Anabolic and catabolic responses to different modes of exercise in patients with chronic kidney disease

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Exercise is recommended, but the molecular responses of skeletal muscle to different exercise modalities remain unclear. This study examined anabolic, catabolic, and myogenic responses to aerobic exercise (AE) versus combined exercise (CE; aerobic plus resistance) in CKD. Methods: Muscle biopsies were collected from participants in a 12-week randomized controlled trial (the ExTra CKD trial) at baseline, 24 hours after initial exercise bout (untrained), and 24 hours after the final session (trained). Western blotting and RT-qPCR assessed markers of protein synthesis, degradation, and regeneration. Complementary in vitro experiments used mechanically stretched primary skeletal muscle cells from CKD patients and healthy controls to investigate the temporal dynamics of anabolic signalling. Results AE did not alter Akt phosphorylation. CE showed no acute effect before training but significantly increased Akt phosphorylation after training, indicating partial restoration of anabolic signalling. CE also upregulated myogenic markers (Pax7, MyoD) and reduced acute catabolic responses, whereas AE effects were minimal. Myostatin was downregulated by AE at both time points, while CE shifted from suppression before training to elevation afterwards. Conclusion: CE, but not AE alone, elicits beneficial anabolic and myogenic adaptations in skeletal in CKD. Combining in vivo and in vitro approaches offers deeper mechanistic insight into exercise-induced molecular adaptations and highlights the importance of including resistance training to overcome anabolic resistance in this population. Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction Chronic kidney disease (CKD) is a global public health emergency with an estimated prevalence of 9.1% [ 1 ]. A common complication at all stages of CKD is muscle wasting, which contributes to reduced physical function independent of age [ 2 ]. This loss of muscle is associated with poor clinical outcomes; for example, diagnosed sarcopenia has been shown to increase the risk of all-cause mortality threefold [ 3 ]. Furthermore, individuals with CKD exhibit high levels of physical inactivity [ 4 ], which is also an independent risk factor for mortality [ 5 ]. Although regular physical activity is strongly recommended for individuals with CKD, and formal exercise guidelines have recently been published for this population [ 6 ], structured exercise programmes remain underutilised. To maximise the benefits of exercise training, it is crucial to understand the underlying molecular mechanisms, particularly how different types of exercise affect skeletal muscle homeostasis. This knowledge could guide the development of adjunctive strategies, such as targeted nutritional or pharmacological interventions. While a few studies have begun to explore this area in humans [ 7 – 9 ], a comprehensive understanding of these mechanisms in the CKD population remains limited. Skeletal muscle mass is maintained by a dynamic balance between protein synthesis and degradation. Anabolic signalling through the Akt/mTOR pathway plays a central role in promoting muscle protein synthesis, while catabolic pathways, including the ubiquitin–proteasome system and myostatin signalling, regulate protein breakdown. In CKD, this balance is often disturbed, exacerbated by systemic factors such as insulin resistance, inflammation, and metabolic acidosis [ 10 – 12 ]. Impairments in anabolic signalling, particularly the reduced phosphorylation of Akt and downstream targets, have been observed in animal models of CKD and are associated with muscle atrophy and impaired regeneration. While resistance exercise is known to activate these anabolic pathways in healthy individuals, the extent to which this occurs in those with CKD remains under investigation. Our previous work has shown that in CKD, the expected anabolic and mitochondrial responses to resistance exercise may be blunted, consistent with the concept of “anabolic resistance” [ 7 , 9 ]. Specifically, we observed attenuated activation of the insulin signalling pathway and limited upregulation of myogenic markers in patients with CKD after a single bout of resistance exercise. However, some of these blunted responses appeared to normalise following a period of training, a finding that has yet to be replicated. Building on this previous work, the aim of this study was to investigate the acute anabolic and catabolic responses of skeletal muscle to aerobic versus combined exercise in individuals with CKD, comparing these responses before and after a structured training period. To achieve this, we used muscle biopsies collected from the previously published ExTra CKD randomised controlled trial [ 13 ]. In addition to analysing these in vivo responses, we used an in vitro stretch model to better understand the temporal dynamics of exercise-induced molecular signalling in primary skeletal muscle cells from CKD and healthy donors. Together, these complementary approaches provide a comprehensive view of how skeletal muscle in CKD responds to exercise and highlight important considerations for optimising interventions aimed at improving muscle health in this vulnerable population. Materials and methods This study is a secondary analysis of the previously reported ExTra CKD randomised controlled trial [ 13 ] and includes complementary in vitro investigations using primary cells obtained from participants in the Explore CKD study. The ExTra CKD trial In brief, 54 non-dialysis patients with CKD stages 3b–5 were enrolled in a 12-week, thrice-weekly supervised exercise intervention and randomised to either combined exercise (CE) or aerobic exercise (AE) alone. Participant characteristics are shown in Table 1 . Each participant served as their own control during a six-week run-in period prior to randomisation. The AE intervention consisted of circuit-based aerobic activities such as treadmill walking or running, cycling, and rowing. The CE group undertook the same aerobic training, with the addition of resistance exercises performed during two of the three weekly sessions. Participants aimed to complete 30 minutes of moderate-intensity aerobic exercise at 70–80% of their maximum heart rate, which was determined by a maximal exercise tolerance test. For the resistance component, participants performed 3 sets of 12–15 repetitions of leg extensions at 70% of their estimated one-repetition maximum, which was determined from a five-repetition maximum test. Table 1 Participant characteristics Aerobic Exercise (n = 10) Combined Exercise (n = 9) Age (years) 65 ± 8 59 ± 18 Gender ( n men/women) 4/6 3/6 Ethnicity White British n = 9 Black Caribbean n = 1 White British n = 8 South Asian n = 1 eGFR (ml/min/1.73m 2 ) 27 ± 9 27 ± 6 Serum Bicarbonate (mmol/l) 25 ± 6 26 ± 5 BMI (kg/m 2 ) 30 ± 6 30 ± 5 Creatinine (µmol/L) 209 ± 75 218 ± 69 Urea (mmol/L) 12 ± 4 13 ± 5 Abbreviations: BMI, body mass index; eGFR, estimated glomerular filtration rate. Data are mean ± SD. A subset of participants (AE, n = 10; CE, n = 9) consented to skeletal muscle biopsies of the vastus lateralis using a needle biopsy technique previously described [ 9 ]. Samples were collected in a fasted state at three time points: baseline, 24 hours after the first training session (untrained), and 24 hours after the final session (trained). Following the removal of visible adipose tissue, biopsies were snap-frozen in liquid nitrogen and stored for later analysis. The Explore CKD Study A single lower leg skeletal muscle biopsy was obtained from six individuals with CKD and eight age- and sex-matched non-CKD controls as part of the Explore CKD study (participant characteristics are detailed in Table 2 ). CKD participants were recruited from outpatient clinics at Leicester General Hospital, UK, between 1st January 2016 and 2nd November 2020. Healthy controls (HC) with no significant medical history were recruited from orthopaedic theatre lists during procedures for benign tumour removal. Muscle biopsies from CKD participants were collected using the needle biopsy technique, while control muscle biopsies were obtained via the open biopsy technique. Table 2 Skeletal muscle biopsy donors for primary cell culture establishment Healthy Controls (n = 8) CKD Patients (n = 6) Age (years) 61 ± 14 63 ± 6 Gender ( n men/women) 4/4 2/3 Ethnicity White British n = 8 White British n = 6 eGFR (ml/min/1.73m 2 ) 25.0 ± 4.7 82.0 ± 9.9 Abbreviations: eGFR, estimated glomerular filtration rate. Data are mean ± SD. Molecular biology techniques Western Blotting Approximately 15–20 mg of wet weight muscle tissue was homogenised in 18µL/mg RIPA buffer (Sigma, UK) supplemented with 1% (v/v) phosphatase inhibitor-3 (Sigma Aldrich, UK). Samples were rotated for 90 min at 4°C and centrifuged at 13,000 rpm for 15 min at 4°C. The supernatant was collected, and protein concentration determined using the Bio-Rad Protein Assay (BioRad, UK,). The pellet was retained for 14-kDa actin fragment analysis [ 14 ]. Lysates were subjected to SDS-PAGE using 10–12% gels on a mini-PROTEAN Tetra system (Bio-Rad, UK). Proteins were transferred onto nitrocellulose membranes and blocked for 1h with Tris-buffered saline with 5% (w/v) skimmed milk and 0.1% (v/v) Tween-20. Membranes were incubated overnight with the primary antibodies against p-Akt (Ser 473 ; 1:2,000; Cell Signalling Technologies, USA) and p-p70S6K (Thr 389 ; 1:500; Cell Signalling Technologies, USA). For 14kDa fragment analysis, an AC-40 Actin clone antibody (1:500; Sigma Aldrich, UK) was used. This antibody also recognises the 42-kDa fragment, which served as a loading control with a shorter exposure time. For all other proteins, GAPDH was used as a loading control. Horseradish Peroxidase (HRP)-linked anti-mouse/rabbit secondary antibodies (Dako, Aglient, UK) were used at 1:1500 for 2h at room temperature. Blots were visualised using ECL Reagents (Geneflow, UK) and captured using a ChemiDoc MP imager (Bio-Rad). Quantitative RT-PCR Total RNA was isolated from 15–20 mg of muscle tissue using TRIzol® (Invitrogen, UK) and reversed transcribed to cDNA using an AMV reverse transcription system (Promega, WI, USA). Primers and probes and internal controls were supplied as TaqMan gene expression assays (Applied Biosystems, UK) were used for the following targets: MAFbx (Hs00369714_m1), MuRF-1 (Hs00822397_m1), Myostatin (Hs00976237_m1), Activin Receptor IIB, (Hs00155658_m1), Myogenin (Hs01072232_m1), MyoD (Hs02330075_g1), Myf5 (Hs00929416), Pax7 (Hs00242962), and 18S (Hs99999901) which served as the housekeeping gene with a coefficient of variation of 2.18%. All reactions were performed in a 20µL- volume containing 1µL cDNA, 10µL 2X Taqman Fast Mastermix, 8µL nuclease-free water, and 1µL primer/probe assay on an Applied Biosystem’s QuantStudio 3 instrument with the following conditions: 95°C 15 s, followed by 40 cycles at 95°C for 15 s and at 60°C for 1 min. Target gene Ct values were normalised to the 18S house-keeping gene, and relative expression levels were calculated using the 2 −ΔΔCt method. Satellite cell isolation procedure Satellite cells were isolated and propagated as previously described [ 15 ]. Briefly, muscle tissue was washed three times in HamsF10 (containing 1% penicillin streptomycin and 1% Gentamycin), minced into small fragments, and enzymatically digested in two