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Parkinson’s disease (PD) is a progressive neurodegenerative condition that pathognomonically involves the death of dopaminergic neurons in the substantia nigra pars compacta, resulting in a myriad of motor and nonmotor symptoms. Given the insurmountable burden of this disease on the population and healthcare system, significant efforts have been put forth toward generating disease modifying therapies. This class of treatments characteristically alters disease course, as opposed to current strategies that focus on managing symptoms. Previous literature has implicated the cell death pathway known as parthanatos in PD progression. Inhibition of this pathway by targeting poly (ADP)-ribose polymerase 1 (PARP1) prevents neurodegeneration in a model of idiopathic PD. However, PARP1 has a vast repertoire of functions within the body, increasing the probability of side effects with the long-term treatment likely necessary for clinically significant neuroprotection. Recent work culminated in the development of a novel agent targeting the macrophage migration inhibitory factor (MIF) nuclease domain, also named parthanatos-associated apoptosis-inducing factor nuclease (PAAN). This nuclease activity specifically executes the terminal step in parthanatos. Parthanatos-associated apoptosis-inducing factor nuclease inhibitor-1 was neuroprotective in multiple preclinical mouse models of PD. This piece will focus on contextualizing this discovery, emphasizing its significance, and discussing its potential implications for parthanatos-directed treatment. © 2024 International Parkinson and Movement Disorder Society. [ABSTRACT FROM AUTHOR]

Leucine-rich repeat kinase-2 (LRRK2) mutations are a common cause of Parkinson's disease. Here we identify inhibitors of LRRK2 kinase that are protective in in vitro and in vivo models of LRRK2-induced neurodegeneration. These results establish that LRRK2-induced degeneration of neurons in vivo is kinase dependent and that LRRK2 kinase inhibition provides a potential new neuroprotective paradigm for the treatment of Parkinson's disease.

In recent years, research into Parkinson's disease and similar neurodegenerative disorders has increasingly suggested that these conditions are synonymous with failures in proteostasis. However, the spotlight of this research has remained firmly focused on the tail end of proteostasis, primarily aggregation, misfolding, and degradation, with protein translation being comparatively overlooked. Now, there is an increasing body of evidence supporting a potential role for translation in the pathogenesis of PD, and its dysregulation is already established in other similar neurodegenerative conditions. In this paper, we consider how altered protein translation fits into the broader picture of PD pathogenesis, working hand in hand to compound the stress placed on neurons, until this becomes irrecoverable. We will also consider molecular players of interest, recent evidence that suggests that aggregates may directly influence translation in PD progression, and the implications for the role of protein translation in our development of clinically useful diagnostics and therapeutics. [ABSTRACT FROM AUTHOR]

Pathologic α-synuclein plays an important role in the pathogenesis of α-synucleinopathies such as Parkinson's disease (PD). Disruption of proteostasis is thought to be central to pathologic α-synuclein toxicity; however, the molecular mechanism of this deregulation is poorly understood. Complementary proteomic approaches in cellular and animal models of PD were used to identify and characterize the pathologic α-synuclein interactome. We report that the highest biological processes that interacted with pathologic α-synuclein in mice included RNA processing and translation initiation. Regulation of catabolic processes that include autophagy were also identified. Pathologic α-synuclein was found to bind with the tuberous sclerosis protein 2 (TSC2) and to trigger the activation of the mammalian target of rapamycin (mTOR) complex 1 (mTORC1), which augmented mRNA translation and protein synthesis, leading to neurodegeneration. Genetic and pharmacologic inhibition of mTOR and protein synthesis rescued the dopamine neuron loss, behavioral deficits, and aberrant biochemical signaling in the α-synuclein preformed fibril mouse model and Drosophila transgenic models of pathologic α-synuclein–induced degeneration. Pathologic α-synuclein furthermore led to a destabilization of the TSC1-TSC2 complex, which plays an important role in mTORC1 activity. Constitutive overexpression of TSC2 rescued motor deficits and neuropathology in α-synuclein flies. Biochemical examination of PD postmortem brain tissues also suggested deregulated mTORC1 signaling. These findings establish a connection between mRNA translation deregulation and mTORC1 pathway activation that is induced by pathologic α-synuclein in cellular and animal models of PD. Editor's summary: Disrupted proteostasis contributes to the development of Parkinson's disease (PD), but underlying mechanisms remain elusive. Khan et al. used cellular and animal models to show that pathologic α-synuclein interacted with tuberous sclerosis protein (TSC) 2 and increased mRNA translation. Inhibition of mammalian target of rapamycin complex 1 mTORC1 normalized protein synthesis, decreased loss of dopaminergic neurons, and ameliorated behavioral deficits in fly and mouse models. Pathologic α-synuclein also disrupted the TSC1-TSC2 complex, a negative regulator of mTORC1. TSC1 and 2 expression was decreased in post-mortem brains of patients with PD, suggesting the TSC1-TSC2/mTORC1 axis as potential treatment target warranting further studies. —Daniela Neuhofer [ABSTRACT FROM AUTHOR]

Regulation of gene expression by epigenetic modifications means lasting and heritable changes in the function of genes without alterations in the DNA sequence. Of all epigenetic mechanisms identified thus far, DNA methylation has been of particular interest in both aging and age-related disease research over the last decade given the consistency of site-specific DNA methylation changes during aging that can predict future health and lifespan. An increasing line of evidence has implied the dynamic nature of DNA (de)methylation events that occur throughout the lifespan has a role in the pathophysiology of aging and age-associated neurodegenerative conditions, including Parkinson's disease (PD). In this regard, PD methylome shows, to some extent, similar genome-wide changes observed in the methylome of healthy individuals of matching age. In this review, we start by providing a brief overview of studies outlining global patterns of DNA methylation, then its mechanisms and regulation, within the context of aging and PD. Considering diverging lines of evidence from different experimental and animal models of neurodegeneration and how they combine to shape our current understanding of tissue-specific changes in DNA methylome in health and disease, we report a high-level comparison of the genomic methylation landscapes of brain, with an emphasis on dopaminergic neurons in PD and in natural aging. We believe this will be particularly useful for systematically dissecting overlapping genome-wide alterations in DNA methylation during PD and healthy aging, and for improving our knowledge of PD-specific changes in methylation patterns independent of aging process. [ABSTRACT FROM AUTHOR]

