FBXL5 Regulates IRP2 Stability in Iron Homeostasis via an Oxygen-Responsive [2Fe2S] Cluster

Protein Ubiquitination Modification in Pulmonary Fibrosis

Pulmonary fibrosis (PF) is a chronic, progressive fibrotic interstitial lung disease characterized by a high incidence and mortality rate, which encompasses features, such as diffuse alveolar inflammation, invasive fibroblast activation, and uncontrolled extracellular matrix (ECM) deposition. Beyond the local pathological processes, PF can be better understood in light of interorgan communication networks that are involved in its progression. Notably, pulmonary inflammation can affect cardiovascular, renal, hepatic, and neural functions, highlighting the importance of understanding these systemic interactions. Posttranslational modifications play a crucial role in regulating protein function, localization, stability, and activity. Specifically, protein ubiquitination modifications are involved in PF induced by various stimuli, involving a range of ubiquitin-modifying enzymes and substrates. In this review, we provide an overview of how E3 ubiquitin ligases and deubiquitinating enzymes (DUBs) modulate PF through several signaling pathways, such as TGF-β, Wnt, metabolic activity, aging, ferroptosis, endoplasmic reticulum stress, and inflammatory responses. This perspective includes the role of ubiquitin-proteasome systems in interorgan communication, affecting the progression of PF and related systemic conditions. Additionally, we also summarize the currently available therapeutic compounds targeting protein ubiquitination-related enzymes or ubiquitination substrates for the treatment of PF. Understanding the interplay between ubiquitination and interorgan communication may pave the way for novel therapeutic strategies.

Distinct Stress Regulators in the CRL Family: Emerging Roles of F-Box Proteins: Cullin-RING Ligases and Stress-Sensing

Cullin-RING ligases (CRLs) are central regulators of environmental and cellular stress responses, orchestrating diverse processes through the ubiquitination of substrate proteins. As modular complexes, CRLs employ substrate-specific adaptors to target proteins for degradation and other ubiquitin-mediated processes, enabling dynamic adaptation to environmental cues. Recent advances have highlighted the largest CRL subfamily SCF (Skp1-cullin-F-box) in environmental sensing, a role historically underappreciated for SCF ubiquitin ligases. Notably, emerging evidence suggests that the F-box domain, a 50-amino acid motif traditionally recognized for mediating protein-protein interactions, can act as a direct environmental sensor due to its ability to bind heavy metals. Despite these advances, the roles of many CRL components in environmental sensing remain poorly understood. This review provides an overview of CRLs in stress response regulation and emphasizes the emerging functions of F-box proteins in environmental adaptation.

Iron-sensing and redox properties of the hemerythrin-like domains of Arabidopsis BRUTUS and BRUTUS-LIKE2 proteins

Iron uptake in plants is negatively regulated by highly conserved hemerythrin (Hr) E3 ubiquitin ligases exemplified by Arabidopsis thaliana BRUTUS (BTS). Physiological studies suggest these are the elusive plant iron sensors, but biochemical evidence is lacking. Here we demonstrate that the N-terminal domains of BTS and BTS-LIKE2 (BTSL2) respectively bind three and two diiron centres within three closely packed Hr-like subdomains. The centres can be reversibly oxidized by O2 and H2O2, resulting in a di-Fe3+ form that is non-labile. In the reduced state, a proportion of the iron becomes labile, based on accessibility to Fe2+ chelators and reconstitution experiments, consistent with dynamic iron binding. Impaired iron binding and altered redox properties in the BTS dgl variant correlate with diminished capacity to suppress the downstream signalling cascade. These data provide the biochemical foundation for a mechanistic model of how BTS/Ls function as iron sensors that are unique to the plant kingdom.

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.

Mathematical modeling reveals ferritin as the strongest cellular driver of dietary iron transfer block in enterocytes

Intestinal mucosal block is the transient reduction in iron absorption ability of intestinal epithelial cells (enterocytes) in response to previous iron exposures that occur at the cell scale. The block characteristics have been shown to depend both on iron exposure magnitude and temporality, and understanding block control will enable deeper understanding of how intestinal iron absorption contributes to pathological iron states. Three biochemical mechanisms implicated in driving the block behavior are divalent metal transporter 1 endocytosis, ferritin iron sequestration, and iron regulatory protein regulation of iron related protein expression. In this work, a model of enterocyte iron metabolism is built based on published experimental data that is capable of reproducing the mucosal block phenomena. The model is then used to estimate the quantitative contribution of each of the three mechanisms on the properties of the mucosal block. Analysis reveals that ferritin and iron regulatory proteins are the main intracellular mechanisms contributing to the mucosal block, findings congruent with experimental predictions. Lastly, DMT1 endocytosis is shown to play a role in limiting total iron uptake by enterocytes but does not contribute to the decrease in total iron transfer across their basal membrane seen in the mucosal block.

Shedding light on iron nutrition: exploring intersections of transcription factor cascades in light and iron deficiency signaling

In the dynamic environment of plants, the interplay between light-dependent growth and iron nutrition is a recurring challenge. Plants respond to low iron levels by adjusting growth and physiology through enhanced iron acquisition from the rhizosphere and internal iron pool reallocation. Iron deficiency response assays and gene co-expression networks aid in documenting physiological reactions and unraveling gene-regulatory cascades, offering insight into the interplay between hormonal and external signaling pathways. However, research directly exploring the significance of light in iron nutrition remains limited. This review provides an overview on iron deficiency regulation and its cross-connection with distinct light signals, focusing on transcription factor cascades and long-distance signaling. The circadian clock and retrograde signaling influence iron uptake and allocation. The light-activated shoot-to-root mobile transcription factor ELONGATED HYPOCOTYL5 (HY5) affects iron homeostasis responses in roots. Blue light triggers the formation of biomolecular condensates containing iron deficiency-induced protein complexes. The potential of exploiting the connection between light and iron signaling remains underutilized. With climate change and soil alkalinity on the rise, there is a need to develop crops with improved nutrient use efficiency and modified light dependencies. More research is needed to understand and leverage the interplay between light signaling and iron nutrition.

Modulation of iron metabolism by new chemicals interacting with the iron regulatory system

Despite the vital role of iron and vulnerability of iron metabolism in disease states, it remains largely unknown whether chemicals interacting with cellular proteins are responsible for perturbation of iron metabolism. We previously demonstrated that cisplatin was an inhibitor of the iron regulatory system by blocking IRP2 (iron regulatory protein 2) binding to an iron-responsive element (IRE) located in the 3'- or 5'-UTR (untranslated region) of key iron metabolism genes such as transferrin receptor 1 (TfR1) and ferritin mRNAs. To guide the development of new chemical probes to modulate the IRP-IRE regulatory system, we used an artificial intelligence (AI)-based ligand design and screened a chemical library composed of cysteine-reactive warheads. Using wild type and mutant IRE-luciferase reporter cells, we identified new IRP-IRE inhibitors such as V004-0872 harboring chloroacetamide, while its analog V011-6261 with chloropropanamide completely lost the inhibitory activity. V004-0872 inhibited the human IRP2 via Cys512 and caused decreased iron levels through reciprocal TfR1 downregulation and ferritin upregulation. V004-0872 increased production of mitochondrial reactive oxygen species (ROS) and exhibited cytotoxicity that was inhibited by N-acetyl cysteine but not the ferroptosis inhibitor ferrostatin-1. Furthermore, we found that widely used haloketone protease inhibitors and acetamide herbicides inhibit the IRP-IRE system. Since IRP2 overexpression is responsible for iron excess conditions to promote growth of several cancers and exacerbation of iron-overload diseases, these results and new compounds lay the groundwork for new reagents and strategies to limit the availability of iron and oxidative stress in iron-overloaded disease conditions.

Recognition of BACH1 quaternary structure degrons by two F-box proteins under oxidative stress

Ubiquitin-dependent proteolysis regulates diverse cellular functions with high substrate specificity, which hinges on the ability of ubiquitin E3 ligases to decode the targets' degradation signals, i.e., degrons. Here, we show that BACH1, a transcription repressor of antioxidant response genes, features two distinct unconventional degrons encrypted in the quaternary structure of its homodimeric BTB domain. These two degrons are both functionalized by oxidative stress and are deciphered by two complementary E3s. FBXO22 recognizes a degron constructed by the BACH1 BTB domain dimer interface, which is unmasked from transcriptional co-repressors after oxidative stress releases BACH1 from chromatin. When this degron is impaired by oxidation, a second BACH1 degron manifested by its destabilized BTB dimer is probed by a pair of FBXL17 proteins that remodels the substrate into E3-bound monomers for ubiquitination. Our findings highlight the multidimensionality of protein degradation signals and the functional complementarity of different ubiquitin ligases targeting the same substrate.

