Brain Iron Metabolism Dysfunction in Parkinson's Disease

Environmental factors in Parkinson's disease: New insights into the molecular mechanisms

Parkinson's disease is a chronic, progressive neurodegenerative disorder affecting 2-3% of the population ≥65 years. It has long been characterized by motor impairment, autonomic dysfunction, and psychological and cognitive changes. The pathological hallmarks are intracellular inclusions containing α-synuclein aggregates and the loss of dopaminergic neurons in the substantia nigra. Parkinson's disease is thought to be caused by a combination of various pathogenic factors, including genetic factors, environmental factors, and lifestyles. Although much research has focused on the genetic causes of PD, environmental risk factors also play a crucial role in the development of the disease. Here, we summarize the environmental risk factors that may increase the occurrence of PD, as well as the underlying molecular mechanisms.

[Regulatory mechanism of interferon regulatory factor 1 by α-synuclein in mouse Parkinson's disease model]

OBJECTIVE

To investigate the molecular mechanism by which α-synuclein (α-Syn) regulates interferon regulatory factor 1 (IRF-1) expression.

METHODS

SH-SY5Y cells overexpressing α-Syn and transgenic mouse model carrying human α-Syn gene with A53T mutation (3 and 6 months old) were examined for IRF-1 mRNA and protein expressions using real-time PCR and Western blotting, respectively. The subcellular localization of IRF-1 was determined with immunofluorescence staining and cytoplasmic/nuclear protein isolation. The optimal concentrations of the proteasome inhibitor MG132 (0.01-2.0 μmol/L) and lysosomal inhibitor chloroquine (5-200 μmol/L) for treatment of SH-SY5Y cells for 24 h were determined by examining the cell viability. SH-SY5Y cells were treated with 0.2 μmol/L MG132 and 30 μmol/L chloroquine for 24 h (the maximum dose that did not cause cell damage), and the changes of IRF-1 protein expressions was analyzed. The effects of α-Syn on MDM2 protein expression and IRF-1 ubiquitylation were analyzed using Western blotting and ubiquitylation assay.

RESULTS

α-Syn overexpression did not affect the mRNA level of IRF-1 but significantly increased its protein level (P < 0.01). In α-Synoverexpressing SH-SY5Y cells, IRF-1 translocation was observed from the cytoplasm to the nucleus (P < 0.001). Treatment of the cells with 0.2 μmol/L MG132 significantly aggravated α-Syn-induced increase of IRF-1 protein expression (P < 0.01) while 30 μmol/L chloroquine produced no significant changes in IRF-1 level. α-Syn overexpression caused an obvious decrease of MDM2 protein level and further inhibited the ubiquitylation of IRF-1 (P < 0.01).

CONCLUSION

α-Syn blocks MDM2-mediated ubiquitylation of IRF-1 through ubiquitin proteasome pathway, thereby enhancing IRF-1 protein expression.

Decrypting the potential role of α-lipoic acid in Alzheimer's disease

Alzheimer's disease (AD) is one of the most prevalent neurodegenerative diseases with motor disturbances, cognitive decline, and behavioral impairment. It is characterized by the extracellular aggregation of amyloid-β plaques and the intracellular accumulation of tau protein. AD patients show a cognitive decline, which has been associated with oxidative stress, as well as mitochondrial dysfunction. Alpha-lipoic acid (α-LA), a natural antioxidant present in food and used as a dietary supplement, has been considered a promising agent for the prevention or treatment of neurodegenerative disorders. Despite multiple preclinical studies indicating beneficial effects of α-LA in memory functioning, and pointing to its neuroprotective effects, to date only a few studies have examined its effects in humans. Studies performed in animal models of memory loss associated with aging and AD have shown that α-LA improves memory in a variety of behavioral paradigms. Furthermore, molecular mechanisms underlying α-LA effects have also been investigated. Accordingly, α-LA shows antioxidant, antiapoptotic, anti-inflammatory, glioprotective, metal chelating properties in both in vivo and in vitro studies. In addition, it has been shown that α-LA reverses age-associated loss of neurotransmitters and their receptors. The review article aimed at summarizing and discussing the main studies investigating the neuroprotective effects of α-LA on cognition as well as its molecular effects, to improve the understanding of the therapeutic potential of α-LA in patients suffering from neurodegenerative disorders, supporting the development of clinical trials with α-LA.

Evidence That HFE H63D Variant Is a Potential Disease Modifier in Cluster Headache

Cluster headache (CH) is a primary headache disorder with a complex genetic background. Several studies indicate a potential link between iron homeostasis and the pathophysiology of primary headaches. The HFE gene encodes for a protein involved in iron metabolism, while genetic variants in HFE have been associated with hereditary hemochromatosis (HH), an iron overload disorder. The objective of the current study was to examine the association of the more common HFE H63D variant, with the susceptibility to develop CH and diverse clinical phenotypes in a population of Southeastern European Caucasian (SEC) origin. Genomic DNA samples from 128 CH patients and 294 neurologically healthy controls were genotyped for the HFE rs1799945 (H63D) variant. H63D genotypic and allelic frequency distribution did not differ significantly between patients and controls (p > 0.05). Subgroup analysis revealed a significantly more frequent occurrence of the variant G allele in chronic compared to episodic CH patients, indicative for a possible correlation of the HFE gene with the susceptibility for disease chronification. Although homozygosity for the less prevalent H63D variant G allele was minimal in the CH cohort, the results of the present study are in accordance with previous studies in CH and migraine patients, suggesting that HFE H63D variant modifies the disease clinical characteristics. Hence, despite the absence of a per se association with CH susceptibility in the current SEC cohort, variability in HFE gene may be potentially regarded as a disease modifier genetic factor in CH.

In vivo Direct Conversion of Astrocytes to Neurons Maybe a Potential Alternative Strategy for Neurodegenerative Diseases

Partly because of extensions in lifespan, the incidence of neurodegenerative diseases is increasing, while there is no effective approach to slow or prevent neuronal degeneration. As we all know, neurons cannot self-regenerate and may not be replaced once being damaged or degenerated in human brain. Astrocytes are widely distributed in the central nervous system (CNS) and proliferate once CNS injury or neurodegeneration occur. Actually, direct reprogramming astrocytes into functional neurons has been attracting more and more attention in recent years. Human astrocytes can be successfully converted into neurons in vitro. Notably, in vivo direct reprogramming of astrocytes into functional neurons were achieved in the adult mouse and non-human primate brains. In this review, we briefly summarized in vivo direct reprogramming of astrocytes into functional neurons as regenerative strategies for CNS diseases, mainly focusing on neurodegenerative diseases such as Parkinson’s disease (PD), Alzheimer’s disease (AD), and Huntington’s disease (HD). We highlight and outline the advantages and challenges of direct neuronal reprogramming from astrocytes in vivo for future neuroregenerative medicine.

The epigenetic mechanisms involved in mitochondrial dysfunction: Implication for Parkinson's disease

Mitochondrial dysfunction is one of the crucial factors involved in PD’s pathogenicity, which emerges from a combination of genetic and environmental factors. These factors cause differential molecular expression in neurons, such as varied transcriptional regulation of genes, elevated oxidative stress, α‐synuclein aggregation and endogenous neurotoxins release, which induces epigenetic modifications and triggers energy crisis by damaging mitochondria of the dopaminergic neurons (DN). So far, these events establish a complicated relationship with underlying mechanisms of mitochondrial anomalies in PD, which has remained unclear for years and made PD diagnosis and treatment extremely difficult. Therefore, in this review, we endeavored to discuss the complex association of epigenetic modifications and other associated vital factors in mitochondrial dysfunction. We propose a hypothesis that describes a vicious cycle in which mitochondrial dysfunction and oxidative stress act as a hub for regulating DA neuron's fate in PD. Oxidative stress triggers the release of endogenous neurotoxins (CTIQs) that lead to mitochondrial dysfunction along with abnormal α‐synuclein aggregation and epigenetic modifications. These disturbances further intensify oxidative stress and mitochondrial damage, amplifying the synthesis of CTIQs and works vice versa. This vicious cycle may result in the degeneration of DN to hallmark Parkinsonism. Furthermore, we have also highlighted various endogenous compounds and epigenetic marks (neurotoxic and neuroprotective), which may help for devising future diagnostic biomarkers and target specific drugs using novel PD management strategies.