incubations with collagenase IV (1mg/mL), BSA (5mg/mL) and trypsin (500µl/mL) at 37°C with gentle agitation. The resultant supernatant was strained through a 70µm nylon filter and centrifuged at 800 g for 7 mins. The cells were washed in Hams F10 with 1% penicillin-streptomycin and pre-plated on uncoated 9cm2 petri dishes in 3mL growth medium (GM; Hams F10 Glutamax, 20% FBS, 1% penicillin streptomycin, 1% fungazone) for 3h. The cell suspension was then moved to collagen I coated 25 cm2 flasks and kept in standard culture environmental conditions (37°C, 5% CO2). For the expansion of satellite cell populations, cells were grown to approximately 70% confluence in GM that was changed every other day. Cells were subsequently trypsinised (Sigma-Aldrich, UK) and counted using the trypan blue exclusion method. Cell Culture and in Vitro Mechanical Stretch Myoblasts were seeded on 6-well Flexcell culture plates, and cyclic multiaxial stretch applied using a Flexcell Fx3000 system set to 2 second sine wave stretch with 4 second release resulting in an 18% maximum stretch for 30 minutes at 37°C. Cells were harvested in 200µl lysis buffer/well RIPA buffer (Sigma, UK) supplemented with 1% v/v phosphatase inhibitor-3 (Sigma Aldrich, UK) prior to stretch, immediately post and at 1,3,7 and 24h post stretch. Protein concentration was determined by the Bio-Rad Protein Assay, and resulting lysates were stored for subsequent western blotting analysis. Availability of data The datasets supporting the conclusions of this article are available in the University of Leicester Figshare repository (Watson, Emma (2025). ExTra CKD Biopsy Analysis. University of Leicester. Dataset. https://figshare.le.ac.uk/articles/dataset/_/30665759 Statistics Data distribution was assessed using the Shapiro-Wilks test. Non-normally distributed variables were log-transformed for analysis and back-transformed for presentation. A primary analysis was performed for each variable using a repeated measures ANOVA to assess the effects of time point (baseline, untrained, trained) and group allocation (AE vs. CE). In addition, paired t-tests were performed to compare specific time points (baseline vs. untrained, baseline vs. trained, and untrained vs. trained) for both AE and CE groups, expressed as mean change (90% CIs). Magnitude-based inferences were used to estimate the mean effects between AE and CE groups. Results Participant characteristics Participant characteristics for the ExTra CKD and Explore CKD studies are presented in Tables 1 and 2 , respectively. Baseline characteristics were well-matched between the exercise groups (AE vs. CE) in the ExTRA CKD trial (Table 1 ) and between the donor groups (CKD vs. HC) in the Explore CKD study (Table 2 ). The anabolic response to exercise in CKD Changes in phosphorylation of Akt and p70S6K are shown in Fig. 1 . Akt phosphorylation is well documented to increase in the hours following exercise, and is a key contributor to the anabolic response to exercise [ 16 ]. In this study, no significant change in Akt phosphorylation was observed at any time point following AE. Similarly, a single bout of CE in the untrained state did not significantly alter Akt phosphorylation from baseline (P = 0.48, Fig. 1 A-D). However, after 12 weeks of CE training, the same exercise stimulus elicited a significant 118% increase in Akt phosphorylation from baseline (P = 0.02), a response that was also significantly greater than that observed in the untrained state (P = 0.02). In contrast, p70S6K phosphorylation was not significantly changed by an acute bout of AE or CE in either the untrained or trained state (Fig. 1 E-H). The catabolic response to exercise in CKD Changes in the 14-kDa actin fragment, a biomarker of skeletal muscle catabolism [ 14 ], are shown in Fig. 2 . The abundance of the 14 kDa fragment remained unchanged at all time points following AE. In contrast, an acute bout of CE in the untrained state resulted in a 253% increase in the 14-kDa fragment relative to baseline (P = 0.04). This response was abrogated after 12 weeks of CE training, with fragment levels returning to baseline (P = 0.68 vs baseline). MuRF-1 and MAFbx are two muscle-specific E3 ligases, commonly used as markers of ubiquitin-proteasome system activity [ 17 ]. A repeated measures ANOVA revealed no effect of acute AE or CE on MuRF-1 mRNA expression (P = 0.46; Fig. 3 ) or MAFbx mRNA expression (P = 0.70; Fig. 3 ). In contrast, the mRNA expression of myostatin, a potent negative regulator of muscle mass [ 18 ], was downregulated from baseline following an acute bout of AE in both the untrained (1.5-fold reduction; P = 0.01; Fig. 3 ) and trained (1.2-fold reduction; P = 0.04) states. In response to CE in the untrained state, myostatin mRNA expression decreased five-fold (P = 0.003). After training, however, the response to CE was reversed, with myostatin mRNA expression being elevated compared to the response in the untrained state (P = 0.007; Fig. 3 ). No changes were observed for the expression of the myostatin receptor, ActIIRB in any condition (P > 0.05; Fig. 3 ). The myogenic response to exercise in CKD The mRNA expression of myogenic regulatory factors (Pax7, MyoD, Myogenin and Myf5), which coordinate muscle repair [ 19 ] are shown in Fig. 4 . No changes in the mRNA expression of any of these factors were observed following AE (P > 0.05). Similarly, there were no changes in Myogenin or Myf5 expression following CE at any time point (P > 0.05). In the untrained state, an acute bout of CE induced a near-significant two-fold decrease in MyoD mRNA expression (P = 0.05); this response was reversed following training, resulting in a significant increase compared to the untrained condition (P = 0.01). Finally, Pax7 mRNA expression in response to CE was greater in the trained state compared to the untrained state (P = 0.025). In Vitro anabolic signalling response to mechanical stretch To examine the temporal dynamics of anabolic signalling, primary myoblasts from CKD and HC donors were subjected to mechanical stretch in vitro . Mechanical stretch induced a significant increase in Akt phosphorylation relative to baseline in both groups immediately post-stretch (CKD: +5651%, P = 0.012; HC: +3437%, P = 0.028; Fig. 5 A–D). This elevation persisted at 1- hour post-stretch (CKD: +61%, P = 0.012; HC: +1472%, P = 0.028). At 3- hours post-stretch, Akt phosphorylation remained elevated in the HC group (+ 388%, P = 0.046) but had returned to baseline in the CKD group (P = 0.31). By 7- and 24-hours post-stretch, phosphorylation levels had returned to baseline in both groups (Fig. 5 A). A repeated measures ANOVA revealed no significant interaction effect, indicating the overall response to stretch did not differ between groups (P = 0.84). A similar phosphorylation pattern was observed for p70S6K (Fig. 5 D-F). p70S6K phosphorylation significantly increased from baseline immediately post-stretch in both groups (CKD: +1076%, P = 0.014; HC + 712%, P = 0.038). In CKD cells, this elevation persisted at 1- hour (+ 306%, P = 0.047) and 7- hours post-stretch (+ 219%, P = 0.004), with a strong trend toward an increase at 3 hours (+ 185%, P = 0.052). In contrast, no further time points showed significant increases from baseline in the HC group. The repeated measures ANOVA showed a trend toward a significant interaction that was not statistically significant (P = 0.052), indicating broadly similar responses to the stretch regime between the two groups. Discussion This study offers new insights into the molecular responses to aerobic versus combined exercise in individuals with CKD, while also supporting our previous findings in a different cohort and exercise modality [ 9 ]. Here we showed the combined aerobic and resistance exercise, but not aerobic exercise alone, elicits beneficial molecular adaptations in skeletal muscle of individuals with CKD. Following 12-weeks of CE participants exhibited a significant restoration of anabolic signalling in response to exercise through increased Akt phosphorylation, activation of myogenic markers and attenuation of acute catabolic responses. Complementary in vitro stretch experiments demonstrated that skeletal muscle cells from people with CKD are capable of mounting anabolic responses, although these were more transient than those observed in healthy controls. Evidence suggests that individuals with CKD do not always exhibit the expected physiological adaptations to exercise. For instance, several studies have reported that aerobic training does not consistently lead to increases in VO₂ peak in patients with CKD [ 20 – 22 ], a finding linked to a blunted activation of mitochondrial biogenesis pathways [ 7 ]. Additionally, it was previously reported that after a single bout of resistance exercise, the expected activation of the insulin signalling pathway was largely absent, but this response was restored after a training period [ 9 ] – a finding we have replicated here. A clear understanding of the molecular responses that underpin these adaptations to exercise is crucial for designing adjunct therapies that maximise the benefits of exercise for patients with CKD. Skeletal muscle homeostasis is maintained through a finely regulated balance between protein synthesis and protein degradation. In CKD, this balance is often disrupted by factors like insulin resistance, which contributes to muscle wasting via reduced phosphorylation of the key proteins in the Akt/mTOR pathway [ 10 – 12 ]. Our previous work indicated that individuals with CKD exhibit a blunted anabolic response to an acute bout of exercise in the untrained state, consistent with the presence of anabolic resistance, but that this response was restored following a period of training [ 9 ]. The current study confirms and extends these findings. In participants undergoing CE, we observed no detectable change in Akt phosphorylation after an acute exercise bout in the untrained state. However, after 12 weeks of training, the same stimulus elicited a significant elevation in Akt phosphorylation, indicating a partial restoration of anabolic signalling. In contrast, no change in Akt or p70S6K phosphorylation was observed in the AE group, aligning with evidence that aerobic exercise does not robustly activate this pathway [ 23 ]. A major limitation of human muscle biopsy studies is the limited temporal resolution. As our in vivo samples were collected 24 hours post-exercise, crucial early molecular responses may have been missed. To address this gap, we conducted in vitro stretch experiments using primary myoblasts from both healthy controls and individuals with CKD, which are known to retain key aspects of their in vivo phenotype [ 15 ] and matched for age, gender and physical activity levels (all had low physical activity levels). These experiments revealed that mechanical stretch robustly increased of Akt and p70S6K phosphorylation in cells from both groups, with peak activation occurring between 0 and 7 hours post-stretch and returning to baseline by 24 hours. This 24-hour result replicates our in vivo observation of no sustained change at that time point. Interestingly, there was no significant difference in Akt phosphorylation response between CKD and control cells. While a trend was observed for a more transient p70S6K phosphorylation in CKD cells compared to a more sustained response in controls, this did not reach statistical significance, possibly due to high inter-donor variability. As