Repair of spinal cord transection and its effects on muscle mass and myosin heavy chain isoform phenotype

A number of significant advances have been developed for treating spinal cord injury during the past two decades. The combination of peripheral nerve grafts and acidic fibroblast growth factor ( hereafter referred to as PNG) has been shown to partially restore hindlimb function. However, very little is known about the effects of such treatments in restoring normal muscle phenotype. The primary goal of the current study was to test the hypothesis that PNG would completely or partially restore 1) muscle mass and muscle fiber cross-sectional area and 2) the slow myosin heavy chain phenotype of the soleus muscle. To test this hypothesis, we assigned female Sprague-Dawley rats to three groups: 1) sham control, 2) spinal cord transection ( Tx), and 3) spinal cord transection plus PNG ( Tx + PNG). Six months following spinal cord transection, the open- field test was performed to assess locomotor function, and then the soleus muscles were harvested and analyzed. SDS- PAGE for single muscle fiber was used to evaluate the myosin heavy chain ( MHC) isoform expression pattern following the injury and treatment. Immunohistochemistry was used to identify serotonin ( 5- HT) fibers in the spinal cord. Compared with the Tx group, the Tx + PNG group showed 1) significantly improved Basso, Beattie, and Bresnahan scores ( hindlimb locomotion test), 2) less muscle atrophy, 3) a higher percentage of slow type I fibers, and 4) 5- HT fibers distal to the lesion site. We conclude that the combined treatment of PNG is partially effective in restoring the muscle mass and slow phenotype of the soleus muscle in a T- 8 spinal cord- transected rat model.