Ferroptosis and cell death mechanisms in Parkinson's disease

Hepcidin and its therapeutic potential in neurodegenerative disorders

Abnormally high brain iron, resulting from the disrupted expression or function of proteins involved in iron metabolism in the brain, is an initial cause of neuronal death in neuroferritinopathy and aceruloplasminemia, and also plays a causative role in at least some of the other neurodegenerative diseases including Alzheimer's disease, Parkinson's disease, Huntington's disease, and Friedreich's ataxia. As such, iron is believed to be a novel target for pharmacological intervention in these disorders. Reducing iron toward normal levels or hampering the increases in iron associated with age in the brain is a promising therapeutic strategy for all iron-related neurodegenerative disorders. Hepcidin is a crucial regulator of iron homeostasis in the brain. Recent studies have suggested that upregulating brain hepcidin levels can significantly reduce brain iron content through the regulation of iron transport protein expression in the blood-brain barrier and in neurons and astrocytes. In this review, we focus on the discussion of the therapeutic potential of hepcidin in iron-associated neurodegenerative diseases and also provide a systematic overview of recent research progress on how misregulated brain iron metabolism is involved in the development of multiple neurodegenerative disorders.

Neuropathology and pathogenesis of extrapyramidal movement disorders: a critical update-I. Hypokinetic-rigid movement disorders

Extrapyramidal movement disorders include hypokinetic rigid and hyperkinetic or mixed forms, most of them originating from dysfunction of the basal ganglia (BG) and their information circuits. The functional anatomy of the BG, the cortico-BG-thalamocortical, and BG-cerebellar circuit connections are briefly reviewed. Pathophysiologic classification of extrapyramidal movement disorder mechanisms distinguish (1) parkinsonian syndromes, (2) chorea and related syndromes, (3) dystonias, (4) myoclonic syndromes, (5) ballism, (6) tics, and (7) tremor syndromes. Recent genetic and molecular-biologic classifications distinguish (1) synucleinopathies (Parkinson's disease, dementia with Lewy bodies, Parkinson's disease-dementia, and multiple system atrophy); (2) tauopathies (progressive supranuclear palsy, corticobasal degeneration, FTLD-17; Guamian Parkinson-dementia; Pick's disease, and others); (3) polyglutamine disorders (Huntington's disease and related disorders); (4) pantothenate kinase-associated neurodegeneration; (5) Wilson's disease; and (6) other hereditary neurodegenerations without hitherto detected genetic or specific markers. The diversity of phenotypes is related to the deposition of pathologic proteins in distinct cell populations, causing neurodegeneration due to genetic and environmental factors, but there is frequent overlap between various disorders. Their etiopathogenesis is still poorly understood, but is suggested to result from an interaction between genetic and environmental factors. Multiple etiologies and noxious factors (protein mishandling, mitochondrial dysfunction, oxidative stress, excitotoxicity, energy failure, and chronic neuroinflammation) are more likely than a single factor. Current clinical consensus criteria have increased the diagnostic accuracy of most neurodegenerative movement disorders, but for their definite diagnosis, histopathological confirmation is required. We present a timely overview of the neuropathology and pathogenesis of the major extrapyramidal movement disorders in two parts, the first one dedicated to hypokinetic-rigid forms and the second to hyperkinetic disorders.

Ferroptosis - An iron- and disorder-dependent programmed cell death

Programmed cell death (PCD) is an integral component of both developmental and pathological features of an organism. Recently, ferroptosis, a new form of PCD that is dependent on reactive oxygen species and iron, has been described. As with apoptosis, necroptosis, and autophagy, ferroptosis is associated with a large set of proteins assembled in protein-protein interaction (PPI) networks, interactability of which is driven by the presence of intrinsically disordered proteins (IDPs) and IDP regions (IDPRs). Previous investigations have identified the prevalence and functionality of IDPs/IDPRs in non-ferroptosis PCD. The intrinsic disorder in protein structures is used to increase the regulatory powers of these processes. As uncontrolled PCD is associated with the onset of various pathological traits, uncovering the association between intrinsic disorder and ferroptosis-related proteins is crucial. To understand this association, 31 human ferroptosis-related proteins were analyzed via a multi-dimensional array of bioinformatics and computational techniques. In addition, a disorder meta-predictor (PONDR® FIT) was implored to look at the evolutionary conservation of intrinsic disorder in these proteins. This study presents evidence that IDPs and IDPRs are prevalent in ferroptosis. The intrinsic disorder found in ferroptosis has far-reaching functional implications related to ferroptosis-related PPIs and molecular interactions.

Iron and oxidizing species in oxidative stress and Alzheimer's disease

Iron species can participate in the Fenton or Fenton-like reaction to generate oxidizing species that can cause oxidative damages to biomolecules and induce oxidative stress in the body. Furthermore, iron accumulation and oxidative stress have been shown to associate with the pathological progression of neurodegenerative disorders, including Alzheimer's disease (AD) and Parkinson's disease (PD). In this review, the role of iron species in generating the most deleterious free radical species (ie, hydroxyl radical) and effects of this species in causing oxidative stress in vivo are described. The implications of oxidative stress and the recently recognized cell death pathway (ie, ferroptosis) to AD are addressed. Strategies to combat this neurodegenerative disease, such as iron chelation and antioxidant therapies, and future research directions on this aspect are also discussed.

GPX4 at the Crossroads of Lipid Homeostasis and Ferroptosis

Oxygen is necessary for aerobic metabolism but can cause the harmful oxidation of lipids and other macromolecules. Oxidation of cholesterol and phospholipids containing polyunsaturated fatty acyl chains can lead to lipid peroxidation, membrane damage, and cell death. Lipid hydroperoxides are key intermediates in the process of lipid peroxidation. The lipid hydroperoxidase glutathione peroxidase 4 (GPX4) converts lipid hydroperoxides to lipid alcohols, and this process prevents the iron (Fe²⁺ )-dependent formation of toxic lipid reactive oxygen species (ROS). Inhibition of GPX4 function leads to lipid peroxidation and can result in the induction of ferroptosis, an iron-dependent, non-apoptotic form of cell death. This review describes the formation of reactive lipid species, the function of GPX4 in preventing oxidative lipid damage, and the link between GPX4 dysfunction, lipid oxidation, and the induction of ferroptosis.

