NCOA4-mediated ferritinophagy in macrophages is crucial to sustain erythropoiesis in mice

Characterization of the Iron-Sulfur Cluster in the NCOA4 Fragment (383-522) and Its Interaction with Ferritin

Ferritin degradation pathways, particularly NCOA4-mediated ferritinophagy, are crucial for maintaining iron homeostasis. Here, we demonstrate the coexistence of two NCOA4 isoforms, one iron-sulfur cluster-free and one iron-sulfur cluster-bound, in oxygenated cell cultures. Using a combination of spectroscopic and analytical techniques, in vitro characterization of the NCOA4 fragment (383-522), denoted NCOA4-D, revealed a predominance of monomeric species with a relatively stable [2Fe-2S] cluster under normoxic conditions. The results demonstrate distinct interactions between NCOA4-D isoforms and ferritin, underscoring the influence of cellular oxygen and iron concentrations on NCOA4's regulatory functions, pathways, and ferritin's fate. Our findings suggest that different NCOA4-initiated degradation pathways may concurrently occur in cells and highlight the necessity of further exploring the role of the Fe-S cluster in NCOA4 as an iron-sensing mechanism for maintaining cellular iron homeostasis.

Loss of FTH1 Induces Ferritinophagy-Mediated Ferroptosis in Anaemia of Myelodysplastic Syndromes

Single-cell sequencing of lineage negative (Lin-) cells from patients with myelodysplastic syndromes (MDS) revealed a reduction in ferritin heavy chain 1 (FTH1) levels, yet the significance of this decrease in FTH1 in the pathophysiology of MDS remains unclear. In this study, we evaluated the role of FTH1 in patients with MDS. The mRNA expression of FTH1 in GlycoA+ nucleated erythrocytes from MDS patients was significantly lower than that in control group. FTH1 was implicated in both ferritinophagy and ferroptosis in MDS patients, processes that are linked to the development of anaemia. To further validate our observations, we employed shRNA to knock down the FTH1 gene in K562 and SKM1 cells. This knockdown confirmed that the elevated ferroptosis levels observed after FTH1 depletion were indeed due to the induction of ferritinophagy. Hemin stimulation promoted the differentiation of K562 cells, while downregulation of FTH1 gene expression had an impact on erythroid differentiation and haemoglobin synthesis. Taken together, our results suggest that FTH1-mediated ferritinophagy may represent a novel therapeutic target for MDS.

The emerging role of nuclear receptor coactivator 4 in health and disease: a novel bridge between iron metabolism and immunity

Nuclear receptor coactivator 4 (NCOA4) has recently been recognized as a selective cargo receptor of ferritinophagy participating in ferroptosis. However, NCOA4 is also a coactivator that modulates the transcriptional activity of many vital nuclear receptors. Recent novel studies have documented the role of NCOA4 in healthy and pathogenic conditions via its modulation of iron- and non-iron-dependent metabolic pathways. NCOA4 exhibits non-ferritinophagic and iron-independent features such as promoting tumorigenesis and erythropoiesis, immunomodulation, regulating autophagy, and participating in DNA replication and mitosis. Full-length human-NCOA4 is composed of 614 amino acids, of which the N-terminal (1-237) contains nuclear-receptor-binding domains, while the C-terminal (238-614) principally contains a ferritin-binding domain. The exploration of the protein structure of NCOA4 suggests that NCOA4 possesses additional significant and complex functions based on its structural domains. Intriguingly, another three isoforms of NCOA4 that are produced by alternative splicing have been identified, which may also display disparate activities in physiological and pathological processes. Thus, NCOA4 has become an important bridge that encompasses interactions between immunity and metabolism. In this review, we outline the latest advances in the important regulating mechanisms underlying NCOA4 actions in health and disease conditions, providing insights into potential therapeutic interventions.

Recent advances in potential therapeutic targets of ferroptosis‑associated pathways for the treatment of stroke (Review)

Stroke is a severe neurological disease that is associated with high rates of morbidity and mortality, and the underlying pathological processes are complex. Ferroptosis fulfills a significant role in the progression and treatment of stroke. It is well established that ferroptosis is a type of programmed cell death that is distinct from other forms or types of cell death. The process of ferroptosis involves multiple signaling pathways and regulatory mechanisms that interact with mechanisms inherent to stroke development. Inducers and inhibitors of ferroptosis have been shown to exert a role in the onset of this cell death process. Furthermore, it has been shown that interfering with ferroptosis affects the occurrence of stroke, indicating that targeting ferroptosis may offer a promising therapeutic approach for treating patients of stroke. Hence, the present review aimed to summarize the latest progress that has been made in terms of using therapeutic interventions for ferroptosis as treatment targets in cases of stroke. It provides an overview of the relevant pathways and molecular mechanisms that have been investigated in recent years, highlighting the roles of inducers and inhibitors of ferroptosis in stroke. Additionally, the intervention potential of various types of Traditional Chinese Medicine is also summarized. In conclusion, the present review provides a comprehensive overview of the potential therapeutic targets afforded by ferroptosis‑associated pathways in stroke, offering new insights into how ferroptosis may be exploited in the treatment of stroke.

Ferroptosis: a new mechanism of traditional Chinese medicine for treating ulcerative colitis

Ulcerative colitis (UC), a subtype of inflammatory bowel disease, manifests with symptoms such as abdominal pain, diarrhea, and mucopurulent, bloody stools. The pathogenesis of UC is not fully understood. At present, the incidence of UC has increased significantly around the world. Conventional therapeutic arsenals are relatively limited, with often poor efficacy and many adverse effects. In contrast, traditional Chinese medicine (TCM) holds promise due to their notable effectiveness, reduced recurrence rates, and minimal side effects. In recent years, significant progress has been made in the basic research on TCM for UC treatment. It has been found that the inhibition of ferroptosis through the intervention of TCM can significantly promote intestinal mucosal healing and reverse UC. The mechanism of action involves multiple targets and pathways.

