The effect of biomechanical and biochemical regulators on the expression of Factor VIII and von Willebrand Factor in endothelial cells

Abstract

The coagulant protein Factor VIII (FVIII) has been the subject of much debate and controversy regarding where, when, and how it is expressed and produced in the human body for much of the past 30-40 years. Expression was only recently linked exclusively to the endothelial cells; its main source is in the liver sinusoidal endothelial cells, while extra-hepatic vascular endothelium is the secondary source. This is highly notable as von Willebrand Factor (VWF), FVIII’s carrier protein, is made primarily in the vascular endothelium. However, FVIII expression is known to not be ubiquitous across the endothelium. The mechanisms behind what allows certain endothelial cells, but not others, to express and produce FVIII are largely unknown. This thesis examined aspects of the endothelial microenvironment that may influence how the endothelium behaves in vivo with a focus on inflammation: biochemical factors in the form of the pro-inflammatory cytokine TNFα, short-term laminar and short- and long-term oscillatory biomechanical shear stress. This study investigated how these conditions were able to modulate the gene expression and protein production of FVIII and VWF, and provides evidence for a role of both these conditions as potential regulators of FVIII and VWF expression and secretion. Through the examination of these conditions in multiple endothelial cell isolates, we propose the significance of accounting for endothelial cell heterogeneity in this type of study. In particular, we have shown that a quiescent phenotype post-inflammation may induce FVIII, and that an inflammatory phenotype, through oscillatory and short-term shear, can induce FVIII in some cases. We also linked our data towards defining the acute phase response in endothelial cells, and provide evidence as to the extra-hepatic FVIII response. Endothelial cells continue to be a major source of interest with reference to FVIII synthesis, storage and secretion, and as we continue to learn more about the molecular regulation of FVIII; this provides new avenues in understanding the balance between hepatic and extra-hepatic FVIII synthesis.