Induction of the Vitamin D Receptor Attenuates Autophagy Dysfunction-Mediated Cell Death Following Traumatic Brain Injury

Abstract

Background/Aims: Traumatic brain injury (TBI) is a major public health problem in the world and causes high rates of mortality and disability. Recent evidence suggests that vitamin D (VD) has neuroprotective actions and can promote function recovery after TBI. In vitro and in vivo studies have demonstrated that autophagy could be enhanced following supplementation with an active metabolite of VD (calcitriol). However, it is unclear whether autophagy participates in the protective effects of calcitriol after TBI. To test this hypothesis, we examined the protective effects of calcitriol on TBI-induced neurological impairment and further investigated whether calcitriol could modulate autophagy dysfunction-mediated cell death in the cortex region of rat brain. Methods: Eighty-five male rats (250-280 g) were randomly assigned to sham (n=15), TBI model (TBI, n=35) and calcitriol treatment (calcitriol, n=35) groups. Rats were injected intraperitoneally with calcitriol (1 µg/kg) at 30 min, 24 h and 48 h post-TBI in the calcitriol group. The lysosomal inhibitor, chloroquine (CQ), was used to evaluate autophagic flux in the TBI and calcitriol groups. Neurological functions were evaluated via the modified neurological severity score test at 1-7 days after TBI or sham operation, and the terminal deoxynucleotidyl transferase-mediated FITC-dUTP nick-end labeling method was used to evaluate the ability of calcitriol to inhibit apoptosis. The expression of VDR, LC3 and p62 proteins was measured by western blot analysis at 1, 3 and 7 days post-injury Results: Calcitriol treatment attenuated mNSS at 2-7 days post-TBI (P < 0.05 versus TBI group). Calcitriol dramatically increased VDR protein expression compared with the untreated counterparts at 1, 3 and 7 days post-TBI (P < 0.05). The rate of apoptotic cells in calcitriol-treated rats was significantly reduced compared to that observed in the TBI group (P < 0.05). The LC3II/LC3I ratio was decreased in the cortex region at 1, 3 and 7 days post-TBI in rats treated with calcitriol (p < 0.05 versus TBI group), and the p62 expression was also attenuated (p < 0.05 versus TBI group). The LC3II/LC3I ratio in the calcitriol group was significantly increased when pretreated with CQ (P < 0.05). Conclusion: Calcitriol treatment activated VDR protein expression and attenuated neurological deficits in this rat TBI model. The protective effects might be associated with the restoration of autophagy flux and the decrease in apoptosis in the cortex region of rat brain.