Fletcher G C, Xue L, Passingham S K, Tolkovsky A M
Department of Biochemistry, University of Cambridge, Cambridge, CB2 1QW, United Kingdom.
J Cell Biol. 2000 Aug 21;150(4):741-54. doi: 10.1083/jcb.150.4.741.
Axotomized neurons have several characteristics that are different from intact neurons. Here we show that, unlike established cultures, the axotomized sympathetic neurons deprived of NGF become committed to die before caspase activation, since the same proportion of NGF-deprived neurons are rescued by NGF regardless of whether caspases are inhibited by the pan-caspase inhibitor Boc-Asp(O-methyl)-CH(2)F (BAF). Despite prolonged Akt and ERK signaling induced by NGF after BAF treatment has prevented death, the neurons fail to increase protein synthesis, recover ATP levels, or grow. Within 3 d, all the mitochondria disappear without apparent removal of any other organelles or loss of membrane integrity. Although NGF does rescue intact BAF-treated 6-d cultures after NGF deprivation, rescue by NGF fails when these neurons are axotomized before NGF deprivation and BAF treatment. Moreover, cytosolic cytochrome c rapidly kills axotomized neurons. We propose that axotomy induces signals that make sympathetic neurons competent to die prematurely. NGF cannot repair these NGF-deprived, BAF-treated neurons because receptor signaling (which is normal) is uncoupled from protein renewal, and the mitochondria (which are damaged) go on to be eliminated. Hence, the order of steps underlying neuronal death commitment is mutable and open to regulation.
轴突切断的神经元具有一些与完整神经元不同的特征。我们在此表明，与已建立的培养物不同，被剥夺神经生长因子（NGF）的轴突切断的交感神经元在半胱天冬酶激活之前就注定要死亡，因为无论泛半胱天冬酶抑制剂Boc-Asp（O-甲基）-CH₂F（BAF）是否抑制半胱天冬酶，相同比例的被剥夺NGF的神经元都能被NGF挽救。尽管BAF处理后NGF诱导的Akt和ERK信号延长可防止死亡，但神经元无法增加蛋白质合成、恢复ATP水平或生长。在3天内，所有线粒体消失，而其他细胞器没有明显清除，膜完整性也没有丧失。尽管在剥夺NGF后，NGF确实能挽救完整的经BAF处理的6天龄培养物，但当这些神经元在剥夺NGF和BAF处理之前被轴突切断时，NGF的挽救作用失败。此外，胞质细胞色素c会迅速杀死轴突切断的神经元。我们提出，轴突切断会诱导信号，使交感神经元易于过早死亡。NGF无法修复这些被剥夺NGF、经BAF处理的神经元，因为受体信号传导（正常）与蛋白质更新解偶联，而受损的线粒体继续被清除。因此，神经元死亡进程的步骤顺序是可变的，且易于调控。
