Sphingosine-1-phosphate lyase is an endogenous suppressor of pulmonary fibrosis: Role of S1P signalling and autophagy

Introduction: Idiopathic pulmonary fibrosis (IPF) is characterised by accumulation of fibroblasts and myofibroblasts and deposition of extracellular matrix proteins. Sphingosine-1-phosphate (S1P) signalling plays a critical role in pulmonary fibrosis. Methods: S1P lyase (S1PL) expression in peripheral blood mononuclear cells (PBMCs) was correlated with pulmonary functions and overall survival; used a murine model to check the role of S1PL on the fibrogenesis and a cell culture system to study the effect of S1PL expression on transforming growth factor (TGF)-β- and S1P-induced fibroblast differentiation. Results: S1PL expression was upregulated in fibrotic lung tissues and primary lung fibroblasts isolated from patients with IPF and bleomycin-challenged mice. TGF-β increased the expression of S1PL in human lung fibroblasts via activation and binding of Smad3 transcription factor to Sgpl1 promoter. Overexpression of S1PL attenuated TGF-β-induced and S1P-induced differentiation of human lung fibroblasts through regulation of the expression of LC3 and beclin1. Knockdown of S1PL (Sgpl1^+/-) in mice augmented bleomycin-induced pulmonary fibrosis, and patients with IPF reduced Sgpl1 mRNA expression in PBMCs exhibited higher severity of fibrosis and lower survival rate. Conclusion: These studies suggest that S1PL is a novel endogenous suppressor of pulmonary fibrosis in human IPF and animal models.