Mechanism and consequences of von Willebrand factor upregulation in response to aging and organ transplantation
Creators: Alavi, Parnian
Publisher: name: University of Alberta Library
Year: 2024

<p>Von Willebrand factor (VWF) is a procoagulant protein, which is crucial for blood clot formation and is exclusively expressed in endothelial cells and megakaryocytes. An unregulated increase in VWF levels is associated with elevating the incidence of thrombosis. Elevated VWF levels are observed in pathological conditions as well as physiological conditions and in response to various stimuli and could be a major contributing factor in the association of such conditions with increased thrombogenicity.<br>
Aging is the primary risk factor for cardiovascular disease, which is the most prevalent cause of morbidity and mortality in elderly populations. Several studies have reported that aging increases the circulating levels of VWF, leading to shifts in the hemostatic balance toward pro coagulability and prothrombotic state. While it has been widely reported that circulating VWF levels rise in normal-aged individuals compared to young individuals, there is a gap in our knowledge regarding the mechanism by which aging leads to increased circulating levels of VWF. In this study, I have explored the mechanism by which an age-associated increase in VWF occurs and determined its functional consequences with respect to increased thrombogenicity.<br>
Our analysis demonstrated plasma levels of the antigen and high molecular weight multimers form of VWF were increased in aged mice compared to young. Both VWF mRNA and cellular protein were increased in an organ-specific manner. It increased in the brains, lungs, and livers but not in the kidneys and hearts of aged mice compared to young. There was an increase in the number of microvascular endothelial cells that exhibited VWF expression in the vasculature of aged organs (liver, lung and brain) compared to young. Investigation of the functional consequences of increased VWF levels demonstrated that it was concomitant with a significant increase in platelet aggregates formation in the vascular beds of target organs of aged but not young mice. In vitro analyses demonstrated that there was a significant increase in VWF mRNA levels, in prolonged culture of endothelial cells; and associated with cells that exhibited senescence. Higher proportion of VWF expressing endothelial cells in vivo exhibited senescent markers β- galactosidase and p53 in aged mice brain compared to young. Knockdown of p53 in cultured endothelial cells eliminated VWF upregulation in time-extended/senescent cultured cells, demonstrating the participation of p53 in this process. Moreover, treatment of aged mice with lipid nanoparticles (LPN), which target p53 expressing senescent cells for destruction, exhibited a significant reduction in senescent brain microvascular endothelial cells, and platelets aggregate formation. These results provide insight into designing potential organ-specific targeted treatments to address age-related thrombogenic complications.<br>
Another condition, which may occur physiologically (embryonic development) or pathophysiologically (tumor progression) and is demonstrated to induce VWF upregulation is hypoxia. Our group has reported hypoxia can upregulate VWF and alter its vascular bed expression pattern in lung. Lung transplantation is an effective therapeutic intervention and conventionally necessitates exposure of donor lung to a period of hyperthermia and hypoxia. Since thrombosis is a major complication of lung transplantation, which may lead to allograft failure and since during organ-transplantation donor organs are exposed to hypoxic conditions, we explored whether this may lead to alterations in VWF expression. We also aimed to determine whether an innovative organ preservation method, ex vivo lung perfusion (EVLP) prior to transplantation, could moderate this potential effect and as a result reduce its thrombogenic consequences.<br>
To test our hypothesis, we procured pig’s lungs maintained under conventional static cold storage conditions (SCS), and those in EVLP. Tissue biopsies were obtained at the beginning and the end of SCS period or EVLP perfusion for further analysis. The results demonstrated that VWF mRNA and protein levels in lungs maintained under SCS were unaltered, but significantly reduced in lungs that were perfused under ex vivo lung perfusion “EVLP” for 12 hours. This result was not limited to lungs; similar results were observed in limb’s blood vessels preserved under ex vivo setting. Furthermore, IF analysis of donor lungs post transplantation demonstrated that the preserving lungs in cold storage conditions, but not EVLP, prior to transplantation altered VWF expression pattern, leading to an increased number of microvascular endothelial cells that express VWF in transplanted lungs. These Results provide insights into developing effective anti- thrombotic approaches that would be advantageous in organ transplant procedures.</p>