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Böttcher RT, Strohmeyer N, Aretz J, Fässler R. New insights into the phosphorylation of the threonine motif of the β1 integrin cytoplasmic domain. Life Sci Alliance 2022; 5:5/4/e202101301. [PMID: 34996844 PMCID: PMC8761493 DOI: 10.26508/lsa.202101301] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2021] [Revised: 12/23/2021] [Accepted: 12/23/2021] [Indexed: 01/18/2023] Open
Abstract
Integrins require an activation step before ligand binding and signaling that is mediated by talin and kindlin binding to the β integrin cytosolic domain (β-tail). Conflicting reports exist about the contribution of phosphorylation of a conserved threonine motif in the β1-tail (β1-pT788/pT789) to integrin activation. We show that widely used and commercially available antibodies against β1-pT788/pT789 integrin do not detect specific β1-pT788/pT789 integrin signals in immunoblots of several human and mouse cell lysates but bind bi-phosphorylated threonine residues in numerous proteins, which were identified by mass spectrometry experiments. Furthermore, we found that fibroblasts and epithelial cells expressing the phospho-mimicking β1-TT788/789DD integrin failed to activate β1 integrins and displayed reduced integrin ligand binding, adhesion initiation and cell spreading. These cellular defects are specifically caused by the inability of kindlin to bind β1-tail polypeptides carrying a phosphorylated threonine motif or phospho-mimicking TT788/789DD substitutions. Our findings indicate that the double-threonine motif in β1-class integrins is not a major phosphorylation site but if phosphorylated would curb integrin function.
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Affiliation(s)
- Ralph T Böttcher
- Department of Molecular Medicine, Max Planck Institute of Biochemistry, Martinsried, Germany
| | - Nico Strohmeyer
- Department of Biosystems Science and Engineering, Eidgenössische Technische Hochschule Zurich, Basel, Switzerland
| | - Jonas Aretz
- Department of Molecular Medicine, Max Planck Institute of Biochemistry, Martinsried, Germany
| | - Reinhard Fässler
- Department of Molecular Medicine, Max Planck Institute of Biochemistry, Martinsried, Germany
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Blackburn JWD, Lau DHC, Liu EY, Ellins J, Vrieze AM, Pawlak EN, Dikeakos JD, Heit B. Soluble CD93 is an apoptotic cell opsonin recognized by α x β 2. Eur J Immunol 2019; 49:600-610. [PMID: 30656676 DOI: 10.1002/eji.201847801] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2018] [Revised: 12/13/2018] [Accepted: 01/16/2019] [Indexed: 11/11/2022]
Abstract
Efferocytosis is essential for homeostasis and prevention of the inflammatory and autoimmune diseases resulting from apoptotic cell lysis. CD93 is a transmembrane glycoprotein previously implicated in efferocytosis, with mutations in CD93 predisposing patients to efferocytosis-associated diseases. CD93 is a cell surface protein, which is proteolytically shed under inflammatory conditions, but it is unknown how CD93 mediates efferocytosis or whether its efferocytic activity is mediated by the soluble or membrane-bound form. Herein, using cell lines and human monocytes and macrophages, we demonstrate that soluble CD93 (sCD93) potently opsonizes apoptotic cells but not a broad range of microorganisms, whereas membrane-bound CD93 has no phagocytic, efferocytic, or tethering activity. Using mass spectrometry, we identified αx β2 as the receptor that recognizes sCD93, and via deletion mutagenesis determined that sCD93 binds to apoptotic cells via its C-type lectin-like domain and to αx β2 by its EGF-like repeats. The bridging of apoptotic cells to αx β2 markedly enhanced efferocytosis by macrophages and was abrogated by αx β2 knockdown. Combined, these data elucidate the mechanism by which CD93 regulates efferocytosis and identifies a previously unreported opsonin-receptor system utilized by phagocytes for the efferocytic clearance of apoptotic cells.
