Sphingosine 1-phosphate receptor 1 governs endothelial barrier function and angiogenesis by upregulating endoglin signaling

Abstract

Background:The sphingosine 1-phosphate (S1P)/S1P receptor (S1pr) 1 signaling plays an essential role in regulating vascular integrity and angiogenesis. We have previously shown that cell-surface expression of endoglin (Eng) is sustained by S1P/S1pr1 signaling in endothelial cells (ECs). However, whether S1pr1 mediates Eng signaling, or vice versa, remains unknown.Methods: S1pr1 inhibitors were used to study whether pharmacological inhibition induces basal vascular leakage in vivo. An acute respiratory distress syndrome (ARDS) model was used to study whether S1pr1 inhibition evoked greater inflammation in lungs. A S1pr1 inhibitor, a bone morphogenetic protein 9 (BMP9) blocking antibody, or lentivirus-mediated expression of soluble extracellular domain of Eng (sEng) were used to test whether blocking both S1P/S1pr1 and BMP9/Eng signaling axes would impose any interaction in retinal angiogenesis. To clarify whether S1P and BMP9 function in a linear pathway, a study of transendothelial electrical resistance (TEER) measurement was carried out using a mouse islet EC line MS1; time course studies were executed to exam downstream effectors of S1P and BMP9 signaling pathways in ECs; two stable MS1 cell lines were generated, one with overexpression of human S1PR1 and the other with knockdown of Eng, to validate S1pr1 and Eng were the key players for the crosstalk. Inhibitor of extracellular regulated protein kinases (ERK) was used to check whether this signaling was involved in S1Pinduced cell-surface localization of Eng.Results: The present study elucidated that S1pr1 and Eng are both pivotal for angiogenesis in the postnatal mouse retina, and that the activation of S1pr1 or Eng increases vascular barrier function. Activation of S1pr1 enhanced the phosphorylation of Smad family members 1, 5, and 8 (pSmad1/5/8), while the inhibition of S1pr1 reduced the levels of pSma1/5/8 induced by BMP9 treatment. Activation or loss of Eng did not affect S1pr1 signaling. Moreover, activation of ERK was involved in promoting EC-surface expression of Eng by S1pr1.Conclusions: Our data demonstrates for the first time that there exists a linear pathway of S1pr1-Eng

An update on preclinical models of hereditary haemorrhagic telangiectasia: Insights into disease mechanisms

“…Additionally, shear stress potentiates BMP9-mediated ALK1 signalling by enhancing the physical interaction between ALK1 and ENG proteins, thereby lowering the EC 50 of BMP9 by approximately 17-fold ( 13 ). As sphingosine-1-phosphate (S1P)/S1PR1 signalling enhances ENG cell surface expression and BMP9-mediated ALK1 signalling ( 71 , 72 ), it is interesting to speculate that shear stress-mediated activation of S1P/S1PR may be a key player in shear stress-induced enhancement of ALK1 signalling. Furthermore, although ALK1 does not seem to interact with the classical shear stress-responsive KLF2 pathway ( 13 , 54 ), it does transduce flow signals to regulate expression of some flow-responsive genes, including cxcr4a and edn1 ( 54 ).…”