Prostaglandin E2inhibits collagen expression and proliferation in patient-derived normal lung fibroblasts via E prostanoid 2 receptor and cAMP signaling

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Abstract
Uncontrolled fibroblast activation is one of the hallmarks of fibrotic lung disease. Prostaglandin E2 (PGE2) has been shown to inhibit fibroblast migration, proliferation, collagen deposition, and myofibroblast differentiation in the lung. Understanding the mechanisms for these effects may provide insight into the pathogenesis of fibrotic lung disease. Previous work has focused on commercially available fibroblast cell lines derived from tissue whose precise origin and histopathology are often unknown. Here, we sought to define the mechanism of PGE2 inhibition in patient-derived fibroblasts from peripheral lung verified to be histologically normal. Fibroblasts were grown from explants of resected lung, and proliferation and collagen I expression was determined following treatment with PGE2 or modulators of its receptors and downstream signaling components. PGE2 inhibited fibroblast proliferation by 33% and collagen I expression by 62%. PGE2 resulted in a 15-fold increase in intracellular cAMP; other cAMP-elevating agents inhibited collagen I in a manner similar to PGE2. These effects were reproduced by butaprost, a PGE2 analog selective for the cAMP-coupled E prostanoid (EP) 2 receptor, but not by selective EP3 or EP4 agonists. Fibroblasts expressed both major cAMP effectors, protein kinase A (PKA) and exchange protein activated by cAMP-1 (Epac-1), but only a selective PKA agonist was able to appreciably inhibit collagen I expression. Treatment with okadaic acid, a phosphatase inhibitor, potentiated the effects of PGE2. Our data indicate that PGE2 inhibits fibroblast activation in primary lung fibroblasts via binding of EP2 receptor and production of cAMP; inhibition of collagen I proceeds via activation of PKA.

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