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Updated: Jul 23, 2025
Three-dimensional Confocal Analysis of Microglia/macrophage Markers of Polarization in Experimental Brain Injury
Published on: September 4, 2013
Central IRF4/5 Signaling Are Critical for Microglial Activation and Impact on Stroke Outcomes
Conelius Ngwa1, Abdullah Al Mamun1, Shaohua Qi1
1Department of Neurology, McGovern Medical School, The University of Texas Health Science Center at Houston, Houston, TX, 77030, USA.
Abstract:
Microglia and monocytes play a critical role in immune responses to cerebral ischemia. Previous studies have demonstrated that interferon regulatory factor 4 (IRF4) and IRF5 direct microglial polarization after stroke and impact outcomes. However, IRF4/5 are expressed by both microglia and monocytes, and it is not clear if it is the microglial (central) or monocytic (peripheral) IRF4-IRF5 regulatory axis that functions in stroke. In this work, young (8-12 weeks) male pep boy (PB), IRF4 or IRF5 flox, and IRF4 or IRF5 conditional knockout (CKO) mice were used to generate 8 types of bone marrow chimeras, to differentiate the role of central (PB-to-IRF CKO) vs. peripheral (IRF CKO-to-PB) phagocytic IRF4-IRF5 axis in stroke. Chimeras generated from PB and flox mice were used as controls. All chimeras were subjected to 60-min middle cerebral artery occlusion (MCAO) model. Three days after the stroke, outcomes and inflammatory responses were analyzed. We found that PB-to-IRF4 CKO chimeras had more robust microglial pro-inflammatory responses than IRF4 CKO-to-PB chimeras, while ameliorated microglial response was seen in PB-to-IRF5 CKO vs. IRF5 CKO-to-PB chimeras. PB-to-IRF4 or IRF5 CKO chimeras had worse or better stroke outcomes respectively than their controls, whereas IRF4 or 5 CKO-to-PB chimeras had similar outcomes compared to controls. We conclude that the central IRF4/5 signaling is responsible for microglial activation and mediates stroke outcomes.
Insights
Central interferon regulatory factor 4 (IRF4) and IRF5 signaling drives microglial activation and stroke outcomes. Peripheral IRF4/IRF5 do not significantly impact stroke in mice.
Area of Science:
- Neuroimmunology
- Stroke Pathophysiology
- Innate Immune Cell Signaling
Background:
- Microglia and monocytes are key immune cells in cerebral ischemia.
- Interferon regulatory factors 4 (IRF4) and 5 (IRF5) influence microglial polarization post-stroke.
- The specific roles of central (microglial) versus peripheral (monocytic) IRF4/IRF5 in stroke remain unclear.
Purpose of the Study:
- To delineate the distinct roles of microglial versus monocytic IRF4 and IRF5 in stroke.
- To investigate the contribution of the central (microglia) and peripheral (monocytes) IRF4-IRF5 axis to stroke pathophysiology and outcomes.
Main Methods:
- Generation of eight types of bone marrow chimeras using young male pep boy (PB), IRF4/IRF5 flox, and IRF4/IRF5 conditional knockout (CKO) mice.
- Subjecting chimeras to a 60-minute middle cerebral artery occlusion (MCAO) model of stroke.
- Analysis of inflammatory responses and stroke outcomes three days post-MCAO.
Main Results:
- Central IRF4 signaling (PB-to-IRF4 CKO) enhanced pro-inflammatory microglial responses compared to peripheral signaling (IRF4 CKO-to-PB).
- Central IRF5 signaling (PB-to-IRF5 CKO) ameliorated microglial responses compared to peripheral signaling (IRF5 CKO-to-PB).
- Central IRF4/IRF5 CKO chimeras exhibited altered stroke outcomes (worse for IRF4, better for IRF5) compared to controls, while peripheral CKO chimeras showed similar outcomes.
Conclusions:
- The central IRF4/IRF5 signaling axis within microglia is primarily responsible for regulating microglial activation after stroke.
- Central IRF4 signaling exacerbates, while central IRF5 signaling ameliorates, stroke outcomes.
- Peripheral IRF4/IRF5 signaling plays a minimal role in mediating stroke outcomes in this model.
