Nuclear Factor Erythroid 2-Related Factor 2 (Nrf2) Mediates Neuroprotection in Traumatic Brain Injury at Least in Part by Inactivating Microglia

BACKGROUND Microglial activation has been reported to be involved in traumatic brain injury (TBI). Nuclear factor erythroid 2-related factor 2 (Nrf2) plays a significant role in protecting against TBI-induced secondary brain injury. However, the exact mechanism is not clearly understood. The present study aimed to explore whether Nrf2 protects against TBI partly by regulating microglia function. MATERIAL AND METHODS Microglia cells were isolated from C57BL/6 mouse brains (postnatal day 1-3). The expression of Nrf2 was suppressed by transfection with Nrf2-specific small interfering RNA (siRNA), and overexpressed by transfections with pcDNA3.1-Nrf2. The expression of Nrf2 was confirmed by real-time PCR and Western blotting. After transfection, cell viability, phagocytic ability, and the expression of pro-inflammatory cytokines (tumor necrosis factor (TNF)-α and interleukin (IL)-6) were determined by 3-(4, 5-dimethylthiazol-2-yl)-2, 5- diphenyltetrazolium bromide (MTT) colorimetric assay, phagocytosis assay, and enzyme-linked immunosorbent assay (ELISA), respectively. RESULTS mRNA and protein expression levels of Nrf2 were significantly reduced by transfection with Nrf2-specific siRNA (both P<0.05) but were elevated by transfection with pcDNA3.1-Nrf2 (both P<0.01). The cell viability, phagocytic ability, and the expression of TNF-α and IL-6 were all significantly reduced by overexpression of Nrf2 but were significantly increased by silencing of Nrf2 compared with the control group. CONCLUSIONS Our results suggest that Nrf2 protects against TBI, at least part by regulating microglia function.