In this project we wanted to look into the mechanism behind von Willebrand disease (VWD). This is the most commonly diagnosed bleeding disorder and will effect ~1:10,000 people. In this disorder, there are defects in the levels of functional von Willebrand Factor (VWF). This is a large protein, that is produced in endothelial cells, which line the blood vessels throughout the body. Most VWF is produced by these cells, but a small percentage (~20%) is carried by platelets, which circulate in the blood stream. VWF is stored in a tubular folded form in Weibel Palade bodies (WPBs), which are vesicles in the endothelial cells. When vascular injury occurs, VWF is secreted by these cells and will unfold in the blood stream. Platelets will bind to these long strands of VWF, forming a clot to stop the bleeding. In the case of VWD, there is not enough functional VWF, and therefore bleedings will continue, and this can lead to life threatening situations.
However, besides some animal models, at the moment there is a lack of good cell models to study VWD, but also other bleeding and vascular diseases. Therefore the precise effects of low levels of VWF remain unknown and new approaches are needed. We are now able to push adult cells back to progenitor cells that can be induced to most cell types of the human body. We used this system on blood cells from healthy donors and VWD patients and made endothelial cells from these progenitor cells, thereby creating a disease in a dish model for VWD.
After several endothelial differentiation rounds, we performed some characterization assays of these cells and concluded that these cells are really endothelial cells, when we look at their shape, cell markers on their surface and their genetics/expression. However, it is known from literature, that these induced endothelial cells have some problems with their maturity, and this is reflected in low production of VWF. Therefore, we focussed on trying to produce more mature endothelial cells with this approach. We have tried different protocols, growth factors and other supplements to induce this maturation, although without too much success. However, we noticed that when the cells are grown in a dish for more than 30 days, some cells do show mature VWF production. However, it is known that these cells can be kept in a dish for a limited length of time, and the cells were deteriorating and did not look like healthy cells anymore
In conclusion, we were able to generate endothelial cells from healthy donors and patients with VWD. However, because of their immaturity problem which is reflected in low VWF production, we were not able to do a full characterization and apply these cells to explore novel therapeutics for VWD. Nevertheless, this maturity issue can be a problem for other studies looking at bleeding and/or vascular disorders. Therefore more research is needed to create a better understanding of VWD, leading to new therapeutics.