Parkinson's disease (PD) is the second most prevalent neurodegenerative disease of the central nervous system, with an estimated 5,000,000 cases worldwide. PD pathology is characterized by the accumulation of misfolded α-synuclein, which is thought to play a critical role in the pathogenesis of the disease. Animal models of PD suggest that activation of Abelson tyrosine kinase (c-Abl) plays an essential role in the initiation and progression of α-synuclein pathology and initiates processes leading to degeneration of dopaminergic and nondopaminergic neurons. Given the potential role of c-Abl in PD, a c-Abl inhibitor library was developed to identify orally bioavailable c-Abl inhibitors capable of crossing the blood-brain barrier based on predefined characteristics, leading to the discovery of IkT-148009. IkT-148009, a brain-penetrant c-Abl inhibitor with a favorable toxicology profile, was analyzed for therapeutic potential in animal models of slowly progressive, α-synuclein–dependent PD. In mouse models of both inherited and sporadic PD, IkT-148009 suppressed c-Abl activation to baseline and substantially protected dopaminergic neurons from degeneration when administered therapeutically by once daily oral gavage beginning 4 weeks after disease initiation. Recovery of motor function in PD mice occurred within 8 weeks of initiating treatment concomitantly with a reduction in α-synuclein pathology in the mouse brain. These findings suggest that IkT-148009 may have potential as a disease-modifying therapy in PD. Protecting dopamine neurons with a c-Abl inhibitor: Neurodegeneration of dopaminergic neurons in Parkinson's disease (PD) leads to activation of the non-receptor tyrosine kinase c-Abl. Karuppagounder et al. now report that IkT-148009, a c-Abl inhibitor that can cross the blood-brain barrier, rescued dopaminergic neuron deficits in mouse models of inherited and sporadic PD. Rescue of dopaminergic neurons occurred even when oral administration of IkT-148009 began 4 weeks after disease initiation. These results suggest that IkT-148009 should be investigated further as a disease-modifying therapy for PD. —OMS [ABSTRACT FROM AUTHOR]

Parkinson’s disease (PD) is characterized by the progressive loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc). In this study, we generated a transgenic model by crossing germline Parkin–/– mice with PolgAD257A mice, an established model of premature aging and mitochondrial stress. We hypothesized that loss of Parkin–/– in PolgAD257A/D257A mice would exacerbate mitochondrial dysfunction, leading to loss of dopamine neurons and nigral-striatal specific neurobehavioral motor dysfunction. We found that aged Parkin–/– /PolgAD257A/D257A male and female mice exhibited severe behavioral deficits, nonspecific to the nigral-striatal pathway, with neither dopaminergic neurodegeneration nor reductions in striatal dopamine. We saw no difference in expression levels of nuclear-encoded subunits of mitochondrial markers and mitochondrial Complex I and IV activities, although we did observe substantial reductions in mitochondrial-encoded COX41I, indicating mitochondrial dysfunction as a result of PolgAD257A/D257A mtDNA mutations. Expression levels of mitophagy markers LC3I/LC3II remained unchanged between cohorts, suggesting no overt mitophagy defects. Expression levels of the parkin substrates, VDAC, NLRP3, and AIMP2 remained unchanged, suggesting no parkin dysfunction. In summary, we were unable to observe dopaminergic neurodegeneration with corresponding nigral-striatal neurobehavioral deficits, nor Parkin or mitochondrial dysfunction in Parkin–/– /PolgAD257A/D257A mice. These findings support a lack of synergism of Parkin loss on mitochondrial dysfunction in mouse models of mitochondrial deficits. [ABSTRACT FROM AUTHOR]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.tins.2005.05.002 Byline: Andrew B. West (a), Valina L. Dawson (a)(b)(c), Ted M. Dawson (a)(b) Abstract: Epidemiological evidence suggests a reduced incidence of many common types of non-smoking-related cancers in individuals with Parkinson's disease (PD). Genes that underlie familial forms of PD are often abnormally expressed in cancer, owing to their differential regulation or mutation. Functional studies implicate these genes in maintenance of the cell cycle, in some cases through interaction in the ubiquitin-proteasome system. Variation in genes associated with familial-linked PD could therefore modify susceptibility to both cancer and PD, implying some degree of overlap in the underlying biochemical dysfunction. When considering the normal function of these PD-linked genes in the periphery and their potential role in cancer, further emphasis might be placed on protein handling relating to cell-cycle control in the etiology of PD. Author Affiliation: (a) Institute for Cell Engineering, and Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA (b) Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA (c) Department of Physiology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA

