Interpretation of exercise-induced changes in human skeletal muscle mRNA expression depends on the timing of the post-exercise biopsies

Abstract

AimExercise elicits a range of adaptive responses in skeletal muscle that include changes in mRNA expression. To better understand the health benefits of exercise training, it is essential to investigate the underlying molecular mechanisms of skeletal muscle adaptations to exercise. However, most studies have assessed the molecular events at a few convenient time points within a short time frame post exercise, and the variations of gene expression kinetics have not been addressed systematically.MethodMuscle biopsies were collected from nine participants at baseline and six time points (0, 3, 9, 24, 48, and 72 h) following a session of high-intensity interval exercise. We assessed the mRNA content of 23 gene isoforms from the muscle samples.ResultThe temporal patterns of target gene expression were highly variable and the mRNA contents detected were largely dependent on the muscle sample timing. The maximal levels of mRNA content of all tested target genes were observed between 3 to 48 h post exercise.ConclusionOur findings highlight a critical gap in knowledge regarding the molecular response to exercise, where the use of a few time points within a short period after exercise has led to an incomplete understanding of the molecular responses to exercise. The timing of muscle sampling for individual studies needs to be carefully chosen based on existing literature and preliminary analysis of the molecular targets of interest. We propose that a comprehensive time-course analysis on the exercise-induced transcriptional response in humans will significantly benefit the field of exercise molecular biology.

Mechanical loading of bioengineered skeletal muscle in vitro recapitulates gene expression signatures of resistance exercise in vivo

“…These genes were therefore analyzed at 0.5, 3, and 24 h post-loading in bioengineered mouse muscle to enable a direct comparison with humans after acute RE. First, the majority of these genes predominantly increased at 3 h post-loading and returned to basal levels at 24 h. This temporal gene regulatory profile has been observed several times in response to exercise in vivo in which gene expression tends to peak at 3-8 h post-exercise (Barrès et al, 2012;Chen et al, 2002;Drummond et al, 2008;Knuiman et al, 2018;Kuang et al, 2020) and generally returns to basal levels within 24 h Liu et al, 2010;Yang et al, 2005).…”

Exercise mitigates sleep-loss-induced changes in glucose tolerance, mitochondrial function, sarcoplasmic protein synthesis, and diurnal rhythms

“…While exercise is known to acutely increase skeletal muscle Glut4 mRNA [ 22 ], we did not observe an increase in the SR+EX group. This may be explained by the timing of our muscle sample, which was collected 48 h post the final exercise session, by which time Glut4 mRNA expression may have returned to baseline levels [ 22 , 51 ]. Therefore, while no changes to Glut4 mRNA or protein content were observed in tandem with changes in glucose tolerance, it is plausible that GLUT4 translocation to the cell membrane may be impaired, which would support previous research that has indicated impairments within the insulin signaling pathway following sleep restriction [ 52 , 53 ].…”

“…However, despite a non-significant 35 ± 28% change in Mfn2 mRNA in the SR group, we observed no changes in the molecular regulators of mitochondrial dynamics. Considering that exercise can also acutely influence markers of mitochondrial dynamics [ 59 ], this suggests the chosen muscle sampling time points may not have been appropriate to detect these potential changes [ 51 ].…”

Omega-3 Supplementation Improves Isometric Strength But Not Muscle Anabolic and Catabolic Signaling in Response to Resistance Exercise in Healthy Older Adults

“…Four biopsies were taken, 2 at baseline (PRE) and 2 after completion of the 14-week intervention (POST). All biopsies were taken at least 72 hours after RE to exclude interference of acute exercise on muscle molecular signaling ( 25 ). The first biopsy (proximal needle orientation, both on the PRE- and POST-session) was taken in a fasted state and the second biopsy (distal needle orientation) was sampled 80 minutes after a standardized, protein-rich breakfast consisting of 4 toasts (4 × 22 g), jam (40 g), and a protein shake (34 g powder in 0.3 L H 2 O) (in total: 565.8 kcal; 38.2 g proteins of which 13 g essential amino acids; 4.1 g fats of which 0.5 g saturated; 93.2 g carbohydrates of which 25.1 g sugars; 3.3 g fibers; 1.4 g NaCl).…”