Calcific aortic valve disease (CAVD) is associated with increased presence of myofibroblasts, osteoblastic cells and, occasionally, adipocytes and chondrocytes in lesions. The ectopic cell types in diseased valves may be elaborated by an unidentified multipotent progenitor subpopulation within the valve interstitial cells (VICs) that populate the valve interstitium. Notably, lesions form preferentially in the fibrosa layer, the stiffer layer of the valve leaflet. It has been shown that differentiation of VICs to myofibroblasts and osteoblasts is modulated by matrix stiffness. However, the molecular mechanisms involved in mediating stiffness-dependent mechanotransduction remain obscure. The objectives of this thesis were: (1) to determine whether VICs contain a subpopulation of multipotent mesenchymal progenitor cells and to measure the frequencies of the mesenchymal progenitors and osteoprogenitors; (2) to determine the role of β-catenin and matrix stiffness in transforming growth factor-β1 (TGF-β1)-induced myofibroblast differentiation of VICs; and (3) to preliminarily investigate the involvement of four and a half LIM domains protein 2 (FHL2) in CAVD and stiffness-dependent mechanotransduction downstream of RhoA in VICs. Firstly, VICs were found to contain a subpopulation of mesenchymal progenitors that are inducible to osteogenic, myofibroblastic, adipogenic, and chondrogenic lineages. The frequencies of mesenchymal progenitors and osteoprogenitors were significantly higher than other reported sources. Secondly, it was demonstrated that β-catenin is required in TGF-β1-induced, matrix stiffness-regulated myofibroblast differentiation. Notably, TGF-β1 was only able to induce β-catenin nuclear translocation and myofibroblast differentiation on matrices with fibrosa-like stiffness, but not on matrices with ventricularis-like stiffness. Thirdly, FHL2 was found to be upregulated and colocalized with runt-related transcriptional factor 2 (Runx2) in lesions in the fibrosa layer of diseased valves, suggesting its role in osteogenic processes in CAVD. Notably, increasing matrix stiffness increased FHL2 nuclear translocation and RhoA activity in VICs. Preliminary data showed that matrix stiffness regulates FHL2 nuclear translocation via RhoA activity. These results suggest that differentiation of the rich valve progenitor subpopulation, regulated by both mechanical and biochemical cues, may contribute to the preferential occurrence of ectopic cell types in the fibrosa in CAVD. More broadly, these results highlight the critical role of mechanical environment in modulating cellular biochemical signaling.

Cardiac and orthopaedic diseases are significant causes of morbidity and mortality in dogs and are therefore critical areas for veterinary research. More information regarding the pathophysiology of these diseases, and the development of novel therapeutics are sorely required and adult stem cells (ASCs) are a promising source of cells for both investigation of these diseases in vitro and also potentially therapeutics in the longer term. ASCs are a readily available source of multipotent cells which bypass the ethical issues surrounding embryonic stem (ES) cells. ASCs have been described in several tissues of the body, and typically differentiate along specific cellular routes related to original source location. This thesis investigates whether ASCs can be isolated and cultured from the dog from two specific locations; cardiac, producing cardiac stem cells (CSCs); and the bone marrow, producing mesenchymal stem cells (MSCs). These cell sources will be extensively characterised at their baseline for morphology, culture behaviour and gene marker expression. Following characterisation each cell source will be subjected to differentiation techniques to examine canine ASC multipotent differentiation potential. CSCs were isolated from cultured atrial cardiac explant tissue taken from dogs post-mortem, with owners’ consent. These cells were able to survive successive passages in serum free media and formed large spherical cell clusters, termed ‘cardiospheres’. CSCs were capable of clonal expansion under controlled culture conditions, demonstrating their ability for self-renewal. Characterisation of these cells demonstrated the expression of CSC markers; c-Kit, GATA 4 and Flk-1 and no expression of cardiac lineage markers including cardiac troponin T and I, Nkx2.5, the cardiac ryanodine receptor and the β1-adrenergic receptor. Primary canine MSCs were isolated from bone marrow aspirates using ficoll separation and cultured on tissue culture plastic. Canine MSCs closely resembled MSCs described from other species, such as the human and mouse, and were found to express CD44 and STRO-1 and were negative for CD34 and CD45. CSCs and MSCs were exposed to published cardiac directed differentiation protocols and differentiation then analysed using cellular morphology and gene expression. Canine CSCs appeared to differentiate partially along cardiac lineages with upregulation of cardiac troponin T and Nkx2.5, and down regulation of c-Kit and endothelial lineage markers. Canine MSCs demonstrated some morphological changes during cardiac differentiation, and demonstrated up-regulation of Nkx2.5 and Flk-1 but no significant alteration in other markers examined. This suggested that cardiac directed differentiation was not as successful with canine MSCs compared to CSCs and conflicting with published data using rodent MSC models. Murine MSCs were used as a positive control cell line for cardiac directed differentiation, based upon published literature. Critically there were key marker expression differences between baseline murine and canine MSCs, including the expression of cardiac markers such as cardiac troponin T and I, and the Ryanodine receptor. Furthermore, expression analysis of cardiac genes changed with time in culture and passage number and no significant alteration was seen when cells were subjected to the cardiac differentiation protocol; thereby bringing into question the data regarding successful cardiac differentiation using murine MSCs. Canine MSCs were further differentiated toward a chondrocyte lineage to investigate the use of MSCs for orthopaedic research. Canine MSCs were successfully differentiated toward articular type cartilage, with demonstration of extracellular matrix secretions, an upregulation of collagen type II with downregulation of collagen type I and the development of SOX9 expression in differentiated cells. This thesis builds the groundwork for future ASC research in the dog. Successful isolation and culture of two ASC sources from the dog is demonstrated. Cardiac and cartilage directed differentiation was successful using primary sourced cells, but differentiation was found to be limited to highly specific routes for each stem cell source. The results presented here highlight the importance of analysing baseline stem cells extensively prior to differentiation and in particular, before making comparisons between cell populations isolated from different locations and species.

