Differential Effects of UCHL1 Modulation on Alpha-Synuclein in PD-Like Models of Alpha-Synucleinopathy

Abstract

Parkinson's disease (PD) is a progressive neurodegenerative disorder caused by genetic and environmental factors. Abnormal accumulation and aggregation of alpha-synuclein (a-syn) within neurons, and mutations in the a-syn and UCH-L1 genes have been shown to play a role in the pathogenesis of PD. In light of recent reports suggesting an interaction between a-synuclein and UCH-L1, we investigated the effects of UCH-L1 inhibition on a-syn distribution and expression levels in primary neurons and hippocampal tissues derived from non transgenic (non tg) and a-syn over expressing tg mice. We show that suppression of UCH-L1 activity increased a-syn levels in control, non tg neurons, and resulted in a concomitant accumulation of presynaptic a-syn in these neurons. In contrast, blocking UCH-L1 activity in a-syn over expressing neurons decreased a-syn levels, and enhanced its synaptic clearance. In vitro studies verified the LDN-induced inhibition of UCH-L1 had minimal effect on LC3 (a marker of autophagy) in control cells, in cells over expressing a-syn UCH-L1 inhibition resulted in increased LC3 activity. These findings suggest a possible differential role of UCH-L1 function under normal and pathological conditions. Furthermore, in the context of a-syn-induced pathology, modulation of UCH-L1 activity could serve as a therapeutic tool to enhance the autophagy pathway and induce clearance of the observed accumulated/aggregated a-syn species in the PD brain.

Catecholamine autotoxicity. Implications for pharmacology and therapeutics of Parkinson disease and related disorders

“…Since UCHL1 inhibition increases cytoplasmic alpha-synuclein levels (Cartier et al, 2012), UCHL1 mutation might interfere with vesicular catecholamine storage in a manner similar to that in PARK1 and PARK4.…”

Proteomic Analysis After Status Epilepticus Identifies UCHL1 as Protective Against Hippocampal Injury

“…LDN is a reversible, competitive, isatin derivative that selectively inhibits UCHL1 hydrolase activity (IC 50 = 0.88 μM) over a closely related DUB, UCHL3 (IC 50 = 25 μM) [35]. Although no data is available on the pharmacokinetics of LDN in mice, LDN and other isatins readily cross the blood-brain barrier [30, 36, 37], Previous work suggests that LDN is capable of exerting an inhibitory effect on UCHL1 in the hippocampus at systemic doses of 0.5 mg/kg [30, 36]; we used this reported effective dose to assess the inhibitory effect of LDN.…”

“…LDN at 1 h, 4 h, 8 h and 24 h prior to sacrifice, and levels of free monomeric ubiquitin were assessed by Western blotting, as a measure of UCHL1 inhibition [36]. These data suggested that the LDN-induced downregulation of free ubiquitin was maximal at 4 h following UCHL1 inhibition, though the effect was not significant ( P = 0.1419, Figures 5a and 5c).…”

Parkin Is Dispensable for Mitochondrial Function, but Its Ubiquitin Ligase Activity Is Critical for Macroautophagy and Neurotransmitters: Therapeutic Potential beyond Parkinson's Disease

“…Parkin-mediated α-synuclein degradation via the ubiquitin-proteasome pathway now appears unlikely, and mounting evidence suggests that α-synuclein is cleared via autophagy [60,69,88,89]. Changes in autophagy are widely recognized in neurodegeneration [90,91,92,93,94,95].…”