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Affiliation(s)
- Jack W D Blackburn
- Department of Microbiology and Immunology, Center for Human Immunology, The University of Western Ontario, London, Ontario, Canada
| | - Darius H C Lau
- Department of Microbiology and Immunology, Center for Human Immunology, The University of Western Ontario, London, Ontario, Canada
| | - Elaine Y Liu
- Department of Microbiology and Immunology, Center for Human Immunology, The University of Western Ontario, London, Ontario, Canada
| | - Jessica Ellins
- Department of Microbiology and Immunology, Center for Human Immunology, The University of Western Ontario, London, Ontario, Canada
| | - Angela M Vrieze
- Department of Microbiology and Immunology, Center for Human Immunology, The University of Western Ontario, London, Ontario, Canada
| | - Emily N Pawlak
- Department of Microbiology and Immunology, Center for Human Immunology, The University of Western Ontario, London, Ontario, Canada
| | - Jimmy D Dikeakos
- Department of Microbiology and Immunology, Center for Human Immunology, The University of Western Ontario, London, Ontario, Canada
| | - Bryan Heit
- Department of Microbiology and Immunology, Center for Human Immunology, The University of Western Ontario, London, Ontario, Canada
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Guo R, Merkel AR, Sterling JA, Davidson JM, Guelcher SA. Substrate modulus of 3D-printed scaffolds regulates the regenerative response in subcutaneous implants through the macrophage phenotype and Wnt signaling. Biomaterials 2015; 73:85-95. [PMID: 26406449 PMCID: PMC4846647 DOI: 10.1016/j.biomaterials.2015.09.005] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2015] [Revised: 08/31/2015] [Accepted: 09/09/2015] [Indexed: 01/15/2023]
Abstract
The growing need for therapies to treat large cutaneous defects has driven recent interest in the design of scaffolds that stimulate regenerative wound healing. While many studies have investigated local delivery of biologics as a restorative approach, an increasing body of evidence highlights the contribution of the mechanical properties of implanted scaffolds to wound healing. In the present study, we designed poly(ester urethane) scaffolds using a templated-Fused Deposition Modeling (t-FDM) process to test the hypothesis that scaffolds with substrate modulus comparable to that of collagen fibers enhance a regenerative versus a fibrotic response. We fabricated t-FDM scaffolds with substrate moduli varying from 5 to 266 MPa to investigate the effects of substrate modulus on healing in a rat subcutaneous implant model. Angiogenesis, cellular infiltration, collagen deposition, and directional variance of collagen fibers were maximized for wounds treated with scaffolds having a substrate modulus (Ks = 24 MPa) comparable to that of collagen fibers. The enhanced regenerative response in these scaffolds was correlated with down-regulation of Wnt/β-catenin signaling in fibroblasts, as well as increased polarization of macrophages toward the restorative M2 phenotype. These observations highlight the substrate modulus of the scaffold as a key parameter regulating the regenerative versus scarring phenotype in wound healing. Our findings further point to the potential use of scaffolds with substrate moduli tuned to that of the native matrix as a therapeutic approach to improve cutaneous healing.
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Affiliation(s)
- R Guo
- Department of Chemical and Biomolecular Engineering, Vanderbilt University, Nashville, TN 37235, USA
| | - A R Merkel
- Research Service, Department of Veterans Affairs Tennessee Valley Healthcare System, Nashville, TN 37212, USA; Center for Bone Biology, Vanderbilt University Medical Center, Nashville, TN 37232, USA; Division of Clinical Pharmacology, Department of Medicine, Vanderbilt University Medical Center, Nashville, TN 37232, USA
| | - J A Sterling
- Research Service, Department of Veterans Affairs Tennessee Valley Healthcare System, Nashville, TN 37212, USA; Center for Bone Biology, Vanderbilt University Medical Center, Nashville, TN 37232, USA; Division of Clinical Pharmacology, Department of Medicine, Vanderbilt University Medical Center, Nashville, TN 37232, USA; Department of Cancer Biology, Vanderbilt University Medical Center, Nashville, TN 37232, USA
| | - J M Davidson
- Research Service, Department of Veterans Affairs Tennessee Valley Healthcare System, Nashville, TN 37212, USA; Department of Pathology, Immunology, and Microbiology, Vanderbilt University, Nashville, TN 37232, USA
| | - S A Guelcher
- Department of Chemical and Biomolecular Engineering, Vanderbilt University, Nashville, TN 37235, USA; Center for Bone Biology, Vanderbilt University Medical Center, Nashville, TN 37232, USA; Department of Biomedical Engineering, Vanderbilt University, Nashville, TN 37235, USA.
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Shin HY, Frechette DM, Rohner N, Zhang X, Puleo DA, Bjursten LM. Dependence of macrophage superoxide release on the pulse amplitude of an applied pressure regime: a potential factor at the soft tissue-implant interface. J Tissue Eng Regen Med 2013; 10:E227-38. [DOI: 10.1002/term.1789] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2012] [Revised: 12/26/2012] [Accepted: 05/27/2013] [Indexed: 01/21/2023]
Affiliation(s)
- Hainsworth Y. Shin
- Center for Biomedical Engineering; University of Kentucky; Lexington KY USA
| | | | - Nathan Rohner
- Center for Biomedical Engineering; University of Kentucky; Lexington KY USA
| | - Xiaoyan Zhang
- Center for Biomedical Engineering; University of Kentucky; Lexington KY USA
| | - David A. Puleo
- Center for Biomedical Engineering; University of Kentucky; Lexington KY USA
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Chaturvedi LS, Zhang P, Basson MD. Effects of extracellular pressure and alcohol on the microglial response to inflammatory stimulation. Am J Surg 2013; 204:602-6. [PMID: 23140827 DOI: 10.1016/j.amjsurg.2012.07.010] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2012] [Revised: 07/10/2012] [Accepted: 07/10/2012] [Indexed: 10/27/2022]
Abstract
BACKGROUND Traumatic brain injury induces a neuroinflammatory response frequently associated with increased intracranial pressure. The aim of this study was to investigate the effects of alcohol and increased extracellular pressure on murine BV-2 microglial proliferation and cytokine responses to lipopolysaccharide (LPS) stimulation. METHODS BV-2 cells were cultured under 0 or 30 mm Hg increased extracellular pressure without or with ethanol (100 mmol/L) or LPS (10 ng/mL) for 24 hours. Cell proliferation was assessed using MTS assay and secretion of the proinflammatory cytokines tumor necrosis factor (TNF)-α, interleukin (IL)-6, and monocyte chemotactic protein (MCP)-1 by enzyme-linked immunosorbent assay. RESULTS Increased pressure and LPS stimulation each promoted proliferation. Ethanol pretreatment blocked these effects. Basal TNF-α and IL-6 secretion was at the limits of delectability. Basal MCP-1 production was stimulated by pressure, which was blocked by ethanol. Even this low LPS dose stimulated microglial secretion of TNF-α, IL-6, and MCP-1. Pressure inhibited LPS-stimulated production of these proinflammatory cytokines, while ethanol pretreatment blocked LPS-stimulated cytokine production. The combination of pressure and ethanol further reduced TNF-α, IL-6, and MCP-1 secretion by LPS-stimulated microglial cells. CONCLUSION Alcohol's anti-inflammatory effects may contribute to the reduced mortality from traumatic brain injury that some have described in acutely intoxicated patients, while pressure down-regulation of inflammatory cytokine release could create a negative feedback that ameliorates inflammation in traumatic brain injury.
