Spatial Regulation of Inflammation by Human Aortic Endothelial Cells in a Linear Gradient of Shear Stress

OBJECTIVE: Atherosclerosis is a focal disease that develops at sites of low and oscillatory shear stress in arteries. This study aimed to understand how endothelial cells sense a gradient of fluid shear stress and transduce signals that regulate membrane expression of cell adhesion molecules and monocyte recruitment. METHODS: Human aortic endothelial cells were stimulated with TNF-alpha and simultaneously exposed to a linear gradient of shear stress that increased from 0 to 16 dyne/cm2. Cell adhesion molecule expression and activation of NFkappa B were quantified by immunofluorescence microscopy with resolution at the level of a single endothelial cell. Monocyte recruitment was imaged using custom microfluidic flow chambers. RESULTS: VCAM-1 and E-selectin upregulation was greatest between 2-4 dyne/cm2 (6 and 4-fold, respectively) and above 8 dyne/cm2 expression was suppressed below that of untreated endothelial cells. In contrast, ICAM-1 expression and NFkappa B nuclear translocation increased with shear stress up to a maximum at 9 dyne/cm2. Monocyte recruitment was most efficient in regions where E-selectin and VCAM-1 expression was greatest. CONCLUSIONS: We found that the endothelium can sense a change in shear stress on the order of 0.25 dyne/cm2 over a length of approximately 10 cells, regulating the level of protein transcription, cellular adhesion molecule expression, and leukocyte recruitment during inflammation.