Both human ferredoxins 1 and 2 and ferredoxin reductase are important for iron-sulfur cluster biogenesis

Copper homeostasis and cuproptosis in gynecological disorders: Pathogenic insights and therapeutic implications

This review comprehensively explores the complex role of copper homeostasis in female reproductive system diseases. As an essential trace element, copper plays a crucial role in various biological functions. Its dysregulation is increasingly recognized as a pivotal factor in the pathogenesis of gynecological disorders. We investigate how copper impacts these diseases, focusing on aspects like oxidative stress, inflammatory responses, immune function, estrogen levels, and angiogenesis. The review highlights significant changes in copper levels in diseases such as cervical, ovarian, endometrial cancer, and endometriosis, underscoring their potential roles in disease mechanisms and therapeutic exploration. The recent discovery of 'cuproptosis,' a novel cell death mechanism induced by copper ions, offers a fresh molecular perspective in understanding these diseases. The review also examines genes associated with cuproptosis, particularly those related to drug resistance, suggesting new strategies to enhance traditional therapy effectiveness. Additionally, we critically evaluate current therapeutic approaches targeting copper homeostasis, including copper ionophores, chelators, and nanoparticles, emphasizing their emerging potential in gynecological disease treatment. This article aims to provide a comprehensive overview of copper's role in female reproductive health, setting the stage for future research to elucidate its mechanisms and develop targeted therapeutic strategies.

Revealing the key role of cuproptosis in osteoporosis via the bioinformatic analysis and experimental validation of cuproptosis-related genes

The incidence of osteoporosis has rapidly increased owing to the ageing population. Cuproptosis, a novel mechanism that regulates cell death, may be a new therapeutic approach. However, the relevance of cuproptosis in the immune microenvironment and osteoporosis immunotherapy is still unknown. We intersected the differentially expressed genes from osteoporotic samples with 75 cuproptosis-related genes to identify 16 significantly expressed cuproptosis genes. We further explored the connection between the cuproptosis pattern, immune microenvironment, and immunotherapy. The weighted gene co-expression network analysis algorithm was used to identify cuproptosis phenotype-associated genes, and we used quantitative real-time PCR and immunohistochemistry in mouse femur tissues to verify hub gene (MAP2K2, FDX1, COX19, VEGFA, CDKN2A, and NFE2L2) expression. Six hub genes and 59 cuproptosis phenotype-associated genes involved in immunisation were identified among the osteoporosis and control groups, and the majority of these 59 genes were enriched in the inflammatory response, as well as in signal transducers, Janus kinase, and transcription pathway activators. In addition, two different clusters of cuproptosis were found, and immune infiltration analysis showed that gene Cluster 1 had a greater immune score and immune infiltration level. Further analysis revealed that three key genes (COX19, MAP2K2, and FDX1) were highly correlated with immune cell infiltration, and external experiments validated the association of these three genes with the prognosis of osteoporosis. We used the three key mRNAs COX19, MAP2K2, and FDX1 as a classification model that may systematically elucidate the complex connection between cuproptosis and the immune microenvironment of osteoporosis. New insights into osteoporosis pathogenesis and immunotherapy prospects may be gained from this study.

Fe-S cluster biosynthesis and maturation: Mass spectrometry-based methods advancing the field

Iron‑sulfur (FeS) clusters are inorganic protein cofactors that perform essential functions in many physiological processes. Spectroscopic techniques have historically been used to elucidate details of FeS cluster type, their assembly and transfer, and changes in redox and ligand binding properties. Structural probes of protein topology, complex formation, and conformational dynamics are also necessary to fully understand these FeS protein systems. Recent developments in mass spectrometry (MS) instrumentation and methods provide new tools to investigate FeS cluster and structural properties. With the unique advantage of sampling all species in a mixture, MS-based methods can be utilized as a powerful complementary approach to probe native dynamic heterogeneity, interrogate protein folding and unfolding equilibria, and provide extensive insight into protein binding partners within an entire proteome. Here, we highlight key advances in FeS protein studies made possible by MS methodology and contribute an outlook for its role in the field.

Examining the Effects of Nutrient Supplementation on Metabolic Pathways via Mitochondrial Ferredoxin in Aging Ovaries

As women age, oocytes are susceptible to a myriad of dysfunctions, including mitochondrial dysfunction, impaired DNA repair mechanisms, epigenetic alterations, and metabolic disturbances, culminating in reduced fertility rates among older individuals. Ferredoxin (FDX) represents a highly conserved iron-sulfur (Fe-S) protein essential for electron transport across multiple metabolic pathways. Mammalian mitochondria house two distinct ferredoxins, FDX1 and FDX2, which share structural similarities and yet perform unique functions. In our investigation into the regulatory mechanisms governing ovarian aging, we employed a comprehensive multi-omics analysis approach, integrating spatial transcriptomics, single-cell RNA sequencing, human ovarian pathology, and clinical biopsy data. Previous studies have highlighted intricate interactions involving excessive lipid peroxide accumulation, redox-induced metal ion buildup, and alterations in cellular energy metabolism observed in aging cells. Through a multi-omics analysis, we observed a notable decline in the expression of the critical gene FDX1 as ovarian age progressed. This observation prompted speculation regarding FDX1's potential as a promising biomarker for ovarian aging. Following this, we initiated a clinical trial involving 70 patients with aging ovaries. These patients were administered oral nutritional supplements consisting of DHEA, ubiquinol CoQ10, and Cleo-20 T3 for a period of two months to evaluate alterations in energy metabolism regulated by FDX1. Our results demonstrated a significant elevation in FDX1 levels among participants receiving nutritional supplementation. We hypothesize that these nutrients potentiate mitochondrial tricarboxylic acid cycle (TCA) activity or electron transport chain (ETC) efficiency, thereby augmenting FDX1 expression, an essential electron carrier in metabolic pathways, while concurrently mitigating lipid peroxide accumulation and cellular apoptosis. In summary, our findings underscore the potential of nutritional intervention to enhance in vitro fertilization outcomes in senescent cells by bolstering electron transport proteins, thus optimizing energy metabolism and improving oocyte quality in aging women.

Activation of Coq6p, a FAD Monooxygenase Involved in Coenzyme Q Biosynthesis, by Adrenodoxin Reductase/Ferredoxin

Adrenodoxin reductase (AdxR) plays a pivotal role in electron transfer, shuttling electrons between NADPH and iron/sulfur adrenodoxin proteins in mitochondria. This electron transport system is essential for P450 enzymes involved in various endogenous biomolecules biosynthesis. Here, we present an in-depth examination of the kinetics governing the reduction of human AdxR by NADH or NADPH. Our results highlight the efficiency of human AdxR when utilizing NADPH as a flavin reducing agent. Nevertheless, akin to related flavoenzymes such as cytochrome P450 reductase, we observe that low NADPH concentrations hinder flavin reduction due to intricate equilibrium reactions between the enzyme and its substrate/product. Remarkably, the presence of MgCl2 suppresses this complex kinetic behavior by decreasing NADPH binding to oxidized AdxR, effectively transforming AdxR into a classical Michaelis-Menten enzyme. We propose that the addition of MgCl2 may be adapted for studying the reductive half-reactions of other flavoenzymes with NADPH. Furthermore, in vitro experiments provide evidence that the reduction of the yeast flavin monooxygenase Coq6p relies on an electron transfer chain comprising NADPH-AdxR-Yah1p-Coq6p, where Yah1p shuttles electrons between AdxR and Coq6p. This discovery explains the previous in vivo observation that Yah1p and the AdxR homolog, Arh1p, are required for the biosynthesis of coenzyme Q in yeast.

[Correlation of serum ferredoxin 1 and lipoic acid levels with severity of coronary artery disease]

OBJECTIVE

To analyze the correlation of copper death inducer ferredoxin 1 (FDX1) and lipoic acid (LA) with the occurrence and severity of coronary atherosclerosis and explore their roles in coronary heart disease (CHD).

METHODS

We analyzed the data of 226 patients undergoing coronary artery angiography (CAG) in our hospital between October, 2021 and October, 2022, including 47 patients with normal CAG findings (control group) and 179 patients with mild, moderate or severe coronary artery stenosis (CHD group). Serum FDX1 and LA levels were determined with ELISA for all the patients. We also examined pathological changes in the aorta of normal and ApoE-/- mice using HE staining and observed collagen fiber deposition with Sirius red staining. Immunohistochemistry was used to detect the expression and distribution of FDX1 and LA in the aorta, and RT-PCR was performed to detect the expressions of FDX1, LIAS and ACO2 mRNAs in the myocardial tissues.

