Thiol peroxidases ameliorate LRRK2 mutant-induced mitochondrial and dopaminergic neuronal degeneration in Drosophila

Understanding role of pesticides in development of Parkinson's disease: Insights from Drosophila and rodent models

Parkinson's disease is a neurodegenerative illness linked to ageing, marked by the gradual decline of dopaminergic neurons in the midbrain. The exact aetiology of Parkinson's disease (PD) remains uncertain, with genetic predisposition and environmental variables playing significant roles in the disease's frequency. Epidemiological data indicates a possible connection between pesticide exposure and brain degeneration. Specific pesticides have been associated with important characteristics of Parkinson's disease, such as mitochondrial dysfunction, oxidative stress, and α-synuclein aggregation, which are crucial for the advancement of the disease. Recently, many animal models have been developed for Parkinson's disease study. Although these models do not perfectly replicate the disease's pathology, they provide valuable insights that improve our understanding of the condition and the limitations of current treatment methods. Drosophila, in particular, has been useful in studying Parkinson's disease induced by toxins or genetic factors. The review thoroughly analyses many animal models utilised in Parkinson's research, with an emphasis on issues including pesticides, genetic and epigenetic changes, proteasome failure, oxidative damage, α-synuclein inoculation, and mitochondrial dysfunction. The text highlights the important impact of pesticides on the onset of Parkinson's disease (PD) and stresses the need for more research on genetic and mechanistic alterations linked to the condition.

Post-translational modification and mitochondrial function in Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disease with currently no cure. Most PD cases are sporadic, and about 5-10% of PD cases present a monogenic inheritance pattern. Mutations in more than 20 genes are associated with genetic forms of PD. Mitochondrial dysfunction is considered a prominent player in PD pathogenesis. Post-translational modifications (PTMs) allow rapid switching of protein functions and therefore impact various cellular functions including those related to mitochondria. Among the PD-associated genes, Parkin, PINK1, and LRRK2 encode enzymes that directly involved in catalyzing PTM modifications of target proteins, while others like α-synuclein, FBXO7, HTRA2, VPS35, CHCHD2, and DJ-1, undergo substantial PTM modification, subsequently altering mitochondrial functions. Here, we summarize recent findings on major PTMs associated with PD-related proteins, as enzymes or substrates, that are shown to regulate important mitochondrial functions and discuss their involvement in PD pathogenesis. We will further highlight the significance of PTM-regulated mitochondrial functions in understanding PD etiology. Furthermore, we emphasize the potential for developing important biomarkers for PD through extensive research into PTMs.

Animal models of Parkinson's disease: bridging the gap between disease hallmarks and research questions

Parkinson's disease (PD) is a progressive neurodegenerative disorder characterized by motor and non-motor symptoms. More than 200 years after its first clinical description, PD remains a serious affliction that affects a growing proportion of the population. Prevailing treatments only alleviate symptoms; there is still neither a cure that targets the neurodegenerative processes nor therapies that modify the course of the disease. Over the past decades, several animal models have been developed to study PD. Although no model precisely recapitulates the pathology, they still provide valuable information that contributes to our understanding of the disease and the limitations of our treatment options. This review comprehensively summarizes the different animal models available for Parkinson's research, with a focus on those induced by drugs, neurotoxins, pesticides, genetic alterations, α-synuclein inoculation, and viral vector injections. We highlight their characteristics and ability to reproduce PD-like phenotypes. It is essential to realize that the strengths and weaknesses of each model and the induction technique at our disposal are determined by the research question being asked. Our review, therefore, seeks to better aid researchers by ensuring a concrete discernment of classical and novel animal models in PD research.

Disturb mitochondrial associated proteostasis: Neurodegeneration and imperfect ageing

The disturbance in mitochondrial functions and homeostasis are the major features of neuron degenerative conditions, like Parkinson’s disease, Amyotrophic Lateral Sclerosis, and Alzheimer’s disease, along with protein misfolding. The aberrantly folded proteins are known to link with impaired mitochondrial pathways, further contributing to disease pathogenesis. Despite their central significance, the implications of mitochondrial homeostasis disruption on other organelles and cellular processes remain insufficiently explored. Here, we have reviewed the dysfunction in mitochondrial physiology, under neuron degenerating conditions. The disease misfolded proteins impact quality control mechanisms of mitochondria, such as fission, fusion, mitophagy, and proteasomal clearance, to the detriment of neuron. The adversely affected mitochondrial functional roles, like oxidative phosphorylation, calcium homeostasis, and biomolecule synthesis as well as its axes and contacts with endoplasmic reticulum and lysosomes are also discussed. Mitochondria sense and respond to multiple cytotoxic stress to make cell adapt and survive, though chronic dysfunction leads to cell death. Mitochondria and their proteins can be candidates for biomarkers and therapeutic targets. Investigation of internetworking between mitochondria and neurodegeneration proteins can enhance our holistic understanding of such conditions and help in designing more targeted therapies.

Redox Modulation of Mitochondrial Proteins in the Neurotoxicant Models of Parkinson's Disease

Significance: Mitochondrial proteins regulate the oxidative phosphorylation, cellular metabolism, and free radical generation. Redox modulation alters the mitochondrial proteins and instigates the damage to dopaminergic neurons. Toxicants contribute to Parkinson's disease (PD) pathogenesis in conjunction with aging and genetic factors. While oxidative modulation of a number of mitochondrial proteins is linked to xenobiotic exposure, little is known about its role in the toxicant-induced PD. Understanding the role of redox modulation of mitochondrial proteins in complex cellular events leading to neurodegeneration is highly relevant. Recent Advances: Many toxicants are shown to inhibit complex I or III and elicit free radical production that alters the redox status of mitochondrial proteins. Implication of redox modulation of the mitochondrial proteins makes them a target to comprehend the underlying mechanism of toxicant-induced PD. Critical Issues: Owing to multifactorial etiology, exploration of onset and progression and treatment outcomes needs a comprehensive approach. The article explains about a few mitochondrial proteins that undergo redox changes along with the promising strategies, which help to alleviate the toxicant-induced redox imbalance leading to neurodegeneration. Future Directions: Although mitochondrial proteins are linked to PD, their role in toxicant-induced parkinsonism is not yet completely known. Preservation of antioxidant defense machinery could alleviate the redox modulation of mitochondrial proteins. Targeted antioxidant delivery, use of metal chelators, and activation of nuclear factor erythroid 2-related factor 2, and combinational therapy that encounters multiple free radicals, could ameliorate the redox modulation of mitochondrial proteins and thereby PD progression.

