Ferredoxins: master regulators in mitochondrial redox homeostasis and programmed cell death.

As the central hub of cellular energy metabolism, the maintenance of mitochondrial functional homeostasis highly depends on the precise regulation of FDX1 and FDX2 (Section 2 ). When the functions of FDXs are abnormal, the core functions of mitochondria will undergo a cascade of disorders, promoting the disease process by triggering mitochondrial-dependent cell death pathways such as cuproptosis and ferroptosis (Section 5 ). As key mitochondrial-targeted Fe–S proteins, FDX1 and FDX2, through their specialized functions, become the core nodes connecting mitochondrial functions and disease phenotypes: Abnormalities in FDX1 disrupt the mitochondrial copper ion reduction balance and lipoylation modification, triggering proteotoxic stress and metabolic reprogramming. Defects in FDX2 directly impede mitochondrial Fe–S cluster assembly, leading to the collapse of the electron transport chain and iron metabolism imbalance. This section systematically elaborates on how FDXs participate in disease development by regulating mitochondrial functions: (i) In cancer, the cuproptosis regulation of FDX1 and the Fe–S cluster-dependent function of FDX2 jointly affect tumor metabolism and the immune microenvironment; (ii) In neurodegenerative diseases, mitochondrial copper toxicity and lipoylation defects mediated by FDX1 exacerbate neuronal damage, while FDX2 deficiency impairs Fe–S cluster biogenesis and respiratory chain activity; (iii) In cardiovascular diseases, the abnormal lipid metabolism regulatory function of FDX1 disrupts vascular homeostasis and myocardial energy supply; (iv) In endocrine diseases, the steroidogenic function of FDX1 and the cuproptosis pathway jointly participate in metabolic disorders; (v) In genetic diseases, the copper metabolism defect of FDX1 and the Fe–S cluster synthesis disorder of FDX2 respectively lead to specific mitochondrial dysfunction syndromes ( Fig. 4 ). These contents will reveal the disease-regulating mechanisms of FDXs as the “gatekeepers” of mitochondrial functions, providing a theoretical basis for therapeutic strategies targeting the mitochondrial-FDXs axis. Fig. 4 FDXs as central regulators of mitochondrial pathology across disease spectrums As core regulators of mitochondrial homeostasis, FDX1 and FDX2 control mitochondrial homeostasis and cell death through multiple pathways, thus linking mitochondrial dysfunction to major diseases. In cancer, FDX1 drives cuproptosis by mediating copper-dependent lipoylation of mitochondrial proteins, while FDX2 regulates Fe–S cluster assembly to control iron metabolism and ferroptosis. Their interplay amplifies oxidative stress, linking tumor metabolism to cell death pathways. In neurodegenerative diseases, FDX1 mediates copper toxicity in AD and PD via impaired copper reduction and lipoylation defects. Copper overload disrupts mitochondrial function and induces cuproptosis, exacerbating neurodegeneration. In cardiovascular diseases, FDX1 dysregulation disrupts lipid metabolism and causes copper-induced cuproptosis in ischemic cardiomyopathy and atherosclerosis. Mitochondrial dysfunction further destabilizes vascular homeostasis. In endocrine diseases, FDX1 integrates steroidogenesis and copper-dependent β-cell cuproptosis in diabetes. Tissue-specific roles in PCOS and T2DM highlight its dual functions. In genetic diseases, FDX1 defects cause copper dyshomeostasis in Menkes/Wilson disease, while FDX2 mutations disrupt Fe–S cluster biogenesis, leading to mitochondrial myopathies and lactic acidosis. Treatment interventions target copper chelation, iron-sulfur cluster restoration, or mitochondrial protection, highlighting FDXs as key nodes linking the regulation of mitochondrial function to disease outcomes. Fig. 4 FDXs as central regulators of mitochondrial pathology across disease spectrums As core regulators of mitochondrial homeostasis, FDX1 and FDX2 control mitochondrial homeostasis and cell death through multiple pathways, thus linking mitochondrial dysfunction to major diseases. In cancer, FDX1 drives cuproptosis by mediating copper-dependent lipoylation of mitochondrial proteins, while FDX2 regulates Fe–S cluster assembly to control iron metabolism and ferroptosis. Their interplay amplifies oxidative stress, linking tumor metabolism to cell death pathways. In neurodegenerative diseases, FDX1 mediates copper toxicity in AD and PD via impaired copper reduction and lipoylation defects. Copper overload disrupts mitochondrial function and induces cuproptosis, exacerbating neurodegeneration. In cardiovascular diseases, FDX1 dysregulation disrupts lipid metabolism and causes copper-induced cuproptosis in ischemic cardiomyopathy and atherosclerosis. Mitochondrial dysfunction further destabilizes vascular homeostasis. In endocrine diseases, FDX1 integrates steroidogenesis and copper-dependent β-cell cuproptosis in diabetes. Tissue-specific roles in PCOS and T2DM highlight its dual functions. In genetic diseases, FDX1 defects cause copper dyshomeostasis in Menkes/Wilson disease, while FDX2 mutations disrupt Fe–S cluster biogenesis, leading to mitochondrial myopathies and lactic acidosis. Treatment interventions target copper chelation, iron-sulfur cluster restoration, or mitochondrial protection, highlighting FDXs as key nodes linking the regulation of mitochondrial function to disease outcomes. Cancer remains one of the most formidable global public health challenges, with escalating incidence and mortality rates significantly impeding improvements in life expectancy worldwide [ 122 ]. Despite advances in oncology, effective cancer treatment continues to face substantial challenges due to the intrinsic complexity of malignant tumors. Tumorigenesis is driven by multiple hallmark biological processes, including: (i) sustained proliferative signaling, (ii) evasion of growth suppression, (iii) resistance to apoptotic cell death, (iv) replicative immortality, (v) angiogenesis induction, (vi) activation of invasion and metastasis, (vii) metabolic reprogramming, and (vii) immune evasion. Furthermore, the dynamic tumor microenvironment adds another layer of complexity to cancer pathogenesis and therapeutic resistance [ 123 ]. At the core of these pathological processes lies mitochondrial function – a hub for energy metabolism, cell death regulation, and redox balance – where members of the ferredoxin family, FDX1 and FDX2, exert unique and critical roles. Their core biological functions are intimately linked to mitochondrial integrity: FDX1 is involved in copper metabolism and lipoylation of mitochondrial proteins [ 124 ]. Emerging evidence highlights cuproptosis, a copper-dependent, mitochondria-mediated cell death pathway, as a critical modulator of tumor immunity and clinical outcomes across various cancer types, with FDX1 serving as its central mediator [ 125 ]. In contrast, FDX2 influences mitochondrial function, iron metabolism, and genomic stability in cancer through its key involvement in iron-sulfur cluster biogenesis. Collectively, FDX1 and FDX2 connect mitochondrial function to cancer hallmarks such as metabolic reprogramming, resistance to cell death, and immune evasion, making their mitochondria-centered mechanisms pivotal for understanding cancer pathogenesis and developing targeted therapies. As an essential mitochondrial iron-sulfur protein, FDX1 exerts diverse roles in cancer through mechanisms deeply rooted in mitochondrial function. Its biological activities, spanning lipoylation of mitochondrial enzymes, regulation of metabolic pathways, and mediation of cuproptosis, are all tightly linked to mitochondrial homeostasis, forming a functional network that extends from basic mitochondrial processes to the complex pathogenesis of tumors. Exploring these roles reveals how FDX1's mitochondrial functions shape cancer development, therapeutic responses, and immune interactions. At the mitochondrial level, FDX1 mediates lipoylation of mitochondrial enzymes (e.g., DLAT), a process critical for TCA cycle function and mitochondrial metabolic integrity. This lipoylation capacity directly underlies its role as the central executor of cuproptosis [ 126 ]. In cancer, FDX1-mediated cuproptosis exhibits a dual role shaped by its mitochondrial lipoylation function. In KIRC/LUAD, downregulated FDX1 impairs lipoylated protein oligomerization, reducing cuproptosis sensitivity and promoting tumor survival. In STAD/GBM, upregulated FDX1 enhances lipoylation-dependent cuproptosis, increasing sensitivity to chemotherapy (e.g., 5-FU) [ 111 , 125 , 127 , 128 ]. The molecular basis for these opposing expression patterns appears to be rooted in the distinct metabolic adaptations of different tumors to their microenvironment. In GBM, which is characterized by severe hypoxia and a reliance on mitochondrial respiration for invasion, FDX1 is upregulated, potentially as an adaptive response to maintain electron transfer and OXPHOS under metabolic stress [ 129 ]. Conversely, in KIRC, where VHL loss leads to constitutive HIF activation and a pseudo-hypoxic state, there may be a selective pressure to downregulate FDX1. This adaptation could serve to decouple the lipoylation-dependent TCA cycle flux from the risk of FDX1-mediated cuproptosis, thereby evading a metabolic vulnerability that might otherwise be