Interaction of free apolipoproteins with macrophages. Formation of high density lipoprotein-like lipoproteins and reduction of cellular cholesterol

• Published in: The Journal of biological chemistry 1991-02, Vol.266 (5), p.3080-3086
• Main Authors: HARA, H, YOKOYAMA, S
• Format: Article
• Language: English
• Subjects: Analytical, structural and metabolic biochemistry; Animals; Apolipoproteins - metabolism; Biological and medical sciences; Cholesterol - metabolism; Electrophoresis, Agar Gel; Female; Fundamental and applied biological sciences. Psychology; Humans; Hydrolysis; Lipoproteins, HDL - metabolism; Lipoproteins, myelin; Macrophages - metabolism; Male; Mice; Phospholipids - metabolism; Proteins; Ultracentrifugation
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/S0021-9258(18)49957-7

Mouse peritoneal macrophages, loaded with cholesteryl ester by incubating with acetylated human low density lipoprotein containing [3H]cholesteryl oleate, were exposed to purified human apolipoproteins (apo) A-I, A-II, C-III, or E in aqueous solutions. Unesterified cholesterol was released into the medium in the presence of apoA-I, -A-II, or -E, accompanied by the decrease in intracellular cholesteryl ester. ApoC-III had no such effects. Apparent Km values of the cholesterol release were estimated as 0.11, 0.14, and 0.24 microM, and Vmax values 35, 11, and 14 micrograms of cholesterol/mg of cell protein/6 h, for apoA-I, -A-II, and -E, respectively. The products formed with apoA-I, -A-II, or -E in the media were analyzed by density gradient ultracentrifugation when the cells were preloaded with [3H]cholesteryl oleate-acetylated low density lipoproteins and [3H]choline. Free [3H]cholesterol, [3H]phosphatidylcholine, and [3H]sphingomyelin were detected coincidentally as a symmetric peak at the density of 1.1 in each case. In the complex of lipids and apoA-I or apoA-II, the weight ratios of apolipoprotein/cholesterol/phosphatidylcholine/sphingomyelin/lysophosphatidyl- choline were estimated as 2.2:1:0.6:0.2:0.07 and 4.0:1:0.5:0.3:0.07, respectively. Both of the products formed with apoA-I and -A-II migrated slower than plasma high density lipoprotein in electrophoresis on agarose gel. Because the Km values are as low as 1:340-400, 1:140-160, and 1:6-8 of plasma concentrations of apoA-I, -A-II, and -E, respectively, the results have physiological relevance for a function of the free apolipoproteins in interstitial fluid to form high density lipoprotein and to reduce cellular cholesterol.