Biology subjects

Kreysing, E.

Publications and source records attributed to Kreysing, E..

4 recordsLinked to original sources

bioRxiv2025

Measurement force, speed and post-mortem time affect the ratio of CNS grey to white matter elasticity

For several decades, many attempts have been made to characterise the mechanical properties of grey and white matter, which constitute the two main compartments of the central nervous system (CNS), with various methods and contradictory results. In particular, the ratio of grey-to-white-matter elasticity is sometimes larger than 1 and sometimes smaller; the reason for this apparent discrepancy is currently unknown. Here, we exploited atomic force microscopy (AFM)-based indentation measurements to systematically investigate how the measurement force, measurement speed, post-mortem interval and temperature affect the measured elasticity of spinal cord tissue, and in particular the ratio of grey-to-white-matter elasticity (Kg/Kw). Within the explored parameter space, increasing measurement force and speed increased the measured elasticity of both grey and white matter. However, Kg/Kw declined from values as high as [~]5 at low forces and speeds to [~]1 for high forces and speeds. Kg/Kw also strongly depended on the anatomical plane in which the measurements were conducted and was considerably higher in transverse sections compared to longitudinal sections. Furthermore, the post-mortem interval impacted both the absolute measured tissue elasticity and Kg/Kw. Grey matter elasticity started decreasing [~]3 hours post-mortem until reaching a plateau after [~]6 hours. In contrast, white matter elasticity started declining from the beginning of the measurements until [~]6 hours post-mortem, when it also levelled off. As a result, Kg/Kw increased until [~]6 hours post-mortem before stabilising. Between 20{degrees}C and 38{degrees}C, both grey and white matter elasticity decreased at a similar rate, without affecting Kg/Kw. We have thus identified differences in the response of grey and white matter to varying strains and strain rates, and the post-mortem interval, and excluded temperature as a factor affecting Kg/Kw. These differential responses likely contribute to the contradictory results obtained with different methods working in different strain regimes. Statement of significanceWe here showed that the mechanical response of CNS grey and white matter to an applied force differentially depends on measurement parameters such as the speed and magnitude of the applied forces, the post-mortem interval, as well as the anatomical axis along which measurements are conducted. These results broaden our understanding of CNS mechanics and pave the way for better and more targeted experimental design of future experiments. Ultimately, they may help to reconcile seemingly contradictory results in the literature concerning the ratio of grey-to-white-matter elasticity.

biophysics↗

bioRxiv2024

Substrate stiffness regulates neuronal maturation via Piezo1-mediated TTR activity

During brain development, neurons extend axons to connect to their target cells while initiating a maturation process during which neurons start expressing voltage-gated ion channels, form synapses, express synaptic transmitters and receptors, and start communicating via action potentials. Little is known about external factors regulating this process. Here, we identified environmental mechanics as an important regulator of neuronal maturation, and a molecular pathway linking tissue stiffness to this process. Using patch clamp electrophysiology, calcium imaging and immunofluorescence, we found that neurons cultured on stiffer substrates showed a delay in voltage-gated ion channel activity, spontaneous and evoked action potentials, and synapse formation. RNA sequencing and CRISPR/Cas9 knockdown revealed that the mechanosensitive ion channel Piezo1 supresses transthyretin (TTR) expression on stiffer substrates, slowing down synapse formation and consequently electrical maturation. In agreement, the stiffness of developing Xenopus laevis brain negatively correlated with local synapse densities, and stiffening of brain tissue resulted in a significant delay of synaptic activity in vivo. Our data indicate that environmental stiffness represents a fundamental regulator of neuronal maturation, which is important for the development of normal circuitry in the brain, and potentially for neurodevelopmental disorders. Furthermore, the mechanical regulation of TTR downstream of Piezo1 may be found in many other biological systems.

developmental biology↗

bioRxiv2021

Effective Cell Membrane Tension is Independent of Substrate Stiffness

Most animal cells are surrounded by a cell membrane and an underlying actomyosin cortex. Both structures are linked, and they are under tension. In-plane membrane tension and cortical tension both influence many cellular processes, including cell migration, division, and endocytosis. However, while actomyosin tension is regulated by substrate stiffness, how membrane tension responds to mechanical substrate properties is currently poorly understood. Here, we probed the effective membrane tension of neurons and fibroblasts cultured on glass and polyacrylamide substrates of varying stiffness using optical tweezers. In contrast to actomyosin-based traction forces, both peak forces and steady state tether forces of cells cultured on hydrogels were independent of substrate stiffness and did not change after blocking myosin II activity using blebbistatin, indicating that tether and traction forces are not directly linked. Peak forces in fibroblasts on hydrogels were about twice as high as those in neurons, indicating stronger membrane-cortex adhesion in fibroblasts. Steady state tether forces were generally higher in cells cultured on hydrogels than on glass, which we explain by a mechanical model. Our results provide new insights into the complex regulation of effective membrane tension and pave the way for a deeper understanding of the biological processes it instructs.

biophysics↗

bioRxiv2019

Correlating surface plasmon resonance microscopy of living and fixated cells with electron microscopy allows for investigation of potential preparation artifacts

AO_SCPLOWBSTRACTC_SCPLOWThe investigation of the cell-substrate interface is of great importance for a broad spectrum of areas such as biomedical engineering, brain-chip interfacing and fundamental research. Due to its unique resolution and the prevalence of instruments, electron microscopy (EM) is used as one of the standard techniques for the analysis of the cell-substrate interface. However, possible artifacts that might be introduced by the required sample preparation have been the subject of speculation for decades. Due to recent advances in Surface plasmon resonance microscopy (SPRM), the technique now offers a label-free alternative for the interface characterization with nanometer resolution in axial direction. In contrast to EM, SPRM studies do not require fixation and can therefore be performed on living cells. Here, we present a workflow that allows us to quantify the impact of chemical fixation on the cell-substrate interface. These measurements confirmed that chemical fixation preserved the average cell-substrate distances in the majority of studied cells. Furthermore, we were able to correlate the SPRM measurements with EM images of the cell-substrate interface of the exact same cells allowing us to identify regions with good agreement between the two methods and reveal artifacts introduced during further sample preparation.

biophysics↗