Dual BACH1 regulation by complementary SCF-type E3 ligases

Broad-complex, tramtrack, and bric-à-brac domain (BTB) and CNC homolog 1 (BACH1) is a key regulator of the cellular oxidative stress response and an oncogene that undergoes tight post-translational control by two distinct F-box ubiquitin ligases, SCFFBXO22 and SCFFBXL17. However, how both ligases recognize BACH1 under oxidative stress is unclear. In our study, we elucidate the mechanism by which FBXO22 recognizes a quaternary degron in a domain-swapped β-sheet of the BACH1 BTB dimer. Cancer-associated mutations and cysteine modifications destabilize the degron and impair FBXO22 binding but simultaneously expose an otherwise shielded degron in the dimer interface, allowing FBXL17 to recognize BACH1 as a monomer. These findings shed light on a ligase switch mechanism that enables post-translational regulation of BACH1 by complementary ligases depending on the stability of its BTB domain. Our results provide mechanistic insights into the oxidative stress response and may spur therapeutic approaches for targeting oxidative stress-related disorders and cancer.

Novel biallelic variants in IREB2 cause an early-onset neurodegenerative disorder in a Chinese pedigree

BACKGROUND

Cellular iron metabolism is essential for maintaining various biological processes in organisms, and this is influenced by the function of iron-responsive element-binding protein 2 (IRP2), encoded by the IREB2 gene. Since 2019, three cases of a genetic neurodegenerative syndrome resulting from compound heterozygous mutations in IREB2 have been documented, highlighting the crucial role of IRP2 in regulating iron metabolism homeostasis. This study aims to investigate the molecular basis in a single proband born to non-consanguineous healthy parents, presenting with severe psychomotor developmental abnormalities and microcytic anemia.

METHODS

Trio-whole exome sequencing (WES) was applied to identify the disease-causing gene in an 8-month-old male patient from China. In silico tools were used to predict the pathogenicity of the identified variants, and in vitro functional studies were performed to evaluate the molecular mechanism.

RESULTS

WES identified novel biallelic variants, c.1111 A > G (P.Ile371Val) and c.2477 A > T (P.Asp826Val), in the IREB2 gene, which encodes the iron metabolism-related protein, IRP2. Functional studies revealed that c.2477 A > T resulted in a significant degradation of IRP2, which led to the misregulation of intracellular ferric iron.

CONCLUSIONS

We report the identification of the first functional domain associated with the degradation of IRP2. The biallelic variants that affect protein degradation likely underlie the pathogenesis of the IRP2-related neurodegenerative disorder. Moreover, the use of proteasome inhibitors can potentially restore the expression of IRP2, highlighting a promising therapeutic target for patients with IRP2deficiency.

Mitochondrial Iron Metabolism as a Potential Key Mediator of PD-L1 Thermal Regulation

Glioblastoma (GBM) is the most common primary brain malignancy in the U.S. with a 5-year overall survival < 5% despite an aggressive standard of care. Laser interstitial thermal therapy (LITT) is a surgical approach to treating GBM that has gained traction, providing a safe option for reducing intracranial tumor burden. LITT is believed to potentially modulate GBM immune responses; however, the biochemical mechanisms underlying the modulation of immune checkpoints in GBM cells have been poorly characterized. The present study aimed to preliminarily evaluate the effects of thermal therapy and radiation on PD-L1 modulation in vitro, as a function of IDH mutational status. U87 cells and their IDH-mutant counterpart (U87R132H), which was generated using a crispr-cas9 knock-in approach, were utilized for this preliminary evaluation. Cell heating was achieved by harvesting with trypsin centrifugation where the cell pellets were treated on a heat block for the associated time and temperature. Following thermal therapy, cells were resuspended and irradiated using a 37-Cesium irradiator at 0.6 Gy min-1. Immediately following treatment, cells were either plated as single cells to allow colonies to form, and stained with Coomassie blue to be counted approximately 10-14 days later or harvested for Western blot analysis. Cell lysates were analyzed for PD-L1 expression with respect to various iron metabolic parameters (mortalin (HSPA9), transferrin receptor, and ferritin heavy chain) using a Western blotting approach. In both U87 and U87R132H cell lines, thermal therapy showed a temperature-dependent cell-killing effect, but U87R132H cells appeared more sensitive to thermal treatment when treated at 43 °C for 10 min. Moreover, thermal therapy had minimal effects on cell responses to 2 Gy irradiation. Treatment with thermal therapy downregulated PD-L1 expression in U87R132H cells, which was associated with increased expression of the mitochondrial iron metabolic enzyme, HSPA9. Thermal therapy reversed the radiation-induced overexpression of PD-L1, transferrin receptor, and ferritin heavy chain in U87R132H cells. No effects were observed in wild-type U87 cells. Moreover, Ga(NO3)3 depleted mitochondrial iron content which, in turn, significantly enhanced the sensitivity of U87R132H cells to thermal therapy and 2 Gy irradiation and caused a significant increase in PD-L1 expression. These results suggest that thermal therapy alone can modulate the immune checkpoint PD-L1. This effect was more pronounced when thermal therapy was combined with radiation. Mechanistically, mitochondrial iron trafficking through HSPA9 may coordinate the regulation of PD-L1 in the context of thermal therapy and ionizing radiation, which can be targeted with gallium-based therapy. These novel, preliminary findings warrant further mechanistic investigations in pre-clinical models of LITT.

Fighting ischemia-reperfusion injury: Focusing on mitochondria-derived ferroptosis

Ischemia-reperfusion injury (IRI) is a major cause of mortality and morbidity. Current treatments for IRI have limited efficacy and novel therapeutic strategies are needed. Mitochondrial dysfunction not only initiates IRI but also plays a significant role in ferroptosis pathogenesis. Recent studies have highlighted that targeting mitochondrial pathways is a promising therapeutic approach for ferroptosis-induced IRI. The association between ferroptosis and IRI has been reviewed many times, but our review provides the first comprehensive overview with a focus on recent mitochondrial research. First, we present the role of mitochondria in ferroptosis. Then, we summarize the evidence on mitochondrial manipulation of ferroptosis in IRI and review recent therapeutic strategies aimed at targeting mitochondria-related ferroptosis to mitigate IRI. We hope our review will provide new ideas for the treatment of IRI and accelerate the transition from bench to bedside.

Ubiquitin-specific protease 38 promotes atrial fibrillation in diabetic mice by stabilizing iron regulatory protein 2

BACKGROUND

Atrial fibrillation (AF) is a common cardiovascular disease often observed in diabetes mellitus, and there is currently no satisfactory therapeutic option. Ubiquitin-specific protease 38 (USP38) has been implicated in the degradation of numerous substrate proteins in the myocardium. Herein, we aim to investigate the role of USP38 in AF induced by diabetes.

METHODS

Cardiac-specific transgenic USP38 mice and cardiac-specific knockout USP38 mice were constructed, and streptozotocin was used to establish diabetic mouse model. Functional, electrophysiological, histologic, biochemical studies were performed.

RESULTS

The expression of USP38 was upregulated in atrial tissues of diabetic mice and HL-1 cells exposed to high glucose. USP38 overexpression increased susceptibility to AF, accompanied by aberrant expression of calcium-handling protein, heightened iron load and oxidation stress in diabetic mice. Conversely, USP38 deficiency reduced vulnerability to AF by hampering ferroptosis. Mechanistically, USP38 bound to iron regulatory protein 2 (IRP2), stabilizing it and remove K48-linked polyubiquitination chains, thereby increasing intracellular iron overload, lipid peroxidation, and ultimately contributing to ferroptosis. In addition, reduced iron overload by deferoxamine treatment alleviated oxidation stress and decreased vulnerability to AF in diabetic mice.

CONCLUSION

Overall, our findings reveal the detrimental role of USP38 in diabetes-related AF, manifested by increased level of iron overload and oxidation stress.

