Entanglement of vimentin shapes the microrheological response of suspended-like melanoma WM35 cells to oscillatory strains induced by different AFM probe geometries

Abstract

Normal and pathological states of cells can be distinguished by their mechanical properties, which are thought to be determined by the organization of the actin network. In the body, cells exist in both adherent and non-adherent (suspended) states, and studies of the rheological properties of spread and suspended cells are needed to gain more insight into their response to strain. Herein, we show that WM35 melanoma cells in adherent and non-adherent states respond differently to oscillatory strain. We used an atomic force microscopy (AFM)-based microrheological approach to study the elasticity and fluidity of the cells, quantified by the storage (G') and loss (G") moduli and the transition frequency f_T (G' = G”). Our results show that spread cells are stiffer than the suspended-like cells (plateau shear modulus of 3.51 ± 0.43 kPa vs 2.67 ± 0.34 kPa). We also found, from measurements made with a conical probe, that suspended-like cells are more tolerant to imposed strains. Combining AFM results and fluorescence microscopy of the cytoskeleton, we conclude that the organization and distribution of actin and vimentin within the cell body strongly influence the rheological properties of spread and suspended-like WM35 cells. The data also suggest that phosphorylated vimentin is predominant in suspended-like cells, whereas in spread cells, vimentin intermittent filaments (VIFs) form an assembled network that contributes to higher G'. The entanglement of the disassembled VIFs in suspended-like WM35 cell influences the rheological properties of such cells.