Yao P M, Tabas I
Departments of Medicine and Anatomy and Cell Biology, Columbia University, New York, New York 10032, USA.
J Biol Chem. 2000 Aug 4;275(31):23807-13. doi: 10.1074/jbc.M002087200.
Macrophage death is an important feature of atherosclerosis, but the cellular mechanism for this process is largely unknown. There is increasing interest in cellular free cholesterol (FC) excess as an inducer of lesional macrophage death because macrophages accumulate large amounts of FC in vivo, and FC loading of macrophages in culture causes cell death. In this study, a cell culture model was used to explore the cellular mechanisms involved in the initial stages of FC-induced macrophage death. After 9 h of FC loading, some of the macrophages exhibited externalization of phosphatidylserine and DNA fragmentation, indicative of an apoptotic mechanism. Incubation of the cells with Z-DEVD-fluoromethylketone blocked these events, indicating dependence upon effector caspases. Macrophages from mice with mutations in either Fas or Fas ligand (FasL) demonstrated substantial resistance to FC-induced apoptosis, and FC-induced death in wild-type macrophages was blocked by an anti-FasL antibody. FC loading had no effect on the expression of cell-surface Fas but caused a small yet reproducible increase in cell-surface FasL. To determine the physiological significance of this finding, unloaded and FC-loaded Fas-deficient macrophages, which can only present FasL, were compared for their ability to induce apoptosis in secondarily added Fas-bearing macrophages. The FC-loaded macrophages were much more potent inducers of apoptosis than the unloaded macrophages, and this effect was almost completely blocked by an inhibitory anti-FasL antibody. In summary, during the early stages of FC loading of macrophages, a fraction of cells exhibited biochemical changes that are indicative of apoptosis. An important part of this event is FC-induced activation of FasL that leads to Fas-mediated apoptosis. In light of recent in vivo findings that show that apoptotic macrophages in atherosclerotic lesions express both Fas and FasL, we present a cellular model of Fas-mediated death in lesional foam cells.
巨噬细胞死亡是动脉粥样硬化的一个重要特征，但这一过程的细胞机制在很大程度上尚不清楚。细胞内游离胆固醇（FC）过量作为损伤性巨噬细胞死亡的诱导因素，受到越来越多的关注，因为巨噬细胞在体内会积累大量的FC，并且培养的巨噬细胞中FC负载会导致细胞死亡。在本研究中，使用细胞培养模型来探索FC诱导巨噬细胞死亡初始阶段所涉及的细胞机制。FC负载9小时后，一些巨噬细胞表现出磷脂酰丝氨酸外化和DNA片段化，这表明存在凋亡机制。用Z-DEVD-氟甲基酮孵育细胞可阻断这些事件，表明其依赖效应半胱天冬酶。来自Fas或Fas配体（FasL）发生突变的小鼠的巨噬细胞对FC诱导的凋亡具有显著抗性，并且野生型巨噬细胞中FC诱导的死亡可被抗FasL抗体阻断。FC负载对细胞表面Fas的表达没有影响，但导致细胞表面FasL出现小幅度但可重复的增加。为了确定这一发现的生理学意义，比较了未负载和FC负载的仅能呈递FasL的Fas缺陷型巨噬细胞在诱导二次添加的带有Fas的巨噬细胞凋亡方面的能力。FC负载的巨噬细胞比未负载的巨噬细胞更有效地诱导凋亡，并且这种效应几乎完全被抑制性抗FasL抗体阻断。总之，在巨噬细胞FC负载的早期阶段，一部分细胞表现出指示凋亡的生化变化。这一事件的一个重要部分是FC诱导的FasL激活，其导致Fas介导的凋亡。鉴于最近的体内研究结果表明动脉粥样硬化病变中的凋亡巨噬细胞同时表达Fas和FasL，我们提出了损伤性泡沫细胞中Fas介导死亡的细胞模型。
