ATP13A2/PARK9 Deficiency Neither Cause Lysosomal Impairment Nor Alter α-Synuclein Metabolism in SH-SY5Y Cells

The Roles of ATP13A2 Gene Mutations Leading to Abnormal Aggregation of α-Synuclein in Parkinson’s Disease

Parkinson’s disease (PD) is the second most common neurodegenerative disease. PARK9 (also known as ATP13A2) is recognized as one of the key genes that cause PD, and a mutation in this gene was first discovered in a rare case of PD in an adolescent. Lewy bodies (LBs) formed by abnormal aggregation of α-synuclein, which is encoded by the SNCA gene, are one of the pathological diagnostic criteria for PD. LBs are also recognized as one of the most important features of PD pathogenesis. In this article, we first summarize the types of mutations in the ATP13A2 gene and their effects on ATP13A2 mRNA and protein structure; then, we discuss lysosomal autophagy inhibition and the molecular mechanism of abnormal α-synuclein accumulation caused by decreased levels and dysfunction of the ATP13A2 protein in lysosomes. Finally, this article provides a new direction for future research on the pathogenesis and therapeutic targets for ATP13A2 gene-related PD from the perspective of ATP13A2 gene mutations and abnormal aggregation of α-synuclein.

Lipid and immune abnormalities causing age-dependent neurodegeneration and Parkinson's disease

This article describes pathogenic concepts and factors, in particular glycolipid abnormalities, that create cell dysfunction and synaptic loss in neurodegenerative diseases. By phenocopying lysosomal storage disorders, such as Gaucher disease and related disorders, age- and dose-dependent changes in glycolipid cell metabolism can lead to Parkinson's disease and related dementias. Recent results show that perturbation of sphingolipid metabolism can precede or is a part of abnormal protein handling in both genetic and idiopathic Parkinson's disease and Lewy body dementia. In aging and genetic predisposition with lipid disturbance, α-synuclein's normal vesicular and synaptic role may be detrimentally shifted toward accommodating and binding such lipids. Specific neuronal glycolipid, protein, and vesicular interactions create potential pathophysiology that is amplified by astroglial and microglial immune mechanisms resulting in neurodegeneration. This perspective provides a new logic for therapeutic interventions that do not focus on protein aggregation, but rather provides a guide to the complex biology and the common sequence of events that lead to age-dependent neurodegenerative disorders.

Endolysosomal dysfunction in Parkinson's disease: Recent developments and future challenges

Increasingly, genetic, cell biological, and in vivo work emphasizes the role of the endolysosomal system dysfunction in Parkinson's disease pathogenesis. Yet many questions remain about the mechanisms by which primary endolysosomal dysfunction causes PD as well as how the endolysosomal system interacts with α-synuclein-mediated neurotoxicity. We recently described a new mouse model of parkinsonism in which loss of the endolysosomal protein Atp13a2 causes behavioral, neuropathological, and biochemical changes similar to those present in human subjects with ATP13A2 mutations. In this Scientific Perspectives, we revisit the evidence implicating the endolysosomal system in PD, current hypotheses of disease pathogenesis, and how recent studies refine these hypotheses and raise new questions for future research. © 2016 International Parkinson and Movement Disorder Society.

ATP13A2/PARK9 regulates endo-/lysosomal cargo sorting and proteostasis through a novel PI(3, 5)P2-mediated scaffolding function

ATP13A2 (also called PARK9), is a transmembrane endo-/lysosomal-associated P5 type transport ATPase. Loss-of-function mutations in ATP13A2 result in the Kufor-Rakeb Syndrome (KRS), a form of autosomal Parkinson's disease (PD). In spite of a growing interest in ATP13A2, very little is known about its physiological role in stressed cells. Recent studies suggest that the N-terminal domain of ATP13A2 may hold key regulatory functions, but their nature remains incompletely understood. To this end, we generated a set of melanoma and neuroblastoma cell lines stably overexpressing wild-type (WT), catalytically inactive (D508N) and N-terminal mutants, or shRNA against ATP13A2. We found that under proteotoxic stress conditions, evoked by the proteasome inhibitor Bortezomib, endo-/lysosomal associated full-length ATP13A2 WT, catalytically-inactive or N-terminal fragment mutants, reduced the intracellular accumulation of ubiquitin-conjugated (Ub) proteins, independent of autophagic degradation. In contrast, ATP13A2 silencing increased the intracellular accumulation of Ub-proteins, a pattern also observed in patient-derived fibroblasts harbouring ATP13A2 loss-of function mutations. In treated cells, ATP13A2 evoked endocytic vesicle relocation and increased cargo export through nanovesicles. Expression of an ATP13A2 mutant abrogating PI(3,5)P2 binding or chemical inhibition of the PI(3,5)P2-generating enzyme PIKfyve, compromised vesicular trafficking/nanovesicles export and rescued intracellular accumulation of Ub-proteins in response to proteasomal inhibition. Hence, our study unravels a novel activity-independent scaffolding role of ATP13A2 in trafficking/export of intracellular cargo in response to proteotoxic stress.

Non-cell-autonomous Neurotoxicity of α-synuclein Through Microglial Toll-like Receptor 2

Synucleinopathies are a collection of neurological diseases that are characterized by deposition of α-synuclein aggregates in neurons and glia. These diseases include Parkinson's disease (PD), dementia with Lewy bodies, and multiple system atrophy. Although it has been increasingly clear that α-synuclein is implicated in the pathogenesis of PD and other synucleinopathies, the precise mechanism underlying the disease process remains to be unraveled. The past studies on how α-synuclein exerts pathogenic actions have focused on its direct, cell-autonomous neurotoxic effects. However, recent findings suggested that there might be indirect, non-cell-autonomous pathways, perhaps through the changes in glial cells, for the pathogenic actions of this protein. Here, we present evidence that α-synuclein can cause neurodegeneration through a non-cell-autonomous manner. We show that α-synuclein can be secreted from neurons and induces inflammatory responses in microglia, which in turn secreted neurotoxic agents into the media causing neurodegeneration. The neurotoxic response of microglia was mediated by activation of toll-like receptor 2 (TLR2), a receptor for neuron-derived α-synuclein. This work suggests that TLR2 is the key molecule that mediates non-cell-autonomous neurotoxic effects of α-synuclein, hence a candidate for the therapeutic target.

Genes associated with Parkinson's disease: regulation of autophagy and beyond

Substantial progress has been made in the genetic basis of Parkinson's disease (PD). In particular, by identifying genes that segregate with inherited PD or show robust association with sporadic disease, and by showing the same genes are found on both lists, we have generated an outline of the cause of this condition. Here, we will discuss what those genes tell us about the underlying biology of PD. We specifically discuss the relationships between protein products of PD genes and show that common links include regulation of the autophagy-lysosome system, an important way by which cells recycle proteins and organelles. We also discuss whether all PD genes should be considered to be in the same pathway and propose that in some cases the relationships are closer, whereas in other cases the interactions are more distant and might be considered separate. Beilina and Cookson review the links between genes for Parkinson's disease (red) and the autophagy-lysosomal system. They propose the hypothesis that many of the known PD genes can be assigned to pathways that affect (I) turnover of mitochondria via mitophagy (II) turnover of several vesicular structures via macroautophagy or chaperone-mediated autophagy or (III) general lysosome function. This article is part of a special issue on Parkinson disease.