Dependence of cyclic stretch-induced stress fiber reorientation on stretch waveform

doi:10.1016/j.jbiomech.2011.11.012

Journal of Biomechanics

Volume 45, Issue 5, 15 March 2012, Pages 728-735

https://doi.org/10.1016/j.jbiomech.2011.11.012 Get rights and content

Abstract

Cyclic uniaxial stretching of adherent nonmuscle cells induces the gradual reorientation of their actin stress fibers perpendicular to the stretch direction to an extent dependent on stretch frequency. By subjecting cells to various temporal waveforms of cyclic stretch, we revealed that stress fibers are much more sensitive to strain rate than strain frequency. By applying asymmetric waveforms, stress fibers were clearly much more responsive to the rate of lengthening than the rate of shortening during the stretch cycle. These observations were interpreted using a theoretical model of networks of stress fibers with sarcomeric structure. The model predicts that stretch waveforms with fast lengthening rates generate greater average stress fiber tension than that generated by fast shortening. This integrated approach of experiment and theory provides new insight into the mechanisms by which cells respond to matrix stretching to maintain tensional homeostasis.

Introduction

Arterial endothelial cells are subjected to cyclic stretch during the cardiac cycle, which affects intracellular signaling and gene expression to regulate cellular functions such as apoptosis, proliferation and morphology (Wang and Thampatty, 2006). Actin stress fibers (SFs) within adherent nonmuscle cells generate isometric tension to counterbalance forces in the extracellular matrix and maintain mechanical equilibrium (Galbraith and Sheetz, 1998). This equilibrium is disrupted by external mechanical cues and SFs can either relax or reorient themselves in an effort to reestablish equilibrium (Hsu et al., 2009, Kaunas and Deguchi, 2011). However, the mechanism by which cells determine their specific response to particular changes in mechanical stretch remains unclear.

We and others have demonstrated that stretch-induced SF remodeling is dependent on the frequency of strain (Hsu et al., 2009, Lee et al., 2010, Jungbauer et al., 2008). These experiments involved applying different cyclic stretch waveforms in which the rates of strain were proportional to the frequency of stretching. Here, we perform experiments in which strain rate and frequency are uncoupled to better understand their respective roles on SF reorganization. We also demonstrate that cells can sense the difference between the strain rates applied during the lengthening and shortening phases of a stretch cycle.

Section snippets

Cell culture

U2OS osteosarcoma cells stably expressing GFP-actin (MarinPharm GmbH) were used between passages 2 and 6 and subcultured in DMEM (GIBCO) supplemented with 10% fetal bovine serum, 2 mM l-glutamine, 1 mM sodium pyruvate and 1 mM penicillin/streptomycin in a humidified incubator kept at 37 °C and 5% CO₂ as described previously (Hsu et al., 2010, Lee et al., 2010).

Stretching experiment

Cells were subjected to cyclic stretch using a custom stretch device capable of generating various temporal strain waveforms (Table 1). The

Dependence of SFs alignment on the rate of strain rather than frequency

We first quantified the extent of SF alignment in non-confluent U2OS cells subjected to 12 h of 10% cyclic uniaxial stretch at 0.01, 0.1 and 1 Hz using a triangular strain pattern (Fig. 1A; hereafter referred to simply as triangle-stretch). Consistent with our previous findings using non-confluent and confluent bovine aortic endothelial cells (Hsu et al., 2009, Lee et al., 2010), the SFs oriented perpendicular to the direction of stretch to an extent that monotonically increased with increasing

Discussion

While fluid shear stress and cyclic stretch each contribute to endothelial cell function, the role of fluid shear stress has been studied in much greater detail. Numerous studies have evaluated the effects of shear stress magnitude, pulsatility and directionality on EC function and morphology with the general consensus being that low and reversing shear stress contributes to atherogenesis, while high and non-reversing shear stress is “athero-protective” (Dai et al., 2004). High and

Conclusions

The common carotid artery proximal to the carotid bulb experiences rapid dilation and slower return during the cardiac cycle (Ramnarine et al., 2003). Our results indicate this asymmetric stretch waveform is the type that ECs would be most responsive to, though at frequencies above 1 Hz the differences may be negligible (cf. Fig. 7). While these experiments were performed using U2OS cells, we expect that similar results would be observed using ECs and many other cell types that respond to cyclic

Acknowledgments

We thank Dr. Wonmuk Hwang for insightful comments that helped to motivate these studies. The authors were supported by grants from the American Heart Association (0730238N) and the National Science Foundation (CBET-0854129) to RK.

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Dependence of cyclic stretch-induced stress fiber reorientation on stretch waveform

Abstract

Introduction

Section snippets

Cell culture

Stretching experiment

Dependence of SFs alignment on the rate of strain rather than frequency

Discussion

Conclusions

Acknowledgments

European Journal of Cell Biology

Current Opinion in Cell Biology

Biophysical Journal

Cell Signal

Biochemical and Biophysical Research Communications

Journal of Biomechanics

European Journal of Cell Biology

Journal of Biomechanics

Models for the specific adhesion of cells to cells

Science

Buckling of actin stress fibers: a new wrinkle in the cytoskeletal tapestry

Cell Motility and the Cytoskeleton

Distinct endothelial phenotypes evoked by arterial waveforms derived from atherosclerosis-susceptible and -resistant regions of human vasculature

Proceedings of the National Academy of Sciences of the USA

Dynamics of Cell Orientation

Nature Physics