2,285 research outputs found

    Computer modelling of haematopoietic stem cells migration

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    AbstractA mathematical model for migration of haematopoietic stem cells towards their niche in the bone marrow has been proposed in the literature. It consists of a chemotaxis system of partial differential equations with nonhomogeneous boundary conditions and an additional ordinary differential equation on a part of the computational boundary. The aim of the current work is to extend appropriately a second order positivity preserving central upwind scheme, originally proposed for a chemotaxis system with zero-flux boundary conditions and to apply it for the numerical solution of the considered problem. This paper introduces a first glance of such modification and outlines open questions in the handling of the nonlinear boundary conditions in a way that preserves the positivity of the solution. The presented numerical tests illustrate the need of the development of new specialized schemes for more complex chemotaxis systems

    Transplantation tolerance, microchimerism, and the two-way paradigm

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    The nonlinear nature of biology

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    In this thesis, we explore the stability and the breakdown of stability of biological systems. The main examples are the blood system and invasion of cancer. However, the models presented in the thesis apply to several other examples. Biological systems are characterised by both competition and cooperation. Cooperation is based on an unsolvable dilemma: Even though mutual cooperation leads to higher payoff than mutual defection, a defector has higher payoff than a co-operator when they meet. It is not possible to represent this dilemma with a linear and deterministic model. Hence, the dilemma of cooperation must have a nonlinear and/or stochastic representation. More general, by using a linearised model to describe a biological system, one might lose dimensions inherent in the complexity of the system. In this thesis, we illustrate that a nonlinear description of a biological system is potentially more accurate and might provide new information. We show that even though a new type of individual is in general not advantageous when it appears in stable population, the newcomers can grow in number due to stochasticity. Moreover, the new type can only become advantageous if it manages to change the environment in such a way that it increases its fitness. We also propose a model that links self-organisation with symmetric and asymmetric cell division, and we illustrate that if symmetric stem cell division is regulated by differentiated cells, then the fitness of the stem cells can be affected by modifying the death rate of the mature cells. This result is interesting because stem cells are less sensitive than mature cells to medical therapy, and our results imply that stem cells can be manipulated indirectly by medical treatments that target the mature cells

    Construction of artificial stem cell microniches

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    Artificial embryonic stem cell niches were made from murine embryonic stem cells (ESCs) and SAOS-2 osteoblast-like cells (a human osteosarcoma cell line) by constructing aggregates with well-defined architectures with dielectrophoresis between the castellations of interdigitated oppositely castellated electrodes. This combination of the cells was chosen to mimic the bone marrow endosteal niche that harbours haematopoietic stem cells in a quiescent stage, with the aim of transforming the embryonic stem cells into hematopoietic precursor cells. Within aggregates made with dielectrophoresis cells are in very close contact, allowing strong cell-cell interactions to occur. Puramatrix gel was used to immobilize the cells; a concentration of 25% Puramatrix was found to be optimal. Aggregates consisting of only ESCs formed embryoid bodies upon aggregation with dielectrophoresis within 24 hours. The size of the electrodes determines the size of embryoid bodies. Embryonic bodies formed at electrodes with a characteristic size larger than 100 μm tended to split; electrodes smaller than 75 μm gave embryonic bodies which tended to merge. 75 to 100 μm was optimal. When aggregates were made containing both SAOS-2 and ESCs, the reorganization of the two cell types after their aggregation was found to be controlled by the different adhesive-cohesive properties of the two cell types and their initial position. Optimum cell-cell interaction was obtained in an aggregate with a layered architecture with the osteoblasts initially in bottom position, and the ESCs in top position. The study of differentiation in ESCs was made by conducting experiments with Bry ESCs, which mark the onset of differentiation along mesenchymal lineage with the production of GFP. The results indicated that aggregation with dielectrophoresis causes the ESCs to take the first steps towards differentiation along the mesenchymal lineage, and that the differentiation is stronger in aggregates formed at electrodes of 75 μm than at electrodes of 100 and 50 μm. Co-culture with SAOS-2 cells did not lead to differentiation along the mesenchymal lineage. Lastly it was shown that optical tweezers could be combined with dielectrophoresis to move individual cells between niches

