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      Removal of the mechanoprotective influence of the cytoskeleton reveals PIEZO1 is gated by bilayer tension

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          Abstract

          Mechanosensitive ion channels are force-transducing enzymes that couple mechanical stimuli to ion flux. Understanding the gating mechanism of mechanosensitive channels is challenging because the stimulus seen by the channel reflects forces shared between the membrane, cytoskeleton and extracellular matrix. Here we examine whether the mechanosensitive channel PIEZO1 is activated by force-transmission through the bilayer. To achieve this, we generate HEK293 cell membrane blebs largely free of cytoskeleton. Using the bacterial channel MscL, we calibrate the bilayer tension demonstrating that activation of MscL in blebs is identical to that in reconstituted bilayers. Utilizing a novel PIEZO1–GFP fusion, we then show PIEZO1 is activated by bilayer tension in bleb membranes, gating at lower pressures indicative of removal of the cortical cytoskeleton and the mechanoprotection it provides. Thus, PIEZO1 channels must sense force directly transmitted through the bilayer.

          Abstract

          PIEZO1 is a mechanosensitive ion channel, but the mechanism of force transduction is unknown. Here Cox and Bae et al. disrupt the cortical cytoskeleton in HEK293 cells to show that PIEZO1 is gated directly by membrane tension.

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          Most cited references59

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          Piezos are pore-forming subunits of mechanically activated channels

          Mechanotransduction plays a crucial role in physiology. Biological processes including sensing touch and sound waves require yet unidentified cation channels that detect pressure. Mouse piezo1 (mpiezo1) and mpiezo2 induce mechanically activated cationic currents in cells; however, it is unknown if piezos are pore-forming ion channels or modulate ion channels. We show that Drosophila piezo (dpiezo) also induces mechanically activated currents in cells, but through channels with remarkably distinct pore properties including sensitivity to the pore blocker ruthenium red and single channel conductances. mpiezo1 assembles as a ~1.2 million-Dalton tetramer, with no evidence of other proteins in this complex. Finally, purified mpiezo1 reconstituted into asymmetric lipid bilayers and liposomes forms ruthenium red-sensitive ion channels. These data demonstrate that piezos are an evolutionarily conserved ion channel family involved in mechanotransduction.
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            Piezo1, a mechanically activated ion channel, is required for vascular development in mice.

            Mechanosensation is perhaps the last sensory modality not understood at the molecular level. Ion channels that sense mechanical force are postulated to play critical roles in a variety of biological processes including sensing touch/pain (somatosensation), sound (hearing), and shear stress (cardiovascular physiology); however, the identity of these ion channels has remained elusive. We previously identified Piezo1 and Piezo2 as mechanically activated cation channels that are expressed in many mechanosensitive cell types. Here, we show that Piezo1 is expressed in endothelial cells of developing blood vessels in mice. Piezo1-deficient embryos die at midgestation with defects in vascular remodeling, a process critically influenced by blood flow. We demonstrate that Piezo1 is activated by shear stress, the major type of mechanical force experienced by endothelial cells in response to blood flow. Furthermore, loss of Piezo1 in endothelial cells leads to deficits in stress fiber and cellular orientation in response to shear stress, linking Piezo1 mechanotransduction to regulation of cell morphology. These findings highlight an essential role of mammalian Piezo1 in vascular development during embryonic development.
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              Non-equilibration of hydrostatic pressure in blebbing cells.

              Current models for protrusive motility in animal cells focus on cytoskeleton-based mechanisms, where localized protrusion is driven by local regulation of actin biochemistry. In plants and fungi, protrusion is driven primarily by hydrostatic pressure. For hydrostatic pressure to drive localized protrusion in animal cells, it would have to be locally regulated, but current models treating cytoplasm as an incompressible viscoelastic continuum or viscous liquid require that hydrostatic pressure equilibrates essentially instantaneously over the whole cell. Here, we use cell blebs as reporters of local pressure in the cytoplasm. When we locally perfuse blebbing cells with cortex-relaxing drugs to dissipate pressure on one side, blebbing continues on the untreated side, implying non-equilibration of pressure on scales of approximately 10 microm and 10 s. We can account for localization of pressure by considering the cytoplasm as a contractile, elastic network infiltrated by cytosol. Motion of the fluid relative to the network generates spatially heterogeneous transients in the pressure field, and can be described in the framework of poroelasticity.
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                Author and article information

                Journal
                Nat Commun
                Nat Commun
                Nature Communications
                Nature Publishing Group
                2041-1723
                20 January 2016
                2016
                : 7
                Affiliations
                [1 ]Victor Chang Cardiac Research Institute , Darlinghurst, New South Wales 2010, Australia
                [2 ]Department of Physiology and Biophysics, State University of New York at Buffalo , Buffalo, New York 14214, USA
                [3 ]St Vincent's Clinical School, University of New South Wales , Darlinghurst, New South Wales 2010, Australia
                [4 ]The Centre for Single Molecule Biophysics, State University of New York at Buffalo , Buffalo, New York 14214, USA
                Author notes
                [*]

                These authors contributed equally to this work.

                [†]

                These authors jointly supervised this work.

                Article
                ncomms10366
                10.1038/ncomms10366
                4735864
                26785635
                d94af733-bfec-4386-a095-d5ad2be118bd
                Copyright © 2016, Nature Publishing Group, a division of Macmillan Publishers Limited. All Rights Reserved.

                This work is licensed under a Creative Commons Attribution 4.0 International License. The images or other third party material in this article are included in the article's Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder to reproduce the material. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/

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