Schröder Rolf, Goudeau Bertrand, Simon Monique Casteras, Fischer Dirk, Eggermann Thomas, Clemen Christoph S, Li Zhenlin, Reimann Jens, Xue Zhigang, Rudnik-Schöneborn Sabine, Zerres Klaus, van der Ven Peter F M, Fürst Dieter O, Kunz Wolfram S, Vicart Patrick
Department of Neurology, University Hospital Bonn, Sigmund-Freud-Str. 25, 53105 Bonn, Germany.
Hum Mol Genet. 2003 Mar 15;12(6):657-69. doi: 10.1093/hmg/ddg060.
Recent studies in desmin (-/-) mice have shown that the targeted ablation of desmin leads to pathological changes of the extrasarcomeric intermediate filament cytoskeleton, as well as structural and functional abnormalities of mitochondria in striated muscle. Here, we report on a novel heterozygous single adenine insertion mutation (c.5141_5143insA) in a 40-year-old patient with a distal myopathy. The insertion mutation leads to a frameshift and a truncated desmin (K239fs242). Using transfection studies in SW13 and BHK21 cells, we show that the K239fsX242 desmin mutant is incapable of forming a desmin intermediate filament network. Furthermore, it induces the collapse of a pre-existing desmin cytoskeleton, alters the subcellular distribution of mitochondria and leads to abnormal cytoplasmic protein aggregates reminiscent of desmin-immunoreactive granulofilamentous material seen in the ultrastructural analysis of the patient's muscle. Analysis of mitochondrial function in isolated saponin-permeablized skeletal muscle fibres from our patient showed decreased maximal rates of respiration with the NAD-dependent substrate combination glutamate and malate, as well as a higher amytal sensitivity of respiration, indicating an in vivo inhibition of complex I activity. Our findings suggest that the heterozygous K239fsX242 desmin insertion mutation has a dominant negative effect on the polymerization process of desmin intermediate filaments and affects not only the subcellular distribution, but also biochemical properties of mitochondria in diseased human skeletal muscle. As a consequence, the intermediate filament pathology-induced mitochondrial dysfunction may contribute to the degeneration/regeneration process leading to progressive muscle dysfunction in human desminopathies.
近期对结蛋白基因敲除（-/-）小鼠的研究表明，结蛋白的靶向缺失会导致肌节外中间丝细胞骨架发生病理变化，以及横纹肌中线粒体的结构和功能异常。在此，我们报告了一名患有远端肌病的40岁患者中，存在一种新型的杂合单腺嘌呤插入突变（c.5141_5143insA）。该插入突变导致移码并产生截短的结蛋白（K239fs242）。通过在SW13和BHK21细胞中的转染研究，我们发现K239fsX242结蛋白突变体无法形成结蛋白中间丝网络。此外，它会诱导预先存在的结蛋白细胞骨架塌陷，改变线粒体的亚细胞分布，并导致异常的细胞质蛋白聚集体，这类似于在患者肌肉的超微结构分析中看到的结蛋白免疫反应性颗粒状丝状物质。对我们患者分离的皂素通透化骨骼肌纤维中线粒体功能的分析表明，使用依赖于NAD的底物组合谷氨酸和苹果酸时，呼吸的最大速率降低，以及呼吸对阿米妥的敏感性更高，表明体内复合物I活性受到抑制。我们的研究结果表明，杂合的K239fsX242结蛋白插入突变对结蛋白中间丝的聚合过程具有显性负性作用，不仅影响亚细胞分布，还影响患病人类骨骼肌中线粒体的生化特性。因此，中间丝病理诱导的线粒体功能障碍可能有助于导致人类结蛋白病中进行性肌肉功能障碍的变性/再生过程。
