The acidity of the tumor microenvironment enhances the immunosuppressive role of MDSCs via activating ASICs

The acidity of the tumor microenvironment enhances the immunosuppressive role of MDSCs via activating ASICs | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article The acidity of the tumor microenvironment enhances the immunosuppressive role of MDSCs via activating ASICs Hui-Hong Gong, Ping Yi, WenLong Zhang, JinHong Liu, YiRong Hu, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7337447/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract A common feature of solid tumors is tumor microenvironment acidification. The acidification triggers immunosuppressive mechanisms that enhance cancer cell survival and growth and facilitate tumor progression. MDSCs (Myeloid-derived suppressor cells) are activated by these mechanisms. Acid-sensing ion channels (ASICs) mainly help to acidify the microenvironment. It's unclear how acidification triggers the activation of MDSCs through ASICs. Research into the mechanisms has demonstrated that MDSCs produce numerous immunosuppressive substances and cytokines through the use of ASICs multiple subunits. The NF-κB and STAT signaling pathways are the main activators of these subunits. Findings of this study suggest that ASICs are implicated in the effect of acidosis on the function of MDSCs in TME. Biological sciences/Cancer Biological sciences/Cell biology MDSCs ASICs immunosuppressive activity TME acidity Figures Figure 1 Figure 2 Figure 3 Figure 4 1. Introduction Myeloid-derived suppressor cells (MDSCs) are a heterogeneous group of cells that interact with the tumor microenvironment via several mechanisms 1 . This cell type is important for the immune escape of tumor cells 2 , it is crucial for tumor progression 3 and it is a key contributor to ineffective tumor immunotherapy 4 . Hence, people try to lessen or completely eliminate the body’s immunosuppressive condition by either removing the MDSCs or blocking their functions 5 – 7 . The modulation of the immunosuppressive signal transduction pathways, electrophysiological characteristics and essential chemicals associated with the immunological effects of MDSCs holds vital significance for tumor disease treatment. Hypoxia and tissue acidification are common phenomena that occur during inflammation and solid tumors, which are important characteristics of the microenvironment. The acidic physical environment of a tumor was found to inhibit several immune cell activities, thus probably inducing immune tolerance. It has been noticed that it can strongly inhibit the cytotoxicity of natural killer (NK) cells in mice 8 . Furthermore, it can activated macrophages to inhibit Fc receptor-mediated phagocytosis and increase production of nitric oxide (NO) 9 . According to a report, acidification impedes the development of LAK cells and reduces the expression of adhesion molecules on cell membranes, thus inhibiting their ability to kill tumor cells 10 . Moreover, it regulates the production and secretion of cytotoxicity-associated cytokines including TNF-α, IFN-γ, TGF-β, IL-10, and IL-12, which further regulates the affinity of receptors in immune response 11 , 12 . Moreover, it has been noted that it can cause a transient rise in the concentration of intracellular calcium ions in human neutrophils 13 . Despite that, it is essential to study if the acidic tumor microenvironment affects MDSCs or not. What is the method via which it exerts influence? The current literature on the subject is rather limited. ASICs, also known as H + non-voltage-gated cation channels or H + -gated cation channels, are a type of ligand-activated ion channel. They are also referred to as Acid-sensing ion channels. The ENaC/degenerin channel family DEG includes these channels as a subclass. So far, cloning of four genes yielded the identification of seven ASICs subunits. The ASIC channel consists of functional subunits ASIC1a, ASIC1b, ASIC2a, and ASIC3. The ASIC2 and ASIC4 functional features have not been clarified 14 . The hydrogen ions (H + ) found outside the cell can stimulate ASICs – ion channels that allow the flow of ions into the cell. Moreover, changes in the H + gradient inside and outside the cell can be detected through these channels 15 . As a result, it can be described as hydrogen ion receptor. Moreover, it has been shown that non-neural cells, such as osteoblasts, vascular smooth muscle cells and immunological cells can express ASICs 16 . T cells, for instance, can make ASICs which help coordinate various cellular functions. Furthermore, bone marrow-derived immature dendritic cells (DCs) can sense the pH drop in the acidic microenvironment through the expression of ASICs 17 . With this detection, it then allows for the DC phagocytosis and the up-regulation of surface major histocompatibility. According to 18 , this mechanism is crucial for the adaptive immune response and immune inflammatory response mediated by dendric cells. The greater inward cation currents in MDSCs observed, as measured in the same MDSCs at various pH levels. Inward cation currents in MDSCs generated from tumor-bearing hosts are much larger and sensitive to pH than those produced from non-tumor-bearing hosts. Is there a link between ASIC expression in MDSCs and their ability to inhibit immunity? Right now, there aren't many academic publications on this topic at the moment. 2. Results 2.1 Detection of ASICs on MDSCs The mRNA expression of ASIC1, ASIC2 and ASIC3 in mouse MDSCs was determined using RT-PCR to evaluate the presence of these ASICs. ASIC1 was found to be 140 bp, ASIC2 139 bp, and ASIC3 was found to be 107 bp. The cortex neurons were seen as a reliable benchmark. MDSCs showed confirmatory mRNA presence for all three ASICs (Fig. 1 A). At the same time, Western Blotting was carried out to detect the expression level of ASICs in MDSCs (Fig. 1 B). Expression of ASICs subunits in T-MDSCs (MDSCs derived from tumor-host individuals) was found to be increased with respect to normal IMCs. Literatures state that ASICs expression might be upregulated in MDSCs owing to acidification and inflammatory lesions. To be specific, the expression of ASIC2 in normal IMCs is lower while T-MDSCs have significantly higher expression. Neither normal nor malignant myeloid-derived suppressor cells express TRPV1, the receptor for capsaicin. Other acid channels cannot interfere because they have been removed. Next, the localization of the ASICs in MDSCs was analyzed by immunocytochemistry in order to observe their distribution at the subcellular and cellular levels. The finding suggests that most of ASIC1 and ASIC3 are in membrane and cytoplasm according to our investigation. In the cytoplasm, ASIC 2 was rarely seen, and only a little amount of the protein was found on the cell membrane (Fig. 1 C). 2.2 Changes of ROS levels in myeloid-derived suppressor cells (MDSCs) subjected to changes in pH. According to the results shown in Fig. 2 , there was a significant increase in ROS (from an average of 38.85–55.13%; p < 0.001) in the T-MDSCs released into the medium with normal physiological pH (pH 7.3) relative to the N-MDSCs (MDSCs derived from normal individuals). At an acidic pH of 5.5, with marked negligible levels of ROS production (55.13% data), T-MDSCs produced a substantially higher level of ROS (139.18% data) as against pH of 7.3. The 62.88% found for N-MDSCs (pH 7.3) was reached at about 2.2 times lower growth rate. The addition of amiloride, a nonspecific blocker of ASICs, PcTx1, a specific blocker of ASICs subunit 1, and APETx2, a specific blocker of ASICs subunit 3, in the cell culture system decreased the expression of ROS in T-MDSCs by 69.44% following APETx2 higher than decrease by 86.6% in the potency of PcTx1. According to this, the high expression of ROS might be related to ASIC3 and ASIC1. There was only a slight decrease in the counts of N-MDSCs. 2.3 Alterations in the expression of TGF-β1 in MDSCs in response to varying pH conditions As you can see in Fig. 3 , TGF-β1 levels differ when pH medium is different during the derivation of MDSCs. When the pH dropped to 5.5, the production of TGF-β1 in T-MDSCs was much greater than in N-MDSCs. It proposes that the acidity of microenvironment could significantly increase TGF-β1 production in T-MDSCs. We then quantified the TGF-β1 levels present in the supernatant of four different pH mediums (pH7.3, 5.5; normal, tumor), after pretreating with amiloride (Fig. 3 D), PcTx1, and APETx2 (Fig. 3 G) as controls. According to recently published findings present in Fig. 3 , a significant reduction of TGF-β1 was observed upon using the following ASICs blocker agents like amiloride ( p < 0.001), PcTx1 ( p < 0.05), and APETx2 ( p < 0.01). It indicates that inhibiting/blocking ASICs in the acidic milieu of T-MDSCs can significantly reduce the release of TGF-β1. 2.4 Changes in ARG-1 expression of myeloid-derived suppressor cells (MDSCs) at varying pH conditions. Figure 3 B, E, H display the results. The expression of the ARG-1 gene in the tumor group was higher than in the normal group. This expression occurred in both the physiological environment (pH 7.3) and acidic environment (pH 5.5). Moreover, in the acidic environment tumor group (Mean tumor diameter: 1.2 ± 0.3 cm), the expression of the ARG-1 gene was significantly increased, which means that a slightly acidic environment increased the expression of MDSCs ARG-1 gene. The expression of ARG-1 in the MDSCs cells significantly reduced by adding amiloride before treatment compared to tumor group without amiloride. This is a paraphrase of the original sentence: In the tumor group, it is believed that amiloride inhibits the express of ARG-1. Also, pre-treating MDSCs cells with PcTx1 and APETx2 hindered the activity of ARG-1 in a mildly acidic environment. Under acidic conditions, Activation of MDSCs can occur either through ASIC1 or ASIC3 or both ASIC1 and ASIC3 working together. As a result of such activation, there will be upregulation of ARG-1 leading to an immunosuppressive effect. 2.5 Alterations in the expression of COX-2 in MDSCs in response to varying pH conditions The tumor group's natural environment had much higher COX-2 expression compared to the normal group, as shown in Fig. 3 C, F, I. Furthermore, at pH 5.5, the expression of COX-2 in the tumor mouse was significantly higher than in normal conditions. The expression of COX-2 get effectively blocked upon adding amiloride. The results showed that ASICs could possibly alter the COX-2 expression of the MDSCs. The increase of COX-2 expression results to the opening of ASICs ion channels due to acid stimulation. Blocking ASICs reduces MDSCs’ COX-2 expression. To investigate the involvement of MDSCs COX-2 expression through ASICs, the involvement of subunits in experimental pretreatment with ASICs subunit specific inhibitor PcTx1 and APETx2 was examined. The results indicate that APETx2 can inhibit COX-2 gene expression while PcTx1 does not disrupt this gene expression. This indicates that the expression of the COX-2 gene may be somewhat related to ASIC3. In contrast, there does not appear to be a direct correlation with ASIC1. ASIC3 may affect the COX-2 gene expression in a similar way as ASIC2, according to these results. However, more experiments are needed to confirm these results. 