Wood Lauren K, Kayupov Erdan, Gumucio Jonathan P, Mendias Christopher L, Claflin Dennis R, Brooks Susan V
Biomedical Engineering, University of Michigan, Ann Arbor, Michigan;
Molecular & Integrative Physiology, University of Michigan, Ann Arbor, Michigan; Orthopaedic Surgery, University of Michigan, Ann Arbor, Michigan; and.
J Appl Physiol (1985). 2014 Aug 15;117(4):363-9. doi: 10.1152/japplphysiol.00256.2014. Epub 2014 Jul 3.
Advanced age is associated with increases in muscle passive stiffness, but the contributors to the changes remain unclear. Our purpose was to determine the relative contributions of muscle fibers and extracellular matrix (ECM) to muscle passive stiffness in both adult and old animals. Passive mechanical properties were determined for isolated individual muscle fibers and bundles of muscle fibers that included their associated ECM, obtained from tibialis anterior muscles of adult (8-12 mo old) and old (28-30 mo old) mice. Maximum tangent moduli of individual muscle fibers from adult and old muscles were not different at any sarcomere length tested. In contrast, the moduli of bundles of fibers from old mice was more than twofold greater than that of fiber bundles from adult muscles at sarcomere lengths >2.5 μm. Because ECM mechanical behavior is determined by the composition and arrangement of its molecular constituents, we also examined the effect of aging on ECM collagen characteristics. With aging, muscle ECM hydroxyproline content increased twofold and advanced glycation end-product protein adducts increased threefold, whereas collagen fibril orientation and total ECM area were not different between muscles from adult and old mice. Taken together, these findings indicate that the ECM of tibialis anterior muscles from old mice has a higher modulus than the ECM of adult muscles, likely driven by an accumulation of densely packed extensively crosslinked collagen.
高龄与肌肉被动僵硬度增加有关，但导致这种变化的因素尚不清楚。我们的目的是确定成年和老年动物中肌纤维和细胞外基质（ECM）对肌肉被动僵硬度的相对贡献。对从成年（8 - 12月龄）和老年（28 - 30月龄）小鼠的胫前肌中分离出的单个肌纤维以及包含其相关ECM的肌纤维束进行被动力学性能测定。在任何测试的肌节长度下，成年和老年肌肉单个肌纤维的最大切线模量均无差异。相比之下，在肌节长度>2.5μm时，老年小鼠纤维束的模量比成年肌肉纤维束的模量高出两倍多。由于ECM的力学行为由其分子成分的组成和排列决定，我们还研究了衰老对ECM胶原蛋白特性的影响。随着衰老，肌肉ECM羟脯氨酸含量增加两倍，晚期糖基化终产物蛋白加合物增加三倍，而成年和老年小鼠肌肉之间的胶原纤维取向和总ECM面积没有差异。综上所述，这些发现表明老年小鼠胫前肌的ECM比成年肌肉的ECM具有更高的模量，这可能是由密集堆积且广泛交联的胶原蛋白积累所致。
