Deubiquitinase Usp8 regulates α-synuclein clearance and modifies its toxicity in Lewy body disease

Abstract

In Parkinson’s disease, misfolded α-synuclein accumulates, often in a ubiquitinated form, in neuronal inclusions termed Lewy bodies. An important outstanding question is whether ubiquitination in Lewy bodies is directly relevant to α-synuclein trafficking or turnover and Parkinson’s pathogenesis. By comparative analysis in human postmortem brains, we found that ubiquitin immunoreactivity in Lewy bodies is largely due to K63-linked ubiquitin chains and markedly reduced in the substantia nigra compared with the neocortex. The ubiquitin staining in cells with Lewy bodies inversely correlated with the content and pathological localization of the deubiquitinase Usp8. Usp8 interacted and partly colocalized with α-synuclein in endosomal membranes and, both in cells and after purification, it deubiquitinated K63-linked chains on α-synuclein. Knockdown of Usp8 in the Drosophila eye reduced α-synuclein levels and α-synuclein–induced eye toxicity. Accordingly, in human cells, Usp8 knockdown increased the lysosomal degradation of α-synuclein. In the dopaminergic neurons of the Drosophila model, unlike knockdown of other deubiquitinases, Usp8 protected from α-synuclein–induced locomotor deficits and cell loss. These findings strongly suggest that removal of K63-linked ubiquitin chains on α-synuclein by Usp8 is a critical mechanism that reduces its lysosomal degradation in dopaminergic neurons and may contribute to α-synuclein accumulation in Lewy body disease.

Extracellular HMGB1 Modulates Glutamate Metabolism Associated with Kainic Acid-Induced Epilepsy-Like Hyperactivity in Primary Rat Neural Cells

“…2 left panel, blue arrow) and indicated that HMGB1 is mono ubiquitinated. This mono ubiquitination regulates the target protein’s cellular functions, such as membrane trafficking [45, 46] and exocytosis [47]. These results provide novel evidence that the shuttling of HMGB1 between the nucleus and extracellular space may be tightly regulated in response to an epileptogenic signal.…”

How is alpha‐synuclein cleared from the cell?

“…) and K63‐linked conjugates are present in Lewy bodies (Alexopoulou et al . ). In mammalian cells, NEDD4 over‐expression promoted the degradation of α‐Syn by an ESCRT‐mediated lysosomal route (Tofaris et al .…”

“…Knockdown of USP8 in the Drosophila model reduced α‐Syn levels and toxicity suggesting that both in cells and simple model organisms, USP8 acts as a negative regulator of α‐Syn clearance (Alexopoulou et al . ). The endoplasmic reticulum (ER)‐associated deubiquitinase USP19 was shown to recruit misfolded proteins, including α‐Syn, to the ER surface for deubiquitination and encapsulation into ER‐associated late endosomes for secretion to the cell exterior (Lee et al .…”

Deubiquitylating enzymes and drug discovery: emerging opportunities

“…Notably, USP8 depletion was found to delay Parkin translocation onto depolarized mitochondria, as well as mitochondrial clearance, and USP8 displayed an ability to remove K6-linked ubiquitin chains from Parkin in vitro 148 . In addition, USP8 has been shown to remove K63-linked ubiquitin chains from α-synuclein 149 , a protein known to aggregate -often in a ubiquitylated form -in Lewy bodies associated with neurodegenerative diseases such as Parkinson disease. Depletion of USP8 in either human SH-SY5Y cells or D. melanogaster resulted in increased lysosomal degradation of α-synuclein 149 .…”