Abstract Rationale Two novel therapies are now being considered for idiopathic pulmonary fibrosis (IPF), Treprostinil, a prostacyclin analog that stimulates prostaglandin I2 receptor (PTGIR), a G protein-coupled receptor to generate cAMP and nerandomilast, a phosphodiesterase 4B (PDE4B) inhibitor that enhances cAMP levels. Although signaling through PTGIR and cAMP has been shown to be anti-fibrotic, whether IPF fibroblasts exhibit differential expression of PTGIR and responsiveness to prostacyclin analogs have not been examined. Methods Lung fibroblasts derived from IPF patients and non-fibrotic controls were examined for relative expression of PTGIR and other G protein-coupled receptors. To compare function of PTGIR in normal and IPF fibroblasts, fibroblasts were treated with transforming growth factor - β1 (TGF-β1) for 48 hours and subsequently treated with PTGIR agonists Iloprost (1 µM), Treprostinil (10 µM) or ACT-333679 (10 µM) with or without nerandomilast (10 µM) for 24 hours. Their ability to affect α-smooth muscle actin (SMA) and collagen I expression were analyzed by RT-PCR and immunoblot. To determine why PTGIR expression may be altered in IPF, we examined epigenetic patterns and expression of transcription factors that regulate PTGIR. Results Treprostinil, Iloprost, and ACT-333679 all demonstrated to varying degrees an ability to reverse myofibroblast differentiation in the context of collagen and α-SMA expression. Compared to normal fibroblasts, IPF fibroblasts demonstrated a relative resistance to the PTGIR agonists. This was overcome when additionally treated with nerandomilast, demonstrating the effect of combined GPCR signaling and PDE4B inhibition. IPF fibroblasts demonstrated a decrease in PTGIR expression, including its transcription factors - specificity protein 1 (Sp1), octamer-binding protein 1 (POU2F1), and sterol regulatory element-binding protein 1 (SREBF1). Although ACT-333679 was found to reduce protein collagen levels most significantly in control fibroblasts, the drug lost some of its effectiveness in IPF fibroblasts. Conclusions Prostacyclin agonists can cause dedifferentiation of myofibroblasts, with a more pronounced effect when supplemented with nerandomilast. The effectiveness of ACT-333679 in IPF patients may be due to its selectivity to the PTGIR receptor, unlike Iloprost and Treprostinil which interact with other G protein-coupled receptors. IPF fibroblasts exhibited reduced expression of PTGIR, which may limit the ability of these cells to be inhibited by prostacyclin analogs; this may be overcome with addition of nerandomilast. This abstract is funded by: NHLBI (HL162963)
Fleck et al. (Fri,) studied this question.
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