Beta-propeller protein-associated neurodegeneration (BPAN) as a genetically simple model of multifaceted neuropathology resulting from defects in autophagy

Autophagy is an essential and conserved cellular homeostatic process. Defects in the core and accessory components of the autophagic machinery would most severely impact terminally differentiated cells, such as neurons. The neurodevelopmental/neurodegenerative disorder β-propeller protein-associated neurodegeneration (BPAN) resulted from heterozygous or hemizygous germline mutations/pathogenic variant of the X chromosome geneWDR45, encoding WD40 repeat protein interacting with phosphoinositides 4 (WIPI4). This most recently identified subtype of the spectrum of neurodegeneration with brain iron accumulation diseases is characterized by a biphasic mode of disease manifestation and progression. The first phase involves early-onset of epileptic seizures, global developmental delay, intellectual disability and autistic syndrome. Subsequently, Parkinsonism and dystonia, as well as dementia, emerge in a subacute manner in adolescence or early adulthood. BPAN disease phenotypes are thus complex and linked to a wide range of other neuropathological disorders. WIPI4/WDR45 has an essential role in autophagy, acting as a phosphatidylinositol 3-phosphate binding effector that participates in autophagosome biogenesis and size control. Here, we discuss recent updates on WIPI4’s mechanistic role in autophagy and link the neuropathological manifestations of BPAN’s biphasic infantile onset (epilepsy, autism) and adolescent onset (dystonic, Parkinsonism, dementia) phenotypes to neurological consequences of autophagy impairment that are now known or emerging in many other neurodevelopmental and neurodegenerative disorders. As monogenicWDR45mutations in BPAN result in a large spectrum of disease phenotypes that stem from autophagic dysfunctions, it could potentially serve as a simple and unique genetic model to investigate disease pathology and therapeutics for a wider range of neuropathological conditions with autophagy defects.

A GPX4-dependent cancer cell state underlies the clear-cell morphology and confers sensitivity to ferroptosis

Clear-cell carcinomas (CCCs) are a histological group of highly aggressive malignancies commonly originating in the kidney and ovary. CCCs are distinguished by aberrant lipid and glycogen accumulation and are refractory to a broad range of anti-cancer therapies. Here we identify an intrinsic vulnerability to ferroptosis associated with the unique metabolic state in CCCs. This vulnerability transcends lineage and genetic landscape, and can be exploited by inhibiting glutathione peroxidase 4 (GPX4) with small-molecules. Using CRISPR screening and lipidomic profiling, we identify the hypoxia-inducible factor (HIF) pathway as a driver of this vulnerability. In renal CCCs, HIF-2α selectively enriches polyunsaturated lipids, the rate-limiting substrates for lipid peroxidation, by activating the expression of hypoxia-inducible, lipid droplet-associated protein (HILPDA). Our study suggests targeting GPX4 as a therapeutic opportunity in CCCs, and highlights that therapeutic approaches can be identified on the basis of cell states manifested by morphological and metabolic features in hard-to-treat cancers.

Iron and manganese-related CNS toxicity: mechanisms, diagnosis and treatment

INTRODUCTION

Iron (Fe) and manganese (Mn) are essential nutrients for humans. They act as cofactors for a variety of enzymes. In the central nervous system (CNS), these two metals are involved in diverse neurological activities. Dyshomeostasis may interfere with the critical enzymatic activities, hence altering the neurophysiological status and resulting in neurological diseases. Areas covered: In this review, the authors cover the molecular mechanisms of Fe/Mn-induced toxicity and neurological diseases, as well as the diagnosis and potential treatment. Given that both Fe and Mn are abundant in the earth crust, nutritional deficiency is rare. In this review the authors focus on the neurological disorders associated with Mn and Fe overload. Expert commentary: Oxidative stress and mitochondrial dysfunction are the primary molecular mechanism that mediates Fe/Mn-induced neurotoxicity. Although increased Fe or Mn concentrations have been found in brain of patients, it remains controversial whether the elevated metal amounts are the primary cause or secondary consequence of neurological diseases. Currently, treatments are far from satisfactory, although chelation therapy can significantly decrease brain Fe and Mn levels. Studies to determine the primary cause and establish the molecular mechanism of toxicity may help to adapt more comprehensive and satisfactory treatments in the future.

Striking while the iron is hot: Iron metabolism and ferroptosis in neurodegeneration

Perturbations in iron homeostasis and iron accumulation feature in several neurodegenerative disorders including Alzheimer's disease (AD), Parkinson's disease (PD) and Amyotrophic lateral sclerosis (ALS). Proteins such as α-synuclein, tau and amyloid precursor protein that are pathologically associated with neurodegeneration are involved in molecular crosstalk with iron homeostatic proteins. Quantitative susceptibility mapping, an MRI based non-invasive technique, offers proximal evaluations of iron load in regions of the brain and powerfully predicts cognitive decline. Further, small molecules that target elevated iron have shown promise against PD and AD in preclinical studies and clinical trials. Despite these strong links between altered iron homeostasis and neurodegeneration the molecular biology to describe the association between enhanced iron levels and neuron death, synaptic impairment and cognitive decline is ill defined. In this review we discuss the current understanding of brain iron homeostasis and how it may be perturbed under pathological conditions. Further, we explore the ramifications of a novel cell death pathway called ferroptosis that has provided a fresh impetus to the "metal hypothesis" of neurodegeneration. While lipid peroxidation plays a central role in the execution of this cell death modality the removal of iron through chelation or genetic modifications appears to extinguish the ferroptotic pathway. Conversely, tissues that harbour elevated iron may be predisposed to ferroptotic damage. These emerging findings are of relevance to neurodegeneration where ferroptotic signalling may offer new targets to mitigate cell death and dysfunction.

The development of the concept of ferroptosis

The term ferroptosis was coined in 2012 to describe an iron-dependent regulated form of cell death caused by the accumulation of lipid-based reactive oxygen species; this type of cell death was found to have molecular characteristics distinct from other forms of regulated cell death. Features of ferroptosis have been observed periodically over the last several decades, but these molecular features were not recognized as evidence of a distinct form of cell death until recently. Here, we describe the history of observations consistent with the current definition of ferroptosis, as well as the advances that contributed to the emergence of the concept of ferroptosis. We also discuss recent implications and applications of manipulations of the ferroptotic death pathway.

