Mitochondrial ferritin limits oxidative damage regulating mitochondrial iron availability: hypothesis for a protective role in Friedreich ataxia

Observation of the Assembly of the Nascent Mineral Core at the Nucleation Site of Human Mitochondrial Ferritin

Ferritins play a crucial role in iron homeostasis and detoxification in organisms from all kingdoms of life. They are composed of 24 α-helical subunits arranged around an interior cavity where an iron-containing mineral core can be reversibly stored. Despite decades of study, leading to significant progress in defining the routes of Fe2+ uptake and the mechanism of its subsequent oxidation to Fe3+ at diiron catalytic sites termed ferroxidase centers, the process of core synthesis from the product of ferroxidase center activity remains poorly understood. In large part, this is due to the lack of high-resolution structural data on ferritin cores anchored to their nucleation sites on the inner surface of the protein. Mitochondrial ferritins are atypical of those found in higher eukaryotes in that they are homopolymers in which all subunits contain both a ferroxidase center and a presumed but undefined core nucleation site. Here, in conjunction with a novel method for producing iron-enriched ferritin crystals, we exploit these unusual features to structurally characterize both the nucleation site of mitochondrial ferritin and a pentanuclear, ferrihydrite-like iron-oxo cluster formed there. Kinetic data for wild-type and variant proteins confirmed the functional importance of this site, indicating a critical role for E61 in the transfer of Fe3+ from the ferroxidase center to the nascent mineral core.

Iron chelators as mitophagy agents: Potential and limitations

Mitochondrial autophagy (mitophagy) is very important process for the maintenance of cellular homeostasis, functionality and survival. Its dysregulation is associated with high risk and progression numerous serious diseases (e.g., oncological, neurodegenerative and cardiovascular ones). Therefore, targeting mitophagy mechanisms is very hot topic in the biological and medicinal research. The interrelationships between the regulation of mitophagy and iron homeostasis are now becoming apparent. In short, mitochondria are central point for the regulation of iron homeostasis, but change in intracellular cheatable iron level can induce/repress mitophagy. In this review, relationships between iron homeostasis and mitophagy are thoroughly discussed and described. Also, therapeutic applicability of mitophagy chelators in the context of individual diseases is comprehensively and critically evaluated.

Exploring the relationship between anastasis and mitochondrial ROS-mediated ferroptosis in metastatic chemoresistant cancers: a call for investigation

Ferroptosis induces significant changes in mitochondrial morphology, including membrane condensation, volume reduction, cristae alteration, and outer membrane rupture, affecting mitochondrial function and cellular fate. Recent reports have described the intrinsic cellular iron metabolism and its intricate connection to ferroptosis, a significant kind of cell death characterized by iron dependence and oxidative stress regulation. Furthermore, updated molecular insights have elucidated the significance of mitochondria in ferroptosis and its implications in various cancers. In the context of cancer therapy, understanding the dual role of anastasis and ferroptosis in chemoresistance is crucial. Targeting the molecular pathways involved in anastasis may enhance the efficacy of ferroptosis inducers, providing a synergistic approach to overcome chemoresistance. Research into how DNA damage response (DDR) proteins, metabolic changes, and redox states interact during anastasis and ferroptosis can offer new insights into designing combinatorial therapeutic regimens against several cancers associated with stemness. These treatments could potentially inhibit anastasis while simultaneously inducing ferroptosis, thereby reducing the likelihood of cancer cells evading death and developing resistance to chemotherapy. The objective of this study is to explore the intricate interplay between anastasis, ferroptosis, EMT and chemoresistance, and immunotherapeutics to better understand their collective impact on cancer therapy outcomes. We searched public research databases including google scholar, PubMed, relemed, and the national library of medicine related to this topic. In this review, we discussed the interplay between the tricarboxylic acid cycle and glycolysis implicated in modulating ferroptosis, adding complexity to its regulatory mechanisms. Additionally, the regulatory role of reactive oxygen species (ROS) and the electron transport chain (ETC) in ferroptosis has garnered significant attention. Lipid metabolism, particularly involving GPX4 and System Xc- plays a significant role in both the progression of ferroptosis and cancer. There is a need to investigate the intricate interplay between anastasis, ferroptosis, and chemoresistance to better understand cancer therapy clinical outcomes. Integrating anastasis, and ferroptosis into strategies targeting chemoresistance and exploring its potential synergy with immunotherapy represent promising avenues for advancing chemoresistant cancer treatment. Understanding the intricate interplay among mitochondria, anastasis, ROS, and ferroptosis is vital in oncology, potentially revolutionizing personalized cancer treatment and drug development.

Exploring the relationship between anastasis and mitochondrial ROS-mediated ferroptosis in metastatic chemoresistant cancers: a call for investigation

Ferroptosis induces significant changes in mitochondrial morphology, including membrane condensation, volume reduction, cristae alteration, and outer membrane rupture, affecting mitochondrial function and cellular fate. Recent reports have described the intrinsic cellular iron metabolism and its intricate connection to ferroptosis, a significant kind of cell death characterized by iron dependence and oxidative stress regulation. Furthermore, updated molecular insights have elucidated the significance of mitochondria in ferroptosis and its implications in various cancers. In the context of cancer therapy, understanding the dual role of anastasis and ferroptosis in chemoresistance is crucial. Targeting the molecular pathways involved in anastasis may enhance the efficacy of ferroptosis inducers, providing a synergistic approach to overcome chemoresistance. Research into how DNA damage response (DDR) proteins, metabolic changes, and redox states interact during anastasis and ferroptosis can offer new insights into designing combinatorial therapeutic regimens against several cancers associated with stemness. These treatments could potentially inhibit anastasis while simultaneously inducing ferroptosis, thereby reducing the likelihood of cancer cells evading death and developing resistance to chemotherapy. The objective of this study is to explore the intricate interplay between anastasis, ferroptosis, EMT and chemoresistance, and immunotherapeutics to better understand their collective impact on cancer therapy outcomes. We searched public research databases including google scholar, PubMed, relemed, and the national library of medicine related to this topic. In this review, we discussed the interplay between the tricarboxylic acid cycle and glycolysis implicated in modulating ferroptosis, adding complexity to its regulatory mechanisms. Additionally, the regulatory role of reactive oxygen species (ROS) and the electron transport chain (ETC) in ferroptosis has garnered significant attention. Lipid metabolism, particularly involving GPX4 and System Xc- plays a significant role in both the progression of ferroptosis and cancer. There is a need to investigate the intricate interplay between anastasis, ferroptosis, and chemoresistance to better understand cancer therapy clinical outcomes. Integrating anastasis, and ferroptosis into strategies targeting chemoresistance and exploring its potential synergy with immunotherapy represent promising avenues for advancing chemoresistant cancer treatment. Understanding the intricate interplay among mitochondria, anastasis, ROS, and ferroptosis is vital in oncology, potentially revolutionizing personalized cancer treatment and drug development.

Ferritinophagy: A novel insight into the double-edged sword in ferritinophagy-ferroptosis axis and human diseases

Nuclear receptor coactive 4 (NCOA4), which functions as a selective cargo receptor, is a critical regulator of the particularly autophagic degradation of ferritin, a process known as ferritinophagy. Mechanistically, NCOA4-mediated ferritinophagy performs an increasingly vital role in the maintenance of intracellular iron homeostasis by promoting ferritin transport and iron release as needed. Ferritinophagy is not only involved in iron-dependent responses but also in the pathogenesis and progression of various human diseases, including metabolism-related, neurodegenerative, cardiovascular and infectious diseases. Therefore, ferritinophagy is of great importance in maintaining cell viability and function and represents a potential therapeutic target. Recent studies indicated that ferritinophagy regulates the signalling pathway associated with ferroptosis, a newly discovered type of cell death characterised by iron-dependent lipid peroxidation. Although accumulating evidence clearly demonstrates the importance of the interplay between dysfunction in iron metabolism and ferroptosis, a deeper understanding of the double-edged sword effect of ferritinophagy in ferroptosis has remained elusive. Details of the mechanisms underlying the ferritinophagy-ferroptosis axis in regulating relevant human diseases remain to be elucidated. In this review, we discuss the latest research findings regarding the mechanisms that regulate the biological function of NCOA4-mediated ferritinophagy and its contribution to the pathophysiology of ferroptosis. The important role of the ferritinophagy-ferroptosis axis in human diseases will be discussed in detail, highlighting the great potential of targeting ferritinophagy in the treatment of diseases.