each replicate represented a different donor, future studies using multiple replicates from the same donor could clarify these responses. Integrating the in vivo and in vitro data suggests that individuals with CKD are capable of mounting an anabolic response to exercise; however, this response appears to be relatively transient. Conducting an in vitro 'training' model using repeated bouts of mechanical stretch could offer valuable insights into how chronic loading influences the durability and magnitude of the anabolic signalling response in CKD patients. An essential component of muscle adaptation is the activation of satellite cells for repair and regeneration. In our study, AE did not stimulate changes in the expression of myogenic regulatory factors. In contrast, CE induced a more pronounced response after the training period, with significant upregulation of Pax7 and MyoD expression. Given that resistance exercise is a potent stimulus for muscle damage and repair, it is plausible that regenerative processes are more strongly activated by CE than by AE alone. This study has several limitations. The timing of muscle biopsy collection restricted to a single time point 24 hours post-exercise limits the conclusions that can be drawn to a narrow temporal window. As such, early molecular events that may have occurred in the immediate hours following exercise could have been missed. This limitation was a key rationale for conducting the complementary in vitro study, which allowed for a more detailed examination of the temporal profile of anabolic signalling. It must be highlighted that whilst a good in vitro model, mechanical stretch of human primary muscle cells does not fully recapitulate exercise in vivo . It does not capture the complex interactions between hormonal changes, neural input or immune responses that can all affect the molecular response within the muscle. 2D cultured primary cells can also lose aspects of their tissue-level organisation and environmental context over time. Factors such as extracellular matrix composition, cell–cell interactions, and 3D architecture, which influence signal transduction in vivo. To better capture the dynamics of molecular responses to exercise in future in vivo studies, multiple biopsy time points across the acute post-exercise period should be considered. In conclusion this study provides novel insight into the molecular responses of skeletal muscle to different modes of exercise in individuals with CKD. Using both in vivo muscle biopsy data and complementary in vitro models, we demonstrate that combined exercise training, but not aerobic training alone, can restore aspects of anabolic signalling, namely Akt phosphorylation, in skeletal muscle, supporting the notion that resistance-based modalities are necessary to elicit beneficial molecular adaptations in this population and confirming our earlier work. While the in vitro stretch model helped clarify the temporal dynamics of early signalling events, it also highlighted the complexity of translating findings across experimental models. Our findings suggest that individuals with CKD are capable of mounting an anabolic and myogenic response to exercise, but that this response may be blunted or short-lived without repeated loading. The observed changes in catabolic and regenerative markers further support the importance of exercise modality in shaping muscle adaptation and further validating the role of exercise training in reversing anabolic resistance in CKD. Future work should focus on longitudinal models, both in vitro and in vivo , to better understand how repeated loading influences anabolic signalling, and how these molecular responses relate to clinically meaningful improvements in muscle mass and function in CKD. Declarations Authors declare no conflict of interest. This is a summary of independent research funded by the Leicester Hospitals Charity Kidney Care Appeal and the Stoneygate Trust, supported by the National Institute for Health and Care Research (NIHR) Leicester Biomedical Research Centre (BRC). The views expressed are those of the author(s) and not necessarily those of the NIHR or the Department of Health and Social Care. For the purpose of open access, the author has applied a Creative Commons Attribution license (CC BY) to any Author Accepted Manuscript version arising from this submission. For the ExTra CKD study: Recruitment occurred between 16 th December 2013 and 30 th April 2016, with all interventions completed by October 2016. Ethical approval was obtained from the UK National Research Ethics Committee (Ref: 13/EM/0344), and the trial was registered with the ISRCTN (no. 36489137). The study was conducted in accordance with the Declaration of Helsinki, and all participants provided written informed consent. For the Explore CKD study: The study received ethical approval from the UK National Research Ethics Committee (Ref: 15/EM/0467) and registered with ISRCTN (No. 18221837). All procedures conformed to the Declaration of Helsinki, and all participants provided written informed consent. Conflict of interest All authors confirm there are no conflicts of interest Author contributions DWG: Conducted the experiments, sample collection, sample and data analysis, revising and reviewing the manuscript LAB: Conducting the experiments, data collection, revising and critically reviewing the manuscript TJW: Conducting the experiments, data collection, revising and critically reviewing the manuscript. NE: Providing participant samples, revising and critically reviewing the manuscript. RUA: Providing participant samples, revising and critically reviewing the manuscript. MD: Conducting the experiments, data collection, revising and critically reviewing the manuscript MGB: Providing participant samples, revising and critically reviewing the manuscript. ACS: Formulating the research idea and aims, oversight and leadership for the research activity, Securing financial support for the project. JLV: Conducting the experiments, data collection, revising and critically reviewing the manuscript AP: Mythological support, revising and critically reviewing the manuscript. ELW: Formulating the research idea and aims, oversight and leadership for the research activity, conducting the experiments, data collection and analysis, preparing the first version of the manuscript. References Global, regional, and national burden of chronic kidney disease, 1990–2017: a systematic analysis for the Global Burden of Disease Study 2017. Lancet, 2020. 395(10225): pp. 709–33. Moorthi RN, Avin KG. Clinical relevance of sarcopenia in chronic kidney disease. Curr Opin Nephrol Hypertens. 2017;26(3):219–28. Pereira RA, et al. Sarcopenia in chronic kidney disease on conservative therapy: prevalence and association with mortality. Nephrol Dial Transpl. 2015;30(10):1718–25. Wilkinson TJ, et al. Prevalence and correlates of physical activity across kidney disease stages: an observational multicentre study. 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Skeletal muscle atrophy and the E3 ubiquitin ligases MuRF1 and MAFbx/atrogin-1. Am J Physiol Endocrinol Metab. 2014;307(6):E469–84. Elkina Y, et al. The role of myostatin in muscle wasting: an overview. J Cachexia Sarcopenia Muscle. 2011;2(3):143–51. O'Sullivan TF, Smith AC, Watson EL. Satellite cell function, intramuscular inflammation and exercise in chronic kidney disease. Clin Kidney J. 2018;11(6):810–21. Graham-Brown MPM, et al. A randomized controlled trial to investigate the effects of intra-dialytic cycling on left ventricular mass. Kidney Int. 2021;99(6):1478–86. Watson EL, et al. Progressive Resistance Exercise Training in CKD: A Feasibility Study. Am J Kidney Dis. 2015;66(2):249–57. Greenwood SA, et al. Effect of exercise training on estimated GFR, vascular health, and cardiorespiratory fitness in patients with CKD: a pilot randomized controlled trial. Am J Kidney Dis. 2015;65(3):425–34. Pasiakos SM, et al. 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Supplementary Files Supplementarymaterial.docx.pptx Cite Share Download PDF Status: Published Journal Publication published 13 Mar, 2026 Read the published version in BMC Nephrology → Version 1 posted Editorial decision: Revision requested 10 Jan, 2026 Reviews received at journal 09 Jan, 2026 Reviews received at journal 08 Jan, 2026 Reviews received at journal 08 Jan, 2026 Reviewers agreed at journal 23 Dec, 2025 Reviewers agreed at journal 21 Dec, 2025 Reviewers agreed at journal 19 Dec, 2025 Reviews received at journal 18 Dec, 2025 Reviewers agreed at journal 18 Dec, 2025 Reviewers invited by journal 18 Dec, 2025 Editor invited by journal 18 Dec, 2025 Editor assigned by journal 17 Dec, 2025 Submission checks completed at journal 17 Dec, 2025 First submitted to journal 16 Dec, 2025 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. 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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-8374768","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":563717701,"identity":"ee19cacd-1504-4dd7-9c5e-cb55c34c400d","order_by":0,"name":"Douglas W Gould","email":"","orcid":"","institution":"Intensive Care National Audit and Research Centre","correspondingAuthor":false,"prefix":"","firstName":"Douglas","middleName":"W","lastName":"Gould","suffix":""},{"id":563717702,"identity":"bb107acb-422e-4c81-8702-4899160193bb","order_by":1,"name":"Luke A Baker","email":"","orcid":"","institution":"University of Leicester","correspondingAuthor":false,"prefix":"","firstName":"Luke","middleName":"A","lastName":"Baker","suffix":""},{"id":563717703,"identity":"ab15c8dd-127b-4861-8fc2-c549ee98e4e1","order_by":2,"name":"Thomas J Wilkinson","email":"","orcid":"","institution":"University of Leicester","correspondingAuthor":false,"prefix":"","firstName":"Thomas","middleName":"J","lastName":"Wilkinson","suffix":""},{"id":563717704,"identity":"9d756601-dde5-47d2-a51c-bbedb2dc5a0a","order_by":3,"name":"Nicholas Eastley","email":"","orcid":"","institution":"University Hospitals of Leicester","correspondingAuthor":false,"prefix":"","firstName":"Nicholas","middleName":"","lastName":"Eastley","suffix":""},{"id":563717705,"identity":"daed9e15-5ef4-4b8a-b14e-e0022d3d1e9e","order_by":4,"name":"Robert U Ashford","email":"","orcid":"","institution":"University Hospitals of Leicester","correspondingAuthor":false,"prefix":"","firstName":"Robert","middleName":"U","lastName":"Ashford","suffix":""},{"id":563717706,"identity":"9b0720e0-0318-4ee3-982c-7c86f08a8044","order_by":5,"name":"Matthew Denniff","email":"","orcid":"","institution":"University of Leicester","correspondingAuthor":false,"prefix":"","firstName":"Matthew","middleName":"","lastName":"Denniff","suffix":""},{"id":563717707,"identity":"e4a1fee3-dcde-4f18-96d2-f1726ddd21c6","order_by":6,"name":"Matthew Graham-Brown","email":"","orcid":"","institution":"University of Leicester","correspondingAuthor":false,"prefix":"","firstName":"Matthew","middleName":"","lastName":"Graham-Brown","suffix":""},{"id":563717708,"identity":"0a337da9-56b7-4a3a-aa97-5e01f7584929","order_by":7,"name":"João L Viana","email":"","orcid":"","institution":"CIDESD, University of Maia","correspondingAuthor":false,"prefix":"","firstName":"João","middleName":"L","lastName":"Viana","suffix":""},{"id":563717709,"identity":"44b8c02e-8639-488e-b7e8-03e9122623fc","order_by":8,"name":"Andrew Philp","email":"","orcid":"","institution":"Centenary