Derepression of the epithelial transcription factor GRHL2 promotes direct hepatocyte-to-cholangiocyte transdifferentiation

Abstract

The liver's regenerative capacity is underscored by the plasticity potential of adult hepatocytes. In this context, hepatocyte-to-cholangiocyte transdifferentiation (HCT) has been ascribed with pro-regenerative functions in animal models and is a feature of end-stage human chronic liver diseases. While dampened activities of hepatocyte identity transcription factors (TFs) underlay HCT, how the cholangiocyte transcriptional program is implemented is poorly defined. Here, we identify that HCT does not involve transitioning through a hepatoblast-like transcriptional program. Furthermore, we show that HCT primarily involves induction of the archetypal transcriptional program of monopolarized epithelial cells initially repressed in hepatocytes. Indeed, HCT requires relieving H3K27me3-mediated and polycomb-dependent epigenetic silencing of epithelial TF encoding genes including Grainyhead Like Transcription Factor 2 (GRHL2). Ectopic expression of GRHL2 in hepatocytes, including in vivo in the adult mouse liver, induces epithelial genes reminiscent of those activated during HCT. Finally, GRHL2 is detected in human hepatocytes undergoing HCT as evidenced using samples from end-stage chronic liver diseases. Hence, HCT is a process chiefly characterized by induction of a conventional epithelial transcriptional program originally lacking in hepatocytes promoted by derepression of the master epithelial TF GRHL2.