Mitochondrial inhibitor models of Huntington's disease and Parkinson's disease induce zinc accumulation and are attenuated by inhibition of zinc neurotoxicity in vitro or in vivo

Dyshomeostasis of Iron and Its Transporter Proteins in Cypermethrin-Induced Parkinson's Disease

The etiology of Parkinson's disease (PD) is highly complex and is still indefinable. However, a number of studies have indicated the involvement of pesticides and transition metals. Copper, magnesium, iron, and zinc have emerged as important metal contributors. Exposure to pesticides causes an accumulation of transition metals in the substantia nigra (SN) region of the brain. The cypermethrin model of PD is characterized by mitochondrial dysfunction, autophagy impairment, oxidative stress, etc. However, the effect of cypermethrin on metal homeostasis is not yet explored. The study was designed to delineate the role of metals and their transporter proteins in cypermethrin-induced animal and cellular models of PD. The level of copper, magnesium, iron, and zinc was checked in the nigrostriatal tissue and serum by atomic absorption spectroscopy. Since cypermethrin consistently increased iron content in the nigrostriatal tissue and serum after 12 weeks of exposure, the level of iron transporter proteins, such as divalent metal transporter-1 (DMT-1), ceruloplasmin, transferrin, ferroportin, and hepcidin, and their in silico interaction with cypermethrin were checked. 3,3'-Diaminobenzidine-enhanced Perl's staining showed an elevated number of iron-positive cells in the SN of cypermethrin-treated rats. Molecular docking studies revealed a strong binding affinity between cypermethrin and iron transporter protein receptors of humans and rats. Furthermore, cypermethrin increased the expression of DMT-1 and hepcidin while reducing the expression of transferrin, ceruloplasmin, and ferroportin in the nigrostriatal tissue and human neuroblastoma cells. These observations suggest that cypermethrin alters the expression of iron transporter proteins leading to iron dyshomeostasis, which could contribute to dopaminergic neurotoxicity.

Monoterpenoid indole alkaloid adducts and dimers from Melodinus fusiformis

Eight unprecedented monoterpenoid indole alkaloid (MIA) adducts and dimers, melofusinines A-H (1-8), and three undescribed melodinus-type MIA monomers, melofusinines I-K (9-11), together with six putative biogenetic precursors were isolated from the twigs and leaves of Melodinus fusiformis Champ. ex Benth. Compounds 1 and 2 are unusual hybrid indole alkaloids incorporating an aspidospermatan-type MIA with a monoterpenoid alkaloid unit via C-C coupling. Compounds 3-8 feature the first MIA dimers constructed through an aspidospermatan-type monomer and a rearranged melodinus-type monomer with two different types of couplings. Their structures were elucidated by spectroscopic data, single crystal X-ray diffraction, and calculated electric circular dichroism spectra analysis. In addition, dimers 5 and 8 showed significant neuroprotection effects on MPP ⁺-injured primary cortical neurons.

Zinc and Central Nervous System Disorders

Zinc (Zn²⁺) is the second most abundant necessary trace element in the human body, exerting a critical role in many physiological processes such as cellular proliferation, transcription, apoptosis, growth, immunity, and wound healing. It is an essential catalyst ion for many enzymes and transcription factors. The maintenance of Zn²⁺ homeostasis is essential for the central nervous system, in which Zn²⁺ is abundantly distributed and accumulates in presynaptic vesicles. Synaptic Zn²⁺ is necessary for neural transmission, playing a pivotal role in neurogenesis, cognition, memory, and learning. Emerging data suggest that disruption of Zn²⁺ homeostasis is associated with several central nervous system disorders including Alzheimer's disease, depression, Parkinson's disease, multiple sclerosis, schizophrenia, epilepsy, and traumatic brain injury. Here, we reviewed the correlation between Zn²⁺ and these central nervous system disorders. The potential mechanisms were also included. We hope that this review can provide new clues for the prevention and treatment of nervous system disorders.

Pyruvate Prevents Dopaminergic Neurodegeneration and Motor Deficits in the 1-Methyl-4-Phenyl-1,2,3,6-Tetrahydropyridine Model of Parkinson's Disease

Parkinson's disease (PD) is a progressive neurodegenerative disorder characterized by the selective loss of dopamine(DA)rgic neurons in the substantia nigra of the midbrain, and primarily causes motor symptoms. While the pathological cause of PD remains uncertain, oxidative damage, neuroinflammation, and energy metabolic perturbation have been implicated. Pyruvate has been shown neuroprotective in animal models for many neurological disorders, presumably owing to its potent anti-oxidative, anti-inflammatory, and energy metabolic properties. We therefore investigated whether exogenous pyruvate could also protect nigral DA neurons from degeneration and reverse the associated motor deficits in an animal model of PD using the DA neuron-specific toxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). MPTP (20 mg/kg) was injected four times every 2 h into the peritoneum of mice, which resulted in a massive loss of DA neurons as well as an increase in neuronal death and cytosolic labile zinc overload. There were rises in inflammatory and oxidative responses, a drop in the striatal DA level, and the emergence of PD-related motor deficits. In comparison, when sodium pyruvate was administered intraperitoneally at a daily dose of 250 mg/kg for 7 days starting 2 h after the final MPTP treatment, significant relief in the MPTP-induced neuropathology, neurodegeneration, DA depletion, and motor symptoms was observed. Equiosmolar dose of NaCl had no neuroprotective effect, and lower doses of sodium pyruvate did not have any statistically significant effects. These findings suggest that pyruvate has therapeutic potential for the treatment of PD and related neurodegenerative diseases.

