Knight B L, Patel D D, Soutar A K
Biochem J. 1983 Feb 15;210(2):523-32. doi: 10.1042/bj2100523.
Human blood monocytes cultured in medium containing 20% whole serum showed the greatest activity of 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase and [14C]acetate incorporation into non-saponifiable lipids around the 7th day after seeding, the period of greatest growth. Although there was enough low-density lipoprotein (LDL) in the medium to saturate the LDL receptors that were expressed by normal cells at that time, HMG-CoA reductase activity and acetate incorporation were as high in normal cells as in cells from familial-hypercholesterolaemic (FH) patients. Both the addition of extra LDL, which interacted with the cells by non-saturable processes, and receptor-mediated uptake of acetylated LDL significantly reduced reductase activity and increased incorporation of [14C]oleate into cholesteryl esters in normal cells and cells from FH patients ('FH cells'), and reduced the expression of LDL receptors in normal cells. Pre-incubation for 20h in lipoprotein-deficient medium apparently increased the number of LDL receptors expressed by normal cells but reduced the activity of HMG-CoA reductase in both normal and FH cells. During subsequent incubations the same rate of degradation of acetylated LDL and of non-saturable degradation of LDL by FH cells was associated with the same reduction in HMG-CoA reductase activity, although LDL produced a much smaller stimulation of oleate incorporation into cholesteryl esters. In normal cells pre-incubated without lipoproteins, receptor-mediated uptake of LDL could abolish reductase activity and the expression of LDL receptors. The results suggested that in these cells, receptor-mediated uptake of LDL might have a greater effect on reductase activity and LDL receptors than the equivalent uptake of acetylated LDL. It is proposed that endogenous synthesis is an important source of cholesterol for growth of normal cells, and that the site at which cholesterol is deposited in the cells may determine the nature and extent of the metabolic events that follow.
在含有20%全血清的培养基中培养的人血单核细胞，在接种后第7天左右，即生长最旺盛的时期，显示出3-羟基-3-甲基戊二酰辅酶A（HMG-CoA）还原酶的最大活性以及[14C]乙酸盐掺入非皂化脂质的量最大。尽管培养基中存在足够的低密度脂蛋白（LDL）以饱和当时正常细胞所表达的LDL受体，但正常细胞中的HMG-CoA还原酶活性和乙酸盐掺入量与家族性高胆固醇血症（FH）患者的细胞一样高。额外添加通过非饱和过程与细胞相互作用的LDL以及受体介导的乙酰化LDL摄取，均显著降低了正常细胞和FH患者细胞（“FH细胞”）中的还原酶活性，并增加了[14C]油酸酯掺入胆固醇酯的量，同时降低了正常细胞中LDL受体的表达。在无脂蛋白培养基中预孵育20小时，显然增加了正常细胞所表达的LDL受体数量，但降低了正常细胞和FH细胞中HMG-CoA还原酶的活性。在随后的孵育过程中，FH细胞对乙酰化LDL的降解速率和对LDL的非饱和降解速率相同，与HMG-CoA还原酶活性的降低程度相同，尽管LDL对油酸酯掺入胆固醇酯的刺激作用要小得多。在未用脂蛋白预孵育的正常细胞中，受体介导的LDL摄取可消除还原酶活性和LDL受体的表达。结果表明，在这些细胞中，受体介导的LDL摄取对还原酶活性和LDL受体的影响可能比等量的乙酰化LDL摄取更大。有人提出，内源性合成是正常细胞生长所需胆固醇的重要来源，并且胆固醇在细胞中的沉积部位可能决定随后代谢事件的性质和程度。
