Lipoylation is dependent on the ferredoxin FDX1 and dispensable under hypoxia in human cells

Shedding Light on the Electron Delocalization Pathway at the [Fe2S2]2+ Cluster of FDX2

In this paper, we investigate the electronic structure of the [Fe2S2]2+ cluster of human ferredoxin 2 by designing NMR experiments tailored to observe hyperfine-shifted and fast relaxing resonances in the immediate proximity of the cluster and adding a quantitative layer of interpretation through quantum chemical calculations. The combination of paramagnetic NMR and density functional theory data provides evidence of the way unpaired electron density map is at the origin of the inequivalence of the two iron(III) ferredoxin centers. An electron spin density transfer is observed between cluster inorganic sulfide ions and aliphatic carbon atoms, occurring via a C-H---S-Fe3+ interaction, suggesting that inorganic cluster sulfide ions have a significant role in the distribution of electron spin density around the prosthetic group. The extended assignment of 1H, 13C, and 15N nuclei allows the identification of all residues of the binding loop and provides an estimate of the magnetic exchange coupling constant between the two Fe3+ ions of the [Fe2S2]2+ cluster of 386 cm-1. The approach developed here can be extended to other iron-sulfur proteins, providing a crucial tool to uncover subtle differences in electronic structures that modulate the functions of this protein family.

FDX1 Regulates the Phosphorylation of ATM, DNA-PKcs Akt, and EGFR and Affects Radioresistance Under Severe Hypoxia in the Glioblastoma Cell Line T98G

Hypoxic cells exhibit radioresistance, which is associated with poor prognosis in cancer patients. Understanding the molecular mechanisms underlying radioresistance in hypoxic tumor cells is crucial for improving radiotherapy efficacy. In this study, we examined the role of FDX1 in regulating cellular responses to severe hypoxia in glioblastoma cell lines T98G and A172. We found that FDX1 expression was upregulated under severe hypoxia, and its knockdown reduced the hypoxia-induced activation of key radioresistance factors and cellular survival mechanisms, including ATM, DNA-PKcs, Akt, and EGFR. FDX1 knockdown also sensitized T98G cells to radiation under severe hypoxia. Furthermore, FDX1 was found to regulate HIF-1α protein level, while HIF-1α did not regulate FDX1 expression. These results suggest that FDX1 may be a novel therapeutic target to overcome radioresistance in glioblastoma under severe hypoxia.

Dying to survive: harnessing inflammatory cell death for better immunotherapy

Immunotherapy has transformed cancer treatment paradigms, but its effectiveness depends largely on the immunogenicity of the tumor. Unfortunately, the high resemblance of cancer to normal tissues makes most tumors immunologically 'cold', with a poor response to immunotherapy. Danger signals are critical for breaking immune tolerance and mobilizing robust, long-lasting antitumor immunity. Recent studies have identified inflammatory cell death modalities and their power in providing danger signals to trigger optimal tumor suppression. However, key mediators of inflammatory cell death are preferentially silenced during early tumor immunoediting. Strategies to rejuvenate inflammatory cell death hold great promise for broadening immunotherapy-responsive tumors. In this review, we examine how inflammatory cell death enhances tumor immunogenicity, how it is suppressed during immunoediting, and the potential of harnessing it for improved immunotherapy.

Pulling back the mitochondria's iron curtain

Mitochondrial functionality and cellular iron homeostasis are closely intertwined. Mitochondria are biosynthetic hubs for essential iron cofactors such as iron-sulfur (Fe-S) clusters and heme. These cofactors, in turn, enable key mitochondrial pathways, such as energy and metabolite production. Mishandling of mitochondrial iron is associated with a spectrum of human pathologies ranging from rare genetic disorders to common conditions. Here, we review mitochondrial iron utilization and its intersection with disease.

Hypoxia as a medicine

Oxygen is essential for human life, yet a growing body of preclinical research is demonstrating that chronic continuous hypoxia can be beneficial in models of mitochondrial disease, autoimmunity, ischemia, and aging. This research is revealing exciting new and unexpected facets of oxygen biology, but translating these findings to patients poses major challenges, because hypoxia can be dangerous. Overcoming these barriers will require integrating insights from basic science, high-altitude physiology, clinical medicine, and sports technology. Here, we explore the foundations of this nascent field and outline a path to determine how chronic continuous hypoxia can be safely, effectively, and practically delivered to patients.