2.6 The molecular mechanism behind the inhibitory activity of MDSCs in an acidic environment Due to the acidification conditions, the MDSCs activation occur through the NF-κB signalling. N-MDSCs and T-MDSCs cells were cultured separately in pH 7.3 and pH 5.5 media for the period of 16 hours. Consequently, the total protein was harvested in order to observe the alteration in the phosphorylation levels of IκB, p65, IKK Proteins of the NF-κB pathway. As illustrated in Fig. 4 , expression of p65 was found to increase significantly with decrease in pH. This suggests that the activation of MDSC's NF-κB is encouraged by acidic conditions. In addition, Amiloride treatment inhibited the p-p65, p-IκB, and p-IKK phosphorylation, consequently inhibiting NF-κB activation. According to these results, MDSC activation of NF-κB pathways occurs in acidic environments and this activation closely correlates to ASICs. To find out which ASIC subunits activate this pathway, we used PcTx1 and APETx2 ahead of time. Both PcTx1 and APETx2 are responsible for the phosphorylation of p-p65, pIκB, and pIKK. As a result, this inhibition prevented the NF-κB signaling pathway from being activated. As per this statement, under acidification conditions, activation of NF-κB signaling may occur because of stimulation of ASIC1 and ASIC3. This subsequently leads to MDSCs activation and immunosuppression. The signalling pathways of STAT1 and STAT6 were involved in the activation of MDSCs during the acidification conditions. It can be seen from above that acidification conditions can activate NF-κB signaling pathway in MDSCs through ASICs. Can we find additional signaling pathways that activate MDSCs? N-MDSCs and T-MDSCs were grown sequentially in a medium with pH 7.3 and pH 5.5 for 16 hours. The total protein was then extracted to assess the changes of protein phosphorylation of the pathways of STAT1 and STAT6. Figure 4 D displays the results. The levels of phosphorylation of STAT1 and STAT6 in T-MDSCs increase at a pH of 5.5. Before the experiment began, Amiloride, PcTx1 and APETx2 were added, which caused a drop in the level of pSTAT1 and pSTAT6 phosphorylation (Fig. 4 E, F). This suggests that acidification conditions may activate transcription factors, namely STAT1 and STAT6, via ASIC1 and ASIC3 stimulation, which subsequently mediates MDSCs. In general, we propose that the acidic conditions menly or along with each other stimulant ASIC1 and 3 on MDSCs derived from tumor-bearing mice. The stimulation causes ASIC channels to activate and open. This activation leads to the initiation of NF-κB and STAT signaling in MDSCs. Thus, these pathways lead to phosphorylation and assist in other molecules. The NF-κB pathway is activated leading to upregulation of COX-2, ARG-1, ROS and other associated molecules. Release of TGF-β1 is greatly enhanced by the activation of transcription factors STAT1 and STAT6. As a result, MDSCs get activated in quick succession and later in high numbers by the production of a large quantity of inhibitory cytokines. The final outcome is the application of an immunosuppressive effect. 3. Discussion MDSCs plays important role to regulate immune response in various disease conditions; and, these have become an important part of tumor immunology. Thus, inhibiting the activity of MDSCs is of great physiological and pathological importance for clinical relevance. Lactate accumulation in the tumor microenvironment, termed extracellular acidosis, is common in many clinical settings 19 – 21 . The increased production of lactate and acidity of tumor microenvironment (TME) enhances several fundamental carcinogenic process including angiogenesis, tissue invasion/metastasis and treatment response. Lactate, a substance that was previously rejected, is no longer rejected 10 . When there is inflammation, a tumor, a viral infection, or the blood supply to a tissue is cut off, H + ions can directly alter the activity of some ion channels (for example ASICs) to help maintain pH balance. As ASICs are cation channels which activated by extracellular protons and have been demonstrated in immune cells (T cells, B cells, macrophages, DCs, and BMMs) in mice. We propose that ASICs may play a role in the response of MDSCs to acidosis by acting as sensors of extracellular acidosis. To test this theory, researchers checked for ASICs in mouse MDSCs. As expected, ASIC expression was higher among T-MDSCs than N-MDSCs. ASIC1 and ASIC3 are mainly located in the cytoplasm and not on the cell membrane is neurons, whereas ASIC2 is located on the cell membrane only (Fig. 1 C). According to earlier studies, several proinflammatory substances are connected with the accumulation and activation of MDSCs in tumour-bearing mice and cancer patients. These include IL-10, IL-6, IL-1β, TGF-β, the bioactive lipid PGE2, S100A8 and C5a. Nonetheless, the research findings on how acidosis affects cytokine secretion are complex. According to the study, a pH of 5.5 activates MDSCs, providing definitive proof. This activation increases inhibitory function by elevating the production and release of ROS (Fig. 2 ), TGF-β1, ARG-1, and COX-2 (Fig. 3 ). The addition of the ASIC blocker amiloride attenuated the production of ROS (refer to Fig. 2 ) and TGF-β1, ARG-1, and COX-2 (Fig. 3 D, E, F). The experiment utilized PcTx1, which is a type of blocker that inhibits ASIC subunit 1; and APETx2, which is a blocker that inhibits ASIC subunit 3. According to the data obtained, PcTx1 and APETx2 suppress the expression of ROS, TGF-β1 and ARG-1. Moreover, down-regulation of COX-2 gene expression by APETx2, but not PcTx1, was observed in the microarray studies. The data show that the expressions of the genes ROS, TGF-β1, and ARG-1 may correlate with ASIC1 and ASIC3. Some studies say that ASIC3 either alone or together with ASIC2 regulates COX-2 gene expression. Yet, more tests are needed to validate this connection. The findings indicate that MDSCs' immunosuppressive ability in tumor mice is markedly potentiated in acidic environment possibly due to acid-induced activation of ASICs. The way MDSCs sense outside acidity is not clear yet As demonstrated by our findings that the activation of MDSCs occurs through NF-κB and STAT pathways associated with ASICs via stimulation by extracellular acidity. This is supported by the following evidence: 1. The phosphorylation levels of p65, IκB, and Ikk in tumor MDSCs were much higher when cultured at pH 5.5 (Fig. 4 A). 2. The activation of STAT was observed in MDSCs from mice with tumors, as indicated by the increased phosphorylation of STAT1 and STAT6. When the amiloride blocker for ASICs was preincubated with MDSCs, the phosphorylation levels of p65, IκB, Ikk, STAT1, and STAT6 returned to the original level (Fig. 4 ). Acidic conditions is likely to cause the group of proteins known as NF-kB and a family of cell signaling molecules known as STAT to become phosphoylative. And that is likely to result in activation of T-MDSCs in tumor bearing animals and inhibit immune function. Additionally, ASICs could be used to inhibit the T-MDSCs in the tumor microenvironment. The study's results sub-stantiating findings from various other recent studies: lactic acid in TME limits the immune response to cancer, inhibits immune cell function; and leads to: (1) inhibition of immune cell proliferation and survival 22 ; (2) induction of immune cell dedifferentiation 23 ; (3) activation of downstream signaling pathways 24 , 25 . Tumor-bearing mice contain a variety of MDSC subtypes, around 80% which are PMN-MDSCs. These cells primarily exert immune suppression in an antigen-specific manner. The prominent feature of these cells is the induction of T-cell tolerance specific to antigen 26 , 27 . The generation of ROS is responsible for inhibiting T-cell responses both against specific antigens and in a non-specific manner. Around a fifth of the M-MDSCs accomplish this by utilizing NO and cytokine production mechanisms. For a comprehensive discussion, refer to reference 28 . Unfortunately, our current study did not classify the MDSCs in tumor-bearing mice nor did we examine expression and localization of ASICs in M-MDSCs and PMN-MDSCs cells. Also we did not consider whether ASICs affect cellular immunosuppression and the mechanisms involved in it. Factors within the tumor microenvironment may induce the generation of a variety of suppressive cells, including regulatory T lymphocytes (Tregs), tumor-associated macrophages (TAMs), mast cells, type II NKT cells, and MDSCs. These cells help fight against both the natural and the adaptive immunity of the body to the tumor. Among these cells, MDSCs are particularly important due to their contribution to the failure of tumor immunotherapy 29 . Accordingly, people try to diminish or eliminate the body’s immunosuppressive condition through the removal of MDSCs or the inhibition of their functions 5 – 7 . Our study revealed that the acidic environment has greatly enhanced the expression of the ASICs in MDSCs. The further addition of extracellular H + ion prompted protein expression, thus causing influx of Na + and/or Ca 2+ ions. This activation of ion channels triggered activation of the NF-κB pathway and/or STAT pathway followed which was manifested in increased expression and secretion of MDSCs inhibitory molecules. The result was increasing the MDSCs immunosuppressive function. The research offers some evidence that an acidic tumor microenvironment can affect the MDSCs. It also explains how this influence occurs at the molecular level. This evidence is important for abolishing immunosuppressive signal transduction pathways and modifying immune effects of MDSCs via inhibiting ASICs. This stops the formation of microenvironments around the tumor and improves the therapy of tumor. Still, the cells’ biological function cannot be verified unless techniques to selectively target them are worked out. In order to achieve this task, distinct markers for these cells must be identified. This can be done by a greater understanding of the molecular pathways that control the growth of these cells. Our study reveals the exact molecular process through which low pH in the tumor microenvironment affects MDSCs. In this article, we explore the biological characteristics of MDSCs with relation to ion channels and offer up new therapeutic targets and strategies for cancer prophylaxis and treatment. 4. Materials and methods 4.1 Cell lines H22 liver cancer cell line is derived from type cultured cells from the Chinese Academy of Sciences (Shanghai, China), catalog number TCHu 98. The cultured process of H22 liver cancer cells took place in the use of RPMI 1640 media with a presence of 10% FBS. Also, this cultured media has a presence of both penicillin and streptomycin. The other components of this cultured media are Culture supplement, recombinant human growth factor, and stem cell factor. 4.2 Tumor inoculations We purchased the BALB/c mice from Hubei Province’s (Wuhan, China) Center of Medical Experimental Animals. Mice 6-week to 12-week age-mice were bred and maintained in specific pathogen-free conditions and treated according to South-Central MinZu University (China) Animal Care Guidelines. All animal experiments were conducted in accordance with ARRIVE guidelines. Approval for the animal study was granted by the Ethics Review Committee at South-Central MinZu University (Approval No: SCXK(Liao)2014-0012). 4.3 Isolation and purification of MDSC We obtained spleens, tibias, and femurs from 6 ~ 8 week-old tumor-bearing (Mean tumor diameter: 1.2 ± 0.3 cm) or normal mice and washed them twice with Iscove’s modified Dulbecco medium. After RBC lysis, bone marrow cells and splenocytes were fractionated by centrifugation on a Percoll (Amersham Biosciences, Uppsala, Sweden) density gradient as described 30 . Cells were harvested from the gradient interfaces that presented between a 50% and 60% density and termed “Fraction 2.” CD11b + /Gr-1 + cells were extracted from miltenyi biotec (Auburn, CA) macrobeads through MACS magnetic microbeads. The purity of cell separation ranged between 90% and 96%. 4.4 Flow cytometry The cells were treated with the FITC, PE, or allophycocyanin-conjugated mAbs specific for CD3 (145–2C11), CD11b (M1/70), Gr-1 (RB6–8C5), CD120a(TNFR1), CD120b(TNFR2), and with isotype controls (rat IgG2a, rat IgG2b, mouse IgG2a, Armenian hamster IgG) from eBioscience (San Diego, CA) or Biolegend (San Diego, CA). Cells were kept in primary antibodies in phosphate buffer saline containing 2% BSA for 30 min at 4°C and washed for twice Data was acquired via a BD Biosciences FACSCanto (MountainView, CA) and analyzed via CellQuest software. For 16 hours, MDSCs were isolated from normal and tumor-bearing mice (Mean tumor diameter: 1.2 ± 0.3 cm), respectively, and grown in media with pH levels of 7.3, 6.5, and 5.5 to assess ROS (reactive oxygen species) levels. Following the collection of cells, centrifugation was used to discard the supernatant. DCFH-DA (dilution 1:1000, final concentration – 10 µmol/L) was subsequently added to the cell concentration of 5 × 10 6 cells/mL. The cells were placed in a 5% CO 2 incubator at 37℃ and were inverted and mixed at intervals of 3 to 5 minutes for 20 minutes. Cells were washed three times with serum-free media to remove excess DCFH-DA. Flow cytometry was used to identify ROS content. 