Tabas I, Marathe S, Keesler G A, Beatini N, Shiratori Y
Department of Medicine, Columbia University College of Physicians and Surgeons, New York, New York 10032, USA.
J Biol Chem. 1996 Sep 13;271(37):22773-81. doi: 10.1074/jbc.271.37.22773.
Macrophages in atherosclerotic lesions accumulate free cholesterol (FC) as well as cholesteryl ester and appear to have high rates of phospholipid (PL) synthesis and increased PL mass. Previous short term (i.e. </=24 h) studies with cultured macrophages have shown that these cells respond to FC loading by up-regulating phosphatidylcholine biosynthesis. We propose that this response is adaptive by keeping the FC:PL ratio in the macrophages from reaching toxic levels. We further propose that one cause of macrophage necrosis, a prominent and important event in atherosclerosis, is an eventual decrease of this adaptive response. To explore these ideas, cultured macrophages were loaded with FC for up to 4 days and assayed for phosphatidylcholine biosynthesis, FC and PL mass, and cytotoxicity. For the first 24 h, cellular phosphatidylcholine biosynthesis and FC and PL mass increased 3-4-fold, and thus the FC:PL molar ratio was prevented from reaching very high levels; at this point, there were no overt signs of cytotoxicity. Over the next 24-48 h, however, phosphatidylcholine biosynthesis, and then phosphatidylcholine mass, began to decrease. Initially, the macrophages remained healthy and continued to accumulate FC, but eventually these macrophages, but not unloaded macrophages, became necrotic (swollen organelles and disrupted membranes). Lipoprotein dose studies indicated a close relationship between the onset of macrophage necrosis and the FC:PL ratio. To test further the causal nature of these relationships, cellular FC and PL mass were independently manipulated by using high density lipoprotein3 (HDL3) to decrease cellular FC and choline depletion to decrease cellular PC. As predicted by our hypotheses, HDL3 protected FC-loaded macrophages from necrosis, whereas choline depletion accelerated cytotoxic changes. These findings support the idea that the initial increase in phosphatidylcholine biosynthesis in FC-loaded macrophages is an adaptive response that prevents cholesterol-induced macrophage necrosis. We propose that an eventual failure of the PL response in foam cells may represent one cause of macrophage necrosis in advanced atherosclerotic lesions.
动脉粥样硬化病变中的巨噬细胞会积累游离胆固醇（FC）以及胆固醇酯，并且似乎具有较高的磷脂（PL）合成速率和增加的PL质量。先前对培养巨噬细胞进行的短期（即≤24小时）研究表明，这些细胞通过上调磷脂酰胆碱生物合成来响应FC负载。我们提出，这种反应具有适应性，可使巨噬细胞中的FC:PL比值不至于达到毒性水平。我们还提出，巨噬细胞坏死是动脉粥样硬化中一个突出且重要的事件，其一个原因是这种适应性反应最终会减弱。为了探究这些观点，将培养的巨噬细胞用FC负载长达4天，并检测磷脂酰胆碱生物合成、FC和PL质量以及细胞毒性。在最初的24小时内，细胞磷脂酰胆碱生物合成以及FC和PL质量增加了3 - 4倍，因此FC:PL摩尔比值被阻止达到非常高的水平；此时，没有明显的细胞毒性迹象。然而，在接下来的24 - 48小时内，磷脂酰胆碱生物合成，然后是磷脂酰胆碱质量开始下降。最初，巨噬细胞仍保持健康并继续积累FC，但最终这些巨噬细胞（而非未负载FC的巨噬细胞）发生坏死（细胞器肿胀和膜破裂）。脂蛋白剂量研究表明巨噬细胞坏死的发生与FC:PL比值密切相关。为了进一步检验这些关系的因果性质，通过使用高密度脂蛋白3（HDL3）降低细胞FC以及胆碱耗竭降低细胞PC来独立调节细胞FC和PL质量。正如我们的假设所预测的，HDL3保护负载FC的巨噬细胞免于坏死，而胆碱耗竭加速了细胞毒性变化。这些发现支持了这样一种观点，即负载FC的巨噬细胞中磷脂酰胆碱生物合成的初始增加是一种适应性反应，可防止胆固醇诱导的巨噬细胞坏死。我们提出，泡沫细胞中PL反应最终失效可能是晚期动脉粥样硬化病变中巨噬细胞坏死的一个原因。
