Background-Sphingosine-1-phosphate (S1P) signaling is a central regulator of resistance artery tone. Therefore, S1P levels need to be tightly controlled through the delicate interplay of its generating enzyme sphingosine kinase 1 and its functional antagonist S1P phosphohydrolase-1. The intracellular localization of S1P phosphohydrolase-1 necessitates the import of extracellular S1P into the intracellular compartment before its degradation. The present investigation proposes that the cystic fibrosis transmembrane conductance regulator transports extracellular S1P and hence modulates microvascular S1P signaling in health and disease. Methods and Results-In cultured murine vascular smooth muscle cells in vitro and isolated murine mesenteric and posterior cerebral resistance arteries ex vivo, the cystic fibrosis transmembrane conductance regulator (1) is critical for S1P uptake; (2) modulates S1P-dependent responses; and (3) is downregulated in vitro and in vivo by tumor necrosis factor-␣, with significant functional consequences for S1P signaling and vascular tone. In heart failure, tumor necrosis factor-␣ downregulates the cystic fibrosis transmembrane conductance regulator across several organs, including the heart, lung, and brain, suggesting that it is a fundamental mechanism with implications for systemic S1P effects. Conclusions-We identify the cystic fibrosis transmembrane conductance regulator as a critical regulatory site for S1P signaling; its tumor necrosis factor-␣-dependent downregulation in heart failure underlies an enhancement in microvascular tone. This molecular mechanism potentially represents a novel and highly strategic therapeutic target for cardiovascular conditions involving inflammation. (Circulation. 2012;125:2739-2750.)Key Words: acute myocardial infarction Ⅲ hemodynamics Ⅲ myogenic vasoconstriction Ⅲ signal transduction Ⅲ vasomotor tone S phingosine-1-phosphate (S1P) is a ubiquitous signaling mediator that directs a diverse array of biological processes. 1 In the microcirculation, S1P is a potent vasoconstrictor and a central mediator regulating myogenic tone. [2][3][4][5] This confers S1P signaling with significant importance in the control of blood flow autoregulation, tissue perfusion, and systemic blood pressure. Editorial see p 2692 Clinical Perspective on p 2750The potent and pleiotropic effects of S1P are confined both spatially and temporally 6 ; however, the molecular mechanisms limiting S1P bioavailability are not completely understood. We have demonstrated that S1P phosphohydrolase-1 (SPP1), an intracellular enzyme primarily localized to the endoplasmic reticulum, 7,8 degrades extracellular S1P. 3 As a consequence, we concluded that an S1P "import" mechanism must be present in vascular smooth muscle cells. Boujaoude et al 9 have provided indirect evidence that the cystic fibrosis transmembrane conductance regulator (CFTR) could act as this S1P transporter and thereby limit S1P receptor-mediated effects. Accordingly, we have observed that CFTR inhibition specifically enhance...

S ubarachnoid hemorrhage (SAH) affects ≈10 in 100 000 people/y.1 Although SAH accounts for only 5% to 10% of all strokes, it is particularly devastating: half of all SAH patients die within 1 month and half of those who survive will require life-long assistance for daily living (ie, ≈75% of patients die or are seriously debilitated).2,3 The poor clinical outcome can be attributed to the biphasic course of the disease, characterized by an initial hemorrhagic stroke that is frequently followed by delayed cerebral ischemia (DCI) within 4 to 12 days. 4,5 The latter is a primary therapeutic concern when treating SAH, because DCI causes at least half of the morbidity and mortality in SAH. 2The transition from the hemorrhagic insult to secondary ischemia is driven by prominent changes in cerebrovascular reactivity, which compromises cerebral autoregulation 6,7 and evokes angiographic vasospasm (ie, radiographically identifiable arterial narrowing in the proximal cerebrovascular circulation).2,8 Conceptually, both events originate from augmentedBackground and Purpose-Subarachnoid hemorrhage (SAH) is a complex stroke subtype characterized by an initial brain injury, followed by delayed cerebrovascular constriction and ischemia. Current therapeutic strategies nonselectively curtail exacerbated cerebrovascular constriction, which necessarily disrupts the essential and