4.5 Cytokine Levels Detection by ELISA MDSCs collected from tumor-bearing mice were used to assess the levels of mouse TGF-β1 in their supernatant using an ELISA Kit (BD Biosciences) as per the manufacturer’s instructions. The Multiscan MC reader measured absorbance at 450 nm, and Delta Soft II software (BioMetallics, Inc.) was used to analyze samples. 4.6 Total protein preparation and Western blot analysis Cells were solubilized in lysis buffer (150 mM NaCl, 50 mM HEPES, pH 7.4 and 1% Triton X-100) for 1 hr at 4°C with a protease inhibitor cocktail (Calbiochem, SanDiego, CA). Centrifugation at 20,000g for 10 mins at a temperature of 4℃ helps to obtain the cell extract. Samples were mixed with Tris-glycine SDS sample buffer (4×) containing 10% 2-ME and boiled at 95℃ for 5 min. Next, 80 µg of soluble protein of each sample was fractionated by 12% SDS-polyacrylamide gel electrophoresis and transferred on to a PVDF membrane. A blocking solution comprising 5% BSA in TBS-Tween-20 or non-fat milk in PBS-Tween-20 (0.05%) was used to block the membrane for 2 h at room temperature. The blots were allowed to incubate overnight at 4°C with the primary antibody (phosphospecific p38 Thr180/182 and phosphospecific JNK G-7, phosphospecific ERK1/2 (Santa Cruz), actin (Biolegend) or TNF-α antibody(R&D), and then follow incubation for 1 ~ 2 h with secondary antibody (horseradish peroxidase-conjugated). Immunogenic marginals were affiliated at the chemiluminescence (Amersham Pharmacia ECL or Pierce ECL). Densitometry was carry-out on the resultant autoradiograms. All experiments were performed at least three times. We used EXCEL 5.0 and Student's two-tailed t-test for statistical analysis. 4.7 Reverse transcription-PCR and quantitative real-time PCR As per the manufacturer’s instructions, total RNA was extracted in TRIzol reagent (Invitrogen). One-step RT-PCR kit, used for the RT-PCR, was by Qiagen. Thirty PCR cycles were used for all the analyses. The intensity of each amplified DNA band was analyzed using IQ Mac version 1.2 software and quantitatively compared by using Actin as the internal control. Gene Link synthesized the primers for all of the genes we tested, including the internal control Actin: Actin: 5V- TCA CCC ACA CTG TGC CCA TCT ACGA-3V (sense) and CAT CGG AAC CGC TCG TTG CCA ATAG − 3V (antisense). ARG-1: 5V- CAG AAG AAT GGA AGA GTC AG -3V (sense) and 5V- CAG ATA TGC AGG GAG TCA CC -3V (antisense). COX-2: 5V- AAT GAG TAC CGC AAA CGC − 3V(sense) and 5V- CCA GAA TGG TGC TCC AAG − 3V (antisense). cDNA was subjected to quantitative real-time PCR using 2 µL reverse Real-time PCR Platinum SYBR Green qPCR SuperMix UDG Kit from Invitrogen, and the testing was performed on Rotor gene 3000 system from Corbett Research. The IQ-Cycler (Bio-Rad) analyzed each sample in duplicate, and the normalized signal level was calculated by dividing the sample by the respective actin housekeeping signal. The cycling conditions consisted of 3 minutes at 94°C followed by 30 seconds at 94°C, 40 seconds at 55°C, and 50 seconds at 72°C for a total of 35 cycles. To standardize the total quantity of RNA that is added to each reaction mixture. The internal control gene TC is used to normalized the Ct values of target genes in qPCR. The 2(-Delta Delta C(T)) method method was used to measure the differential expression 31 . Statistical investigation Statistical analysis was performed using the SPSS software (Version 18.0). The data was presented as means ± standard deviation (SD). Using one-way analysis of variance and Dunnett's several comparisons were made. Statistical significance was the probability (P) value 0.05. Abbreviation letters: MDSCs, myeloid-derived suppressor cells; T-MDSCs, tumor-bearing mice-derived myeloid-derived suppressor cells; N-MDSCs, myeloid-derived suppressor cells obtained from normal sources; ASICs, acid-sensing ion channels; TME, tumor microenvironment; IL-1β, Interleukin-1β; IL-8, Interleukin-8; iNOS, Inducible nitric oxide synthase; LPS, Lipopolysaccharides; NF-κB, Nuclear factor-kappa B; ROS, Reactive oxygen species; TNF-α, Tumor necrosis factor-α; IFN-γ, interferon-gamma; TGF-β1, transforming growth factor-beta 1; IL-10, interleukin-10; IL-12, interleukin-12. Declarations Acknowledgements This study would not have been complete without the valuable assistance received from HUST(Huazhong University of Science and Technology,WuHan, China) Professor Zhuo-ya Li, Professor Bin-jiao Yin, and Professor Jing Wang in interpreting the significance of our results and in constructive discussions. Funding Statement The authors also thank the support of the Fundamental Research Funds for the Central Universities, South-Central MinZu University (Grant No. CZY17014) and Natural Science Foundation of HuBei Province of China (Grant No. 2023AFB681). This work was also supported by the Young Scientists Fund of the National Natural Science Foundation of China (Grant No. 81201610) and the Fund for Academic Innovation Teams of South-Central MinZu University (Grant No. XTZ24025). Data availability statement The authors of this article will provide the raw data that supports its conclusions without giving any undue reservation. Ethics statement The Animal Ethics Committee of South-Central Minzu University approved this experiment according to License Number SCXK(Liao)2014-0012. All mice were housed in a specific pathogen-free (SPF) facility in the Experimental Animal Centre. Our procedures for handling animals conformed to the requirements of the Committee and the Guidelines of the National Institutes of Health (NIH). Author contributions The examination was designed by Hui-Hong Gong, Xin Hu. Ping Yi , Shenglan Tong and Hui Yao performed the experiments. Xin Hu, WenLong Zhang, JinHong Liu , YiRong Hu and Hui-Hong Gong analyzed the data. Xin Hu, Shenglan Tong wrote the manuscript. All authors have read and approved the final manuscript before submitting. Conflict of interest statement The authors declare that there are no conflicts of interest. Generative AI statement The authors affirm that generative AI played no role in developing this manuscript. References Youn, J. I., Nagaraj, S., Collazo, M. & Gabrilovich, D. I. Subsets of myeloid-derived suppressor cells in tumor-bearing mice. J Immunol . 15;181(8):5791 – 802. (2008). 10.4049/jimmunol.181.8.5791 Ostrand-Rosenberg, S. & Sinha, P. Myeloid-derived suppressor cells: linking inflammation and cancer. J Immunol . 15;182(8):4499 – 506. (2009). 10.4049/jimmunol.0802740 Cheng, P. et al. Inhibition of dendritic cell differentiation and accumulation of myeloid-derived suppressor cells in cancer is regulated by S100A9 protein. J. Exp. Med. 29 (10), 2235–2249. 10.1084/jem.20080132 (2008). Gabrilovich, D. I. & Nagaraj, S. Myeloid-derived suppressor cells as regulators of the immune system. Nat. Rev. Immunol. 9 (3), 162–174. 10.1038/nri2506 (2009). Bronte, V. et al. IL-4-induced arginase 1 suppresses alloreactive T cells in tumor-bearing mice. J Immunol . 1;170(1):270-8. (2003). 10.4049/jimmunol.170.1.270 Kusmartsev, S., Nefedova, Y., Yoder, D. & Gabrilovich, D. I. Antigen-specific inhibition of CD8 + T cell response by immature myeloid cells in cancer is mediated by reactive oxygen species. J. Immunol. 15 (2), 989–999. 10.4049/jimmunol.172.2.989 (2004). Sinha, P., Clements, V. K., Fulton, A. M. & Ostrand-Rosenberg, S. Prostaglandin E2 promotes tumor progression by inducing myeloid-derived suppressor cells. Cancer Res . 1;67(9):4507-13. (2007). 10.1158/0008-5472.CAN-06-4174 Jedlička, M., Feglarova, T. & Janstova, L. Lactate from the tumor microenvironment-A key obstacle in NK cell-based immunotherapies. FRONT. IMMUNO . 13 , 932055 (2022). Palmieri, E. M., McGinity, C., Wink, D. A. & McVicar, D. W. Nitric Oxide in Macrophage Immunometabolism: Hiding in Plain Sight. Metabolites . 26;10(11):429. (2020). 10.3390/metabo10110429 Wang, J. X. et al. Lactic Acid and an Acidic Tumor Microenvironment suppress Anticancer Immunity. Int. J. Mol. Sci. 7 (21), 8363. 10.3390/ijms21218363 (2020). Certo, M. et al. Lactate modulation of immune responses in inflammatory versus tumour microenvironments. Nat. Rev. Immunol. 21 , 151–161. doi.org/10.1038/s41577-020-0406-2 (2021). Dietl, K. et al. Lactic acid and acidification inhibit TNF secretion and glycolysis of human monocytes. J Immunol . 1;184(3):1200-9. (2010). 10.4049/jimmunol.0902584 Immler, R., Simon, S. I. & Sperandio, M. Calcium signalling and related ion channels in neutrophil recruitment and function. Eur. J. Clin. Invest. 48 (Suppl 2), e12964. 10.1111/eci.12964 (2018). Ruan, N. et al. Acid-Sensing Ion Channels and Mechanosensation. Int. J. Mol. Sci. 1 (9), 4810. 10.3390/ijms22094810 (2021). Holzer, P. et al. Acid-sensitive ion channels and receptors. Handb Exp Pharmac ol. (194): pp. 283–332 (2009). Foster, V. S., Rash, L. D., King, G. F. & Rank, M. M. Acid-Sensing Ion Channels: Expression and Function in Resident and Infiltrating Immune Cells in the Central Nervous System. Front. Cell. Neurosci. 17 , 15:738043. 10.3389/fncel.2021.738043 (2021). Leblanc-Hotte, A. et al. Immature and mature bone marrow-derived dendritic cells exhibit distinct intracellular mechanical properties. Sci Rep . 3;13(1):1967. (2023). 10.1038/s41598-023-28625-w Kong, X. et al. Extracellular acidosis modulates the endocytosis and maturation of macrophages. Cell. Immunol. 281 (1), 44–50. 10.1016/j.cellimm.2012.12.009 (2013). De Milito, A. et al. pH-dependent antitumor activity of proton pump inhibitors against human melanoma is mediated by inhibition of tumor acidity. Int J Cancer . 1;127(1):207 – 19. (2010). 10.1002/ijc.25009 Fukumura, D. & Jain, R. K. Tumor microenvironment abnormalities: causes, consequences, and strategies to normalize. J Cell Biochem . 1;101(4):937 – 49. (2007). 10.1002/jcb.21187 Helmlinger, G., Yuan, F., Dellian, M. & Jain, R. K. Interstitial pH and pO2 gradients in solid tumors in vivo: high-resolution measurements reveal a lack of correlation. Nat. Med. 3 (2), 177–182. 10.1038/nm0297-177 (1997). Huber, V. et al. Cancer acidity: An ultimate frontier of tumor immune escape and a novel target of immunomodulation. Semin Cancer Biol. 43 , 74–89. 10.1016/j.semcancer.2017.03.001 (2017). Zhang, D. et al. Metabolic regulation of gene expression by histone lactylation. Nature 574 , 575–580. doi.org/10.1038/s41586-019-1678-1( (2019). Choi, S. Y., Collins, C. C., Gout, P. W. & Wang, Y. Cancer-generated lactic acid: a regulatory, immunosuppressive metabolite? J. Pathol. 230 (4), 350–355. 10.1002/path.4218 (2013). Feichtinger, R. G. & Lang, R. Targeting L-Lactate Metabolism to Overcome Resistance to Immune Therapy of Melanoma and Other Tumor Entities. J Oncol . 3;2019:2084195. (2019). 10.1155/2019/2084195 Koehn, B. H. et al. GVHD-associated, inflammasome-mediated loss of function in adoptively transferred myeloid-derived suppressor cells. Blood . 24;126(13):1621-8. 10.1182/blood-2015-03-634691(2015 ). Marigo, I. et al. Tumor-induced tolerance and immune suppression depend on the C/EBPbeta transcription factor. Immunity 25 (6), 790–802. 10.1016/j.immuni.2010.05.010 (2010). Gabrilovich, D. I., Ostrand-Rosenberg, S. & Bronte, V. Coordinated regulation of myeloid cells by tumours. Nat Rev Immunol . 22;12(4):253 – 68. (2012). 10.1038/nri3175 Sui, H. et al. Immunotherapy of targeting MDSCs in tumor microenvironment. Front. Immunol. 5 , 13:990463. 10.3389/fimmu.2022.990463 (2022). Pan, P. Y. et al. Reversion of immune tolerance in advanced malignancy: modulation of myeloid-derived suppressor cell development by blockade of stem-cell factor function. Blood . 