Vitamin D mitigates oxidative and endoplasmic reticulum stress and protects cardiac tissue from apoptotic cell death in vivo and in vitro.

Vitamin D deficiency is linked to cardiovascular disease (CVD), with oxidative stress (OS) playing a key role in the etiology of CVD. We hypothesized that vitamin D deficiency induces cardiac oxidative and endoplasmic reticulum stress (ERS), leading to apoptotic cell death. A rat model of vitamin D deficiency and insufficiency was employed for in vivo studies, while the rat cardiomyoblast cell line (H9C2) was used for in vitro experiments. (OS) parameters were assessed by spectrophotometry, gene and protein expression were determined using qPCR and western blotting. OS markers were elevated while antioxidant enzyme activities were decreased in the left ventricle of vitamin D deficient (VDD) rats compared to control rats. VDD downregulated nuclear factor-erythroid factor 2-related factor 2 (Nrf2) and its downstream proteins in the heart. Since elevated OS leads to ERS, we assessed ERS markers in the heart. Levels of ERS markers were elevated in both the VDD and insufficient rats. Pro-apoptotic and autophagy markers such as BAX, BIM and caspase 8 were upregulated in the heart of VDD rats. Experiments with the H9C2 cell line demonstrated that induction of mild OS using H2O2 upregulates ERS, autophagy and apoptotic markers. VD pretreatment of H9C2 cells led to increase in antioxidant enzyme activities, decrease in ERS and autophagy markers and apoptosis. 4PBA, an ERS inhibitor inhibited apoptosis indicative of a direct role for ERS. The findings suggest that vitamin D protects the heart from oxidative injury and cell death by antioxidant defence mechanism, upregulating Nrf2/HO-1 signaling while alleviating ER stress.