Mechanics of Individual Keratin Bundles in Living Cells

Abstract

Along with microtubules and microfilaments, intermediate filaments are a major component of the eukaryotic cytoskeleton and play a key role in cell mechanics. In cells, keratin intermediate filaments form networks of bundles that are sparser in structure and have lower connectivity than, for example, actin networks. Because of this, bending and buckling play an important role in these networks. Buckling events, which occur due to compressive intracellular forces and cross-talk between the keratin network and other cytoskeletal components, are measured here in situ. By applying a mechanical model for the bundled filaments, we can access the mechanical properties of both the keratin bundles themselves and the surrounding cytosol. Bundling is characterized by a coupling parameter that describes the strength of the linkage between the individual filaments within a bundle. Our findings suggest that coupling between the filaments is mostly complete, although it becomes weaker for thicker bundles, with some relative movement allowed.

Investigating Cellular Nanoscale with X-rays

“…On average, the radius of each filament was 5.5 nm and the distance between two filaments (centre of mass to centre of mass) was 15.2 nm. These values are in good agreement with the literature values issued from EM and confocal images-a radius of 4 to 5 nm and an inter-distance of 11 to 14 nm [117,232]. But here, the preparation of the samples was much less than the ones for EM.…”

“…On a similar degree of importance, in chapter 5 [78], by combining ptychography and scanning nano-diffraction, the structure of keratin networks in whole cells could be retrieved by the use of a prior model assumption: the filaments are packed on a hexagonal lattice as shown by EM [117,232]. Ptychograms of whole cells were recorded at 65 nm resolution while scanning nano-diffraction had a resolution of few nanometres owing to the reciprocal space information.…”

“…These bundles have an average diameter of 81±22 nm, as measured by confocal microscopy [117]. Furthermore, these bundles have been shown to arrange themselves hexagonally [117]. This was shown by recording EM pictures of the cross section and longitudinal section of the keratin networks.…”

“…In cells, keratin proteins form bundles and networks. The mechanical and structural properties of keratin bundles have been studied by microscopy techniques [103,117,[183][184][185][186][187][188][189][190][191], but the internal structure could not be accessed. One way to access the internal architecture of these bundles is by the use of X-rays.…”

Desmosomes and Intermediate Filaments: Their Consequences for Tissue Mechanics

“…Intriguingly, disulfide bonding of K14 coincided with formation of networks enriched in the nuclear periphery, a region reactive to mechanical cues (Feng and Coulombe 2015;Wallrath et al 2016). Disulfide bonding may also alter bending and buckling of keratin networks, which occur on compressive intracellular forces (Nolting et al 2014). Finally, disulfide bonds in keratins not only alter keratin organization and dynamics on mechanical signals but could tie them to the highly dynamic cellular redox network controlled by the antioxidant transcription factor Nrf2 (Schafer et al 2012).…”