Aim of the review

This review summarizes the experimental studies on the targeted regulation of ferroptosis by TCM and its impact on UC in recent years, aiming to provide theoretical basis for the prevention, treatment, and further drug development for UC.

Results

Ferroptosis disrupts antioxidant mechanisms in intestinal epithelial cells, damages the intestinal mucosa, and participates in the pathological process of UC. TCM acts on various pathways such as Nrf2/HO-1 and GSH/GPX4, blocking the pathological progression of ferroptosis in intestinal epithelial cells, inhibiting pathological damage to the intestinal mucosa, and thereby alleviating UC.

Conclusion

The diverse array of TCM single herbs, extracts and herbal formulas facilitates selective and innovative research and development of new TCM methods for targeting UC treatment. Although progress has been made in studying TCM compound formulas, single herbs, and extracts, there are still many issues in clinical and basic experimental designs, necessitating further in-depth scientific exploration and research.

Melatonin alleviates septic ARDS by inhibiting NCOA4-mediated ferritinophagy in alveolar macrophages

Ferroptosis is a novel form of programmed cell death which can exacerbate lung injury in septic acute respiratory distress syndrome (ARDS). Alveolar macrophages, crucial innate immune cells, play a pivotal role in the pathogenesis of ARDS. Ferritinophagy is a process of ferritin degradation mediated by nuclear receptor coactivator 4 (NCOA4) which releases large amounts of iron ions thus promoting ferroptosis. Recent evidence revealed that inhibiting macrophage ferroptosis can effectively attenuate pulmonary inflammatory injury. Melatonin (MT), an endogenous neurohormone, has antioxidant and anti-inflammatory effects and can reduce septic ARDS. However, it is not clear whether MT's pulmonary protective effect is related to the inhibition of macrophage ferritinophagy. Our in vitro experiments demonstrated that MT decreased intracellular malondialdehyde (MDA), Fe2+, and lipid peroxidation levels, increased glutathione (GSH) levels and cell proliferation, and upregulated glutathione peroxidase 4 (GPX4) and ferritin heavy chain 1 (FTH1) protein levels in LPS-treated macrophages. Mechanistically, the antiferroptotic effect of MT on LPS-treated macrophages was significantly compromised by the overexpression of NCOA4. Our in vivo experiments revealed that MT alleviated the protein expression of NCOA4 and FTH1 in the alveolar macrophages of septic mice. Furthermore, MT improved lipid peroxidation and mitigated damage in alveolar macrophages and lung tissue, ultimately increasing the survival rates of septic mice. These findings indicate that MT can inhibit ferroptosis in an NCOA4-mediated ferritinophagy manner, thereby ameliorating septic ARDS.

Mechanisms of Ferritinophagy and Ferroptosis in Diseases

The discovery of the role of autophagy, particularly the selective form like ferritinophagy, in promoting cells to undergo ferroptosis has inspired us to investigate functional connections between diseases and cell death. Ferroptosis is a novel model of procedural cell death characterized by the accumulation of iron-dependent reactive oxygen species (ROS), mitochondrial dysfunction, and neuroinflammatory response. Based on ferroptosis, the study of ferritinophagy is particularly important. In recent years, extensive research has elucidated the role of ferroptosis and ferritinophagy in neurological diseases and anemia, suggesting their potential as therapeutic targets. Besides, the global emergence and rapid transmission of COVID-19, which is caused by SARS-CoV-2, represents a considerable risk to public health worldwide. The potential involvement of ferroptosis in the pathophysiology of brain injury associated with COVID-19 is still unclear. This review summarizes the pathophysiological changes of ferroptosis and ferritinophagy in neurological diseases, anemia, and COVID-19, and hypothesizes that ferritinophagy may be a potential mechanism of ferroptosis. Advancements in these fields will enhance our comprehension of methods to prevent and address neurological disorders, anemia, and COVID-19.

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.

Iron chelation improves ineffective erythropoiesis and iron overload in myelodysplastic syndrome mice

Myelodysplastic syndrome (MDS) is a heterogeneous group of bone marrow stem cell disorders characterized by ineffective hematopoiesis and cytopenias, most commonly anemia. Red cell transfusion therapy for anemia in MDS results in iron overload, correlating with reduced overall survival. Whether the treatment of iron overload benefits MDS patients remains controversial. We evaluate underlying iron-related pathophysiology and the effect of iron chelation using deferiprone on erythropoiesis in NUP98-HOXD13 transgenic mice, a highly penetrant well-established MDS mouse model. Our results characterize an iron overload phenotype with aberrant erythropoiesis in these mice which was reversed by deferiprone-treatment. Serum erythropoietin levels decreased while erythroblast erythropoietin receptor expression increased in deferiprone-treated MDS mice. We demonstrate, for the first time, normalized expression of the iron chaperones Pcbp1 and Ncoa4 and increased ferritin stores in late-stage erythroblasts from deferiprone-treated MDS mice, evidence of aberrant iron trafficking in MDS erythroblasts. Importantly, erythroblast ferritin is increased in response to deferiprone, correlating with decreased erythroblast ROS. Finally, we confirmed increased expression of genes involved in iron uptake, sensing, and trafficking in stem and progenitor cells from MDS patients. Taken together, our findings provide evidence that erythroblast-specific iron metabolism is a novel potential therapeutic target to reverse ineffective erythropoiesis in MDS.

