Activation of EphrinB2 Signaling Promotes Adaptive Venous Remodeling in Murine Arteriovenous Fistulae

Abstract

Background: Arteriovenous fistulae (AVF) are the preferred mode of vascular access for hemodialysis. Before use, AVF remodel by thickening and dilating to achieve a functional conduit via an adaptive process characterized by expression of molecular markers characteristic of both venous and arterial identity. Although signaling via EphB4, a determinant of venous identity, mediates AVF maturation, the role of its counterpart EphrinB2, a determinant of arterial identity, remains unclear. We hypothesize that EphrinB2 signaling is active during AVF maturation and may be a mechanism of venous remodeling. Methods: Aortocaval fistulae were created or sham laparotomy was performed in C57Bl/6 mice, and specimens were examined on Days 7 or 21. EphrinB2 reverse signaling was activated with EphB4-Fc applied periadventitially in vivo and in endothelial cell culture medium in vitro. Downstream signaling was assessed using immunoblotting and immunofluorescence. Results: Venous remodeling during AVF maturation was characterized by increased expression of EphrinB2 as well as Akt1, extracellular signal-regulated kinases 1/2 (ERK1/ 2), and p38. Activation of EphrinB2 with EphB4-Fc increased phosphorylation of Eph-rinB2, endothelial nitric oxide synthase, Akt1, ERK1/2, and p38 and was associated with increased diameter and wall thickness in the AVF. Both mouse and human endothelial cells treated with EphB4-Fc increased phosphorylation of EphrinB2, endothelial nitric oxide synthase, Akt1, ERK1/2, and p38 and increased endothelial cell tube formation and migration. Conclusions: Activation of EphrinB2 signaling by EphB4-Fc was associated with adaptive venous remodeling in vivo while activating endothelial cell function in vitro.

Sex differences in arterial identity correlate with neointimal hyperplasia after balloon injury

“…Since vessel identity can be altered in adults, including increased EphrinB2 expression in veins exposed to the fistula environment [ 22 , 23 ], we determined whether there are differences in EphrinB2 expression after balloon injury and if there are sex differences in these changes. The baseline expression of EphrinB2 in the carotid artery was similar before balloon injury between female and male animals (Fig.…”

“…Since EphrinB2 signaling is mediated through several downstream signaling pathways including Akt1, Extracellular signal-regulated kinases (ERK)1/2 and p38 [ 10 , 24 ], we determined if there are sex differences in these pathways that could be consistent with the sex differences in arterial identity markers (Fig. 5 ).…”

“…The transmembrane-ligand EphrinB2 is an embryonic determinant of arterial identity, whereas its corresponding receptor EphB4 is a determinant of venous fate [ 7 , 8 ]. Although EphrinB2-EphB4 function regulates venous remodeling [ 22 , 23 , 42 , 43 ], the function of this pathway in arterial injury, as well as potential sex differences, have not been well characterized. Cyclic stretch increases expression of EphrinB2 in arterial endothelial cells [ 44 ], suggesting a function for EphrinB2 in the response to stretch injury such as occurs with balloon injury.…”

“…EphrinB2 is a preferred ligand for erythropoietin-producing hepatocellular B4 (EphB4) and functions as an important regulator of blood vessel formation and remodeling [ 8 , 9 ]. We have previously shown that activation of EphrinB2 signaling promotes venous remodeling including increased venous and arterial diameter and wall thickness in arteriovenous fistulae [ 10 ]. Furthermore, exposure to exogenous 17β-estradiol (E2) during vascular niche development significantly disrupts EphrinB2 arterial identity by decreasing the expression of VEGF-A and its downstream Notch pathway [ 11 ].…”

EphrinB2 promotes the human aortic smooth muscle cell growth and migration via mediating F-actin remodeling

“…16 Studies in developmental biology have proved that Eph-rinB2 is a stable protein molecule in adult animals' artery staining structure and function; it is also one molecular fingerprint of the artery. 17,18 A series of studies have indicated that EphrinB2 is associated with several vascular diseases in murine. [17][18][19] However, the role of EphrinB2 on human arterial cells remains unexplored.…”