Atomic-level design of biomimetic iron-sulfur clusters for biocatalysis

Designing biomimetic materials with high activity and customized biological functions by mimicking the central structure of biomolecules has become an important avenue for the development of medical materials. As an essential electron carrier, the iron-sulfur (Fe-S) clusters have the advantages of simple structure and high electron transport capacity. To rationally design and accurately construct functional materials, it is crucial to clarify the electronic structure and conformational relationships of Fe-S clusters. However, due to the complex catalytic mechanism and synthetic process in vitro, it is hard to reveal the structure-activity relationship of Fe-S clusters accurately. This review introduces the main structural types of Fe-S clusters and their catalytic mechanisms first. Then, several typical structural design strategies of biomimetic Fe-S clusters are systematically introduced. Furthermore, the development of Fe-S clusters in the biocatalytic field is enumerated, including tumor treatment, antibacterial, virus inhibition and plant photoprotection. Finally, the problems and development directions of Fe-S clusters are summarized. This review aims to guide people to accurately understand and regulate the electronic structure of Fe-S at the atomic level, which is of great significance for designing biomimetic materials with specific functions and expanding their applications in biocatalysis.

Iron regulatory protein two facilitates ferritinophagy and DNA damage/repair through guiding ATG9A trafficking

Trace elemental iron is an essential nutrient that participates in diverse metabolic processes. Dysregulation of cellular iron homeostasis, both iron deficiency and iron overload, is detrimental and tightly associated with disease pathogenesis. IRPs-IREs system is located at the center for iron homeostasis regulation. Additionally, ferritinophagy, the autophagy-dependent ferritin catabolism for iron recycling, is emerging as a novel mechanism for iron homeostasis regulation. It is still unclear whether IRPs-IREs system and ferritinophagy are synergistic or redundant in determining iron homeostasis. Here we report that IRP2, but not IRP1, is indispensable for ferritinophagy in response to iron depletion. Mechanistically, IRP2 ablation results in compromised AMPK activation and defective ATG9A endosomal trafficking, leading to the decreased engulfment of NCOA4-ferritin complex by endosomes and the subsequent dysregulated endosomal microferritinophagy. Moreover, this defective endosomal microferritinophagy exacerbates DNA damage and reduces colony formation in IRP2-depleted cells. Collectively, this study expands the physiological function of IRP2 in endosomal microferritinophagy and highlights potential crosstalk between IRPs-IREs and ferritinophagy in manipulating iron homeostasis.

Gallium Uncouples Iron Metabolism to Enhance Glioblastoma Radiosensitivity

Gallium-based therapy has been considered a potentially effective cancer therapy for decades and has recently re-emerged as a novel therapeutic strategy for the management of glioblastoma tumors. Gallium targets the iron-dependent phenotype associated with aggressive tumors by mimicking iron in circulation and gaining intracellular access through transferrin-receptor-mediated endocytosis. Mechanistically, it is believed that gallium inhibits critical iron-dependent enzymes like ribonucleotide reductase and NADH dehydrogenase (electron transport chain complex I) by replacing iron and removing the ability to transfer electrons through the protein secondary structure. However, information regarding the effects of gallium on cellular iron metabolism is limited. As mitochondrial iron metabolism serves as a central hub of the iron metabolic network, the goal of this study was to investigate the effects of gallium on mitochondrial iron metabolism in glioblastoma cells. Here, it has been discovered that gallium nitrate can induce mitochondrial iron depletion, which is associated with the induction of DNA damage. Moreover, the generation of gallium-resistant cell lines reveals a highly unstable phenotype characterized by impaired colony formation associated with a significant decrease in mitochondrial iron content and loss of the mitochondrial iron uptake transporter, mitoferrin-1. Moreover, gallium-resistant cell lines are significantly more sensitive to radiation and have an impaired ability to repair any sublethal damage and to survive potentially lethal radiation damage when left for 24 h following radiation. These results support the hypothesis that gallium can disrupt mitochondrial iron metabolism and serve as a potential radiosensitizer.

Focus on the role of calcium signaling in ferroptosis: a potential therapeutic strategy for sepsis-induced acute lung injury

By engaging in redox processes, ferroptosis plays a crucial role in sepsis-induced acute lung injury (ALI). Although iron stimulates calcium signaling through the stimulation of redox-sensitive calcium pathways, the function of calcium signals in the physiological process of ferroptosis in septic ALI remains unidentified. Iron homeostasis disequilibrium in ferroptosis is frequently accompanied by aberrant calcium signaling. Intracellular calcium overflow can be a symptom of dysregulation of the cellular redox state, which is characterized by iron overload during the early phase of ferroptosis. This can lead to disruptions in calcium homeostasis and calcium signaling. The mechanisms controlling iron homeostasis and ferroptosis are reviewed here, along with their significance in sepsis-induced acute lung injury, and the potential role of calcium signaling in these processes is clarified. We propose that the development of septic acute lung injury is a combined process involving the bidirectional interaction between iron homeostasis and calcium signaling. Our goal is to raise awareness about the pathophysiology of sepsis-induced acute lung injury and investigate the relationship between these mechanisms and ferroptosis. We also aimed to develop calcium-antagonistic therapies that target ferroptosis in septic ALI and improve the quality of survival for patients suffering from acute lung injury.

The involvement of IRP2-induced ferroptosis through the p53-SLC7A11-ALOX12 pathway in Parkinson's disease

Disturbance in iron homeostasis has been described in Parkinson's disease (PD), in which iron regulatory protein 2 (IRP2) plays a crucial role. IRP2 deletion resulted in the misregulation of iron metabolism and subsequent neurodegeneration. However, growing evidence showed that the levels of IRP2 were increased in the substantia nigra (SN) in MPTP-induced PD mice. To further clarify the role of increased IRP2 in PD, we developed IRP2-overexpressed mice by microinjecting AAV-Ireb2 in the SN. These mice showed decreased motor ability, abnormal gait and anxiety. Iron deposits induced by increased TFR1 and dopaminergic neuronal loss were observed in the SN. When these mice were treated with MPTP, exacerbated dyskinesia and dopaminergic neuronal loss were observed. In addition, TP53 was post-transcriptionally upregulated by IRP2 binding to the iron regulated element (IRE) in its 3' untranslated region. This resulted in increased lipid peroxidation levels and induced ferroptosis through the SLC7A11-ALOX12 pathway, which was independent of GPX4. This study revealed that IRP2 homeostasis in the SN was critical for PD progression and clarified the molecular mechanism of ferroptosis caused by IRP2.

Inhibition of IRP2-dependent reprogramming of iron metabolism suppresses tumor growth in colorectal cancer

BACKGROUND

Dysregulation of iron metabolism is implicated in malignant transformation, cancer progression, and therapeutic resistance. Here, we demonstrate that iron regulatory protein 2 (IRP2) preferentially regulates iron metabolism and promotes tumor growth in colorectal cancer (CRC).

METHODS

IRP2 knockdown and knockout cells were generated using RNA interference and clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9 methodologies, respectively. Cell viability was evaluated using both CCK-8 assay and cell counting techniques. Furthermore, IRP2 inhibition was determined by surface plasmon resonance (SPR) and RNA immunoprecipitation (IP). The suppressive effects of IRP2 were also corroborated in both organoid and mouse xenograft models, providing a comprehensive validation of IRP2's role.

RESULTS

We have elucidated the role of IRP2 as a preferential regulator of iron metabolism, actively promoting tumorigenesis within CRC. Elevated levels of IRP2 expression in patient samples are correlated with diminished overall survival, thereby reinforcing its potential role as a prognostic biomarker. The functional suppression of IRP2 resulted in a pronounced delay in tumor growth. Building on this proof of concept, we have developed IRP2 inhibitors that significantly reduce IRP2 expression and hinder its interaction with iron-responsive elements in key iron-regulating proteins, such as ferritin heavy chain 1 (FTH1) and transferrin receptor (TFRC), culminating in iron depletion and a marked reduction in CRC cell proliferation. Furthermore, these inhibitors are shown to activate the AMPK-ULK1-Beclin1 signaling cascade, leading to cell death in CRC models.

CONCLUSIONS

Collectively, these findings highlight the therapeutic potential of targeting IRP2 to exploit the disruption of iron metabolism in CRC, presenting a strategic advancement in addressing a critical area of unmet clinical need.