exacerbated by the hypoxic tumor milieu [ 125 , 130 ]. This duality is further regulated by mitochondrial redox and copper metabolism: FDX1 reduces Cu 2+ to Cu + in mitochondria, and the FDX1-Cu + complex drives lipoylated protein aggregation, triggering cuproptosis [ 111 , 131 ]. Therapeutically, this mitochondrial mechanism is targetable. Copper ionophores like ES may enhance FDX1-mediated cuproptosis in FDX1-high cancers [ 131 , 132 ]. However, AKT1-mediated phosphorylation of FDX1 at Ser63 disrupts its mitochondrial function, reducing DLAT lipoylation and shifting metabolism from mitochondrial oxidative phosphorylation to glycolysis, thereby resisting cuproptosis [ 65 ]. This resistance is reversible: Combining AKT inhibitor MK2206 with ES restores FDX1's mitochondrial lipoylation capacity, re-sensitizing TNBC to cuproptosis in vitro and in vivo [ 65 ]. Additionally, multiple regulatory axes control FDX1 activity in cuproptosis. In esophageal squamous cell carcinoma (ESCC), l -lactate induces NUDT21 lactylation via AARS1, promoting 3′ UTR lengthening of FDX1 mRNA and translational suppression, correlating with poor prognosis in LDHA/NUDT21-high tumors [ 64 ]. In HCC, copper activates SEC14L3, which suppresses ERK/YY1 signaling to elevate FDX1 expression, forming a feed-forward loop that enhances cuproptosis sensitivity and establishes the SEC14L3-ERK-YY1-FDX1 axis [ 61 ]. MiR-3130–5p inhibits FDX1 by binding its 3′ UTR, worsening HCC prognosis [ 63 ]. In colorectal cancer, lncRNA PVT1 activates FDX1 transcription via direct promoter binding (with H3K27ac deposition) and recruiting transcription factor SF1 [ 59 ]. In OC, FDX1 expression governs sensitivity to ES-Cu-driven cuproptosis in a dose-dependent manner; its depletion confers resistance, whereas enforced overexpression heightens susceptibility. This same axis also modulates the cellular response to cisplatin [ 132 ]. In pancreatic cancer (PC), chlorophyllin (CHL) induces cuproptosis sequentially: depletes GSH/elevates ROS, releases free Cu 2+ , which binds FDX1 to drive DLAT oligomerization. It is important to note that this synergistic activity, mediated through the FDX1 pathway, has been demonstrated in preclinical studies including cell-based assays and mouse xenograft models, and its efficacy in human patients remains to be evaluated [ 133 ]. In STAD, FDX1 knockdown increases 5-FU/cisplatin IC50, confirming its role in chemosensitivity [ 127 ]. In multiple myeloma, elesclomol overcomes proteasome inhibitor resistance by disrupting the mitochondrial Fe–S cluster pathway [ 67 ]. FDX1's mitochondrial functions extend to metabolic regulation, linking mitochondrial metabolism to tumor progression. Its role in the TCA cycle regulation influences cancer cell metabolic reprogramming, a hallmark of malignancy. In KIRC, FDX1 expression correlates with genes involved in the TCA cycle and OXPHOS, indicating its role in maintaining mitochondrial energy metabolism [ 125 , 130 , 134 ]. Pan-cancer analyses further link FDX1 to fatty acid metabolism and PPAR signaling pathways intertwined with mitochondrial lipid metabolism [ 41 , [135] , [136] , [137] ]. In OC cells, FDX1 activation during chronic cuproptosis induction upregulates mitochondrial cholesterol biosynthesis genes, elevating total cholesterol levels. This suggests cross-talk between FDX1's mitochondrial function and cholesterol metabolism, as cholesterol depletion mitigates cuproptosis cytotoxicity [ 132 ]. Building upon the observation that FDX1 upregulation enhances chemosensitivity in STAD, comprehensive bioinformatic analyses provide deeper mechanistic and clinical insights. A landmark study by Zuo et al. integrating data from TCGA, GTEx, and GEO, established FDX1 as a pivotal cuproptosis regulator in this malignancy. They demonstrated that high FDX1 expression is a significant prognostic factor associated with improved survival. It was significantly correlated with elevated tumor mutation burden (TMB, r = 0.240, p < 0.001) and microsatellite instability (MSI, r = 0.247, p < 0.001), suggesting enhanced tumor immunogenicity. However, this coexisted with an overall reduction in immune cell infiltration, presenting a complex interplay. Crucially, their drug sensitivity analysis confirmed that FDX1-high tumors exhibit significantly increased sensitivity to first-line chemotherapeutic agents, including cisplatin (p = 0.012) and 5-fluorouracil (p = 0.034). These findings collectively position FDX1 as a multifaceted biomarker with utility in prognostic prediction and chemotherapy guidance, underscoring its value in formulating individualized treatment strategies for STAD patients [ 127 ]. Under extreme hypoxia, glioblastoma cells upregulate FDX1 to preserve mitochondrial function. FDX1 interacts with DNA damage response kinases (ATM/DNA-PKcs) in mitochondria, activating AKT and enhancing DNA repair, enabling tumor cells to survive hypoxic stress and resist radiation [ 129 ]. These metabolic roles directly affect therapeutic responses. High FDX1 expression increases sensitivity to 17-AAG (a mitochondrial HSP90 inhibitor) in pan-cancer analyses, while conferring cisplatin resistance in ovarian/cervical cancers and enhancing oxaliplatin sensitivity in HCC [ 14 , 25 , 138 , 139 ]. FDX1's immune regulatory roles in cancer are indirectly linked to its mitochondrial functions, as mitochondrial metabolism shapes the tumor microenvironment (TIME). Single-cell sequencing shows FDX1 is highly expressed in tumor-associated macrophages (TAMs), cells dependent on mitochondrial metabolism for function [ 134 ]. In KIRC, low FDX1 correlates with abnormal immune infiltration and advanced disease [ 140 ]. In STAD, high FDX1 associates with favorable profiles: activated CD4 + T memory cells, follicular helper T cells, M1 macrophages, and negatively correlates with resting NK cells/monocytes [ 127 ]. FDX1 upregulates PD-L1 (CD274), likely via mitochondrial redox-dependent transcriptional control. In KIRC, LUSC, glioma, and melanoma, FDX1 expression positively correlates with PD-L1 [ 125 , 141 , 142 ]. In gliomas, FDX1 regulates PD-L1 via NOD-like receptor signaling activation, pathways influenced by mitochondrial stress [ 141 ]. In gliomas, this is mediated by NOD-like receptor signaling activation, pathways associated with mitochondrial stress [ 141 ]. Copper-doped nanoparticles (CACuPDA) were found to effectively compromise mitochondrial function and trigger dual FDX1-dependent cuproptosis and ferroptosis through depletion of the GSH/GPX4 antioxidant axis. This dual cell death mechanism causes extensive tumor lysis and significantly reprograms the immunosuppressive microenvironment, as evidenced by increased cytotoxic T cells and reduced regulatory T cells. Notably, this approach synergizes remarkably with anti -PD-L1 therapy, enhancing tumor suppression by approximately 5-fold compared to anti -PD-L1 monotherapy [ 143 ]. This synergy highlights how FDX1's mitochondrial-mediated cell death modulates immune responses. The expression patterns of FDX1 are closely related to its mitochondrial functions. In KIRC, LUAD, LIHC, and CRC, FDX1 is downregulated, impairing mitochondrial lipoylation/cuproptosis and promoting survival [ 125 , 130 ]. In KIRC, reduced FDX1 correlates with higher grades, advanced TNM stages, and poor survival, partly via EMT promotion through FMR1-ALCAM dysregulation [ 140 , 144 ]. In OC, FDX1 mRNA is decreased in tumors vs. normal ovarian epithelium [ 132 ]. Conversely, FDX1 is overexpressed in glioblastoma, gastric adenocarcinoma, and endometrial carcinoma, potentially supporting mitochondrial metabolism for proliferation [ 25 , 145 ]. In STAD, high FDX1 associates with better survival, 5-FU/cisplatin sensitivity, and higher tumor mutational burden (TMB) and microsatellite instability (MSI) [ 127 ]. In glioma, FDX1 is part of a cuproptosis-related gene signature with prognostic value [ 128 ]. The activity of FDX1 is regulated by phosphorylation, lactylation, and multiple mechanisms at the transcriptional and epigenetic levels. These mechanisms act together on mitochondrial function, providing entry points for targeted interventions [ 59 , 61 , [63] , [64] , [65] ]. For example, LDHA inhibitors targeting lactate-mediated FDX1 suppression could restore mitochondrial-dependent cuproptosis in ESCC [ 64 ]. Collectively, FDX1's roles in cancer stem from mitochondrial functions, connecting lipoylation, metabolism, cuproptosis, immune modulation, and clinical outcomes, supporting its potential as a mitochondrial-centric therapeutic target. As the master regulator of Fe–S cluster biogenesis, FDX2 contributes to cancer pathogenesis by playing a fundamental role in mitochondrial function, iron metabolism, and the maintenance of genomic stability. Its function is critical for the activity of numerous mitochondrial and nuclear proteins, including ETC complexes, key metabolic enzymes, and DNA repair machinery [ 12 ]. Deficiency in FDX2 disrupts Fe–S cluster biogenesis, leading to a cascade of detrimental effects: impaired mitochondrial ETC function reduces ATP production, dysregulated iron homeostasis causes mitochondrial Fe 2+ overload, and subsequent oxidative stress elevates ROS. This convergence of metabolic and genotoxic stress is a hallmark of cancer cell vulnerability. In ovarian cancer cells, loss of FDX2 creates a state of heightened