RESULTS

Compared with the control patients, CHD patients had significantly lower serum FDX1 and LA levels, which decreased progressively as coronary artery stenosis worsened (P < 0.01) and as the number of involved coronary artery branches increased (P < 0.05). Serum FDX1 and LA levels were positively correlated (r=0.451, P < 0.01) and they both negatively correlated with the Gensini score (r=-0.241 and -0.273, respectively; P < 0.01). Compared with normal mice, ApoE-/- mice showed significantly increased lipid levels (P < 0.01) and atherosclerosis index, obvious thickening, lipid aggregation, and collagen fiber hyperplasia in the aorta, and significantly reduced expressions of FDX1, LA, LIAS, and ACO2 (P < 0.05).

CONCLUSION

Serum FDX1 and LA levels decrease with worsening of coronary artery lesions, and theirs expressions are correlated with coronary artery lesions induced by hyperlipidemia.

UCHL1 deficiency upon HCMV infection induces vascular endothelial inflammatory injury mediated by mitochondrial iron overload

Human cytomeglovirus (HCMV) infection predisposes blood vessels to atherosclerosis (AS) and post-transplantation restenosis, but the underlying molecular basis remains elusive. Here, we found that HCMV infection activates AIM2 inflammasome and pyroptosis in vascular endothelial cells by inducing mitochondrial iron overload. Mechanistically, under normal conditions, ubiquitin carboxyl terminal hydrolase-L1 (UCHL1) was identified as a DUB enzyme that interacts with, deubiquitylates, and stabilizes ferredoxin reductase (FDXR), an important mitochondrial protein that regulates mitochondral iron homeostasis. However, HCMV infection induces the aberrantly elevated m6A modification and R-loops, the three-stranded DNA-DNA:RNA hybrid structures. The expression of UCHL1 was remarkably reduced by m6A modification-mediated mRNA decay and R-loop-dependent transcriptional termination after HCMV infection. Deficiency of UCHL1 causes ubiquitination and degradation of FDXR. Loss of FDXR induces the mitochondrial iron overload, which consequently leads to AIM2 inflammasome activation and endothelial injury. Moreover, both downregulation expression of UCHL1 and related inflammatory injury in vascular endothelium was observed in MCMV-infected mice. Notably, STM2457, a METTL3 specific inhibitor, restores the expression of UCHL1 upon HCMV infection, thereby inhibiting the inflammatory injury of vascular endothelial cells. Our findings delineate a novel mechnism involved in HCMV-induced inflammatory injury to vascular endothelium and implicate the role of METTL3 inhibitor as a potential therapeutic approach.

FDX1 Is Required for the Biogenesis of Mitochondrial Cytochrome c Oxidase in Mammalian Cells

Ferredoxins (FDXs) are evolutionarily conserved iron-sulfur (Fe-S) proteins that function as electron transfer proteins in diverse metabolic pathways. Mammalian mitochondria contain two ferredoxins, FDX1 and FDX2, which share a high degree of structural similarity but exhibit different functionalities. Previous studies have established the unique role of FDX2 in the biogenesis of Fe-S clusters; however, FDX1 seems to have multiple targets in vivo, some of which are only recently emerging. Using CRISPR-Cas9-based loss-of-function studies in rat cardiomyocyte cell line, we demonstrate an essential requirement of FDX1 in mitochondrial respiration and energy production. We attribute reduced mitochondrial respiration to a specific decrease in the abundance and assembly of cytochrome c oxidase (CcO), a mitochondrial heme-copper oxidase and the terminal enzyme of the mitochondrial respiratory chain. FDX1 knockout cells have reduced levels of copper and heme a/a3, factors that are essential for the maturation of the CcO enzyme complex. Copper supplementation failed to rescue CcO biogenesis, but overexpression of heme a synthase, COX15, partially rescued COX1 abundance in FDX1 knockout cells. This finding links FDX1 function to heme a biosynthesis, and places it upstream of COX15 in CcO biogenesis like its ancestral yeast homolog. Taken together, our work has identified FDX1 as a critical CcO biogenesis factor in mammalian cells.

Interactions of human mitochondrial Ferredoxin 1 (Adrenodoxin) by NMR; modulation by cytochrome P450 substrate and by truncation of the C-terminal tail

Human Ferredoxin 1, also referred to as Adrenodoxin (Adx), is the sole electron carrier supporting the function of all seven mitochondrial cytochrome P450 (CYP) enzymes. Adx utilizes conserved negatively charged residues along its α-helix3 to interact with either the proximal surface of CYP enzymes or the binding surface of Adrendodoxin Reductase (AdR). However, in the oxidized state, Adx assumes a monomer-homodimer equilibrium that requires the presence of its unstructured C-terminal tail. Crystallographic structures of full-length human Adx dimers indicate that part of the binding surface necessary for its interactions with CYPs or with AdR is partially occluded by the dimer interface. In this study, protein NMR spectroscopy was used to interrogate the interactions between full-length (2-124) or truncated monomeric (2-108) human Adx and human CYP24A1 (with and without its vitamin-D substrate) as well as interactions with AdR. Here, monomeric Adx induced a similar pattern of peak broadening as that induced by addition of CYP24A1 substrate, consistent with a 1:1 Adx:CYP interaction as the functional complex. Additionally, removal of the C-terminal tail appears to enhance the interaction with AdR, despite removal of some of the AdR contacts in the tail region. This finding was also supported by an NMR competition assay. These findings suggest that the Adx dimers do not undergo meaningful interactions with either CYP or AdR, but may instead be responsible for regulating access to monomeric Adx. These conclusions are discussed in the context of a revised model of the Adx electron shuttle mechanism.

Progress in the research of cuproptosis and possible targets for cancer therapy

Developing novel cancer therapies that exploit programmed cell death pathways holds promise for advancing cancer treatment. According to a recently published study in Science, copper death (cuproptosis) occurs when intracellular copper is overloaded, triggering aggregation of lipidated mitochondrial proteins and Fe-S cluster proteins. This intriguing phenomenon is triggered by the instability of copper ions. Understanding the molecular mechanisms behind cuproptosis and its associated genes, as identified by Tsvetkov, including ferredoxin 1, lipoic acid synthase, lipoyltransferase 1, dihydrolipid amide dehydrogenase, dihydrolipoamide transacetylase, pyruvate dehydrogenase α1, pyruvate dehydrogenase β, metallothionein, glutaminase, and cyclin-dependent kinase inhibitor 2A, may open new avenues for cancer therapy. Here, we provide a new understanding of the role of copper death and related genes in cancer.

FDX1 regulates cellular protein lipoylation through direct binding to LIAS

Ferredoxins are a family of iron-sulfur (Fe-S) cluster proteins that serve as essential electron donors in numerous cellular processes that are conserved through evolution. The promiscuous nature of ferredoxins as electron donors enables them to participate in many metabolic processes including steroid, heme, vitamin D, and Fe-S cluster biosynthesis in different organisms. However, the unique natural function(s) of each of the two human ferredoxins (FDX1 and FDX2) are still poorly characterized. We recently reported that FDX1 is both a crucial regulator of copper ionophore-induced cell death and serves as an upstream regulator of cellular protein lipoylation, a mitochondrial lipid-based post-translational modification naturally occurring on four mitochondrial enzymes that are crucial for TCA cycle function. Here we show that FDX1 directly regulates protein lipoylation by binding the lipoyl synthase (LIAS) enzyme promoting its functional binding to the lipoyl carrier protein GCSH and not through indirect regulation of cellular Fe-S cluster biosynthesis. Metabolite profiling revealed that the predominant cellular metabolic outcome of FDX1 loss of function is manifested through the regulation of the four lipoylation-dependent enzymes ultimately resulting in loss of cellular respiration and sensitivity to mild glucose starvation. Transcriptional profiling established that FDX1 loss-of-function results in the induction of both compensatory metabolism-related genes and the integrated stress response, consistent with our findings that FDX1 loss-of-function is conditionally lethal. Together, our findings establish that FDX1 directly engages with LIAS, promoting its role in cellular protein lipoylation, a process essential in maintaining cell viability under low glucose conditions.

FDXR-associated disease in a Chinese cohort: Unraveling expanded ocular phenotypes and genetic spectrum

FDXR: associated disease is characterized by optic atrophy, acoustic neuropathy, and developmental delays. This study evaluated the ocular phenotypes and genetic features of patients with biallelic FDXR variants. Five individuals from unrelated non-consanguineous Chinese families with biallelic FDXR variants were identified using whole exome sequencing, Sanger sequencing, and co-segregation validation. In addition to optic atrophy and diverse extraocular manifestations, all patients presented with retinal dystrophy, and electroretinogram showed severely impaired cone and rod functions in their first decades. Three of the five patients showed attenuated retinal vessels that appeared as white lines on the fundus, and fundus fluorescein angiography (FFA) further revealed vascular abnormalities including delayed filling, completely occluded retinal vasculature, and severe retinal vascular nonperfusion of the peripheral retina. Five novel FDXR variants were identified: c.383C > T (p.A128V), c.963delG (p.R322fs*7), c.1052_1053delTC (p.L351Pfs*12), c.394-11T > G and c.1002+1G > A. Retinal dystrophy with attenuated retinal vessels appearing as white lines was observed in this cohort, and the FFA images revealed that retinal vascular occlusion could be a distinct clinical characteristic of FDXR-associated disease. Probands with FDXR revealed severe early onset ophthalmic features with rapid-progression, indicating the importance of early diagnosis and treatment. Moreover, this is the first study to report FFA manifestations in an FDXR cohort, expanding the FDXR-associated ocular disease phenotype and genetic spectrum.

