The role of fatty acids and caveolin-1 in tumor necrosis factor α-induced endothelial cell activation

Hypertriglyceridemia and associated high circulating free fatty acids are important risk factors for atherosclerosis. In contrast to omega-3 fatty acids, linoleic acid, the major omega-6 unsaturated fatty acid in the American diet, may be atherogenic by amplifying an endothelial inflammatory response. We hypothesize that omega-6 and omega-3 fatty acids can differentially modulate tumor necrosis factor α (TNF-α)-induced endothelial cell activation and that functional plasma membrane microdomains called caveolae are required for endothelial cell activation. Caveolae are particularly abundant in endothelial cells and play a major role in endothelial trafficking and the regulation of signaling pathways associated with the pathology of vascular diseases. To test our hypothesis, endothelial cells were preenriched with either linoleic acid or α-linolenic acid before TNF-α-induced endothelial activation. Measurements included oxidative stress and nuclear factor κB-dependent induction of cyclooxygenase-2 (COX-2) and prostaglandin E₂ (PGE₂) under experimental conditions with intact caveolae and with cells in which caveolin-1 was silenced by small interfering RNA. Exposure to TNF-α induced oxidative stress and inflammatory mediators, such as p38 mitogen-activated protein kinase (MAPK), nuclear factor κB, COX-2, and PGE₂, which were all amplified by preenrichment with linoleic acid but blocked or reduced by α-linolenic acid. The p38 MAPK inhibitor SB203580 blocked TNF-α-mediated induction of COX-2 protein expression, suggesting a regulatory mechanism through p38 MAPK signaling. Image overlay demonstrated TNF-α-induced colocalization of TNF receptor type 1 with caveolin-1. Caveolin-1 was significantly induced by TNF-α, which was further amplified by linoleic acid and blocked by α-linolenic acid. Furthermore, silencing of the caveolin-1 gene completely blocked TNF-α-induced production of COX-2 and PGE₂ and significantly reduced the amplified response of linoleic acid plus TNF-α. These data suggest that omega-6 and omega-3 fatty acids can differentially modulate TNF-α-induced inflammatory stimuli and that caveolae and its fatty acid composition play a regulatory role during TNF-α-induced endothelial cell activation and inflammation.