We propose to build and analyze the first reported animal models of myosin storage myopathy (MSM), a degenerative disease of human skeletal and cardiac muscles that arises from point mutations in the C-terminal rod region of slow/beta-cardiac myosin heavy chain. Our transgenic Drosophila melanogaster models will be used to dissect the molecular and developmental bases of MSM and to test possible therapeutic modalities. The Drosophila system will allow us to examine both homozygotes and heterozygotes (mutant/+) for each MSM allele in a standardized genetic background. This will define the importance of interactions between wild- type and mutant myosin molecules to disease pathology and will obviate genetic heterogeneity that leads to phenotypic variability in the human disease. We will test the hypotheses that: 1) MSM mutant myosin expressed in Drosophila leads to specific cell biological and physiological abnormalities similar to those seen in human MSM patients, 2) MSM myosin molecules a) are defective in filament assembly, b) show abnormal filament degradation and/or c) are prone to aggregation, 3) preventing MSM myosin aggregate formation or enhancing MSM myosin turnover can improve mutant muscle structure and performance. To test these hypotheses, we will pursue the following specific aims: 1) Examine the structural and functional effects of four different MSM mutations on skeletal and cardiac muscles during aging. We will explore the progressive nature of MSM via microscopy and physiological assays and correlate our results with extant human data. 2) Isolate mutant myosin molecules and assess their filament-forming ability, filament stability to proteolysis and aggregation propensity. This will help define the molecular basis of the disease. 3) Attempt to ameliorate disease phenotypes in organisms a) by over-expressing the molecular chaperones alphaB-crystallin, Hsp70, Hsp90 or UNC-45 (all known to aid in myosin folding and/or protection from stress);b) by using small molecule inducers of the heat shock response to more broadly elicit expression of molecular chaperones;c) by using transgenic or pharmacological approaches to induce autophagy as a mechanism to clear myosin aggregates. This multifaceted approach will provide novel insights into the developmental and biophysical bases of MSM and yield potential therapeutic approaches that may be useful for treating MSM and other inclusion body diseases.
Myosin storage myopathy is a genetic disease that results in defects in both heart and skeletal muscles due to mutation and aggregation of the protein myosin. In this project, we will construct and analyze models of this disease in the fruit fly, Drosophila melanogaster, in order to better understand the basis of the human disease and to further the development of potential therapies. We will use our mutant Drosophila lines to 1) determine how the mutations alter the structure and function of skeletal and cardiac muscles during aging, 2) define the biophysical defects present in the mutant myosin and 3) employ genetic and drug therapies designed to remove the abnormal myosin and reduce its effect on muscle and heart function.
|Viswanathan, Meera C; Tham, Rick C; Kronert, William A et al. (2017) Myosin storage myopathy mutations yield defective myosin filament assembly in vitro and disrupted myofibrillar structure and function in vivo. Hum Mol Genet 26:4799-4813|