Down-regulation of miR-181a promotes microglial M1 polarization through increasing expression of NDRG2

Abstract

Background: Microglia exist in two polarized states: a classical activation state (M1) and an alternative activation state (M2). Accumulating evidence has suggested an involvement of miR-181a in neuronal development, survival, function, and plasticity, but its exact functional role in microglial polarization still requires clarification. We investigated the impact of miR-181a on microglial polarization using a rat chronic social stress model of depression. Methods: N9 microglia were stimulated with lipopolysaccharide (LPS; 100 ng/mL ) or IL-4 (10 ng/mL ) for 12h. Expression of Nos2, Arg-1, miR-181a, and NDRG2 was determined using real-time PCR. NDRG2 and syntaxin-1A protein expressions were analyzed by western blotting. The cell viability of N2A neuron was measured by an MTT assay. Body weight gain and adrenal weight were also evaluated. Results: Five weeks of daily social defeat significantly increased Nos2 and NDRG2 mRNA expression and dramatically reduced miR-181a expression in the hippocampus. Microglia were also polarized into different functional phenotypes. LPS treatment significantly enhanced mRNA expression of Nos2 and dramatically inhibited the expression of miR-181a. Conversely, treatment with IL-4 markedly increased the mRNA levels of Arg-1 and the expression of miR-181a. Expression of miR-181a regulated microglia differentiation by targeting NDRG2, while inhibition of miR-181a expression in N9 microglia induced N2A neuron death, which could be reversed by NDRG2 interference. Overexpression of miR-181a overcame the impacts of chronic psychosocial stress on body weight gain, adrenal weight, and syntaxin-1A expression in the hippocampus. Conclusion: Down-regulation of miR-181a promoted microglial M1 polarization by enhancing NDRG2 expression. Keywords: miR-181a, microglial M1 polarization, NDRG2