Biology subjects

Rölleke, U.

Publications and source records attributed to Rölleke, U..

2 recordsLinked to original sources

bioRxiv2026

Force generation of cardiomyocytes in engineered environments

Cardiomyocyte contraction is essential for the pumping action of the heart and deteriorates after myocardial damage, either as a consequence of irreversible cardiomyocyte injury or stiffening of the extracellular matrix, a process described as fibrosis. Cell geometry and substrate stiffness not only influence sarcomere architecture and contractility, they also determine how much work the cardiomyocytes can transfer to their environment. Human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes provide a model system to examine these effects in a controlled manner, enabling us to mimic key features of the cardiac environment in vitro. Here we show that geometric confinement and substrate stiffness influence different aspects of cardiomyocyte force generation. By combining traction force microscopy and live-cell imaging of hiPSC-derived cardiomyocytes on soft and patterned substrates, we find that geometric confinement leads to longer resting sarcomeres and more pronounced sarcomere shortening on substrates with both physiological (10 kPa) and fibrotic (30 kPa) stiffness. Interestingly, the substrate stiffness itself has little effect on resting sarcomere length, but influences the peak contractile stress. On 10 kPa substrates, confined cells generate higher peak contractile stresses than unconfined cells, whereas this difference is not observed at 30 kPa. Confinement also results in faster mechanical relaxation at 10 kPa, with no detectable difference at 30 kPa. The combination of defined cell geometry and physiological stiffness leads to longer resting sarcomere lengths, more pronounced sarcomere shortening, higher peak contractile stress, and faster relaxation, features associated with a more mature cardiomyocyte phenotype. These findings show that the mechanical consequences of cell geometry depend on substrate stiffness and, therefore, both aspects have to be considered when employing hiPSC-derived cardiomyocytes as a model system in mechanobiology research, disease modeling and drug testing.

biophysics↗

bioRxiv2025

The keratin cortex stabilizes cells at high strains

The eukaryotic cytoskeleton consists of three filament types: actin filaments, microtubules and intermediate filaments (IFs). IF proteins are expressed in a cell-type specific manner, and keratins are found in epithelial cells. In certain cell types, keratin forms a layer close to the membrane which may be referred to as an "IF-cortex". It is hypothesized that this IF-cortex arranges with radial bundles in a "rim-and-spokes" structure in epithelia. Based on this hypothesis, IFs and actin filaments might add complementary mechanical properties to the cortex. It was previously shown that single IFs in vitro remain undamaged at high strains and display a non-linear stretching behavior. We now ask the question of whether this unique force-extension behavior of single IFs is also relevant in the context of a filament network within a cell. We show that keratin-deficient (KO) MDCK II cells readily form 2D cell layers and 3D cysts and withstand high equibiaxial strains. High-resolution imaging using STED microscopy reveals altered actin cortex structures in KO cells, presumably in response to the missing keratin. We investigate the influence of the equibiaxial strain on the viscoelastic properties of wild-type (WT) and KO cells using atomic force microscopy. We find that the KO cells exhibit a higher pre-stress than the WT cells, likely due to the change of the cortical structure. Interestingly, both the pre-stress and the fluidity of the KO cells are altered already at intermediate strains, whereas the WT cells show a response only at high strain. Similarly, the KO cysts are stretched more easily at low strains than the WT cysts during injection experiments. The compressibility modulus is analyzed in a spatially resolved manner and we find this modulus to be increased at the cell rim, compared to the inside region, due to the geometry of the cell layer. Our results indicate that KO cells compensate for the missing keratin, but are nevertheless very sensitive to external strain, whereas the intricate interplay between the actin and keratin cortices in WT cells preserves the mechanical state and cell stability.

biophysics↗