Smad7 prevents activation of hepatic stellate cells and liver fibrosis in rats.
OBJECTIVE
Numerous studies implicate transforming growth factor (TGF)-beta signaling in liver fibrogenesis. To perturb the TGF-beta pathway during this process, we overexpressed Smad7, an intracellular antagonist of TGF-beta signaling, in vivo and in primary-cultured hepatic stellate cells (HSCs).


METHODS
Ligation of the common bile duct (BDL) was used to induce liver fibrosis in rats. Animals received injections of an adenovirus carrying Smad7 cDNA into the portal vein during surgery and via the tail vein at later stages. The effect of Smad7 on TGF-beta signaling and activation of HSC was further analyzed in primary-cultured cells.


RESULTS
Smad7-overexpressing BDL rats displayed reduced collagen and alpha-SMA expression and reduced hydroxyproline content in the liver, when compared with animals administered AdLacZ. Such a beneficial effect was also observed when Smad7 was expressed in animals with established fibrosis. Accordingly, Smad7 arrested transdifferentiation of primary-cultured HSCs. AdSmad7 infected cells remained in a quiescent stage and retained storage of vitamin A droplets. Smad7 expression totally blocked TGF-beta signal transduction, shown by inhibiting Smad2/3 phosphorylation, nuclear translocation of activated Smad complexes, and activation of (CAGA)(9)-MLP-Luc, resulting in decreased collagen I expression. Smad7 also abrogated TGF-beta-dependent proliferation inhibition of HSC. Smad7 did not decrease expression of alpha-SMA, but immunofluorescent staining with anti alpha-SMA antibodies displayed destruction of the fibrillar organization of the actin cytoskeleton.


CONCLUSIONS
In summary, gene transfer of Smad7 inhibits experimental fibrogenesis in vivo. Studies with isolated HSC suggest that the underlying mechanisms involve inhibition of TGF-beta signaling and HSC transdifferentiation.
Dooley
Steven
S
Institüt für Klinische Chemie und Pathobiochemie, RWTH-Universitätsklinikum, Aachen, Germany. sdooley@ukaachen.de
Hamzavi
Jafar
J
Breitkopf
Katja
K
Wiercinska
Eliza
E
Said
Harun M
HM
Lorenzen
Johann
J
Ten Dijke
Peter
P
Gressner
Axel M
AM
D000199:Actins / Q000235:genetics; D000818:Animals; D019898:Autocrine Communication; D002455:Cell Division; D002478:Cells, Cultured; D024042:Collagen Type I / Q000096:biosynthesis; D004268:DNA-Binding Proteins / Q000235:genetics*; D015870:Gene Expression; D015316:Genetic Therapy; D008099:Liver / Q000166:cytology*; D008103:Liver Cirrhosis / Q000473:pathology / Q000517:prevention & control*; D051379:Mice; D019899:Paracrine Communication; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction; D051906:Smad7 Protein; D015534:Trans-Activators / Q000235:genetics*; D016212:Transforming Growth Factor beta / Q000378:metabolism; D019076:Transgenes
D000199:Actins; D024042:Collagen Type I; D004268:DNA-Binding Proteins; D051906:Smad7 Protein; C497807:Smad7 protein, mouse; C497808:Smad7 protein, rat; D015534:Trans-Activators; D016212:Transforming Growth Factor beta