Vitamin D alleviates neuronal injury in cerebral ischemia-reperfusion via enhancing the Nrf2/HO-1 antioxidant pathway to counteract NLRP3-mediated pyroptosis

Abstract

Vitamin D supplementation is reported to have anti-inflammatory and neuroprotective effects during cerebral ischemia-reperfusion injury (CIRI), but the protective mechanism has not been fully elucidated. In this study, rats were given prior administrations of 1,25-vitamin D3 (1,25-VitD3) for a week and subjected to 2 hours of middle cerebral artery occlusion (MCAO) followed by 24 hours of reperfusion. Supplementation with 1,25-VitD3 significantly reduced neurological deficit scores and cerebral infarction areas, and increased surviving neurons. Oxygen-glucose deprivation/reoxygenation (OGD/R)-induced rat cortical neuron cells (RN-C) were subjected to 1,25-VitD3 treatment. Administration of 1,25-VitD3 improved cell viability and inhibited lactate dehydrogenase (LDH) activity and cell apoptosis in OGD/R-stimulated RN-C, as assessed by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-h-tetrazolium bromide (MTT) assay, LDH activity assays and TdT-mediated dUTP nick end labeling (TUNEL) staining, respectively. Notably, western blot assay showed that 1,25-VitD3 upregulated nuclear factor erythroid 2-related factor 2 (Nrf2) and heme oxygenase 1 (HO-1) to alleviate oxidative stress, but reduced proteins and inflammatory cytokines related to NLR pyrin domain containing 3 (NLRP3)-mediated pyroptosis, resulting in decreased pyroptosis and neuroinflammation in vivo and in vitro. Transfection of pcDNA-Nrf2 in RN-C also inhibited pyroptosis and OGD/R-induced cell death whereas breakdown of Nrf2 signals destroyed the protective effect of 1,25-VitD3 on OGD/R-stimulated RN-C. In conclusion, 1,25-VitD3 protects neurons against CIRI through activating the antioxidant Nrf2/HO-1 pathway to restrain NLRP3-mediated pyroptosis.