In idiopathic Parkinson's disease (PD), pathologic αSyn aggregates drive oxidative and nitrative stress that may cause genomic and mitochondrial DNA damage. These events are associated with activation of the cyclic GMP-AMP synthase (cGAS)/stimulator of interferon genes (STING) immune pathway, but it is not known whether STING is activated in or contributes to α-synucleinopathies. Herein, we used primary cell cultures and the intrastriatal αSyn preformed fibril (αSyn-PFF) mouse model of PD to demonstrate that αSyn pathology causes STING-dependent neuroinflammation and dopaminergic neurodegeneration. In microglia-astrocyte cultures, αSyn-PFFs induced DNA double-strand break (DSB) damage response signaling (γH2A.X), as well as TBK1 activation that was blocked by STING inhibition. In the αSyn-PFF mouse model, we similarly observed TBK1 activation and increased γH2A.X within striatal microglia prior to the onset of dopaminergic neurodegeneration. Using STING-deficient (Stinggt) mice, we demonstrated that striatal interferon activation in the α-Syn PFF model is STINGdependent. Furthermore, Stinggt mice were protected from α-Syn PFF-induced motor deficits, pathologic αSyn accumulation, and dopaminergic neuron loss. We also observed upregulation of STING protein in the substantia nigra pars compacta (SNpc) of human PD patients that correlated significantly with pathologic αSyn accumulation. STING was similarly upregulated in microglia cultures treated with αSyn-PFFs, which primed the pathway to mount stronger interferon responses when exposed to a STING agonist. Our results suggest that microglial STING activation contributes to both the neuroinflammation and neurodegeneration arising from α-synucleinopathies, including PD. [ABSTRACT FROM AUTHOR]

A recent breakthrough paper published in Science Translational Medicine has provided compelling evidence that inhibition of Parkin Interacting Substrate (PARIS) may offer clinical researchers an important new therapeutic approach since it shows considerable promise as an important biological target potentially capable of pharmaceutical intervention to slow long term neurodegeneration in patients with Parkinson's disease (PD). We present several PD-relevant perspectives on this paper that were not discussed in that otherwise entirely scientific narrative. We also outline the some of the work leading up to it, including the massive drug screen that proved necessary to discover a clinically suitable inhibitor of PARIS (Farnesol), as well as relevant PD research within the wider drug class, issues surrounding its future formulation, and next steps in translating this new knowledge into the clinic to evaluate possible long-term PD patient benefits. [ABSTRACT FROM AUTHOR]

Aberrant activation of the non-receptor kinase c-Abl is implicated in the development of pathogenic hallmarks of Parkinson's disease, such as α-synuclein aggregation and progressive neuronal loss. c-Abl-mediated phosphorylation and inhibition of parkin ligase function lead to accumulation of parkin interacting substrate (PARIS) that mediates α-synuclein pathology-initiated dopaminergic neurodegeneration. Here we show that, in addition to PARIS accumulation, c-Abl phosphorylation of PARIS is required for PARIS-induced cytotoxicity. c-Abl-mediated phosphorylation of PARIS at Y137 (within the Krüppel-associated box domain) drives its association with KAP1 and the repression of genes with diverse functions in pathways such as chromatin remodelling and p53-dependent cell death. One phosphorylation-dependent PARIS target, MDM4 (a p53 inhibitor that associates with MDM2; also known as MDMX), is transcriptionally repressed in a histone deacetylase-dependent manner via PARIS binding to insulin response sequence motifs within the MDM4 promoter. Virally induced PARIS transgenic mice develop c-Abl activity-dependent Parkinson's disease features such as motor deficits, dopaminergic neuron loss and neuroinflammation. PARIS expression in the midbrain resulted in c-Abl activation, PARIS phosphorylation, MDM4 repression and p53 activation, all of which are blocked by the c-Abl inhibitor nilotinib. Importantly, we also observed aberrant c-Abl activation and PARIS phosphorylation along with PARIS accumulation in the midbrain of adult parkin knockout mice, implicating c-Abl in recessive Parkinson's disease. Inhibition of c-Abl or PARIS phosphorylation by nilotinib or Y137F-PARIS expression in adult parkin knockout mice blocked MDM4 repression and p53 activation, preventing motor deficits and dopaminergic neurodegeneration. Finally, we found correlative increases in PARIS phosphorylation, MDM4 repression and p53 activation in post-mortem Parkinson's disease brains, pointing to clinical relevance of the c-Abl-PARIS-MDM4-p53 pathway. Taken together, our results describe a novel mechanism of epigenetic regulation of dopaminergic degeneration downstream of pathological c-Abl activation in Parkinson's disease. Since c-Abl activation has been shown in sporadic Parkinson's disease, PARIS phosphorylation might serve as both a useful biomarker and a potential therapeutic target to regulate neuronal loss in Parkinson's disease. [ABSTRACT FROM AUTHOR]

The transcriptional repressor called parkin interacting substrate (PARIS; ZNF746) was initially identified as a novel co-substrate of parkin and PINK1 that leads to Parkinson's disease (PD) by disrupting mitochondrial biogenesis through peroxisome proliferator-activated receptor gamma (PPARγ) coactivator -1α (PGC-1α) suppression. Since its initial discovery, growing evidence has linked PARIS to defective mitochondrial biogenesis observed in PD pathogenesis. Yet, dopaminergic (DA) neuron-specific mechanistic underpinnings and genome-wide PARIS binding landscape has not been explored. We employed conditional translating ribosome affinity purification (TRAP) followed by RNA sequencing (TRAP-seq) for transcriptome profiling of DA neurons in transgenic Drosophila lines expressing human PARIS wild type (WT) or mutant (C571A). We also generated genome-wide maps of PARIS occupancy using ChIP-seq in human SH-SY5Y cells. The results demonstrated that PPARγ functions as a master regulator of PARIS-induced molecular changes at the transcriptome level, confirming that PARIS acts primarily on PGC-1α to lead to neurodegeneration in PD. Moreover, we identified that PARIS actively modulates expression of PPARγ target genes by physically binding to the promoter regions. Together, our work revealed how PARIS drives adverse effects on modulation of PPAR-γ associated gene clusters in DA neurons. [ABSTRACT FROM AUTHOR]