NAD+ Metabolism and Diseases with Motor Dysfunction

Neurodegenerative diseases result in the progressive deterioration of the nervous system, with motor and cognitive impairments being the two most observable problems. Motor dysfunction could be caused by motor neuron diseases (MNDs) characterized by the loss of motor neurons, such as amyotrophic lateral sclerosis and Charcot-Marie-Tooth disease, or other neurodegenerative diseases with the destruction of brain areas that affect movement, such as Parkinson's disease and Huntington's disease. Nicotinamide adenine dinucleotide (NAD+) is one of the most abundant metabolites in the human body and is involved with numerous cellular processes, including energy metabolism, circadian clock, and DNA repair. NAD+ can be reversibly oxidized-reduced or directly consumed by NAD+-dependent proteins. NAD+ is synthesized in cells via three different paths: the de novo, Preiss-Handler, or NAD+ salvage pathways, with the salvage pathway being the primary producer of NAD+ in mammalian cells. NAD+ metabolism is being investigated for a role in the development of neurodegenerative diseases. In this review, we discuss cellular NAD+ homeostasis, looking at NAD+ biosynthesis and consumption, with a focus on the NAD+ salvage pathway. Then, we examine the research, including human clinical trials, focused on the involvement of NAD+ in MNDs and other neurodegenerative diseases with motor dysfunction.

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.

Synaptic Zinc: An Emerging Player in Parkinson's Disease

Alterations of zinc homeostasis have long been implicated in Parkinson's disease (PD). Zinc plays a complex role as both deficiency and excess of intracellular zinc levels have been incriminated in the pathophysiology of the disease. Besides its role in multiple cellular functions, Zn²⁺ also acts as a synaptic transmitter in the brain. In the forebrain, subset of glutamatergic neurons, namely cortical neurons projecting to the striatum, use Zn²⁺ as a messenger alongside glutamate. Overactivation of the cortico-striatal glutamatergic system is a key feature contributing to the development of PD symptoms and dopaminergic neurotoxicity. Here, we will cover recent evidence implicating synaptic Zn²⁺ in the pathophysiology of PD and discuss its potential mechanisms of actions. Emphasis will be placed on the functional interaction between Zn²⁺ and glutamatergic NMDA receptors, the most extensively studied synaptic target of Zn²⁺.

Explorative Combined Lipid and Transcriptomic Profiling of Substantia Nigra and Putamen in Parkinson's Disease

Parkinson’s disease (PD) is characterized by the loss of dopaminergic neurons from the substantia nigra (SN) that project to the dorsal striatum (caudate-putamen). To better understand the molecular mechanisms underlying PD, we performed combined lipid profiling and RNA sequencing of SN and putamen samples from PD patients and age-matched controls. SN lipid analysis pointed to a neuroinflammatory component and included elevated levels of the endosomal lipid Bis (Monoacylglycero)Phosphate 42:8, while two of the three depleted putamen lipids were saturated sphingomyelin species. Remarkably, we observed gender-related differences in the SN and putamen lipid profiles. Transcriptome analysis revealed that the top-enriched pathways among the 354 differentially expressed genes (DEGs) in the SN were “protein folding” and “neurotransmitter transport”, and among the 261 DEGs from putamen “synapse organization”. Furthermore, we identified pathways, e.g., “glutamate signaling”, and genes, encoding, e.g., an angiotensin receptor subtype or a proprotein convertase, that have not been previously linked to PD. The identification of 33 genes that were common among the SN and putamen DEGs, which included the α-synuclein paralog β-synuclein, may contribute to the understanding of general PD mechanisms. Thus, our proof-of-concept data highlights new genes, pathways and lipids that have not been explored before in the context of PD.

New insight into Parkinson's disease pathogenesis from reactive oxygen species-mediated extracellular Zn2+ influx

BACKGROUND

Parkinson's disease (PD) is the common neurodegenerative disorder in the elderly characterized by motor symptoms such as tremors, which is caused by selective loss of nigral dopaminergic neurons. Oxidative stress induced by the auto-oxidation of dopamine has been implicated as a key cause of the selective loss of dopaminergic neurons.

METHODS

To understand the selective loss of nigral dopaminergic neurons, the PD pathogenesis is reviewed focused on paraquat (PQ) and 6-hydroxydopamine (6-OHDA)-induced PD in rats.

RESULTS

Reactive oxygen species (ROS), which are produced by PQ and 6-OHDA, are retrogradely transported to presynaptic glutamatergic neuron terminals. ROS activate presynaptic transient receptor potential melastatin 2 (TRPM2) cation channels and induce extracellular glutamate accumulation in the substantia nigra pars compacta (SNpc), followed by age-related intracellular Zn2+ dysregulation. Loss of nigral dopaminergic neurons is accelerated by age-related intracellular Zn2+ dysregulation in the SNpc of rat PD models. The intracellular Zn2+ dysregulation in nigral dopaminergic neurons is linked with the rapid influx of extracellular Zn2+ via postsynaptic AMPA receptor activation, suggesting that PQ- and 6-OHDA-induced pathogenesis is linked with age-related intracellular Zn2+ dysregulation in the SNpc. Postsynaptic TRPM2 channels may be also involved in intracellular Zn2+ dysregulation in the SNpc.