sensitivity to ferroptosis. The resulting iron overload and lipid peroxidation predispose cells to this iron-dependent form of cell death. This vulnerability is profoundly exposed when combined with pharmacological inhibition of the GPX4 or FSP1 pathways [ 12 ]. This synthetic lethal interaction underscores that FDX2 deficiency, while manageable under basal conditions, pushes cells beyond a survivable threshold upon disruption of parallel antioxidant systems. Consequently, FDX2 status emerges as a critical biomarker for predicting sensitivity to therapeutic ferroptosis inducers. FDX2-deficient mice develop lipid metabolism disorders, spontaneous tumors (lymphomas, sarcomas), and steatohepatitis; lipidomics shows disrupted cardiolipin and ceramide metabolism, which may promote malignancy by altering membrane dynamics and signaling [ 58 ]. FDX2 maintains genomic stability, as Fe–S cluster-containing proteins are essential for DNA repair. Impaired Fe–S cluster formation due to FDX2 dysfunction can lead to genomic instability, a driver of tumor initiation. Mendelian randomization and co-localization analyses highlight the 19q13.32 region tagged by rs78295726, a locus adjacent to FDX2, as contributing to multiple myeloma risk specifically in the context of COVID-19 hospitalization. This genomic convergence implicates COVID-19-driven cellular stress and potentially perturbed Fe–S cluster homeostasis in myelomagenesis [ 146 ]. FDX2's role in cancer is context-dependent: its deficiency can promote tumorigenesis in some cases, while in others, it may act as a tumor suppressor by maintaining mitochondrial and genomic integrity. Elucidating the precise regulatory networks governing FDX2 in different cancer types, and exploring its synergistic potential with existing modalities, represent critical avenues for future research that could unlock novel, FDX2-directed therapeutic strategies. In tumors, FDX1 and FDX2 crosstalk through Fe–S cluster homeostasis: FDX1-mediated cuproptosis disrupts Fe–S clusters assembled by FDX2, amplifying oxidative stress and synergizing with ferroptosis inducers (e.g., CHL in PC) [ 133 ]. Beyond cuproptosis, they interact through iron and copper metabolism. FDX2's role in Fe–S cluster biogenesis affects iron availability, which influences FDX1-mediated copper homeostasis. Conversely, FDX1-regulated copper levels may impact FDX2's Fe–S cluster synthesis, as copper can displace iron in some metalloproteins. In ovarian cancer, FDX2 deficiency-induced ferroptosis can be enhanced by FDX1-mediated copper accumulation, with both pathways contributing to lipid peroxidation and mitochondrial damage [ 12 ]. Mitochondrial metabolism is another area of cross-talk. FDX1's involvement in the TCA cycle and FDX2's role in ETC function coordinate to maintain mitochondrial integrity. Disruption of either leads to mitochondrial dysfunction, and combined dysregulation exacerbates metabolic stress, driving tumor cells toward death or enhancing dependence on alternative energy sources. In hypoxic tumor microenvironments, FDX1 upregulation supports survival through DNA repair and metabolic adaptation, while FDX2 ensures functionality of Fe–S cluster-containing enzymes involved in hypoxia responses [ 35 , 129 ]. Their cross-talk extends to immune modulation in the TIME. FDX1's regulation of PD-L1 and immune cell infiltration can be influenced by FDX2-mediated Fe–S cluster metabolism, as immune cell function depends on Fe–S cluster-containing proteins [ 147 ]. FDX2-induced ferroptosis can release immunogenic cell death markers, which may synergize with FDX1-dependent cuproptosis to enhance anti-tumor immune responses. This is seen in copper-doped nanoparticles (CACuPDA), which induce FDX1-dependent cuproptosis and ferroptosis, reprogramming the tumor immune microenvironment and enhancing anti -PD-L1 therapy efficacy [ 143 ]. Combining copper ionophores that trigger FDX1-dependent cuproptosis with inhibitors of Fe–S cluster synthesis, which impair FDX2 activity, could induce synthetic lethality in tumors reliant on both pathways. This dual-targeting strategy may enhance therapeutic efficacy across diverse cancers. Looking forward, the emerging technology of single-cell spatial transcriptomics holds immense potential to advance our understanding of FDX-mediated intercellular crosstalk fundamentally. This approach could directly interrogate the proposed metabolic symbiosis within the TME by simultaneously mapping the transcriptional profiles of cancer and stromal cells while preserving their spatial context. A critical hypothesis to test is whether ‘FDX1-high’ tumor cells, which are primed for cuproptosis and reliant on oxidative phosphorylation, coexist in specific niches with ‘FDX2-high’ TAMs that possess enhanced capacity for Fe–S cluster biogenesis. Such spatial association would suggest a previously unrecognized form of metabolic cooperation, potentially mediated by the exchange of iron/copper-containing metabolites or other signaling molecules. Decoding this intricate communication network could unveil novel therapeutic vulnerabilities. For instance, simultaneously targeting FDX1 in tumor cells to induce cuproptosis while disrupting the FDX2-supported pro-tumor functions of TAMs, thereby achieving a synergistic combined therapy that remodels the entire TME. Neurodegenerative diseases (NDs), including Alzheimer's disease (AD), Parkinson's disease (PD), Amyotrophic Lateral Sclerosis (ALS), and Friedreich's Ataxia (FRDA), are driven by protein misfolding, mitochondrial dysfunction, and disrupted metal homeostasis [ 148 ]. These processes are tightly linked to the roles of FDX1 in copper reduction and lipoylated protein stability, as well as the role of FDX2 in Fe–S cluster biogenesis, making FDXs key players in the pathogenesis of NDs. Experimental evidence demonstrates that chronic copper exposure induces oxidative stress by generating ROS, impairing mitochondrial membrane potential, and exacerbating dopaminergic neuron loss in PD [ [149] , [150] , [151] ]. Mechanistically, abnormal FDX1 activity reduces GSH antioxidant capacity, leading to copper overload and cuproptosis [ [149] , [150] , [151] ], which is consistent with FDX1's role in mediating cuproptosis through lipoylated protein aggregation as described in earlier sections. In AD, copper ions significantly accelerate amyloid-β (Aβ) aggregation. Under copper overload conditions, redox cycling promotes Aβ aggregation and plaque formation, generating ROS that damages mitochondrial membranes and proteins. This further depletes mitochondrial iron-sulfur clusters, impairs complex IV activity, and compromises ATP synthesis and mitochondrial function [ 152 ]. Studies in mice show that copper overload exacerbates cognitive deficits, causing cerebral and urinary copper accumulation. It also upregulates FDX1, DLAT, and HSP70 while reducing iron-sulfur cluster protein expression, collectively leading to neuronal degeneration and oxidative damage [ 153 ]. Single-cell transcriptomics has revealed cell-type-specific expression patterns of FDX1 in NDs. For example, while some studies report downregulated FDX1 mRNA in peripheral blood mononuclear cells (PBMCs) of AD patients, qPCR analysis of whole-blood samples shows upregulation, a discrepancy likely due to methodological differences and cell-sorting effects [ 154 , 155 ]. Importantly, FDX1 upregulation is specifically observed in B cells, NK cells, and CD4 + T cells, suggesting its potential involvement in AD pathogenesis via immune-regulatory mechanisms [ 154 ]. As a critical gene in cuproptosis, FDX1 is intricately linked to mitochondrial function, particularly oxidative phosphorylation, and contributes to immune microenvironment remodeling. This makes FDX1 a promising therapeutic target, with potential drugs like LANRAPLENIB already identified as candidates for AD research [ 154 ]. Though direct evidence linking FDX1 to copper-induced Aβ aggregation is lacking, its roles in mitochondrial function and cuproptosis suggest it may indirectly influence Aβ oligomerization by modulating copper ion distribution and activity, warranting further investigation [ 152 , 153 ]. Additionally, copper-FDX1 interactions in AD impair synaptic energy metabolism, contributing to cognitive decline [ 155 ]. Mitochondrial dysfunction emerges as a convergent mechanism across NDs [ 156 , 157 ]. This is particularly evident in PD, copper disrupts α-synuclein (α-Syn) homeostasis, facilitating Lewy body formation via interactions with copper-binding residues (e.g., His 50) [ [158] , [159] , [160] ]. FDX1 expression is upregulated in PD, where it acts as a core molecular switch linking mitochondrial dysfunction, oxidative stress, and α-Syn pathology by driving the cuproptosis pathway – emerging as a novel target for PD treatment. Specifically, FDX1 overexpression directly induces dopaminergic neuron death and motor function impairment, confirming its critical role in PD pathogenesis [ 159 ]. This axis represents a promising therapeutic target, as guanidinium-modified calixarene/cyclodextrin (GCA-CD) nanomedicine rescues motor deficits in Parkinson's disease models by inhibiting FDX1/LIAS-mediated cuproptosis, reducing α-synuclein aggregation, and restoring mitochondrial function [ 159 ]. Copper homeostasis dysregulation, which is associated with the pathogenesis of both AD and