TNF-alpha-induced endothelium-independent vasodilation: a role for phospholipase A2-dependent ceramide signaling.
Ceramide is a novel second messenger generated by hydrolysis of membrane sphingomyelin by a neutral sphingomyelinase (nSMase). Cytokines such as tumor necrosis factor-alpha (TNF-alpha) have been shown to increase intracellular ceramide through phospholipase A2 (PLA2)-dependent activation of nSMase. TNF-alpha has been shown to cause endothelium-independent relaxation in isolated blood vessels. We have previously shown that exogenously applied sphingomyelinase and ceramide cause endothelium-independent vasodilation in rat thoracic aortas (D. G. Johns, H. Osborn, and R. C. Webb. Biochem. Biophys. Res. Commun. 237: 95-97, 1997). In the present study, we tested the hypothesis that ceramide mediates TNF-alpha-induced vasodilation. In phenylephrine-contracted rat thoracic aortic rings (no endothelium), TNF-alpha caused concentration-dependent relaxation in the presence of cyclooxygenase and lipoxygenase inhibitors. The phospholipase A2 antagonist 7,7-dimethyl-(5Z, 8Z)-eicosadienoic acid (DEDA; 50 microM) and the nonselective PLA2 antagonist quinacrine (30 microM) inhibited TNF-alpha-induced relaxation. In cultured rat aortic vascular smooth muscle cells, TNF-alpha (10(-7) g/ml) increased intracellular ceramide 1.5-fold over basal level (0.08 nmol/mg protein), which was blocked by the PLA2 antagonist DEDA (50 microM). We conclude that PLA2 activation and increased ceramide generation play a role in mediating TNF-alpha-induced endothelium-independent vasodilation.
Johns
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DG
Department of Physiology, University of Michigan, Ann Arbor, Michigan 48109, USA.
Webb
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RC
D000818:Animals; D001013:Aorta, Thoracic / Q000502:physiology*; D002518:Ceramides / Q000502:physiology*; D004730:Endothelium, Vascular / Q000502:physiology; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology; D008297:Male; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D010741:Phospholipases A / Q000037:antagonists & inhibitors / Q000502:physiology*; D054467:Phospholipases A2; D011796:Quinacrine / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*; D014664:Vasodilation / Q000187:drug effects / Q000502:physiology*
D002518:Ceramides; D005231:Fatty Acids, Unsaturated; D010726:Phosphodiesterase Inhibitors; D014409:Tumor Necrosis Factor-alpha; C059778:7,7-dimethyl-5,8-eicosadienoic acid; D010741:Phospholipases A; D054467:Phospholipases A2; D011796:Quinacrine