The Effects of Hepatic Fibrosis on Ito Cell Gene Expression

Abstract

While Ito cells appear to be a major source of increased matrix synthesis during hepatic fibrogenesis, the cellular changes that occur in these cells during liver fibrosis have not been well delineated. In this study we examined Ito cell gene expression in isolated cells from normal rats, and rats with carbon tetrachloride-induced fibrosis, in order to better define the changes occurring in these cells during this pathologic process. Specifically, we addressed three questions: (1) which matrix genes are over expressed in Ito cells in fibrotic liver; (2) do these cells increase their expression of the fibrogenic cytokine transforming growth factor-β1 (TGF-β1); and (3) do Ito cells change their phenotype during hepatic fibrogenesis as reflected by alterations in the expression of their intermediate filament genes? Northern hybridization analysis revealed that Ito cells isolated from fibrotic livers had significant increases in mRNA levels of types I, III and IV procollagen compared to normal cells, while no increases were found in hepatocytes, and Kupffer/endothelial cells had only an increase in type I procollagen mRNA. Analysis of other matrix proteins which increase during hepatic fibrogenesis revealed elevations in laminin B and fibronectin mRNA levels only in Ito cells. Increased Ito cell matrix gene expression was also associated with a 4-fold increase in TGF-β1 levels in these cells. No increase in TGF-β1 mRNA was found in hepatocytes, and less than a 2-fold increase was found in Kupffer/endothelial cells isolated from fibrotic livers. Ito cells isolated from both normal and fibrotic livers expressed vimentin, desmin and β-actin mRNA, but no α-actin mRNA, implying that Ito cells in these fibrotic livers retained a normal Ito cell phenotype. These studies suggest that increases in Ito cell mRNA levels of matrix proteins contribute to the development of hepatic fibrosis. Furthermore, enhanced Ito cell expression of TGF-β1 mRNA may further augment this cell's matrix synthesis. Finally, the increases in the mRNA of these matrix proteins appear to occur in Ito cells which are not phenotypically altered by this pathologic process.