Autosomal recessive limb-girdle muscular dystrophy (AR-LGMD) refers to a number of genetically and clinically heterogenous neuromuscular disorders that affect mainly skeletal muscle. Over the last few years, it has become clear that a number of genes encoding protein components of the sarcoglycan complex are responsible for several forms of AR-LGMDs. The sarcoglycans are expressed at the sarcolemma of muscle fibers and, along with other proteins, constitute the dystrophin-glycoprotein complex (DGC). These proteins are believed to play a role in maintaining the normal architecture of the muscle cell membrane by constituting a link between the subsarcolemmal cytoskeleton and the extracellular matrix. In particular, we have shown that alpha-sarcoglycan, a 50 kDa component of the DGC, is a deficient in skeletal muscle from patients having limb- girdle muscular dystrophy type 2D, and that the expression of all the other sarcoglycan proteins is also strongly reduced in muscle from these patients. Although these findings constitute great progress in our understanding of the genetic basis for AR-LGMDs, there have been no improvements in the treatment of these invalidating diseases. The long-term goal of this research proposal is the development of a gene transfer strategy for AR-LGMDs. We recently generated an animal model for LGMD2D by disrupting the alpha-sarcoglycan gene in mice and preliminary analyses of homozygous mutant mice indicate that their skeletal muscle displays a dystrophic phenotype, as expected, thus providing a valuable animal mode for LGMD2D. The overall objective of this pilot project is to develop a virally-mediated gene transfer of alpha-sarcoglycan and to investigate its therapeutic potential in alpha-sarcoglycan deficient mice.
Our first aim will be the construction of recombinant adenovirus and adeno-associated virus vectors containing the human alpha-sarcoglycan deficient mice.
Our first aim will be the construction of recombinant adenovirus and adeno-associated virus vectors containing the human alpha- sarcoglycan cDNA. These vectors will first be tested for their ability to induce expression of alpha-sarcoglycan, both in cultured myoblasts and myotubes. We will then proceed to in vivo experiments designed to test the following hypotheses: i) direct intra-muscular injections of adenoviral- based vectors containing the alpha-sarcoglycan cDNA will efficiently allow expression of the protein and restoration of the DGC in of skeletal muscle of mutant mice (Aim 2) and ii) gene transfer of alpha-sarcoglycan will support functional restoration of muscle fibers in these mice (Aim 3). Overall, the experiments outlined in our proposal will yield new information about alpha-sarcoglycan and the potential for virally-mediated alpha-sarcoglycan gene transfer in mutant mice. In addition, our findings should constitute a foundation for future investigations directed towards developing gene therapy for LGMD2D patients.
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