Ferritinophagy: research advance and clinical significance in cancers

Ferritinophagy, a process involving selective autophagy of ferritin facilitated by nuclear receptor coactivator 4 (NCOA4), entails the recognition of ferritin by NCOA4 and subsequent delivery to the autophagosome. Within the autophagosome, ferritin undergoes degradation, leading to the release of iron in the lysosome. It is worth noting that excessive iron levels can trigger cell death. Recent evidence has elucidated the significant roles played by ferritinophagy and ferroptosis in regulation the initiation and progression of cancer. Given the crucial role of ferritinophagy in tumor biology, it may serve as a potential target for future anti-tumor therapeutic interventions. In this study, we have provided the distinctive features of ferritinophagy and its distinctions from ferroptosis. Moreover, we have briefly examined the fundamental regulatory mechanisms of ferritinophagy, encompassing the involvement of the specific receptor NCOA4, the Nrf2/HO-1 signaling and other pathways. Subsequently, we have synthesized the current understanding of the impact of ferritinophagy on cancer progression and its potential therapeutic applications, with a particular emphasis on the utilization of chemotherapy, nanomaterials, and immunotherapy to target the ferritinophagy pathway for anti-tumor purposes.

Managing the Dual Nature of Iron to Preserve Health

Because of its peculiar redox properties, iron is an essential element in living organisms, being involved in crucial biochemical processes such as oxygen transport, energy production, DNA metabolism, and many others. However, its propensity to accept or donate electrons makes it potentially highly toxic when present in excess and inadequately buffered, as it can generate reactive oxygen species. For this reason, several mechanisms evolved to prevent both iron overload and iron deficiency. At the cellular level, iron regulatory proteins, sensors of intracellular iron levels, and post-transcriptional modifications regulate the expression and translation of genes encoding proteins that modulate the uptake, storage, utilization, and export of iron. At the systemic level, the liver controls body iron levels by producing hepcidin, a peptide hormone that reduces the amount of iron entering the bloodstream by blocking the function of ferroportin, the sole iron exporter in mammals. The regulation of hepcidin occurs through the integration of multiple signals, primarily iron, inflammation and infection, and erythropoiesis. These signals modulate hepcidin levels by accessory proteins such as the hemochromatosis proteins hemojuvelin, HFE, and transferrin receptor 2, the serine protease TMPRSS6, the proinflammatory cytokine IL6, and the erythroid regulator Erythroferrone. The deregulation of the hepcidin/ferroportin axis is the central pathogenic mechanism of diseases characterized by iron overload, such as hemochromatosis and iron-loading anemias, or by iron deficiency, such as IRIDA and anemia of inflammation. Understanding the basic mechanisms involved in the regulation of hepcidin will help in identifying new therapeutic targets to treat these disorders.

Iron-tracking strategies: Chaperones capture iron in the cytosolic labile iron pool

Cells express hundreds of iron-dependent enzymes that rely on the iron cofactors heme, iron-sulfur clusters, and mono-or di-nuclear iron centers for activity. Cells require systems for both the assembly and the distribution of iron cofactors to their cognate enzymes. Proteins involved in the binding and trafficking of iron ions in the cytosol, called cytosolic iron chaperones, have been identified and characterized in mammalian cells. The first identified iron chaperone, poly C-binding protein 1 (PCBP1), has also been studied in mice using genetic models of conditional deletion in tissues specialized for iron handling. Studies of iron trafficking in mouse tissues have necessitated the development of new approaches, which have revealed new roles for PCBP1 in the management of cytosolic iron. These approaches can be applied to investigate use of other nutrient metals in mammals.

Iron as a therapeutic target in chronic liver disease

It was clearly realized more than 50 years ago that iron deposition in the liver may be a critical factor in the development and progression of liver disease. The recent clarification of ferroptosis as a specific form of regulated hepatocyte death different from apoptosis and the description of ferritinophagy as a specific variation of autophagy prompted detailed investigations on the association of iron and the liver. In this review, we will present a brief discussion of iron absorption and handling by the liver with emphasis on the role of liver macrophages and the significance of the iron regulators hepcidin, transferrin, and ferritin in iron homeostasis. The regulation of ferroptosis by endogenous and exogenous mod-ulators will be examined. Furthermore, the involvement of iron and ferroptosis in various liver diseases including alcoholic and non-alcoholic liver disease, chronic hepatitis B and C, liver fibrosis, and hepatocellular carcinoma (HCC) will be analyzed. Finally, experimental and clinical results following interventions to reduce iron deposition and the promising manipulation of ferroptosis will be presented. Most liver diseases will be benefited by ferroptosis inhibition using exogenous inhibitors with the notable exception of HCC, where induction of ferroptosis is the desired effect. Current evidence mostly stems from in vitro and in vivo experimental studies and the need for well-designed future clinical trials is warranted.

Quantitative omics analyses of NCOA4 deficiency reveal an integral role of ferritinophagy in iron homeostasis of hippocampal neuronal HT22 cells

Introduction

Neurons require iron to support their metabolism, growth, and differentiation, but are also susceptible to iron-induced oxidative stress and cytotoxicity. Ferritin, a cytosolic iron storage unit, mediates cellular adaptation to fluctuations in iron delivery. NCOA4 has been characterized as a selective autophagic cargo receptor facilitating the mobilization of intracellular iron from ferritin. This process named ferritinophagy results in the degradation of ferritin and the consequent release of iron into the cytosol.

Methods

Here we demonstrate that NCOA4 is important for the adaptation of the HT22 mouse hippocampal neuronal cell line to cellular iron restriction. Additionally, we determined the pathophysiological implications of impaired ferritinophagy via functional analysis of the omics profile of HT22 cells deficient in NCOA4.

Results

NCOA4 silencing impaired ferritin turnover and was cytotoxic when cells were restricted of iron. Quantitative proteomics identified IRP2 accumulation among the most prominent protein responses produced by NCOA4 depletion in HT22 cells, which is indicative of functional iron deficiency. Additionally, proteins of apoptotic signaling pathway were enriched by those responsive to NCOA4 deficiency. Transcriptome profiles of NCOA4 depletion revealed neuronal cell death, differentiation of neurons, and development of neurons as potential diseases and bio functions affected by impaired ferritinophagy, particularly, when iron was restricted.

