Abstract
The research presented in this thesis focusses on the development of new model systems that allow deeper understanding of biology of diseases. Described model systems make use of adult stem cells. Adult stem cells can be identified throughout the adult lifetime of the organism and are retained within the organ
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of interest. These adult stem cells replace the tissues in which they reside by undergoing cell division and subsequent differentiation into various other cell types. This replacement is required when cells are lost due to damage or because of natural organ turnover. We can make use of this epithelial renewal capacity to establish model systems that closely recapitulate the organ of origin.
Adult stem cell-derived organoids are close representatives of the organ of interest due to the capabilities of self-renewal and differentiation of the stem cell population present in the culture. The organoids and their derivatives are useful tools to study fundamental biology but also human disease. Both disease biology as therapeutic interventions are characterised in a higher throughput setting when compared to clinical trials or mouse studies. Presented adult stem cell-derived organoids, therefore, show great promise for the modelling of disease as well as provide potential new therapeutic opportunities. The studies in this thesis make use of the earlier developed intestinal or airway organoids as well as present the development of a new organoid culture of the thyroid.
Many signals are required to sustain the above-mentioned adult stem cells in vivo as well as in vitro. External regulators of this homeostatic condition, like the molecule R-spondin, can potentiate Wnt signalling by decreasing Wnt receptor breakdown, stabilising the receptor on the membrane and maintaining or even increasing stem cell numbers. In vivo manipulation of the R-spondin-Wnt axis could therefore allow for faster organ regeneration by potentiating stem cell population expansion.
Chapter 1 and 2 describes and applies airway organoids to model human disease, respectively. We present a new differentiation protocol that allows extensive visualisation of ciliated cells in airway organoids. This protocol is applied to organoids derived from patients suffering from primary ciliary dyskinesia to study the biology of the disease.
Chapter 3, 4, 5 and 6 describe the use of organoids to study SARS-CoV-2 infection. While Chapter 4 shows the application of intestinal organoids in SARS-CoV-2 research, chapter 6 describes a novel model system of the bronchioalveolar space to study COVID-19.
Chapter 7 describes the generation of a novel organoid system of thyroid follicular cells. The cells in the organoids express thyroid hormone machinery genes and show active secretion of thyroid hormones after stimulation. Moreover, we show the potential of using these organoids as models for Graves’ disease.
Chapter 8 extends the knowledge of adult stem cells and the requirement of Wnt signalling in organoid culture to in vivo. We optimised earlier developed R-spondin production methods to allow systemic injection of the Wnt potentiator in mice. We show increased proliferation in hepatocytes over seven days after injection. This proliferation is not limited to Wnt-active zones in the liver.
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