Mitochondria-mediated Ferroptosis in Diseases Therapy: From Molecular Mechanisms to Implications

Ferroptosis, a type of cell death involving iron and lipid peroxidation, has been found to be closely associated with the development of many diseases. Mitochondria are vital components of eukaryotic cells, serving important functions in energy production, cellular metabolism, and apoptosis regulation. Presently, the precise relationship between mitochondria and ferroptosis remains unclear. In this study, we aim to systematically elucidate the mechanisms via which mitochondria regulate ferroptosis from multiple perspectives to provide novel insights into mitochondrial functions in ferroptosis. Additionally, we present a comprehensive overview of how mitochondria contribute to ferroptosis in different conditions, including cancer, cardiovascular disease, inflammatory disease, mitochondrial DNA depletion syndrome, and novel coronavirus pneumonia. Gaining a comprehensive understanding of the involvement of mitochondria in ferroptosis could lead to more effective approaches for both basic cell biology studies and medical treatments.

Iron imbalance in neurodegeneration

Iron is an essential element for the development and functionality of the brain, and anomalies in its distribution and concentration in brain tissue have been found to be associated with the most frequent neurodegenerative diseases. When magnetic resonance techniques allowed iron quantification in vivo, it was confirmed that the alteration of brain iron homeostasis is a common feature of many neurodegenerative diseases. However, whether iron is the main actor in the neurodegenerative process, or its alteration is a consequence of the degenerative process is still an open question. Because the different iron-related pathogenic mechanisms are specific for distinctive diseases, identifying the molecular mechanisms common to the various pathologies could represent a way to clarify this complex topic. Indeed, both iron overload and iron deficiency have profound consequences on cellular functioning, and both contribute to neuronal death processes in different manners, such as promoting oxidative damage, a loss of membrane integrity, a loss of proteostasis, and mitochondrial dysfunction. In this review, with the attempt to elucidate the consequences of iron dyshomeostasis for brain health, we summarize the main pathological molecular mechanisms that couple iron and neuronal death.

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.

The Therapeutic Potential of Targeting Ferroptosis in the Treatment of Mitochondrial Cardiomyopathies and Heart Failure

ABSTRACT

Ferroptosis is a form of iron-regulated cell death implicated in a wide array of diseases, including heart failure, hypertension, and numerous cardiomyopathies. In addition, mitochondrial dysfunction has been associated with several of these same disease states. However, the role of the mitochondrion in ferroptotic cell death remains debated. As a major regulator of cellular iron levels, the mitochondria may very well play a crucial role in the mechanisms behind ferroptosis, but at this point, this has not been adequately defined. Emerging evidence from our laboratory and others indicates a critical role of mitochondrial Sirtuin 3, a deacetylase linked with longevity and protection against numerous conditions, in the prevention of cardiovascular diseases. Here, we provide a brief overview of the potential roles of Sirtuin 3 in mitochondrial iron homeostasis and its contribution to the mitochondrial cardiomyopathy of Friedreich's ataxia and diabetic cardiomyopathy. We also discuss the current knowledge of the involvement of ferroptosis and the mitochondria in these and other cardiovascular disease states, including doxorubicin-induced cardiomyopathy, and provide insight into areas requiring further investigation.

The diversified role of mitochondria in ferroptosis in cancer

Ferroptosis is a form of regulated cell death induced by iron-dependent lipid peroxidation, and it has been studied extensively since its discovery in 2012. Induced by iron overload and ROS accumulation, ferroptosis is modulated by various cellular metabolic and signaling pathways. The GSH-GPX4 pathway, the FSP1-CoQ10 pathway, the GCH1-BH4 pathway, the DHODH-CoQH2 system and the sex hormones suppress ferroptosis. Mitochondrial iron metabolism regulates ferroptosis and mitochondria also undergo a morphological change during ferroptosis, these changes include increased membrane density and reduced mitochondrial cristae. Moreover, mitochondrial energy metabolism changes during ferroptosis, the increased oxidative phosphorylation and ATP production rates lead to a decrease in the glycolysis rate. In addition, excessive oxidative stress induces irreversible damage to mitochondria, diminishing organelle integrity. ROS production, mitochondrial membrane potential, mitochondrial fusion and fission, and mitophagy also function in ferroptosis. Notably, some ferroptosis inhibitors target mitochondria. Ferroptosis is a major mechanism for cell death associated with the progression of cancer. Metastasis-prone or metastatic cancer cells are more susceptible to ferroptosis. Inducing ferroptosis in tumor cells shows very promising potential for treating drug-resistant cancers. In this review, we present a brief retrospect of the discovery and the characteristics of ferroptosis, then we discuss the regulation of ferroptosis and highlight the unique role played by mitochondria in the ferroptosis of cancer cells. Furthermore, we explain how ferroptosis functions as a double-edged sword as well as novel therapies aimed at selectively manipulating cell death for cancer eradication.

Newly uncovered biochemical and functional aspects of ferritin

Iron homeostasis is strictly regulated at both the systemic and cellular levels by complex mechanisms because of its indispensability and toxicity. Among the various iron-regulatory proteins, ferritin is the earliest discovered regulator of iron metabolism and is a molecule that safely retains excess intracellular iron in the cores of its shells. Two types of ferritin, cytosolic ferritin and mitochondrial ferritin (FTMT), have been identified in a range of organisms from plants to humans. FTMT was identified approximately 60 years after the discovery of cytosolic ferritin. Cytosolic ferritin expression is regulated in an iron-responsive manner. Recently, the molecular mechanisms of iron-dependent degradation of cytosolic ferritin or its secretion into serum have been clarified. FTMT, which shares a high degree of sequence homology with cytosolic ferritin, has distinct functions and is regulated in different ways from cytosolic ferritin. Although knowledge of the physiological role of FTMT is still incomplete, recent studies have shed light on the function and regulation of FTMT. The accumulating biological evidence of both ferritins has made it possible to deepen our knowledge about iron metabolism and its significance in diseases. In this review, we discuss the biological properties of both ferritins, focusing on their newly uncovered behaviors.

Iron accumulation and lipid peroxidation: implication of ferroptosis in diabetic cardiomyopathy

Diabetic cardiomyopathy (DC) is a serious heart disease caused by diabetes. It is unrelated to hypertension and coronary artery disease and can lead to heart insufficiency, heart failure and even death. Currently, the pathogenesis of DC is unclear, and clinical intervention is mainly symptomatic therapy and lacks effective intervention objectives. Iron overdose mediated cell death, also known as ferroptosis, is widely present in the physiological and pathological processes of diabetes and DC. Iron is a key trace element in the human body, regulating the metabolism of glucose and lipids, oxidative stress and inflammation, and other biological processes. Excessive iron accumulation can lead to the imbalance of the antioxidant system in DC and activate and aggravate pathological processes such as excessive autophagy and mitochondrial dysfunction, resulting in a chain reaction and accelerating myocardial and microvascular damage. In-depth understanding of the regulating mechanisms of iron metabolism and ferroptosis in cardiovascular vessels can help improve DC management. Therefore, in this review, we summarize the relationship between ferroptosis and the pathogenesis of DC, as well as potential intervention targets, and discuss and analyze the limitations and future development prospects of these targets.

