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 were 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 up-regulation by TGF-beta 1 might represent a mechanism by which the receptor complex regulates TGF-beta signalling in Ito cells.
Knittel
T
T
Department of Internal Medicine, University of Göttingen, Germany.
Janneck
T
T
Müller
L
L
Fellmer
P
P
Ramadori
G
G
D017667:Adipocytes / Q000378:metabolism*; D000818:Animals; D001483:Base Sequence; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D016326:Extracellular Matrix Proteins / Q000235:genetics; D005786:Gene Expression Regulation / Q000187:drug effects*; D008099:Liver / Q000166:cytology*; D008969:Molecular Sequence Data; D011817:Rabbits; D051381:Rats; D017208:Rats, Wistar; D018125:Receptors, Transforming Growth Factor beta / Q000235:genetics; D016212:Transforming Growth Factor beta / Q000494:pharmacology*
D016326:Extracellular Matrix Proteins; D018125:Receptors, Transforming Growth Factor beta; D016212:Transforming Growth Factor beta