Enhanced ubiquitin-dependent degradation by Nedd4 protects against α-synuclein accumulation and toxicity in animal models of Parkinson's disease

Abstract

Parkinson's disease is a neurodegenerative disorder, characterized by accumulation and misfolding of α-synuclein. Although the level of α-synuclein in neurons is fundamentally linked to the onset of neurodegeneration, multiple pathways have been implicated in its degradation, and it remains unclear which are the critical ubiquitination enzymes that protect against α-synuclein accumulation in vivo. The ubiquitin ligase Nedd4 targets α-synuclein to the endosomal–lysosomal pathway in cultured cells. Here we asked whether Nedd4-mediated degradation protects against α-synuclein-induced toxicity in the Drosophila and rodent models of Parkinson's disease. We show that overexpression of Nedd4 can rescue the degenerative phenotype from ectopic expression of α-synuclein in the Drosophila eye. Overexpressed Nedd4 in the Drosophila brain prevented the α-synuclein-induced locomotor defect whereas reduction in endogenous Nedd4 by RNAi led to worsening motor function and increased loss of dopaminergic neurons. Accordingly, AAV-mediated expression of wild-type but not the catalytically inactive Nedd4 decreased the α-synuclein-induced dopaminergic cell loss in the rat substantia nigra and reduced α-synuclein accumulation. Collectively, our data in two evolutionarily distant model organisms strongly suggest that Nedd4 is a modifier of α-synuclein pathobiology and thus a potential target for neuroprotective therapies.

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

“…It is likely that Usp8 is important in the trafficking of both normal as well as misfolded α-synuclein, opposing its clearance by either an endosomal-or autophagic-lysosomal route, respectively. For example, the Nedd4 ortholog in yeast Rsp5, which functions in endosomal trafficking, also regulates ubiquitin-mediated autophagy (39), and aggregated α-synuclein is also ubiquitinated by Nedd4 in vitro (24). Whether additional DUBs such as Usp7 serve a direct role in α-synuclein pathobiology requires further investigation.…”

“…Interestingly, Usp8 knockdown in dopaminergic cells reduced the loss of the TH-immunoreactive PPM1/2 cluster of dopaminergic neurons (Fig. 6H) that is most vulnerable in the Drosophila α-synuclein model (23)(24)(25) and typically correlates with the locomotor deficit.…”

“…Our neuropathological and cell-based studies suggest that in α-synucleinopathies, increased deubiquitination by Usp8 in nigral neurons may be harmful, at least partly by increasing α-synuclein levels. We tested this prediction by expressing α-synuclein in the fly eye, which has proven to be a valuable experimental model of α-synuclein-induced toxicity (23,24). This assay showed that the rough eye phenotype caused by ectopic expression of either human wild-type α-synuclein or A53T mutant α-synuclein was prevented by concomitant knockdown of Usp8 (Fig.…”

Lys-63-linked Ubiquitination by E3 Ubiquitin Ligase Nedd4-1 Facilitates Endosomal Sequestration of Internalized α-Synuclein

“…Among the E3 ligases that catalyze aS ubiquitination, researchers have focused on Nedd4 (neural precursor cell expressed developmentally down-regulated protein 4) because this E3 ligase is highly expressed in neurons containing LBs and catalyzes the Lys-63-linked ubiquitination of aS (9,10). Mammalian Nedd4 exists in two isoforms, Nedd4-1 and Nedd4-2.…”

Glutamine promotes Hsp70 and inhibits α-Synuclein accumulation in pheochromocytoma PC12 cells

“…Recently, it has been determined that the dysfunction of the lysosome and ubiquitin-proteasome system is associated with the abnormal aggregation of α-Syn in neuroblastoma PC12 cells (22). Furthermore, enhanced ubiquitin-dependent degradation of α-Syn by neural precursor cell expressed developmentally down-regulated protein 4 was confirmed in an animal model of PD (24). However, the association between the molecular chaperone-and the ubiquitin/proteasome system-mediated degradation of α-Syn in neuroblastoma cells remains to be elucidated.…”