title: Inhibition of transglutaminase 2 reduces efferocytosis in human macrophages: Role of CD14 and SR-AI receptors.
abstract: Transglutaminase 2 (TGM2), a member of the transglutaminase family of enzymes, is a multifunctional protein involved in numerous events spanning from cell differentiation, to signal transduction, apoptosis, and wound healing. It is expressed in a variety of cells, macrophages included. Macrophage TGM2 promotes the clearance of apoptotic cells (efferocytosis) and emerging evidence suggests that defective efferocytosis contributes to the consequences of inflammation-associated diseases, including atherosclerotic lesion progression and its sequelae. Of interest, active TGM2 identified in human atherosclerotic lesions plays critical roles in plaque stability through effects on matrix cross-linking and TGFβ activity. This study explores the mechanisms by which TGM2 controls efferocytosis in human macrophages.
  
  
  
  Herein we show that TGM2 increases progressively during monocyte differentiation towards macrophages and controls their efferocytic potential as well as morphology and viability. Two experimental approaches that took advantage of the inhibition of TGM2 activity and protein silencing give proof that TGM2 reduction significantly impairs macrophage efferocytosis. Among the mechanisms involved we highlighted a role of the receptors CD14 and SR-AI whose levels were markedly reduced by TGM2 inhibition. Conversely, CD36 receptor and αvβ3 integrin levels were not influenced. Of note, lipid accumulation and IL-10 secretion were reduced in macrophages displaying defective efferocytosis.
  
  
  
  Overall, our data define a crucial role of TGM2 activity during macrophage differentiation via mechanisms involving CD14 and SR-AI receptors and show that TGM2 inhibition triggers a pro-inflammatory phenotype.
authors.affiliation: Centro Cardiologico Monzino I.R.C.C.S., Milan, Italy. Electronic address: sonia.eligini@cardiologicomonzino.it.
authors.forename: S
authors.initials: S
authors.lastname: Eligini
authors.affiliation: Centro Cardiologico Monzino I.R.C.C.S., Milan, Italy.
authors.forename: S
authors.initials: S
authors.lastname: Fiorelli
authors.affiliation: Centro Cardiologico Monzino I.R.C.C.S., Milan, Italy.
authors.forename: E
authors.initials: E
authors.lastname: Tremoli
authors.affiliation: Dipartimento di Scienze Farmacologiche e Biomolecolari, Università degli Studi di Milano, Milan, Italy.
authors.forename: S
authors.initials: S
authors.lastname: Colli
mesh_terms: D017209:Apoptosis; D002103:Cadaverine / Q000031:analogs & derivatives / Q000494:pharmacology; D002454:Cell Differentiation; D048430:Cell Shape; D002470:Cell Survival; D018920:Coculture Techniques; D003538:Cystamine / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D019204:GTP-Binding Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D006801:Humans; D016753:Interleukin-10 / Q000378:metabolism; D019169:Jurkat Cells; D018950:Lipopolysaccharide Receptors / Q000378:metabolism*; D008264:Macrophages / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D010587:Phagocytosis / Q000187:drug effects*; D010641:Phenotype; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D034622:RNA Interference; D000068103:Serine-Arginine Splicing Factors / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D013601:T-Lymphocytes / Q000473:pathology; D013997:Time Factors; D014162:Transfection; D011503:Transglutaminases / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism
chemical_list: D004791:Enzyme Inhibitors; C508609:IL10 protein, human; D018950:Lipopolysaccharide Receptors; C503566:SCAF1 protein, human; C000717608:TGM2 protein, human; D016753:Interleukin-10; D000068103:Serine-Arginine Splicing Factors; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D011503:Transglutaminases; D019204:GTP-Binding Proteins; C008542:monodansylcadaverine; D002103:Cadaverine; D003538:Cystamine
keywords: CD14 antigen; Cystamine; Efferocytosis; Interleukin-10; Macrophages; Scavenger receptor SR-AI; Transglutaminase 2