FtMt reduces oxidative stress-induced trophoblast cell dysfunction via the HIF-1α/VEGF signaling pathway

BACKGROUND

Preeclampsia (PE) is a complication of pregnancy that causes long-term adverse outcomes for the mother and fetus and may even lead to death. Oxidative stress caused by the imbalance of oxidants and antioxidants in the placenta has been considered as one of the key mechanisms of preeclampsia (together with inflammation, etc.), in which the placental mitochondria play an important role. The expression of hypoxia-inducible factor-1 (HIF-1α) and vascular endothelial growth factor (VEGF) is known to be increased in patients with PE. Mitochondrial ferritin (FtMt) is known to protect the mitochondria from oxidative stress, although its specific role in PE remains unclear.

METHODS

We used qRT-PCR and western blotting to detect the expression levels of FtMt, HIF-1α, and VEGF in placental tissues from patients with PE. Human chorionic trophoblast cells were also administered with hypoxia treatment, followed by the detection of cell proliferation, invasion and angiogenic capacity by CCK8, Transwell, and endothelial cell angiogenesis assays; we also detected the expression of HIF-1α and VEGF in these cells. Finally, overexpression or inhibitory FtMt lentiviral vectors, along with negative control vectors, were constructed and transfected into hypoxia-treated human chorionic trophoblast cells; this was followed by analyses of cell function.

RESULTS

The expression levels of FtMt, HIF-1α and VEGF in the PE group were higher than those in the control group (P < 0.05). Following hypoxia, there was an increase in the expression levels of HIF-1α and VEGF protein in trophoblast cells. There was also an increase in invasion ability and vascular formation ability along with a reduction in cell proliferation ability. These effects were reversed by transfecting cells with the knockout FtMt lentivirus vector. The differences were statistically significant.

CONCLUSION

Analyses showed that FtMt plays a key role in the vascular regulation of PE trophoblast cells after hypoxia possibly acting via the HIF-1α/VEGF signaling pathway. These results provide us an enhanced understanding of the pathogenesis of PE and suggest that the HIF-1α/VEGF signaling pathway represents a new target for the treatment of PE.

Iron Metabolism in Cardiovascular Disease: Physiology, Mechanisms, and Therapeutic Targets

The cardiovascular system requires iron to maintain its high energy demands and metabolic activity. Iron plays a critical role in oxygen transport and storage, mitochondrial function, and enzyme activity. However, excess iron is also cardiotoxic due to its ability to catalyze the formation of reactive oxygen species and promote oxidative damage. While mammalian cells have several redundant iron import mechanisms, they are equipped with a single iron-exporting protein, which makes the cardiovascular system particularly sensitive to iron overload. As a result, iron levels are tightly regulated at many levels to maintain homeostasis. Iron dysregulation ranges from iron deficiency to iron overload and is seen in many types of cardiovascular disease, including heart failure, myocardial infarction, anthracycline-induced cardiotoxicity, and Friedreich's ataxia. Recently, the use of intravenous iron therapy has been advocated in patients with heart failure and certain criteria for iron deficiency. Here, we provide an overview of systemic and cellular iron homeostasis in the context of cardiovascular physiology, iron deficiency, and iron overload in cardiovascular disease, current therapeutic strategies, and future perspectives.

Mitochondrial ferritin expression in human macrophages is facilitated by thrombin-mediated cleavage under hypoxia

Ferritins are iron storage proteins, which maintain cellular iron homeostasis. Among these proteins, the ferritin heavy chain is well characterized, but the regulatory principles of mitochondrial ferritin (FTMT) remain elusive. FTMT appears to be cleaved from a 27 kDa to a 22 kDa form. In human macrophages, FTMT increased under hypoxia in a hypoxia-inducible factor 2-dependent manner. Occurrence of FTMT resulted from cleavage by thrombin, which was supplied by serum. Inhibition of thrombin as well as serum removal decreased FTMT, while supplementation of thrombin under serum-deprived conditions restored its expression. Besides hypoxia, thrombin facilitated FTMT expression after treatment with the ferroptosis inducer RSL3 and the pro-inflammatory stimulus lipopolysaccharide. This study provides insights into the regulation of FTMT under hypoxia and identifies thrombin as a FTMT maturation-associated peptidase.

Neurogenetic motor disorders

Advances in the field of neurogenetics have practical applications in rapid diagnosis on blood and body fluids to extract DNA, obviating the need for invasive investigations. The ability to obtain a presymptomatic diagnosis through genetic screening and biomarkers can be a guide to life-saving disease-modifying therapy or enzyme replacement therapy to compensate for the deficient disease-causing enzyme. The benefits of a comprehensive neurogenetic evaluation extend to family members in whom identification of the causal gene defect ensures carrier detection and at-risk counseling for future generations. This chapter explores the many facets of the neurogenetic evaluation in adult and pediatric motor disorders as a primer for later chapters in this volume and a roadmap for the future applications of genetics in neurology.

Ferritinophagy, a form of autophagic ferroptosis: New insights into cancer treatment

Ferritinophagy, a form of autophagy, is also an important part of ferroptosis, a type of regulated cell death resulting from abnormal iron metabolism involving the production of reactive oxygen species. As ferroptosis, autophagy and cancer have been revealed, ferritinophagy has attracted increasing attention in cancer development. In this review, we discuss the latest research progress on ferroptosis, autophagy-associated ferroptosis led by ferritinophagy, the regulators of ferritinophagy and promising cancer treatments that target ferritinophagy. Ferritinophagy is at the intersection of ferroptosis and autophagy and plays a significant role in cancer development. The discussed studies provide new insights into the mechanisms of ferritinophagy and promising related treatments for cancer.

The critical role of ferritinophagy in human disease

Ferritinophagy is a type of autophagy mediated by nuclear receptor activator 4 (NCOA4), which plays a role in inducing ferroptosis by regulating iron homeostasis and producing reactive oxygen species in cells. Under physiological conditions, ferritinophagy maintains the stability of intracellular iron by regulating the release of free iron. Studies have demonstrated that ferritinophagy is necessary to induce ferroptosis; however, under pathological conditions, excessive ferritinophagy results in the release of free iron in large quantities, which leads to lipid peroxidation and iron-dependent cell death, known as ferroptosis. Ferritinophagy has become an area of interest in recent years. We here in review the mechanism of ferritinophagy and its association with ferroptosis and various diseases to provide a reference for future clinical and scientific studies.

Iron Metabolism in the Disorders of Heme Biosynthesis

Given its remarkable property to easily switch between different oxidative states, iron is essential in countless cellular functions which involve redox reactions. At the same time, uncontrolled interactions between iron and its surrounding milieu may be damaging to cells and tissues. Heme-the iron-chelated form of protoporphyrin IX-is a macrocyclic tetrapyrrole and a coordination complex for diatomic gases, accurately engineered by evolution to exploit the catalytic, oxygen-binding, and oxidoreductive properties of iron while minimizing its damaging effects on tissues. The majority of the body production of heme is ultimately incorporated into hemoglobin within mature erythrocytes; thus, regulation of heme biosynthesis by iron is central in erythropoiesis. Additionally, heme is a cofactor in several metabolic pathways, which can be modulated by iron-dependent signals as well. Impairment in some steps of the pathway of heme biosynthesis is the main pathogenetic mechanism of two groups of diseases collectively known as porphyrias and congenital sideroblastic anemias. In porphyrias, according to the specific enzyme involved, heme precursors accumulate up to the enzyme stop in disease-specific patterns and organs. Therefore, different porphyrias manifest themselves under strikingly different clinical pictures. In congenital sideroblastic anemias, instead, an altered utilization of mitochondrial iron by erythroid precursors leads to mitochondrial iron overload and an accumulation of ring sideroblasts in the bone marrow. In line with the complexity of the processes involved, the role of iron in these conditions is then multifarious. This review aims to summarise the most important lines of evidence concerning the interplay between iron and heme metabolism, as well as the clinical and experimental aspects of the role of iron in inherited conditions of altered heme biosynthesis.

