In cholestatic liver diseases, cholangiocytes, through the secretion of neuroendocrine factors, are the key link between bile duct injury and the subepithelial fibrosis that characterizes chronic hepatobiliary injury. Targeting the factors that respond to the mechanical stress resulting from tissue injury may limit inflammation and liver fibrosis that occur in hepatobiliary damage and diseases such as primary biliary cirrhosis (PBC), primary sclerosing cholangitis (PSC) and liver fibrosis. Although mechanical stress occurs with biliary distention (commonly observed in PSC and extrahepatic cholestasis) and activates cholangiocytes, the cellular and molecular mechanisms responsible for this activated neuroendocrine phenotypes remain unclear. While advances have been made to further our understanding of the paracrine and autocrine neuroendocrine factors that modulate biliary proliferation during cholestasis, unfortunately, viable therapies for management of cholangiopathies remain elusive. There remains, therefore, a critical need to understand the triggers of cholangiocyte growth and their responses to damage during cholestasis, which may help identify key signaling pathways that represent viable targets for the development of effective therapeutic agents. Preliminary data from the analysis of the activated neuroendocrine cholangiocyte phenotypes demonstrated that: (i) cholangiocytes express serotonin receptors (5-HTR) (2A, 2B and 2C); (ii) mechanical stress-dependent activation of 5-HTR2B stimulates 5-HT synthesis and secretion and an activated neuroendocrine cholangiocyte phenotype in a PKA and miR-16 mediated mechanism; (iii) activation of mechanosensitive 5-HTR2B signaling in concert with increased cholangiocyte expression and secretion of FGF1 (regulated by miR-16) stimulates biliary proliferation during in vitro mechanical stress and bile duct ligation (BDL). Based upon these findings, we propose the overall central hypothesis that the mechanosensitive 5-HT5-HTR2A/BCFGF1 signaling axis is a key pathway responsible for mediating the proliferative and profibrogenic cholangiocyte phenotype. This postulate will be tested in three specific aims, which will demonstrate that: (i) mechanical stress-dependent 5-HT synthesis and release induces an activated neuroendocrine and profibrogenic cholangiocyte phenotype mediated by activation of 5-HTR2A/B/C receptor family; (ii) FGF1 secretion by cholangiocytes during cholestasis mediates biliary proliferation and the activated neuroendocrine cholangiocyte phenotype in a 5-HTR2A/B/C receptor family and miR-16- dependent autocrine/paracrine mechanism; and (iii) inhibition of the 5-HTR2A/B/CFGF1 axis attenuates the activated neuroendocrine biliary phenotype and fibrosis during cholestasis. Completion of proposed studies will provide a framework for understanding how mechanical stimuli trigger local and systemic responses mediate hepatobiliary fibrosis.
The health relatedness of this grant proposal is that effective treatments are lacking for chronic cholestatic liver diseases, such as primary biliary cirrhosis (PBC) and primary sclerosing cholangitis (PSC). Chronic cholestatic liver diseases (cholangiopathies) cause proliferation/damage of bile ducts inside the liver. The rationale for our research is that the successful completion of the studies can provide a greater understanding of the progressive mechanisms of cholestatic liver injuries, and increase opportunities for the development of novel treatment paradigms for the management of chronic liver diseases.
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