Institute","correspondingAuthor":false,"prefix":"","firstName":"Andrew","middleName":"","lastName":"Philp","suffix":""},{"id":563717710,"identity":"cf40cefd-40ec-45d0-bacb-cd6c40b682ef","order_by":9,"name":"Emma L Watson","email":"data:image/png;base64,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","orcid":"","institution":"University of Leicester","correspondingAuthor":true,"prefix":"","firstName":"Emma","middleName":"L","lastName":"Watson","suffix":""}],"badges":[],"createdAt":"2025-12-16 10:09:04","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8374768/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8374768/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1186/s12882-026-04891-4","type":"published","date":"2026-03-13T16:00:04+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":98845696,"identity":"a708cb17-6f74-43b8-9e08-e5f76324941c","added_by":"auto","created_at":"2025-12-23 04:29:06","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":86374,"visible":true,"origin":"","legend":"","description":"","filename":"BMCNephrologyFinalVersion.docx","url":"https://assets-eu.researchsquare.com/files/rs-8374768/v1/555daa381c7379ea94c65c57.docx"},{"id":99308187,"identity":"a8ccb8a4-858d-4189-b065-e639b28f40e4","added_by":"auto","created_at":"2025-12-31 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04:29:06","extension":"xml","order_by":9,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":88809,"visible":true,"origin":"","legend":"","description":"","filename":"6bcfb8314a0948579e2a6f5f910aad261enriched.xml","url":"https://assets-eu.researchsquare.com/files/rs-8374768/v1/5df7078000ccfd615151aaeb.xml"},{"id":98845709,"identity":"0138f30c-0935-4b53-ab22-c6800a8189f1","added_by":"auto","created_at":"2025-12-23 04:29:06","extension":"xml","order_by":10,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":82316,"visible":true,"origin":"","legend":"","description":"","filename":"6bcfb8314a0948579e2a6f5f910aad261structuring.xml","url":"https://assets-eu.researchsquare.com/files/rs-8374768/v1/51ecd22246f0b9c4809bc6b8.xml"},{"id":98845710,"identity":"4bd67d06-6617-4af7-8759-33944da0997e","added_by":"auto","created_at":"2025-12-23 04:29:06","extension":"html","order_by":11,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":98803,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-8374768/v1/207a48007e9678ce6b47eb44.html"},{"id":98845701,"identity":"7888e59b-e970-4bb7-8776-4b61401b370d","added_by":"auto","created_at":"2025-12-23 04:29:06","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":473745,"visible":true,"origin":"","legend":"\u003cp\u003eChanges in phosphorylation of Akt and P70S6K in skeletal muscle biopsies in response to unaccustomed and accustomed bouts of AE or CE. People with CKD undertook 12 weeks of either AE or CE training. Vastus lateralis muscle biopsies were collected at baseline, 24h after a bout of unaccustomed exercise (untrained) and 24h after a bout of accustomed exercise (Trained) in both groups. A) shows a representative western blot image for P-AktSer\u003csup\u003e473\u003c/sup\u003e at baseline, untrained and trained time points with GAPDH that was used as a loading control in those people randomised to AE, and B) in those randomised CE.\u0026nbsp; C-D) Histograms displaying densitometric data. E)\u0026nbsp; shows a representative western blot image for P-70S6KThr\u003csup\u003e389\u003c/sup\u003e at baseline, untrained and trained time points with GAPDH that was used as a loading control in those people randomised to AE and F) in those randomised to CE. For both proteins, AE n= 9, CE n=8. Data are presented as mean±SD.\u0026nbsp; * denotes P\u0026lt;0.05. Abbreviations: AE, aerobic exercise, CE, combined exercise.\u003c/p\u003e","description":"","filename":"Figure1.png","url":"https://assets-eu.researchsquare.com/files/rs-8374768/v1/4efa2290e0c3e59e54137a29.png"},{"id":98845698,"identity":"774edca6-1b01-4132-9073-3a09e86a2861","added_by":"auto","created_at":"2025-12-23 04:29:06","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":279873,"visible":true,"origin":"","legend":"\u003cp\u003eAbundance of the 14kDa actin fragment in skeletal muscle biopsies in response to unaccustomed and accustomed bouts of AE or CE. People with CKD undertook 12 weeks of either AE or CE training. Vastus lateralis muscle biopsies were collected at baseline, 24h after a bout of unaccustomed exercise (untrained) and 24h after a bout of accustomed exercise (Trained) in both groups. A) shows a representative full western blot image that are labelled to show the 42kDa and the 14kDa actin fragments from people within the AE group and B) CE group. Histograms in C-D show densitometric data. AE n= 6, CE n=5. Data are presented as mean±SD. * denotes P\u0026lt;0.05. Abbreviations: AE, aerobic exercise, CE, combined exercise.\u003c/p\u003e","description":"","filename":"Figure2.png","url":"https://assets-eu.researchsquare.com/files/rs-8374768/v1/c3b7f0ada97b6e5ba40c4a30.png"},{"id":99308264,"identity":"795301b6-016a-4ef2-84a3-9107e22cf27e","added_by":"auto","created_at":"2025-12-31 16:08:08","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":344457,"visible":true,"origin":"","legend":"\u003cp\u003eChanges in mRNA expression of genes related to atrophy processes in response to unaccustomed and accustomed bouts of AE or CE. People with CKD undertook 12 weeks of either AE or CE training. Vastus lateralis muscle biopsies were collected at baseline, 24h after a bout of unaccustomed exercise (untrained) and 24h after a bout of accustomed exercise (Trained) in both groups. mRNA expression of MuRF-1 and MAFbx were analysed by RT-PCR in the A) AE group, and B) CE group. Myostatin and ActIIRB were analysed by RT-PCR in the C) AE group, and D) CE group. \u0026nbsp;Expression is displayed as relative change from baseline according to 2−ΔΔCt method and normalized to 18S. Data are presented as mean±SD. MuRF-1 AE n= 9, CE n=8; MAFbx AE n=8 CE = 10; Myostatin AE=10, CE=9; AC2BR AE=10, CE=9. * denotes P\u0026lt;0.05 vs baseline, ** denotes P\u0026lt;0.01 vs baseline, # denotes P\u0026lt;0.05 vs untrained. Abbreviations: AE, aerobic exercise; CE, combined exercise.\u003c/p\u003e","description":"","filename":"Figure3.png","url":"https://assets-eu.researchsquare.com/files/rs-8374768/v1/3374be3135ccfb18c2701abd.png"},{"id":99308324,"identity":"165aed51-fb15-4ab3-8532-25be33809712","added_by":"auto","created_at":"2025-12-31 16:08:16","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":211650,"visible":true,"origin":"","legend":"\u003cp\u003eChanges in mRNA expression of genes related to myogenesis in response to unaccustomed and accustomed bouts of AE or CE. People with CKD undertook 12 weeks of either AE or CE training. Vastus lateralis muscle biopsies were collected at baseline, 24h after a bout of unaccustomed exercise (untrained) and 24h after a bout of accustomed exercise (Trained) in both groups. mRNA expression of genes within the myogenic pathways were analysed by RT-PCR in the A) AE group and B) CE group. Expression is displayed as relative change from baseline according to 2−ΔΔCt method and normalized to 18S. Data are presented as mean±SD. \u0026nbsp;MyoD AE n=10, CE n=9; Myogenin AE n=10, CE n=9, Myf5 AE n=8, CE n=9; Pax 7 AE n=10, CE n=8.* denotes P\u0026lt;0.05 vs untrained. # denotes P=0.05 vs baseline. Abbreviations: AE, aerobic exercise; CE, combined exercise.\u003c/p\u003e","description":"","filename":"Figure4.png","url":"https://assets-eu.researchsquare.com/files/rs-8374768/v1/3c5b4af6c6c1e951392bef3c.png"},{"id":98845703,"identity":"23a042d2-3fc6-4892-b5cd-4d55164622f7","added_by":"auto","created_at":"2025-12-23 04:29:06","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":676224,"visible":true,"origin":"","legend":"\u003cp\u003eThe effect of 18% cyclic stretch on the phosphorylation of Akt and P70S6K in primary skeletal muscle myotubes from healthy control or CKD donors. Myotubes were stretched on 6-well Flexcell culture plates for 30 minutes using a Flexcell Fx3000 system set to 2 second sine wave stretch with 4 second release. Cells were harvested for western blotting prior to stretch (baseline), immediately post, and at 1,3,7 and 24h post stretch for the analysis of P-Akt and P-P70S6K. A) Time course of % change from baseline of P-Akt, n=8 healthy control, n=6 CKD, and B) P-P70S6K n=7 healthy control, n=5 CKD. Representative western blot images of C) P-Akt normalised to GAPDH in a healthy control donor and D) P-Akt normalised to GAPDH in a CKD donor E) P-P70S6K normalised to GAPDH in a healthy control donor and F) P-P70S6K normalised to GAPDH in a CKD donor. Data are presented as mean±SD. * Denotes P\u0026lt;0.05 vs baseline in HC. † denotes P\u0026lt;0.05 vs baseline in CKD. Abbreviations: BL, Baseline; CKD, chronic kidney disease; h, hour; IM, immediately post stretch.\u003c/p\u003e","description":"","filename":"Figure5.png","url":"https://assets-eu.researchsquare.com/files/rs-8374768/v1/252ea4bc1933d3a9fe395921.png"},{"id":104740426,"identity":"d7e9e506-4b99-4992-bf73-c3e905a0faf4","added_by":"auto","created_at":"2026-03-16 16:18:02","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2591891,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8374768/v1/1b01cda1-38cf-4128-804f-768c4e8addf0.pdf"},{"id":98845713,"identity":"033be0c2-1084-4115-bc7b-8da700f8cdd4","added_by":"auto","created_at":"2025-12-23 04:29:07","extension":"pptx","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":49816688,"visible":true,"origin":"","legend":"","description":"","filename":"Supplementarymaterial.docx.pptx","url":"https://assets-eu.researchsquare.com/files/rs-8374768/v1/efb769352262b24e10506c58.pptx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Anabolic and catabolic responses to different modes of exercise in patients with chronic kidney disease","fulltext":[{"header":"Introduction","content":"\u003cp\u003eChronic kidney disease (CKD) is a global public health emergency with an estimated prevalence of 9.1% [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. A common complication at all stages of CKD is muscle wasting, which contributes to reduced physical function independent of age [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. This loss of muscle is associated with poor clinical outcomes; for example, diagnosed sarcopenia has been shown to increase the risk of all-cause mortality threefold [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Furthermore, individuals with CKD exhibit high levels of physical inactivity [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e], which is also an independent risk factor for mortality [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eAlthough regular physical activity is strongly recommended for individuals with CKD, and formal exercise guidelines have recently been published for this population [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e], structured exercise programmes remain underutilised. To maximise the benefits of exercise training, it is crucial to understand the underlying molecular mechanisms, particularly how different types of exercise affect skeletal muscle homeostasis. This knowledge could guide the development of adjunctive strategies, such as targeted nutritional or pharmacological interventions. While a few studies have begun to explore this area in humans [\u003cspan additionalcitationids=\"CR8\" citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e], a comprehensive understanding of these mechanisms in the CKD population remains limited.