Institute of Medical Biotechnology, Friedrich-Alexander-University Erlangen-Nürnberg, Paul-Gordan-Str. 3, 91052 Erlangen, Bavaria, Germany.
Graduate School in Advanced Optical Technologies, Paul-Gordan-Str. 6, 91052 Erlangen, Bavaria, Germany.
Int J Mol Sci. 2020 Jul 31;21(15):5501. doi: 10.3390/ijms21155501.
Muscle biomechanics relies on active motor protein assembly and passive strain transmission through cytoskeletal structures. The desmin filament network aligns myofibrils at the z-discs, provides nuclear-sarcolemmal anchorage and may also serve as memory for muscle repositioning following large strains. Our previous analyses of R349P desmin knock-in mice, an animal model for the human R350P desminopathy, already depicted pre-clinical changes in myofibrillar arrangement and increased fiber bundle stiffness. As the effect of R349P desmin on axial biomechanics in fully differentiated single muscle fibers is unknown, we used our to compare passive visco-elasticity and active contractile biomechanics in single fibers from fast- and slow-twitch muscles from adult to senile mice, hetero- or homozygous for the R349P desmin mutation with wild type littermates. We demonstrate that R349P desmin presence predominantly increased axial stiffness in both muscle types with a pre-aged phenotype over wild type fibers. Axial viscosity and Ca2+-mediated force were largely unaffected. Mutant single fibers showed tendencies towards faster unloaded shortening over wild type fibers. Effects of aging seen in the wild type appeared earlier in the mutant desmin fibers. Our single-fiber experiments, free of extracellular matrix, suggest that compromised muscle biomechanics is not exclusively attributed to fibrosis but also originates from an impaired intermediate filament network.
肌肉生物力学依赖于通过细胞骨架结构主动的运动蛋白组装和被动的应变传递。结蛋白丝网络将肌原纤维定位于 Z 盘，提供核-肌膜锚定，并且在经受大应变后，可能也有助于肌肉重新定位的记忆。我们之前对 R349P 结蛋白敲入小鼠（一种人类 R350P 结蛋白病的动物模型）的分析已经描述了肌原纤维排列的临床前变化和纤维束刚度的增加。由于 R349P 结蛋白对完全分化的单肌纤维的轴向生物力学的影响尚不清楚，我们使用我们的方法比较了快速和慢速抽搐肌肉的成年到衰老的小鼠的单纤维的被动粘弹性和主动收缩生物力学，这些小鼠是 R349P 结蛋白突变的杂合子或纯合子，与野生型同窝仔相比。我们证明，R349P 结蛋白的存在主要增加了两种肌肉类型的轴向刚度，具有预老化表型，超过了野生型纤维。轴向粘度和 Ca2+介导的力基本不受影响。与野生型纤维相比，突变的单纤维表现出更快的空载缩短趋势。在野生型中看到的衰老效应在突变结蛋白纤维中更早出现。我们的单纤维实验，没有细胞外基质，表明受损的肌肉生物力学不仅归因于纤维化，而且还源于受损的中间丝网络。
