Realistic Temporal Variations of Shear Stress Modulate MMP-2 and MCP-1 Expression in Arteriovenous Vascular Access

Venous neointimal hyperplasia (VNH) lesions are prone to localized development within the vascular access junction (VAJ) and efferent vein of arteriovenous (AV) fistulae and grafts. The creation of VAJ dramatically alters the local venous hemodynamics with high pulsatile flow velocities enter the vein resulting in blood-flow separation, recirculation and flow reversal. This study conducted a computational hemodynamic investigation of an idealized AV graft and realistic AV fistula which demonstrated a complex hemodynamic environment within the VAJ, producing elevated wall shear stress (WSS) magnitudes and significant spatial and temporal WSS gradients in the VAJ. These hemodynamic patterns and non-physiological WSSs are postulated to initiate VNH development at the transcriptional level. Human umbilical vein endothelial cells (HUVEC) were exposed to elevated temporal WSS waveforms obtained from the aforementioned computational analysis, using a cone-and-plate bioreactor. Using real-time RT-PCR, early induction of MMP-2 and delayed transcriptional upregulation of MCP-1 was observed following EC exposure to VAJ high wall shear forces. These results indicate that MMP-2 and MCP-1 may be induced by high WSS present in the VAJ, suggesting a link between elevated WSS magnitudes and temporal gradients, extracellular matrix decomposition, smooth muscle cell migration and proliferation, and the subsequent VNH development in AV VAJs.