High density lipoproteins (HDL) are major plasma carriers of sphingosine 1-phosphate (S1P). Here we show that HDL increases endothelial barrier integrity as measured by electric cell substrate impedance sensing. S1P was implicated as the mediator in this process through findings showing that pertussis toxin, an inhibitor of G i -coupled S1P receptors, as well as antagonists of the S1P receptor, S1P1, inhibited barrier enhancement by HDL. Additional findings show that HDL stimulates endothelial cell activation of Erk1/2 and Akt, signaling pathway intermediates that have been implicated in S1P-dependent endothelial barrier activity. HDL was also found to promote endothelial cell motility, a process that may also relate to endothelial barrier function in the context of a vascular injury response. The effects of HDL on endothelial cell Erk1/2 and Akt activation and motility were suppressed by pertussis toxin and S1P1 antagonists. However, both HDL-induced barrier enhancement and HDL-induced motility showed a greater dependence on Akt activation as compared with Erk1/2 activation. Together, the findings indicate that HDL has endothelial barrier promoting activities, which are attributable to its S1P component and signaling through the S1P1/Akt pathway.Sphingosine 1-phosphate (S1P) 2 is a plasma-borne lysosphingolipid that has been shown to regulate endothelial barrier integrity (1). For example, treatment of cultured endothelial cells with S1P associated with the carrier albumin acts to increase endothelial barrier activity as indicated by increased transendothelial electrical resistance (2, 3). Moreover, S1P administration greatly reduces lung capillary leakage induced in mice by lipopolysaccharide treatment (4). Mechanistically, S1P acts to enhance tight junction formation in neighboring endothelial cells by influencing subcellular distributions of tight junction components including ZO-1 and claudin-5 (5). In addition, S1P induces endothelial cortical actin assembly (1) and relocation of endothelial cell junctional adhesion molecules including platelet endothelial cell adhesion molecule and vascular endothelial-cadherin to cell-cell junctional areas (5).In plasma, S1P is found associated with multiple lipoproteins including low density lipoproteins, very low density lipoproteins, and high density lipoproteins (HDL). However, the bulk of the lipoprotein particle-associated S1P (54%) is bound to HDL (6). A number of recent studies point to the S1P cargo of HDL as being a mediator of many of the cardiovascular effects of HDL including the ability to promote vasodilation, vasoconstriction, and angiogenesis, protect against ischemia/reperfusion injury, and inhibit/reverse atherosclerosis (7). One important cardiovascular-related effect of S1P that has not yet been attributed to HDL is regulation of endothelial barrier activity, a major physiological function of the endothelium. Here we investigate the role of HDL as a regulator of endothelial barrier integrity processes known to be dependent on S1P signaling. EXPERIMEN...

BackgroundThe lysosphingolipid sphingosine 1-phosphate (S1P) is carried in the blood in association with lipoproteins, predominantly high density lipoproteins (HDL). Emerging evidence suggests that many of the effects of HDL on cardiovascular function may be attributable to its S1P cargo.MethodsHere we have evaluated how levels of S1P and related sphingolipids in an HDL-containing fraction of human serum correlate with occurrence of ischemic heart disease (IHD). To accomplish this we used liquid chromatography-mass spectrometry to measure S1P levels in the HDL-containing fraction of serum (depleted of LDL and VLDL) from 204 subjects in the Copenhagen City Heart Study (CCHS). The study group consisted of individuals having high serum HDL cholesterol (HDL-C) (females:≥73.5 mg/dL; males:≥61.9 mg/dL) and verified IHD; subjects with high HDL-C and no IHD; individuals with low HDL-C (females:≤38.7 mg/dL; males:≤34.1 mg/dL) and IHD, and subjects with low HDL-C and no IHD.ResultsThe results show a highly significant inverse relationship between the level of S1P in the HDL-containing fraction of serum and the occurrence of IHD. Furthermore, an inverse relationship with IHD was also observed for two other sphingolipids, dihydro-S1P and C24:1-ceramide, in the HDL-containing fraction of serum. Additionally, we demonstrated that the amount of S1P on HDL correlates with the magnitude of HDL-induced endothelial cell barrier signaling.ConclusionsThese findings indicate that compositional differences of sphingolipids in the HDL-containing fraction of human serum are related to the occurrence of IHD, and may contribute to the putative protective role of HDL in IHD.

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We have recently established the critical importance of sphingosine‐1‐phosphate (S1P) signaling in the process of vasculogenesis. Specifically, S1P signaling influences behaviors of angioblasts and early endothelial cells (e.g., motility) that lead to expansion of embryonic vascular networks. Our current investigations focus on establishing a mechanistic basis for the motility‐related effects of S1P on angioblasts and early endothelial cells required for blood vessel formation. First, using qPCR analysis we found that S1P receptors S1P1, S1P2, S1P3, Gpr3 and Gpr63 are expressed by angioblasts and early endothelial cells with S1P1 and S1P2 expressed at highest levels. Consistent with these findings are those showing that embryonic vascular network formation is sensitive to pertussis toxin, a known inhibitor of S1P1 and S1P2‐mediated signaling. We have also established that the physiological carrier of S1P, high‐density lipoproteins (HDL), can mediate the expansion of embryonic vascular networks in a pertussis toxin‐sensitive manner. Finally, we have found that S1P acts as a modulator of filopodial extension by tip cells engaged in vascular network formation. Furthermore, that the effects of S1P on filopodial extension were found to be dependent on expression of the gap junction protein, connexin 43.