Abstract
Background: Traumatic brain injury (TBI) initiates an oxidative cascade that contributes to the delayed progressive damage, whereas autophagy is critical in maintaining homeostasis during stressful challenge. We previously demonstrated that vitamin D (VitD) shows strong neuroprotective and anti-oxidative properties in the animal models of TBI. Therefore, the present study aimed to further explore the potential interrelationship between oxidative stress and autophagy in the progression of TBI and therapeutic mechanism of VitD. Methods: Neuroprotective effects of calcitriol, the active form of VitD, were examined following TBI. We further evaluated the impacts of TBI and VitD treatment on autophagic process and nuclear factor E2-related factor 2 (Nrf2) signaling. To confirm the mechanism, chloroquine (CQ) treatment and Nrf2−/− mice were used to block autophagy and Nrf2 pathway, respectively. Results: We found that treatment of calcitriol markedly ameliorated the neurological deficits and histopathological changes following TBI. The brain damage impaired autophagic flux and impeded Nrf2 signaling, the major regulator in antioxidant response, consequently leading to uncontrolled and excessive oxidative stress. Meanwhile, calcitriol promoted autophagic process and activated Nrf2 signaling as evidenced by the reduced Keap1 expression and enhanced Nrf2 translocation, thereby mitigating TBI-induced oxidative damage. To further confirm whether autophagy was responsible for Keap1 degradation and Nrf2 activation, the lysosomal inhibitor, CQ, was used to block autophagy. Our data suggested that CQ treatment abrogated calcitriol-induced autophagy and compromised Nrf2 activation with increased Keap1 accumulation and reduced expression of Nrf2-targeted genes. Additionally, both CQ treatment and Nrf2 genetic knockout abolished the protective effects of VitD against both TBI-induced neurological deficits and neuronal apoptosis. Conclusions: Therefore, our work demonstrated a neuroprotective role of VitD in TBI by triggering Nrf2 activation, which might be mediated by autophagy.
NADPH Oxidase 2 Regulates NLRP3 Inflammasome Activation in the Brain after Traumatic Brain Injury
