Lung Myofibroblasts Are Characterized by Down-Regulated Cyclooxygenase-2 and Its Main Metabolite, Prostaglandin E2

Marta Gabasa,Dolores Royo,Jordi Roca-Ferrer,Antoni Xaubet,Cesar Picado,Maria Molina-Molina,Laura Pujols,Javier Pereda,Mauricio Rojas

doi:10.1371/journal.pone.0065445

Abstract

BackgroundProstaglandin E2 (PGE2), the main metabolite of cyclooxygenase (COX), is a well-known anti-fibrotic agent. Moreover, myofibroblasts expressing α-smooth muscle actin (α-SMA), fibroblast expansion and epithelial-mesenchymal transition (EMT) are critical to the pathogenesis of idiopathic pulmonary fibrosis (IPF). Our aim was to investigate the expression of COX-2 and PGE2 in human lung myofibroblasts and establish whether fibroblast-myofibroblast transition (FMT) and EMT are associated with COX-2 and PGE2 down-regulation.MethodsFibroblasts obtained from IPF patients (n = 6) and patients undergoing spontaneous pneumothorax (control, n = 6) and alveolar epithelial cell line A549 were incubated with TGF-β1 and FMT and EMT markers were evaluated. COX-2 and α-SMA expression, PGE2 secretion and cell proliferation were measured after IL-1β and PGE2 incubation.ResultsMyofibroblasts from both control and IPF fibroblast cultures stimulated with IL-1β showed no COX-2 expression. IPF fibroblasts showed increased myofibroblast population and reduced COX-2 expression in response to IL-1β. TGF-β1 increased the number of myofibroblasts in a time-dependent manner. In contrast, TGF-β1 induced slight COX-2 expression at 4 h (without increase in myofibroblasts) and 24 h, but not at 72 h. Both IPF and control cultures incubated with TGF-β1 for 72 h showed diminished COX-2 induction, PGE2 secretion and α-SMA expression after IL-1β addition. The latter decreased proliferation in fibroblasts but not in myofibroblasts. A549 cells incubated with TGF-β1 for 72 h showed down-regulated COX-2 expression and low basal PGE2 secretion in response to IL-1β. Immuno-histochemical analysis of IPF lung tissue showed no COX-2 immuno-reactivity in myofibroblast foci.ConclusionsMyofibroblasts are associated with COX-2 down-regulation and reduced PGE2 production, which could be crucial in IPF development and progression.

Highlights

Prostaglandin E2 (PGE2), the main metabolite of cyclooxygenase (COX), is a well-known anti-fibrotic agent
A-SMA positive cells showed little or no expression of COX-2 in response to IL-1b (Table 1, Fig. 1). This finding demonstrates that spontaneous myofibroblasts present in culture are characterized by diminished COX-2 expression in response to IL-1b
idiopathic pulmonary fibrosis (IPF) is characterized by increased expression of transforming growth factor (TGF)-b1, increased myofibroblast numbers and reduced production of PGE2 resulting from a limited induction of COX-2

Summary

Introduction

Prostaglandin E2 (PGE2), the main metabolite of cyclooxygenase (COX), is a well-known anti-fibrotic agent. Idiopathic pulmonary fibrosis (IPF) is a progressive and fatal interstitial lung disease of uncertain etiology, characterized by the histopathological pattern of usual interstitial pneumonia. This fibrotic process involves the loss of lung architecture through increased epithelial cell apoptosis and abnormal wound healing, followed by the formation of fibroblast foci and excessive collagen deposition. In this context, the crucial role of myofibroblasts in tissue remodeling has been well described [1]. EMT involves a transition from epithelial cells to mesenchymal myofibroblast-like cells that involves a decreased expression of epithelial markers such as E-cadherin [2]

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