Low-frequency stimulation regulates metabolic gene expression in paralyzed muscle

Abstract

The altered metabolic state after a spinal cord injury compromises systemic glucose regulation. Skeletal muscle atrophies and transforms into fast, glycolytic, and insulin-resistant tissue. Osteoporosis is common after spinal cord injury and limits the ability to exercise paralyzed muscle. We used a novel approach to study the acute effect of two frequencies of stimulation (20 and 5 Hz) on muscle fatigue and gene regulation in people with chronic paralysis. Twelve subjects with chronic (>1 yr) and motor complete spinal cord injury (ASIA A) participated in the study. We assessed the twitch force before and after a single session of electrical stimulation (5 or 20 Hz). We controlled the total number of pulses delivered for each protocol (10,000 pulses). Three hours after the completion of the electrical stimulation (5 or 20 Hz), we sampled the vastus lateralis muscle and examined genes involved with metabolic transcription, glycolysis, oxidative phosphorylation, and mitochondria remodeling. We discovered that the 5-Hz stimulation session induced a similar amount of fatigue and a five- to sixfold increase (P < 0.05) in key metabolic transcription factors, including PGC-1α, NR4A3, and ABRA as the 20-Hz session. Neither session showed a robust regulation of genes for glycolysis, oxidative phosphorylation, or mitochondria remodeling. We conclude that a low-force and low-frequency stimulation session is effective at inducing fatigue and regulating key metabolic transcription factors in human paralyzed muscle. This strategy may be an acceptable intervention to improve systemic metabolism in people with chronic paralysis.

Keywords: diabetes; electrical stimulation; health quality; metabolic syndrome; spinal cord injury.

Copyright © 2015 the American Physiological Society.

Figures

Fig. 1.

Timeline for each experimental session. Sessions A and B: in these first 2 sessions, the physiological response to a 5- or 20-Hz stimulation protocol was assessed using pre- and post-3-Hz stimulation. These first 2 sessions were separated by ≥2 wk. Sessions C and D: in these last 2 sessions, bilateral vastus lateralis muscle biopsies were taken 3 h after unilateral activation of the vastus lateralis (quadriceps) muscle with the 5- or 20-Hz stimulation protocol. These last 2 sessions were separated by ≥6 wk.

Fig. 2.

Representative example of the force-time curve. An example of the force generated using 5-Hz (black) and 20-Hz (gray) electrical muscle stimulation with the knee extended to 10° of horizontal in a single subject. The associated electrical stimulation train is below each force-time curve.

Fig. 3.

Assessment of fatigue after low- and high-force exercise. The mean and SE of the maximum twitch force generated before (pre) and after (post) a session of low- (5 Hz) and high-frequency (20 Hz) exercise using electrical stimulation. There was a significant decrease in the peak twitch force after low- (P < 0.001) and high-force (P < 0.001) exercise. There was no difference in the peak twitch force observed between the low- and high-force exercise sessions (P = 0.31).

Fig. 4.

Expression of transcription factor, fast-twitch fiber, and slow-twitch fiber genes following acute exercise. A: peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) was increased 3 h after a dose of low- and high-frequency muscle stimulation (P < 0.001 and P = 0.003, respectively). B: nuclear receptor subfamily 4 group A member 3 (NR4A3) was increased 3 h after a dose of low- and high-frequency muscle stimulation (P < 0.001 and P < 0.001, respectively). C: actin-binding rho-activating protein (ABRA) was increased 3 h after a dose of low- and high-frequency muscle stimulation (P = 0.001 and P = 0.003, respectively). D: myostatin (MSTN) was decreased 3 h after a dose of low- but not high-frequency muscle stimulation (P = 0.05 and P = 0.11, respectively). E–H: genes associated with a fast-twitch muscle fiber phenotype were unaltered 3 h after either low- or high-frequency muscle stimulation. In a single subject, parvalbumin (PVALB) was increased after electrical muscle stimulation, but this was inconsistent with the remaining subjects. I and J: genes associated with a slow-twitch muscle fiber phenotype were unaltered 3 h after either low- or high-frequency muscle stimulation. Fold change values represent the mean of the exercised limb compared with the opposite (nonexercised) limb from the same subjects. †P < 0.05 for a within-group paired t-test; ‡P < 0.10 for a within-group paired t-test.

Fig. 5.

Expression of glycolysis and fatty acid oxidation genes following acute or chronic stimulation. A–D: genes associated with glucose metabolism were consistently unaltered 3 h after low- or high-frequency muscle stimulation. However, pyruvate dehydrogenase kinase 4 (PDK4) appears to be increased in most subjects after both low- and high-frequency muscle stimulation and PDHA1 decreased after low-frequency muscle stimulation. E–H: genes associated with fatty acid metabolism were unaltered 3 h after either low- or high-frequency muscle stimulation. Fold change values represent the mean of the exercised limb compared with the opposite (nonexercised) limb from the same subjects. †P < 0.05 for a within-group paired t-test; ‡P < 0.10 for a within-group paired t-test.

Fig. 6.

Expression of tricarboxylic acid cycle, oxidative phosphorylation, and mitochondrial fission/fusion genes following acute or chronic stimulation A–D: genes associated with the tricarboxylic acid cycle were unaltered 3 h after low- and high-frequency muscle stimulation. E–H: most genes associated with oxidative phosphorylation were unaltered 3 h after either low- or high-frequency muscle stimulation; however, COQ10A was decreased after high- but not low-frequency electrical muscle stimulation. I and J: most genes associated with the mitochondrial fission or fusion were unaltered 3 h after either low- or high-frequency muscle stimulation. However, MFF was decreased in most subjects after low-frequency muscle stimulation, and MFN2 was decreased in most subjects after high-frequency muscle stimulation. Fold change values represent the mean of the exercised limb compared with the opposite (nonexercised) limb from the same subjects. †P < 0.05 for a within-group paired t-test; ‡P < 0.10 for a within-group paired t-test.