Acute inhibition of iron-sulfur cluster biosynthesis disrupts metabolic flexibility in mice

Iron-sulfur clusters (ISCs) are cell-essential cofactors present in ∼60 proteins including subunits of OXPHOS complexes I-III, DNA polymerases, and iron-sensing proteins. Dysfunctions in ISC biosynthesis are associated with anemias, neurodegenerative disorders, and metabolic diseases. To assess consequences of acute ISC inhibition in a whole body setting, we developed a mouse model in which key ISC biosynthetic enzyme NFS1 can be acutely and reversibly suppressed. Contrary to in vitro ISC inhibition and pharmacological OXPHOS suppression, global NFS1 inhibition rapidly enhances lipid utilization and decreases adiposity without affecting caloric intake and physical activity. ISC proteins decrease, including key proteins involved in OXPHOS (SDHB), lipoic acid synthesis (LIAS), and insulin mRNA processing (CDKAL1), causing acute metabolic inflexibility. Age-related metabolic changes decelerate loss of adiposity substantially prolonged survival of mice with NFS1 inhibition. Thus, the observation that ISC metabolism impacts organismal fuel choice will aid in understanding the mechanisms underlying ISC diseases with increased risk for diabetes.

Graphical abstract

Highlights

Acute ISC inhibition leads to rapid loss of adiposity in miceMulti-metabolic pathway disruption upon ISC deficiency blocks energy storageNfs1 inhibition induces glucose dyshomeostasis due to ISC deficiency in β-cellsEnergy distress caused by inhibition of ISC synthesis is attenuated in aged mice.

Iron-dependent KDM4D activity controls the quiescence-activity balance of MSCs via the PI3K-Akt-Foxo1 pathway

Iron deficiency is a prevalent nutritional deficit associated with organ damage and dysfunction. Recent research increasingly associates iron deficiency with bone metabolism dysfunction, although the precise underlying mechanisms remain unclear. Some studies have proposed that iron-dependent methylation-erasing enzyme activity regulates cell proliferation and differentiation under physiological or pathological conditions. However, it remains uncertain whether iron deficiency inhibits the activation of quiescent mesenchymal stem cells (MSCs) by affecting histone demethylase activity. In our study, we identified KDM4D as a key player in the activation of quiescent MSCs. Under conditions of iron deficiency, the H3K9me3 demethylase activity of KDM4D significantly decreased. This alteration resulted in increased heterochromatin with H3K9me3 near the PIK3R3 promoter, suppressing PIK3R3 expression and subsequently inhibiting the activation of quiescent MSCs via the PI3K-Akt-Foxo1 pathway. Iron-deficient mice displayed significantly impaired bone marrow MSCs activation and decreased bone mass compared to normal mice. Modulating the PI3K-Akt-Foxo1 pathway could reverse iron deficiency-induced bone loss.

FGFR1 governs iron homeostasis via regulating intracellular protein degradation pathways of IRP2 in prostate cancer cells

The acquisition of ectopic fibroblast growth factor receptor 1 (FGFR1) expression is well documented in prostate cancer (PCa) progression, notably in conferring tumor growth advantage and facilitating metastasis. However, how FGFR1 contributes to PCa progression is not fully revealed. Here we report that ectopic FGFR1 in PCa cells promotes transferrin receptor 1 (TFR1) expression and expands the labile iron pool (LIP), and vice versa. We further demonstrate that FGFR1 stabilizes iron regulatory proteins 2 (IRP2) and therefore, upregulates TFR1 via promoting IRP2 binding to the IRE of TFR1. Deletion of FGFR1 in DU145 cells decreases the LIP, which potentiates the anticancer efficacy of iron chelator. Intriguingly, forced expression of IRP2 in FGFR1 depleted cells reinstates TFR1 expression and LIP, subsequently restoring the tumorigenicity of the cells. Together, our results here unravel a new mechanism by which FGFR1 drives PCa progression and suggest a potential novel target for PCa therapy.

Selenium represses microRNA-202-5p/MICU1 aixs to attenuate mercuric chloride-induced kidney ferroptosis

Mercuric chloride (HgCl2) is a nephrotoxic contaminant that is widely present in the environment. Selenium (Se) can effectively antagonize the biological toxicity caused by heavy metals. Here, in vivo and in vitro models of Se antagonism to HgCl2-induced nephrotoxicity in chickens were established, with the aim of exploring the specific mechanism. Morphological observation and kidney function analysis showed that Se alleviated HgCl2-induced kidney tissue injury and cytotoxicity. The results showed that ferroptosis was the primary mechanism for the toxicity of HgCl2, as indicated by iron overload and lipid peroxidation. On the one hand, Se significantly prevented HgCl2-induced iron overload. On the other hand, Se alleviated the intracellular reactive oxygen species (ROS) levels caused by HgCl2. Subsequently, we focused on the sources of ROS during HgCl2-induced ferroptosis. Mechanically, Se reduced ROS overproduction induced by HgCl2 through mitochondrial calcium uniporter (MCU)/mitochondrial calcium uptake 1 (MICU1)-mediated mitochondrial calcium ion (Ca2+) overload. Furthermore, a dual luciferase reporter assay demonstrated that MICU1 was the direct target of miR-202-5p. Overall, Se represses miR-202-5p/MICU1 axis to attenuate HgCl2-induced kidney ferroptosis.

Distinct Perception Mechanisms of BACH1 Quaternary Structure Degrons by Two F-box Proteins under Oxidative Stress

The transcription factor BACH1 regulates heme homeostasis and oxidative stress responses and promotes cancer metastasis upon aberrant accumulation. Its stability is controlled by two F-box protein ubiquitin ligases, FBXO22 and FBXL17. Here we show that the homodimeric BTB domain of BACH1 functions as a previously undescribed quaternary structure degron, which is deciphered by the two F-box proteins via distinct mechanisms. After BACH1 is released from chromatin by heme, FBXO22 asymmetrically recognizes a cross-protomer interface of the intact BACH1 BTB dimer, which is otherwise masked by the co-repressor NCOR1. If the BACH1 BTB dimer escapes the surveillance by FBXO22 due to oxidative modifications, its quaternary structure integrity is probed by a pair of FBXL17, which simultaneously engage and remodel the two BTB protomers into E3-bound monomers for ubiquitination. By unveiling the multifaceted regulatory mechanisms of BACH1 stability, our studies highlight the abilities of ubiquitin ligases to decode high-order protein assemblies and reveal therapeutic opportunities to block cancer invasion via compound-induced BACH1 destabilization.

Mitochondria function in cytoplasmic FeS protein biogenesis

Iron‑sulfur (FeS) clusters are cofactors of numerous proteins involved in essential cellular functions including respiration, protein translation, DNA synthesis and repair, ribosome maturation, anti-viral responses, and isopropylmalate isomerase activity. Novel FeS proteins are still being discovered due to the widespread use of cryogenic electron microscopy (cryo-EM) and elegant genetic screens targeted at protein discovery. A complex sequence of biochemical reactions mediated by a conserved machinery controls biosynthesis of FeS clusters. In eukaryotes, a remarkable epistasis has been observed: the mitochondrial machinery, termed ISC (Iron-Sulfur Cluster), lies upstream of the cytoplasmic machinery, termed CIA (Cytoplasmic Iron‑sulfur protein Assembly). The basis for this arrangement is the production of a hitherto uncharacterized intermediate, termed X-S or (Fe-S)int, produced in mitochondria by the ISC machinery, exported by the mitochondrial ABC transporter Atm1 (ABCB7 in humans), and then utilized by the CIA machinery for the cytoplasmic/nuclear FeS cluster assembly. Genetic and biochemical findings supporting this sequence of events are herein presented. New structural views of the Atm1 transport phases are reviewed. The key compartmental roles of glutathione in cellular FeS cluster biogenesis are highlighted. Finally, data are presented showing that every one of the ten core components of the mitochondrial ISC machinery and Atm1, when mutated or depleted, displays similar phenotypes: mitochondrial and cytoplasmic FeS clusters are both rendered deficient, consistent with the epistasis noted above.

