Molecular Attributes of Human Skeletal Muscle at Rest and After Unaccustomed Exercise: An Age Comparison

Abstract

The current study examined muscle DNA and protein concentrations ([ ]) and the [RNA] (assumed to represent translational capacity), [RNA]:[DNA] (assumed to represent transcriptional efficiency) and [protein]:[RNA] (assumed to represent translational efficiency) in younger vs. older participants during a resting state. Further, changes in muscle [DNA], translational capacity, and transcriptional efficiency were analyzed 24 hours after an unaccustomed resistance exercise bout. Younger (20.9 +/- 0.5 years, 84.0 +/- 5.2 kg, 26.6 +/- 1.8 kg x m(-2); n = 13) and older men (67.6 +/- 1.3 years, 88.7 +/- 4.8 kg, 28.6 +/- 1.4 kg x m(-2); n = 13) reported to the laboratory and completed an unaccustomed bout of lower-body resistance training (i.e., 3 sets of 10 repetitions at 80% 1 repetition maximum for Smith squat, leg press, and leg extensions). Muscle biopsies from the vastus lateralis were obtained before and 24 hours after exercise. Baseline [RNA], [DNA], [protein], and [RNA]:[DNA] were not different between age groups (p > 0.05). Baseline [protein]:[RNA] was greater in younger vs. older men (p = 0.045), whereas 24-hour postexercise [RNA]:[DNA] tended to be greater in older men (p = 0.087). These findings suggest that a decrease in the efficiency of translational processes occurs in older human skeletal muscle, whereas global transcriptional processes appear to be unaltered when compared with those in younger men. In lieu of these data, it remains apparent that muscle-protein synthesis is impaired in aging skeletal muscle and effective countermeasures such as resistance exercise and nutritional adequacy must be undertaken by older populations to offset this phenomenon.

Impaired Ribosomal Biogenesis by Noncanonical Degradation of β-Catenin during Hyperammonemia

“…Our observations of reduced ribosome content and biogen- esis during hyperammonemia-induced muscle loss are consistent with those reported for disuse-related muscle atrophy, where lower skeletal muscle RNA content was noted in rats during hindlimb immobilization and spinal cord injury (66,67) or in humans during inactivity (68). Importantly, this phenomenon is different from aging-related sarcopenia and sciatic denervation-induced atrophy, where the skeletal muscle total RNA concentration is not decreased (31,65). Also, our data show that ribosomal alterations in muscle atrophy are not necessarily the reverse of hypertrophy, because the changes in hypertrophy are believed to be due to translational rather than transcriptional perturbations (27).…”

“…The reduction in ribosomal biogenesis in this model was shown to be due to an increase in proteasomal activity, suggesting translational deficits rather than global transcriptional mechanisms as mediators of aging-related muscle loss (28). In contrast, others have reported unaltered or even increased skeletal muscle ribosomal biogenesis with aging (29)(30)(31). These conflicting observations may be indicative of a compensatory increase in ribosome biogenesis during muscle atrophy or a context-dependent response.…”

Aging in Rats Differentially Affects Markers of Transcriptional and Translational Capacity in Soleus and Plantaris Muscle

“…While this observation contrasts prior literature reporting that skeletal muscle ribosome density is similar in younger vs. older humans (Roberts et al, 2010; Stec et al, 2015) or is greater in older rats (Haddad and Adams, 2006), this finding may be due to our examination of the plantaris muscle vs. the examination of vastus lateralis tissue in humans or gastrocnemius muscles in rats in the aforementioned studies; both which contain a heterogeneous mixture of type I and II fibers. Notably, soleus muscle total RNA levels did not differ between age groups which suggests that slow-twitch fiber ribosome density does not decrease with aging in Fisher rats.…”

No adverse effects of statins on muscle function and health‐related parameters in the elderly: An exercise study

“…It was also suggested that tissue damage, a stimulus for repair and tissue hypertrophy resulting from muscle‐damaging exercise, may be sufficient to contribute to the increased total energy during recovery (Burleson et al., ). Although the findings of the above investigations are based on young individuals, they could be applied in the present study considering the observation that the intrinsic regenerative capacity of skeletal muscle and satellite cells is not impaired with age (Conboy et al., ; Roberts et al., ).…”