Delayed Satellite Cell Activation in Relation to Myostatin Expression Following Acute Resistance Exercise in Older and Younger Adults
Bibliographic record
Abstract
Muscle growth is regulated by a unique population of muscle stem cells (satellite cells: SC). Depletion or dysfunction of SC leads to a loss in muscle mass and capacity for muscle growth. It remains unknown if this cell population is adversely affected by the aging process. PURPOSE: To quantify the SC pool size and SC cell-cycle response to acute resistance exercise in healthy young (Y) and Old (O) humans in relation to muscle myostatin. METHODS: Subjects (young (Y) 21.3±3.1y; N=9; Older adults (O) 69.6±3.9y; N=9) preformed 4 sets of 10 rep of unilateral leg extensions and leg press at 75% of 1RM. Blood and muscle biopsies (vastus lateralis) were obtained pre-exercise (PRE) and 3, 24 and 48h post exercise. SC number and cell-cycle kinetics were analyzed via flow cytometry. Gene analysis was analyzed via qRT-PCR and muscle cross-sections were analyzed for Pax7, myostatin, and activin IIb (ActRIIb) via IHC. RESULTS: PRE SC numbers were 53.9% lower in O vs. Y (8665 vs 13 345 Pax7+ cells/mg p<0.05). At 24h, SC remained 48.6% lower in O vs Y. SC increased significantly in both Y and O at 48h (32 342.7 vs 32 0161.1 Pax7+ cells/mg, Y vs O respectively). There were more SC in G0/ G1 at PRE and 24h in Y vs O (p<0.05), with no age effect at 48h. SC in S-phase and G2/M were not significantly elevated until 48h (no age effect) with a trend for more SC in S-phase in Y at 24h and 48h (p=0.08). PRE myostatin mRNA was 47% higher in O vs Y (p=0.06). Myostatin was similar across time in Y and O, significantly decreasing at 3, 24 and 48h post exercise (p<0.05). However, myostatin expression was 141% and 148% higher in O vs Y at 24h and 48h (p<0.001). Both follistatin and follistatin-like-1mRNA expression did not change post exercise. However basal follistatin expression was 59% higher in O vs Y (p=0.04). Myf5 expression in O was unchanged while Myf5 mRNA in Y increased 1.5-fold at 48h (p=0.04). IHC confirmed Pax7+ cells were positive for myostatin and co-localized with ActRIIb. CONCLUSION: These data illustrate an effect of age on the SC pool. The SC pool remained lower at 24h, with fewer cells in G1 suggesting a blunted SC activation in O. This deficit in the SC response is supported by the expression pattern of Myf5. Localization of myostatin and ActRIIb with Pax7 and higher expression of myostatin in O vs Y suggest a potential mechanism for the blunted SC response.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".