Distinct Skeletal Muscle Gene Regulation from Active Contraction, Passive Vibration, and Whole Body Heat Stress in Humans

Abstract

Skeletal muscle exercise regulates several important metabolic genes in humans. We know little about the effects of environmental stress (heat) and mechanical stress (vibration) on skeletal muscle. Passive mechanical stress or systemic heat stress are often used in combination with many active exercise programs. We designed a method to deliver a vibration stress and systemic heat stress to compare the effects with active skeletal muscle contraction.

Purpose: The purpose of this study is to examine whether active mechanical stress (muscle contraction), passive mechanical stress (vibration), or systemic whole body heat stress regulates key gene signatures associated with muscle metabolism, hypertrophy/atrophy, and inflammation/repair.

Methods: Eleven subjects, six able-bodied and five with chronic spinal cord injury (SCI) participated in the study. The six able-bodied subjects sat in a heat stress chamber for 30 minutes. Five subjects with SCI received a single dose of limb-segment vibration or a dose of repetitive electrically induced muscle contractions. Three hours after the completion of each stress, we performed a muscle biopsy (vastus lateralis or soleus) to analyze mRNA gene expression.

Results: We discovered repetitive active muscle contractions up regulated metabolic transcription factors NR4A3 (12.45 fold), PGC-1α (5.46 fold), and ABRA (5.98 fold); and repressed MSTN (0.56 fold). Heat stress repressed PGC-1α (0.74 fold change; p < 0.05); while vibration induced FOXK2 (2.36 fold change; p < 0.05). Vibration similarly caused a down regulation of MSTN (0.74 fold change; p < 0.05), but to a lesser extent than active muscle contraction. Vibration induced FOXK2 (p < 0.05) while heat stress repressed PGC-1α (0.74 fold) and ANKRD1 genes (0.51 fold; p < 0.05).

Conclusion: These findings support a distinct gene regulation in response to heat stress, vibration, and muscle contractions. Understanding these responses may assist in developing regenerative rehabilitation interventions to improve muscle cell development, growth, and repair.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Fig 1. Study Timeline.

The muscle contraction stressor was unilaterally delivered in two ~4-minute bouts with a 5-minute rest period between bout 1 and bout 2. The vibration stressor was unilaterally delivered in a single 30-minute bout at a oscillation frequency of 30Hz and an amplitude of 0.6g. The whole-body heat stressor was delivered in a single 30-minute bout. Three hours after the completion of each stressor a percuatneous muscle biopsy was performed. Muscle biopsies were performed bilaterally on the experimental and control limb for the muscle contractions and vibration stressors. A unilateral muscle biopsy was performed before the heat stressor on the control limb and after the heat stressor on the opposite limb due to the systemic effects of whole-body heat stress.

Fig 2. Physiological Effects after Muscle Contraction, Vibration, and Heat.

(A and B) The torque curve from the soleus muscle during bout 1 and bout 2 during the muscle contraction stressor with decreased torque production by the end and between the bout 1 and bout 2. Representative example of the level of EMG muscle activity compared to the maximum M-wave during the bout of unilateral muscle vibration. (D, E, F) The temperature, self-reported comfort, and heart rate during the passive, whole-body heat stressor.

Fig 3. Comparative Gene Stress Responses following Muscle Contractions, Vibration, and Heat.

We compared the expression levels of the top 10 up and down regulated genes after each stressor to the other stressors. Of particular note is the order of magnitude change of the top 10 genes increased after muscle contractions compared to the other stressors. Additionally, the increased expression of FOXK2 (2.36±0.56) only after vibration, and the difference in ANKRD1 expression after heat (downregulated, 0.51±0.07) and muscle contractions (upregulated, 2.19±0.08).

Fig 4. Expression of Transcription Factors following Muscle Contractions, Vibration, and Heat.

(A)PGC-1α expression increased after muscle contractions (5.46±0.64, p

Fig 5. Expression of Mitochondrial Genes following Muscle Contractions, Vibration, and Heat.

(A) BRP44 expression was unchanged after muscle contractions and vibration (1.14±0.10, p = 0.25; 0.93±0.09, p = 0.42) and decreased in most participants after heat (0.77±0.12, p = 0.12). (B) BRP44L expression was unchanged after muscle contractions and vibration (1.02±0.09, p = 0.97; 0.88±0.10, p = 0.27) and decreased after heat (0.82±0.06, p = 0.03). (C) MFN1 expression was unchanged after muscle contractions and vibration (1.18±0.16, p = 0.42; 0.98±0.07, p = 0.67), and slightly decreased after heat (0.87±0.06, p = 0.07). (D) MFN2 expression was unchanged after muscle contractions and vibration (0.97±0.06, p = 0.54; 1.13±0.11, p = 0.44) and slightly decreased after heat (0.79±0.07, p = 0.05). † indicates a p-value

Fig 6. Expression of Glucose Metabolism Genes following Muscle Contractions, Vibration, and Heat.

(A) PDK4 expression was increased after muscle contractions (3.37±0.83, p