There is considerable interest in understanding the mechanistic relationships between biliary damage and portal fibrosis, the main mechanism of progression in chronic cholangiopathies. Congenital Hepatic Fibrosis (CHF) and Caroli disease (CD) are genetic cholangiopathies caused by mutations in PKHD1, the gene encoding for fibrocystin, characterized by biliary dysgenesis, segmental ductal dilations and progressive portal fibrosis with portal hypertension. In CHF and CD, cholangiocyte dysfunction and portal fibrosis are caused by a genetic defect in the biliary epithelium, rather than by necroinflammatory damage and thus, represent a model disease for elucidating the role of cholangiocytes in portal fibrosis of biliary diseases. We propose to study these mechanisms in a mouse model of CHF/CD, harboring a deleting mutation in Pkhd1 (Pkhd1del4/del4 mice). Our preliminary data highlights several interesting features of Pkhd1del4/del4 mice. Including: a) sevee biliary fibrosis and portal hypertension develop slowly over 12 months, along with worsening biliary dysgenesis; b) during early disease phases there is progressive accumulation of a peribiliary cell infiltrate that is comprised about 60% macrophages and up to 20% by aSMA-negative, collagen positive cells (fibrocytes), whereas the accumulation of a-SMA-positive portal myofibroblasts becomes significant after the first sixth months; c) Pkhd1del4/del4 isolated cholangiocytes secrete increased amount of CXCL1 and CXCL10 and show an increased PKA-dependent phosphorylation of -catenin at Ser675; d) secretion of CXCL1 and CXCL10 is -catenin- mediated in Pkhd1del4/del4 cholangiocytes. Based on these observations, we propose that, as a consequence of the increased transcriptional activation of pSer-675--catenin, Pkhd1del4/del4 cholangiocytes secrete chemokines able to recruit macrophages (and possibly fibrocytes) to the pericystic area; macrophages orchestrate the deposition of fibrosis and the transition from the early slow fibrosis phase to the later more brisk phase marked by an increase in macrophage M2 polarization. Thus, establishment of portal fibrosis in Pkhd1del4/del4 mice is initiated by a -catenin-dependent cholangiocyte secretion of chemokines from the biliary epithelium. This sequence of events is a paradigmatic example of para-inflammation i.e. an adaptive response to a persistent cellular dysfunction, generating a low grade inflammatory response and resulting in activation of fibrogenic mechanisms. To demonstrate this novel hypothesis, we will pursue the following Specific Aims:
Aim#1 : Elucidate how increased pSer675--catenin signaling stimulates the secretion of CXCL1 and CXCL10.
Aim#2 : Examine the role of macrophages in the establishment of fibrosis in Pkhd1del4/del4 mice.
Aim#3 : Investigate the histogenesis of myofibroblasts in Pkhd1del4/del4 mice, and the role of fibrocytes. These studies will provide a new model for role of cholangiocyte dysfunction and para-inflammation in portal fibrosis. Knowledge of the regulatory signaling could lead to new therapeutic strategies.
Autosomal Recessive Polycystic Kidney Disease (ARPKD), Congenital Hepatic Fibrosis (CHF) and Caroli's Disease (CD), are genetic disorders of the liver and kidney caused by deficiency in fibrocystin, the protein encoded by the PKHD1 gene. In this proposal, we will study the mechanisms of portal fibrosis in a mouse model of CHF/CD. These studies has a strong translational potential and proximity to cure, understanding the mechanism linking cholangiocyte dysfunction to fibrosis will generate therapeutic strategies not only of patients with CHF/CD, but also of those suffering from other chronic liver diseases.