The spread of pathological α-synuclein (α-syn) is a crucial event in the progression of Parkinson's disease (PD). Cell surface receptors such as lymphocyte activation gene 3 (LAG3) and amyloid precursor-like protein 1 (APLP1) can preferentially bind α-syn in the amyloid over monomeric state to initiate cell-to-cell transmission. However, the molecular mechanism underlying this selective binding is unknown. Here, we perform an array of biophysical experiments and reveal that LAG3 D1 and APLP1 E1 domains commonly use an alkaline surface to bind the acidic C terminus, especially residues 118 to 140, of α-syn. The formation of amyloid fibrils not only can disrupt the intramolecular interactions between the C terminus and the amyloid-forming core of α-syn but can also condense the C terminus on fibril surface, which remarkably increase the binding affinity of α-syn to the receptors. Based on this mechanism, we find that phosphorylation at serine 129 (pS129), a hallmark modification of pathological α-syn, can further enhance the interaction between α-syn fibrils and the receptors. This finding is further confirmed by the higher efficiency of pS129 fibrils in cellular internalization, seeding, and inducing PD-like α-syn pathology in transgenic mice. Our work illuminates the mechanistic understanding on the spread of pathological α-syn and provides structural information for therapeutic targeting on the interaction of α-syn fibrils and receptors as a potential treatment for PD. [ABSTRACT FROM AUTHOR]

Aggregation of misfolded α-synuclein (α-syn) is the major component of Lewy bodies and neurites in Parkinson's disease (PD) and related α-synucleinopathies. Some α-syn mutations (e.g., A53T) in familial PD recapitulate the α-syn pathology in transgenic mice, which supports the importance of pathologic α-syn in driving the pathogenesis of α-synucleinopathies. Lymphocyte activation gene 3 (Lag3) is a receptor of α-syn fibrils facilitating pathologic α-syn spread; however, the role of Lag3 in mediating the pathogenesis in α-syn transgenic mice is not clear. Here, we report that depletion of Lag3 in human α-syn A53T transgenic (hA53T) mice significantly reduces the level of detergent-insoluble α-syn aggregates and phosphorylated ser129 α-syn, and inhibits activation of microglia and astrocytes. The absence of Lag3 significantly delays disease progression and reduces the behavioral deficits in hA53T transgenic mice leading to prolonged survival. Taken together, these results show that Lag3 contributes to the pathogenesis in the α-syn A53T transgenic mouse model. [ABSTRACT FROM AUTHOR]

That certain cell types in the central nervous system are more likely to undergo neurodegeneration in Parkinson's disease is a widely appreciated but poorly understood phenomenon. Many vulnerable subpopulations, including dopamine neurons in the substantia nigra pars compacta, have a shared phenotype of large, widely distributed axonal networks, dense synaptic connections, and high basal levels of neural activity. These features come at substantial bioenergetic cost, suggesting that these neurons experience a high degree of mitochondrial stress. In such a context, mechanisms of mitochondrial quality control play an especially important role in maintaining neuronal survival. In this review, we focus on understanding the unique challenges faced by the mitochondria in neurons vulnerable to neurodegeneration in Parkinson's and summarize evidence that mitochondrial dysfunction contributes to disease pathogenesis and to cell death in these subpopulations. We then review mechanisms of mitochondrial quality control mediated by activation of PINK1 and Parkin, two genes that carry mutations associated with autosomal recessive Parkinson's disease. We conclude by pinpointing critical gaps in our knowledge of PINK1 and Parkin function, and propose that understanding the connection between the mechanisms of sporadic Parkinson's and defects in mitochondrial quality control will lead us to greater insights into the question of selective vulnerability. [ABSTRACT FROM AUTHOR]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.cell.2009.09.026 Byline: Joo-Ho Shin, Valina L. Dawson, Ted M. Dawson

We recently demonstrated that NLY01, a novel glucagon-like peptide-1 receptor agonist, exerts neuroprotective effects in two mouse models of PD in a glia-dependent manner. NLY01 prevented microglia from releasing inflammatory mediators known to convert astrocytes into a neurotoxic A1 reactive subtype. Importantly, we provided evidence that this neuroprotection was not mediated by a direct action of NLY01 on neurons or astrocytes (e.g., by activating neurotrophic pathways or modulating astrocyte reactivity per se). In the present article, we provide a generalist review of microglia and astrocytes in neurodegeneration and discuss the emerging paradigm of A1 astrocyte neurotoxicity in more detail. We comment on specific inferences that are naturally suggested by our work in this area and the differential level of support it offers to each. Finally, we discuss implications for the overall goal of creating disease-modifying therapies for PD, survey emerging methodologies for accelerating translational research on glia in neurodegeneration, and describe expected challenges for developing glia-directed therapies that do not impede essential physiological functions carried out by glia in the CNS. © 2019 International Parkinson and Movement Disorder Society. [ABSTRACT FROM AUTHOR]

Mutations in LRRK2 are known to be the most common genetic cause of sporadic and familial Parkinson's disease (PD). Multiple lines of LRRK2 transgenic or knockin mice have been developed, yet none exhibit substantial dopamine (DA)-neuron degeneration. Here we develop human tyrosine hydroxylase (TH) promotercontrolled tetracycline-sensitive LRRK2 G2019S (GS) and LRRK2 G2019S kinase-dead (GS/DA) transgenic mice and show that LRRK2 GS expression leads to an age- and kinase-dependent cell-autonomous neurodegeneration of DA and norepinephrine (NE) neurons. Accompanying the loss of DA neurons are DAdependent behavioral deficits and α-synuclein pathology that are also LRRK2 GS kinase-dependent. Transmission EM reveals that that there is an LRRK2 GS kinase-dependent significant reduction in synaptic vesicle number and a greater abundance of clathrin-coated vesicles in DA neurons. These transgenic mice indicate that LRRK2-induced DA and NE neurodegeneration is kinasedependent and can occur in a cell-autonomous manner. Moreover, these mice provide a substantial advance in animal model development for LRRK2-associated PD and an important platform to investigate molecular mechanisms for how DA neurons degenerate as a result of expression of mutant LRRK2. [ABSTRACT FROM AUTHOR]