FDX1 enhances endometriosis cell cuproptosis via G6PD-mediated redox homeostasis

Cuproptosis is a new form of programmed cell death, which is associated with the mitochondrial TCA (tricarboxylic acid) cycle. But the functions of cuproptosis in endometriosis progression are still unknown. Here, we find that cuproptosis suppresses the growth of endometriosis cells and the growth of ectopic endometrial tissues in a mouse model. FDX1 as a key regulator in cuproptosis pathway could promote cuproptosis in endometriosis cells. Interestingly, FDX1 interacts with G6PD, and reduces its protein stability, which predominantly affects the cellular redox-regulating systems. Then, the reduced G6PD activity enhances cuproptosis via down-regulating NADPH and GSH levels. Collectively, our study demonstrates that FDX1 mediates cuproptosis in endometriosis via G6PD pathway, resulting in repression of endometriosis cell proliferation and metastasis.

Critical role of antioxidant programs in enzalutamide-resistant prostate cancer

Therapy resistance to second-generation androgen receptor (AR) antagonists, such as enzalutamide, is common in patients with advanced prostate cancer (PCa). To understand the metabolic alterations involved in enzalutamide resistance, we performed metabolomic, transcriptomic, and cistromic analyses of enzalutamide-sensitive and -resistant PCa cells, xenografts, patient-derived organoids, patient-derived explants, and tumors. We noted dramatically higher basal and inducible levels of reactive oxygen species (ROS) in enzalutamide-resistant PCa and castration-resistant PCa (CRPC), in comparison to enzalutamide-sensitive PCa cells or primary therapy-naive tumors respectively. Unbiased metabolomic evaluation identified that glutamine metabolism was consistently upregulated in enzalutamide-resistant PCa cells and CRPC tumors. Stable isotope tracing studies suggest that this enhanced glutamine metabolism drives an antioxidant program that allows these cells to tolerate higher basal levels of ROS. Inhibition of glutamine metabolism with either a small-molecule glutaminase inhibitor or genetic knockout of glutaminase enhanced ROS levels, and blocked the growth of enzalutamide-resistant PCa. The critical role of compensatory antioxidant pathways in maintaining enzalutamide-resistant PCa cells was validated by targeting another antioxidant program driver, ferredoxin 1. Taken together, our data identify a metabolic need to maintain antioxidant programs and a potentially targetable metabolic vulnerability in enzalutamide-resistant PCa.

Iron regulatory proteins: players or pawns in ferroptosis and cancer?

Cells require iron for essential functions like energy production and signaling. However, iron can also engage in free radical formation and promote cell proliferation thereby contributing to both tumor initiation and growth. Thus, the amount of iron within the body and in individual cells is tightly regulated. At the cellular level, iron homeostasis is maintained post-transcriptionally by iron regulatory proteins (IRPs). Ferroptosis is an iron-dependent form of programmed cell death with vast chemotherapeutic potential, yet while IRP-dependent targets have established roles in ferroptosis, our understanding of the contributions of IRPs themselves is still in its infancy. In this review, we present the growing circumstantial evidence suggesting that IRPs play critical roles in the adaptive response to ferroptosis and ferroptotic cell death and describe how this knowledge can be leveraged to target neoplastic iron dysregulation more effectively.

Cuproptosis: mechanisms and links with cancers

Cuproptosis was a copper-dependent and unique kind of cell death that was separate from existing other forms of cell death. The last decade has witnessed a considerable increase in investigations of programmed cell death, and whether copper induced cell death was an independent form of cell death has long been argued until mechanism of cuproptosis has been revealed. After that, increasing number of researchers attempted to identify the relationship between cuproptosis and the process of cancer. Thus, in this review, we systematically detailed the systemic and cellular metabolic processes of copper and the copper-related tumor signaling pathways. Moreover, we not only focus on the discovery process of cuproptosis and its mechanism, but also outline the association between cuproptosis and cancers. Finally, we further highlight the possible therapeutic direction of employing copper ion ionophores with cuproptosis-inducing functions in combination with small molecule drugs for targeted therapy to treat specific cancers.

4-Octyl itaconate inhibits aerobic glycolysis by targeting GAPDH to promote cuproptosis in colorectal cancer

Cuproptosis, a novel copper-induced cell death pathway, is linked to mitochondrial respiration and mediated by protein lipoylation. The discovery of cuproptosis unfolds new areas of investigation, particularly in cancers. The present study aimed to explore the role of cuproptosis in colorectal cancer progression. The genetic alterations of cuproptosis in colon cancer were evaluated using a database. MTT assays, colony formation, and flow cytometry were used to examine the effect of elesclomol-Cu and 4-Octyl itaconate (4-OI) on colorectal cancer cell and oxaliplatin-resistant cell viability. The anti-tumor effect of elesclomol with 4-OI was verified in vivo assay. The results showed that FDX1, SDHB, DLAT, and DLST genes were more highly expressed in normal tissues than those in primary tumor tissues. Patients with high expressions of these genes in tumor tissues had a better prognosis. Using MTT assay and colony formation analysis, elesclomol-Cu pulse treatment showed significant inhibition of cell viability in HCT116, LoVo, and HCT116-R cells. In addition, flow cytometry revealed elesclomol-Cu significantly promoted apoptosis. Tetrathiomolybdate, a copper chelator, markedly inhibited cuproptosis. Subsequently, we found 2-deoxy-D-glucose, a glucose metabolism inhibitor, sensitized cuproptosis. Furthermore, galactose further promoted cuproptosis. Interestingly, 4-OI significantly enhanced cuproptosis which was irrelevant to ROS production, apoptosis, necroptosis, or pyroptosis pathways. Aerobic glycolysis was inhibited by 4-OI through GAPDH, one of the key enzymes of glycolysis, sensitizing cuproptosis. Meanwhile, FDX1 knockdown weakened the ability of 4-OI to promote cuproptosis. In vivo experiments, 4-OI with elesclomol-Cu showed better anti-tumor effects. These results indicated that elesclomol-Cu rapidly halted cell growth in colorectal cancer cells and oxaliplatin-resistant cell line. Importantly, we revealed that 4-OI inhibited aerobic glycolysis by targeting GAPDH to promote cuproptosis.

FDX1 regulates cellular protein lipoylation through direct binding to LIAS

Ferredoxins are a family of iron-sulfur (Fe-S) cluster proteins that serve as essential electron donors in numerous cellular processes that are conserved through evolution. The promiscuous nature of ferredoxins as electron donors enables them to participate in many metabolic processes including steroid, heme, vitamin D and Fe-S cluster biosynthesis in different organisms. However, the unique natural function(s) of each of the two human ferredoxins (FDX1 and FDX2) are still poorly characterized. We recently reported that FDX1 is both a crucial regulator of copper ionophore induced cell death and serves as an upstream regulator of cellular protein lipoylation, a mitochondrial lipid-based post translational modification naturally occurring on four mitochondrial enzymes that are crucial for TCA cycle function. Here we show that FDX1 regulates protein lipoylation by directly binding to the lipoyl synthase (LIAS) enzyme and not through indirect regulation of cellular Fe-S cluster biosynthesis. Metabolite profiling revealed that the predominant cellular metabolic outcome of FDX1 loss-of-function is manifested through the regulation of the four lipoylation-dependent enzymes ultimately resulting in loss of cellular respiration and sensitivity to mild glucose starvation. Transcriptional profiling of cells growing in either normal or low glucose conditions established that FDX1 loss-of-function results in the induction of both compensatory metabolism related genes and the integrated stress response, consistent with our findings that FDX1 loss-of-functions is conditionally lethal. Together, our findings establish that FDX1 directly engages with LIAS, promoting cellular protein lipoylation, a process essential in maintaining cell viability under low glucose conditions.

