BACH1 acts as a pioneer repressor to enable macrophage plasticity and adaptation across tissues and inflammatory contexts [RNA-seq/ATAC-seq]

Here, we show that BACH1, a heme-sensitive transcriptional repressor, acts as such a pervasive epigenomic safeguard to regulate tissue macrophage identity. We show that BACH1 is part of the core hardwired transcriptional program of ground-state macrophages shaping the chromatin accessibility of thousands of distal regulatory elements. Furthermore, BACH1 cistrome is extensive, not static but dynamic, and expanding upon different inflammatory stimuli and correlates with pre-formed and de novo formed enhancer-promoter networks.

We further show that myeloid BACH1 is indispensable in vivo for tissue regeneration upon injury as it regulates the kinetics of Ly6C+ to Ly6C- transition of inflammatory macrophages and regulates the onset, the kinetics and magnitude of expression of critical inflammatory and repair-related genes. Finally, BACH1 was found to be required in vivo for competitive fitness and tissue adaptation of several tissue-resident macrophage populations (eg. lung, peritoneal macrophages), further supporting its pervasive role in acquiring and maintaining the functional specificity and diversity of tissue macrophages.

Taken together, our data suggest that BACH1 acts as a signal-dependent master regulator that directly controls key transcriptional circuits during tissue macrophage subtype function, specification and inflammatory responses in vivo.