Project 2

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Project Summary/Abstract for Project 2 Duchenne muscular dystrophy (DMD) is a recessive X-linked neuromuscular disorder resulting from mutations in the dystrophin gene, which ultimately produces progressive muscle wasting and atrophy. Importantly, DMD patients develop cardiac fibrosis and a decrease in cardiac function leading to advanced cardiomyopathy, which is currently the major contributor to mortality in DMD patients. The mission of the UT Southwestern Wellstone Center is to develop CRISPR/Cas9 genome editing as a therapeutic modality for DMD patients; however, issues related to DMD-associated cardiomyopathy will continue to persist. Project 1 proposes to use genome editing to target the 12 “hot spots” within the dystrophin gene making a truncated dystrophin protein and converting a DMD patient into a Becker muscular dystrophy (BMD) patient. Thus, the overall goal of Project 2 is to develop novel therapies to attenuate the morbidity and mortality associated with DMD- associated cardiomyopathy. Significant strides have been made in treating non-DMD cardiomyopathy; however, there are no definitive therapies to effectively induce long term reverse cardiac remodeling and improve overall cardiac function within DMD patients. Our group has undertaken a cardiac MRI study demonstrating that adult DMD patients have very low left ventricular (LV) mass as well as low LV concentricity as compared to age-, sex-, and weight-matched control patients. Once a DMD patient develops symptoms related to advanced cardiomyopathy, the DMD heart starts to dilate and enlarge resembling the structure of advanced dilated non-ischemic cardiomyopathy. These observations raise the question whether the development of pathological cardiac hypertrophy is the primary mechanism underlying DMD-associated cardiomyopathy. Does the observed low LV mass and concentricity arise due to prolonged immobility or are independent of a DMD patient’s ability to ambulate? Data from the Mammen Laboratory indicates that mdx mice, a murine model of DMD, have altered cardiac metabolism and also have low cardiac mass due to a decrease in proliferative gene expression during the first week of life. Therefore, the central hypothesis of Project 2 is that low LV mass and concentricity in DMD-associated cardiomyopathy leads to progressive cardiomyopathy independent of a DMD patient’s ability to ambulate. To test our central hypothesis, we will pursue the following three specific aims: Specific Aim 1: Characterize the clinical and molecular phenotypes in ambulatory and non-ambulatory DMD patients as a function of patient age. Specific Aim 2: Define the cardiac phenotype in BMD-associated cardiomyopathy as a function of patient age and site of the genetic mutation. Specific Aim 3: Determine the molecular phenotypes of human DMD and BMD cardiomyocytes.