CONCLUSION

A novel mechanism of nigral dopaminergic degeneration, in which ROS induce rapid intracellular Zn2+ dysregulation, figures out the PD pathogenesis induced by PQ and 6-OHDA in rats. This review deals with new insight into PD pathogenesis from ROS-mediated extracellular Zn2+ influx and its proposed defense strategy.

Synaptic zinc contributes to motor and cognitive deficits in 6-hydroxydopamine mouse models of Parkinson's disease

Hyperactivity of glutamatergic corticostrial pathways is recognized as a key pathophysiological mechanism contributing to development of PD symptoms and dopaminergic neurotoxicity. Subset of corticostriatal projection neurons uses Zn²⁺ as a co-transmitter alongside glutamate, but the role of synaptically released Zn²⁺ in PD remains unexplored. We used genetically modified mice and pharmacological tools in combination with 6-hydroxydopamine (6-OHDA) lesion models of PD to investigate the contribution of synaptic zinc to disease associated behavioral deficits and neurodegeneration. Vesicular zinc transporter-3 (ZnT3) knockout mice lacking releasable Zn²⁺ were more resistant to locomotor deficit and memory impairment of nigrostriatal dopamine (DA) denervation compared to wildtype littermates. The loss of striatal dopaminergic fibers was comparable between genotypes, indicating that synaptically released Zn²⁺ contributes to behavioral deficits but not neurotoxic effects of 6-OHDA. To gain further insight into the mechanisms of Zn²⁺ actions, we used the extracellular Zn²⁺ chelator CaEDTA and knock-in mice lacking the high affinity Zn²⁺ inhibition of GluN2A-containing NMDA receptors (GluN2A-NMDARs). Acute chelation of extracellular Zn²⁺ in the striatum restored locomotor deficit of 6-OHDA lesion, confirming that synaptic Zn²⁺ suppresses locomotor behavior. Disruption of the Zn²⁺-GluN2A interaction had, on the other hand, no impact on locomotor deficit or neurotoxic effect of 6-OHDA. Collectively, these findings provide clear evidence for the implication of striatal synaptic Zn²⁺ in the pathophysiology of PD. They unveil that synaptic Zn²⁺ plays predominantly a detrimental role by promoting motor and cognitive deficits caused by nigrostriatal DA denervation, pointing towards new therapeutic interventions.

Neurotoxicity Linked to Dysfunctional Metal Ion Homeostasis and Xenobiotic Metal Exposure: Redox Signaling and Oxidative Stress

SIGNIFICANCE

Essential metals such as copper, iron, manganese, and zinc play a role as cofactors in the activity of a wide range of processes involved in cellular homeostasis and survival, as well as during organ and tissue development. Throughout our life span, humans are also exposed to xenobiotic metals from natural and anthropogenic sources, including aluminum, arsenic, cadmium, lead, and mercury. It is well recognized that alterations in the homeostasis of essential metals and an increased environmental/occupational exposure to xenobiotic metals are linked to several neurological disorders, including neurodegeneration and neurodevelopmental alterations. Recent Advances: The redox activity of essential metals is key for neuronal homeostasis and brain function. Alterations in redox homeostasis and signaling are central to the pathological consequences of dysfunctional metal ion homeostasis and increased exposure to xenobiotic metals. Both redox-active and redox-inactive metals trigger oxidative stress and damage in the central nervous system, and the exact mechanisms involved are starting to become delineated.

CRITICAL ISSUES

In this review, we aim to appraise the role of essential metals in determining the redox balance in the brain and the mechanisms by which alterations in the homeostasis of essential metals and exposure to xenobiotic metals disturb the cellular redox balance and signaling. We focus on recent literature regarding their transport, metabolism, and mechanisms of toxicity in neural systems.

FUTURE DIRECTIONS

Delineating the specific mechanisms by which metals alter redox homeostasis is key to understand the pathological processes that convey chronic neuronal dysfunction in neurodegenerative and neurodevelopmental disorders. Antioxid. Redox Signal. 28, 1669-1703.

Extracellular Zn2+ Influx into Nigral Dopaminergic Neurons Plays a Key Role for Pathogenesis of 6-Hydroxydopamine-Induced Parkinson's Disease in Rats

Parkinson's disease (PD) is a progressive neurological disease characterized by a selective loss of nigrostriatal dopaminergic neurons. The exact cause of the neuronal loss remains unclear. Here, we report a unique mechanism of nigrostriatal dopaminergic neurodegeneration, in which extracellular Zn²⁺ influx plays a key role for PD pathogenesis induced with 6-hydroxydopamine (6-OHDA) in rats. 6-OHDA rapidly increased intracellular Zn²⁺ only in the substantia nigra pars compacta (SNpc) of brain slices and this increase was blocked in the presence of CaEDTA, an extracellular Zn²⁺ chelator, and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), an α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptor antagonist, indicating that 6-OHDA rapidly increases extracellular Zn²⁺ influx via AMPA receptor activation in the SNpc. Extracellular Zn²⁺ concentration was decreased under in vivo SNpc perfusion with 6-OHDA and this decrease was blocked by co-perfusion with CNQX, supporting 6-OHDA-induced Zn²⁺ influx via AMPA receptor activation in the SNpc. Interestingly, both 6-OHDA-induced loss of nigrostriatal dopaminergic neurons and turning behavior to apomorphine were ameliorated by co-injection of intracellular Zn²⁺ chelators, i.e., ZnAF-2DA and N,N,N',N'-Tetrakis(2-pyridylmethyl)ethylenediamine (TPEN). Co-injection of TPEN into the SNpc blocked 6-OHDA-induced increase in intracellular Zn²⁺ but not in intracellular Ca²⁺. These results suggest that the rapid influx of extracellular Zn²⁺ into dopaminergic neurons via AMPA receptor activation in the SNpc induces nigrostriatal dopaminergic neurodegeneration, resulting in 6-OHDA-induced PD in rats.