Discussion

These findings identify an integral role of NCOA4-mediated ferritinophagy in the maintenance of iron homeostasis by HT22 cells, and its potential implications in controlling genetic pathways of neurodevelopment and neurodegenerative diseases.

Autophagy and Its Lineage-Specific Roles in the Hematopoietic System

Autophagy is a dynamic process that regulates the selective and nonselective degradation of cytoplasmic components, such as damaged organelles and protein aggregates inside lysosomes to maintain tissue homeostasis. Different types of autophagy including macroautophagy, microautophagy, and chaperon-mediated autophagy (CMA) have been implicated in a variety of pathological conditions, such as cancer, aging, neurodegeneration, and developmental disorders. Furthermore, the molecular mechanism and biological functions of autophagy have been extensively studied in vertebrate hematopoiesis and human blood malignancies. In recent years, the hematopoietic lineage-specific roles of different autophagy-related (ATG) genes have gained more attention. The evolution of gene-editing technology and the easy access nature of hematopoietic stem cells (HSCs), hematopoietic progenitors, and precursor cells have facilitated the autophagy research to better understand how ATG genes function in the hematopoietic system. Taking advantage of the gene-editing platform, this review has summarized the roles of different ATGs at the hematopoietic cell level, their dysregulation, and pathological consequences throughout hematopoiesis.

The dual role of autophagy in periprosthetic osteolysis

Periprosthetic osteolysis (PPO) induced by wear particles is an important cause of aseptic loosening after artificial joint replacement, among which the imbalance of osteogenesis and osteoclastic processes occupies a central position. The cells involved in PPO mainly include osteoclasts (macrophages), osteoblasts, osteocytes, and fibroblasts. RANKL/RANK/OGP axis is a typical way for osteolysis. Autophagy, a mode of regulatory cell death and maintenance of cellular homeostasis, has a dual role in PPO. Although autophagy is activated in various periprosthetic cells and regulates the release of inflammatory cytokines, osteoclast activation, and osteoblast differentiation, its beneficial or detrimental role remains controversy. In particular, differences in the temporal control and intensity of autophagy may have different effects. This article focuses on the role of autophagy in PPO, and expects the regulation of autophagy to become a powerful target for clinical treatment of PPO.

Inhibitory Effects of Esculetin on Liver Cancer Through Triggering NCOA4 Pathway-Mediation Ferritinophagy in vivo and in vitro

Objective

To explore the effects of Esculetin on liver cancer and explore potential mechanisms of Esculetin-inducing cells death.

Methods

Esculetin's effects on the proliferation, migration and apoptosis of HUH7 and HCCLM3 cells were detected by using CCK8, crystal violet staining, wound healing, Transwell^TM and Annexin V-FITC/PI. Flow cytometry, fluorescence staining, Western blot, T-AOC, DPPH radical scavenging assay, hydroxyl radical's inhibitory capability and GSH test were used to examine the esculetin's effects on the ROS level, the oxidation-related substances and proteins' expression in hepatoma cells. In vivo experiment was performed by xenograft model. Ferrostatin-1 was used to determine the death way of hepatoma cells induced by esculetin. Live cell probe, Western blot, Fe²⁺ content, MDA, HE staining, Prussian blue staining and immunohistochemistry were used to examine the ferritinophagy-related phenomenon induced by esculetin in hepatoma cells. The relationship between esculetin and NCOA4-mediated ferritinophagy was confirmed through gene silence and overexpression, immunofluorescence staining and Western blot.

Results

Esculetin suppressed the proliferation, migration and apoptosis of HUH7 and HCCLM3 cells significantly, influenced the oxidative stress level, altered the autophagy and iron metabolism levels in cells, and produced a ferritinophagy-related phenomena. Esculetin increased the levels of cellular lipid peroxidation and reactive oxygen species. In vivo, esculetin could decrease tumour volume, promote LC3 and NCOA4 expressions, suppresse hydroxyl radical's inhibiting capacity and GSH, increase Fe²⁺ and MDA levels, decrease antioxidant proteins expression in tumour tissue. In addition, Esculetin could also increase the iron deposition of tumour tissues, promote ferritinophagy, and induce tumours' ferroptosis.

Conclusion

Esculetin has an inhibitory effect on liver cancer in vivo and in vitro through triggering NCOA4 pathway-mediation ferritinophagy.

Genetic regulation of iron homeostasis in sideropenic patients with mild COVID-19 disease under a new oral iron formulation: Lessons from a different perspective

Background

Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) needs iron to replicate itself. Coronaviruses are able to upregulate Chop/Gadd153 and Arg1 genes, consequently leading to CD8 lymphocytes decrease, degradation of asparagine and decreased nitric oxide (NO), thus impairing immune response and antithrombotic functions. Little is known about regulation of genes involved in iron metabolism in paucisymptomatic patients with COVID-19 disease or in patients with iron deficiency treated with sucrosomial iron.

Methods

Whole blood was taken from the COVID-19 patients and from patients with sideropenic anemia, treated or not (control group) with iron supplementations. Enrolled patients were: affected by COVID19 under sucrosomal iron support (group A), affected by COVID-19 not under oral iron support (group B), iron deficiency not under treatment, not affected by COVID19 (control group). After RNA extraction and complementary DNA (cDNA) synthesis of Arg1, Hepcidin and Chop/Gadd153, gene expression from the 3 groups was measured by qRT-PCR. M2 macrophages were detected by cytofluorimetry using CD163 and CD14 markers.

