To clarify the molecular changes of sublesional muscle in the acute phase of spinal cord injury (SCI), a moderately severe injury (40 g cm) was induced in the spinal cord (T10 vertebral level) of adult male Sprague-Dawley rats (injury) and compared with sham (laminectomy only). Rats were sacrificed at 48 h (acute) post injury, and gastrocnemius muscles were excised. Morphological examination revealed no significant changes in the muscle fiber diameter between the sham and injury rats. Western blot analyses performed on the visibly red, central portion of the gastrocnemius muscle showed significantly higher expression of muscle specific E3 ubiquitin ligases (muscle ring finger-1 and muscle atrophy f-box) and significantly lower expression of phosphorylated Akt-1/2/3 in the injury group compared to the sham group. Cyclooxygenase 2, tumor necrosis factor alpha (TNF-α), and caspase-1, also had a significantly higher expression in the injury group; although, the mRNA levels of TNF-α and IL-6 did not show any significant difference between the sham and injury groups. These results suggest activation of protein degradation, deactivation of protein synthesis, and development of inflammatory reaction occurring in the sublesional muscles in the acute phase of SCI before overt muscle atrophy is seen.
Keywords: E3-ubiquitin ligases; Inflammation; Muscle atrophy; Protein degradation; Protein synthesis; Spinal cord injury.