Technical Brief

Study of Cholesterol Repletion Effect on Nanomechanical Properties of Human Umbilical Vein Endothelial Cell Via Rapid Broadband Atomic Force Microscopy

[+] Author and Article Information
Bo Yan

School of Electrical Engineering,
University of Electrical Science and Engineering,
Chengdu 60054, China

Juan Ren

Department of Mechanical Engineering,
Iowa State University,
Ames, IA 50011

Yue Liu, Xi Zheng

Department of Chemical Biology,
Rutgers University,
Piscataway, NJ 08854

Huarong Huang

Allan H. Conney Laboratory,
Guangdong University of Technology,
Guangzhou 510006, China

Qingze Zou

Department of Mechanical and Aerospace Engineering,
Rutgers University,
Piscataway, NJ 08854
e-mail: qzzou@rci.rutgers.edu

1B. Yan and J. Ren contributed equally to this work.

2Corresponding author.

Manuscript received December 8, 2015; final manuscript received November 4, 2016; published online January 23, 2017. Assoc. Editor: Mohammad Mofrad.

J Biomech Eng 139(3), 034501 (Jan 23, 2017) (5 pages) Paper No: BIO-15-1627; doi: 10.1115/1.4035260 History: Received December 08, 2015; Revised November 04, 2016

Abnormalities of blood cholesterol concentration are associated with increased risks for vascular disease, especially heart attacks and strokes. As one of the main lipid components of plasma membrane in all mammalian cells, cholesterol has a major impact on the mechanical properties of the membrane of endothelial cells. Although the effect of cholesterol depletion on cell mechanical properties has been studied, no results yet have been reported on quantitative investigation of cholesterol repletion effect. In this study, the cholesterol repletion effect on the nanomechanical properties of human umbilical vein endothelial cell (EA.hy926) was studied using a control-based atomic force microscope (AFM) nanomechanical measurement protocol. The viscoelasticity of EA.hy926 cells were measured over a large frequency range (0.1–100 Hz) using both constant-rate excitation force with different loading rates and a broadband excitation force. The viscoelasticity oscillation of the cell membranes under the cholesterol effect was also monitored in real-time. The experiment results showed that under the effect of cholesterol repletion, both the Young's modulus and the complex modulus of EA.hy926 cell were increased over 30%, respectively, and moreover, the amplitudes of both the elasticity oscillation and the viscosity oscillation at a period of around 200 s were increased over 70%, respectively. Therefore, this work is among the first to investigate the mechanical properties, particularly, the broadband viscoelasticity variations of EA.hy926 cells under cholesterol repletion treatment. The results revealed that cholesterol repletion may reinforce the coupling of F-actin to plasma membrane by increasing actin stability, and the cholesterol might have modified the submembrane cytoskeletal organization of EA.hy926 cell by causing the involvement of the motor protein nonmuscle myosin II.

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Grahic Jump Location
Fig. 1

Force–indentation curve on cholesterol-enriched EA.hy926 cell

Grahic Jump Location
Fig. 2

Comparison of the frequency-dependent Young's modulus

Grahic Jump Location
Fig. 3

Real-time monitoring of the Young's modulus of the cholesterol-treated EA.hy926 cell with force load rate at 1 Hz for 800 s. Adjacent-averaging with a 20-points window (the solid line) is shown to highlight the periodic elasticity oscillations.

Grahic Jump Location
Fig. 4

The complex modulus of (a) the cholesterol-treated EA.hy926 cells and (b) the control, where the data are plotted in log-linear scale, and each oblique line plotted shows the complex modulus measured under a 20-s broadband excitation over the frequency range of [2, f] Hz (f = 100), with all the lines plotted in chronological order (from the first 20-s period to the last 20-s period) for the total of 60 measurement periods, and (c) the zoomed-in view of two consecutive measurements each of 20-s period

Grahic Jump Location
Fig. 5

Comparison of (a) the power law constant E0 and (b) the power exponent α for the cholesterol-enriched cells versus the control, measured during the elasticity oscillation monitoring experiments



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