Hypoxia Signaling in Parkinson's Disease: There Is Use in Asking "What HIF?"

Hypoxia is a condition characterized by insufficient tissue oxygenation, which results in impaired oxidative energy production. A reduction in cellular oxygen levels induces the stabilization of hypoxia inducible factor α (HIF-1α), master regulator of the molecular response to hypoxia, involved in maintaining cellular homeostasis and driving hypoxic adaptation through the control of gene expression. Due to its high energy requirement, the brain is particularly vulnerable to oxygen shortage. Thus, hypoxic injury can cause significant metabolic changes in neural cell populations, which are associated with neurodegeneration. Recent evidence suggests that regulating HIF-1α may ameliorate the cellular damage in neurodegenerative diseases. Indeed, the hypoxia/HIF-1α signaling pathway has been associated to several processes linked to Parkinson's disease (PD) including gene mutations, risk factors and molecular pathways such as mitochondrial dysfunction, oxidative stress and protein degradation impairment. This review will explore the impact of hypoxia and HIF-1α signaling on these specific molecular pathways that influence PD development and will evaluate different novel neuroprotective strategies involving HIF-1α stabilization.

Succinate accumulation contributes to oxidative stress and iron accumulation in pentylenetetrazol-induced epileptogenesis and kainic acid-induced seizure

This study explored the role of succinate accumulation in the oxidative stress and iron accumulation in both pentylenetetrazol (PTZ)-induced epileptogenesis and kainic acid (KA)-induced status epilepticus (SE). The levels of succinate, oxidative stress, iron content, iron-related protein expression, and the severity of neuronal injury and seizures were measured in both models. We found that increased concentrations of succinate were associated with increased levels of oxidative stress, iron content, iron regulator protein, and iron importer divalent metal transporter 1, as well as decreased levels of iron exporter ferropotin 1. Aggravated neuronal injury was observed in the hippocampi and cortices of both models. The cell-permeable molecule dimethyl malonate (DM), a competitive inhibitor of succinate dehydrogenase (SDH), significantly attenuated succinate accumulation, reduced the oxidative stress and iron levels, and mitigated the severity of the seizures and neuronal injury. Our results thus indicate that the accumulation of succinate due to the reverse catalysis of SDH may exacerbate oxidative stress and thus induce iron accumulation and neuronal injury in both models. Targeting succinate accumulation may achieve neuroprotective and anti-seizure effects.

Mechanisms of Metal-Induced Mitochondrial Dysfunction in Neurological Disorders

Metals are actively involved in multiple catalytic physiological activities. However, metal overload may result in neurotoxicity as it increases formation of reactive oxygen species (ROS) and elevates oxidative stress in the nervous system. Mitochondria are a key target of metal-induced toxicity, given their role in energy production. As the brain consumes a large amount of energy, mitochondrial dysfunction and the subsequent decrease in levels of ATP may significantly disrupt brain function, resulting in neuronal cell death and ensuing neurological disorders. Here, we address contemporary studies on metal-induced mitochondrial dysfunction and its impact on the nervous system.

Protection of Iron-Induced Oxidative Damage in Neuroblastoma (SH-SY5Y) Cells by Combination of 1-(N-Acetyl-6-aminohexyl)-3-hydroxy-2-methylpyridin-4-one and Green Tea Extract

Iron is a crucial trace element and essential for many cellular processes; however, excessive iron accumulation can induce oxidative stress and cell damage. Neurodegenerative disorders, such as Alzheimer's disease and Parkinson's disease, have been associated with altered iron homoeostasis causing altered iron distribution and accumulation in brain tissue. This study aims to investigate the protective effect of 1-(N-acetyl-6-aminohexyl)-3-hydroxy-2-methylpyridin-4-one (CM1) in combination with green tea extract (GTE) on iron-induced oxidative stress in neuroblastoma (SH-SY5Y) cells. Cells were cultured in medium with or without ferric chloride loading. Their viability and mitochondrial activity were assessed using MTT and JC-1 staining methods. Levels of the cellular labile iron pool (LIP), reactive oxygen species (ROS), and lipid-peroxidation products were determined using calcein acetoxymethyl ester, 2',7'-dichlorohydrofluorescein diacetate, and TBARS-based assays, respectively. The viability of iron-loaded cells was found to be significantly increased after treatment with CM1 (10 µM) for 24 h. CM1 co-treatment with GTE resulted in a greater protective effect than their monotherapy. Combination of CM1 and GTE also reduced mitochondrial disruption and LIP content and ROS and TBARS production. In conclusion, the combination of CM1 and GTE exhibits protection against iron-induced oxidative stress in neuroblastoma cells.

Extracellular α-Synuclein Modulates Iron Metabolism Related Proteins via Endoplasmic Reticulum Stress in MES23.5 Dopaminergic Cells

Alpha-synuclein plays a vital role in the pathology of Parkinson's disease (PD). Spreading of α-synuclein in neighboring cells was believed to contribute to progression in PD. How α-synuclein transmission affects adjacent cells is not full elucidated. Here, we used recombinant α-synuclein to mimic intercellular transmitted α-synuclein in MES23.5 dopaminergic cells, to investigate whether and how it could modulate iron metabolism. The results showed that α-synuclein treatment up-regulated divalent metal transporter 1 (DMT1) and down-regulated iron transporter (FPN), also up-regulated iron regulatory protein 1 (IRP1) protein levels and hepcidin mRNA levels. Endocytosis inhibitor dynasore pretreatment completely abolished and even reversed the upregulation of DMT1 and IRP1 induced by α-synuclein, however, FPN down-regulation was partially blocked by dynasore. Autophagy-inducing agent rapamycin reversed DMT1 up-regulation and FPN down-regulation, and fully blocked the upregulation of IRP1. Elevated hepcidin levels induced by α-synuclein was fully blocked by dynasore pretreatment, however, even higher with rapamycin pretreatment. Alpha-synuclein treatment triggered endoplasmic reticulum (ER) stress. ER stress inducer thapsigargin induced similar responses elicited by α-synuclein. ER stress inhibitor salubrinal blocked the up-regulation of IRP1 and hepcidin, as well as DMT1 up-regulation and FPN down-regulation, also dramatically abolished cAMP-response elements binding protein phosphorylation induced by α-synuclein. Taken together, these finding indicated that extracellular α-synuclein could regulate cellular iron metabolism, probably mediated by ER stress. It provides novel evidence to elucidate the relationships between transmitted α-synuclein and iron metabolism disturbance in PD.