Comparison of quantitative T2 and ADC mapping in the assessment of 3-nitropropionic acid-induced neurotoxicity in rats

To assess the relative performance of MRI T₂ relaxation and ADC mapping as potential biomarkers of neurotoxicity, a model of 3-nitropropionic acid (NP)-induced neurodegeneration in rats was employed. Male Sprague-Dawley rats received NP (N = 20, 16-20 mg/kg, ip or sc) or saline (N = 6, 2 ml/kg, ip) daily for 3 days. MRI was performed using a 7 T system employing quantitative T₂ and ADC mapping based on spin echo pulse sequence. All maps were skull stripped and co-registered and the changes were quantified using baseline subtraction and anatomical segmentation. Following the in vivo portion of the study, rat brains were histologically examined. Four NP-treated rats were considered responders based on their MRI and histology data. T₂ values always increased in the presence of toxicity, while ADC changes were bidirectional, decreasing in some lesion areas and increasing in others. In contrast to T₂ in some cases, ADC did not change. The effect sizes of T₂ and ADC signals suggestive of neurotoxicity were 2.64 and 1.66, respectively, and the variability of averaged T₂ values among anatomical regions was consistently lower than that for ADC. The histopathology data confirmed the presence of neurotoxicity, however, a more detailed assessment of the correlation of MRI with histology is needed. T₂ mapping provides more sensitive and specific information than ADC about changes in the rat brain thought to be associated with neurotoxicity due to a higher signal-to-noise ratio, better resolution, and unidirectional changes, and presents a better opportunity for biomarker development.

Striatal mitochondria response to 3-nitropropionic acid and fish oil treatment

BACKGROUND

Mitochondrial dysfunction is involved in neurodegenerative diseases, such as Huntington's disease (HD). 3-Nitropropionic acid (3-NP) is a mitochondrial toxin that specifically inhibits complex II of the electron transport chain (ETC) and is used to generate an experimental model of HD.

OBJECTIVE

To study the effect of fish liver oil (FO) over the mitochondrial dysfunction induced via partial ETC inhibition by 3-NP.

METHODS

This study was performed in rats and consisted of two phases: (i) administration of increasing doses of 3-NP and (ii) administration of FO for 14 days before to 3-NP. The rats' exploratory activity; complex I, II, III, and IV activities; and rearing behavior were observed. Additionally, the number of TUNEL-positive cells and various mitochondrial parameters, including oxygen consumption, transmembrane potential, adenosine triphosphate synthesis, and ETC activity, were measured.

RESULTS

We observed that FO exerted a protective effect against the 3-NP-induced toxicity, although complex II inhibition still occurred. Instead, this effect was related to strengthened mitochondrial complex III and IV activities.

DISCUSSION

Our results show that FO exerts a beneficial prophylactic effect against mitochondrial damage. Elucidating the mechanisms linking the effects of FO with its prevention of neurodegeneration could be the key to developing recommendations for FO consumption in neurological pathologies.

Cell death caused by the synergistic effects of zinc and dopamine is mediated by a stress sensor gene Gadd45b - implication in the pathogenesis of Parkinson's disease

The pathogenesis of Parkinson's disease (PD) is not completely understood, Zinc (Zn(2+) ) and dopamine (DA) have been shown to involve in the degeneration of dopaminergic cells. By microarray analysis, we identified Gadd45b as a candidate molecule that mediates Zn(2+) and DA-induced cell death; the mRNA and protein levels of Gadd45b are increased by Zn(2+) treatment and raised to an even higher level by Zn(2+) plus DA treatment. Zn(2+) plus DA treatment-induced PC12 cell death was enhanced when there was over-expression of Gadd45b and was decreased by knock down of Gadd45b. MAPK p38 and JNK signaling was able to cross-talk with Gadd45b during Zn(2+) and DA treatment. The synergistic effects of Zn(2+) and DA on PC12 cell death can be accounted for by an activation of the Gadd45b-induced cell death pathway and an inhibition of p38/JNK survival pathway. Furthermore, the in vivo results show that the levels of Gadd45b protein expression and phosphorylation of p38 were increased in the substantia nigra by the infusion of Zn(2+) /DA in the mouse brain and the level of Gadd45b mRNA is significantly higher in the substantia nigra of male PD patients than normal controls. The novel role of Gadd45b and its interactions with JNK and p38 will help our understanding of the pathogenesis of PD and help the development of future treatments for PD. Zinc and dopamine are implicated in the degeneration of dopaminergic neurons. We previously demonstrated that zinc and dopamine induced synergistic effects on PC12 cell death. Results from this study show that these synergistic effects can be accounted for by activation of the Gadd45b-induced cell death pathway and inhibition of the p38/JNK survival pathway. We provide in vitro and in vivo evidence to support a novel role for Gadd45b in the pathogenesis of Parkinson's disease.

