Evaluation of basal and stimulated von Willebrand factor release from endothelial colony forming cells derived from Type 1 von Willebrand disease patients
Type 1 von Willebrand disease (VWD) is the most common bleeding disorder and is thought to be caused by a quantitative deficiency in von Willebrand factor (VWF). Endothelial cells release VWF into the circulation in an unstimulated manner through basal secretion, but they can also be stimulated to release large stores of VWF in response to hemostatic challenge. VWF levels measured during the diagnostic workup for Type 1 VWD are taken at baseline and therefore only represent the contributions of basal VWF secretion. It has been consistently reported that baseline VWF levels exhibit no correlation to bleeding severity in Type 1 VWD which greatly complicates diagnosis, management, and stratification of patients based on future risk of bleeding. Our lab has previously shown that Type 1 VWD patients exhibit a blunted response to surrogates of hemostatic challenge that correlates with their bleeding severity, but the underlying cause of this poor response is not understood. This thesis aims to use endothelial colony forming cells (ECFCs), a population of circulating endothelial progenitor cells, from Type 1 VWD patients and healthy controls to further explore this question. We employed VWF secretion analysis and transcriptomic analysis to identify differences between control and Type 1 VWD-derived ECFCs during basal and stimulated VWF release. Through VWF secretion analysis, we found that control and Type 1 VWD-derived ECFCs secrete comparable amounts of VWF during basal release, but during stimulated release, VWF secretion was reduced in the Type 1 VWD group. mRNA-seq showed differential regulation of coagulation, cell shape, the cell cortex, and cellular receptor complexes between control and Type 1 VWD-derived ECFCs during stimulated VWF release. Finally, we identified seven miRNAs during basal VWF release and five miRNAs during stimulated VWF release that are differentially regulated between control and Type 1 VWD-derived ECFCs. We have shown for the first time distinct transcriptional differences between control and Type 1 VWD-derived ECFCs. These differences are more apparent during stimulated VWF release, which supports the notion that the ability to respond to hemostatic challenge may be a better predictor of bleeding severity than baseline VWF levels alone.