No description available.

The cost of drug development is high with many drugs failing during toxicity testing. This is a particular problem in veterinary medicine where the pharmaceutical market size is so small that it may not be economically viable to develop drugs. The liver and specifically hepatocytes have a crucial role in drug metabolism via oxidation by cytochrome enzymes (CYP), conjugation and excretion into the biliary system. This drug metabolism is unpredictable between species as each has unique CYP profiles. Furthermore there is breed variation of CYP profiles within the canine species. The ability to produce an in vitro source of canine hepatocytes to model drug metabolism in this species and in different breeds would greatly reduce the expense of candidate drug testing. If an unlimited supply could be produced in vitro this would reduce the number of animals required in pre-clinical testing. The aim of this thesis was to produce an in vitro supply of canine hepatocyte-like cells from stem cell sources, namely hepatic progenitor cells (HPC), mesenchymal stem cells (MSC) or induced pluripotent stem cells (iPSC). Cultures of canine primary hepatocytes were produced to use as a gold standard, but also to develop and refine tests of hepatocyte characterisation and function. A panel of primers was developed for use in real time polymerase chain reaction (PCR) as well as optimising tests for low density lipoprotein (LDL) and indocyanine green uptake, albumin production, periodic acid- Schiff staining for glycogen and CYP activity using a luciferase-based system. As primary hepatocytes rapidly lost their defining characteristics and function in vitro, methods of maintaining function using CYP inducers and culture substrates were assessed. Isodensity centrifugation and magnetic-activated cell sorting was employed to isolate HPCs. Selection of cells from the non-parenchymal cell fraction with stem cell marker Prominin 1 demonstrated that these were keratin 7 positive, a HPC marker. Cells morphologically consistent with HPC appeared and expanded in culture after 2 weeks. On passaging, these cells failed to continue expanding, despite plating onto collagen, laminin, SNL feeder cells or using Kubota’s medium (known to allow rapid expansion of rodent and human HPCs). Canine adipose (Ad-MSC) and bone marrow-derived mesenchymal stromal cells (BM-MSC) were isolated post mortem. These were characterised as CD45, 105 and STRO-1 positive, CD11b, 19 and 45 negative cells which could be differentiated into adipocytes, chondrocytes and osteocytes based on staining characteristics and relative gene expression. Protocols published for other species were used to differentiate both Ad-MSC and BM-MSC towards a hepatocyte phenotype. Although a dramatic change in morphology and a reduction in vimentin gene expression were noted, suggesting a loss of mesenchymal phenotype, these protocols did not induce a hepatocyte phenotype. Pre-treatment with 5-Aza-2′-deoxycytidine to cause DNA demethylation and valproic acid to inhibit histone deacetylation also failed to allow transdifferentiation. A polycistronic vector containing Oct-4, c-Myc, Sox2 and Klf4 was successfully transfected into canine epidermal keratinocyte progenitor cells which became alkaline phosphatase positive and assumed a morphology consistent with iPSC. After colony selection and expansion, PCR evidence of plasmid presence was lost, colony morphology changed, and alkaline phosphatase activity reduced, consistent with vector expression factor and pluripotency loss. Canine iPSCs produced by lentiviral method were then differentiated towards hepatocyte phenotype using a published protocol for mouse and human iPSC. These cells were then assessed for hepatocyte characteristics using the developed reagents and primers. These cells demonstrated increased gene expression and morphology consistent with differentiation towards a hepatocyte-like phenotype. This thesis demonstrates successful culture of canine primary hepatocytes and validation of tests of hepatocyte phenotype. This provides a basis for optimising primary hepatocyte function in vitro and assessment of the success of differentiation protocols on stem cell sources. Canine mesenchymal stromal cells do not appear to transdifferentiate towards a hepatocyte-like phenotype using published protocols for other species. Canine iPSC are a promising candidate for an in-vitro source of hepatocyte-like cells.