"Metal elements and pesticides as risk factors for Parkinson's disease - A review"

Essential metals including iron (Fe) and manganese (Mn) with known physiological functions in human body play an important role in cell homeostasis. Excessive exposure to these essential as well as non-essential metals including mercury (Hg) and Aluminum (Al) may contribute to pathological conditions, including PD. Each metal could be toxic through specific pathways. Epidemiological evidences from occupational and ecological studies besides various in vivo and in vitro studies have revealed the possible pathogenic role and neurotoxicity of different metals. Pesticides are substances that aim to mitigate the harm done by pests to plants and crops, and are extensively used to boost agricultural production. This review provides an outline of our current knowledge on the possible association between metals and PD. We have discussed the potential association between these two, furthermore the chemical properties, biological and toxicological aspects as well as possible mechanisms of Fe, Mn, Cu, Zn, Al, Ca, Pb, Hg and Zn in PD pathogenesis. In addition, we review recent evidence on deregulated microRNAs upon pesticide exposure and possible role of deregulated miRNA and pesticides to PD pathogenesis.

miR‑335 promotes ferroptosis by targeting ferritin heavy chain 1 in in vivo and in vitro models of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disease characterized by the selective loss of dopaminergic neurons in the substantia nigra (SN). In a previous study, the authors demonstrated that ferritin heavy chain 1 (FTH1) inhibited ferroptosis in a model of 6-hydroxydopamine (6-OHDA)-induced PD. However, whether and how microRNAs (miRNAs/miRs) modulate FTH1 in PD ferroptosis is not yet well understood. In the present study, in vivo and in vitro models of PD induced by 6-OHDA were established. The results in vivo and in vitro revealed that the levels of the ferroptosis marker protein, glutathione peroxidase 4 (GPX4), and the PD marker protein, tyrosine hydroxylase (TH), were decreased in the model group, associated with a decreased FTH1 expression and the upregulation of miR-335. In both the in vivo and in vitro models, miR-335 mimic led to a lower FTH1 expression, exacerbated ferroptosis and an enhanced PD pathology. The luciferase 3′-untranslated region reporter results identified FTH1 as the direct target of miR-335. The silencing of FTH1 in 6-OHDA-stimulated cells enhanced the effects of miR-335 on ferroptosis and promoted PD pathology. Mechanistically, miR-335 enhanced ferroptosis through the degradation of FTH1 to increase iron release, lipid peroxidation and reactive oxygen species (ROS) accumulation, and to decrease mitochondrial membrane potential (MMP). On the whole, the findings of the present study reveal that miR-335 promotes ferroptosis by targeting FTH1 in in vitro and in vivo models of PD, providing a potential therapeutic target for the treatment of PD.

Benefits of Iron Chelators in the Treatment of Parkinson's Disease

As a novel discovered regulated cell death pattern, ferroptosis has been associated with the development of Parkinson's disease (PD) and has attracted widespread attention. Nevertheless, the relationship between ferroptosis and PD pathogenesis is still unclear. This study aims to investigate the effect of iron overload on dopaminergic (DA) neurons and its correlation with ferroptosis. Here we use nerve growth factor (NGF) induced PC12 cells which are derived from pheochromocytoma of the rat adrenal to establish a classical PD in vitro model. We found significantly decreased cell viability in NGF-PC12 cell under ammonium ferric citrate (FAC) administration. Moreover, excessive intracellular iron ions induced the increase of (reactive oxygen species) ROS release as well as the decrease of mitochondrial membrane potential in PC12-NGF cells. In addition, we also found that overloaded iron can activate cell apoptosis and ferroptosis pathways, which led to cell death. Furthermore, MPP-induced PD cells were characterized by mitochondrial shrinkage, decreased expression of glutathione peroxidase 4 (Gpx4) and ferritin heavy chain (FTH1), and increased divalent metal transporter (DMT1) and transferrin receptor 1 (TfR1) expression level. In contrast, Lip-1 and DFO increased the expression level of GPX4 and FTH1 compared to MPP-induced PD cell. In conclusion, we indicated that overloaded intracellular iron contributes to neurons death via apoptosis and ferroptosis pathways, while DFO, an iron chelator, can inhibit ferroptosis in order to protect the neurons in vitro.

Polyphenols as Prebiotics in the Management of High-Fat Diet-Induced Obesity: A Systematic Review of Animal Studies

Obesity is a disease growing at an alarming rate and numerous preclinical studies have proven the role of polyphenols in managing this disease. This systematic review explores the prebiotic effect of polyphenols in the management of obesity among animals fed on a high-fat diet. A literature search was carried out in PubMed, Scopus, CINAHL, Web of Science, and Embase databases following the PRISMA guidelines. Forty-four studies reported a significant reduction in obesity-related parameters. Most notably, 83% of the studies showed a decrease in either body weight/visceral adiposity/plasma triacylglyceride. Furthermore, 42 studies reported a significant improvement in gut microbiota (GM), significantly affecting the genera Akkermansia, Bacteroides, Blautia, Roseburia, Bifidobacteria, Lactobacillus, Alistipes, and Desulfovibrio. Polyphenols’ anti-obesity, anti-hyperglycaemic, and anti-inflammatory properties were associated with their ability to modulate GM. This review supports the notion of polyphenols as effective prebiotics in ameliorating HFD-induced metabolic derangements in animal models.

New Insights into the Role of Ferritin in Iron Homeostasis and Neurodegenerative Diseases

Growing evidence has indicated that iron deposition is one of the key factors leading to neuronal death in the neurodegenerative diseases. Ferritin is a hollow iron storage protein composed of 24 subunits of two types, ferritin heavy chain (FTH) and ferritin light chain (FTL), which plays an important role in maintaining iron homeostasis. Recently, the discovery of extracellular ferritin and ferritin in exosomes indicates that ferritin might be not only an iron storage protein within the cell, but might also be an important factor in the regulation of tissue and body iron homeostasis. In this review, we first described the structural characteristics, regulation and the physiological functions of ferritin. Secondly, we reviewed the current evidence concerning the mechanisms underlying the secretion of ferritin and the possible role of secreted ferritin in the brain. Then, we summarized the relationship between ferritin and the neurodegenerative diseases including Parkinson's disease (PD), Alzheimer's disease (AD) and neuroferritinopathy (NF). Given the importance and relationship between iron and neurodegenerative diseases, understanding the role of ferritin in the brain can be expected to contribute to our knowledge of iron dysfunction and neurodegenerative diseases.

Iron Dysregulation and Inflammagens Related to Oral and Gut Health Are Central to the Development of Parkinson's Disease

Neuronal lesions in Parkinson's disease (PD) are commonly associated with α-synuclein (α-Syn)-induced cell damage that are present both in the central and peripheral nervous systems of patients, with the enteric nervous system also being especially vulnerable. Here, we bring together evidence that the development and presence of PD depends on specific sets of interlinking factors that include neuroinflammation, systemic inflammation, α-Syn-induced cell damage, vascular dysfunction, iron dysregulation, and gut and periodontal dysbiosis. We argue that there is significant evidence that bacterial inflammagens fuel this systemic inflammation, and might be central to the development of PD. We also discuss the processes whereby bacterial inflammagens may be involved in causing nucleation of proteins, including of α-Syn. Lastly, we review evidence that iron chelation, pre-and probiotics, as well as antibiotics and faecal transplant treatment might be valuable treatments in PD. A most important consideration, however, is that these therapeutic options need to be validated and tested in randomized controlled clinical trials. However, targeting underlying mechanisms of PD, including gut dysbiosis and iron toxicity, have potentially opened up possibilities of a wide variety of novel treatments, which may relieve the characteristic motor and nonmotor deficits of PD, and may even slow the progression and/or accompanying gut-related conditions of the disease.