The thymic stroma primarily comprises epithelial, mesenchymal and endothelial cells, interspersed with those of haematopoietic origin. Thymic epithelial cells (TECs) are highly heterogeneous, but can be divided into two broad lineages, cortical and medullary, based on phenotype, functionality and location. A population of Plet1+ TEC progenitors have been identified which, when isolated from mouse E12.5 or E15.5 fetal thymus, reaggregated, and grafted, can produce a functional thymus. However, the potential of individual progenitors to form cortex and/or medulla is undefined. The main aim of this thesis was to use retrospective clonal analysis to ascertain the point during thymus ontogeny at which the cortical and medullary lineages diverge. To this end, I used transgenic mice carrying a ubiquitous ROSA26laacZ reporter gene (where a duplication within lacZ encodes non-functional b-galactosidase). Here, rare, random laacZ-lacZ genetic recombinations result in heritable expression of functional b-gal, producing labelled clones. As this occurs at a known frequency, determination of TEC numbers would enable calculation of the expected number of TEC clones present throughout ontogeny. Due to the lack of quantitative data on all thymic cell populations, I determined the size not only of TEC (lin-EpCAM+), but also haematopoietic (CD45+), mesenchymal (lin-PDGFRa+ and/or lin-PDGFRb+) and endothelial (lin-CD31+) populations from E12.5 until E17.5. I then showed that the absolute number of Plet1+ TECs remains constant during this time, although the proportion of Plet1+ cells in cycle decreases. From these collective data, I propose a model for the role of the Plet1+ population in thymus development, in which Plet1+ cells continually give rise to Plet1- TECs in a self-renewing manner. Finally, I present a ‘dual origin coefficient’ strategy for analysis of a library of prospective TEC clones. I calculated the number of TEC lacZ+ clones expected to be present throughout thymus ontogeny, selecting an appropriate developmental stage for analysis. Although I observed several clones of apparent mesenchymal origin, supporting a single origin for intrathymic and capsular mesenchyme at E15.5, I observed no TEC clones in this extensive analysis. The CpG content of the ROSA26 promoter suggests a possibility of methylation-induced silencing brought about by de novo methylation of the lacZ reporter gene.

No description available.

