Keratin Networks in Live Cells

Intermediate filaments are a major component of the eukaryotic cytoskeleton along with microtubules and microfilaments and play a key role in cell mechanics. One representative of this class of proteins, which exemplifies the mechanical importance of intermediate filaments, is keratin. In specific cells, keratin intermediate filaments can form bundles, which are organized in a cell wide network. One function of this network is to provide the cell with the ability to withstand potentially harmful mechanical forces and to ensure the integrity of the cell. In this study, the dynamic motion of the keratin network is investigated under the influence of external forces. To this end, living cells are exposed to shear stress using microfluidic methods, while the network is observed in situ. The data show that the keratin motion is reduced upon the application of shear flow and indicate an involvement of cytoskeletal cross-talk. Furthermore, buckling events caused by intracellular forces are observed for keratin bundles in living cells. By investigating these buckling events in situ and applying a mechanical model, both the mechanical properties of the keratin bundles themselves as well as the surrounding cytosol can be assessed. Here, a coupling-parameter which describes the strength of linkage between individual filaments within a bundle is introduced. The data suggest that there is mostly full coupling between the individual filaments with no relative movement of filaments against each other, although the coupling becomes weaker for thicker bundles