Mechanisms of Ferroptosis and Emerging Links to the Pathology of Neurodegenerative Diseases

Neurodegenerative diseases are a diverse class of diseases attributed to chronic progressive neuronal degeneration and synaptic loss in the brain and/or spinal cord, including Alzheimer’s disease, Parkinson’s disease, Huntington’s disease, amyotrophic lateral sclerosis and multiple sclerosis. The pathogenesis of neurodegenerative diseases is complex and diverse, often involving mitochondrial dysfunction, neuroinflammation, and epigenetic changes. However, the pathogenesis of neurodegenerative diseases has not been fully elucidated. Recently, accumulating evidence revealed that ferroptosis, a newly discovered iron-dependent and lipid peroxidation-driven type of programmed cell death, provides another explanation for the occurrence and progression of neurodegenerative diseases. Here, we provide an overview of the process and regulation mechanisms of ferroptosis, and summarize current research progresses that support the contribution of ferroptosis to the pathogenesis of neurodegenerative diseases. A comprehensive understanding of the emerging roles of ferroptosis in neurodegenerative diseases will shed light on the development of novel therapeutic technologies and strategies for slowing down the progression of these diseases.

Ferritinophagy and α-Synuclein: Pharmacological Targeting of Autophagy to Restore Iron Regulation in Parkinson's Disease

A major hallmark of Parkinson’s disease (PD) is the fatal destruction of dopaminergic neurons within the substantia nigra pars compacta. This event is preceded by the formation of Lewy bodies, which are cytoplasmic inclusions composed of α-synuclein protein aggregates. A triad contribution of α-synuclein aggregation, iron accumulation, and mitochondrial dysfunction plague nigral neurons, yet the events underlying iron accumulation are poorly understood. Elevated intracellular iron concentrations up-regulate ferritin expression, an iron storage protein that provides cytoprotection against redox stress. The lysosomal degradation pathway, autophagy, can release iron from ferritin stores to facilitate its trafficking in a process termed ferritinophagy. Aggregated α-synuclein inhibits SNARE protein complexes and destabilizes microtubules to halt vesicular trafficking systems, including that of autophagy effectively. The scope of this review is to describe the physiological and pathological relationship between iron regulation and α-synuclein, providing a detailed understanding of iron metabolism within nigral neurons. The underlying mechanisms of autophagy and ferritinophagy are explored in the context of PD, identifying potential therapeutic targets for future investigation.

Apoptosis versus survival of African horse sickness virus serotype 4-infected horse peripheral blood mononuclear cells

Expanding on our previous work, this study used transcriptome analysis of RNA sequences to investigate the various factors that contributed to either inducing apoptosis that resulted in cell death or promoting the survival of African horse sickness virus serotype 4 (AHSV4)-infected horse peripheral blood mononuclear cells (PBMC) after 24 h. Apoptosis is a host defense mechanism that prevents virus replication, accumulation and spread of progeny viruses. AHSV4-infected PBMC were killed via the intrinsic and the perforin/granzyme pathways of apoptosis during the attenuated AHSV4 (attAHSV4) in vivo primary and secondary immune responses. Trained innate immunity played an important role in circumventing viral interference that resulted in the elimination of AHSV4-infected PBMC through the intrinsic and the extrinsic pathways of apoptosis during the virulent AHSV4 (virAHSV4) in vitro secondary immune response. Oxidative stress in conjunction with IRE1α pro-apoptotic signaling played a major role in the induction of the intrinsic pathway of apoptosis and cytotoxic lymphocytes induced the perforin/granzyme or extrinsic pathways of apoptosis. In contrast, AHSV4-infected PBMC survived during the virAHSV4 in vitro primary immune response, which allows unrestrained viral replication. The virAHSV4 interference with the innate immune response resulted in impaired NK cell responses and delayed immune responses, which together with the antioxidant defense system promoted AHSV4-infected PBMC survival.

A Novel Insight Into the Fate of Cardiomyocytes in Ischemia-Reperfusion Injury: From Iron Metabolism to Ferroptosis

Ischemia-reperfusion injury (IRI), critically involved in the pathology of reperfusion therapy for myocardial infarction, is closely related to oxidative stress the inflammatory response, and disturbances in energy metabolism. Emerging evidence shows that metabolic imbalances of iron participate in the pathophysiological process of cardiomyocyte IRI [also termed as myocardial ischemia-reperfusion injury (MIRI)]. Iron is an essential mineral required for vital physiological functions, including cellular respiration, lipid and oxygen metabolism, and protein synthesis. Nevertheless, cardiomyocyte homeostasis and viability are inclined to be jeopardized by iron-induced toxicity under pathological conditions, which is defined as ferroptosis. Upon the occurrence of IRI, excessive iron is transported into cells that drive cardiomyocytes more vulnerable to ferroptosis by the accumulation of reactive oxygen species (ROS) through Fenton reaction and Haber–Weiss reaction. The increased ROS production in ferroptosis correspondingly leads cardiomyocytes to become more sensitive to oxidative stress under the exposure of excess iron. Therefore, ferroptosis might play an important role in the pathogenic progression of MIRI, and precisely targeting ferroptosis mechanisms may be a promising therapeutic option to revert myocardial remodeling. Notably, targeting inhibitors are expected to prevent MIRI deterioration by suppressing cardiomyocyte ferroptosis. Here, we review the pathophysiological alterations from iron homeostasis to ferroptosis together with potential pathways regarding ferroptosis secondary to cardiovascular IRI. We also provide a comprehensive analysis of ferroptosis inhibitors and initiators, as well as regulatory genes involved in the setting of MIRI.

Dietary Iron Overload and Hfe-/- Related Hemochromatosis Alter Hepatic Mitochondrial Function

Iron is an essential co-factor for many cellular metabolic processes, and mitochondria are main sites of utilization. Iron accumulation promotes production of reactive oxygen species (ROS) via the catalytic activity of iron species. Herein, we investigated the consequences of dietary and genetic iron overload on mitochondrial function. C57BL/6N wildtype and Hfe^-/- mice, the latter a genetic hemochromatosis model, received either normal diet (ND) or high iron diet (HI) for two weeks. Liver mitochondrial respiration was measured using high-resolution respirometry along with analysis of expression of specific proteins and ROS production. HI promoted tissue iron accumulation and slightly affected mitochondrial function in wildtype mice. Hepatic mitochondrial function was impaired in Hfe^-/- mice on ND and HI. Compared to wildtype mice, Hfe^-/- mice on ND showed increased mitochondrial respiratory capacity. Hfe^-/- mice on HI showed very high liver iron levels, decreased mitochondrial respiratory capacity and increased ROS production associated with reduced mitochondrial aconitase activity. Although Hfe^-/- resulted in increased mitochondrial iron loading, the concentration of metabolically reactive cytoplasmic iron and mitochondrial density remained unchanged. Our data show multiple effects of dietary and genetic iron loading on mitochondrial function and linked metabolic pathways, providing an explanation for fatigue in iron-overloaded hemochromatosis patients, and suggests iron reduction therapy for improvement of mitochondrial function.