Chemically Induced Models of Parkinson's Disease: History and Perspectives for the Involvement of Ferroptosis

Ferroptosis is a newly discovered form of necrotic cell death characterized by its dependency on iron and lipid peroxidation. Ferroptosis has attracted much attention recently in the area of neurodegeneration since the involvement of ferroptosis in Parkinson’s disease (PD), a major neurodegenerative disease, has been indicated using animal models. Although PD is associated with both genetic and environmental factors, sporadic forms of PD account for more than 90% of total PD. Following the importance of environmental factors, various neurotoxins are used as chemical inducers of PD both in vivo and in vitro. In contrast to other neurodegenerative diseases such as Alzheimer’s and Huntington’s diseases (AD and HD), many of the characteristics of PD can be reproduced in vivo by the use of specific neurotoxins. Given the indication of ferroptosis in PD pathology, several studies have been conducted to examine whether ferroptosis plays role in the loss of dopaminergic neurons in PD. However, there are still few reports showing an authentic form of ferroptosis in neuronal cells during exposure to the neurotoxins used as PD inducers. In this review article, we summarize the history of the uses of chemicals to create PD models in vivo and in vitro. Besides, we also survey recent reports examining the possible involvement of ferroptosis in chemical models of PD.

Therapeutic effect of a histone demethylase inhibitor in Parkinson's disease

Iron accumulation in the substantia nigra is recognized as a hallmark of Parkinson's disease (PD). Therefore, reducing accumulated iron and associated oxidative stress is considered a promising therapeutic strategy for PD. However, current iron chelators have poor membrane permeability and lack cell-type specificity. Here we identified GSK-J4, a histone demethylase inhibitor with the ability to cross blood brain barrier, as a potent iron suppressor. Only a trace amount of GSK-J4 significantly and selectively reduced intracellular labile iron in dopaminergic neurons, and suppressed H2O2 and 6-OHDA-induced cell death in vitro. The iron-suppressive effect was mainly mediated by inducing an increase in the expression of the iron exporter ferroportin-1. In parallel, GSK-J4 rescued dopaminergic neuron loss and motor defects in 6-OHDA-induced PD rats, which was accompanied by reduction of oxidative stress. Importantly, GSK-J4 rescued the abnormal changes of histone methylation, H3K4me3 and H3K27me3 during 6-OHDA treatment although the iron-suppressive and neuroprotective effects were sensitive to H3K4me3 inhibition only. Also, upregulating H3K4me3 increased ferroportin-1 expression and neuroprotection. Taken together, we demonstrate a previously unappreciated action of GSK-J4 on cell-specific iron suppression and neuroprotection via epigenetic mechanism. Compared with conventional iron chelators, this compound has a stronger therapeutic potential for PD.

The S-nitrosylation of parkin attenuated the ubiquitination of divalent metal transporter 1 in MPP+-treated SH-SY5Y cells

Abnormal iron accumulation caused by elevated levels of divalent metal transporter 1 (DMT1) contributes to progressive neurodegeneration in Parkinson's disease (PD). Parkin is a E3 ubiquitin ligase for the ubiquitination of DMT1. S-nitrosylated parkin (SNO-parkin) is commonly observed in PD. However, the effects of S-nitrosylation on the E3 ubiquitin ligase activity of parkin for the ubiquitination of DMT1 in PD are largely unknown. To elucidate the role of S-nitrosylated parkin and DMT1 in PD, SH-SY5Y cells were transfected with parkin, being treated with S-nitrosoglutathione (GSNO) and 1-methyl-4-phenylpyridinium (MPP⁺). The results showed increased levels of oxidized nitric oxide (NO) and S-nitrosylated parkin after the treatment of GSNO and MPP⁺ in parkin-transfected cells. Consistently, increased levels of DMT1, iron uptake and cell viability were observed. Interestingly, inhibition of S-nitrosylated parkin reduced the level of DMT1. Further, S-nitrosylation of parkin significantly inhibited the ubiquitination of DMT1. When HEK293T cells were transfected with plasmid of parkin with single site mutation (Cys241A, Cys260A, Cys323A), ubiquitination of DMT1 was also inhibited. However, the cells cotransfected with plasmids containing all three mutations, GSNO treatment did not affect the ubiquitination of DMT1. The expression of SNO-parkin and DMT1 protein in substantia nigra increased significantly gradually after 2 h, 4 h and 24 h with MPTP injection. These results indicate that the S-nitrosylation of parkin inhibits its E3 ubiquitin ligase activity for the ubiquitination of DMT1, which contributes to iron accumulation and degenerative process in PD. Targeted S-nitrosylation could provide a potential therapeutic strategy against PD.

Iron-responsive-like elements and neurodegenerative ferroptosis

A set of common-acting iron-responsive 5′untranslated region (5′UTR) motifs can fold into RNA stem loops that appear significant to the biology of cognitive declines of Parkinson's disease dementia (PDD), Lewy body dementia (LDD), and Alzheimer's disease (AD). Neurodegenerative diseases exhibit perturbations of iron homeostasis in defined brain subregions over characteristic time intervals of progression. While misfolding of Aβ from the amyloid-precursor-protein (APP), alpha-synuclein, prion protein (PrP) each cause neuropathic protein inclusions in the brain subregions, iron-responsive-like element (IRE-like) RNA stem–loops reside in their transcripts. APP and αsyn have a role in iron transport while gene duplications elevate the expression of their products to cause rare familial cases of AD and PDD. Of note, IRE-like sequences are responsive to excesses of brain iron in a potential feedback loop to accelerate neuronal ferroptosis and cognitive declines as well as amyloidosis. This pathogenic feedback is consistent with the translational control of the iron storage protein ferritin. We discuss how the IRE-like RNA motifs in the 5′UTRs of APP, alpha-synuclein and PrP mRNAs represent uniquely folded drug targets for therapies to prevent perturbed iron homeostasis that accelerates AD, PD, PD dementia (PDD) and Lewy body dementia, thus preventing cognitive deficits. Inhibition of alpha-synuclein translation is an option to block manganese toxicity associated with early childhood cognitive problems and manganism while Pb toxicity is epigenetically associated with attention deficit and later-stage AD. Pathologies of heavy metal toxicity centered on an embargo of iron export may be treated with activators of APP and ferritin and inhibitors of alpha-synuclein translation.

Co-Administration of Iron and a Bioavailable Curcumin Supplement Increases Serum BDNF Levels in Healthy Adults

Brain-derived neurotrophic factor (BDNF) is key for the maintenance of normal neuronal function and energy homeostasis and has been suggested to improve cognitive function, including learning and memory. Iron and the antioxidant curcumin have been shown to influence BDNF homeostasis. This 6-week, double blind, randomized, placebo-controlled study examined the effects of oral iron supplementation at low (18 mg) and high (65 mg) ferrous (FS) iron dosages, compared to a combination of these iron doses with a bioavailable formulated form of curcumin (HydroCurcTM; 500 mg) on BDNF levels in a healthy adult cohort of 155 male (26.42 years ± 0.55) and female (25.82 years ± 0.54) participants. Participants were randomly allocated to five different treatment groups: both iron and curcumin placebo (FS0+Plac), low dose iron and curcumin placebo (FS18+Plac), low dose iron and curcumin (FS18+Curc), high dose iron and curcumin placebo (FS65+Plac) and high dose iron and curcumin (FS65+Curc). Results showed a significant increase in BDNF over time (26%) in the FS18+Curc group (p = 0.024), and at end-point between FS18+Curc and FS18+Plac groups (35%, p = 0.042), demonstrating for the first time that the combination with curcumin, rather than iron supplementation alone, results in increased serum BDNF. The addition of curcumin to iron supplementation may therefore provide a novel approach to further enhance the benefits associated with increased BDNF levels.

