Mechanical, Molecular Myofibrillar and Proteomic Modifications in Muscle Aging: A Pilot Study

Introduction: Skeletal muscle tissue is a complex and very important organ for movement, metabolism and thermoregulation, but its relevance to health is not always taken in consideration. The muscle is made by a set of syncital fusiform cells called myocytes, which contein sarcomeres, the real protein contractile apparatus, composed of myofibrillar cytoskeleton proteins. Muscle tissue undergoes significant remodeling with aging and it changes its contractile phenotype. Aging significantly influences the proteomic structure of the cell as well as the nervous component. We assist to a physiopathological framework where the slowing of protein synthesis is accompanied by an axonal atrophy essential for efficient muscle contraction. The result of those factors leads to a loss of volume of the muscle fibers, a lower strength and performance. Aim: The objective of this study is to analyze the modifications of muscle tissue in aging. The qualitative (strength), quantitative (section) and the proteomics differences of the whole muscle and of the single fiber between young and old were studied. Methods: A sample of muscle tissue from the m. vastus lateral quadriceps was taken with an open technique by eight volunteers, four young donors (22-27 years) and four elderly (66-75 years). As regards in vivo analyzes, the measurements of maximum voluntary isometric strength were evaluated. Finally, a magnetic resonance was performed to calculate the volume. Results: The maximum isometric strength performed, the specific strength and the section of the individual fibers assessed in vitro tests are significantly lower in the elderly (p <.05). Elderly subjects also present a modest decline in the number of type II fibers (p = .043). The maximum voluntary contraction and the percentage of muscle recruitment assessed in vivo undergo a significant decrease (p <.005). The proteomic analysis show an alteration of the sarcoplasmic reticulum (RS) and of the myofibrils (Line M). Conclusion: In the aging process there is a negative modification of all the components of the contractile system and of the systems connected to the translation of the force (Ca+2 ATP-asi and sarcolumenina) and to the stabilization of myofibers (proteins M).