PPAR-γ Ligands Repress TGFβ-Induced Myofibroblast Differentiation by Targeting the PI3K/Akt Pathway: Implications for Therapy of Fibrosis

Abstract

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 AktS473. 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 J2 (15d-PGJ2), 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 A1 (PGA1), a structural analogue of 15d-PGJ2 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-PGJ2 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.

Lactic Acid Is Elevated in Idiopathic Pulmonary Fibrosis and Induces Myofibroblast Differentiation via pH-Dependent Activation of Transforming Growth Factor-β

“…Primary human lung fibroblasts were cultured to subconfluence on glass chamber slides under standard conditions described above, and slides were prepared using aSMA (Sigma Aldrich) and Alexa Fluor 488 (Invitrogen, Carlsbad, CA) as previously described (33).…”

PPARγ Alleviates Right Ventricular Failure Secondary to Pulmonary Arterial Hypertension in Rats

“…[3][4][5][6] Activation of PPARγ provides beneficial effects in anti-inflammation and anti-apoptosis, suggesting that activation of PPARγ may be vital in a variety of diseases. [7][8][9] Accumulating evidence demonstrated that activation of PPARγ may be a novel PAH therapeutic target. 10) PPARγ agonist rosiglitazone (Rosi) has been proved to alleviate PAH in rats, including regulating endothelial dysfunction, 11) sustaining angiogenic potential in mature pulmonary microvascular endotheliai cells (PMVECs), 12) preventing PASMCs proliferation, 13,14) etc.…”

Differential expression of long non-coding RNAs in bleomycin-induced lung fibrosis

“…Recent studies have indicated that PPAR-γ ligands inhibit TGFβ signaling by affecting two pro-survival pathways that culminate in myofibroblast differentiation. Further investigation of PPAR-γ ligands and small electrophilic molecules may lead to a new generation of anti-fibrotic therapeutics (42,43).…”