Results

Forty patients with COVID-19 (group A), 20 patients with iron deficiency treated with sucrosomial iron (group B) and 20 patients with iron deficiency not under treatment (control group) were enrolled. In all the patients supported with oral sucrosomial iron, the gene expression of Chop, Arg1 and Hepcidin genes was lower than in sideropenic patients not supported with iron, M1 macrophages polarization and functional iron deficiency was also lower in group A and B, than observed in the control group.

Conclusions

New oral iron formulations, as sucrosomial iron, are able to influence the expression of genes like Chop and Arg1 and to influence M2 macrophage polarization mainly in the early phase of COVID-19 disease.

Ferroptosis, a Rising Force against Renal Fibrosis

Ferroptosis is a type of programmed cell death characterized by iron overload, oxidative stress, imbalance in lipid repair, and mitochondria-specific pathological manifestations. Growing number of molecular mechanisms and signaling pathways have been found to be involved in ferroptosis progression, including iron metabolism, amino acid metabolism, lipid metabolism, and energy metabolism. It is worth noting that ferroptosis is involved in the progression of fibrotic diseases such as liver cirrhosis, cardiomyopathy, and idiopathic pulmonary fibrosis, and inhibition of ferroptosis has acquired beneficial outcomes in rodent models, while studies on ferroptosis and renal fibrosis remains limited. Recent studies have revealed that targeting ferroptosis can effectively mitigate chronic kidney injury and renal fibrosis. Moreover, myofibroblasts suffer from ferroptosis during fiber and extracellular matrix deposition in the fibrotic cascade reaction and pharmacological modulation of ferroptosis shows great therapeutic effect on renal fibrosis. Here, we summarize the latest molecular mechanisms of ferroptosis from high-quality studies and review its therapeutic potential in renal fibrosis.

NCOA4 Regulates Iron Recycling and Responds to Hepcidin Activity and Lipopolysaccharide in Macrophages

Macrophages, via erythrophagocytosis, recycle iron from effete erythrocytes to newly developing red blood cells. Conversion of potentially cytotoxic levels of iron from its heme into nonheme form during iron recycling is safely accomplished via coordinated regulations of cellular iron transport and homeostasis. Herein, we demonstrate the roles and regulation of NCOA4 (nuclear receptor coactivator 4)-mediated ferritinophagy in macrophages after erythrophagocytosis using the mouse macrophage cell line J774 cells. Ferritin in J774 cells increased with the rise of nonheme iron by erythrocyte ingestion and declined when total cellular iron contents subsequently decreased. NCOA4, a selective autophagic cargo receptor for ferritin, was responsible for the control of cellular ferritin and total iron contents at the later stage of erythrophagocytosis. A hepcidin analog, which limits the flux of iron through iron-recycling by inhibiting iron export at the plasma membrane, repressed NCOA4 expression and led to accumulation of ferritin in the mouse macrophages. Transcriptome analyses revealed a functional association of immune response with NCOA4-dependent gene expressions, and we confirmed repression of Ncoa4 by lipopolysaccharide (LPS) in J774 cells and the spleen of mice. Collectively, our studies indicate that NCOA4 facilitates cellular ferritin turnover and the release of iron by macrophages after erythrophagocytosis and functions as a regulatory target for molecular signals of systemic iron overload and inflammation. These identify macrophage NCOA4 as a potential therapeutic target for disorders of systemic iron dysregulation, including anemia of inflammation and hemochromatosis.

Silver Nanoparticles Induce a Size-dependent Neurotoxicity to SH-SY5Y Neuroblastoma Cells via Ferritinophagy-mediated Oxidative Stress

Silver nanoparticles (AgNPs) are widely used in a variety of consumer products because of their antibacterial and antifungal characteristics, but little is known about their toxicity to the brain. In this study, we investigated AgNP-induced neurotoxicity using the human neuroblastoma cancer (SH-SY5Y) cell line. After a 24 h treatment of AgNPs with two primary sizes (5 and 50 nm labeled as Ag-5 and Ag-50, respectively), a series of toxicological endpoints including cell viability, expression of proteins and genes in amyloid precursor protein (APP) amyloid hydrolysis process and ferritinophagy signaling pathways, oxidative stress, intracellular iron levels, and molecular regulators of iron metabolism were evaluated. Our results showed that both Ag-5 and Ag-50 induced notable neurotoxic effects on SH-SY5Y cells indicated by cell proliferation inhibition, increased BACE1 protein expression, and decreased APP and ADAM10 gene expression. Activation of nuclear receptor coactivator 4-mediated ferritinophagy and blockade of autophagic flux were induced by AgNPs, accompanied by intracellular iron accumulation and overexpression of divalent metal-ion transporter-1 and ferroportin1 in SH-SY5Y cells. In addition, AgNPs significantly decreased glutathione peroxidase 4 protein expression but increased malondialdehyde concentration, suggesting that AgNP-induced iron accumulation may trigger oxidative stress by disruption of the intracellular oxidant and antioxidant systems. In addition, compared with Ag-50, Ag-5 with higher cellular uptake efficiency caused more detrimental effects on SH-SY5Y cells. In conclusion, our findings demonstrated a size-dependent neurotoxicity in SH-SY5Y cells by AgNPs via ferritinophagy-mediated oxidative stress.

