Biology subjects

Schnauss, J.

Publications and source records attributed to Schnauss, J..

3 recordsLinked to original sources

bioRxiv2021

A science friction story. Molecular interactions in semiflexible polymer networks

Established model theories, developed to capture the mechanical behavior of soft complex materials composed of semiflexible polymers assume entropic interactions between filaments to determine the mechanical response. In recent studies, the general accepted tube model has been challenged in terms of its basic assumption about filament-filament interactions, but also because of its predictions regarding the frequency dependence of the elastic modulus in the intermediate frequency regime. A central question is how molecular interactions and friction between network constituents influence the rheological response of isotropic entangled networks of semiflexible polymers. It was shown that friction forces between aligned pairs of actin filaments are not negligible. Here, we systematically investigate the influence of friction forces and attractive interactions on network rheology by means of a targeted surface modification. We show that these forces have a qualitative and quantitative influence on the viscoelastic properties of semiflexible polymer networks and contribute to the response to nonlinear deformations. By comparing two polymer model systems with respect to their surface compositions we give a possible explanation about the origin of acting forces on a molecular level.

biophysics↗

bioRxiv2020

Keratins determine network stress responsiveness in reconstituted actin-keratin filament systems

The cytoskeleton is a major determinant of cell mechanics, a property that is altered during many pathological situations. To understand these alterations, it is essential to investigate the interplay between the main filament systems of the cytoskeleton in the form of composite networks. Here, we investigate the role of keratin intermediate filaments (IFs) in network strength by studying in vitro reconstituted actin and keratin 8/18 composite networks via bulk shear rheology. We co-polymerized these structural proteins in varying ratios and recorded how their relative content affects the overall mechanical response of the various composites. For relatively small deformations, we found that all composites exhibited an intermediate linear viscoelastic behavior compared to that of the pure networks. In stark contrast, the composites displayed increasing strain stiffening behavior as a result of increased keratin content when larger deformations were imposed. This strain stiffening behavior is fundamentally different from behavior encountered with vimentin IF as a composite network partner for actin. Our results provide new insights into the mechanical interplay between actin and keratin in which keratin provides reinforcement to actin. This interplay may contribute to the overall integrity of cells, providing an explanation for the stability of stressed epithelial tissues due to their high keratin contents. Additionally, this helps us to understand the physiological necessity to exchange IF systems during epithelial-mesenchymal transition (EMT) in order to suppress strain stiffening of the network, making cells more elastic and, thus, facilitating their migration through dense tissues.

biophysics↗

bioRxiv2020

Activation of Macrophages by CpG DNA and LPS: an FTIR Spectroscopic Study

The innate immune response triggered by CpG DNA can improve host survival following pathogen challenge. Whether CpG ODN-mediated immune activation leads to global molecular changes in cells that are detectable by FTIR spectroscopy is currently unknown. Here, we used Attenuated Total Reflectance (ATR) Fourier Transform Infrared (FTIR) spectroscopy to monitor the molecular changes in murine macrophage RAW 264.7 cells upon activation with CpG DNA and lipopolysaccharide (LPS). By PCA analysis, we identified the sources of variation to follow with detailed spectral analysis. CpG DNA and LPS treatment increase the total nucleic acid concentration from the early periods post-activation, and DNA synthesis follows RNA synthesis. RNA-specific peak shows the activation state of macrophages in early periods post-treatment. CpG DNA and LPS result in an initial rapid increase in the total protein concentration, leveling off two hours post-activation. Both activated groups increase the concentration of fatty acids, triglycerides, and cholesterol, pointing out to a shared synthesis pathway and de novo lipogenesis. This study, for the first time, demonstrates the use of FTIR spectroscopy as an independent modality to monitor the activation dynamics of murine macrophages upon activation with CpG DNA and LPS.

biophysics↗