Genetic repair of muscular degeneration associated with Duchenne muscular dystrophy

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Project Summary/Abstract: Duchenne Muscular dystrophy (Dmd) is a lethal degenerative disease affecting 1 in 5,000 males. Dmd is caused by mutations in the gene encoding dystrophin, a highly conserved protein linking muscle cell membranes with the extracellular matrix and the contractile machinery within them. Dystrophin has structural and signaling functions. Loss of dystrophin is linked to muscular and neural degeneration. While traditional analyses of mice, worms and other animals modeling Dmd genetically, through loss-of-function mutations in the dystrophin gene, resulted in great advances, these systems have only produced relatively mild muscular and behavioral phenotypes. To date there is no cure for Dmd. To model the acute muscle degeneration observed in Dmd patients in a model system amenable to genetics we developed a fast and inexpensive nematode assay. Our assay elicits strong behavioral and cellular phenotypes in dystrophic (dys-1) nematodes to a degree not previously attained in other systems. During our previous award cycle, we improved our assay to allow automatization and medium to high throughput screening of candidate treatments. We went on to characterize many dystrophic phenotypes and found that they first arise during embryogenesis. We also identified the first neurological impairments in dystrophic worms, where the sensory function of ASH neurons is impaired. A suppressor mutant, and an RNA-interference screen both pointed to calmodulin as a therapeutic target. The first specific aim of this project is to characterize the onset of dystrophic phenotypes during myogenesis, and to separate the contribution of dystrophin’s signaling and structural roles to these deficits. This will identify the mechanism by which muscles become impaired during development. The second aim is to characterize the role dystrophin plays in the structure and function of the ASH neurons. These well-studied neurons will provide an amenable springboard to study the neuropathophysiology of Dmd. In the third aim, we will use our assay to identify downstream effectors of calmodulin responsible for the prevention of dystrophic phenotypes observed following reduction of calmodulin function in dys-1 animals. Identifying these effectors will be key to finding safe treatment avenues, sparing additional processes mediated by calmodulin. To validate our findings and bridge the gap to humans, we will use humanized dystrophic nematodes and human myogenic cell lines. Completion of these aims will provide key insights into Dmd pathophysiology and identify new molecular targets and pathways that can be used to treat this disease.