Mitogen-activated protein kinase (MAPK) pathway activation: effects of age and acute exercise on human skeletal muscle

Abstract

The purpose of this investigation was to examine the activation (phosphorylation) and total protein content of MAPK signalling cascade proteins (ERK 1/2, p90RSK, Mnk 1, eIF4E, p38 MAPK, JNK/SAPK, MKP 1) at rest and following exercise, in sedentary young and old men. Eight young (22 +/- 1 years; YM) and eight old (79 +/- 3 years; OM) men underwent a resting muscle biopsy of the vastus lateralis; they then performed a knee extensor resistance exercise session (29 contractions at approximately 70 % of max), followed by a post-exercise biopsy. Western immunoblot analysis demonstrated that the OM had higher resting phosphorylation of ERK 1/2, p90RSK, Mnk 1, p38 MAPK and JNK/SAPK proteins versus YM (P < 0.05). The resistance exercise bout caused an increase in phosphorylation of the ERK 1/2, p90RSK and Mnk 1 proteins (P < 0.05) in the YM. Conversely, the OM had a decrease in ERK 1/2, p90RSK, Mnk 1, p38 MAPK and JNK/SAPK phosphorylation (P < 0.05) after the exercise bout. Neither group showed a change in eIF4E phosphorylation. The total amount of protein expression of the MAPK signalling proteins was not different between the YM and OM, except that there was a higher (P < 0.05) MKP 1 protein content in the OM. This investigation is the first to provide evidence that MAPK proteins are differentially activated at rest and in response to a bout of resistance exercise in skeletal muscle of young and old men. These findings may have implications for other processes (e.g. transcription and translation) involved in skeletal muscle type and growth, when examining the changes occurring with ageing muscle before and after resistance exercise/training.

Figure 1. Effects of one bout of resistance exercise on ERK 1/2 phosphorylation in young (YM) and old (OM) men

The ERK 1/2 phosphorylation state was determined from vastus lateralis samples (at rest and post-exercise) using Western blot analysis with antibodies specific for phosphorylation of ERK 1/2 (Thr²⁰² and Tyr²⁰⁴). Equal loading was verified by Ponceau S staining. Data are expressed as arbitrary units (means ±s.e.m.). *P < 0.05 vs. resting. †P < 0.05 vs. age.

Figure 2. Effects of one bout of resistance exercise on p90RSK phosphorylation in YM and OM

The p90RSK phosphorylation state was determined from vastus lateralis samples (at rest and post-exercise) using Western blot analysis with antibodies specific for p90RSK phosphorylation (Thr⁵⁷³). Equal loading was verified by Ponceau S staining. Data are expressed as arbitrary units (means ±s.e.m.). *P < 0.05 vs. resting. †P < 0.05 vs. age.

Figure 3. Effects of one bout of resistance exercise on Mnk 1 phosphorylation in YM and OM

The Mnk 1 phosphorylation state was determined from vastus lateralis samples (at rest and post-exercise) using Western blot analysis with antibodies specific for Mnk 1 phosphorylation (Thr¹⁹⁷ and Thr²⁰²). Equal loading was verified by Ponceau S staining. Data are expressed as arbitrary units (means ±s.e.m.). *P < 0.05 vs. resting. †P < 0.05 vs. age.

Figure 4. Effects of one bout of resistance exercise on eIF4E phosphorylation in YM and OM

The eIF4E phosphorylation state was determined from vastus lateralis samples (at rest and post-exercise) using Western blot analysis with antibodies specific for eIF4E phosphorylation (Ser²⁰⁹). Equal loading was verified by Ponceau S staining. Data are expressed as arbitrary units (means ±s.e.m.).

Figure 5. Effects of one bout of resistance exercise on p38 MAPK phosphorylation in YM and OM

The p38 MAPK phosphorylation state was determined from vastus lateralis samples (at rest and post-exercise) using Western blot analysis with antibodies specific for p38 MAPK phosphorylation (Thr¹⁸⁰ and Tyr¹⁸²). Data are expressed as arbitrary units (means ±s.e.m.). *P < 0.05 vs. resting. †P < 0.05 vs. age.

Figure 6. Effects of one bout of resistance exercise on JNK/SAPK phosphorylation in YM and OM

The JNK/SAPK phosphorylation state was determined from vastus lateralis (at rest and post-exercise) using Western blot analysis with antibodies specific for JNK/SAPK phosphorylation (Thr¹⁸³ and Tyr¹⁸⁵). Equal loading was verified by Ponceau S staining. Data are expressed as arbitrary units (means ±s.e.m.). *P < 0.05 vs. resting. †P < 0.05 vs. age.

Figure 7. MKP 1 total protein content in YM and OM

MKP 1 protein content was determined from vastus lateralis samples (at rest and post-exercise) using Western blot analysis with antibodies specific for MKP 1. Equal loading was verified by probing the same blot with antibodies for actin, as well staining the blot with Ponceau S. Data are expressed as arbitrary units (means ±s.e.m.). †P < 0.05 vs. age.