Shear stress patterns affect the secreted chemokine profile in endothelial cells.

Background: Atherosclerotic plaques are initiated by pro-inflammatory endothelial activation at arterial regions subjected to non-uniform shear stress. We applied the in vitro flow-through cell culture slides to investigate whether different patterns of shear stress affect the secreted cytokine and chemokine profile in endothelial cells.

Methods: Human umbilical vein endothelial cells (ECs) were exposed to 24 h of flow in straight or bifurcating flow-through slides, in some experiments followed by 6 h stimulation with 2.5 ng/mL TNF-α. IL-1β, IL-6, IL-8, IL-12p70, MIP-1α, MCP-1 and sICAM-1 were measured in conditioned medium samples by flow cytometry using antibodies conjugated with fluorescent beads.

Results: The release of IL-1β, IL-12p70 and MIP-1α from endothelial cells exposed to shear stress was below detectable levels. Strongly increased level of sICAM and significantly increased IL-8 concentration were detected in conditioned medium from endothelial cells exposed to flow in bifurcating slides as compared with cells grown under laminar flow in straight channels. The release of IL-6 and MCP-1 was not significantly induced in bifurcating slides. Treatment with TNF-α for 6 h induced 2-3 fold increase in secreted chemokines and cytokines. In particular, significantly increased MCP-1 and increased IL-8 levels were released from endothelial cells grown in bifurcating slides. This release was partly prevented in cells grown in straight channels, i.e. under exposure to laminar flow only.

Conclusions: Although the endothelial monolayer areas exposed to non-uniform shear stress are relatively small, the activation of cells in these regions is strong enough to produce a detectable change in cytokine and chemokine profile, which represents the earliest step in atherogenic endothelial dysfunction.