Sphingosine Kinase–Dependent Activation of Endothelial Nitric Oxide Synthase by Angiotensin II

Abstract

Objective-In addition to their role in programmed cell death, cell survival, and cell growth, sphingolipid metabolites such as ceramide, sphingosine, and sphingosine-1-phosphate have vasoactive properties. Besides their occurrence in blood, they can also be formed locally in the vascular wall itself in response to external stimuli. This study was performed to investigate whether vasoactive compounds modulate sphingolipid metabolism in the vascular wall and how this might contribute to the vascular responses. Methods and Results-In isolated rat carotid arteries, the contractile responses to angiotensin II are enhanced by the sphingosine kinase inhibitor dimethylsphingosine. Endothelium removal or NO synthase inhibition by N -nitro-Larginine results in a similar enhancement. Angiotensin II concentration-dependently induces NO production in an endothelial cell line, which can be diminished by dimethylsphingosine. Using immunoblotting and intracellular calcium measurements, we demonstrate that this sphingosine kinase-dependent endothelial NO synthase activation is mediated via both phosphatidylinositol 3-kinase/Akt and calcium-dependent pathways. Sphingomyelinase catalyzes the hydrolysis of sphingomyelin to form ceramide. 1,2 The sequential action of ceramidase and sphingosine kinase converts ceramide to sphingosine and sphingosine-1-phosphate (S1P), and ceramide synthase and S1P phosphatase can reverse this process to form ceramide from S1P. 3,4 The sphingomyelin metabolites ceramide, sphingosine, and S1P are biologically active mediators that play important roles in cellular homeostasis. In this regard, ceramide and sphingosine on the one hand and S1P on the other hand frequently have opposite biological effects. For example, ceramide and sphingosine are generally involved in apoptotic responses to various stress stimuli and in growth arrest, 5,6 whereas S1P is implicated in mitogenesis, differentiation, and migration. 7,8 This homeostatic system is frequently referred to as the ceramide/S1P rheostat. 9 It can be hypothesized that this rheostat also plays a role in vascular contraction and relaxation because S1P, sphingosine, and ceramide are potentially counteracting, vasoactive compounds. 10,11 The molecular basis of ceramide effects has not been explored fully but is believed to involve stress-activated protein kinases, protein phosphatases such as protein phosphatases 1 and 2, guanylyl cyclase, and charybdotoxinsensitive K ϩ channels. 11,12 The molecular basis of S1P effects has been characterized in more detail. S1P can act on specific G protein-coupled receptors, of which 5 subtypes have been identified thus far, termed S1P 1-5 . These receptors couple to intracellular second messenger systems including intracellular Ca 2ϩ , adenylyl cyclase, phospholipase C, phosphatidylinositol 3 (PI3)-kinase, protein kinase Akt, mitogen-activated protein kinases, and Rho-and Ras-dependent pathways. 13 The cardiovascular system primarily expresses the receptor subtypes S1P 1-3 , and within the vasculature they are express...

Sphingosine-1-Phosphate-Induced Inflammation Involves Receptor Tyrosine Kinase Transactivation in Vascular Cells

“…6,16 -19 S1P is generated from membrane phospholipids in various cell types, and its production is stimulated by many vasoactive factors, including angiotensin II. 20 In the vasculature, the precise distribution of S1P receptors has still not been clearly established, although S1P1, S1P2, and S1P3 seem to be expressed in vascular cells, with endothelial cells expressing primarily S1P1 and S1P3 and VSMCs expressing S1P1, S1P2, and S1P3. 4 -8,21-26 In the present study, we found that S1P1 and S1P2 but not S1P3 receptors are present in VSMCs from WKYs and SHRSPs.…”

Signaling pathway involved in the inhibitory effect of FTY720P on the Na+/K+ ATPase in HepG2 cells

“…For instance, eNOS activation by TNF-α in human endothelial cells was blocked by inhibitors of sphingomyelinase, sphingosine kinase, and blockers of S1P receptors (Mulders et al 2006). This work showed that ERK is another mediator of FTY720P's action on the pump.…”

Sphingosine-1-Phosphate–Dependent Activation of p38 MAPK Maintains Elevated Peripheral Resistance in Heart Failure Through Increased Myogenic Vasoconstriction

“…For example, Gschwend et al showed that blockade of AT 1 receptors with angiotensin receptor blockers reversed the increased myogenic constriction observed in HF in rat, 7 suggesting participation of RAS, which has also been linked directly (and indirectly via NADPH oxidase-derived ROS 48 ) to Sphk-dependent vasomotor effects in isolated vessel preparations from nondiseased animals 20,49 and to p38 MAPK activation in VSMCs. 48 Further studies will be needed to dissect the precise contributions of RAS, other neurohormones, or even cytokines implicated in HF such as tumor necrosis factor-␣, 50 to Sphk activity, 51,52 S1P receptor expression, 52 and myogenic responses.…”