Coherent and Contradictory Facts, Feats and Fictions Associated with Metal Accumulation in Parkinson's Disease: Epicenter or Outcome, Yet a Demigod Question

Unwarranted exposure due to liberal use of metals for maintaining the lavish life and to achieve the food demand for escalating population along with an incredible boost in the average human life span owing to orchestrated progress in rejuvenation therapy have gradually increased the occurrence of Parkinson's disease (PD). Etiology is albeit elusive; association of PD with metal accumulation has never been overlooked due to noteworthy similitude between metal-exposure symptoms and a few cardinal features of disease. Even though metals are entailed in the vital functions, a hysterical shift, primarily augmentation, escorts the stern nigrostriatal dopaminergic neurodegeneration. An increase in the passage of metals through the blood brain barrier and impaired metabolic activity and elimination system could lead to metal accumulation in the brain, which eventually makes dopaminergic neurons quite susceptible. In the present article, an update on implication of metal accumulation in PD/Parkinsonism has been provided. Moreover, encouraging and paradoxical facts and fictions associated with metal accumulation in PD/Parkinsonism have also been compiled. Systematic literature survey of PD is performed to describe updated information if metal accumulation is an epicenter or merely an outcome. Finally, a perspective on the association of metal accumulation with pesticide-induced Parkinsonism has been explained to unveil the likely impact of the former in the latter.

Neuroprotective effect of ethyl pyruvate against Zn(2+) toxicity via NAD replenishment and direct Zn(2+) chelation

Ethyl pyruvate (EP) is a simple aliphatic ester of pyruvic acid and has been shown to have robust protective effect in various pathological conditions. A variety of mechanisms have been reported to underlie the protective effects of EP, which include anti-inflammatory, anti-oxidative, and anti-apoptotic functions. Recently, we reported that EP suppressed high mobility group box 1 (HMGB1) release from primary microglial cells via direct Ca(2+) chelation. In the present study, we investigated whether and how EP chelates Zn(2+) in neurons when it is present at toxic levels. In cortical neurons treated with 40 μM of Zn(2+) for 24 h, both EP and pyruvate significantly suppressed neuronal cell death, although the potency of pyruvate was greater than that of EP, and that NAD replenishment contributed to the neuroprotective effects of both pyruvate and EP. However, when cortical neurons were exposed to acute treatment of Zn(2+) (400 μM, 15 min), EP, but not pyruvate, significantly suppressed neuronal death, despite the fact that NAD replenishment by EP was weaker than that by pyruvate. Spectrophotometric studies revealed that EP directly chelates Zn(2+), and this was confirmed in physiological contexts, such as, NMDA-treated primary cortical cultures and OGD-subjected hippocampal slice cultures, in which EP suppressed intracellular Zn(2+) elevation and neuronal cell death. In addition, EP markedly reduced the expressions of PARP-1 and of the NADPH oxidase subunit in Zn(2+)-treated primary cortical neurons, well known Zn(2+)-induced downstream processes. Together, these results show EP suppresses Zn(2+) induced neurotoxicity via dual functions, chelating Zn(2+) and promoting NAD replenishment.

New iboga-type alkaloids from Ervatamia hainanensis

The structures and absolute configurations of seven new iboga-type alkaloids 1–7 were determined by spectroscopic data, Mosher's method, single crystal X-ray diffraction and ECD analyses.

Targeting mitochondrial metal dyshomeostasis for the treatment of neurodegeneration

Mitochondrial impairment and metal dyshomeostasis are suggested to be associated with many neurodegenerative disorders including Alzheimer's disease, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis and Friedreich's ataxia. Treatments aimed at restoring metal homeostasis are highly effective in models of these diseases, and clinical trials hold promise. However, in general, the effect of these treatments on mitochondrial metal homeostasis is unclear, and the contribution of mitochondrial metal dyshomeostasis to disease pathogenesis requires further investigation. This review describes the role of metals in mitochondria in health, how mitochondrial metals are disrupted in neurodegenerative diseases, and potential therapeutics aimed at restoring mitochondrial metal homeostasis and function.

Transition metals activate TFEB in overexpressing cells

Exposure of cells to micromolar Cu activates recombinant transcription factor EB (TFEB), leading to expression of the lysosomal network genes. Whereas TFEB overexpression has a cytoprotective effect under moderate Cu exposure, it enhances oxidative stress and mitochondrial damage caused by high levels of Cu.

Transition metal toxicity is an important factor in the pathogenesis of numerous human disorders, including neurodegenerative diseases. Lysosomes have emerged as important factors in transition metal toxicity because they handle transition metals via endocytosis, autophagy, absorption from the cytoplasm and exocytosis. Transcription factor EB (TFEB) regulates lysosomal biogenesis and the expression of lysosomal proteins in response to lysosomal and/or metabolic stresses. Since transition metals cause lysosomal dysfunction, we proposed that TFEB may be activated to drive gene expression in response to transition metal exposure and that such activation may influence transition metal toxicity. We found that transition metals copper (Cu) and iron (Fe) activate recombinant TFEB and stimulate the expression of TFEB-dependent genes in TFEB-overexpressing cells. In cells that show robust lysosomal exocytosis, TFEB was cytoprotective at moderate levels of Cu exposure, decreasing oxidative stress as reported by the expression of heme oxygenase-1 (HMOX1) gene. However, at high levels of Cu exposure, particularly in cells with low levels of lysosomal exocytosis, activation of overexpressed TFEB was toxic, increasing oxidative stress and mitochondrial damage. Based on these data, we conclude that TFEB-driven gene network is a component of the cellular response to transition metals. These data suggest limitations and disadvantages of TFEB overexpression as a therapeutic approach.