Circadian control of BDNF-mediated Nrf2 activation in astrocytes protects dopaminergic neurons from ferroptosis

Astrocyte-neuron interactions protect neurons from iron-mediated toxicity. As dopamine can be metabolized to reactive quinones, dopaminergic neurons are susceptible to oxidative damage and ferroptosis-like induced cell death. Detoxification enzymes are required to protect neurons. Brain-derived neurotrophic factor (BDNF) plays a key role in the regulation of redox sensitive transcription factor Nrf2 in astrocytes and metabolic cooperation between astrocytes and neurons. This article reviews the importance of BDNF and astrocyte-neuron interactions in the protection of neurons against oxidative damages in rodent brains. We previously proposed that BDNF activates Nrf2 via the truncated TrkB.T1 and p75^NTR receptor complex in astrocytes. Stimulation by BDNF generates the signaling molecule ceramide, which activates PKCζ leading to induction of the CK2-Nrf2 signaling axis. As a cell clock regulates p75^NTR expression, we suggested that BDNF effectively activates Nrf2 in astrocytes during the rest phase. In contrast, neurons express both TrkB.FL and TrkB.T1, and TrkB.FL tyrosine kinase activity inhibits p75^NTR-dependent ceramide generation and internalizes p75^NTR. Therefore, BDNF may not effectively activate Nrf2 in neurons. Notably, neurons only weakly activate detoxification and antioxidant enzymes/proteins via the Nrf2-ARE signaling axis. Thus, astrocytes may provide relevant transcripts and/or proteins to neurons via microparticles/exosomes increasing neuronal resistance to oxidative stress. Circadian increases in the levels of circulating glucocorticoids may further facilitate material transfer from astrocytes to neurons via the stimulation of pannexin 1 channels-P2X7R signaling pathway in astrocytes at the beginning of the active phase. Dysregulation of astrocyte-neuron interactions could therefore contribute to the pathogenesis of neurodegenerative diseases including Parkinson's disease.

The pathological features of regulated necrosis

Necrosis of a cell is defined by the loss of its plasma membrane integrity. Morphologically, necrosis occurs in several forms such as coagulative necrosis, colliquative necrosis, caseating necrosis, fibrinoid necrosis, and others. Biochemically, necrosis was demonstrated to represent a number of genetically determined signalling pathways. These include (i) kinase-mediated necroptosis, which depends on receptor interacting protein kinase 3 (RIPK3)-mediated phosphorylation of the pseudokinase mixed lineage kinase domain like (MLKL); (ii) gasdermin-mediated necrosis downstream of inflammasomes, also referred to as pyroptosis; and (iii) an iron-catalysed mechanism of highly specific lipid peroxidation named ferroptosis. Given the molecular understanding of the nature of these pathways, specific antibodies may allow direct detection of regulated necrosis and correlation with morphological features. Necroptosis can be specifically detected by immunohistochemistry and immunofluorescence employing antibodies to phosphorylated MLKL. Likewise, it is possible to generate cleavage-specific antibodies against epitopes in gasdermin protein family members. In ferroptosis, however, specific detection requires quantification of oxidative lipids by mass spectrometry (oxylipidomics). Together with classical cell death markers, such as TUNEL staining and detection of cleaved caspase-3 in apoptotic cells, the extension of the arsenal of necrosis markers will allow pathological detection of specific molecular pathways rather than isolated morphological descriptions. These novel pieces of information will be extraordinarily helpful for clinicians as inhibitors of necroptosis (necrostatins), ferroptosis (ferrostatins), and inflammasomes have emerged in clinical trials. Anatomical pathologists should embrace these novel ancillary tests and the concepts behind them and test their impact on diagnostic precision, prognostication, and the prediction of response to the upcoming anti-necrotic therapies. Copyright © 2019 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Deferoxamine promotes recovery of traumatic spinal cord injury by inhibiting ferroptosis

Ferroptosis is an iron-dependent novel cell death pathway. Deferoxamine, a ferroptosis inhibitor, has been reported to promote spinal cord injury repair. It has yet to be clarified whether ferroptosis inhibition represents the mechanism of action of Deferoxamine on spinal cord injury recovery. A rat model of Deferoxamine at thoracic 10 segment was established using a modified Allen's method. Ninety 8-week-old female Wistar rats were used. Rats in the Deferoxamine group were intraperitoneally injected with 100 mg/kg Deferoxamine 30 minutes before injury. Simultaneously, the Sham and Deferoxamine groups served as controls. Drug administration was conducted for 7 consecutive days. The results were as follows: (1) Electron microscopy revealed shrunken mitochondria in the spinal cord injury group. (2) The Basso, Beattie and Bresnahan locomotor rating score showed that recovery of the hindlimb was remarkably better in the Deferoxamine group than in the spinal cord injury group. (3) The iron concentration was lower in the Deferoxamine group than in the spinal cord injury group after injury. (4) Western blot assay revealed that, compared with the spinal cord injury group, GPX4, xCT, and glutathione expression was markedly increased in the Deferoxamine group. (5) Real-time polymerase chain reaction revealed that, compared with the Deferoxamine group, mRNA levels of ferroptosis-related genes Acyl-CoA synthetase family member 2 (ACSF2) and iron-responsive element-binding protein 2 (IREB2) were up-regulated in the Deferoxamine group. (6) Deferoxamine increased survival of neurons and inhibited gliosis. These findings confirm that Deferoxamine can repair spinal cord injury by inhibiting ferroptosis. Targeting ferroptosis is therefore a promising therapeutic approach for spinal cord injury.

