Muscle Aging and Regenerative Medicine, Tokyo Metropolitan Institute of Gerontology, 35-2 Sakae-cho, Itabashi, Tokyo 173-0015, Japan.
Department of Regenerative and Transplant Medicine, Division of Orthopedic Surgery, Graduate School of Medical and Dental Sciences, Niigata University, 1-757 Asahimachi-Dori, Tyuo-Ku, Niigata 951-8510, Japan.
Int J Mol Sci. 2021 Nov 16;22(22):12356. doi: 10.3390/ijms222212356.
The main function of skeletal muscles is to generate force. The force developed by myofiber contraction is transmitted to the tendon. There are two pathways of force transmission from myofibers to tendons: longitudinal transmission that depends on tension elicited via the myotendinous junction and lateral transmission that depends on shear elicited via the interface between the myofiber surface and surrounding connective tissue. Experiments using animal muscle and mathematical models indicated that lateral transmission is the dominant pathway in muscle force transmission. Studies using rat muscle showed that the efficiency of lateral force transmission declines with age. Here, the lateral transmission of force was measured using the extensor digitorum longus muscle from young and old mice. Dependence on longitudinal transmission increased in the old muscle, and there was a trend for lower efficiency of lateral force transmission in the old muscle compared to the young muscle. There was a noticeable increase in the connective tissue volume in the old muscle; however, there was no significant change in the expression of dystrophin, a critical molecule for the link between the myofiber cytoskeleton and extracellular matrix. This study demonstrates the measurement of lateral force transmission in mouse muscles and that alteration in force transmission property may underlie age-related muscle weakness.
骨骼肌的主要功能是产生力。肌纤维收缩产生的力传递到肌腱。肌纤维向肌腱传递力有两种途径：纵向传递依赖于肌腱连接所引起的张力，而横向传递依赖于肌纤维表面和周围结缔组织界面所引起的剪切。使用动物肌肉进行的实验和数学模型表明，横向传递是肌肉力传递的主要途径。使用大鼠肌肉进行的研究表明，横向力传递的效率随年龄的增长而下降。在这里，使用年轻和老年小鼠的伸趾长肌测量了力的横向传递。老年肌肉对纵向传递的依赖性增加，与年轻肌肉相比，老年肌肉的横向力传递效率呈下降趋势。老年肌肉中的结缔组织体积明显增加；然而，肌营养不良蛋白的表达没有显著变化，肌营养不良蛋白是肌纤维细胞骨架和细胞外基质之间连接的关键分子。这项研究证明了在小鼠肌肉中测量横向力传递，并且力传递特性的改变可能是与年龄相关的肌肉无力的基础。
