The Single Cell Landscape of the Human Vein After Arteriovenous Fistula Creation and Implications for Maturation Failure
The biological mechanisms underlying arteriovenous fistula (AVF) maturation in hemodialysis patients remain poorly understood despite decades of research. To address this gap, we investigated the cellular changes in the venous wall after fistula creation in histological biopsies of longitudinal veins and AVF samples (N=23 patients). Using single-cell RNA sequencing of 70,281 cells from pre-access veins, mature, and failed AVFs (N=20 patients), we created a complementary transcriptomic atlas of the human vein before and after anastomosis. Postoperatively, the fistula exhibited increased intimal hyperplasia and cell number but reduced cell density, indicating that extracellular matrix (ECM) deposition was more prominent than cell accumulation. Analysis of 14,475 cells from fistulas obtained within one week of creation revealed that inflammation drives early adaptation across all vascular cell types. This includes the pro-inflammatory activation of endothelial cells (ECs) and production of a hyaluronic acid-rich neointima by fibroblasts. By 13 {+/-} 6 weeks, transcriptomic profiles continue to reflect active healing of the vasculature by ECM-producing myofibroblasts and fibroblasts that were found localized throughout the vascular wall, including the intima, using immunofluorescence and in-situ hybridization. Postoperative ECs maintained significant hemostatic adaptations and upregulation of inflammatory molecules (ACKR3, ICAM1, IL1R1, COL8A1) supporting their role as gatekeepers of immune cell infiltration. Comparative analyses of failed versus mature AVFs revealed persistent inflammatory signaling among macrophages, ECs, myofibroblasts, and fibroblasts in association with AVF failure. These findings uncover previously unrecognized cellular and molecular patterns in human veins following AVF creation, providing novel insights and potential therapeutic targets to improve AVF outcomes. TRANSLATIONAL STATEMENTArteriovenous fistulas (AVF) are a special type of blood vessels that provides access to a patients bloodstream during hemodialysis treatments. The AVF is surgically created by connecting an artery and a vein, after which the vein heals and enlarges in a process called "maturation". We do not fully understand how maturation occurs. This prevents us from designing therapies that ensure proper enlargement of the AVF, which fails in up to 40% of patients. This study investigates how a vein transforms into an AVF in 43 patients with end-stage kidney disease undergoing surgery for AVF creation. We analyze the modifications of structural components of the vein and of diverse populations of cells that direct healing and maturation. Our findings suggest that, contrary to current beliefs, the best therapies to improve AVF maturation should target the accumulation of non-cellular components in the vein and the inflammatory factors that trigger such accumulation.