Abstract 284: Cholesterol Handling in Bone Marrow--Derived Macrophages from Apoe-Deficient AKR and DBA/2 Mice
It has been demonstrated in humans that about 50% of the susceptibility to atherosclerosis is heritable. Therefore, it is not surprising that mice from distinct genetic backgrounds present different susceptibility to atherosclerosis. For example, apoE-/- DBA/2 mice have aortic root atherosclerosis lesion areas >10-fold larger than apoE-/- AKR mice. In order to better understand the mechanisms underlying this difference, we studied cholesterol metabolism in bone marrow-derived macrophages from these two strains. In the unloaded state, macrophages from both strains had equivalent amounts of total, esterified, and free cholesterol (TC, CE, and FC, respectively). Cells were loaded with acetylated low density lipoproteins (AcLDL) for 48h and DBA/2 macrophages had 36% higher TC (p<0.0001) vs. AKR macrophages, mainly due to 72% higher CE accumulation (p<0.0001). In contrast the loaded DBA/2 macrophages had 6% lower FC than the AKR macrophages (p<0.05). No difference was seen in AcLDL uptake or acetyl-coenzyme A acyltransferase (ACAT) activity between the two strains. When cells were loaded with AcLDL, the DBA/2 cells released cholesterol less efficiently than the AKR cells to apoAI (18% lower, p=0.01) or HDL (25% lower, p=0.001). However when the loading was performed in presence of ACAT inhibitor, blocking the formation of CE, the efflux from the two strains was equivalent suggesting a blockage of CE hydrolysis in DBA/2 cells. In loaded cells, when a 24h chase period was done in presence of ACAT inhibitor to prevent cholesterol re-esterification, the CE was reduce by 69% in AKR cells (t1/2 = 47h) compared to chase without inhibitor while it was only reduced by 42% in DBA/2 cells (t1/2 = 101h). Furthermore, when lalistat, an inhibitor of lysosomal acid lipase (LAL), and ACAT inhibitor were added during the chase, CE levels were equivalent to the one observed in chase without any inhibitors, suggesting that CE hydrolysis occurs primarily in the lysosome. In conclusion, our data support the hypothesis that DBA/2 cells accumulate more CE than AKR cells due to a defect in CE hydrolysis by LAL. Autophagy has been recently described as the pathway in macrophages by which lipid droplets can be delivered to the lysosome, and we are investigating the role of this pathway in our cells.
- © 2012 by American Heart Association, Inc.