Abstract: Background: Phosphodiesterase 4 (PDE4) is a promising target for the treatment of Parkinson's disease (PD). However, the underlying mechanism has not yet been well elucidated. Additionally, most of current PDE4 inhibitors produce severe nausea and vomiting response in patients, which limit their clinical application. FCPR16 is a novel PDE4 inhibitor with little emetic potential. In the present study, the neuroprotective effect and underlying mechanism of FCPR16 against cellular apoptosis induced by 1-methyl-4-phenylpyridinium (MPP+) were examined in SH-SY5Y cells and primary cultured neurons. Methods: CCK-8 assay, Hoechst staining, lactate dehydrogenase release and flow cytometry were used to study the protective effect of FCPR16 against cell damage caused by MPP+. Mitochondrial membrane potential (Δψm) was measured by JC-1 staining. The extent of oxidation was evaluated using Cell ROXs Deep Red Reagent and malonaldehyde (MDA) kit. Pretreatments with various pathway inhibitors were used to investigate the possible pathways involved in the protection of FCPR16. The phosphorylated and total levels of various proteins were analyzed by Western blot.  Results: FCPR16 (12.5–50 μM) dose-dependently reduced MPP+-induced loss of cell viability, accompanied by reductions in nuclear condensation and lactate dehydrogenase release. The level of cleaved caspase 3 and the ratio of Bax/Bcl-2 were also decreased after treatment with FCPR16 in MPP+-treated cells. Furthermore, FCPR16 (25 μM) significantly suppressed the accumulation of reactive oxygen species (ROS), prevented the decline of Δψm and attenuated the expression of MDA level. Further studies disclosed that FCPR16 enhanced the levels of cAMP and the exchange protein directly activated by cAMP (Epac) in SH-SY5Y cells. Western blotting analysis revealed that FCPR16 increased the phosphorylation of cAMP response element-binding protein (CREB) and protein kinase B (Akt) down-regulated by MPP+ in SH-SY5Y cells. Moreover, the inhibitory effects of FCPR16 on the production of ROS and Δψm loss could be blocked by PKA inhibitor H-89 and Akt inhibitor KRX-0401. We also found that MPP+ induced a dose-dependent apoptosis in cultured neurons, and 500 μM MPP+ caused an approximately 50% loss of cortical neurons, while treatment with FCPR16 reversed the toxic effect of MPP+ and enhanced the cell viability in a dose-dependent manner. Conclusions: These results suggest that FCPR16 attenuates MPP+-induced dopaminergic degeneration via lowering ROS and preventing the loss of Δψm in SH-SY5Y cells. Mechanistically, cAMP/PKA/CREB and Epac/Akt signaling pathways are involved in these processes

Key words: Phosphodiesterase 4, FCPR16, Oxidative stress, Mitochondrial membrane potential, Parkinson's disease