    Bomapin is a redox-sensitive nuclear serpin that affects responsiveness of myeloid progenitor cells to growth environment

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    <p>Abstract</p> <p>Background</p> <p>Haematopoiesis is a process of formation of mature blood cells from hematopoietic progenitors in bone marrow. Haematopoietic progenitors are stimulated by growth factors and cytokines to proliferate and differentiate, and they die via apoptosis when these factors are depleted. An aberrant response to growth environment may lead to haematological disorders. Bomapin (serpinb10) is a hematopoietic- and myeloid leukaemia-specific protease inhibitor with unknown function.</p> <p>Results</p> <p>We found that the majority of naturally expressed bomapin was located in the nucleus. Both the natural and recombinant bomapin had a disulfide bond which linked the only two bomapin cysteines: one located in the CD-loop and the other near the C-terminus. Computer modelling showed that the cysteines are distant in the reduced bomapin, but can easily be disulfide-linked without distortion of the overall bomapin structure. Low-level ectopic expression of bomapin in bomapin-deficient K562 cells resulted in about 90% increased cell proliferation under normal growth conditions. On the other hand, antisense-downregulation of natural bomapin in U937 cells resulted in a decreased cell proliferation. Bomapin C395S mutant, representing the reduced form of the serpin, had no effect on cell proliferation, suggesting that the disulfide bond-linked conformation of bomapin is biologically important. The bomapin-dependent effect was specific for myeloid cells, since ectopic expression of the serpin in HT1080 cells did not change cell proliferation. In contrast to the survival-promoting activity of bomapin in cells cultured under optimal growth conditions, bomapin enhanced cell apoptosis following growth factor withdrawal.</p> <p>Conclusions</p> <p>We propose that bomapin is a redox-sensitive nuclear serpin that augments proliferation or apoptosis of leukaemia cells, depending on growth factors availability.</p

    Towards a new understanding of decision-making by hematopoietic stem cells

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    Cells within the hematopoietic stem cell compartment selectively express receptors for cytokines that have a lineage(s) specific role; they include erythropoietin, macrophage colony-stimulating factor, granulocyte colony-stimulating factor, granulocyte/macrophage colony-stimulating factor and the ligand for the fms-like tyrosine kinase 3. These hematopoietic cytokines can instruct the lineage fate of hematopoietic stem and progenitor cells in addition to ensuring the survival and proliferation of cells that belong to a particular cell lineage(s). Expression of the receptors for macrophage colony-stimulating factor and granulocyte colony-stimulating factor is positively autoregulated and the presence of the cytokine is therefore likely to enforce a lineage bias within hematopoietic stem cells that express these receptors. In addition to the above roles, macrophage colony-stimulating factor and granulocyte/macrophage colony-stimulating factor are powerful chemoattractants. The multiple roles of some hematopoietic cytokines leads us towards modelling hematopoietic stem cell decision-making whereby these cells can &lsquo;choose&rsquo; just one lineage fate and migrate to a niche that both reinforces the fate and guarantees the survival and expansion of cells as they develop

    The in vitro differentiation of prostate epithelial cells and gonadal adipocytes from mouse embryonic stem cells

