Microglia Display Altered Spatial Morphology and Proteome After Stroke.

Microglia are abundantly distributed throughout the central nervous system (CNS) to play critical roles in neural development and homeostasis, and act as immune sentinels to constantly monitor their surrounding neural environment. Given their high reactivity to brain insults, we hypothesised that the cerebral microenvironment altered by ischaemic stroke would significantly impact microglial morphology and function in a spatially dependent manner. To investigate this, we examined regional gene expression changes associated with microglial activation and neuroinflammation, microglial morphology using 3D image reconstruction and unbiased proteomics at 24 h after transient middle cerebral artery occlusion (tMCAO). We found the microenvironment within the ischaemic infarct core has a distinct proinflammatory profile versus that of the sham-operated controls. Moreover, stroke induces region-specific changes to microglia morphology with those closer to the infarct displaying a more ameboid shape and less complex dendritic processes. Additionally, we identified 108 differentially expressed proteins in microglia that were isolated from the ipsilateral ischaemic hemisphere compared to those isolated from the contralateral hemisphere. These differentially expressed proteins are predicted to influence signalling pathways that mediate TNFα superfamily cytokine production, chemokine activities and leukocyte chemotaxis and migration. These findings support microglia as critical regulators of the inflammatory signalling after stroke.