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Atherosclerosis and Mechanical Forces
Published in Michel R. Labrosse, Cardiovascular Mechanics, 2018
Mechanical stretch primarily affects the tunica media, that is, vascular SMCs; however, it also triggers biochemical signaling in ECs (Figure 7.5). Mechanoreceptor proteins that participate in stretch signal mechanotransduction in ECs are stretch-activated channels, integrin and focal adhesion kinase (Naruse 1998; Katsumi 2005; Zebda 2012). Within the cell, the stretch stimulates the occurrence of stress fibers, that is, actin filaments, which increase the resistance of the cell against the applied stress (Tojkander 2012). To minimize the alteration in intracellular strain, the stress fibers reorient perpendicularly to the direction of stretch (Wang 2001).
Structure, Biochemical Properties, and Biological Functions of Integrin Cytoplasmic Domains
Published in Yoshikazu Takada, Integrins: The Biological Problems, 2017
Martin E. Hemler, Jonathan B. Weitzman, Renata Pasqualini, Satoshi Kawaguchi, Paul D. Kassner, Feodor B. Berdichevsky
Focal adhesions are discrete subcellular regions where the plasma membrane is in tight association with the underlying substrate. These subcellular complexes, which are specialized for anchoring microfilament bundles known as stress fibers,97 contain several cytoskeletal proteins, including α-actinin, vinculin, and talin. In a substrate-dependent manner, integrins also localize to focal adhesions, thus providing a transmembrane linkage between the extracellular matrix and the cytoskeleton.56,57,60,97,151 Protein kinase C152 and the majority of tyrosine-phosphorylated proteins71,153 also appear to concentrate within focal adhesions, suggesting that these complexes are important sites of cellular signaling.
Quantification of Cellular Elasticity
Published in Malgorzata Lekka, Cellular Analysis by Atomic Force Microscopy, 2017
As an example, the comparison between two cell types will be provided here [51]. Fibroblasts are the cells characterized by highly organized internal structure with well-differentiated both actin and microtubule cytoskeleton (Fig. 4.15a). Actin filaments are dispersed within the entire cell but they are mostly concentrated in the cortex layer beneath the cell membrane. They are organized into two groups: (i) stress fibers visible as a long and thick fibers and (ii) short actin filaments whose presence is barely detected under the fluorescent microscope. Microtubules extend from location close to cell nucleus toward membrane. The length of these cytoskeletal elements can reach even more than 100 microns. The incubation of fibroblasts with 5 μg/ml cytochalasin D leads to depolymerization of actin filaments and, as a consequence, to more homogenous spatial distribution of actin filaments (no stress fibers visible, Fig. 4.15b).
S1P in the development of atherosclerosis: roles of hemodynamic wall shear stress and endothelial permeability
Published in Tissue Barriers, 2021
Christina M Warboys, Peter D Weinberg
EC undergo dynamic cytoskeletal remodeling in response to mechanical forces that alter endothelial cell shape and orientation.67,68 Broadly, there are three phases of cytoskeletal remodeling and adaptation, with consequent alterations in barrier function. There appears to be an immediate compensatory response following application of shear stress (up to 20 min) that is associated with an enhanced cortical actin cytoskeleton and increased barrier function.52,69 This is followed by a phase of enhanced motility, remodeling and realignment associated with stress fiber formation, disruption of cell–cell junctions and thus increased permeability.70,71 Recent studies by our group have shown that EC re-orient and align themselves so as to minimize transverse wall shear stress.72 Once endothelial cells have remodeled, the dense cortical actin cytoskeleton reforms73 and junctions and cell contacts are reestablished, resulting in enhanced barrier function.21,71
A computational model to predict cell traction-mediated prestretch in the mitral valve
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2019
M. A. J. van Kelle, M. K. Rausch, E. Kuhl, S. Loerakker
In the present study we aim to understand how cell-mediated traction forces may lead to the development of anisotropic tissue prestretch in the mitral valve. Towards this end, a model is required which predicts the development of traction forces by cellular actin stress fibers. Different models have been developed which use physically-motivated remodeling laws to predict cellular actin stress fiber remodeling. These models rely on stress and strain homeostasis (Deshpande et al. 2006, 2007; Vernerey and Farsad 2011; Obbink-Huizer et al. 2014) or on a thermodynamic equilibrium (Foucard and Vernerey 2012; Vigliotti et al. 2016) to predict stress fiber assembly and dissociation in response to topological and mechanical cues. Loerakker et al. (2014) coupled the cell-mediated remodeling laws of Obbink-Huizer et al. (2014) to an algorithm for collagen remodeling, and showed that cellular contractility is a very important affector of remodeling in tissue engineered heart valves in the pulmonary position (Loerakker et al. 2016).
Formin proteins in megakaryocytes and platelets: regulation of actin and microtubule dynamics
Published in Platelets, 2019
Malou Zuidscherwoude, Hannah L.H. Green, Steven G. Thomas
Formin proteins were first identified in mice from studies on abnormal limb development (1,2) with homologues subsequently being found in drosophila and yeast (3). A list of the formin proteins expressed in mammalian cells is given in Table I. Formins have the ability to both nucleate and accelerate the elongation of linear actin filaments. They play a crucial role in the assembly of cytoskeletal structures such as filopodia, lamellipodia and stress fibres and are therefore required for a range of cellular processes including cell adhesion, cell division and cell motility (4). These multidomain proteins are defined by the presence of highly conserved Formin Homology 1 (FH1) and Formin Homology 2 (FH2) domains and a less well-conserved FH3 domain (Figure 1(a)). Formins function as a homodimer with dimerisation mediated via the dimerisation domain (DD), a component of the FH3 domain (5) and the FH2 domains (Figure 1(b)). The FH2 domains form a doughnut-shaped head-to-tail dimer which nucleates actin filaments. Indeed, it has been shown that the FH2 domains alone are sufficient for actin filament nucleation probably via the stabilisation of spontaneously formed actin dimers (6). The FH2 domain remains processively attached to actin filament barbed ends facilitating addition of actin monomers to support elongation and shielding the filament from abundant capping proteins (7–9). The FH1 domains recruit profilin bound G-actin molecules, bringing them into close proximity with the barbed end and thus accelerating filament elongation (10) (Figure 1(c)).