1;111(1):219 – 28. (2008). 10.1182/blood-2007-04-086835 Rao, X., Huang, X., Zhou, Z. & Lin, X. An improvement of the 2ˆ(-delta delta CT) method for quantitative real-time polymerase chain reaction data analysis. Biostat Bioinforma Biomath . 3 (3), 71–85 (2013). Additional Declarations No competing interests reported. Supplementary Files SupplementaryFigureS4.pdf Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7337447","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":508420286,"identity":"11ff93a5-8162-445f-b4ca-ba452af2bd38","order_by":0,"name":"Hui-Hong Gong","email":"","orcid":"","institution":"Hubei University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Hui-Hong","middleName":"","lastName":"Gong","suffix":""},{"id":508420287,"identity":"2cfb3070-c94e-470c-ae12-22487b0b2970","order_by":1,"name":"Ping Yi","email":"","orcid":"","institution":"Kindstar Globalgene Technology, Inc","correspondingAuthor":false,"prefix":"","firstName":"Ping","middleName":"","lastName":"Yi","suffix":""},{"id":508420288,"identity":"cf9e1d3b-eae5-49a5-a04e-bc779a48e706","order_by":2,"name":"WenLong Zhang","email":"","orcid":"","institution":"South-Central Minzu University","correspondingAuthor":false,"prefix":"","firstName":"WenLong","middleName":"","lastName":"Zhang","suffix":""},{"id":508420289,"identity":"8841e7df-563d-45e1-b3d9-bedf23247044","order_by":3,"name":"JinHong Liu","email":"","orcid":"","institution":"South-Central Minzu University","correspondingAuthor":false,"prefix":"","firstName":"JinHong","middleName":"","lastName":"Liu","suffix":""},{"id":508420290,"identity":"d28874b8-1991-4710-9878-23eff9320bef","order_by":4,"name":"YiRong Hu","email":"","orcid":"","institution":"South-Central Minzu University","correspondingAuthor":false,"prefix":"","firstName":"YiRong","middleName":"","lastName":"Hu","suffix":""},{"id":508420291,"identity":"3bd5ce22-73f0-485a-97c8-5fbc808026ee","order_by":5,"name":"Shenglan Tong","email":"","orcid":"","institution":"The First People’s Hospital of Jiangxia District","correspondingAuthor":false,"prefix":"","firstName":"Shenglan","middleName":"","lastName":"Tong","suffix":""},{"id":508420292,"identity":"95386e88-825f-4e9a-ade8-f8d2fd43240c","order_by":6,"name":"Hui Yao","email":"","orcid":"","institution":"South-Central Minzu University","correspondingAuthor":false,"prefix":"","firstName":"Hui","middleName":"","lastName":"Yao","suffix":""},{"id":508420293,"identity":"3c3161d4-1c07-4dbc-b90e-7a3c8c763217","order_by":7,"name":"Xin Hu","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAyElEQVRIiWNgGAWjYBACAyA+wPjnHzMbe2Pjgw/Ea2k4wM7Pc7jZcAaxWhiAWvglZ6S3SXMQo8VcIsfwcOGOO9IGNx82SDMw2MnpNhDQYjkjLeHwzDPPjA1uJzYYFzAkG5sdIOSwG8kHDvOwMSeDtCTPYDiQuI2wlsQGkJb6DTcPAhnEaQHawtt2mFlyBmNjM3FazjxLOMxzJo2ZnyexmXGGATF+OZ5j/JmnwgYYlcef//hQYSdHUAu6CaQpHwWjYBSMglGAAwAAltRJOA2Ny4sAAAAASUVORK5CYII=","orcid":"","institution":"South-Central Minzu University","correspondingAuthor":true,"prefix":"","firstName":"Xin","middleName":"","lastName":"Hu","suffix":""}],"badges":[],"createdAt":"2025-08-10 07:53:07","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7337447/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7337447/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":90417312,"identity":"27c152c6-3b8e-4ee8-a16a-dec10b136433","added_by":"auto","created_at":"2025-09-02 13:24:56","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":404465,"visible":true,"origin":"","legend":"\u003cp\u003eInvestigation of the presence and distribution of ASIC1, ASIC2, and ASIC3 in MDSCs.\u003c/p\u003e\n\u003cp\u003eTranscripts of A, ASICs were identified in MDSCs using RT-PCR. Cortical neurons (B) were employed as a positive control. N: MDSCs from normal mice; T: MDSCs from animals with tumors Perform Western blot analysis to assess the protein expression of ASICs in MDSCs. The cortex protein was employed as a positive control. To control for specificity, antibodies for ASICs were preincubated with the matching peptide antigens. Localization of ASICs subunit proteins in MDSCs was detected using double-staining immunofluorescence with a Nikon microscope. The nuclei were stained with Hoechst33342, resulting in a blue coloration. The color red represents ASICs, while the color green represents Gr-1.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-7337447/v1/62790be7360a1302eb3a60dc.png"},{"id":90417766,"identity":"5b7a57cf-6b49-44be-9d43-d05fceb5e648","added_by":"auto","created_at":"2025-09-02 13:32:56","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":277945,"visible":true,"origin":"","legend":"\u003cp\u003eTumor acidification microenvironment is characterized by an elevation in ROS levels and a decrease in the presence of ASICs subunit blocker. The generation of reactive oxygen species (ROS) by both N-MDSCs and T-MDSCs was assessed after incubation in an environment with a pH of 7.3 and 5.5, and 5% carbon dioxide (CO\u003csub\u003e2\u003c/sub\u003e) for a duration of 16 hours. This assessment was conducted using the DEFH-DA method. At a pH of 5.5, there was a considerable rise in active oxygen levels, rising from about 62.88% to 139.18%. Additionally, the growth rate was almost 2.2 times higher than that of normal mice. Amiloride significantly reduced the expression of ROS in T-MDSCs from 139.18% to 56.15% at pH 5.5. Additionally, PcTx1 decreased the expression by 86.6%, while APETx2 decreased it by 69.44%.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-7337447/v1/4f82782386e8d5e6011e3ff6.png"},{"id":90417313,"identity":"8ba9042c-f408-4089-b0e1-e06197bc887c","added_by":"auto","created_at":"2025-09-02 13:24:56","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":170562,"visible":true,"origin":"","legend":"\u003cp\u003eshows the collection of the liquid portion (supernatant) by both N-MDSCs and T-MDSCs after being exposed to an environment with a pH of 7.3 and 5.5, with 5% CO\u003csub\u003e2\u003c/sub\u003e, for a duration of 16 hours. The quantification of TGF-β1 (A) released by MDSCs was assessed using the enzyme-linked immunosorbent assay (ELISA). Extracellular acidosis leads to an elevation in TGF-β1 levels, which can be suppressed by amiloride, PcTx1, and APETx2(D, G). The expression of ARG-1 and COX-2 gene in the tumor group was considerably higher than that in the normal group, particularly at pH 5.5. The addition of amiloride prior to the experiment resulted in a notable decrease in the expression of ARG-1 and COX-2 in MDSCs cells compared to the tumor group without amiloride (E, F). The addition of PcTx1 and APETx2 before to experimentation resulted in the inhibition of ARG-1 expression in MDSCs cells under mildly acidic conditions (H). Figure I demonstrates that APETx2 has the ability to suppress the expression of the COX-2 gene, while PcTx1 does not possess the capability to reduce its gene expression. The results are quantified as the proliferating index and presented as the average value plus or minus the standard deviation from three separate tests. Statistical significance was observed with p-values of less than 0.001 , 0.01and 0.05 denoted as ***\u003cem\u003ep\u003c/em\u003e\u0026lt;0.001 , **\u003cem\u003ep\u003c/em\u003e\u0026lt;0.01 and *\u003cem\u003ep\u003c/em\u003e\u0026lt;0.05, respectively. There is a notable distinction between the normal pH level of 5.5 and the pH level of 5.5 in tumors.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-7337447/v1/d6ca98f53ad6ac7879ca7cbd.png"},{"id":90420948,"identity":"3b3688c3-ca35-4a4f-914e-e7fcedbc5bc1","added_by":"auto","created_at":"2025-09-02 13:56:56","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":278655,"visible":true,"origin":"","legend":"\u003cp\u003eExtracellular acidosis triggers the activation of MDSCs through the signaling pathways of NF-κB, STAT1, and STAT6. MDSCs were collected following a 16-hour culture in a medium with pH levels of 7.3 and 5.5. Prior to this, N- and T-MDSCs were incubated with amiloride in a pH of 7.3, 5.5, and 5% CO\u003csub\u003e2\u003c/sub\u003e for 16 hours (A, D). Additionally, N- and T-MDSCs were preincubated with PcTx1 for 16 hours (B, E), and with APETx2 for 16 hours (C, F). The cells were disrupted, and the phosphorylation of p65, IκB, Ikk in NF-κB, and the phosphorylation of STAT1 and STAT6 were examined by western blotting. Actin and the five signaling molecules were used as loading controls. The results are indicative of five separate tests.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-7337447/v1/e491e8b4024a5b40c1e5d239.png"},{"id":91817561,"identity":"8c86108d-9f94-46d4-8bf8-fb37574cfbac","added_by":"auto","created_at":"2025-09-22 06:56:54","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1932052,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7337447/v1/2c3c8a13-ad5f-4cbb-ac8b-82bf2e401c1e.pdf"},{"id":90417315,"identity":"32bf3a20-55a2-49cc-b419-1478a8889f2c","added_by":"auto","created_at":"2025-09-02 13:24:56","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":2207276,"visible":true,"origin":"","legend":"","description":"","filename":"SupplementaryFigureS4.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7337447/v1/93447a4ff9ac15c14729f197.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"The acidity of the tumor microenvironment enhances the immunosuppressive role of MDSCs via activating ASICs","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eMyeloid-derived suppressor cells (MDSCs) are a heterogeneous group of cells that interact with the tumor microenvironment via several mechanisms\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e. This cell type is important for the immune escape of tumor cells\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e, it is crucial for tumor progression \u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e and it is a key contributor to ineffective tumor immunotherapy\u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e. Hence, people try to lessen or completely eliminate the body\u0026rsquo;s immunosuppressive condition by either removing the MDSCs or blocking their functions\u003csup\u003e\u003cspan additionalcitationids=\"CR6\" citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e. The modulation of the immunosuppressive signal transduction pathways, electrophysiological characteristics and essential chemicals associated with the immunological effects of MDSCs holds vital significance for tumor disease treatment.\u003c/p\u003e\u003cp\u003eHypoxia and tissue acidification are common phenomena that occur during inflammation and solid tumors, which are important characteristics of the microenvironment. The acidic physical environment of a tumor was found to inhibit several immune cell activities, thus probably inducing immune tolerance. It has been noticed that it can strongly inhibit the cytotoxicity of natural killer (NK) cells in mice\u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e. Furthermore, it can activated macrophages to inhibit Fc receptor-mediated phagocytosis and increase production of nitric oxide (NO) \u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e. According to a report, acidification impedes the development of LAK cells and reduces the expression of adhesion molecules on cell membranes, thus inhibiting their ability to kill tumor cells \u003csup\u003e\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u003c/sup\u003e. Moreover, it regulates the production and secretion of cytotoxicity-associated cytokines including TNF-α, IFN-γ, TGF-β, IL-10, and IL-12, which further regulates the affinity of receptors in immune response\u003csup\u003e\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e. Moreover, it has been noted that it can cause a transient rise in the concentration of intracellular calcium ions in human neutrophils \u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e. Despite that, it is essential to study if the acidic tumor microenvironment affects MDSCs or not. What is the method via which it exerts influence? The current literature on the subject is rather limited.