Transcriptomic responses to low temperature stress in the Nile tilapia, Oreochromis niloticus

The Nile tilapia, Oreochromis niloticus, is a species of high economic value and extensively cultured. The limited stress tolerance of this species to a low temperature usually leads to mass mortality and great loss. Nevertheless, there is limited information on the molecular mechanisms underlying the susceptibility to low temperature in the tilapia. In this study, tilapia was treated at 28 °C to a lethal temperature of 8 °C by a gradual decrement. Transcriptomic response of the immune organ, kidney, in tilapia was characterized using RNA-seq. In total, 2191 genes were annotated for significant expression, which were mainly associated with metabolism and immunity. Pathway analysis showed that immune-related pathways of phagosome and cell adhesion molecules (CAMs) pathway were significantly down-regulated under low temperature. Moreover, ferroptosis, a significantly changed pathway involved in tissue damage and acute renal failure, is reported here for the first time. The levels of serum parameters associated with kidney damage such as urea and uric acid (UA) increased significantly under low temperature. The immunofluorescence staining of the kidney showed that cell apoptosis occurred at low temperature. The results of the present study indicate that exposure to low temperature can cause kidney disfunction and down-regulate the immune-related pathway in the kidney of tilapia. This study provides new insight into the mechanism of kidney damage in fish under low temperature.

Functional Effects of a Neuromelanin Analogue on Dopaminergic Neurons in 3D Cell Culture

The substantia nigra pars compacta (SNpc) is a discrete region of the brain that exhibits a dark pigment, neuromelanin (NM), a biomaterial with unique properties and the subject of ongoing research pertaining to neurodegenerative conditions like Parkinson's disease (PD). Obtaining human tissue to isolate this pigment is costly and labor intensive, making it necessary to find alternatives to model the biochemical interaction of NM and its implications on PD. To address this limitation, we modified our established silk 3D brain tissue model to emulate key characteristics of the SNpc by using a structural analogue of NM to examine the effects of the material on dopaminergic neurons using Lund's human mesencephalon (LUHMES) cells. We utilized a sepia-melanin, squid ink, derived NM analogue (NM-sim) to chelate ferric iron, and this iron-neuromelanin precipitate (Fe-NM) was purified and characterized. We then exposed LUHMES dopaminergic cells to the NM-sim, Fe-NM-sim, and control vehicle within 3D silk protein scaffolds. The presence of both NM-sim and Fe-NM-sim in the scaffolds negatively impacted spontaneous electrical activity from the LUMES networks, as evidenced by changes in local field potential (LFP) electrophysiological recordings. Furthermore, the Fe-NM-sim precipitate generated peroxides, depleted nutrients/antioxidants, and increased protein oxidation by carbonylation in sustained (>2 weeks) 3D cultures, thereby contributing to cell dysfunction. The results suggest that this 3D tissue engineered brain-like model may provide useful readouts related to PD neuro-toxicology research.

Empowerment of 15-Lipoxygenase Catalytic Competence in Selective Oxidation of Membrane ETE-PE to Ferroptotic Death Signals, HpETE-PE

sn2-15-Hydroperoxy-eicasotetraenoyl-phosphatidylethanolamines ( sn2-15-HpETE-PE) generated by mammalian 15-lipoxygenase/phosphatidylethanolamine binding protein-1 (15-LO/PEBP1) complex is a death signal in a recently identified type of programmed cell demise, ferroptosis. How the enzymatic complex selects sn2-ETE-PE as the substrate among 1 of ∼100 total oxidizable membrane PUFA phospholipids is a central, yet unresolved question. To unearth the highly selective and specific mechanisms of catalytic competence, we used a combination of redox lipidomics, mutational and computational structural analysis to show they stem from (i) reactivity toward readily accessible hexagonally organized membrane sn2-ETE-PEs, (ii) relative preponderance of sn2-ETE-PE species vs other sn2-ETE-PLs, and (iii) allosteric modification of the enzyme in the complex with PEBP1. This emphasizes the role of enzymatic vs random stochastic free radical reactions in ferroptotic death signaling.

Reduced expression of the ferroptosis inhibitor glutathione peroxidase-4 in multiple sclerosis and experimental autoimmune encephalomyelitis

Glutathione peroxidase 4 (GPx4) is the only enzyme capable of reducing toxic lipid hydroperoxides in biological membranes to the corresponding alcohols using glutathione as the electron donor. GPx4 is the major inhibitor of ferroptosis, a non-apoptotic and iron-dependent programmed cell death pathway, which has been shown to occur in various neurological disorders with severe oxidative stress. In this study, we investigate whether GPx4 expression is altered in multiple sclerosis and its animal model experimental autoimmune encephalomyelitis (EAE). The results clearly show that mRNA expression for all three GPx4 isoforms (cytoplasmic, mitochondrial and nuclear) decline in multiple sclerosis gray matter and in the spinal cord of MOG_35-55 peptide-induced EAE. The amount of GPx4 protein is also reduced in EAE, albeit not in all cells. Neuronal GPx4 immunostaining, mostly cytoplasmic, is lower in EAE spinal cords than in control spinal cords, while oligodendrocyte GPx4 immunostaining, mainly nuclear, is unaltered. Neither control nor EAE astrocytes and microglia cells show GPx4 labeling. In addition to GPx4, two other negative modulators of ferroptosis (γ-glutamylcysteine ligase and cysteine/glutamate antiporter), which are critical to maintain physiological levels of glutathione, are diminished in EAE. The decrease in the ability to eliminate hydroperoxides was also evidenced by the accumulation of lipid peroxidation products and the reduction in the proportion of the docosahexaenoic acid in non-myelin lipids. These findings, along with presence of abnormal neuronal mitochondria morphology, which includes an irregular matrix, disrupted outer membrane and reduced/absent cristae, are consistent with the occurrence of ferroptotic damage in inflammatory demyelinating disorders.

Golgi stress mediates redox imbalance and ferroptosis in human cells

Cytotoxic activities of several Golgi-dispersing compounds including AMF-26/M-COPA, brefeldin A and golgicide A have previously been shown to induce autophagy or apoptosis. Here, we demonstrate that these Golgi disruptors also trigger ferroptosis, a non-apoptotic form of cell death characterized by iron-dependent oxidative degradation of lipids. Inhibitors of ferroptosis not only counteract cell death, but they also protect from Golgi dispersal and inhibition of protein secretion in response to several Golgi stress agents. Furthermore, the application of sublethal doses of ferroptosis-inducers such as erastin and sorafenib, low cystine growth conditions, or genetic knockdown of SLC7A11 and GPX4 all similarly protect cells from Golgi stress and lead to modulation of ACSL4, SLC7A5, SLC7A11 or GPX4 levels. Collectively, this study suggests a previously unrecognized function of the Golgi apparatus, which involves cellular redox control and prevents ferroptotic cell death.

