A novel mechanism underlying the protective effect of PDE4 inhibitor against cognitive impairment:inhibiting neuroinflammation through inducing autophagy in microglial cells

OBJECTIVE Inhibition of phosphodiesterase 4(PDE4) improves the learning and memory abilities in Alzheimer disease animal models. The cognition-enhancing effects of PDE4 inhibition involve reduced inflammatory responses in the brain. However,the underlying mechanisms are illunderstood. cA MP induces autophagy,and deficiency of autophagy leads to elevated inflammatory factors.In the present study,we aimed to investigate the contribution of autophagy to the anti-inflammatory effect of PDE4 inhibitor ROF. METHODS Acidic vesicles were traced by Lysotracker(LYT) red and acridine orange(AO) staining. Autophagosomes in BV-2 cells was observed by immunofluorescence staining of microtubule-associated protein 1 light chain 3(LC3). Aβ_(25-35) or lipopolysaccharide(LPS) with ATP were used to activate microglial cells and inflammasome. Cytokine levels were measured by ELISA method. The levels of pro-inflammatory factors and essential proteins involved in the formation of autophagosome were detected by Western blotting. RESULTS ROF increased the level of LC3-Ⅱ,while the level of p62 was decreased. Enhanced fluorescent signals were observed in BV-2 cells treated with ROF by AO and LYT red staining. In addition,immunofluorescence indicated a significant increase in punctate LC3. Both LPS plus ATP and Aβ_(25-35) enhanced the conversion of pro-caspase-1 to cleaved-caspase-1 and increased the production of mature IL-1β. Interestingly,these effects were blocked by the treatment of ROF. Moreover,ROF decreased the apoptosis of neuronal N2 a cells in conditioned media from BV-2 microglia. These effects were reversed by inhibition of microglial autophagy.Treatment with ROF also showedenhanced autophagy in mcie treated with LPS. CONCLUSION PDE4 inhibitor ROF inhibits inflammasome activities and reduces the release of IL-1β by inducing autophagy.