Transforming growth factor beta(1)-regulated gene expression of Ito cells

During liver fibrogenesis, Ito cells are regarded as the principal matrix synthesizing cells and transforming growth factor beta 1 (TGF-beta 1) appears to be the main fibrogenic mediator. This study analyzed the effects of TGF-beta 1 on Ito cell activation, proliferation, and on the expression of a set of matrix proteins, antiproteases, and TGF-beta receptors both in ''early cultured'' and ''culture-activated'' Ito cells. Rat liver Ito cells at day 2 of primary culture (''early cultured'' cells) were mainly smooth muscle alpha actin (SMA)-negative, whereas cells at day 6 were judged as ''activated'' cells (SMA-positive), Following 24-hour exposure to 1 ng/mL TGF-beta 1, total protein synthesis, cell proliferation, and expression of the ''activation'' marker SMA mere not significantly changed. In addition to previously described stimulatory effects on collagen types I and III, fibronectin, undulin, and proteoglycan-gene expression, TGF-beta also dose-dependently increased synthesis and secretion of tenascin, laminin, entactin, collagen type IV, and alpha(2)-macroglobulin, but decreased C1-esterase inhibitor production by Ito cells, as revealed by immunoprecipitation of endogenously labeled proteins and by Northern blot analysis, The stimulatory effect of TGF-beta was evident both in ''early cultured'' as well as ''culture-activated'' Ito cells, By reverse-transcription polymerase chain reaction (RT-PCR) analysis, TGF-beta type II, III, and TGF-beta/activin type I receptors were present in Ito cells, and their expression pattern was not changed upon TGF-beta exposure, Northern blot analysis demonstrated that type I TGF-beta/activin receptor was induced during in vitro activation and that TGF-beta exposure resulted in a slight increase of type I and III receptor messenger RNAs. In summary, the data illustrate that TGF-beta is an important fibrogenic mediator acting both on ''early cultured'' as well as ''culture-activated'' Ito cells, rather than a mitogenic or morphogenic mediator. The differential regulation of TGF-beta/activin receptors during in vitro activation and their upregulation by TGF-beta 1 might represent a mechanism by which the receptor complex regulates TGF-beta signalling in Ito cells.