Hyperoxia-induced S1P signaling reduced angiogenesis by suppression of TIE-2 leading to experimental bronchopulmonary dysplasia.

Introduction: We have earlier shown that hyperoxia (HO)-induced sphingosine kinase 1 (SPHK1)/sphingosine-1-phosphate (S1P) signaling contribute to bronchopulmonary dysplasia (BPD). S1P acts through G protein-coupled receptors, S1P through S1P. Further, we noted that heterozygous deletion of S1pr1 ameliorated the HO-induced BPD in the murine model. The mechanism by which S1P signaling contributes to HO-induced BPD was explored.

Methods: S1pr1 and S1pr1 mice pups were exposed to either room air (RA) or HO (75% oxygen) for 7 days from PN 1-7. Lung injury and alveolar simplification was evaluated. Lung protein expression was determined by Western blotting and immunohistochemistry (IHC). In vitro experiments were performed using human lung microvascular endothelial cells (HLMVECs) with S1P inhibitor, NIBR0213 to interrogate the S1P signaling pathway.

Results: HO increased the expression of S1pr1 gene as well as S1P protein in both neonatal lungs and HLMVECs. The S1pr1 neonatal mice showed significant protection against HO-induced BPD which was accompanied by reduced inflammation markers in the bronchoalveolar lavage fluid. HO-induced reduction in ANG-1, TIE-2, and VEGF was rescued in S1pr1 mouse, accompanied by an improvement in the number of arterioles in the lung. HLMVECs exposed to HO increased the expression of KLF-2 accompanied by reduced expression of TIE-2, which was reversed with S1P inhibition.

Conclusion: HO induces S1P followed by reduced expression of angiogenic factors. Reduction of S1P signaling restores ANG-1/ TIE-2 signaling leading to improved angiogenesis and alveolarization thus protecting against HO-induced neonatal lung injury.