Shear stress regulates occludin and VEGF expression in porcine arterial endothelial cells.

Background: One of the initiating factors of atherosclerosis is the accumulation of low-density lipoprotein in the intima. Despite the correlation between low shear stress and vascular lesion formation, there is little research on the effects of shear stress on the molecular regulators of endothelial cell permeability. In this study, the effects of shear stress on the expression of occludin and vascular endothelial growth factor (VEGF), two important regulators of endothelial permeability, were investigated.

Methods: Porcine carotid arteries were cultured in perfusion culture systems for 24 h with 100 mm Hg pressure and low or physiologic shear stress. Subsequently, vessel sections were taken for histology and endothelial cells were isolated for RNA and protein extraction. Reverse transcription polymerase chain reaction (RT-PCR) was used to determine occludin and VEGF mRNA levels. Western blotting and immunohistochemistry were performed to examine occludin and VEGF protein levels.

Results: RT-PCR showed that endothelial cells from vessels cultured with low shear stress had an 11% decrease in occludin/GAPDH band density ratio (P < 0.05) and a 16% increase in VEGF/beta-actin band density ratio (P < 0.05) relative to the physiologic shear stress group. Western blot showed a 50% decrease in occludin protein expression (P < 0.01) and a 95% increase in VEGF protein expression in endothelial cells from vessels cultured with low shear stress relative to the physiologic shear stress group. Immunoreactivity of occludin and VEGF in vessels also reflected these changes.

Conclusions: These results demonstrate that low shear stress both decreases endothelial cell occludin mRNA and protein expression and increases endothelial cell VEGF mRNA and protein expression. These changes may suggest a possible molecular mechanism for increased endothelial permeability due to low shear stress.