Decreased Jagged1 expression in vascular smooth muscle cells delays endothelial regeneration in arteriovenous graft

AIMS: It is well-established that endothelial dysfunction promotes activation of vascular smooth muscle cell (VSMC). Whether decreased accumulation of VSMCs affects endothelial regeneration and functions in arteriovenous graft (AVG) remodeling has not been studied. We sought to identify mechanisms by which the Notch ligand, Jagged1, in VSMCs regulates endothelial cell (EC) functions in AVGs. METHODS AND RESULTS: AVGs were created in transgenic mice bearing VSMC-specific knockout (KO) or overexpression of Jagged1. VSMC migration, EC regeneration and its barrier functions as well as AVG remodeling were evaluated. Jagged1 expression was induced in VSMCs of neointima in the AVGs. Jagged1 KO in VSMCs inhibited the accumulation of extracellular matrix as well as VSMC migration. Fewer alpha-SMA-positive VSMCs were found in AVGs created in VSMC-specific Jagged1 KO mice (VSMCJagged1 KO mice) vs. in WT mice. Decreased VSMCs in AVGs were associated with deterioration of EC functions. In AVGs created in transgenic mice bearing Jagged1 KO in VSMCs exhibited delayed EC regeneration and impaired EC barrier function. Barrier dysfunction of ECs increased inflammatory cell infiltration and dysregulation of AVG remodeling and arterialization. The increased expression of IL-1beta in macrophages was associated with expression of adhesion markers in ECs in AVGs created in VSMCJagged1 KO mice. In contrast, AVGs created in mice with overexpression of Jagged1 in VSMCs exhibited improved EC regeneration plus decreased macrophage infiltration. This led to AVG remodeling and arterialization. In co-cultures of ECs and VSMCs, Jagged1 deficiency in VSMCs suppressed N-cadherin and integrin beta3 expression in ECs. Inhibition of integrin beta3 activation delayed EC spreading and migration. Notably, Jagged1 overexpression in VSMCs or treatment with recombinant Jagged1 stimulated the expression of N-cadherin and integrin beta3 in ECs. Jagged1-induced responses were blocked by inhibition of Notch signaling. CONCLUSIONS: Jagged1 expression in VSMCs maintains EC barrier functions and blocks infiltration of macrophages. These responses promote remodeling and arterialization of AVGs. TRANSLATIONAL PERSPECTIVE: The vein is subjected to arterial environment immediately after AVG or arteriovenous fistula surgery. ECs in the vein of the AVGs and arteriovenous fistulae are denuded and regenerated later. Deficiency of Jagged1 expression in VSMCs inhibits VSMC migration, proliferation, and interferes with arterialization of vein of the AVGs. These responses also delay EC regeneration and EC barrier function with increased inflammation leading to failed vascular remodeling of AVGs. Thus, a strategy to regulate Jagged1 expression will improve AVG arterialization and function.