PD, triggers a series of harmful events. In AD models under copper stress, for example, upregulation of FDX1 is associated with aggregation of lipoylated proteins (e.g., DLAT) and induction of oxidative stress; simultaneously, copper overload inhibits CREB phosphorylation and BDNF expression, leading to impaired synaptic plasticity [ 153 , 155 , 157 ]. In PD, copper homeostasis dysregulation similarly activates FDX1 to induce cuproptosis, promotes α-Syn aggregation, and depletes GSH, jointly exacerbating proteotoxic stress and the loss of dopaminergic neurons. Importantly, CREB inactivation is also a key feature of PD, driving dopaminergic neurodegeneration [ 153 , 161 ]. This dual pathway of cuproptosis and CREB inhibition highlights the common mechanisms of neurodegeneration in AD and PD. FRDA is the most common autosomal recessive ataxia. It is caused by GAA repeat expansion in the FXN gene, which encodes frataxin, a mitochondrial protein involved in ISC biogenesis [ 162 ]. FRDA is characterized by the degeneration of large sensory neurons and spinocerebellar tracts, as well as an increased incidence of cardiomyopathy and diabetes [ 163 ]. A deficiency in FXN protein impairs the biosynthesis of Fe–S clusters [ 164 ]. FXN acts as a kinetic activator, accelerating persulfide transfer from NFS1 to ISCU. FXN deficiency slows persulfide transfer by ∼6-fold, leading to toxic accumulation and impaired [2Fe–2S] cluster assembly on ISCU. This disrupts FDX2-dependent electron transfer, causing mitochondrial failure and oxidative stress. Indirectly, Fe–S defects impair lipoylation via LIAS dysfunction, contributing to metabolic disturbances. A key research gap is understanding the precise role of FDX2 in FRDA pathogenesis and whether it can be targeted therapeutically. While FXN is the primary defect, FDX2 dysfunction exacerbates pathology, as Zn 2+ dysregulation may further inhibit FDX2 under FXN-deficient conditions. This dual hit of FXN deficiency and zinc imbalance amplifies mitochondrial dysfunction [ 28 , 52 ]. Additionally, calcitriol (1,25-dihydroxyvitamin D3) has shown potential in treating FRDA. Studies have demonstrated that calcitriol supplementation significantly increases frataxin protein levels and restores mitochondrial function in dorsal root ganglion (DRG) neurons, cardiomyocytes with frataxin deficiency, and lymphoblasts from FRDA patients [ 165 ]. Mechanistically, calcitriol may bind to the promoter region of the frataxin gene via the vitamin D receptor (VDR) to enhance its transcription. Meanwhile, calcitriol restores the level of FDX1, an electron donor for the calcitriol-synthesizing enzyme CYP27B1. It also improves the expression of the mitochondrial calcium exchanger (NCLX) and mitochondrial membrane potential (ΔΨm), reduces oxidative stress and calcium dysregulation, and decreases apoptosis and neurite degeneration. Ultimately, these effects lead to increased cell survival. These findings support calcitriol as an accessible and affordable therapeutic strategy for FRDA [ 165 ]. However, the direct involvement of FDX2 in this process remains unclear, highlighting another area for investigation. Future studies should also examine whether targeting FDX2 activation or zinc chelation could modulate disease progression, and how FDXs interact with other ISC biogenesis components in FRDA models. ALS is a fatal neurodegenerative disorder characterized by the progressive degeneration of motor neurons in the brain and spinal cord, leading to muscle weakness, paralysis, and ultimately respiratory failure within 3–5 years of onset [ 166 ]. Superoxide dismutase 1(SOD1) is a classic pathogenic gene for ALS. Mutations in this gene play a key role in the pathogenesis of ALS by mediating toxic gain-of-function mechanisms, including protein aggregation and oxidative stress [ 167 ]. A significant research gap exists in understanding the direct role of FDXs, particularly FDX2, in ALS pathogenesis. While mutations in SOD1 are known to cause familial ALS by promoting toxic gain-of-function, including aberrant peroxidase activity and protein aggregation [ 168 ], the connection to mitochondrial Fe–S cluster damage warrants further investigation. Studies have shown that the superoxide radical (O 2 • - ) can oxidize [4Fe–4S] clusters to [3Fe–4S] clusters in neural tissues of the SOD1G93A ALS rat model, concurrently releasing iron [ 169 ]. This Fe–S cluster damage is associated with mitochondrial dysfunction and is considered a potential source of redox-active iron contributing to oxidative stress in ALS [ 169 ]. This presents a critical research gap regarding whether the observed Fe–S cluster deficiency in ALS models is related to impaired FDX2 function. As the primary electron donor for Fe–S cluster biogenesis, FDX2 dysfunction could directly lead to the collapse of [4Fe–4S] clusters in critical mitochondrial complexes (I, II, III) and enzymes like aconitase, mirroring the damage induced by superoxide [ 29 , 169 ]. Future studies should investigate whether mutant SOD1 or the resulting oxidative stress directly or indirectly impacts FDX2 expression, activity, or its interaction with the Fe–S cluster assembly machinery (e.g., NFS1-ISD11-ACP1 complex, ISCU, ISCA1-ISCA2). Establishing a link between FDX2 dysfunction and the Fe–S cluster pathology observed in ALS would identify a novel mechanistic pathway and highlight FDX2 as a potential therapeutic target for stabilizing mitochondrial function in ALS. Despite diverse genetic and clinical presentations in neurodegenerative diseases, mitochondrial dysfunction mediated by FDX1 and FDX2 represents a unifying pathogenic mechanism. FDX1 dysregulation disrupts copper homeostasis and triggers cuproptosis, whereas FDX2 deficiency impairs Fe–S cluster biogenesis, compromises respiratory chain activity, and heightens ferroptosis susceptibility. Both pathways converge on extensive mitochondrial ROS accumulation, promoting neuronal death via oxidative damage and energy failure [ 152 , 156 ]. Importantly, crosstalk exists between FDX1-modulated copper metabolism and FDX2-driven Fe–S cluster assembly: copper ions disrupt Fe–S cluster stability, and impaired Fe–S biogenesis aggravates iron dyshomeostasis, creating a self-reinforcing vicious cycle. Ultimately, FDX dysfunction culminates in respiratory chain failure and ATP depletion. Interventional strategies targeting FDXs, such as metal ion chelators and supplementation with the antioxidant GSH, provide potential therapeutic directions for various neurodegenerative diseases by stabilizing metal ion homeostasis and redox balance [ 158 ]. Future therapies should consider cell-type-specific FDX modulation to ameliorate neuronal loss and neuroinflammation simultaneously. Current research still needs to address key gaps, particularly the role of FDX2 in amyotrophic lateral sclerosis-related Fe–S cluster deficiency and Friedreich's ataxia pathogenesis, as well as the potential value of FDXs in other neurodegenerative diseases. Cardiovascular diseases (CVDs) are one of the major causes of death and disability worldwide [ 170 ]. FDX1's role in cardiovascular health is deeply rooted in its core functions spanning lipid metabolism regulation and mitochondrial redox balance maintenance, with copper homeostasis serving as a critical intersecting factor [ 171 ]. Experimental studies highlight how disruptions in these functions drive vascular and myocardial damage through interconnected pathways. FDX1's involvement in lipid metabolism is central to atherosclerotic processes. Functional validation shows FDX1 knockout decreases 3BH5C secretion by 82–90 % in hepatocytes and reduces macrophage cholesterol efflux by 15 %, while overexpression rescues these phenotypes [ 57 ]. This aligns with its role in regulating cholesterol transport, as single-cell analyses link FDX1 to CD52-high lipid-handling macrophage subpopulations in plaques, where it drives reverse cholesterol transport via CYP27A1 and LXR signaling [ 57 ]. Genetic association analyses identify an atherosclerosis-risk locus near FDX1 (rs10488763) where the minor allele(T) disrupts AP-1/CEBPβ-mediated transcriptional activation, reducing FDX1 expression by 13 % in lipid-loaded macrophages [ 62 ]. This impairment compromises mitochondrial Fe–S cluster biogenesis, resulting in depressed respiratory chain activity and attenuated lipid clearance. The variant confers significant coronary artery disease risk, mechanistically linking FDX1 deficiency to foam cell formation in atherosclerotic plaques [ 62 ]. Metabolomics studies have shown that FDX1 influences the atherosclerotic process by regulating the synthesis of 3BH5C, a cholesterol metabolite in the acidic pathway, thereby affecting cholesterol efflux. A study of 8124 Asian individuals revealed that the risk allele rs10488763-T exhibits a significant population-specific effect. The impact of the FDX1-3BH5C pathway, marked by this allele, on coronary artery disease is substantially stronger in Asian populations compared to European populations, with a 5- to 6-fold difference in the effect size. This disparity highlights the population-specific regulatory mechanisms of the cholesterol metabolic pathway and reflects the unique pathophysiological characteristics of Asian populations in FDX1-mediated metabolism [ 57 ]. Mitochondrial dysfunction, another core FDX1 function, underpins