title: Transglutaminase 2 interacts with syndecan-4 and CD44 at the surface of human macrophages to promote removal of apoptotic cells.
abstract: Tissue transglutaminase (TG2) is a multifunctional protein cross-linking enzyme that has been implicated in apoptotic cell clearance but is also important in many other cell functions including cell adhesion, migration and monocyte to macrophage differentiation. Cell surface-associated TG2 regulates cell adhesion and migration, via its association with receptors such as syndecan-4 and β1 and β3 integrins. Whilst defective apoptotic cell clearance has been described in TG2-deficient mice, the precise role of TG2 in apoptotic cell clearance remains ill-defined. Our work addresses the role of macrophage extracellular TG2 in apoptotic cell corpse clearance. Here we reveal TG2 expression and activity (cytosolic and cell surface) in human macrophages and demonstrate that inhibitors of protein crosslinking activity reduce macrophage clearance of dying cells. We show also that cell-impermeable TG2 inhibitors significantly inhibit the ability of macrophages to migrate and clear apoptotic cells through reduced macrophage recruitment to, and binding of, apoptotic cells. Association studies reveal TG2-syndecan-4 interaction through heparan sulphate side chains, and knockdown of syndecan-4 reduces cell surface TG2 activity and apoptotic cell clearance. Furthermore, inhibition of TG2 activity reduces crosslinking of CD44, reported to augment AC clearance. Thus our data define a role for TG2 activity at the surface of human macrophages in multiple stages of AC clearance and we propose that TG2, in association with heparan sulphates, may exert its effect on AC clearance via a mechanism involving the crosslinking of CD44.
authors.affiliation: School of Life & Health Sciences, Aston University, Birmingham B4 7ET, UK; Aston Research Centre for Healthy Ageing, Aston University, Birmingham B4 7ET, UK.
authors.forename: Vinod
authors.initials: V
authors.lastname: Nadella
authors.affiliation: School of Life & Health Sciences, Aston University, Birmingham B4 7ET, UK; Aston Research Centre for Healthy Ageing, Aston University, Birmingham B4 7ET, UK.
authors.forename: Zhuo
authors.initials: Z
authors.lastname: Wang
authors.affiliation: Academic Nephrology Unit (Sheffield Kidney Inst.), School of Medicine, University of Sheffield, Beech Hill Rd., Sheffield S10 2RZ, UK.
authors.forename: Timothy S
authors.initials: TS
authors.lastname: Johnson
authors.affiliation: School of Life & Health Sciences, Aston University, Birmingham B4 7ET, UK; Aston Research Centre for Healthy Ageing, Aston University, Birmingham B4 7ET, UK. Electronic address: m.griffin@aston.ac.uk.
authors.forename: Martin
authors.initials: M
authors.lastname: Griffin
authors.affiliation: School of Life & Health Sciences, Aston University, Birmingham B4 7ET, UK; Aston Research Centre for Healthy Ageing, Aston University, Birmingham B4 7ET, UK. Electronic address: a.devitt1@aston.ac.uk.
authors.forename: Andrew
authors.initials: A
authors.lastname: Devitt
mesh_terms: D017209:Apoptosis; D002450:Cell Communication; D002465:Cell Movement; D002478:Cells, Cultured; D019204:GTP-Binding Proteins / Q000502:physiology*; D006801:Humans; D018960:Hyaluronan Receptors / Q000502:physiology*; D008264:Macrophages / Q000502:physiology*; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D053671:Syndecan-4 / Q000502:physiology*; D011503:Transglutaminases / Q000502:physiology*
chemical_list: C497483:CD44 protein, human; D018960:Hyaluronan Receptors; D053671:Syndecan-4; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D011503:Transglutaminases; D019204:GTP-Binding Proteins
keywords: Apoptotic cell clearance; CD44; Heparan sulphate proteoglycan; Macrophages; Syndecan 4; Transglutaminase 2