Tidball J G, Albrecht D E, Lokensgard B E, Spencer M J
Department of Physiological Science, University of California, Los Angeles 90024-1527, USA.
J Cell Sci. 1995 Jun;108 ( Pt 6):2197-204. doi: 10.1242/jcs.108.6.2197.
The current view that death of dystrophin-deficient muscle fibers is a necrotic process relies primarily upon the histological appearance of the tissue after the degenerative process is well advanced. Here, we tested this view by examining the possibility that apoptosis is a component of dystrophin-deficient muscle cell death. Three assays for apoptosis were employed in analyzing prenecrotic, peak necrotic and regenerated hindlimb muscle of mdx mice: (1) terminal deoxynucleotidyl transferase (TdT) mediated end-labeling of DNA in nuclei in tissue sections; (2) assays for DNA ladders; and (3) electron microscopic assays for the presence of organelles undergoing structural changes characteristic of apoptosis. At all ages sampled, mdx muscle contained apoptotic nuclei, according to TdT-mediated dUTP labeling of tissue sections. Nuclei in regenerated mdx muscle fibers did not display apoptosis. dUTP-labeled nuclei in control C57 muscles were rare or absent at all ages sampled. DNA from 4-week-old mdx mice was found to be cleaved into fragments indicative of preferential cleavage at internucleosomal sites. Electron microscopic analysis showed that organelle structural changes indicating apoptosis appear before pathological changes diagnostic of necrosis. For example, condensed mitochondria, fragmented sarcoplasmic reticulum and nuclei with chromatin condensations resembling apoptosis appear in fibers that otherwise possess normal morphology. Together, the findings show that apoptosis precedes any detectable necrotic change in mdx muscle, and that apoptotic events continue into the stage of dystrophic pathology that is currently viewed as necrosis. Thus, apoptosis characterizes the onset of pathology in dystrophin-deficient muscle which is followed secondarily by necrotic processes.
目前认为抗肌萎缩蛋白缺乏的肌纤维死亡是一个坏死过程，这一观点主要基于退行性变过程充分进展后组织的组织学表现。在此，我们通过研究凋亡是否是抗肌萎缩蛋白缺乏的肌肉细胞死亡的一个组成部分来检验这一观点。我们采用了三种凋亡检测方法来分析mdx小鼠坏死前期、坏死高峰期和再生期的后肢肌肉：（1）末端脱氧核苷酸转移酶（TdT）介导的组织切片细胞核中DNA的末端标记；（2）DNA梯状条带检测；（3）通过电子显微镜检测是否存在具有凋亡特征性结构变化的细胞器。在所检测的所有年龄段，根据TdT介导的组织切片dUTP标记，mdx肌肉中均含有凋亡细胞核。再生的mdx肌纤维中的细胞核未显示凋亡。在所有检测的年龄段，对照C57肌肉中dUTP标记的细胞核很少见或不存在。发现4周龄mdx小鼠的DNA被切割成片段，表明在核小体间位点有优先切割。电子显微镜分析表明，指示凋亡的细胞器结构变化出现在诊断坏死的病理变化之前。例如，在形态 otherwise 正常的纤维中出现了线粒体浓缩、肌浆网断裂以及染色质浓缩类似凋亡的细胞核。总之，这些发现表明凋亡先于mdx肌肉中任何可检测到的坏死变化出现，并且凋亡事件持续到目前被视为坏死的营养不良病理阶段。因此，凋亡是抗肌萎缩蛋白缺乏肌肉病理发生的特征，其次才是坏死过程。
