Abstract
The capability of regeneration for skeletal muscle after injury depends on the differentiation and proliferation ability of the resident stem cells called satellite cells. It has been reported that electrical stimulation was widely used in clinical conditions to facilitate muscle regeneration after injury, but the characterization of satellite cell responses to the context of low-frequency electrical stimulation in early-phase muscle strain conditions has not been fully clarified. In this study, we aim to investigate the effects of low-frequency electrical stimulation (frequency: 20 Hz; duration: 30 minutes, twice daily) on satellite cell activities in a rat model for the early phase of muscle strain. Firstly, we adopted our previously developed rat model to mimic the early phase of muscle strain in human. After then, we examined the effects of low-frequency electrical stimulation on histopathological changes of the muscle fiber by hematoxylin and eosin (H&E) staining. Finally, we investigated the effects of low-frequency electrical stimulation on satellite cell proliferation and differentiation by quantification of the expression level of the specific proteins using western blot analyses. The muscle strain in biceps femoris muscles of rats can be induced by high-speed rotation from knee flexion 50° to full knee extension at 960°·s−1 angular velocity during its tetany by activating the sciatic nerve, as evidenced by a widening of the interstitial space between fibers, and more edema or necrosis fibers were detected in the model rats without treatment than in control rats. After treatment with low-frequency electrical stimulation (frequency: 20 Hz; duration: 30 minutes, twice daily), the acute strained biceps femoris muscles of rats showed obvious improvement of histomorphology as indicated by more mature muscle fibers with well-ordered formation with clear boundaries. Consistently, the expression levels of the MyoD and myogenin were marked higher than those in the rats in the animal model group, indicating increased satellite cell proliferating and differentiating activities by low-frequency electrical stimulation. This study shows that low-frequency electrical stimulation provides an effective stimulus to upregulate the protein expression of MyoD/myogenin and accelerate the restoration of structure during the early phase of muscle strain. This may have significance for clinical practice. Optimization of low-frequency electrical stimulation parameters may enhance the therapeutic outcome in patients.
Highlights
Muscle injuries are the most common injuries sustained by athletes
hematoxylin and eosin (H&E) staining indicated that normal fibers with polygonal aspects are multinucleated syncytia with their nuclei located at the periphery as seen in the biceps femoris muscle cross section (Figure 1(a))
We have explored the effectiveness of lowfrequency electrical stimulation on satellite cell activity and restoration of structure in the strained biceps femoris muscles during the early phase of muscle strain
Summary
Muscle injuries are the most common injuries sustained by athletes. The high prevalence of muscle strains is well documented in sports, for example, football [1], soccer [2], cricket [3], and rugby [4]. Even a mild muscle strain can cause a delay in returning to sport or even lead to a failure in the sporting activity one is able to do. Rehabilitation of injured skeletal muscle is an area that continues to present a challenge for the athletes and sports medicine clinicians. Skeletal muscles exhibit a high plasticity for morphological and functional adaptations to growth, training, mechanical overload, and injury. The processes by which these adaptations occur are largely dependent on a small population of satellite cells, which are resident between the basal
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