multiple CVD pathologies. In ischemic cardiomyopathy (IC), FDX1 downregulation correlates with mitochondrial respiratory chain defects and oxidative damage, underscoring its potential as an immunobiomarker [ 172 ]. Pharmacological activation of FDX1 (e.g., dexmedetomidine) mitigates cerebral ischemia-reperfusion injury by reducing copper accumulation and preserving mitochondrial membrane potential, while FDX1 deficiency disrupts ETC activity, amplifying ROS production and lipid peroxidation in endothelial cells to destabilize atherosclerotic plaques [ 173 , 174 ]. This mitochondrial vulnerability extends to myocardial infarction (MI), where copper ion overload in infarcted tissue triggers FDX1-mediated cuproptosis, a process involving copper-dependent aggregation of lipoylated proteins (refer to Section 5.1 ). Cardiomyocytes respond through LRP6 nuclear translocation, which interacts with ALKBH5 to inhibit m 6 A modification of FDX1, exacerbating copper toxicity [ 175 ]. Therapeutic strategies targeting this axis show promise: tribromobimane (TLB) improves cardiac function in doxorubicin-induced cardiotoxicity (DIC) by binding FDX1, reducing mitochondrial oxidative stress and cuproptosis [ 176 ]. DSF also protects against cerebral ischemia-reperfusion injury by inhibiting FDX1, regulating copper homeostasis, and alleviating inflammation via the HSP70/TLR4/NLRP3 pathway [ 177 ]. Broadly, alleviating oxidative stress and inhibiting cuproptosis exert cardioprotective effects [ 176 , 178 , 179 ]. FDX1's dual functions in lipid metabolism and mitochondrial health also influence vascular calcification. In vascular smooth muscle cells (VSMCs), elevated FDX1 and Slc31a1 levels coincide with increased copper levels and decreased Elabela expression. Administration of Elabela hinders calcification progression in VitD3-overloaded models by activating PPAR-γ signaling, which suppresses FDX1 expression and rescues mitochondrial function [ 180 ]. Similarly, in post-MI contexts, chrysin-7- O -glucuronide (C7Og) reduces myocardial damage by inhibiting LRP6, thereby modulating FDX1-dependent mitochondrial stability [ 175 ]. These findings position FDX1 as a pleiotropic regulator of cardiovascular health, with its core functions in lipid metabolism and mitochondrial homeostasis driving pathogenesis across atherosclerosis, ischemia, and calcification. Targeting FDX1's context-specific roles through lipid metabolism modulation, mitochondrial protection, or cuproptosis inhibition offers diverse therapeutic avenues for CVD. FDX1 exerts pivotal effects in endocrine diseases through its dual core functions: steroidogenesis and copper metabolism-mediated cell death. These functions converge in conditions like type 2 diabetes mellitus (T2DM) and polycystic ovary syndrome (PCOS), driving pathological processes through tissue-specific mechanisms. FDX1's role in steroid hormone synthesis, rooted in its function as an electron transporter for cytochrome P450 enzymes, underpins its tissue-specific effects in PCOS. As a key component of the FDXR-FDX1-P450scc complex, it supports cholesterol side-chain cleavage via CYP11A1, a rate-limiting step in steroidogenesis [ 181 , 182 ]. This process exhibits dysregulated tissue specificity in PCOS: in granulosa cells, FDX1 downregulation reduces CYP11A1 activity, impairing progesterone synthesis and disrupting the hormonal balance; conversely, in theca cells, FDX1 upregulation enhances mitochondrial steroidogenesis, accelerating cholesterol-to-androgen conversion and exacerbating hyperandrogenemia [ 183 , 184 ]. This imbalance in steroidogenesis, driven by FDX1's tissue-specific expression, directly contributes to PCOS pathophysiology. Therapeutically, GLP-1 agonists like liraglutide improve PCOS symptoms by upregulating FDX1 and mitigating oxidative stress, restoring the balance between androgen and progesterone synthesis [ 185 ]. In T2DM, FDX1's role in copper homeostasis and cuproptosis takes center stage, mirroring its cell death mechanisms in cancer but with distinct pathological consequences. Serum copper metabolism imbalance leads to mitochondrial copper accumulation in β-cells, activating FDX1-dependent cuproptosis [ 186 , 187 ]. This cuproptotic pathway impairs insulin secretion by compromising β-cell viability, a key feature of T2DM progression. The pathological reach of FDX1-mediated copper dysregulation extends beyond β-cells. In diabetes-associated cognitive dysfunction (DACD), neuronal copper overload exacerbates cuproptosis, as evidenced by reduced expression of FDX1, LIAS, and DLAT under high glucose/palmitic acid conditions [ 188 ]. Mitochondrial ROS production amplifies β-cell oxidative damage, while in diabetic retinopathy, FDX1 downregulation is linked to STAT1-mediated SLC31A1 overexpression, promoting microglial inflammation under hyperglycemic conditions [ 189 , 190 ]. Therapeutic strategies targeting FDX1's copper metabolic function show promise. Peripheral mitochondrial transplantation (Mito-PLt) suppresses cuproptosis by restoring copper homeostasis and neuronal function, while copper chelators or FDX1 agonists may preserve β-cell function by rebalancing copper levels [ 187 , 188 , 190 ]. These interventions align with FDX1's core role in regulating copper-dependent cell death, highlighting its potential as a target for T2DM and its complications. The dual functions of FDX1, steroidogenesis and copper metabolism, position it as a critical regulator of endocrine-metabolic disorders. In PCOS, its role in steroidogenesis drives hormonal imbalance, while in T2DM, its mediation of cuproptosis disrupts β-cell function. These processes, though distinct, share a reliance on FDX1's mitochondrial localization and interaction with metal ions, linking back to its fundamental mechanisms outlined in earlier sections. Future research should focus on tissue-specific modulation of FDX1 to target these distinct pathways, optimizing therapeutic strategies for endocrine diseases. FDX1 and FDX2 contribute to distinct genetic disorders through their core functions – copper metabolism and Fe–S cluster biogenesis – both converging on mitochondrial integrity. Disruption of either pathway impairs mitochondrial function, driving distinct genetic disorders while sharing a common root in mitochondrial dysfunction. FDX1's role in mitochondrial copper metabolism is pivotal in two copper-related genetic disorders, with pathogenicity rooted in impaired mitochondrial copper utilization and redox homeostasis. In Menkes syndrome, an X-linked recessive disorder from ATP7A mutations, FDX1's ability to reduce Cu 2+ to Cu + (a step critical for mitochondrial copper import) is compromised [ 191 ]. This impairs mitochondrial copper-dependent processes, including COX activity, a key component of the respiratory chain. Research shows FDX1-dependent reduction of ES-Cu 2+ to ES-Cu + enables mitochondrial copper release and respiratory function recovery; FDX1 knockout exacerbates mitochondrial dysfunction (e.g., decreased COX activity) and diminishes the therapeutic effect of ES, highlighting its role in sustaining mitochondrial respiratory chain function [ 20 ]. Conversely, Wilson's disease, caused by ATP7B mutations, leads to copper accumulation in mitochondria [ 192 ]. FDX1 expression is upregulated here, with its copper-reducing activity amplifying toxic Cu + levels in the mitochondrial matrix. This overload disrupts redox balance, inducing mitochondrial ROS production and impairing respiratory chain function. Clinical studies show FDX1 levels decrease after treatment with sodium dimercaptosulphonate, linking its activity directly to mitochondrial copper toxicity [ 193 ]. FDX1 dysfunction disrupts mitochondrial copper homeostasis in both Menkes and Wilson's diseases through opposing mechanisms. In Menkes disease, impaired FDX1 activity leads to mitochondrial copper deficiency, starving respiratory enzymes of their essential cofactor. Conversely, in Wilson's disease, excessive FDX1-mediated Cu 2+ reduction results in toxic Cu  +  overload. Both scenarios ultimately cause mitochondrial respiratory failure. FDX2's role in mitochondrial Fe–S cluster biogenesis makes it critical for maintaining mitochondrial enzyme activity, with mutations disrupting this process and inducing mitochondrial energy failure. Mutations in FDX2 disrupt [4Fe–4S] cluster synthesis, a process essential for mitochondrial respiratory chain complexes I-III and Fe–S-dependent enzymes like aconitase [ 48 ]. This directly impairs mitochondrial energy metabolism: homozygous FDX2 c.431C > T (p.P144L) mutations cause childhood-onset optic atrophy, myopathy, and leukoencephalopathy, with muscle biopsies showing SDH/COX deficiency (key mitochondrial enzymes) and iron deposition [ 45 , 194 ]. Other mutations (e.g., c.1A > T) reduce aconitase activity by 75 %, while c.12G > T and c.10A > T mutations induce rhabdomyolysis and lactic acidosis, all reflecting mitochondrial energy metabolism collapse due to Fe–S cluster depletion [ [195] , [196] , [197] ]. The interaction between FDX2 and FDXR is critical for electron transfer in Fe–S cluster synthesis: FDXR mutations (e.g., R392W, c.1174C > T) impair electrostatic interactions with FDX2, reducing electron transfer efficiency to just 30 % of normal levels [ [198] , [199] , [200] ]. This disruption in electron supply to FDX2 hinders Fe–S cluster