Functional spectrum and specificity of mitochondrial ferredoxins FDX1 and FDX2

Ferredoxins comprise a large family of iron-sulfur (Fe-S) proteins that shuttle electrons in diverse biological processes. Human mitochondria contain two isoforms of [2Fe-2S] ferredoxins, FDX1 (aka adrenodoxin) and FDX2, with known functions in cytochrome P450-dependent steroid transformations and Fe-S protein biogenesis. Here, we show that only FDX2, but not FDX1, is involved in Fe-S protein maturation. Vice versa, FDX1 is specific not only for steroidogenesis, but also for heme a and lipoyl cofactor biosyntheses. In the latter pathway, FDX1 provides electrons to kickstart the radical chain reaction catalyzed by lipoyl synthase. We also identified lipoylation as a target of the toxic antitumor copper ionophore elesclomol. Finally, the striking target specificity of each ferredoxin was assigned to small conserved sequence motifs. Swapping these motifs changed the target specificity of these electron donors. Together, our findings identify new biochemical tasks of mitochondrial ferredoxins and provide structural insights into their functional specificity.

Mitochondrial [2Fe-2S] ferredoxins: new functions for old dogs

Ferredoxins (FDXs) comprise a large family of iron-sulfur proteins that shuttle electrons from NADPH and FDX reductases into diverse biological processes. This review focuses on the structure, function and specificity of mitochondrial [2Fe-2S] FDXs that are related to bacterial FDXs due to their endosymbiotic inheritance. Their classical function in cytochrome P450-dependent steroid transformations was identified around 1960, and is exemplified by mammalian FDX1 (aka adrenodoxin). Thirty years later the essential function in cellular Fe/S protein biogenesis was discovered for the yeast mitochondrial FDX Yah1 that is additionally crucial for the formation of haem a and ubiquinone CoQ₆ . In mammals, Fe/S protein biogenesis is exclusively performed by the FDX1 paralog FDX2, despite the high structural similarity of both proteins. Recently, additional and specific roles of human FDX1 in haem a and lipoyl cofactor biosyntheses were described. For lipoyl synthesis, FDX1 transfers electrons to the radical S-adenosyl methionine-dependent lipoyl synthase to kickstart its radical chain reaction. The high target specificity of the two mammalian FDXs is contained within small conserved sequence motifs, that upon swapping change the target selection of these electron donors.

Development and validation of a novel diagnostic model for musculoskeletal aging (sarcopenia) based on cuproptosis-related genes associated with immunity

OBJECTIVE

Sarcopenia is a geriatric disease characterized by accelerated skeletal muscle mass and function loss due to aging. Cell death plays a pivotal role in the onset and progress of sarcopenia. The purpose of this study was to investigate the role of cuproptosis-related genes (CRGs) and immune infiltration in sarcopenia development.

METHODS

Three microarray expression datasets from the Gene Expression Omnibus (GEO) database were merged and batch-corrected by R software to identify differentially expressed genes (DEGs) between old and young skeletal muscles. Subsequently, DEGs were subjected to functional enrichment and gene set enrichment analysis (GSEA) to investigate the roles of DEGs and immune infiltration in the pathogenesis of musculoskeletal aging. Then, ssGSEA was performed to calculate the proportion of immune cells and functions within each muscle sample to analyze the differences between the older and young healthy muscle groups. In order to select candidate CRGs, the correlation between CRGs and immune infiltration was analyzed. Finally, a novel nomogram model of musculoskeletal aging was constructed based on candidate CRGs associated with immunity. Additionally, the diagnostic model based on key CRGs was tested using a validation dataset, and its diagnostic performance was evaluated by the area under curve (AUC) value.

RESULTS

141 DEGs were identified between 45 older samples and 50 young healthy samples. Compared to young healthy muscle tissues, significantly lower infiltration levels of T-regulatory cells were identified in older muscle tissues, while dendritic cells (DCs) and mast cells were relatively higher. Based on the CRGs from seven candidates, a novel model with high prediction efficiency (AUC = 0.856) was established to diagnose and screen for sarcopenia.

CONCLUSION

The CRGs associated with immunity may play a vital role in the development of musculoskeletal aging, providing a novel avenue for early diagnosis. Furthermore, immune cell infiltration is essential for the progression of musculoskeletal aging.

Iron and liver cancer: an inseparable connection

Iron is an essential element for all organisms. Iron-containing proteins play critical roles in cellular functions. The biological importance of iron is largely attributable to its chemical properties as a transitional metal. However, an excess of 'free' reactive iron damages the macromolecular components of cells and cellular DNA through the production of harmful free radicals. On the contrary, most of the body's excess iron is stored in the liver. Not only hereditary haemochromatosis but also some liver diseases with mild-to-moderate hepatic iron accumulation, such as chronic hepatitis C, alcoholic liver disease and nonalcoholic steatohepatitis, are associated with a high risk for liver cancer development. These findings have attracted attention to the causative and promotive roles of iron in the development of liver cancer. In the last decade, accumulating evidence regarding molecules regulating iron metabolism or iron-related cell death programmes such as ferroptosis has shed light on the relationship between hepatic iron accumulation and hepatocarcinogenesis. In this review, we briefly present the current molecular understanding of iron regulation in the liver. Next, we describe the mechanisms underlying dysregulated iron metabolism depending on the aetiology of liver diseases. Finally, we discuss the causative and promotive roles of iron in cancer development.

The Role of Copper Homeostasis in Brain Disease

In the human body, copper is an important trace element and is a cofactor for several important enzymes involved in energy production, iron metabolism, neuropeptide activation, connective tissue synthesis, and neurotransmitter synthesis. Copper is also necessary for cellular processes, such as the regulation of intracellular signal transduction, catecholamine balance, myelination of neurons, and efficient synaptic transmission in the central nervous system. Copper is naturally present in some foods and is available as a dietary supplement. Only small amounts of copper are typically stored in the body and a large amount of copper is excreted through bile and urine. Given the critical role of copper in a breadth of cellular processes, local concentrations of copper and the cellular distribution of copper transporter proteins in the brain are important to maintain the steady state of the internal environment. The dysfunction of copper metabolism or regulatory pathways results in an imbalance in copper homeostasis in the brain, which can lead to a myriad of acute and chronic pathological effects on neurological function. It suggests a unique mechanism linking copper homeostasis and neuronal activation within the central nervous system. This article explores the relationship between impaired copper homeostasis and neuropathophysiological progress in brain diseases.

A Novel Cuprotosis-Related Gene FDX1 Signature for Overall Survival Prediction in Clear Cell Renal Cell Carcinoma Patients

Background

Ferredoxin 1 (FDX1) is a newly discovered gene regulating cuprotosis. However, the effect of FDX1 expression on clear renal cell carcinoma (ccRCC) is unknown.

Methods

Gene expression profiles and clinical data of ccRCC patients were downloaded from the Cancer Genome Atlas (TCGA) database. The differences in FDX1 expression between ccRCC and nonneoplastic tissues adjacent to cancer were analyzed by R software. The results were validated by GEO data, quantitative real-time polymerase chain reaction (qRT-PCR), western blotting (WB), and immunohistochemistry (IHC). Chi-square test was used to analyze the clinical pathological parameters. Kaplan-Meier survival analysis and Cox proportional hazard regression model selection were used to evaluate the effect of FDX1 expression on overall survival. Protein interaction networks were used to analyze other proteins that interact with FDX1. Signal pathway analysis was performed for possible FDX1 enrichment using GSEA and ssGSEA algorithms. Pan-cancer analysis of FDX1 was carried out through TCGA database.

Results

The FDX1 expression in nontumor tissues was significantly higher than that in ccRCC, and the expression difference was verified by GEO data, qRT-PCR, WB, and IHC. The high expression of FDX1 was significantly related to the well overall survival rate (P < 0.05). The chi-square test showed that the high expression of FDX1 was related to gender, TNM stage, T stage, lymph node metastasis, and pathological grade. Additionally, the FDX1 expression level was different in groups classified based on pathological grade, gender, TNM stage, T stage, lymph node metastasis, and distant metastasis (P < 0.05). The multivariate analysis revealed the high expression of FDX1 as an important independent predictor for overall survival. STRING database results showed that LIAS and LIPT1 may interact with FDX1 in the PPI network, which are also involved in the regulation of cuprotosis. The GSEA and ssGSEA results showed that the FDX1 was enriched in the anticancer pathway. The FDX1 high expression is associated with better prognosis in many cancers, as revealed by pan-cancer analysis.

Conclusion

FDX1 may play a role in the progression of ccRCC as a tumor suppressor gene. It can be used as a potential prognostic indicator and therapeutic target of ccRCC. However, the cuprotosis regulatory role in the development of ccRCC needs to be further verified.

Cuproptosis-Related Gene - SLC31A1, FDX1 and ATP7B - Polymorphisms are Associated with Risk of Lung Cancer

Background

Cuproptosis is a novel copper-dependent cell death, and the copper level was increased in lung cancer patients. However, few studies evaluated the association between single-nucleotide polymorphisms (SNPs) in cuproptosis-related genes and lung cancer risk.

