Cellular sources of matrix proteins in experimentally induced cholestatic rat liver

Collagens (I, III, and IV), fibronectin, and laminin were localized using the indirect immunoperoxidase technique 14 days after bile duct ligation, i.e., when extensive fibrosis and numerous neoformed bile ducts were observed. Extensive fibrous septa in enlarged portal spaces were stained for collagens I, III and IV, fibronectin, and laminin. Collagen IV and laminin were abundant around proliferative bile ducts. In addition, collagen IV was nearly continuous in the sinusoids. At the ultrastructural level, antigens were localized in the endoplasmic reticulum of several liver cell types. In portal spaces, bile duct cells and cells that form the transitional canal of Hering were strongly labelled for basement membrane components, particularly laminin, but not for collagens I and III and fibronectin, which were abundant in fibroblast-like cells. Inside the lobule, only Ito cells and, to a lesser extent, endothelial cells contained collagens, fibronectin, and laminin. Ito cells were found to be heavily stained for collagens III and IV, and laminin. Except for fibronectin, which was always abundant, precursors of extracellular matrix proteins were only slightly detectable in the endoplasmic reticulum of some hepatocytes, particularly those located close to altered areas. This study demonstrates that experimental extrahepatic cholestasis in the rat induces periportal fibrosis and continuous deposition of collagen IV in the sinusoids. Several cell types participate in the formation of extracellular matrix components, particularly bile duct cells and Ito cells, with a possible involvement of hepatocytes, thus suggesting that cholestasis provokes changes in the pattern of matrix protein production in liver cells.

Reversibility of hepatic fibrosis in experimentally induced cholestasis in rat

The reversibility of hepatic fibrosis was investigated in an experimental model of extrahepatic cholestasis in the rat after common bile duct ligation for 2 weeks, followed by bilioduodenal anastomosis for 3 weeks. Bile duct ligation resulted in a transitory marked elevation in the serum concentration of 5'-nucleotidase, alkaline phosphatase, and bilirubin during the first 3 days. Then these levels decreased to threefold, twofold, and 100-fold the normal values, respectively, during the following 4 weeks. Histologic examination of the liver disclosed extensive bile duct proliferation and the formation of periportal fibrosis, with only slight inflammation and necrosis. The distribution of the major components of the hepatic extracellular matrix was analyzed 2 weeks after bile duct ligation, using the indirect immunoperoxidase method. Fibrous septa were found to be strongly stained for collagens I, pro-III, III and IV, fibronectin, and laminin. The most intense staining was found in enlarged periportal areas, collagen IV and laminin being particularly abundant around newly formed bile ducts. These changes paralleled high steady-state levels of alpha 1(I) and alpha 1(IV) collagen and B2 chain laminin mRNAs. Relief of the obstruction for 2 weeks resulted in a shift in the serum concentration of 5'-nucleotidase, alkaline phosphatase, and bilirubin toward normal values. A dramatic resorption of bile duct proliferations and periportal fibrosis were observed. Three weeks after bile duct repermeabilization, immunohistochemical study showed that the pattern of distribution of extracellular matrix components was almost normal, except for collagen IV, which remained abundant in the sinusoids when compared with the normal liver. In parallel, the steady-state B2-chain laminin mRNA level became lower than in cholestatic livers, whereas alpha 1(I) and alpha 1(IV) mRNAs were almost undetectable. These results show that hepatic fibrosis induced by experimental extrahepatic cholestasis in rat disappears in less than 3 weeks after relief of bile duct obstruction, suggesting that an active degradation of matrix protein occurs, except for collagen IV in the sinusoid.