Molecular Mechanisms and Therapeutic Targeting of Ferroptosis in Doxorubicin-Induced Cardiotoxicity

Ferroptosis, an iron-dependent form of regulated cell death, has received increasing attention for its pathophysiologic contribution to the onset and development of doxorubicin-induced cardiotoxicity. Moreover, modulation of ferroptosis with specific inhibitors may provide new therapeutic opportunities for doxorubicin-induced cardiotoxicity. Here, we will review the molecular mechanisms and therapeutic promise of targeting ferroptosis in doxorubicin-induced cardiotoxicity.

Requirements for the biogenesis of [2Fe-2S] proteins in the human and yeast cytosol

The biogenesis of iron-sulfur (Fe/S) proteins entails the synthesis and trafficking of Fe/S clusters, followed by their insertion into target apoproteins. In eukaryotes, the multiple steps of biogenesis are accomplished by complex protein machineries in both mitochondria and cytosol. The underlying biochemical pathways have been elucidated over the past decades, yet the mechanisms of cytosolic [2Fe-2S] protein assembly have remained ill-defined. Similarly, the precise site of glutathione (GSH) requirement in cytosolic and nuclear Fe/S protein biogenesis is unclear, as is the molecular role of the GSH-dependent cytosolic monothiol glutaredoxins (cGrxs). Here, we investigated these questions in human and yeast cells by various in vivo approaches. [2Fe-2S] cluster assembly of cytosolic target apoproteins required the mitochondrial ISC machinery, the mitochondrial transporter Atm1/ABCB7 and GSH, yet occurred independently of both the CIA system and cGrxs. This mechanism was strikingly different from the ISC-, Atm1/ABCB7-, GSH-, and CIA-dependent assembly of cytosolic-nuclear [4Fe-4S] proteins. One notable exception to this cytosolic [2Fe-2S] protein maturation pathway defined here was yeast Apd1 which used the CIA system via binding to the CIA targeting complex through its C-terminal tryptophan. cGrxs, although attributed as [2Fe-2S] cluster chaperones or trafficking proteins, were not essential in vivo for delivering [2Fe-2S] clusters to either CIA components or target apoproteins. Finally, the most critical GSH requirement was assigned to Atm1-dependent export, i.e. a step before GSH-dependent cGrxs function. Our findings extend the general model of eukaryotic Fe/S protein biogenesis by adding the molecular requirements for cytosolic [2Fe-2S] protein maturation.

Baicalin enhances the chemotherapy sensitivity of oxaliplatin-resistant gastric cancer cells by activating p53-mediated ferroptosis

Gastric cancer is one of the most common malignant tumors, and chemotherapy is the main treatment for advanced gastric cancer. However, chemotherapy resistance leads to treatment failure and poor prognosis in patients with gastric cancer. Multidrug resistance (MDR) is a major challenge that needs to be overcome in chemotherapy. According to recent research, ferroptosis activation is crucial for tumor therapeutic strategies. In this work, we explored the solution to chemoresistance in gastric cancer by investigating the effects of the Chinese medicine monomer baicalin on ferroptosis. Baicalin with different concentrations was used to treat the parent HGC27 and drug-resistant HGC27/L cells of gastric cancer. Cell viability was measured by CCK8, and synergistic effects of baicalin combined with oxaliplatin were evaluated using Synergy Finder software. The effects of baicalin on organelles and cell morphology were investigated using projective electron microscopy. Iron concentration, MDA production and GSH inhibition rate were measured by colorimetry. ROS accumulation was detected by flow cytometry. The ferroptosis-related genes (IREB2, TfR, GPX4, FTH1), P53, and SLC7A11 were analysed by Western blot, and the expression differences of the above proteins between pretreatment and pretreatment of different concentrations of baicalin, were assayed in both parental HGC27 cells and Oxaliplatin-resistant HGC27/L cells. Mechanically, Baicalin disrupted iron homeostasis and inhibits antioxidant defense, resulting in iron accumulation, lipid peroxide aggregation, and specifically targeted and activated ferroptosis by upregulating the expression of tumor suppressor gene p53, thereby activating the SLC7A11/GPX4/ROS pathway mediated by it. Baicalin activates ferroptosis through multiple pathways and targets, thereby inhibiting the viability of oxaliplatin-resistant gastric cancer HGC27/L cells and enhancing the sensitivity to oxaliplatin chemotherapy.

The redox requirement and regulation during cell proliferation

The intracellular metabolic network comprises a variety of reduction-oxidation (redox) reactions that occur in a temporally and spatially distinct manner. In order to coordinate these redox processes, mammalian cells utilize a collection of electron-carrying molecules common to many redox reactions, including NAD, NADP, coenzyme Q (CoQ), and glutathione (GSH). This review considers the metabolic basis of redox regulation in the context of cell proliferation by analyzing how cells acquire and utilize electron carriers to maintain directional carbon flux, sustain reductive biosynthesis, and support antioxidant defense. Elucidating the redox requirement during cell proliferation can advance the understanding of human diseases such as cancer, and reveal effective therapeutic opportunities in the clinic.

Using Biotinylated Iron-Responsive Element to Analyze the Activity of Iron Regulatory Proteins

Iron regulatory proteins (IRP1 and IRP2) are the master regulators of mammalian iron homeostasis. They bind to the iron-responsive elements (IREs) of the transcripts of iron-related genes to regulate their expression, thereby maintaining cellular iron availability. The primary method to measure the IRE-binding activity of IRPs is the electrophoresis mobility shift assay (EMSA). This method is particularly useful for evaluating IRP1 activity, since IRP1 is a bifunctional enzyme and its protein levels remain similar during conversion between the IRE-binding protein and cytosolic aconitase forms. Here, we exploited a method of using a biotinylated-IRE probe to separate IRE-binding IRPs followed by immunoblotting to analyze the IRE-binding activity. This method allows for the successful measurement of IRP activity in cultured cells and mouse tissues under various iron conditions. By separating IRE-binding IRPs from the rest of the lysates, this method increases the specificity of IRP antibodies and verifies whether a band represents an IRP, thereby revealing some previously unrecognized information about IRPs. With this method, we showed that the S711-phosphorylated IRP1 was found only in the IRE-binding form in PMA-treated Hep3B cells. Second, we found a truncated IRE-binding IRP2 isoform that is generated by proteolytic cleavage on sites in the 73aa insert region of the IRP2 protein. Third, we found that higher levels of SDS, compared to 1-2% SDS in regular loading buffer, could dramatically increase the band intensity of IRPs in immunoblots, especially in HL-60 cells. Fourth, we found that the addition of SDS or LDS to cell lysates activated protein degradation at 37 °C or room temperature, especially in HL-60 cell lysates. As this method is more practical, sensitive, and cost-effective, we believe that its application will enhance future research on iron regulation and metabolism.

Abnormal mitochondrial iron metabolism damages alveolar type II epithelial cells involved in bleomycin-induced pulmonary fibrosis

Rationale: Pulmonary fibrosis is a chronic progressive lung disease with limited therapeutic options. We previously revealed that there is iron deposition in alveolar epithelial type II cell (AECII) in pulmonary fibrosis, which can be prevented by the iron chelator deferoxamine. However, iron in the cytoplasm and the mitochondria has two relatively independent roles and regulatory systems. In this study, we aimed to investigate the role of mitochondrial iron deposition in AECII injury and pulmonary fibrosis, and to find potential therapeutic strategies. Methods: BLM-treated mice, MLE-12 cells, and primary AECII were employed to establish the mouse pulmonary fibrosis model and epithelial cells injury model, respectively. Mitochondrial transplantation, siRNA and plasmid transfection, western blotting (WB), quantitative real-time polymerase chain reaction (RT-qPCR), polymerase chain reaction (PCR), immunofluorescence, immunoprecipitation (IP), MitoSOX staining, JC-1 staining, oxygen consumption rate (OCR) measurement, and Cell Counting Kit-8 (CCK8) assay were utilized to elucidate the role of mitochondrial iron deposition in cell and lung fibrosis and determine its mechanism. Results: This study showed that prominent mitochondrial iron deposition occurs within AECII in bleomycin (BLM)-induced pulmonary fibrosis mouse model and in BLM-treated MLE-12 epithelial cells. Further, the study revealed that healthy mitochondria rescue BLM-damaged AECII mitochondrial iron deposition and cell damage loss. Mitoferrin-2 (MFRN2) is the main transporter that regulates mitochondrial iron metabolism by transferring cytosolic iron into mitochondria, which is upregulated in BLM-treated MLE-12 epithelial cells. Direct overexpression of MFRN2 causes mitochondrial iron deposition and cell damage. In this study, decreased ubiquitination of the ubiquitin ligase F-box/LRR-repeat protein 5 (FBXL5) degraded iron-reactive element-binding protein 2 (IREB2) and promoted MFRN2 expression as well as mitochondrial iron deposition in damaged AECII. Activation of the prostaglandin E2 receptor EP4 subtype (EP4) receptor signaling pathway counteracted mitochondrial iron deposition by downregulating IREB2-MFRN2 signaling through upregulation of FBXL5. This intervention not only reduced mitochondrial iron content but also preserved mitochondrial function and protected against AECII damage after BLM treatment. Conclusion: Our findings highlight the unexplored roles, mechanisms, and regulatory approaches of abnormal mitochondrial iron metabolism of AECII in pulmonary fibrosis. Therefore, this study deepens the understanding of the mechanisms underlying pulmonary fibrosis and offers a promising strategy for developing effective therapeutic interventions using the EP4 receptor activator.

