Principal Investigator: Deborah Ferrington, Ph.D.
The proposed work will focus on the proteasome, the principal proteolytic enzyme responsible for degrading muscle proteins. Previous research has shown upregulation of proteasome activity under conditions of muscle wasting, such as in cancer, diabetes, and muscular dystrophy (MD). A very recent report of the rescue of dystrophin and dystrophin-associated proteins with proteasome inhibition in mdx mice suggests proteasome inhibitors could be a viable therapeutic intervention for MD. Requisite for designing safe and effective inhibitors for patients with MD is a thorough understanding of the molecular changes associated with the proteasome during muscle wasting. Research from my own laboratory has shown significant changes in proteasome structure and function in atrophied muscle induced by either aging or hindlimb unweighting (Nash funding 2004). The proposed research will follow up on our initial observations that hindlimb unweighting in young rats recapitulate many of the features of proteasome in aged (atrophied) muscle. We will investigate the molecular details responsible for these changes in young rats hindlimb unweighted for either 2 or 4 weeks. We will also extend our investigations of proteasome function, composition, and regulation to the mdx mouse model. These mice provide an alternative system for examining proteasome structure/function under conditions of rapidly changing muscle architecture. Proteasome in mdx mice will be examined at 2 and 6 months, ages where there is significant atrophy and hypertrophy, respectively. We hypothesize that proteasome will share similar structural and functional features under both conditions of muscle remodeling. The following aims will be pursued. (1) Evaluate proteasome activity using model protein substrates and peptides that measure catalytic site-specific function. (2) Determine the content of the proteasome, its catalytic subunits, and the regulatory proteins PA700 and PA28. (3) Monitor the extent of muscle wasting or hypertrophy. This will be the first thorough characterization of proteasome in mdx mice. Defining how the proteasome behaves under conditions of muscle remodeling will provide important mechanistic information that could be applied to developing therapies specifically targeted at proteasome in MD muscle and other diseases associated with muscle wasting.