Lipopolysaccharide–induced preconditioning protects against traumatic spinal cord injury by upregulating Nrf2 expression in rats

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Aims:Lipopolysaccharide (LPS)-induced preconditioning protects neurons against traumatic spinal cord injury (TSCI) in rats. This study sought to test whether Nrf2, a transcription factor, mediated LPS-induced preconditioning.Main methods:The TSCI model was established using a standardized NYU impactor on adult female rats. Rats were pretreated with LPS (0.2 mg/kg, IP; 72 h before injury). Nrf2 was silenced by injecting a lentivirus encoding RNAi against Nrf2 into injured spinal cords. Neurologic function was assessed by Basso, Beattie and Bresnahan (BBB) scores 6 h, 12 h, 24 h, 48 h, 72 h, 7 d and 14 d after TSCI. Neuronal apoptosis was measured by a TUNEL staining. Ultrastructure was observed using transmission electron microscope (TEM). The protein expression of HO-1, NQO1 and GCLC was examined using immunohistochemistry and immunoblotting.Key findings:The injection of a lentivirus effectively transfected GFP into injured spinal cords. The expression of Nrf2 was significantly decreased in spinal cords receiving a lentivirus encoding RNAi against Nrf2. BBB scores showed that TSCI markedly impaired nervous function, which was markedly preserved by LPS pretreatment. Nrf2 knockdown significantly suppressed LPS pretreatment–induced protection of nervous function. TEM images and TUNEL staining showed an increase in apoptotic cells when Nrf2 was silenced. Moreover, immunohistochemistry and immunoblotting analysis exhibited that LPS pretreatment significantly upregulated the expression of anti–oxidative proteins including HO-1, NQO1 and GCLC, which was suppressed when Nrf2 expression was silenced in injured spinal cords.Significance:LPS preconditioning effectively alleviates TSCI–induced impairment and preserves nervous function in a Nrf2–dependent manner.

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