Pharmacological approaches for targeting lysosomes to induce ferroptotic cell death in cancer

Lysosomes are crucial organelles responsible for the degradation of cytosolic materials and bulky organelles, thereby facilitating nutrient recycling and cell survival. However, lysosome also acts as an executioner of cell death, including ferroptosis, a distinctive form of regulated cell death that hinges on iron-dependent phospholipid peroxidation. The initiation of ferroptosis necessitates three key components: substrates (membrane phospholipids enriched with polyunsaturated fatty acids), triggers (redox-active irons), and compromised defence mechanisms (GPX4-dependent and -independent antioxidant systems). Notably, iron assumes a pivotal role in ferroptotic cell death, particularly in the context of cancer, where iron and oncogenic signaling pathways reciprocally reinforce each other. Given the lysosomes' central role in iron metabolism, various strategies have been devised to harness lysosome-mediated iron metabolism to induce ferroptosis. These include the re-mobilization of iron from intracellular storage sites such as ferritin complex and mitochondria through ferritinophagy and mitophagy, respectively. Additionally, transcriptional regulation of lysosomal and autophagy genes by TFEB enhances lysosomal function. Moreover, the induction of lysosomal iron overload can lead to lysosomal membrane permeabilization and subsequent cell death. Extensive screening and individually studies have explored pharmacological interventions using clinically available drugs and phytochemical agents. Furthermore, a drug delivery system involving ferritin-coated nanoparticles has been specifically tailored to target cancer cells overexpressing TFRC. With the rapid advancements in understandings the mechanistic underpinnings of ferroptosis and iron metabolism, it is increasingly evident that lysosomes represent a promising target for inducing ferroptosis and combating cancer.

Iron, Copper, and Selenium: Cancer's Thing for Redox Bling

Cells require micronutrients for numerous basic functions. Among these, iron, copper, and selenium are particularly critical for redox metabolism, and their importance is heightened during oncogene-driven perturbations in cancer. In this review, which particularly focuses on iron, we describe how these micronutrients are carefully chaperoned about the body and made available to tissues, a process that is designed to limit the toxicity of free iron and copper or by-products of selenium metabolism. We delineate perturbations in iron metabolism and iron-dependent proteins that are observed in cancer, and describe the current approaches being used to target iron metabolism and iron-dependent processes.

A regulatory module comprising G3BP1-FBXL5-IRP2 axis determines sodium arsenite-induced ferroptosis

Arsenic contamination is extremely threatening to the global public health. It was reported that sodium arsenite exposure induces serious kidney injury. However, the underlying mechanism is unclear. Ferroptosis is a newly characterized form of iron-dependent programmed cell death, which is implicated in the pathogenesis of various human diseases, including kidney injury. The lethal accumulation of iron-catalyzed lipid peroxidation is the fundamental biochemical characteristic of ferroptosis. Herein we report that sodium arsenite exposure initiates ferroptosis in mammalian HEK293, MEF and HT1080 cells, and induces ferroptosis-associated acute kidney injury in mice. RNA-binding protein G3BP1, the switch component of stress granules, is indispensable for sodium arsenite-induced ferroptosis in a stress granule-independent manner. Mechanistically, G3BP1 stabilizes IRP2, the master regulator of cellular iron homeostasis, through binding to and suppressing the translation of FBXL5 mRNA, which encodes the E3 ligase component to mediate IRP2 ubiquitination and proteasomal degradation. Sodium arsenite intoxication expedites this G3BP1-FBXL5-IRP2 axis and elevates cellular labile free iron, which is responsible for sodium arsenite exposure-induced lipid peroxidation and ferroptotic cell death. In summary, this study highlights a regulatory module comprising G3BP1-FBXL5-IRP2 axis in determining sodium arsenite-induced ferroptosis and ferroptosis-associated acute kidney injury in mice.

E3 ubiquitin ligase Hul6 modulates iron-dependent metabolism by regulating Php4 stability

Schizosaccharomyces pombe Php4 is the regulatory subunit of the CCAAT-binding complexes and plays an important role in the regulation of iron homeostasis and iron-dependent metabolism. Here, we show that Php4 undergoes ubiquitin-dependent degradation in the late logarithmic and stationary phases. The degradation and ubiquitination of Php4 could be attenuated by deletion of hul6, a gene encoding a putative HECT-type E3 ubiquitin ligase. The expression levels of Hul6 and Php4 are oppositely regulated during cell growth. Hul6 interacts with the C-terminal region of Php4. Two lysine residues (K217 and K274) located in the C-terminal region of Php4 are required for its polyubiquitination. Increasing the levels of Php4 by deletion of hul6 or overexpression of php4 decreased expression of Php4 target proteins involved in iron-dependent metabolic pathways such as the tricarboxylic cycle and mitochondrial oxidative phosphorylation, thus causing increased sensitivity to high-iron and reductions in succinate dehydrogenase and mitochondrial complex II activities. Hul6 is located primarily in the mitochondrial outer membrane and most likely targets cytosolic Php4 for ubiquitination and degradation. Taken together, our data suggest that Hul6 regulates iron-dependent metabolism through degradation of Php4 under normal growth conditions. Our results also suggest that Hul6 promotes iron-dependent metabolism to help the cell to adapt to a nutrient-starved growth phase.

Tumor iron homeostasis and immune regulation

Abnormal iron metabolism has long been regarded as a key metabolic hallmark of cancer. As a critical cofactor, iron contributes to tumor progression by participating in various processes such as mitochondrial electron transport, gene regulation, and DNA synthesis or repair. Although the role of iron in tumor cells has been widely studied, recent studies have uncovered the interplay of iron metabolism between tumor cells and immune cells, which may affect both innate and adaptive immune responses. In this review, we discuss the current understanding of the regulatory networks of iron metabolism between cancer cells and immune cells and how they contribute to antitumor immunity, and we analyze potential therapeutics targeting iron metabolism. Also, we highlight several key challenges and describe potential therapeutic approaches for future investigations.

Mechanisms controlling cellular and systemic iron homeostasis

In mammals, hundreds of proteins use iron in a multitude of cellular functions, including vital processes such as mitochondrial respiration, gene regulation and DNA synthesis or repair. Highly orchestrated regulatory systems control cellular and systemic iron fluxes ensuring sufficient iron delivery to target proteins is maintained, while limiting its potentially deleterious effects in iron-mediated oxidative cell damage and ferroptosis. In this Review, we discuss how cells acquire, traffick and export iron and how stored iron is mobilized for iron-sulfur cluster and haem biogenesis. Furthermore, we describe how these cellular processes are fine-tuned by the combination of various sensory and regulatory systems, such as the iron-regulatory protein (IRP)-iron-responsive element (IRE) network, the nuclear receptor co-activator 4 (NCOA4)-mediated ferritinophagy pathway, the prolyl hydroxylase domain (PHD)-hypoxia-inducible factor (HIF) axis or the nuclear factor erythroid 2-related factor 2 (NRF2) regulatory hub. We further describe how these pathways interact with systemic iron homeostasis control through the hepcidin-ferroportin axis to ensure appropriate iron fluxes. This knowledge is key for the identification of novel therapeutic opportunities to prevent diseases of cellular and/or systemic iron mismanagement.

