Targeted disruption of Smad3 confers resistance to the development of dimethylnitrosamine-induced hepatic fibrosis in mice.
BACKGROUND
Hepatic fibrosis is characterized by a progressive accumulation of fibrillar extracellular matrix (ECM) proteins including collagen, which occurs in most types of chronic liver diseases. Transforming growth factor-beta (TGF-beta)/Smad3 signalling plays a central role in tissue fibrogenesis, acting as a potent stimulus of ECM accumulation.


OBJECTIVE
To evaluate the potential protective role of Smad3 deficiency in the pathogenesis of liver fibrosis induced by dimethylnitrosamine (DMN) in Smad3 null mice.


METHODS
Chronic hepatitis-associated fibrosis was induced in 13 Smad3 null and 13 wild-type (WT) mice by intraperitoneal DMN administration (10 microg/g body weight/day) for three consecutive days per week for 6 weeks. The liver was excised for macroscopic examination and histological, morphometric and immunohistochemical (IHC) analyses. For IHC, alpha-smooth muscle actin (alpha-SMA), collagen types I-III, TGF-beta1, connective tissue growth factor (CTGF), Smad3, Smad7 and CD3 antibodies were used.


RESULTS
At macroscopic examination, the liver of DMN-treated Smad3 WT appeared harder with a dark brown colouring and necrotic areas compared with that from null mice. Histological and morphometric evaluation revealed a significantly higher degree of hepatic fibrosis and accumulation of connective tissue in the Smad3 WT compared with null mice. IHC evaluation showed a marked increase in alpha-SMA, CTGF, collagen I-III, TGF-beta and Smad3 staining in the liver of Smad3 WT compared with that in null mice, whereas Smad7 was increased only in null mice.


CONCLUSIONS
The results indicate that Smad3 loss confers resistance to the development of DMN-induced hepatic fibrosis. The reduced fibrotic response appears to be due to a reduction of fibrogenic myofibroblast activation and ECM production and accumulation. Smad3 could be a novel target for potential treatment of fibrosis complicating chronic hepatitis.
Department of Internal Medicine, GI Unit, University of L'Aquila, L'Aquila, Italy. giolatel@tin.it
Giovanni
G
Latella
Antonella
A
Vetuschi
Roberta
R
Sferra
Valentina
V
Catitti
Angela
A
D'Angelo
Giuliana
G
Zanninelli
Kathleen C
KC
Flanders
Eugenio
E
Gaudio
D000199:Actins / Q000378:metabolism; D000375:Aging; D000818:Animals; D017252:CD3 Complex / Q000378:metabolism; D055513:Connective Tissue Growth Factor / Q000378:metabolism; D004128:Dimethylnitrosamine; D024022:Fibrillar Collagens / Q000378:metabolism; D007150:Immunohistochemistry; D008099:Liver / Q000378:metabolism* / Q000473:pathology; D008103:Liver Cirrhosis / Q000139:chemically induced / Q000235:genetics / Q000378:metabolism / Q000473:pathology / Q000517:prevention & control*; D051379:Mice; D018345:Mice, Knockout; D012720:Severity of Illness Index; D051900:Smad3 Protein / Q000172:deficiency* / Q000235:genetics; D051906:Smad7 Protein / Q000378:metabolism; D053773:Transforming Growth Factor beta1 / Q000378:metabolism
D000199:Actins; C526318:CCN2 protein, mouse; D017252:CD3 Complex; D024022:Fibrillar Collagens; D051900:Smad3 Protein; C497791:Smad3 protein, mouse; D051906:Smad7 Protein; C497807:Smad7 protein, mouse; D053773:Transforming Growth Factor beta1; D055513:Connective Tissue Growth Factor; D004128:Dimethylnitrosamine