Hepatocyte Hippo Signaling Drives Inflammation in Liver Injury and Regeneration

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Project Summary The short-term goal of this proposal is to define how hepatocyte Yap signaling influences the recruitment and characteristics of immune cell infiltration during liver injury and regeneration. Our long-term goal is to understand the intimate cell-cell interactions that hepatocytes have with the tissue microenvironment to drive liver fibrosis. Successful completion of this project would augment our ability to develop tailored medical therapies for cirrhosis by focusing on particular arms of the Hippo Signaling pathway. For several years, we studied the role that hepatocytes play in orchestrating regenerative responses, primarily through the lens of Hippo Signaling, a potent growth regulatory pathway. In a prior proposal (K08DK105351), we identified that by inducibly targeting hepatocytic Yap expression, this rapidly led to liver inflammation and fibrosis. We predicted that in a similar fashion, chronic liver injury would increase hepatocytic Yap activity and that this would directly lead to the development of liver inflammation/fibrosis. We have subsequently confirmed the predictions of that study. In the process, we identified that inflammation is directly related to Yap levels in hepatocytes and that Cyr61 is a key transcriptional target of Yap that is directly responsible for macrophage cell recruitment and liver fibrosis. This proposal seeks to extend these findings by using new tools to interrogate liver biology. In Aim 1, we will characterize the origin, phenotype and contribution of the monocytes/macrophages that respond to hepatocyte-specific Yap (Yap-Tg) activity in driving fibrosis. Using a combination of chemical and genetic strategies to modify monocytes/macrophages activity we will define their contribution to inflammation/fibrosis in the context of Yap-Tg. In Aim 2, we will interrogate the role of hepatocyte-derived Cyr61 in recruiting and polarizing monocytes through in vivo overexpression and genetic knockout experiments. Mass cytometry and high throughput RNA sequencing will be used to probe the immune landscape and changes in cellular signaling in the context of Cyr61 loss and gain of function. We propose that hepatocytes actively drive genetic programs after injury that remodel their local microenvironment. Hepatocytic Yap activity plays a critical role in directing these programs with Cyr61 being a particularly important downstream cytokine. Understanding the canonical and non-canonical mechanisms by which Yap/Cyr61 recruit and polarize the immune cell environment will lead to improved models of predicting the liver’s response to disease and facilitate directed treatment for cirrhosis.