Vitamin D Promotes Neuronal Survival via Nrf2 Upregulation in D-Galactose-Induced Mice: An In-Vivo and In-Silico Study.

Abstract

Gradual loss of the homeostatic balance owing to deregulation of endogenous antioxidant defense pathways, such as nuclear factor erythroid 2-related factor 2 (Nrf2), contributes, at least in part, to the characteristic oxidative stress, neuronal loss, and cognitive decline associated with aging. Here, we adopted an integrated approach using behavioral, biochemical, histological, molecular, and in silico methods, exploring the neuroprotective efficacy of vitamin D against D-galactose-induced oxidative stress, neuroinflammation, and neurodegeneration. Chronic D-galactose administration (150 mg/kg, s.c) led to profound deficits in spatial learning, working memory, and recognition memory, besides increased oxidative stress, reduced antioxidant enzyme activity, suppression of Nrf2 and heme oxygenase-1 (HO-1) expression, and frank hippocampal neurodegeneration, as revealed by nissl staining. Vitamin D treatment (5 µg/kg i.p) significantly improved such deficits by restoring cognitive performance, reducing ROS and lipid peroxidation, enhancing endogenous antioxidant activities such as superoxide dismutase (SOD), catalase (CAT), reduced glutathione (GSH) and glutathione peroxidase (GPx), and upregulating Nrf2 and HO-1 expression comparable to positive control, dimethyl fumarate (DMF). Co-administration of all-trans retinoic acid (ATRA), an antagonist for Nrf2, abrogated these protective effects, confirming the pathway specificity. Molecular docking studies have shown a strong binding affinity of Vitamin D to the regulatory domain of Nrf2, supporting a direct stabilizing interaction that may facilitate the activation of Nrf2. Nissl quantification has further demonstrated substantial preservation of neuronal integrity in hippocampal CA1, CA3, and DG regions following the treatment with vitamin D. Altogether, findings from this study show that vitamin D confers robust neuroprotection through Nrf2-dependent antioxidant mechanisms and mitigates aging-related neurodegeneration induced by D-galactose. The results highlighted vitamin D as a readily accessible therapeutic candidate for mitigating oxidative stress-driven cognitive decline.