The Vascular Fibroblast: An Understudied Culprit In Postoperative Venous Stenosis

The Vascular Fibroblast: An Understudied Culprit in Postoperative Venous Stenosis ABSTRACT Creating a stenosis-free arteriovenous fistula (AVF) is a significant challenge even for highly skilled vascular surgeons. The surgery involves anastomosing a vein to a nearby artery in the arm of patients with end-stage kidney disease (ESKD). However, approximately 40% of newly created AVFs are never usable for dialysis without subsequent salvage procedures due to significant narrowing in the venous limb of the access (maturation failure). A major concern is that therapies designed to enhance reendothelialization or inhibit cellular proliferation have not succeeded in improving surgical outcomes. Consequently, the success of future anti-stenotic therapies will depend on our ability to update the existing theoretical framework by incorporating evidence emerging from human observational studies and clinical trials. This translational proposal utilizes emerging transcriptomic data from individual cells within the human vein and AVF to investigate the mechanisms by which fibroblasts and myofibroblasts control postoperative inflammation, medial fibrosis, and expansion of the intima that combined lead to constrictive remodeling and stenosis. Our fundamental hypothesis is that genetic and pharmacological inhibition of collagen VIII biosynthesis in venous fibroblasts decreases postoperative inflammation, myofibroblast accumulation, and stiffness in the venous wall, thereby improving AVF maturation. We will test this hypothesis using an integrated molecular and cellular approach, encompassing in vivo and in vitro models. Aim 1 will demonstrate the central role of venous fibroblasts in stenotic remodeling of human and murine AVFs. We will trace the contribution of fibroblasts to the myofibroblast population responsible for the remodeling of experimental fistulas created in transgenic mice. Additionally, we will investigate the clonal expansion, pro-fibrotic activation, and fate of human venous fibroblasts after fistula creation using genomic tracing. Aim 2 will demonstrate the causality of fibroblast-derived type VIII collagen on AVF failure. We will elucidate the upstream mechanisms responsible for the transcriptional activation of COL8A1 in fibroblasts. We will then demonstrate the role of collagen VIII as the link between inflammation, fibroblast activation, and excessive extracellular matrix (ECM) deposition in AVF failure. Mechanistically, we hypothesize that collagen VIII activates the complement C1 complex and Wnt/b-catenin signaling, ultimately leading to exacerbation of both pro-fibrotic and inflammatory pathways. Lastly, Aim 3 will test the benefits of COL8A1-targeted gene therapy and the anti-fibrotic drug pirfenidone, which also inhibits COL8A1 deposition, in a preclinical model of AVF failure in swine. We expect to show that both approaches are feasible and can enhance AVF maturation. We anticipate that these investigations will provide a comprehensive understanding of the cellular and molecular processes underlying AVF failure in humans and pave the way for novel therapeutic strategies to enhance maturation and durability of hemodialysis accesses.