Endothelial cell layer subjected to flow mimicking the apex of an arterial bifurcation

Endothelial cell response to shear stress and shear stress gradients is widely accepted as a mediator of vascular pathology, including intracranial aneurysms. To this point, most in vitro research on endothelial cells focuses on low to normal shear stress environments, rather than on the high shear stress and complex impinging flow environments seen at the apices of bifurcations, where intracranial aneurysms usually form. The impinging flow environments are usually characterized by high wall shear stress (WSS > 40 dynes/cm 2) and high wall shear stress gradients (WSSG > 300 dynes/cm 3). To expose endothelial cells to this complex high-flow environment, a T-shaped impinging flow chamber was designed, and confluent bovine aortic endothelial cells were placed at the apex and surrounding regions of flow. After 72 hours under flow, cells around the stagnation point remained polygonal and presented a low density. Downstream, cells under very high WSS and WSSG in adjacent branch regions remained confluent and were elongated and aligned with the flow by 24 hours of flow exposure. Observations of cell density over time indicate that cells accumulated, forming areas of high cell density in the high WSS and high WSSG region and moved downstream and diminished over time. Such behavior indicates that cells are migrating downstream from the stagnation point as a response to impinging flow and that WSSG is responsible for this migration. A preliminary study of proliferation revealed that cells appear to proliferate at the impingement as a response to cell loss by migration, though this process is likely highly dependant on the cell density of the monolayer. These preliminary results demonstrate a unique endothelial response to aneurysm-prone flow environments at bifurcation apices.