\u003c/p\u003e\u003cp\u003eASICs, also known as H\u003csup\u003e+\u003c/sup\u003e non-voltage-gated cation channels or H\u003csup\u003e+\u003c/sup\u003e-gated cation channels, are a type of ligand-activated ion channel. They are also referred to as Acid-sensing ion channels. The ENaC/degenerin channel family DEG includes these channels as a subclass. So far, cloning of four genes yielded the identification of seven ASICs subunits. The ASIC channel consists of functional subunits ASIC1a, ASIC1b, ASIC2a, and ASIC3. The ASIC2 and ASIC4 functional features have not been clarified\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e. The hydrogen ions (H\u003csup\u003e+\u003c/sup\u003e) found outside the cell can stimulate ASICs \u0026ndash; ion channels that allow the flow of ions into the cell. Moreover, changes in the H\u003csup\u003e+\u003c/sup\u003e gradient inside and outside the cell can be detected through these channels\u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e. As a result, it can be described as hydrogen ion receptor. Moreover, it has been shown that non-neural cells, such as osteoblasts, vascular smooth muscle cells and immunological cells can express ASICs\u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e. T cells, for instance, can make ASICs which help coordinate various cellular functions. Furthermore, bone marrow-derived immature dendritic cells (DCs) can sense the pH drop in the acidic microenvironment through the expression of ASICs\u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e. With this detection, it then allows for the DC phagocytosis and the up-regulation of surface major histocompatibility. According to\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e, this mechanism is crucial for the adaptive immune response and immune inflammatory response mediated by dendric cells. The greater inward cation currents in MDSCs observed, as measured in the same MDSCs at various pH levels. Inward cation currents in MDSCs generated from tumor-bearing hosts are much larger and sensitive to pH than those produced from non-tumor-bearing hosts. Is there a link between ASIC expression in MDSCs and their ability to inhibit immunity? Right now, there aren't many academic publications on this topic at the moment.\u003c/p\u003e"},{"header":"2. Results","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1 Detection of ASICs on MDSCs\u003c/h2\u003e\u003cp\u003eThe mRNA expression of ASIC1, ASIC2 and ASIC3 in mouse MDSCs was determined using RT-PCR to evaluate the presence of these ASICs. ASIC1 was found to be 140 bp, ASIC2 139 bp, and ASIC3 was found to be 107 bp. The cortex neurons were seen as a reliable benchmark. MDSCs showed confirmatory mRNA presence for all three ASICs (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eA). At the same time, Western Blotting was carried out to detect the expression level of ASICs in MDSCs (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eB). Expression of ASICs subunits in T-MDSCs (MDSCs derived from tumor-host individuals) was found to be increased with respect to normal IMCs. Literatures state that ASICs expression might be upregulated in MDSCs owing to acidification and inflammatory lesions. To be specific, the expression of ASIC2 in normal IMCs is lower while T-MDSCs have significantly higher expression. Neither normal nor malignant myeloid-derived suppressor cells express TRPV1, the receptor for capsaicin. Other acid channels cannot interfere because they have been removed. Next, the localization of the ASICs in MDSCs was analyzed by immunocytochemistry in order to observe their distribution at the subcellular and cellular levels. The finding suggests that most of ASIC1 and ASIC3 are in membrane and cytoplasm according to our investigation. In the cytoplasm, ASIC 2 was rarely seen, and only a little amount of the protein was found on the cell membrane (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eC).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u0026lt;Insert Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e here\u0026gt;\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e2.2 Changes of ROS levels in myeloid-derived suppressor cells (MDSCs) subjected to changes in pH.\u003c/h2\u003e\u003cp\u003eAccording to the results shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, there was a significant increase in ROS (from an average of 38.85\u0026ndash;55.13%; \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001) in the T-MDSCs released into the medium with normal physiological pH (pH 7.3) relative to the N-MDSCs (MDSCs derived from normal individuals). At an acidic pH of 5.5, with marked negligible levels of ROS production (55.13% data), T-MDSCs produced a substantially higher level of ROS (139.18% data) as against pH of 7.3. The 62.88% found for N-MDSCs (pH 7.3) was reached at about 2.2 times lower growth rate. The addition of amiloride, a nonspecific blocker of ASICs, PcTx1, a specific blocker of ASICs subunit 1, and APETx2, a specific blocker of ASICs subunit 3, in the cell culture system decreased the expression of ROS in T-MDSCs by 69.44% following APETx2 higher than decrease by 86.6% in the potency of PcTx1. According to this, the high expression of ROS might be related to ASIC3 and ASIC1. There was only a slight decrease in the counts of N-MDSCs.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u0026lt;Insert Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e here\u0026gt;\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\u003ch2\u003e2.3 Alterations in the expression of TGF-β1 in MDSCs in response to varying pH conditions\u003c/h2\u003e\u003cp\u003eAs you can see in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, TGF-β1 levels differ when pH medium is different during the derivation of MDSCs. When the pH dropped to 5.5, the production of TGF-β1 in T-MDSCs was much greater than in N-MDSCs. It proposes that the acidity of microenvironment could significantly increase TGF-β1 production in T-MDSCs. We then quantified the TGF-β1 levels present in the supernatant of four different pH mediums (pH7.3, 5.5; normal, tumor), after pretreating with amiloride (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eD), PcTx1, and APETx2 (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eG) as controls. According to recently published findings present in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, a significant reduction of TGF-β1 was observed upon using the following ASICs blocker agents like amiloride (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001), PcTx1 (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05), and APETx2 (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01). It indicates that inhibiting/blocking ASICs in the acidic milieu of T-MDSCs can significantly reduce the release of TGF-β1.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\u003ch2\u003e2.4 Changes in ARG-1 expression of myeloid-derived suppressor cells (MDSCs) at varying pH conditions.\u003c/h2\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eB, E, H display the results. The expression of the ARG-1 gene in the tumor group was higher than in the normal group. This expression occurred in both the physiological environment (pH 7.3) and acidic environment (pH 5.5). Moreover, in the acidic environment tumor group (Mean tumor diameter: 1.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3 cm), the expression of the ARG-1 gene was significantly increased, which means that a slightly acidic environment increased the expression of MDSCs ARG-1 gene. The expression of ARG-1 in the MDSCs cells significantly reduced by adding amiloride before treatment compared to tumor group without amiloride. This is a paraphrase of the original sentence: In the tumor group, it is believed that amiloride inhibits the express of ARG-1. Also, pre-treating MDSCs cells with PcTx1 and APETx2 hindered the activity of ARG-1 in a mildly acidic environment. Under acidic conditions, Activation of MDSCs can occur either through ASIC1 or ASIC3 or both ASIC1 and ASIC3 working together. As a result of such activation, there will be upregulation of ARG-1 leading to an immunosuppressive effect.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\u003ch2\u003e2.5 Alterations in the expression of COX-2 in MDSCs in response to varying pH conditions\u003c/h2\u003e\u003cp\u003eThe tumor group's natural environment had much higher COX-2 expression compared to the normal group, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eC, F, I. Furthermore, at pH 5.5, the expression of COX-2 in the tumor mouse was significantly higher than in normal conditions. The expression of COX-2 get effectively blocked upon adding amiloride. The results showed that ASICs could possibly alter the COX-2 expression of the MDSCs.\u003c/p\u003e\u003cp\u003eThe increase of COX-2 expression results to the opening of ASICs ion channels due to acid stimulation. Blocking ASICs reduces MDSCs\u0026rsquo; COX-2 expression.\u003c/p\u003e\u003cp\u003eTo investigate the involvement of MDSCs COX-2 expression through ASICs, the involvement of subunits in experimental pretreatment with ASICs subunit specific inhibitor PcTx1 and APETx2 was examined. The results indicate that APETx2 can inhibit COX-2 gene expression while PcTx1 does not disrupt this gene expression. This indicates that the expression of the COX-2 gene may be somewhat related to ASIC3. In contrast, there does not appear to be a direct correlation with ASIC1. ASIC3 may affect the COX-2 gene expression in a similar way as ASIC2, according to these results. However, more experiments are needed to confirm these results.\u003c/p\u003e\u003cp\u003e\u0026lt;Insert Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e here\u0026gt;\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003e2.6 The molecular mechanism behind the inhibitory activity of MDSCs in an acidic environment\u003c/h2\u003e\u003cp\u003eDue to the acidification conditions, the MDSCs activation occur through the NF-κB signalling. N-MDSCs and T-MDSCs cells were cultured separately in pH 7.3 and pH 5.5 media for the period of 16 hours. Consequently, the total protein was harvested in order to observe the alteration in the phosphorylation levels of IκB, p65, IKK Proteins of the NF-κB pathway. As illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, expression of p65 was found to increase significantly with decrease in pH. This suggests that the activation of MDSC's NF-κB is encouraged by acidic conditions. In addition, Amiloride treatment inhibited the p-p65, p-IκB, and p-IKK phosphorylation, consequently inhibiting NF-κB activation. According to these results, MDSC activation of NF-κB pathways occurs in acidic environments and this activation closely correlates to ASICs. To find out which ASIC subunits activate this pathway, we used PcTx1 and APETx2 ahead of time. Both PcTx1 and APETx2 are responsible for the phosphorylation of p-p65, pIκB, and pIKK. As a result, this inhibition prevented the NF-κB signaling pathway from being activated. As per this statement, under acidification conditions, activation of NF-κB signaling may occur because of stimulation of ASIC1 and ASIC3. This subsequently leads to MDSCs activation and immunosuppression.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe signalling pathways of STAT1 and STAT6 were involved in the activation of MDSCs during the acidification conditions.\u003c/p\u003e\u003cp\u003eIt can be seen from above that acidification conditions can activate NF-κB signaling pathway in MDSCs through ASICs. Can we find additional signaling pathways that activate MDSCs? N-MDSCs and T-MDSCs were grown sequentially in a medium with pH 7.3 and pH 5.5 for 16 hours. The total protein was then extracted to assess the changes of protein phosphorylation of the pathways of STAT1 and STAT6. