PURPOSE: Idiopathic pulmonary fibrosis (IPF) is a fatal lung disease characterized by progressive destruction of alveolar structures, excessive fibroproliferation, and unrestrained extracellular matrix deposition. Transforming growth factor beta (TGF-β), a profibrotic cytokine aberrantly expressed in IPF lungs, is a potent regulator of fibrogenesis and connective tissue synthesis. We recently reported that pirfenidone binds competitively to the ATP-binding site of two isoforms of p38 MAPK (p38α and p38γ), a key intracellular mediator of TGF-β-induced collagen synthesis. In order to further explore the potential therapeutic utility of pirfenidone in IPF, we sought to confirm the expression of p38γ in human lung fibroblasts and investigate the inhibitory activity of pirfenidone against TGF-β-induced p38α and p38γ activation in these cells.
METHODS: Human lung fibroblasts (HFL-1) were cultured in F12K medium; serum-starved cells were pre-treated with medium or with pirfenidone (1 mM), then treated with TGF-β. Cellular lysates were prepared and Western blot was used to measure expression and activation of p38α and p38γ. Using a human in vitro kinase panel, we also discovered that p38α and p38γ are directly inhibited by pirfenidone.
RESULTS: Western blot analysis revealed that both p38α and p38γ are expressed in normal and IPF human lung fibroblasts. Additionally, activation of p38α and p38γ was induced by the exposure of cells to TGF-β. Pretreatment of lung fibroblasts with 1mM pirfenidone significantly attenuated TGF-β-induced activation of p38α and p38γ, and comparative analysis of collagen synthesis in HFL-1 cells over-expressing wild-type and pirfenidone-resistant mutants of p38α and p38γ confirmed inhibition in wild-type, but not mutant forms of p38 following exposure to pirfenidone.
CONCLUSION: Our results demonstrate that p38γ MAPK, previously believed to be expressed only in smooth muscle cells, is expressed in normal and IPF human lung fibroblasts. The inhibition of TGF-β-induced p38α and p38γ activation/activity in fibroblasts suggests that pirfenidone’s antifibrotic activity is mediated at least partly through inhibition of the p38 MAPK signal transduction pathway.
CLINICAL IMPLICATIONS: Further study is warranted to elucidate the clinical utility of this novel compound.
DISCLOSURE: Osman Ozes, University grant monies No; Grant monies (from sources other than industry) No; Grant monies (from industry related sources) No; Shareholder O. Ozes, S. Stevens, R. Phillips, L. Blatt: InterMune shareholders; Employee O. Ozes, S. Stevens, R. Phillips, L. Blatt: InterMune employees; Fiduciary position (of any organization, association, society, etc, other than ACCP No; Consultant fee, speaker bureau, advisory committee, etc. No; Other No; Product/procedure/technique that is considered research and is NOT yet approved for any purpose, All.