The overall goal of this proposal is to use animal models to test the efficacy of biglycan as a protein therapeutic for muscular dystrophy. Duchenne's muscular dystrophy (DMD) is a heritable disease that affects approximately 1 in 3,500 boys. These children are usually wheelchair-bound by age 12 and rarely survive past their early twenties. There are currently no effective treatments for the underlying pathology of DM0. The molecular pathogenesis of Duchenne's and many other muscular dystrophies has been traced to a specialized ensemble of proteins at the muscle cell surface known as the dystrophin-associated protein complex (DAPC). Mutation of dystrophin leads to disruption in the organization of the DAPC. The resulting failure of DAPC function results in muscle cell damage and loss. We have recently discovered that the extracellular matrix molecule biglycan is expressed at the muscle cell surface and binds, by distinct mechanisms, to the ectodomains of three core constituents of the DAPC: alpha-dystroglycan, aipha-sarcoglycan and gamma-sarcoglycan. These molecular interactions indicate that biglycan can bridge the component subcomplexes of the DAPC and thus coordinate and stabilize the entire complex from outside the cell. Indeed, biglycan null (bgn-/o) mice display a dystrophic phenotype as evidenced by weakened muscle cell membranes and cell death. These observations suggest that biglycan could serve as a therapeutic to stabilize the DAPC from its extracellular aspect when dystrophin is absent. Biglycan thus represents a new path for developing therapies for muscular dystrophies. Importantly, since the biglycan-DAPC interactions are wholly extracellular, biglycan can be introduced to the muscle by systemic delivery of the purified recombinant protein. This program will utilize unique production methods to produce sufficient quantities of high quality biglycan, .and test efficacy in several animal models of muscular dystrophy.