Brown M S, Goldstein J L, Krieger M, Ho Y K, Anderson R G
J Cell Biol. 1979 Sep;82(3):597-613. doi: 10.1083/jcb.82.3.597.
Mouse peritoneal macrophages accumulate large amounts of cholesteryl ester when incubated with human low-density lipoprotein that has been modified by chemical acetylation (acetyl-LDL). This accumulation is related to a high-affinity cell surface binding site that mediates the uptake of acetyl-LDL by adsorptive endocytosis and its delivery to lysosomes. The current studies demonstrate that the cholesteryl ester accumulation can be considered in terms of a two-compartment model: (a) the incoming cholesteryl esters of acetyl-LDL are hydrolyzed in lysosomes, and (b) the resultant free cholesterol is re-esterified in the cytosol where the newly formed esters are stored as lipid droplets. The following biochemical and morphologic evidence supports the hydrolysis-re-esterification mechanism: (a) Incubation of macrophages with acetyl-LDL markedly increased the rate of cholesteryl ester synthesis from [14C]oleate, and this was accompanied by an increase in the acyl-CoA:cholesteryl acyltransferase activity of cell-free extracts. (b) When macrophages were incubated with reconstituted acetyl-LDL in which the endogenous cholesterol was replaced with [3H]-cholesteryl linoleate, the [3H]cholesteryl linoleate was hydrolyzed, and at least one-half of the resultant [3H]cholesterol was re-esterified to form [3H]cholesteryl oleate, which accumulated within the cell. The lysosomal enzyme inhibitor chloroquine inhibited the hydrolysis of the [3H]cholesteryl linoleate, thus preventing the formation of [3H]cholesteryl oleate and leading to the accumulation of unhydrolyzed [3H]cholesteryl linoleate within the cells. (c) In the electron microscope, macrophages incubated with acetyl-LDL had numerous cytoplasmic lipid droplets that were not surrounded by a limiting membrane. The time course of droplet accumulation was similar to the time course of cholesteryl ester accumulation as measured biochemically. (d) When acetyl-LDL was removed from the incubation medium, biochemical and morphological studies showed that cytoplasmic cholesteryl esters were rapidly hydrolyzed and that the resultant free cholesterol was excreted from the cell.
当与经化学乙酰化修饰的人低密度脂蛋白（乙酰化低密度脂蛋白，acetyl-LDL）一起孵育时，小鼠腹腔巨噬细胞会积累大量胆固醇酯。这种积累与一种高亲和力的细胞表面结合位点有关，该位点通过吸附性胞吞作用介导乙酰化低密度脂蛋白的摄取并将其递送至溶酶体。当前的研究表明，胆固醇酯的积累可以用双室模型来解释：（a）乙酰化低密度脂蛋白进入的胆固醇酯在溶酶体中被水解，（b）产生的游离胆固醇在细胞质中重新酯化，新形成的酯以脂滴的形式储存。以下生化和形态学证据支持水解 - 重新酯化机制：（a）巨噬细胞与乙酰化低密度脂蛋白孵育显著增加了[14C]油酸酯合成胆固醇酯的速率，同时无细胞提取物的酰基辅酶A：胆固醇酰基转移酶活性也增加。（b）当巨噬细胞与用[3H] - 亚油酰胆固醇酯替代内源性胆固醇的重组乙酰化低密度脂蛋白一起孵育时，[3H] - 亚油酰胆固醇酯被水解，至少一半产生的[3H]胆固醇重新酯化形成[3H] - 油酰胆固醇酯，并在细胞内积累。溶酶体酶抑制剂氯喹抑制了[3H] - 亚油酰胆固醇酯的水解，从而阻止了[3H] - 油酰胆固醇酯的形成，并导致未水解的[3H] - 亚油酰胆固醇酯在细胞内积累。（c）在电子显微镜下，与乙酰化低密度脂蛋白孵育的巨噬细胞有许多没有被界膜包围的细胞质脂滴。脂滴积累的时间进程与生化测量的胆固醇酯积累的时间进程相似。（d）当从孵育培养基中去除乙酰化低密度脂蛋白时，生化和形态学研究表明细胞质胆固醇酯迅速水解，产生的游离胆固醇从细胞中排出。
