Iron-induced oxidative stress contributes to α-synuclein phosphorylation and up-regulation via polo-like kinase 2 and casein kinase 2

alpha-Synuclein plays a central role in synucleinopathies pathogenesis such as Parkinson's disease (PD). Phosphorylation is the most common and important protein modification linked to alpha-synuclein pathologies. There is mounting evidence suggested iron and alpha-synuclein are closely related in PD. We previously reported iron up-regulated alpha-synuclein mRNA levels and induced alpha-synuclein aggregation. In the present study, we aimed to investigate whether and how phosphorylation was involved in iron-induced alpha-synuclein regulations. The results showed that iron could induce pS129 alpha-synuclein (phosphorylation at Ser129) and alpha-synuclein upregulation in the substantia nigra of iron-overloaded rats and iron-treated SH-SYSY cells, accompanied by the elevated levels of polo-like kinase 2 (PLK2) and casein kinase 2 (CK2). Over-expression of CK2 or PLK2 induced pS129 alpha-synuclein up-regulation and inhibitors of CK2 or PLK2 could suppress iron-induced alpha-synuclein phosphorylation. Antioxidant NAC could fully block iron-induced upregulation of CK2, PLK2 and pS129 alpha-synuclein levels, indicating oxidative stress plays a critical role in iron-induced alpha-synuclein phosphorylation. However, iron-induced alpha-synuclein up-regulation could only be partially blocked by CK2/PLK2 inhibitor or NAC. These findings demonstrate that iron-induced oxidative stress is largely responsible for alpha-synuclein phosphorylation and upregulation via CK2 and PLK2, and alpha-synuclein upregulation is not fully phosphorylation-dependent.