Russell Katelyn A, Ng Rainer, Faulkner John A, Claflin Dennis R, Mendias Christopher L
Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, United States.
Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, United States; Department of Molecular & Integrative Physiology, University of Michigan, Ann Arbor, MI, United States.
Exp Gerontol. 2015 May;65:42-5. doi: 10.1016/j.exger.2015.03.003. Epub 2015 Mar 8.
A progressive loss of skeletal muscle mass and force generating capacity occurs with aging. Mice are commonly used in the study of aging-associated changes in muscle size and strength, with most models of aging demonstrating 15-35% reductions in muscle mass, cross-sectional area (CSA), maximum isometric force production (Po) and specific force (sPo), which is Po/CSA. The lumbrical muscle of the mouse forepaw is exceptionally small, with corresponding short diffusion distances that make it ideal for in vitro pharmacological studies and measurements of contractile properties. However, the aging-associated changes in lumbrical function have not previously been reported. To address this, we tested the hypothesis that compared to adult (12month old) mice, the forepaw lumbrical muscles of old (30month old) mice exhibit aging-related declines in size and force production similar to those observed in larger limb muscles. We found that the forepaw lumbricals were composed exclusively of fibers with type II myosin heavy chain isoforms, and that the muscles accumulated connective tissue with aging. There were no differences in the number of fibers per whole-muscle cross-section or in muscle fiber CSA. The whole muscle CSA in old mice was increased by 17%, but the total CSA of all muscle fibers in a whole-muscle cross-section was not different. No difference in Po was observed, and while sPo normalized to total muscle CSA was decreased in old mice by 22%, normalizing Po by the total muscle fiber CSA resulted in no difference in sPo. Combined, these results indicate that forepaw lumbrical muscles from 30month old mice are largely protected from the aging-associated declines in size and force production that are typically observed in larger limb muscles.
随着年龄增长，骨骼肌质量和力量产生能力会逐渐丧失。小鼠常用于研究与衰老相关的肌肉大小和力量变化，大多数衰老模型显示肌肉质量、横截面积（CSA）、最大等长力产生（Po）和比力（sPo，即Po/CSA）会减少15%-35%。小鼠前爪的蚓状肌非常小，相应的扩散距离短，这使其成为体外药理学研究和收缩特性测量的理想对象。然而，此前尚未报道过蚓状肌功能与衰老相关的变化。为了解决这个问题，我们测试了一个假设，即与成年（12个月大）小鼠相比，老年（30个月大）小鼠前爪的蚓状肌在大小和力量产生方面表现出与衰老相关的下降，类似于在较大肢体肌肉中观察到的情况。我们发现前爪蚓状肌仅由具有II型肌球蛋白重链亚型的纤维组成，并且随着年龄增长，肌肉中结缔组织会积累。全肌横截面上的纤维数量或肌纤维CSA没有差异。老年小鼠的全肌CSA增加了17%，但全肌横截面上所有肌纤维的总CSA没有差异。未观察到Po有差异，虽然以总肌肉CSA标准化的sPo在老年小鼠中降低了22%，但以总肌纤维CSA标准化Po后，sPo没有差异。综合这些结果表明，30个月大小鼠的前爪蚓状肌在很大程度上免受了通常在较大肢体肌肉中观察到的与衰老相关的大小和力量产生下降的影响。