"The effectiveness of exogenous cellular therapies has been limited by the ability to efficiently and locally deliver cells to a region of interest. We have developed biological sutures, formed from fibrin microthreads, to overcome these delivery issues and demonstrated increased cell engraftment compared to the current gold standard. However, the cell seeding efficiency onto the sutures is low and during implantation cells are subjected to shear forces as the sutures are pulled through the tissue. As a result, cells go unused after seeding and an uneven distribution of cells from the entry point to exit of the suture. By adding cell attachment and adhesion promoters and increasing culture time we proposed to overcome these issues. We have developed a shear loading method to evaluate the changes in cellular adhesion. Either poly-l-lysine or vitronectin was used to coat sutures. Uncoated control and coated sutures were then seeded with 100,000 human mesenchymal stem cells (hMSCs) for 24hrs or control sutures were seeded for 48hrs. An in vitro shear stress model was created by spinning seeded sutures with a centrifuge. Cell number per unit length prior to and post spinning were compared. To compare the effect of modifications on cell morphology cells were qualitatively assessed and nuclear alignment was evaluated as a robust measurement for overall cellular angle. Control sutures were found to have 6,821±739cells/cm prior to spinning, while sutures modified with poly-l-lysine resulted in 4,226±1,003cells/cm and vitronectin had 19,604±1,829cells/cm (p<0.05 vs. control and poly-l-lysine). 48hrs seeding resulted in a cell number to 4,417±2,266 cells/cm. Spinning resulted in relative decreases in cell number for control and coated sutures. Cells remained attached after sutures were spun after increased incubation time. Cells aligned along the long axis of individual microthreads; the alignment on control sutures was significantly different from all modifications. There was no difference in alignment between modifications, although they were significantly different compared to cells grown on topographically flat tissue culture plastic. These results demonstrated increased cell seeding efficiency and cell number for vitronectin coated biological sutures and increased cell adhesion following increased incubation time. The combination of these two modifications may lead to increased quantity and more evenly distributed cells delivered to diseased tissues by increasing initial cell number, increasing cell engraftment, and increased resistance to shear."

No description available.

abstract / Medicine / Doctoral / Doctor of Philosophy

Despite major advances in pharmacological and surgical treatments of cardiovascular diseases (CVDs), clinical outcomes of patients with severe CVDs remain very poor. Most of medication and interventions currently available are only playing roles of preventing further damage to myocardium, declining the risk of on-going cardiovascular events, lifting the cardiac pumping efficiency and lower early mortality rates, none of these treatments can regenerate or repair damaged cardiac tissue or restore heart function. As a result, several new strategies have been explored to overcome limitations of current therapeutic approaches. One prospective is to replace dead cardiac vascular cells with young and green cells to repair or regenerate damaged heart myocardium. Several types of stem cells, including bone marrow hematopoietic stem cells, mesenchymal stem cells (MSCs), embryonic stem cell (ESCs)and induced pluripotent stem cells (iPSCs),have been tested as the candidates for treatment of CVDs. Among a myriad of types of stem cells, bone marrow derived MSCs(BM-MSCs) has received great attention based on several unique properties such as easy isolation and expansion, stable genetic background and low immunogenicity. However, the therapeutic efficacy of BM-MSCs derived from aging or diseased donors is impaired. The differentiation potential of BM-MSCs is gradually reduced with the increased culture time. Thus, it is urgent to identify some novel alternative sources for MSCs. Moreover, the potential mechanisms of MSCs therapy have not been understood totally. This thesis is designed to investigate the therapeutic efficacy and potential mechanisms of several novel types of MSCs, including hESC-MSCs and hiPSC-MSCs and Rap1-/--BM-MSCson several types of CVDs, including pulmonary arterial hypertension (PAH), dilated cardiomyopathy (DCM)and myocardial infarction (MI). In Chapter 4, it disclosed that hESC-MSCs have a better therapeutic efficacy than BM-MSCs in attenuation of PAH induced by monocrotaline in mice. The greater therapeutic potential of hESC-MSCs on PAH was not only attributed to the higher capacity of differentiation into de-novo vascular cells, but also attributed to higher cell survival rate and greater paracrine effects post-transplantation. In Chapter 5, it demonstrated that compared with BM-MSCs, iPSC-MSCs have a better therapeutic effect on doxorubicin-induced cardiomyopathy. Several potential mechanisms of action were involved in iPSC-MSCs-based therapy for cardiomyopathy. It demonstrated that iPSC-MSCs transplantation not only attenuated the generation of reactive oxygen species(ROS)and the level of inflammation, but also restored depletion of cardiac progenitor cells and promoted endogenous myocardial regeneration against doxorubicin induced cardiomyopathy. Moreover, mitochondrial transfer and paracrine actions of iPSC-MSCs played critical roles in the rescue for doxorubicin-induced cardiomyopathy. In Chapter 6, it uncovered that compared with wild type BM-MSCs,Rap1-/--BM-MSCs transplantation achieved a better benefit to MI induced by ligation of left anterior descending (LAD)coronary artery. Rap1-mediated NF-κB activity plays a key role in regulation MSCscytokine secretion profiles. The absence of Rap1 in MSCs leads to reduced pro-inflammatory cytokines secretion and enhanced MSCs survival capacity, thus yielding a better therapeutic efficacy. In conclusion, findings presented in this thesis provide important new insights regarding different novel types of MSCs, including those derived from ESC and iPSC. They have distinct mechanisms of action from BM-MSCs and provide superior therapeutic efficacy in various form of severe CVDs, including PAH and DCM. The safety and efficacy of these novel types of MSCs for treatment of CVDs deserve further investigations. / published_or_final_version / Medicine / Doctoral / Doctor of Philosophy

