Characterizing Fibrotic Tissue in Duchenne Muscular Dystrophy Cardiomyopathy

Duchenne Muscular Dystrophy (DMD) is an X-linked recessive disease caused by the lack of a functional dystrophin protein, which anchors the muscle cell cytoskeleton to the extracellular matrix. DMD is characterized by muscle degeneration leading to wheelchair use by the age of 12, use of ventilation assistance by the age of 20, and a progression into cardiac failure, leading to an approximate lifespan of 25 years. Prior DMD animal models were inadequate for studying cardiac failure, prompting the development and subsequent characterization of the Fiona/dko model, a mouse line that is dystrophin deficient, utrophin deficient, and possesses a human utrophin transgene expressed only in skeletal muscles, but not the heart. Investigation into the Fiona/dko model illustrated a gap in knowledge, as it was found that while cardiac function continues to decline through 12 months of age, quantity of fibrotic tissue plateaus after 6 months. Micro-dystrophin-5 gene therapy, currently being tested in clinical trials, was shown to prevent cardiac functional decline and pathology in Fiona/dko mice. To determine the cause of declining function with sustained fibrosis and subsequently locate therapeutic targets, it is necessary to further characterize fibrosis composition in the Fiona/dko model. Investigation of the extracellular matrix components comprising cardiac scars in Fiona mice was completed through immunofluorescence staining for Fibronectin, Elastin, Tenascin, and Collagen I, as well as staining of activated myofibroblasts using alpha-smooth muscle actin. A significant reduction of fibronectin and tenascin was present in treated Fiona/dko mice as compared to untreated Fiona/dko. Collagen I and Fibronectin localization was compared and shown to be localized to the same areas of fibrosis. Elastin was not found to be present in fibrotic scars of Fiona/dko hearts. Staining for alpha-smooth muscle actin was not prominent compared to other dystrophic tissues such as diaphragm, suggesting myofibroblast in dystrophic hearts may have a different phenotype. Immunostaining of extracellular matrix proteins suggest that their contribution to fibrotic scars does not change during heart failure progression and that micro-dystrophin gene therapies are able to prevent cardiac fibrosis in dystrophic hearts.A one-year embargo was granted for this item.Academic Major: Biomedical Scienc