Hamed Alborzinia et al. show that Golgi-dispersing compounds trigger iron-dependent oxidative degradation of lipids, inducing a non-apoptotic cell death called ferroptosis. This study provides insight into the role of Golgi apparatus for preventing ferroptotic cell death through its cellular redox control.

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.

The Role of NCOA4-Mediated Ferritinophagy in Health and Disease

Nuclear receptor coactivator 4 (NCOA4) is a selective cargo receptor that mediates the autophagic degradation of ferritin ("ferritinophagy"), the cytosolic iron storage complex. NCOA4-mediated ferritinophagy maintains intracellular iron homeostasis by facilitating ferritin iron storage or release according to demand. Ferritinophagy is involved in iron-dependent physiological processes such as erythropoiesis, where NCOA4 mediates ferritin iron release for mitochondrial heme synthesis. Recently, ferritinophagy has been shown to regulate ferroptosis, a newly described form of iron-dependent cell death mediated by excess lipid peroxidation. Dysregulation of iron metabolism and ferroptosis have been described in neurodegeneration, cancer, and infection, but little is known about the role of ferritinophagy in the pathogenesis of these diseases. Here, we will review the biochemical regulation of NCOA4, its contribution to physiological processes and its role in disease. Finally, we will discuss the potential of activating or inhibiting ferritinophagy and ferroptosis for therapeutic purposes.

Ferroptosis inhibitor SRS 16-86 attenuates ferroptosis and promotes functional recovery in contusion spinal cord injury

Cell death is a key issue in spinal cord secondary injury. Ferroptosis is recently discovered as an iron-dependent type of cell death that is distinct from other forms of cell death pathways such as apoptosis and necrosis. This research is aimed to investigate the role of ferroptosis in spinal cord injury (SCI) pathophysiology, and to explore the effectiveness of ferroptosis inhibitor on SCI. We examined the ferroptosis markers and the factors in a rat contusion SCI model. Seen from transmission electron microscopy (TEM) following SCI, mitochondria showed ferroptotic characteristic changes. Treatment with a ferroptosis inhibitor SRS 16-86 enhanced functional recovery after SCI through the upregulation of anti-ferroptosis factor GPX4, GSH and xCT, and the downregulation of the lipid peroxidation marker 4HNE. SRS 16-86 treatment alleviated astrogliosis and enhanced neuronal survival after SCI. The inflammatory cytokine levels (IL-1β, TNF-α and ICAM-1) were decreased significantly post SRS 16-86 treatment after SCI. These findings suggest strong correlation between ferroptosis and the secondary injury of SCI. The effectiveness of ferroptosis inhibitor SRS-16-86 on SCI repair leads to the identification of a novel therapeutic target for SCI.

Inhibition of ferroptosis attenuates tissue damage and improves long-term outcomes after traumatic brain injury in mice

AIMS

Ferroptosis, a new form of iron-dependent programmed cell death, has been shown to be involved in a range of diseases. However, the role of ferroptosis in traumatic brain injury (TBI) has yet to be elucidated. We aimed to investigate whether ferroptosis is induced after TBI and whether the inhibition of ferroptosis would protect against traumatic brain injury in a controlled cortical impact injury (CCI) mouse model.

METHODS

After establishing the TBI model in mice, we determined the biochemical and morphological changes associated with ferroptosis, including iron accumulation with Perl's staining, neuronal cell death with Fluoro-Jade B (FJB) staining, iron metabolism dysfunction with Western blotting, reactive oxygen species (ROS) accumulation with malondialdehyde (MDA) assays, and shrunken mitochondria with transmission electron microscopy. Furthermore, a specific inhibitor of ferroptosis, ferrostatin-1(fer-1), was administrated by cerebral ventricular injection after CCI. We used cresyl violet (CV) staining to assess lesion volume, along with the Morris water maze and beam walk test to evaluate long-term outcomes.

RESULTS

TBI was followed by iron accumulation, dysfunctional iron metabolism, the upregulation of ferroptosis-related genes, reduced glutathione peroxidase (GPx) activity, and the accumulation of lipid-reactive oxygen species (ROS). Three days (d) after TBI, transmission electron microscopy (TEM) confirmed that the mitochondria had shrunk a typical characteristic of ferroptosis. Importantly, the administration of Fer-1 by cerebral ventricular injection significantly reduced iron deposition and neuronal degeneration while attenuating injury lesions and improving long-term motor and cognitive function.

CONCLUSION

This study demonstrated an effective method with which to treat TBI by targeting ferroptosis.

Targeting Nrf2 to Suppress Ferroptosis and Mitochondrial Dysfunction in Neurodegeneration

Ferroptosis is a newly described form of regulated cell death, distinct from apoptosis, necroptosis and other forms of cell death. Ferroptosis is induced by disruption of glutathione synthesis or inhibition of glutathione peroxidase 4, exacerbated by iron, and prevented by radical scavengers such as ferrostatin-1, liproxstatin-1, and endogenous vitamin E. Ferroptosis terminates with mitochondrial dysfunction and toxic lipid peroxidation. Although conclusive identification of ferroptosis in vivo is challenging, several salient and very well established features of neurodegenerative diseases are consistent with ferroptosis, including lipid peroxidation, mitochondrial disruption and iron dysregulation. Accordingly, interest in the role of ferroptosis in neurodegeneration is escalating and specific evidence is rapidly emerging. One aspect that has thus far received little attention is the antioxidant transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2). This transcription factor regulates hundreds of genes, of which many are either directly or indirectly involved in modulating ferroptosis, including metabolism of glutathione, iron and lipids, and mitochondrial function. This potentially positions Nrf2 as a key deterministic component modulating the onset and outcomes of ferroptotic stress. The minimal direct evidence currently available is consistent with this and indicates that Nrf2 may be critical for protection against ferroptosis. In contrast, abundant evidence demonstrates that enhancing Nrf2 signaling is potently neuroprotective in models of neurodegeneration, although the exact mechanism by which this is achieved is unclear. Further studies are required to determine to extent to which the neuroprotective effects of Nrf2 activation involve the prevention of ferroptosis.