The fundamental principle of tissue engineering is to use appropriate cell source, combined with scaffolds and bioactive factors to develop tissue constructs which restore, maintain or improve tissue function. There is increasing data emphasizing the importance of mechanical signals and extracellular matrix (ECM) proteins presented by the scaffold in determining stem cell fate/functions which are critical to tissue construct maturation and success of stem cell-based therapies. Cell-matrix adhesions are one of the major mechanosensing machineries cells use to convert information provided by ECM ligands and mechanical signals presented by scaffolds into intracellular biochemical signaling cascades which lead to particular functional responses. Therefore, understanding how ECM ligands and mechanical signals regulate cell-matrix adhesion formation and activation of associated intracellular signaling proteins is fundamental to rational design of biomaterial and loading protocol for optimal cell functional responses in tissue constructs. In this study, we attempted to understand the regulatory effects of external mechanical signal and exogenous ECM protein on cell-matrix adhesion formation and associated intracellular signaling proteins of human mesenhymal stem cells, and in particular, to test the hypothesis that mechanical stimulation or exogenous ECM protein can lead to adhesion maturation into 3D-matrix adhesions in 3D collagen environment. We used microencapsulation technique to embed cells in 3D collagen environment, forming disc-shaped hMSC-collagen constructs. By immunofluorescent staining and confocal microscopy, we visualized changes in size, morphologies and molecular composition of the adhesions. First of all, 2D adhesions of hMSCs were characterized. We showed that hMSCs form well-organized αv integrin-based focal adhesions and fibrillar adhesions in 2D culture. To investigate the regulatory effects of mechanical signals on adhesion signaling and maturation, we used micromanipulator-based loading device to impose dynamic compression to hMSC-collagen constructs. We found that dynamic compression lead to enlargement of integrin αv adhesions which recruit focal adhesion kinase (FAK), vinculin and extracellular signal-regulated kinase (ERK). In addition, FAK was activated at enlarged integrin αv adhesions and translocated to peri-nuclear region after compression, suggesting that loading induces activation of FAK signaling pathways through increased integrin αv clustering. Moreover, we demonstrated that dynamic compression can induce 3D-matrix adhesion formation, indicating the role of external force in integrin α5-based adhesion maturation in 3D collagen environment. We explored the effect of exogenous ECM proteins on adhesion maturation of hMSCs by adding fibronectin into cell-collagen mixture during fabrication of collagen constructs. Our results demonstrated that the exogenous fibronectin can induce α5 integrin-based adhesion maturation into 3D-matrix adhesions in our collagen constructs in a dose-dependent manner. This study demonstrated that the effect of external mechanical signals and exogenous ECM ligands on adhesion signaling and maturation of hMSCs in 3D collagen environment. Our findings contribute towards mechanobiology of hMSCs in 3D context. In particular, our results showed that exogenous proteins or external loading can lead to 3D-matrix adhesion formation, which may serve as a potential way to enhance biological functions of hMSCs in collagen constructs, facilitating stem cell-based therapies. / published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

No description available.

