Endothelial dysfunction, a hallmark of vascular disease, is restored by plasma high-density lipoprotein (HDL). However, a generalized increase in HDL abundance is not beneficial, suggesting that specific HDL species mediate protective effects. Apolipoprotein M–containing HDL (ApoM+HDL), which carries the bioactive lipid sphingosine 1-phosphate (S1P), promotes endothelial function by activating G protein–coupled S1P receptors. Moreover, HDL-bound S1P is limiting in several inflammatory, metabolic, and vascular diseases. We report the development of a soluble carrier for S1P, ApoM-Fc, which activated S1P receptors in a sustained manner and promoted endothelial function. In contrast, ApoM-Fc did not modulate circulating lymphocyte numbers, suggesting that it specifically activated endothelial S1P receptors. ApoM-Fc administration reduced blood pressure in hypertensive mice, attenuated myocardial damage after ischemia/reperfusion injury, and reduced brain infarct volume in the middle cerebral artery occlusion model of stroke. Our proof-of-concept study suggests that selective and sustained targeting of endothelial S1P receptors by ApoM-Fc could be a viable therapeutic strategy in vascular diseases.

Ceramides are sphingolipids that modulate a variety of cellular processes via 2 major mechanisms: functioning as second messengers and regulating membrane biophysical properties, particularly lipid rafts, important signaling platforms. Altered sphingolipid levels have been implicated in many cardiovascular diseases, including hypertension, atherosclerosis, and diabetes mellitus–related conditions; however, molecular mechanisms by which ceramides impact endothelial functions remain poorly understood. In this regard, we generated mice defective of endothelial sphingolipid de novo biosynthesis by deleting the Sptlc2 (long chain subunit 2 of serine palmitoyltransferase)—the first enzyme of the pathway. Our study demonstrated that endothelial sphingolipid de novo production is necessary to regulate (1) signal transduction in response to NO agonists and, mainly via ceramides, (2) resting eNOS (endothelial NO synthase) phosphorylation, and (3) blood pressure homeostasis. Specifically, our findings suggest a prevailing role of C16:0-Cer in preserving vasodilation induced by tyrosine kinase and GPCRs (G-protein coupled receptors), except for Gq-coupled receptors, while C24:0- and C24:1-Cer control flow-induced vasodilation. Replenishing C16:0-Cer in vitro and in vivo reinstates endothelial cell signaling and vascular tone regulation. This study reveals an important role of locally produced ceramides, particularly C16:0-, C24:0-, and C24:1-Cer in vascular and blood pressure homeostasis, and establishes the endothelium as a key source of plasma ceramides. Clinically, specific plasma ceramides ratios are independent predictors of major cardiovascular events. Our data also suggest that plasma ceramides might be indicative of the diseased state of the endothelium.

We recently discovered that endothelial Nogo-B, a membrane protein of the ER, regulates vascular function by inhibiting the rate-limiting enzyme, serine palmitoyltransferase (SPT), in de novo sphingolipid biosynthesis. Here, we show that endothelium-derived sphingolipids, particularly sphingosine-1-phosphate (S1P), protect the heart from inflammation, fibrosis, and dysfunction following pressure overload and that Nogo-B regulates this paracrine process. SPT activity is upregulated in banded hearts in vivo as well as in TNF-α–activated endothelium in vitro, and loss of Nogo removes the brake on SPT, increasing local S1P production. Hence, mice lacking Nogo-B, systemically or specifically in the endothelium, are resistant to the onset of pathological cardiac hypertrophy. Furthermore, pharmacological inhibition of SPT with myriocin restores permeability, inflammation, and heart dysfunction in Nogo-A/B–deficient mice to WT levels, whereas SEW2871, an S1P1 receptor agonist, prevents myocardial permeability, inflammation, and dysfunction in WT banded mice. Our study identifies a critical role of endothelial sphingolipid biosynthesis and its regulation by Nogo-B in the development of pathological cardiac hypertrophy and proposes a potential therapeutic target for the attenuation or reversal of this clinical condition.

Bioactive sphingolipids are emerging as key regulators of vascular function and homeostasis. While most of the clinical studies have been devoted to profile circulating sphingolipids in maternal plasma, little is known about the role of the sphingolipid at the feto-placental vasculature, which is in direct contact with the offspring circulation. Our study aims to compare the sphingolipid profile of normal with preeclamptic (PE) placental chorionic arteries and isolated endothelial cells, with the goal of unveiling potential underlying pathomechanisms in the vasculature. Dihydrosphingosine and sphingomyelin (SM) concentrations (C16:0-, C18:0-, and C24:0- sphingomyelin) were significantly increased in chorionic arteries of preeclamptic placentas, whereas total ceramide, although showing a downward trend, were not statistically different. Moreover, RNA and immunofluorescence analysis showed impaired sphingosine-1-phosphate (S1P) synthesis and signaling in PE vessels. Our data reveal that the exposure to a deranged maternal intrauterine environment during PE alters the sphingolipid signature and gene expression on the fetal side of the placental vasculature. This pathological remodeling consists in increased serine palmitoyltransferase (SPT) activity and SM accrual in PE chorionic arteries, with concomitance impairment endothelial S1P signaling in the endothelium of these vessels. The increase of endothelial S1P phosphatase, lyase and S1PR2, and blunted S1PR1 expression support the onset of the pathological phenotype in chorionic arteries.