Activation of the Hepcidin-Ferroportin1 pathway in the brain and astrocytic-neuronal crosstalk to counteract iron dyshomeostasis during aging

During physiological aging, iron accumulates in the brain with a preferential distribution in regions that are more vulnerable to age-dependent neurodegeneration such as the cerebral cortex and hippocampus. In the brain of aged wild-type mice, alteration of the Brain Blood Barrier integrity, together with a marked inflammatory and oxidative state lead to increased permeability and deregulation of brain-iron homeostasis. In this context, we found that iron accumulation drives Hepcidin upregulation in the brain and the inhibition of the iron exporter Ferroportin1. We also observed the transcription and the increase of NCOA4 levels in the aged brain together with the increase of light-chain enriched ferritin heteropolymers, more efficient as iron chelators. Interestingly, in cerebral cortex and hippocampus, Ferroportin1 is mainly expressed by astrocytes, while the iron storage protein ferritin light-chain by neurons. This differential distribution suggests that astrocytes mediate iron shuttling in the nervous tissue and that neurons are unable to metabolize it. Our findings highlight for the first time that Hepcidin/Ferroportin1 axis and NCOA4 are directly involved in iron metabolism in mice brain during physiological aging as a response to a higher brain iron influx.

The mutual crosstalk between iron and erythropoiesis

Iron homeostasis and erythropoiesis are strongly interconnected. On one side iron is essential to terminal erythropoiesis for hemoglobin production, on the other erythropoiesis may increase iron absorption through the production of erythroferrone, the erythroid hormone that suppresses hepcidin expression Also erythropoietin production is modulated by iron through the iron regulatory proteins-iron responsive elements that control the hypoxia inducible factor 2-α. The second transferrin receptor, an iron sensor both in the liver and in erythroid cells modulates erythropoietin sensitivity and is a further link between hepcidin and erythropoiesis. When erythropoietin is decreased in iron deficiency the erythropoietin sensitivity is increased because the second transferrin receptor is removed from cell surface. A deranged balance between erythropoiesis and iron/hepcidin may lead to anemia, as in the case of iron deficiency, defective iron uptake and erythroid utilization or subnormal recycling. Defective control of hepcidin production may cause iron deficiency, as in the recessive disorder iron refractory iron deficiency anemia or in anemia of inflammation, or in iron loading anemias, which are characterized by excessive but ineffective erythropoiesis. The elucidation of the mechanisms that regulates iron homeostasis and erythropoiesis is leading to the development of drugs for the benefit of both iron and erythropoiesis disorders.

Macrophages and Iron: A Special Relationship

Macrophages perform a variety of different biological functions and are known for their essential role in the immune response. In this context, a principal function is phagocytic clearance of pathogens, apoptotic and senescent cells. However, the major targets of homeostatic phagocytosis by macrophages are old/damaged red blood cells. As such, macrophages play a crucial role in iron trafficking, as they recycle the large quantity of iron obtained by hemoglobin degradation. They also seem particularly adapted to handle and store amounts of iron that would be toxic to other cell types. Here, we examine the specific and peculiar iron metabolism of macrophages.

Using the Zebrafish as a Genetic Model to Study Erythropoiesis

Vertebrates generate mature red blood cells (RBCs) via a highly regulated, multistep process called erythropoiesis. Erythropoiesis involves synthesis of heme and hemoglobin, clearance of the nuclei and other organelles, and remodeling of the plasma membrane, and these processes are exquisitely coordinated by specific regulatory factors including transcriptional factors and signaling molecules. Defects in erythropoiesis can lead to blood disorders such as congenital dyserythropoietic anemias, Diamond–Blackfan anemias, sideroblastic anemias, myelodysplastic syndrome, and porphyria. The molecular mechanisms of erythropoiesis are highly conserved between fish and mammals, and the zebrafish (Danio rerio) has provided a powerful genetic model for studying erythropoiesis. Studies in zebrafish have yielded important insights into RBC development and established a number of models for human blood diseases. Here, we focus on latest discoveries of the molecular processes and mechanisms regulating zebrafish erythropoiesis and summarize newly established zebrafish models of human anemias.

Macrophages form erythropoietic niches and regulate iron homeostasis to adapt erythropoiesis in response to infections and inflammation

It has recently emerged that tissue-resident macrophages are key regulators of several stem cell niches orchestrating tissue formation during development, as well as postnatally, when they also organize the repair and regeneration of many tissues including the hemopoietic tissue. The fact that macrophages are also master regulators and effectors of innate immunity and inflammation allows them to coordinate hematopoietic response to infections, injuries, and inflammation. After recently reviewing the roles of phagocytes and macrophages in regulating normal and pathologic hematopoietic stem cell niches, we now focus on the key roles of macrophages in regulating erythropoiesis and iron homeostasis. We review herein the recent advances in understanding how macrophages at the center of erythroblastic islands form an erythropoietic niche that controls the terminal differentiation and maturation of erythroblasts into reticulocytes; how red pulp macrophages in the spleen control iron recycling and homeostasis; how these macrophages coordinate emergency erythropoiesis in response to blood loss, infections, and inflammation; and how persistent infections or inflammation can lead to anemia of inflammation via macrophages. Finally, we discuss the technical challenges associated with the molecular characterization of erythroid island macrophages and red pulp macrophages.

The Multiple Facets of Iron Recycling

The production of around 2.5 million red blood cells (RBCs) per second in erythropoiesis is one of the most intense activities in the body. It continuously consumes large amounts of iron, approximately 80% of which is recycled from aged erythrocytes. Therefore, similar to the “making”, the “breaking” of red blood cells is also very rapid and represents one of the key processes in mammalian physiology. Under steady-state conditions, this important task is accomplished by specialized macrophages, mostly liver Kupffer cells (KCs) and splenic red pulp macrophages (RPMs). It relies to a large extent on the engulfment of red blood cells via so-called erythrophagocytosis. Surprisingly, we still understand little about the mechanistic details of the removal and processing of red blood cells by these specialized macrophages. We have only started to uncover the signaling pathways that imprint their identity, control their functions and enable their plasticity. Recent findings also identify other myeloid cell types capable of red blood cell removal and establish reciprocal cross-talk between the intensity of erythrophagocytosis and other cellular activities. Here, we aimed to review the multiple and emerging facets of iron recycling to illustrate how this exciting field of study is currently expanding.