N-Acetylcysteine Nanocarriers Protect against Oxidative Stress in a Cellular Model of Parkinson's Disease

Oxidative stress is a key mediator in the development and progression of Parkinson's disease (PD). The antioxidant n-acetylcysteine (NAC) has generated interest as a disease-modifying therapy for PD but is limited due to poor bioavailability, a short half-life, and limited access to the brain. The aim of this study was to formulate and utilise mitochondria-targeted nanocarriers for delivery of NAC alone and in combination with the iron chelator deferoxamine (DFO), and assess their ability to protect against oxidative stress in a cellular rotenone PD model. Pluronic F68 (P68) and dequalinium (DQA) nanocarriers were prepared by a modified thin-film hydration method. An MTT assay assessed cell viability and iron status was measured using a ferrozine assay and ferritin immunoassay. For oxidative stress, a modified cellular antioxidant activity assay and the thiobarbituric acid-reactive substances assay and mitochondrial hydroxyl assay were utilised. Overall, this study demonstrates, for the first time, successful formulation of NAC and NAC + DFO into P68 + DQA nanocarriers for neuronal delivery. The results indicate that NAC and NAC + DFO nanocarriers have the potential characteristics to access the brain and that 1000 μM P68 + DQA NAC exhibited the strongest ability to protect against reduced cell viability (p = 0.0001), increased iron (p = 0.0033) and oxidative stress (p ≤ 0.0003). These NAC nanocarriers therefore demonstrate significant potential to be transitioned for further preclinical testing for PD.

Alpha-Lipoic Acid Mediates Clearance of Iron Accumulation by Regulating Iron Metabolism in a Parkinson's Disease Model Induced by 6-OHDA

The disruption of neuronal iron homeostasis and oxidative stress are related to the pathogenesis of Parkinson's disease (PD). Alpha-lipoic acid (ALA) is a naturally occurring enzyme cofactor with antioxidant and iron chelator properties and has many known effects. ALA has neuroprotective effects on PD. However, its underlying mechanism remains unclear. In the present study, we established PD models induced by 6-hydroxydopamine (6-OHDA) to explore the neuroprotective ability of ALA and its underlying mechanism in vivo and in vitro. Our results showed that ALA could provide significant protection from 6-OHDA-induced cell damage in vitro by decreasing the levels of intracellular reactive oxygen species and iron. ALA significantly promoted the survival of the dopaminergic neuron in the 6-OHDA-induced PD rat model and remarkably ameliorated motor deficits by dramatically inhibiting the decrease in tyrosine hydroxylase expression and superoxide dismutase activity in the substantia nigra. Interestingly, ALA attenuated 6-OHDA-induced iron accumulation both in vivo and in vitro by antagonizing the 6-OHDA-induced upregulation of iron regulatory protein 2 and divalent metal transporter 1. These results indicated that the neuroprotective mechanism of ALA against neurological injury induced by 6-OHDA may be related to the regulation of iron homeostasis and reduced oxidative stress levels. Therefore, ALA may provide neuroprotective therapy for PD and other diseases related to iron metabolism disorder.

α-Synuclein Regulates Iron Homeostasis via Preventing Parkin-Mediated DMT1 Ubiquitylation in Parkinson's Disease Models

Iron metabolism imbalance plays a key role in the neurodegeneration of Parkinson's disease (PD), thus iron homeostasis should be tightly controlled by iron transporters. α-Synuclein (α-Syn) serves as a ferrireductase and iron-binding protein, which is supposed to be linked with iron metabolism, but little is known about how α-Syn affects iron homeostasis in PD. Our previous findings that up-regulation of divalent metal transporter 1 (DMT1) accounted for the nigral iron accumulation in PD raised the question whether α-Syn disturbed iron homeostasis by modulating DMT1 expression. Using α-Syn overexpressed SH-SY5Y cells and mutant human A53T α-Syn transgenic mice, we found that α-Syn could up-regulate DMT1 protein levels, followed by enhanced ferrous iron influx and subsequent aggravated oxidative stress injury. Mechanistic studies identified that α-Syn-induced p38 mitogen-activated protein kinase (MAPK) activation phosphorylated parkin at Ser131, which inactivated parkin's E3 ubiquitin ligase activity and further reduced DMT1 ubiquitylation level. Our findings revealed that α-Syn affected brain iron homeostasis through modulating DMT1 protein stability and altering cellular iron uptake, which might provide direct evidence for the involvement of α-Syn in iron metabolism dysfunction and provide insight into PD-associated nigral iron deposition.

Recent progress in nanotechnology based ferroptotic therapies for clinical applications

Ferroptosis is a new iron and reactive oxygen species dependent programmed cell death process which is different from apoptosis, necrosis, and autophagy. It is closely related to a number of disease progression including cancers, neurodegenerative disease, cerebral hemorrhage, liver disease, and renal failure. The development of different ferroptotic inducers has been proved as an efficient therapeutic strategy for a variety of chemoradiotherapy-resistant cancer cells and cancer stem cells. In addition, the development of ferroptotic inhibitors is also becoming an emerging research hotspot for the treatment of many non-cancerous diseases. Furthermore, the combination of nanotechnology with ferroptotic therapies has exhibited additional advantages such as enhanced targeting and/or stimuli-responsive ability to tumor microenvironment, ameliorated drug solubility, ease of preparation and the integration of multifunctional theranostic platforms to develop synergetic combined therapies of great clinical importance. This paper reviews the latest advances of using tailored ferroptotic nanoparticles and ferroptotic molecular probes to be relevant for the accurate diagnosis and treatment of different diseases. Finally, the opportunities and challenges of this burgeoning field were spotlighted to promote the rational design of nano-ferroptotic drugs or theranostic probes in the near future.

Substantia nigra echogenicity is associated with serum ferritin, gender and iron-related genes in Parkinson's disease

Substantia nigra (SN) hyperechogenicity is present in most Parkinson’s disease (PD) cases but is occasionally absent in some. To date, age, gender, disease severity, and other factors have been reported to be associated with SN hyperechogenicity in PD. Previous studies have discovered that excess iron deposition in the SN underlies its hyperechogenicity in PD, which may also indicate the involvement of genes associated with iron metabolism in hyperechogenicity. The objective of our study is to explore the potential associations between variants in iron metabolism-associated genes and SN echogenicity in Han Chinese PD. Demographic profiles, clinical data, SN echogenicity and genotypes were obtained from 221 Han Chinese PD individuals with a sufficient bone window. Serum ferritin levels were quantified in 92 of these individuals by immunochemical assay. We then compared factors between PD individuals with SN hyperechogenicity and those with SN hypoechogenicity to identify factors that predispose to SN hyperechogenicity. Of our 221 participants, 122 (55.2%) displayed SN hyperechogenicity, and 99 (44.8%) displayed SN hypoechogenicity. Gender and serum ferritin levels were found to be associated with SN hyperechogenicity. In total, 14 genes were included in the sequencing part. After data processing, 34 common single nucleotide polymorphisms were included in our further analyses. In our data, we also found a significantly higher frequency of PANK2 rs3737084 (genotype: OR = 2.07, P = 0.013; allele: OR = 2.51, P = 0.002) in the SN hyperechogenic group and a higher frequency of PLA2G6 rs731821 (genotype: OR = 0.45, P = 0.016; allele: OR = 0.44, P = 0.011) in the SN hypoechogenic group. However, neither of the two variants was found to be correlated with serum ferritin. This study demonstrated that genetic factors, serum ferritin level, and gender may explain the interindividual variability in SN echogenicity in PD. This is an explorative study, and further replication is warranted in larger samples and different populations.

