Mitochondrial enzyme defects in normal and low-frequency-stimulated muscles of young and aging rats

Exercise Promotes Healthy Aging of Skeletal Muscle

Primary aging is the progressive and inevitable process of bodily deterioration during adulthood. In skeletal muscle, primary aging causes defective mitochondrial energetics and reduced muscle mass. Secondary aging refers to additional deleterious structural and functional age-related changes caused by diseases and lifestyle factors. Secondary aging can exacerbate deficits in mitochondrial function and muscle mass, concomitant with the development of skeletal muscle insulin resistance. Exercise opposes deleterious effects of secondary aging by preventing the decline in mitochondrial respiration, mitigating aging-related loss of muscle mass and enhancing insulin sensitivity. This review focuses on mechanisms by which exercise promotes "healthy aging" by inducing modifications in skeletal muscle.

Blunted angiogenesis and hypertrophy are associated with increased fatigue resistance and unchanged aerobic capacity in old overloaded mouse muscle

We hypothesize that the attenuated hypertrophic response in old mouse muscle is (1) partly due to a reduced capillarization and angiogenesis, which is (2) accompanied by a reduced oxidative capacity and fatigue resistance in old control and overloaded muscles, that (3) can be rescued by the antioxidant resveratrol. To investigate this, the hypertrophic response, capillarization, oxidative capacity, and fatigue resistance of m. plantaris were compared in 9- and 25-month-old non-treated and 25-month-old resveratrol-treated mice. Overload increased the local capillary-to-fiber ratio less in old (15 %) than in adult (59 %) muscle (P < 0.05). Although muscles of old mice had a higher succinate dehydrogenase (SDH) activity (P < 0.05) and a slower fiber type profile (P < 0.05), the isometric fatigue resistance was similar in 9- and 25-month-old mice. In both age groups, the fatigue resistance was increased to the same extent after overload (P < 0.01), without a significant change in SDH activity, but an increased capillary density (P < 0.05). Attenuated angiogenesis during overload may contribute to the attenuated hypertrophic response in old age. Neither was rescued by resveratrol supplementation. Changes in fatigue resistance with overload and aging were dissociated from changes in SDH activity, but paralleled those in capillarization. This suggests that capillarization plays a more important role in fatigue resistance than oxidative capacity.

Expression of respiratory chain enzyme mRNA and the morphological properties of mitochondria in the masseter muscles of klotho mutant mice

The activity of respiratory chain enzymes in a rat's masseter muscle changes as the animal ages; however, there is little information about the RNA transcript levels of mitochondrial enzymes in klotho mutant mice as they age. We measured the activities of NADH-ferricyanide oxidoreductase and NADH-O2 oxidoreductase, and the RNA transcript levels of NADH dehydrogenase, the mitochondrial isoform of ND1, the nuclear isoforms of the 51 kDa and 75 kDa subunits of Complex I, the nuclear isoform of cytochrome c, and the mitochondrial isoform of beta subunits of ATPase (Complex V). In addition, we measured the RNA transcript levels of catalase (CAT) and superoxide dismutase (SOD), which are associated with antioxidant proteins. Moreover, we measured ATP concentrations using a luciferin-luciferase assay, and we determined the amount of cytochrome c associated with mitochondria in both klotho mutant mice and wild-type mice. However, the mRNA levels of cytochrome c and Complex V components, the mRNA levels of CAT, SOD, and apoptosis-inducing factor (Aifm), and the protein level of cytochrome c remained constant as klotho mutant mice aged from 5 weeks to 7 weeks. In wild-type mice, these components (except for those of Complex I) increased over time. NADH-ferricyanide oxidoreductase and NADH-O2 oxidoreductase activities decreased in klotho mutant mice as they aged from 5 weeks to 7 weeks. A few large mitochondria were scattered between myofibrils, and 7-week-old klotho mutant mice displayed an increased number of irregular mitochondria with fewer cristae. Our results indicate that the klotho protein plays a role in the diminished functional adaptability of enzymes in the masseter muscle of klotho mutant mice throughout the aging process.

Bioreactors for guiding muscle tissue growth and development

Muscle tissue bioreactors are devices which are employed to guide and monitor the development of engineered muscle tissue. These devices have a modern history that can be traced back more than a century, because the key elements of muscle tissue bioreactors have been studied for a very long time. These include barrier isolation and culture of cells, tissues and organs after isolation from a host organism; the provision of various stimuli intended to promote growth and maintain the muscle, such as electrical and mechanical stimulation; and the provision of a perfusate such as culture media or blood derived substances. An accurate appraisal of our current progress in the development of muscle bioreactors can only be made in the context of the history of this endeavor. Modern efforts tend to focus more upon the use of computer control and the application of mechanical strain as a stimulus, as well as substrate surface modifications to induce cellular organization at the early stages of culture of isolated muscle cells.

Fiber-type transitions and satellite cell activation in low-frequency-stimulated muscles of young and aging rats

We examined satellite cell content and the activity of satellite cell progeny in tibialis anterior muscles of young (15 weeks) and aging (101 weeks) Brown Norway (BN) rats, after they were exposed for 50 days to a standardized and highly reproducible regime of chronic low-frequency electrical stimulation. Chronic low-frequency electrical stimulation was successful in inducing fast-to-slow fiber-type transformation, characterized by a 2.3-fold increase in the proportion of IIA fibers and fourfold and sevenfold decreases in the proportion of IID/X and IIB fibers in both young and aging BN rats. These changes were accompanied by a twofold increase in the satellite cell content in both the young and aging groups; satellite cell content reached a level that was significantly higher in the young group (p <.04). The total muscle precursor cell content (i.e., satellite cells plus progeny), however, did not differ between groups, because there was a greater number of satellite cell progeny passing through the proliferative and differentiative compartments of the aging group. The resulting 1.5-fold increase in myonuclear content was similar in the young and aging groups. We conclude that satellite cells and satellite cell progeny of aging BN rats possess an unaltered capacity to contribute to the adaptive response.