Skeletal muscle IL-15/IL-15Rα and myofibrillar protein synthesis after resistance exercise.
TL;DR: In conclusion, IL‐15/IL‐15Rα signaling pathway is activated in skeletal muscle in response to a session of resistance exercise.
Abstract: In vitro and in vivo studies described the myokine IL-15 and its receptor IL-15Rα as anabolic/anti-atrophy agents, however, the protein expression of IL-15Rα has not been measured in human skeletal muscle and data regarding IL-15 expression remain inconclusive. The purpose of the study was to determine serum and skeletal muscle IL-15 and IL-15Rα responses to resistance exercise session and to analyze their association with myofibrillar protein synthesis (MPS). Fourteen participants performed a bilateral leg resistance exercise composed of four sets of leg press and four sets of knee extension at 75% 1RM to task failure. Muscle biopsies were obtained at rest, 0, 4 and 24 hours post-exercise and blood samples at rest, mid-exercise, 0, 0.3, 1, 2, 4 and 24 hours post-exercise. Serum IL-15 was increased by ~5.3-fold immediately post-exercise, while serum IL-15Rα decreased ~75% over 1 hour post-exercise (P<.001). Skeletal muscle IL-15Rα mRNA and protein expression were increased at 4 hours post-exercise by ~2-fold (P<.001) and ~1.3-fold above rest (P=.020), respectively. At 24 hours post-exercise, IL-15 (P=.003) and IL-15Rα mRNAs increased by ~2-fold (P=.002). Myofibrillar fractional synthetic rate between 0-4 hours was associated with IL-15Rα mRNA at rest (r=.662, P=.019), 4 hours (r=.612, P=.029), and 24 hours post-exercise (r=.627, P=.029). Finally, the muscle IL-15Rα protein up-regulation was related to Leg press 1RM (r=.688, P=.003) and total weight lifted (r=.628, P=.009). In conclusion, IL-15/IL-15Rα signaling pathway is activated in skeletal muscle in response to a session of resistance exercise.
Summary (2 min read)
Take down policy
- IL-15Rα has not been determined in human skeletal muscle.
- Therefore, despite the 67 fact that in vitro studies indicate a role for skeletal muscle IL-15 in anabolism, studies in 68 humans are inconclusive.
- Of 119 the 16 participants included in the original study, 14 were analysed in the present investigation 120 due to insufficient muscle tissue in the two subjects excluded.
Experimental protocol 123
- A detailed description of the experimental protocol and analytical methods can be found 124 elsewhere (McKendry et al., 2016) .
- Thereafter, one-repetition maximum (1RM) strength during leg press and 127 knee extension was assessed (Cybex VR-3, MA, USA).
- The following morning at 7.00 h, participants returned to the 142 laboratory after a 10-12h overnight fast and a cannula was inserted into a forearm vein to obtain 143 a blood sample followed by the fourth and last biopsy, which was obtained from the vastus 144 lateralis of the contralateral leg.
- The participants received three standardised meals for consumption the evening prior to 147 the experimental trial, as well as the afternoon and evening after the experimental trial.
Serum IL-15 and IL-15Rα 154
- After collection, all blood samples were centrifuged for 15 minutes at 1000 g, aliquoted and 155 stored at -80 ºC.
- Two high-sensitivity enzyme-linked immunosorbent assay kits were 156 used to determine the serum concentration of IL-15 and IL-15Rα in duplicates.
Both antibodies were diluted into BSA-blocking buffer containing 4% bovine serum albumin in 175
- Antibody specific labelling was revealed by 176 incubation with an HRP-conjugated goat anti-rabbit (IL-15) or anti-mouse (IL-15Rα) antibodies 177 (1:5000), both diluted in 5% blotto blocking buffer and visualised with ECL Western blotting 178 detection system using a ChemiDoc XRS (Bio-Rad, Copenhagen, Denmark).
- Imaging and band 179 quantification were performed using the Quantity One 1-D Analysis software (Bio-Rad, 180 Copenhagen, Denmark).
- Test samples were run together with a control sample from a subject 181 who did not take part in the study.
- The control sample was loaded in three different lanes and 182 used as an internal control for inter-gel variability.
RNA Isolation and quantitative real-time reverse transcription polymerase chain reaction 187 (qRT-PCR). 188
- Approximately 15-20 mg of skeletal muscle tissue was used for the RNA isolation.
- The RNA 189 was extracted by guanine-phenol-chloroform isothiocyanate procedures using TRIzol 190 (AUC) was determined using trapezoid method and compared between groups using a paired 242 Student's t-test.
- Since no significant differences were observed between the 1-and 5-min 243 recovery, both groups were combined for further analyses.
- To determine time effects of the intervention on serum, protein and mRNA levels of IL-245 15 and IL-15Rα, ANOVA for repeated measures was performed.
- Tukey HSD correction was 246 used as post-hoc test when significant differences were detected.
Skeletal muscle IL-15/IL-15Rα expression and myofibrillar protein synthesis. 306
- This lack of 328 differences could be interpreted as evidence to refute the association between skeletal muscle 329 IL-15/IL-15Rα and MPS.
- Nevertheless, the effect sizes and statistical outputs (P<0.10) indicate 330 that a potential difference between groups may actually exist.
- In agreement, the authors have observed a positive association between serum concentration of 395 IL-15 and IL-15 protein levels in skeletal muscle, suggesting that muscle may be an important 396 source of IL-15 in the basal state.
- In the present study, the authors observed that basal IL-15 protein 397 levels in skeletal muscle were associated with serum concentration immediately post-exercise, 398 also suggesting that the size of the intramuscular pool could determine the magnitude of the 399 increase in serum IL-15 elicited by resistance exercise.
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Cites background from "Skeletal muscle IL-15/IL-15Rα and m..."
...IL-15 has been shown to exert pro-inflammatory effects when this cytokine is chronically elevated at baseline ; however, in response to a single session of exercise, serum IL-15 is upregulated [115,116], and instead of showing a pro-inflammatory function, this myokine exerts oxidative effects in adipose tissue ....
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`` This is the peer reviewed version of the following article: Pérez-López A, McKendry J, Martin-Rincon M, et al. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving. ``