Doctor of Philosophy, University of Akron, 2018, Biomedical Engineering

Neurodegenerative diseases that are caused by deterioration of nerve cells in the brain and spinal cord affect more than 6 million Americans and cost nearly 0.8 trillion dollars annually in patient care. With a growing number of elderly population, the statistics are expected to worsen as there is currently no cure for these disorders. Modern medicines are at best palliative and only manage the symptoms. Therapeutic interventions to deliver functional neural cells to the ravaged tissue are essential to restore lost tissue functions. The use of stem cell-derived neural cells is a promising strategy for cell replacement therapies of neurodegenerative diseases. Embryonic stem cells (ESCs) are promising cell sources for therapeutic uses including cell replacement therapy of neural tissues. This is because ESCs have unlimited self-renewal and proliferation capabilities and the ability to differentiate into various neural cells. Nevertheless, despite significant investment and research, therapeutic uses of ESCs for neural cell replacement has been largely unsuccessful. Low and inconsistent yield of neural cells from ESCs and lack of a complete understanding of molecular mechanisms of neural differentiation of ESCs are major obstacles against clinical uses of ESC-based therapies. A cohort of cell surface bound and soluble factors, interactions of ESCs with their neighboring cells and extracellular matrix proteins, and various epigenetic factors may act synergistically to drive differentiation of stem cells. While most of current research is centered on functionalizing specific biomolecules on scaffolds and tuning the matrix stiffness, or altering media compositions to gain a better control over the neural differentiation of stem cells, the role of niche-mediated factors is less understood. In this study, we showed that intrinsic niche parameters such as stem cell colony size and interspacing between the two colonies can significantly impact the differentiation effic (open full item for complete abstract)

Committee: Hossein Tavana (Advisor); Marnie Saunders (Committee Member); Nic Leipzig (Committee Member); Yang Yun (Committee Member); Sailaja Paruchuri (Committee Member) Subjects: Biomedical Engineering; Biomedical Research; Engineering; Neurobiology

PhD, University of Cincinnati, 2011, Medicine: Developmental Biology

Primordial germ cells (PGCs) are the embryonic precursors of adult gametes. In the mouse, they arise around E7.5 in the allantois, and migrate through the developing hindgut and midline dorsal body wall mesenchyme to colonize the gonad primordia by E11.5. PGC behavior, including proliferation, survival, and motility, is controlled by cellular signaling during migration. Steel factor is known as an essential survival factor for PGCs. It is the protein product of the Steel locus, and the ligand for the receptor tyrosine kinase c-kit, which is expressed by PGCs throughout migration. Steel factor exists in two forms, membrane-bound and the soluble, generated by alternative splicing. This thesis addresses two general questions: 1) Is PGC behavior controlled by Steel factor from the beginning of their migration? 2) Do the two different forms of Steel factor control different aspects of PGC behavior? Using the mouse reporter line Stella-GFP, in which PGCs express GFP under the control of the promoter of Stella gene, I demonstrate that PGC number is significantly reduced in Steel-/- embryos at E7.5. Similarly, in the absence of Steel factor, either by null mutation or antibody blockade, PGCs aggregate together and show dramatically decreased motility, but their directionality is maintained. These data indicate an essential role for Steel factor in PGC survival and motility. I then show that Steel factor-expressing cells surround PGCs from the time of their initial specification in the allantois, to the time of their colonization of the gonad primordia, providing a “spatio-temporal niche” that travels with PGCs to regulate their survival, proliferation and motility throughout migration. Further, I show that these functions of Steel factor in PGC behavior are distributed between the membrane-bound and soluble forms by analyzing PGC behavior in Steel-dickie mutant embryos, which make only the soluble form. Soluble Steel factor alone is sufficient for PGC survival at E7.5. How (open full item for complete abstract)

Committee: Christopher Wylie PhD (Committee Chair); Aaron Zorn PhD (Committee Member); Kenneth Campbell PhD (Committee Member); Iain Cartwright PhD (Committee Member); James Wells PhD (Committee Member) Subjects: Developmental Biology

PhD, University of Cincinnati, 2011, Medicine: Developmental Biology

Cdc42 is a member of Rho GTPase family. Cdc42 integrates signals from multiple cell surface receptors including c-kit, CXCR4 and ß1-integrin, thus regulating cytoskeleton dynamics which impacts on cell adhesion and migration properties. All these are crucial for the retention of hematopietic stem cells (HSCs) in their bone marrow (BM) microenvironment. Our laboratory has shown that conditional deletion of Cdc42 in BM led to massive egress of hematopoietic stem and progenitor cells (HSPCs) into circulation, a phenotype of HSPC mobilization, attributable to deficiencies of Cdc42-/- BM HSPCs in F-actin polymerization, adhesion and migration. This and other related studies allow us to hypothesize that Cdc42 might be a valid target for HSC mobilization. In chapter 2, we characterize a Cdc42-specific inhibitor, termed CASIN (Cdc42 Activity-Specific Inhibitor). CASIN inhibits Cdc42 activity of BM progenitors specifically and reversibly. Administration of CASIN in mice and a mouse model of human xenograft leads to significant mobilization of HSPCs transiently. Serial transplantations of CASIN-mobilized peripheral blood stem cells (PBSCs) demonstrate a better long-term reconstitution capacity than those mobilized by AMD3100. Recent studies have suggested that mobilization can be used as a preparative regimen for hematopoietic stem cell transplantation (HSCT) without myeloablation. This allows us to further hypothesize that deletion/inhibition of Cdc42 might be able to facilitate the engraftment of transplanted HSPCs without myeloablation. In chapter 3, we demonstrate that both genetic deletion and pharmacological inhibition of Cdc42 allow efficient engraftment of murine HSPCs and human cord blood progenitors in mice. This CASIN-facilitated engraftment can be applied to FA model of Fanca-/- mice in settings of both allogeneic HSCT and gene therapy using autologous HSCs. Taken together, our studies identified a lead Cdc42-specific inhibitor that is efficient in HSC mobilizatio (open full item for complete abstract)

Committee: Yi Zheng PhD (Committee Chair); Hartmut Geiger PhD (Committee Member); Jose Cancelas-Perez MD (Committee Member); Tim Cripe MD, PhD (Committee Member); James Mulloy PhD (Committee Member) Subjects: Surgery