Apelin-13 ameliorates LPS-induced BV-2 microglia inflammatory response through promoting autophagy and inhibiting H3K9ac enrichment of TNF-α and IL-6 promoter

Microglia is activated and polarized to pro-inflammatory M1 phenotype or anti-inflammatory M2 phenotype in neuroinflammation. Apelin-13 exerts protective properties against neuroinflammation in several neurological disorders. We aimed to investigate whether apelin-13 played a protective role on BV-2 microglia and explore its underlying mechanisms. Lipopolysaccharide (LPS)-stimulated BV-2 microglia cells were treated with apelin-13. Microglia activation was evaluated by immunofluorescence with F-actin. Western blot was performed to measure the expression of autophagy associated proteins. CD16/32 and CD206 were detected to assess microglia polarization by western blot and flow cytometry. qRT-PCR was utilized to measure inducible nitric oxide synthase (iNOS), arginase-1 (Arg-1), interleukin-10 (IL-10), interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha). Histone H3 acetyl lysine 9 (H3K9ac) enrichment of TNF-alpha and IL-6 promoter was detected by ChIP. We discovered that apelin-13 impacted the actin cytoskeleton, recovering the control phenotype following LPS exposure. Apelin-13 improved autophagy-mediated microglia polarization towards M2 phenotype to alleviate inflammatory response in LPS-stimulated cells. Autophagy flux inhibitor chloroquine antagonized these effects of apelin-13 on LPS-stimulated cells. Besides, apelin-13 decreased the enrichment of H3K9ac at the promoter region of TNF-alpha and IL-6 to inhibit inflammatory response, which was reversed by histone deacetylase antagonist valproate. Taken together, apelin-13 alleviated inflammation via facilitating microglia M2 polarization due to autophagy promotion, and inhibiting H3K9ac enrichment on promoter regions of TNF-alpha and IL-6.