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eD displays the results. The levels of phosphorylation of STAT1 and STAT6 in T-MDSCs increase at a pH of 5.5. Before the experiment began, Amiloride, PcTx1 and APETx2 were added, which caused a drop in the level of pSTAT1 and pSTAT6 phosphorylation (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eE, F). This suggests that acidification conditions may activate transcription factors, namely STAT1 and STAT6, via ASIC1 and ASIC3 stimulation, which subsequently mediates MDSCs.\u003c/p\u003e\u003cp\u003eIn general, we propose that the acidic conditions menly or along with each other stimulant ASIC1 and 3 on MDSCs derived from tumor-bearing mice. The stimulation causes ASIC channels to activate and open. This activation leads to the initiation of NF-κB and STAT signaling in MDSCs. Thus, these pathways lead to phosphorylation and assist in other molecules. The NF-κB pathway is activated leading to upregulation of COX-2, ARG-1, ROS and other associated molecules. Release of TGF-β1 is greatly enhanced by the activation of transcription factors STAT1 and STAT6. As a result, MDSCs get activated in quick succession and later in high numbers by the production of a large quantity of inhibitory cytokines. The final outcome is the application of an immunosuppressive effect.\u003c/p\u003e\u003cp\u003e\u0026lt;Insert Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e here\u0026gt;\u003c/p\u003e\u003c/div\u003e"},{"header":"3. Discussion","content":"\u003cp\u003eMDSCs plays important role to regulate immune response in various disease conditions; and, these have become an important part of tumor immunology. Thus, inhibiting the activity of MDSCs is of great physiological and pathological importance for clinical relevance.\u003c/p\u003e\u003cp\u003eLactate accumulation in the tumor microenvironment, termed extracellular acidosis, is common in many clinical settings \u003csup\u003e\u003cspan additionalcitationids=\"CR20\" citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e. The increased production of lactate and acidity of tumor microenvironment (TME) enhances several fundamental carcinogenic process including angiogenesis, tissue invasion/metastasis and treatment response. Lactate, a substance that was previously rejected, is no longer rejected\u003csup\u003e\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u003c/sup\u003e. When there is inflammation, a tumor, a viral infection, or the blood supply to a tissue is cut off, H\u003csup\u003e+\u003c/sup\u003e ions can directly alter the activity of some ion channels (for example ASICs) to help maintain pH balance. As ASICs are cation channels which activated by extracellular protons and have been demonstrated in immune cells (T cells, B cells, macrophages, DCs, and BMMs) in mice. We propose that ASICs may play a role in the response of MDSCs to acidosis by acting as sensors of extracellular acidosis.\u003c/p\u003e\u003cp\u003eTo test this theory, researchers checked for ASICs in mouse MDSCs. As expected, ASIC expression was higher among T-MDSCs than N-MDSCs. ASIC1 and ASIC3 are mainly located in the cytoplasm and not on the cell membrane is neurons, whereas ASIC2 is located on the cell membrane only (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eC).\u003c/p\u003e\u003cp\u003eAccording to earlier studies, several proinflammatory substances are connected with the accumulation and activation of MDSCs in tumour-bearing mice and cancer patients. These include IL-10, IL-6, IL-1β, TGF-β, the bioactive lipid PGE2, S100A8 and C5a. Nonetheless, the research findings on how acidosis affects cytokine secretion are complex. According to the study, a pH of 5.5 activates MDSCs, providing definitive proof. This activation increases inhibitory function by elevating the production and release of ROS (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e), TGF-β1, ARG-1, and COX-2 (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). The addition of the ASIC blocker amiloride attenuated the production of ROS (refer to Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) and TGF-β1, ARG-1, and COX-2 (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eD, E, F). The experiment utilized PcTx1, which is a type of blocker that inhibits ASIC subunit 1; and APETx2, which is a blocker that inhibits ASIC subunit 3. According to the data obtained, PcTx1 and APETx2 suppress the expression of ROS, TGF-β1 and ARG-1. Moreover, down-regulation of COX-2 gene expression by APETx2, but not PcTx1, was observed in the microarray studies. The data show that the expressions of the genes ROS, TGF-β1, and ARG-1 may correlate with ASIC1 and ASIC3. Some studies say that ASIC3 either alone or together with ASIC2 regulates COX-2 gene expression. Yet, more tests are needed to validate this connection. The findings indicate that MDSCs' immunosuppressive ability in tumor mice is markedly potentiated in acidic environment possibly due to acid-induced activation of ASICs.\u003c/p\u003e\u003cp\u003eThe way MDSCs sense outside acidity is not clear yet As demonstrated by our findings that the activation of MDSCs occurs through NF-κB and STAT pathways associated with ASICs via stimulation by extracellular acidity. This is supported by the following evidence: 1. The phosphorylation levels of p65, IκB, and Ikk in tumor MDSCs were much higher when cultured at pH 5.5 (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eA). 2. The activation of STAT was observed in MDSCs from mice with tumors, as indicated by the increased phosphorylation of STAT1 and STAT6. When the amiloride blocker for ASICs was preincubated with MDSCs, the phosphorylation levels of p65, IκB, Ikk, STAT1, and STAT6 returned to the original level (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). Acidic conditions is likely to cause the group of proteins known as NF-kB and a family of cell signaling molecules known as STAT to become phosphoylative. And that is likely to result in activation of T-MDSCs in tumor bearing animals and inhibit immune function. Additionally, ASICs could be used to inhibit the T-MDSCs in the tumor microenvironment. The study's results sub-stantiating findings from various other recent studies: lactic acid in TME limits the immune response to cancer, inhibits immune cell function; and leads to: (1) inhibition of immune cell proliferation and survival\u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e; (2) induction of immune cell dedifferentiation \u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e; (3) activation of downstream signaling pathways \u003csup\u003e\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e. Tumor-bearing mice contain a variety of MDSC subtypes, around 80% which are PMN-MDSCs. These cells primarily exert immune suppression in an antigen-specific manner. The prominent feature of these cells is the induction of T-cell tolerance specific to antigen \u003csup\u003e\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e. The generation of ROS is responsible for inhibiting T-cell responses both against specific antigens and in a non-specific manner. Around a fifth of the M-MDSCs accomplish this by utilizing NO and cytokine production mechanisms. For a comprehensive discussion, refer to reference\u003csup\u003e\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e. Unfortunately, our current study did not classify the MDSCs in tumor-bearing mice nor did we examine expression and localization of ASICs in M-MDSCs and PMN-MDSCs cells. Also we did not consider whether ASICs affect cellular immunosuppression and the mechanisms involved in it.\u003c/p\u003e\u003cp\u003eFactors within the tumor microenvironment may induce the generation of a variety of suppressive cells, including regulatory T lymphocytes (Tregs), tumor-associated macrophages (TAMs), mast cells, type II NKT cells, and MDSCs. These cells help fight against both the natural and the adaptive immunity of the body to the tumor. Among these cells, MDSCs are particularly important due to their contribution to the failure of tumor immunotherapy \u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e. Accordingly, people try to diminish or eliminate the body\u0026rsquo;s immunosuppressive condition through the removal of MDSCs or the inhibition of their functions \u003csup\u003e\u003cspan additionalcitationids=\"CR6\" citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eOur study revealed that the acidic environment has greatly enhanced the expression of the ASICs in MDSCs. The further addition of extracellular H\u003csup\u003e+\u003c/sup\u003e ion prompted protein expression, thus causing influx of Na\u003csup\u003e+\u003c/sup\u003e and/or Ca\u003csup\u003e2+\u003c/sup\u003e ions. This activation of ion channels triggered activation of the NF-κB pathway and/or STAT pathway followed which was manifested in increased expression and secretion of MDSCs inhibitory molecules. The result was increasing the MDSCs immunosuppressive function. The research offers some evidence that an acidic tumor microenvironment can affect the MDSCs. It also explains how this influence occurs at the molecular level. This evidence is important for abolishing immunosuppressive signal transduction pathways and modifying immune effects of MDSCs via inhibiting ASICs. This stops the formation of microenvironments around the tumor and improves the therapy of tumor.\u003c/p\u003e\u003cp\u003eStill, the cells\u0026rsquo; biological function cannot be verified unless techniques to selectively target them are worked out. In order to achieve this task, distinct markers for these cells must be identified. This can be done by a greater understanding of the molecular pathways that control the growth of these cells. Our study reveals the exact molecular process through which low pH in the tumor microenvironment affects MDSCs. In this article, we explore the biological characteristics of MDSCs with relation to ion channels and offer up new therapeutic targets and strategies for cancer prophylaxis and treatment.\u003c/p\u003e"},{"header":"4. Materials and methods","content":"\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\u003ch2\u003e4.1 Cell lines\u003c/h2\u003e\u003cp\u003eH22 liver cancer cell line is derived from type cultured cells from the Chinese Academy of Sciences (Shanghai, China), catalog number TCHu 98. The cultured process of H22 liver cancer cells took place in the use of RPMI 1640 media with a presence of 10% FBS. Also, this cultured media has a presence of both penicillin and streptomycin. The other components of this cultured media are Culture supplement, recombinant human growth factor, and stem cell factor.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\u003ch2\u003e4.2 Tumor inoculations\u003c/h2\u003e\u003cp\u003eWe purchased the BALB/c mice from Hubei Province\u0026rsquo;s (Wuhan, China) Center of Medical Experimental Animals. Mice 6-week to 12-week age-mice were bred and maintained in specific pathogen-free conditions and treated according to South-Central MinZu University (China) Animal Care Guidelines. All animal experiments were conducted in accordance with ARRIVE guidelines. Approval for the animal study was granted by the Ethics Review Committee at South-Central MinZu University (Approval No: SCXK(Liao)2014-0012).\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\u003ch2\u003e\u003cb\u003e4.3 Isolation and purification of MDSC\u003c/b\u003e\u003c/h2\u003e\u003cp\u003eWe obtained spleens, tibias, and femurs from 6\u0026thinsp;~\u0026thinsp;8 week-old tumor-bearing (Mean tumor diameter: 1.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3 cm) or normal mice and washed them twice with Iscove\u0026rsquo;s modified Dulbecco medium. After RBC lysis, bone marrow cells and splenocytes were fractionated by centrifugation on a Percoll (Amersham Biosciences, Uppsala, Sweden) density gradient as described\u003csup\u003e\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/sup\u003e. Cells were harvested from the gradient interfaces that presented between a 50% and 60% density and termed \u0026ldquo;Fraction 2.