biogenesis, leading to mitochondrial iron overload, complex I/II deficiencies, and lactate accumulation [ [199] , [200] , [201] ]. Concurrently, this electron transfer dysfunction compromises mitochondrial membrane potential and exacerbates ROS production, further amplifying mitochondrial damage [ [199] , [200] , [201] ]. Diagnostic markers such as elevated serum FGF21 and impaired respiratory chain enzyme activity further reflect mitochondrial stress induced by FDX2 defects [ 45 , 198 , 199 ]. Antioxidant therapies target mitochondrial ROS to mitigate this damage [ 195 , 202 ]. It is important to note that comprehensive epidemiological data, such as the population frequency of FDX2 mutations, remain undefined due to the extreme rarity of these disorders. The current clinical understanding is built upon a constellation of consistent findings from individual case reports. These have firmly established that specific serum biomarkers, most notably lactic acid and FGF21, are consistently elevated in affected individuals and serve as reliable hallmarks of the severe mitochondrial dysfunction caused by FDX2 deficiency. FDX1 and FDX2 drive genetic diseases through distinct pathways but converge on mitochondrial impairment. FDX1's copper metabolism defects disrupt mitochondrial redox balance and respiratory chain activity, while FDX2's Fe–S cluster defects cripple mitochondrial enzymes and energy production. Both pathways induce mitochondrial stress through mechanisms such as copper toxicity, Fe–S cluster depletion, or ROS overproduction, which underscores mitochondria as the central effector in FDX-related genetic disorders. This convergence highlights the need for therapies that target mitochondrial resilience while also modulating FDX1/FDX2 in an isoform-specific manner, as such approaches can address the root causes of these conditions. As summarized in Sections 6.1-6 .5, FDX1 and FDX2 exert distinct yet interconnected roles in disease pathogenesis, stemming from their core biological functions. FDX1, through its roles in copper metabolism and lipid metabolism, drives cuproptosis in malignancies and modulates metabolic balance in cardiovascular diseases and endocrine disorders. Its dysfunction disrupts mitochondrial redox homeostasis, linking copper overload/toxicity to pathologies like Wilson's disease and β-cell cuproptosis in T2DM. FDX2, centered on Fe–S cluster biogenesis, maintains mitochondrial enzyme function; its deficiency triggers Fe–S cluster defects, leading to mitochondrial myopathies, genomic instability, and tumor susceptibility. These mechanistic insights have accelerated targeted therapy development: strategies range from restoring FDX activity (e.g., copper chelators in Wilson's disease) to exploiting FDX-dependent vulnerabilities (e.g., cuproptosis inducers in chemotherapy-resistant cancers). To systematize these advances, we summarize disease-specific FDX dysregulation mechanisms and clinical associations, and overview FDX-targeting drugs with their mechanisms and therapeutic impacts ( Table 3 , Table 4 ). Together, these analyses highlight FDXs as pivotal nodes bridging mitochondrial metabolism and cell death pathways, underscoring their potential in precision medicine. Future efforts should prioritize isoform-specific drug design – leveraging FDX1's copper/lipid metabolism vs. FDX2's Fe–S cluster roles – and combinatorial strategies to address context-dependent functions across tissues. Table 3 Molecular mechanisms and clinical associations of FDXs-related diseases. Table 3 Disease Type FDX1-Related Mechanisms FDX2-Related Mechanisms References Cancer Tissue-specific expression patterns (decreased in KIRC/LUAD/LIHC/CRC; increased in GBM/STAD); Regulates EMT through FMR1-ALCAM axis in KIRC; Induces cuproptosis via DLAT lipoylation; AKT1-mediated phosphorylation at Ser63 confers resistance; Correlates with PD-L1 expression and immune infiltration. Deficiency causes lipid metabolism disorders and spontaneous tumors; Disrupts cardiolipin/ceramide metabolism; Induces ferroptosis through mitochondrial Fe 2+ overload; rs78295726 locus associated with multiple myeloma risk. [ 22 , 25 , 65 , 67 , 125 , 127 , 128 , 130 , 132 , 140 , 144 ] Neurodegenerative Diseases Upregulated in specific immune cells (B cells, NK cells, CD4 + T cells)in AD; Mediates dopaminergic neuron death in PD; mpairs synaptic plasticity via CREB/BDNF suppression. FDX2 dysfunction may contribute to ALS-related Fe–S cluster damage; In FRDA, FDX2 electron transfer is disrupted by FXN deficiency, impairing Fe–S cluster assembly. [ 22 , [148] , [149] , [150] , [151] , 153 , [155] , [156] , [157] , [158] , [159] , [160] , 165 , 169 ] Cardiovascular Diseases rs10488763 polymorphism affects macrophage lipid metabolism; LRP6-ALKBH5 axis regulates m6A modification post-MI; Elabela/PPAR-γ axis regulates vascular calcification. Not directly implicated. [ 57 , 62 , [170] , [171] , [172] , [173] , [174] , [175] , [176] , [177] , [178] , [179] , [180] ] Endocrine Diseases T2DM: Induces β-cell cuproptosis through copper overload; PCOS: Differentially regulates steroidogenesis in granulosa/theca cells; Diabetic retinopathy: Associated with STAT1/SLC31A1 pathway. Not directly implicated. [ [181] , [182] , [183] , [184] , [185] , [186] , [187] , [188] , [189] , [190] ] Genetic Disorders Menkes disease: Mediates ES-Cu redox cycling; Wilson disease: Expression decreases after chelation therapy. Mutations cause: Optic atrophy, Mitochondrial myopathy, Rhabdomyolysis (elevated CK), Leukoencephalopathy; Impairs FDXR interaction (reduced to 30 % electron transfer). [ 20 , 45 , 48 , [191] , [192] , [193] , [194] , [195] , [196] , [197] , [198] , [199] , [200] , [201] , [202] ] Table 4 Drugs targeting FDXs. Table 4 Drug/Intervention Disease Mechanism Impact/Findings Reference Elesclomol-Cu Ovarian cancer, TNBC, HCC FDX1-mediated Cu 2+ -Cu + reduction. First-in-class cuproptosis inducer; overcomes cisplatin resistance (synergizes with AKT inhibitor MK2206). [ 22 , 25 , 65 , 67 , 68 , 132 ] Disulfiram-Cu MDS FDX1-mediated Cu 2+ -Cu + reduction – cuproptosis induction. Synergizes with ferroptosis inducers (erastin); penetrates the blood-brain barrier. [ 100 , 101 ] Chlorophyllin Pancreatic cancer Depletes GSH – activates FDX1-Cu + . Shows synergistic anti-tumor activity with gemcitabine in mouse models; clinical efficacy remains unknown. [ 133 ] Erastin/Sorafenib Ovarian cancer Exploits FDX2 deficiency-induced lipid peroxidation. In FDX2-deficient cells, the sensitivity to GPX4 inhibitors can be greatly enhanced. [ 12 , 99 ] Simvastatin MDS Suppresses the mevalonate pathway. Upregulates FDX1 to enhance cuproptosis sensitivity. [ 101 ] Liraglutide PCOS GLP-1 receptor-mediated FDX1 upregulation. Improves granulosa cell mitochondrial function; reduces hyperandrogenemia. [ 185 ] DHEA/CoQ10 Ovarian aging Restores FDX1-dependent steroidogenesis. Rescues oocyte quality in animal models by restoring mitochondrial metabolism. [ 120 , 121 ] Guanidinium-modified calixarene/cyclodextrin Parkinson's disease Inhibits FDX1-LIAS cuproptosis axis. Reduces α-synuclein aggregation; improves motor function in PD models. [ 159 ] Phillygenin Myocardial ischemia-reperfusion CTR1 degradation reducing FDX1 activity. Protects cardiomyocytes from copper overload-induced damage. [ 112 ] Tribromobimane Doxorubicin cardiotoxicity Direct binding to FDX1 inhibiting cuproptosis. Dose-dependently improves cardiac function (15 % LVEF increase). [ 176 ] Elabela Vascular calcification PPARγ-FDX1 axis regulation. Inhibits vascular smooth muscle calcification by suppressing FDX1 overexpression. [ 180 ] Copper chelators (e.g., Penicillamine) Wilson's disease Copper load reduction modulating FDX1. Normalizes FDX1 expression post-treatment; reduces liver copper accumulation. [ 193 ] Mitochondrial transplantation Diabetes-associated cognitive dysfunction Functional FDX1 replenishment. Rescues neurons from cuproptosis; improves cognitive function in diabetes models. [ 188 ] Hypoxia-targeted radiotherapy Glioblastoma Inhibition of FDX1-ATM/DNA-PKcs pathway. Doubles radiosensitivity in FDX1-knockout hypoxic tumor cells. [ 129 ] CACuPDA nanoparticles Lung cancer Concurrent induction of cuproptosis and ferroptosis. 5-fold enhanced tumor suppression when combined with anti -PD-L1 therapy. [ 143 ] Molecular mechanisms and clinical associations of FDXs-related diseases. Drugs targeting FDXs.

Yajuan Lu: Writing – original draft. Yunyi Wu: Data curation. Chen Yang: Writing – original draft. Yi Zhou: Writing – original draft. Xueying Ren: Visualization. Haoran Li: Methodology. Hangqi Huang: Writing – original draft. Feifan Pan: Writing – original draft. Aoli Deng: Writing – original draft. Yi Lu: Visualization. Jiayi Yang: Resources. Xiangmin Tong: Conceptualization, Visualization. Yanchun Li: Funding acquisition, Supervision. Jing Du: Conceptualization, Writing – review & editing.

Not applicable.

All authors agree to publish.

This research was supported by the Construction Fund of Key Medical Disciplines of Hangzhou (No. 2025HZZD01 , 2025HZGF04 ); 10.13039/501100001809 National Natural Science Foundation of China (No. 82202429 ); 10.13039/501100017594 Medical and Health Science and Technology Project of Zhejiang Province (No. 2025KY125 , 2023RC131 , 2022KY074 ); Zhejiang Provincial Natural Science Foundation of China (No. LBY23H080001 ).

