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TECHNICAL PAPERS: Cell

Effect of Combined Cyclic Stretch and Fluid Shear Stress on Endothelial Cell Morphological Responses

[+] Author and Article Information
Tomas B. Owatverot, Sara J. Oswald, Yong Chen, Jeremiah J. Wille

Department of Biomedical Engineering  Washington University in St. Louis, St. Louis, MO 63130

Frank C-P Yin

Department of Biomedical Engineering and Department of Medicine  Washington University in St. Louis, St Louis MO 63130

J Biomech Eng 127(3), 374-382 (Feb 01, 2005) (9 pages) doi:10.1115/1.1894180 History: Received March 04, 2004; Accepted February 01, 2005; Revised February 01, 2005

Endothelial cells in vivo are normally subjected to multiple mechanical stimuli such as stretch and fluid shear stress (FSS) but because each stimulus induces magnitude-dependent morphologic responses, the relative importance of each stimulus in producing the normal in vivo state is not clear. Using cultured human aortic endothelial cells, this study first determined equipotent levels of cyclic stretch, steady FSS, and oscillatory FSS with respect to the time course of cell orientation. We then tested whether these levels of stimuli were equipotent in combination with each other by imposing simultaneous cyclic stretch and steady FSS or cyclic stretch and oscillatory FSS so as to reinforce or counteract the cells’ orientation responses. Equipotent levels of the three stimuli were 2% cyclic stretch at 2%s, 80dynescm2 steady FSS and 20±10dynescm2 oscillatory FSS at 20dynecm2-s. When applied in reinforcing fashion, cyclic stretch and oscillatory, but not steady, FSS were additive. Both pairs of stimuli canceled when applied in counteracting fashion. These results indicate that this level of cyclic stretch and oscillatory FSS sum algebraically so that they are indeed equipotent. In addition, oscillatory FSS is a stronger stimulus than steady FSS for inducing cell orientation. Moreover, arterial endothelial cells in vivo are likely receiving a stronger stretch than FSS stimulus.

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Copyright © 2005 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic and photograph of the fluid shear device showing (A) the three bearings that hold the silicone belt creating Couette flow and (B) the motor-driven pulley driving the belt

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Figure 2

Images showing the position of neutrally buoyant bubbles in the first 1.5 s after injection into the gap between the belt and the bottom of the chamber

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Figure 3

Axial velocities calculated from the bubble positions shown in Fig. 2 as a function of distance across the gap compared with the theoretical ideal linear velocity profile of Couette flow

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Figure 4

Axial fluid velocities calculated from the CFD model as a function of distance across the gap at different y-positions across the width of the belt. For clarity, the theoretical linear velocity profile of 0cm∕s to 31.2cm∕s at gap distances of 0 mm to 1 mm is not shown.

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Figure 5

Changes in median cell angles from that of unstimulated cells in response to different levels of cyclic strain after varying durations. At each duration, all pairs of responses are significantly different from one another. For each level of stimulus the effect of duration was tested by performing all pairwise comparisons with the * denoting a significant difference compared to the succeeding duration. In addition, for 5% strain, the difference between 1.5 h and 6 h is significant.

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Figure 6

Changes in median cell angles from that of unstimulated cells in response to different levels of steady FSS after varying durations. Brackets connect pairs of significantly different responses at each duration. The nomenclature for the effect of each succeeding duration for each stimulus level is the same as in Fig. 5. In addition, for 20dyne∕cm2, the difference between 3 h and 6 h is significant.

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Figure 7

Changes in median cell angles from that of unstimulated cells in response to different levels of oscillatory FSS after varying durations. Nomenclature is the same as in Fig. 6. Despite the lack of significant differences at succeeding durations for some stimulus levels, differences across more than one duration are all significant.

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Figure 8

Changes in median cell angles from that of unstimulated cells in response to the equipotent levels of each individual stimulus: cyclic strain at 2%, 2%∕s; steady FSS at 80dyne∕cm2; oscillatory FSS at 20±10dyne∕cm2, 20dyne∕cm2‐s. Brackets connect pairs of significantly different responses at each duration.

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Figure 9

Actin stress fiber responses to each of the individual equipotent stimuli after varying durations. Arrows indicate direction of applied stimuli. Scale bar is 20μm.

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Figure 10

Changes in median cell angles from that of unstimulated cells in response to cyclic stretch and steady FSS applied in reinforcing (a) and counteracting (b) fashion. At each duration in (a), all pairs of responses are statistically similar. At each duration except 1.5 h in (b), the counteracting response is significantly different from the individual responses.

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Figure 11

Changes in median cell angles from that of unstimulated cells in response to cyclic stretch and oscillatory FSS applied in reinforcing (a) and counteracting (b) fashion. At each duration, the combined response is significantly different from the individual responses.

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Figure 12

Actin stress fiber responses to cyclic stretch and steady or oscillatory FSS after 3 h and 6 h. Arrows indicate direction of applied stimuli. Scale bar is 20μm.

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Figure 13

Mean cell shape for unstimulated cells, cells subjected to equipotent levels of individual stimuli, and cells subjected to reinforcing (+) and counteracting (−) pairs of stimuli. The results of all stimuli differ significantly from the unstimulated results. Compared to cyclic strain response, * denotes those results that differ significantly.

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