Abstract TP538: Dynamic of Microglial Polarization in Experimental Subarachnoid Hemorrhage

Abstract

Introduction: Subarachnoid hemorrhage (SAH) is a devastating stroke type. Microglia/Macrophage, in neuroinflammation response, are capable of classic M1 and alternative M2 polarization after activation. However, the profile of microglial activation was not well studied in SAH. In this study, we aimed to unravel the polarization-specific dynamic of microglia after SAH. Methods: Wild-type C57BL/6 mice and Cx3cr1 GFP/GFP Ccr2 RFP/RFP mice were used and SAH was induced by endovascular perforation. The Immunohistochemistry and Immunofluorescence were employed to characterize the profile of microglia activation on day 1, day 3, day 5, day 10 (n=6-8). Results: Iba1-positive microglia accumulated significantly in the cortex adjacent to the bleeding site (CAPS) on day 1 and sustained to increase till the delayed phase in SAH. Microglial accumulation was also observed on motor cortex and hippocampus on the early phase. Immunofluorescence showed the CD16/32-positive M1-predominant phenotype appeared in 3 days, then gradually transformed into the CD206-positive M2 phenotype. The functionally microglial polarization advanced along with the morphological changes through ramified to amoeboid shape. The bipolar microglia appeared through the morphological transformation with the colocalization of M1/M2 markers. In addition, Ccr2 low expressed and Cx3Cr1 highly expressed (CCR2 - /Cx3Cr1 + ) cells are observed on CAPS with a co-existing of a small group of CCR2 + /Cx3Cr1 + cell. The results suggested the preponderant microglial activation rather than the infiltrated macrophage. Conclusions: Microglia demonstrated a preponderant and early accumulation and this accumulation showed a centrifugal spreading through CAPS to remote motor cortex. Pro-inflammatory response occurred early and transform to the anti-inflammation on the delayed phase. The dynamic of microglial morphological changes and polarization implied the function-related neuroinflammatory response and pathophysiologic process of restoration upon the hemorrhage attack.