Dystrophin insufficiency causes selective muscle histopathology and loss of dystrophin-glycoprotein complex assembly in pig skeletal muscle

Authors: HOLLINGER, KATRIN - Iowa State University; YANG, CAIXIA - Iowa State University; MONTZ, ROBYN - Iowa State University; Nonneman, Danny - Dan; ROSS, JASON - Iowa State University; SELSBY, JOSHUA - Iowa State University

Submitted to: Journal of Federation of American Societies for Experimental Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/9/2013
Publication Date: 4/1/2014
Publication URL: http://handle.nal.usda.gov/10113/59654
Citation: Hollinger, K., Yang, C.X., Montz, R.E., Nonneman, D., Ross, J.W., Selsby, J.T. 2014. Dystrophin insufficiency causes selective muscle histopathology and loss of dystrophin-glycoprotein complex assembly in pig skeletal muscle. Journal of Federation of American Societies for Experimental Biology. 28(4):1600-1609.

Interpretive Summary: Because of limitations in existing animal models of Duchenne and Becker muscular dystrophies, there has been great interest in the development of novel large animal models for these diseases. Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) are caused by mutations in dystrophin that result in deficiency or a non-functional protein product. Both of these diseases are most commonly studied using a knockout mouse and a golden retriever dog model, which have some inconsistencies with the human disease. A line of pigs was recently identified that are more susceptible to stress-mediated death due to a defect in the dystrophin gene. This defect is associated with a reduction of dystrophin, a necessary structural protein, in heart and skeletal muscle. This report evaluates dystrophin protein levels and severity of disease in muscles of eight-week-old pigs. Affected pigs had about 70% less dystrophin protein in diaphragm and skeletal muscle and greater variation in muscle fiber size. Other membrane proteins that associate with dystrophin were also reduced. Histology of muscle from affected pigs also showed signs of muscle injury in load-bearing muscles. At eight weeks of age, pigs with a deficiency in dystrophin protein have a phenotype consistent with human muscular dystrophy patients. Affected pigs resemble many aspects of human disease and their body size, relevant to humans, should provide an ideal model for this human disease.

Technical Abstract: Duchenne muscular dystrophy (DMD) is caused by a dystrophin deficiency while Becker muscular dystrophy (BMD) is caused by a dystrophin insufficiency or expression of a partially functional protein product. Both of these dystrophinopathies are most commonly studied using the mdx mouse and a golden retriever dog model. While these models contribute to our understanding of the disease, deficiencies of both models necessitate the development of a novel large animal model. We evaluated eight week old male dystrophin insufficient pigs for suitability as a large animal model of dystrophinopathy. Affected pigs had a 70% reduction in full length dystrophin protein in the diaphragm, psoas major and longissimus lumborum along with a fivefold increase in serum creatine kinase activity compared to healthy littermates. Dystrophin insufficiency in the diaphragm and the longissimus lumborum resulted in muscle injury with disorganized fibrosis often co-localized with fatty infiltration, but not in the psoas major. Further fiber size variability increased 20% in the diaphragm and fivefold in the longissimus compared to muscle from healthy animals. Affected animals also had a 50% reduction in a-sarcoglycan in all three muscles indicating compromised assembly of the dystrophin associated protein complex. Other membrane associated proteins, including laminin and desmin, were not reduced as demonstrated by immunohistochemistry. We conclude that at only eight weeks of age pigs with insufficient dystrophin protein expression have a phenotype consistent with human dystrophinopathy patients. Affected pigs recapitulate many aspects of human disease and their body size is relevant to humans indicating pigs are an ideal translational model for dystrophinopathies.