Modulation of transforming growth factor beta response and signaling during transdifferentiation of rat hepatic stellate cells to myofibroblasts

Hepatology. 2000 May;31(5):1094-106. doi: 10.1053/he.2000.6126.

Abstract

Activation of hepatic stellate cells (HSCs) is the key step in liver fibrogenesis. Increased transforming growth factor beta (TGF-beta) expression and extracellular matrix production in patients with hepatic fibrosis and experimental models of liver fibrogenesis support implication of TGF-beta in the pathogenesis of this disease. However, a causative role for TGF-beta during transdifferentiation of HSCs has not been delineated in molecular detail. Using a rat cell culture model of HSC transdifferentiation, we analyzed TGF-beta signal transduction and identified changes between stellate cells and their transdifferentiated phenotype. Fully transdifferentiated myofibroblasts, opposed to HSCs, were not inhibited in proliferation activity on treatment with TGF-beta1. Furthermore, stimulation of alpha2 (I) collagen and Smad7 messenger RNA (mRNA) expression by TGF-beta1 was achieved in stellate cells but not in myofibroblasts. Northern and Western blot analyses indicated significant expression of TGF-beta receptors I and II in both cell types. In contrast, [(125)I]-TGF-beta1 receptor affinity labeling displayed strongly reduced types I, II, and III receptor presentation at the cell surface of myofibroblasts. Moreover, myofibroblasts did not display DNA-binding SMAD proteins in electrophoretic mobility shift assays with a CAGA box. These data indicate that stellate cells are responsive to TGF-beta1 treatment and transduce a signal that may play an important role in liver fibrogenesis. Myofibroblasts display decreased availability of surface receptors for TGF-beta, which could be based on autocrine stimulation. However, lack of activated SMAD complexes with DNA-binding activity and absence of alpha2 (I) collagen transcription inhibition by latency-associated peptide (LAP)/anti-TGF-beta antibody raise the possibility of TGF-beta signaling independent receptor down-regulation in myofibroblasts.

MeSH terms

  • Activin Receptors, Type I*
  • Animals
  • Cell Differentiation / drug effects
  • Collagen / genetics
  • DNA / metabolism
  • DNA-Binding Proteins / genetics
  • Fibroblasts / cytology
  • Liver / cytology*
  • Male
  • Protein-Serine-Threonine Kinases / genetics
  • Rats
  • Rats, Sprague-Dawley
  • Receptor, Transforming Growth Factor-beta Type I
  • Receptor, Transforming Growth Factor-beta Type II
  • Receptors, Transforming Growth Factor beta / genetics
  • Signal Transduction*
  • Smad7 Protein
  • Trans-Activators / genetics
  • Transforming Growth Factor beta / pharmacology*

Substances

  • DNA-Binding Proteins
  • Receptors, Transforming Growth Factor beta
  • Smad7 Protein
  • Smad7 protein, rat
  • Trans-Activators
  • Transforming Growth Factor beta
  • Collagen
  • DNA
  • Protein-Serine-Threonine Kinases
  • Activin Receptors, Type I
  • Receptor, Transforming Growth Factor-beta Type I
  • Receptor, Transforming Growth Factor-beta Type II
  • Tgfbr1 protein, rat