protective process of cerebral blood flow autoregulation. This study identifies a smooth muscle cell autocrine/paracrine signaling network that augments myogenic tone in a murine model of experimental SAH: it links tumor necrosis factor-α (TNFα), the cystic fibrosis transmembrane conductance regulator, and sphingosine-1-phosphate signaling. Methods-Mouse olfactory cerebral resistance arteries were isolated, cannulated, and pressurized for in vitro vascular reactivity assessments. Cerebral blood flow was measured by speckle flowmetry and magnetic resonance imaging. Standard Western blot, immunohistochemical techniques, and neurobehavioral assessments were also used. Results-We demonstrate that targeting TNFα and sphingosine-1-phosphate signaling in vivo has potential therapeutic application in SAH. Both interventions (1) eliminate the SAH-induced myogenic tone enhancement, but otherwise leave vascular reactivity intact; (2) ameliorate SAH-induced neuronal degeneration and apoptosis; and (3) improve neurobehavioral performance in mice with SAH. Furthermore, TNFα sequestration with etanercept normalizes cerebral perfusion in SAH. Conclusions-Vascular smooth muscle cell TNFα and sphingosine-1-phosphate signaling significantly enhance cerebral artery tone in SAH; anti-TNFα and anti-sphingosine-1-phosphate treatment may significantly improve clinical outcome.

The S1P 2 receptor is a member of a family of G protein-coupled receptors that bind the extracellular sphingolipid metabolite sphingosine 1-phosphate with high affinity. The receptor is widely expressed and linked to multiple G protein signaling pathways, but its physiological function has remained elusive. Here we have demonstrated that S1P 2 receptor expression is essential for proper functioning of the auditory and vestibular systems. Auditory brainstem response analysis revealed that S1P 2 receptor-null mice were deaf by one month of age. These null mice exhibited multiple inner ear pathologies. However, some of the earliest cellular lesions in the cochlea were found within the stria vascularis, a barrier epithelium containing the primary vasculature of the inner ear. Between 2 and 4 weeks after birth, the basal and marginal epithelial cell barriers and the capillary bed within the stria vascularis of the S1P 2 receptor-null mice showed markedly disturbed structures. JTE013, an S1P 2 receptor-specific antagonist, blocked the S1P-induced vasoconstriction of the spiral modiolar artery, which supplies blood directly to the stria vascularis and protects its capillary bed from high perfusion pressure. Vascular disturbance within the stria vascularis is a potential mechanism that leads to deafness in the S1P 2 receptor-null mice. Sphingosine 1-phosphate (S1P)3 is a sphingolipid metabolite that functions as a signaling ligand through interactions with G protein-coupled S1P receptors. Five high affinity receptors (S1P 1 -S1P 5 ) have been described that trigger distinctive intracellular signaling pathways (1, 2) following binding of the S1P ligand. Three of these receptors, S1P 1 , S1P 2 , and S1P 3 , are widely expressed on cells and tissues, whereas expression of the S1P 4 and S1P 5 receptors are largely confined to cells of the immune and nervous systems. The ligand S1P is produced through the phosphorylation of sphingosine by sphingosine kinases 1 and 2 and can be degraded by S1P-specific enzymes that include phosphatases and a lyase (3). Micromolar levels of the S1P ligand, bound primarily to high density lipoproteins, are found in plasma and may provide a source for tonic signaling. Acute S1P signaling may result from enhanced secretion of S1P from cells, such as platelets and mast cells, upon activation.Genetic deletion of receptors within mice has been an important means of identifying the physiologic roles of S1P receptor signaling. These studies have demonstrated that the signaling pathways are biologically significant and potentially clinically relevant within the vascular (4 -6), immune (7, 8), pulmonary (9), and nervous systems (10).Here we report that S1P 2 receptor expression is essential for proper functioning of the auditory and vestibular systems. S1P 2 receptor-null mice exhibit profound deafness early in life with severe associated pathologic changes within the cochlea. Early cellular defects were found to be in the stria vascularis, a compartment that harbors the main vasculature of the inner ea...