Interferon regulatory factor 4/5 signaling impacts on microglial activation after ischemic stroke in mice

Abstract

Microglial activation is a key element in initiating and perpetuating inflammatory responses to stroke. Interferon regulatory factor 5 (IRF5) and IRF4 signaling have been found critical in mediating macrophage pro-inflammatory (M1) and anti-inflammatory (M2) phenotypes respectively in peripheral inflammation. We hypothesize that the IRF5/4 regulatory axis also mediates microglial activation after stroke. C57BL6 mice of 8–12 weeks were subject to a 90-minute middle cerebral artery occlusion and the brains evaluated at 24h, 3d, 10d and 30d after reperfusion. Flow cytometry was utilized to examine microglial activation and cytokine expression. RT-PCR was performed for mRNA levels of IRF5/4 in sorted microglia. Microglial expression of IRF5/4 was examined by immunohistochemistry, and brain cytokine levels were determined by ELISA. Our results revealed that the IRF5 mRNA level in sorted microglia increased at 3d of stroke; whereas IRF4 mRNA level exhibited bi-phasic increases, with a transient rise at 24h and a peak at 10d. The same pattern was seen in IRF5/4 protein colocalization with Iba-1+ cells by IHC. Intracellular levels of TNFα and IL-1β in microglia peaked at 3d 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 3d vs. 10d of stroke. We conclude that microglia phenotypes are dynamic to ischemic stroke and IRF5/4 signaling may regulate microglial M1/M2 activation and impact on stroke outcomes.

Anti-inflammatory and Neuroprotective Effects of Fungal Immunomodulatory Protein Involving Microglial Inhibition

“…The pro-inflammatory phenotypes of microglia are characterized by several upstream activators and downstream effectors, including IRF5, IRF8, P2X4R, P2X7R, P2Y12R, iNOS, COX-2, and CD68 [ 28 , 29 , 30 ]. In neuron/glia cultures, LPS/IFN-γ elevated the protein levels of IRF5, IRF8, P2X4R, P2X7R, P2Y12R, iNOS, COX-2, and CD68.…”

Interferon Regulatory Factor 5 Mediates Lipopolysaccharide Induced Neuroinflammation

“…Manipulating the polarization of microglia towards the M2 phenotype might attenuate neuroin ammation related brain injuries 7,20 . A recently study showed that down-regulation of IRF5 in transient middle cerebral artery occlusion mice attenuated M1, but enhanced M2 activation of microglia, quenched pro-in ammatory responses, and improved stroke outcomes 7,21 . Therefore, IRF5 mediated pro-in ammatory activation of microglia are not disease speci c, but can also be seen in other pathogenic conditions.…”

“…However, the role of IRF5 in CNS remains elusive. A recent study found that the expression of IRF5 in uenced stroke outcomes 7 , which was related to IRF5 mediated activation of microglia and regulation of neuroin ammation. Thus, our study intends to clarify the role of IRF5 in microglia associated neuroin ammation.…”

Thrombin Inhibition Reduces the Expression of Brain Inflammation Markers upon Systemic LPS Treatment

“…Inflammation initiates clotting while decreasing the activity of natural anticoagulant mechanisms and impairing the fibrinolytic system [ 15 , 22 ]. Inflammatory cytokines are the major mediators involved in the activation of coagulation [ 4 , 10 , 15 ]. The natural anticoagulants function to dampen the elevation of cytokine levels [ 15 , 36 ].…”

“…A growing body of evidence links systemic inflammation and disease pathogenesis in the brain [ 1 – 3 ]. Upon stimulation by endogenous (e.g., injury, stroke, and autoimmune processes) or exogenous challenges (e.g., pathogens or severe psychological stressors), the immune system upregulates the expression of several cytokines in the brain [ 4 – 10 ]. This results in microglia alteration and ultimately disruption of the delicate neuroglial interactive balance causing alteration of cognition and behavior [ 11 , 12 ].…”