Inhibition of transforming growth factor-beta/Smad signaling improves regeneration of small-for-size rat liver grafts.
Transforming growth factor-beta (TGF-beta) is a potent inhibitor of cell proliferation. This study investigated whether overexpression of Smad7, which blocks TGF-beta-induced activation of Smad2/3, could prevent the suppression of regeneration of small-for-size liver grafts. Rats were intravenously given adenoviruses (2 x 10(10) pfu/rat) carrying the LacZ gene or the Smad7 gene (Ad-Smad7) 3 days prior to liver harvesting. Half-size livers were implanted into recipients of the same weight or twice the donor weight, and this resulted in half-size or quarter-size liver grafts. Cell proliferation, detected by 5-bromo-2'-deoxyuridine (BrdU) incorporation, increased to 23% in half-size grafts at 38 hours after implantation but was only 4% in quarter-size grafts. Graft weight did not increase after 38 hours in full-size and quarter-size grafts but increased 28% in half-size grafts. Ad-Smad7 restored BrdU labeling to 32%, and the graft weight increased to 43% in quarter-size grafts. Serum total bilirubin increased approximately 30-fold after the implantation of quarter-size grafts. Ad-Smad7 blunted hyperbilirubinemia by 80%. The basal hepatic TGF-beta(1) level was 7 ng/g of liver wet weight, and this increased to 30 ng/g at 1.5 hours after the transplantation of full-size grafts but decreased rapidly afterwards. After the transplantation of quarter-size grafts, however, TGF-beta(1) progressively increased to 159 ng/g in 38 hours. Nuclear phosphorylated Smad2/3 was barely detectable, and p21Cip1 expression was negligible in full-size grafts but increased markedly in quarter-size grafts. Ad-Smad7 blocked Smad2/3 activation and expression of p21Cip1. Together, these data show that TGF-beta is responsible, at least in part, for the defective liver regeneration in small-for-size grafts by activating the Smad signaling pathway.
Zhong
Zhi
Z
Department of Pharmaceutical and Biomedical Sciences, Medical University of South Carolina, Charleston, SC 29425, USA. zhong@musc.edu
Tsukada
Shigeki
S
Rehman
Hasibur
H
Parsons
Christopher J
CJ
Theruvath
Tom P
TP
Rippe
Richard A
RA
Brenner
David A
DA
Lemasters
John J
JJ
D021581:Active Transport, Cell Nucleus / Q000502:physiology; D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000235:genetics / Q000378:metabolism; D018014:Gene Transfer Techniques; D007763:Lac Operon; D008115:Liver Regeneration / Q000502:physiology*; D016031:Liver Transplantation; D009929:Organ Size; D051381:Rats; D015398:Signal Transduction / Q000502:physiology*; D051899:Smad2 Protein / Q000378:metabolism; D051900:Smad3 Protein / Q000378:metabolism; D051906:Smad7 Protein / Q000235:genetics / Q000378:metabolism*; D053773:Transforming Growth Factor beta1 / Q000378:metabolism*; D001616:beta-Galactosidase / Q000235:genetics
C493958:Cdkn1a protein, rat; D050759:Cyclin-Dependent Kinase Inhibitor p21; C497806:SMAD7 protein, human; D051899:Smad2 Protein; C497784:Smad2 protein, rat; D051900:Smad3 Protein; C497787:Smad3 protein, rat; D051906:Smad7 Protein; D053773:Transforming Growth Factor beta1; D001616:beta-Galactosidase