Mammalian copper homeostasis: physiological roles and molecular mechanisms

In the past decade, evidence for the numerous roles of copper (Cu) in mammalian physiology has grown exponentially. The discoveries of Cu involvement in cell signaling, autophagy, cell motility, differentiation, and regulated cell death (cuproptosis) have markedly extended the list of already known functions of Cu, such as a cofactor of essential metabolic enzymes, a protein structural component, and a regulator of protein trafficking. Novel and unexpected functions of Cu transporting proteins and enzymes have been identified, and new disorders of Cu homeostasis have been described. Significant progress has been made in the mechanistic studies of two classic disorders of Cu metabolism, Menkes disease and Wilson's disease, which paved the way for novel approaches to their treatment. The discovery of cuproptosis and the role of Cu in cell metastatic growth have markedly increased interest in targeting Cu homeostatic pathways to treat cancer. In this review, we summarize the established concepts in the field of mammalian Cu physiology and discuss how new discoveries of the past decade expand and modify these concepts. The roles of Cu in brain metabolism and in cell functional speciation and a recently discovered regulated cell death have attracted significant attention and are highlighted in this review.

Hypoxia-induced autophagy attenuates ferredoxin 1-mediated cuproptosis in colorectal cancer cells

IntroductionCuproptosis has emerged as a potential therapeutic target for colorectal cancer (CRC). This study investigated the role of ferredoxin 1 (FDX1) in regulating cuproptosis under hypoxic conditions and explored the impact of autophagy on this process in CRC.MethodsCRC patient samples and cell lines were used in this study. Cells were exposed to hypoxia and treated with Es-Cu (a copper supplement) and rapamycin, an autophagy inducer. FDX1 expression in clinical tissues was assessed in clinical tissues using qPCR and Western blot. The CCK8 assay, EdU staining, and Transwell assay were employed to evaluate the malignant behavior of tumor cells. Copper content and DLAT oligomerization were measured. A nude mouse xenograft model was used to explore the role of FDX1 under hypoxic conditions.ResultsCompared with adjacent normal tissues, elevated FDX1 expression was observed in CRC tissues. In vitro, hypoxia or Es-Cu treatment upregulated FDX1 expression in CRC cell lines, resulting in reduced cell proliferation and increased cellular damage. FDX1 overexpression under hypoxic conditions suppressed migration, invasion, and proliferation while promoting cellular damage and DLAT oligomerization. Rapamycin-induced autophagy reversed the inhibitory effects of FDX1 overexpression on CRC cells. In vivo, rapamycin treatment attenuated the tumor-suppressive effects of FDX1 overexpression in nude mouse xenograft models.DiscussionThis study demonstrated that hypoxia-induced autophagy inhibits FDX1-mediated cuproptosis, leading to resistance to copper-induced cell death in CRC cells. Targeting the autophagy pathway may provide a novel therapeutic strategy to overcome resistance to cuproptosis and improving CRC treatment outcomes.

Structural aspects of iron‑sulfur protein biogenesis: An NMR view

Over the last decade, structural aspects involving iron‑sulfur (Fe/S) protein biogenesis have played an increasingly important role in understanding the high mechanistic complexity of mitochondrial and cytosolic machineries maturing Fe/S proteins. In this respect, solution NMR has had a significant impact because of its ability to monitor transient protein-protein interactions, which are abundant in the networks of pathways leading to Fe/S cluster biosynthesis and transfer, as well as thanks to the developments of paramagnetic NMR in both terms of new methodologies and accurate data interpretation. Here, we review the use of solution NMR in characterizing the structural aspects of human Fe/S proteins and their interactions in the framework of Fe/S protein biogenesis. We will first present a summary of the recent advances that have been achieved by paramagnetic NMR and then we will focus our attention on the role of solution NMR in the field of human Fe/S protein biogenesis.

Exploring Copper's role in stroke: progress and treatment approaches

Copper is an important mineral, and moderate copper is required to maintain physiological processes in nervous system including cerebral ischemia/reperfusion (I/R) injury. Over the past few decades, copper induced cell death, named cuprotosis, has attracted increasing attention. Several lines of evidence have confirmed cuprotosis exerts pivotal role in diverse of pathological processes, such as cancer, neurodegenerative diseases, and I/R injury. Therefore, an in-depth understanding of the interaction mechanism between copper-mediated cell death and I/R injury may reveal the significant alterations about cellular copper-mediated homeostasis in physiological and pathophysiological conditions, as well as therapeutic strategies deciphering copper-induced cell death in cerebral I/R injury.