Methods

Six SNPs of the SLC31A1, FDX1 and ATP7B genes were genotyped in a case-control cohort including 650 lung cancer cases and 650 controls using the MassARRAY platform.

Results

The minor alleles of SLC31A1-rs10981694 and FDX1-rs10488764 were associated with an increased risk of lung cancer (rs10981694: OR=1.455, 95% CI: 1.201-1.763, p<0.001; rs10488764: OR=1.483, 95% CI: 1.244-1.768, p<0.001). In contrast, the minor alleles of rs9535826 and rs9535828 in ATP7B were related to a decreased risk of the disease (rs9535826: OR=0.714, 95% CI: 0.608-0.838 p<0.001; rs9535828: OR=0.679, 95% CI: 0.579-0.796, p<0.001). The frequencies of rs10981694-TG/GG and rs10488764-GA/AA genotypes were significantly higher in lung cancer cases than that in controls, making them risk genotypes for the disease (p < 0.001); while the rs9535826-TG/GG and rs9535828-GA/AA genotypes were protective genotypes and associated with a reduced risk of the disease (p<0.001). Genetic model evaluation revealed that SLC31A1-rs10981694 and FDX1-rs10488764 were associated with a growing risk of lung cancer in dominant, recessive and log-additive models (p<0.001). Moreover, rs9535826 and rs9535828 in ATP7B were related to a declining risk of the disease in three genetic models (p<0.001). In addition, stratification analysis showed that FDX1-rs10488764 was risk variant for lung cancer in both smokers and nonsmokers, and was associated with risk of each pathological type of lung cancer (p<0.008).

Conclusion

The results shed new light on the correlation between cuproptosis-related genes and risk of lung cancer.

Pan-cancer analyses confirmed the cuproptosis-related gene FDX1 as an immunotherapy predictor and prognostic biomarker

Background: The latest research identified cuproptosis as an entirely new mechanism of cell death. However, as a key regulator in copper-induced cell death, the prognostic and immunotherapeutic value of FDX1 in pan-cancer remains unclear.

Methods: Data from the UCSC Xena, GEPIA, and CPTAC were analyzed to conduct an inquiry into the overall differential expression of FDX1 across multiple cancer types. The expression of FDX1 in GBM, LUAD and HCC cell lines as well as their control cell lines was verified by RT-QPCR. The survival prognosis, clinical features, and genetic changes of FDX1 were also evaluated. Finally, the relationship between FDX1 and immunotherapy response was further explored through Gene Set Enrichment Analysis enrichment analysis, tumor microenvironment, immune cell infiltration, immune gene co-expression and drug sensitivity analysis.

Results: The transcription and protein expression of FDX1 were significantly reduced in most cancer types and had prognostic value for the survival of certain cancer patients such as ACC, KIRC, HNSC, THCA and LGG. In some cancer types, FDX1 expression was also markedly correlated with the clinical characteristics, TMB, MSI, and antitumor drug susceptibility or resistance of different tumors. Gene set enrichment analysis showed that FDX1 was significantly associated with immune-related pathways. Moreover, the expression level of FDX1 was confirmed to be strongly correlated with immune cell infiltration, immune checkpoint genes, and immune regulatory genes to a certain extent.

Conclusion: This study comprehensively explored the potential value of FDX1 as a prognostic and immunotherapeutic marker for pan-cancer, providing new direction and evidence for cancer therapy.

Cuproptosis-Related Risk Score Predicts Prognosis and Characterizes the Tumor Microenvironment in Hepatocellular Carcinoma

Aims

Cuproptosis is a recently identified form of programmed cell death; however, its role in hepatocellular carcinoma (HCC) remains unclear.

Methods

A set of bioinformatic tools was integrated to analyze the expression and prognostic significance of ferredoxin 1 (FDX1), the key regulator of cuproptosis. A cuproptosis-related risk score (CRRS) was developed via correlation analyses, least absolute shrinkage and selection operator (LASSO) Cox regression, and multivariate Cox regression. The metabolic features, mutation signatures, and immune profile of CRRS-classified HCC patients were investigated, and the role of CRRS in therapy guidance was analyzed.

Results

FDX1 was significantly downregulated in HCC, and its high expression was associated with longer survival time. HCC patients in the high-CRRS group showed a significantly lower overall survival (OS) and enriched in cancer-related pathways. Mutation analyses revealed that the high-CRRS HCC patients had a high mutational frequency of some tumor suppressors such as tumor protein P53 (TP53) and Breast-cancer susceptibility gene 1 (BRCA1)-associated protein 1 (BAP1) and a low frequency of catenin beta 1 (CTNNB1). Besides, HCC patients with high CRRS showed an increase of protumor immune infiltrates and a high expression of immune checkpoints. Moreover, the area under the curve (AUC) values of CRRS in predicting the efficiency of sorafenib and the non-responsiveness to transcatheter arterial chemoembolization (TACE) in HCC patients reached 0.877 and 0.764, respectively.

Significance

The cuproptosis-related signature is helpful in prognostic prediction and in guiding treatment for HCC patients.

Hydrogel platform with tunable stiffness based on magnetic nanoparticles cross-linked GelMA for cartilage regeneration and its intrinsic biomechanism

Cartilage injury affects numerous individuals, but the efficient repair of damaged cartilage is still a problem in clinic. Hydrogel is a potent scaffold candidate for tissue regeneration, but it remains a big challenge to improve its mechanical property and figure out the interaction of chondrocytes and stiffness. Herein, a novel hybrid hydrogel with tunable stiffness was fabricated based on methacrylated gelatin (GelMA) and iron oxide nanoparticles (Fe₂O₃) through chemical bonding. The stiffness of Fe₂O₃/GelMA hybrid hydrogel was controlled by adjusting the concentration of magnetic nanoparticles. The hydrogel platform with tunable stiffness modulated its cellular properties including cell morphology, microfilaments and Young's modulus of chondrocytes. Interestingly, Fe₂O₃/GelMA hybrid hydrogel promoted oxidative phosphorylation of mitochondria and facilitated catabolism of lipids in chondrocytes. As a result, more ATP and metabolic materials generated for cellular physiological activities and organelle component replacements in hybrid hydrogel group compared to pure GelMA hydrogel. Furthermore, implantation of Fe₂O₃/GelMA hybrid hydrogel in the cartilage defect rat model verified its remodeling potential. This study provides a deep understanding of the bio-mechanism of Fe₂O₃/GelMA hybrid hydrogel interaction with chondrocytes and indicates the hydrogel platform for further application in tissue engineering.

Therapeutic Targeting of Ovarian Cancer Stem Cells Using Estrogen Receptor Beta Agonist

Ovarian cancer (OCa) is the deadliest gynecologic cancer. Emerging studies suggest ovarian cancer stem cells (OCSCs) contribute to chemotherapy resistance and tumor relapse. Recent studies demonstrated estrogen receptor beta (ERβ) exerts tumor suppressor functions in OCa. However, the status of ERβ expression in OCSCs and the therapeutic utility of the ERβ agonist LY500307 for targeting OCSCs remain unknown. OCSCs were enriched from ES2, OV90, SKOV3, OVSAHO, and A2780 cells using ALDEFLUOR kit. RT-qPCR results showed ERβ, particularly ERβ isoform 1, is highly expressed in OCSCs and that ERβ agonist LY500307 significantly reduced the viability of OCSCs. Treatment of OCSCs with LY500307 significantly reduced sphere formation, self-renewal, and invasion, while also promoting apoptosis and G2/M cell cycle arrest. Mechanistic studies using RNA-seq analysis demonstrated that LY500307 treatment resulted in modulation of pathways related to cell cycle and apoptosis. Western blot and RT-qPCR assays demonstrated the upregulation of apoptosis and cell cycle arrest genes such as FDXR, p21/CDKN1A, cleaved PARP, and caspase 3, and the downregulation of stemness markers SOX2, Oct4, and Nanog. Importantly, treatment of LY500307 significantly attenuated the tumor-initiating capacity of OCSCs in orthotopic OCa murine xenograft models. Our results demonstrate that ERβ agonist LY500307 is highly efficacious in reducing the stemness and promoting apoptosis of OCSCs and shows significant promise as a novel therapeutic agent in treating OCa.

