Spontaneous formation and spatial self-organization of mechanically induced mesenchymal-like cells within geometrically confined cancer cell monolayers

Effects of cell shape and nucleus shape on epithelial-mesenchymal transition revealed using chimeric micropatterns

Epithelial-mesenchymal transition (EMT) is a key phenotypic switch in cancer metastasis, leading to fatal consequences for patients. Under geometric constraints, the morphology of cancer cells changes in both cellular and subcellular levels, whose effects on EMT are, however, not fully understood. Herein, we designed and fabricated chimeric micropatterns of polystyrene (PS) with adhesion contrast to reveal the impacts of cell shapes and nuclear shapes on EMT in a decoupled way. Cell elongation was modulated via microwell aspect ratios (ARs), and nuclear deformation was generated through a micropillar array in the microwell. Human non-small cell lung cancer cells (A549) were cultured on the quasi-three dimensional micropatterned surfaces, and transforming growth factor-β1 (TGF-β1) was added to induce EMT. We found that chimeric micropatterns upregulated EMT with an increase of cellular AR and nuclear indentation under given TGF-β1. The subsequent assessment of the contractility and oriented assembly of microfilaments elucidated the key role of mechanotransduction in cell elongation and EMT, as proved by myosin inhibition, while it was obstructed by micropillars in the chimeric micropattern. Hence, the micropillar array possessed a nonmonotonic influence, enhancing the EMT of cells with AR of 1, but hindering the EMT with an impact more significant on microwells with large ARs due to the impeded cytoskeleton assembly. This fundamental research has illustrated the complex of cellular and subcellular geometries on cell behaviors including phenotype transition in cancer metastasis.

Tissue geometry spatiotemporally drives bacterial infections

Epithelial tissues serve as the first line of host against bacterial infections. The self-organization of epithelial tissues continuously adapts to the architecture and mechanics of microenvironments, thereby dynamically impacting the initial niche of infections. However, the mechanism by which tissue geometry regulates bacterial infection remains poorly understood. Here, we showed geometry-guided infection patterns of bacteria in epithelial tissues using bioengineering strategies. We discovered that cellular traction forces play a crucial role in the regulation of bacterial invasive sites and marginal infection patterns in epithelial monolayers through triggering co-localization of mechanosensitive ion channel protein Piezo1 with bacteria. Further, we developed precise mechanobiology-based strategies to potentiate the antibacterial efficacy in animal models of wound and intestinal infection. Our findings demonstrate that tissue geometry exerts a key impact on mediating spatiotemporal infections of bacteria, which has important implications for the discovery and development of alternative strategies against bacterial infections.

Biological boundary conditions regulate the internalization of Aspergillus fumigatus conidia by alveolar cells

Introduction

The lung environment is defined by unique biological boundary conditions, including complex alveolar geometry, extracellular matrix composition and mechanical forces generated during respiration. These factors were shown to regulate alveolar permeability, surfactant secretion, cell contractility and apoptosis, but their role in fungal infections remains unknown. Aspergillus fumigatus is a critical fungal pathogen that causes severe pulmonary infections in immunocompromised individuals. Our study addresses a knowledge gap by investigating how boundary conditions affect A. fumigatus conidia interactions with alveolar epithelial cells.

Methods

We applied micropatterned substrates to confine cells into defined shapes and densities, allowing precise control over geometric conditions and extracellular matrix composition. Using cell line stably expressing the phagolysosomal protein Lamp1-NeonGreen and multiplane fluorescent microscopy, we evaluated A. fumigatus conidia binding and internalization efficiency.

Results

We observed significantly faster and more efficient A. fumigatus conidia internalization in cells confined on micropatterns compared to previously reported studies using cell monolayers. Altering cell geometry, density and extracellular matrix composition strongly affected conidia binding and localization to Lamp1+ phagolysosomes. Cells on X-shaped or multicellular micropatterns showed higher internalization rates, particularly at the periphery, suggesting spatial heterogeneity in pathogen uptake. Additionally, changes in extracellular matrix composition influenced the intracellular trafficking of A. fumigatus conidia.

Discussion

Our findings emphasize the essential role that local mechanical and biochemical cues play in shaping the interactions between fungal pathogens and alveolar cells. Understanding how lung boundary conditions change in disease states will provide important insights into fungal infection outcomes.

Epithelial-Mesenchymal Plasticity and Epigenetic Heterogeneity in Cancer

The tumor microenvironment comprises various cell types and experiences dynamic alterations in physical and mechanical properties as cancer progresses. Intratumoral heterogeneity is associated with poor prognosis and poses therapeutic challenges, and recent studies have begun to identify the cellular mechanisms that contribute to phenotypic diversity within tumors. This review will describe epithelial-mesenchymal (E/M) plasticity and its contribution to phenotypic heterogeneity in tumors as well as how epigenetic factors, such as histone modifications, histone modifying enzymes, DNA methylation, and chromatin remodeling, regulate and maintain E/M phenotypes. This review will also report how mechanical properties vary across tumors and regulate epigenetic modifications and E/M plasticity. Finally, it highlights how intratumoral heterogeneity impacts therapeutic efficacy and provides potential therapeutic targets to improve cancer treatments.

