Project leaders: Timo van den Berg PhD
In 2011 a new line of research dedicated to basic aspects of platelets was initiated. We developed a novel FACS based assay for the analysis of platelet aggregation using a variety of agonists. In contrary to the standard aggregometer test this test is suitable for analyzing platelet function in thrombocytopenic patients. Our research also shows that this test allows for the relatively simple functional discrimination of patients with related integrin-based but nevertheless genetically distinct bleeding disorders, including Glanzmann disease and LAD-1/variant syndrome, the latter of which was originally described in our laboratory. Glanzmann patients have a genetic defect in the integrin-β3 chain, which selectively affects fibrinogen-mediated binding. On the other hand, as we have recently shown for the first time, patients with LAD-1/variant syndrome carry mutations in the kindling-3 protein that is involved in integrin inside-outpotentiated signaling. This leads to a more generalized defect in integrin activation, which affects both fibrinogen- as well as collagen-mediated aggregation, of which the latter is mediated via the α2β1-integrin. Our results were confirmed with adhesion assays performed under physiologic flow conditions. It is hypothesized that the difference in the adhesion to collagen is representative for the initial binding of platelets to the damaged blood vessel wall. These findings also provide an explanation for the more severe bleeding tendency observed in LAD-1/variant syndrome as compared to Glanzmann disease. We are also continuing our investigations on the role of kindling-3 in phagocytes.
In addition, we have investigated the role of the caprin-2 protein in platelet formation and function. Caprin-2-deficient mice were shown to be thrombocytopenic and this appears to be due to an intrinsic defect in the megakaryocyte/platelet lineage. The results are supported by caprin-2 knock-down studies in human megakaryocytic cell lines and current efforts are focused on characterizing the role of caprin-2 in the different stages of platelet development. We are also optimizing the available flow-based assays for the analysis of platelet function.