During FeS cluster biogenesis, ferredoxin and frataxin use overlapping binding sites on yeast cysteine desulfurase Nfs1

In mitochondria, cysteine desulfurase (Nfs1) plays a central role in the biosynthesis of iron-sulfur (FeS) clusters, cofactors critical for activity of many cellular proteins. Nfs1 functions both as a sulfur donor for cluster assembly and as a binding platform for other proteins functioning in the process. These include not only the dedicated scaffold protein (Isu1) on which FeS clusters are synthesized but also accessory FeS cluster biogenesis proteins frataxin (Yfh1) and ferredoxin (Yah1). Yfh1 has been shown to activate cysteine desulfurase enzymatic activity, whereas Yah1 supplies electrons for the persulfide reduction. While Yfh1 interaction with Nfs1 is well understood, the Yah1-Nfs1 interaction is not. Here, based on the results of biochemical experiments involving purified WT and variant proteins, we report that in Saccharomyces cerevisiae, Yah1 and Yfh1 share an evolutionary conserved interaction site on Nfs1. Consistent with this notion, Yah1 and Yfh1 can each displace the other from Nfs1 but are inefficient competitors when a variant with an altered interaction site is used. Thus, the binding mode of Yah1 and Yfh1 interacting with Nfs1 in mitochondria of S. cerevisiae resembles the mutually exclusive binding of ferredoxin and frataxin with cysteine desulfurase reported for the bacterial FeS cluster assembly system. Our findings are consistent with the generally accepted scenario that the mitochondrial FeS cluster assembly system was inherited from bacterial ancestors of mitochondria.

FDX2 and ISCU Gene Variations Lead to Rhabdomyolysis With Distinct Severity and Iron Regulation

Background and Objectives

To determine common clinical and biological traits in 2 individuals with variants in ISCU and FDX2, displaying severe and recurrent rhabdomyolyses and lactic acidosis.

Methods

We performed a clinical characterization of 2 distinct individuals with biallelic ISCU or FDX2 variants from 2 separate families and a biological characterization with muscle and cells from those patients.

Results

The individual with FDX2 variants was clinically more affected than the individual with ISCU variants. Affected FDX2 individual fibroblasts and myoblasts showed reduced oxygen consumption rates and mitochondrial complex I and PDHc activities, associated with high levels of blood FGF21. ISCU individual fibroblasts showed no oxidative phosphorylation deficiency and moderate increase of blood FGF21 levels relative to controls. The severity of the FDX2 individual was not due to dysfunctional autophagy. Iron was excessively accumulated in ISCU-deficient skeletal muscle, which was accompanied by a downregulation of IRP1 and mitoferrin2 genes and an upregulation of frataxin (FXN) gene expression. This excessive iron accumulation was absent from FDX2 affected muscle and could not be correlated with variable gene expression in muscle cells.

Discussion

We conclude that FDX2 and ISCU variants result in a similar muscle phenotype, that differ in severity and skeletal muscle iron accumulation. ISCU and FDX2 are not involved in mitochondrial iron influx contrary to frataxin.

Rare presentation of FDX2-related disorder and untargeted global metabolomics findings

We present the case of a 20-year-old male with a history of myopathy and multiple episodes of rhabdomyolysis, and lactic acidosis. He needed hemodialysis for severe rhabdomyolysis-related acute renal failure at the time of initial presentation (age 10 years). Exome sequencing detected a homozygous likely pathogenic variant in FDX2 (c.12G>T, p.M4I). The FDX2 gene encodes a mitochondrial protein, ferredoxin 2, that is involved in the biogenesis of Fe-S clusters. Biallelic pathogenic variants in FDX2 have previously been associated with episodic mitochondrial myopathy with or without optic atrophy and reversible leukoencephalopathy. Only two cases with FDX2-related rhabdomyolysis as a predominant feature have been reported in medical literature. Here, we report a third patient with FDX2-related recurrent, severe episodes of rhabdomyolysis and lactic acidosis. He does not have optic atrophy or leukoencephalopathy. This is the oldest patient reported with FDX2-related disorder and he has significantly elevated CK during episodes of rhabdomyolysis. In addition, we describe untargeted global metabolomic findings during an episode of metabolic decompensation, shedding light on the biochemical pathway perturbation associated with this ultra-rare genetic disorder.

Molecular characteristics of proteins within the mitochondrial Fe-S cluster assembly complex

Iron-Sulfur (Fe-S) clusters are essential for life, as they are widely utilized in nearly every biochemical pathway. When bound to proteins, Fe-S clusters assist in catalysis, signal recognition, and energy transfer events, as well as additional cellular pathways including cellular respiration and DNA repair and replication. In Eukaryotes, Fe-S clusters are produced through coordinated activity by mitochondrial Iron-Sulfur Cluster (ISC) assembly pathway proteins through direct assembly, or through the production of the activated sulfur substrate used by the Cytosolic Iron-Sulfur Cluster Assembly (CIA) pathway. In the mitochondria, Fe-S cluster assembly is accomplished through the coordinated activity of the ISC pathway protein complex composed of a cysteine desulfurase, a scaffold protein, the accessory ISD11 protein, the acyl carrier protein, frataxin, and a ferredoxin; downstream events that accomplish Fe-S cluster transfer and delivery are driven by additional chaperone/delivery proteins that interact with the ISC assembly complex. Deficiency in human production or activity of Fe-S cluster containing proteins is often detrimental to cell and organism viability. Here we summarize what is known about the structure and functional activities of the proteins involved in the early steps of assembling [2Fe-2S] clusters before they are transferred to proteins devoted to their delivery. Our goal is to provide a comprehensive overview of how the ISC assembly apparatus proteins interact to make the Fe-S cluster which can be delivered to proteins downstream to the assembly event.

FDX1 can Impact the Prognosis and Mediate the Metabolism of Lung Adenocarcinoma

Background: Lung cancer has emerged as one of the most common cancers in recent years. The mitochondrial electron transport chain (ETC) is closely connected with metabolic pathways and inflammatory response. However, the influence of ETC-associated genes on the tumor immune response and the pathogenesis of lung cancer is not clear and needs further exploration.

Methods: The RNA-sequencing transcriptome and clinical characteristic data of LUAD were downloaded from the Cancer Genome Atlas (TCGA) database. The LASSO algorithm was used to build the risk signature, and the prediction model was evaluated by the survival analysis and receiver operating characteristic curve. We explored the function of FDX1 through flow cytometry, molecular biological methods, and liquid chromatography–tandem mass spectrometry/mass spectrometry (LC–MS/MS).

Results: 12 genes (FDX1, FDX2, LOXL2, ASPH, GLRX2, ALDH2, CYCS, AKR1A1, MAOB, RDH16, CYBB, and CYB5A) were selected to build the risk signature, and the risk score was calculated with the coefficients from the LASSO algorithm. The 1-year, 3-year, and 5-year area under the curve (AUC) of ROC curves of the dataset were 0.7, 0.674, and 0.692, respectively. Univariate Cox analysis and multivariate Cox regression analysis indicated that the risk signature is an independent risk factor for LUAD patients. Among these genes, we focused on the FDX1 gene, and we found that knockdown of FDX1 neither inhibited tumor cell growth nor did it induce apoptosis or abnormal cell cycle distribution. But FDX1 could promote the ATP production. Furthermore, our study showed that FDX1 was closely related to the glucose metabolism, fatty acid oxidation, and amino acid metabolism.

Conclusion: Collectively, this study provides new clues about carcinogenesis induced by ETC-associated genes in LUAD and paves the way for finding potential targets of LUAD.

Steroidogenic electron-transfer factors and their diseases

Most steroidogenesis disorders are caused by mutations in genes encoding the steroidogenic enzymes, but work in the past 20 years has identified related disorders caused by mutations in the genes encoding the cofactors that transport electrons from NADPH to P450 enzymes. Most P450s are microsomal and require electron donation by P450 oxidoreductase (POR); by contrast, mitochondrial P450s require electron donation via ferredoxin reductase (FdxR) and ferredoxin (Fdx). POR deficiency is the most common and best-described of these new forms of congenital adrenal hyperplasia. Severe POR deficiency is characterized by the Antley-Bixler skeletal malformation syndrome and genital ambiguity in both sexes, and hence is easily recognized, but mild forms may present only with infertility and subtle disorders of steroidogenesis. The common POR polymorphism A503V reduces catalysis by P450c17 (17-hydroxylase/17,20-lyase) and the principal drugmetabolizing P450 enzymes. The 17,20-lyase activity of P450c17 requires the allosteric action of cytochrome b5, which promotes interaction of P450c17 with POR, with consequent electron transfer. Rare b5 mutations are one of several causes of 17,20-lyase deficiency. In addition to their roles with steroidogenic mitochondrial P450s, Fdx and FdxR participate in the synthesis of iron-sulfur clusters used by many enzymes. Disruptions in the assembly of Fe-S clusters is associated with Friedreich ataxia and Parkinson disease. Recent work has identified mutations in FdxR in patients with neuropathic hearing loss and visual impairment, somewhat resembling the global neurologic disorders seen with mitochondrial diseases. Impaired steroidogenesis is to be expected in such individuals, but this has not yet been studied.

