Prestressed cells are prone to cytoskeleton failures under localized shear strain: an experimental demonstration on muscle precursor cells

Laura Streppa,Evelyne Goillot,Françoise Argoul,Anne Devin,Alain Arneodo,Laurent Schaeffer,Francesca Ratti

doi:10.1038/s41598-018-26797-4

Abstract

We report on a wavelet based space-scale decomposition method for analyzing the response of living muscle precursor cells (C2C12 myoblasts and myotubes) upon sharp indentation with an AFM cantilever and quantifying their aptitude to sustain such a local shear strain. Beyond global mechanical parameters which are currently used as markers of cell contractility, we emphasize the necessity of characterizing more closely the local fluctuations of the shear relaxation modulus as they carry important clues about the mechanisms of cytoskeleton strain release. Rupture events encountered during fixed velocity shear strain are interpreted as local disruptions of the actin cytoskeleton structures, the strongest (brittle) ones being produced by the tighter and stiffer stress fibers or actin agglomerates. These local strain induced failures are important characteristics of the resilience of these cells, and their aptitude to maintain their shape via a quick recovery from local strains. This study focuses on the perinuclear region because it can be considered as a master mechanical organizing center of these muscle precursor cells. Using this wavelet-based method, we combine the global and local approaches for a comparative analysis of the mechanical parameters of normal myoblasts, myotubes and myoblasts treated with actomyosin cytoskeleton disruptive agents (ATP depletion, blebbistatin).

Highlights

Living cells are active mechanical machines which can withstand forces and deformations and can adapt quite rapidly to their mechanical environment
C2C12 myoblast cells are immortalized cells derived from mouse satellite cells that can be switched to differentiation into myotubes by replacing their proliferation growth factor rich medium (GM) by a growth factor deprived medium (DM)
We focused on the perinuclear region because it is the thickest part of an adherent cell and because this area can be considered as a master mechanical organizing center

Summary

Introduction

Living cells are active mechanical machines which can withstand forces and deformations and can adapt quite rapidly to their mechanical environment This malleability is mediated by three major cytoskeleton (CSK) filament networks, namely microtubules (MTs), actin filaments (F-actin), and intermediate filaments (IFs)[1,2]. Sharper tips (conical, pyramidal, single needle) produce a greater and more localized shearing and lead to higher Young’s modulus than spherical tips[33,34] They are better suited to probe local (nanoscale) mechanical properties[35,36] and to investigate local perturbations including disruptions of the CSK network. Sharp (conical or pyramidal) indenters are better suited for the characterization of the spatial inhomogeneity of cell mechanics, and more precisely of their stress fiber resistance to deformation This explains that we selected very sharp AFM tips (pyramidal shape) for the present study. The muscle cell precursors were the best candidates to perform such a demonstration

Methods

Results

Conclusion