Abstract 157: Nur77 Ameliorate Brain Ischemic Injury Through Polarize Microglia From M1 to M2 Phenotype

Introduction: The immune response to cerebral ischemia is a major contributor to stroke pathobiology in which microglia play a crucial role. Microglia are present in the classical M1 pro-inflammatory and the alternative M2 anti-inflammatory microglia. The Nur77 is a member of orphan nuclear receptor family, has been implicated in the regulation of macrophage M1/M2 polarization. However, the function of Nur77 in microglia and stroke pathology has not been studied yet. We investigated the role of Nur77 in modulating microglial M1/M2 polarization and improve brain injury. Methods: Wild type and Nur77 -/- mice were subjected to right middle cerebral artery occlusion (MCAO). Behavior test, infarction volume, inflammation factors, and microglial phenotypes were determined at 1d, 3d, 7d after MCAO. In vitro , wild type and Nur77 -/- microglia were simulated with conditional medium of oxygen glucose deprivation neuron. M1/M2 markers were measured at different time points. To explore mechanisms, proteomics analysis was conducted. Then we induced a lentivirus into the microglial cells for abrogation of Nur77 downstream protein in Nur77 -/- microglia. Results: Nur77 expression in ipsilateral peri-infarction is markedly decreased. Nur77 deficiency enlarged infarction size, exacerbated sensorimotor and cognitive function, increased the expression of pro-inflammatory mediators (COX-2, TNFα), and decreased anti-inflammatory mediators (IL-4, IL-10) at 3d and 7d after MCAO. Nur77 -/- mice present more CD16 + Iba-1 + and CD86 + Iba-1 + M1 microglia and less CD206 + Iba-1 + M2 microglia than wild type mice. In vitro conditional medium treated Nur77 -/- primary microglia express more pro-inflammation mediators and less anti-inflammation factors. LPS-treated Nur77 -/- and wild type microglia was used for mass spectrometry and we found that Nur77 down-regulate the expression of dedicator of cytokinesis 2 (DOCK2), which promote release of proinflammation mediators in microglia. After knockdown of DOCK2 in Nur77 -/- microglia, up-regulated pro-inflammation mediators in Nur77 -/- microglia have been reversed. Conclusions: Nur77 protects against ischemic brain injury by promoting M2 polarization, which probably be mediated by DOCK2-dependent pathway.