Role of zinc and copper ions in the pathogenetic mechanisms of Alzheimer's and Parkinson's diseases

Disbalance of zinc (Zn2+) and copper (Cu2+) ions in the central nervous system is involved in the pathogenesis of numerous neurodegenerative disorders such as multisystem atrophy, amyotrophic lateral sclerosis, Creutzfeldt-Jakob disease, Wilson-Konovalov disease, Alzheimer's disease, and Parkinson's disease. Among these, Alzheimer's disease (AD) and Parkinson's disease (PD) are the most frequent age-related neurodegenerative pathologies with disorders in Zn2+ and Cu2+ homeostasis playing a pivotal role in the mechanisms of pathogenesis. In this review we generalized and systematized current literature data concerning this problem. The interactions of Zn2+ and Cu2+ with amyloid precursor protein (APP), β-amyloid (Abeta), tau-protein, metallothioneins, and GSK3β are considered, as well as the role of these interactions in the generation of free radicals in AD and PD. Analysis of the literature suggests that the main factors of AD and PD pathogenesis (oxidative stress, structural disorders and aggregation of proteins, mitochondrial dysfunction, energy deficiency) that initiate a cascade of events resulting finally in the dysfunction of neuronal networks are mediated by the disbalance of Zn2+ and Cu2+.

Mitochondrial metals as a potential therapeutic target in neurodegeneration

Transition metals are critical for enzyme function and protein folding, but in excess can mediate neurotoxic oxidative processes. As mitochondria are particularly vulnerable to oxidative damage due to radicals generated during ATP production, mitochondrial biometal homeostasis must therefore be tightly controlled to safely harness the redox potential of metal enzyme cofactors. Dysregulation of metal functions is evident in numerous neurological disorders including Alzheimer's disease, stroke, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis and Friedrich's ataxia. This review describes the mitochondrial metal defects in these disorders and highlights novel metal-based therapeutic approaches that target mitochondrial metal homeostasis in neurological disorders.

Mutations in the ATP13A2 gene and Parkinsonism: a preliminary review

Parkinson's disease (PD) is a major neurodegenerative disorder for which the etiology and pathogenesis remain as elusive as for Alzheimer's disease. PD appears to be caused by genetic and environmental factors, and pedigree and cohort studies have identified numerous susceptibility genes and loci related to PD. Autosomal recessive mutations in the genes Parkin, Pink1, DJ-1, ATP13A2, PLA2G6, and FBXO7 have been linked to PD susceptibility. Such mutations in ATP13A2, also named PARK9, were first identified in 2006 in a Chilean family and are associated with a juvenile-onset, levodopa-responsive type of Parkinsonism called Kufor-Rakeb syndrome (KRS). KRS involves pyramidal degeneration, supranuclear palsy, and cognitive impairment. Here we review current knowledge about the ATP13A2 gene, clinical characteristics of patients with PD-associated ATP13A2 mutations, and models of how the ATP13A2 protein may help prevent neurodegeneration by inhibiting α-synuclein aggregation and supporting normal lysosomal and mitochondrial function. We also discuss another ATP13A2 mutation that is associated with the family of neurodegenerative disorders called neuronal ceroid lipofuscinoses (NCLs), and we propose a single pathway whereby ATP13A2 mutations may contribute to NCLs and Parkinsonism. Finally, we highlight how studies of mutations in this gene may provide new insights into PD pathogenesis and identify potential therapeutic targets.

Regulation of the VHL/HIF-1 pathway by DJ-1

DJ-1 (PARK7) is a gene linked to autosomal recessive Parkinson disease (PD). We showed previously that DJ-1 loss sensitizes neurons in models of PD and stroke. However, the biochemical mechanisms underlying this protective role are not completely clear. Here, we identify Von Hippel Lindau (VHL) protein as a critical DJ-1-interacting protein. We provide evidence that DJ-1 negatively regulates VHL ubiquitination activity of the α-subunit of hypoxia-inducible factor-1 (HIF-1α) by inhibiting HIF-VHL interaction. Consistent with this observation, DJ-1 deficiency leads to lowered HIF-1α levels in models of both hypoxia and oxidative stress, two stresses known to stabilize HIF-1α. We also demonstrate that HIF-1α accumulation rescues DJ-1-deficient neurons against 1-methyl-4-phenylpyridinium-induced toxicity. Interestingly, lymphoblast cells extracted from DJ-1-related PD patients show impaired HIF-1α stabilization when compared with normal individuals, indicating that the DJ-1-VHL link may also be relevant to a human context. Together, our findings delineate a model by which DJ-1 mediates neuronal survival by regulation of the VHL-HIF-1α pathway.

Cellular function and pathological role of ATP13A2 and related P-type transport ATPases in Parkinson's disease and other neurological disorders

Mutations in ATP13A2 lead to Kufor-Rakeb syndrome, a parkinsonism with dementia. ATP13A2 belongs to the P-type transport ATPases, a large family of primary active transporters that exert vital cellular functions. However, the cellular function and transported substrate of ATP13A2 remain unknown. To discuss the role of ATP13A2 in neurodegeneration, we first provide a short description of the architecture and transport mechanism of P-type transport ATPases. Then, we briefly highlight key P-type ATPases involved in neuronal disorders such as the copper transporters ATP7A (Menkes disease), ATP7B (Wilson disease), the Na(+)/K(+)-ATPases ATP1A2 (familial hemiplegic migraine) and ATP1A3 (rapid-onset dystonia parkinsonism). Finally, we review the recent literature of ATP13A2 and discuss ATP13A2's putative cellular function in the light of what is known concerning the functions of other, better-studied P-type ATPases. We critically review the available data concerning the role of ATP13A2 in heavy metal transport and propose a possible alternative hypothesis that ATP13A2 might be a flippase. As a flippase, ATP13A2 may transport an organic molecule, such as a lipid or a peptide, from one membrane leaflet to the other. A flippase might control local lipid dynamics during vesicle formation and membrane fusion events.

