Lineage tracing demonstrates no evidence of cholangiocyte epithelial-to-mesenchymal transition in murine models of hepatic fibrosis.

UNLABELLED: Whether or not cholangiocytes or their hepatic progenitors undergo an epithelial-to-mesenchymal transition (EMT) to become matrix-producing myofibroblasts during biliary fibrosis is a significant ongoing controversy. To assess whether EMT is active during biliary fibrosis, we used Alfp-Cre × Rosa26-YFP mice, in which the epithelial cells of the liver (hepatocytes, cholangiocytes, and their bipotential progenitors) are heritably labeled at high efficiency with yellow fluorescent protein (YFP). Primary cholangiocytes isolated from our reporter strain were able to undergo EMT in vitro when treated with transforming growth factor-ß1 alone or in combination with tumor necrosis factor-α, as indicated by adoption of fibroblastoid morphology, intracellular relocalization of E-cadherin, and expression of α-smooth muscle actin (α-SMA). To determine whether EMT occurs in vivo, we induced liver fibrosis in Alfp-Cre × Rosa26-YFP mice using the bile duct ligation (BDL) (2, 4, and 8 weeks), carbon tetrachloride (CCl(4) ) (3 weeks), and 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC; 2 and 3 weeks) models. In no case did we find evidence of colocalization of YFP with the mesenchymal markers S100A4, vimentin, α-SMA, or procollagen 1α2, although these proteins were abundant in the peribiliary regions. CONCLUSION: Hepatocytes and cholangiocytes do not undergo EMT in murine models of hepatic fibrosis.

Histologic predictors of fibrosis progression in liver allografts in patients with hepatitis C virus infection.

BACKGROUND & AIMS: Recurrent hepatitis C with ensuing fibrosis is the leading cause of liver allograft loss. We investigated whether histologic features in early posttransplant liver biopsies could predict the rate of fibrosis progression in this population. METHODS: From 1999 to 2007 there were 476 liver transplants performed for hepatitis C at our center. We reviewed all available posttransplant biopsies for these patients; patients were categorized as rapid, intermediate, or slow fibrosers based on their METAVIR fibrosis score at 24 months. Stage F0 biopsies for rapid and slow fibrosers were analyzed histologically and immunohistochemically. RESULTS: We identified 52 rapid fibrosers and 61 slow fibrosers in our cohort. There was a significant increase in the fibrosis progression rate in the group transplanted between 2003 and 2007 compared with between 1999 and 2002. The course of fibrosis progression was determined early in the posttransplant period and the rate was constant. Rapid fibrosers had more hepatocyte apoptosis than slow fibrosers (P = .001), but no difference in hepatitis activity on stage F0 biopsies. Rapid fibrosers also experienced more episodes of acute rejection after transplantation (P < .001). Cytokeratin 19 (CK19) and vimentin expression on F0 stage biopsies could distinguish rapid from slow fibrosers (CK19: area under the curve, 0.71; P = .0034; vimentin: P = .0219). CONCLUSIONS: CK19, vimentin, and hepatocellular apoptosis are promising early markers of rapid fibrosis progression in patients transplanted for hepatitis C. The rate of fibrosis progression is established early in the posttransplant period; this initial rate dictates long-term outcome.

Evidence for the epithelial to mesenchymal transition in biliary atresia fibrosis.

The epithelial to mesenchymal transition has recently been implicated as a source of fibrogenic myofibroblasts in organ fibrosis, particularly in the kidney. There is as yet minimal evidence for the epithelial to mesenchymal transition in the liver. We hypothesized that this process in biliary epithelial cells plays an important role in biliary fibrosis and might be found in patients with especially rapid forms, such as is seen in biliary atresia. We therefore obtained liver tissue from patients with biliary atresia as well as a variety of other pediatric and adult liver diseases. Tissues were immunostained with antibodies against the biliary epithelial cell marker CK19 as well as with antibodies against proteins characteristically expressed by cells undergoing the epithelial to mesenchymal transition, including fibroblast-specific protein 1, the collagen chaperone heat shock protein 47, the intermediate filament protein vimentin, and the transcription factor Snail. The degree of colocalization was quantified using a multispectral imaging system. We observed significant colocalization between CK19 and other markers of the epithelial to mesenchymal transition in biliary atresia as well as other liver diseases associated with significant bile ductular proliferation, including primary biliary cirrhosis. There was minimal colocalization seen in healthy adult and pediatric livers, or in livers not also demonstrating bile ductular proliferation. Multispectral imaging confirmed significant colocalization of the different markers in biliary atresia. In conclusion, we present significant histologic evidence suggesting that the epithelial to mesenchymal transition occurs in human liver fibrosis, particularly in diseases such as biliary atresia and primary biliary cirrhosis with prominent bile ductular proliferation.

Increased stiffness of the rat liver precedes matrix deposition: implications for fibrosis.

Liver fibrosis, the response to chronic liver injury, results from the activation of mesenchymal cells to fibrogenic myofibroblasts. We have recently shown that two key myofibroblast precursor populations, hepatic stellate cells and portal fibroblasts, undergo activation in culture in response to increasing substrate stiffness. We therefore hypothesized that alterations in liver stiffness precede myofibroblast activation and fibrosis in vivo as well. To test this hypothesis, we induced fibrosis in rats by twice weekly injections of carbon tetrachloride (CCl(4)) and then killed the animals at various time points ranging from 3 to 70 days after the initiation of injury. The shear storage modulus of the whole liver was measured on fresh tissue; fixed and frozen tissue from the same livers was used to quantify fibrosis. We observed that liver stiffness increased immediately and continued to increase, leveling out by day 28. Fibrosis, measured histologically by trichrome staining as well as by quantitative sirius red staining, increased with time, although these increases were delayed relative to changes in stiffness. There was no direct correlation between stiffness and fibrosis at early or late time points. Treatment of a second cohort of rats with the lysyl oxidase inhibitor, beta-aminopropionitrile (BAPN), partially prevented early increases in liver stiffness. We concluded that increases in liver stiffness precede fibrosis and potentially myofibroblast activation. Liver stiffness appears to result from matrix cross-linking and possibly other unknown variables in addition to matrix quantity. We suggest that increased liver stiffness may play an important role in initiating the early stages of fibrosis.