PPAR-γ ligands repress TGFβ-induced myofibroblast differentiation by targeting the PI3K/Akt pathway: implications for therapy of fibrosis.
Transforming growth factor beta (TGFβ) induced differentiation of human lung fibroblasts to myofibroblasts is a key event in the pathogenesis of pulmonary fibrosis. Although the typical TGFβ signaling pathway involves the Smad family of transcription factors, we have previously reported that peroxisome proliferator-activated receptor-γ (PPAR-γ) ligands inhibit TGFβ-mediated differentiation of human lung fibroblasts to myofibroblasts via a Smad-independent pathway. TGFβ also activates the phosphatidylinositol 3 kinase/protein kinase B (PI3K/Akt) pathway leading to phosphorylation of Akt(S473). Here, we report that PPAR-γ ligands, 2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid (CDDO) and 15-deoxy-(12,14)-15d-prostaglandin J(2) (15d-PGJ(2)), inhibit human myofibroblast differentiation of normal and idiopathic pulmonary fibrotic (IPF) fibroblasts, by blocking Akt phosphorylation at Ser473 by a PPAR-γ-independent mechanism. The PI3K inhibitor LY294002 and a dominant-negative inactive kinase-domain mutant of Akt both inhibited TGFβ-stimulated myofibroblast differentiation, as determined by Western blotting for α-smooth muscle actin and calponin. Prostaglandin A(1) (PGA(1)), a structural analogue of 15d-PGJ(2) with an electrophilic center, also reduced TGFβ-driven phosphorylation of Akt, while CAY10410, another analogue that lacks an electrophilic center, did not; implying that the activity of 15d-PGJ(2) and CDDO is dependent on their electrophilic properties. PPAR-γ ligands inhibited TGFβ-induced Akt phosphorylation via both post-translational and post-transcriptional mechanisms. This inhibition is independent of MAPK-p38 and PTEN but is dependent on TGFβ-induced phosphorylation of FAK, a kinase that acts upstream of Akt. Thus, PPAR-γ ligands inhibit TGFβ signaling by affecting two pro-survival pathways that culminate in myofibroblast differentiation. Further studies of PPAR-γ ligands and small electrophilic molecules may lead to a new generation of anti-fibrotic therapeutics.
The Division of Pulmonary and Critical Care Medicine, Department of Medicine, University of Rochester School of Medicine and Dentistry, Rochester, New York, United States of America.
Ajit A
AA
Kulkarni
Thomas H
TH
Thatcher
Keith C
KC
Olsen
Sanjay B
SB
Maggirwar
Richard P
RP
Phipps
Patricia J
PJ
Sime
D002454:Cell Differentiation / Q000187:drug effects*; D005355:Fibrosis / Q000188:drug therapy; D006801:Humans; D008024:Ligands; D047495:PPAR gamma / Q000378:metabolism*; D058539:Phosphatidylinositol 3-Kinase / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D016212:Transforming Growth Factor beta / Q000494:pharmacology*
D008024:Ligands; D047495:PPAR gamma; D016212:Transforming Growth Factor beta; D058539:Phosphatidylinositol 3-Kinase; D051057:Proto-Oncogene Proteins c-akt
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