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Mechanosensing and Mechanochemical Transduction: How Is Mechanical Energy Sensed and Converted into Chemical Energy in an Extracellular Matrix?

Department of Pathology and Laboratory Medicine, UMDNJ-Robert Wood Johnson Medical School, Piscataway, New Jersey 08854, USA.
Critical Reviews in Biomedical Engineering 02/2003; 31(4):255-331. DOI: 10.1615/CritRevBiomedEng.v31.i4.10
Source: PubMed

ABSTRACT Gravity plays a central role in vertebrate development and evolution. Gravitational forces acting on mammalian tissues cause the net muscle forces required for locomotion to be higher on earth than on a body subjected to a microgravitational field. As body mass increases during development, the musculoskeleton must be able to adapt by increasing the size of its functional units. Thus mechanical forces required to do the work (mechanical energy) of locomotion must be sensed by cells and converted into chemical energy (synthesis of new tissue). Extracellular matrices (ECMs) are multicomponent tissues that transduce internal and external mechanical signals into changes in tissue structure and function through a process termed mechanochemical transduction. Under the influence of an external gravitational field, both mineralized and unmineralized vertebrate tissues exhibit internal tensile forces that serve to preserve a synthetic phenotype in the resident cell population. Application of additional external forces alters the balance between the external gravitational force and internal forces acting on resident cells leading to changes in the expression of genes and production of protein that ultimately may alter the exact structure and function of the extracellular matrix. Changes in the equilibrium between internal and external forces acting on ECMs and changes in mechanochemical transduction processes at the cellular level appear to be important mechanisms by which mammals adjust their needs to store, transmit, and dissipate energy that is required during development and for bodily movements. Mechanosensing is postulated to involve many different cellular and extracellular components. Mechanical forces cause direct stretching of protein-cell surface integrin binding sites that occur on all eukaryotic cells. Stress-induced conformational changes in the extracellular matrix may alter integrin structure and lead to activation of several secondary messenger pathways within the cell. Activation of these pathways leads to altered regulation of genes that synthesize and catabolize extracellular matrix proteins as well as to alterations in cell division. Another aspect by which mechanal signals are transduced involves deformation of gap junctions containing calcium-sensitive stretch receptors. Once activated, these channels trigger secondary messenger activation through pathways similar to those involved in integrin-dependent activation and allow cell-to-cell communications between cells with similar and different phenotypes. Another process by which mechanochemical transduction occurs is through the activation of ion channels in the cell membrane. Mechanical forces have been shown to alter cell membrane ion channel permeability associated with Ca(+2) and other ion fluxes. In addition, the application of mechanical forces to cells leads to the activation of growth factor and hormone receptors even in the absence of ligand binding. These are some of the mechanisms that have evolved in vertebrates by which cells respond to changes in external forces that lead to changes in tissue strcture and function.

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    • "Another study reported that FFSS opens Cx43 HC on the plasma membrane in osteocytes to trigger the release of ATP by a protein-kinase-C-mediated pathway (Genetos et al., 2007). Given that mechanical forces are also known to deform the extracellular matrix, they can alter the integrin protein conformation leading to activation of secondary messenger pathways or exert their effect directly on the cell surface protein–integrin complex (Silver and Siperko, 2003). We have previously shown that FFSS increases the assembly and cell surface expression of Cx43 HC (Siller-Jackson et al., 2008). "
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    ABSTRACT: Intracellular signaling in osteocytes activated by mechanical loading is important for bone formation and remodeling. These signaling events are mediated by small modulators released from Cx43 hemichannels (HC). We have recently shown that integrin α5 senses the mechanical stimulation and induces the opening of Cx43 HC; however, the underlying mechanism is unknown. Here, we show that both Cx43 and integrin α5 interact with 14-3-3θ, and this interaction is required for the opening of Cx43 HC upon mechanical stress. Ablation of 14-3-3θ prevented the interaction between Cx43 and integrin α5, and blocked HC opening. It further decreased the transport of Cx43 and integrin α5 from the Golgi to the plasma membrane. Moreover, mechanical loading promoted the movement of Cx43 to the surface which was associated not only with an increase in 14-3-3θ levels but also its interaction with Cx43 and integrin α5. This stimulatory effect on forward transport by mechanical loading was attenuated in the absence of 14-3-3θ and majority of the Cx43 was accumulated in the Golgi. Disruption of Golgi apparatus by brefeldin A reduced the association of Cx43 and integrin α5 with 14-3-3θ, further suggesting that the interaction is likely to occur in the Golgi. Together, these results define a novel, scaffolding role of 14-3-3θ in assisting the delivery of Cx43 and integrin α5 to the plasma membrane for the formation of mechanosensitive HC in osteocytes.
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    • "Snowhill et al., however, inferred that there appeared to be connections between collagen and elastic fibres. The view generally held is that close association of collagen and elastic fibres in the aortic wall provides the anatomical basis for functioning of tunica media in a biphasic manner (Mcveigh et al., 2002; Silver & Siperko, 2003). In this arrangement, it is thought that below physiological pressures, the strain is born by elastic fibres of long range reversible stretchability (Kielty et al., 2002). "
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    • "Mechanical stretching has different effects on cells, depending on the tissue environment considered. Many in vitro and in vivo studies have shown the effects of mechanical stretching in terms of alteration of intracellular molecular events [Silver and Siperko, 2003; Yano et al., 2006; Vogel and Sheetz, 2009]. In fact, the balance between cell survival, proliferation and differentiation is essential for physiological behaviours as well as in the maintenance of tissue homeostasis. "
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