alpha-Synuclein (ASN) play important role in pathogenesis of Parkinson’s disease (PD) and other neurodegenerative disorders. Novel and most interesting data showed elevated tauopathy in PD and suggested relationship between ASN and Tau protein. However, the mechanism of ASN-evoked Tau protein modification is not fully elucidated. In this study, we investigated the role of glycogen synthase kinase-3β (Gsk-3β) and cyclin-dependent kinase 5 (Cdk5) in ASN-evoked Tau modification in dopaminergic PC12 cells. We used real-time quantitative PCR (qRT-PCR) analysis to assess Gsk3β gene expression and Western blot technique to analyse protein phosphorylation. The presence of apoptotic cells was assessed by Hoechst 33258 fluorescent staining, and cell viability was determined by the 2-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) colorimetric assay. Our data showed that exogenously added ASN (10 μM) increases Tau phosphorylation on Ser396 and specific Gsk-3β inhibitor (SB-216763, 10 µM) opposite to Cdk5 inhibitor protects cells against Tau hyperphosphorylation. Western blot analysis showed that ASN affected Gsk-3β via increasing of protein level and activation of this enzyme. From immunochemical studies, was found that ASN treatment leads to significant increase in GSK-3β immunoreactivity by about 20%. GSK-3β activity evaluated by its phosphorylation status assay showed that ASN significantly increased the phosphorylation of this enzyme at Tyr216 with parallel decrease in phosphorylation at Ser9, indicative of stimulation of GSK-3β activity. ASN-induced apoptotic processes leads to decrease of PC12 cells viability, the apoptotic cells determined by phase contrast together with Hoechst 33258 fluorescent staining, indicated significantly increase of apoptosis in the presence of ASN. SB-216763 prevented ASN-induced cytotoxicity and enhanced PC12 cell viability. In conclusion, all these findings suggested that extracellular ASN is involved in Gsk-3β-dependent Tau modulation and its proapoptotic effect might be mediated at least in part by the Gsk-3β catalysed Tau hyperphosphorylation and impairment of cytoskeleton stability. GSK-3β inhibitors may offer promising tool against ASN-induced Tau modification and cytotoxicity in neurodegenerative disorders. Supported by statutory theme 9.
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