Impact of resistance exercise on ribosome biogenesis is acutely regulated by post-exercise recovery strategies

Abstract

Muscle hypertrophy occurs following increased protein synthesis, which requires activation of the ribosomal complex. Additionally, increased translational capacity via elevated ribosomal RNA (rRNA) synthesis has also been implicated in resistance training-induced skeletal muscle hypertrophy. The time course of ribosome biogenesis following resistance exercise (RE) and the impact exerted by differing recovery strategies remains unknown. In the present study, the activation of transcriptional regulators, the expression levels of pre-rRNA, and mature rRNA components were measured through 48 h after a single-bout RE. In addition, the effects of either low-intensity cycling (active recovery, ACT) or a cold-water immersion (CWI) recovery strategy were compared. Nine male subjects performed two bouts of high-load RE randomized to be followed by 10 min of either ACT or CWI. Muscle biopsies were collected before RE and at 2, 24, and 48 h after RE. RE increased the phosphorylation of the p38-MNK1-eIF4E axis, an effect only evident with ACT recovery. Downstream, cyclin D1 protein, total eIF4E, upstream binding factor 1 (UBF1), and c-Myc proteins were all increased only after RE with ACT. This corresponded with elevated abundance of the pre-rRNAs (45S, ITS-28S, ITS-5.8S, and ETS-18S) from 24 h after RE with ACT. In conclusion, coordinated upstream signaling and activation of transcriptional factors stimulated pre-rRNA expression after RE. CWI, as a recovery strategy, markedly blunted these events, suggesting that suppressed ribosome biogenesis may be one factor contributing to the impaired hypertrophic response observed when CWI is used regularly after exercise.

Keywords: Cyclin D1; hypertrophy; pre‐rRNA; ribosomal RNA; skeletal muscle; upstream binding factor.

Figure 1

Effect of resistance exercise on the p38‐MNK1‐eIF4E axis. Phosphorylation levels of p38 (A), MNK1 (B), and eIF4E (C), and total levels of eIF4E (D), total cyclin D1 protein (E), and mRNA levels (F). Representative Western blot figures (closest molecular weight marker is shown in the left‐hand side) (G). Western blot data were normalized to GAPDH, with the exception of eIF4E Ser209, which was normalized to its respective total protein. Cyclin D1 mRNA expression was normalized to the geometric mean of three reference genes. Values are mean ± SEM. *different from PRE within the same trial (P < 0.05), ^#different between trials within the same time point (P < 0.05). Main effects and interactions are presented in the text.

Figure 2

Effect of resistance exercise on Akt signaling. Phosphorylation levels of AKT (A) and PRAS40 (B). Representative Western blot figures (closest molecular weight marker is shown in the left‐hand side) (C). Western blot data were normalized to their respective total proteins. Values are mean ± SEM. *different from PRE within the same trial (P < 0.05); ^#different between trials within the same time point (P < 0.05). Main effects and interactions are presented in the text.

Figure 3

Effect of resistance exercise on rDNA transcription factors. Protein levels of UBF1 (A), UBF2 (B), phosphorylation of UBF at Ser388 (C) and Ser484 (D), TIF‐IA at Ser649 (E), and protein levels of c‐Myc (F). Representative Western blots figures (closest molecular weight marker is shown in the left‐hand side) (G). Western blot data were normalized to GAPDH. Values are mean ± SEM. *different from PRE within the same trial (P < 0.05); ^#different between trials within the same time point (P < 0.05). Main effects and interaction are presented in the text.

Figure 4

Effect of resistance exercise on rDNA transcription. Expression of pre‐rRNA as detected by primers against: 5′ETS (A), ITS‐5.8S (B), ITS‐28S (C), ETS‐18S (D), and mature 28S rRNA (E). rRNA expression was normalized by geometric mean of three reference genes. Values are mean ± SEM. *different from PRE within the same trial (P < 0.05); ^#different between trials within the same time point (P < 0.05). Main effects and interaction are presented in the text.

Figure 5

Effect of resistance exercise on mRNA levels of genes involved in rDNA transcription. Expression of UBF (A), TIF‐IA (B), PolR1B (C), NIP7 (D) mRNAs. mRNA expression was normalized by geometric mean of three reference genes. Values are mean ± SEM. *different from PRE within the same trial (P < 0.05); ^#different between trials within the same time point (P < 0.05). Main effects and interaction are presented in the text.

Figure 6

Schematic representation of the signaling pathway affecting rRNA synthesis following resistance exercise and where CWI might interfere with this pathway.