Protective effect of SIRT1 on toxicity of microglial-derived factors induced by LPS to PC12 cells via the p53-caspase-3-dependent apoptotic pathway

Sirtuin1 (SIRT1) has protective effects in some neurodegenerative disease models, but it is not clear whether SIRT1 play the same role on inflammation-mediated Parkinson's disease (PD) models. In this study, we firstly established an inflammation environment by stimulating microglial BV-2 cells with the inflammatory agent lipopolysaccharides (LPS), which demonstrated by increasing of the levels of TNF-a, and IL-6 in cultured medium. Then we exposed PC12 cells (a model of catecholaminergic neuronal cells) with the supernant from LPS stimulated BV-2 cells (activated BV-2). PC12 cell apoptosis and SIRT1 involved protection were investigated. The results indicated that treatment with LPS caused significant decrease in SIRT1 expression in activated BV-2 cells, and increased the levels of TNF-a and IL-6, as measured by ELISA, whereas resveratrol (a known SIRT1 activator) suppressed this effect, which was conversely strengthened by sirtinol (a SIRT1 inhibitor), suggesting that SIRT1 may be involved in regulating proinflammatory cytokines from microglial activation. Further, we found that factors derived from activated microglia significantly decreased the level of deacetylation of p53 by reducing the expression of SIRT1, an effect that increased the apoptosis of PC12 and reduced cell viability. The addition of resveratrol could protect PC12 cells from inflammation-mediated damage above-mentioned, while nicotinamide (another SIRT1 inhibitor) treatment had the opposite effect of resveratrol. Together, these data suggests that: SIRT1 inhibits LPS-mediated proinflammatory cytokines release in microglia, and circumvents dopaminergic neurons injury induced by activated microglial-derived factors via p53-caspase-3-dependent mechanism of apoptosis. Thus, upregulation of SIRT1 provides a promising research field for therapeutic intervention in neuroinflammation diseases.