The effects of dexamethasone on in vitro collagen gene expression

Glucocorticoids have been shown to be useful in the treatment of certain types of chronic liver disease both by inhibiting fibrosis and by improving liver function. We have previously demonstrated in an in vivo model of hepatic fibrogenesis that dexamethasone inhibits the synthesis of types I and IV collagen. In the present study we have evaluated the level of regulation responsible for the dexamethasone-induced changes in collagen gene expression in a defined in vitro system. Primary cultures of adult rat hepatocytes treated with and without dexamethasone under classical cell culture conditions or using defined media were evaluated for synthesis and abundance of procollagen and beta-actin mRNAs. Cells treated with dexamethasone had decreased types I and IV procollagen mRNA steady state levels due in part to diminished transcription rates of the genes. On the other hand, beta-actin mRNA levels were unaffected by dexamethasone. Transient expression experiments were performed to more precisely define the mechanism whereby dexamethasone affects type I procollagen gene transcription. The recombinant plasmid, pAZ1009, containing the mouse alpha 2(I) procollagen gene promoter linked to the chloramphenicol acetyltransferase gene, was transfected into mouse fibroblast cell lines. Cells transfected with the pAZ1009 plasmid in the presence of dexamethasone had a significant decrease in chloramphenicol acetyltransferase activity when compared to cells not exposed to dexamethasone. These data suggest that dexamethasone inhibits collagen synthesis through a direct effect on the collagen gene promoter and appears also to have a post-transcriptional effect on procollagen mRNA content.