Sphingosine-1-phosphate receptor type 2 (S1P2) inhibits bleomycininduced cellular senescence in murine lung fibroblasts

The lysophospholipid mediator sphingosine-1-phosphate (S1P) exerts diverse biological activities including the regulation of leukocyte migration and vascular barrier integrity, suggesting that S1P signaling could be involved in inflammatory fibrotic diseases. Pulmonary fibrosis is a devastating disease characterized by fibroblast accumulation and extracellular matrix deposition in lungs, and bleomycin–induced pulmonary fibrosis is the most widely used experimental model. We studied the effects of the S1P–specific receptor S1P2 on the phenotypes of lung fibroblasts isolated from bleomycin- and saline-administered wild-type and S1P2–null (S1pr2-/-) mice. The lung fibroblasts from bleomycin-administered wild-type and S1pr2-/- mice failed to proliferate in the presence of serum, unlike fibroblasts from saline-administered mice. The fibroblasts from bleomycin-administered mice also showed the enlarged and flattened morphology compared with fibroblasts from control mice. Bleomycin administration increased the protein expression of the cell cycle inhibitor p16INK4a in fibroblasts and the number of senescence–associated β-galactosidase (SA-β-gal)-positive fibroblasts. In S1pr2-/- fibroblasts, bleomycin administration-induced increases in p16INK4a protein expression and SA–β-gal–positive cells were augmented. Furthermore, bleomycin increased mRNA expression of interleukin-6 and matrix metalloproteinases in S1pr2-/- fibroblasts compared with wild-type fibroblasts. In addition, the activation of Akt in response to platelet–derived growth factor and S1P was enhanced in S1pr2-/- fibroblasts compared with wild-type fibroblasts. These results indicate that S1P2 deletion enhances bleomycin administration–induced cellular senescence of lung fibroblasts, which may lead to inhibition of lung fibrosis through the mechanisms involving increased matrix metalloproteinases expression. Thus, S1P2 may be a novel therapeutic target for lung fibrosis