BACH1 orchestrates macrophage state transitions to coordinate regenerative inflammation [Individualmouse]

To delineate the transcriptional changes, we used the cardiotoxin (CTX) acute muscle injury model and profiled the chromatin accessibility (ATAC-seq) and gene expression (RNA-seq) in sorted macrophage populations at different time-points during muscle regeneration. We identified BACH1 a heme-responsive transcriptional repressor, as a novel regulator of this process. Histological analysis reveals that Bach1 myeloid-specific knockout mice present a persistent necrotic fiber as well as delayed tissue repair while FACS and bulk RNA-seq show an abnormal macrophage phenotype switch and deregulation of critical genes involved in regenerative inflammation. To study how BACH1 affects the macrophage subtype specification and cellular composition during muscle repair, we have performed single-cell RNA-seq (scRNA-seq) experiments in control and myeloid specific Bach1 knockout models at different time points post CTX injury in mice. Our results indicate significant differences in the macrophage subsets composition and gene expression profiles demonstrated by the magnitude of expression of critical inflammatory and repair-related genes. In conclusion, by combining single-cell transcriptomics and macrophage-specific knockouts, we revealed a crucial role for BACH1 in regulating macrophage subtype specification and subsequently skeletal muscle regeneration.