Dynamic cell type‐specific expression of Nrf2 after traumatic brain injury in mice

Abstract Nrf2 plays a pivotal role in antioxidant response and anti‐inflammation after traumatic brain injury ( TBI ), and its deletion aggravates TBI ‐induced brain damage. Previous studies have demonstrated that Nrf2 is activated post TBI , but dynamic changes in expression and cell type‐specific characteristics remain unclear. In this study, the Feeney weight‐drop contusion model was conducted to mimic TBI , and the ipsilateral cerebral cortex was collected at 1, 3, 7 and 14 days post TBI (dpi). Nrf2 protein levels were observed by western blot. Cell type‐specific localization of Nrf2 after TBI was detected at different time intervals by double immunofluorescence staining. NeuN, GFAP , IBA 1 and NG 2 were used as cell type‐specific markers to neurons, astrocytes, microglia and NG 2 glia, respectively. After TBI , Nrf2 protein levels peaked at 1 dpi. Robust transient Nrf2 accumulation was co‐localized with neurons, which was predominant at 1 dpi. Continuous weak Nrf2 expression was detected in activated astrocytes, and the number of double positive cells peaked at 7 dpi. Inducible widespread immunostaining of Nrf2 was observed in the nucleus of the microglia, and the number of Nrf2+ microglia peaked at 7 dpi. In addition, we also explored colocalization of Nrf2 in NG 2 glia, in which the percentage of Nrf2+ in NG 2 glia reached a climax at 3 dpi. This study reveals that the accumulation of endogenous Nrf2 might mediate different pathophysical roles in neurons and glias after TBI , the cell‐type specific and time‐dependent expression provide insights to explain the roles of Nrf2 in different neural cells.