End stage liver disease, a consequence common to various hepatic diseases, both acute and chronic, continues to be a major cause of morbidity and mortality worldwide. In fact, chronic liver disease and cirrhosis, are the 12th leading cause of death in the US. Liver transplantation is the only effective available treatment, which is plagued by a dearth of available organs. Continued research is focusing on innovative surgical techniques, cell therapy, stem cell differentiation, artificial liver devices and generation of organs de novo. Broadly defined as Hepatic Regenerative Medicine, this field has gained momentum with the advent of induced pluripotential stem cells, liver-on-chip including the use of micro-physiological systems (MPS) and the use of decellularized liver matrices for differentiation. However, the relative success of these modalities has been limited, mandating improved and thorough understanding of liver physiology for application to these technologies. Continued explication of the complex cell-molecule circuitry for the most relevant pathways in hepatic physiology will be pertinent to the continued success of hepatic regenerative medicine, which may yield novel ways to treat patients with acute liver failure, toxicant- and drug- induced injury. Improved understanding of signaling pathways enabling LR will also have applications in improving liver transplantation outcomes, treatment of complications like small-for-size syndrome and accelerating post-transplantation recovery in both recipients and living donors. One major master regulator of hepatocyte biology that others and we have contributed in identifying, is the Wnt/b-catenin pathway. We have helped identify its key roles in hepatic growth and development, metabolic zonation and liver regeneration (LR). The impetus behind requesting continuation of our study are important observations made over the last 4 years. Liver-specific b-catenin- KO or b-Cat-LKO mice lack pericentral gene expression, thus liver zonation (LZ) is a key function of b-catenin. Likewise, liver regeneration (LR) after partial hepatectomy (PH) depends on hepatocyte-b-catenin, which regulates cyclin-D1 expression at 24h, & in turn induces proliferation at 40h. b-Catenin, for both LZ and LR, is under the control of Wnt since LRP5-6-LKO mice lacking these Wnt co-receptors, phenocopy b-Cat-LKO. To address cell source of Wnt, Wntless (Wls), critical for Wnt secretion, was deleted by breeding Wls-floxed mice to cell-specific cre lines: LysM-cre (macrophages or Mac), Alb-cre (liver epithelial cells). Lrat-cre (hepatic stellate cells or HSC) and Lyve1-cre (endothelial cells or EC). Only EC-Wls-KO phenocopied b-Cat-LKO and LRP5-6-LKO in both loss of LZ and delay in LR after PH. Using microdissection and cell fractionation, Wnt2 and Wnt9b, from central vein (CV) EC and sinusoidal EC (SEC) were shown to be important for LZ and during LR, respectively. The current proposal has three specific aims. Aim 1 will determine e...