Epithelial-Mesenchymal Transition of Cancer Cells on Micropillar Arrays

Epithelial-mesenchymal transition (EMT) is critical for tumor invasion and many other cell-relevant processes. While much progress has been made about EMT, no report concerns the EMT of cells on topological biomaterial interfaces with significant nuclear deformation. Herein, we prepared a poly(lactide-co-glycolide) micropillar array with an appropriate dimension to enable significant deformation of cell nuclei and examined EMT of a human lung cancer epithelial cell (A549). We show that A549 cells undergo serious nuclear deformation on the micropillar array. The cells express more E-cadherin and less vimentin on the micropillar array than on the smooth surface. After transforming growth factor-β1 (TGF-β1) treatment, the expression of E-cadherin as an indicator of the epithelial phenotype is decreased and the expression of vimentin as an indicator of the mesenchymal phenotype is increased for the cells both on smooth surfaces and on micropillar arrays, indicating that EMT occurs even when the cell nuclei are deformed and the culture on the micropillar array more enhances the expression of vimentin. Expression of myosin phosphatase targeting subunit 1 is reduced in the cells on the micropillar array, possibly affecting the turnover of myosin light chain phosphorylation and actin assembly; this makes cells on the micropillar array prefer the epithelial-like phenotype and more sensitive to TGF-β1. Overall, the micropillar array exhibits a promoting effect on the EMT.

Geometric constraint-triggered collagen expression mediates bacterial-host adhesion

Cells living in geometrically confined microenvironments are ubiquitous in various physiological processes, e.g., wound closure. However, it remains unclear whether and how spatially geometric constraints on host cells regulate bacteria-host interactions. Here, we reveal that interactions between bacteria and spatially constrained cell monolayers exhibit strong spatial heterogeneity, and that bacteria tend to adhere to these cells near the outer edges of confined monolayers. The bacterial adhesion force near the edges of the micropatterned monolayers is up to 75 nN, which is ~3 times higher than that at the centers, depending on the underlying substrate rigidities. Single-cell RNA sequencing experiments indicate that spatially heterogeneous expression of collagen IV with significant edge effects is responsible for the location-dependent bacterial adhesion. Finally, we show that collagen IV inhibitors can potentially be utilized as adjuvants to reduce bacterial adhesion and thus markedly enhance the efficacy of antibiotics, as demonstrated in animal experiments.

Mechanotransduction pathways in regulating epithelial-mesenchymal plasticity

The extracellular matrix (ECM) provides structural support for cells and mediates cell-stromal communications. In addition to ECM proteins, mechanical force exerted from the ECM serves as a critical regulator of many biological processes. Epithelial-mesenchymal transition (EMT) is a cellular process by which epithelial cells loosen their cellular junctions and migrate and invade in a more mesenchymal fashion. Recent studies show that increasing ECM stiffness can impinge on cellular signaling pathways through mechanotransduction to promote carcinoma cells to undergo EMT, suggesting that mechanical force exerted by the ECM plays a critical role in tumor invasion and metastasis. Here, we highlight recent work utilizing innovative approaches to study mechanotransduction and summarize newly discovered mechanisms by which mechanosensors and responders regulate EMT during tumor progression and metastasis.

Advanced Mechanical Testing Technologies at the Cellular Level: The Mechanisms and Application in Tissue Engineering

Mechanics, as a key physical factor which affects cell function and tissue regeneration, is attracting the attention of researchers in the fields of biomaterials, biomechanics, and tissue engineering. The macroscopic mechanical properties of tissue engineering scaffolds have been studied and optimized based on different applications. However, the mechanical properties of the overall scaffold materials are not enough to reveal the mechanical mechanism of the cell-matrix interaction. Hence, the mechanical detection of cell mechanics and cellular-scale microenvironments has become crucial for unraveling the mechanisms which underly cell activities and which are affected by physical factors. This review mainly focuses on the advanced technologies and applications of cell-scale mechanical detection. It summarizes the techniques used in micromechanical performance analysis, including atomic force microscope (AFM), optical tweezer (OT), magnetic tweezer (MT), and traction force microscope (TFM), and analyzes their testing mechanisms. In addition, the application of mechanical testing techniques to cell mechanics and tissue engineering scaffolds, such as hydrogels and porous scaffolds, is summarized and discussed. Finally, it highlights the challenges and prospects of this field. This review is believed to provide valuable insights into micromechanics in tissue engineering.

Spatial Gradients of E-Cadherin and Fibronectin in TGF-β1-Treated Epithelial Colonies Are Independent of Fibronectin Fibril Assembly

Epithelial to Mesenchymal Transition (EMT) is a dynamic, morphogenetic process characterized by a phenotypic shift in epithelial cells towards a motile and often invasive mesenchymal phenotype. We have previously demonstrated that EMT is associated with an increase in assembly of the extracellular matrix protein fibronectin (FN) into insoluble, viscoelastic fibrils. We have also demonstrated that Transforming Growth Factor-β1 (TGF-β1) localizes to FN fibrils, and disruption of FN assembly or disruption of TGF-β1 localization to FN fibrils attenuates EMT. Previous studies have shown that TGF-β1 induces spatial gradients of EMT in mammary epithelial cells cultured on FN islands, with cells at free edges of the island preferentially undergoing EMT. In the current work, we sought to investigate: (a) whether FN fibril assembly is also spatially patterned in response to TGF-β1, and (b) what effects FN fibril inhibition has on spatial gradients of E-Cadherin and FN fibrillogenesis. We demonstrate that mammary epithelial cells cultured on square micropatterns have fewer E-Cadherin-containing adherens junctions and assemble more FN fibrils at the periphery of the micropattern in response to increasing TGF-β1 concentration, indicating that TGF-β1 induces a spatial gradient of both E-Cadherin and FN fibrils. Inhibition of FN fibril assembly globally diminished E-Cadherin-containing adherens junctions and FN fibrillogenesis, but did not eliminate the spatial gradient of either. This suggests that global inhibition of FN reduces the degree of both FN fibrillogenesis and E-Cadherin-containing adherens junctions, but does not eliminate the spatial gradient of either, suggesting that spatial gradients of EMT and FN fibrillogenesis are influenced by additional factors.