Stiffness of MDCK II Cells Depends on Confluency and Cell Size

Abstract

Mechanical phenotyping of adherent cells has become a serious tool in cell biology to understand how cells respond to their environment and eventually to identify disease patterns such as the malignancy of cancer cells. In the steady state, homeostasis is of pivotal importance, and cells strive to maintain their internal stresses even in challenging environments and in response to external chemical and mechanical stimuli. However, a major problem exists in determining mechanical properties because many techniques, such as atomic force microscopy, that assess these properties of adherent cells locally can only address a limited number of cells and provide elastic moduli that vary substantially from cell to cell. The origin of this spread in stiffness values is largely unknown and might limit the significance of measurements. Possible reasons for the disparity are variations in cell shape and size, as well as biological reasons such as the cell cycle or polarization state of the cell. Here, we show that stiffness of adherent epithelial cells rises with increasing projected apical cell area in a nonlinear fashion. This size stiffening not only occurs as a consequence of varying cell-seeding densities, it can also be observed within a small area of a particular cell culture. Experiments with single adherent cells attached to defined areas via microcontact printing show that size stiffening is limited to cells of a confluent monolayer. This leads to the conclusion that cells possibly regulate their size distribution through cortical stress, which is enhanced in larger cells and reduced in smaller cells.

On the mechanical regulation of epithelial tissue homeostasis

“…Individual MDCK-II cells show mechanoresponse in the between 0.6 to 5 kPa, while no signicant dierences were noted on 11, 20, 34 kPa [34]. That coincides with the range reported for in vivo stiness of kidneys [66,67] and stiness of MDCK-II cells themselves [68]. This range also coincides with the range at which we observe major changes in tissue organization and mechanoresponse.…”

Shigella flexneri Disruption of Cellular Tension Promotes Intercellular Spread

“…In HeLa cells, treatment with the myosin II inhibitor blebbistatin fully rescued protrusion formation of S. flexneri that produces IpaC R362W (Figures 3C and 3D) but did not affect protrusion formation by bacteria producing WT IpaC, demonstrating that protrusion formation requires IpaC-mediated reduction in membrane tension. The membrane tension of cells is inversely proportional to their density in a monolayer (Nehls et al, 2019). We therefore hypothesized that the role of IpaC R362 in protrusion formation might be more pronounced in sub-confluent cells than in confluent cells.…”

Mechanism of tissue expansion in the early stage of the migration

“…With time, the area of growing or winner cells becomes larger than the neighbouring or loser cells (Figure 10B). Stefan et al (Nehls et al, 2019) reported that the stiffness of MDCK cells depends upon their size, i.e., big cells have high stiffness, and small cells have less stiffness. Therefore, it suggests that the winner cells of the colonies have higher stiffness compared to the loser cells.…”