Articular cartilage is an extraordinary tissue, allowing frictionless movements of articulated joints, and acting as a load-bearing cushion to protect joints from damage. Breakdown of articular cartilage may result in crippling diseases such as osteoarthritis (OA) and, since articular cartilage has a limited repair capacity, a greater understanding of the mechanisms of joint homeostasis and its response to injury are of great clinical need. In this project the hypothesis that endogenous mesenchymal stem cells (MSCs) may contribute to the healing process of a full-thickness articular cartilage defect was investigated by combining a mouse model of joint surface injury and repair with a nucleoside analogue labelling scheme in DBA/1 mice. Following injury, proliferative responses of nucleoside analogue-retaining cells were detected between 4 and 12 days post injury (dpi) in both the bone marrow and the synovial membrane of the knee joint. Phenotypic analysis of these label-retaining cells using immunofluorescence staining revealed an MSC-compatible phenotype (CD44+, CD105+, CD146+, PDGFRα+ and p75NGFR+), with differences observed between the two tissues in expression of CD105 and CD146. The response of the label-retaining cells to the injury was associated with early activation of Notch signalling (4 dpi), followed by BMP signalling at 8 dpi and TGF-β at 12 dpi. Conversely, canonical Wnt signalling, which was active in uninjured knee joints and in injured knee joints up to 8 dpi, was attenuated at 12 dpi. The contribution of nerve growth factor (NGF), known as a pain mediator in OA, to the repair process was then investigated in vitro. NGF was released by both cartilage explants and femoral head cultures following injury. Using a Transwell-based cell migration assay, NGF was revealed to have a chemotactic effect on human bone marrow derived MSCs, but not synovial membrane derived MSCs. High-density micromass cultures also revealed NGF had a potent stimulatory effect on the chondrogenic differentiation of mesenchymal cells. The data presented here demonstrate a contribution of endogenous MSCs to the repair of articular cartilage in vivo and suggest a possible new therapeutic strategy: stimulation of in vivo recruitment of MSCs by modulating signalling pathways activated during the healing process. Furthermore, a novel role for NGF as a factor involved in migration and the chondrogenic differentiation of MSCs is suggested.

Mesenchymal stem cells (MSCs) have the potential to differentiate into various cell types, possess potent immunomodulatory properties and can influence various functions of immune cells. Since the immunomodulatory properties of MSCs can be modified by cytokines, we compered the effect of unstimulated MSCs and MSCs pretreated with interleukin (IL)-1, interferon (IFN)- , transforming growth factor (TGF)- and IL-10 on the development of regulatory T cells (Treg) and T helper 17 (Th17) cells in vitro and on the inflammatory environment in the eye. MSCs can produce significant levels of TGF- and IL-6. These cytokines represent the key factors that reciprocally regulate the development of naive T cells into Treg and Th17 cells. Unstimulated MSCs produce TGF- , but not IL-6, and the production of TGF- can be further enhanced by IL-10 or TGF- . In the presence of IL-1, MSCs secrete significant levels of IL-6, in addition to spontaneous production of TGF- . MSC producing TGF- induced preferentially expression of Foxp3 and activation of Treg lymphocytes, whereas MSCs supernatants containing TGF- together with IL-6 supported ROR t expression and development of Th17 cells. We demonstrated that MSCs and their products effectively control the development of Tregs and Th17 cells in a population of...