Unraveling Parkinson's Disease Neurodegeneration: Does Aging Hold the Clues?

Aging is the greatest risk factor for Parkinson's disease (PD), suggesting that mechanisms driving the aging process promote PD neurodegeneration. Several lines of evidence support a role for aging in PD. First, hallmarks of brain aging such as mitochondrial dysfunction and oxidative stress, loss of protein homeostasis, and neuroinflammation are centrally implicated in PD development. Second, mutations that cause monogenic PD are present from conception, yet typically only cause disease following a period of aging. Third, lifespan-extending genetic, dietary, or pharmacological interventions frequently attenuate PD-related neurodegeneration. These observations support a central role for aging in disease development and suggest that new discoveries in the biology of aging could be leveraged to elucidate novel mechanisms of PD pathophysiology. A recent rapid growth in our understanding of conserved molecular pathways that govern model organism lifespan and healthspan has highlighted a key role for metabolism and nutrient sensing pathways. Uncovering how metabolic pathways involving NAD+ consumption, insulin, and mTOR signaling link to the development of PD is underway and implicates metabolism in disease etiology. Here, we assess areas of convergence between nervous system aging and PD, evaluate the link between metabolism, aging, and PD and address the potential of metabolic interventions to slow or halt the onset of PD-related neurodegeneration drawing on evidence from cellular and animal models.

Altered Cortical Palmitoylation Induces Widespread Molecular Disturbances in Parkinson's Disease

The relationship between Parkinson's disease (PD), the second-most common neurodegenerative disease after Alzheimer's disease, and palmitoylation, a post-translational lipid modification, is not well understood. In this study, to better understand the role of protein palmitoylation in PD and the pathways altered in this disease, we analyzed the differential palmitoyl proteome (palmitome) in the cerebral cortex of PD patients compared to controls (n = 4 per group). Data-mining of the cortical palmitome from PD patients and controls allowed us to: (i) detect a set of 150 proteins with altered palmitoylation in PD subjects in comparison with controls; (ii) describe the biological pathways and targets predicted to be altered by these palmitoylation changes; and (iii) depict the overlap between the differential palmitome identified in our study with protein interactomes of the PD-linked proteins α-synuclein, LRRK2, DJ-1, PINK1, GBA and UCHL1. In summary, we partially characterized the altered palmitome in the cortex of PD patients, which is predicted to impact cytoskeleton, mitochondrial and fibrinogen functions, as well as cell survival. Our study suggests that protein palmitoylation could have a role in the pathophysiology of PD, and that comprehensive palmitoyl-proteomics offers a powerful approach for elucidating novel cellular pathways modulated in this neurodegenerative disease.

Mitophagy and reactive oxygen species interplay in Parkinson's disease

Mitophagy impairment and oxidative stress are cardinal pathological hallmarks in Parkinson's disease (PD), a common age-related neurodegenerative condition. The specific interactions between mitophagy and reactive oxygen species (ROS) have attracted considerable attention even though their exact interplay in PD has not been fully elucidated. We highlight the interactions between ROS and mitophagy, with a focus on the signalling pathways downstream to ROS that triggers mitophagy and draw attention to potential therapeutic compounds that target these pathways in both experimental and clinical models. Identifying a combination of ROS inhibitors and mitophagy activators to provide a physiologic balance in this complex signalling pathways may lead to a more optimal outcome. Deciphering the exact temporal relationship between mitophagy and oxidative stress and their triggers early in the course of neurodegeneration can unravel mechanistic clues that potentially lead to the development of compounds for clinical drug trials focusing on prodromic PD or at-risk individuals.

Intestine-derived α-synuclein initiates and aggravates pathogenesis of Parkinson's disease in Drosophila

Background

Aberrant aggregation of α-synuclein (α-syn) is a key pathological feature of Parkinson’s disease (PD), but the precise role of intestinal α-syn in the progression of PD is unclear. In a number of genetic Drosophila models of PD, α-syn was frequently ectopically expressed in the neural system to investigate the pathobiology.

Method

We investigated the potential role of intestinal α-syn in PD pathogenesis using a Drosophila model. Human α-syn was overexpressed in Drosophila guts, and life span, survival, immunofluorescence and climbing were evaluated. Immunofluorescence, Western blotting and reactive oxygen species (ROS) staining were performed to assess the effects of intestinal α-syn on intestinal dysplasia. High‐throughput RNA and 16S rRNA gene sequencing, quantitative RT‐PCR, immunofluorescence, and ROS staining were performed to determine the underlying molecular mechanism.

Results

We found that the intestinal α-syn alone recapitulated many phenotypic and pathological features of PD, including impaired life span, loss of dopaminergic neurons, and progressive motor defects. The intestine-derived α-syn disrupted intestinal homeostasis and accelerated the onset of intestinal ageing. Moreover, intestinal expression of α-syn induced dysbiosis, while microbiome depletion was efficient to restore intestinal homeostasis and ameliorate the progression of PD. Intestinal α-syn triggered ROS, and eventually led to the activation of the dual oxidase (DUOX)–ROS–Jun N-terminal Kinase (JNK) pathway. In addition, α-syn from both the gut and the brain synergized to accelerate the progression of PD.

Conclusions

The intestinal expression of α-syn recapitulates many phenotypic and pathologic features of PD, and induces dysbiosis that aggravates the pathology through the DUOX–ROS–JNK pathway in Drosophila. Our findings provide new insights into the role of intestinal α-syn in PD pathophysiology.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40035-022-00318-w.

Ebselen, a multi-target compound: its effects on biological processes and diseases

Ebselen is a well-known synthetic compound mimicking glutathione peroxidase (GPx), which catalyses some vital reactions that protect against oxidative damage. Based on a large number of in vivo and in vitro studies, various mechanisms have been proposed to explain its actions on multiple targets. It targets thiol-related compounds, including cysteine, glutathione, and thiol proteins (e.g., thioredoxin and thioredoxin reductase). Owing to this, ebselen is a unique multifunctional agent with important effects on inflammation, apoptosis, oxidative stress, cell differentiation, immune regulation and neurodegenerative disease, with anti-microbial, detoxifying and anti-tumour activity. This review summarises the current understanding of the multiple biological processes and molecules targeted by ebselen, and its pharmacological applications.

