Effect of betulinic acid nanoparticles activating CB2 receptor on microglial polarization in ischemic brain injury

Ischemic stroke is a leading cause of mortality and permanent disability worldwide. Microglia, as the brain-resident immune cells, play a biphasic role in ischemic stroke depending on its polarization toward M1 or M2 phenotype. Betulinic acid (BA) is a natural bioactive molecule with the potential to active CB2 receptor on microglia and promote its M2 polarization. Herein, we set to explore the regulation of self-assembled BA nanoparticles (BA NPs) on CB2 receptor mediated microglial polarization after brain ischemia. The in vitro studies showed that BA could regulate the polarization of BV2 micorglia treated with lipopolysaccharide (LPS), which could be blocked by CB2 inhibitor. For in vivo studies, transient middle cerebral artery occlusion (MCAO) model mice receiving self-assembled BA NPs had the least infarct volume and neurological deficit, which could be reversed by CB2 inhibitor. Moreover, microglia at ischemic site were polarized into M2 phenotype after treatment with BA NPs. Our results demonstrates that BA nanoparticles can significantly regulate the M1/M2 polarization of microglia by activating CB2 signal in ischemic stroke.