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TGF ‐β1 Up‐Regulates the Expression of PDGF ‐β Receptor m RNA and Induces a Delayed PI 3 K ‐, AKT ‐, and p70 S6K ‐Dependent Proliferative Response in Activated Hepatic Stellate Cells
Author(s) -
Shah Ruchi,
ReyesGordillo Karina,
ArellanesRobledo Jaime,
Lechuga Carmen G.,
HernándezNazara Zamira,
Cotty Adam,
Rojkind Marcos,
Lakshman M. Raj
Publication year - 2013
Publication title -
alcoholism: clinical and experimental research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.267
H-Index - 153
eISSN - 1530-0277
pISSN - 0145-6008
DOI - 10.1111/acer.12167
Subject(s) - platelet derived growth factor receptor , platelet derived growth factor , biology , hepatic stellate cell , protein kinase b , pi3k/akt/mtor pathway , microbiology and biotechnology , growth factor , cell growth , receptor , signal transduction , endocrinology , biochemistry
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 m RNA and induces a delayed proliferation of HSC , we used proliferation and apoptosis assays as well as RT‐PCR , W estern 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 m RNA and associated increase in PDGF ‐β receptor protein after 48 hours. TGF ‐β1‐dependent HSC proliferation is mimicked by H 2 O 2 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 PI 3 K / 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.