Background: Ischemic stroke (IS) is a leading cause of death and disability worldwide, yet therapeutic options remain limited and largely ineffective in promoting long-term recovery. Increasing evidence shows that beyond its classical role in bone metabolism, the active metabolite of vitamin D, 1,25-dihydroxyvitamin D3 (1,25-VitD3), exerts neuroprotective actions through anti-inflammatory, antioxidant, and anti-apoptotic pathways. However, its specific molecular mechanisms in IS remain incompletely defined. Here, we investigate whether 1,25-VitD3 alleviates ischemic brain injury and promotes neurogenesis via peroxisome proliferator-activated receptor γ (PPARγ)-dependent microglial polarization. Methods: To test this, we employ transient middle cerebral artery occlusion/reperfusion (MCAO) in mice and oxygen-glucose deprivation/reoxygenation (OGD/R) in primary microglial cultures. We assess neurological outcomes and infarct volumes following the 1,25-VitD3 treatment. We analyze microglial phenotype and PPARγ expression using qPCR and Western blotting. Neural stem cell (NSC) proliferation and differentiation are evaluated in vivo and in vitro through immunofluorescence. Additionally, we quantify brain-derived neurotrophic factor (BDNF) and insulin-like growth factor-1 (IGF-1) levels. Results: We find that 1,25-VitD3 significantly improves both short- and long-term neurological functions and reduces infarct volume following IS. Mechanistic studies reveal that 1,25-VitD3 promotes microglial polarization toward the anti-inflammatory M2 phenotype, accompanied by increased PPARγ expression. Furthermore, conditioned medium from 1,25-VitD3-treated microglia enhances NSC proliferation and neuronal differentiation, effects associated with upregulation of BDNF and IGF-1. Importantly, pharmacological inhibition of PPARγ abolishes these neuroprotective and neurogenic benefits, confirming a PPARγ-dependent mechanism. Conclusion: This study provides compelling evidence that 1,25-VitD3 protects against ischemic injury and facilitates post-stroke neurogenesis through PPARγ-mediated microglial M2 polarization and neurotrophic factor release. These findings highlight 1,25-VitD3 as a promising therapeutic candidate for ischemic stroke, warranting further translational investigation. This work is financially supported by the American Heart Association grants TPA-971566, 24TPA1304527, and 25TPA1481773, which are greatly acknowledged.
Rekapally et al. (Thu,) studied this question.