Cell Death Pathways: a Novel Therapeutic Approach for Neuroscientists

In the first part, the following mechanisms involved in different forms of cell death are considered, with a view to identifying potential therapeutic targets: tumour necrosis factor receptors (TNFRs) and their engagement by tumour necrosis factor-alpha (TNF-α); poly [ADP-ribose] polymerase (PARP)-1 cleavage; the apoptosis signalling kinase (ASK)-c-Jun N-terminal kinase (JNK) axis; lysosomal permeability; activation of programmed necrotic cell death; oxidative stress, caspase-3 inhibition and parthanatos; activation of inflammasomes by reactive oxygen species and the development of pyroptosis; oxidative stress, calcium dyshomeostasis and iron in the development of lysosomal-mediated necrosis and lysosomal membrane permeability; and oxidative stress, lipid peroxidation, iron dyshomeostasis and ferroptosis. In the second part, there is a consideration of the role of lethal and sub-lethal activation of these pathways in the pathogenesis and pathophysiology of neurodegenerative and neuroprogressive disorders, with particular reference to the TNF-α-TNFR signalling axis; dysregulation of ASK-1-JNK signalling; prolonged or chronic PARP-1 activation; the role of pyroptosis and chronic inflammasome activation; and the roles of lysosomal permeabilisation, necroptosis and ferroptosis. Finally, it is suggested that, in addition to targeting oxidative stress and inflammatory processes generally, neuropsychiatric disorders may respond to therapeutic targeting of TNF-α, PARP-1, the Nod-like receptor NLRP3 inflammasome and the necrosomal molecular switch receptor-interacting protein kinase-3, since their widespread activation can drive and/or exacerbate peripheral inflammation and neuroinflammation even in the absence of cell death. To this end, the use is proposed of a combination of the tetracycline derivative minocycline and N-acetylcysteine as adjunctive treatment for a range of neuropsychiatric disorders.

GPx4, Lipid Peroxidation, and Cell Death: Discoveries, Rediscoveries, and Open Issues

SIGNIFICANCE

Iron-dependent lipid peroxidation is a complex oxidative process where phospholipid hydroperoxides (PLOOH) are produced in membranes and finally transformed into a series of decomposition products, some of which are endowed with biological activity. It is specifically prevented by glutathione peroxidase 4 (GPx4), the selenoenzyme that reduces PLOOH by glutathione (GSH). PLOOH is both a product and the major initiator of peroxidative chain reactions, as well as an activator of lipoxygenases. α-Tocopherol both specifically breaks peroxidative chain propagation and inhibits lipoxygenases. Thus, GPx4, GSH, and α-tocopherol are integrated in a concerted anti-peroxidant mechanism. Recent Advances: Ferroptosis has been recently identified as a cell death subroutine that is specifically activated by missing GPx4 activity and inhibited by iron chelation or α-tocopherol supplementation. Ferroptosis induction may underlie spontaneous human diseases, such as major neurodegeneration and neuroinflammation, causing an excessive cell death. The basic mechanism of ferroptosis, therefore, fits the features of activation of lipid peroxidation.

CRITICAL ISSUES

Still lacking are convincing proofs that lipoxygenases are involved in ferroptosis. Also, unknown are the molecules eventually killing cells and the mechanisms underlying the drop of the cellular anti-peroxidant capacity.

FUTURE DIRECTIONS

Molecular events and mechanisms of ferroptosis to be unraveled and validated on animal models are GPx4 inactivation, role of GSH concentration, increased iron availability, and membrane structure and composition. This is expected to drive drug discovery that is aimed at halting cell death in degenerative diseases or boosting it in cancer cells. Antioxid. Redox Signal. 29, 61-74.

12/15 lipoxygenase: A crucial enzyme in diverse types of cell death

The 12/15-lipoxygenase (12/15-LOX) enzymes react with polyunsaturated fatty acids producing active lipid metabolites that are involved in plethora of human diseases including neurological disorders. A great many of elegant studies over the last decades have contributed to unraveling the mechanism how 12/15-lipoxygenase play a role in these diseases. And the way it works is mainly through apoptosis. However, recent years have found that the way 12/15-lipoxygenase works is also related to autophagy and ferroptosis, a newly defined type of cell death by Stockwell's lab in 2012. Figuring out how 12/15-lipoxygenase participate in these modes of cell death is of vital importance to understand its role in disease. The review aims to give a sight on our current knowledge on the role of this enzyme in apoptosis, autophagy and ferroptosis. And the relevant diseases that 12/15-lipoxygenase may be involved.

ENPP2 protects cardiomyocytes from erastin-induced ferroptosis

Ferroptosis is an iron- and oxidative-dependent form of regulated cell death and may play important roles in maintaining myocardium homeostasis and pathology of cardiovascular diseases. Currently, the regulatory roles of lipid signals in regulating cardiomyocytes ferroptosis has not been explored. In this study, we show that ENPP2, as a lipid kinase involved in lipid metabolism, protects against erastin-induced ferroptosis in cardiomyocytes. The classical ferroptosis inducer erastin remarkably inhibits the growth which could be rescued by the small molecule Fer-1 in H9c2 cells. Adenovirus mediated ENPP2 overexpression modestly promotes migration and proliferation and significantly inhibits erastin-induced ferroptosis of H9c2 cells. ENPP2 overexpression leads to increase the LPA level in supernatant of H9c2 cells. H9c2 cells express the LPAR1, LPAR3, LPAR4 and LPAR5 receptors. The supernatant of ENPP2 transduced cardiomyocytes could protects the cells from erastin-induced ferroptosis of H9c2 cells. Furthermore, we observed that ENPP2 overexpression regulates ferroptosis-associated gene GPX4, ACSL4 and NRF2 expression and modulates MAPK and AKT signal in H9c2 cells. Collectively, these findings demonstrated that ENPP2/LPA protects cardiomyocytes from erastin-induced ferroptosis through modulating GPX4, ACSL4 and NRF2 expression and enhancing AKT survival signal.

