Varying effects of hemodynamic forces on tissue factor RNA expression in human endothelial cells

Background: Atherosclerotic lesions predominantly localize in areas exposed to distinct hemodynamic conditions. In such lesions, tissue factor (TF) is over-expressed. Therefore, we hypothesized that varying types of mechanical forces may induce different effects on TF expression in endothelial cell, and may also influence the effects of chemical stimuli.

Materials and methods: TF RNA expression in human umbilical vein endothelial cells (HUVEC) exposed to mechanical stress in the presence or absence of chemical stimulation with thrombin (Th) was determined. The forces examined were: steady unidirectional laminar flow (LF), pulsatile unidirectional laminar flow (PF), constant oscillatory flow (OF), pulsatile to-fro flow (TFF), and cyclic strain (CS).

Results: Mechanical stimulation of HUVEC with LF for 2 h induced an 8.7 ± 0.7-fold increase in TF RNA expression, while PF induced 4.7 ± 0.9 and TFF induced 8.6 ± 1.7-fold, respectively. These responses were significantly higher than static controls. Exposure to OF or CS did not result in any significant increase, whereas chemical stimulation with Th led to significant TF expression (4.9 ± 0.3-fold). The combination of mechanical-chemical stimuli induced significantly higher TF expression than mechanical stresses alone, and this effect was synergistic. Combination of LF+Th for 2 h induced significantly increased TF expression (16.6 ± 1.7-fold), as did PF+Th (14.8 ± 2.4) and TFF+Th (17.4 ± 1.0). Furthermore, after 6 h exposure, only TFF demonstrated significantly higher TF expression both with and without Th.

Conclusions: While uniform laminar flow resulted in transient TF expression, disturbed flow induced sustained amplification of TF expression. Further investigation is needed to elucidate the mechanism of localized atherosclerosis in areas exposed to disturbed flow.