FCPR16 induces AMPK-dependent autophagy and provides neuroprotection in SH-SY5Y cells and neurons exposed to MPP^+-induced oxidative damage

摘要

OBJECTIVE The cause of Parkinson disease (PD) is generally not clear, but it is considered to be related to excessive oxidative damage. Therefore, the identification of therapeutic targets and compounds with antioxidant damage is a reasonable strategy to slow down the progress of PD. FCPR16 is a novel phosphodiesterase4 inhibitor with little emetic potential. Our previous studies showed that FCPR16 was an effective compound for blocking 1-methyl-4-phenylpyridine(MPP+)-induced oxidative damage in SH-SY5Y cells and neurons. However, the detailed mechanisms underlying its protective effect have not been investigated. The level of oxidative stress in neurons is closely related to the balance of mitochondria mass, while autophagy strongly regulates mitochondrial activity in neurons. Our previous study indicated that inhibition of PDE4 or PDE4 knockdown enhanced the activation of autophagy in microglial cells. While whether PDE4 inhibition mediates autophagy in neurons is largely unknown. As described above, autophagy plays a pivotal role in maintaining redox and mitochondrial homeostasis. We were interested in exploring the impact of PDE4 inhibition on autophagy in neurons. METHODS SH-SY5Y cells and neurons was induced with MPP+to mimic PD cell injury in vitro, and MTT assay was used to investigate the viability effects of FCPR16 (50μmol·L-1) with or without different autophagy inhibitors on MPP+-injured SH-SY5Y cells. Detection of apoptosis was performed by PI staining fluorescence. Lysosomes are essential in autophagy, so LYT Red Stain was used to detect lysosomes in SY5Y cells and neurons. Cells were exposed to Cell ROX Deep Red Reagent to detect intracellular reactive oxygen species (ROS). Mitochondrial membrane potential (Δψm)measurement was executed by 5, 5′, 6, 6′-tetrachloro-1, 1′, 3, 3′-tetraethylbenzimidazolyl-carbocyanineiodide (JC-1).To better detect intracellular autophagy, we used the CYTO-ID Autophagy detection kit to detect the autophagic vacuoles and monitor autophagic flux. The expression of autophagy related proteins and other related signal molecules were demonstrated by Western blot. As relevant indicators of oxidative stress, 3-nitrotyrosine (3-NT) and highly toxic peroxide4-hydroxynonenal (4-HNE) were detected with 3-NT and 4-HNE ELISA kits. RESULTS FCPR16 could significantly decrease the expression of p62, an autophagy substrate, at 6 and 12 h, while FCPR16 enhanced the level of LC3-Ⅱ. Similarly, FCPR16 increased the lysosomes fluorescence and CYTO-ID signal in cells and neurons, while it could be blockby 3-methyladenine (3-MA) and hydroxychloroquine sulfate (HCQ). Simultaneously, Treatment of SH-SY5Y cells with FCPR16 prevented MPP+-induced production of ROS and the decline ofΔψm. Importantly, we also found that FCPR16 phosphorylated and thus activated AMPK in SH-SY5Y cells treated with MPP+. In contrast, blockade of the AMPK pathway with compound C blocked the role of FCPR16 in autophagy enhancement. MPP+-induced a significant increase in PI-positive cells, while FCPR16 decreased the ratio of PI positive cells and 3-MA and compound C could block the protective effect. Additionally, FCPR16 reduced MPP+-induced decline of cell viability, and 3-MA and compound C could block the protective effect. CONCLUSION Deficits in autophagy have been proven to participate the pathology of PD and targeting autophagic function has been viewed as a potential therapeutic strategy for the clearance of toxic proteins (such asα-synuclein) and of impaired mitochondria. this is the first time that PDE4 inhibition has been shown to induce autophagic enhancement both in SH-SY5Y cells and in primary cultured neurons. In addition, our findings indicate that inhibition of PDE4 by FCPR16 protects against MPP+-induced oxidative stress and cellular injury in SH-SY5Y cells and neurons through the activation of AMPK-dependent autophagy. Taken together, these results show that PDE4 is a promising target for developing novel drugs against neuronal apoptosis and FCPR16 may be a potential compound for the prevention and treatment of PD.