The role of membrane lipids in the induction of macrophage apoptosis by microparticles
The role of membrane lipids in the induction of macrophage apoptosis by microparticles
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DOI：
10.1007/s10495-006-0622-7
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发表时间：
2007-02-01
期刊：
影响因子：
7.2
通讯作者：
Distler, Oliver
中科院分区：
文献类型：
--
作者：
Huber, Lars C.;Juengel, Astrid;Distler, Oliver
微粒是膜衍生的囊泡，其在活化或细胞死亡期间从细胞释放。这些颗粒可以作为细胞间串扰的介质，并诱导各种细胞反应。先前的研究表明，巨噬细胞吞噬微粒后发生凋亡。在这里，我们已经解决了微粒通过脂质途径触发这一过程的假设。在这些实验中，微粒诱导原代巨噬细胞或细胞系（RAW 264.7或U937）的凋亡，增加高达5倍。用磷脂酰肌醇-3，5-二磷酸（PtdIns（3，5）BP）预孵育巨噬细胞以剂量依赖性方式减少微粒诱导的凋亡。PtdIns（3，5）BP是酸性鞘磷脂酶的特异性抑制剂，因此可以阻断促凋亡神经酰胺的产生。类似地，巨噬细胞与PtdIns（3，5）BP的预孵育防止微粒诱导的半胱天冬酶8的上调，半胱天冬酶8是细胞凋亡途径中神经酰胺作用的主要靶分子。PtdIns（3，5）BP对自发凋亡率无影响。为了评估微粒诱导的进一步信号传导途径，研究了细胞外信号调节激酶（ERK-）1。这种激酶在激活磷脂酶A2中起作用，磷脂酶A2将膜磷脂裂解为花生四烯酸;微粒已被认为是磷脂酶A2的优选底物。如我们的实验所示，微粒以时间依赖性方式强烈增加RAW 264.7巨噬细胞中磷酸化ERK 1/2的量，在共孵育后15分钟达到峰值。加入ERK 1的特异性抑制剂PD 98059可阻止RAW 264.7巨噬细胞凋亡的增加。总之，这些数据表明，微粒扰乱巨噬细胞的脂质稳态，从而诱导细胞凋亡。这些结果强调了生物脂质在免疫细胞的细胞串扰中的重要性。基于这样的事实，即在具有过度细胞死亡的临床情况下，例如恶性肿瘤、自身免疫性疾病和化疗后，高水平的循环微粒可能调节吞噬细胞，由于巨噬细胞的损失，可能发生免疫应答的抑制。
Microparticles are membrane-derived vesicles that are released from cells during activation or cell death. These particles can serve as mediators of intercellular cross-talk and induce a variety of cellular responses. Previous studies have shown that macrophages undergo apoptosis after phagocytosing microparticles. Here, we have addressed the hypothesis that microparticles trigger this process via lipid pathways. In these experiments, microparticles induced apoptosis in primary macrophage cells or cell lines (RAW 264.7 or U937) with up to a 5-fold increase. Preincubation of macrophages with phosphatidylinositol-3,5-bisphosphate (PtdIns(3,5)BP) reduced the microparticle-induced apoptosis in a dose-dependent manner. PtdIns(3,5)BP is a specific inhibitor of the acid sphingomyelinase and thus can block the generation of pro-apoptotic ceramides. Similarly, the pre-incubation of macrophages with PtdIns(3,5)BP prevented microparticle-induced upregulation of caspase 8, which is a major target molecule of ceramide action in the apoptosis pathway. PtdIns(3,5)BP, however, had no effect on the spontaneous rate of apoptosis. To evaluate further signaling pathways induced by microparticles, the extracellular signal regulated kinase (ERK-) 1 was investigated. This kinase plays a role in activating phospholipases A2 which cleaves membrane phospholipids into arachidonic acid; microparticles have been suggested to be a preferred substrate for phospholipases A2. As shown in our experiments, microparticles strongly increased the amount of phosphorylated ERK1/2 in RAW 264.7 macrophages in a time-dependent manner, peaking 15 min after co-incubation. Addition of PD98059, a specific inhibitor of ERK1, prevented the increase in apoptosis of RAW 264.7 macrophages. Together, these data suggest that microparticles perturb lipid homeostasis of macrophages and thereby induce apoptosis. These results emphasize the importance of biolipids in the cellular cross-talk of immune cells. Based on the fact that in clinical situations with excessive cell death such as malignancies, autoimmune diseases and following chemotherapies high levels of circulating microparticles might modulate phagocytosing cells, a suppression of the immune response might occur due to loss of macrophages.