Upregulation of M-creatine kinase and glyceraldehyde-3-phosphate dehydrogenase: two markers of muscle disuse

Muscle disuse induces substantial alterations in the highly plastic skeleta l muscle tissues, which occur especially in antigravity slow muscles. We di fferentially screened a muscle cDNA array to identify modifications in gene profile expression induced in slow rat soleus muscle mechanically unloaded by hindlimb suspension as a model for muscle disuse. This study focused on muscle creatine kinase mRNA and protein and glyceraldehyde-3-phosphate deh ydrogenase mRNA, which were found to be upregulated in unweighted muscles. These upregulations were analyzed over a 4-wk time course of hindlimb suspe nsion and compared with variations in myosin heavy chain (MHC) isoforms whi le specifically focusing on type IIx MHC mRNA and protein. The two metaboli c marker upregulations clearly preceded IIx MHC contractile protein upregul ation. Muscle creatine kinase upregulation was shown to be an excellent, an d the earliest, marker of muscle disuse at mRNA and protein levels.