SS6. Venous Specific Eph-B4 Regulates Vein Graft Thickening via Caveolin-1

Successful vein graft adaptation to the arterial environment is critical to maintain long-term vascular graft patency. However, the mechanism of vein graft adaptation remains unclear. Since Eph-B4, an embryonic determinant of venous identity, expression is reduced during vein graft adaptation, we determined whether Eph-B4, and the shear stress-sensing caveolin-1 (cav-1), play mechanistic roles to limit wall thickening during vein graft adaptation. Full length mouse Eph-B4 cDNA was inserted into the pShuttle-IRES-hrGFP2 vector and the cav-1 binding domain (CBD) was mutated at w804. Intrathoracic inferior vena cava was harvested from wild-type (WT) or cav-1 knockout (cav-1-KO) mice and placed as an interposition aortic graft in WT mice. In some mice Eph-B4 was stimulated with Ephrin-B2/Fc injected IP every other day until harvest; other vein grafts were locally treated with WT or mutated Eph-B4 coding adenovirus (1.0x109 pfu). Vein grafts were harvested and analyzed after 3-4 weeks. Stimulation of Eph-B4 with Ephrin-B2/Fc limited wall thickness (0.03 ± 0.01 mm vs 0.06 ± 0.01 mm, n = 5-7). Eph-B4 colocalized with cav-1 in sucrose gradient separation and co-immunoprecipitation. Vein grafts derived from cav-1-KO mice had increased wall thickness (0.09 ± 0.01 mm vs 0.05 ± 0.01 mm, n = 3-5). Unlike WT grafts, Ephrin-B2/Fc treated Cav-1 KO vein grafts did not have reduced wall thickness (0.09 ± 0.01 mm, n = 4). CBD mutated Eph-B4 was unable to phosphorylate tyrosine in vitro; adenovirus incorporating the CBD mutated Eph-B4 did not limit vein graft wall thickness compared to reduced wall thickness with WT Eph-B4 adenovirus (0.09 ± 0.01 mm vs 0.06 ± 0.01 mm, n = 6). Eph-B4 is functional in adult veins and actively limits vein graft wall thickening during adaptation to the arterial environment. Caveolin-1 may act as the shear stress sensor for Eph-B4, suggesting that the Eph-B4-caveolin-1 pathway may be a therapeutic target to improve vein graft patency.