Project Summary Ischemic heart disease is the leading cause of morbidity, mortality, and healthcare expenditure worldwide due to an inability of the heart to regenerate following injury. Following myocardial infarction (MI), cardiomyocytes undergo massive cell death and through activation of resident cardiac fibroblasts (CFs), are replaced by non- contractile fibrotic scar, ultimately leading to heart failure. Novel heart failure therapies aimed at promoting cardiomyocyte regeneration are desperately needed. In recent years, direct reprogramming of resident CFs to induced cardiac-like myocytes (iCLMs) has emerged as a promising therapeutic strategy to repurpose the fibrotic response of the injured heart toward a functional myocardium. Direct cardiac reprogramming was initially achieved through the overexpression of the transcription factors (TFs) Gata4, Mef2c, and Tbx5 (GMT); later, Hand2 (GHMT) and Akt1 (AGHMT) were found to enhance this process in embryonic and neonatal cell types. However, these cocktails have demonstrated limited success in reprogramming adult human and mouse fibroblasts, constraining the clinical translation of this therapy. Our laboratory undertook a screen of mammalian gene regulatory factors to discover novel regulators of cardiac reprogramming in adult fibroblasts and identified the histone reader PHF7 as the most potent activating factor. In work currently under revision, we have demonstrated the ability of PHF7 to markedly activate reprogramming in adult human and mouse fibroblasts by increasing chromatin accessibility at cardiac super enhancers when added to a five-factor reprogramming cocktail. However, it is not yet known which transcription factors are necessary for PHF7 to optimally facilitate adult cardiac reprogramming. Our preliminary data support the overall hypothesis that PHF7 is a critical regulator of cardiac cell fate conversion and potently reprograms adult fibroblasts to functional cardiomyocytes in vitro and in vivo in the presence of fewer cardiac transcription factors. To explore this hypothesis, I will address the following aims: (1) to define the factors necessary to achieve adult cardiac reprogramming with PHF7, and (2) to define the ability of PHF7 to improve cardiac function following myocardial infarction in vivo. Completion of these studies will enhance our understanding of the factors necessary to achieve cardiac reprogramming in adult cell types and elucidate the mechanisms necessary for this conversion. Further, these studies will potentially provide the basis for development of a novel therapeutic factor in cardiac reprogramming for the treatment of ischemic heart disease. The proposed studies will be performed in the large and highly productive laboratory of Dr. Eric N. Olson, PhD at University of Texas Southwestern Medical Center. All studies and career development will be carried out under the guidance of Dr. Olson, a pioneer in the field of direct cardiac reprogramming.