Brennan M A, Cookson B T
Departments of Microbiology and Laboratory Medicine, Box 357110, University of Washington, Seattle, WA 98195, USA.
Mol Microbiol. 2000 Oct;38(1):31-40. doi: 10.1046/j.1365-2958.2000.02103.x.
We provide evidence that Salmonella typhimurium kills phagocytes by an unusual proinflammatory mechanism of necrosis that is distinguishable from apoptosis. Infection stimulated a distinctly diffuse pattern of DNA fragmentation in macrophages, which contrasted with the marked nuclear condensation displayed by control cells undergoing chemically induced apoptosis. In apoptotic cells, DNA fragmentation and nuclear condensation result from caspase-3-mediated proteolysis; caspases also subvert necrotic cell death by cleaving and inactivating poly ADP-ribose polymerase (PARP). Caspase-3 was not activated during Salmonella infection, and PARP remained in its active, uncleaved state. Another hallmark of apoptosis is sustained membrane integrity during cell death; yet, infected macrophages rapidly lost membrane integrity, as indicated by simultaneous exposure of phosphatidylserine with the uptake of vital dye and the release of the cytoplasmic enzyme lactate dehydrogenase. During experimentally induced necrosis, lethal ion fluxes through the plasma membrane can be prevented by exogenous glycine; similarly, glycine completely blocked Salmonella-induced cytotoxicity. Finally, inhibition of the interleukin (IL)-1-converting enzyme caspase-1 blocked the death of infected macrophages, but not control cells induced to undergo apoptosis or necrosis. Thus, Salmonella-infected macrophages are killed by an unusual caspase-1-dependent mechanism of necrosis.
我们提供的证据表明，鼠伤寒沙门氏菌通过一种不同于凋亡的异常促炎坏死机制杀死吞噬细胞。感染刺激巨噬细胞中出现明显弥散的DNA片段化模式，这与化学诱导凋亡的对照细胞中明显的核浓缩形成对比。在凋亡细胞中，DNA片段化和核浓缩是由caspase-3介导的蛋白水解引起的；caspase还通过切割和灭活聚ADP-核糖聚合酶（PARP）来颠覆坏死性细胞死亡。在沙门氏菌感染期间，caspase-3未被激活，PARP仍处于其活性、未切割状态。凋亡的另一个标志是细胞死亡期间膜的持续完整性；然而，受感染的巨噬细胞迅速丧失膜完整性，这通过磷脂酰丝氨酸与活性染料摄取同时暴露以及细胞质酶乳酸脱氢酶的释放得以表明。在实验诱导的坏死过程中，外源性甘氨酸可阻止致命离子通过质膜；同样，甘氨酸完全阻断了沙门氏菌诱导的细胞毒性。最后，白细胞介素（IL）-1转换酶caspase-1的抑制阻断了受感染巨噬细胞的死亡，但未阻断诱导凋亡或坏死的对照细胞的死亡。因此，受沙门氏菌感染的巨噬细胞通过一种异常的caspase-1依赖性坏死机制被杀死。
