Metabolism of cholesteryl ester lipid droplets in a J774 macrophage foam cell model.
J774 macrophages rapidly incorporated [3H]cholesteryl oleate droplets by a non-saturable phagocytic process. In less than 2 h, foam cell morphology was acquired. The extent of loading obtained after 2 h was a linear function of the mass of cholesteryl oleate provided to the cells. The cholesteryl oleate incorporated was hydrolyzed in the cells at a linear rate over 24 h and the fractional hydrolysis was constant over a wide range of cellular esterified cholesterol contents. The rate of hydrolysis was influenced by the physical state of the cholesteryl ester; cholesteryl oleate in isotropic droplets was hydrolyzed 2-3-fold more rapidly than cholesteryl oleate in anisotropic droplets. The hydrolysis of both types of droplets was inhibited by lysosomotropic agents, indicating that hydrolysis occurred in the lysosomes. Only a small fraction (less than 10% after 24 h) of the free [3H]cholesterol generated in the lysosomes was esterified by ACAT resulting in a doubling of the cell free cholesterol content. Electron microscopy of cells treated with digitonin revealed the accumulation of free cholesterol in lipid-laden lysosomes. ACAT was active as endogenous free [14C]cholesterol was esterified in a linear manner over 24 h and was responsive to the presence of lysosomally-derived cholesterol, as the extent of esterification of the endogenous pool was directly proportional to the mass of [3H]cholesterol generated in the lysosomes.
Mahlberg
F H
FH
Department of Physiology and Biochemistry, Medical College of Pennsylvania, Philadelphia 19129.
Glick
J M
JM
Jerome
W G
WG
Rothblat
G H
GH
D000818:Animals; D001692:Biological Transport; D002451:Cell Compartmentation; D002460:Cell Line; D002784:Cholesterol / Q000378:metabolism; D002788:Cholesterol Esters / Q000378:metabolism*; D005487:Foam Cells / Q000378:metabolism* / Q000648:ultrastructure; D006868:Hydrolysis; D066298:In Vitro Techniques; D007700:Kinetics; D008247:Lysosomes / Q000378:metabolism; D008264:Macrophages / Q000378:metabolism*; D051379:Mice; D008854:Microscopy, Electron
D002788:Cholesterol Esters; D002784:Cholesterol