RESUMEN
Cell adhesion is crucial for cells to not only physically interact with each other but also sense their microenvironment and respond accordingly. In fact, adherent cells can generate physical forces that are transmitted to the surrounding matrix, regulating the formation of cell-matrix adhesions. The main purpose of this work is to develop a computational model to simulate the dynamics of cell-matrix adhesions through a cohesive formulation within the framework of the finite element method and based on the principles of continuum damage mechanics. This model enables the simulation of the mechanical adhesion between cell and extracellular matrix (ECM) as regulated by local multidirectional forces and thus predicts the onset and growth of the adhesion. In addition, this numerical approach allows the simulation of the cell as a whole, as it models the complete mechanical interaction between cell and ECM. As a result, we can investigate and quantify how different mechanical conditions in the cell (e.g., contractile forces, actin cytoskeletal properties) or in the ECM (e.g., stiffness, external forces) can regulate the dynamics of cell-matrix adhesions.
Asunto(s)
Simulación por Computador , Modelos Biológicos , Adhesión Celular/fisiología , Uniones Célula-Matriz/fisiología , Citoesqueleto/metabolismo , Matriz Extracelular/fisiología , HumanosRESUMEN
Finite element (FE) simulations of contractile responses of vascular muscular thin films (vMTFs) and endothelial cells resting on an array of microposts under stimulation of soluble factors were conducted in comparison with experimental measurements reported in the literature. Two types of constitutive models were employed in the simulations, i.e. smooth muscle cell type and non-smooth muscle cell type. The time histories of the effects of soluble factors were obtained via calibration against experimental measurements of contractile responses of tissues or cells. The numerical results for vMTFs with micropatterned tissues suggest that the radius of curvature of vMTFs under stimulation of soluble factors is sensitive to width of the micropatterned tissue, i.e. the radius of curvature increases as the tissue width decreases. However, as the tissue response is essentially isometric, the time history of the maximum principal stress of the micropatterned tissues is not sensitive to tissue width. Good agreement has been achieved for predictions of the vasoconstrictor endothelin-1-induced contraction stress between the FE numerical simulation and the experiment-based approach of Alford (Integr Biol 3:1063-1070, 2011) for the vMTFs with 40, 60, 80 and 100 [Formula: see text] width patterns. This may suggest the contraction stress is weakly sensitive to the tissue width for these patterns. However, for 20 [Formula: see text] width tissue patterning, the numerical simulation result for contraction stress is less than the average value of experimental measurements, which may suggest the thinner and more elongated spindle-like cells within the 20 [Formula: see text] width tissue patterning have higher contractile output. The constitutive model for non-smooth muscle cells was used to simulate the contractile response of the endothelial cells. The substrate was treated as an effective continuum. For agonists such as lysophosphatidic acid and vascular endothelial growth factor, the deformation of the cell diminishes from edge to centre and the central part of the cell is essentially under isometric state. Numerical studies demonstrated the scenarios that cell polarity can be triggered via manipulation of the effective stiffness and Possion's ratio of the substrate.
Asunto(s)
Fenómenos Biomecánicos , Simulación por Computador , Modelos Biológicos , Células Cultivadas , Contracción Muscular/fisiología , Miocitos del Músculo LisoRESUMEN
Differential cadherin (Cdh) expression is a classical mechanism for in vitro cell sorting. Studies have explored the roles of differential Cdh levels in cell aggregates and during vertebrate gastrulation, but the role of differential Cdh activity in forming in vivo tissue boundaries and boundary extracellular matrix (ECM) is unclear. Here, we examine the interactions between cell-cell and cell-ECM adhesion during somitogenesis, the formation of the segmented embryonic precursors of the vertebral column and musculature. We identify a sawtooth pattern of stable Cdh2 adhesions in which there is a posterior-to-anterior gradient of stable Cdh2 within each somite, while there is a step-like drop in stable Cdh2 along the somite boundary. Moreover, we find that the posterior somite boundary cells with high levels of stable Cdh2 have the most columnar morphology. Cdh2 is required for maximal cell aspect ratio and thus full epithelialization of the posterior somite. Loss-of-function analysis also indicates that Cdh2 acts with the fibronectin (FN) receptor integrin α5 (Itgα5) to promote somite boundary formation. Using genetic mosaics, we demonstrate that differential Cdh2 levels are sufficient to induce boundary formation, Itgα5 activation, and FN matrix assembly in the paraxial mesoderm. Elevated cytoskeletal contractility is sufficient to replace differential Cdh2 levels in genetic mosaics, suggesting that Cdh2 promotes ECM assembly by increasing cytoskeletal and tissue stiffness along the posterior somite boundary. Throughout somitogenesis, Cdh2 promotes ECM assembly along tissue boundaries and inhibits ECM assembly in the tissue mesenchyme.
Asunto(s)
Cadherinas/genética , Morfogénesis , Somitos/embriología , Proteínas de Pez Cebra/genética , Pez Cebra/embriología , Pez Cebra/genética , Animales , Cadherinas/metabolismo , Matriz Extracelular/metabolismo , Mesodermo/metabolismo , Pez Cebra/metabolismo , Proteínas de Pez Cebra/metabolismoRESUMEN
Pluripotent human embryonic stem cells (hESCs) have the capability of differentiating into different lineages based on specific environmental cues. We had previously shown that hESCs can be primed to differentiate into either neurons or glial cells, depending on the arrangement, geometry and size of their substrate topography. In particular, anisotropically patterned substrates like gratings were found to favour the differentiation of hESCs into neurons rather than glial cells. In this study, our aim is to elucidate the underlying mechanisms of topography-induced differentiation of hESCs towards neuronal lineages. We show that high actomyosin contractility induced by a nano-grating topography is crucial for neuronal maturation. Treatment of cells with the myosin II inhibitor (blebbistatin) and myosin light chain kinase inhibitor (ML-7) greatly reduces the expression level of microtubule-associated protein 2 (MAP2). On the other hand, our qPCR array results showed that PAX5, BRN3A and NEUROD1 were highly expressed in hESCs grown on nano-grating substrates as compared to unpatterned substrates, suggesting the possible involvement of these genes in topography-mediated neuronal differentiation of hESCs. Interestingly, YAP was localized to the cytoplasm of differentiating hESCs. Taken together, our study has provided new insights in understanding the mechanotransduction of topographical cues during neuronal differentiation of hESCs.