NCOA4 requires a [3Fe-4S] to sense and maintain the iron homeostasis

NCOA4 is a selective cargo receptor for ferritinophagy, the autophagic turnover of ferritin (FTH), a process critical for regulating intracellular iron bioavailability. However, how ferritinophagy flux is controlled through NCOA4 in iron-dependent processes needs to be better understood. Here, we show that the C-terminal FTH-binding domain of NCOA4 harbors a [3Fe-4S]-binding site with a stoichiometry of approximately one labile [3Fe-4S] cluster per NCOA4 monomer. By analyzing the interaction between NCOA4 and HERC2 ubiquitin ligase or NCOA4 and FTH, we demonstrate that NCOA4 regulates ferritinophagy by sensing the intracellular iron-sulfur cluster levels. Under iron-repletion conditions, HERC2 recognizes and recruits holo-NCOA4 as a substrate for polyubiquitination and degradation, favoring ferritin iron storage. Under iron-depletion conditions, NCOA4 exists in the form of apo-protein and binds ferritin to promote the occurrence of ferritinophagy and release iron. Thus, we identify an iron-sulfur cluster [3Fe-4S] as a critical cofactor in determining the fate of NCOA4 in favoring iron storage in ferritin or iron release via ferritinophagy and provide a dual mechanism for selective interaction between HERC2 and [3Fe-4S]-NCOA4 for proteasomal degradation or between ferritin and apo-NCOA4 for ferritinophagy in the control of iron homeostasis.

METTL17 is an Fe-S cluster checkpoint for mitochondrial translation

Friedreich's ataxia (FA) is a debilitating, multisystemic disease caused by the depletion of frataxin (FXN), a mitochondrial iron-sulfur (Fe-S) cluster biogenesis factor. To understand the cellular pathogenesis of FA, we performed quantitative proteomics in FXN-deficient human cells. Nearly every annotated Fe-S cluster-containing protein was depleted, indicating that as a rule, cluster binding confers stability to Fe-S proteins. We also observed depletion of a small mitoribosomal assembly factor METTL17 and evidence of impaired mitochondrial translation. Using comparative sequence analysis, mutagenesis, biochemistry, and cryoelectron microscopy, we show that METTL17 binds to the mitoribosomal small subunit during late assembly and harbors a previously unrecognized [Fe4S4]2+ cluster required for its stability. METTL17 overexpression rescued the mitochondrial translation and bioenergetic defects, but not the cellular growth, of FXN-depleted cells. These findings suggest that METTL17 acts as an Fe-S cluster checkpoint, promoting translation of Fe-S cluster-rich oxidative phosphorylation (OXPHOS) proteins only when Fe-S cofactors are replete.

Iron homeostasis and post-hemorrhagic hydrocephalus: a review

Iron physiology is regulated by a complex interplay of extracellular transport systems, coordinated transcriptional responses, and iron efflux mechanisms. Dysregulation of iron metabolism can result in defects in myelination, neurotransmitter synthesis, and neuronal maturation. In neonates, germinal matrix-intraventricular hemorrhage (GMH-IVH) causes iron overload as a result of blood breakdown in the ventricles and brain parenchyma which can lead to post-hemorrhagic hydrocephalus (PHH). However, the precise mechanisms by which GMH-IVH results in PHH remain elusive. Understanding the molecular determinants of iron homeostasis in the developing brain may lead to improved therapies. This manuscript reviews the various roles iron has in brain development, characterizes our understanding of iron transport in the developing brain, and describes potential mechanisms by which iron overload may cause PHH and brain injury. We also review novel preclinical treatments for IVH that specifically target iron. Understanding iron handling within the brain and central nervous system may provide a basis for preventative, targeted treatments for iron-mediated pathogenesis of GMH-IVH and PHH.

TFEB regulates cellular labile iron and prevents ferroptosis in a TfR1-dependent manner

Autophagy is a major clearance pathway for misfolded α-synuclein which promotes ferroptosis through NCOA4-mediated ferritin degradation. The regulation of these two processes to achieve improved neuroprotection in Parkinson's disease (PD) must be elucidated. Transcription factor EB (TFEB) is a master regulator of both autophagy and lysosome biogenesis, and lysosomes are important cellular iron storage organelles; however, the role of TFEB in ferroptosis and iron metabolism remains unclear. In this study, TFEB overexpression promoted the clearance of misfolded α-synuclein and prevented ferroptosis and iron overload. TFEB overexpression up-regulated transferrin receptor 1 (TfR1) synthesis and increased the localization of TfR1 in the lysosome, facilitating lysosomal iron import and transient lysosomal iron storage. TFEB overexpression increased the levels of cellular iron-safe storage proteins (both ferritin light and heavy chains). These functions in iron metabolism maintain the cellular labile iron at a low level and electrical activity, even under iron overload conditions. Notably, lower levels of cellular labile iron and the upregulation of ferritin light and heavy chains were reversed after TfR1 knockdown in cells overexpressing TFEB, indicating that TFEB regulates cellular labile iron and suppresses ferroptosis in a TfR1 dependent manner. Taken together, this evidence of the regulation of iron metabolism enriches our understanding of the function of TFEB. In addition, TFEB overexpression protects against ferroptosis and iron overload and provides a new direction and perspective for autophagy regulation in PD.

Cardiac iron metabolism during aging - Role of inflammation and proteolysis

Iron is the most abundant trace element in the human body. Since iron can switch between its 2-valent and 3-valent form it is essential in various physiological processes such as energy production, proliferation or DNA synthesis. Especially high metabolic organs such as the heart rely on iron-associated iron-sulfur and heme proteins. However, due to switches in iron oxidation state, iron overload exhibits high toxicity through formation of reactive oxygen species, underlining the importance of balanced iron levels. Growing evidence demonstrates disturbance of this balance during aging. While age-associated cardiovascular diseases are often related to iron deficiency, in physiological aging cardiac iron accumulates. To understand these changes, we focused on inflammation and proteolysis, two hallmarks of aging, and their role in iron metabolism. Via the IL-6-hepcidin axis, inflammation and iron status are strongly connected often resulting in anemia accompanied by infiltration of macrophages. This tight connection between anemia and inflammation highlights the importance of the macrophage iron metabolism during inflammation. Age-related decrease in proteolytic activity additionally affects iron balance due to impaired degradation of iron metabolism proteins. Therefore, this review accentuates alterations in iron metabolism during aging with regards to inflammation and proteolysis to draw attention to their implications and associations.

Molecular Insight into Iron Homeostasis of Acute Myeloid Leukemia Blasts

Acute myeloid leukemia (AML) remains a disease of gloomy prognosis despite intense efforts to understand its molecular foundations and to find efficient treatments. In search of new characteristic features of AML blasts, we first examined experimental conditions supporting the amplification of hematological CD34+ progenitors ex vivo. Both AML blasts and healthy progenitors heavily depended on iron availability. However, even if known features, such as easier engagement in the cell cycle and amplification factor by healthy progenitors, were observed, multiplying progenitors in a fully defined medium is not readily obtained without modifying their cellular characteristics. As such, we measured selected molecular data including mRNA, proteins, and activities right after isolation. Leukemic blasts showed clear signs of metabolic and signaling shifts as already known, and we provide unprecedented data emphasizing disturbed cellular iron homeostasis in these blasts. The combined quantitative data relative to the latter pathway allowed us to stratify the studied patients in two sets with different iron status. This categorization is likely to impact the efficiency of several therapeutic strategies targeting cellular iron handling that may be applied to eradicate AML blasts.

