Pathophysiology of Biliary Disease

PROJECT SUMMARY/ABSTRACT Our OVERALL OBJECTIVE is to clarify the pathogenesis of Primary Sclerosing Cholangitis (PSC) and identify new therapies. PSC accounts for 6% of liver transplants, costs ~$125 million annually, affects ~40,000 Americans, has a median survival of ~15 years, and is associated with inflammatory bowel disease and increased risk of colon, bile duct and gallbladder cancers. There are no regulatory approved drugs for PSC because its pathogenesis is obscure. We reported that stress-induced cholangiocyte senescence (cell cycle arrest, apoptosis resistance, bioactive secretome) is a feature of PSC, informing its pathogenesis and revealing new therapeutic targets. Experiments proposed here extending this observation address the concept that the cholangiocyte response to injury in PSC is not uniform: some cholangiocytes arrest in the cell cycle (become senescent) while others acquire a ductular reactive, proliferative phenotype (resist senescence). We discovered fundamental differences in epigenetic and downstream signaling pathways that influence this binary cholangiocyte injury response. Our preliminary data show: i) we can isolate enriched subpopulations of senescent-sensitive and senescent-resistant cholangiocytes with distinct epigenetic signatures from human and rodent tissue, and from cholangiocyte cell lines; ii) chromatin modifiers, AP1 (transcription factor) and p300 (histone acetyltransferase), establish an epigenetic profile promoting senescence; iii) destabilization of the effector protooncogene, c-Myc, via the kinase, GSK3, drives senescence and cell-cycle arrest; in contrast, stabilization of c-Myc via the kinase, AKT, promotes senescence resistance and cholangiocyte proliferation; and iv) the cholangiocyte subtypes exhibit distinct bioactive secretomes that differentially affect portal fibroblasts (PF) and hepatic stellate cells (HSC). The data support our CENTRAL HYPOTHESIS that, in PSC, the cholangiocyte epigenome drives kinase cascades that determine if cholangiocytes develop senescent or proliferative phenotypes that influence the periductal and bridging fibrogenic responses of PF and HSC. Our integrated SPECIFIC AIMS test 3 hypotheses. Aim 1 Hypothesis: The epigenetic modifiers, AP1 & p300, promote open chromatin and active transcription via histone acetylation at senescence-associated enhancers/promoters and drive cholangiocytes to stress-induced senescence. Aim 2 Hypothesis: The epigenetic profiles of senescent resistant or sensitive cholangiocytes establish kinase cascades that either promote proliferation via c-Myc stabilization (AKT) or senescence via c-Myc destabilization (GSK3) and activation of the senescence effector, ETS1. Aim 3 Hypothesis: Genetic or pharmacologic inhibition of c-Myc or p300 alters the secretomes of proliferative and senescent cholangiocytes, their communication with PF and HSC, and periductal and bridging fibrosis. Thus, we will clarify how the epigenome determines the cholangiocyte injury response, how this binary response drives fibrogenesis, and how pharmacologic modification of the cholangiocyte epigenome can inhibit PSC progression.