Table_1_Mitochondrial Dysfunction Is an Early Consequence of Partial or Complete Dystrophin Loss in mdx Mice.XLSX

Duchenne muscular dystrophy (DMD) is characterized by rapid wasting of skeletal muscle. Mitochondrial dysfunction is a well-known pathological feature of DMD. However, whether mitochondrial dysfunction occurs before muscle fiber damage in DMD pathology is not well known. Furthermore, the impact upon heterozygous female mdx carriers (mdx/+), who display dystrophin mosaicism, has received little attention. We hypothesized that dystrophin deletion leads to mitochondrial dysfunction, and that this may occur before myofiber necrosis. As a secondary complication to mitochondrial dysfunction, we also hypothesized metabolic abnormalities prior to the onset of muscle damage. In this study, we detected aberrant mitochondrial morphology, reduced cristae number, and large mitochondrial vacuoles from both male and female mdx mice prior to the onset of muscle damage. Furthermore, we systematically characterized mitochondria during disease progression starting before the onset of muscle damage, noting additional changes in mitochondrial DNA copy number and regulators of mitochondrial size. We further detected mild metabolic and mitochondrial impairments in female mdx carrier mice that were exacerbated with high-fat diet feeding. Lastly, inhibition of the strong autophagic program observed in adolescent mdx male mice via administration of the autophagy inhibitor leupeptin did not improve skeletal muscle pathology. These results are in line with previous data and suggest that before the onset of myofiber necrosis, mitochondrial and metabolic abnormalities are present within the mdx mouse.

杜氏肌营养不良症（Duchenne muscular dystrophy, DMD）以骨骼肌快速萎缩为典型特征，线粒体功能障碍是公认的DMD病理特征。然而，在DMD的病理进程中，线粒体功能障碍是否先于肌纤维损伤发生，目前仍未得到明确阐释。此外，表现出肌营养不良蛋白（dystrophin）镶嵌现象的杂合雌性mdx携带者（mdx/+），其相关病理影响却鲜少受到关注。我们提出两项假说：其一，肌营养不良蛋白缺失会引发线粒体功能障碍，且该过程可能早于肌纤维坏死出现；其二，作为线粒体功能障碍的继发并发症，肌肉损伤发作前也可存在代谢异常。在本研究中，我们于肌肉损伤发作前的雄性与雌性mdx小鼠体内，检测到异常线粒体形态、减少的线粒体嵴数量以及大型线粒体空泡。此外，我们从肌肉损伤发作前便开始系统表征疾病进程中的线粒体特征，观测到线粒体DNA拷贝数与线粒体大小调控因子出现额外变化。我们还在雌性mdx携带者小鼠中检测到轻度代谢与线粒体损伤，且该损伤会因高脂饮食喂养而加剧。最后，通过给予自噬抑制剂亮肽素（leupeptin）抑制青春期雄性mdx小鼠中观测到的强自噬程序，但并未改善其骨骼肌病理状况。上述结果与既往研究数据相符，表明在肌纤维坏死发作前，mdx小鼠体内已存在线粒体与代谢异常。