The endogenous store-operated calcium entry (SOCE) mechanism via transient receptor potential canonical type 1 (TRPC1) channel is important to the maintenance of endoplasmic reticulum function. In recent years, a decreased expression level of TRPC1 was shown in the autopsied brain of Parkinson's disease patients, and it has been considered that failure of the SOCE mechanism affects the condition of Parkinson's disease. In addition, soluble oligomer of α-synuclein, a major component protein of Lewy body, is also known to have cytotoxicity to the dopaminergic cell. However, the detailed mechanism has not been elucidated how α-synuclein is related to the dysfunction of SOCE. Therefore, in this study, we constructed PC12 cell line which overexpressed human α-synuclein with tetracycline-regulated system and investigated the association with SOCE.
We investigated whether neurotoxins affected TRPC1 expression. In addition, we examined the influence of α-synuclein overexpression using tetracycline-regulated system. We exposed rotenone or MPTP, known as mitochondrial stressors, and reserpine which was inhibitor against vesicular monoamine transporter, and examined the expression level of TRPC1 protein by Western blot. TRPC1 expression was suppressed with rotenone and MPTP, but not with reserpine. Overexpression of human α-synuclein did not affect the TRPC1 suppression seen in rotenone and MPTP exposures. Furthermore, we evaluated the association between α-synuclein and SOCE following SKF-96365 exposure which was a suppressor of TRPC1 channel. MTT assay with SKF-96365 exposure showed 7.2 % decline of cell viability in α-synuclein overexpressed condition compared to non-overexpressed condition (p<0.05).
According to these results, it is considered that mitochondrial stressors causes dysfunction of SOCE by inhibition of TRPC1 expression, and TRPC1 inhibition may lead to enhance the α-synuclein cytotoxicity.