TY - JOUR
T1 - Constitutive Smad signaling and Smad-dependent collagen gene expression in mouse embryonic fibroblasts lacking peroxisome proliferator-activated receptor-γ
AU - Ghosh, Asish K.
AU - Wei, Jun
AU - Wu, Minghua
AU - Varga, John
N1 - Funding Information:
We are grateful to Drs. Christopher K. Glass (University of California, San Diego, CA) for providing the mPPAR-γ expression vectors and Evan D. Rosen (Beth Israel Deaconess Medical Center, Boston, MA) for PPAR-γ null and heterozygous MEFs. This work was supported by Grants from Scleroderma Foundation to AKG and the NIH (AR-42309) to JV.
PY - 2008/9/19
Y1 - 2008/9/19
N2 - Transforming growth factor-β (TGF-β), a potent inducer of collagen synthesis, is implicated in pathological fibrosis. Peroxisome proliferator-activated receptor-γ (PPAR-γ) is a nuclear hormone receptor that regulates adipogenesis and numerous other biological processes. Here, we demonstrate that collagen gene expression was markedly elevated in mouse embryonic fibroblasts (MEFs) lacking PPAR-γ compared to heterozygous control MEFs. Treatment with the PPAR-γ ligand 15d-PGJ2 failed to down-regulate collagen gene expression in PPAR-γ null MEFs, whereas reconstitution of these cells with ectopic PPAR-γ resulted in their normalization. Compared to control MEFs, PPAR-γ null MEFs displayed elevated levels of the Type I TGF-β receptor (TβRI), and secreted more TGF-β1 into the media. Furthermore, PPAR-γ null MEFs showed constitutive phosphorylation of cellular Smad2 and Smad3, even in the absence of exogenous TGF-β, which was abrogated by the ALK5 inhibitor SB431542. Constitutive Smad2/3 phosphorylation in PPAR-γ null MEFs was associated with Smad3 binding to its cognate DNA recognition sequences, and interaction with coactivator p300 previously implicated in TGF-β responses. Taken together, these results indicate that loss of PPAR-γ in MEFs is associated with upregulation of collagen synthesis, and activation of intracellular Smad signal transduction, due, at least in part, to autocrine TGF-β stimulation.
AB - Transforming growth factor-β (TGF-β), a potent inducer of collagen synthesis, is implicated in pathological fibrosis. Peroxisome proliferator-activated receptor-γ (PPAR-γ) is a nuclear hormone receptor that regulates adipogenesis and numerous other biological processes. Here, we demonstrate that collagen gene expression was markedly elevated in mouse embryonic fibroblasts (MEFs) lacking PPAR-γ compared to heterozygous control MEFs. Treatment with the PPAR-γ ligand 15d-PGJ2 failed to down-regulate collagen gene expression in PPAR-γ null MEFs, whereas reconstitution of these cells with ectopic PPAR-γ resulted in their normalization. Compared to control MEFs, PPAR-γ null MEFs displayed elevated levels of the Type I TGF-β receptor (TβRI), and secreted more TGF-β1 into the media. Furthermore, PPAR-γ null MEFs showed constitutive phosphorylation of cellular Smad2 and Smad3, even in the absence of exogenous TGF-β, which was abrogated by the ALK5 inhibitor SB431542. Constitutive Smad2/3 phosphorylation in PPAR-γ null MEFs was associated with Smad3 binding to its cognate DNA recognition sequences, and interaction with coactivator p300 previously implicated in TGF-β responses. Taken together, these results indicate that loss of PPAR-γ in MEFs is associated with upregulation of collagen synthesis, and activation of intracellular Smad signal transduction, due, at least in part, to autocrine TGF-β stimulation.
KW - Collagen
KW - Fibrosis
KW - PPAR-γ
KW - Smad
KW - TGF-β
KW - TbRI
KW - p300
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U2 - 10.1016/j.bbrc.2008.07.014
DO - 10.1016/j.bbrc.2008.07.014
M3 - Article
C2 - 18627765
AN - SCOPUS:48349108129
VL - 374
SP - 231
EP - 236
JO - Biochemical and Biophysical Research Communications
JF - Biochemical and Biophysical Research Communications
SN - 0006-291X
IS - 2
ER -