Flow-induced focal adhesion remodeling mediated by local cytoskeletal stresses and reorganization

Deepika Verma,Fanjie Meng,Frederick Sachs,Susan Z Hua

doi:10.1080/19336918.2015.1089379

Abstract

Cells respond to fluid shear stress through dynamic processes involving changes in actomyosin and other cytoskeletal stresses, remodeling of cell adhesions, and cytoskeleton reorganization. In this study we simultaneously measured focal adhesion dynamics and cytoskeletal stress and reorganization in MDCK cells under fluid shear stress. The measurements used co-expression of fluorescently labeled paxillin and force sensitive FRET probes of α-actinin. A shear stress of 0.74 dyn/cm2 for 3 hours caused redistribution of cytoskeletal tension and significant focal adhesion remodeling. The fate of focal adhesions is determined by the stress state and stability of the linked actin stress fibers. In the interior of the cell, the mature focal adhesions disassembled within 35-40 min under flow and stress fibers disintegrated. Near the cell periphery, the focal adhesions anchoring the stress fibers perpendicular to the cell periphery disassembled, while focal adhesions associated with peripheral fibers sustained. The diminishing focal adhesions are coupled with local cytoskeletal stress release and actin stress fiber disassembly whereas sustaining peripheral focal adhesions are coupled with an increase in stress and enhancement of actin bundles. The results show that flow induced formation of peripheral actin bundles provides a favorable environment for focal adhesion remodeling along the cell periphery. Under such condition, new FAs were observed along the cell edge under flow. Our results suggest that the remodeling of FAs in epithelial cells under flow is orchestrated by actin cytoskeletal stress redistribution and structural reorganization.

Highlights

Mechanical forces provide key signals that regulate functions of mammalian cells and provide guidance for the tissue development.[1]
We show that under flow, the dynamics of focal adhesion (FA) depends on the stability of the linked stress fibers that is regulated by local cytoskeletal tension
The bottom and top layers are separated by »40 nm.[30]. This unique structure enables us to image paxillin and a-actinin simultaneously without fluorescence crosstalk (Fig. 1A), the former is used to analyze the focal adhesion remodeling and the latter is used to measure the forces in a-actinin as well as the assembly/disassembly of actin stress fibers

Summary

Introduction

Mechanical forces provide key signals that regulate functions of mammalian cells and provide guidance for the tissue development.[1]. Cells respond to long-term shear stress through cell typedependent processes, involving cytoskeleton assembly/disassembly, focal adhesion (FA) displacement, and lamellipodia formation.[8,9,10] In endothelial cells, exposure to shear stress causes the peripheral actin bundles on the basal side of the cell to disassociate. This is followed by the formation of actin networks close to the apical membrane allowing the alignment of cells with the flow.[11,12] Shear stress causes rapid formation of lamellipodia and focal adhesions, and lateral displacement of stress fibers in endothelial cells.[8] Epithelial cells respond to shear stress differently. Shear stress causes disassociation of the thick and randomly aligned actin bundles at the basement cortex, followed by the formation of peripheral structure that does not affect the overall cell shape.[7,13] There are limited studies on FA remodeling and force transduction in epithelial cells under flow, and these cells might use different mechanisms for force transduction than endothelial cells

Methods

Results

Conclusion