Skeletal muscle denervation eventually causes atrophy as a result of interrupted nerve conduction and the lack of nutritional factors. Myogenin is a myogenic regulatory factor that plays a key role in myoblast differentiation. Changes in myogenin expression in denervated rat skeletal muscle have been demonstrated, but myogenin expression in denervated human skeletal muscle has not been reported. Human muscle samples were analysed at different time-points post-denervation to evaluate changes in myogenin expression and their relationship with skeletal muscle atrophy. Post-denervation, myogenin mRNA levels peaked at 7 months and were 37.5 times the normal level. Expression levels then declined to 21 and 11 times the normal level at 12 and 26 months postdenervation, respectively. Prolonged denervation resulted in pathological changes characterized by decreased numbers of intact muscle fibres.
It is reported that neural stem cells (NSC)can arrest denervated muscle atrophy and promote nerve regeneration when transplanted into injured peripheral nerves, and that regenerated host axons can form synapses with transplanted and differentiated NSC. In this study, F344 rat nerve segments and F344 rat NSC were transplanted into host green fluorescence protein (GFP) transgenic F344 rats. This allowed transplanted F344 rat tissue to be used as a nonluminous background for the clear visualization of regenerated host GFP axons. Regenerated host axons grew into the transplanted F344 nerve segment 2 weeks after nerve anastomosis. Immunohistochemical staining and confocal microscope analysis revealed that regenerated host axons formed synapses with NSC-derived neurons. The findings confirmed that regenerated peripheral axons form synapses with neurons in peripheral nerves, possibly forming the basis for clinical application in peripheral nerve injury.
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