Assembly of the [4Fe-4S] cluster of NFU1 requires the coordinated donation of two [2Fe-2S] clusters from the scaffold proteins, ISCU2 and ISCA1

NFU1, a late-acting iron-sulfur (Fe-S) cluster carrier protein, has a key role in the pathogenesis of the disease, multiple mitochondrial dysfunctions syndrome. In this work, using genetic and biochemical approaches, we identified the initial scaffold protein, mitochondrial ISCU (ISCU2) and the secondary carrier, ISCA1, as the direct donors of Fe-S clusters to mitochondrial NFU1, which appears to dimerize and reductively mediate the formation of a bridging [4Fe-4S] cluster, aided by ferredoxin 2. By monitoring the abundance of target proteins that acquire their Fe-S clusters from NFU1, we characterized the effects of several novel pathogenic NFU1 mutations. We observed that NFU1 directly interacts with each of the Fe-S cluster scaffold proteins known to ligate [2Fe-2S] clusters, ISCU2 and ISCA1, and we mapped the site of interaction to a conserved hydrophobic patch of residues situated at the end of the C-terminal alpha-helix of NFU1. Furthermore, we showed that NFU1 lost its ability to acquire its Fe-S cluster when mutagenized at the identified site of interaction with ISCU2 and ISCA1, which thereby adversely affected biochemical functions of proteins that are thought to acquire their Fe-S clusters directly from NFU1, such as lipoic acid synthase, which supports the Fe-S-dependent process of lipoylation of components of multiple key enzyme complexes, including pyruvate dehydrogenase, alpha-ketoglutarate dehydrogenase and the glycine cleavage complex.

Down the Iron Path: Mitochondrial Iron Homeostasis and Beyond

Cellular iron homeostasis and mitochondrial iron homeostasis are interdependent. Mitochondria must import iron to form iron–sulfur clusters and heme, and to incorporate these cofactors along with iron ions into mitochondrial proteins that support essential functions, including cellular respiration. In turn, mitochondria supply the cell with heme and enable the biogenesis of cytosolic and nuclear proteins containing iron–sulfur clusters. Impairment in cellular or mitochondrial iron homeostasis is deleterious and can result in numerous human diseases. Due to its reactivity, iron is stored and trafficked through the body, intracellularly, and within mitochondria via carefully orchestrated processes. Here, we focus on describing the processes of and components involved in mitochondrial iron trafficking and storage, as well as mitochondrial iron–sulfur cluster biogenesis and heme biosynthesis. Recent findings and the most pressing topics for future research are highlighted.

Large scale RNA-binding proteins/LncRNAs interaction analysis to uncover lncRNA nuclear localization mechanisms

Long non-coding RNAs (lncRNAs) are key regulators of major biological processes and their functional modes are dictated by their subcellular localization. Relative nuclear enrichment of lncRNAs compared to mRNAs is a prevalent phenomenon but the molecular mechanisms governing their nuclear retention in cells remain largely unknown. Here in this study, we harness the recently released eCLIP data for a large number of RNA-binding proteins (RBPs) in K562 and HepG2 cells and utilize multiple bioinformatics methods to comprehensively survey the roles of RBPs in lncRNA nuclear retention. We identify an array of splicing RBPs that bind to nuclear-enriched lincRNAs (large intergenic non-coding RNAs) thus may act as trans-factors regulating their nuclear retention. Further analyses reveal that these RBPs may bind with distinct core motifs, flanking sequence compositions, or secondary structures to drive lincRNA nuclear retention. Moreover, network analyses uncover potential co-regulatory RBP clusters and the physical interaction between HNRNPU and SAFB2 proteins in K562 cells is further experimentally verified. Altogether, our analyses reveal previously unknown factors and mechanisms that govern lincRNA nuclear localization in cells.

Expanding the FDXR-Associated Disease Phenotype: Retinal Dystrophy Is a Recurrent Ocular Feature

Purpose

The purpose of this study was to report retinal dystrophy as a novel clinical feature and expand the ocular phenotype in patients harboring biallelic candidate FDXR variants.

Methods

Patients carrying biallelic candidate FDXR variants were identified by whole genome sequencing (WGS) as part of the National Institute for Health Research BioResource rare-disease and the UK's 100,000 Genomes Project (100KGP) with an additional case identified by exome sequencing. Retrospective clinical data were collected from the medical records. Haplotype reconstruction was performed in families harboring the same missense variant.

Results

Ten individuals from 8 unrelated families with biallelic candidate variants in FDXR were identified. In addition to bilateral optic atrophy and variable extra-ocular findings, 7 of 10 individuals manifested retinal dystrophy comprising dysfunction and degeneration of both rod and cone photoreceptors. Five of 10 subjects had sensorineural hearing loss. The previously unreported missense variant (c.1115C > A, p.(Pro372His)) was found in 5 of 8 (62.5%) study families. Haplotype reconstruction using WGS data demonstrated a likely ancestral haplotype.

Conclusions

FDXR-associated disease is a phenotypically heterogeneous disorder with retinal dystrophy being a major clinical feature observed in this cohort. In addition, we hypothesize that a number of factors are likely to drive the pathogenesis of optic atrophy, retinal degeneration, and perhaps the associated systemic manifestations.

Defective palmitoylation of transferrin receptor triggers iron overload in Friedreich ataxia fibroblasts

Friedreich ataxia (FRDA) is a frequent autosomal recessive disease caused by a GAA repeat expansion in the FXN gene encoding frataxin, a mitochondrial protein involved in iron-sulfur cluster (ISC) biogenesis. Resulting frataxin deficiency affects ISC-containing proteins and causes iron to accumulate in the brain and heart of FRDA patients. Here we report on abnormal cellular iron homeostasis in FRDA fibroblasts inducing a massive iron overload in cytosol and mitochondria. We observe membrane transferrin receptor 1 (TfR1) accumulation, increased TfR1 endocytosis, and delayed Tf recycling, ascribing this to impaired TfR1 palmitoylation. Frataxin deficiency is shown to reduce coenzyme A (CoA) availability for TfR1 palmitoylation. Finally, we demonstrate that artesunate, CoA, and dichloroacetate improve TfR1 palmitoylation and decrease iron overload, paving the road for evidence-based therapeutic strategies at the actionable level of TfR1 palmitoylation in FRDA.

Report of a case with ferredoxin reductase (FDXR) gene variants in a Chinese boy exhibiting hearing loss, visual impairment, and motor retardation

Ferredoxin reductase (FDXR), located in 17q25.1, encodes for a mitochondrial NADPH: adrenodoxin oxidoreductase or ferredoxin reductase, the sole human ferredoxin reductase involved in the biosynthesis of iron-sulfur (Fe-S) clusters and heme formation. Iron-sulfur (Fe-S) clusters are involved in enzymatic catalysis, gene expression, and DNA replication and repair. Variants in FDXR lead to sensorial neuropathies, damage optic, and auditory neurons. Here, we report a Chinese boy with hearing loss, visual impairment, and motor retardation, with two novel compound heterozygous variants in FDXR (NM_004110), namely, c.250C > T (p.P84S) and c.634G > C (p.D212H), identified by whole-exome sequencing. Compared with the reported cases, except hearing loss and visual impairment, the clinical manifestations of this boy were more serious, who also had motor retardation and died in infancy after infection. The present study expands our knowledge of FDXR variants and related phenotypes, and provides new information on the genetic defects associated with this disease for clinical diagnosis.

Iron-sulfur proteins in plant mitochondria: roles and maturation

Iron-sulfur (Fe-S) clusters are prosthetic groups ensuring electron transfer reactions, activating substrates for catalytic reactions, providing sulfur atoms for the biosynthesis of vitamins or other cofactors, or having protein-stabilizing effects. Hence, metalloproteins containing these cofactors are essential for numerous and diverse metabolic pathways and cellular processes occurring in the cytoplasm. Mitochondria are organelles where the Fe-S cluster demand is high, notably because the activity of the respiratory chain complexes I, II, and III relies on the correct assembly and functioning of Fe-S proteins. Several other proteins or complexes present in the matrix require Fe-S clusters as well, or depend either on Fe-S proteins such as ferredoxins or on cofactors such as lipoic acid or biotin whose synthesis relies on Fe-S proteins. In this review, we have listed and discussed the Fe-S-dependent enzymes or pathways in plant mitochondria including some potentially novel Fe-S proteins identified based on in silico analysis or on recent evidence obtained in non-plant organisms. We also provide information about recent developments concerning the molecular mechanisms involved in Fe-S cluster synthesis and trafficking steps of these cofactors from maturation factors to client apoproteins.