Blood Differential Gene Expression in Patients with Chronic Heart Failure and Systemic Iron Deficiency: Pathways Involved in Pathophysiology and Impact on Clinical Outcomes

Background: Iron deficiency is a common disorder in patients with heart failure and is related with adverse outcomes and poor quality of life. Previous experimental studies have shown biological connections between iron homeostasis, mitochondrial metabolism, and myocardial function. However, the mechanisms involved in this crosstalk are yet to be unfolded. Methods: The present research attempts to investigate the intrinsic biological mechanisms between heart failure and iron deficiency and to identify potential prognostic biomarkers by determining the gene expression pattern in the blood of heart failure patients, using whole transcriptome and targeted TaqMan^® low-density array analyses. Results: We performed a stepwise cross-sectional longitudinal study in a cohort of chronic heart failure patients with and without systemic iron deficiency. First, the full transcriptome was performed in a nested case-control exploratory cohort of 7 paired patients and underscored 1128 differentially expressed transcripts according to iron status (cohort1#). Later, we analyzed the messenger RNA levels of 22 genes selected by their statistical significance and pathophysiological relevance, in a validation cohort of 71 patients (cohort 2#). Patients with systemic iron deficiency presented lower mRNA levels of mitochondrial ferritin, sirtuin-7, small integral membrane protein 20, adrenomedullin and endothelin converting enzyme-1. An intermediate mitochondrial ferritin gene expression and an intermediate or low sirtuin7 and small integral membrane protein 20 mRNA levels were associated with an increased risk of all-cause mortality and heart failure admission ((HR 2.40, 95% CI 1.04–5.50, p-value = 0.039), (HR 5.49, 95% CI 1.78–16.92, p-value = 0.003), (HR 9.51, 95% CI 2.69–33.53, p-value < 0.001), respectively). Conclusions: Patients with chronic heart failure present different patterns of blood gene expression depending on systemic iron status that affect pivotal genes involved in iron regulation, mitochondrial metabolism, endothelial function and cardiovascular physiology, and correlate with adverse clinical outcomes.

Down the Iron Path: Mitochondrial Iron Homeostasis and Beyond

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

Mitochondrial Ferritin: Its Role in Physiological and Pathological Conditions

In 2001, a new type of human ferritin was identified by searching for homologous sequences to H-ferritin in the human genome. After the demonstration that this ferritin is located specifically in the mitochondrion, it was called mitochondrial ferritin. Studies on the properties of this new type of ferritin have been limited by its very high homology with the cytosolic H-ferritin, which is expressed at higher levels in cells. This great similarity made it difficult to obtain specific antibodies against the mitochondrial ferritin devoid of cross-reactivity with cytosolic ferritin. Thus, the knowledge of the physiological role of mitochondrial ferritin is still incomplete despite 20 years of research. In this review, we summarize the literature on mitochondrial ferritin expression regulation and its physical and biochemical properties, with particular attention paid to the differences with cytosolic ferritin and its role in physiological condition. Until now, there has been no evidence that the alteration of the mitochondrial ferritin gene is causative of any disorder; however, the identified association of the mitochondrial ferritin with some disorders is discussed.

The role of iron in doxorubicin-induced cardiotoxicity: recent advances and implication for drug delivery

As an anthracycline antibiotic, doxorubicin (DOX) is one of the most potent and widely used chemotherapeutic agents for treating various types of tumors. Unfortunately, the clinical application of this drug results in severe side effects, particularly dose-dependent cardiotoxicity. There are multiple mechanisms involved with the cardiotoxicity caused by DOX, among which intracellular iron homeostasis plays an essential role based on a recent discovery. In this mini-review, we summarize the clinical features and symptoms of DOX-dependent cardiotoxicity, discuss the correlation between iron and cardiotoxicity, and highlight the involvement of iron-dependent ferroptotic cell death therein. Recent advances in this topic will aid the development of novel DOX delivery systems with reduced adverse effects, and expand the clinical application of anthracycline.

Chemistry and biology of ferritin

Iron is an essential element required by cells and has been described as a key player in ferroptosis. Ferritin operates as a fundamental iron storage protein in cells forming multimeric assemblies with crystalline iron cores. We discuss the latest findings on ferritin structure and activity and its link to cell metabolism and ferroptosis. The chemistry of iron, including its oxidation states, is important for its biological functions, its reactivity, and the biology of ferritin. Ferritin can be localized in different cellular compartments and secreted by cells with a variety of functions depending on its spatial context. Here, we discuss how cellular ferritin localization is tightly linked to its function in a tissue-specific manner, and how impairment of iron homeostasis is implicated in diseases, including cancer and coronavirus disease 2019. Ferritin is a potential biomarker and we discuss latest research where it has been employed for imaging purposes and drug delivery.

Distinct Effects of Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus Cell Wall Component-Induced Inflammation on the Iron Metabolism of THP-1 Cells

Macrophages are essential immune cells of the innate immune system. They participate in the development and regulation of inflammation. Macrophages play a fundamental role in fighting against bacterial infections by phagocytosis of bacteria, and they also have a specific role in immunomodulation by secreting pro-inflammatory cytokines. In bacterial infection, macrophages decrease the serum iron concentration by removing iron from the blood, acting as one of the most important regulatory cells of iron homeostasis. We examined whether the Gram-positive and Gram-negative cell wall components from various bacterial strains affect the cytokine production and iron transport, storage and utilization of THP-1 monocytes in different ways. We found that S. aureus lipoteichoic acid (LTA) was less effective in activating pro-inflammatory cytokine expression that may related to its effect on fractalkine production. LTA-treated cells increased iron uptake through divalent metal transporter-1, but did not elevate the expression of cytosolic and mitochondrial iron storage proteins, suggesting that the cells maintained iron efflux via the ferroportin iron exporter. E. coli and P. aeruginosa lipopolysaccharides (LPSs) acted similarly on THP-1 cells, but the rates of the alterations of the examined proteins were different. E. coli LPS was more effective in increasing the pro-inflammatory cytokine production, meanwhile it caused less dramatic alterations in iron metabolism. P. aeruginosa LPS-treated cells produced a smaller amount of pro-inflammatory cytokines, but caused remarkable elevation of both cytosolic and mitochondrial iron storage proteins and intracellular iron content compared to E. coli LPS. These results prove that LPS molecules from different bacterial sources alter diverse molecular mechanisms in macrophages that prepossess the outcome of the bacterial infection.

The Role of GSH in Intracellular Iron Trafficking

Evidence is reviewed for the role of glutathione in providing a ligand for the cytosolic iron pool. The possibility of histidine and carnosine forming ternary complexes with iron(II)glutathione is discussed and the physiological significance of these interactions considered. The role of carnosine in muscle, brain, and kidney physiology is far from established and evidence is presented that the iron(II)-binding capability of carnosine relates to this role.

Mitochondrial iron metabolism and its role in diseases

Iron is one of the most important elements for life, but excess iron is toxic. Intracellularly, mitochondria are the center of iron utilization requiring sufficient amounts to maintain normal physiologic function. Accordingly, disruption of iron homeostasis could seriously impact mitochondrial function leading to impaired energy state and potential disease development. In this review, we discuss mechanisms of iron metabolism including transport, processing, heme synthesis, iron-sulfur cluster biogenesis and storage. We highlight the vital role of mitochondrial iron in pathologic states including neurodegenerative disorders and sideroblastic anemia.

