More than 14 000 enrolled veterans depend on an arteriovenous (A-V) fistula or other type of vascular access to receive hemodialysis and prolong their lives. The transformation of a vein to a fistula is one of the most intriguing processes in vascular biology. The desired scenario is that the fistula matures becoming a larger vessel with increased luminal area and a thicker wall. Unfortunately, A-V fistulas frequently fail (~40%) because venous stenosis compromises blood flow. We recently discovered that stenosis occurs due to excessive medial fibrosis, and is aggravated by intimal hyperplasia (IH). Our specific goal is to demonstrate that up-regulated lysyl oxidase (LOX) in the venous limb of the A-V fistula mediates improper extracellular matrix (ECM) remodeling and pathological expansion of the intima, which causes stenosis and failure. This proposal establishes the cause- effect relationship among LOX and fistula outcomes in order to design targeted therapies. Our proposal is built on strong scientific premises (manuscripts and unique preliminary data) that suggest a mechanistic relationship between postoperative upregulation of LOX in native fistulas and the improper remodeling that causes fistula failure. Specifically, we hypothesize that LOX disrupts the epigenetic marks that secure contractile gene expression in smooth muscle cells (SMC), thereby facilitating the phenotypic switch of SMCs, neointima formation, and fibrosis of newly created A-V fistulas. We also postulate that extracellular LOX simultaneously increases stiffness and altered collagen configuration in this type of vascular access. We will test our hypothesis in three specific aims and five experimental layouts that will prove: 1) the contribution of vascular LOX to postoperative A-V fistula stenosis; 2) the role of LOX in the epigenetic control of the SMC phenotype after fistula creation; and 3) the relationship between pre- existing LOX and A-V fistula outcomes in a human cohort. We will use fine microsurgical techniques in a novel conditional knockout mice and in vitro and in situ models to successfully achieve our goals. We will also interrogate a human biorepository of >300 patients undergoing creation of a two- stage brachiobasilic transposition fistula to search for associations between the levels of LOX and maturation failure. In conclusion, with the successful accomplishment of this proposal, we are paving the way for the design of new drugs and cell type-specific interventions to effectively target A-V fistula fibrosis and reduce vascular access complications.