Domazetovska Ana, Ilkovski Biljana, Kumar Vikash, Valova Valentina A, Vandebrouck Aurelie, Hutchinson David O, Robinson Phillip J, Cooper Sandra T, Sparrow John C, Peckham Michelle, North Kathryn N
Institute for Neuromuscular Research, Children's Hospital at Westmead, New South Wales, Australia.
Ann Neurol. 2007 Dec;62(6):597-608. doi: 10.1002/ana.21200.
Mutations in the alpha-skeletal actin gene (ACTA1) result in a variety of inherited muscle disorders characterized by different pathologies and variable clinical phenotypes. Mutations at Val163 in ACTA1 result in pure intranuclear rod myopathy; however, the molecular mechanisms by which mutations at Val163 lead to intranuclear rod formation and muscle weakness are unknown.
We investigated the effects of the Val163Met mutation in ACTA1 in tissue culture and Drosophila models, and in patient muscle. In cultured cells, the mutant actin tends to aggregate rather than incorporate into cytoplasmic microfilaments, and it affects the dynamics of wild-type actin, causing it to accumulate with the mutant actin in the nucleus. In Drosophila, the Val163Met mutation severely disrupts the structure of the muscle sarcomere. The intranuclear aggregates in patient muscle biopsies impact on nuclear structure and sequester normal Z-disc-associated proteins within the nucleus; however, the sarcomeric structure is relatively well preserved, with evidence of active regeneration. By mass spectrometry, the levels of mutant protein are markedly reduced in patient muscle compared with control.
Data from our tissue culture and Drosophila models show that the Val163Met mutation in alpha-skeletal actin can affect the dynamics of other actin isoforms and severely disrupt sarcomeric structure, processes that can contribute to muscle weakness. However, in human muscle, there is evidence of regeneration, and the mutant protein tends to aggregate rather than incorporate into cytoplasmic microfilaments in cells. These are likely compensatory processes that ameliorate the effects of the mutant actin and contribute to the milder clinical and pathological disease phenotype.
α-骨骼肌动蛋白基因（ACTA1）突变会导致多种遗传性肌肉疾病，其特征为不同的病理表现和多样的临床表型。ACTA1基因第163位缬氨酸（Val）发生突变会导致单纯核内杆状体肌病；然而，第163位Val突变导致核内杆状体形成和肌肉无力的分子机制尚不清楚。
我们在组织培养、果蝇模型以及患者肌肉中研究了ACTA1基因Val163Met突变的影响。在培养细胞中，突变型肌动蛋白倾向于聚集而不是整合到细胞质微丝中，并且它会影响野生型肌动蛋白的动力学，导致其与突变型肌动蛋白在细胞核中积累。在果蝇中，Val163Met突变严重破坏了肌肉肌节的结构。患者肌肉活检中的核内聚集体影响核结构，并在核内隔离正常的Z盘相关蛋白；然而，肌节结构相对保存完好，有活跃再生的迹象。通过质谱分析，与对照组相比，患者肌肉中突变蛋白的水平明显降低。
我们组织培养和果蝇模型的数据表明，α-骨骼肌动蛋白中的Val163Met突变会影响其他肌动蛋白异构体的动力学，并严重破坏肌节结构，这些过程可能导致肌肉无力。然而，在人类肌肉中，有再生的证据，并且突变蛋白在细胞中倾向于聚集而不是整合到细胞质微丝中。这些可能是补偿过程，可减轻突变型肌动蛋白的影响，并导致临床和病理疾病表型较轻。