Hippocampal Lipocalin 2 Is Associated With Neuroinflammation and Iron-Related Oxidative Stress in ob/ob Mice

Obesity causes brain injuries with inflammatory and structural changes, leading to neurodegeneration. Although increased circulating lipocalin 2 (LCN2) level has been implicated in neurodegenerative diseases, the precise mechanism of neurodegeneration in obesity is not clear. Here, we investigated whether LCN2-mediated signaling promotes neurodegeneration in the hippocampus of leptin-deficient ob/ob mice, which are characterized by obesity, insulin resistance, systemic inflammation, and neuroinflammation. In particular, there was significant upregulation of both LCN2 and matrix metalloproteinase 9 levels from serum and hippocampus in ob/ob mice. Using RNA-seq analysis, we found that neurodegeneration- sortilin-related receptor 1 (Sorl1) and brain-derived neurotrophic factor (Bdnf) genes were significantly reduced in the hippocampus of ob/ob mice. We additionally found that the endosome-related WD repeat and FYVE-domain-containing 1 (Wdfy1) gene were upregulated in ob/ob mice. In particular, iron overload-related mitochondrial ferritin and nuclear factor erythroid 2-related factor 2 (Nrf2)/heme oxygenase-1 (HO-1) proteins were increased in the hippocampus of ob/ob. Thus, these findings indicate that iron-binding protein LCN2-mediated oxidative stress promotes neurodegeneration in ob/ob mice.

An Overview of the Ferroptosis Hallmarks in Friedreich's Ataxia

BACKGROUND

Friedreich's ataxia (FRDA) is a neurodegenerative disease characterized by early mortality due to hypertrophic cardiomyopathy. FRDA is caused by reduced levels of frataxin (FXN), a mitochondrial protein involved in the synthesis of iron-sulphur clusters, leading to iron accumulation at the mitochondrial level, uncontrolled production of reactive oxygen species and lipid peroxidation. These features are also common to ferroptosis, an iron-mediated type of cell death triggered by accumulation of lipoperoxides with distinct morphological and molecular characteristics with respect to other known cell deaths.

SCOPE OF REVIEW

Even though ferroptosis has been associated with various neurodegenerative diseases including FRDA, the mechanisms leading to disease onset/progression have not been demonstrated yet. We describe the molecular alterations occurring in FRDA that overlap with those characterizing ferroptosis.

MAJOR CONCLUSIONS

The study of ferroptotic pathways is necessary for the understanding of FRDA pathogenesis, and anti-ferroptotic drugs could be envisaged as therapeutic strategies to cure FRDA.

Frataxin gene editing rescues Friedreich's ataxia pathology in dorsal root ganglia organoid-derived sensory neurons

Friedreich's ataxia (FRDA) is an autosomal-recessive neurodegenerative and cardiac disorder which occurs when transcription of the FXN gene is silenced due to an excessive expansion of GAA repeats into its first intron. Herein, we generate dorsal root ganglia organoids (DRG organoids) by in vitro differentiation of human iPSCs. Bulk and single-cell RNA sequencing show that DRG organoids present a transcriptional signature similar to native DRGs and display the main peripheral sensory neuronal and glial cell subtypes. Furthermore, when co-cultured with human intrafusal muscle fibers, DRG organoid sensory neurons contact their peripheral targets and reconstitute the muscle spindle proprioceptive receptors. FRDA DRG organoids model some molecular and cellular deficits of the disease that are rescued when the entire FXN intron 1 is removed, and not with the excision of the expanded GAA tract. These results strongly suggest that removal of the repressed chromatin flanking the GAA tract might contribute to rescue FXN total expression and fully revert the pathological hallmarks of FRDA DRG neurons.

Hypoxia inhibits ferritinophagy, increases mitochondrial ferritin, and protects from ferroptosis

Cellular iron, at the physiological level, is essential to maintain several metabolic pathways, while an excess of free iron may cause oxidative damage and/or provoke cell death. Consequently, iron homeostasis has to be tightly controlled. Under hypoxia these regulatory mechanisms for human macrophages are not well understood. Hypoxic primary human macrophages reduced intracellular free iron and increased ferritin expression, including mitochondrial ferritin (FTMT), to store iron. In parallel, nuclear receptor coactivator 4 (NCOA4), a master regulator of ferritinophagy, decreased and was proven to directly regulate FTMT expression. Reduced NCOA4 expression resulted from a lower rate of hypoxic NCOA4 transcription combined with a micro RNA 6862-5p-dependent degradation of NCOA4 mRNA, the latter being regulated by c-jun N-terminal kinase (JNK). Pharmacological inhibition of JNK under hypoxia increased NCOA4 and prevented FTMT induction. FTMT and ferritin heavy chain (FTH) cooperated to protect macrophages from RSL-3-induced ferroptosis under hypoxia as this form of cell death is linked to iron metabolism. In contrast, in HT1080 fibrosarcome cells, which are sensitive to ferroptosis, NCOA4 and FTMT are not regulated. Our study helps to understand mechanisms of hypoxic FTMT regulation and to link ferritinophagy and macrophage sensitivity to ferroptosis.

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Hypoxia decreases NCOA4 transcription in primary human macrophages.

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NCOA4 mRNA is a target of miR-6862-5p.

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Lowering NCOA4 increases FTMT abundance under hypoxia.

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FTMT and FTH protect from ferroptosis.

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Tumor cells lack the hypoxic decrease of NCOA4 and fail to stabilize FTMT.

Ferroptosis and Cancer: Mitochondria Meet the "Iron Maiden" Cell Death

Ferroptosis is a new type of oxidative regulated cell death (RCD) driven by iron-dependent lipid peroxidation. As major sites of iron utilization and master regulators of oxidative metabolism, mitochondria are the main source of reactive oxygen species (ROS) and, thus, play a role in this type of RCD. Ferroptosis is, indeed, associated with severe damage in mitochondrial morphology, bioenergetics, and metabolism. Furthermore, dysregulation of mitochondrial metabolism is considered a biochemical feature of neurodegenerative diseases linked to ferroptosis. Whether mitochondrial dysfunction can, per se, initiate ferroptosis and whether mitochondrial function in ferroptosis is context-dependent are still under debate. Cancer cells accumulate high levels of iron and ROS to promote their metabolic activity and growth. Of note, cancer cell metabolic rewiring is often associated with acquired sensitivity to ferroptosis. This strongly suggests that ferroptosis may act as an adaptive response to metabolic imbalance and, thus, may constitute a new promising way to eradicate malignant cells. Here, we review the current literature on the role of mitochondria in ferroptosis, and we discuss opportunities to potentially use mitochondria-mediated ferroptosis as a new strategy for cancer therapy.

Effects of FTMT Expression by Retinal Pigment Epithelial Cells on Features of Angiogenesis

Aberrant angiogenesis is a pathological feature of a number of diseases and arises from the uncoordinated expression of angiogenic factors as response to different cellular stresses. Age-related macular degeneration (AMD), a leading cause of vision loss, can result from pathological angiogenesis. As a mutation in the mitochondrial ferritin (FTMT) gene has been associated with AMD, its possible role in modulating angiogenic factors and angiogenesis was investigated. FTMT is an iron-sequestering protein primarily expressed in metabolically active cells and tissues with high oxygen demand, including retina. In this study, we utilized the human retinal pigment epithelial cell line ARPE-19, both as undifferentiated and differentiated cells. The effects of proinflammatory cytokines, FTMT knockdown, and transient and stable overexpression of FTMT were investigated on expression of pro-angiogenic vascular endothelial growth factor (VEGF) and anti-angiogenic pigment epithelial-derived factor (PEDF). Proinflammatory cytokines induced FTMT and VEGF expression, while NF-κB inhibition significantly reduced FTMT expression. VEGF protein and mRNA expression were significantly increased in FTMT-silenced ARPE-19 cells. Using an in vitro angiogenesis assay with endothelial cells, we showed that conditioned media from FTMT-overexpressing cells had significant antiangiogenic effects. Collectively, our findings indicate that increased levels of FTMT inhibit angiogenesis, possibly by reducing levels of VEGF and increasing PEDF expression. The cellular models developed can be used to investigate if increased FTMT may be protective in angiogenic diseases, such as AMD.