Oxidative stress factors in Parkinson's disease

Parkinson's disease (PD) is the second most common cause of neurodegeneration. Over the last two decades, various hypotheses have been proposed to explain the etiology of PD. Among these is the oxidant-antioxidant theory, which asserts that local and systemic oxidative damage triggered by reactive oxygen species and other free radicals may promote dopaminergic neuron degeneration. Excessive reactive oxygen species formation, one of the underlying causes of pathology in the course of PD has been evidenced by various studies showing that oxidized macromolecules including lipids, proteins, and nucleic acids accumulate in brain tissues of PD patients. DNA oxidation may produce various lesions in the course of PD. Mutations incurred as a result of DNA oxidation may further enhance reactive oxygen species production in the brains of PD patients, exacerbating neuronal loss due to defects in the mitochondrial electron transport chain, antioxidant depletion, and exposure to toxic oxidized dopamine. The protein products of SNCA, PRKN, PINK1, DJ1, and LRRK2 genes are associated with disrupted oxidoreductive homeostasis in PD. SNCA is the first gene linked with familial PD and is currently known to be affected by six mutations correlated with the disorder: A53T, A30P, E46K, G51D, H50Q and A53E. PRKN encodes Parkin, an E3 ubiquitin ligase which mediates the proteasome degradation of redundant and disordered proteins such as glycosylated α-synuclein. Over 100 mutations have been found among the 12 exons of PRKN. PINK1, a mitochondrial kinase highly expressed in the brain, may undergo loss of function mutations which constitute approximately 1-8% of early onset PD cases. More than 50 PD-promoting mutations have been found in PINK1. Mutations in DJ-1, a neuroprotective protein, are a rare cause of early onset PD and constitute only 1% of cases. Around 20 mutations have been found in DJ1 among PD patients thus far. Mutations in the LRRK2 gene are the most common known cause of familial autosomal dominant PD and sporadic PD. Treatment of PD patients, especially in the advanced stages of the disease, is very difficult. The first step in managing progressive PD is to optimize dopaminergic therapy by increasing the doses of dopamine agonists and L-dopa. The next step is the introduction of advanced therapies, such as deep brain stimulation. Genetic factors may influence the response to L-dopa and deep brain stimulation therapy and the regulation of oxidative stress. Consequently, research into minimally invasive surgical interventions, as well as therapies that target the underlying etiology of PD is warranted.

LRRK2 at the Crossroad of Aging and Parkinson's Disease

Parkinson's disease (PD) is a heterogeneous neurodegenerative disease characterized by the progressive loss of dopaminergic neurons in the substantia nigra pars compacta and the widespread occurrence of proteinaceous inclusions known as Lewy bodies and Lewy neurites. The etiology of PD is still far from clear, but aging has been considered as the highest risk factor influencing the clinical presentations and the progression of PD. Accumulating evidence suggests that aging and PD induce common changes in multiple cellular functions, including redox imbalance, mitochondria dysfunction, and impaired proteostasis. Age-dependent deteriorations in cellular dysfunction may predispose individuals to PD, and cellular damages caused by genetic and/or environmental risk factors of PD may be exaggerated by aging. Mutations in the LRRK2 gene cause late-onset, autosomal dominant PD and comprise the most common genetic causes of both familial and sporadic PD. LRRK2-linked PD patients show clinical and pathological features indistinguishable from idiopathic PD patients. Here, we review cellular dysfunctions shared by aging and PD-associated LRRK2 mutations and discuss how the interplay between the two might play a role in PD pathologies.

Mitochondrial Redox Signaling Is Critical to the Normal Functioning of the Neuronal System

Mitochondrial dysfunction often leads to neurodegeneration and is considered one of the main causes of neurological disorders, such as Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS) and other age-related diseases. Mitochondrial dysfunction is tightly linked to oxidative stress and accumulating evidence suggests the association between oxidative stress and neurological disorders. However, there is insufficient knowledge about the role of pro-oxidative shift in cellular redox and impairment of redox-sensitive signaling in the development of neurodegenerative pathological conditions. To gain a more complete understanding of the relationship between mitochondria, redox status, and neurodegenerative disorders, we investigated the effect of mitochondrial thiol-dependent peroxidases, peroxiredoxins (Prxs), on the physiological characteristics of flies, which change with pathologies such as PD, ALS and during aging. We previously found that through their ability to sense changes in redox and regulate redox-sensitive signaling, Prxs play a critical role in maintaining global thiol homeostasis, preventing age-related apoptosis and chronic activation of the immune response. We also found that the phenotype of flies under-expressing Prxs in mitochondria shares many characteristics with the phenotype of Drosophila models of neurological disorders such as ALS, including impaired locomotor activity and compromised redox balance. Here, we expanded the study and found that under-expression of mitochondrial Prxs leads to behavioral changes associated with neural function, including locomotor ability, sleep-wake behavior, and temperature-sensitive paralysis. We also found that under-expression of mitochondrial Prxs with a motor-neuron-specific driver, D42-GAL4, was a determining factor in the development of the phenotype of shortened lifespan and impaired motor activity in flies. The results of the study suggest a causal link between mitochondrial Prx activity and the development of neurological disorders and pre-mature aging.

Mitochondrial Kinases and the Role of Mitochondrial Protein Phosphorylation in Health and Disease

The major role of mitochondria is to provide cells with energy, but no less important are their roles in responding to various stress factors and the metabolic changes and pathological processes that might occur inside and outside the cells. The post-translational modification of proteins is a fast and efficient way for cells to adapt to ever changing conditions. Phosphorylation is a post-translational modification that signals these changes and propagates these signals throughout the whole cell, but it also changes the structure, function and interaction of individual proteins. In this review, we summarize the influence of kinases, the proteins responsible for phosphorylation, on mitochondrial biogenesis under various cellular conditions. We focus on their role in keeping mitochondria fully functional in healthy cells and also on the changes in mitochondrial structure and function that occur in pathological processes arising from the phosphorylation of mitochondrial proteins.