\u003c/p\u003e \u003cp\u003eSkeletal muscle mass is maintained by a dynamic balance between protein synthesis and degradation. Anabolic signalling through the Akt/mTOR pathway plays a central role in promoting muscle protein synthesis, while catabolic pathways, including the ubiquitin\u0026ndash;proteasome system and myostatin signalling, regulate protein breakdown. In CKD, this balance is often disturbed, exacerbated by systemic factors such as insulin resistance, inflammation, and metabolic acidosis [\u003cspan additionalcitationids=\"CR11\" citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. Impairments in anabolic signalling, particularly the reduced phosphorylation of Akt and downstream targets, have been observed in animal models of CKD and are associated with muscle atrophy and impaired regeneration. While resistance exercise is known to activate these anabolic pathways in healthy individuals, the extent to which this occurs in those with CKD remains under investigation.\u003c/p\u003e \u003cp\u003eOur previous work has shown that in CKD, the expected anabolic and mitochondrial responses to resistance exercise may be blunted, consistent with the concept of \u0026ldquo;anabolic resistance\u0026rdquo; [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Specifically, we observed attenuated activation of the insulin signalling pathway and limited upregulation of myogenic markers in patients with CKD after a single bout of resistance exercise. However, some of these blunted responses appeared to normalise following a period of training, a finding that has yet to be replicated.\u003c/p\u003e \u003cp\u003eBuilding on this previous work, the aim of this study was to investigate the acute anabolic and catabolic responses of skeletal muscle to aerobic versus combined exercise in individuals with CKD, comparing these responses before and after a structured training period. To achieve this, we used muscle biopsies collected from the previously published ExTra CKD randomised controlled trial [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. In addition to analysing these \u003cem\u003ein vivo\u003c/em\u003e responses, we used an \u003cem\u003ein vitro\u003c/em\u003e stretch model to better understand the temporal dynamics of exercise-induced molecular signalling in primary skeletal muscle cells from CKD and healthy donors. Together, these complementary approaches provide a comprehensive view of how skeletal muscle in CKD responds to exercise and highlight important considerations for optimising interventions aimed at improving muscle health in this vulnerable population.\u003c/p\u003e"},{"header":"Materials and methods","content":"\u003cp\u003eThis study is a secondary analysis of the previously reported ExTra CKD randomised controlled trial [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e] and includes complementary \u003cem\u003ein vitro\u003c/em\u003e investigations using primary cells obtained from participants in the Explore CKD study.\u003c/p\u003e \u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eThe ExTra CKD trial\u003c/h2\u003e \u003cp\u003eIn brief, 54 non-dialysis patients with CKD stages 3b\u0026ndash;5 were enrolled in a 12-week, thrice-weekly supervised exercise intervention and randomised to either combined exercise (CE) or aerobic exercise (AE) alone. Participant characteristics are shown in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Each participant served as their own control during a six-week run-in period prior to randomisation. The AE intervention consisted of circuit-based aerobic activities such as treadmill walking or running, cycling, and rowing. The CE group undertook the same aerobic training, with the addition of resistance exercises performed during two of the three weekly sessions. Participants aimed to complete 30 minutes of moderate-intensity aerobic exercise at 70\u0026ndash;80% of their maximum heart rate, which was determined by a maximal exercise tolerance test. For the resistance component, participants performed 3 sets of 12\u0026ndash;15 repetitions of leg extensions at 70% of their estimated one-repetition maximum, which was determined from a five-repetition maximum test.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eParticipant characteristics\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAerobic Exercise (n\u0026thinsp;=\u0026thinsp;10)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCombined Exercise (n\u0026thinsp;=\u0026thinsp;9)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAge (years)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e65\u0026thinsp;\u0026plusmn;\u0026thinsp;8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e59\u0026thinsp;\u0026plusmn;\u0026thinsp;18\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGender (\u003cem\u003en\u003c/em\u003e men/women)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e4/6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3/6\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eEthnicity\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eWhite British n\u0026thinsp;=\u0026thinsp;9\u003c/p\u003e \u003cp\u003eBlack Caribbean n\u0026thinsp;=\u0026thinsp;1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eWhite British n\u0026thinsp;=\u0026thinsp;8\u003c/p\u003e \u003cp\u003eSouth Asian n\u0026thinsp;=\u0026thinsp;1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eeGFR (ml/min/1.73m\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e27\u0026thinsp;\u0026plusmn;\u0026thinsp;9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e27\u0026thinsp;\u0026plusmn;\u0026thinsp;6\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSerum Bicarbonate (mmol/l)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e25\u0026thinsp;\u0026plusmn;\u0026thinsp;6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e26\u0026thinsp;\u0026plusmn;\u0026thinsp;5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBMI (kg/m\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e30\u0026thinsp;\u0026plusmn;\u0026thinsp;6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e30\u0026thinsp;\u0026plusmn;\u0026thinsp;5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCreatinine (\u0026micro;mol/L)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e209\u0026thinsp;\u0026plusmn;\u0026thinsp;75\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e218\u0026thinsp;\u0026plusmn;\u0026thinsp;69\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eUrea (mmol/L)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e12\u0026thinsp;\u0026plusmn;\u0026thinsp;4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e13\u0026thinsp;\u0026plusmn;\u0026thinsp;5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"3\"\u003eAbbreviations: BMI, body mass index; eGFR, estimated glomerular filtration rate. Data are mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD.\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eA subset of participants (AE, n\u0026thinsp;=\u0026thinsp;10; CE, n\u0026thinsp;=\u0026thinsp;9) consented to skeletal muscle biopsies of the vastus lateralis using a needle biopsy technique previously described [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Samples were collected in a fasted state at three time points: baseline, 24 hours after the first training session (untrained), and 24 hours after the final session (trained). Following the removal of visible adipose tissue, biopsies were snap-frozen in liquid nitrogen and stored for later analysis.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eThe Explore CKD Study\u003c/h3\u003e\n\u003cp\u003eA single lower leg skeletal muscle biopsy was obtained from six individuals with CKD and eight age- and sex-matched non-CKD controls as part of the Explore CKD study (participant characteristics are detailed in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). CKD participants were recruited from outpatient clinics at Leicester General Hospital, UK, between 1st January 2016 and 2nd November 2020. Healthy controls (HC) with no significant medical history were recruited from orthopaedic theatre lists during procedures for benign tumour removal. Muscle biopsies from CKD participants were collected using the needle biopsy technique, while control muscle biopsies were obtained via the open biopsy technique.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eSkeletal muscle biopsy donors for primary cell culture establishment\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eHealthy Controls (n\u0026thinsp;=\u0026thinsp;8)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCKD Patients (n\u0026thinsp;=\u0026thinsp;6)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAge (years)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e61\u0026thinsp;\u0026plusmn;\u0026thinsp;14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e63\u0026thinsp;\u0026plusmn;\u0026thinsp;6\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGender (\u003cem\u003en\u003c/em\u003e men/women)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e4/4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2/3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eEthnicity\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eWhite British n\u0026thinsp;=\u0026thinsp;8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eWhite British n\u0026thinsp;=\u0026thinsp;6\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eeGFR (ml/min/1.73m\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e25.0\u0026thinsp;\u0026plusmn;\u0026thinsp;4.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e82.0\u0026thinsp;\u0026plusmn;\u0026thinsp;9.9\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"3\"\u003eAbbreviations: eGFR, estimated glomerular filtration rate. Data are mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD.\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e\n\u003ch3\u003eMolecular biology techniques\u003c/h3\u003e\n\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003eWestern Blotting\u003c/h2\u003e \u003cp\u003eApproximately 15\u0026ndash;20 mg of wet weight muscle tissue was homogenised in 18\u0026micro;L/mg RIPA buffer (Sigma, UK) supplemented with 1% (v/v) phosphatase inhibitor-3 (Sigma Aldrich, UK). Samples were rotated for 90 min at 4\u0026deg;C and centrifuged at 13,000 rpm for 15 min at 4\u0026deg;C. The supernatant was collected, and protein concentration determined using the Bio-Rad Protein Assay (BioRad, UK,). The pellet was retained for 14-kDa actin fragment analysis [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. Lysates were subjected to SDS-PAGE using 10\u0026ndash;12% gels on a mini-PROTEAN Tetra system (Bio-Rad, UK). Proteins were transferred onto nitrocellulose membranes and blocked for 1h with Tris-buffered saline with 5% (w/v) skimmed milk and 0.1% (v/v) Tween-20. Membranes were incubated overnight with the primary antibodies against p-Akt (Ser\u003csup\u003e473\u003c/sup\u003e; 1:2,000; Cell Signalling Technologies, USA) and p-p70S6K (Thr\u003csup\u003e389\u003c/sup\u003e; 1:500; Cell Signalling Technologies, USA). For 14kDa fragment analysis, an AC-40 Actin clone antibody (1:500; Sigma Aldrich, UK) was used. This antibody also recognises the 42-kDa fragment, which served as a loading control with a shorter exposure time. For all other proteins, GAPDH was used as a loading control. Horseradish Peroxidase (HRP)-linked anti-mouse/rabbit secondary antibodies (Dako, Aglient, UK) were used at 1:1500 for 2h at room temperature. Blots were visualised using ECL Reagents (Geneflow, UK) and captured using a ChemiDoc MP imager (Bio-Rad).