Epithelial-mesenchymal transitions (EMTs) play an important role in tissue construction during embryogenesis, and evidence suggests that this process may also help to remodel some adult tissues after injury. Activation of the hedgehog (Hh) signaling pathway regulates EMT during development. This pathway is also induced by chronic biliary injury, a condition in which EMT has been suggested to have a role. We evaluated the hypothesis that Hh signaling promotes EMT in adult bile ductular cells (cholangiocytes). In liver sections from patients with chronic biliary injury and in primary cholangiocytes isolated from rats that had undergone bile duct ligation (BDL), an experimental model of biliary fibrosis, EMT was localized to cholangiocytes with Hh pathway activity. Relief of ductal obstruction in BDL rats reduced Hh pathway activity, EMT, and biliary fibrosis. In mouse cholangiocytes, coculture with myofibroblastic hepatic stellate cells, a source of soluble Hh ligands, promoted EMT and cell migration. Addition of Hh-neutralizing antibodies to cocultures blocked these effects. Finally, we found that EMT responses to BDL were enhanced in patched-deficient mice, which display excessive activation of the Hh pathway. Together, these data suggest that activation of Hh signaling promotes EMT and contributes to the evolution of biliary fibrosis during chronic cholestasis.

Clinicians rely upon the severity of liver fibrosis to segregate patients with well-compensated nonalcoholic fatty liver disease (NAFLD) into sub-populations at high versus low-risk for eventual liver-related morbidity and mortality. We compared hepatic gene expression profiles in high- and low-risk NAFLD patients to identify processes that distinguish the two groups and hence, might be novel biomarkers or treatment targets. Microarray analysis was used to characterize gene expression in percutaneous liver biopsies from low-risk, “mild” NAFLD patients (fibrosis stage 0–1, n=40) and high risk, “severe” NAFLD patients (fibrosis stage 3–4, n=32). Findings were validated in a second, independent cohort and confirmed by real time PCR and immunohistochemistry. As a group, patients at risk for bad NAFLD outcomes had significantly worse liver injury and more advanced fibrosis (severe NAFLD) than clinically-indistinguishable NAFLD patients with a good prognosis (mild NAFLD). A 64 gene profile reproducibly differentiated severe NAFLD from mild NAFLD, and a 20 gene subset within this profile correlated with NAFLD severity, independent of other factors known to influence NAFLD progression. Multiple genes involved with tissue repair/regeneration and certain metabolism-related genes were induced in severe NAFLD. Ingenuity Pathway Analysis and immunohistochemistry confirmed deregulation of metabolic and regenerative pathways in severe NAFLD, and revealed overlap among the gene expression patterns of severe NAFLD, cardiovascular disease, and cancer. Conclusion By demonstrating specific metabolic and repair pathways that are differentially activated in livers with severe NAFLD, gene profiling identified novel targets that can be exploited to improve diagnosis and treatment of patients who are at greatest risk for NAFLD-related morbidity and mortality.

Nonalcoholic fatty liver disease (NAFLD) encompasses a spectrum of hepatic pathology, ranging from simple steatosis (also called nonalcoholic fatty liver or NAFL) in its most benign form, to cirrhosis in its most advanced form. Nonalcoholic steatohepatitis (NASH) is an intermediate level of hepatic pathology. Hepatocyte accumulation of triglyceride is a hallmark of NAFL and NASH, but this sometimes subsides once cirrhosis has developed. Triglyceride storage per se is not hepatotoxic. Rather, it is a marker of increased exposure of hepatocytes to potentially toxic fatty acids. NAFL progresses to NASH when adaptive mechanisms that protect hepatocytes from fatty acid-mediated lipotoxicity become overwhelmed and rates of hepatocyte death begin to outstrip mechanisms that normally regenerate dead hepatocytes. This triggers repair responses that involve activation of hepatic stellate cells to myofibroblasts. The myofibroblasts generate excessive matrix and produce factors that stimulate expansion of liver progenitor populations. The progenitor cells produce chemokines to attract various kinds of inflammatory cells to the liver. They also differentiate to replace the dead hepatocytes. The intensity of these repair responses generally parallel the degree of hepatocyte death, resulting in variable distortion of the hepatic architecture with fibrosis, infiltrating immune cells, and regenerating epithelial nodules. As in other types of chronic liver injury, cirrhosis ensues in patients with NAFLD when repair is extreme and sustained, but ultimately unsuccessful, at reconstituting healthy hepatic epithelia.

Glutaminolysis controls accumulation of myofibroblast HSCs in mice and might be a therapeutic target for cirrhosis.