Congenital myopathy (CM) is a group of clinically and genetically heterogeneous muscle disorders, characterized by muscle weakness and hypotonia from birth. Currently, no definite treatment exists for CM. A de novo mutation in Tropomyosin 3-TPM3(E151G) was identified from a boy diagnosed with CM, previously TPM3(E151A) was reported to cause CM. However, the role of TPM3(E151G) in CM is unknown. Histopathological, swimming behavior, and muscle endurance were monitored in TPM3 wild-type and mutant transgenic fish, modelling CM. Gene expression profiling of muscle of the transgenic fish were studied through RNAseq, and mitochondria respiration was investigated. While TPM3(WT) and TPM3(E151A) fish show normal appearance, amazingly a few TPM3(E151G) fish display either no tail, a crooked body in both F0 and F1 adults. Using histochemical staining for the muscle biopsy, we found TPM3(E151G) displays congenital fiber type disproportion and TPM3(E151A) resembles nemaline myopathy. TPM3(E151G) transgenic fish dramatically swimming slower than those in TPM3(WT) and TPM3(E151A) fish measured by DanioVision and T-maze, and exhibit weaker muscle endurance by swimming tunnel instrument. Interestingly, l-carnitine treatment on TPM3(E151G) transgenic larvae significantly improves the muscle endurance by restoring the basal respiration and ATP levels in mitochondria. With RNAseq transcriptomic analysis of the expression profiling from the muscle specimens, it surprisingly discloses large downregulation of genes involved in pathways of sodium, potassium, and calcium channels, which can be rescued by l-carnitine treatment, fatty acid metabolism was differentially dysregulated in TPM3(E151G) fish and rescued by l-carnitine treatment. These results demonstrate that TPM3(E151G) and TPM3(E151A) exhibit different pathogenicity, also have distinct gene regulatory profiles but the ion channels were downregulated in both mutants, and provides a potential mechanism of action of TPM3 pathophysiology. Our results shed a new light in the future development of potential treatment for TPM3-related CM.

中文翻译：

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左旋肉碱改善原肌球蛋白 3 从头突变转基因斑马鱼的先天性肌病

先天性肌病 (CM) 是一组临床和遗传异质性肌肉疾病，其特征是出生时肌无力和肌张力减退。目前，对 CM 没有明确的治疗方法。从一名被诊断患有 CM 的男孩身上发现了原肌球蛋白 3-TPM3(E151G) 的从头突变，之前有报道称 TPM3(E151A) 会导致 CM。然而，TPM3(E151G) 在 CM 中的作用尚不清楚。在模拟 CM 的 TPM3 野生型和突变转基因鱼中监测组织病理学、游泳行为和肌肉耐力。通过RNAseq研究了转基因鱼肌肉的基因表达谱，并研究了线粒体呼吸。虽然 TPM3(WT) 和 TPM3(E151A) 鱼表现出正常的外观，但令人惊讶的是，一些 TPM3(E151G) 鱼要么没有尾巴，要么在 F0 和 F1 成年鱼中都显示出弯曲的身体。使用组织化学染色进行肌肉活检，我们发现 TPM3(E151G) 显示先天性纤维类型不成比例，TPM3(E151A) 类似于线状体肌病。TPM3(E151G) 转基因鱼的游泳速度明显慢于 DanioVision 和 T-maze 测量的 TPM3(WT) 和 TPM3(E151A) 鱼，游泳隧道仪器显示肌肉耐力较弱。有趣的是，左旋肉碱对 TPM3(E151G) 转基因幼虫的处理通过恢复线粒体中的基础呼吸和 ATP 水平显着提高了肌肉耐力。通过对肌肉标本表达谱的 RNAseq 转录组学分析，它令人惊讶地揭示了参与钠、钾和钙通道途径的基因的大量下调，这些基因可以通过左旋肉碱治疗来挽救，脂肪酸代谢在 TPM3(E151G) 鱼中存在差异性失调，并通过左旋肉碱治疗得以挽救。这些结果表明 TPM3(E151G) 和 TPM3(E151A) 表现出不同的致病性，也具有不同的基因调控谱，但两种突变体中的离子通道均下调，并提供了 TPM3 病理生理学的潜在作用机制。我们的研究结果为 TPM3 相关 CM 潜在治疗的未来发展提供了新的启示。