The diaphragm rapidly increases expression of muscle atrophy genes following acute cervical spinal cord injury (cSCI)

Abstract

High cSCI typically leads to diaphragm dysfunction. The purpose of the current work was to explore changes in gene expression in the diaphragm following acute cSCI. Our primary hypothesis was that following unilateral cSCI induced by hemisection of the cervical (C2) spinal cord (C2Hx), the ipsilateral hemidiaphragm would show an increase in the mRNA level of specific proteolytic biomarkers. Diaphragm tissue was harvested from uninjured adult male Sprague-Dawley rats or rats at 1 or 7 days following C2Hx. Tissue samples were obtained from the medial costal diaphragm ipsilateral to C2Hx. In pilot studies, an 84 well gene array was used to screen for mRNA changes in genes associated with muscle plasticity. Results were subsequently validated using qRT-PCR. At 1 day post-C2Hx, the following atrophy biomarkers showed substantial relative increases: MAFbx/atrogin-1 (5-fold); MuRF1 (42-fold); Caspase-3 (3-fold); FoxO3 (2-fold). Genes associated with myogenesis also showed increased expression at both 1 (myogenin, 22-fold; Myf6, 4-fold) and 7 days post injury (MyoD, 11-fold). These data indicate that following C2Hx, the ipsilateral hemidiaphragm undergoes rapid plasticity with increased expression of genes related to muscle atrophy and plasticity.