\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eQuantitative RT-PCR\u003c/h3\u003e\n\u003cp\u003eTotal RNA was isolated from 15\u0026ndash;20 mg of muscle tissue using TRIzol\u0026reg; (Invitrogen, UK) and reversed transcribed to cDNA using an AMV reverse transcription system (Promega, WI, USA). Primers and probes and internal controls were supplied as TaqMan gene expression assays (Applied Biosystems, UK) were used for the following targets: MAFbx (Hs00369714_m1), MuRF-1 (Hs00822397_m1), Myostatin (Hs00976237_m1), Activin Receptor IIB, (Hs00155658_m1), Myogenin (Hs01072232_m1), MyoD (Hs02330075_g1), Myf5 (Hs00929416), Pax7 (Hs00242962), and 18S (Hs99999901) which served as the housekeeping gene with a coefficient of variation of 2.18%. All reactions were performed in a 20\u0026micro;L- volume containing 1\u0026micro;L cDNA, 10\u0026micro;L 2X Taqman Fast Mastermix, 8\u0026micro;L nuclease-free water, and 1\u0026micro;L primer/probe assay on an Applied Biosystem\u0026rsquo;s QuantStudio 3 instrument with the following conditions: 95\u0026deg;C 15 s, followed by 40 cycles at 95\u0026deg;C for 15 s and at 60\u0026deg;C for 1 min. Target gene Ct values were normalised to the 18S house-keeping gene, and relative expression levels were calculated using the 2\u003csup\u003e\u0026minus;ΔΔCt\u003c/sup\u003e method.\u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eSatellite cell isolation procedure\u003c/h2\u003e \u003cp\u003eSatellite cells were isolated and propagated as previously described [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. Briefly, muscle tissue was washed three times in HamsF10 (containing 1% penicillin streptomycin and 1% Gentamycin), minced into small fragments, and enzymatically digested in two incubations with collagenase IV (1mg/mL), BSA (5mg/mL) and trypsin (500\u0026micro;l/mL) at 37\u0026deg;C with gentle agitation. The resultant supernatant was strained through a 70\u0026micro;m nylon filter and centrifuged at 800 g for 7 mins. The cells were washed in Hams F10 with 1% penicillin-streptomycin and pre-plated on uncoated 9cm2 petri dishes in 3mL growth medium (GM; Hams F10 Glutamax, 20% FBS, 1% penicillin streptomycin, 1% fungazone) for 3h. The cell suspension was then moved to collagen I coated 25 cm2 flasks and kept in standard culture environmental conditions (37\u0026deg;C, 5% CO2). For the expansion of satellite cell populations, cells were grown to approximately 70% confluence in GM that was changed every other day. Cells were subsequently trypsinised (Sigma-Aldrich, UK) and counted using the trypan blue exclusion method.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eCell Culture and in Vitro Mechanical Stretch\u003c/h3\u003e\n\u003cp\u003eMyoblasts were seeded on 6-well Flexcell culture plates, and cyclic multiaxial stretch applied using a Flexcell Fx3000 system set to 2 second sine wave stretch with 4 second release resulting in an 18% maximum stretch for 30 minutes at 37\u0026deg;C. Cells were harvested in 200\u0026micro;l lysis buffer/well RIPA buffer (Sigma, UK) supplemented with 1% v/v phosphatase inhibitor-3 (Sigma Aldrich, UK) prior to stretch, immediately post and at 1,3,7 and 24h post stretch. Protein concentration was determined by the Bio-Rad Protein Assay, and resulting lysates were stored for subsequent western blotting analysis.\u003c/p\u003e\n\u003ch3\u003eAvailability of data\u003c/h3\u003e\n\u003cp\u003eThe datasets supporting the conclusions of this article are available in the University of Leicester Figshare repository (Watson, Emma (2025). ExTra CKD Biopsy Analysis. University of Leicester. Dataset. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://figshare.le.ac.uk/articles/dataset/_/30665759\u003c/span\u003e\u003cspan address=\"https://figshare.le.ac.uk/articles/dataset/_/30665759\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eStatistics\u003c/h2\u003e \u003cp\u003eData distribution was assessed using the Shapiro-Wilks test. Non-normally distributed variables were log-transformed for analysis and back-transformed for presentation. A primary analysis was performed for each variable using a repeated measures ANOVA to assess the effects of time point (baseline, untrained, trained) and group allocation (AE vs. CE). In addition, paired t-tests were performed to compare specific time points (baseline vs. untrained, baseline vs. trained, and untrained vs. trained) for both AE and CE groups, expressed as mean change (90% CIs). Magnitude-based inferences were used to estimate the mean effects between AE and CE groups.\u003c/p\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003eParticipant characteristics\u003c/h2\u003e \u003cp\u003eParticipant characteristics for the ExTra CKD and Explore CKD studies are presented in Tables\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e and \u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, respectively. Baseline characteristics were well-matched between the exercise groups (AE vs. CE) in the ExTRA CKD trial (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) and between the donor groups (CKD vs. HC) in the Explore CKD study (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003eThe anabolic response to exercise in CKD\u003c/h2\u003e \u003cp\u003eChanges in phosphorylation of Akt and p70S6K are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Akt phosphorylation is well documented to increase in the hours following exercise, and is a key contributor to the anabolic response to exercise [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. In this study, no significant change in Akt phosphorylation was observed at any time point following AE. Similarly, a single bout of CE in the untrained state did not significantly alter Akt phosphorylation from baseline (P\u0026thinsp;=\u0026thinsp;0.48, Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eA-D). However, after 12 weeks of CE training, the same exercise stimulus elicited a significant 118% increase in Akt phosphorylation from baseline (P\u0026thinsp;=\u0026thinsp;0.02), a response that was also significantly greater than that observed in the untrained state (P\u0026thinsp;=\u0026thinsp;0.02).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn contrast, p70S6K phosphorylation was not significantly changed by an acute bout of AE or CE in either the untrained or trained state (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eE-H).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003eThe catabolic response to exercise in CKD\u003c/h2\u003e \u003cp\u003eChanges in the 14-kDa actin fragment, a biomarker of skeletal muscle catabolism [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e], are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. The abundance of the 14 kDa fragment remained unchanged at all time points following AE. In contrast, an acute bout of CE in the untrained state resulted in a 253% increase in the 14-kDa fragment relative to baseline (P\u0026thinsp;=\u0026thinsp;0.04). This response was abrogated after 12 weeks of CE training, with fragment levels returning to baseline (P\u0026thinsp;=\u0026thinsp;0.68 vs baseline).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eMuRF-1 and MAFbx are two muscle-specific E3 ligases, commonly used as markers of ubiquitin-proteasome system activity [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. A repeated measures ANOVA revealed no effect of acute AE or CE on MuRF-1 mRNA expression (P\u0026thinsp;=\u0026thinsp;0.46; Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e) or MAFbx mRNA expression (P\u0026thinsp;=\u0026thinsp;0.70; Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn contrast, the mRNA expression of myostatin, a potent negative regulator of muscle mass [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e], was downregulated from baseline following an acute bout of AE in both the untrained (1.5-fold reduction; P\u0026thinsp;=\u0026thinsp;0.01; Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e) and trained (1.2-fold reduction; P\u0026thinsp;=\u0026thinsp;0.04) states. In response to CE in the untrained state, myostatin mRNA expression decreased five-fold (P\u0026thinsp;=\u0026thinsp;0.003). After training, however, the response to CE was reversed, with myostatin mRNA expression being elevated compared to the response in the untrained state (P\u0026thinsp;=\u0026thinsp;0.007; Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). No changes were observed for the expression of the myostatin receptor, ActIIRB in any condition (P\u0026thinsp;\u0026gt;\u0026thinsp;0.05; Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003eThe myogenic response to exercise in CKD\u003c/h2\u003e \u003cp\u003eThe mRNA expression of myogenic regulatory factors (Pax7, MyoD, Myogenin and Myf5), which coordinate muscle repair [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e] are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. No changes in the mRNA expression of any of these factors were observed following AE (P\u0026thinsp;\u0026gt;\u0026thinsp;0.05). Similarly, there were no changes in Myogenin or Myf5 expression following CE at any time point (P\u0026thinsp;\u0026gt;\u0026thinsp;0.05). In the untrained state, an acute bout of CE induced a near-significant two-fold decrease in MyoD mRNA expression (P\u0026thinsp;=\u0026thinsp;0.05); this response was reversed following training, resulting in a significant increase compared to the untrained condition (P\u0026thinsp;=\u0026thinsp;0.01). Finally, Pax7 mRNA expression in response to CE was greater in the trained state compared to the untrained state (P\u0026thinsp;=\u0026thinsp;0.025).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eIn Vitro\u003c/b\u003e \u003cb\u003eanabolic signalling response to mechanical stretch\u003c/b\u003e\u003c/p\u003e \u003cp\u003eTo examine the temporal dynamics of anabolic signalling, primary myoblasts from CKD and HC donors were subjected to mechanical stretch \u003cem\u003ein vitro\u003c/em\u003e. Mechanical stretch induced a significant increase in Akt phosphorylation relative to baseline in both groups immediately post-stretch (CKD: +5651%, P\u0026thinsp;=\u0026thinsp;0.012; HC: +3437%, P\u0026thinsp;=\u0026thinsp;0.028; Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eA\u0026ndash;D). This elevation persisted at 1- hour post-stretch (CKD: +61%, P\u0026thinsp;=\u0026thinsp;0.012; HC: +1472%, P\u0026thinsp;=\u0026thinsp;0.028). At 3- hours post-stretch, Akt phosphorylation remained elevated in the HC group (+\u0026thinsp;388%, P\u0026thinsp;=\u0026thinsp;0.046) but had returned to baseline in the CKD group (P\u0026thinsp;=\u0026thinsp;0.31). By 7- and 24-hours post-stretch, phosphorylation levels had returned to baseline in both groups (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eA). A repeated measures ANOVA revealed no significant interaction effect, indicating the overall response to stretch did not differ between groups (P\u0026thinsp;=\u0026thinsp;0.84).