Genetic Analysis of EGLN1 C127S Variant in Taiwanese Parkinson’s Disease

Parkinson's disease (PD) is a neurodegenerative disorder related to nigrostriatal dopaminergic neuron degeneration and iron accumulation. As a cellular oxygen sensor, prolyl hydroxylase domain containing protein 2 (PHD2, encoded by egl-9 family hypoxia inducible factor 1, EGLN1) modifies hypoxia-inducible factor alpha (HIF-α) protein for proteasomal destruction under normoxic condition. In addition, 2-oxoglutarate- (OG-) dependent dioxygenase activity of PHD2 is involved in the oxygen and iron regulation of iron-responsive element binding protein 2 (IRP2) stability. Previously increased expression of EGLN1 was found in the substantia nigra of the parkinsonian brain. We investigated the possible role of c.380 G > C (p.C127S) of EGLN1 gene in Taiwanese patients with PD. 479 patients and 435 healthy controls were recruited. Polymerase chain reaction and BsmAI restriction enzyme analysis were applied for analysis. An association between CC genotype and reduced PD risk in the recessive model (CC vs. GG + GC) was found. Our study provides a link between EGLN1 c.380 G > C SNP and the development of PD.

Mitophagy and iron: two actors sharing the stage in age-associated neuronal pathologies

Aging is characterized by the deterioration of different cellular and organismal structures and functions. A typical hallmark of the aging process is the accumulation of dysfunctional mitochondria and excess iron, leading to a vicious cycle that promotes cell and tissue damage, which ultimately contribute to organismal aging. Accordingly, altered mitochondrial quality control pathways such as mitochondrial autophagy (mitophagy) as well as altered iron homeostasis, with consequent iron overload, can accelerate the aging process and the development and progression of different age-associated disorders. In this review we first briefly introduce the aging process and summarize molecular mechanisms regulating mitophagy and iron homeostasis. We then provide an overview on how dysfunction of these two processes impact on aging and age-associated neurodegenerative disorders with a focus on Alzheimer's disease, Parkinson's disease and Amyotrophic Lateral Sclerosis. Finally, we summarize some recent evidence showing mechanistic links between iron metabolism and mitophagy and speculate on how regulating the crosstalk between the two processes may provide protective effects against aging and age-associated neuronal pathologies.

The Promise and Challenges of Developing miRNA-Based Therapeutics for Parkinson's Disease

MicroRNAs (miRNAs) are small double-stranded RNAs that exert a fine-tuning sequence-specific regulation of cell transcriptome. While one unique miRNA regulates hundreds of mRNAs, each mRNA molecule is commonly regulated by various miRNAs that bind to complementary sequences at 3’-untranslated regions for triggering the mechanism of RNA interference. Unfortunately, dysregulated miRNAs play critical roles in many disorders, including Parkinson’s disease (PD), the second most prevalent neurodegenerative disease in the world. Treatment of this slowly, progressive, and yet incurable pathology challenges neurologists. In addition to L-DOPA that restores dopaminergic transmission and ameliorate motor signs (i.e., bradykinesia, rigidity, tremors), patients commonly receive medication for mood disorders and autonomic dysfunctions. However, the effectiveness of L-DOPA declines over time, and the L-DOPA-induced dyskinesias commonly appear and become highly disabling. The discovery of more effective therapies capable of slowing disease progression –a neuroprotective agent–remains a critical need in PD. The present review focus on miRNAs as promising drug targets for PD, examining their role in underlying mechanisms of the disease, the strategies for controlling aberrant expressions, and, finally, the current technologies for translating these small molecules from bench to clinics.

Observation of magnetic susceptibility changes within the thalamus: a comparative study between healthy and Parkinson’s disease afflicted cynomolgus monkeys using 7 T MRI

Background

Although the thalamus is known to modulate basal ganglia function related to motor control activity, the abnormal changes within the thalamus during distinct medical complications have been scarcely investigated. In order to explore the feasibility of assessing iron accumulation in the thalamus as an informative biomarker for Parkinson’s disease (PD), this study was designed to employ quantitative susceptibility mapping using a 7 T magnetic resonance imaging system in cynomolgus monkeys. A 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-injected cynomolgus monkey and a healthy control (HC) were examined by 7 T magnetic resonance imaging. Positron emission tomography with 18F-N-(3-fluoro propyl)-2ß-carboxymethoxy-3ß-(4-iodophenyl) nortropane was also employed to identify the relationship between iron deposits and dopamine depletion. All acquired values were averaged within the volume of interest of the nigrostriatal pathway.

Findings

Compared with the HC, the overall elevation of iron deposition within the thalamus in the Parkinson’s disease model (about 53.81% increase) was similar to that in the substantia nigra (54.81%) region. Substantial susceptibility changes were observed in the intralaminar part of the thalamus (about 70.78% increase). Additionally, we observed that in the Parkinson’s disease model, binding potential values obtained from positron emission tomography were considerably decreased in the thalamus (97.51%) and substantia nigra (92.48%).

Conclusions

The increased iron deposition in the thalamus showed negative correlation with dopaminergic activity in PD, supporting the idea that iron accumulation affects glutaminergic inputs and dopaminergic neurons. This investigation indicates that the remarkable susceptibility changes in the thalamus could be an initial major diagnostic biomarker for Parkinson’s disease-related motor symptoms.

Interrogating Parkinson's disease associated redox targets: Potential application of CRISPR editing

Loss of dopaminergic neurons in the substantia nigra is one of the pathogenic hallmarks of Parkinson's disease, yet the underlying molecular mechanisms remain enigmatic. While aberrant redox metabolism strongly associated with iron dysregulation and accumulation of dysfunctional mitochondria is considered as one of the major contributors to neurodegeneration and death of dopaminergic cells, the specific anomalies in the molecular machinery and pathways leading to the PD development and progression have not been identified. The high efficiency and relative simplicity of a new genome editing tool, CRISPR/Cas9, make its applications attractive for deciphering molecular changes driving PD-related impairments of redox metabolism and lipid peroxidation in relation to mishandling of iron, aggregation and oligomerization of alpha-synuclein and mitochondrial injury as well as in mechanisms of mitophagy and programs of regulated cell death (apoptosis and ferroptosis). These insights into the mechanisms of PD pathology may be used for the identification of new targets for therapeutic interventions and innovative approaches to genome editing, including CRISPR/Cas9.

Iron overload resulting from the chronic oral administration of ferric citrate induces parkinsonism phenotypes in middle-aged mice

Iron homeostasis is critical for maintaining normal brain physiological functions, and its mis-regulation can cause neurotoxicity and play a part in the development of many neurodegenerative disorders. The high incidence of iron deficiency makes iron supplementation a trend, and ferric citrate is a commonly used iron supplement. In this study, we found that the chronic oral administration of ferric citrate (2.5 mg/day and 10 mg/day) for 16 weeks selectively induced iron accumulation in the corpus striatum (CPu), substantia nigra (SN) and hippocampus, which typically caused parkinsonism phenotypes in middle-aged mice. Histopathological analysis showed that apoptosis- and oxidative stress-mediated neurodegeneration and dopaminergic neuronal loss occurred in the brain, and behavioral tests showed that defects in the locomotor and cognitive functions of these mice developed. Our research provides a new perspective for ferric citrate as a food additive or in clinical applications and suggests a new potential approach to develop animal models for Parkinson's disease (PD).

Bayesian inference for parameter estimation in lactoferrin-mediated iron transport across blood-brain barrier

BACKGROUND

In neurodegenerative diseases such as Alzheimer's and Parkinson's, excessive irons as well as lactoferrin (Lf), but not transferrin (Tf), have been found in and around the affected regions of the brain. These evidences suggest that lactoferrin plays a critical role during neurodegenerative diseases, although Lf-mediated iron transport across blood-brain barrier (BBB) is negligible compared to that of transferrin in normal condition. However, the kinetics of lactoferrins and lactoferrin-mediated iron transport are still unknown.

METHOD

To determine the kinetic rate constants of lactoferrin-mediated iron transport through BBB, a mass-action based ordinary differential equation model has been presented. A Bayesian framework is developed to estimate the kinetic rate parameters from posterior probability density functions. The iron transport across BBB is studied by considering both Lf- and Tf-mediated pathways for both normal and pathologic conditions.

