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Interferon regulatory factor 4/5 signaling impacts on microglial activation after ischemic stroke in mice
Author(s) -
Al Mamun Abdullah,
Chauhan Anjali,
Yu Haifu,
Xu Yan,
Sharmeen Romana,
Liu Fudong
Publication year - 2018
Publication title -
european journal of neuroscience
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.346
H-Index - 206
eISSN - 1460-9568
pISSN - 0953-816X
DOI - 10.1111/ejn.13778
Subject(s) - microglia , interferon regulatory factors , cytokine , inflammation , immunology , irf5 , tumor necrosis factor alpha , stroke (engine) , medicine , biology , immune system , innate immune system , mechanical engineering , engineering
Microglial activation is a key element in initiating and perpetuating inflammatory responses to stroke. Interferon regulatory factor 5 ( IRF 5) and IRF 4 signaling have been found critical in mediating macrophage pro‐inflammatory (M1) and anti‐inflammatory (M2) phenotypes, respectively, in peripheral inflammation. We hypothesize that the IRF 5/4 regulatory axis also mediates microglial activation after stroke. C57 BL 6 mice of 8–12 weeks were subject to a 90‐min middle cerebral artery occlusion, and the brains evaluated at 24 h, 3, 10 and 30 days after reperfusion. Flow cytometry was utilized to examine microglial activation and cytokine expression. RT ‐ PCR was performed for mRNA levels of IRF 5/4 in sorted microglia. Microglial expression of IRF 5/4 was examined by immunohistochemistry, and brain cytokine levels were determined by ELISA . Our results revealed that the IRF 5 mRNA level in sorted microglia increased at 3 days of stroke; whereas IRF 4 mRNA level exhibited biphasic increases, with a transient rise at 24 h and a peak at 10 days. The same pattern was seen in IRF 5/4 protein colocalization with Iba‐1 + cells by IHC . Intracellular levels of TNF ‐α and IL ‐1β in microglia peaked at 3 days of stroke, and IL ‐4 + IL ‐10 + double‐positive microglia significantly increased at day 10. Brain levels of these cytokines were consistent with microglial cytokine changes. Worse behavior test results were seen at 3 days vs. 10 days of stroke. We conclude that microglia phenotypes are dynamic to ischemic stroke, and IRF 5/4 signaling may regulate microglial M1/M2 activation and impact on stroke outcomes.