Abstract 5475: A Novel Lipase, Neutral Cholesteryl Ester Hydrolase, is a Major Regulator of Neutral Cholesteryl Ester Hydrolysis in Murine Macrophages.
Macrophage-derived foam cells, which contain excessive cholesteryl esters (CEs), play integral roles in the pathogenesis of atherosclerosis. The breakdown of the accumulated CEs is controlled by the neutral cholesteryl ester hydrolase (nCEH), although the molecular identity has long been debated. Several observations suggested that hormone-sensitive lipase (HSL) might account for the nCEH. However, additional nCEH(s) is suggested since peritoneal macrophages of HSL−/− mice still show nCEH activity. We identified a novel nCEH in macrophages (NCEH; neutral cholesteryl ester hydrolase), and generated NCEH−/− mice to gain insights into the physiological roles. NCEH accounted for approximately 50% of the nCEH activity in peritoneal macrophages (NCEH+/+: 38.9±1.8 pmol/min/mg vs NCEH−/−: 19.1±1.0 pmol/min/mg, n=7–8). Upon exposure to acetylated low density lipoprotein (acLDL), the intracellular CE content was increased by 50% (NCEH+/+: 36.3±3.7 μg/mg vs NCEH−/−: 55.1±5.2 μg/mg, n=7) and CE formation from [14C] oleate was increased 2 fold in NCEH−/−. Cholesterol efflux from NCEH−/− was decreased by 35% (NCEH+/+: 38.9±2.9% vs NCEH−/−: 24.8±1.2%, n=5). When NCEH−/− mice were crossbred with apoE−/− mice, the offspring demonstrated an increase of atherosclerotic lesion development without affecting the serum lipids (2.2 fold increase analyzed by en face aorta analysis, and 1.8 fold increase analyzed by cross-sectional analysis, n=10–15). Furthermore, we crossbred NCEH−/− mice with HSL−/− mice. The nCEH activity in the NCEH/HSL double deficient (DKO) macrophages was reduced to approximately 10% of that in wild-type macrophages (WT: 37.9±1.9 pmol/min/mg vs DKO: 4.8±0.4 pmol/min/mg, n=6–7). Deficiencies in NCEH and HSL had an additive effect in the CE accumulation upon exposure to acLDL and in cholesterol efflux. Acyl-CoA:cholesterol acyl-transferase activity in the DKO macrophages was reduced to 55% of that in wild-type. Neither NCEH nor HSL affected lipoprotein uptake and degradation. In conclusion, a novel lipase, NCEH, contributes to macrophage nCEH in vitro and to atherosclerotic lesion development in vivo. NCEH and HSL are the major nCEHs in macrophages and account for 90% of nCEH activity in murine macrophages.