Abstract 17092: Apolipoprotein-A1 (ApoA-1) Diminishes Lipid Raft Content and Reduces Vascular Inflammation
Background: Although it is known the inflammatory effects of free-fatty acids are mediated via Toll-Like Receptor 4 (TLR4) and NF-κB signaling, the mechanism by which High Density Lipoprotein (HDL) attenuates this response remains unclear. Cholesterol rich lipid rafts are critical platforms for TLR4 signaling. ApoA-1, the primary protein component in HDL, sequesters cholesterol. Consequently we propose that ApoA-1 can attenuate diet-induced vascular inflammation and that this is mediated via its affects on lipid rafts.
Methods/Results: C57BL/6 wild-type (WT) and ApoA-1 transgenic mice were fed a chow or a Diabetogenic Diet with Cholesterol (DDC) for 24 weeks. Their aortic tissues were analyzed for markers of NF-κB activation including IL-6 and MCP-1 expression. The DDC fed WT mice had a significant up-regulation in NF-κB signaling. This was accompanied by a robust increase in lipid raft content as measured by Caveolin-1 and Flotillin-1, known lipid raft markers. This lipid raft response was abrogated in the DDC fed ApoA-1 transgenic mice. Moreover these mice were protected from vascular inflammation. In vitro, we show palmitate (C16:0)-treated human microvascular endothelial cells (HMECs) recruit TLR4 into lipid rafts. This is associated with NF-κB activation as measured by increased IL-6 production and expression of cell adhesion molecules. To test if disruption of lipid rafts is sufficient to inhibit palmitate-induced inflammation, we treated HMECs with methyl-β cyclodextrin (MβCD), a pharmacologic agent that sequesters cholesterol thereby disrupting lipid rafts. MβCD significantly reduces fluorescent-conjugated Cholera-toxin-B (CTX-B) staining, an alternative measurement of lipid raft content. MβCD also inhibits palmitate recruitment of TLR4 into lipid rafts subsequently impairing its pro-inflammatory response. We also show that ApoA-1 mimics MβCD's effects in endothelial cells. Like MβCD, ApoA-1 reduces CTX-B staining. In addition, it attenuates palmitate-induced NF-κB activation.
Conclusion: The present study demonstrates that ApoA-1 diminishes lipid raft content and attenuates diet-induced vascular inflammation, possibly via impaired TLR4 signaling.
- © 2010 by American Heart Association, Inc.