Parkinson's disease-linked human PARK9/ATP13A2 maintains zinc homeostasis and promotes α-Synuclein externalization via exosomes

α-Synuclein plays a central causative role in Parkinson's disease (PD). Increased expression of the P-type ATPase ion pump PARK9/ATP13A2 suppresses α-Synuclein toxicity in primary neurons. Our data indicate that ATP13A2 encodes a zinc pump; neurospheres from a compound heterozygous ATP13A2(-/-) patient and ATP13A2 knockdown cells are sensitive to zinc, whereas ATP13A2 over-expression in primary neurons confers zinc resistance. Reduced ATP13A2 expression significantly decreased vesicular zinc levels, indicating ATP13A2 facilitates transport of zinc into membrane-bound compartments or vesicles. Endogenous ATP13A2 localized to multi-vesicular bodies (MVBs), a late endosomal compartment located at the convergence point of the endosomal and autophagic pathways. Dysfunction in MVBs can cause a range of detrimental effects including lysosomal dysfunction and impaired delivery of endocytosed proteins/autophagy cargo to the lysosome, both of which have been observed in cells with reduced ATP13A2 function. MVBs also serve as the source of intra-luminal nanovesicles released extracellularly as exosomes that can contain a range of cargoes including α-Synuclein. Elevated ATP13A2 expression reduced intracellular α-Synuclein levels and increased α-Synuclein externalization in exosomes >3-fold whereas ATP13A2 knockdown decreased α-Synuclein externalization. An increased export of exosome-associated α-Synuclein may explain why surviving neurons of the substantia nigra pars compacta in sporadic PD patients were observed to over-express ATP13A2. We propose ATP13A2's modulation of zinc levels in MVBs can regulate the biogenesis of exosomes capable of containing α-Synuclein. Our data indicate that ATP13A2 is the first PD-associated gene involved in exosome biogenesis and indicates a potential neuroprotective role of exosomes in PD.

Parkinson's disease-associated human ATP13A2 (PARK9) deficiency causes zinc dyshomeostasis and mitochondrial dysfunction

Human ATP13A2 (PARK9), a lysosomal type 5 P-type ATPase, has been associated with autosomal recessive early-onset Parkinson's disease (PD). ATP13A2 encodes a protein that is highly expressed in neurons and is predicted to function as a cation pump, although the substrate specificity remains unclear. Accumulation of zinc and mitochondrial dysfunction are established aetiological factors that contribute to PD; however, their underlying molecular mechanisms are largely unknown. Using patient-derived human olfactory neurosphere cultures, which harbour loss-of-function mutations in both alleles of ATP13A2, we identified a low intracellular free zinc ion concentration ([Zn²⁺]_i), altered expression of zinc transporters and impaired sequestration of Zn²⁺ into autophagy-lysosomal pathway-associated vesicles, indicating that zinc dyshomeostasis occurs in the setting of ATP13A2 deficiency. Pharmacological treatments that increased [Zn²⁺]_i also induced the production of reactive oxygen species and aggravation of mitochondrial abnormalities that gave rise to mitochondrial depolarization, fragmentation and cell death due to ATP depletion. The toxic effect of Zn²⁺ was blocked by ATP13A2 overexpression, Zn²⁺ chelation, antioxidant treatment and promotion of mitochondrial fusion. Taken together, these results indicate that human ATP13A2 deficiency results in zinc dyshomeostasis and mitochondrial dysfunction. Our data provide insights into the molecular mechanisms of zinc dyshomeostasis in PD and its contribution to mitochondrial dysfunction with ATP13A2 as a molecular link between the two distinctive aetiological factors of PD.

Neurodegeneration in Parkinson's disease: interactions of oxidative stress, tryptophan catabolites and depression with mitochondria and sirtuins

The biological underpinnings to the etiology and course of neurodegeneration in Parkinson's disease are an area of extensive research that has yet to produce an early biological marker or disease-slowing or preventative treatment. Recent conceptualizations of Parkinson's disease have integrated immuno-inflammation and oxidative and nitrosative stress occurring in depression, somatization and peripheral inflammation into the course of Parkinson's disease. We review the data showing the importance of immuno-inflammatory processes and oxidative and nitrosative stress in such classically conceived 'comorbidities', suggesting that lifetime, prodromal and concurrent depression and somatization may be intricately involved in the etiology and course of Parkinson's disease, rather than psychiatric comorbidities. This produces a longer term developmental perspective of Parkinson's disease, which incorporates tryptophan catabolites (TRYCATs), lipid peroxidation, sirtuins, cyclic adenosine monophosphate, aryl hydrocarbon receptor, and circadian genes. This integrates wider bodies of data pertaining to neuronal loss in Parkinson's disease, emphasizing how these interact with susceptibility genes to drive changes in mitochondria, blood-brain barrier permeability and intercellular signalling. We review this data here in the context of neurodegeneration in Parkinson's disease and to the future directions indicated for slowing disease progression.