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eA similar phosphorylation pattern was observed for p70S6K (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eD-F). p70S6K phosphorylation significantly increased from baseline immediately post-stretch in both groups (CKD: +1076%, P\u0026thinsp;=\u0026thinsp;0.014; HC\u0026thinsp;+\u0026thinsp;712%, P\u0026thinsp;=\u0026thinsp;0.038). In CKD cells, this elevation persisted at 1- hour (+\u0026thinsp;306%, P\u0026thinsp;=\u0026thinsp;0.047) and 7- hours post-stretch (+\u0026thinsp;219%, P\u0026thinsp;=\u0026thinsp;0.004), with a strong trend toward an increase at 3 hours (+\u0026thinsp;185%, P\u0026thinsp;=\u0026thinsp;0.052). In contrast, no further time points showed significant increases from baseline in the HC group. The repeated measures ANOVA showed a trend toward a significant interaction that was not statistically significant (P\u0026thinsp;=\u0026thinsp;0.052), indicating broadly similar responses to the stretch regime between the two groups.\u003c/p\u003e \u003c/div\u003e"},{"header":"Discussion","content":"\u003cp\u003eThis study offers new insights into the molecular responses to aerobic versus combined exercise in individuals with CKD, while also supporting our previous findings in a different cohort and exercise modality [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Here we showed the combined aerobic and resistance exercise, but not aerobic exercise alone, elicits beneficial molecular adaptations in skeletal muscle of individuals with CKD. Following 12-weeks of CE participants exhibited a significant restoration of anabolic signalling in response to exercise through increased Akt phosphorylation, activation of myogenic markers and attenuation of acute catabolic responses. Complementary in vitro stretch experiments demonstrated that skeletal muscle cells from people with CKD are capable of mounting anabolic responses, although these were more transient than those observed in healthy controls.\u003c/p\u003e \u003cp\u003eEvidence suggests that individuals with CKD do not always exhibit the expected physiological adaptations to exercise. For instance, several studies have reported that aerobic training does not consistently lead to increases in VO₂\u003csub\u003epeak\u003c/sub\u003e in patients with CKD [\u003cspan additionalcitationids=\"CR21\" citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e], a finding linked to a blunted activation of mitochondrial biogenesis pathways [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Additionally, it was previously reported that after a single bout of resistance exercise, the expected activation of the insulin signalling pathway was largely absent, but this response was restored after a training period [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e] \u0026ndash; a finding we have replicated here. A clear understanding of the molecular responses that underpin these adaptations to exercise is crucial for designing adjunct therapies that maximise the benefits of exercise for patients with CKD.\u003c/p\u003e \u003cp\u003eSkeletal muscle homeostasis is maintained through a finely regulated balance between protein synthesis and protein degradation. In CKD, this balance is often disrupted by factors like insulin resistance, which contributes to muscle wasting via reduced phosphorylation of the key proteins in the Akt/mTOR pathway [\u003cspan additionalcitationids=\"CR11\" citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. Our previous work indicated that individuals with CKD exhibit a blunted anabolic response to an acute bout of exercise in the untrained state, consistent with the presence of anabolic resistance, but that this response was restored following a period of training [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. The current study confirms and extends these findings. In participants undergoing CE, we observed no detectable change in Akt phosphorylation after an acute exercise bout in the untrained state. However, after 12 weeks of training, the same stimulus elicited a significant elevation in Akt phosphorylation, indicating a partial restoration of anabolic signalling. In contrast, no change in Akt or p70S6K phosphorylation was observed in the AE group, aligning with evidence that aerobic exercise does not robustly activate this pathway [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eA major limitation of human muscle biopsy studies is the limited temporal resolution. As our \u003cem\u003ein vivo\u003c/em\u003e samples were collected 24 hours post-exercise, crucial early molecular responses may have been missed. To address this gap, we conducted \u003cem\u003ein vitro\u003c/em\u003e stretch experiments using primary myoblasts from both healthy controls and individuals with CKD, which are known to retain key aspects of their \u003cem\u003ein vivo\u003c/em\u003e phenotype [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e] and matched for age, gender and physical activity levels (all had low physical activity levels). These experiments revealed that mechanical stretch robustly increased of Akt and p70S6K phosphorylation in cells from both groups, with peak activation occurring between 0 and 7 hours post-stretch and returning to baseline by 24 hours. This 24-hour result replicates our \u003cem\u003ein vivo\u003c/em\u003e observation of no sustained change at that time point. Interestingly, there was no significant difference in Akt phosphorylation response between CKD and control cells. While a trend was observed for a more transient p70S6K phosphorylation in CKD cells compared to a more sustained response in controls, this did not reach statistical significance, possibly due to high inter-donor variability. As each replicate represented a different donor, future studies using multiple replicates from the same donor could clarify these responses. Integrating the \u003cem\u003ein vivo\u003c/em\u003e and \u003cem\u003ein vitro\u003c/em\u003e data suggests that individuals with CKD are capable of mounting an anabolic response to exercise; however, this response appears to be relatively transient. Conducting an \u003cem\u003ein vitro\u003c/em\u003e 'training' model using repeated bouts of mechanical stretch could offer valuable insights into how chronic loading influences the durability and magnitude of the anabolic signalling response in CKD patients.\u003c/p\u003e \u003cp\u003eAn essential component of muscle adaptation is the activation of satellite cells for repair and regeneration. In our study, AE did not stimulate changes in the expression of myogenic regulatory factors. In contrast, CE induced a more pronounced response after the training period, with significant upregulation of Pax7 and MyoD expression. Given that resistance exercise is a potent stimulus for muscle damage and repair, it is plausible that regenerative processes are more strongly activated by CE than by AE alone.\u003c/p\u003e \u003cp\u003eThis study has several limitations. The timing of muscle biopsy collection restricted to a single time point 24 hours post-exercise limits the conclusions that can be drawn to a narrow temporal window. As such, early molecular events that may have occurred in the immediate hours following exercise could have been missed. This limitation was a key rationale for conducting the complementary \u003cem\u003ein vitro\u003c/em\u003e study, which allowed for a more detailed examination of the temporal profile of anabolic signalling. It must be highlighted that whilst a good \u003cem\u003ein vitro\u003c/em\u003e model, mechanical stretch of human primary muscle cells does not fully recapitulate exercise \u003cem\u003ein vivo\u003c/em\u003e. It does not capture the complex interactions between hormonal changes, neural input or immune responses that can all affect the molecular response within the muscle. 2D cultured primary cells can also lose aspects of their tissue-level organisation and environmental context over time. Factors such as extracellular matrix composition, cell\u0026ndash;cell interactions, and 3D architecture, which influence signal transduction \u003cem\u003ein vivo.\u003c/em\u003e To better capture the dynamics of molecular responses to exercise in future \u003cem\u003ein vivo\u003c/em\u003e studies, multiple biopsy time points across the acute post-exercise period should be considered.\u003c/p\u003e \u003cp\u003eIn conclusion this study provides novel insight into the molecular responses of skeletal muscle to different modes of exercise in individuals with CKD. Using both in vivo muscle biopsy data and complementary in vitro models, we demonstrate that combined exercise training, but not aerobic training alone, can restore aspects of anabolic signalling, namely Akt phosphorylation, in skeletal muscle, supporting the notion that resistance-based modalities are necessary to elicit beneficial molecular adaptations in this population and confirming our earlier work. While the in vitro stretch model helped clarify the temporal dynamics of early signalling events, it also highlighted the complexity of translating findings across experimental models. Our findings suggest that individuals with CKD are capable of mounting an anabolic and myogenic response to exercise, but that this response may be blunted or short-lived without repeated loading. The observed changes in catabolic and regenerative markers further support the importance of exercise modality in shaping muscle adaptation and further validating the role of exercise training in reversing anabolic resistance in CKD. Future work should focus on longitudinal models, both \u003cem\u003ein vitro\u003c/em\u003e and \u003cem\u003ein vivo\u003c/em\u003e, to better understand how repeated loading influences anabolic signalling, and how these molecular responses relate to clinically meaningful improvements in muscle mass and function in CKD.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003eAuthors declare no conflict of interest. This is a summary of independent research funded by the Leicester Hospitals Charity Kidney Care Appeal and the Stoneygate Trust, supported by the National Institute for Health and Care Research (NIHR) Leicester Biomedical Research Centre (BRC). The views expressed are those of the author(s) and not necessarily those of the NIHR or the Department of Health and Social Care. \u0026nbsp;For the purpose of open access, the author has applied a Creative Commons Attribution license (CC BY) to any Author Accepted Manuscript version arising from this submission. For the ExTra CKD study:\u0026nbsp;Recruitment occurred between 16\u003csup\u003eth\u003c/sup\u003e December 2013 and 30\u003csup\u003eth\u003c/sup\u003e April 2016, with all interventions completed by October 2016. Ethical approval was obtained from the UK National Research Ethics Committee (Ref: 13/EM/0344), and the trial\u0026nbsp;was registered with the ISRCTN (no. 36489137).\u0026nbsp;The study was conducted in accordance with the Declaration of Helsinki, and all participants provided written informed consent.\u003c/p\u003e\n\u003cp\u003eFor the Explore CKD study:\u0026nbsp;The study received ethical approval from the UK National Research Ethics Committee (Ref: 15/EM/0467) and registered with ISRCTN (No. 18221837). All procedures conformed to the Declaration of Helsinki, and all participants provided written informed consent.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll authors confirm there are no conflicts of interest\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eDWG: Conducted the experiments, sample collection, sample and data analysis, revising and reviewing the manuscript\u003c/p\u003e\n\u003cp\u003eLAB: Conducting the experiments, data collection, revising and critically reviewing the manuscript\u003c/p\u003e\n\u003cp\u003eTJW: Conducting the experiments, data collection, revising and critically reviewing the manuscript.