Regulation of the calpain and ubiquitin-proteasome systems in a canine model of muscular dystrophy

Introduction: Previous studies have tested the hypothesis that calpain and/or proteasome inhibition is beneficial in Duchenne muscular dystrophy, based largely on evidence that calpain and proteasome activities are enhanced in the mdx mouse. Methods: mRNA expression of ubiquitin‐proteasome and calpain system components were determined using real‐time polymerase chain reaction in skeletal muscle and heart in the golden retriever muscular dystrophy model. Similarly, calpain 1 and 2 and proteasome activities were determined using fluorometric activity assays. Results: We found that less than half of the muscles tested had increases in proteasome activity, and only half had increased calpain activity. In addition, transcriptional regulation of the ubiquitin‐proteasome system was most pronounced in the heart, where numerous components were significantly decreased. Conclusion: This study illustrates the diversity of expression and activities of the ubiquitin‐proteasome and calpain systems, which may lead to unexpected consequences in response to pharmacological inhibition. Muscle Nerve, 2011