Limb-Girdle Muscular Dystrophies (LGMD) are a collection of progressive muscle wasting disorders that result in muscle weakness in the shoulder and pelvic girdles. Symptoms can vary from reduced movement and strength through the shoulders, to an abnormal walking gait, to a loss of walking ability. The age of onset ranges from childhood to late adulthood, with childhood onset typically leading to more severe forms of the disease. LGMD are caused by mutations in over 30 different genes with diverse functions, though how these genes interact or how they contribute to a common disease pathology is not well understood. In order to explore the relationship between various LGMD causative and associated genes, we are utilizing the genetically tractable model system Drosophila melanogaster, a well-established model for studying muscular dystrophies. Two LGMD causative/associated genes, BAG-3 and HspB8, are members of a protein quality control mechanism called the Chaperone Assisted Selective Autophagy (CASA) complex. We now find that the CASA complex interacts with the stress response p38 MAPK (p38Kb), which is also associated with other LGMD causing genes. We find that p38Kb and the CASA complex interact to regulate locomotor functions and to regulate protein aggregation in response to both aging and oxidative stress, two factors associated with LGMD. In order to identify potential targets of the CASA complex, we have performed a large-scale proteomics screen and have identified several candidates that have been linked to LGMD or other muscular dystrophies. Therefore, we hypothesize that p38Kb and the CASA complex regulate the degradation of specific proteins in response to aging and oxidative stress, and disruption of this process may lead to the development of LGMD. In addition, we have also screened a library of drug compounds generated by Dr. Andrei Kutateladze at the University of Denver for the ability to restore the locomotor activity of the p38Kb mutants and have identified a potential therapeutic compound. We propose to: 1) Analyze the relationship between p38Kb and the CASA complex in response to oxidative stress, 2) Characterize p38Kb and CASA complex target proteins that aggregate with age and oxidative stress exposure, and 3) Identify potential LGMD therapeutics, using Drosophila genetics, behavioral assays, and molecular biology and biochemical approaches. By exploring the mechanisms that underlie LGMD, we expect to uncover fundamental principles that contribute to disease pathology and to identify new molecular targets and compounds for the treatment of LGMD and potentially other muscular dystrophies.
Limb-Girdle Muscular Dystrophies (LGMD) are a collection of disorders that affect the muscles of the shoulder and pelvic girdles. This proposal will explore how different LGMD associated genes interact with each other to result in a common disease pathology. By understanding the factors that contribute to the disease state, we may have a greater understanding of disease causality and may identify new molecular targets for the development of therapeutics for the treatment of LGMD.
