Arresting the Bad Seed: HDAC3 Regulates Proliferation of Different Microglia after Ischemic Stroke [ATAC-seq]

The rapid accumulation of self-renewed polarized microglia in the penumbra is the critical neuroinflammatory process after the onset of ischemic stroke, leading to secondary demyelination and neuronal loss. HDAC3 has been reported to regulate cell proliferation of tumour cells and modulate neuroinflammation. However, the mechanism by which HDAC3 regulates microgliosis and microglial polarization remains ambiguous. Herein, we demonstrated that microglia-specific ablation of HDAC3 (HDAC3-miKO) ameliorated poststroke long-term functional and histological outcomes. Starting with unbiased RNA seq of microglia, we identified mitosis as the most significant process reversed by loss of HDAC3. Notably, HDAC3-miKO specifically inhibited the proliferation of M1-like microglia but not M2-like microglia, resulting in microglial transition to an M1-like state. Moreover, ATAC-seq (Assay for Transposase-Accessible Chromatin using sequencing) revealed that HDAC3 deletion induced drastic closing of accessible regions enriched with motifs for PU.1. Taken together, we uncovered for the first time that HDAC3/PU.1-mediated differential proliferation-related reprogramming in different microglia populations drives poststroke inflammatory state transition of microglia and thereby contributes to the pathophysiology of ischemic stroke.