Hepatocyte Stress Increases Expression of YAP and TAZ in Hepatocytes to Promote Parenchymal Inflammation and Fibrosis.

Background and Aims Activated hepatocytes are hypothesized to be a major source of signals that drive cirrhosis, but the biochemical pathways that convert hepatocytes into such a state are unclear. We examined the role of the Hippo pathway transcriptional coactivators Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) in hepatocytes to facilitate cell-cell interactions that stimulate liver inflammation and fibrosis. Approach and Results Using a variety of genetic, metabolic, and liver injury models in mice, we manipulated Hippo signaling in hepatocytes and examined its effects in nonparenchymal cells to promote liver inflammation and fibrosis. YAP-expressing hepatocytes rapidly and potently activate the expression of proteins that promote fibrosis (collagen type I alpha 1 chain, tissue inhibitor of metalloproteinase 1, platelet-derived growth factor c, transforming growth factor beta 2) and inflammation (tumor necrosis factor, interleukin 1 beta). They stimulate expansion of myofibroblasts and immune cells, followed by aggressive liver fibrosis. In contrast, hepatocyte-specific YAP and YAP/TAZ knockouts exhibit limited myofibroblast expansion, less inflammation, and decreased fibrosis after CCl4 injury despite a similar degree of necrosis as controls. We identified cellular communication network factor 1 (CYR61) as a chemokine that is up-regulated by hepatocytes during liver injury but is expressed at significantly lower levels in mice with hepatocyte-specific deletion of YAP or TAZ. Gain-of-function and loss-of-function experiments with CYR61 in vivo point to it being a key chemokine controlling liver fibrosis and inflammation in the context of YAP/TAZ. There is a direct correlation between levels of YAP/TAZ and CYR61 in liver tissues of patients with high-grade nonalcoholic steatohepatitis. Conclusions Liver injury in mice and humans increases levels of YAP/TAZ/CYR61 in hepatocytes, thus attracting macrophages to the liver to promote inflammation and fibrosis.