S. Lee1, K. Brownson1, R. Khosravi1, K. Goldstein1, T. Isaji1, J. Humphrey1, A. Dardik1 1Yale University School Of Medicine,New Haven, CT, USA
Introduction:
Veins are typically thin-walled and compliant at low pressures, optimal for their dual roles as conduits for blood returning to the heart and reservoirs for holding most of the blood volume. Surgically connecting a vein to the arterial system as an arteriovenous fistula (AVF) exposes the vein to higher pressure, flow magnitudes and frequencies, triggering a set of molecular pathways that result in venous remodeling, such as dilatation and thickening. Recent work showed that the venous identity marker EphB4 is upregulated and required for the venous remodeling that occurs during AVF maturation. However, it is not known how EphB4 function or fistula creation affects the mechanical properties of veins; we hypothesize that increased EphB4 function during fistula remodeling enhances venous compliance.
Methods:
C57BL/6 wild type (WT) and Ephb4+/- (heterozygous) mice were treated with sham surgery or abdominal aortocaval fistulae creation via needle puncture (n=4-6 per group). The thoracic IVC were harvested at post-operative day 21 for uniaxial mechanical testing and subsequent histology. Veins were axially stretched to their in vivo length, then cyclically distended from 1 to ~20 mmHg with phosphate buffered saline while simultaneously recording outer diameter with a side-mounted video camera. Compliance was calculated as the change in cross-sectional luminal area per unit pressure. Veins were sectioned at 5 μm with wall (intima-media) thickness measured manually. Statistical analyses were performed with one-way ANOVA, using the Tukey post-hoc test for multiple comparisons.
Results:
WT AVF distended to a greater maximal diameter compared to WT control veins (1290±35μm vs. 986±55μm; p = 0.04). Similarly, Ephb4+/- AVF distended to a greater diameter compared to Ephb4+/- control veins (1231±75μm vs. 878±77μm, p = 0.007). At physiologic venous pressures (0-5 mmHg), Ephb4+/- veins were less compliant than WT veins (<ΔCWT,EphB4> = -0.05 mm2/mmHg, p = 0.015). Veins became more compliant with fistula creation in both WT (<ΔCWT,F> = 0.17 mm2/mmHg, p = 0.01) and Ephb4+/- (<ΔCEphB4,F> = 0.12 mm2/mmHg, p = 0.006) mice, with Ephb4+/- fistulae remaining less compliant than WT fistulae (<ΔCEphB4F,WTF> = 0.1 mm2/mmHg, p = 0.01). Ephb4+/- veins were significantly thicker than WT veins with (73.2±5.9μm vs 41.9±1.6μm, p = 0.03) or without (81.5±12μm vs 46.3±4.5μm, p = 0.01) fistula creation.
Conclusion:
Although creation of an AVF results in more distensible and circumferentially compliant veins in both WT and Ephb4+/- mice, veins from Ephb4+/- mice are thicker and stiffer than veins in WT mice both at baseline and after AVF creation. These results suggest that the structural changes of EphB4-regulated venous remodeling are accompanied by functional changes that support venous adaptation to the fistula environment.