The proper association of muscle fibers with laminin in the extracellular matrix is essential for normal muscle function. The alpha7Beta1 integrin and the dystrophin-glycoprotein complex both bind laminin and appear to be complementary linkage systems between fibers and the extracellular matrix. Congenital and acquired defects in the dystrophin-glycoprotein complex underlie the pathology associated with Duchenne and other muscular dystrophies, as well as cardiomyopathies. Mutations in the human alpha7 gene cause an additional myopathy. We recently discovered that enhanced expression of the alpha7 integrin mediated linkage system can compensate for the absence of the dystrophin-glycoprotein complex. Dystrophin/utrophin null mice develop an acute muscular dystrophy and die prematurely. Enhanced expression of the alpha7 integrin inhibits the development of muscular dystrophy and restores longevity to these animals. We propose to expand on this result and determine the level of alpha7Beta1 integrin that best prevents development of skeletal muscle pathology in these animals and whether transgene expression in the heart and smooth muscle can prevent cardiovascular disease. We will also analyze whether enhanced expression of the alpha7 integrin in the heart reduces development of cardiomyopathy associated with enterovirus-induced cleavage of dystrophin. Additional skeletal muscle and cardiomyopathies result from other defects in the dystrophin-glycoprotein linkage system. We will use transgenic animals that over-express the alpha7Beta1 integrin in different genetic backgrounds to determine whether the integrin can prevent these myopathies. Whereas mutations in the sarcoglycan genes perturb the dystrophin-glycoprotein transmembrane linkage system and cause cardiomyopathy and muscular dystrophy, we will determine whether over-expression of the alpha7 integrin can inhibit the development of muscle disease in sarcoglycan deficient mice. Likewise, we will assess whether enhanced integrin expression will ameliorate alpha2-laminin congenital muscular dystrophy. Lastly, experiments are proposed that aim at understanding the mechanism by which enhanced integrin expression inhibits development of muscle pathology. This research will reveal whether increasing alpha7 integrin levels in humans may be worth pursuing in the future as treatments for Duchenne and other muscular dystrophies and cardiomyopathies.
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