The Ketone Body Metabolite ?-hydroxybutyrate Induces Microglial Ramification Via The HDACs Inhibition-triggered Akt-small RhoGTPase Signal

Purpose The major aim of this study is to investigate the functional ramification of microglia induced by the ketone body metabolite ?-hydroxybutyrate(BHB),and elucidate its molecular mechanisms.Methods The immunofluorescence technique was used to detect the morphological changes in primary cultured microglia and cerebral cortex microglia.The Western blot and real time-PCR experiment were applied to measure the changes in protein and mRNA expressions.The effect of BHB on depression-like behavior induced by lipopolysaccharide(LPS)was detected by behavioral assays in C57BL6/J mice.Results BHB as well as its producing stimuli,fasting and KD,induced obvious ramifications of murine microglia in basal and inflammatory conditions in a reversible manner,and these ramifications were accompanied with microglial profile toward M2 polarization and phagocytosis.The protein kinase B(Akt)-small RhoGTPase axis was found to mediate the effect of BHB on microglial shape change,as(i)BHB activated the microglial small RhoGTPase(Rac1,Cdc42)and Akt;(ii)Akt and Rac1-Cdc42 inhibition abolished the pro-ramification effect of BHB;(iii)Akt inhibition prevented the activation of Rac1-Cdc42 induced by BHB treatment.Incubation of microglia with other classical histone deacetylases(HDACs)inhibitors,but not G protein-coupled receptor 109a(GPR109a)activators,also induced microglial ramification and Akt activation.Functionally,Akt inhibition abrogated the effects of BHB on microglial polarization and phagocytosis.In a neuroinflammatory model induced by LPS,BHB prevented the microglial process retraction and depression-like behaviors,and these effects were abolished by Akt inhibition.Conclusions BHB induces a functional ramification of murine microglia in both basal and inflammatory conditions in vitro and in vivo.The pro-ramification effect of BHB on microglia is mediated by the HDACs inhibition-triggered Akt-small RhoGTPase signal.In a neuroinflammation model,the Akt inhibitor abrogates the reversal effect of BHB on LPS-induced retraction of microglial process as well as LPS-induced depression-like behaviors.