The significance, trafficking and determination of labile iron in cytosol, mitochondria and lysosomes

The labile iron pool (LIP) is a pool of chelatable and redox-active iron, not only essential for a wide variety of metabolic process, but also as a catalyst in the Fenton reaction, causing the release of hazardous reactive oxygen species (ROS) with potential for inducing oxidative stress and cell damage. The cellular LIP represents the entirety of every heterogenous sub-pool of iron, not only present in the cytosol, but also in mitochondria, lysosomes and the nucleus, which have all been detected and characterized by various fluorescent methods. Accumulated evidence indicates that alterations in the intracellular LIP can substantially contribute to a variety of injurious processes and initiate pathological development. Herein, we present our understanding of the role of the cellular LIP. To fully review the LIP, firstly, the significance of cellular labile iron in different subcellular compartments is presented. And then, the trafficking processes of cellular labile iron between/in cytosol, mitochondria and lysosomes are discussed in detail. Then, the recent progress in uncovering and assessing the cellular LIP by fluorescent methods have been noted. Overall, this summary may help to comprehensively envision the important physiological and pathological roles of the LIP and shed light on profiling the LIP in a real-time and nondestructive manner with fluorescent methods. Undoubtedly, with the advent and development of iron biology, a better understanding of iron, especially the LIP, may also enhance treatments for iron-related diseases.

Identification of multiple ferritin genes in Macrobrachium nipponense and their involvement in redox homeostasis and innate immunity

Based on the transcriptome database, we screened out four ferritin subunit genes (MnFer2-5) from the oriental river prawn Macrobrachium nipponense, which encode two non-secretory and two secretory peptides. MnFer2 and 4 possess a strictly conserved ferroxidase site, and MnFer3 has a non-typical ferroxidase site. MnFer5 seems to be a number of ferritin families, which has a distinct dinuclear metal binding motif, but lacks an iron ion channel, a ferroxidase site and a nucleation site. Diverse tissue-specific transcriptions of the four genes indicate their functional diversity in the prawn. Among them, MnFer2 is mainly expressed in hepatopancreas and intestines, MnFer3 and 4 are predominantly expressed in gills, and MnFer5 is widely expressed in various tissues with high presence in intestines, hepatopancreas and haemocytes. The transcription of all the four MnFer genes can be strongly induced by doxorubicin, indicating the involvement of these ferritin subunits in protection from oxidative stress. Upon Aeromonas hydrophila infection, only MnFer5 is persistently up-regulated, while other subunits including MnFer2-4 are down-regulated during the early stage, followed by recovery and even a slight increase at 48 h post bacterial challenge. Moreover, the iron binding capacity of recombinant MnFer2 is also demonstrated in vitro. The E. coli expressing MnFer2 displays increased resistance to hydrogen peroxidase cytotoxicity. These results suggest a protective role of ferritins from M. nipponense in iron homeostasis, redox biology and antibacterial immunity and shed light on the molecule evolution of crustacean ferritin subunits.

The Role of Iron in Friedreich's Ataxia: Insights From Studies in Human Tissues and Cellular and Animal Models

Friedreich's ataxia (FRDA) is a rare early-onset degenerative disease that affects both the central and peripheral nervous systems, and other extraneural tissues, mainly the heart and endocrine pancreas. This disorder progresses as a mixed sensory and cerebellar ataxia, primarily disturbing the proprioceptive pathways in the spinal cord, peripheral nerves and nuclei of the cerebellum. FRDA is an inherited disease with an autosomal recessive pattern caused by an insufficient amount of the nuclear-encoded mitochondrial protein frataxin, which is an essential and highly evolutionary conserved protein whose deficit results in iron metabolism dysregulation and mitochondrial dysfunction. The first experimental evidence connecting frataxin with iron homeostasis came from Saccharomyces cerevisiae; iron accumulates in the mitochondria of yeast with deletion of the frataxin ortholog gene. This finding was soon linked to previous observations of iron deposits in the hearts of FRDA patients and was later reported in animal models of the disease. Despite advances made in the understanding of FRDA pathophysiology, the role of iron in this disease has not yet been completely clarified. Some of the questions still unresolved include the molecular mechanisms responsible for the iron accumulation and iron-mediated toxicity. Here, we review the contribution of the cellular and animal models of FRDA and relevance of the studies using FRDA patient samples to gain knowledge about these issues. Mechanisms of mitochondrial iron overload are discussed considering the potential roles of frataxin in the major mitochondrial metabolic pathways that use iron. We also analyzed the effect of iron toxicity on neuronal degeneration in FRDA by reactive oxygen species (ROS)-dependent and ROS-independent mechanisms. Finally, therapeutic strategies based on the control of iron toxicity are considered.

Mitochondrial Ferritin Is a Hypoxia-Inducible Factor 1α-Inducible Gene That Protects from Hypoxia-Induced Cell Death in Brain

Aims: Mitochondrial ferritin (protein [FtMt]) is preferentially expressed in cell types of high metabolic activity and oxygen consumption, which is consistent with its role of sequestering iron and preventing oxygen-derived redox damage. As of yet, the mechanisms of FtMt regulation and the protection FtMt affords remain largely unknown. Results: Here, we report that hypoxia-inducible factor 1α (HIF-1α) can upregulate FtMt expression. We verify one functional hypoxia-response element (HRE) in the positive regulatory region and two HREs possessing HIF-1α binding activity in the minimal promoter region of the human FTMT gene. We also demonstrate that FtMt can alleviate hypoxia-induced brain cell death by sequestering uncommitted iron, whose levels increase with hypoxia in these cells. Innovation: In the absence of FtMt, this catalytic metal excess catalyzes the production of cytotoxic reactive oxygen species. Conclusion: Thus, the cell ability to increase expression of FtMt during hypoxia may be a skill to avoid tissue damage derived from oxygen limitation.

Role of frataxin protein deficiency and metabolic dysfunction in Friedreich ataxia, an autosomal recessive mitochondrial disease

Friedreich ataxia (FRDA) is a progressive neurodegenerative disease with developmental features caused by a genetic deficiency of frataxin, a small, nuclear-encoded mitochondrial protein. Frataxin deficiency leads to impairment of iron–sulphur cluster synthesis, and consequently, ATP production abnormalities. Based on the involvement of such processes in FRDA, initial pathophysiological hypotheses focused on reactive oxygen species (ROS) production as a key component of the mechanism. With further study, a variety of other events appear to be involved, including abnormalities of mitochondrially related metabolism and dysfunction in mitochondrial biogenesis. Consequently, present therapies focus not only on free radical damage, but also on control of metabolic abnormalities and correction of mitochondrial biogenesis. Understanding the multitude of abnormalities in FRDA thus offers possibilities for treatment of this disorder.

Pathological Roles of Iron in Cardiovascular Disease

Iron is an essential mineral required for a variety of vital biological functions. Despite being vital for life, iron also has potentially toxic aspects. Iron has been investigated as a risk factor for coronary artery disease (CAD), however, iron's toxicity in CAD patients still remains controversial. One possible mechanism behind the toxicity of iron is "ferroptosis", a newly described form of irondependent cell death. Ferroptosis is an iron-dependent form of regulated cell death that is distinct from apoptosis, necroptosis, and other types of cell death. Ferroptosis has been reported in ischemiareperfusion (I/R) injury and several other diseases. Recently, we reported that ferroptosis is a significant form of cell death in cardiomyocytes. Moreover, myocardial hemorrhage, a major event in the pathogenesis of heart failure, could trigger the release of free iron into cardiac muscle and is an independent predictor of adverse left ventricular remodeling after myocardial infarction. Iron deposition in the heart can now be detected with advanced imaging methods, such as T2 star (T2*) cardiac magnetic resonance imaging, which can non-invasively predict iron levels in the myocardium and detect myocardial hemorrhage, thus existing technology could be used to assess myocardial iron. We will discuss the role of iron in cardiovascular diseases and especially with regard to myocardial I/R injury.

