PROJECT SUMMARY Duchenne muscular dystrophy (DMD) is one of the most severe neuromuscular diseases, with a median life expectancy of 22 years. DMD results from the absence of the protein dystrophin, reducing the ability of muscle to respond to stresses imposed by force generation and resulting in significant contractile dysfunction. In human patients with DMD, this manifests in progressive skeletal muscle weakness beginning around 3-5 years of age and cardiomyopathy and respiratory insufficiency around age 25, leading to death. In the mdx mouse model of DMD, the absence of dystrophin also results in rapid and robust deficits in contractility, particularly loss of force with repetitive eccentric contractions (ECCs) in skeletal muscle. The mechanisms by which mdx mice undergo ECC force loss, and those which result in broader contractile deficits of striated muscle, are poorly understood. Preliminary data from the Ervasti lab implicates elevated reactive oxygen species (ROS) and subsequent hyperoxidation of the thiol proteome in DMD pathophysiology. Moreover, supplementation with the gasotransmitter hydrogen sulfide (H2S), which is reduced in mdx muscle, completely protects mdx extensor digitorum longus (EDL) muscle from ECC force loss in vitro. The mechanisms by which H2S protects from ECC force loss, and its contributions to contractility in general, are not well characterized in the context of dystrophin- deficient muscular dystrophy. The studies I designed in my proposal will test the hypothesis that elevations in H2S will increase the persulfidation of reactive thiol residues on cysteines of contractile proteins, thereby preventing hyperoxidation and associated contractile dysfunction. The experiments proposed here will strive to characterize the effect of chronic, systemic H2S supplementation on DMD pathophysiology in vivo (Aim 1) and define the effects of low H2S levels on oxidative post-translational modifications in mdx contractile proteins (Aim 2). A more complete understanding of contractile dysfunction and protection from force loss in mdx muscle is critical to generating more efficacious therapeutics. In addition to the research proposal, the following documents include a comprehensive and rigorous set of research and clinical training plans that will allow for the successful completion of my MD and PhD degrees and will enhance my development into a productive physician-scientist, able to drive cutting-edge translational research and clinical care for my patients.