Loss of hepatocyte identity following aberrant YAP activation: A key mechanism in alcoholic hepatitis

Abstract

Background & aims: Alcoholic hepatitis (AH) is a life-threatening disease with limited therapeutic options, as the molecular mechanisms leading to death are not well understood. This study evaluates the Hippo/Yes-associated protein (YAP) pathway which has been shown to play a role in liver regeneration.

Method: The Hippo/YAP pathway was dissected in explants of patients transplanted for AH or alcohol-related cirrhosis and in control livers, using RNA-seq, real-time PCR, western blot, immunohistochemistry and transcriptome analysis after laser microdissection. We transfected primary human hepatocytes with constitutively active YAP (YAPS127A) and treated HepaRG cells and primary hepatocytes isolated from AH livers with a YAP inhibitor. We also used mouse models of ethanol exposure (Lieber de Carli) and liver regeneration (carbon tetrachloride) after hepatocyte transduction of YAPS127A.

Results: In AH samples, RNA-seq analysis and immunohistochemistry of total liver and microdissected hepatocytes revealed marked downregulation of the Hippo pathway, demonstrated by lower levels of active MST1 kinase and abnormal activation of YAP in hepatocytes. Overactivation of YAP in hepatocytes in vitro and in vivo led to biliary differentiation and loss of key biological functions such as regeneration capacity. Conversely, a YAP inhibitor restored the mature hepatocyte phenotype in abnormal hepatocytes taken from patients with AH. In ethanol-fed mice, YAP activation using YAPS127A resulted in a loss of hepatocyte differentiation. Hepatocyte proliferation was hampered by YAPS127A after carbon tetrachloride intoxication.

Conclusion: Aberrant activation of YAP plays an important role in hepatocyte transdifferentiation in AH, through a loss of hepatocyte identity and impaired regeneration. Thus, targeting YAP is a promising strategy for the treatment of patients with AH.

Lay summary: Alcoholic hepatitis is characterized by inflammation and a life-threatening alteration of liver regeneration, although the mechanisms behind this have not been identified. Herein, we show that liver samples from patients with alcoholic hepatitis are characterized by profound deregulation of the Hippo/YAP pathway with uncontrolled activation of YAP in hepatocytes. We used human cell and mouse models to show that inhibition of YAP reverts this hepatocyte defect and could be a novel therapeutic strategy for alcoholic hepatitis.

Keywords: Hippo/YAP; alcoholic hepatitis; hepatocyte; regeneration; transdifferentiation.