Objective: To explore the mechanism of CTSD inhibition in the dysfunction of autophagy-lysosome pathway and aggregation of α-synuclein in Parkinson’s disease.

Background: α-synuclein, the main component of lewy bodies, is likely to play a key role in the development of Parkinson’s disease. Cathepsin D (CTSD) is previously demonstrated to be a main lysosomal protease involved in processing α-synuclein, but the underlying mechanism remains unclear.

Methods: Rotenone treatment of Lewis rats was used to establish model Parkinson’s disease. CTSD gene was knocked down by VshRNA-CtsD-GFP and CTSD activity was inhibited by Pepstatin A in Lewis rats and human neuroblastoma SH-SY5Y cells. Immunofluorescence staining and western blotting were used to analyze protein expression.

Results: Neuronal α-synuclein accumulation was observed in both dopaminergic neurons in rotenone-treated rats, and rotenone-treated SH-SY5Y cells. Correspondingly, decrease of CTSD protein expression and reduction of enzyme activity were induced by rotenone in vivo and in vitro. When CTSD gene was knocked down by VshRNA-CtsD-GFP in the substatia nigra pars compata (SNc), immunofluorescent staining showed significant increase of α-synuclein accumulation and aggregation in rat nigral neurons. In rat nigral neurons and SH-SY5Y cells, lysosome marker lysosomal-associated membrane protein1 (Lamp-1), the autophagy protein light chain 3 (LC3)-II and the autophagy substrate P62 protein were upregulated by rotenone, suggesting the impairment of autophagic flux. When pretreated with pepstatin A, the accumulation of P62 and α-synuclein induced by rotenone was aggravated, while the induction of LC3-II was alleviated in SH-SY5Y cells. These results demonstrated that inactivation of CTSD could be responsible for α-synuclein aggregation. Furthermore, inhibiton of CTSD impaired the autophagy flux in environmental toxic condition, resulting in dysfunction of autophagy lysosome pathway (ALP), which is crucial for clearance of α-synuclein aggregation.

Conclusions: Our data suggest that regulation the expression level of CTSD, maintaining its enzymatic activity in dopaminergic neurons, could be served as a novel approach for Parkinson’s disease.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/inhibition-of-cathepsin-d-enhances-the-autophagy-lysosome-pathway-dysfunction-and-synuclein-aggregation-in-experimental-parkinsonism/