Abstract
Pirfenidone is a pyridinone derivative that has been shown to inhibit fibrosis in animal models and in patients with idiopathic pulmonary fibrosis. Its effect on orbital fibroblasts remains poorly understood. We investigated the in vitro effect of pirfenidone in transforming growth factor-β1 (TGF-β1)-induced myofibroblast transdifferentiation and extracellular matrix (ECM) homeostasis in primary cultured orbital fibroblasts from patients with Graves' ophthalmopathy (GO). The expression of fibrotic proteins, including α-smooth muscle actin (α-SMA), connective tissue growth factor (CTGF), fibronectin, and collagen type I, was determined by Western blots. The activities of matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) responsible for the ECM homeostasis were examined. After pretreating the GO orbital fibroblasts with pirfenidone (250, 500, and 750 μg/mL, respectively) for one hour followed by TGF-β1 for another 24 h, the expression of α-SMA, CTGF, fibronectin, and collagen type I decreased in a dose-dependent manner. Pretreating the GO orbital fibroblasts with pirfenidone not only abolished TGF-β1-induced TIMP-1 expression but recovered the MMP-2/-9 activities. Notably, pirfenidone inhibited TGF-β1-induced phosphorylation of p38 and c-Jun N-terminal kinase (JNK), the critical mediators in the TGF-β1 pathways. These findings suggest that pirfenidone modulates TGF-β1-mediated myofibroblast differentiation and ECM homeostasis by attenuating downstream signaling of TGF-β1.