Thesis (Ph. D.)--Rutgers University, 2009. / "Graduate Program in Chemical and Biochemical Engineering." Includes bibliographical references (p. 74-78).

published_or_final_version / Medical Sciences / Master / Master of Medical Sciences

Diabetes is a chronic disorder of the pancreas, where a decline in the insulin-producing β-cell population disrupts metabolic homeostasis. Pancreatic transplantation has shown to be effective in circumventing the problem of β-cell insufficiency. However, availability of donor islets remains an obstacle. Although progressive differentiation of embryonic stem cells (ESCs) to pancreatic β-cells is a solution, current protocols are wrought with inefficiencies. It is obvious that to realize ESC differentiation for therapy many steps need to be optimized, and this study describes improvement of Pdx1+pancreatic progenitor derivation, a critical determinant of pancreatic fate. The compounds melatonin and sPDZD2 have been suggested to act through the Protein Kinase A (PKA) pathway to exert transcriptional effects, and in particular sPDZD2 stimulates the expression of pancreatic genes in INS-1E rat pancreatic cells. This led to the hypothesis that the PKA-targeting characteristics of said molecules could be exploited for pancreatic specification through post-translational activation ofPdx1. hESCs were first induced to form definitive endoderm before treatment with melatonin and sPDZD2. Pdx1 expression induced by these molecules was then compared with levels triggered by known pancreatic progenitor inducer Indolactam V (ILV). A secondary objective of this study was to assess the endoderm induction potential of small molecules in hESCs, which claim to be potentially useful in differentiation. In this research, I show that small molecules are noticeably more challenging to use in the hESC context. Between the TGF-β pathwayactivatorsIDE-1 and 2, the latter is more potent at inducing endoderm formation, though it does not surpass the capabilities of Stauprimide, a molecule originally thought to only serve a priming purpose in mESCs.IDE-2 and Stauprimide consistently perform better than Activin A, the near universal factor for endoderm induction. Possible synergy between IDE-2 and Stauprimide was explored, but their combination appears detrimental to Sox17expression. Subsequent pancreatic differentiation was also inefficient, and my results affirm the immaturity of chemically-induced endoderm by contrasting with mainstream means of endoderm induction; levels of endoderm marker expression between the two methods are millions of folds apart. This work exposes the risks of using small molecules, and they necessitate proper characterization before being adopted for differentiation. Most favorably, both sPDZD2 and melatonin were able to trigger Pdx1 expression in STEMDiffTm derived definitive endoderm; 10 and 30folds respectively, comparable to the known Pdx1 inducer ILV (25 folds). I also reveal concentration-mediated differentiation and proliferative purposes of ILV and sPDZD2, which are highly reminiscent of the signaling mechanisms involved during pancreatic development. Preliminary quantification of Pdx1+ cells suggest that high concentrations of ILV and sPDZD2 favor self-renewal of Pdx1+ progenitors, whilst lower doses elevate Pdx1 expression. Demonstration of Pdx1 at both gene and protein expression levels was encouraging, but it remains uncertain if melatonin and sPDZD2 manipulate PKA signaling to exert Pdx1 promoting effects. My work supports the use of melatonin as a candidate for pancreatic differentiation, and suggests involvement of sPDZD2 in deriving and expanding progenitors during pancreatic organogenesis. / published_or_final_version / Biochemistry / Master / Master of Philosophy

published_or_final_version / Paediatrics / Master / Master of Philosophy

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Telomeres are the repetitive DNA sequence and associated proteins found at the ends of linear chromosomes. They have a role in biological processes including meiosis and aging as well as implications in a number of genomic instability disorders and cancers. Telomeres maintain genomic stability by protecting chromosome ends from terminal fusions and misidentification as DNA damage sites. Their wide range of functions has resulted in an increased interest in developing tools to study the dynamics of telomeres in live cells. To do this, current studies use the ubiquitously expressed protein Telomere Repeat Factor 1 (TRF1) tagged with a fluorescent protein. TRF1 is a negative regulator of telomere length that binds exclusively to telomere repeats. Over-expression of the fluorescent protein fused to TRF1 has been a useful tool to track telomere movement. The foci formed by the tagged TRF1 protein accurately represent the number of telomeres expected in the cells and the localization is maintained throughout the cell cycle. A caveat with this system is that over-expression of TRF1 leads to accelerated telomere shortening, as well as replication defects that can stall telomere replication. These caveats make it difficult to draw conclusions about telomere dynamics based solely on observations of cells over-expressing fluorescently tagged TRF1. To eliminate problems associated with protein over-expression, I have tried to develop knock-in embryonic stem (ES) cells expressing fluorescently tagged TRF1 from the endogenous Trf1 promoter. To do this, I have used a recombineering technique using Bacterial Artificial Chromosomes (BACs). BAC recombineering allows for the direct knock-in of a fluorescent tag into the mouse Trf1gene locus. Genetic constructs with the correct sequence inserts have been obtained and have been used for transfection of ES cells. While no correctly targeted ES cells have been identified so far, the expectation is that ES cell lines with correctly targeted fluorescently tagged TRF1 will be obtained in the near future. Such lines will be used to study telomere dynamics in ES cells, differentiated cells generated from ES cells, as well as to generate mice.

