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

Abstract

Hypertriglyceridemia and associated high circulating free fatty acids are important risk factors of 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 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 pre-enriched with either linoleic acid or α-linolenic acid prior to TNF-α-induced endothelial activation. Measurements included oxidative stress and NF-κB-dependent induction of COX-2 and PGE2 under experimental conditions with intact caveolae and with cells in which caveolin-1 was silenced by siRNA. Exposure to TNF-α induced oxidative stress and inflammatory mediators, such as p38 MAPK, NF-κB, COX-2 and PGE2, which were all amplified by pre-enrichment 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 co-localization of TNF receptor type 1 (TNFR-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.

NFĸB is an Unexpected Major Mediator of Interleukin-15 Signaling in Cerebral Endothelia

“…We showed that TNF suppressed claudin-2 expression in cerebral endothelia; however, TNF acts through NF B and increases claudin-2 in HT-29/B6 human colon cells [44]. Nonetheless, the TNF-induced increase of caveolin [48] and decrease of occludin expression in endothelial cells [49] is consistent with our results. We chose the hCMEC/ D3 cell line as a model system since TNF activates NF B in these cells and they express TNF receptors [50,51].…”

Time‐dependent regulation of muscle caveolin activation and insulin signalling in response to high‐fat diet

“…Cav-1 is also slightly upregulated, as reported by other authors using similar diets [22]. This early response of Cav-1 could be related to the high amount of cholesterol and the overload of fatty acids in the diet [22], but also to the release of the inflammatory cytokine TNF-alpha [23]. Therefore, we suggest that, in this prompt response, insulin-related pathways might be activated by a coordinated mechanism mediated by both caveolins and IR, in an attempt to effectively fight against the excess of dietary nutrients in order to maintain glucose balance.…”

Fatty acids and postprandial inflammation

“…As a result, the anti-inflammatory effects of n-3 PUFA are counteracted by the proinflammatory effects of n-6 PUFA. This hypothesis has been confirmed in a recently published elegant study where endothelial cells in vitro were preexposed to either linoleic acid (n-6 PUFA) or a-linolenic acid (n-3 PUFA) and subsequently exposed to TNF-a [37]. Cells preexposed to linoleic acid (the n-6 PUFA precursor molecule) had an increase of their response to the proinflammatory cytokine TNF-a including induction of p38 mitogen-activated protein kinase (MAPK), NF-kB, COX-2, and PGE2.…”