title: Microglia use multiple mechanisms to mediate interactions with vitronectin; non-essential roles for the highly-expressed αvβ3 and αvβ5 integrins.
abstract: BACKGROUND
  As the primary resident immune cells, microglia play a central role in regulating inflammatory processes in the CNS. The extracellular matrix (ECM) protein vitronectin promotes microglial activation, switching microglia into an activated phenotype. We have shown previously that microglia express two vitronectin receptors, αvβ3 and αvβ5 integrins. As these integrins have well-defined roles in activation and phagocytic processes in other cell types, the purpose of the current study was to investigate the contribution of these two integrins in microglial activation.
  
  
  METHODS
  Microglial cells were prepared from wild-type, β3 integrin knockout (KO), β5 integrin KO or β3/β5 integrin DKO mice, and their interactions and activation responses to vitronectin examined in a battery of assays, including adhesion, expression of activation markers, MMP-9 expression, and phagocytosis. Expression of other αv integrins was examined by flow cytometry and immunoprecipitation.
  
  
  RESULTS
  Surprisingly, when cultured on vitronectin, microglia from the different knockout strains showed no obvious defects in adhesion, activation marker expression, MMP-9 induction, or phagocytosis of vitronectin-coated beads. To investigate the reason for this lack of effect, we examined the expression of other αv integrins. Flow cytometry showed that β3/β5 integrin DKO microglia expressed residual αv integrin at the cell surface, and immunoprecipitation confirmed this finding by revealing the presence of low levels of the αvβ1 and αvβ8 integrins. β1 integrin blockade had no impact on adhesion of β3/β5 integrin DKO microglia to vitronectin, suggesting that in addition to αvβ1, αvβ3, and αvβ5, αvβ8 also serves as a functional vitronectin receptor on microglia.
  
  
  CONCLUSIONS
  Taken together, this demonstrates that the αvβ3 and αvβ5 integrins are not essential for mediating microglial activation responses to vitronectin, but that microglia use multiple redundant receptors to mediate interactions with this ECM protein.
authors.affiliation: Department of Molecular and Experimental Medicine, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA.
authors.forename: Jennifer V
authors.initials: JV
authors.lastname: Welser-Alves
authors.forename: Amin
authors.initials: A
authors.lastname: Boroujerdi
authors.forename: Ulrich
authors.initials: U
authors.lastname: Tigges
authors.forename: Richard
authors.initials: R
authors.lastname: Milner
mesh_terms: D000818:Animals; D002448:Cell Adhesion / Q000502:physiology; D018929:Cell Culture Techniques; D002478:Cells, Cultured; D005353:Fibronectins / Q000378:metabolism; D039302:Integrin alphaVbeta3 / Q000235:genetics / Q000378:metabolism*; D020780:Matrix Metalloproteinase 9 / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D017628:Microglia / Q000166:cytology / Q000378:metabolism*; D019030:Receptors, Vitronectin / Q000235:genetics / Q000378:metabolism*; D019096:Vitronectin / Q000378:metabolism*
chemical_list: D005353:Fibronectins; D039302:Integrin alphaVbeta3; D019030:Receptors, Vitronectin; D019096:Vitronectin; C064660:integrin alphaVbeta5; D020780:Matrix Metalloproteinase 9
references.citation: Annu Rev Immunol. 1990;8:365-400
references.pmid: 2188667
references.citation: J Exp Med. 1999 Sep 20;190(6):861-74
references.pmid: 10499924
references.citation: Nat Neurosci. 2007 Nov;10(11):1387-94
references.pmid: 17965659
references.citation: Development. 1998 Aug;125(16):3167-77
references.pmid: 9671589
references.citation: Nat Med. 2002 Jan;8(1):27-34
references.pmid: 11786903
references.citation: J Biol Chem. 2002 Jul 5;277(27):24835-41
references.pmid: 11997396
references.citation: J Clin Invest. 2000 Feb;105(4):433-40
references.pmid: 10683372
references.citation: Invest Ophthalmol Vis Sci. 1997 Jul;38(8):1588-97
references.pmid: 9224287
references.citation: Glia. 2002 Nov;40(2):218-31
references.pmid: 12379909
references.citation: J Exp Med. 2004 Dec 20;200(12):1539-45
references.pmid: 15596525
references.citation: J Clin Invest. 1999 Jan;103(2):229-38
references.pmid: 9916135
references.citation: S Afr Med J. 1982 May 15;61(20):733-6
references.pmid: 7079880
references.citation: J Neuroimmunol. 1999 Jul 1;98(1):49-56
references.pmid: 10426362
references.citation: Ann Neurol. 2004 Apr;55(4):458-68
references.pmid: 15048884
references.citation: Am J Pathol. 1989 Jul;135(1):161-8
references.pmid: 2528301
references.citation: Development. 1994 Dec;120(12):3497-506
references.pmid: 7821217
references.citation: J Neuroimmunol. 1999 Jul 1;98(1):57-68
references.pmid: 10426363
references.citation: J Neuropathol Exp Neurol. 1995 Mar;54(2):202-13
references.pmid: 7533209
references.citation: Brain Res Brain Res Rev. 1999 Jul;30(1):77-105
references.pmid: 10407127
references.citation: Am J Pathol. 1996 Jul;149(1):37-44
references.pmid: 8686760
references.citation: J Biol Chem. 1990 Apr 15;265(11):5938-41
references.pmid: 1690718
references.citation: Stroke. 2001 Sep;32(9):2179-84
references.pmid: 11546914
references.citation: Curr Opin Cell Biol. 1993 Oct;5(5):864-8
references.pmid: 7694604
references.citation: J Immunol. 2007 Jun 15;178(12):8158-67
references.pmid: 17548654
references.citation: J Cell Sci. 1999 Dec;112 ( Pt 23):4271-9
references.pmid: 10564645
references.citation: Glia. 1997 Dec;21(4):350-60
references.pmid: 9419010
references.citation: Science. 1994 Apr 22;264(5158):569-71
references.pmid: 7512751
references.citation: Am J Pathol. 2001 Dec;159(6):2227-37
references.pmid: 11733372
references.citation: Glia. 2009 May;57(7):714-23
references.pmid: 18985734
references.citation: Nature. 2008 Feb 28;451(7182):1076-81
references.pmid: 18278032
references.citation: J Neurosci. 2002 Mar 1;22(5):1562-72
references.pmid: 11880486
references.citation: J Immunol. 2003 Apr 1;170(7):3850-8
references.pmid: 12646653
references.citation: J Cereb Blood Flow Metab. 2010 May;30(5):1031-43
references.pmid: 20087368
references.citation: Proc Natl Acad Sci U S A. 1997 Nov 25;94(24):12932-7
references.pmid: 9371778
references.citation: Mol Cell Biol. 2000 Feb;20(3):755-9
references.pmid: 10629031
references.citation: J Cereb Blood Flow Metab. 1999 Jun;19(6):624-33
references.pmid: 10366192
references.citation: Science. 1995 Dec 1;270(5241):1500-2
references.pmid: 7491498
references.citation: J Neuroimmunol. 1999 Jul 1;98(1):37-44
references.pmid: 10426360