The limited treatment options available for heart disease patients has lead to increased interest in the development of embryonic stem cell (ESC) therapies to replace heart muscle. The challenges of developing usable ESC therapeutic strategies are associated with the limited ability to obtain a pure, defined population of differentiated cardiomyocytes, and the design of in vivo cell delivery platforms to minimize cardiomyocyte loss. These challenges were addressed in Chapter 2 by designing a cardiomyocyte selectable progenitor cell line that permitted evaluation of a collagen-based scaffold for its ability to sustain stem cell-derived cardiomyocyte function (“A P19 Cardiac Cell Line as a Model for Evaluating Cardiac Tissue Engineering Biomaterials”). P19 cells enriched for cardiomyocytes were viable on a transglutaminase cross-linked collagen scaffold, and maintained their cardiomyocyte contractile phenotype in vitro while growing on the scaffold. The potential for a novel cell-surface marker to purify cardiomyocytes within ESC cultures was evaluated in Chapter 3, “Dihydropyridine Receptor (DHP-R) Surface Marker Enrichment of ES-derived Cardiomyocytes”. DHP-R is demonstrated to be upregulated at the protein and RNA transcript level during cardiomyogenesis. DHP-R positive mouse ES cells were fluorescent activated cell sorted, and the DHP-R positive cultured cells were enriched for cardiomyocytes compared to the DHP-R negative population. Finally, in Chapter 4, mouse ESCs were characterized while growing on a clinically approved collagen I/III-based scaffold modified with the RGD integrin-binding motif, (“Collagen (+RGD and –RGD) scaffolds support cardiomyogenesis after aggregation of mouse embryonic stem cells”). The collagen I/III RGD+ and RGD- scaffolds sustained ESC-derived cardiomyocyte growth and function. Notably, no significant differences in cell survival, cardiac phenotype, and cardiomyocyte function were detected with the addition of the RGD domain to the collagen scaffold. Thus, in summary, these three studies have resulted in the identification of a potential cell surface marker for ESC-derived cardiomyocyte purification, and prove that collagen-based scaffolds can sustain ES-cardiomyocyte growth and function. This has set the framework for further studies that will move the field closer to obtaining a safe and effective delivery strategy for transplanting ESCs onto human hearts.

Telomeres are the repetitive DNA sequence and associated proteins found at the ends of linear chromosomes. They have a role in biological processes including meiosis and aging as well as implications in a number of genomic instability disorders and cancers. Telomeres maintain genomic stability by protecting chromosome ends from terminal fusions and misidentification as DNA damage sites. Their wide range of functions has resulted in an increased interest in developing tools to study the dynamics of telomeres in live cells. To do this, current studies use the ubiquitously expressed protein Telomere Repeat Factor 1 (TRF1) tagged with a fluorescent protein. TRF1 is a negative regulator of telomere length that binds exclusively to telomere repeats. Over-expression of the fluorescent protein fused to TRF1 has been a useful tool to track telomere movement. The foci formed by the tagged TRF1 protein accurately represent the number of telomeres expected in the cells and the localization is maintained throughout the cell cycle. A caveat with this system is that over-expression of TRF1 leads to accelerated telomere shortening, as well as replication defects that can stall telomere replication. These caveats make it difficult to draw conclusions about telomere dynamics based solely on observations of cells over-expressing fluorescently tagged TRF1. To eliminate problems associated with protein over-expression, I have tried to develop knock-in embryonic stem (ES) cells expressing fluorescently tagged TRF1 from the endogenous Trf1 promoter. To do this, I have used a recombineering technique using Bacterial Artificial Chromosomes (BACs). BAC recombineering allows for the direct knock-in of a fluorescent tag into the mouse Trf1gene locus. Genetic constructs with the correct sequence inserts have been obtained and have been used for transfection of ES cells. While no correctly targeted ES cells have been identified so far, the expectation is that ES cell lines with correctly targeted fluorescently tagged TRF1 will be obtained in the near future. Such lines will be used to study telomere dynamics in ES cells, differentiated cells generated from ES cells, as well as to generate mice.