Age-related alterations in the level and expression pattern of Von Willebrand Factor (VWF)
Von Willebrand Factor (VWF) is a multimeric adhesive glycoprotein that is exclusively expressed in endothelial cells (EC) and megakaryocytes. This procoagulant protein is involved in maintaining primary hemostasis and thrombus formation. However, there are pathological and physiological conditions that alter the circulating levels and pattern of VWF expression in vasculature. Unregulated increase in VWF levels may contribute to elevate the incidence of thrombosis. Since increased
... is observed with aging, we explored whether aging is associated with alterations in the level and/or pattern of VWF expression. This study compared circulating VWF levels in the blood of young and aged mice and rats, using ELISA. Additionally, immunofluorescence confocal microscopy, Western blot analyses, and RT-PCR analyses were used to determine VWF expression pattern, cellular protein and mRNA levels. The expression pattern of the VWF protein was determined in combination with the endothelial marker CD31 and micro vessels marker (Isolectin-GS-IB4), in various organs of young and aged mice. Furthermore, to explore the functional consequences of altered VWF expression with regard to platelet aggregation, which is a major contributing factor to thrombus formation, CD41 a marker of activated platelets was used for immunofluorescence confocal microscopy. iii The results of these analyses demonstrated that circulating VWF protein levels were higher in blood of aged rats and mice compared to young. Also with age VWF expression at mRNA levels were significantly increased in livers, brains, and lungs, but not in hearts and kidneys. Consistent with the mRNA analyses, the cellular protein levels were determined in lungs and livers and shown to be significantly increased in aged compared to young mice. Moreover, the endothelial staining for VWF was observed significantly in microvessels of brains, lungs, and livers of aged but not young mice, demonstrating a phenotypic shift of microvascular endothelial cells of these organs with aging towards a procoagulant state with de novo expression of VWF. Additionally, activated platelet aggregates and occluded vessels were significantly increased in livers, brains, and lungs, but not in hearts and kidneys of aged mice compared to young, consistently with the mRNA and protein levels, and redistribution patterns of VWF expression. These results demonstrate that with aging, VWF levels are increased in circulation, and vasculature of distinct organs exhibit an altered VWF expression pattern. Specifically in liver, lung, and brain, but not heart and kidney, with aging increased VWF levels and de novo expression in microvascular endothelial cells are observed. Furthermore, the increased VWF levels specifically in these organs were concomitant with detection of significantly increased platelet aggregate formation and occluded vessels. Overexpression of VWF in circulation and microvasculature vessels of distinct organs as a result of aging may contribute to vascular diseases such as thrombosis. iv Preface The information in this thesis is the original work performed by Radya Yousef Abdualla. Experimental design, performance and analysis of data were completed by Radya Yousef Abdualla and her supervisor Dr. Nadia Jahroudi. v Dedication "The aim of science is, on the one hand, as complete a comprehension as possible of the connection between perceptible experiences in their totality, and, on the other hand, the achievement of this aim by employing a minimum of primary concepts and relations." -Albert Einstein I dedicate this to my family, for their great support and love throughout this journey. vi Acknowledgment I would like to express my sincerest appreciation and deepest thanks to my supervisor, Dr. Nadia Jahroudi. I appreciate her support, patience and inspiration. She was a true mentor and a great teacher.