Role for microglia in sex differences after ischemic stroke: importance of M2

Abstract

Inflammation plays a critical role in the pathogenesis of ischemic stroke. This process depends, in part, upon proinflammatory factors released by activated resident central nervous system (CNS) microglia (MG). Previous studies demonstrated that transfer of IL-10+ B-cells reduced infarct volumes in male C57BL/6J recipient mice when given 24 h prior to or therapeutically at 4 h or 24 h after experimental stroke induced by 60 min middle cerebral artery occlusion (MCAO). The present study assesses possible sex differences in immunoregulation by IL-10+ B-cells on primary male vs. female MG cultured from naïve and ischemic stroke-induced mice. Thus, MG cultures were treated with recombinant (r)IL-10, rIL-4 or IL-10+ B-cells after lipopolysaccharide (LPS) activation and evaluated by flow cytometry for production of proinflammatory and anti-inflammatory factors. We found that IL-10+ B-cells significantly reduced MG production of TNF-α, IL-1β and CCL3 post-MCAO and increased their expression of the anti-inflammatory M2 marker, CD206, by cell-cell interactions. Moreover, MG from female vs. male mice had higher expression of IL-4 and IL-10 receptors and increased production of IL-4, especially after treatment with IL-10+ B-cells. These findings indicate that IL-10-producing B-cells play a crucial role in regulating MG activation, proinflammatory cytokine release and M2 phenotype induction, post-MCAO, with heightened sensitivity of female MG to IL-4 and IL-10. This study, coupled with our previous demonstration of increased numbers of transferred IL-10+ B-cells in the ischemic hemisphere, provide a mechanistic basis for local regulation by secreted IL-10 and IL-4 as well as direct B-cell/MG interactions that promote M2+-MG.

Estrogen induces multiple regulatory B cell subtypes and promotes M2 microglia and neuroprotection during experimental autoimmune encephalomyelitis

“…Previously we demonstrated in the middle cerebral artery occlusion (MCAO) model that regulatory B10 cells can reduce microglial production of pro-inflammatory cytokines and increase the expression of M2 markers by cell-cell interaction. This effect was more pronounced in female mice compared to male mice (Bodhankar, Lapato, 2015). Hence, it is possible that the estrogen induced Bregs that migrate into the CNS during EAE promote an anti-inflammatory M2 phenotype in microglia and enhance neuroprotection.…”

“…as described before (Bodhankar et al, 2015). The glial cell cultures were incubated at 37°C at 5% CO 2 and replenished with fresh medium containing GM-CSF every 3 days.…”

Interleukin-4 Is Essential for Microglia/Macrophage M2 Polarization and Long-Term Recovery After Cerebral Ischemia

“…Interestingly, recent studies support the importance of IL-4 in sex differences in stroke models. 12, 29 IL-4 is critical for neuroprotection during the estrus phase of the estrous cycle in females. 12 Furthermore, microglia isolated from female mice after MCAO express higher levels of the IL-4 receptor upon further inflammatory stimulation.…”

“…12 Furthermore, microglia isolated from female mice after MCAO express higher levels of the IL-4 receptor upon further inflammatory stimulation. 29 Therefore, the effect of IL-4 on long-term outcomes after stroke in female warrants further investigation.…”

Estrogen protects both sexes against EAE by promoting common regulatory cell subtypes independent of endogenous estrogen

“…Bregs are known to secrete IL-10 and have also been shown to influence microglia polarization by secreting IL-4, resulting in more anti-inflammatory microglia (Bodhankar et al 2015b). The frequency of anti-inflammatory splenic macrophages (CD11b + CD206 + or CD11b + Arg-1 + ) is significantly increased in E2 treated intact females (Benedek et al 2017), male and OVX females during EAE compared to sham treated mice.…”