Prostaglandin E₂ inhibits profibrotic function of human pulmonary fibroblasts by disrupting Ca²⁺ signaling

Abstract

We have shown that calcium (Ca2+) 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 E2 (PGE2) exerts antifibrotic effects in the lung, but the mechanisms for this action are not well defined. We thus sought to explore interactions between PGE2 and the profibrotic agent TGF-β in pulmonary fibroblasts (PFs) isolated from patients with or without idiopathic pulmonary fibrosis (IPF). PGE2 inhibited TGF-β-promoted [Ca2+] oscillations and prevented the activation of Akt and Ca2+/calmodulin-dependent protein kinase-II (CaMK-II) but did not prevent activation of Smad-2 or ERK. PGE2 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 EP2 receptors relative to other prostanoid receptor subtypes: EP2 expression is ~10-fold higher than that of EP4 receptors; EP1 and EP3 receptors are barely detectable; and EP2-receptor expression is ~3.5-fold lower in PFs from IPF patients than in normal HPFs. The inhibitory effects of PGE2 on synthetic function and stress fiber formation were blocked by selective EP2 or EP4 antagonists and mimicked by selective EP2 or EP4 agonists, the phosphodiesterase inhibitor isobutylmethylxanthine and forskolin, all of which elevate cellular cAMP concentrations. We conclude that PGE2, likely predominantly via EP2 receptors, interferes with Ca2+ signaling, CaMK-II activation, and Akt activation in IPF-HPFs and HPFs treated with TGF-β. Moreover, a decreased expression of EP2 receptors in pulmonary fibroblasts from IPF patients may contribute to the pathophysiology of this disease.

Therapeutic Targeting of 15-PGDH in Murine Idiopathic Pulmonary Fibrosis

“…These data extend previous work demonstrating the capacity for PGE2 or specific agonism of EP2/EP4 receptors to attenuate TGFβ-mediated pro-fibrotic signaling in pulmonary fibroblasts 19,23-25 , and provide a well-tolerated and efficacious alternative to the delivery of long-acting prostaglandin analogs 18 . Our dual therapeutic effect on both acute inflammation and chronic fibrosis, as well as, our finding that pulmonary endothelial cells, mast cells, and macrophages are highly 15-PGDH active, suggest multiple discrete mechanisms contribute to PGDHi-mediated protection.…”

“…The concept that PGDHi protects in part by improving alveolar stem and progenitor cell function is consistent with recent reports that senescent epithelial cells and fibroblasts drive IPF pathology 34 . Later in disease, and of particular clinical relevance, PGDHi reduces ECM protein expression and fibrotic remodeling in the lung, consistent with the impact of PGE2 administration or specific EP2/EP4 agonism, on human pulmonary fibroblasts from IPF patients 19 . Notably, PGDHi was associated with fewer fibrotic foci, preservation of alveolar architecture, and striking improvements to the dynamic compliance, resistance, and parenchymal rigidity of lungs upon forced oscillation analysis.…”

Inhibiting eicosanoid degradation exerts antifibrotic effects in a pulmonary fibrosis mouse model and human tissue

“…20,57 The finding that PGE 2 decreased fibrocyte differentiation in PBMCs from healthy donors in an EP2 and EP4 receptor-dependent manner led us to investigate cells from patients with IPF, because alterations in EP2 receptor expression and signaling pathways have been described in IPF lung tissue, in patient-derived fibroblasts, and in the bleomycin mouse model, thereby reducing sensibility to the antifibrotic effects of PGE 2 . 58,59,73,74 However, in our in vitro approach, we could see no such changes. PGE 2 reduced fibrocyte differentiation at similar concentrations as compared with healthy donors.…”

Sphingosine Kinase 1/S1P Signaling Contributes to Pulmonary Fibrosis by Activating Hippo/YAP Pathway and Mitochondrial Reactive Oxygen Species in Lung Fibroblasts

“…There is evidence for the involvement of bioactive lipid mediators, such as prostaglandin (PGE2) [8][9][10], lysophosphatidic acid [11][12][13], and its G-protein coupled receptors in the pathophysiology of IPF and experimental pulmonary fibrosis [14,15]. Recent evidence strongly suggests a role for sphingolipids-specifically S1P signaling and homeostasis-in the pathogenesis of IPF, as well as animal models of PF [12,[16][17][18].…”