Roflupram attenuates alpha-synuclein-induced cytotoxicity and promotes the mitochondrial translocation of Parkin in SH-SY5Y cells overexpressing A53T mutant alpha-synuclein

We have previously shown that inhibition of cAMP-specific 3',5'-cyclic phosphodiesterase 4 (PDE4) protects against cellular toxicity in neuronal cells. Since alpha-synuclein (alpha-syn) toxicity contributes to the neurodegeneration of Parkinson's disease (PD). The aim of this study was to explore the effects and mechanisms of PDE4 on alpha-syn-induced neuronal toxicity. Using mutant human A53T alpha-syn overexpressed SH-SY5Y cells, we found that PDE4B knockdown reduced cellular apoptosis. Roflupram (ROF, 20 mu M), a selective PDE4 inhibitor, produced similar protective effects and restored the morphological alterations of mitochondria. Mechanistic studies identified that alpha-syn enhanced the phosphorylation of Parkin at Ser131, followed by the decreased mitochondrial translocation of Parkin. Whereas both PDE4B knockdown and PDE4 inhibition by ROF blocked the effects of alpha-syn on Parkin phosphorylation and mitochondrial translocation. Moreover, PDE4 inhibition reversed the increase in the phosphorylation of p38 mitogen-activated protein kinase (MAPK) induced by alpha-syn. ROF treatment also reduced the binding of p38 MAPK to Parkin. Consistently, overexpression of PDE4B blocked the roles of ROF on p38 MAPK phosphorylation, Parkin phosphorylation, and the subsequent mitochondrial translocation of parkin. Furthermore, PDE4B overexpression attenuated the protective role of ROF, as evidenced by reduced mitochondria membrane potential and increased cellular apoptosis. Interestingly, ROF failed to suppress alpha-syn-induced cytotoxicity in the presence of a protein kinase A (PKA) inhibitor H-89. Our findings indicate that PDE4 facilitates alpha-syn-induced cytotoxicity via the PKA/p38 MAPK/Parkin pathway in SH-SY5Y cells overexpressing A53T mutant alpha-synuclein. PDE4 inhibition by ROF is a promising strategy for the prevention and treatment of alpha-syn-induced neurodegeneration.