Release of Iron-Loaded Ferritin in Sodium Iodate-Induced Model of Age Related Macular Degeneration: An In-Vitro and In-Vivo Study

To evaluate the role of iron in sodium iodate (NaIO3)-induced model of age-related macular degeneration (AMD) in ARPE-19 cells in-vitro and in mouse models in-vivo. ARPE-19 cells, a human retinal pigment epithelial cell line, was exposed to 10 mM NaIO3 for 24 h, and the expression and localization of major iron modulating proteins was evaluated by Western blotting (WB) and immunostaining. Synthesis and maturation of cathepsin-D (cat-D), a lysosomal enzyme, was evaluated by quantitative reverse-transcriptase polymerase chain reaction (RT-qPCR) and WB, respectively. For in-vivo studies, C57BL/6 mice were injected with 40 mg/kg mouse body weight of NaIO3 intraperitoneally, and their retina was evaluated after 3 weeks as above. NaIO3 induced a 10-fold increase in ferritin in ARPE-19 cells, which co-localized with LC3II, an autophagosomal marker, and LAMP-1, a lysosomal marker. A similar increase in ferritin was noted in retinal lysates and retinal sections of NaIO3-injected mice by WB and immunostaining. Impaired synthesis and maturation of cat-D was also noted. Accumulated ferritin was loaded with iron, and released from retinal pigmented epithelial (RPE) cells in Perls' and LAMP-1 positive vesicles. NaIO3 impairs lysosomal degradation of ferritin by decreasing the transcription and maturation of cat-D in RPE cells. Iron-loaded ferritin accumulates in lysosomes and is released in lysosomal membrane-enclosed vesicles to the extracellular milieu. Accumulation of ferritin in RPE cells and fusion of ferritin-containing vesicles with adjacent photoreceptor cells is likely to create an iron overload, compromising their viability. Moreover, reduced activity of cat-D is likely to promote accumulation of other cellular debris in lysosomal vesicles, contributing to AMD-like pathology.

Newcastle-disease-virus-induced ferroptosis through nutrient deprivation and ferritinophagy in tumor cells

A number of new cell death processes have been discovered in recent years, including ferroptosis, which is characterized by the accumulation of lipid peroxidation products derived from iron metabolism. The evidence suggests that ferroptosis has a tumor-suppressor function. However, the mechanism by which ferroptosis mediates the response of tumor cells to oncolytic viruses remains poorly understood. The Newcastle disease virus (NDV) can selectively replicate in tumor cells. We show that NDV-induced ferroptosis acts through p53-SLC7A11-GPX4 pathway. Meanwhile, the levels of intracellular reactive oxygen species and lipid peroxides increased in tumor cells. Ferritinophagy was induced by NDV promotion of ferroptosis through the release of ferrous iron and an enhanced Fenton reaction. Collectively, these observations demonstrated that the NDV can kill tumor cells through ferroptosis. Our study provides novel insights into the mechanisms of NDV-induced ferroptosis and highlights the critical role of viruses in treating therapy-resistant cancers.

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Oncolytic viruses NDV caused tumor cells death through ferroptosis

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NDV-induced ferroptosis acts through nutrient deprivation by suppression of System Xc⁻

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P53 activation is required for NDV-induced ferroptosis initiation

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Ferritinophagy induced by NDV promotes ferroptosis through release of ferrous iron

Mechanisms of cellular iron sensing, regulation of erythropoiesis and mitochondrial iron utilization

To maintain an adequate iron supply for hemoglobin synthesis and essential metabolic functions while counteracting iron toxicity, humans and other vertebrates have evolved effective mechanisms to conserve and finely regulate iron concentration, storage, and distribution to tissues. At the systemic level, the iron-regulatory hormone hepcidin is secreted by the liver in response to serum iron levels and inflammation. Hepcidin regulates the expression of the sole known mammalian iron exporter, ferroportin, to control dietary absorption, storage and tissue distribution of iron. At the cellular level, iron regulatory proteins 1 and 2 (IRP1 and IRP2) register cytosolic iron concentrations and post-transcriptionally regulate the expression of iron metabolism genes to optimize iron availability for essential cellular processes, including heme biosynthesis and iron-sulfur cluster biogenesis. Genetic malfunctions affecting the iron sensing mechanisms or the main pathways that utilize iron in the cell cause a broad range of human diseases, some of which are characterized by mitochondrial iron accumulation. This review will discuss the mechanisms of systemic and cellular iron sensing with a focus on the main iron utilization pathways in the cell, and on human conditions that arise from compromised function of the regulatory axes that control iron homeostasis.

On Iron Metabolism and Its Regulation

Iron is a critical metal for several vital biological processes. Most of the body’s iron is bound to hemoglobin in erythrocytes. Iron from senescent red blood cells is recycled by macrophages in the spleen, liver and bone marrow. Dietary iron is taken up by the divalent metal transporter 1 (DMT1) in enterocytes and transported to portal blood via ferroportin (FPN), where it is bound to transferrin and taken up by hepatocytes, macrophages and bone marrow cells via transferrin receptor 1 (TfR1). While most of the physiologically active iron is bound hemoglobin, the major storage of most iron occurs in the liver in a ferritin-bound fashion. In response to an increased iron load, hepatocytes secrete the peptide hormone hepcidin, which binds to and induces internalization and degradation of the iron transporter FPN, thus controlling the amount of iron released from the cells into the blood. This review summarizes the key mechanisms and players involved in cellular and systemic iron regulation.