The Wilms' tumour suppressor gene Wt1 is a key regulator of embryonic development and tissue homeostasis. In humans, mutation in the gene may lead to childhood kidney cancer, severe glomerular kidney diseases, gonadal dysgenesis and, in rare cases, heart diseases. The importance of WT1 in embryonic development is related to its crucial function in the regulation of two cellular plasticity processes: the epithelial to mesenchymal transition (EMT) and the reverse process, the mesenchymal to epithelial transition (MET). WT1 expression persists during the waves of EMT and MET that generate certain mesodermal tissues. In fact, WT1 is a major regulator of both transitions and it is essential for the survival of mesenchyme progenitors. Furthermore, it has been proposed that WT1 is required for the derivation of progenitors from different mesothelia, possibly through an EMT. Progenitors expressing WT1 are believed to differentiate into different cell types, giving rise to coronary vasculature, adipocytes and hepatic stellate cells. In my PhD I aimed to investigate the instructive role of different WT1 isoforms. To address this, the first goal was to generate a single plasmid that would accommodate all necessary components of an inducible system, in order to derive cellular models for the inducible expression of WT1 single isoforms. Second, I aimed to understand the processes that the single variants were sufficient to drive. Therefore, I started with the establishment of two cellular models for the inducible expression of the main four isoforms of WT1 (with or without the exon 5 and/or the KTS, here referred as +/+, +/-, -/+ and -/-). I cloned different plasmids carrying doxycycline inducible WT1 isoforms and derived single stable clones in two epithelial kidney cell lines that do not express WT1: the MDCK and the IMCD3 cells. I then analysed the expression profiles of the clones, using either microarray or RNA sequencing, and performed cellular assays to characterize the cells after WT1 induction. Overall, WT1 induction did not affect cell growth, cell cycle, cell migration or anchorage independent growth, suggesting that the expression of WT1 in these two cell lines does not change their oncogenic potential. The expression analysis of the MDCK cells suggested that the induction of WT1 isoforms activates an inflammatory response, leading to the overexpression of several cytokines. Moreover, the -/+ isoform speciffically caused the upregulation of fibrotic markers and the rearrangement of the actin cytoskeleton. Interestingly, the expression of the mesothelial marker UPK3B increased following the induction of the -/+ isoform. Because the expression of the -/+ variant led to the most signifficant isoform-specific changes in both cell lines, I focused on this isoform for the validation of the transcriptomic data of the IMCD3 cells. I confirmed that the induction of WT1 -/+ in the IMCD3 cells leads to the upregulation of fibrotic markers, increases cell adhesion and activates the AKT and MAPK pathways. Moreover, there was a significant overexpression of different mesothelial markers and, importantly, of key regulators and markers of developmental processes, such as adipogenesis, skeletal and cartilage development, as well as angiogenesis. I then dissected the timing of expression of some specific markers and regulators, analysing the levels of the genes at different time points after WT1 -/+ induction. The preliminary results intimate that WT1 -/+ might induce epithelial cells in the direction of cartilage-skeletal tissue and fat, possibly through a mesothelial intermediate. The data also suggest that the induction of this isoform initiates an EMT, possibly followed by an MET, as the levels of expression of the differentiation markers and regulators increase. To validate the proposed instructive role of WT1, it will be of crucial importance to determine both RNA and protein levels of markers and regulators at even later time points, both in IMCD3 cells and in a model of inducible embryonic stem cells, which is currently under development. In the future, it will be important to address the relevance of these findings in vivo and to dissect the molecular mechanisms.

Current treatment options are limited for patients with myocardial infarction or heart failure. Cellular cardiomyoplasty is a promising therapeutic strategy being investigated as a potential treatment, which aims to deliver exogenous cells to the infarcted heart, for the purpose of restoring healthy myocardial mass and mechanical cardiac function. While several cell types have been studied for this application, only bone marrow cells and human mesenchymal stem cells (hMSCs) have been shown to be safe and effective for improving cardiac function in clinical trials. In both human and animal studies, the delivery of hMSCs to infarcted myocardium decreased inflammatory response, promoted cardiomyocyte survival, and improved cardiac functional indices. While the benefits of using hMSCs as a cell therapy for cardiac repair are encouraging, the desired expectation of cardiomyoplasty is to increase cardiomyocyte content that will contribute to active cardiac mechanical function. Delivered cells may increase myocyte content by several different mechanisms such as differentiating to a cardiomyocyte lineage, secreting paracrine factors that increase native stem cell differentiation, or secreting factors that increase native myocyte proliferation. Considerable work suggests that hMSCs can differentiate towards a cardiomyocyte lineage based on measured milestones such as cardiac-specific marker expression, sarcomere formation, ion current propagation, and gap junction formation. However, current methods for cardiac differentiation of hMSCs have significant limitations. Current differentiation techniques are complicated and tedious, signaling pathways and mechanisms are largely unknown, and only a small percentage of hMSCs appear to exhibit cardiogenic traits. In this body of work, we developed a simple strategy to initiate cardiac differentiation of hMSCs in vitro. Incorporating environmental cues typically found in a myocardial infarct (e.g. decreased oxygen tension and increased concentrations of cell-signaling factors), our novel in vitro conditioning regimen combines reduced-O2 culture and hepatocyte growth factor (HGF) treatment. Reduced-O2 culturing of hMSCs has shown to enhance differentiation, tissue formation, and the release of cardioprotective signaling factors. HGF is a pleiotropic cytokine involved in several biological processes including developmental cardiomyogenesis, through its interaction with the tyrosine kinase receptor c-Met. We hypothesize that applying a combined conditioning treatment of reduced-O2 and HGF to hMSCs in vitro will enhance cardiac-specific gene and protein expression. Additionally, the transplantation of conditioned hMSCs into an in vivo infarct model will result in differentiation of delivered hMSCs and improved cardiac mechanical function. In testing our hypothesis, we show that reduced-O2 culturing can enhance hMSC growth kinetics and total c-Met expression. Combining reduced-O2 culturing with HGF treatment, hMSCs can be conditioned to express cardiac-specific genes and proteins in vitro. Using small-molecule inhibitors to target specific effector proteins in a proposed HGF/c-Met signaling pathway, treated reduced-O2/HGF hMSCs show a decrease in cardiac gene expression. When implanted into rat infarcts in vivo, reduced-O2/HGF conditioned hMSCs increase regional cardiac mechanics within the infarct region at 1 week and 1 month. Further analysis from the in vivo study showed a significant increase in the retention of reduced-O2/HGF conditioned hMSCs. Immunohistochemistry showed that some of the reduced-O2/HGF conditioned hMSCs express cardiac-specific proteins in vivo. These results suggest that a combined regimen of reduced-O2 and HGF conditioning increases cardiac-specific marker expression in hMSCs in vitro. In addition, the implantation of reduced-O2/HGF conditioned hMSCs into an infarct significantly improves cardiac function, with contributing factors of improved cell retention and possible increases in myocyte content. Overall, we developed a simple in vitro conditioning regimen to improve cardiac differentiation capabilities in hMSCs, in order to enhance the outcomes of using hMSCs as a cell therapy for the diseased heart.