FDX2, an iron-sulfur cluster assembly factor, is essential to prevent cellular senescence, apoptosis or ferroptosis of ovarian cancer cells

Recent studies reveal that biosynthesis of iron-sulfur clusters (Fe-Ss) is essential for cell proliferation, including that of cancer cells. Nonetheless, it remains unclear how Fe-S biosynthesis functions in cell proliferation/survival. Here, we report that proper Fe-S biosynthesis is essential to prevent cellular senescence, apoptosis, or ferroptosis, depending on cell context. To assess these outcomes in cancer, we developed an ovarian cancer line with conditional KO of FDX2, a component of the core Fe-S assembly complex. FDX2 loss induced global downregulation of Fe-S-containing proteins and Fe2+ overload, resulting in DNA damage and p53 pathway activation, and driving the senescence program. p53 deficiency augmented DNA damage responses upon FDX2 loss, resulting in apoptosis rather than senescence. FDX2 loss also sensitized cells to ferroptosis, as evidenced by compromised redox homeostasis of membrane phospholipids. Our results suggest that p53 status and phospholipid homeostatic activity are critical determinants of diverse biological outcomes of Fe-S deficiency in cancer cells.

FDX1 downregulation activates mitophagy and the PI3K/AKT signaling pathway to promote hepatocellular carcinoma progression by inducing ROS production

BACKGROUND

Mitochondrial dysfunction and metabolic reprogramming can lead to the development and progression of hepatocellular carcinoma (HCC). Ferredoxin 1 (FDX1) is a small mitochondrial protein and recent studies have shown that FDX1 plays an important role in tumor cuproptosis, but its role in HCC is still elusive. In this study, we aim to investigate the expression and novel functions of FDX1 in HCC.

METHODS

FDX1 expression was first analyzed in publicly available datasets and verified by immunohistochemistry, qRT-PCR and Western blot. In vitro and in vivo experiments were applied to explore the functions of FDX1. Non-targeted metabolomics and RNA-sequencing were used to determine molecular mechanism. mRFP-GFP-LC3 lentivirus transfection, Mito-Tracker Red and Lyso-Tracker Green staining, transmission electron microscopy, flow cytometry, JC-1 staining, etc. were used to analyze mitophagy or ROS levels. Hydrodynamic tail vein injection (HTVi) and patient-derived organoid (PDO) models were used to analyze effect of FDX1 overexpression.

RESULTS

FDX1 expression is significantly downregulated in HCC tissues. FDX1 downregulation promotes HCC cell proliferation, invasion in vitro and growth, metastasis in vivo. In addition, FDX1 affects metabolism of HCC cells and is associated with autophagy. We then confirmed that FDX1 deficiency increases ROS levels, activates mitophagy and the PI3K/AKT signaling pathway in HCC cells. Interestingly, scavenging ROS attenuates the tumor-promoting role and mitophagy of FDX1 downregulation. The results of HTVi and PDO models both find that FDX1 elevation significantly inhibits HCC progression. Moreover, low FDX1 expression is associated with shorter survival and is an independent risk factor for prognosis in HCC patients.

CONCLUSIONS

Our research had investigated novel functions of FDX1 in HCC. Downregulation of FDX1 contributes to metabolic reprogramming and leads to ROS-mediated activation of mitophagy and the PI3K/AKT signaling pathway. FDX1 is a potential prognostic biomarker and increasing FDX1 expression may be a potential therapeutic approach to inhibit HCC progression.

Cuproptosis in cancer: biological implications and therapeutic opportunities

Cuproptosis, a newly identified copper (Cu)-dependent form of cell death, stands out due to its distinct mechanism that sets it apart from other known cell death pathways. The molecular underpinnings of cuproptosis involve the binding of Cu to lipoylated enzymes in the tricarboxylic acid cycle. This interaction triggers enzyme aggregation and proteotoxic stress, culminating in cell death. The specific mechanism of cuproptosis has yet to be fully elucidated. This newly recognized form of cell death has sparked numerous investigations into its role in tumorigenesis and cancer therapy. In this review, we summarized the current knowledge on Cu metabolism and its link to cancer. Furthermore, we delineated the molecular mechanisms of cuproptosis and summarized the roles of cuproptosis-related genes in cancer. Finally, we offered a comprehensive discussion of the most recent advancements in Cu ionophores and nanoparticle delivery systems that utilize cuproptosis as a cutting-edge strategy for cancer treatment.

The role of lipoylation in mitochondrial adaptation to methionine restriction

Dietary methionine restriction (MR) is associated with a spectrum of health-promoting benefits. Being conducive to prevention of chronic diseases and extension of life span, MR can activate integrated responses at metabolic, transcriptional, and physiological levels. However, how the mitochondria of MR influence metabolic phenotypes remains elusive. Here, we provide a summary of cellular functions of methionine metabolism and an overview of the current understanding of effector mechanisms of MR, with a focus on the aspect of mitochondria-mediated responses. We propose that mitochondria can sense and respond to MR through a modulatory role of lipoylation, a mitochondrial protein modification sensitized by MR.