The Aging of Iron Man

Brain iron is tightly regulated by a multitude of proteins to ensure homeostasis. Iron dyshomeostasis has become a molecular signature associated with aging which is accompanied by progressive decline in cognitive processes. A common theme in neurodegenerative diseases where age is the major risk factor, iron dyshomeostasis coincides with neuroinflammation, abnormal protein aggregation, neurodegeneration, and neurobehavioral deficits. There is a great need to determine the mechanisms governing perturbations in iron metabolism, in particular to distinguish between physiological and pathological aging to generate fruitful therapeutic targets for neurodegenerative diseases. The aim of the present review is to focus on the age-related alterations in brain iron metabolism from a cellular and molecular biology perspective, alongside genetics, and neuroimaging aspects in man and rodent models, with respect to normal aging and neurodegeneration. In particular, the relationship between iron dyshomeostasis and neuroinflammation will be evaluated, as well as the effects of systemic iron overload on the brain. Based on the evidence discussed here, we suggest a synergistic use of iron-chelators and anti-inflammatories as putative anti-brain aging therapies to counteract pathological aging in neurodegenerative diseases.

Neuroprotective effect of gold nanoparticles composites in Parkinson's disease model

Parkinson's disease (PD) is second most common neurodegenerative disorder worldwide. Although drugs and surgery can relieve the symptoms of PD, these therapies are incapable of fundamentally treating the disease. For PD patients, over-expression of α-synuclein (SNCA) leads to the death of dopaminergic neurons. This process can be prevented by suppressing SNCA over-expression through RNA interference. Here, we successfully synthesized gold nanoparticles (GNP) composites (CTS@GNP-pDNA-NGF) via the combination of electrostatic adsorption and photochemical immobilization, which could load plasmid DNA (pDNA) and target specific cell types. GNP was transfected into cells via endocytosis to inhibiting the apoptosis of PC12 cells and dopaminergic neurons. Simultaneously, GNP composites are also used in PD models in vivo, and it can successfully cross the blood-brain barrier by contents of GNP in the mice brain. In general, all the works demonstrated that GNP composites have good therapeutic effects for PD models in vitro and in vivo.

O-Phenylenediamine: a privileged pharmacophore of ferrostatins for radical-trapping reactivity in blocking ferroptosis

Ferroptosis is a non-apoptotic, iron dependent form of regulated cell death that is characterized by the accumulation of lipid hydroperoxides.

Why should neuroscientists worry about iron? The emerging role of ferroptosis in the pathophysiology of neuroprogressive diseases

Ferroptosis is a unique form of programmed death, characterised by cytosolic accumulation of iron, lipid hydroperoxides and their metabolites, and effected by the fatal peroxidation of polyunsaturated fatty acids in the plasma membrane. It is a major driver of cell death in neurodegenerative neurological diseases. Moreover, cascades underpinning ferroptosis could be active drivers of neuropathology in major psychiatric disorders. Oxidative and nitrosative stress can adversely affect mechanisms and proteins governing cellular iron homeostasis, such as the iron regulatory protein/iron response element system, and can ultimately be a source of abnormally high levels of iron and a source of lethal levels of lipid membrane peroxidation. Furthermore, neuroinflammation leads to the upregulation of divalent metal transporter1 on the surface of astrocytes, microglia and neurones, making them highly sensitive to iron overload in the presence of high levels of non-transferrin-bound iron, thereby affording such levels a dominant role in respect of the induction of iron-mediated neuropathology. Mechanisms governing systemic and cellular iron homeostasis, and the related roles of ferritin and mitochondria are detailed, as are mechanisms explaining the negative regulation of ferroptosis by glutathione, glutathione peroxidase 4, the cysteine/glutamate antiporter system, heat shock protein 27 and nuclear factor erythroid 2-related factor 2. The potential role of DJ-1 inactivation in the precipitation of ferroptosis and the assessment of lipid peroxidation are described. Finally, a rational approach to therapy is considered, with a discussion on the roles of coenzyme Q₁₀, iron chelation therapy, in the form of deferiprone, deferoxamine (desferrioxamine) and deferasirox, and N-acetylcysteine.

Live or let die: Neuroprotective and anti-cancer effects of nutraceutical antioxidants

Diet sources are closely involved in the pathogenesis of diverse neuropsychiatric disorders and cancers, in addition to inherited factors. Currently, natural products or nutraceuticals (commonly called medical foods) are increasingly employed for adjunctive therapy of these patients. However, the potential molecular mechanisms of the nutrient efficacy remain elusive. In this review, we summarized the neuroprotective and anti-cancer mechanisms of nutraceuticals. It was concluded that the nutraceuticals exerted neuroprotection and suppressed tumor growth possibly through the differential modulations of redox homeostasis. In addition, the balance between reactive oxygen species (ROS) production and ROS elimination was manipulated by multiple molecular mechanisms, including cell signaling pathways, inflammation, transcriptional regulation and epigenetic modulation, which were involved in the therapeutic potential of nutraceutical antioxidants against neurological diseases and cancers. We specifically proposed that ROS scavenging was integral in the neuroprotective potential of nutraceuticals, while alternation of ROS level (either increase or decrease) or disruption of redox homeostasis (ROS addiction) constituted the anti-cancer property of these compounds. We also hypothesized that ROS-associated ferroptosis, a novel type of lipid ROS-dependent regulatory cell death, was likely to be a critical mechanism for the nutraceutical antioxidants. Targeting ferroptosis is advantageous to develop new nutraceuticals with more effective and lower adverse reactions for curing patients with neuropsychiatric diseases or carcinomas.

Subcellular compartmentalisation of copper, iron, manganese, and zinc in the Parkinson's disease brain

Elevated iron and decreased copper levels are cardinal features of the degenerating substantia nigra pars compacta in the Parkinson's disease brain. Both of these redox-active metals, and fellow transition metals manganese and zinc, are found at high concentrations within the midbrain and participate in a range of unique biological reactions. We examined the total metal content and cellular compartmentalisation of manganese, iron, copper and zinc in the degenerating substantia nigra, disease-affected but non-degenerating fusiform gyrus, and unaffected occipital cortex in the post mortem Parkinson's disease brain compared with age-matched controls. An expected increase in iron and a decrease in copper concentration was isolated to the soluble cellular fraction, encompassing both interstitial and cytosolic metals and metal-binding proteins, rather than the membrane-associated or insoluble fractions. Manganese and zinc levels did not differ between experimental groups. Altered Fe and Cu levels were unrelated to Braak pathological staging in our cases of late-stage (Braak stage V and VI) disease. The data supports our hypothesis that regional alterations in Fe and Cu, and in proteins that utilise these metals, contribute to the regional selectively of neuronal vulnerability in this disorder.