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Integrins and small GTPases as modulators of phagocytosis. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2013; 302:321-54. [PMID: 23351714 DOI: 10.1016/b978-0-12-407699-0.00006-6] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Phagocytosis is the mechanism whereby cells engulf large particles. This process has long been recognized as a critical component of the innate immune response, which constitutes the organism's defense against microorganisms. In addition, phagocytic internalization of apoptotic cells or cell fragments plays important roles in tissue homeostasis and remodeling. Phagocytosis requires target interactions with receptors on the plasma membrane of the phagocytic cell. Integrins have been identified as important mediators of particle clearance, in addition to their well-established roles in cell adhesion, migration and mechanotransduction. Indeed, these ubiquitously expressed proteins impart phagocytic capacity to epithelial, endothelial and mesenchymal cell types. The importance of integrins in particle internalization is emphasized by the ability of microbial and viral pathogens to exploit their signaling pathways to invade host cells, and by the wide variety of disorders that arise from abnormalities in integrin-dependent phagocytic uptake.
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Propofol's effects on phagocytosis, proliferation, nitrate production, and cytokine secretion in pressure-stimulated microglial cells. Surgery 2011; 150:887-96. [PMID: 21676422 DOI: 10.1016/j.surg.2011.04.002] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2010] [Accepted: 04/22/2011] [Indexed: 01/05/2023]
Abstract
BACKGROUND Intracranial hypertension complicates severe traumatic brain injury frequently and might be associated with poor outcomes. Traumatic brain injury induces a neuroinflammatory response by microglial activation and upregulation of proinflammatory cytokines, such as interleukin-1β, tumor necrosis factor alpha, and interleukin-6. To elucidate the effect of increased intracranial pressure on microglial function, we studied the effects of increased extracellular pressure on primary human microglial cell phagocytosis, proliferation, cytokine secretion, and total nitrate production. In addition, because many patients receive propofol during anesthesia or intensive care unit sedation, we evaluated whether propofol alters the effects of pressure. METHODS Human microglial cells were pretreated with (2.5-20 μg/mL) propofol or Intralipid as a vehicle control were incubated at ambient atmospheric pressure or at 15 or 30 mm Hg increased pressure for 2 h for phagocytosis assays or 24 h for proliferation, cytokine secretion, and total nitrate production studies. Phagocytosis was determined by incorporation of intracellular fluorescent latex beads. Tumor necrosis factor alpha, interleukin-1β, and interleukin-6 were assayed by sandwich enzyme-linked immunosorbent assay and total nitrate by Greiss reagent. RESULTS Increased extracellular pressure stimulated phagocytosis versus untreated microglial cells or cells treated with an Intralipid vehicle control. Propofol also stimulated microglial phagocytosis at ambient pressure. Increased pressure, however, decreased phagocytosis in the presence of propofol. Pressure also increased microglial tumor necrosis factor-α and interleukin-1β secretion and propofol pretreatment blocked the pressure-stimulated effect. Interleukin-6 production was not altered either by pressure or by propofol. Pressure also induced total nitrate secretion, and propofol pretreatment decreased basal as well as pressure-induced microglial nitrate production. CONCLUSION Extracellular pressures consistent with increased intracranial pressure after a head injury activate inflammatory signals in human primary microglial cells in vitro, stimulating phagocytosis, proliferation, tumor necrosis factor-α, interleukin-1β, and total nitrate secretion but not affecting interleukin-6. Such inflammatory events may contribute to the worsened prognosis of traumatic brain injury after increased intracranial pressure. Because propofol alleviated these potentially proinflammatory effects, these results suggest that the inflammatory cascade activated by intracranial pressure might be targeted by propofol in patients with increased intracranial pressure after traumatic brain injury.
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