Epithelial cells sacrifice excess area to preserve fluidity in response to external mechanical stress

Abstract

Viscoelastic properties of epithelial cells subject to shape changes were monitored by indentation-retraction/relaxation experiments. MDCK II cells cultured on extensible polydimethylsiloxane substrates were laterally stretched and, in response, displayed increased cortex contractility and loss of excess surface area. Thereby, the cells preserve their fluidity but inevitably become stiffer. We found similar behavior in demixed cell monolayers of ZO-1/2 double knock down (dKD) cells, cells exposed to different temperatures and after removal of cholesterol from the plasma membrane. Conversely, the mechanical response of single cells adhered onto differently sized patches displays no visible rheological change. Sacrificing excess surface area allows the cells to respond to mechanical challenges without losing their ability to flow. They gain a new degree of freedom that permits resolving the interdependence of fluidity β on stiffness $${K}_{{{{{{{{\rm{A}}}}}}}}}^{0}$$ K A 0 . We also propose a model that permits to tell apart contributions from excess membrane area and excess cell surface area.

Mechanical Implications of Cellular Viscoelasticity, Cortex Polarity, Superelasticity, and Cell-Cell Junctions in Curved Tissues

“…As recently demonstrated, the stiffness of cells mirrors both the cortex architecture and the excess surface area. 14,28 Hence, we infer, supported by confocal and SICM-imaging (Fig. 1), that this excess area is apically larger.…”

“…Employing conventional nanometer-sized AFM-probes, we centrally indented the cells of curved epithelia and fitted the indentation-relaxation curve to a recently developed model, giving access to the cortical tension, the cortex's area compressibility modulus, and its fluidity. [13][14][15] Crucially, we encounter two distinct orientations of the cells: in hemicysts, the more bulged apical side faces towards the probe, whereas we target the rather flat basolateral membrane/cortex of the cells in cysts (Fig. 1).…”

“…6 On a single cell level, excess surface area in conjunction with the contractile actomyosin cortex permits to absorb external stress and to dissipate the associated energy reminiscent of a soft glassy material. [11][12][13][14][15] However, on tissue length scales, the number of experiments is sparse and our knowledge how cells organized in epithelia respond to lateral, in-plane, forces and their ability to dissipate the elastic energy remains limited. [4][5][6] Here, we examine how cysts 16,17 and hemicysts (domes) with opposing polarity generated from MDCK-II cells respond to external deformation with micrometer-sized colloidal probes on short time scales of seconds.…”

Membrane-Bound Vimentin Filaments Reorganize and Elongate under Strain

“…A uniaxial motorized stretching device (M-111.1DG, linear stage, Physik Instrumente, Karlsruhe, Germany) was employed as described in Bodenschatz et al ( Figure 1 ). 27 The motor pulled on one side of the sample holder, stretching the PDMS substrate up to a motor position (mp) of 10 mm. The PDMS (Sylgard 184, Farnell GmbH, Oberhaching, Germany) chamber was composed of a thick PDMS frame (5.5 × 2.5 × 0.5 cm 3 ) and a thin sheet (2.0 × 2.0 × 0.02 cm 3 ) that were assembled on the stretching device.…”

Structure and Mechanics of Membrane-bound Vimentin Filaments and Networks under Strain

“…For further details concerning the design of the stretching device, read the dissertation of JONATHAN BODENSCHATZ. [118]…”