\u003c/p\u003e\n\u003cp\u003eNE: Providing participant samples,\u0026nbsp;revising and critically reviewing the manuscript.\u003c/p\u003e\n\u003cp\u003eRUA: Providing participant samples,\u0026nbsp;revising and critically reviewing the manuscript.\u003c/p\u003e\n\u003cp\u003eMD: Conducting the experiments, data collection, revising and critically reviewing the manuscript\u003c/p\u003e\n\u003cp\u003eMGB: Providing participant samples,\u0026nbsp;revising and critically reviewing the manuscript.\u003c/p\u003e\n\u003cp\u003eACS:\u0026nbsp;Formulating the research idea and aims, oversight and leadership for the research activity, Securing financial support for the project.\u003c/p\u003e\n\u003cp\u003eJLV: Conducting the experiments, data collection, revising and critically reviewing the manuscript\u003c/p\u003e\n\u003cp\u003eAP: Mythological support,\u0026nbsp;revising and critically reviewing the manuscript.\u003c/p\u003e\n\u003cp\u003eELW:\u0026nbsp;Formulating the research idea and aims, oversight and leadership for the research activity, conducting the experiments, data collection and analysis, preparing the first version of the manuscript.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eGlobal, regional, and national burden of chronic kidney disease, 1990\u0026ndash;2017: a systematic analysis for the Global Burden of Disease Study 2017. Lancet, 2020. 395(10225): pp. 709\u0026ndash;33.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMoorthi RN, Avin KG. Clinical relevance of sarcopenia in chronic kidney disease. Curr Opin Nephrol Hypertens. 2017;26(3):219\u0026ndash;28.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePereira RA, et al. Sarcopenia in chronic kidney disease on conservative therapy: prevalence and association with mortality. Nephrol Dial Transpl. 2015;30(10):1718\u0026ndash;25.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWilkinson TJ, et al. Prevalence and correlates of physical activity across kidney disease stages: an observational multicentre study. Nephrol Dial Transpl. 2021;36(4):641\u0026ndash;9.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSchmid D, Ricci C, Leitzmann MF. Associations of objectively assessed physical activity and sedentary time with all-cause mortality in US adults: the NHANES study. PLoS ONE. 2015;10(3):e0119591.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBaker LA, et al. Clinical practice guideline exercise and lifestyle in chronic kidney disease. BMC Nephrol. 2022;23(1):75.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWatson EL, et al. Reductions in skeletal muscle mitochondrial mass are not restored following exercise training in patients with chronic kidney disease. Faseb j. 2020;34(1):1755\u0026ndash;67.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWatson EL, et al. Inflammation and physical dysfunction: responses to moderate intensity exercise in chronic kidney disease. Nephrol Dial Transpl. 2022;37(5):860\u0026ndash;8.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWatson EL, et al. The Effect of Resistance Exercise on Inflammatory and Myogenic Markers in Patients with Chronic Kidney Disease. Front Physiol. 2017;8:541.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang XH, Mitch WE. Muscle wasting from kidney failure-a model for catabolic conditions. Int J Biochem Cell Biol. 2013;45(10):2230\u0026ndash;8.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang XH, et al. Exercise ameliorates chronic kidney disease-induced defects in muscle protein metabolism and progenitor cell function. Kidney Int. 2009;76(7):751\u0026ndash;9.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBailey JL. \u003cem\u003eInsulin resistance and muscle metabolism in chronic kidney disease.\u003c/em\u003e ISRN Endocrinol, 2013. 2013: p. 329606.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWatson EL, et al. Twelve-week combined resistance and aerobic training confers greater benefits than aerobic training alone in nondialysis CKD. Am J Physiol Ren Physiol. 2018;314(6):F1188\u0026ndash;96.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWorkeneh BT, et al. Development of a diagnostic method for detecting increased muscle protein degradation in patients with catabolic conditions. J Am Soc Nephrol. 2006;17(11):3233\u0026ndash;9.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBaker LA et al. \u003cem\u003eEstablishment and characterisation of primary skeletal muscle cell cultures from patients with advanced Chronic Kidney Disease.\u003c/em\u003e bioRxiv, 2020: p. 2020.11.16.384263.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSchiaffino S, et al. Mechanisms regulating skeletal muscle growth and atrophy. Febs j. 2013;280(17):4294\u0026ndash;314.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBodine SC, Baehr LM. Skeletal muscle atrophy and the E3 ubiquitin ligases MuRF1 and MAFbx/atrogin-1. Am J Physiol Endocrinol Metab. 2014;307(6):E469\u0026ndash;84.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eElkina Y, et al. The role of myostatin in muscle wasting: an overview. J Cachexia Sarcopenia Muscle. 2011;2(3):143\u0026ndash;51.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eO'Sullivan TF, Smith AC, Watson EL. Satellite cell function, intramuscular inflammation and exercise in chronic kidney disease. Clin Kidney J. 2018;11(6):810\u0026ndash;21.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGraham-Brown MPM, et al. A randomized controlled trial to investigate the effects of intra-dialytic cycling on left ventricular mass. Kidney Int. 2021;99(6):1478\u0026ndash;86.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWatson EL, et al. Progressive Resistance Exercise Training in CKD: A Feasibility Study. Am J Kidney Dis. 2015;66(2):249\u0026ndash;57.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGreenwood SA, et al. Effect of exercise training on estimated GFR, vascular health, and cardiorespiratory fitness in patients with CKD: a pilot randomized controlled trial. Am J Kidney Dis. 2015;65(3):425\u0026ndash;34.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePasiakos SM, et al. Molecular responses to moderate endurance exercise in skeletal muscle. Int J Sport Nutr Exerc Metab. 2010;20(4):282\u0026ndash;90.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"bmc-nephrology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"bnep","sideBox":"Learn more about [BMC Nephrology](http://bmcnephrol.biomedcentral.com/)","snPcode":"","submissionUrl":"https://www.editorialmanager.com/bnep/default.aspx","title":"BMC Nephrology","twitterHandle":"BMC_series","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"em","reportingPortfolio":"BMC Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-8374768/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8374768/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eBackground: Muscle wasting is a common in chronic kidney disease (CKD), contributing to impaired function and poor outcomes. Exercise is recommended, but the molecular responses of skeletal muscle to different exercise modalities remain unclear. This study examined anabolic, catabolic, and myogenic responses to aerobic exercise (AE) versus combined exercise (CE; aerobic plus resistance) in CKD.\u003c/p\u003e\n\u003cp\u003eMethods: Muscle biopsies were collected from participants in a 12-week randomized controlled trial (the ExTra CKD trial) at baseline, 24 hours after initial exercise bout (untrained), and 24 hours after the final session (trained). Western blotting and RT-qPCR assessed markers of protein synthesis, degradation, and regeneration. Complementary \u003cem\u003ein vitro\u003c/em\u003e experiments used mechanically stretched primary skeletal muscle cells from CKD patients and healthy controls to investigate the temporal dynamics of anabolic signalling.\u003c/p\u003e\n\u003cp\u003eResults AE did not alter Akt phosphorylation. CE showed no acute effect before training but significantly increased Akt phosphorylation after training, indicating partial restoration of anabolic signalling. CE also upregulated myogenic markers (Pax7, MyoD) and reduced acute catabolic responses, whereas AE effects were minimal. Myostatin was downregulated by AE at both time points, while CE shifted from suppression before training to elevation afterwards.\u003c/p\u003e\n\u003cp\u003eConclusion: CE, but not AE alone, elicits beneficial anabolic and myogenic adaptations in skeletal in CKD. Combining in vivo and in vitro approaches offers deeper mechanistic insight into exercise-induced molecular adaptations and highlights the importance of including resistance training to overcome anabolic resistance in this population.\u003c/p\u003e","manuscriptTitle":"Anabolic and catabolic responses to different modes of exercise in patients with chronic kidney disease","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-12-23 04:29:01","doi":"10.21203/rs.3.rs-8374768/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-01-11T04:33:36+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-01-09T15:00:26+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-01-08T23:18:49+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-01-08T05:15:11+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"124997275917105527984514349702639517199","date":"2025-12-23T16:55:10+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"143430025534237968477747605954414168140","date":"2025-12-21T19:33:53+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"334846939940306736542690050340034986493","date":"2025-12-19T05:51:49+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-12-18T17:31:02+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"215761100340529739593289777587448336125","date":"2025-12-18T16:44:30+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-12-18T15:21:07+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2025-12-18T09:18:41+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-12-17T14:00:17+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-12-17T13:59:41+00:00","index":"","fulltext":""},{"type":"submitted","content":"BMC Nephrology","date":"2025-12-16T10:00:06+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"bmc-nephrology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"bnep","sideBox":"Learn more about [BMC Nephrology](http://bmcnephrol.biomedcentral.com/)","snPcode":"","submissionUrl":"https://www.editorialmanager.com/bnep/default.aspx","title":"BMC Nephrology","twitterHandle":"BMC_series","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"em","reportingPortfolio":"BMC Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"d2886749-12b8-40f6-87f7-5f1f4e1f991e","owner":[],"postedDate":"December 23rd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2026-03-16T16:15:56+00:00","versionOfRecord":{"articleIdentity":"rs-8374768","link":"https://doi.org/10.1186/s12882-026-04891-4","journal":{"identity":"bmc-nephrology","isVorOnly":false,"title":"BMC Nephrology"},"publishedOn":"2026-03-13 16:00:04","publishedOnDateReadable":"March 13th, 2026"},"versionCreatedAt":"2025-12-23 04:29:01","video":"","vorDoi":"10.1186/s12882-026-04891-4","vorDoiUrl":"https://doi.org/10.1186/s12882-026-04891-4","workflowStages":[]},"version":"v1","identity":"rs-8374768","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8374768","identity":"rs-8374768","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}