Doctor of Philosophy, The Ohio State University, 2016, Biomedical Engineering

Volume overload (VO) induced heart failure results from an increase in blood volume (preload) to the heart. The heart responds to increases in hemodynamic load through compensative remodeling. VO has a distinct pattern of remodeling compared to pressure overload induced heart failure, which results in fibrosis. VO results in a net decrease in extracellular matrix (ECM). This loss of ECM contributes to the progression of the disease due to the loss of structural integrity. Since cardiac fibroblasts (CFs) are the main cells responsible for maintaining ECM in the heart, we characterized the in vitro phenotype of CFs isolated from a rat VO model, aortocaval fistula (ACF). Compared to sham operated animals, ACF fibroblasts displayed a phenotype that we described as “hypofibrotic”. ACF CFs secreted relatively less collagen and profibrotic molecules, such as a-smooth muscle actin (aSMA) and connective tissue growth factor (CTGF). Interestingly, ACFs produce approximately twice as much transforming growth factor-ß1 (TGF-ß), a key profibrotic stimulus, as their sham counterparts. However, there were no changes in the canonical TGF-ß pathway that could account for the hypofibrotic phenotype observed in ACF fibroblasts. Since others have shown that the cytoskeleton and the Rho/ROCK pathway play a role in fibroblast phenotype, we characterized the actin cytoskeleton in sham and ACF fibroblasts. We found that ACF CFs have significantly less F-actin than sham CFs. We were able to show that it is possible the actin cytoskeleton might account for phenotypic differences in CFs by chemically altering the amounts of F-actin and G-actin. When the cells were treated with a ROCK inhibitor, which allows F-actin to depolymerize into G-actin, CFs displayed a more hypofibrotic phenotype. Conversely, enhancement of F-actin with jasplakinolide treatment forced the CFs to have a profibrotic phenotype. Numerous studies have linked substrate modulus with effects on the cytoskeleton. S (open full item for complete abstract)

Committee: Keith Gooch PhD (Advisor); Jun Liu PhD (Committee Member); Pamela Lucchesi PhD (Committee Member); Aaron Trask PhD (Committee Member) Subjects: Biomedical Engineering

Doctor of Philosophy, Case Western Reserve University, 2012, Cell Biology

Cardiovascular disease is the leading cause of death in the industrialized world and its prevalence is increasing worldwide. Regenerative medicine represents a new medical frontier for the treatment of heart failure. This therapeutic approach has mainly focused on the delivery of exogenous stem cells. While clinical trials have shown no major safety concerns, the outcomes associated with the use of exogenous stem cells have shown some degree of efficacy in selected cases. In addition to exogenous stem cells, endogenous populations of stem cells exist and can be activated to promote tissue healing. However, the exact role of endogenous stem cells in cardiac regeneration is far from clear. In Chapter Three, we examined the response of endogenous stem cells to trans-aortic constriction (TAC) in a mouse model. Our results demonstrated an early, orchestrated systemic response of cardiac stem cells (CSC), endothelial progenitor cells (EPC), and SSEA1+ stem cells following TAC. The most significant response found was in the splenic and bone marrow EPC and SSEA1+ populations. These cells showed early mobilization and accumulation in the heart, prior to any proliferative response. Peak stem cell content in the myocardium occurred at 7 days post-TAC. These data identify stem cell sources and populations respondent to TAC. Chapter Four focuses on bone marrow SSEA1+ cells. Through chimeric bone marrow studies, we found that SSEA1+ cells can differentiate into other cells types, including hematopoietic stem cells, EPC, and endothelial cells. We also determined that bone marrow SSEA1+ cell support is essential in maintaining cardiac homeostasis after TAC. Depletion of bone marrow SSEA1+ cells quickened cardiac dysfunction and increased vessel rarefaction after TAC. These results have begun to define the fate and function of bone marrow SSEA1+ cells. The data presented in this dissertation demonstrate a strong support of the myocardium by peripheral stem cells. The next gen (open full item for complete abstract)

Committee: Paul DiCorleto PhD (Advisor); Marc Penn MD PhD (Advisor); Piet de Boer PhD (Committee Chair); Horst von Recum PhD (Committee Member) Subjects: Cellular Biology

Doctor of Philosophy, Case Western Reserve University, 2011, Cell Biology

Heart disease remains the leading cause of death in western society. Many clinicians and researchers have looked to stem cells (SC) for the next generation of heart failure therapies. To date, the majority of reports have focused on their effects when given exogenously. However, it is becoming increasingly understood that endogenous SC play an important role in myocardial repair responses. In contrast to early expectations, adult SC have little regenerative potential. Instead, their observed benefits are largely attributed to pro-survival, trophic, anti-inflammatory, and angiogenic paracrine effects. Little is known about the effects of age on SC function. Recent research suggests aging of the organism may be in part due to attenuation of the SC response to injury. Indeed, studies indicate exogenously given aged SC have decreased beneficial effects. In Chapter 2 of this dissertation, we demonstrate by a series of heterochronic bone marrow (BM) transplantations between young and old mice that aged BM is associated with a decreased compensatory response after transverse aortic constriction which causes pressure overload (PO). This diminished response is associated with decreased myocyte hypertrophy, increased myocyte dropout, increased fibrosis and interestingly, no change in vessel density. These findings suggest endogenous stem cells provide trophic and anti-apoptotic support to the myocardium. There was reduced BM cell migration to the heart and activated cardiac progenitor cells in mice with old BM although no difference in ex vivo migration between young and old BM to SC homing chemokines was observed. Additionally, intravenous mesenchymal stem cell injections failed to improve cardiac function after transverse aortic constriction (TAC). These results suggest a loss of a specific SC population and/or exhaustion of the SC response with age following PO. Chapter 3 investigates the possible involvement of deficient Notch1 signaling in age related declines in cardi (open full item for complete abstract)

Committee: Alan Levine PhD (Committee Chair); Marc Penn MD, PhD (Advisor); Roy Silverstein MD (Committee Member); Horst von Recum PhD (Committee Member) Subjects: Cellular Biology