For more than 10 years abnormalities of dystrophin have been known to be the major cause of muscle cell degeneration. Dystrophin is part of a larger complex of proteins, some of which are also involved in distinct forms of limb girdle muscular dystrophy (LGMD). This complex of proteins links the internal cytoskeleton to the extracellular matrix and alteration in this linkage causes membrane instability, and ultimately muscle cell degeneration. In LGMD, caused by abnormalities in the sarcoglycans, this linkage is preserved, yet muscles still degenerate. The recent identification of FLNC as a sarcoglycan-interacting protein raises the possibility that there is a signaling role to the sarcoglycans, and it is this signaling that is necessary to maintain the muscle cell integrity.

Directed by the Program Director, Dr. Lou Kunkel, this project will continue his laboratory’s interest in understanding the underlying basis of the muscular dystrophies and using that information to develop targeted treatments. Project 1 will focus on a subset of the Kunkel laboratory’s effort, with emphasis on the role of the sarcoglycans and newly identified filamin-2 in the pathogenesis of the limb girdle muscular dystrophies (LGMD). We will explore this function via conventional biochemical and genetic analysis, and by the new expression array (Core C). We will have the unique opportunity to study the mRNA expression profiles of the different muscle biopsies we have collected over the years and plan to collect as part of this program in collaboration with Core B. These expression patterns will be confirmed by our ongoing biochemical work on muscle proteins in the muscular dystrophies. We also are very excited about the possibilities of our recently described muscle stem cells and their potential role in developing a therapy for muscle disorders. These will be studied in collaboration with project 4 to determine their existence in dystrophies and whether normal cells will be equally effective as they were in dystrophin-deficient mice.

AIMS:

• To continue the analysis of Filamin 2 as a new component of the dystrophin associated protein complex and its role in LGMD.
• To identify additional novel FLNC/sarcoglycan-associated interacting proteins by yeast two-hybrid and biochemical cross-linking of proteins made in muscle.
• To use chip-based mRNA expression arrays to analyze/compare dystrophin, sarcoglycan, calpain-3 and filamin-deficient muscle to normal muscle in order to identify changes that are common among the dystrophies or specific to a particular form of dystrophy.
• To validate results of expression arrays and characterize genes that are unique to each of the dystrophies as potential modifiers of the phenotype and begin to test new hypotheses about the molecular pathogenesis of muscle degeneration.
• To analyze SP stem cell populations within sarcoglycan-deficient mouse models of human dystrophy, studying the influence these mutations have on the stem cells and whether normal stem cells can be corrective in these respective dystrophies.