PARK9-associated ATP13A2 localizes to intracellular acidic vesicles and regulates cation homeostasis and neuronal integrity

Abstract

Mutations in the ATP13A2 gene (PARK9, OMIM 610513) cause autosomal recessive, juvenile-onset Kufor-Rakeb syndrome and early-onset parkinsonism. ATP13A2 is an uncharacterized protein belonging to the P(5)-type ATPase subfamily that is predicted to regulate the membrane transport of cations. The physiological function of ATP13A2 in the mammalian brain is poorly understood. Here, we demonstrate that ATP13A2 is localized to intracellular acidic vesicular compartments in cultured neurons. In the human brain, ATP13A2 is localized to pyramidal neurons within the cerebral cortex and dopaminergic neurons of the substantia nigra. ATP13A2 protein levels are increased in nigral dopaminergic and cortical pyramidal neurons of Parkinson's disease brains compared with normal control brains. ATP13A2 levels are increased in cortical neurons bearing Lewy bodies (LBs) compared with neurons without LBs. Using short hairpin RNA-mediated silencing or overexpression to explore the function of ATP13A2, we find that modulating the expression of ATP13A2 reduces the neurite outgrowth of cultured midbrain dopaminergic neurons. We also find that silencing of ATP13A2 expression in cortical neurons alters the kinetics of intracellular pH in response to cadmium exposure. Furthermore, modulation of ATP13A2 expression leads to reduced intracellular calcium levels in cortical neurons. Finally, we demonstrate that silencing of ATP13A2 expression induces mitochondrial fragmentation in neurons. Oppositely, overexpression of ATP13A2 delays cadmium-induced mitochondrial fragmentation in neurons consistent with a neuroprotective effect. Collectively, this study reveals a number of intriguing neuronal phenotypes due to the loss- or gain-of-function of ATP13A2 that support a role for this protein in regulating intracellular cation homeostasis and neuronal integrity.

LIMP-2 expression is critical for β-glucocerebrosidase activity and α-synuclein clearance

“…This increase could be a compensatory measure to overcome impaired targeting of GC to the lysosome due to accumulated α-syn, and could therefore protect neurons from α-syn toxicity. A similar up-regulation as a protective mechanism is also discussed for other PD-linked lysosomal proteins, such as ATP13A2/Park9 in neurons that are exposed to pathologically accumulated α-syn (26). Our data are in conflict with the data of Gegg et al (35), who did not report changes in immunoblot levels of LIMP-2 in PD midbrain lysates.…”

“…In order to accurately quantify LIMP-2 levels in DA neurons of synucleinopathy cases (n = 5) and appropriate controls (n = 7), we have used LIMP-2 immunofluorescence and confocal laser scanning microscopy of postmortem midbrain samples. A similar approach has been used by other groups investigating expression of the lysosomal protein Park9/ATP13A2 in human synucleinopathies (24)(25)(26). Nonspecific binding of the LIMP-2 antibody in DA neurons was controlled using another rabbit-IgG antibody (Fig.…”

Genetic perspective on the role of the autophagy-lysosome pathway in Parkinson disease

“…154 Similarly, silencing of ATP13A2 induces fragmentation of mitochondria in a neuronal cell model, and its overexpression delays mitochondrial fragmentation. 155 These and similar findings 156 suggest a role for ATP13A2 in quality control of mitochondria, probably through mitophagy. A more general role in lysosomal function and autophagy was suggested for ATP13A2, as fibroblasts from patients with Kufor-Rakeb syndrome as well as mouse primary neurons with ATP13A2 deficiency lead to reduced capacity of lysosomal degradation, resulting in SNCA accumulation and neurotoxicity.…”

Mutual Neurotoxic Mechanisms Controlling Manganism and Parkisonism

“…[102][103][104] Subjects normally display generalized brain atrophy with evidence of diminished nigrostriatal dopaminergic function consistent with the observation that ATP13A2 is particularly enriched in the substantia nigra. 103,105,106 Mutations of ATP13A2 results in its re-localization from intracellular acidic vesicular compartments to the endoplasmic reticulum in mammalian cells where it is subsequently digested via the proteasomal ERassociated degradation pathway. 105,107 Homozygous mutations of ATP13A2 have been reported to cause juvenile-onset Parkinsonism (10-22 years) whereas other heterozygous modifications are associated with early-onset Parkinsonism (o50 years), 108-111 suggesting a gene graded response to these mutations.…”

“…103,105,106 Mutations of ATP13A2 results in its re-localization from intracellular acidic vesicular compartments to the endoplasmic reticulum in mammalian cells where it is subsequently digested via the proteasomal ERassociated degradation pathway. 105,107 Homozygous mutations of ATP13A2 have been reported to cause juvenile-onset Parkinsonism (10-22 years) whereas other heterozygous modifications are associated with early-onset Parkinsonism (o50 years), 108-111 suggesting a gene graded response to these mutations. However, the mechanism by which missense mutations cause Parkinson disease is still unclear.…”