T. Foster1,2, C. Protack1,2, T. Hashimoto1, K. Yamamoto1, H. Bai1, J. Hanisch1,2, A. Dardik1,2 1Yale University School Of Medicine,New Haven, CT, USA 2VA Connecticut Healthcare System,West Haven, CT, USA
Introduction:
Although the arteriovenous fistula (AVF) is the gold standard for dialysis access, low rates of fistula maturation prevent optimal fistula use. We have previously shown that stimulation of Eph-B4 in vein grafts prevents wall thickening during venous remodeling. Since Akt-1 is a downstream mediator of Eph-B4 signaling in endothelial cells, we hypothesized that Akt-1 mediates Eph-B4 function during AVF maturation.
Methods:
The infrarenal aorto-caval AVF model was created in wild type C57BL/6 mice and Akt-1 knockout mice as previously described. To stimulate Eph-B4 activity, mice were treated with either EphrinB2/Fc (20 μg IP) or a control vehicle at 48 hr intervals over a 21 day study period. Fistula maturation was monitored with weekly ultrasound measurements; AVF were harvested at day 21 and infrarenal IVC wall thickness was measured using computerized morphometry. Eph-B4 and Akt-1 expression were measured with immunofluorescence.
Results:
In WT mice, Eph-B4 expression increased 4.6-fold in the vein after AVF surgery compared to veins that had a sham operation (p=0.007, t-test). Stimulation of Eph-B4 in WT mice resulted in increased merged Eph-B4 and phospho-tyrosine signal (60% vs 92%; p=0.04, t-test) as well as an 8.2-fold increase in phospho-Akt-1 signal (p=0.04, t-test). Eph-B4 stimulation in WT mice was associated with reduced fistula diameter (45% vs. 98.6%; p<0.05, ANOVA) and reduced fistula wall thickness (8.9μm vs. 20.0μm; p=0.0261, t-test). However, in Akt-1 KO mice, Eph-B4 stimulation resulted in no change in fistula diameter (38% vs 22%; p=0.09, ANOVA) and no change in fistula wall thickness (15.3 vs 17μm; p=0.46, t-test).
Conclusion:
Although Eph-B4 expression is increased in an AVF, Eph-B4 in the AVF is not phosphorylated. However, stimulation of Eph-B4 increases the percentage of phosphorylated Eph-B4 that appears to be active with reduced fistula diameter and wall thickness. Akt-1 knockout abolishes the effects of Eph-B4 stimulation on wall thickness and diameter suggesting that Akt-1 mediates the effect of Eph-B4 on venous adaptation to the arterial environment.