title: TGF-β1 up-regulates the expression of PDGF-β receptor mRNA and induces a delayed PI3K-, AKT-, and p70(S6K) -dependent proliferative response in activated hepatic stellate cells.
abstract: BACKGROUND
  Transforming growth factor beta 1 (TGF-β1) is a pleiotropic cytokine that activates hepatic stellate cell (HSC) proliferation, but inhibits parenchymal cell proliferation. Therefore, we hypothesize that TGF-β1 regulates HSC proliferation and elucidated its molecular action.
  
  
  METHODS
  In order to elucidate the molecular mechanism whereby TGF-β1 up-regulates platelet derived growth factor beta (PDGF-β) receptor mRNA and induces a delayed proliferation of HSC, we used proliferation and apoptosis assays as well as RT-PCR, Western blot analysis, immunostaining, and flow cytometry in mouse and rat HSC.
  
  
  RESULTS
  We show that TGF-β1 markedly induces the proliferation of mouse HSC in culture with concomitant 2.1-fold (p < 0.001) stimulation in [(3) H]-thymidine incorporation into cellular DNA. This induction is maximal between 24 and 36 hours postcytokine exposure that is triggered by 7.6-fold (p < 0.001) up-regulation of PDGF-β receptor mRNA and associated increase in PDGF-β receptor protein after 48 hours. TGF-β1-dependent HSC proliferation is mimicked by H2 O2 that is inhibited by catalase, implying that TGF-β1 action is mediated via reactive oxygen species. HSC proliferation is blunted by PDGF-β receptor-neutralizing antibody as well as by specific inhibitors of PI3 kinase (PI3K), AKT, and p70(S6K) , indicating that the action of TGF-β1 involves the activation of PDGF-β receptor via the PI3K/AKT/p70(S6K) signaling pathway. TGF-β1 also induces a reorganization of actin and myosin filaments and cell morphology leading to the formation of palisades although their myosin and actin contents remained constant. These findings suggest that TGF-β1-mediated oxidative stress causes the transdifferentiation of HSC and primes them for extracellular matrix (ECM) deposition and scar contraction.
  
  
  CONCLUSIONS
  We conclude that liver injury up-regulates TGF-β1 that inhibits parenchymal cell proliferation, but stimulates HSC proliferation leading to the production of ECM and type I collagen resulting in fibrosis.
authors.affiliation: Lipid Research Laboratory, VA Medical Center, Washington, District of Columbia; Department of Biochemistry and Molecular Biology, The George Washington University Medical Center, Washington, District of Columbia.
authors.forename: Ruchi
authors.initials: R
authors.lastname: Shah
authors.forename: Karina
authors.initials: K
authors.lastname: Reyes-Gordillo
authors.forename: Jaime
authors.initials: J
authors.lastname: Arellanes-Robledo
authors.forename: Carmen G
authors.initials: CG
authors.lastname: Lechuga
authors.forename: Zamira
authors.initials: Z
authors.lastname: Hernández-Nazara
authors.forename: Adam
authors.initials: A
authors.lastname: Cotty
authors.forename: Marcos
authors.initials: M
authors.lastname: Rojkind
authors.forename: M Raj
authors.initials: MR
authors.lastname: Lakshman
mesh_terms: D000818:Animals; D000077214:Becaplermin; D049109:Cell Proliferation; D048429:Cell Size; D002478:Cells, Cultured; D055166:Hepatic Stellate Cells / Q000166:cytology / Q000201:enzymology*; D006861:Hydrogen Peroxide / Q000378:metabolism; D051379:Mice; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D020574:Proto-Oncogene Proteins c-sis / Q000378:metabolism; D051381:Rats; D020797:Receptor, Platelet-Derived Growth Factor beta / Q000378:metabolism*; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism*; D015398:Signal Transduction; D053773:Transforming Growth Factor beta1 / Q000378:metabolism*
chemical_list: D020574:Proto-Oncogene Proteins c-sis; D053773:Transforming Growth Factor beta1; D000077214:Becaplermin; D006861:Hydrogen Peroxide; D019869:Phosphatidylinositol 3-Kinases; D020797:Receptor, Platelet-Derived Growth Factor beta; D051057:Proto-Oncogene Proteins c-akt; D038762:Ribosomal Protein S6 Kinases, 70-kDa
keywords: Hepatic Stellate Cells; Liver Fibrosis; PDGF-β Receptor; Proliferation; TGF-β1