RESULTS

Using the point estimates of kinetic parameters, our model can effectively reproduce the experimental data of iron transport through BBB endothelial cells. The robustness of the model and parameter estimation process are further verified by perturbation of kinetic parameters. Our results show that surge in high-affinity receptor density increases lactoferrin as well as iron in the brain.

CONCLUSIONS

Due to the lack of a feedback loop such as iron regulatory proteins (IRPs) for lactoferrin, iron can transport to the brain continuously, which might increase brain iron to pathological levels and can contribute to neurodegeneration.

GENERAL SIGNIFICANCE

This study provides an improved understanding of presence of lactoferrin and iron in the brain during neurodegenerative diseases.

Interactions between iron and α-synuclein pathology in Parkinson's disease

Both iron deposition and α-synuclein aggregation are neuropathological hallmarks of Parkinson's disease (PD). We aimed to summarize the extensive interactions between these two factors. The direct structural links between iron and α-synuclein suggest that structural reorganization provokes α-synuclein conformational change. Iron post-transcriptionally regulates α-synuclein synthesis in the presence of iron-responsive element. Increased oxidative/nitrative stress induced by iron is believed to be involved in the post-translational modulation of α-synuclein. Iron modulates proteolytic pathways and therefore participates in the regulation of α-synuclein levels. Meanwhile, the recycling of iron through ferritin degradation suggests a link from the aspects of the degradation signaling pathway. Finally, α-synuclein might regulate iron metabolism through its ferrireductase activity. A prominent role of α-synuclein in iron homeostasis is involved in the uptake of transferrin-Fe. These findings suggest that intracellular iron and α-synuclein are closely related to each other, contributing to the vulnerability of dopaminergic neurons or even to a vicious cycle of toxicity in the pathology of PD.

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.

Case of Early-Onset Parkinson's Disease in a Heterozygous Mutation Carrier of the ATP7B Gene

In this paper, we report a clinically proven case of Parkinson’s disease (PD) with early onset in a patient who is a heterozygous mutation carrier of ATP7B (the Wilson’s disease gene). The patient was observed from 2011 to 2018 in the Center for Neurodegenerative Diseases, Institute of Experimental Medicine (St. Petersburg, Russia). During this period, the patient displayed aggravation of PD clinical symptoms that were accompanied by a decrease in the ceruloplasmin concentration (from 0.33 to 0.27 g/L) and an increase in serum nonceruloplasmin copper, which are typical of the late stages of Wilson’s disease. It was found that one of the alleles of exon 14 in the ATP7B gene, which partially codes of the nucleotide-binding domain (N-domain), carries a mutation not previously reported corresponding to Cys1079Gly substitution. Alignment of the ATP7B N-domain amino acid sequences of representative vertebrate species has shown that the Cys at 1079 position is conserved throughout the evolution. Molecular dynamic analysis of a polypeptide with Cys1079Gly substitution showed that the mutation causes profound conformational changes in the N-domain, which could potentially lead to impairment of its functions. The role of ATP7B gene mutations in PD development is discussed.

Glial S100A6 Degrades β-amyloid Aggregation through Targeting Competition with Zinc Ions

Evidence has been accumulating that zinc ions can trigger β-amyloid (Aβ) deposition and senile plaque formation in the brain, a pathological hallmark of Alzheimer's disease (AD). Chelating zinc inhibits Aβ aggregation and may hold promise as a therapeutic strategy for AD. S100A6 is an acidic Ca²⁺/Zn²⁺-binding protein found only in a small number of astrocytes in the normal brain. However, in the AD brain, S100A6 is highly expressed in astrocytes around Aβ plaques. The role of the astrocytic S100A6 upregulation in AD is unknown. In the present study, we examined the effects of S100A6 on Aβ plaques and intracellular zinc levels in a mouse model of AD. Chronic exposure to zinc increased Aβ deposition and S100A6 expression, both reversible by the zinc chelator clioquinol, in the brains of amyloid precursor protein/presenilin 1 (APP/PS1) transgenic mice. To examine whether exogenous S100A6 could induce Aβ plaque disaggregation through competition for zinc in vitro, we incubated APP/PS1 mouse brain sections with recombinant human S100A6 protein or co-incubated them with human S100A6-expressing cells. Both treatments efficiently reduced the Aβ plaque burden in situ. In addition, treatment with exogenous S100A6 protected cultured COS-7 cells against zinc toxicity. Our results show for the first time that increased S100A6 levels correlate with both Aβ disaggregation and decrease of Aβ plaque-associated zinc contents in brain sections with AD-like pathology. Astrocytic S100A6 in AD may protect from Aβ deposition through zinc sequestration.

Matching ex vivo MRI With Iron Histology: Pearls and Pitfalls

Iron levels in the brain can be estimated using newly developed specific magnetic resonance imaging (MRI) sequences. This technique has several applications, especially in neurodegenerative disorders like Alzheimer's disease or Parkinson's disease. Coupling ex vivo MRI with histology allows neuroscientists to better understand what they see in the images. Iron is one of the most extensively studied elements, both by MRI and using histological or physical techniques. Researchers were initially only able to make visual comparisons between MRI images and different types of iron staining, but the emergence of specific MRI sequences like R2* or quantitative susceptibility mapping meant that quantification became possible, requiring correlations with physical techniques. Today, with advances in MRI and image post-processing, it is possible to look for MRI/histology correlations by matching the two sorts of images. For the result to be acceptable, the choice of methodology is crucial, as there are hidden pitfalls every step of the way. In order to review the advantages and limitations of ex vivo MRI correlation with iron-based histology, we reviewed all the relevant articles dealing with the topic in humans. We provide separate assessments of qualitative and quantitative studies, and after summarizing the significant results, we emphasize all the pitfalls that may be encountered.

Long-term iron exposure causes widespread molecular alterations associated with memory impairment in mice

Limited literature available indicates the neurotoxic effects of excessive iron, however, a deep understanding of iron neurotoxicity needs to be developed. In this study, we evaluated the toxic effects of excessive iron on learning and cognitive function in long-term iron exposure (oral, 10 mg/L, 6 months) of mice by behavioral tests including novel object recognition test, step-down passive avoidance test and Morris water maze test, and further analyzed differential expression of hippocampal proteins. The behavioral tests consistently showed that iron treatment caused cognitive defects of the mice. Proteomic analysis revealed 66 differentially expressed hippocampal proteins (30 increased and 36 decreased) in iron-treated mice as compared with the control ones. Bioinformatics analysis showed that the dysregulated proteins mainly included: synapse-associated proteins (i.e. synaptosomal-associated protein 25 (SNAP25), complexin-1 (CPLX1), vesicle-associated membrane protein 2 (VAMP2), neurochondrin (NCDN)); mitochondria-related proteins (i.e. ADP/ATP translocase 1 (SLC25A4), 14-3-3 protein zeta/delta (YWHAZ)); cytoskeleton proteins (i.e. neurofilament light polypeptide (NEFL), tubulin beta-2B chain (TUBB2B), tubulin alpha-4A chain (TUBA4A)). The findings suggest that the dysregulations of synaptic, mitochondrial, and cytoskeletal proteins may be involved in iron-triggered memory impairment. This study provides new insights into the molecular mechanisms of iron neurotoxicity.

