HBO1 is an epigenetic determinant of hepatocyte-to-ductal reprogramming

Spontaneous cellular reprogramming is rare, but has been observed in adult cells. This is most evident in the mammalian liver, where hepatocytes undergo physiological reprogramming to generate functional biliary epithelial cells (BECs) in response to injury. The underlying mechanisms driving this cell fate switch remain unclear, however. Here, we characterize epigenetic changes occurring during this transition at the single cell level, and show that reprogramming occurs synchronously and deterministically, though reprogrammed cells retain epigenetic hepatocyte memory. An in vivo CRISPR screen reveals the histone acetyltransferase-HBO1 functions as a critical barrier to hepatocyte reprogramming via acetylation of H3K14. HBO1 depletion accelerates BEC-specific chromatin remodeling and allows for the full resolution of the hepatocyte chromatin landscape. Mechanistically, HBO1 is recruited by the YAP to TEAD target sites to negatively its modulate chromatin-accessibility, DNA-binding, and transcriptional-output, thus acting as an epigenetic brake for YAP/TEAD function. Our work here delineates epigenetic trajectories of a physiological reprogramming process and identifies HBO1 as potential target for hepatocyte trans-differentiation therapeutic strategies. Overall design: Single-cell ATAC-seq profile of sorted BEC and hepatocytes isolated from TetO-YAP S127A mice at different time point post Dox administration. ATAC-seq, RNA-seq, and ChIP-seq was done for primary hepatocytes of TetO-YAP S127A mice with or without HBO1 KO place on Dox for different time points. For in vivo CRISPR screen, GFP+/EPCAM+ hepatocytes were isolated and sorted from TetO-YAP S127A mice carrying different sgRNA libraries 6 weeks post Dox administration.