Cathepsin D Dysfunction Contributes To α-synuclein Accumulation

Aim: To explore the mechanism of cathepsin D dysfunction involved in the accumulation of α-synuclein in SNpc of Parkinson’s disease model rats, and to investigate the regulation of cathepsin D in dopaminergic neural cells.Method: In vivo model of PD was established by rotenone(2mg/kg/day) administered subcutaneously for 8 weeks. Human neuroblastoma SH-SY5 Y cells treated with rotenone were used as in vitro model. LAMP-1 immunostaining was used as lysosome marker to detect lysosome function. α-synuclein and cathepsin D protein level was detected by Western blot analysis and immunofluorescence analysis. The expression of α-synuclein and cathepsin D mRNA was assessed with RT-PCR. Lentivirus-RNAi-GFP of cathepsin D was injected into SNpc of Lewis rat brain. Infection rate and protein expression of cathepsin D were detected with immunofluorescence and Western blot. CCK-8 was used to detect cell viability and cell proliferation. In SH-SY5 Y cells, effects of cathepsin D in the autophagy lysosome pathway were also studied. Pretreatment with cathepsin L specific inhibitor Z-FY-CHO was used to explore the regulation of cathepsin D in SH-SY5 Y cells. Western blot was used to analysis the level of autophagic substrate protein.Results:Rotenone administration caused a loss of tyrosine hydroxylase in SNpc and behavior changes of Lewis rats. The degeneration of dopaminergic neurons was accompanied by the deposition of α-synuclein aggregates, lysosome dysfunction and mature cathepsin D inhibition. In SH-SY5 Y cells, rotenone also induced accumulation of α-synuclein, and reduction of cathepsin D activity. Cathepsin D knock down induced the accumulation of α-synuclein in vivo and in vitro. Knock down of cathepsin D aggaravated the accumulation of autophagy substrate protein induced by rotenone. Cathepsin L inhibitor Z-FY-CHO pretreatment upregulated cathepsin D and alleviated the accumulation of autophagic substrate proteins induced by rotenone.Conclusions: These studies indicate that cathepsin D inhibition contributes to autophagy lysosome pathway dysfunction and α-synuclein accumulation. Recovery of cathepsin D function could be a new therapeutic strategy for Parkinson’s disease.