Doctor of Philosophy, Rijksuniversiteit Groningen (2018)
Master of Science, Rijksuniversiteit Groningen (2012)
Bachelor of Science, Jimma University (2009)
Suzanne Pfeffer, Postdoctoral Faculty Sponsor
PPM1H phosphatase counteracts LRRK2 signaling by selectively dephosphorylating Rab proteins.
Mutations that activate LRRK2 protein kinase cause Parkinson's disease. LRRK2 phosphorylates a subset of Rab GTPases within their Switch-II motif controlling interaction with effectors. An siRNA screen of all human protein phosphatases revealed that a poorly studied protein phosphatase, PPM1H, counteracts LRRK2 signaling by specifically dephosphorylating Rab proteins. PPM1H knockout increased endogenous Rab phosphorylation and inhibited Rab dephosphorylation in human A549 cells. Overexpression of PPM1H suppressed LRRK2-mediated Rab phosphorylation. PPM1H also efficiently and directly dephosphorylated Rab8A in biochemical studies. A 'substrate-trapping' PPM1H mutant (Asp288Ala) binds with high affinity to endogenous, LRRK2-phosphorylated Rab proteins, thereby blocking dephosphorylation seen upon addition of LRRK2 inhibitors. PPM1H is localized to the Golgi and its knockdown suppresses primary cilia formation, similar to pathogenic LRRK2. Thus, PPM1H acts as a key modulator of LRRK2 signaling by controlling dephosphorylation of Rab proteins. PPM1H activity enhancers could offer a new therapeutic approach to prevent or treat Parkinson's disease.
View details for DOI 10.7554/eLife.50416
View details for PubMedID 31663853
Human VPS13A is associated with multiple organelles and influences mitochondrial morphology and lipid droplet motility
The VPS13A gene is associated with the neurodegenerative disorder Chorea Acanthocytosis. It is unknown what the consequences are of impaired function of VPS13A at the subcellular level. We demonstrate that VPS13A is a peripheral membrane protein, associated with mitochondria, the endoplasmic reticulum and lipid droplets. VPS13A is localized at sites where the endoplasmic reticulum and mitochondria are in close contact. VPS13A interacts with the ER residing protein VAP-A via its FFAT domain. Interaction with mitochondria is mediated via its C-terminal domain. In VPS13A-depleted cells, ER-mitochondria contact sites are decreased, mitochondria are fragmented and mitophagy is decreased. VPS13A also localizes to lipid droplets and affects lipid droplet motility. In VPS13A-depleted mammalian cells lipid droplet numbers are increased. Our data, together with recently published data from others, indicate that VPS13A is required for establishing membrane contact sites between various organelles to enable lipid transfer required for mitochondria and lipid droplet related processes.
View details for DOI 10.7554/eLife.43561
View details for Web of Science ID 000459683300001
View details for PubMedID 30741634
View details for PubMedCentralID PMC6389287
Drosophila Vps13 Is Required for Protein Homeostasis in the Brain
2017; 12 (1): e0170106
Chorea-Acanthocytosis is a rare, neurodegenerative disorder characterized by progressive loss of locomotor and cognitive function. It is caused by loss of function mutations in the Vacuolar Protein Sorting 13A (VPS13A) gene, which is conserved from yeast to human. The consequences of VPS13A dysfunction in the nervous system are still largely unspecified. In order to study the consequences of VPS13A protein dysfunction in the ageing central nervous system we characterized a Drosophila melanogaster Vps13 mutant line. The Drosophila Vps13 gene encoded a protein of similar size as human VPS13A. Our data suggest that Vps13 is a peripheral membrane protein located to endosomal membranes and enriched in the fly head. Vps13 mutant flies showed a shortened life span and age associated neurodegeneration. Vps13 mutant flies were sensitive to proteotoxic stress and accumulated ubiquitylated proteins. Levels of Ref(2)P, the Drosophila orthologue of p62, were increased and protein aggregates accumulated in the central nervous system. Overexpression of the human Vps13A protein in the mutant flies partly rescued apparent phenotypes. This suggests a functional conservation of human VPS13A and Drosophila Vps13. Our results demonstrate that Vps13 is essential to maintain protein homeostasis in the larval and adult Drosophila brain. Drosophila Vps13 mutants are suitable to investigate the function of Vps13 in the brain, to identify genetic enhancers and suppressors and to screen for potential therapeutic targets for Chorea-Acanthocytosis.
View details for DOI 10.1371/journal.pone.0170106
View details for Web of Science ID 000392405300076
View details for PubMedID 28107480
View details for PubMedCentralID PMC5249141
HDAC6 Is a Bruchpilot Deacetylase that Facilitates Neurotransmitter Release
2014; 8 (1): 94–102
Presynaptic densities are specialized structures involved in synaptic vesicle tethering and neurotransmission; however, the mechanisms regulating their function remain understudied. In Drosophila, Bruchpilot is a major constituent of the presynaptic density that tethers vesicles. Here, we show that HDAC6 is necessary and sufficient for deacetylation of Bruchpilot. HDAC6 expression is also controlled by TDP-43, an RNA-binding protein deregulated in amyotrophic lateral sclerosis (ALS). Animals expressing TDP-43 harboring pathogenic mutations show increased HDAC6 expression, decreased Bruchpilot acetylation, larger vesicle-tethering sites, and increased neurotransmission, defects similar to those seen upon expression of HDAC6 and opposite to hdac6 null mutants. Consequently, reduced levels of HDAC6 or increased levels of ELP3, a Bruchpilot acetyltransferase, rescue the presynaptic density defects in TDP-43-expressing flies as well as the decreased adult locomotion. Our work identifies HDAC6 as a Bruchpilot deacetylase and indicates that regulating acetylation of a presynaptic release-site protein is critical for maintaining normal neurotransmission.
View details for DOI 10.1016/j.celrep.2014.05.051
View details for Web of Science ID 000341403000011
View details for PubMedID 24981865