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Background: Mutations in glucocerebrosidase (GBA) cause Gaucher disease (GD) and increase the risk of developing Parkinson's disease (PD) and Dementia with Lewy Bodies (DLB). Since both genetic and environmental factors contribute to the pathogenesis of sporadic PD, we investigated the susceptibility of nigrostriatal dopamine (DA) neurons in L444P GBA heterozygous knock-in (GBA+/L444P) mice to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), a selective dopaminergic mitochondrial neurotoxin. Method: We used GBA+/L444P mice, α-synuclein knockout (SNCA-/-) mice at 8 months of age, and adeno-associated virus (AAV)-human GBA overexpression to investigate the rescue effect of DA neuronal loss and susceptibility by MPTP. Mitochondrial morphology and functional assay were used to identify mitochondrial defects in GBA+/L444P mice. Motor behavioral test, immunohistochemistry, and HPLC were performed to measure dopaminergic degeneration by MPTP and investigate the relationship between GBA mutation and α-synuclein. Mitochondrial immunostaining, qPCR, and Western blot were also used to study the effects of α-synuclein knockout or GBA overexpression on MPTP-induced mitochondrial defects and susceptibility. Results: L444P GBA heterozygous mutation reduced GBA protein levels, enzymatic activity and a concomitant accumulation of α-synuclein in the midbrain of GBA+/L444P mice. Furthermore, the deficiency resulted in defects in mitochondria of cortical neurons cultured from GBA+/L444P mice. Notably, treatment with MPTP resulted in a significant loss of dopaminergic neurons and striatal dopaminergic fibers in GBA+/L444P mice compared to wild mice. type (WT) mice. Levels of striatal DA and its metabolites were more depleted in the striatum of GBA+/L444P mice. Behavioral deficits, neuroinflammation, and mitochondrial defects were more exacerbated in GBA+/L444P mice after MPTP treatment. Importantly, MPTP induced PD-like symptoms were significantly improved by knockout of α-synuclein or augmentation of GBA via AAV5-hGBA injection in both WT and GBA+/L444P mice. Intriguingly, the degree of reduction in MPTP induced PD-like symptoms in GBA+/L444P α-synuclein (SNCA)-/- mice was nearly equal to that in SNCA-/- mice after MPTP treatment. Conclusion: Our results suggest that GBA deficiency due to L444P GBA heterozygous mutation and the accompanying accumulation of α-synuclein render DA neurons more susceptible to MPTP intoxication. Thus, GBA and α-synuclein play dual physiological roles in the survival of DA neurons in response to the mitochondrial dopaminergic neurotoxin, MPTP. [ABSTRACT FROM AUTHOR]

Although the etiology of Parkinson's disease (PD) is poorly understood, oxidative stress has long been implicated in the pathogenesis of the disease. However, multifaceted and divergent signaling cascades downstream of oxidative stress have posed challenges for researchers to identify a central component of the oxidative stress-induced pathways causing neurodegeneration in PD. Since 2010, c-Abl-a non-receptor tyrosine kinase and an indicator of oxidative stress-has shown remarkable potential as a future promising drug target in PD therapeutics. Although, the constitutively active form of c-Abl, Bcr-Abl, has a long history in chronic myeloid leukemia and acute lymphocytic leukemia, the role of c-Abl in PD and relevant neurodegenerative diseases was completely unknown. Recently, others and we have identified and validated c-Abl as an important pathogenic mediator of the disease, where activated c-Abl emerges as a common link to various PD-related inducers of oxidative stress relevant to both sporadic and familial forms of PD and α-synucleinopathies. This review discusses the role of c-Abl in PD and the latest advancement on c-Abl as a drug target and as a prospective biomarker. [ABSTRACT FROM AUTHOR]

Monogenetic, familial forms of Parkinson's disease (PD) only account for 5-10% of the total number of PD cases, but analysis of the genes involved therein is invaluable to understanding PD-associated neurodegenerative signaling. One such gene, parkin, encodes a 465 amino acid E3 ubiquitin ligase. Of late, there has been considerable interest in the role of parkin signaling in PD and in identifying its putative substrates, as well as the elucidation of the mechanisms through which parkin itself is activated. Its dysfunction underlies both inherited and idiopathic PD-associated neurodegeneration. Here, we review recent literature that provides a model of activation of parkin in the setting of mitochondrial damage that involves PINK1 (PTEN-induced kinase-1) and phosphoubiquitin. We note that neuronal parkin is primarily a cytosolic protein (with various non-mitochondrial functions), and discuss potential cytosolic parkin activation mechanisms. [ABSTRACT FROM AUTHOR]

Background: Mutations in PINK1 and PARKIN are the most common causes of recessive early-onset Parkinson's disease (EOPD). Together, the mitochondrial ubiquitin (Ub) kinase PINK1 and the cytosolic E3 Ub ligase PARKIN direct a complex regulated, sequential mitochondrial quality control. Thereby, damaged mitochondria are identified and targeted to degradation in order to prevent their accumulation and eventually cell death. Homozygous or compound heterozygous loss of either gene function disrupts this protective pathway, though at different steps and by distinct mechanisms. While structure and function of PARKIN variants have been well studied, PINK1 mutations remain poorly characterized, in particular under endogenous conditions. A better understanding of the exact molecular pathogenic mechanisms underlying the pathogenicity is crucial for rational drug design in the future. Methods: Here, we characterized the pathogenicity of the PINK1 p.I368N mutation on the clinical and genetic as well as on the structural and functional level in patients' fibroblasts and in cell-based, biochemical assays. Results: Under endogenous conditions, PINK1 p.I368N is expressed, imported, and N-terminally processed in healthy mitochondria similar to PINK1 wild type (WT). Upon mitochondrial damage, however, full-length PINK1 p.I368N is not sufficiently stabilized on the outer mitochondrial membrane (OMM) resulting in loss of mitochondrial quality control. We found that binding of PINK1 p.I368N to the co-chaperone complex HSP90/CDC37 is reduced and stress-induced interaction with TOM40 of the mitochondrial protein import machinery is abolished. Analysis of a structural PINK1 p.I368N model additionally suggested impairments of Ub kinase activity as the ATP-binding pocket was found deformed and the substrate Ub was slightly misaligned within the active site of the kinase. Functional assays confirmed the lack of Ub kinase activity. Conclusions: Here we demonstrated that mutant PINK1 p.I368N can not be stabilized on the OMM upon mitochondrial stress and due to conformational changes in the active site does not exert kinase activity towards Ub. In patients' fibroblasts, biochemical assays and by structural analyses, we unraveled two pathomechanisms that lead to loss of function upon mutation of p.I368N and highlight potential strategies for future drug development. [ABSTRACT FROM AUTHOR]

