This study is to further reveal the role of microglia and microglia-astrocyte crosstalk in acute ischemic stroke (AIS).

Inflammation and lymphocytes invasion occur within a few hours after AIS. Microglia are the first responders to microenvironmental changes and also engaged in communicating with other cells, such as astrocytes and periphery cells. However, our understanding of microglial immunomodulation still remains unclear.

A mouse model of transient focal cerebral ischemic stroke and reperfusion was achieved by tMCAo (temporary Middle Cerebral Artery occlusion). Motor coordination and neurological function was accessed by Rotarod Test and neurological deficit score. Oxygen glucose deprivation (OGD) in vitro was taken to simulate AIS. Depletion of microglia in Cx3cr1-Cre: Rosa^YFP/iDTR mice was done via administration of tamoxifen and diphtheria toxin. Next generation sequencing was conducted to figure out differential genes. Primary glia cells were used.  Exogenous IL1RA and neutralizing antibody were used in vitro study. CXCL1 neutralizing antibody or exogenous IL1RA was to treat AIS in vivo.

Compared to control group with tMCAo, we demonstrated that depletion of microglia exacerbated neurological deficits and brain infarction accompanying with more infiltrated neutrophils. And a significant upregulation of CXCL1 expression and downregulation of IL1RN expression following tMCAO were found in microglia depleted group. Tissue immunochemistry and in vitro studies revealed microglia were the main source of IL1RA and astrocytes secreted CXCL1. In vitro, IL1RA recombinant protein suppressed astrocyte-derived CXCL1 expression while the neutralizing antibody against IL1RA promoted CXCL1 expression. In vivo, treating with CXCL1 antibody or exogenous IL1RA ameliorated brain injury, accompanying with reduction in neutrophils invasion in brain parenchyma. Furtherly, IL1RA treatment inhibited CXCL1 expression in vivo.

Our findings identified microglia played a neuroprotective role in AIS and microglia-derived IL1RA mediated the microglia-astrocyte crosstalk by suppressing CXCL1 from astrocytes, thus ameliorating neutrophils invasion and brain injury following AIS.