Biology subjects

Zahler, S.

Publications and source records attributed to Zahler, S..

4 recordsLinked to original sources

bioRxiv2023

Unravelling the metastasis-preventing effect of miR-200c in vitro and in vivo

Advanced breast cancer as well as insufficient treatment can lead to the dissemination of malignant cells from the primary tumor to distant organs. Recent research has shown that miR-200c can hamper certain steps of the invasion-metastasis cascade. However, it is still unclear, whether sole miR-200c expression is sufficient to prevent breast cancer cells from metastasis formation. Hence, we performed a xenograft mouse experiment with inducible miR-200c expression in MDA-MB 231 cells. The ex vivo analysis of metastatic sites in a multitude of organs including lung, liver, brain, and spleen has revealed a dramatically reduced metastatic burden of mice with miR-200c expressing tumors. A fundamental prerequisite for metastasis formation is the motility of cancer cells and, therefore, their migration. Consequently, we analyzed the effect of miR-200c on collective and single cell migration in vitro, utilizing MDA-MB 231 and MCF7 cell systems with genetically modified miR-200c expression. Analysis of collective cell migration has resulted in confluence dependent motility of cells with altered miR-200c expression. Additionally, scratch assays have shown enhanced predisposition of miR-200c negative cells to leave cell clusters. The in-between stage of collective and single cell migration was validated using transwell assays, which have displayed reduced migration of miR-200c positive cells. Finally, to measure migration on single cell level, a novel assay on dumbbell shaped micropatterns was performed, which revealed that miR-200c critically determines confined cell motility. All of these results demonstrate that exclusive expression of miR-200c impedes metastasis formation in vivo and migration in vitro and highlight miR-200c as metastatic suppressor in breast cancer.

cancer biology↗

bioRxiv2022

Matrix stiffness regulates Notch signaling activity in endothelial cells

The Notch signaling pathway plays a critical role in many developmental and disease related processes. It is widely accepted that Notch has a mechano-transduction module that regulates cleavage of the receptor. However, the role of biomechanical properties of the cellular environment on this module and on Notch signaling in general is still poorly understood. During angiogenesis, differentiation into tip and stalk cells is regulated by Notch. The endothelial cells in this process respond to biochemical and mechanical cues triggered by local stiffening of the ECM. Here, we investigated the influence of substrate stiffness on the Notch signaling pathway in endothelial cells. Using stiffness tuned PDMS substrates we show that Notch signaling pathway activity inversely correlates with the physiologically relevant substrate stiffness, with increased Notch activity on softer substrates. We show that trans-endocytosis of the Notch extracellular domain, but not the overall endocytosis, is regulated by substrate stiffness. Furthermore, we could show that integrin cell-matrix connections are both stiffness-dependent and influenced by Notch. Cadherin mediated cell-cell adhesion and Notch, however, influence each other in that basal Notch signaling is cell-cell contact dependent, but inhibition of the Notch signaling pathway also results in a reduction of VE-cadherin levels. We conclude that mechano-transduction of Notch activation depends on substrate stiffness highlighting the role of substrate rigidity as a modulator of Notch signaling. This may have important implications in pathological situations, such as tumor growth, associated with stiffening of the extracellular matrix.

cell biology↗

bioRxiv2021

Disentangling cadherin-mediated cell-cell interactions in collective cancer cell migration

Cell dispersion from a confined area is fundamental in a number of biological processes, including cancer metastasis. To date, a quantitative understanding of the interplay of single cell motility, cell proliferation, and intercellular contacts remains elusive. In particular, the role of E- and N-Cadherin junctions, central components of intercellular contacts, is still controversial. Combining theoretical modeling with in vitro observations, we investigate the collective spreading behavior of colonies of human cancer cells (T24). Inhibition of E- and N-Cadherin junctions decreases colony spreading and average spreading velocities, without affecting the strength of correlations in spreading velocities of neighboring cells. Based on a biophysical simulation model for cell migration, we show that the behavioral changes upon disruption of these junctions can be explained by reduced repulsive excluded volume interactions between cells. This suggests that cadherin-based intercellular contacts sharpen cell boundaries leading to repulsive rather than cohesive interactions between cells, thereby promoting efficient cell spreading during collective migration.

biophysics↗

bioRxiv2019

Cell based strain stiffening of a non-fibrous matrix as organizing principle for morphogenesis

Endothelial tube formation on a reconstituted extracellular matrix (Matrigel) is a well-established in vitro model for studying the processes of angiogenesis and vasculogenesis. However, to date, the organizing principles that underlie the morphogenesis of this network, and that shape the initial process of cell-cell finding remain elusive. Furthermore, it is unclear how in vitro results extrapolate to in vivo morphogenesis. Here, we identify a mechanism that allows cells to form networks by mechanically reorganizing and stiffening their extracellular matrix, independent of chemical guidance cues. Interestingly, we find that this cellular self-organization strongly depends on the connectivity and topology of the surrounding matrix, as well as on cell contractility and cell density. Cells rearrange the matrix, and form bridges of matrix material that are stiffer than their surroundings, thus creating a durotactic track for the initiation of cell-cell contacts. This contractility-based communication via strain stiffening and matrix rearrangement might be a general organizing principle during tissue development or regeneration.\n\nSignificance StatementIn addition to chemotactic gradients, biomechanical cues are important for guiding biological pattern formation. Self-assembly of cells has often been ascribed to reorganization of collagen fibres in the extracellular matrix. However, the basement membrane surrounding vascular cells, is per se non-fibrous. Here, we find that this difference in matrix topology can crucially influence cell behaviour and pattern formation. In a homogeneously elastic environment like the basement membrane, endothelial cells rearrange extracellular matrix proteins by contractile force, forming stiff intercellular bridges as tracks for cell-cell contacts. Our findings shine some light why there is a lot of merit in having multiple approaches to matrix elasticity (like continuum theories or dilated network approaches). Our observations might help to understand why vascular nets look different in different tissues and after rearrangement of the extracellular matrix during disease.

cell biology↗