Barbaras R, Grimaldi P, Negrel R, Ailhaud G
Biochim Biophys Acta. 1986 Sep 19;888(2):143-56. doi: 10.1016/0167-4889(86)90015-7.
Binding of high-density lipoproteins to cultured mouse Ob1771 adipose cells was studied, using labeled human HDL3, mouse HDL and apolipoprotein AI- or AII-containing liposomes. In each case, saturation curves were obtained, yielding linear Scatchard plots. The Kd values were found to be respectively 18, 42, 30 and 3.4 micrograms/ml, whereas the maximal binding capacities were found to be 160, 100, 90 and 21 ng/mg of cell protein. Apoprotein AI not inserted into liposomes did not bind. The binding of 125I-HDL3 was competitively inhibited by apolipoprotein AI-containing liposomes greater than mouse HDL greater than HDL3. The binding of 125I-labeled apolipoprotein AI- and 125I-labeled apolipoprotein AII-containing liposomes was competitively inhibited by HDL3, apolipoprotein AI- and apolipoprotein AII-containing liposomes. Dimyristoylphosphatidylcholine liposomes containing or not cholesterol did not interfere with the binding of labeled HDL3 or apolipoprotein-containing liposomes. Binding studies on crude membranes of Ob1771 adipose cells revealed the presence of intracellular binding sites for LDL and HDL3. Thus, adipose cells have specific binding sites for apolipoprotein E-free HDL and apolipoprotein AI (or AII) is the ligand for these binding sites. Long-term exposure of adipose cells to LDL cholesterol as a function of LDL concentration led to an accumulation of cellular unesterified cholesterol. This process was saturable and reversible as a function of time and concentration by exposure to HDL3 or apolipoprotein AI-containing liposomes, whereas apolipoprotein AII-containing liposomes did not promote any cholesterol efflux. Since long-term exposure of adipose cells to LDL and HDL3 did not affect the number of apolipoprotein B,E receptors and apolipoprotein E-free binding sites, respectively, it appears that adipose cells do not show efficient cholesterol homeostasis and thus could accumulate or mobilize unesterified cholesterol.
利用标记的人HDL3、小鼠HDL以及含载脂蛋白AI或AII的脂质体，研究了高密度脂蛋白与培养的小鼠Ob1771脂肪细胞的结合情况。在每种情况下，均获得了饱和曲线，并得出线性Scatchard图。发现Kd值分别为18、42、30和3.4微克/毫升，而最大结合容量分别为160、100、90和21纳克/毫克细胞蛋白。未插入脂质体的载脂蛋白AI不发生结合。含载脂蛋白AI的脂质体对125I-HDL3结合的竞争性抑制作用大于小鼠HDL大于HDL3。含125I标记的载脂蛋白AI和含125I标记的载脂蛋白AII的脂质体的结合受到HDL3、含载脂蛋白AI和含载脂蛋白AII的脂质体的竞争性抑制。含有或不含胆固醇的二肉豆蔻酰磷脂酰胆碱脂质体不干扰标记的HDL3或含载脂蛋白脂质体的结合。对Ob1771脂肪细胞粗膜的结合研究揭示了存在LDL和HDL3的细胞内结合位点。因此，脂肪细胞具有无载脂蛋白E的HDL的特异性结合位点，且载脂蛋白AI（或AII）是这些结合位点的配体。脂肪细胞长期暴露于LDL胆固醇，其胆固醇积累量随LDL浓度而变化。通过暴露于HDL3或含载脂蛋白AI的脂质体，该过程在时间和浓度方面是可饱和且可逆的，而含载脂蛋白AII 的脂质体则不促进任何胆固醇流出。由于脂肪细胞长期暴露于LDL和HDL3分别不影响载脂蛋白B、E受体和无载脂蛋白E结合位点的数量，因此看来脂肪细胞未表现出有效的胆固醇稳态，从而可能积累或动员未酯化胆固醇。
