Betulinic acid regulates microglial polarization by inhibiting the phosphorylation of CB2 receptors thereby improving ischemic brain injury.

Ischemic stroke is a leading cause of mortality and permanent disability worldwide, with a lack of effective drug therapy. Microglia, as the intrinsic immune cells of the brain, play a biphasic role in ischemic stroke depending on its polarization toward M1 or M2 phenotype. Betulinic acid (BA) is a natural bioactive compound has antioxidant, anti-inflammatory, anti-tumor, and other biological activities, holds potential to active CB2 receptor on microglia and promote a shift towards the M2 polarization. This study delves into the regulatory impact of self-assembled BA on CB2 receptor-mediated microglial polarization after cerebral ischemia. In vitro studies revealed BA's ability to modulate the polarization of BV2 microglia subjected to lipopolysaccharide (LPS) treatment, an effect impeded by CB2 inhibition. For in vivo studies, transient middle cerebral artery occlusion (MCAO) model mice receiving self-assembled BA NPs exhibited the smallest infarct volume and least neurological deficits. However, these benefits were reversible with the administration of a CB2 inhibitor. Notably, microglia at the ischemic site displayed a shift towards the M2 phenotype upon BA treatment. Our results demonstrates that BA can significantly regulate the M1/M2 polarization of microglia by activating CB2 signal and inhibiting its phosphorylation level in ischemic stroke, thereby reducing the brain inflammatory response and playing a neuroprotective role.