The role of Smad3 in mediating mouse hepatic stellate cell activation.
Transforming growth factor beta (TGF-beta) is the most potent profibrogenic mediator in liver fibrosis. Although Smad proteins have been identified as intracellular mediators in the TGF-beta signaling pathway, the function of individual Smad proteins remains poorly understood. The aim of this study was to explore the contribution of Smad3 in mediating TGF-beta responses in a model of acute liver injury in vivo and in culture-activated hepatic stellate cells (HSCs). Wild-type, Smad3 heterozygous or Smad3 homozygous knockout mice were treated with a single intragastric administration of CCl(4). After 72 hours, the induction of hepatic collagen alpha1(I) and alpha2(I) messenger RNA (mRNA) levels in Smad3 knockout mice was only 42% and 64%, respectively, of the levels induced in wild-type mice. However, smooth muscle alpha-actin (alpha-SMA) was expressed at a slightly higher level in livers from knockout mice compared with wild-type mice. In culture-activated HSCs from Smad3 knockout mice, collagen alpha1(I) mRNA was 73% of wild-type HSCs, but alpha-SMA expression was the same. HSCs from knockout mice showed a higher proliferation rate than wild-type HSCs. Smad3-deficient HSCs did not form TGF-beta1-induced Smad-containing DNA-binding complexes. In conclusion, (1) maximal expression of collagen type I in activated HSCs requires Smad3 in vivo and in culture; (2) Smad3 is not necessary for HSC activation as assessed by alpha-SMA expression; (3) Smad3 is necessary for inhibition of proliferation of HSCs, which might be TGF-beta-dependent; and (4) Smad3 is required for TGF-beta1-mediated Smad-containing DNA-binding complex formation in cultured HSCs.
Schnabl
B
B
Department of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA.
Kweon
Y O
YO
Frederick
J P
JP
Wang
X F
XF
Rippe
R A
RA
Brenner
D A
DA
D000199:Actins / Q000235:genetics; D000818:Animals; D002251:Carbon Tetrachloride; D002417:Cattle; D002455:Cell Division; D002478:Cells, Cultured; D056486:Chemical and Drug Induced Liver Injury; D003094:Collagen / Q000235:genetics; D004247:DNA / Q000096:biosynthesis / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D004789:Enzyme Activation; D005312:Fetal Blood; D022781:Hepatocytes / Q000378:metabolism / Q000473:pathology*; D017403:In Situ Hybridization; D008107:Liver Diseases / Q000378:metabolism / Q000473:pathology*; D051379:Mice; D018345:Mice, Knockout; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009130:Muscle, Smooth / Q000737:chemistry; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology; D012333:RNA, Messenger / Q000032:analysis / Q000096:biosynthesis; D051900:Smad3 Protein; D015534:Trans-Activators / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D016212:Transforming Growth Factor beta / Q000032:analysis / Q000494:pharmacology / Q000502:physiology
D000199:Actins; D004268:DNA-Binding Proteins; D010982:Platelet-Derived Growth Factor; D012333:RNA, Messenger; D051900:Smad3 Protein; C497791:Smad3 protein, mouse; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D003094:Collagen; D004247:DNA; D002251:Carbon Tetrachloride; D020928:Mitogen-Activated Protein Kinases