Cell stiffness and receptors: evidence for cytoskeletal subnetworks

Abstract

Viscoelastic models of cells often treat cells as homogeneous objects. However, studies have demonstrated that cellular properties are local and can change dramatically on the basis of the location probed. Because membrane receptors are linked in various ways to the intracellular space, with some receptors linking to the cytoskeleton and others diffusing freely without apparent linkages, the cellular physical response to mechanical stresses is expected to depend on the receptor engaged. In this study, we tested the hypothesis that cellular mechanical stiffness as measured via cytoskeletally linked receptors is greater than stiffness measured via receptors that are not cytoskeletally linked. We used a magnetic micromanipulator to apply linear stresses to magnetic beads attached to living cells via selected receptors. One of the receptor classes probed, the dystroglycan receptors, is linked to the cytoskeleton, while the other, the transferrin receptors, is not. Fibronectincoated beads were used to test cellular mechanical properties of the cytoskeleton without membrane dependence by allowing the beads to endocytose. For epithelial cells, transferrin-dependent stiffness and endocytosed bead-dependent stiffness were similar, while dystroglycan-dependent stiffness was significantly lower. For smooth muscle cells, dystroglycan-dependent stiffness was similar to the endocytosed bead-dependent stiffness, while the transferrin-dependent stiffness was lower. The conclusion of this study is that the measured cellular stiffness is critically influenced by specific receptor linkage and by cell type and raises the intriguing possibility of the existence of separate cytoskeletal networks with distinct mechanical properties that link different classes of receptors. magnetic micromanipulator; dystroglycan; transferrin THE MECHANISM BY WHICH CELLS sense and respond to mechanical forces is relevant to many pathological conditions, such as atherosclerosis and myopathies. While there is no consensus regarding the specific response mechanism, it is thought that the cytoskeleton plays an important role in sensing the cell's physical environment (9,32,33). To study the cellular response to mechanical stresses, different methods have been used, including membrane strain studies (6,8,11,15,28,37,39,50) and cone viscometer experiments (49). More recently, new techniques have allowed greater control of the applied forces and the targeting of specific membrane receptors (1,5,12,21,23,35,42,47,48). Magnetic micromanipulation applies stresses via magnetic beads and is capable of generating either linear (1, 4, 42) or twisting stress (10,43,44,52,53).Mechanical stresses applied to different receptors using magnetic micromanipulation result in molecular signaling that is strongly present only when the receptor stressed is cytoskeletally linked (2, 41-43). These results support the notion that cytoskeletally linked receptors serve as a link between the external mechanical environment and the internal signaling domains of the cell. Tensegrity-ba...

Cathelicidin LL-37 Increases Lung Epithelial Cell Stiffness, Decreases Transepithelial Permeability, and Prevents Epithelial Invasion by Pseudomonas aeruginosa

“…LL-37's ability to interact with lipid rafts is suggested by its high surface activity (52), the caveolae-independent membrane raft-dependent endocytosis of an LL-37/DNA plasmid complex (53), and LL-37-mediated/raft-dependent LPS internalization (54). Because LL-37 activates multiple plasma receptors, and the cellular mechanical response to agonists depends on the receptor engaged (55), it is also possible that the LL-37-mediated increase in F-actin concentration results in the formation of distinct cytoskeletal networks with mechanical properties that affect bacterial invasion.…”

A theoretical model for F-actin remodeling in vascular smooth muscle cells subjected to cyclic stretch

“…Many families of CSK proteins contribute to overall cell stiffness, but F-actin tends to dominate in many cases (Pourati et al, 1998;Wu et al, 1998;Smith et al, 2003;Na et al, 2004;Huang et al, 2005) and thus was the focus herein. There is increasing information available on the elasticity of F-actin, including isolated filaments, networks having different degrees of crosslinks, and stress fibers (e.g., Liu and Pollack, 2002;Gardel et al, 2004;Deguchi et al, 2006).…”

Time-dependent Changes in Smooth Muscle Cell Stiffness and Focal Adhesion Area in Response to Cyclic Equibiaxial Stretch

“…18,33,48,51 Relationships between cytoskeletal structure and the mechanical properties of cells have been studied extensively given recent developments of techniques capable of manipulating forces and displacements less than a piconewton and a nanometer, respectively (for reviews, see Huang et al, 17 Vliet et al, 44 Zhu et al 52 ). Nonetheless, there remains a need for data that are sufficient to develop quantitative relationships between dynamically changing cell properties (e.g., overall stiffness) and the cytoskeletal remodeling (e.g., F-actin) that associates with the dynamic reorganization of focal adhesions (FAs) that occurs in response to altered cell stretching.…”