Effects of ageing in muscle tissue: the contribution of proteomics

Ageing induces a progressive functional decline affecting the entire organism, therefore, the loss of muscle mass and function (sarcopenia) contributes significantly to a loss of functional autonomy. In muscles, the age-related degenerative changes produce alteration of morphology associated to muscle fiber atrophy, loss of satellite cells, and remodelling of neuronal structures. Morphological changes induced by ageing indicate a decrement of muscle fiber size, a change in fiber type distribution and appearance of mitochondrial aggregates with an increment of lipofuscin. This functional and morphological changes are also observed in nerves, in which ageing induces biochemical, morphological and functional variations both in myelin and in axons. Beside that, mitochondrial metabolism plays a pivotal role in aging, as its alteration influences the muscle function. In particular, the two morphologically distinct mitochondrial sub-fractions, named sub-sarcolemmal (SS) and inter-myofibrillar (IMF) according to their diverse cellular localization, play different roles in muscle tissue. The modulation of the respiration rate, proteins and lipids composition, and the diverse biochemical (e.g. protein import) properties, contributes to muscle cell adaptation during ageing. The SS sub-fraction is more influenced by muscle changes and is more affected by ageing. Proteomics has been utilized to monitor, at the molecular level, the decline of muscle tissue, nerves innervating it and mitochondrial machinery