Eccentric Exercise Activates Novel Transcriptional Regulation of Hypertrophic Signaling Pathways Not Affected by Hormone Changes

Unaccustomed eccentric exercise damages skeletal muscle tissue, activating mechanisms of recovery and remodeling that may be influenced by the female sex hormone 17β-estradiol (E2). Using high density oligonucleotide based microarrays, we screened for differences in mRNA expression caused by E2 and eccentric exercise. After random assignment to 8 days of either placebo (CON) or E2 (EXP), eighteen men performed 150 single-leg eccentric contractions. Muscle biopsies were collected at baseline (BL), following supplementation (PS), +3 hours (3H) and +48 hours (48H) after exercise. Serum E2 concentrations increased significantly with supplementation (P<0.001) but did not affect microarray results. Exercise led to early transcriptional changes in striated muscle activator of Rho signaling (STARS), Rho family GTPase 3 (RND3), mitogen activated protein kinase (MAPK) regulation and the downstream transcription factor FOS. Targeted RT-PCR analysis identified concurrent induction of negative regulators of calcineurin signaling RCAN (P<0.001) and HMOX1 (P = 0.009). Protein contents were elevated for RND3 at 3H (P = 0.02) and FOS at 48H (P<0.05). These findings indicate that early RhoA and NFAT signaling and regulation are altered following exercise for muscle remodeling and repair, but are not affected by E2

The order of exercise during concurrent training for rehabilitation does not alter acute genetic expression, mitochondrial enzyme activity or improvements in muscle function.

Concurrent exercise combines different modes of exercise (e.g., aerobic and resistance) into one training protocol, providing stimuli meant to increase muscle strength, aerobic capacity and mass. As disuse is associated with decrements in strength, aerobic capacity and muscle size concurrent training is an attractive modality for rehabilitation. However, interference between the signaling pathways may result in preferential improvements for one of the exercise modes. We recruited 18 young adults (10 ♂, 8 ♀) to determine if order of exercise mode during concurrent training would differentially affect gene expression, protein content and measures of strength and aerobic capacity after 2 weeks of knee-brace induced disuse. Concurrent exercise sessions were performed 3x/week for 6 weeks at gradually increasing intensities either with endurance exercise preceding (END>RES) or following (RES>END) resistance exercise. Biopsies were collected from the vastus lateralis before, 3 h after the first exercise bout and 48 h after the end of training. Concurrent exercise altered the expression of genes involved in mitochondrial biogenesis (PGC-1α, PRC, PPARγ), hypertrophy (PGC-1α4, REDD2, Rheb) and atrophy (MuRF-1, Runx1), increased electron transport chain complex protein content, citrate synthase and mitochondrial cytochrome c oxidase enzyme activity, muscle mass, maximum isometric strength and VO 2peak. However, the order in which exercise was completed (END>RES or RES>END) only affected the protein content of mitochondrial complex II subunit. In conclusion, concurrent exercise training is an effective modality for the rehabilitation of the loss of skeletal muscle mass, maximum strength, and peak aerobic capacity resulting from disuse, regardless of the order in which the modes of exercise are performed

Concurrent exercise alters mRNA content of genes involved in mitochondrial biogenesis and metabolism and increases protein content of subunits of the ETC.

<p>A - Gene expression changes in skeletal muscle 3 hours after concurrent rehabilitative exercise for genes involved in aerobic exercise adaption. Peroxisome proliferative activated receptor (PPAR) gamma coactivator-1α (PGC-1α), PGC-1-related coactivator (PRC), PGC-1β, and PPARγ. B - Fold changes in protein content from pre-exercise for subunits of the 5 complexes of the ETC (CI-CV) following 6 weeks of concurrent rehabilitative exercise. Light bars indicate END>RES group, dark bars indicate RES>END group. Representative western blotting image for pre-exercise and post included. *Significant difference from baseline (P<0.05). **Significant difference from baseline (P<0.01). ***Significant difference from baseline (P<0.001). Bar indicates main effect for time and not exercise group. Mean ± SD.</p

Concurrent exercise recovers maximum isometric strength loss induced by disuse and increases aerobic performance.

<p>A - Values for maximum isometric strength of the knee extensors before immobilization (BL), before exercise (pre-exercise) and after 6 weeks of rehabilitative concurrent exercise (Post). B - peak oxygen consumption (VO_2peak) before immobilization (BL) and after 6 weeks of concurrent exercise (Post). Light bars indicate END>RES group, dark bars indicate RES>END group. **Significant difference from baseline (P<0.01). ***Significant difference from baseline (P<0.001). Bar indicates main effect for time and not exercise group. Mean ± SD.</p

Subject characteristics before interventions.

<p>Mean ± SD.</p><p>Subject characteristics before interventions.</p

Concurrent exercise alters mRNA content of genes involved in the regulation of mTOR signaling, and proposed IGF-1 and myostatin gene expression.

<p>Gene expression changes in skeletal muscle 3 hours after concurrent rehabilitative exercise for genes involved in resistance exercise adaption. Light bars indicate END>RES group, dark bars indicate RES>END group. Regulated in DNA damage 1 (REDD1) and 2 (REDD2), Ras homolog enriched in brain (Rheb), and peroxisome proliferative activated receptor (PPAR) gamma coactivator-1α, isoform 4 (PGC-1α4), ***Significant difference from baseline (P<0.001). Bar indicates main effect for time and not exercise group. Mean ± SD.</p

Primer design.

<p>Primer design.</p

Fold change of gene expression after 3 hours of recovery from eccentric exercise using DNA microarray analysis (n = 18).

<p>Fold change of gene expression after 3 hours of recovery from eccentric exercise using DNA microarray analysis (n = 18).</p

Regulatory and downstream targets of NFAT transcriptionally active following a single bout of eccentric exercise.

<p>p38MAPK – p38 mitogen activated protein kinase; GSK-3β – glycogen synthase kinase 3 beta; MAF – v-maf musculoaponeurotic fibrosarcoma oncogene homologue (avian).</p