New iron export pathways acting via holo-ferritin secretion

Ferritin is a spherical nanocage protein for iron storage, composed of 24 light- or heavy-polypeptide chain subunits. A single ferritin molecule can carry up to 4500 iron atoms in its core, which plays an important role in suppressing intracellular iron toxicity. Serum ferritin levels are used as a marker for the total amount of iron stored in the body. Most serum ferritin is iron-free (apo-ferritin) and it is unclear how ferritin is released from cells. Ferritin is secreted into serum via extracellular vesicles (EVs) or the secretory autophagy pathway but not via the classical endoplasmic reticulum (ER)-to-Golgi secretion pathway. We recently discovered that the level of tetraspanin CD63, a common EV marker, is post-transcriptionally regulated by the intracellular iron level and both CD63 and ferritin expression is induced by iron loading. Ferritin is incorporated into CD63(+)-EVs through the ferritin-specific autophagy adapter molecule, NCOA4, and then secreted from cells. EV production differs drastically depending on cell type and physiological conditions. Extracellular matrix detached cells express pentaspanin prominin 2 and prominin 2(+)-EVs secrete ferritin independently of NCOA4 trafficking. Ferritin is tightly bound to iron in EVs and functions as an iron-carrier protein in the extracellular environment. Cells can suppress ferroptosis by secreting holo-ferritin, which reduces intracellular iron concentration. However, this exposes the neighboring cells receiving the secreted holo-ferritin to a large excess of iron. This results in cellular toxicity through increased generation of reactive oxygen species (ROS). Here we review the machinery by which ferritin is incorporated into EVs and its role as an intercellular communication molecule.

Gut microbiota bridges the iron homeostasis and host health

The gut microbiota acts as a symbiotic microecosystem that plays an indispensable role in the regulation of a number of metabolic processes in the host by secreting secondary metabolites and impacting the physiology and pathophysiology of numerous organs and tissues through the circulatory system. This relationship, referred to as the "gut-X axis", is associated with the development and progression of disorders, including obesity, fatty liver and Parkinson's disease. Given its importance, the gut flora is a vital research area for the understanding and development of the novel therapeutic approaches for multiple disorders. Iron is a common but necessary element required by both mammals and bacteria. As a result, iron metabolism is closely intertwined with the gut microbiota. The host's iron homeostasis affects the composition of the gut microbiota and the interaction between host and gut microbiota through various mechanisms such as nutrient homeostasis, intestinal peaceability, gut immunity, and oxidative stress. Therefore, understanding the relationship between gut microbes and host iron metabolism is not only of enormous significance to host health but also may offer preventative and therapeutic approaches for a number of disorders that impact both parties. In this review, we delve into the connection between the dysregulation of iron metabolism and dysbiosis of gut microbiota, and how it contributes to the onset and progression of metabolic and chronic diseases.

Ferroptosis Nanomedicine: Clinical Challenges and Opportunities for Modulating Tumor Metabolic and Immunological Landscape

Ferroptosis, a type of regulated cell death driven by iron-dependent phospholipid peroxidation, has captured much attention in the field of nanomedicine since it was coined in 2012. Compared with other regulated cell death modes such as apoptosis and pyroptosis, ferroptosis has many distinct features in the molecular mechanisms and cellular morphology, representing a promising strategy for treating cancers that are resistant to conventional therapeutic modalities. Moreover, recent insights collectively reveal that ferroptosis is tightly connected to the maintenance of the tumor immune microenvironment (TIME), suggesting the potential application of ferroptosis therapies for evoking robust antitumor immunity. From a biochemical perspective, ferroptosis is intricately regulated by multiple cellular metabolic pathways, including iron metabolism, lipid metabolism, redox metabolism, etc., highlighting the importance to elucidate the relationship between tumor metabolism and ferroptosis for developing antitumor therapies. In this review, we provide a comprehensive discussion on the current understanding of ferroptosis-inducing mechanisms and thoroughly discuss the relationship between ferroptosis and various metabolic traits of tumors, which offer promising opportunities for direct tumor inhibition through a nanointegrated approach. Extending from the complex impact of ferroptosis on TIME, we also discussed those important considerations in the development of ferroptosis-based immunotherapy, highlighting the challenges and strategies to enhance the ferroptosis-enabled immunostimulatory effects while avoiding potential side effects. We envision that the insights in this study may facilitate the development and translation of ferroptosis-based nanomedicines for tumor treatment.

Hepcidin deficiency in mice impairs white adipose tissue browning possibly due to a defect in de novo adipogenesis

The role of iron in the two major sites of adaptive thermogenesis, namely the beige inguinal (iWAT) and brown adipose tissues (BAT) has not been fully understood yet. Body iron levels and distribution is controlled by the iron regulatory peptide hepcidin. Here, we explored iron homeostasis and thermogenic activity in brown and beige fat in wild-type and iron loaded Hepcidin KO mice. Hepcidin-deficient mice displayed iron overload in both iWAT and BAT, and preferential accumulation of ferritin in stromal cells compared to mature adipocytes. In contrast to BAT, the iWAT of Hepcidin KO animals featured with defective thermogenesis evidenced by an altered beige signature, including reduced UCP1 levels and decreased mitochondrial respiration. This thermogenic modification appeared cell autonomous and persisted after a 48 h-cold challenge, a potent trigger of thermogenesis, suggesting compromised de novo adipogenesis. Given that WAT browning occurs in both mice and humans, our results provide physiological results to interrogate the thermogenic capacity of patients with iron overload disorders.

The Imbalance of p53-Park7 Signaling Axis Induces Iron Homeostasis Dysfunction in Doxorubicin-Challenged Cardiomyocytes

Doxorubicin (DOX)-induced cardiotoxicity (DoIC) is a major side effect for cancer patients. Recently, ferroptosis, triggered by iron overload, is demonstrated to play a role in DoIC. How iron homeostasis is dysregulated in DoIC remains to be elucidated. Here, the authors demonstrate that DOX challenge exhibits reduced contractile function and induction of ferroptosis-related phenotype in cardiomyocytes, evidenced by iron overload, lipid peroxide accumulation, and mitochondrial dysfunction. Compared to Ferric ammonium citrate (FAC) induced secondary iron overload, DOX-challenged cardiomyocytes show a dysfunction of iron homeostasis, with decreased cytoplasmic and mitochondrial iron-sulfur (FeS) cluster-mediated aconitase activity and abnormal expression of iron homeostasis-related proteins. Mechanistically, mass spectrometry analysis identified DOX-treatment induces p53-dependent degradation of Parkinsonism associated deglycase (Park7) which results in iron homeostasis dysregulation. Park7 counteracts iron overload by regulating iron regulatory protein family transcription while blocking mitochondrial iron uptake. Knockout of p53 or overexpression of Park7 in cardiomyocytes remarkably restores the activity of FeS cluster and iron homeostasis, inhibits ferroptosis, and rescues cardiac function in DOX treated animals. These results demonstrate that the iron homeostasis plays a key role in DoIC ferroptosis. Targeting of the newly identified p53-Park7 signaling axis may provide a new approach to prevent DoIC.

Ferroptosis landscape in prostate cancer from molecular and metabolic perspective

Prostate cancer is a major disease that threatens men's health. Its rapid progression, easy metastasis, and late castration resistance have brought obstacles to treatment. It is necessary to find new effective anticancer methods. Ferroptosis is a novel iron-dependent programmed cell death that plays a role in various cancers. Understanding how ferroptosis is regulated in prostate cancer will help us to use it as a new way to kill cancer cells. In this review, we summarize the regulation and role of ferroptosis in prostate cancer and the relationship with AR from the perspective of metabolism and molecular pathways. We also discuss the feasibility of ferroptosis in prostate cancer treatment and describe current limitations and prospects, providing a reference for future research and clinical application of ferroptosis.

Oxygen modulates iron homeostasis by switching iron-sensing of NCOA4

To ensure proper utilization of iron and avoid its toxicity, cells are equipped with iron-sensing proteins to maintain cellular iron homeostasis. We showed previously that NCOA4, a ferritin-specific autophagy adapter, intricately regulates the fate of ferritin; upon binding to Fe³⁺, NCOA4 forms insoluble condensates and regulates ferritin autophagy in iron-replete conditions. Here, we demonstrate an additional iron-sensing mechanism of NCOA4. Our results indicate that the insertion of an Fe-S cluster enables preferential recognition of NCOA4 by the HERC2 ubiquitin ligase in iron-replete conditions, resulting in degradation by the proteasome and subsequent inhibition of ferritinophagy. We also found that both condensation and ubiquitin-mediated degradation of NCOA4 can occur in the same cell, and the cellular oxygen tension determines the selection of these pathways. Fe-S cluster-mediated degradation of NCOA4 is enhanced under hypoxia, whereas NCOA4 forms condensates and degrades ferritin at higher oxygen levels. Considering the involvement of iron in oxygen handling, our findings demonstrate that the NCOA4/ferritin axis is another layer of cellular iron regulation in response to oxygen levels.