Abstract 110: RNA Sequencing Reveals Novel Macrophage Transcriptome Favoring Neurovascular Plasticity After Ischemic Stroke

Abstract

Introduction: Blood monocytes/macrophages (MΦ) infiltrate the brain in massive numbers after ischemic stroke, but their functional roles in the post-stroke brain remain elusive. Methods: We sorted CD11b + CD45 high monocytes/MΦ from mouse blood and brain 5d after distal MCAO (dMCAO) and investigated their transcriptomic profiles by RNA-seq (n=3/group). Results: Robust genomic changes occurred in MΦ invading the post-dMCAO brain compared to their counterparts in the blood (3196 differentially expressed genes with >2 fold changes; FDR<0.05). In addition to their canonical role in immune responses, brain MΦ expressed unique transcriptomic programs which may favor post-stroke neurovascular repair. Functional enrichment analysis of brain MΦ transcriptome revealed significant overrepresentation (p<0.01) of 110 biological processes linked to neurovascular remodeling and plasticity (e.g., angiogenesis and axonal regeneration), suggesting a previously underappreciated role for MΦ in post-stroke brain repair. Upstream Regulator analysis predicted PPARγ as a master regulator (z-score=2.64, p<10 -15 ) that drives the transcriptional reprogramming in post-stroke brain MΦ and dictates their functional phenotype. Accordingly, tamoxifen-induced, myeloid cell-specific PPARγ knockout mice demonstrated less post-stroke angiogenesis (BrdU+CD31 staining) and neurogenesis (BrdU+NeuN) than WT mice (n=9/group, p<0.01), which correlated significantly with the exacerbation of neurological deficits in these mice (n=9/group, p<0.01 vs WT in foot fault and adhesive removal tests) at 35d after dMCAO. Conclusions: Our study reveals a novel repair-enhancing transcriptome in brain MΦ during post-stroke neurovascular remodeling. As a master molecule controlling genomic reprogramming, PPARγ is a rational therapeutic target for promoting beneficial MΦ functions, and facilitating neurorestoration and long term functional recovery after ischemic stroke.