The FDXs family, as a key hub linking mitochondrial metabolic reprogramming and programmed cell death, embodies its co-evolution from a basic electron transport role to disease-specific regulatory functions. This review clarifies how FDX proteins dynamically coordinate mitochondrial homeostasis through metabolic remodeling and precisely regulate multiple cell death signaling pathways, thus playing an important role in various diseases. The functions of FDX1 and FDX2 are both specific and synergistic, profoundly reflecting their integrated role in cell physiology. First, the functional differentiation between FDX1 and FDX2 reveals their complex roles in coordinating metabolism with cell death pathways. As a core metabolic sensor, FDX1 directly regulates TCA cycle flux through protein lipoylation while governing copper metabolism and cuproptosis induction. FDX2, as the primary mediator of iron-sulfur cluster biogenesis, maintains respiratory chain function by supporting [4Fe–4S] cluster assembly in complexes I-III. Their interaction forms a central “metabolism-death axis” where FDX1-driven cuproptosis triggers Fe–S cluster dysfunction through Cu + -mediated protein aggregation, while FDX2 deficiency promotes ferroptosis via iron overload and impaired antioxidant defenses due to loss of Fe–S enzymes like Aconitase 1. Beyond these pathways, FDX1 modulates apoptosis in granulosa cells by disrupting mitochondrial membrane potential, and FDX2 deficiency induces p53-dependent apoptosis in ovarian cancer through impaired DNA repair resulting from MUTYH/NTHL1 dysfunction. The regulatory dichotomy extends to autophagy-FDX1, which promotes autophagic flux in PCOS theca cells while suppressing it in cardiomyocytes during ischemia-reperfusion. This bidirectional regulatory network exerts its effects through mitochondrial redox balance, and its regulation may be related to shared substrates such as NADPH or the cross-regulation of ROS levels. Second, the clinical significance of FDX biology is increasingly prominent across multiple disease areas. In cancer, the differential expression patterns of FDX1 across tumor types and its role in regulating cuproptosis sensitivity offer opportunities for targeted therapy, with copper ionophores like ES showing promise for overcoming therapeutic resistance. Furthermore, the emerging role of FDX1 in regulating the tumor immune microenvironment, such as its influence on PD-L1 expression, highlights its significant potential as an immunotherapeutic target. Nevertheless, it is essential to carefully balance its pro-death efficacy against potential pro-survival effects. Beyond oncology, FDX dysregulation contributes to diverse pathologies through distinct mechanisms. In neurodegenerative diseases, FDX1-mediated copper toxicity drives neuronal damage in Alzheimer's and Parkinson's diseases, suggesting copper homeostasis modulation as a potential intervention strategy. Cardiovascular disorders reveal another dimension, where FDX1 polymorphisms impair lipid metabolism in macrophages, exacerbating atherosclerosis, while its overexpression in vascular smooth muscle cells promotes calcification. The endocrine system demonstrates FDX1's dual role in POCS – enhancing androgen production in theca cells while suppressing progesterone synthesis in granulosa cells. Genetic disorders further highlight this dichotomy: FDX1 deficiency worsens Menkes disease through impaired copper utilization, whereas its overexpression contributes to Wilson's disease pathology. Meanwhile, FDX2 mutations cause severe mitochondrial myopathies and leukoencephalopathy through defective Fe–S cluster assembly. Notably, FDX2's clinical relevance extends beyond rare genetic disorders to cancer metabolism and therapeutic targeting. As the cornerstone of Fe–S cluster biogenesis, FDX2 deficiency creates a unique vulnerability in tumors, sensitizing them to ferroptosis induction through mitochondrial iron overload and impaired antioxidant defense. This synthetic lethality with GPX4 inhibition positions FDX2 as both a biomarker for patient stratification and a potential indirect target for combinatorial therapies. Future clinical investigations should prioritize defining FDX2 expression patterns across cancer subtypes and validating its utility in predicting response to ferroptosis-inducing regimens. This spectrum of disease associations underscores the necessity of precise, tissue-specific therapeutic targeting to maximize efficacy while minimizing off-target effects. Third, previous sections have detailed the essential mechanistic role of FDX1 in copper-dependent cell death and mitochondrial metabolism. To evaluate the clinical potential of targeting FDX1, the following summarizes key clinical trial data. These studies investigate FDX1-directed therapeutics across specific oncology indications, focusing on copper-induced cytotoxicity and phosphorylation modulation mechanisms. The compiled data confirm the effectiveness of FDX1 as a viable clinical target. They provide key insights into the therapeutic breakthroughs of FDX1-targeted cuproptosis in solid tumors through copper ion release and phosphorylation regulation. They also reveal the clinical value and potential for future expansion to other diseases, as well as deeper research into regulatory mechanisms ( Table 5 ). Table 5 Summary of clinical trials involving FDX1. Table 5 Disease Medicine Targets/Mechanism of Action NCT Phase Conclusion of NCT Solid tumors Elesclomol FDX1-dependent copper ion release induces cuproptosis. NCT00827203 I The drug is well-tolerated, and its toxicity profile is similar to that of paclitaxel alone. Solid Tumors Elesclomol + Paclitaxel FDX1-dependent copper ion release induces cuproptosis and improves chemotherapy resistance. NCT00088114 I Unknown Ovarian Epithelial Cancer, Fallopian Tube Cancer, or Primary Peritoneal Cancer Elesclomol + Paclitaxel FDX1-dependent copper ion release induces cuproptosis and improves chemotherapy resistance. NCT00888615 II The drug combination was well-tolerated but lacked sufficient promise to merit further investigation. Melanoma Elesclomol + Paclitaxel FDX1-dependent copper ion release induces cuproptosis and improves chemotherapy resistance. NCT00084214 II The combination regimen not only achieved a statistically significant doubling of the median PFS but also had an acceptable toxicity profile, while the OS data were also encouraging. Melanoma Elesclomol + Paclitaxel FDX1-dependent copper ion release induces cuproptosis and improves chemotherapy resistance. NCT00522834 III The combination of elesclomol and paclitaxel did not significantly improve PFS, but this combination therapy improved PFS in patients with normal serum LDH levels. Relapsed or Refractory Acute Myeloid Leukemia Elesclomol FDX1-dependent copper ion release induces cuproptosis. NCT01280786 I Unknown Soft Tissue Sarcomas Elesclomol + Paclitaxel FDX1-dependent copper ion release induces cuproptosis and improves chemotherapy resistance. NCT00087997 II Unknown Stage IIIB or Stage IV Non-Small Cell Lung Cancer (NSCLC) Elesclomol+ Paclitaxel + Carboplatin FDX1-dependent copper ion release induces cuproptosis and improves chemotherapy resistance. NCT00088088 II Unknown Summary of clinical trials involving FDX1. Fourth, the tissue-specific expression of FDX1 and FDX2 is influenced by functional demands, but the molecular mechanisms are distinct and not fully elucidated for both isoforms. For FDX1, which specializes in steroidogenesis, expression is directly regulated by cell type-specific transcription factors such as SF1, as demonstrated in colorectal cancer, where the lncRNA PVT1 activates FDX1 by recruiting SF1 to its promoter and depositing the H3K27ac mark. For FDX2, which supports Fe–S cluster biogenesis and iron metabolism, its enrichment in metabolically active tissues (e.g., liver, heart) suggests a response to high metabolic demands, but the specific regulatory factors remain less clear. While iron-sensing regulators like IRP1/2 are involved in systemic iron homeostasis, the article does not provide direct evidence that IRP1/2 control FDX2 expression; instead, FDX2 may be regulated by other mechanisms related to mitochondrial function or stress responses. In summary, FDX expression likely involves a collaborative interplay where tissue-specific contexts activate transcription factors and epigenetic machinery, but this model is more firmly established for FDX1, and further research is needed to define the precise pathways for FDX2. Fifth, FDX function is dynamically regulated by PTMs, and an intriguing frontier is the potential cell cycle dependency of these modifications. It remains an open question whether key regulatory events, such as the AKT1-mediated phosphorylation of FDX1 at Ser63, are dynamically regulated across the cell cycle—for instance, being enhanced during the G2/M phase to meet the high bioenergetic and biosynthetic demands of mitosis. Investigating the temporal dynamics of FDX PTMs in synchronized cell models could reveal novel mechanisms through which mitochondrial function is coupled to cell division. Elucidating this link would not only answer a fundamental biological question but also have profound implications for cancer therapy, as it could identify a metabolic vulnerability in rapidly proliferating cells. Sixth, FDXs function as central hubs that integrate the mitochondrial metal ion landscape. Directly, Cu + /Cu 2+ and Fe 2+ serve as their primary redox substrates, while Zn 2+ acts as a competitive inhibitor. Beyond these direct substrates, the broader ionic milieu, particularly Ca 2+ and Mg 2+ , may exert indirect metabolic influence. Calcium signaling fluctuations could modulate FDX efficiency by altering membrane potential and redox balance, while Mg 2+ is crucial for powering the FDXR-FDX system by sustaining NADPH production. These plausible models of indirect regulation await validation, representing a promising frontier for understanding FDX function in physiology and disease. While direct binding evidence between Ca 2+ /Mg 2+ and FDXs is currently lacking, their profound influence on overall mitochondrial energy and redox metabolism positions them as key components of the ionic environment that modulates FDX activity. Investigating how FDX function is tuned within altered ionic microenvironments, especially under pathological conditions characterized by Ca 2+ signaling dysregulation, represents a compelling and fruitful avenue for future research. Seventh, the potential role of FDX2 in copper metabolism remains a core unanswered question. Currently, no experimental evidence indicates that FDX2 participates in the metallation of copper-binding proteins like COX17, nor has functional redundancy with FDX1 in copper redox cycling been observed. In fact, a paradigm of strict functional separation is well-established: FDX1 is dedicated to copper reduction, while FDX2 specializes in iron-sulfur cluster biogenesis. This division is strongly supported by their distinct redox potentials and specific protein interactomes. Therefore, shifting the research focus from seeking redundancy to precisely defining functional boundaries is more valuable. A key direction for the future lies in precisely defining the non-redundant role of FDX2 in copper biology through strategies such as analyzing the interaction between FDX2 and copper chaperone proteins, or evaluating FDX2 function under copper metabolism stress conditions, thereby more completely depicting the regulatory network of mitochondrial metal ion homeostasis. Eighth, the tissue-specific and developmental regulation of FDX1-FDX2 homeostasis requires further investigation, as elucidating these mechanisms could identify novel therapeutic opportunities. From a therapeutic perspective, the development of isoform-specific modulators is both a challenge and an opportunity. For example, in-depth analysis of unique structural features such as the electronegative surface of FDX1 and the interaction interface between FDX2 and ISCA1/2, as well as how dynamic subcellular localization regulates the crosstalk between metabolic plasticity and death signals, can provide guidance for rational drug design. Exploring tissue-targeted delivery systems to improve specificity is also crucial. Combining multi-omics approaches with advanced structural biology techniques is essential for unraveling the complex regulatory networks centered on FDX proteins. In conclusion, the co-evolution of FDXs embodies the functional expansion of mitochondria from energy factories to signaling hubs, and their ability to intricately integrate metabolic reprogramming with the execution of cell death is of great significance. As a critical nexus linking mitochondrial stress to the pathogenesis of human diseases, future research on FDXs should prioritize the integration of multi-omics stratification, the design of engineered biological agents targeting isoform-specific interfaces, and the clinical validation of dual-target strategies to decipher the spatiotemporal specificity of FDX networks – a crucial step in translating these mechanistic insights into precision therapies for cancer, cardiovascular diseases, neurodegenerative diseases, metabolic diseases, and hereditary diseases.

