Vimentin intermediate filaments structure and mechanically support microtubules in cells

Abstract

The eukaryotic cytoskeleton comprises three types of mechanically distinct biopolymers – actin filaments, microtubules and intermediate filaments (IFs)– along with passive crosslinkers and active molecular motors. Among these filament types, IFs are expressed in a cell-type specific manner and vimentin is found in cells of mesenchymal origin. The composite cytoskeletal network determines the mechanical and dynamic properties of the cell and is specifically governed by the interplay of the three different filament systems. We study the influence of vimentin IFs on the mechanics and network structure of microtubules by analyzing fluorescence micrographs of fibroblasts on protein micropatterns. We develop and apply quantitative, automated data analysis to a large number of cells, thus mitigating the considerable natural variance in data from biological cells. We find that the presence of a vimentin IF network structures and aligns microtubules in the cell interior. On a local scale, we observe higher microtubule curvatures when vimentin IFs are present, irrespective of whether the cells are polarized or not. Our results suggest that the vimentin IF network laterally supports microtubules against compressive buckling forces and further helps to structure the microtubule network, thus possibly leading to a more efficient intracellular transport system along the microtubules.