Inhibition of sphingosine-1-phosphate receptor-2 attenuates idiopathic pulmonary fibrosis by preventing its binding to dapper1 in bronchial epithelial cells

Background and purpose: Activation of the sphingosine-1-phosphate receptor-2 (S1P₂ receptor) promotes idiopathic pulmonary fibrosis (IPF). However, the mechanisms associated with IPF development via S1P₂ receptor signalling are poorly understood and no S1P₂ receptor antagonists have been approved for clinical use.

Experimental approach: Western blotting and immunohistochemical assays analysed inflammatory factors and epithelial-mesenchymal transition (EMT) markers. Co-immunoprecipitation and immunofluorescence analysed the binding of S1P₂ receptor to dapper1 (Dpr1) and cyclic AMP response-binding protein 1 (CREB1). X-ray-based computed tomography diagnosed IPF in bleomycin (BLM)-treated mice. Barometric whole-body plethysmography tested pulmonary function of mice. Masson's trichrome and Sirius red staining analysed extracellular matrix deposition. Enzyme-linked immunosorbent assays analysed inflammatory factors and hydroxyproline.

Key results: Activation of S1P₂ receptors promoted IPF through the binding of S1P₂ receptor to Dpr1, decreasing dishevelled (Dvl) degradation to accumulate β-catenin. The β-catenin accumulated in the nucleus, upregulating its target genes by binding to T-cell factor/lymphoid enhancer factor. The binding of S1_P2 receptor to Dpr1 also led to S1P₂ receptor translocation to the nucleus, where it promoted EMT by activating CREB1. BLM-induced IPF in mice was characterised by activated-S1P₂ receptor signalling. Inhibition of S1P₂ receptor prevented the binding of S1P2 receptor to Dpr1, resulting in decreased β-catenin accumulation and blocking nuclear translocation of S1P₂ receptor. The S1P₂ receptor antagonist S118 was more effective than pirfenidone in attenuating IPF through anti-inflammatory, anti-fibrosis, and anti-EMT effects.

Conclusions and implications: Activation of S1P₂ receptors promotes IPF through the binding of S1P₂ receptor to Dpr1 and the nuclear translocation of S1P₂ receptor to activate CREB1. Thus, the S1P₂ receptor antagonist S118 has potential clinical application in attenuating IPF.

Dapper1 (Dpr1); S1P2 receptor antagonist; Sphingosine‐1‐phosphate receptor‐2 (S1P2 receptor); Wnt/β‐catenin pathway; epithelial–mesenchymal transition (EMT); idiopathic pulmonary fibrosis (IPF).