Abstract 1455: Athero-protective Role of IL10 Involves Regulation of Lipid Metabolism in Macrophages
Introduction Previous studies utilizing interleukin (IL)10-overexpressing mice and IL10-deficient mice have demonstrated an anti-atherogenic role of IL10. Internalization of modified low density lipoprotein (LDL) that leads to foam cell formation has long been considered one of the requisite initiating events in atherogenesis. We sought to determine if IL10 exerts its anti-atherogenic effect by modulating lipid metabolism in the macrophage.
Methods & results In lipid uptake studies, IL10 substantially stimulated Dil-acetylated (Ac)LDL uptake by 187% in murine macrophage-like RAW264.7 cells. IL10 induced the expression of SR-AII and CD36 by 15.1 fold and 6.5 fold, respectively, in macrophage-derived foam cells. Moreover, CD36 protein levels were increased by IL10, suggesting that these scavenger receptors account, at least in part, for the increase in modified LDL uptake by the macrophages. Accordingly, IL10 treatment for 24hr significantly increased cholesteryl ester content by 1.5 folds compared with untreated controls (p<0.05). Interestingly, IL10 also markedly promoted ATP-binding cassette protein A1 (ABCA1)-mediated free cholesterol efflux to lipid-free apoAI acting as a cholesterol acceptor. This was peroxisome proliferator-activated receptor (PPAR)γ-dependent because specific PPARγ antagonist GW9226 completely blocked the IL10-triggered cholesterol efflux to lipid-free apoAI. In addition, expression of pro-inflammatory molecules such as TNFα, MCP-1 and iCAM-1 was dramatically inhibited by IL10 in the lipid-laden foam cells. Using immunofluorescence assay of caspase 3 fragment and TUNEL assay, we demonstrated that IL10 significantly suppressed apoptosis of foam cells (27.3 ± 2.1% for AcLDL-treated cells vs. 8.3 ± 1.0 %for AcLDL plus IL10-treated cells, n=8).
Conclusion Our results indicate that IL10 can mediate both the uptake of cholesterol from modified LDL and the efflux of stored cholesterol. Therefore, IL10 may facilitate the removal of harmful atherogenic lipoprotein molecules from the vessel wall. These characteristics along with its ability to suppress the expression of inflammatory molecules and apoptosis of foam cells make IL10 a highly anti-atherogenic agent.