Endothelial cell responses to atheroprone flow are driven by two separate flow components: low time-average shear stress and fluid flow reversal

Abstract

To simulate the effects of shear stress in regions of the vasculature prone to developing atherosclerosis, we subjected human umbilical vein endothelial cells to reversing shear stress to mimic the hemodynamic conditions at the wall of the carotid sinus, a site of complex, reversing blood flow and commonly observed atherosclerosis. We compared the effects of reversing shear stress (time-average: 1 dyn/cm(2), maximum: +11 dyn/cm(2), minimum: -11 dyn/cm(2), 1 Hz), arterial steady shear stress (15 dyn/cm(2)), and low steady shear stress (1 dyn/cm(2)) on gene expression, cell proliferation, and monocyte adhesiveness. Microarray analysis revealed that most differentially expressed genes were similarly regulated by all three shear stress regimens compared with static culture. Comparisons of the three shear stress regimens to each other identified 138 genes regulated by low average shear stress and 22 genes regulated by fluid reversal. Low average shear stress induced increased cell proliferation compared with high shear stress. Only reversing shear stress exposure induced monocyte adhesion. The adhesion of monocytes was partially inhibited by the incubation of endothelial cells with ICAM-1 blocking antibody. Increased heparan sulfate proteoglycan expression was observed on the surface of cells exposed to reversing shear stress. Heparinase III treatment significantly reduced monocyte adhesion. Our results suggest that low steady shear stress is the major impetus for differential gene expression and cell proliferation, whereas reversing flow regulates monocyte adhesion.

Pulsatile Atheroprone Shear Stress Affects the Expression of Transient Receptor Potential Channels in Human Endothelial Cells

“…16,[20][21][22] Morphological changes represent a late response of endothelial cells on flow exposure. 23 The experiments performed confirmed typical morphological changes of human endothelial cells under the influence of atheroprotective shear stress 24 versus atheroprone 25 and static …”

Discovery of novel mechanosensitive genes in vivo using mouse carotid artery endothelium exposed to disturbed flow

“…Similarly, we found that approximately 50% of the in vivo genes were also conserved, whereas approximately 50% were not when our in vivo data were compared with another independent study recently reported by Conway et al (supplemental Table 7). 14 These results demonstrate that approximately half of the mechanosensitive genes found in vivo can be confirmed in vitro, whereas the other half may not be found in vitro because of phenotypic changes in cultured cells. These findings clearly demonstrate the critical need of in vivo models in studying flow-dependent vascular responses and diseases.…”

“…In most studies, gene expression profiles in endothelial cells exposed to laminar shear were compared with that of static culture conditions, 9-17 whereas a few compared laminar shear with that of oscillatory or turbulent shear, 14,43,45 better simulating pathophysiologic conditions. These microarray studies have identified many mechanosensitive genes, such as Klf2, Klf4, BMP-4, cathepsins, and Angpt2, and subsequent studies have revealed functional significance of these mechanosensitive genes in regulation of inflammation, thrombosis, vascular remodeling, angiogenesis, and arteriogenesis, 11,[19][20][21][22][26][27][28][29][30] demonstrating the critical use of these microarray studies in studying vascular biology and diseases.…”

“…[5][6][7][8] To define molecular mechanisms responsible for these changes, investigators have carried out DNA microarray studies using endothelial cells [9][10][11][12][13][14][15][16][17] and have subsequently identified numerous shear-sensitive genes, such as kruppel-like factor 2 and 4 (Klf2, Klf4), endothelial nitric oxide synthase (eNOS), vascular cell adhesion molecule-1 (VCAM-1), intercellular adhesion molecule-1 (ICAM-1), bone morphogenic protein 4 (BMP-4), cathepsins, and angiopoietin-2 (Angpt2). 11,14,[18][19][20][21][22][23][24][25][26][27][28][29] Functional studies based on these shear-sensitive genes and their protein products have revealed the critical roles that they play in regulation of inflammation, thrombosis, vascular remodeling, angiogenesis, and arteriogenesis. 11,[19][20][21][22][26][27][28][29][30] Although these in vitro studies have provided critical insights regarding shear-sensitive mechanisms in cultured endothelial cells using modeled flow conditions, it cannot be assumed that identical mechanosensitive genes and pathways are involved in vivo regulating flow-dependent vascular responses and diseases.…”

Targeting cell adhesion molecules with nanoparticles usingin vivoand flow-basedin vitromodels of atherosclerosis

“…76 HUVECs exposed to high steady shear stress (15 dyn/cm 2 ) for 24 h aligned to the direction of flow, while cells exposed to low steady shear stress of 1 dyn/cm 2 or to the reversing flow were randomly oriented. Upon stopping the perfusion of THP-1 monocytes after 24 h, significant increase for adhesion was observed in the cells exposed to the reversing flow compared to static, low and high stress.…”