Dexmedetomidine reverses MTX-induced neurotoxicity and inflammation in hippocampal HT22 cell lines via NCOA4-mediated ferritinophagy

The incidence of chemotherapy-induced cognitive impairment (CICI) has attracted massive attention. Some studies have demonstrated the neuroprotective effects of dexmedetomidine (DEX). Here, alterations in nuclear receptor coactivator 4 (NCOA4)-mediated ferritinophagy were investigated as the possible causes of DEX’s neuroprotection of HT22 cells against methotrexate (MTX)-induced neurotoxicity. We used various concentrations of DEX and NCOA4-siRNA to treat MTX-induced neurotoxicity and inflammation in HT22 cells. The biomarkers of HT22 cells viability, apoptosis and inflammatory were tested. The expression of ferritinophagy markers were detected in the HT22 cells by using western blot and Immunofluorescence. We found that 10 and 50 ng/mL of DEX alleviated MTX-induced hippocampal neuronal inflammatory injuries. Meanwhile, DEX also reversed MTX-induced iron and ROS overproduction. Increasing DEX concentrations caused significant falls in the expression of ferritin heavy chain 1 (FTH1). DEX also increased vital ferritinophagy markers, NCOA4 and LC3II. NCOA4-siRNA transfection annulled the neuroprotective effects of DEX on MTX-induced inflammation in HT22 cells. Additionally, because NCOA4-siRNA disrupted ferritinophagy, DEX’s inhibitory impact on MTX-induced iron and ROS overproduction in HT22 cells was also annihilated. DEX weakened MTX-provoked neurontoxicity in HT22 cells, possibly by improving NCOA4-mediated ferritinophagy. Our discoveries present further mechanisms for understanding the protective effects of DEX against MTX-induced cognitive impairment.

NCOA4-mediated ferritinophagy promoted inflammatory responses in periodontitis

BACKGROUND/OBJECTIVES

Iron homeostasis plays a crucial role in the combat against pathogen invasion. Ferrous iron can trigger generous production of reactive oxygen species (ROS) by Fenton reaction. Nuclear receptor coactivator 4 (NCOA4), a selective cargo receptor to deliver ferritin to lysosome, may trigger release of ferritin-bound iron into the cytosol. The aim of the present study was to explore whether NCOA4-mediated ferritinophagy participated in the pathogenesis of periodontitis, and its role in promoting the periodontal inflammation.

METHODS

Inflamed and healthy periodontal tissues were harvested for immunobiological staining of ferritinophagy-related genes in the periodontal tissues, while real-time quantitative PCR (qPCR) was utilized to detect mRNA transcription. Periodontal ligament fibroblasts (PDLFs) were isolated and infected with Porphyromonas gingivalis. The mRNA transcription and protein expression of genes involved in the iron metabolism, including NCOA4, transferrin receptor 1 (TFR1), and ferroportin (SLC40A1) were detected by qPCR and western blot. Levels of labile iron pool and ROS production were detected by flow cytometry and confocal endoscopy. Small interference RNA was utilized to knock down NCOA4.

RESULTS

Elevated expression of NCOA4, ferritin heavy chain, and light chain were observed in the diseased periodontal tissues. P. gingivalis infection promoted expression of TFR1, NCOA4, and microtubule-associated protein 1-light chain 3 B (LC3B), enhanced levels of intracellular labile iron pool and ROS production. NCOA4 knockdown reduced ROS generation in PDLFs in response to P. gingivalis and mitigated production of pro-inflammatory monocyte chemoattractant protein-1 and interleukin 6. P. gingivalis triggered activation of c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase signaling pathway. In addition, inhibitors of JNK, SP600125, and inhibitors of p38, SB203580 blocked NCOA4 transcription.

CONCLUSION

NCOA4-ferritinophagy participated in the progress of periodontitis progression. P. gingvalis-triggered ferritinophagy aggravated production of ROS and inflammatory responses in PDLFS. These findings suggest iron homeostasis plays an important role in the pathogenesis of periodontitis.

Cell-type-specific insights into iron regulatory processes

Despite its essential role in many biological processes, iron is toxic when in excess due to its propensity to generate reactive oxygen species. To prevent diseases associated with iron deficiency or iron loading, iron homeostasis must be tightly controlled. Intracellular iron content is regulated by the Iron Regulatory Element-Iron Regulatory Protein (IRE-IRP) system, whereas systemic iron availability is adjusted to body iron needs chiefly by the hepcidin-ferroportin (FPN) axis. Here, we aimed to review advances in the field that shed light on cell-type-specific regulatory mechanisms that control or modify systemic and local iron balance, and how shifts in cellular iron levels may affect specialized cell functions.

Practical implications of the 2019 Nobel Prize in Physiology or Medicine: from molecular adaptation to hypoxia to novel anti-anemic drugs in the clinic

The 2019 Nobel Prize for Medicine or Physiology was assigned to three prestigious physician-scientists, Gregg L. Semenza, William G. Kaelin, and Peter J. Ratcliffe, who clarified the molecular mechanisms of hypoxia adaptation. This viewpoint traces their fundamental findings, which have paved the way for the development of innovative drugs for a wide range of common diseases, including cancer and anemia.

Basics and principles of cellular and systemic iron homeostasis

Iron is a constituent of many metalloproteins involved in vital metabolic functions. While adequate iron supply is critical for health, accumulation of excess iron promotes oxidative stress and causes tissue injury and disease. Therefore, iron homeostasis needs to be tightly controlled. Mammals have developed elegant homeostatic mechanisms at the cellular and systemic level, which serve to satisfy metabolic needs for iron and to minimize the risks posed by iron's toxicity. Cellular iron metabolism is post-transcriptionally controlled by iron regulatory proteins, IRP1 and IRP2, while systemic iron balance is regulated by the iron hormone hepcidin. This review summarizes basic principles of mammalian iron homeostasis at the cellular and systemic level. Particular attention is given on pathways for hepcidin regulation and on crosstalk between cellular and systemic homeostatic mechanisms.