Iron metabolism in erythroid cells and patients with congenital sideroblastic anemia

Sideroblastic anemias are anemic disorders characterized by the presence of ring sideroblasts in a patient's bone marrow. These disorders are typically divided into two types, congenital or acquired sideroblastic anemia. Recently, several genes were reported as responsible for congenital sideroblastic anemia; however, the relationship between the function of the gene products and ring sideroblasts is largely unclear. In this review article, we will focus on the iron metabolism in erythroid cells as well as in patients with congenital sideroblastic anemia.

Lack of mitochondrial ferritin aggravated neurological deficits via enhancing oxidative stress in a traumatic brain injury murine model

Oxidative stress has been strongly implicated in the pathogenesis of traumatic brain injury (TBI). Mitochondrial ferritin (Ftmt) is reported to be closely related to oxidative stress. However, whether Ftmt is involved in TBI-induced oxidative stress and neurological deficits remains unknown. In the present study, the controlled cortical impact model was established in wild-type and Ftmt knockout mice as a TBI model. The Ftmt expression, oxidative stress, neurological deficits, and brain injury were measured. We found that Ftmt expression was gradually decreased from 3 to 14 days post-TBI, while oxidative stress was gradually increased, as evidenced by reduced GSH and superoxide dismutase levels and elevated malondialdehyde and nitric oxide levels. Interestingly, the extent of reduced Ftmt expression in the brain was linearly correlated with oxidative stress. Knockout of Ftmt significantly exacerbated TBI-induced oxidative stress, intracerebral hemorrhage, brain infarction, edema, neurological severity score, memory impairment, and neurological deficits. However, all these effects in Ftmt knockout mice were markedly mitigated by pharmacological inhibition of oxidative stress using an antioxidant, N-acetylcysteine. Taken together, these results reveal an important correlation between Ftmt and oxidative stress after TBI. Ftmt deficiency aggravates TBI-induced brain injuries and neurological deficits, which at least partially through increasing oxidative stress levels. Our data suggest that Ftmt may be a promising molecular target for the treatment of TBI.

Mitochondrial Ferritin Protects Hydrogen Peroxide-Induced Neuronal Cell Damage

Oxidative stress and iron accumulation are tightly associated with neurodegenerative diseases. Mitochondrial ferritin (FtMt) is identified as an iron-storage protein located in the mitochondria, and its role in regulation of iron hemeostasis in neurodegenerative diseases has been reported. However, the role of FtMt in hydrogen peroxide (H₂O₂)-induced oxidative stress and iron accumulation in neuronal cells has not been studied. Here, we overexpressed FtMt in neuroblastoma SH-SY5Y cells and induced oxidative stress by treating with extracellular H₂O₂. We found that overexpression of FtMt significantly prevented cell death induced by H₂O₂, particularly the apoptosis-dependent cell death. The protective effects involved inhibiting the generation of cellular reactive oxygen species, sustaining mitochondrial membrane potential, maintaining the level of anti-apoptotic protein Bcl-2, and inhibiting the activation of pro-apoptotic protein caspase 3. We further explored the mechanism of these protective effects and found that FtMt expression markedly altered iron homeostasis of the H₂O₂ treated cells as compared to that of controls. The FtMt overexpression significantly reduced cellular labile iron pool (LIP) and protected H₂O₂-induced elevation on LIP. While in H₂O₂ treated SH-SY5Y cells, the increased iron uptake and reduced iron release, in correlation with levels of DMT1(-IRE) and ferroportin 1, resulted in heavy iron accumulation, the FtMt overexpressing cells didn’t show any significant changes in levels of iron transport proteins and in the level of LIP. These results implicate a neuroprotective role of FtMt on H₂O₂-induced oxidative stress, which may provide insights into the treatment of iron accumulation associated neurodegenerative diseases.

Drosophila melanogaster Models of Metal-Related Human Diseases and Metal Toxicity

Iron, copper and zinc are transition metals essential for life because they are required in a multitude of biological processes. Organisms have evolved to acquire metals from nutrition and to maintain adequate levels of each metal to avoid damaging effects associated with its deficiency, excess or misplacement. Interestingly, the main components of metal homeostatic pathways are conserved, with many orthologues of the human metal-related genes having been identified and characterized in Drosophila melanogaster. Drosophila has gained appreciation as a useful model for studying human diseases, including those caused by mutations in pathways controlling cellular metal homeostasis. Flies have many advantages in the laboratory, such as a short life cycle, easy handling and inexpensive maintenance. Furthermore, they can be raised in a large number. In addition, flies are greatly appreciated because they offer a considerable number of genetic tools to address some of the unresolved questions concerning disease pathology, which in turn could contribute to our understanding of the metal metabolism and homeostasis. This review recapitulates the metabolism of the principal transition metals, namely iron, zinc and copper, in Drosophila and the utility of this organism as an experimental model to explore the role of metal dyshomeostasis in different human diseases. Finally, a summary of the contribution of Drosophila as a model for testing metal toxicity is provided.

Molecular regulation of cellular iron balance

Handling a life-supporting yet redox-active metal like iron represents a significant challenge to cells and organisms that must not only tightly balance intra- and extracellular iron concentrations but also chaperone it during its journey from its point of entry to final destinations, to prevent inappropriate generation of damaging reactive oxygen species. Accordingly, regulatory mechanisms have been developed to maintain appropriate cellular and body iron levels. In intracellular compartments, about 95% of iron is protein-bound and the expression of the major proteins of iron metabolism is controlled by an integrated and dynamic system involving multilayered levels of regulation. However, dysregulation of iron homeostasis, which could result from both iron-related and unrelated effectors, may occur and have important pathological consequences in a number of human disorders. In this review, we describe the current understanding of the mechanisms that keep cellular iron balance and outline recent advances that increased our knowledge of the molecular physiology of iron metabolism. © 2017 IUBMB Life, 69(6):389-398, 2017.

Characterization of a Novel Monoclonal Antibody against Human Mitochondrial Ferritin and Its Immunohistochemical Application in Human and Monkey Substantia Nigra

Mitochondrial ferritin (FtMt) is a novel iron storage protein with high homology to H-ferritin. Unlike the ubiquitously expressed H- and L-ferritin, FtMt is expressed in specific tissues such as the testis, heart, and brain. The function of FtMt is not fully understood; however, evidence suggests that it has a neuroprotective role in neurodegenerative diseases. We have previously reported that FtMt is expressed in catecholaminergic neurons of the monkey brainstem. To explore FtMt expression in human dopaminergic neurons, we designed a novel monoclonal antibody, C65-2, directed against human FtMt. Here, we report the properties of our C65-2 antibody. Western blots analysis and immunoabsorption tests demonstrated that the C65-2 antibody specifically recognized FtMt with no cross-reactivity to H-ferritin. Immunohistochemistry showed that the C65-2 antibody detected FtMt in neurons of the substantia nigra pars compacta (SNc) in humans and monkeys. We confirmed that FtMt is expressed in dopaminergic neurons of the human SNc. Our results suggest that FtMt is involved in various physiological and pathological mechanisms in human dopaminergic neurons, and the C65-2 monoclonal antibody promises to be a useful tool for determining the localization and biological functions of FtMt in the brain.