The mitochondrial localized CISD-3.1/CISD-3.2 proteins are required to maintain normal germline structure and function in Caenorhabditis elegans

Reproductive organs and developing tissues have high energy demands that require metabolic functions primarily supported by mitochondria function. The highly conserved CISD/NEET iron-sulfur (Fe-S) protein family regulates iron and reactive oxygen homeostasis, both of which are important for mitochondrial function. Disruption of iron and reactive oxygen homeostasis typically leads to detrimental effects. In humans, CISD dysfunction is associated with human health issues including Wolfram syndrome 2. Using C. elegans, we previously determined that the cisd-1, cisd-3.1 and cisd-3.2 have an overlapping role in the regulation of physiological germline apoptosis through the canonical programmed cell death pathway. Here, we isolated the cisd-3.2(pnIs68) mutant that resulted in physiological and fitness defects including germline abnormalities that are associated with abnormal stem cell niche and disrupted formation of bivalent chromosomes. The cisd-3.2(pnIs68) mutation led to complete disruption of the cisd-3.2 gene expression and a decrease in expression of genetically intact cisd-1 and cisd-3.1 genes suggesting an indirect impact of the cisd-3.2(pnIs68) allele. The CISD-3.2 and CISD-3.1 proteins localize to the mitochondria in many tissues throughout development. The cisd-3.2(pnIs68) mutant displays phenotypes associated with mitochondrial dysfunction, including disruption of the mitochondrial network within the germline. These results further support the idea that the CISD protein family is required for mitochondrial function that supports important functions in animals including overall fitness and germline viability.

Mechanism of the Affinity-Enhancing Effect of Isatin on Human Ferrochelatase and Adrenodoxin Reductase Complex Formation: Implication for Protein Interactome Regulation

Isatin (indole-2, 3-dione) is a non-peptide endogenous bioregulator exhibiting a wide spectrum of biological activity, realized in the cell via interactions with numerous isatin-binding proteins, their complexes, and (sub) interactomes. There is increasing evidence that isatin may be involved in the regulation of complex formations by modulating the affinity of the interacting protein partners. Recently, using Surface Plasmon Resonance (SPR) analysis, we have found that isatin in a concentration dependent manner increased interaction between two human mitochondrial proteins, ferrochelatase (FECH), and adrenodoxine reductase (ADR). In this study, we have investigated the affinity-enhancing effect of isatin on the FECH/ADR interaction. The SPR analysis has shown that FECH forms not only homodimers, but also FECH/ADR heterodimers. The affinity-enhancing effect of isatin on the FECH/ADR interaction was highly specific and was not reproduced by structural analogues of isatin. Bioinformatic analysis performed using three dimensional (3D) models of the interacting proteins and in silico molecular docking revealed the most probable mechanism involving FECH/isatin/ADR ternary complex formation. In this complex, isatin is targeted to the interface of interacting FECH and ADR monomers, forming hydrogen bonds with both FECH and ADR. This is a new regulatory mechanism by which isatin can modulate protein-protein interactions (PPI).

Mechanism of Iron–Sulfur Cluster Assembly: In the Intimacy of Iron and Sulfur Encounter

Iron–sulfur (Fe–S) clusters are protein cofactors of a multitude of enzymes performing essential biological functions. Specialized multi-protein machineries present in all types of organisms support their biosynthesis. These machineries encompass a scaffold protein on which Fe–S clusters are assembled and a cysteine desulfurase that provides sulfur in the form of a persulfide. The sulfide ions are produced by reductive cleavage of the persulfide, which involves specific reductase systems. Several other components are required for Fe–S biosynthesis, including frataxin, a key protein of controversial function and accessory components for insertion of Fe–S clusters in client proteins. Fe–S cluster biosynthesis is thought to rely on concerted and carefully orchestrated processes. However, the elucidation of the mechanisms of their assembly has remained a challenging task due to the biochemical versatility of iron and sulfur and the relative instability of Fe–S clusters. Nonetheless, significant progresses have been achieved in the past years, using biochemical, spectroscopic and structural approaches with reconstituted system in vitro. In this paper, we review the most recent advances on the mechanism of assembly for the founding member of the Fe–S cluster family, the [2Fe2S] cluster that is the building block of all other Fe–S clusters. The aim is to provide a survey of the mechanisms of iron and sulfur insertion in the scaffold proteins by examining how these processes are coordinated, how sulfide is produced and how the dinuclear [2Fe2S] cluster is formed, keeping in mind the question of the physiological relevance of the reconstituted systems. We also cover the latest outcomes on the functional role of the controversial frataxin protein in Fe–S cluster biosynthesis.

Mitochondrial diseases: expanding the diagnosis in the era of genetic testing

Mitochondrial diseases are clinically and genetically heterogeneous. These diseases were initially described a little over three decades ago. Limited diagnostic tools created disease descriptions based on clinical, biochemical analytes, neuroimaging, and muscle biopsy findings. This diagnostic mechanism continued to evolve detection of inherited oxidative phosphorylation disorders and expanded discovery of mitochondrial physiology over the next two decades. Limited genetic testing hampered the definitive diagnostic identification and breadth of diseases. Over the last decade, the development and incorporation of massive parallel sequencing has identified approximately 300 genes involved in mitochondrial disease. Gene testing has enlarged our understanding of how genetic defects lead to cellular dysfunction and disease. These findings have expanded the understanding of how mechanisms of mitochondrial physiology can induce dysfunction and disease, but the complete collection of disease-causing gene variants remains incomplete. This article reviews the developments in disease gene discovery and the incorporation of gene findings with mitochondrial physiology. This understanding is critical to the development of targeted therapies.

Systemic Delivery of AAV-Fdxr Mitigates the Phenotypes of Mitochondrial Disorders in Fdxr Mutant Mice

Gene therapy now provides a novel approach for treating inherited monogenetic disorders, including nuclear gene mutations associated with mitochondrial diseases. In this study, we have utilized a mouse model carrying a p.Arg389Gln mutation of the mitochondrial Ferredoxin Reductase gene (Fdxr) and treated them with neurotropic AAV-PHP.B vector loaded with the mouse Fdxr cDNA sequence. We then used immunofluorescence staining and western blot to test the transduction efficiency of this vector. Toluidine blue staining and electronic microscopy were also utilized to assess the morphology of optic and sciatic nerves, and the mitochondrial respiratory chain activity was determined as well. The AAV vector effectively transduced in the central nervous system and peripheral organs, and AAV-Fdxr treatment reversed almost all the symptoms of the mutants (Fdxr^R389Q/R389Q). This therapy also improved the electronic conductivity of the sciatic nerves, prevented optic atrophy, improved mobility, and restored mitochondrial complex function. Most notably, the sensory neuropathy, neurodegeneration, and chronic neuroinflammation in the brain were alleviated. Overall, we present the first demonstration of a potential definitive treatment that significantly improves optic and sciatic nerve atrophy, sensory neuropathy, and mitochondrial dysfunction in FDXR-related mitochondriopathy. Our study provides substantial support for the translation of AAV-based Fdxr gene therapy into clinical applications.

Cardiolipin-deficient cells have decreased levels of the iron-sulfur biogenesis protein frataxin

Cardiolipin (CL) is the signature phospholipid of mitochondrial membranes, where it is synthesized locally and plays an important role in mitochondrial bioenergetics. Previous studies in the yeast model have indicated that CL is required for optimal iron homeostasis, which is disrupted by a mechanism not yet determined in the yeast CL mutant, crd1Δ. This finding has implications for the severe genetic disorder, Barth syndrome (BTHS), in which CL metabolism is perturbed because of mutations in the CL-remodeling enzyme, tafazzin. Here, we investigate the effects of tafazzin deficiency on iron homeostasis in the mouse myoblast model of BTHS tafazzin knockout (TAZ-KO) cells. Similarly to CL-deficient yeast cells, TAZ-KO cells exhibited elevated sensitivity to iron, as well as to H2O2, which was alleviated by the iron chelator deferoxamine. TAZ-KO cells exhibited increased expression of the iron exporter ferroportin and decreased expression of the iron importer transferrin receptor, likely reflecting a regulatory response to elevated mitochondrial iron. Reduced activities of mitochondrial iron-sulfur cluster enzymes suggested that the mechanism underlying perturbation of iron homeostasis was defective iron-sulfur biogenesis. We observed decreased levels of Yfh1/frataxin, an essential component of the iron-sulfur biogenesis machinery, in mitochondria from TAZ-KO mouse cells and in CL-deleted yeast crd1Δ cells, indicating that the role of CL in iron-sulfur biogenesis is highly conserved. Yeast crd1Δ cells exhibited decreased processing of the Yfh1 precursor upon import, which likely contributes to the iron homeostasis defects. Implications for understanding the pathogenesis of BTHS are discussed.