Novel CH25H and OASL microglia subclusters play distinct roles in cerebral ischemic stroke.

Background: Microglial polarization is one of the most promising therapeutic targets for multiple central nervous system (CNS) disorders, including ischemic stroke. However, detailed transcriptional alteration of microglia following cerebral ischemic stroke remains largely unclear.

Methods: Focal cerebral ischemia was induced by transient middle cerebral artery occlusion (tMCAO) for 60 min in mice. Single-cell RNA sequencing (scRNA-seq) was performed using ischemic brain tissues from tMCAO and sham mice 3 days after surgery. Ch25h mice were used to investigate the role of specific microglia subcluster on post-stroke infarct volume and neuroinflammation.

Results: We identified a relatively homeostatic subcluster with enhanced antigen processing and three "ischemic stroke associated microglia" (ISAM): MKI67, CH25H and OASL subclusters. We found the MKI67 subcluster undergo proliferation and differentiation into CH25H and OASL subclusters. CH25H microglia was a critical subcluster of ISAM that exhibited increased phagocytosis and neuroprotective property after stroke. Ch25h mice developed significantly increased infarct volume following ischemic stroke compared to Ch25h. Meanwhile, the OASL subcluster accumulated in the ischemic brain and was associated with the evolving of neuroinflammation after stroke, which was further aggravated in the aged mice brain.

Conclusions: Our data reveal previously unrecognized roles of the newly defined CH25H and OASL microglia subclusters following ischemic stroke, with novel insights for precise microglia modulation towards stroke therapy.