Summary Mutations in PTEN-induced putative kinase 1 ( PINK1 ) and parkin cause autosomal-recessive Parkinson’s disease through a common pathway involving mitochondrial quality control. Parkin inactivation leads to accumulation of the parkin interacting substrate (PARIS, ZNF746) that plays an important role in dopamine cell loss through repression of proliferator-activated receptor gamma coactivator-1-alpha (PGC-1α) promoter activity. Here, we show that PARIS links PINK1 and parkin in a common pathway that regulates dopaminergic neuron survival. PINK1 interacts with and phosphorylates serines 322 and 613 of PARIS to control its ubiquitination and clearance by parkin. PINK1 phosphorylation of PARIS alleviates PARIS toxicity, as well as repression of PGC-1α promoter activity. Conditional knockdown of PINK1 in adult mouse brains leads to a progressive loss of dopaminergic neurons in the substantia nigra that is dependent on PARIS. Altogether, these results uncover a function of PINK1 to direct parkin-PARIS-regulated PGC-1α expression and dopaminergic neuronal survival. [ABSTRACT FROM AUTHOR]

Mitochondrial dynamics and mitophagy have been linked to cardiovascular and neurodegenerative diseases. Here, we demonstrate that the mitochondrial division dynamin Drp1 and the Parkinson's disease-associated E3 ubiquitin ligase parkin synergistically maintain the integrity of mitochondrial structure and function in mouse heart and brain. Mice lacking cardiac Drp1 exhibited lethal heart defects. In Drp1 KO cardiomyocytes, mitochondria increased their connectivity, accumulated ubiquitinated proteins, and decreased their respiration. In contrast to the current views of the role of parkin in ubiquitination of mitochondrial proteins, mitochondrial ubiquitination was independent of parkin in Drp1 KO hearts, and simultaneous loss of Drp1 and parkin worsened cardiac defects. Drp1 and parkin also play synergistic roles in neuronal mitochondrial homeostasis and survival. Mitochondrial degradation was further decreased by combination of Drp1 and parkin deficiency, compared with their single loss. Thus, the physiological importance of parkin in mitochondrial homeostasis is revealed in the absence of mitochondrial division in mammals. [ABSTRACT FROM AUTHOR]

c-Abl is activated in the brain of Parkinson's disease (PD) patients and in 1-methyl-4-phenyl-1,2,3, 6-tetrahydropyridine (MPTP)-intoxicated mice where it inhibits parkin through tyrosine phosphorylation leading to the accumulation of parkin substrates, and neuronal cell death. In the present study, we evaluated the in vivo efficacy of nilotinib, a brain penetrant c-Abl inhibitor, in the acute MPTP-induced model of PD. Our results show that administration of nilotinib reduces c-Abl activation and the levels of the parkin substrate, PARIS, resulting in prevention of dopamine (DA) neuron loss and behavioral deficits following MPTP intoxication. On the other hand, we observe no reduction in the tyrosine phosphorylation of parkin and the parkin substrate, AIMP2 suggesting that the protective effect of nilotinib may, in part, be parkin-independent or to the pharmacodynamics properties of nilotinib. This study provides a strong rationale for testing other brain permeable c-Abl inhibitors as potential therapeutic agents for the treatment of PD. [ABSTRACT FROM AUTHOR]

The defining pathogenic feature of Parkinson's disease is the age-dependent loss of dopaminergic neurons. Mutations and inactivation of parkin, an ubiquitin E3 ligase, induce Parkinson's disease through accumulation of pathogenic substrates. We found that transgenic overexpression of a parkin substrate, aminoacyl-tRNA synthetase complex interacting multifunctional protein-2 (AIMP2), led to a selective, age-dependent, progressive loss of dopaminergic neurons via activation of poly(ADP-ribose) polymerase-1 (PARP1). AIMP2 accumulation in vitro and in vivo resulted in PARP1 overactivation and dopaminergic cell toxicity via direct association of these proteins in the nucleus, providing a path to PARP1 activation other than DNA damage. Inhibition of PARP1 through gene deletion or drug inhibition reversed behavioral deficits and protected against dopamine neuron death in AIMP2 transgenic mice. These data indicate that brain-permeable PARP inhibitors could effectively delay or prevent disease progression in Parkinson's disease. [ABSTRACT FROM AUTHOR]

The leucine-rich repeat kinase 2 (LRRK2) gene was found to play a role in the pathogenesis of both familial and sporadic Parkinson’s disease (PD). LRRK2 encodes a large multi-domain protein that is expressed in different tissues. To date, the physiological and pathological functions of LRRK2 are not clearly defined. In this study we have explored the role of LRRK2 in controlling vesicle trafficking in different cellular or animal models and using various readouts. In neuronal cells, the presence of LRRK2G2019S pathological mutant determines increased extracellular dopamine levels either under basal conditions or upon nicotine stimulation. Moreover, mutant LRRK2 affects the levels of dopamine receptor D1 on the membrane surface in neuronal cells or animal models. Ultrastructural analysis of PC12-derived cells expressing mutant LRRK2G2019S shows an altered intracellular vesicle distribution. Taken together, our results point to the key role of LRRK2 to control vesicle trafficking in neuronal cells. [ABSTRACT FROM AUTHOR]

