Evaluation of the Influence of Wall Shear Stress Features from Newly Fashioned Arteriovenous Fistulae on Endothelial Cell Phenotypes In Vitro

Abstract

Objective: Patency rates for autogenous arteriovenous fistulae (AVFs) range between 60% and 80% at two years. The wall shear stress (WSS) is the frictional force per unit area exerted at the interface of the flowing blood and the endothelium and is a potent stimulus capable of evoking differential phenotypes in endothelial cells (ECs). The aim of this study was to investigate the influence of WSS on EC phenotypes. Methods: The intraluminal pressures and waveforms from the arterial and venous limbs of 14 newly fashioned human AVFs (four radiocephalic, 10 brachiocephalic) were measured using a microcatheter transducer and pull through technique. Human umbilical vein endothelial cells (HUVECs) were exposed for 24 hours to 10 idealised physiological waveforms (using calculations from in vivo experiments) with WSS peak magnitude 0.5 – 2.5 Pa, temporal wall shear stress gradient (t-WSSG) from 2 to 20 Pa/s, and from 0 to 0.5 of the oscillatory shear index value. Differential protein and gene expression was evaluated using reverse transcription polymerase chain reaction, western blot, and immunofluorescence staining. Results: In vitro results indicate that WSS waveforms with a peak magnitude of 1.5 or 2.5 Pa can induce a protective phenotype in ECs in culture (Krüppel-like factor-2 (KLF-2), KLF-4, Interleukin-8 (IL-8), and vascular cell adhesion molecule -1 (VCAM-1) expression). By presenting a reverse phase or decreasing time averaged WSS of the waveforms with a peak of 1.5 or 2.5 Pa, the flow induced protective effect is maintained. A WSS peak of 1.5 Pa is shown to be sufficient to induce protective pathways. Pro-inflammatory gene analysis showed no differences in the expression of two subunits of nuclear factor kappa B. Conclusion: The differential effects of WSS profiles can induce protective or pro-inflammatory EC profiles. These results suggest that geometrical variations may influence AVF patency rates and outcomes.