Perturbation of transcription factor Nur77 expression mediated by myocyte enhancer factor 2D (MEF2D) regulates dopaminergic neuron loss in response to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)

We have earlier reported the critical nature of calpain-CDK5-MEF2 signaling in governing dopaminergic neuronal loss in vivo. CDK5 mediates phosphorylation of the neuronal survival factor myocyte enhancer factor 2 (MEF2) leading to its inactivation and loss. However, the downstream factors that mediate MEF2-regulated survival are unknown. Presently, we define Nur77 as one such critical downstream survival effector. Following 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) treatment in vivo, Nur77 expression in the nigrostriatal region is dramatically reduced. This loss is attenuated by expression of MEF2. Importantly, MEF2 constitutively binds to the Nur77 promoter in neurons under basal conditions. This binding is lost following 1-methyl-4-phenylpyridinium treatment. Nur77 deficiency results in significant sensitization to dopaminergic loss following 1-methyl-4-phenylpyridinium/MPTP treatment, in vitro and in vivo. Furthermore, Nur77-deficient MPTP-treated mice displayed significantly reduced levels of dopamine and 3,4-Dihydroxyphenylacetic acid in the striatum as well as elevated post synaptic FosB activity, indicative of increased nigrostriatal damage when compared with WT MPTP-treated controls. Importantly, this sensitization in Nur77-deficient mice was rescued with ectopic Nur77 expression in the nigrostriatal system. These results indicate that the inactivation of Nur77, induced by loss of MEF2 activity, plays a critical role in nigrostriatal degeneration in vivo.

Copper/zinc chelation by clioquinol reduces spinal cord white matter damage and behavioral deficits in a murine MOG-induced multiple sclerosis model

The present study aimed to evaluate the therapeutic potential of clioquinol (CQ), a metal chelator, on multiple sclerosis pathogenesis. Experimental autoimmune encephalomyelitis was induced by immunization with myelin oligodendrocyte glycoprotein (MOG(35-55)) in female mice. Three weeks after the initial immunization, demyelination and immune cell infiltration in the spinal cord were analyzed. CQ (30mg/kg) was given by gavage once per day for the entire experimental course. CQ profoundly reduced the daily clinical score and incidence rate of EAE mice. The CQ-mediated inhibition of the clinical course of EAE was accompanied by suppression of demyelination and reduced infiltration by encephalitogenic immune cells including CD4, CD8, CD20 and F4/80 positive cells. CQ also remarkably inhibited EAE-associated BBB disruption and MMP-9 activation. Autophagy contributes to clearance of aggregated proteins in astrocytes and neurons. The present study found that EAE increased the induction of autophagy and CQ further increased this expression. Furthermore, the present study found that post-treatment with CQ also reduced the clinical score of EAE and spinal cord demyelination. These results demonstrate that CQ inhibits the clinical features and neuropathological changes associated with EAE. The present study suggests that transition metals may be involved in several steps of multiple sclerosis pathogenesis.

The relevance of metals in the pathophysiology of neurodegeneration, pathological considerations

Neurodegenerative disorders are featured by a variety of pathological conditions that share similar critical processes, such as oxidative stress, free radical activity, proteinaceous aggregations, mitochondrial dysfunctions, and energy failure. They are mediated or triggered by an imbalance of metal ions leading to changes of critical biological systems and initiating a cascade of events finally leading to neurodegeneration and cell death. Their causes are multifactorial, and although the source of the shift in oxidative homeostasis is still unclear, current evidence points to changes in the balance of redox transition metals, especially iron, copper, and other trace metals. They are present at elevated levels in Alzheimer disease, Parkinson disease, multisystem atrophy, etc., while in other neurodegenerative disorders, copper, zinc, aluminum, and manganese are involved. This chapter will review the recent advances of the role of metals in the pathogenesis and pathophysiology of major neurodegenerative diseases and discuss the use of chelating agents as potential therapies for metal-related disorders.

NAD(+) maintenance attenuates light induced photoreceptor degeneration

Light-induced retinal damage (LD) occurs after surgery or sun exposure. We previously showed that zinc (Zn(2+)) accumulated in photoreceptors and RPE cells after LD but prior to cell death, and pyruvate or nicotinamide attenuated the resultant death perhaps by restoring nicotinamide adenine dinucleotide (NAD(+)) levels. We first examined the levels of NAD(+) and the efficacy of pyruvate or nicotinamide in oxidative toxicities using primary retinal cultures. We next manipulated NAD(+) levels in vivo and tested the affect on LD to photoreceptors and RPE. NAD(+) levels cycle with a 24-h rhythm in mammals, which is affected by the feeding schedule. Therefore, we tested the affect of increasing NAD(+) levels on LD by giving nicotinamide, inverting the feeding schedule, or using transgenic mice which overexpress cytoplasmic nicotinamide mononucleotide adenyl-transferase-1 (cytNMNAT1), an NAD(+) synthetic enzyme. Zn(2+) accumulation was also assessed in culture and in retinal sections. Retinas of light damaged animals were examined by OCT and plastic sectioning, and retinal NAD(+) levels were measured. Day fed, or nicotinamide treated rats showed less NAD(+) loss, and LD compared to night fed rats or untreated rats without changing the Zn(2+) staining pattern. CytNMNAT1 showed less Zn(2+) staining, NAD(+) loss, and cell death after LD. In conclusion, intense light, Zn(2+) and oxidative toxicities caused an increase in Zn(2+), NAD(+) loss, and cell death which were attenuated by NAD(+) restoration. Therefore, NAD(+) levels play a protective role in LD-induced death of photoreceptors and RPE cells.