Lactate modulates microglial inflammatory responses after oxygen-glucose deprivation through HIF-1α-mediated inhibition of NF-κB

Metabolic adaption drives microglial inflammatory responses, and lactate shapes immunological and inflammatory states. However, whether lactate was involved in the regulation of microglial inflammatory responses after cerebral ischemia remains unclear. In this study, the expression of iNOS, arginase-1, phosphorylated NF-kappa B p65 and I kappa B-alpha, and HIF-1 alpha in BV2 cells after oxygen-glucose deprivation (OGD) were detected by western blotting and immunofluorescence. The mRNA levels of microglial responsive markers and inflammatory factors were assessed by real-time-qPCR. The effect of lactate-treated BV2 cells on the survival of primary neurons was observed using transwell co-culture. The results showed that the protein levels of iNOS and arginase-1, the ratio of mRNA levels of iNOS/CD206, CD86/Ym1, IL-6/IL-10, TNF-alpha/IL-10 and the mRNA levels of IL-6 and TNF-alpha, as well as the protein levels of phosphorylated NF-kappa B p65 and I kappa B-alpha, were increased after OGD. Lactate treatment inhibited the OGD-induced increase in the protein levels of iNOS, phosphorylated NF-kappa B p65 and I kappa B-alpha, as well as iNOS/CD206, CD86/Ym1, IL-6/IL-10, TNF-alpha/IL-10, IL-6 and TNF-alpha mRNA levels in BV2 cells, while promoted arginase-1 protein expression as well as IL-10 and TGF-beta mRNA level. Interestingly, lactate activated HIF-1 alpha and the HIF-1 alpha inhibitor YC-1 reversed the effect of lactate on levels of microglial responsive markers and phosphorylated NF-kappa B p65 and I kappa B-alpha in BV2 cells. Moreover, knockdown of HIF-1 alpha by lentivirus-delivered shRNA also reversed the effect of lactate on phosphorylated NF-kappa B p65 and I kappa B-alpha in BV2 cells after OGD. Finally, and importantly, lactate-treated BV2 microglia increased the viability and decreased the apoptosis of neurons after OGD. These findings revealed that lactate inhibited NF-kappa B pathway and skewed BV2 microglia toward the protective response through activation of HIF-1 alpha after OGD, thereby improving neuronal survival.