Identification of Targets from LRRK2 Rescue Phenotypes

Parkinson’s disease (PD) is an age-dependent neurodegenerative condition. Leucine-rich repeat kinase 2 (LRRK2) mutations are the most frequent cause of sporadic and autosomal dominant PD. The exact role of LRRK2 protective variants (R1398H, N551K) together with a pathogenic mutant (G2019S) in aging and neurodegeneration is unknown. We generated the following myc-tagged UAS-LRRK2 transgenic Drosophila: LRRK2 (WT), N551K, R1398H, G2019S single allele, and double-mutants (N551K/G2019S or R1398H/G2019S). The protective variants alone were able to suppress the phenotypic effects caused by the pathogenic LRRK2 mutation. Next, we conducted RNA-sequencing using mRNA isolated from dopaminergic neurons of these different groups of transgenic Drosophila. Using pathway enrichment analysis, we identified the top 10 modules (p < 0.05), with “LRRK2 in neurons in Parkinson’s disease” among the candidates. Further dissection of this pathway identified the most significantly modulated gene nodes such as eEF1A2, ACTB, eEF1A, and actin cytoskeleton reorganization. The induction of the pathway was successfully restored by the R1398H protective variant and R1398H-G2019S or N551K-G2019S rescue experiments. The oxidoreductase family of genes was also active in the pathogenic mutant and restored in protective and rescue variants. In summary, we provide in vivo evidence supporting the neuroprotective effects of LRRK2 variants. RNA sequencing of dopaminergic neurons identified upregulation of specific gene pathways in the Drosophila carrying the pathogenic variant, and this was restored in the rescue phenotypes. Using protective gene variants, our study identifies potential new targets and provides proof of principle of a new therapeutic approach that will further our understanding of aging and neurodegeneration in PD.

Mechanisms of ebselen as a therapeutic and its pharmacology applications

Ebselen is a synthetic organoselenium radical scavenger compound that possesses glutathione peroxidase-like activity and its own unique bioactivity by reacting with thiols, hydroperoxides and peroxynitrites. Owing to its high affinity toward several essential reactions, ebselen protects cellular components from oxidative and free radical damage, and it has been employed as a useful tool for studying redox-related mechanisms. Based on numerous in vitro and in vivo research, mechanisms are proposed to understand the biomedical and molecular actions of ebselen in health and disease, and it is currently under clinical trials for the prevention and treatment of various human disorders. Based on these outstanding discoveries, this review summarizes the current understanding of the biochemical and molecular characteristics, pharmacological applications and future directions of ebselen.

The New Frontiers in Neurodegenerative Diseases Treatment: Liposomal-Based Strategies

In the last decade, the onset of neurodegenerative (ND) diseases is strongly widespread due to the age increase of the world population. Despite the intensive investigations boosted by the scientific community, an efficacious therapy has not been outlined yet. The drugs commonly used are only able to relieve symptom severity; following their oral or intravenous administration routes, their effectiveness is strictly limited due to their low ability to reach the Central Nervous System (CNS) overcoming the Blood Brain Barrier (BBB). Starting from these assumptions, the engineered-nanocarriers, such as lipid-nanocarriers, are suitable agents to enhance the delivery of drugs into the CNS due to their high solubility, bioavailability, and stability. Liposomal delivery systems are considered to be the ideal carriers, not only for conventional drugs but also for neuroprotective small molecules and green-extracted compounds. In the current work, the LP-based drug delivery improvements in in vivo applications against ND disorders were carefully assessed.

Chetomin rescues pathogenic phenotype of LRRK2 mutation in drosophila

Leucine-rich repeat kinase 2 (LRRK2) is a complex protein kinase involved in a diverse set of functions. Mutations in LRRK2 are a common cause of autosomal dominant familial Parkinson's disease. Peroxiredoxin 2 (PRDX2) belongs to a family of anti-oxidants that protect cells from oxidative stress. Importantly, PRDX2 is a cytoplasmic protein, similar to Leucine-rich repeat kinase 2, which localizes predominantly in the cytosol. Here, we demonstrated that Leurice-rich repeat kinase 2 phosphorylates PRDX2 in Drosophila, leading to a loss of dopaminergic neurons, climbing ability and shortened lifespan. These pathogenic phenotypes in the LRRK2 Drosophila were rescued with transgenic expression of PRDX2. Chetomin, a PRDX2 mimic, belongs to a class of epidithio-diketopiperazine fungal secondary metabolites (containing a dithiol group that has hydrogen peroxide-reducing activity). As proof of principle, we demonstrated that Chetomin recapitulated the rescue in these mutant Drosophila. Our findings suggest that Chetomin can be a potential therapeutic compound in LRRK2 linked Parkinson's disease.

From Synaptic Dysfunction to Neuroprotective Strategies in Genetic Parkinson's Disease: Lessons From LRRK2

The pathogenesis of Parkinson’s disease (PD) is thought to rely on a complex interaction between the patient’s genetic background and a variety of largely unknown environmental factors. In this scenario, the investigation of the genetic bases underlying familial PD could unveil key molecular pathways to be targeted by new disease-modifying therapies, still currently unavailable. Mutations in the leucine-rich repeat kinase 2 (LRRK2) gene are responsible for the majority of inherited familial PD cases and can also be found in sporadic PD, but the pathophysiological functions of LRRK2 have not yet been fully elucidated. Here, we will review the evidence obtained in transgenic LRRK2 experimental models, characterized by altered striatal synaptic transmission, mitochondrial dysfunction, and α-synuclein aggregation. Interestingly, the processes triggered by mutant LRRK2 might represent early pathological phenomena in the pathogenesis of PD, anticipating the typical neurodegenerative features characterizing the late phases of the disease. A comprehensive view of LRRK2 neuronal pathophysiology will support the possible clinical application of pharmacological compounds targeting this protein, with potential therapeutic implications for patients suffering from both familial and sporadic PD.

In Vivo Visual Screen for Dopaminergic Rab ↔ LRRK2-G2019S Interactions in Drosophila Discriminates Rab10 from Rab3

LRRK2 mutations cause Parkinson's, but the molecular link from increased kinase activity to pathological neurodegeneration remains undetermined. Previous in vitro assays indicate that LRRK2 substrates include at least 8 Rab GTPases. We have now examined this hypothesis in vivo in a functional, electroretinogram screen, expressing each Rab with/without LRRK2-G2019S in selected Drosophila dopaminergic neurons. Our screen discriminated Rab10 from Rab3. The strongest Rab/LRRK2-G2019S interaction is with Rab10; the weakest with Rab3. Rab10 is expressed in a different set of dopaminergic neurons from Rab3. Thus, anatomical and physiological patterns of Rab10 are related. We conclude that Rab10 is a valid substrate of LRRK2 in dopaminergic neurons in vivo We propose that variations in Rab expression contribute to differences in the rate of neurodegeneration recorded in different dopaminergic nuclei in Parkinson's.

