Hypercholesterolemia in Cardiac Function, Survival and Repair

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DESCRIPTION (provided by applicant): Mounting mechanistic and translational studies support the use of cell-based therapies to repair myocardial tissue destroyed by infarction and to restore cardiac function. Several phenotypically distinct subsets of adult primitive cell populations have been shown to improve cardiac structure and function in animal models of myocardial infarction (MI) and heart failure. Small clinical trials of stem cell therapy have recapitulated these beneficial effects in patients with ischemic cardiomyopathy. Recent discovery of cardiac stem cells (CSCs) has sparked intense hope for the development of promising stem cell therapies for cardiac repair/regeneration because CSCs are inherently programmed to reconstitute cardiac tissue. In recent studies, we found that intracoronary delivery of CSCs to rats with either acute or chronic MI and to pigs with chronic MI ameliorated cardiac function and regenerated new cardiac cells. However, human patients needing cardiac reparative therapies generally possess an array of cardiovascular risk factors such as hypercholesterolemia (HC), diabetes, hypertension etc. With the recent surge of interest in cell therapies for patients, it is important to understand the impact of these risk factors on cell-mediated cardiac repair. In particular, HC is a highly prevalent risk factor and contributes to a range of pathophysiological consequences. Hence, the overall goal of this proposal is to investigate the impact of HC on CSC-mediated cardiac repair. Our fundamental hypothesis is that depending on the specific conditions, cholesterol can be beneficial or detrimental in CSC-mediated cardiac repair. We propose that mild elevations of plasma cholesterol or the presence of the minimally oxidatively modified form of LDL-cholesterol precondition both the myocardium and the CSCs; the resulting combination of a primed myocardial microenvironment for cell engraftment and enhanced paracrine signaling mechanisms of preconditioned CSCs work in concert to enhance CSC-mediated cardiac repair. We further propose that marked elevations of plasma cholesterol or the presence of the completely oxidized form of LDL- cholesterol provoke oxidative injury to both the CSCs and the myocardium, leading to loss of efficacy of cell therapies for cardiac repair. We will test these hypotheses under 3 specific aims using both in vitro cultured CSCs and cardiomyocytes in the presence of differently modified LDLs and in vivo rat models of MI with different levels of plasma cholesterol. Aim 1 will determine the effects of HC on CSC-mediated cardiac repair in vivo; Aim 2 will determine the effects of LDLs on CSC function and reparative capability in vitro; and Aim 3 will determine whether pretreatment of CSCs with differently modified LDLs in vitro alters the efficacy of cardiac reparative therapy in vivo. Given that plasma cholesterol is a modifiable risk factor, but is also essential for cellular function, understanding the effects of this prevalent risk factor on stem cell-based therapies will have translational and mechanistic importance. This project will provide novel insights into a much-needed preclinical framework to develop cell-based therapies for cardiac repair in patients with cardiovascular risk factors. PUBLIC HEALTH RELEVANCE: Increasing evidence has demonstrated that adult stem/progenitor cells can repair myocardium with functional benefits in animal models of myocardial infarction and heart failure. Small clinical trials of stem cell therapy in human patients with myocardial infarction and ischemic cardiomyopathy have recapitulated these beneficial effects. Recent discovery that heart itself contains cardiac stem cells (CSCs) has sparked intense hope for the development of most promising stem cell therapies for cardiac repair because CSCs are inherently programmed to reconstitute cardiac tissue. However, in the clinical arena patients who need cardiac reparative therapies are mostly associated with cardiovascular risk factors such hypercholesterolemia, diabetes, hypertension etc. With the recent surge of interest in cell therapies for patients, it is important to understand the impacts of these risk factors on stem cell-mediated cardiac repair. Hypercholesterolemia is a most prevalent risk factor and imposes various pathophysiological impacts in the biological system. In this application, we will conduct experiements to investigate the impacts of hypercholesterolemia on CSC-mediated cardiac repaie. We will use both normocholesterolemic and hypercholesterolemic rat models of myocardial infarction. Rats with myocardial infarction will receive CSC therapy. The efficacy of CSC therapy for cardiac repair will be assessed using comprehensive evaluation of myocardial performance including echocardiography and hemodynamic pressure-volume catheterization and tissue structure repair including morphology, immunohistochemistry, light and confocal microscopy. Regardless our results are "positive" or "negative", this project will provide novel insights into preclinical framework to develop effective cell-based therapies for cardiac repair in patients with cardiovascular risk factors. Given that plasma cholesterol is a modifiable risk factor and essential for cellular function, understanding the effects of this prevalent risk factor on stem cell- based cardiac repair will have translational and mechanistic importance.