The transcription factor BACH1 couples chromatin priming and repression to enable macrophage plasticity and adaptation.

Abstract

Macrophage activation and tissue adaptation involve precise transcriptional control by lineage-determining transcription factors (LDTFs) and stimulus-dependent TFs. The heme-regulated transcriptional repressor BACH1 clusters with myeloid LDTFs in unstimulated macrophages, suggesting a role in shaping macrophage identity and function. We found that BACH1 bound to both inactive and active regulatory regions, including latent enhancers. BACH1 recruited the NuRD complex and had dual functions, establishing early chromatin accessibility while actively repressing transcription. Upon inflammatory stimulation, BACH1 rapidly redistributed in cis to nearby promoters, reshaping chromatin occupancy, motif specificity, and enhancer-promoter interactions. BACH1 constrained 3D chromatin architecture, limiting enhancer mobility and TF complex dynamics. In vivo, Bach1 deletion impaired macrophage polarization and tissue adaptation and limited resilience during systemic and regenerative inflammation. Thus, BACH1 acts as an early chromatin accessibility-priming factor while actively repressing transcription-a regulatory activity that can be defined as pioneer repression-thereby shaping the macrophage epigenome in response to inflammatory and tissue contexts.