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    Mouse embryonic stem (ES) cells are pluripotent, undifferentiated cells that can differentiate into any cell of the three germ layers: the ectoderm, the mesoderm and the endoderm. Mammalian development is challenging to study due to the in utero gestation and small size of early embryos. Mouse ES cells overcome this hurdle by recapitulating in vivo organogenesis in an in vitro setting. There are currently no in vitro models of prostate development from mouse ES cells. The prostate is an endoderm derived exocrine organ that functions to provide the seminal constituents for sperm. The initial aim of this study was to differentiate mouse ES cells into mature, prostatic epithelial cells in vitro in stepwise manner. The prostate is derived from the urogenital sinus which in turn is derived from the endoderm. The endoderm and urothelium have been generated from mouse ES cells in vitro with the addition of Activin-A and alltrans retinoic acid respectively. It was hypothesised that treatment of mouse ES cell-derived urothelial cells with dihydrotestosterone (DHT), TGFb1 and FGF10 would induce prostate epithelial cell differentiation. Gene expression of homeobox protein Nkx3.1 and prostate marker probasin (Pbsn) were identified in day 16 and day 22 differentiated cultures treated with the aforementioned growth factors. Additionally, day 22 cultures treated with DHT, TGFb1 and FGF10 developed cyst-like acinus structures with a lumen. In conjunction with prostate epithelial cell differentiation, adipocyte-like cells were unexpectedly generated. Brown and white adipocytes are thought to arise from the mesoderm germ layer. Mouse ES cell culture conditions used to generate prostate epithelial cells were primed for endoderm specification. The question was then asked if the adipocytes generated were indicative of a particular adipose depot and if the endoderm could be a source of adipocytes. In order to identify the adipocyte-like cells differentiated in vitro, a method was developed to characterise brown, subcutaneous and visceral white adipocytes by flow cytometry. Multi-parametric flow cytometric analyses of adipocytes stained with Nile Red, MitoTracker Deep Red, Nile Blue, fatty acid translocase CD36 and laminin receptor integrins a6b1 established adipocyte heterogeneity at the single cell level. Comparisons in dye uptake and surface protein expression between adipocytes revealed a code that was applied to the adipocyte-like cells differentiated under endoderm culture conditions. Adipocytes generated in mouse ES cell cultures treated with DHT, TGFb1 and FGF10 matched the profile of gonadal adipocytes. Here, I report the first protocol describing prostate epithelial cell differentiation from mouse ES cells. As mouse ES cells can be genetically modified, the development of prostate epithelial cells may serve as an alternative approach for the study of prostate disease in vitro. The generation of adipocytes from mouse ES cells under endoderm conditions prompted the development of a flow cytometric method to characterise adipocyte heterogeneity at the single cell level. The method can potentially be used for the diagnosis of a range of metabolic disorders stemming from obesity such as diabetes. Contrary to reports of a mesoderm origin of adipocytes, a possible endoderm origin of gonadal adipocytes is hypothesised, the adipose depot closest to the prostate. The development of the prostate in conjunction with gonadal adipocytes has yet to be reported

    A roadmap for the Human Developmental Cell Atlas

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    The Human Developmental Cell Atlas (HDCA) initiative, which is part of the Human Cell Atlas, aims to create a comprehensive reference map of cells during development. This will be critical to understanding normal organogenesis, the effect of mutations, environmental factors and infectious agents on human development, congenital and childhood disorders, and the cellular basis of ageing, cancer and regenerative medicine. Here we outline the HDCA initiative and the challenges of mapping and modelling human development using state-of-the-art technologies to create a reference atlas across gestation. Similar to the Human Genome Project, the HDCA will integrate the output from a growing community of scientists who are mapping human development into a unified atlas. We describe the early milestones that have been achieved and the use of human stem-cell-derived cultures, organoids and animal models to inform the HDCA, especially for prenatal tissues that are hard to acquire. Finally, we provide a roadmap towards a complete atlas of human development

    Pluripotent stem cells and their dynamic niche

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    Cell-seeded implants are a regenerative medicine strategy that aims to replace injured tissue and restore tissue function. Pluripotent stem cells are promising cell candidates for the development of regenerative medicine therapies as they have the ability to self-renew and commit towards numerous cell types. In vivo, stem cells reside in a dynamic niche, a stem cell-specific microenvironment that possesses chemical, biological and mechanical cues, which drive the stem cell fate and renewal. The connection between stem cells and their niche is a two-way relationship consisting of both cell–cell interac‐tion and cell–extracellular matrix (ECM) interactions. An alternative regenerative medicine approach is the manipulation of the stem cell microenvironment. Hence, novel strategies have been developed including 3D biomaterials and bioreactor technologies providing topographical, chemical and mechanical cues to recreate the stem cell niche. Understanding the mechanisms controlling stem cell fate and the dynamic nature of thestem cell niche will enable researchers to replicate this stem cell-specific microenvironment, and therefore, harness and control the valuable attributes which stem cells possess. This chapter elucidates the importance of pluripotent stem cells and their dynamic niche in regenerative medicine. It further presents novel strategies to replicate chemical, topographical and mechanical stimuli which are essential for the regulation of stem cell fate and hence tissue regeneration
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