Ferroptosis: A Regulated Cell Death Nexus Linking Metabolism, Redox Biology, and Disease

Ferroptosis is a form of regulated cell death characterized by the iron-dependent accumulation of lipid hydroperoxides to lethal levels. Emerging evidence suggests that ferroptosis represents an ancient vulnerability caused by the incorporation of polyunsaturated fatty acids into cellular membranes, and cells have developed complex systems that exploit and defend against this vulnerability in different contexts. The sensitivity to ferroptosis is tightly linked to numerous biological processes, including amino acid, iron, and polyunsaturated fatty acid metabolism, and the biosynthesis of glutathione, phospholipids, NADPH, and coenzyme Q10. Ferroptosis has been implicated in the pathological cell death associated with degenerative diseases (i.e., Alzheimer's, Huntington's, and Parkinson's diseases), carcinogenesis, stroke, intracerebral hemorrhage, traumatic brain injury, ischemia-reperfusion injury, and kidney degeneration in mammals and is also implicated in heat stress in plants. Ferroptosis may also have a tumor-suppressor function that could be harnessed for cancer therapy. This Primer reviews the mechanisms underlying ferroptosis, highlights connections to other areas of biology and medicine, and recommends tools and guidelines for studying this emerging form of regulated cell death.

Therapeutic Potential of Baicalein in Alzheimer's Disease and Parkinson's Disease

Alzheimer's disease and Parkinson's disease are the two most common, progressive central neurodegenerative diseases affecting the population over the age of 60 years. Apart from treatments that temporarily improve symptoms, there is no medicine currently available to inhibit or reverse the progression of Alzheimer's disease and Parkinson's disease. In traditional Chinese medicine, the root of Scutellaria baicalensis Georgi is a classic compatible component in the decoction of herbal medicine used for treating central nervous system diseases. Modern pharmacokinetic studies have confirmed that baicalein (5,6,7-trihydroxyflavone) is a major bioactive flavone constituent root of S. baicalensis Georgi. Studies showed that baicalein possesses a range of key pharmacological properties, such as reducing oxidative stress, anti-inflammatory properties, inhibiting aggregation of disease-specific amyloid proteins, inhibiting excitotoxicity, stimulating neurogenesis and differentiation action, and anti-apoptosis effects. Based on these properties, baicalein shows therapeutic potential for Alzheimer's disease and Parkinson's disease. In this review, we summarize the pharmacological protective actions of baicalein that make it suitable for the treatment of Alzheimer's disease and Parkinson's disease, and discuss the potential mechanisms underlying the effects.

Small molecule probes for cellular death machines

The past decade has witnessed a significant expansion of our understanding about the regulated cell death mechanisms beyond apoptosis. The application of chemical biological approaches had played a major role in driving these exciting discoveries. The discovery and use of small molecule probes in cell death research has not only revealed significant insights into the regulatory mechanism of cell death but also provided new drug targets and lead drug candidates for developing therapeutics of human diseases with huge unmet need. Here, we provide an overview of small molecule modulators for necroptosis and ferroptosis, two non-apoptotic cell death mechanisms, and discuss the molecular pathways and relevant pathophysiological mechanisms revealed by the judicial applications of such small molecule probes. We suggest that the development and applications of small molecule probes for non-apoptotic cell death mechanisms provide an outstanding example showcasing the power of chemical biology in exploring novel biological mechanisms.

Nexus between mitochondrial function, iron, copper and glutathione in Parkinson's disease

Parkinson's disease is neuropathologically characterised by loss of catecholamine neurons in vulnerable brain regions including substantia nigra pars compacta and locus coeruleus. This review discusses how the susceptibility of these regions is defined by their shared biochemical characteristics that differentiate them from other neurons. Parkinson's disease is biochemically characterised by mitochondrial dysfunction, accumulation of iron, diminished copper content and depleted glutathione levels in these regions. This review also discusses this neuropathology, and provides evidence for how these pathological features are mechanistically linked to each other. This leads to the conclusion that disruption of mitochondrial function, or iron, copper or glutathione metabolism in isolation provokes the pathological impairment of them all. This creates a vicious cycle that drives pathology leading to mitochondrial failure and neuronal cell death in vulnerable brain regions.

Chromatin-Bound Oxidized α-Synuclein Causes Strand Breaks in Neuronal Genomes in in vitro Models of Parkinson's Disease

Alpha-synuclein (α-Syn) overexpression and misfolding/aggregation in degenerating dopaminergic neurons have long been implicated in Parkinson's disease (PD). The neurotoxicity of α-Syn is enhanced by iron (Fe) and other pro-oxidant metals, leading to generation of reactive oxygen species in PD brain. Although α-Syn is predominantly localized in presynaptic nerve terminals, a small fraction exists in neuronal nuclei. However, the functional and/or pathological role of nuclear α-Syn is unclear. Following up on our earlier report that α-Syn directly binds DNA in vitro, here we confirm the nuclear localization and chromatin association of α-Syn in neurons using proximity ligation and chromatin immunoprecipitation analysis. Moderate (∼2-fold) increase in α-Syn expression in neural lineage progenitor cells (NPC) derived from induced pluripotent human stem cells (iPSCs) or differentiated SHSY-5Y cells caused DNA strand breaks in the nuclear genome, which was further enhanced synergistically by Fe salts. Furthermore, α-Syn required nuclear localization for inducing genome damage as revealed by the effect of nucleus versus cytosol-specific mutants. Enhanced DNA damage by oxidized and misfolded/oligomeric α-Syn suggests that DNA nicking activity is mediated by the chemical nuclease activity of an oxidized peptide segment in the misfolded α-Syn. Consistent with this finding, a marked increase in Fe-dependent DNA breaks was observed in NPCs from a PD patient-derived iPSC line harboring triplication of the SNCA gene. Finally, α-Syn combined with Fe significantly promoted neuronal cell death. Together, these findings provide a novel molecular insight into the direct role of α-Syn in inducing neuronal genome damage, which could possibly contribute to neurodegeneration in PD.