LRRK2 Biology from structure to dysfunction: research progresses, but the themes remain the same

Since the discovery of leucine-rich repeat kinase 2 (LRRK2) as a protein that is likely central to the aetiology of Parkinson’s disease, a considerable amount of work has gone into uncovering its basic cellular function. This effort has led to the implication of LRRK2 in a bewildering range of cell biological processes and pathways, and probable roles in a number of seemingly unrelated medical conditions. In this review we summarise current knowledge of the basic biochemistry and cellular function of LRRK2. Topics covered include the identification of phosphorylation substrates of LRRK2 kinase activity, in particular Rab proteins, and advances in understanding the activation of LRRK2 kinase activity via dimerisation and association with membranes, especially via interaction with Rab29. We also discuss biochemical studies that shed light on the complex LRRK2 GTPase activity, evidence of roles for LRRK2 in a range of cell signalling pathways that are likely cell type specific, and studies linking LRRK2 to the cell biology of organelles. The latter includes the involvement of LRRK2 in autophagy, endocytosis, and processes at the trans-Golgi network, the endoplasmic reticulum and also key microtubule-based cellular structures. We further propose a mechanism linking LRRK2 dimerisation, GTPase function and membrane recruitment with LRRK2 kinase activation by Rab29. Together these data paint a picture of a research field that in many ways is moving forward with great momentum, but in other ways has not changed fundamentally. Many key advances have been made, but very often they seem to lead back to the same places.

The role of NOX inhibitors in neurodegenerative diseases

Oxidative stress is a key player in both chronic and acute brain disease due to the higher metabolic demand of the brain. Among the producers of free radicals, NADPH-oxidase (NOX) is a major contributor to oxidative stress in neurological disorders. In the brain, the superoxide produced by NOX is mainly found in leukocytes. However, recent studies have reported that it can be found in several other cell types. NOX has been reported to regulate neuronal signaling, memory processing, and central cardiovascular homeostasis. However, overproduction of NOX can contribute to neurotoxicity, CNS degeneration, and cardiovascular disorders. Regarding the above functions, NOX has been shown to play a crucial role in chronic CNS diseases like Parkinson's disease (PD), Alzheimer's disease (AD), Huntington's disease (HD), multiple sclerosis (MS), and amyotrophic lateral sclerosis (ALS), and in acute CNS disorders such as stroke, spinal cord injury, traumatic brain injury (TBI), and related cerebrovascular diseases. NOX is a multi-subunit complex consisting of two membrane-associated and four cytosolic subunits. Thus, in recent years, inhibition of NOX activity has drawn a great deal of attention from researchers in the field of treating chronic and acute CNS disorders and preventing secondary complications. Mounting evidence has shown that NOX inhibition is neuroprotective and that inhibiting NOX in circulating immune cells can improve neurological disease conditions. This review summarizes recent studies on the therapeutic effects and pharmacological strategies regarding NOX inhibitors in chronic and acute brain diseases and focuses on the hurdles that should be overcome before their clinical implementation.

Exploring the "Multiple-Hit Hypothesis" of Neurodegenerative Disease: Bacterial Infection Comes Up to Bat

Despite major strides in personalized genomics, it remains poorly understood why neurodegenerative diseases occur in only a fraction of individuals with a genetic predisposition and conversely, why individuals with no genetic risk of a disorder develop one. Chronic diseases like Alzheimer's, Parkinson's, and Multiple sclerosis are speculated to result from a combination of genetic and environmental factors, a concept commonly referred to as the “multiple hit hypothesis.” A number of bacterial infections have been linked to increased risk of neurodegeneration, and in some cases, clearance of bacterial pathogens has been correlated with amelioration of central nervous system (CNS) deficits. Additionally, mutations in several genes known to contribute to CNS disorders like Parkinson's Disease have repeatedly been implicated in susceptibility to intracellular bacterial infection. Recent data has begun to demonstrate roles for these genes (PARK2, PINK1, and LRRK2) in modulating innate immune outcomes, suggesting that immune dysregulation may play an even more important role in neurodegeneration than previously appreciated. This review will broadly explore the connections between bacterial infection, immune dysregulation, and CNS disorders. Understanding this interplay and how bacterial pathogenesis contributes to the “multiple-hit hypothesis” of neurodegeneration will be crucial to develop therapeutics to effectively treat both neurodegeneration and infection.

Phosphoregulation on mitochondria: Integration of cell and organelle responses

Mitochondria are highly integrated organelles that are crucial to cell adaptation and mitigating adverse physiology. Recent studies demonstrate that fundamental signal transduction pathways incorporate mitochondrial substrates into their biological programs. Reversible phosphorylation is emerging as a useful mechanism to modulate mitochondrial function in accordance with cellular changes. Critical serine/threonine protein kinases, such as the c-Jun N-terminal kinase (JNK), protein kinase A (PKA), PTEN-induced kinase-1 (PINK1), and AMP-dependent protein kinase (AMPK), readily translocate to the outer mitochondrial membrane (OMM), the interface of mitochondria-cell communication. OMM protein kinases phosphorylate diverse mitochondrial substrates that have discrete effects on organelle dynamics, protein import, respiratory complex activity, antioxidant capacity, and apoptosis. OMM phosphorylation events can be tempered through the actions of local protein phosphatases, such as mitogen-activated protein kinase phosphatase-1 (MKP-1) and protein phosphatase 2A (PP2A), to regulate the extent and duration of signaling. The central mediators of OMM signal transduction are the scaffold proteins because the relative abundance of these accessory proteins determines the magnitude and duration of a signaling event on the mitochondrial surface, which dictates the biological outcome of a local signal transduction pathway. The concentrations of scaffold proteins, such as A-kinase anchoring proteins (AKAPs) and Sab (or SH3 binding protein 5-SH3BP5), have been shown to influence neuronal survival and vulnerability, respectively, in models of Parkinson's disease (PD), highlighting the importance of OMM signaling to health and disease. Despite recent progress, much remains to be discovered concerning the mechanisms of OMM signaling. Nonetheless, enhancing beneficial OMM signaling events and inhibiting detrimental protein-protein interactions on the mitochondrial surface may represent highly selective approaches to restore mitochondrial health and homeostasis and mitigate organelle dysfunction in conditions such as PD.

