A CHANGE OF HEART: NOVEL APPROACHES TO DIRECT CARDIAC REPROGRAMMING

Heart disease remains the leading cause of death in the United States, despite enormous progress in prevention, diagnosis, and treatment. Further reductions in heart disease mortality are hindered by the lack of regenerative capacity of the human myocardium. Direct cardiac reprogramming is a promising therapeutic strategy for creating new myocardium by converting cardiac fibroblasts into cardiomyocytes. While a number of technical hurdles to clinical translation remain, the past twelve years of study have borne important lessons that can be leveraged to improve cardiac reprogramming and make it more amenable for use in patients. This dissertation is comprised of work aimed both at developing new reprogramming approaches and deepening knowledge about the reprogramming process. A CRISPR activation-based method of reprogramming human fibroblasts is developed, demonstrating that endogenous Mef2c, Gata4, and Tbx5 expression is sufficient for transdifferentiation. Second, an unbiased, genome-wide comparative study of direct reprogramming of neurons, hepatocytes, and cardiomyocytes is undertaken, revealing shared features between these disparate cell types. Driven by these data, the cardiogenic potential of Ascl1 – a neuron reprogramming factor – is tested; cardiac reprogramming via Mef2c and Ascl1 is demonstrated and, furthermore, found to be more efficient. Unbiased transcriptomic and epigenomic assessment reveals that co-operation between Mef2c and Ascl1 is key to their cardiogenic activities. These results leave open the possibility that other cross-lineage reprogramming factors exist and are awaiting discovery. Exploration of this question and others may lead to insights that have broad implications.