X-linked myotubular myopathy (XLMTM) is a life-threatening skeletal muscle disease caused by mutations in the MTM1 gene. XLMTM fibres display a population of nuclei mispositioned in the centre. In the present study, we aimed to explore whether positioning and overall distribution of nuclei affects cellular organization and contractile function, thereby contributing to muscle weakness in this disease. We also assessed whether gene therapy alters nuclear arrangement and function. We used tissue from human patients and animal models, including XLMTM dogs that had received increasing doses of recombinant AAV8 vector restoring MTM1 expression (rAAV8-cMTM1). We then used single isolated muscle fibres to analyze nuclear organization and contractile function. In addition to the expected mislocalization of nuclei in the centre of muscle fibres, a novel form of nuclear mispositioning was observed: irregular spacing between those located at the fibre periphery, and an overall increased number of nuclei, leading to dramatically smaller and inconsistent myonuclear domains. Nuclear mislocalization was associated with decreases in global nuclear synthetic activity, contractile protein content and intrinsic myofilament force production. A contractile deficit originating at the myofilaments, rather than mechanical interference by centrally positioned nuclei, was supported by experiments in regenerated mouse muscle. Systemic administration of rAAV8-cMTM1 at doses higher than 2.5 × 1013 vg kg−1 allowed a full rescue of all these cellular defects in XLMTM dogs. Altogether, these findings identify previously unrecognized pathological mechanisms in human and animal XLMTM, associated with myonuclear defects and contractile filament function. These defects can be reversed by gene therapy restoring MTM1 expression in dogs with XLMTM.

中文翻译：

---

rAAV 相关治疗完全挽救 X 连锁肌管肌病中的肌核和肌丝功能

X 连锁肌管肌病 (XLMTM) 是一种由 MTM1 基因突变引起的危及生命的骨骼肌疾病。XLMTM 纤维显示了一组错误定位在中心的细胞核。在本研究中，我们旨在探索细胞核的定位和整体分布是否会影响细胞组织和收缩功能，从而导致这种疾病的肌肉无力。我们还评估了基因治疗是否会改变核排列和功能。我们使用来自人类患者和动物模型的组织，包括接受增加剂量的重组 AAV8 载体恢复 MTM1 表达 (rAAV8-cMTM1) 的 XLMTM 狗。然后我们使用单个分离的肌肉纤维来分析核组织和收缩功能。除了预期的核在肌纤维中心的错误定位外，观察到一种新形式的核错位：位于纤维外围的核之间的间距不规则，并且总体上增加的核数量，导致肌核区域显着变小和不一致。核错误定位与全球核合成活动、收缩蛋白含量和内在肌丝力产生的减少有关。源自肌丝的收缩缺陷，而不是中央定位的细胞核的机械干扰，得到了再生小鼠肌肉实验的支持。以高于 2.5 × 1013 vg kg-1 的剂量全身施用 rAAV8-cMTM1 可以完全挽救 XLMTM 狗的所有这些细胞缺陷。总之，这些发现确定了人类和动物 XLMTM 中以前未被识别的病理机制，与肌核缺陷和收缩丝功能有关。这些缺陷可以通过基因疗法在患有 XLMTM 的狗中恢复 MTM1 表达来逆转。