No description available.

Atrophic non-union is a major complication following fracture of a bone. It represents a biological failure of the fracture healing process and occurs in 5-10% of cases. A number of factors predispose to atrophic non-union including high energy injuries, open fractures, diabetes, and smoking. Atrophic non-unions cause immense patient morbidity and consume large amount of health care resources. Bone grafts taken from the iliac crest contain biologic components required for fracture healing and are considered as the gold standard treatment of aseptic atrophic non-union. However, harvesting bone grafts from the iliac crest is associated with significant patient morbidity which can reduce quality of life. Mesenchymal stem cells (MSCs) have the ability to proliferate and undergo multilineage differentiation. The emergence of MSC therapy provides an alternative strategy for treating impaired fracture healing. MSCs contribute to normal fracture healing both directly as bone progenitor cells and indirectly as mediator secreting cells. Although a number of studies have shown that MSCs can promote bone regeneration in small animal fresh critical size defects, this is not analogous to most clinical aseptic atrophic non-unions which do not have a significant bone gap. There remains therefore a clinical need for an appropriate strategy for using stem cells in atrophic non-unions. Thus, the aim of this study aim was to develop a clinically relevant strategy to promote fracture healing in an atrophic non-union model using the percutaneous injection of MSCs as a minimally invasive technique. An atrophic non-union model was established and validated. A small (1 mm) non-critical size defect was created at the mid shaft tibia and the fracture site was stabilised using an external fixator. Atrophic non-union was induced by stripping the periosteum for one bone diameter either side of the osteotomy site and curettage of the intramedullary canal over the same distance. The procedure reliably created an atrophic non-union. Fracture healing was evaluated using (1) serial radiography, (2) micro-computed tomography, (3) histomorphology and (5) biomechanical testing. Fracture scoring systems including the radiographic union scale in tibia (RUST) and the Lane & Sandhu score were validated in a preclinical model. A simple sample preparation technique for evaluating bone mechanical properties was developed and used to assess the stiffness and strength of the fracture repair. Percutaneous injection of MSCs locally into the fracture site in the early ‘post-injury’ period at three weeks after induction of atrophic non-union was found to improve the fracture healing process significantly (83% of cases), while MSCs implantation in the late ‘post-injury’ period at eight weeks after induction of atrophic non-union showed no significant improvement of fracture healing (20% of cases). Percutaneous local implantation of MSCs rescued the fracture healing process in cases destined to progress to atrophic non-union. In clinical practice, there may be an advantage using MSCs from a universal donor as the processes of MSC isolation and preparation are expensive and time consuming. To investigate the feasibility of using non-autologous cells, the atrophic non-union was used to determine the bone regenerative potential of using xenogeneic donor hMSCs in an atrophic non-union. The results demonstrated that the therapeutic effect of using hMSCs in a xenogeneic manner to promote fracture healing in the rat atrophic non-union model was comparable with rMSCs (88% of cases in both hMSCs and rMSCs) and there were neither significant clinical adverse effects nor adverse immune responses with the xenogeneic transplantation. However, MSCs did not persist at the fracture following injection. Perivascular stem cells (PSCs) taken from adipose tissue, which is an expendable source, have advantages over conventional MSCs as they are a defined and homogenous population and can be used without culture expansion. The administration of PSC using percutaneous injection improved the fracture healing process in atrophic non-union (60% of cases). This suggested that PSCs may present an appropriate choice for use in cell therapies to promote fracture healing in atrophic non-union. The results from this thesis can be applied to the development of a clinically relevant strategy using MSCs as a minimally invasive technique to promote fracture healing in atrophic non-union, in particular (1) the effectiveness of a cell therapy is likely to be highly dependent of the timing of injection relative to the stage of fracture healing, (2) hMSCs were as effective as rMSCs in promoting fracture healing, suggesting that it may be feasible to use an allogeneic strategy in humans, (3) the injected MSCs were not detectable even in case of successful repair, suggesting that they may act through a paracrine effect and (4) PSCs isolated from adipose tissue contributed to fracture healing in the atrophic non-union model, suggesting that adipose tissues can be used as an alternative cell sources for bone repair.