Response of rat muscle to acute resistance exercise defined by transcriptional and translational profiling - PubMed (original) (raw)

Response of rat muscle to acute resistance exercise defined by transcriptional and translational profiling

Yi-Wen Chen et al. J Physiol. 2002.

Abstract

To further understand molecular mechanisms underlying skeletal muscle hypertrophy, expression profiles of translationally and transcriptionally regulated genes were characterized following an acute bout of maximally activated eccentric contractions. Experiments demonstrated that translational mechanisms contribute to acute gene expression changes following high resistance contractions with two candidate mRNAs, basic fibroblast growth factor (bFGF) and elongation factor-1 alpha (EF1alpha), targeted to the heavier polysomal fractions after a bout of contractions. Gene profiling was performed using Affymetrix Rat U34A GeneChips with either total RNA or polysomal RNA at one and six hours following contractions. There were 18 genes that changed expression at one hour and 70 genes that were different (60 genes increased:10 genes decreased)at six hours after contractions. The model from this profiling suggests that following high resistance contractions skeletal muscle shares a common growth profile with proliferating cells exposed to serum. This cluster of genes can be classified as "growth" genes and is commonly associated with progression of the cell cycle. However, a unique aspect was that there was induction of a cluster of tumour suppressor or antigrowth genes. We propose that this cluster of "antigrowth" genes is induced by the stress of contractile activity and may act to maintain skeletal muscle in the differentiated state. From the profiling results, further experiments determined that p53 levels increased in skeletal muscle at 6 h following contractions. This novel finding of p53 induction following exercise also demonstrates the power of expression profiling for identification of novel pathways involved in the response to muscle contraction.

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Figures

Figure 1

Figure 1. mRNA distribution in polysomes following an acute bout of high resistance contractions

Each fraction represents the untranslated RNAs (fractions 1-3) and the heavier, translated mRNAs (fractions 4-6). Representative Northern blots are provided in the top panels with control muscle on the left and exercised muscle on the right. Results from the Northern blots were quantified using densitometry and the relative proportion of mRNA in each fraction has been quantified and presented graphically (lower panel). A, distribution of EF1α (elongation factor 1 α); B, distribution of basic fibroblast growth factor (bFGF); C, distribution of α-skeletal actin mRNA. For each graph, continuous line represents control and dashed line represents exercised.

Figure 2

Figure 2. Examples of hybridization patterns for specific genes regulated in response to acute muscle contractions

Each gene shown was queried with 16 ‘perfect match’ 25 bp oligonucleotides (top rows), with paired ‘mismatched’ oligonucleotides designed with a single mismatch in the centre (lower rows). Signal intensities are represented by different colour codes: (from high to low) white, red, yellow, green, blue and black A, hybridization of the Egr1 mRNA shows very low level in unexercised muscle. After a bout of exercise, Egr1 shows strong induction of expression, in both total RNA pools (transcriptional regulation) and polysomal pools (translational regulation). Hybridization only to the perfect match probes is seen, with relatively consistent hybridization signals to all 16 perfect match oligonucleotides. B, GADD45 shows strong translational induction after exercise. The gene does not show significant changes in the total RNA pools.

Figure 3

Figure 3. Immunological confirmation of c-fos gene expression changes

Cold acetone-fixed cryosections of control and exercised muscle are shown, immunostained with c-fos (Cy3; red signal) and Hoechst 358 (nuclear marker, blue signal).

Figure 4

Figure 4. Bar graph of means ± standard errors from densitometric scans of p53 Western blots

# statistically significant at P < 0.05: one-tailed t test.

Figure 5

Figure 5. Proposed biochemical cascades in skeletal muscle tissue following a bout of high resistance exercise

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