Decreased serum ferritin may be associated with increased restless legs syndrome in Parkinson's disease (PD): a meta-analysis for the diagnosis of RLS in PD patients

Objective: Restless legs syndrome (RLS) is one of the most common non-motor symptoms of Parkinson's disease (PD), but its pathogenesis in a PD background is unclear. Abnormal iron metabolism may be involved, in which case it may be a marker of RLS risk. Here, the literature was systematically searched and meta-analyzed to compare iron metabolism markers between PD patients with or without RLS. Method: The databases PubMed, Embase, Chinese National Knowledge Infrastructure, Wanfang, Web of Science, and SinoMed were searched for case-control and observational studies examining RLS-related changes in iron metabolism in PD, in terms of serum iron, serum ferritin and hemoglobin. Eligible studies were meta-analyzed using Stata 12.0. Results: Meta-analysis of 11 case-control studies showed that serum ferritin concentration was lower in PD patients with RLS than in those without RLS. (95%CI -0.32 to -0.03, p = 0.018). In contrast, levels of serum iron or hemoglobin did not differ significantly between PD patients with or without RLS. Conclusion: This meta-analysis may provide the first reliable pooled estimate of the correlation between abnormal iron metabolism and RLS in PD. The available evidence indicates that levels of ferritin, but not of serum iron or hemoglobin, correlate significantly with RLS in PD, with lower ferritin levels correlating to greater prevalence of RLS.

The Role of the Antioxidant Response in Mitochondrial Dysfunction in Degenerative Diseases: Cross-Talk between Antioxidant Defense, Autophagy, and Apoptosis

The mitochondrion is an essential organelle important for the generation of ATP for cellular function. This is especially critical for cells with high energy demands, such as neurons for signal transmission and cardiomyocytes for the continuous mechanical work of the heart. However, deleterious reactive oxygen species are generated as a result of mitochondrial electron transport, requiring a rigorous activation of antioxidative defense in order to maintain homeostatic mitochondrial function. Indeed, recent studies have demonstrated that the dysregulation of antioxidant response leads to mitochondrial dysfunction in human degenerative diseases affecting the nervous system and the heart. In this review, we outline and discuss the mitochondrial and oxidative stress factors causing degenerative diseases, such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, Huntington's disease, and Friedreich's ataxia. In particular, the pathological involvement of mitochondrial dysfunction in relation to oxidative stress, energy metabolism, mitochondrial dynamics, and cell death will be explored. Understanding the pathology and the development of these diseases has highlighted novel regulators in the homeostatic maintenance of mitochondria. Importantly, this offers potential therapeutic targets in the development of future treatments for these degenerative diseases.

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.

Iron Dysregulation in Parkinson's Disease: Focused on the Autophagy-Lysosome Pathway

Parkinson's disease (PD) is the second most common neurodegenerative disease and is characterized by dopaminergic neuron loss in the substantia nigra pars compacta (SNpc). Although both iron accumulation and a defective autophagy-lysosome pathway contribute to the pathological development of PD, the connection between these two causes is poorly documented. The autophagy-lysosome pathway not only responds to regulation by iron chelators and channels but also participates in cellular iron recycling through the degradation of ferritin and other iron-containing components. Previously, ferritin has been posited to be the bridge between iron accumulation and autophagy impairment in PD. In addition, iron directly interacts with α-synuclein in Lewy bodies, which are primarily digested through the autophagy-lysosome pathway. These findings indicate that some link exists between iron deposition and autophagy impairment in PD. In this review, the basic mechanisms of the autophagy-lysosome pathway and iron trafficking are introduced, and then their interaction under physiological conditions is explained. Finally, we finish by discussing the dysfunction of iron deposition and autophagy in PD, as well as their potential relationship, which will provide some insight for further study.

A Golgi-targeting fluorescent probe for labile Fe(ii) to reveal an abnormal cellular iron distribution induced by dysfunction of VPS35

Iron is involved in numerous physiologically essential processes in our body. However, excessive iron is a pathogenic factor in neurodegenerative diseases, causing aberrant oxidative stress. Divalent metal transporter 1 (DMT1) acts as a primary transporter of Fe(ii) ions. The intracellular delivery of DMT1 toward the cellular membrane via the trans-Golgi network during the endocytotic process is partially regulated by a retromer-mediated protein-sorting system comprising vacuolar protein-sorting proteins (VPSs). Thus, together with DMT1, the Golgi-apparatus acts as a hub organelle in the delivery system for intracellular Fe(ii) ions. Dysfunction of the VPS-relevant protein sorting system can induce the abnormal delivery of DMT1 toward lysosomes concomitantly with Fe(ii) ions. To explore this issue, we developed a fluorescent probe, Gol-SiRhoNox, for the Golgi-specific detection of Fe(ii) ions by integrating our original N-oxide-based Fe(ii)-specific chemical switch, a new Golgi-localizable chemical motif, and polarity-sensitive fluorogenic scaffold. Our synchronous imaging study using Gol-SiRhoNox and LysoRhoNox, a previously developed fluorescent probe for lysosomal Fe(ii), revealed that the intracellular distribution balance of Fe(ii) ions between the Golgi apparatus and lysosomes is normally Golgi-dominant, whereas the lysosome-specific elevation of Fe(ii) ions was observed in cells with induced dysfunction of VPS35, a member of the retromer complex. Treatment of cells with dysfunctional VPS35 with R55, a molecular chaperone, resulted in the restoration of the subcellular distribution of Fe(ii) ions to the Golgi-dominant state. These results indicate that the impairment of the DMT1 traffic machinery affects subcellular iron homeostasis, promoting Fe(ii) leakage at the Golgi and lysosomal accumulation of Fe(ii) through missorting of DMT1.

The Contribution of Iron to Protein Aggregation Disorders in the Central Nervous System

The homeostasis of iron is of fundamental importance in the central nervous system (CNS) to ensure biological processes such as oxygen transport, mitochondrial respiration or myelin synthesis. Dyshomeostasis and accumulation of iron can be observed during aging and both are shared characteristics of several neurodegenerative diseases. Iron-mediated generation of reactive oxygen species (ROS) may lead to protein aggregation and cellular toxicity. The process of misfolding and aggregation of neuronal proteins such as α-synuclein, Tau, amyloid beta (Aβ), TDP-43 or SOD1 is a common hallmark of many neurodegenerative disorders and iron has been shown to facilitate protein aggregation. Thus, both, iron and aggregating proteins are proposed to amplify their detrimental effects in the disease state. In this review, we give an overview on effects of iron on aggregation of different proteins involved in neurodegeneration. Furthermore, we discuss the proposed mechanisms of iron-mediated toxicity and protein aggregation emphasizing the red-ox chemistry and protein-binding properties of iron. Finally, we address current therapeutic approaches harnessing iron chelation as a disease-modifying intervention in neurodegenerative disorders, such as Parkinson’s disease, Alzheimer’s disease, and amyotrophic lateral sclerosis.

Iron Pathophysiology in Parkinson Diseases

The key molecular events that provoke Parkinson's disease (PD) are not fully understood. Iron deposit was found in the substantia nigra pars compacta (SNpc) of PD patients and animal models, where dopaminergic neurons degeneration occurred selectively. The mechanisms involved in disturbed iron metabolism remain unknown, however, considerable evidence indicates that iron transporters dysregulation, activation of L-type voltage-gated calcium channel (LTCC) and ATP-sensitive potassium (KATP) channels, as well as N-methyl-D-aspartate (NMDA) receptors (NMDARs) contribute to this process. There is emerging evidence on the structural links and functional modulations between iron and α-synuclein, and the key player in PD which aggregates in Lewy bodies. Iron is believed to modulate α-synuclein synthesis, post-translational modification, and aggregation. Furthermore, glia, especially activated astroglia and microglia, are involved in iron deposit in PD. Glial contributions were largely dependent on the factors they released, e.g., neurotrophic factors, pro-inflammatory factors, lactoferrin, and those undetermined. Therefore, iron chelation using iron chelators, the extracts from many natural foods with iron chelating properties, may be an effective therapy for prevention and treatment of the disease.