Liver fibrogenesis due to cholestasis is associated with increased Smad7 expression and Smad3 signaling.
OBJECTIVE
Profibrogenic TGF-beta signaling in hepatic stellate cells is modulated during transdifferentiation. Strategies to abrogate TGF-beta effects provide promising antifibrotic results, however, in vivo data regarding Smad activation during fibrogenesis are scarce.


METHODS
Here, liver fibrosis was assessed subsequent to bile duct ligation by determining liver enzymes in serum and collagen deposition in liver tissue. Activated hepatic stellate cells were identified by immunohistochemistry and immunoblots for alpha smooth muscle actin. Cellular localization of Smad3 and Smad7 proteins was demonstrated by immunohistochemistry. RTPCR for Smad4 and Smad7 was conducted with total RNA and Northern blot analysis for Smad7 with mRNA. Whole liver lysates were prepared to detect Smad2/3/4 and phospho- Smad2/3 by Western blotting.


RESULTS
Cholestasis induces TGF-beta signaling via Smad3 in vivo, whereas Smad2 phosphorylation was only marginally increased. Smad4 expression levels were unchanged. Smad7 expression was continuously increasing with duration of cholestasis. Hepatocytes of fibrotic lesions exhibited nuclear staining Smad3. In contrast to this, Smad7 expression was localized to activated hepatic stellate cells.


CONCLUSIONS
Hepatocytes of damaged liver tissue display increased TGF-beta signaling via Smad3. Further, negative feedback regulation of TGF-beta signaling by increased Smad7 expression in activated hepatic stellate cells occurs, however does not interfere with fibrogenesis.
Seyhan
H
H
Department of Plastic and Hand Surgery, University Medical Center Erlangen, Germany.
Hamzavi
J
J
Wiercinska
Eliza
E
Gressner
A M
AM
Mertens
P R
PR
Kopp
J
J
Horch
R E
RE
Breitkopf
Katja
K
Dooley
S
S
D000818:Animals; D001652:Bile Ducts / Q000473:pathology; D002779:Cholestasis / Q000150:complications*; D007150:Immunohistochemistry; D008026:Ligation; D008099:Liver / Q000201:enzymology / Q000473:pathology; D008103:Liver Cirrhosis / Q000209:etiology / Q000473:pathology*; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction; D051900:Smad3 Protein / Q000378:metabolism / Q000502:physiology*; D051901:Smad4 Protein / Q000096:biosynthesis; D051906:Smad7 Protein / Q000096:biosynthesis*; D016212:Transforming Growth Factor beta / Q000502:physiology
D051900:Smad3 Protein; C497787:Smad3 protein, rat; D051901:Smad4 Protein; C490811:Smad4 protein, rat; D051906:Smad7 Protein; C497808:Smad7 protein, rat; D016212:Transforming Growth Factor beta