Prostaglandin E inhibits profibrotic function of human pulmonary fibroblasts by disrupting Ca signaling.

We have shown that calcium (Ca) oscillations in human pulmonary fibroblasts (HPFs) contribute to profibrotic effects of transforming growth factor-β (TGF-β) and that disruption of these oscillations blunts features of pulmonary fibrosis. Prostaglandin E (PGE) exerts antifibrotic effects in the lung, but the mechanisms for this action are not well defined. We thus sought to explore interactions between PGE and the profibrotic agent TGF-β in pulmonary fibroblasts (PFs) isolated from patients with or without idiopathic pulmonary fibrosis (IPF). PGE inhibited TGF-β-promoted [Ca] oscillations and prevented the activation of Akt and Ca/calmodulin-dependent protein kinase-II (CaMK-II) but did not prevent activation of Smad-2 or ERK. PGE also eliminated TGF-β-stimulated expression of collagen A1, fibronectin, and α-smooth muscle actin and reduced stress fiber formation in the HPFs. RNA sequencing revealed that HPFs preferentially express EP receptors relative to other prostanoid receptor subtypes: EP expression is ~10-fold higher than that of EP receptors; EP and EP receptors are barely detectable; and EP-receptor expression is ~3.5-fold lower in PFs from IPF patients than in normal HPFs. The inhibitory effects of PGE on synthetic function and stress fiber formation were blocked by selective EP or EP antagonists and mimicked by selective EP or EP agonists, the phosphodiesterase inhibitor isobutylmethylxanthine and forskolin, all of which elevate cellular cAMP concentrations. We conclude that PGE, likely predominantly via EP receptors, interferes with Ca signaling, CaMK-II activation, and Akt activation in IPF-HPFs and HPFs treated with TGF-β. Moreover, a decreased expression of EP receptors in pulmonary fibroblasts from IPF patients may contribute to the pathophysiology of this disease.