A Comparative Analysis of Age-Related Changes in the Structure of the Mitochondrial Apparatus in Skeletal Muscles of Species with Different Lifespan

A comparative electron microscopic and morphometric analysis of age-related transformations in the ultrastructure of the skeletal muscle mitochondrial apparatus was carried out in animal species with different aging programs: short-lived classical objects, such as C57BL/6 mice and Wistar rats, prematurely aging OXYS rats, and the longest-living rodents, naked mole-rats ( Heterocephalus glaber ), characterized by delayed aging. In C57BL/6 mice, age-related reorganization of the skeletal muscle mitochondrial apparatus corresponds to that reported previously for Wistar rats: the mitochondrial reticulum forms by the age of 2.5–3 months; by the age of 30 months, it undergoes a drastic reduction, due to which the number of mitochondrial cross-sections in muscle fibers decreases almost twofold, from 0.45 ± 0.074 to 0.23 ± 0.017 profiles per µm 2 . In C57BL/6 mice, no destructive changes in the mitochondrial ultrastructure were observed, in contrast to OXYS rats, in which age-related changes in the chondriome affect both the overall structure and internal ultrastructure of the muscle fiber mitochondrial apparatus. At the same time, in naked mole-rats, which are comparable with mice in their size, the number and size of mitochondria in skeletal muscles increase significantly by the age of five years, although no mitochondrial reticulum forms. It is hypothesized that a special organization of the mitochondrial apparatus in naked mole-rat skeletal muscles provide a proper level of redox processes in muscles, thus preventing a decline in their physical efficiency and the development of sarcopenia, whereas in C57BL/6 mice, Wistar and OXYS rats, age-related abnormalities in the structural organization of skeletal muscle mitochondrial apparatus may be one of the major causes for the development of age-related pathologies, including sarcopenia.