The Frequency Dependent Response of the Vascular Endothelium to Pulsatile Shear Stress

Abstract

Objective To advance the understanding of how in vivo arterial shear forces affect vascular endothelial gene expression. Methods Experiments were performed to test the effects of pulsatile shear stress frequency and mean shear on endothelial gene expression. Steady flow, three sinusoidal waveforms (1, 2, and 3 Hz), and one physiological waveform were used. At each frequency, three levels of mean shear stress (0, 7.5, and 15 dyn/cm2) were used. Porcine aortic endothelial cells were exposed for 24 hours to each combination of waveform and mean shear, replicated four times. Following shear exposure, phase contrast images were acquired, and RNA was extracted for microarray analysis. Results Cell alignment with the flow was positively correlated with mean shear (p < 0.001) and independent of frequency. A two-way ANOVA identified 232 genes that were differentially regulated by frequency. The largest response was seen at 2 Hz. At this frequency, several inflammatory molecules were upregulated, including VCAM, c-jun, and IL-8, indicating a potential endothelial atherosusceptibility at this frequency. Mean shear significantly affected the expression of ~3,000 genes. Purely oscillatory flow enhanced the expression of several growth factors and adhesion molecules (E-selectin, VCAM, MCP-1, IL-8, c-jun), relative to non-reversing flow. Non-reversing flow enhanced the expression of antioxidant enzymes (SOD, catalase), relative to oscillatory or reversing flow. The 2 Hz upregulation of certain atherogenic molecules was enhanced as the mean shear was reduced. Conclusion Arterial regions that experience particular combinations of frequency and mean shear may be particularly susceptible to lesion formation. Supported by NIH grant H50442.