Abstract
BackgroundAlthough muscle dysfunction caused by unfamiliar lengthening contraction is one of most important issues in sports medicine, there is little known about the molecular events on regeneration process. The purpose of this study was to investigate the temporal and spatial expression patterns of myogenin, myoD, pax7, and myostatin after acute lengthening contraction (LC)-induced injury in the rat hindlimb.MethodsWe employed our originally developed device with LC in rat gastrocnemius muscle (n = 24). Male Wistar rats were anesthetized with isoflurane (aspiration rate, 450 ml/min, concentration, 2.0%). The triceps surae muscle of the right hindlimb was then electrically stimulated with forced isokinetic dorsi-flexion (180°/sec and from 0 to 45°). Tissue contents of myoD, myogenin, pax7, myostatin were measured by western blotting and localizations of myoD and pax7 was measured by immunohistochemistry. After measuring isometric tetanic torque, a single bout of LC was performed in vivo.ResultsThe torque was significantly decreased on days 2 and 5 as compared to the pre-treatment value, and recovered by day 7. The content of myoD and pax7 showed significant increases on day 2. Myogenin showed an increase from day 2 to 5. Myostatin on days 5 and 7 were significantly increased. Immunohistochemical analysis showed that myoD-positive/pax7-positive cells increased on day 2, suggesting that activated satellite cells play a role in the destruction and the early recovery phases.ConclusionWe, thus, conclude that myogenic events associate with torque recovery after LC-induced injury.
Highlights
Muscle dysfunction caused by unfamiliar lengthening contraction is one of most important issues in sports medicine, there is little known about the molecular events on regeneration process
Protein levels of muscles We measured the muscle contents of myogenin, myoD, pax7, and myostatin to assess the process of muscle regeneration
We examined the relationship between the expression of myogenic proteins and functional changes in the skeletal muscle after a single bout of lengthening contraction (LC) in vivo
Summary
Muscle dysfunction caused by unfamiliar lengthening contraction is one of most important issues in sports medicine, there is little known about the molecular events on regeneration process. The healing process of muscle injury consists of 3 phases: the destruction phase, the repair phase, and the remodeling phase [9]. During these 3 phases, activation of the quiescent satellite cells (SCs) plays a key role [10,11]. Activated SCs eventually become myoblasts, characterized by upregulated myogenin and downregulated pax7 [15,16,17]. These activated myogenic cells contribute to hyperplasia or hypertrophy of the injured muscles
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