\u0026rdquo; CD11b\u003csup\u003e+\u003c/sup\u003e/Gr-1\u003csup\u003e+\u003c/sup\u003e cells were extracted from miltenyi biotec (Auburn, CA) macrobeads through MACS magnetic microbeads. The purity of cell separation ranged between 90% and 96%.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e\u003ch2\u003e\u003cb\u003e4.4 Flow cytometry\u003c/b\u003e\u003c/h2\u003e\u003cp\u003eThe cells were treated with the FITC, PE, or allophycocyanin-conjugated mAbs specific for CD3 (145\u0026ndash;2C11), CD11b (M1/70), Gr-1 (RB6\u0026ndash;8C5), CD120a(TNFR1), CD120b(TNFR2), and with isotype controls (rat IgG2a, rat IgG2b, mouse IgG2a, Armenian hamster IgG) from eBioscience (San Diego, CA) or Biolegend (San Diego, CA). Cells were kept in primary antibodies in phosphate buffer saline containing 2% BSA for 30 min at 4\u0026deg;C and washed for twice Data was acquired via a BD Biosciences FACSCanto (MountainView, CA) and analyzed via CellQuest software.\u003c/p\u003e\u003cp\u003eFor 16 hours, MDSCs were isolated from normal and tumor-bearing mice (Mean tumor diameter: 1.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3 cm), respectively, and grown in media with pH levels of 7.3, 6.5, and 5.5 to assess ROS (reactive oxygen species) levels. Following the collection of cells, centrifugation was used to discard the supernatant. DCFH-DA (dilution 1:1000, final concentration \u0026ndash; 10 \u0026micro;mol/L) was subsequently added to the cell concentration of 5 \u0026times; 10\u003csup\u003e6\u003c/sup\u003e cells/mL. The cells were placed in a 5% CO\u003csub\u003e2\u003c/sub\u003e incubator at 37℃ and were inverted and mixed at intervals of 3 to 5 minutes for 20 minutes. Cells were washed three times with serum-free media to remove excess DCFH-DA. Flow cytometry was used to identify ROS content.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec15\" class=\"Section2\"\u003e\u003ch2\u003e4.5 Cytokine Levels Detection by ELISA\u003c/h2\u003e\u003cp\u003eMDSCs collected from tumor-bearing mice were used to assess the levels of mouse TGF-β1 in their supernatant using an ELISA Kit (BD Biosciences) as per the manufacturer\u0026rsquo;s instructions. The Multiscan MC reader measured absorbance at 450 nm, and Delta Soft II software (BioMetallics, Inc.) was used to analyze samples.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec16\" class=\"Section2\"\u003e\u003ch2\u003e4.6 Total protein preparation and Western blot analysis\u003c/h2\u003e\u003cp\u003eCells were solubilized in lysis buffer (150 mM NaCl, 50 mM HEPES, pH 7.4 and 1% Triton X-100) for 1 hr at 4\u0026deg;C with a protease inhibitor cocktail (Calbiochem, SanDiego, CA). Centrifugation at 20,000g for 10 mins at a temperature of 4℃ helps to obtain the cell extract. Samples were mixed with Tris-glycine SDS sample buffer (4\u0026times;) containing 10% 2-ME and boiled at 95℃ for 5 min. Next, 80 \u0026micro;g of soluble protein of each sample was fractionated by 12% SDS-polyacrylamide gel electrophoresis and transferred on to a PVDF membrane. A blocking solution comprising 5% BSA in TBS-Tween-20 or non-fat milk in PBS-Tween-20 (0.05%) was used to block the membrane for 2 h at room temperature. The blots were allowed to incubate overnight at 4\u0026deg;C with the primary antibody (phosphospecific p38 Thr180/182 and phosphospecific JNK G-7, phosphospecific ERK1/2 (Santa Cruz), actin (Biolegend) or TNF-α antibody(R\u0026amp;D), and then follow incubation for 1\u0026thinsp;~\u0026thinsp;2 h with secondary antibody (horseradish peroxidase-conjugated). Immunogenic marginals were affiliated at the chemiluminescence (Amersham Pharmacia ECL or Pierce ECL). Densitometry was carry-out on the resultant autoradiograms. All experiments were performed at least three times. We used EXCEL 5.0 and Student's two-tailed t-test for statistical analysis.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec17\" class=\"Section2\"\u003e\u003ch2\u003e4.7 Reverse transcription-PCR and quantitative real-time PCR\u003c/h2\u003e\u003cp\u003eAs per the manufacturer\u0026rsquo;s instructions, total RNA was extracted in TRIzol reagent (Invitrogen). One-step RT-PCR kit, used for the RT-PCR, was by Qiagen. Thirty PCR cycles were used for all the analyses. The intensity of each amplified DNA band was analyzed using IQ Mac version 1.2 software and quantitatively compared by using Actin as the internal control. Gene Link synthesized the primers for all of the genes we tested, including the internal control Actin: Actin: 5V- TCA CCC ACA CTG TGC CCA TCT ACGA-3V (sense) and CAT CGG AAC CGC TCG TTG CCA ATAG \u0026minus;\u0026thinsp;3V (antisense). ARG-1: 5V- CAG AAG AAT GGA AGA GTC AG -3V (sense) and 5V- CAG ATA TGC AGG GAG TCA CC -3V (antisense). COX-2: 5V- AAT GAG TAC CGC AAA CGC \u0026minus;\u0026thinsp;3V(sense) and 5V- CCA GAA TGG TGC TCC AAG \u0026minus;\u0026thinsp;3V (antisense).\u003c/p\u003e\u003cp\u003ecDNA was subjected to quantitative real-time PCR using 2 \u0026micro;L reverse Real-time PCR Platinum SYBR Green qPCR SuperMix UDG Kit from Invitrogen, and the testing was performed on Rotor gene 3000 system from Corbett Research. The IQ-Cycler (Bio-Rad) analyzed each sample in duplicate, and the normalized signal level was calculated by dividing the sample by the respective actin housekeeping signal. The cycling conditions consisted of 3 minutes at 94\u0026deg;C followed by 30 seconds at 94\u0026deg;C, 40 seconds at 55\u0026deg;C, and 50 seconds at 72\u0026deg;C for a total of 35 cycles. To standardize the total quantity of RNA that is added to each reaction mixture. The internal control gene TC is used to normalized the Ct values of target genes in qPCR. The 2(-Delta Delta C(T)) method method was used to measure the differential expression\u003csup\u003e\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003e\u003cb\u003eStatistical investigation\u003c/b\u003e\u003c/p\u003e\u003cp\u003eStatistical analysis was performed using the SPSS software (Version 18.0). The data was presented as means\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation (SD). Using one-way analysis of variance and Dunnett's several comparisons were made. Statistical significance was the probability (P) value 0.05.\u003c/p\u003e\u003cp\u003eAbbreviation letters: MDSCs, myeloid-derived suppressor cells; T-MDSCs, tumor-bearing mice-derived myeloid-derived suppressor cells; N-MDSCs, myeloid-derived suppressor cells obtained from normal sources; ASICs, acid-sensing ion channels; TME, tumor microenvironment; IL-1β, Interleukin-1β; IL-8, Interleukin-8; iNOS, Inducible nitric oxide synthase; LPS, Lipopolysaccharides; NF-κB, Nuclear factor-kappa B; ROS, Reactive oxygen species; TNF-α, Tumor necrosis factor-α; IFN-γ, interferon-gamma; TGF-β1, transforming growth factor-beta 1; IL-10, interleukin-10; IL-12, interleukin-12.\u003c/p\u003e\u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study would not have been complete without the valuable assistance received from HUST(Huazhong University of Science and Technology,WuHan, China) Professor Zhuo-ya Li, Professor Bin-jiao Yin, and Professor Jing Wang in interpreting the significance of our results and in constructive discussions.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding Statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors also thank the support of the Fundamental Research Funds for the Central Universities, South-Central MinZu University (Grant No. CZY17014) and Natural Science Foundation of\u0026nbsp;HuBei Province of China (Grant No. 2023AFB681).\u0026nbsp;This work was also supported by\u0026nbsp;the\u0026nbsp;Young Scientists Fund of the National Natural Science Foundation of China (Grant No. 81201610)\u0026nbsp;\u0026nbsp;and\u0026nbsp;the\u0026nbsp;Fund\u0026nbsp;for\u0026nbsp;Academic\u0026nbsp;Innovation\u0026nbsp;Teams\u0026nbsp;of\u0026nbsp;South-Central MinZu University (Grant\u0026nbsp;No.\u0026nbsp;XTZ24025).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors of this article will provide the raw data that supports its conclusions without giving any undue reservation.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe Animal Ethics Committee of South-Central Minzu University approved this experiment according to License Number SCXK(Liao)2014-0012. All mice were housed in a specific pathogen-free (SPF) facility in the Experimental Animal Centre. Our procedures for handling animals conformed to the requirements of the Committee and the Guidelines of the National Institutes of Health (NIH).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe examination was designed by Hui-Hong Gong, Xin Hu. Ping Yi , Shenglan Tong and\u0026nbsp;Hui Yao\u0026nbsp;performed the experiments. Xin Hu, WenLong Zhang, JinHong Liu ,\u0026nbsp;YiRong Hu\u0026nbsp;and\u0026nbsp;Hui-Hong Gong analyzed the data. Xin Hu, Shenglan Tong wrote the manuscript. All authors have read and approved the final manuscript before submitting.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of interest statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that there are no conflicts of interest.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eGenerative AI statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors affirm that generative AI played no role in developing this manuscript.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eYoun, J. I., Nagaraj, S., Collazo, M. \u0026amp; Gabrilovich, D. I. Subsets of myeloid-derived suppressor cells in tumor-bearing mice. \u003cem\u003eJ Immunol\u003c/em\u003e. 15;181(8):5791\u0026thinsp;\u0026ndash;\u0026thinsp;802. (2008). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.4049/jimmunol.181.8.5791\u003c/span\u003e\u003cspan address=\"10.4049/jimmunol.181.8.5791\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eOstrand-Rosenberg, S. \u0026amp; Sinha, P. Myeloid-derived suppressor cells: linking inflammation and cancer. \u003cem\u003eJ Immunol\u003c/em\u003e. 15;182(8):4499\u0026thinsp;\u0026ndash;\u0026thinsp;506. (2009). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.4049/jimmunol.0802740\u003c/span\u003e\u003cspan address=\"10.4049/jimmunol.0802740\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eCheng, P. et al. Inhibition of dendritic cell differentiation and accumulation of myeloid-derived suppressor cells in cancer is regulated by S100A9 protein. \u003cem\u003eJ. Exp. Med.\u003c/em\u003e \u003cb\u003e29\u003c/b\u003e (10), 2235\u0026ndash;2249. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1084/jem.20080132\u003c/span\u003e\u003cspan address=\"10.1084/jem.20080132\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2008).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eGabrilovich, D. I. \u0026amp; Nagaraj, S. Myeloid-derived suppressor cells as regulators of the immune system. \u003cem\u003eNat. Rev. Immunol.\u003c/em\u003e \u003cb\u003e9\u003c/b\u003e (3), 162\u0026ndash;174. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1038/nri2506\u003c/span\u003e\u003cspan address=\"10.1038/nri2506\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2009).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBronte, V. et al. IL-4-induced arginase 1 suppresses alloreactive T cells in tumor-bearing mice. \u003cem\u003eJ Immunol\u003c/em\u003e. 1;170(1):270-8. (2003). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.4049/jimmunol.170.1.270\u003c/span\u003e\u003cspan address=\"10.4049/jimmunol.170.1.270\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eKusmartsev, S., Nefedova, Y., Yoder, D. \u0026amp; Gabrilovich, D. I. Antigen-specific inhibition of CD8\u0026thinsp;+\u0026thinsp;T cell response by immature myeloid cells in cancer is mediated by reactive oxygen species. \u003cem\u003eJ. Immunol.\u003c/em\u003e \u003cb\u003e15\u003c/b\u003e (2), 989\u0026ndash;999. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.4049/jimmunol.172.2.989\u003c/span\u003e\u003cspan address=\"10.4049/jimmunol.172.2.989\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2004).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eSinha, P., Clements, V. K., Fulton, A. M. \u0026amp; Ostrand-Rosenberg, S. Prostaglandin E2 promotes tumor progression by inducing myeloid-derived suppressor cells. \u003cem\u003eCancer Res\u003c/em\u003e. 1;67(9):4507-13. (2007). