S1PR3 Inhibition in alveolar epithelial cells alleviates pulmonary fibrosis by enhancing alveolar barrier function.

BACKGROUND: Pulmonary fibrosis (PF) is a chronic and progressive respiratory disease characterized by the destruction of the alveolar-capillary barrier. Repeated injury and abnormal repair of alveolar epithelial cells lead to barrier dysfunction and fibroblast activation. The sphingosine-1-phosphate (S1P) and sphingosine-1-phosphate receptor (S1PR) signaling pathways are critical for regulating physiological barrier function. Among the five receptor subtypes, S1PR3 is highly expressed in alveolar epithelial cells, especially after injury, but its specific role in PF remains unclear. METHODS: Public single-cell RNA sequencing datasets were analyzed to examine S1PR3 expression in idiopathic pulmonary fibrosis (IPF) patients. The expression pattern of S1PR3 was validated in bleomycin (BLM)-induced PF mice. To explore its functional role, lung epithelial-specific S1pr3 conditional knockout mice were generated. In vitro, S1PR3 expression was knocked down by siRNA or inhibited by the selective antagonist TY52156 to evaluate its effect on epithelial barrier integrity and tight junction proteins. RESULTS: S1PR3 expression was markedly upregulated in the epithelial cells of both IPF patients and BLM-induced fibrotic mice. Epithelial-specific deletion of S1pr3 significantly attenuated fibrosis, as evidenced by reduced inflammatory cytokine levels, decreased collagen deposition, and improved alveolar-capillary barrier integrity. Furthermore, pharmacological or genetic inhibition of S1PR3 enhanced the expression of tight junction proteins, including ZO-1, Occludin, and Claudin-4, thereby mitigating epithelial barrier disruption. CONCLUSIONS: S1PR3 in alveolar epithelial cells plays a critical role in maintaining alveolar-capillary barrier integrity during pulmonary fibrosis. Targeted inhibition of S1PR3 strengthens tight junctions and alleviates inflammation, suggesting that S1PR3 may serve as a promising therapeutic target for PF.