End-stage renal disease (ESRD) in the United States is prevalent, morbid, costly, and associated with significant mortality. More than half a million people in the United States have ESRD with more than 100,000 new cases per year. Due to the scarcity of kidneys available for transplantation and no medical therapeutic to reverse ESRD, hemodialysis represents the most prevalent and durable alternative for renal replacement therapy. Despite the successes and advancements of arteriovenous fistula (AVF) creation for hemodialysis access over the past fifty years, the morbidity, failure and re-intervention rates remain unacceptably high. AVFs fail to mature in 20-50 percent of cases and posses an early 1-year primary patency rate of 60-65 percent. The biology of normal AV fistula formation and maladaptive formation remains poorly characterized.;The goal of this research was to systematically characterize the venous limb adaptation process of AVFs and identify potential molecular therapeutic sites. Through the use of a mouse aorta-caval model a six-week time course identified the gene expression changes of several groups of genes known to previously have been involved in vascular remodeling: collagens, proteases, protease inhibitors, Akt-eNOS, VEGF, determinants of embryonic vessel identity, and extracellular matrix-related proteins. Together, the structural and gene associated alterations provide a framework for venous remodeling under AV fistula conditions so that when evaluating a specific gene loss of function or over-expression studies, mechanisms of action can be identified.;The remaining focus of the research presented examines the role of EphB4 and Ephrin-B2 (critical determinants of embryonic vascular morphogenesis) on AVF venous limb remodeling. As opposed to vein-graft adaptation, the maturation of AVFs exhibit a maintenance of venous identity (EphB4 expression) while gaining arterial identity (Ephrin-B2 expression). Ephrin-B2 has not previously been described to exist within either the embryonic or adult venous circulatory system. The reduction of EphR4 during AVF maturation results in clinically beneficial outcomes: increased wall thickening, decreased wall shear stress profile, and improved potency. The over-expression of EphB4 using a lentiviral construct was found to impede arterial and venous limb dilation during AVF maturation.;Further investigations into EphB4 function identified Y774 as a critical tyrosine residue for receptor function. The loss of Y774 resulted in an abrogation of receptor tyrosine phosphorylation, altered Akt and Ertk1/2 activity, and distorted cell migration. The Y774 site may be of interest as a future therapeutic target to limit EphB4 activity during AVF maturation, and improved clinical outcomes.
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