Recent advances in molecular mechanisms of skin wound healing and its treatments

The skin, being a multifaceted organ, performs a pivotal function in the complicated wound-healing procedure, which encompasses the triggering of several cellular entities and signaling cascades. Aberrations in the typical healing process of wounds may result in atypical scar development and the establishment of a persistent condition, rendering patients more vulnerable to infections. Chronic burns and wounds have a detrimental effect on the overall quality of life of patients, resulting in higher levels of physical discomfort and socio-economic complexities. The occurrence and frequency of prolonged wounds are on the rise as a result of aging people, hence contributing to escalated expenditures within the healthcare system. The clinical evaluation and treatment of chronic wounds continue to pose challenges despite the advancement of different therapeutic approaches. This is mainly owing to the prolonged treatment duration and intricate processes involved in wound healing. Many conventional methods, such as the administration of growth factors, the use of wound dressings, and the application of skin grafts, are used to ease the process of wound healing across diverse wound types. Nevertheless, these therapeutic approaches may only be practical for some wounds, highlighting the need to advance alternative treatment modalities. Novel wound care technologies, such as nanotherapeutics, stem cell treatment, and 3D bioprinting, aim to improve therapeutic efficacy, prioritize skin regeneration, and minimize adverse effects. This review provides an updated overview of recent advancements in chronic wound healing and therapeutic management using innovative approaches.

Targeting cuproplasia and cuproptosis in cancer

Copper, an essential trace element that exists in oxidized and reduced forms, has pivotal roles in a variety of biological processes, including redox chemistry, enzymatic reactions, mitochondrial respiration, iron metabolism, autophagy and immune modulation; maintaining copper homeostasis is crucial as both its deficiency and its excess are deleterious. Dysregulated copper metabolism has a dual role in tumorigenesis and cancer therapy. Specifically, cuproplasia describes copper-dependent cell growth and proliferation, including hyperplasia, metaplasia and neoplasia, whereas cuproptosis refers to a mitochondrial pathway of cell death triggered by excessive copper exposure and subsequent proteotoxic stress (although complex interactions between cuproptosis and other cell death mechanisms, such as ferroptosis, are likely and remain enigmatic). In this Review, we summarize advances in our understanding of copper metabolism, the molecular machineries underlying cuproplasia and cuproptosis, and their potential targeting for cancer therapy. These new findings advance the rapidly expanding field of translational cancer research focused on metal compounds.

SF3B1 mutations provide genetic vulnerability to copper ionophores in human acute myeloid leukemia

In a phenotypical screen of 56 acute myeloid leukemia (AML) patient samples and using a library of 10,000 compounds, we identified a hit with increased sensitivity toward SF3B1-mutated and adverse risk AMLs. Through structure-activity relationship studies, this hit was optimized into a potent, specific, and nongenotoxic molecule called UM4118. We demonstrated that UM4118 acts as a copper ionophore that initiates a mitochondrial-based noncanonical form of cell death known as cuproptosis. CRISPR-Cas9 loss-of-function screen further revealed that iron-sulfur cluster (ISC) deficiency enhances copper-mediated cell death. Specifically, we found that loss of the mitochondrial ISC transporter ABCB7 is synthetic lethal to UM4118. ABCB7 is misspliced and down-regulated in SF3B1-mutated leukemia, creating a vulnerability to copper ionophores. Accordingly, ABCB7 overexpression partially rescued SF3B1-mutated cells to copper overload. Together, our work provides mechanistic insights that link ISC deficiency to cuproptosis, as exemplified by the high sensitivity of SF3B1-mutated AMLs. We thus propose SF3B1 mutations as a biomarker for future copper ionophore-based therapies.

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.

Mitochondrial fatty acid synthesis is an emergent central regulator of mammalian oxidative metabolism

Contrary to their well-known functions in nutrient breakdown, mitochondria are also important biosynthetic hubs and express an evolutionarily conserved mitochondrial fatty acid synthesis (mtFAS) pathway. mtFAS builds lipoic acid and longer saturated fatty acids, but its exact products, their ultimate destination in cells, and the cellular significance of the pathway are all active research questions. Moreover, why mitochondria need mtFAS despite their well-defined ability to import fatty acids is still unclear. The identification of patients with inborn errors of metabolism in mtFAS genes has sparked fresh research interest in the pathway. New mammalian models have provided insights into how mtFAS coordinates many aspects of oxidative mitochondrial metabolism and raise questions about its role in diseases such as obesity, diabetes, and heart failure. In this review, we discuss the products of mtFAS, their function, and the consequences of mtFAS impairment across models and in metabolic disease.

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.