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1158/0008-5472.CAN-06-4174\u003c/span\u003e\u003cspan address=\"10.1158/0008-5472.CAN-06-4174\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eJedlička, M., Feglarova, T. \u0026amp; Janstova, L. Lactate from the tumor microenvironment-A key obstacle in NK cell-based immunotherapies. \u003cem\u003eFRONT. IMMUNO\u003c/em\u003e. \u003cb\u003e13\u003c/b\u003e, 932055 (2022).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003ePalmieri, E. M., McGinity, C., Wink, D. A. \u0026amp; McVicar, D. W. Nitric Oxide in Macrophage Immunometabolism: Hiding in Plain Sight. \u003cem\u003eMetabolites\u003c/em\u003e. 26;10(11):429. (2020). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.3390/metabo10110429\u003c/span\u003e\u003cspan address=\"10.3390/metabo10110429\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eWang, J. X. et al. Lactic Acid and an Acidic Tumor Microenvironment suppress Anticancer Immunity. \u003cem\u003eInt. J. Mol. Sci.\u003c/em\u003e \u003cb\u003e7\u003c/b\u003e (21), 8363. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.3390/ijms21218363\u003c/span\u003e\u003cspan address=\"10.3390/ijms21218363\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2020).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eCerto, M. et al. Lactate modulation of immune responses in inflammatory versus tumour microenvironments. \u003cem\u003eNat. Rev. Immunol.\u003c/em\u003e \u003cb\u003e21\u003c/b\u003e, 151\u0026ndash;161. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003edoi.org/10.1038/s41577-020-0406-2\u003c/span\u003e\u003cspan address=\"10.1038/s41577-020-0406-2\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2021).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eDietl, K. et al. Lactic acid and acidification inhibit TNF secretion and glycolysis of human monocytes. \u003cem\u003eJ Immunol\u003c/em\u003e. 1;184(3):1200-9. (2010). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.4049/jimmunol.0902584\u003c/span\u003e\u003cspan address=\"10.4049/jimmunol.0902584\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eImmler, R., Simon, S. I. \u0026amp; Sperandio, M. Calcium signalling and related ion channels in neutrophil recruitment and function. \u003cem\u003eEur. J. Clin. Invest.\u003c/em\u003e \u003cb\u003e48\u003c/b\u003e (Suppl 2), e12964. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1111/eci.12964\u003c/span\u003e\u003cspan address=\"10.1111/eci.12964\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2018).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eRuan, N. et al. Acid-Sensing Ion Channels and Mechanosensation. \u003cem\u003eInt. J. Mol. Sci.\u003c/em\u003e \u003cb\u003e1\u003c/b\u003e (9), 4810. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.3390/ijms22094810\u003c/span\u003e\u003cspan address=\"10.3390/ijms22094810\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2021).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHolzer, P. et al. Acid-sensitive ion channels and receptors. \u003cem\u003eHandb Exp Pharmac\u003c/em\u003eol. (194): pp. 283\u0026ndash;332 (2009).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eFoster, V. S., Rash, L. D., King, G. F. \u0026amp; Rank, M. M. Acid-Sensing Ion Channels: Expression and Function in Resident and Infiltrating Immune Cells in the Central Nervous System. \u003cem\u003eFront. Cell. Neurosci.\u003c/em\u003e \u003cb\u003e17\u003c/b\u003e, 15:738043. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.3389/fncel.2021.738043\u003c/span\u003e\u003cspan address=\"10.3389/fncel.2021.738043\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2021).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eLeblanc-Hotte, A. et al. Immature and mature bone marrow-derived dendritic cells exhibit distinct intracellular mechanical properties. \u003cem\u003eSci Rep\u003c/em\u003e. 3;13(1):1967. (2023). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1038/s41598-023-28625-w\u003c/span\u003e\u003cspan address=\"10.1038/s41598-023-28625-w\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eKong, X. et al. Extracellular acidosis modulates the endocytosis and maturation of macrophages. \u003cem\u003eCell. Immunol.\u003c/em\u003e \u003cb\u003e281\u003c/b\u003e (1), 44\u0026ndash;50. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.cellimm.2012.12.009\u003c/span\u003e\u003cspan address=\"10.1016/j.cellimm.2012.12.009\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2013).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eDe Milito, A. et al. pH-dependent antitumor activity of proton pump inhibitors against human melanoma is mediated by inhibition of tumor acidity. \u003cem\u003eInt J Cancer\u003c/em\u003e. 1;127(1):207\u0026thinsp;\u0026ndash;\u0026thinsp;19. (2010). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1002/ijc.25009\u003c/span\u003e\u003cspan address=\"10.1002/ijc.25009\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eFukumura, D. \u0026amp; Jain, R. K. Tumor microenvironment abnormalities: causes, consequences, and strategies to normalize. \u003cem\u003eJ Cell Biochem\u003c/em\u003e. 1;101(4):937\u0026thinsp;\u0026ndash;\u0026thinsp;49. (2007). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1002/jcb.21187\u003c/span\u003e\u003cspan address=\"10.1002/jcb.21187\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHelmlinger, G., Yuan, F., Dellian, M. \u0026amp; Jain, R. K. Interstitial pH and pO2 gradients in solid tumors in vivo: high-resolution measurements reveal a lack of correlation. \u003cem\u003eNat. Med.\u003c/em\u003e \u003cb\u003e3\u003c/b\u003e (2), 177\u0026ndash;182. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1038/nm0297-177\u003c/span\u003e\u003cspan address=\"10.1038/nm0297-177\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (1997).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHuber, V. et al. Cancer acidity: An ultimate frontier of tumor immune escape and a novel target of immunomodulation. \u003cem\u003eSemin Cancer Biol.\u003c/em\u003e \u003cb\u003e43\u003c/b\u003e, 74\u0026ndash;89. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.semcancer.2017.03.001\u003c/span\u003e\u003cspan address=\"10.1016/j.semcancer.2017.03.001\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2017).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eZhang, D. et al. Metabolic regulation of gene expression by histone lactylation. \u003cem\u003eNature\u003c/em\u003e \u003cb\u003e574\u003c/b\u003e, 575\u0026ndash;580. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003edoi.org/10.1038/s41586-019-1678-1(\u003c/span\u003e\u003cspan address=\"10.1038/s41586-019-1678-1(\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2019).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eChoi, S. Y., Collins, C. C., Gout, P. W. \u0026amp; Wang, Y. Cancer-generated lactic acid: a regulatory, immunosuppressive metabolite? \u003cem\u003eJ. Pathol.\u003c/em\u003e \u003cb\u003e230\u003c/b\u003e (4), 350\u0026ndash;355. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1002/path.4218\u003c/span\u003e\u003cspan address=\"10.1002/path.4218\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2013).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eFeichtinger, R. G. \u0026amp; Lang, R. Targeting L-Lactate Metabolism to Overcome Resistance to Immune Therapy of Melanoma and Other Tumor Entities. \u003cem\u003eJ Oncol\u003c/em\u003e. 3;2019:2084195. (2019). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1155/2019/2084195\u003c/span\u003e\u003cspan address=\"10.1155/2019/2084195\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eKoehn, B. H. et al. GVHD-associated, inflammasome-mediated loss of function in adoptively transferred myeloid-derived suppressor cells. \u003cem\u003eBlood\u003c/em\u003e. 24;126(13):1621-8. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1182/blood-2015-03-634691(2015\u003c/span\u003e\u003cspan address=\"10.1182/blood-2015-03-634691(2015\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMarigo, I. et al. Tumor-induced tolerance and immune suppression depend on the C/EBPbeta transcription factor. \u003cem\u003eImmunity\u003c/em\u003e \u003cb\u003e25\u003c/b\u003e (6), 790\u0026ndash;802. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.immuni.2010.05.010\u003c/span\u003e\u003cspan address=\"10.1016/j.immuni.2010.05.010\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2010).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eGabrilovich, D. I., Ostrand-Rosenberg, S. \u0026amp; Bronte, V. Coordinated regulation of myeloid cells by tumours. \u003cem\u003eNat Rev Immunol\u003c/em\u003e. 22;12(4):253\u0026thinsp;\u0026ndash;\u0026thinsp;68. (2012). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1038/nri3175\u003c/span\u003e\u003cspan address=\"10.1038/nri3175\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eSui, H. et al. Immunotherapy of targeting MDSCs in tumor microenvironment. \u003cem\u003eFront. Immunol.\u003c/em\u003e \u003cb\u003e5\u003c/b\u003e, 13:990463. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.3389/fimmu.2022.990463\u003c/span\u003e\u003cspan address=\"10.3389/fimmu.2022.990463\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2022).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003ePan, P. Y. et al. Reversion of immune tolerance in advanced malignancy: modulation of myeloid-derived suppressor cell development by blockade of stem-cell factor function. \u003cem\u003eBlood\u003c/em\u003e. 1;111(1):219\u0026thinsp;\u0026ndash;\u0026thinsp;28. (2008). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1182/blood-2007-04-086835\u003c/span\u003e\u003cspan address=\"10.1182/blood-2007-04-086835\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eRao, X., Huang, X., Zhou, Z. \u0026amp; Lin, X. An improvement of the 2ˆ(-delta delta CT) method for quantitative real-time polymerase chain reaction data analysis. \u003cem\u003eBiostat Bioinforma Biomath\u003c/em\u003e. \u003cb\u003e3\u003c/b\u003e (3), 71\u0026ndash;85 (2013).\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"MDSCs, ASICs, immunosuppressive activity, TME, acidity","lastPublishedDoi":"10.21203/rs.3.rs-7337447/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7337447/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eA common feature of solid tumors is tumor microenvironment acidification. The acidification triggers immunosuppressive mechanisms that enhance cancer cell survival and growth and facilitate tumor progression. MDSCs (Myeloid-derived suppressor cells) are activated by these mechanisms. Acid-sensing ion channels (ASICs) mainly help to acidify the microenvironment. It's unclear how acidification triggers the activation of MDSCs through ASICs. Research into the mechanisms has demonstrated that MDSCs produce numerous immunosuppressive substances and cytokines through the use of ASICs multiple subunits. The NF-κB and STAT signaling pathways are the main activators of these subunits. Findings of this study suggest that ASICs are implicated in the effect of acidosis on the function of MDSCs in TME.\u003c/p\u003e","manuscriptTitle":"The acidity of the tumor microenvironment enhances the immunosuppressive role of MDSCs via activating ASICs","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-09-02 13:24:51","doi":"10.21203/rs.3.rs-7337447/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"689056f1-5ab6-4112-8f2c-38efaceb7f1f","owner":[],"postedDate":"September 2nd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":53993154,"name":"Biological sciences/Cancer"},{"id":53993155,"name":"Biological sciences/Cell biology"}],"tags":[],"updatedAt":"2025-09-22T05:23:39+00:00","versionOfRecord":[],"versionCreatedAt":"2025-09-02 13:24:51","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7337447","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7337447","identity":"rs-7337447","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}