Muscular dystrophy is a genetic disease for which there is no cure. One of the most severe forms of muscular dystrophy is Duchenne Muscular Dystrophy (DMD). DMD and a subset of the limb girdle muscular dystrophies have in common disruption of the dystrophin protein complex. Disrupting the dystrophin complex lead to a fragile muscle membrane, loss of myofibers and replacement of the muscle with fibrosis or scarring. Multiple lines of evidence point to fibrosis is as a driver of muscular dystrophy pathology. We hypothesize that fibrosis provides a scaffold that promotes an unfavorable cytokine profile that further damages muscle. We further hypothesize that the primary components of the unfavorable cytokine profile are TGFp and the related TGFp family member myostatin. Together, TGFp and myostatin, lead to increased fibrosis, reduced muscle mass and regeneration, and aggravated membrane fragility. Therefore, we propose to determine the means by which TGFp and myostatin are normally sequestered by the matrix and held unavailable for receptor engagement and signaling and to determine how to promote inactivation of TGFp and myostatin in muscular dystrophy (Project 1). We will also demonstrate necessary proteolytic cleavage steps for release and processing of myostatin, and related molecules, and the degree to which soluble receptors can be effective in treating muscular dystrophy (Project 2). We will also sequentially assess the distinct intracellular signaling pathways that are triggered by TGFp and myostatin and test whether inhibiting these pathways improves muscle function and pathology in muscular dystrophy (Project 3). Three established investigators (McNally, Lee, and Molkentin) will lead these projects forming a distinctive team where their combined expertise will define the TGFp/myostatin pathway for therapeutic intent in muscular dystrophy. Three Cores will support the Projects; Core A will integrate the efforts at our three institutions to assure seamless collaboration and transfer of materials. Core B will provide histopathological assessment of muscular dystrophy after genetic manipulation and treatments, and Core C will perform functional analysis in vivo and provide support to Core B.