Signals Getting Crossed in the Entanglement of Redox and Phosphorylation Pathways: Phosphorylation of Peroxiredoxin Proteins Sparks Cell Signaling

Reactive oxygen and nitrogen species have cell signaling properties and are involved in a multitude of processes beyond redox homeostasis. The peroxiredoxin (Prdx) proteins are highly sensitive intracellular peroxidases that can coordinate cell signaling via direct reactive species scavenging or by acting as a redox sensor that enables control of binding partner activity. Oxidation of the peroxidatic cysteine residue of Prdx proteins are the classical post-translational modification that has been recognized to modulate downstream signaling cascades, but increasing evidence supports that dynamic changes to phosphorylation of Prdx proteins is also an important determinant in redox signaling. Phosphorylation of Prdx proteins affects three-dimensional structure and function to coordinate cell proliferation, wound healing, cell fate and lipid signaling. The advent of large proteomic datasets has shown that there are many opportunities to understand further how phosphorylation of Prdx proteins fit into intracellular signaling cascades in normal or malignant cells and that more research is necessary. This review summarizes the Prdx family of proteins and details how post-translational modification by kinases and phosphatases controls intracellular signaling.

LRRK2 and mitochondria: Recent advances and current views

Mutations in the leucine-rich repeat kinase 2 (LRRK2) gene account for most common causes of familial and sporadic Parkinson's disease (PD) and are one of the strongest genetic risk factors in sporadic PD. Pathways implicated in LRRK2-dependent neurodegeneration include cytoskeletal dynamics, vesicular trafficking, autophagy, mitochondria, and calcium homeostasis. However, the exact molecular mechanisms still need to be elucidated. Both genetic and environmental causes of PD have highlighted the importance of mitochondrial dysfunction in the pathogenesis of PD. Mitochondrial impairment has been observed in fibroblasts and iPSC-derived neural cells from PD patients with LRRK2 mutations, and LRRK2 has been shown to localize to mitochondria and to regulate its function. In this review we discuss recent discoveries relating to LRRK2 mutations and mitochondrial dysfunction.

The Sources of Reactive Oxygen Species and Its Possible Role in the Pathogenesis of Parkinson's Disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder characterized by progressive loss of dopaminergic neurons in the substantia nigra. The precise mechanism underlying pathogenesis of PD is not fully understood, but it has been widely accepted that excessive reactive oxygen species (ROS) are the key mediator of PD pathogenesis. The causative factors of PD such as gene mutation, neuroinflammation, and iron accumulation all could induce ROS generation, and the later would mediate the dopaminergic neuron death by causing oxidation protein, lipids, and other macromolecules in the cells. Obviously, it is of mechanistic and therapeutic significance to understand where ROS are derived and how ROS induce dopaminergic neuron damage. In the present review, we try to summarize and discuss the main source of ROS in PD and the key pathways through which ROS mediate DA neuron death.

Varied pathological and therapeutic response effects associated with CHCHD2 mutant and risk variants

Mutations and polymorphic risk variant of coiled-coil-helix-coiled-coil-helix domain containing 2 (CHCHD2) have been associated with late-onset Parkinson disease. In vivo pathological evidence of CHCHD2 mutations is currently lacking. Utilizing transgenic Drosophila model, we examined the relative pathophysiologic effect of the pathogenic (c.182C>T, p.Thr61Ile and c.434G>A, p.Arg145Gln) and the risk (c.5C>T, p.Pro2Leu) CHCHD2 variants. All the transgenic models exhibited locomotor dysfunction that could be exacerbated by rotenone exposure, dopaminergic neuron degeneration, reduction in lifespan, mitochondrial dysfunction, oxidative stress, and impairment in synaptic transmission. However, both mutants showed more severe early motor dysfunction, dopaminergic neuronal loss, and higher hydrogen peroxide production compared with the risk variant. p.Thr61Ile (co-segregated in three independent PD families) displayed the most severe phenotype followed by p.Arg145Gln (present only in index patient). We treated the transgenic flies with Ebselen, a mitochondrial hydrogen peroxide scavenger compound; Ebselen appears to be more effective in ameliorating motor function in the mutant than the risk variant models. We provide the first in vivo evidence of the pathological effects associated with CHCHD2 mutations. There was a difference in the pathological and drug response effects between the pathogenic and the risk variants. Ebselen may be a useful neuroprotective drug for carriers of CHCHD2 mutations.

Targeting LRRK2 in Parkinson's disease: an update on recent developments

INTRODUCTION

LRRK2 research has progressed significantly in recent years with more reports of LRRK2 interactors and the development of more specific and sophisticated LRRK2 kinase inhibitors. Identification of bone fide LRRK2 substrates will provide new therapeutic targets in LRRK2-linked Parkinson's disease (PD). Areas covered: This review aims to put current LRRK2 research into perspective. Beginning with recent LRRK2 mammalian models employed for in vivo validation of LRRK2 substrates, followed by updates on reported LRRK2 interactors and their inferred mechanisms. Finally an overview of commonly used LRRK2 kinase inhibitors will be depicted. Expert opinion: Identification of LRRK2 non-kinase functions suggests the possibility of alternative LRRK2 drug target sites and these should be further explored. Studies on the effects of LRRK2 kinase inhibition on its non-kinase function and its self-regulatory role will provide further insights on its pathophysiologic mechanisms. Development of robust measurements of LRRK2 inhibitor efficacy will be required. These would include identification of specific imaging ligands or direct biochemical assays that can accurately capture its intrinsic activity. Testing of new therapeutic drug targets in both LRRK2 carriers and non LRRK2-linked patients will be important since their phenotype is similar.

Mitochondrial peroxiredoxins are essential in regulating the relationship between Drosophila immunity and aging

Previously, we have shown that flies under-expressing the two mitochondrial peroxiredoxins (Prxs), dPrx3 and dPrx5, display increases in tissue-specific apoptosis and dramatically shortened life span, associated with a redox crisis, manifested as changes in GSH:GSSG and accumulation of protein mixed disulfides. To identify specific pathways responsible for the observed biological effects, we performed a transcriptome analysis. Functional clustering revealed a prominent group enriched for immunity-related genes, including a considerable number of NF-kB-dependent antimicrobial peptides (AMP) that are up-regulated in the Prx double mutant. Using qRT-PCR analysis we determined that the age-dependent changes in AMP levels in mutant flies were similar to those observed in controls when scaled to percentage of life span. To further clarify the role of Prx-dependent mitochondrial signaling, we expressed different forms of dPrx5, which unlike the uniquely mitochondrial dPrx3 is found in multiple subcellular compartments, including mitochondrion, nucleus and cytosol. Ectopic expression of dPrx5 in mitochondria but not nucleus or cytosol partially extended longevity under normal or oxidative stress conditions while complete restoration of life span occurred when all three forms of dPrx5 were expressed from the wild type dPrx5 transgene. When dPrx5 was expressed in mitochondria or in all three compartments, it substantially delayed the development of hyperactive immunity while expression of cytosolic or nuclear forms had no effect on the immune phenotype. The data suggest a critical role of mitochondria in development of chronic activation of the immune response triggered by impaired redox control.

