Modelling hypertrophy in dystrophic cardiomyocytes

Abstract

Duchenne Muscular Dystrophy (DMD) is an X-linked disorder, caused by mutations in the DMD gene. This gene encodes dystrophin, a structural protein that links the sarcomere to the extracellular matrix via a trans-membrane protein complex. In the absence of dystrophin the associated glycoprotein complex fails to assemble, leading to sarcolemmal instability, impaired ion handling, skeletal muscle wasting and fibrosis. Patients become non-ambulant in their teens and seldom live past their third decade. Cardiac failure is one of the leading causes of death. The heart initially compensates for reduced functional capacity by becoming hypertrophic, but eventually becomes fibrotic and develops dilated cardiomyopathy. Several proposed therapies have now reached clinical trial phase, but there is still no cure available for all DMD patients. Some of these therapies target skeletal muscle better than the heart. Sample availability restricts research into cardiac mechanisms of disease and testing treatments. This thesis presents a model that can potentially be used as an in vitro outcome measure for testing DMD therapies. Cardiomyocytes isolated from hearts collected from the DMD mouse model (mdx) embryos became larger than control mouse embryo-derived cardiomyocytes in response to serum starvation in culture. Control and mdx cardiomyocytes were collected at five timepoints of serum starvation and RNA-Seq was performed on the samples to identify pathways responsible for this hypertrophic response observed in dystrophic cells. Several pharmacological compounds as well as a proposed gene therapy method were trialled for their ability to reduce the hypertrophic response. Serum starved cardiomyocytes from mdx mouse embryos were transduced with adeno-associated viruses containing a gene construct expressing a functional internally truncated version of dystrophin. The viral rescue therapy and some pharmacological compounds significantly reduced the dystrophic hypertrophy caused by serum starvation. This model of mdx cardiomyocyte hypertrophy could therefore be used for testing therapies in pre-clinical trials.