Satellite cell and myonuclear accretion is related to training-induced skeletal muscle fiber hypertrophy in young males and females

Abstract

Satellite cells (SC) play an integral role in the recovery from skeletal muscle damage and supporting muscle hypertrophy. Acute resistance exercise typically elevates type I and type II SC content 24-96 hours post-exercise in healthy young males, although comparable research in females is lacking. We aimed to elucidate whether sex-based differences exist in fiber type-specific SC content after resistance exercise in the untrained (UT) and trained (T) states. Ten young males (23.0 ± 4.0y) and females (23.0 ± 4.8y) completed an acute bout of resistance exercise before and after 8 weeks of whole-body resistance training. Muscle biopsies were taken from the vastus lateralis immediately prior to and 24 and 48-hours after each bout to determine SC and myonuclear content by immunohistochemistry. Males had greater SC associated with type II fibers (P ≤ 0.03). There was no effect of acute resistance exercise on SC content in either fiber type (P ≥ 0.58) for either sex, however, training increased SC in type II fibers (P < 0.01) irrespective of sex. The change in mean 0-48 h type II SC was positively correlated with muscle fiber hypertrophy in type II fibers (r = 0.47; P = 0.035). Furthermore, the change in myonuclei per fiber was positively correlated with type I and type II fiber hypertrophy (both r = 0.68; P < 0.01). Our results suggest that SC responses to acute and chronic resistance exercise are similar in males and females and that SC and myonuclear accretion is related to training-induced muscle fiber hypertrophy.

Trained Integrated Postexercise Myofibrillar Protein Synthesis Rates Correlate with Hypertrophy in Young Males and Females

“…Fibers were excluded from analysis if they had a circularity <0.65. Fiber cross-sectional area was determined via the average of type I and type II fibers obtained from our previous publication (28).…”

Weight Pulling: A Novel Mouse Model of Human Progressive Resistance Exercise

“…In addition to inducing hypertrophy, numerous human studies have shown that the PRE-induced hypertrophic response is associated with myonuclear accretion [26,35]. Therefore, to determine whether WP induces this effect, we measured the myonuclei to fiber ratio in the mid-belly crosssections and found that WP increased this ratio.…”

“…It has also been shown that the PRE-induced increase in muscle mass can be attributed to an increase in the cross-sectional area of muscle fibers (i.e., hypertrophy), and/or an increase in the length of muscle fascicles/fibers [23,24]. Moreover, these changes are often accompanied by an increase in the number of myonuclei per fiber, as well as a fast→slow transition in the composition of the Type II fibers [25,26]. Accordingly, we used a variety of different assays to determine whether these types of responses were elicited by our model which we refer to as "weight pulling".…”

Fusion and beyond: Satellite cell contributions to loading‐induced skeletal muscle adaptation

“…Uncovering all the ways by which satellite cells affect non‐satellite cell populations during adult muscle adaptation, and translating these results to human populations, will be an exciting challenge for future investigations. More attention should also be paid to sex differences in satellite cell contributions to muscle adaptation, as this is incompletely understood 27,220,228,229 . Unfortunately, the vast majority of knowledge on satellite cell behavior during adaptation is extrapolated from developmental myogenesis or injury and regeneration experiments.…”

“… 212 , 213 , 214 , 215 , 216 , 217 Collectively, the amount and source of myonuclear turnover in adult skeletal muscle, and whether this is affected by exercise, are open questions that deserve further exploration. While muscle can adapt to an extent without satellite cells, it is currently unclear whether having augmented satellite cell number or function could enhance exercise adaptation through development and/or in adulthood; human resistance training studies point to this possibility in some instances, 35 , 182 , 218 , 219 , 220 , 221 but correlation does not mean causation. How satellite cells contribute to neuromuscular junction stability, as well as the myotendinous junction, are also provocative areas of inquiry, 50 , 222 , 223 , 224 , 225 especially in the context of exercise adaptation during aging.…”