Regulation of DJ-1 by Glutaredoxin 1 in Vivo: Implications for Parkinson's Disease

Parkinson's disease (PD) is the second most common neurodegenerative disease worldwide, caused by the degeneration of the dopaminergic neurons in the substantia nigra. Mutations in PARK7 (DJ-1) result in early onset autosomal recessive PD, and oxidative modification of DJ-1 has been reported to regulate the protective activity of DJ-1 in vitro. Glutathionylation is a prevalent redox modification of proteins resulting from the disulfide adduction of the glutathione moiety to a reactive cysteine-SH, and glutathionylation of specific proteins has been implicated in regulation of cell viability. Glutaredoxin 1 (Grx1) is the principal deglutathionylating enzyme within cells, and it has been reported to mediate protection of dopaminergic neurons in Caenorhabditis elegans; however many of the functional downstream targets of Grx1 in vivo remain unknown. Previously, DJ-1 protein content was shown to decrease concomitantly with diminution of Grx1 protein content in cell culture of model neurons (SH-SY5Y and Neuro-2A lines). In the current study we aimed to investigate the regulation of DJ-1 by Grx1 in vivo and characterize its glutathionylation in vitro. Here, with Grx(-/-) mice we provide show that Grx1 regulates protein levels of DJ-1 in vivo. Furthermore, with model neuronal cells (SH-SY5Y) we observed decreased DJ-1 protein content in response to treatment with known glutathionylating agents, and with isolated DJ-1 we identified two distinct sites of glutathionylation. Finally, we found that overexpression of DJ-1 in the dopaminergic neurons partly compensates for the loss of the Grx1 homologue in a C. elegans in vivo model of PD. Therefore, our results reveal a novel redox modification of DJ-1 and suggest a novel regulatory mechanism for DJ-1 content in vivo.

Mechanisms of Parkinson's Disease: Lessons from Drosophila

The power of Drosophila genetics has attracted attention in tackling important biomedical challenges such as the understanding and prevention of neurodegenerative diseases. Parkinson's disease (PD) is the most common neurodegenerative movement disorder which results from the relentless degeneration of midbrain dopaminergic neurons. Over the past two decades tremendous advances have been made in identifying genes responsible for inherited forms of PD. The ease of genetic manipulation in Drosophila has spurred the development of numerous models of PD, including expression of human genes carrying pathogenic mutations or the targeted mutation of conserved orthologs. The genetic and cellular analysis of these models is beginning to reveal fundamental insights into the pathogenic mechanisms. Numerous pathways and processes are disrupted in these models but some common themes are emerging. These often implicate aberrant synaptic function, protein aggregation, autophagy, oxidative stress, and mitochondrial dysfunction. Moreover, an impressive list of small molecule compounds have been identified as effective in reversing pathogenic phenotypes, paving the way to explore these for therapeutic interventions.

FUS-linked essential tremor associated with motor dysfunction in Drosophila

Essential tremor (ET) is one of the most common adult-onset neurological disorders which produce motor and non-motor symptoms. To date, there are no gold standard pathological hallmarks of ET, and despite a strong genetic contribution toward ET development, only a few pathogenic mutations have been identified. Recently, a pathogenic FUS-Q290X mutation has been reported in a large ET-affected family; however, the pathophysiologic mechanism underlying FUS-linked ET is unknown. Here, we generated transgenic Drosophila expressing hFUS-WT and hFUS-Q290X and targeted their expression in different tissues. We found that the targeted expression of hFUS-Q290X in the dopaminergic and the serotonergic neurons did not cause obvious neuronal degeneration, but it resulted in motor dysfunction which was accompanied by impairment in the GABAergic pathway. The involvement of the GABAergic pathway was supported by rescue of motor symptoms with gabapentin. Interestingly, we observed gender specific downregulation of GABA-R and NMDA-R expression and reduction in serotonin level. Overexpression of hFUS-Q290X also caused an increase in longevity and this was accompanied by downregulation of the IIS/TOR signalling pathway. Our in vivo studies of the hFUS-Q290X mutation in Drosophila link motor dysfunction to impairment in the GABAergic pathway. Our findings would facilitate further efforts in unravelling the pathophysiology of ET.

Linking F-box protein 7 and parkin to neuronal degeneration in Parkinson's disease (PD)

Mutations of F-box protein 7 (FBXO7) and Parkin, two proteins in ubiquitin-proteasome system (UPS), are both implicated in pathogenesis of dopamine (DA) neuron degeneration in Parkinson's disease (PD). Parkin is a HECT/RING hybrid ligase that physically receives ubiquitin on its catalytic centre and passes ubiquitin onto its substrates, whereas FBXO7 is an adaptor protein in Skp-Cullin-F-box (SCF) SCF(FBXO7) ubiquitin E3 ligase complex to recognize substrates and mediate substrates ubiquitination by SCF(FBXO7) E3 ligase. Here, we discuss the overlapping pathophysiologic mechanisms and clinical features linking Parkin and FBXO7 with autosomal recessive PD. Both proteins play an important role in neuroprotective mitophagy to clear away impaired mitochondria. Parkin can be recruited to impaired mitochondria whereas cellular stress can promote FBXO7 mitochondrial translocation. PD-linked FBXO7 can recruit Parkin into damaged mitochondria and facilitate its aggregation. WT FBXO7, but not PD-linked FBXO7 mutants can rescue DA neuron degeneration in Parkin null Drosophila. A better understanding of the common pathophysiologic mechanisms of these two proteins could unravel specific pathways for targeted therapy in PD.