Parkinson's disease (PD) is a progressive neurodegenerative disease caused by the interaction of genetic and environmental factors. However, the etiology of PD remains largely unknown. Macroautophagy is known to play an essential role in the degradation of abnormal proteins and organelles. Furthermore, the loss of autophagy-related (Atg) genes results in neurodegeneration and abnormal protein accumulation. Since these are also pathologic features of Parkinson's disease, the conditional impairment of autophagy may lead to improved animal models for the study of PD. Using transgenic mice expressing Cre recombinase under the control of either the dopamine transporter or the engrailed-1 promoters, we generated mice with the conditional deletion of Atg7 in the dopamine neurons of the substantia nigra pars compacta, other regions of the midbrain, and also the hindbrain. This conditional impairment of autophagy results in the age-related loss of dopaminergic neurons and corresponding loss of striatal dopamine, the accumulation of low-molecular-weight α-synuclein, and the presence of ubiquitinated protein aggregates, recapitulating many of the pathologic features of PD. These conditional knock-out animals provide insight into the process of autophagy in Parkinson's disease pathology. [ABSTRACT FROM AUTHOR]

Mutations in the LRRK2 (leucine-rich repeat kinase 2) gene are the most frequent genetic cause of PD (Parkinson’s disease), and these mutations play important roles in sporadic PD. The LRRK2 protein contains GTPase and kinase domains and several protein–protein interaction domains. The kinase and GTPase activity of LRRK2 seem to be important in regulating LRRK2-dependent cellular signalling pathways. LRRK2’s GTPase and kinase domains may reciprocally regulate each other to direct LRRK2’s ultimate function. Although most LRRK2 investigations are centred on LRRK2’s kinase activity, the present review focuses on the function of LRRK2’s GTPase activity in LRRK2 physiology and pathophysiology. [ABSTRACT FROM AUTHOR]

Both sporadic and autosomal dominant forms of Parkinson's disease (PD) have been causally linked to mutations in leucine-rich repeat kinase 2 (LRRK2), a large protein with multiple domains. The kinase domain plays an important role in LRRK2-mediated toxicity. Although a number of investigations have focused on LRRK2 kinase activity, less is known about the GTPase function of LRRK2. The activity of GTPases is regulated by GTPase activating proteins (GAPs) and GTP exchange factors. Here, we identify ArfGAP1 as the first GAP for LRRK2. ArfGAP1 binds LRRK2 predominantly via the WD40 and kinase domain of LRRK2, and it increases LRRK2 GTPase activity and regulates LRRK2 toxicity both in vitro and in vivo in Drosophila melanogaster. Unexpectedly, ArfGAP1 is an LRRK2 kinase substrate whose GAP activity is inhibited by LRRK2, whereas wild-type and G2019S LRRK2 autophosphorylation and kinase activity are significantly reduced in the presence of ArfGAP1. Overexpressed ArfGAP1 exhibits toxicity that is reduced by LRRK2 both in vitro and in vivo. &Dgr;64 -ArfGAP1, a dominant-negative ArfGAP1, and shRNA knockdown of ArfGAP1 reduce LRRK2 toxicity. Thus, LRRK2 and ArfGAP1 reciprocally regulate the activity of each other. Our results provide insight into the basic pathobiology of LRRK2 and indicate an important role for the GTPase domain and ArfGAP1 in LRRK2-mediated toxicity. These data suggest that agents targeted toward regulation of LRRK2 GTP hydrolysis might be therapeutic agents for the treatment of PD. [ABSTRACT FROM AUTHOR]

Genetic studies have provided valuable insight into the pathological mechanisms underlying Parkinson's disease (PD). The elucidation of genetic components to what was once largely considered a nongenetic disease has given rise to a multitude of cell and animal models enabling the dissection of molecular pathways involved in disease etiology. Here, we review advances obtained from models of dominant mutations in α-synuclein and LRRK2 as well as recessive PINK1, parkin and DJ-1 mutations. Recent genome-wide association studies have implicated genetic variability at two of these loci, α-synuclein and LRRK2, as significant risk factors for developing sporadic PD. This, coupled with the established role of mitochondrial impairment in both familial and sporadic PD, highlights the likelihood of common mechanisms fundamental to the etiology of both. [ABSTRACT FROM AUTHOR]

Genetic and biochemical abnormalities of α-synuclein are associated with the pathogenesis of Parkinson's disease. In the present study we investigated the in vivo interaction of mouse and human α-synuclein with the potent parkinsonian neurotoxin, MPTP. We find that while lack of mouse α-synuclein in mice is associated with reduced vulnerability to MPTP, increased levels of human α-synuclein expression is not associated with obvious changes in the vulnerability of dopaminergic neurons to MPTP. However, expressing human α-synuclein variants (human wild type or A53T) in the asynuclein null mice completely restores the vulnerability of nigral dopaminergic neurons to MPTP. These results indicate that human α-synuclein can functionally replace mouse α-synuclein in regard to vulnerability of dopaminergic neurons to MPTP-toxicity. Significantly, α-synuclein null mice and wild type mice were equally sensitive to neurodegeneration induced by 29NH2-MPTP, a MPTP analog that is selective for serotoninergic and noradrenergic neurons. These results suggest that effects of α-synuclein on MPTP like compounds are selective for nigral dopaminergic neurons. Immunoblot analysis of bsynuclein and Akt levels in the mice reveals selective increases in b-synuclein and phosphorylated Akt levels in ventral midbrain, but not in other brain regions, of α-synuclein null mice, implicating the α-synuclein-level dependent regulation of b-synuclein expression in modulation of MPTP-toxicity by α-synuclein. Together these findings provide new mechanistic insights on the role α-synuclein in modulating neurodegenerative phenotypes by regulation of Akt-mediated cell survival signaling in vivo. [ABSTRACT FROM AUTHOR]

