Transcriptomic analysis of mouse brain microglia on aging-associated changes in response to cerebral ischemia

Senescence-associated alterations in microglia may have profound impact on cerebral homeostasis and stroke outcomes. However, the lack of a transcriptome-wide comparison between young and aged microglia in the context of ischemia limits our understanding of aging-related mechanisms. Herein, we performed bulk RNA sequencing analysis of microglia purified from cerebral hemispheres of young adult (10-week-old) and aged (18-month-old) mice 5 days after distal middle cerebral artery occlusion or sham operation. Considerable transcriptional differences were observed between young and aged microglia in healthy brains, indicating heightened chronic inflammation in aged microglia. Following stroke, the overall transcriptional activation was more robust in young microglia than in aged microglia. Gene clusters with functional implications in immune inflammatory responses, immune cell chemotaxis, tissue remodeling, and cell-cell interactions were markedly activated in microglia of young but not aged stroke mice. These alterations in microglial gene response may contribute to aging-driven vulnerability and poorer recovery after ischemic stroke. Overall design: Young adult (10 weeks old) and aged (18 months old) male C57BL/6 mice were subjected to focal cerebral ischemia induced by permanent occlusion of the left distal middle cerebral artery and left common carotid artery (abbreviated as "dMCAO"). The CD11b+CD45low cell population was collected by fluorescence-activated cell sorting from the brain after sham operation, or 5 days after brain ischemia. There were 4 groups: young sham, young dMCAO 5d, aged sham, and aged dMCAO 5d. In each group there were 2 biological replicates. Each replicate was pooled from 5 mouse brains. The sorted cells were subjected to mRNA sequencing.