Antioxidants inhibit neuronal toxicity in Parkinson's disease-linked LRRK2

Mutations in leucine‐rich repeat kinase‐2 are the most common cause of familial Parkinson's disease. The prevalent G2019S mutation increase oxidative, kinase and toxic activity and inhibit endogenous peroxidases. We initially screened a library of 84 antioxidants and identified seven phenolic compounds that inhibited kinase activity on leucine‐rich repeat kinase‐2 substrates. The representative antioxidants (piceatannol, thymoquinone, and esculetin) with strong kinase inhibitor activity, reduced loss in dopaminergic neurons, oxidative dysfunction, and locomotor defects in G2019S‐expressing neuronal and Drosophila models compared to weak inhibitors. We provide proof of principle that natural antioxidants with dual antioxidant and kinase inhibitor properties could be useful for leucine‐rich repeat kinase‐2‐linked Parkinson's disease.

The prion hypothesis of Parkinson's disease

The discovery of alpha-synuclein's prion-like behaviors in mammals, as well as a non-Mendelian type of inheritance, has led to a new concept in biology, the "prion hypothesis" of Parkinson's disease. The misfolding and aggregation of alpha-synuclein (α-syn) within the nervous system occur in many neurodegenerative diseases including Parkinson's disease (PD), Lewy body dementia (LBD), and multiple system atrophy (MSA). The molecular basis of synucleinopathies appears to be tightly coupled to α-syn's conformational conversion and fibril formation. The pathological form of α-syn consists of oligomers and fibrils with rich in β-sheets. The conversion of its α-helical structure to the β-sheet rich fibril is a defining pathologic feature of α-syn. These kinds of disorders have been classified as protein misfolding diseases or proteopathies which share key biophysical and biochemical characteristics with prion diseases. In this review, we highlight α-syn's prion-like activities in PD and PD models, describe the idea of a prion-like mechanism contributing to PD pathology, and discuss several key molecules that can modulate the α-syn accumulation and propagation.

A visual review of the interactome of LRRK2: Using deep-curated molecular interaction data to represent biology

Molecular interaction databases are essential resources that enable access to a wealth of information on associations between proteins and other biomolecules. Network graphs generated from these data provide an understanding of the relationships between different proteins in the cell, and network analysis has become a widespread tool supporting –omics analysis. Meaningfully representing this information remains far from trivial and different databases strive to provide users with detailed records capturing the experimental details behind each piece of interaction evidence. A targeted curation approach is necessary to transfer published data generated by primarily low-throughput techniques into interaction databases. In this review we present an example highlighting the value of both targeted curation and the subsequent effective visualization of detailed features of manually curated interaction information. We have curated interactions involving LRRK2, a protein of largely unknown function linked to familial forms of Parkinson's disease, and hosted the data in the IntAct database. This LRRK2-specific dataset was then used to produce different visualization examples highlighting different aspects of the data: the level of confidence in the interaction based on orthogonal evidence, those interactions found under close-to-native conditions, and the enzyme–substrate relationships in different in vitro enzymatic assays. Finally, pathway annotation taken from the Reactome database was overlaid on top of interaction networks to bring biological functional context to interaction maps.

Mitochondrial diseases: Drosophila melanogaster as a model to evaluate potential therapeutics

While often presented as a single entity, mitochondrial diseases comprise a wide range of clinical, biochemical and genetic heterogeneous disorders. Among them, defects in the process of oxidative phosphorylation are the most prevalent. Despite intense research efforts, patients are still without effective treatment. An important part of the development of new therapeutics relies on predictive models of the pathology in order to assess their therapeutic potential. Since mitochondrial diseases are a heterogeneous group of progressive multisystemic disorders that can affect any organ at any time, the development of various in vivo models for the different diseases-associated genes defects will accelerate the search for effective therapeutics. Here, we review existing Drosophila melanogaster models for mitochondrial diseases, with a focus on alterations in oxidative phosphorylation, and discuss the potential of this powerful model organism in the process of drug target discovery. This article is part of a Directed Issue entitled: Energy Metabolism Disorders and Therapies.

The role of the LRRK2 gene in Parkinsonism

Parkinson’s disease (PD), like many common age-related conditions, has been recognized to have a substantial genetic component. Multiple lines of evidence suggest that Leucine-rich repeat kinase 2 (LRRK2) is a crucial factor to understanding the etiology of PD. LRRK2 is a large, widely expressed, multi-domain and multifunctional protein. LRRK2 mutations are the major cause to inherited and sporadic PD. In this review, we discuss the pathology and clinical features which show diversity and variability of LRRK2-associated PD. In addition, we do a thorough literature review and provide theoretical data for gene counseling. Further, we present the evidence linking LRRK2 to various possible pathogenic mechanism of PD such as α-synuclein, tau, inflammatory response, oxidative stress, mitochondrial dysfunction, synaptic dysfunction as well as autophagy-lysosomal system. Based on the above work, we investigate activities both within GTPase and outside enzymatic regions in order to obtain a potential therapeutic approach to solve the LRRK2 problem.

Glutaredoxin deficiency exacerbates neurodegeneration in C. elegans models of Parkinson's disease

Parkinson's disease (PD) is characterized by selective degeneration of dopaminergic neurons. Although the etiology of PD remains incompletely understood, oxidative stress has been implicated as an important contributor in the development of PD. Oxidative stress can lead to oxidation and functional perturbation of proteins critical to neuronal survival. Glutaredoxin 1 (Grx1) is an evolutionally conserved antioxidant enzyme that repairs protein oxidation by reversing the oxidative modification of cysteine known as S-glutathionylation. We aimed to explore the regulatory role of Grx1 in PD. We first examined the levels of Grx1 in postmortem midbrain samples from PD patients, and observed that Grx1 content is decreased in PD, specifically within the dopaminergic neurons. We subsequently investigated the potential role of Grx1 deficiency in PD pathogenesis by examining the consequences of loss of the Caenorhabditis elegans Grx1 homolog in well-established worm models of familial PD caused by overexpression of pathogenic human LRRK2 mutants G2019S or R1441C. We found that loss of the Grx1 homolog led to significant exacerbation of the neurodegenerative phenotype in C. elegans overexpressing the human LRRK2 mutants. Re-expression in the dopaminergic neurons of the active, but not a catalytically inactive form of the Grx1 homolog rescued the exacerbated phenotype. Loss of the Grx1 homolog also exacerbated the neurodegenerative phenotype in other C. elegans models, including overexpression of human α-synuclein and overexpression of tyrosine hydroxylase (a model of sporadic PD). Therefore, our results reveal a novel neuroprotective role of glutaredoxin against dopaminergic neurodegeneration in models of familial and sporadic PD.