Cell therapy, including human mesenchymal stem cell (hMSC) therapy, has the potential to treat different pathologies, including myocardial infarctions (heart attacks). Biological sutures composed of fibrin have been shown to effectively deliver hMSCs to infarcted hearts. However, hMSCs rapidly degrade fibrin making cell seeding and delivery time sensitive. To delay the degradation process, we propose using aprotinin, a proteolytic enzyme inhibitor that has been shown to slow fibrinolysis. This project investigated the effects of aprotinin on hMSCs and suture integrity. Viability of hMSCs incubated with aprotinin, examined using a LIVE/DEAD stain, was similar to controls. No differences in proliferation, as determined by Ki-67 presence, and were observed. hMSCs incubated in aprotinin differentiated into adipocytes, osteocytes, and chondrocytes, confirming multipotency. CyQuant assays were used to determine the number of cells adhered to fibrin sutures. The number of adhered cells was increased through aprotinin supplementation at Days 2, 3, and 5 time points. To examine the effect of aprotinin on suture integrity, sutures were loaded to failure to determine ultimate tensile strength (UTS) and modulus (E). Sutures exposed to aprotinin had higher UTS and E when compared to sutures exposed to standard growth media. Degradation of fibrin was quantified using an ELISA to quantify fibrin degradation products (FDP) and by measuring suture diameter. Fibrin sutures incubated in aprotinin had larger diameters and less FDP compared to the controls, confirming decreased fibrinolysis. These data suggest that aprotinin can reduce degradation of biological sutures, providing a novel method for extending the implantation window and increasing the number of cells delivered for hMSC seeded biological sutures.

Mesenchymal stem cells (MSCs) are promising candidates for treating diverse inflammatory disorders due to their capacity to be immunosuppressive. This phenotype is not present at baseline but develops in response to instructive cues. To date, clinical trials use cells grown in basic culture conditions, anticipating the cells will acquire a useful phenotype in response to in vivo cues. This strategy has failed to produce any FDA approved therapies, based on inconsistent efficacy. This thesis explores whether priming MSCs prior to administration can lead to a more uniformly therapeutic phenotype, and it details the design of an optimal in vitro priming regimen. Because interferon gamma (IFN-γ) is known to induce an anti-inflammatory state in MSCs, hypoxia can confer survival benefits, and both cues coexist in known situations of immune tolerance, we hypothesized dual IFN-γ/hypoxia priming would yield a superior immunosuppressive MSC therapy. We show that priming MSCs with hypoxia or IFN-γ alone improves their ability to inhibit T-cells in vitro, but combining these cues results in additive improvements. We next characterize the proteomic and metabolomic changes MSCs undergo when exposed to single or dual IFN-γ/hypoxia priming. While IFN-γ induces MSCs to suppress inflammation and fibrosis, hypoxia leads to cell adaptations to low oxygen, including upregulation of proteins involved in anaerobic metabolism, autophagy, angiogenesis, and cell migration. Dual priming results in additive effects, with many instances of synergy. Finally, we show initial evidence that dual primed MSCs are better able to inhibit disease progression in a mouse model of acute graft-vs-host disease (GvHD).