Ito‐cell gene expression and collagen regulation

Ito cells are perisinusoidal cells thought to be a major source of collagen in normal and fibrotic livers. These cells appear to have features similar to several cell types but when cultured assume a fibroblast‐like morphology. In this study we evaluated the phenotype of both freshly isolated and cultured Ito cells by examining their gene expression. To better define the modulators of Ito‐cell collagen synthesis, we also examined the effect of transforming growth factor‐β1, tumor necrosis factor‐α and dexamethasone on collagen synthesis by these cells. Northern hybridization analysis revealed that cultured Ito cells expressed different types of procollagen mRNAs than did freshly isolated cells. Cultured cells contained large amounts of type I procollagen mRNA and lesser amounts of types III and IV, whereas freshly isolated cells contained more type IV procollagen mRNA than types I and III. Treatment of cultured cells with either transforming growth factor‐β1 or tumor necrosis factor‐α resulted in a greater than threefold increase in total collagen content, and the effects of these cytokines on Ito‐cell collagen synthesis involved different levels of gene regulation. Transforming growth factor‐β1‐treated cells had an approximately threefold increase in their type I procollagen mRNA levels, whereas no increase in this mRNA level was found in tumor necrosis factor‐α‐treated cells. Transforming growth factor‐β1 treatment induced a twofold increase in transforming growth factor‐β1 mRNA content in cultured cells. In contrast to transforming growth factor‐β1, dexamethasone inhibited type I procollagen and transforming growth factor‐β1 mRNA content by at least twofold in cultured cells. These results suggest that cultured Ito cells alter their collagen gene expression such that they become phenotypically more fibroblast‐like. Furthermore, transforming growth factor‐β1's induction of its own mRNA in Ito cells suggests that these cells are capable of amplifying their collagen synthesis. Finally, the inhibition of transforming growth factor‐β1 and procollagen type I gene expression by dexamethasone suggests another way steroids may be beneficial in the treatment of certain forms of chronic liver disease.