Ferredoxins (FDXs) are a large class of iron-sulfur proteins first discovered in the obligate anaerobic non-photosynthetic bacterium, Clostridium pasteurianum in 1962 [ 1 ]. They are named for their unique property of being able to transfer electrons while containing only iron, without heme or flavin cofactors [ 1 ]. Ferredoxins are widely found in various organisms such as plants, animals, bacteria, and archaea and play roles in many fundamental biological processes, including photosynthesis, lipid metabolism, cellular respiration, iron-sulfur (Fe–S) cluster synthesis, steroidogenesis, bile acid production, and vitamin metabolism [ [2] , [3] , [4] , [5] ]. In particular, their involvement in redox processes makes them essential proteins in organisms ranging from non-photosynthetic anaerobic bacteria to photosynthetic single-cell and multicellular life forms [ 5 ]. Moreover, FDXs have been well-characterized as multifunctional regulatory proteins, demonstrating diverse roles in cellular processes. These include: modulating the expression of photooxidative stress-responsive genes [ 6 ]; orchestrating the dynamic reorganization of key protein complexes, particularly in photosynthetic and respiratory electron transport chains [ [7] , [8] , [9] ]; and governing posttranslational protein lipoylation, a crucial modification for cellular metabolism [ 10 ]. Humans possess two mitochondrially localized FDXs, namely ferredoxin 1 (FDX1) and ferredoxin 2 (FDX2, previously known as ferredoxin1L), encoded by adjacent genes on chromosome 11q22 [ 11 ]. These Fe–S proteins serve as crucial electron carriers in mitochondrial metabolic pathways, forming an essential redox chain with ferredoxin reductase (FDXR) to support fundamental processes including oxidative phosphorylation (OXPHOS), the tricarboxylic acid (TCA) cycle, and Fe–S cluster biogenesis. Notably, FDX1 and FDX2 exhibit distinct functional specialization: FDX1 primarily mediates steroid hormone biosynthesis and protein lipoylation, while FDX2 specifically drives [4Fe–4S] cluster assembly and maturation [ 11 ]. This functional dichotomy establishes FDXs as master regulators of mitochondrial metabolic homeostasis. Emerging research has further revealed their pivotal role as molecular nodes integrating metabolic signaling with cell fate determination. FDXs dynamically interface with multiple programmed cell death pathways, including apoptosis [ 12 ], autophagy [ 13 ], ferroptosis [ 12 , 14 ], and cuproptosis [ 15 ]. This paradigm shift highlights FDXs as central players in the crosstalk between cellular metabolism and death signaling networks. This review synthesizes mechanistic insights into how FDX1 and FDX2 govern mitochondrial bioenergetics, Fe–S cluster dynamics, and redox balance, while their dysregulation propagates death signals through cuproptosis, ferroptosis, autophagy, and apoptosis. We further highlight how isoform-specific targeting offers promising therapeutic avenues for oncogenesis and cancer progression, particularly in chemoresistant malignancies, neurodegenerative disorders, cardiovascular pathologies, metabolic disorders, and genetic diseases. By systematically dissecting the co-evolution of FDXs from electron carriers to death regulators, we illuminate their emerging translational potential in precision medicine.

We confirm that there are no known conflicts of interest associated with this publication. All funding sources for this study are disclosed in the manuscript under the “Declarations” section. The authors declare no financial or non-financial competing interests that could influence the work reported in this paper.

The precise control of FDX1 and FDX2 is paramount for mitochondrial integrity, extending beyond their core functions to encompass a sophisticated, multi-layered regulatory network. This network operates at the transcriptional, post-transcriptional, and post-translational levels to dynamically fine-tune FDX abundance and activity in response to cellular cues. In addition to these dynamic mechanisms, FDX function is also influenced by genetic variations. These range from common polymorphisms that modulate disease susceptibility by affecting expression levels, to rare, inactivating mutations that directly cause severe monogenic disorders. The following sections detail this regulatory landscape, with the dysregulation of these layers being a hallmark of diverse pathological states. An intricate network of regulatory mechanisms fine-tunes the functionality of FDXs. In terms of transcriptional and epigenetic control, the transcription of FDX1 is activated in colorectal cancer by the long non-coding RNA PVT1, which recruits transcription factors like SF1 to its promoter [ 59 ]. In glioma, FDX1 expression is upregulated through an m6A methylation-mediated mechanism, where the oncogene C-MYC enhances FDX1 expression via the reader protein YTHDF1 [ 60 ]. At the transcriptional level, the SREBP2, a master regulator of cholesterol synthesis, has been implicated in regulating FDX s expression, although direct binding to the FDX s promoter warrants further experimental validation [ 5 , 58 ]. Additionally, the transcription factor YY1 has been shown to suppress FDX1 expression in hepatocellular carcinoma as part of the SEC14L3-ERK-YY1 axis [ 61 ]. Furthermore, common genetic polymorphisms can set the baseline for FDX1 expression. A prominent example is the rs10488763 variant, which disrupts transcription factor binding and reduces FDX1 expression in macrophages, thereby increasing susceptibility to complex diseases such as coronary artery disease, as detailed in Section 6.3 [ 57 , 62 ]. Regarding post-transcriptional regulation, microRNAs enable rapid fine-tuning of FDX1 levels. For example, miR-3130–5p directly targets the 3′ untranslated region of FDX1 mRNA to trigger its degradation in hepatocellular carcinoma [ 63 ]. Additionally, RNA processing mechanisms contribute to FDX1 regulation; one such mechanism is lactate-induced NUDT21 lactylation, which promotes the formation of a longer 3′ untranslated region that is less efficiently translated, thereby suppressing FDX1 synthesis [ 64 ]. In the context of post-translational modification, these modifications can directly modulate FDX1 activity without changing its abundance. A key regulatory mechanism here is the phosphorylation of FDX1 at the Ser63 site by AKT1. This phosphorylation event inhibits FDX1's reductase activity, disrupts lipoylation processes, and leads to the induction of resistance to cuproptosis in triple-negative breast cancer [ 65 ]. Beyond transcriptional, post-translational, and direct inhibitory control, the human core iron-sulfur cluster (ISC) assembly machinery is also subject to a precise allosteric switch. A prime example is the FDX2-containing complex. Structural studies reveal a structural basis for this regulation, showing that FDX2 binds the NFS1-ISD11-ACP1 complex in two distinct conformations: a ‘distal’ state, where its [2Fe–2S] cluster is positioned ∼23 Å from the ISCU2 active site, and a ‘proximal’ state, where key interactions bring the cluster within ∼14 Å to enable efficient electron transfer for synthesis [ 30 ]. This conformational switch represents a natural allosteric system. Targeting these allosteric interfaces with small molecules designed to stabilize the inactive distal conformation provides a promising strategy to fine tune Fe–S cluster biogenesis. This strategy aims to modulate the synthesis rate in a context-dependent fashion, enabling precise therapeutic intervention while potentially circumventing the systemic toxicity that results from complete inhibition of this essential pathway. Pathological suppression of FDX activity transcends simple downregulation at the expression level. These microenvironments employ direct and indirect mechanisms to impair FDX function. In terms of inhibitory post-translational modifications, the hyperactivation of oncogenic signaling pathways in cancers directly inactivates FDX1, with AKT1-mediated phosphorylation serving as a typical example; this modification converts FDX1 from a pro-death protein into a pro-survival factor [ 65 ]. Under conditions of severe oxidative stress, another direct inhibitory mechanism comes into play: the iron-sulfur clusters within FDXs themselves can be damaged, resulting in the loss of their electron transfer capability. This damage creates a vicious cycle, where mitochondrial dysfunction further exacerbates FDX impairment. Competitive ion inhibition represents yet another direct regulatory mechanism. As detailed in Section 2.1.2 , zinc ions (Zn 2+ ) competitively inhibit FDX2's binding to the ISCU scaffold, directly hindering Fe–S cluster biogenesis [ 28 ]. This mechanism underscores how the dysregulation of other metal ions can specifically exert pathological suppression on FDX2 activity. Transcriptional silencing also contributes to the function suppression of FDXs. In addition to direct mechanisms, indirect inhibition occurs through energetic substrate depletion. Pathological conditions that deplete cellular NADPH pools, including metabolic syndrome and oxidative stress, indirectly cripple the entire FDXR-FDX electron transfer chain. This is because FDXR relies on NADPH as its primary electron donor, and the depletion of this substrate disrupts the chain's normal function. Collectively, these mechanisms demonstrate that the pathological impairment of FDXs is an active process driven by the disease microenvironment. This acquired dysregulation, as well as underlying genetic alterations, can disrupt FDX homeostasis, with the consequences of rare loss-of-function mutations detailed in Section 6.5 . This sets the stage for the execution of specific cell death pathways and the manifestation of diverse diseases, as elaborated in the following sections.