Publication Date

2016-12-13

Availability

Open access

Embargo Period

2016-12-13

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PHD)

Department

Molecular and Cellular Pharmacology (Medicine)

Date of Defense

2016-11-21

First Committee Member

Joshua M. Hare

Second Committee Member

Roberto I. Vazquez-Padron

Third Committee Member

Omaida C. Velazquez

Fourth Committee Member

Bradley J. Goldstein

Fifth Committee Member

Krishna V. Komanduri

Abstract

Cardiovascular disease (CVD) is a leading cause of morbidity and mortality in the United States and worldwide. Furthermore, CVD is heavily linked to frailty, a comorbidity afflicting elderly patients. Endothelial dysfunction-characterized by diminished endothelial progenitor cell (EPC) function and flow-mediated vasodilation (FMD)-is central to the pathophysiology of heart failure (HF) and frailty. Current therapies are unable to reverse or stop the progression of these diseases, lending way to the emergence of regenerative medicine approaches and the use of stem cells, most notably mesenchymal stem cells (MSCs). MSCs are pro-angiogeneic, immunomodulatory, antifibrotic, and also stimulate endogenous endothelial cell proliferation and function, thus having the potential to restore endothelial dysfunction. Recent clinical trials in HF patients with ischemic and non-ischemic cardiomyopathy illustrate that MSC therapy improves cardiac function. However, the specific mechanisms underlying this therapeutic effect remain controversial. In this study, we tested the hypothesis that allogeneic MSCs preferentially improve endothelial function by increasing EPC function and restoring FMD via a mechanism involving the suppression of pathologic vascular endothelial growth factor (VEGF), stromal derived factor-1 alpha (SDF-1a), and tumor necrosis factor alpha (TNFa). Accordingly, EPC-colony forming units (EPC-CFUs) and FMD were measured in patients with dilated cardiomyopathy (DCM), ischemic cardiomyopathy (ICM), and frailty at baseline and three months post either allogeneic or autologous MSC therapy. The mechanism was studied in patients with DCM. More specifically, the vasculogenic potential of allogeneic versus autologous MSCs was measured in vitro. Additionally, patient serum VEGF and TNFa were measured at baseline and three months post MSC treatment, as well as MSC secretion of SDF-1a and TNFa. Our results revealed exciting and important implications for the future design of stem cell trials. We found that patients with DCM, ICM, and frailty have endothelial dysfunction at baseline, evident by reduced EPC-CFUs and FMD. Allogeneic, but not autologous, MSCs were able to improve this dysfunction three months post treatment in patients with DCM and ICM. Mechanistically, we found human umbilical vein endothelial cells (HUVECs) with impaired vasculogenesis due to pharmacologic nitric oxide (NO) synthase inhibition, were rescued by allogeneic MSC-conditioned medium. Furthermore, circulating VEGF and TNFa were profoundly elevated in DCM patients and only allogeneic MSCs were able to restore these levels towards normal. Additionally, autologous MSCs secreted significantly higher levels of SDF-1a than allogeneic MSCs. There were strong correlations between EPC-CFUs and FMD, EPC- CFUs and VEGF, EPC-CFUs and SDF-1a, EPC-CFUs and TNFa, VEGF and TNFa, and VEGF and SDF-1a. Ultimately, these findings reveal a novel mechanism by which allogeneic MSCs secrete normal levels of SDF-1a, which results in normal levels of VEGF signaling, an increase in EPC bioactivity, an improvement in FMD and NO bioavailability, and a reduction in the pro-inflammatory signaling of TNFa, resulting in a significant improvement in endothelial function. These findings have significant clinical and biological implications for the use of MSCs in HF and other disorders associated with endothelial dysfunction.

Keywords

mesenchymal stem cells; endothelial function; heart failure; frailty; endothelial progenitor cells; flow mediated vasodilation

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