Developing Bioinstructive Materials for Cardiac Repair

Abstract

Cardiovascular disease (CVD) is a leading cause of death in the United States and worldwide, and coronary heart disease is the largest contributor of CVD. Coronary heart disease occurs when the coronary arteries in the heart become blocked and the cells surrounding the blockage die, resulting in a heart attack or myocardial infarction. After a heart attack the necrotic tissue is replaced with non-contractile scar tissue, as healthy adult cardiomyocytes do not naturally proliferate to regenerate the heart. Current approaches for cardiac regeneration attempt to stimulate proliferation of existing cardiomyocytes by modulating known cell cycle genes, with one study demonstrating that using a combination of viral vectors and small molecules increases cardiomyocyte proliferation and results in moderate functional benefit, although significant therapeutic benefit is still lacking. Using a new approach to identify novel factors to induce proliferation may yield more significant results. Simultaneously, while identifying factors that stimulate cardiomyocyte proliferation has been a challenge, an additional challenge lies in achieving localized delivery of these factors, as systemic injection can lead to negative side-effects. The purpose of this dissertation was to develop a new approach to identify factors that can stimulate cardiomyocyte proliferation and to develop biomaterial strategies to locally deliver these factors. Viral vectors typically require a fast release to induce factor production, whereas small molecules need a more sustained release in order to elicit a cellular response, and subsequently two different delivery systems are needed. In Chapter 2, an adhesive and thermosensitive hydrogel that could locally deliver viral vectors was developed from blends of Pluronic F127 and polycarbophil. The Pluronic F127 and polycarbophil blends had tunable sol-gel temperature transitions, were cytocompatible, and kept adenovirus vectors localized to the heart when applied to an in vivo mouse model. Chapter 3 discusses the development of a pipeline to identify novel factors to induce cardiomyocyte proliferation. Instead of focusing on known cell cycle regulators, we studied a naturally regenerative organ, the liver, and compared the transcriptomes between proliferating liver cells and quiescent cardiomyocytes. Pathway analysis revealed many pathways that may be important in cellular proliferation and tissue regeneration, including the HIF1α (hypoxia inducible factor 1) pathway. HIF1α is a component of the hypoxic microenvironment and is known to be important regulator for wound healing and proliferation of other cell types. Previous studies have demonstrated that hypoxia may be important in stimulating cardiomyocyte proliferation, however these studies were conducted using a hypoxia chamber, which is not a practical therapeutic option. In this work we screened CoCl2, a well-studied HIF1α inducer, on our hiPSC-derived cardiomyocyte cell model and observed that CoCl2 was able to stabilize HIF1α expression in cardiomyocytes and led to an increase in cell proliferation. In Chapter 4 we developed a process to 3D print blends of poly(glycerol sebacate) and polycaprolactone polymers. This process allows for the fabrication of a biomaterial patch that can provide mechanical support and deliver small molecules. CoCl2 was easily incorporated into the polymer blend and it was observed that small molecule release was sustained for at least 96 hours, and CoCl2 was still functional after polymer processing. Finally, recommendations for future studies were discussed in Chapter 5. Altogether, the experimental and biomaterial strategies developed in this dissertation may help lead to the development of a novel therapeutic approach to locally stimulate cardiomyocyte proliferation and lead to cardiac regeneration.