Characterization of zebrafish models of filamin C related cardiomyopathy
Date
2019
Authors
Alnefaie, Rasha M., author
Garrity, Deborah, advisor
Reddy, A. S. N., committee member
Lybourn, Paul, committee member
Muller, Racheal, committee member
Journal Title
Journal ISSN
Volume Title
Abstract
Cardiomyopathies are a group of cardiac muscle diseases characterized by abnormal function and/or structure of the myocardium which cause arrhythmia, heart failure or sudden death. In many cases, cardiomyopathy is a genetic disease and the majority of inherited cases are caused by mutations in genes that encode cardiac costameric and sarcomeric proteins. Cardiomyopathies include different types, such as dilated cardiomyopathy (DCM), hypertrophic cardiomyopathy (HCM), restrictive cardiomyopathy (RCM), and arrythmogenic cardiomyopathy (ARCM). These groups of disorders can have common cellular phenotypes and mechanisms. To date, few studies have described the roles of filamin C in cardiac development or explained how mutations in filamin C cause cardiomyopathic disease. Due to the lack of a suitable animal model, the pathological mechanisms underlying this disease and the role of filamin C in cardiac development remain unclear. Here, we created a zebrafish loss-of-function model for two flnc paralogous genes. We investigated several genetic lines bearing mutations in filamin C that target different sites of the gene. As for humans, zebrafish mutants exhibited variable penetrance and variable expressivity. Double flnca and flncb mutant hearts exhibited more pronounced cardiac morphological defects compared to single mutants, leading to the conclusion that these paralogs play redundant roles in zebrafish heart development. The cardiac morphological phenotype of double flnc mutant embryos is characterized by a decrease in cardiac output and stroke volume as is also observed in patients who suffer from cardiomyopathies. Using a transgenic line expressing GFP in cardiac z-discs, we find that knockdown of flnca and flncb via morpholinos and double flnca and flncb mutant hearts exhibited irregular z-discs. In support of this finding, ultrastructural analysis by transmission electronic microscopy for flncb morphant embryos and double flnca and flncb mutants indicated disorganized myofibrils with fewer consecutive sarcomeres. Particularly, z-discs were irregular or apparently absent, and numerous small vacuoles and potentially autophagous vesicles were observed. Additionally, through double flnca and flncb mutant, we demonstrated that filamin C is required for normal cardiomyocyte morphology and microfilament arrangement. In summary, the zebrafish model demonstrates an essential requirement for filamin C function during heart and skeletal muscle development. Depletion of filamin C impairs both sarcomerogenesis and alters the cytoskeletal architecture of cardiomyocytes.