Gut microbiota modulation of regulatory DNA elements revealed by massively parallel functional characterization

Cis-regulatory elements (CREs) are central to dynamic gene regulation in hepatocytes, yet most functional annotations derive from in vitro models that poorly capture physiological regulation. We systematically profiled 109,386 human liver-derived CREs using massively parallel reporter assays in hepatocytes under matched in vitro and in vivo conditions. In vivo-active functional CREs (fCREs) were enriched for H3K27ac and chromatin accessibility and were regulated by diverse transcription factors in the human liver. We further demonstrate that gut microbiota-derived signals modulate fCRE activity and target gene expression in vivo, in part via the KEAP1/NFE2L2 antioxidant pathway. Specific microbial metabolites directly altered the activity of selected fCREs, and genetic variation within fCREs modified their responsiveness to microbial signals. Together, these findings reveal microbiota-dependent regulation of hepatic CREs and highlight condition-specific gene regulatory mechanisms in vivo.