Maintaining mitochondrial function and dynamics is crucial for cellular health. In muscle, defects in mitochondria result in severe myopathies where accumulation of damaged mitochondria causes deterioration and dysfunction. Importantly, understanding the role of mitochondria in disease is a necessity to determine future therapeutics. One of the most common myopathies is mitochondrial encephalopathy lactic acidosis stroke-like episodes (MELAS), which has no current treatment. Recently, MELAS patients treated with rapamycin exhibited improved clinical outcomes. However, the cellular mechanisms of rapamycin effects in MELAS patients are currently unknown. In this study, we used cultured skin fibroblasts as a window into the mitochondrial dysfunction evident in MELAS cells, as well as to study the mechanisms of rapamycin action, compared to control, healthy individuals. We observed that mitochondria from patients were fragmented, had a 3-fold decline in the average speed of motility, a 2-fold reduced mitochondrial membrane potential and a 1.5-2-fold decline in basal respiration. Despite the reduction in mitochondrial function, mitochondrial import protein Tim23 was elevated in patient cell lines. MELAS fibroblasts exhibited increased MnSOD levels and lysosomal function when compared to healthy controls. Treatment of MELAS fibroblasts with rapamycin for 24 hrs resulted in increased mitochondrial respiration compared to control cells, a higher lysosome content, and a greater localization of mitochondria to lysosomes. Our studies suggest that rapamycin has the potential to improve cellular health even in the presence of mtDNA defects, primarily via an increase in lysosomal content.

中文翻译：

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雷帕霉素对mtDNA突变患者成纤维细胞线粒体和溶酶体的影响

维持线粒体功能和动力学对细胞健康至关重要。在肌肉中，线粒体缺陷会导致严重的肌病，其中受损线粒体的积累会导致退化和功能障碍。重要的是，了解线粒体在疾病中的作用是确定未来治疗方法的必要条件。最常见的肌病之一是线粒体脑病乳酸性酸中毒中风样发作 (MELAS)，目前尚无治疗方法。最近，用雷帕霉素治疗的 MELAS 患者表现出改善的临床结果。然而，雷帕霉素在 MELAS 患者中作用的细胞机制目前尚不清楚。在这项研究中，我们使用培养的皮肤成纤维细胞作为了解 MELAS 细胞中明显线粒体功能障碍的窗口，并研究了雷帕霉素与对照相比的作用机制，健康的个体。我们观察到患者的线粒体是碎片化的，平均运动速度下降了 3 倍，线粒体膜电位下降了 2 倍，基础呼吸下降了 1.5-2 倍。尽管线粒体功能降低，但患者细胞系中线粒体输入蛋白 Tim23 升高。与健康对照相比，MELAS 成纤维细胞表现出更高的 MnSOD 水平和溶酶体功能。与对照细胞相比，用雷帕霉素处理 MELAS 成纤维细胞 24 小时导致线粒体呼吸增加，溶酶体含量更高，以及线粒体对溶酶体的更大定位。我们的研究表明，即使存在 mtDNA 缺陷，雷帕霉素也有可能改善细胞健康，主要是通过增加溶酶体含量。