Mutations in the leucine-rich repeat kinase 2 (LRRK2) gene are associated with late-onset, autosomal-dominant, familial Parkinson's disease (PD) and also contribute to sporadic disease. The LRRK2 gene encodes a large protein with multiple domains, including functional Roc GTPase and protein kinase domains. Mutations in LRRK2 most likely cause disease through a toxic gain-of-function mechanism. The expression of human LRRK2 variants in cultured primary neurons induces toxicity that is dependent on intact GTP binding or kinase activities. However, the mechanism(s) underlying LRRK2-induced neuronal toxicity is poorly understood, and the contribution of GTPase and/or kinase activity to LRRK2 pathobiology is not well defined. To explore the pathobiology of LRRK2, we have developed a model of LRRK2 cytotoxicity in the baker's yeast Saccharomyces cerevisiae. Protein domain analysis in this model reveals that expression of GTPase domain-containing fragments of human LRRK2 are toxic. LRRK2 toxicity in yeast can be modulated by altering GTPase activity and is closely associated with defects in endocytic vesicular trafficking and autophagy. These truncated LRRK2 variants induce similar toxicity in both yeast and primary neuronal models and cause similar vesicular defects in yeast as full-length LRRK2 causes in primary neurons. The toxicity induced by truncated LRRK2 variants in yeast acts through a mechanism distinct from toxicity induced by human a-synuclein. A genome-wide genetic screen identified modifiers of LRRK2-induced toxicity in yeast including components of vesicular trafficking pathways, which can also modulate the trafficking defects caused by expression of truncated LRRK2 variants. Our results provide insight into the basic pathobiology of LRRK2 and suggest that the GTPase domain may contribute to the toxicity of LRRK2. These findings may guide future therapeutic strategies aimed at attenuating LRRK2-mediated neurodegeneration. [ABSTRACT FROM AUTHOR]

Mutations in the leucine-rich repeat kinase 2 (LRRK2) gene are the most common known cause of Parkinson's disease (PD). Whether loss of LRRK2 function accounts for neurodegeneration of dopamine neurons in PD is not known, nor is it known whether LRRK2 kinase activity modulates the susceptibility of dopamine (DA) neurons to the selective dopaminergic toxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). To better understand the role of LRRK2 in DA neuronal survival and its role in the susceptibility of DA neurons to MPTP, we generated LRRK2 knock-out (KO) mice lacking the kinase domain of LRRK2. Here, we show that LRRK2 KO mice are viable and have no major abnormalities and live to adulthood. The dopaminergic system is normal in LRRK2 KO mice as assessed via HPLC for DA and its metabolites and via stereologic assessment of DA neuron number in young and aged mice. Importantly, there is no significant difference in the susceptibility of LRRK2 KO and wild-type mice to MPTP. These results suggest that LRRK2 plays little if any role in the development and survival of DA neurons under physiologic conditions. Thus, PD due to LRRK2 mutations are likely not due to a loss of function. Moreover, LRRK2 is not required for the susceptibility of DA neurons to MPTP. [ABSTRACT FROM AUTHOR]

Mutations in the leucine-rich repeat kinase 2 (LRRK2) gene are currently recognized as the most common genetic cause of parkinsonism. Among the large number of LRRK2 mutations identified to date, the G2019S variant is the most common. In Asia, however, another LRRK2 variant, G2385R, appears to occur more frequently. To better understand the contribution of different LRRK2 variants toward disease pathogenesis, we generated transgenic Drosophila over-expressing various human LRRK2 alleles, including wild type, G2019S, Y1699C, and G2385R LRRK2. We found that transgenic flies harboring G2019S, Y1699C, or G2385R LRRK2 variant, but not the wild-type protein, exhibit late-onset loss of dopaminergic (DA) neurons in selected clusters that is accompanied by locomotion deficits. Furthermore, LRRK2 mutant flies also display reduced lifespan and increased sensitivity to rotenone, a mitochondrial complex I inhibitor. Importantly, coexpression of human parkin in LRRK2 G2019S-expressing flies provides significant protection against DA neurodegeneration that occurs with age or in response to rotenone. Together, our results suggest a potential link between LRRK2, parkin, and mitochondria in the pathogenesis of LRRK2-related parkinsonism. [ABSTRACT FROM AUTHOR]

Inhibitors of apoptosis (IAPs) are a family of highly-conserved proteins that regulate cell survival through binding to caspases, the final executioners of apoptosis. X-linked IAP (XIAP) is the most widely expressed IAP and plays an important function in regulating cell survival. XIAP contains 3 baculoviral IAP repeats (BIRs) followed by a RING finger domain at the C terminal. The BIR domains of XIAP possess anticaspase activities, whereas the RING finger domain enables XIAP to function as an E3 ubiquitin ligase in the ubiquitin and proteasomal system. Our previous study showed that parkin, a protein that is important for the survival of dopaminergic neurons in Parkinson's disease (PD), is S-nitrosylated both in vitro and in vivo in PD patients. S-nitrosylation of parkin compromises its ubiquitin E3 ligase activity and its protective function, which suggests that nitrosative stress is an important factor in regulating neuronal survival during the pathogenesis of PD. In this study we show that XIAP is S-nitrosylated in vitro and in vivo in an animal model of PD and in PD patients. Nitric oxide modifies mainly cysteine residues within the BIR domains. In contrast to parkin, S-nitrosylation of XIAP does not affect its E3 ligase activity, but instead directly compromises its anti-caspase-3 and antiapoptotic function. Our results confirm that nitrosative stress contributes to PD pathogenesis through the impairment of prosurvival proteins such as parkin and XIAP through different mechanisms, indicating that abnormal S-nitrosylation plays an important role in the process of neurodegeneration. [ABSTRACT FROM AUTHOR]