title: Interferon regulatory factor 8/interferon consensus sequence binding protein is a critical transcription factor for the physiological phenotype of microglia.
abstract: BACKGROUND
  Recent fate-mapping studies establish that microglia, the resident mononuclear phagocytes of the CNS, are distinct in origin from the bone marrow-derived myeloid lineage. Interferon regulatory factor 8 (IRF8, also known as interferon consensus sequence binding protein) plays essential roles in development and function of the bone marrow-derived myeloid lineage. However, little is known about its roles in microglia.
  
  
  METHODS
  The CNS tissues of IRF8-deficient mice were immunohistochemically analyzed. Pure microglia isolated from wild-type and IRF8-deficient mice were studied in vitro by proliferation, immunocytochemical and phagocytosis assays. Microglial response in vivo was compared between wild-type and IRF8-deficient mice in the cuprizon-induced demyelination model.
  
  
  RESULTS
  Our analysis of IRF8-deficient mice revealed that, in contrast to compromised development of IRF8-deficient bone marrow myeloid lineage cells, development and colonization of microglia are not obviously affected by loss of IRF8. However, IRF8-deficient microglia demonstrate several defective phenotypes. In vivo, IRF8-deficient microglia have fewer elaborated processes with reduced expression of IBA1/AIF1 compared with wild-type microglia, suggesting a defective phenotype. IRF8-deficient microglia are significantly less proliferative in mixed glial cultures than wild-type microglia. Unlike IRF8-deficient bone marrow myeloid progenitors, exogenous macrophage colony stimulating factor (colony stimulating factor 1) (M-CSF (CSF1)) restores their proliferation in mixed glial cultures. In addition, IRF8-deficient microglia exhibit an exaggerated growth response to exogenous granulocyte-macrophage colony stimulating factor (colony stimulating factor 2) (GM-CSF (CSF2)) in the presence of other glial cells. IRF8-deficient microglia also demonstrate altered cytokine expressions in response to interferon-gamma and lipopolysaccharide in vitro. Moreover, the maximum phagocytic capacity of IRF8-deficient microglia is reduced, although their engulfment of zymosan particles is not overtly impaired. Defective scavenging activity of IRF8-deficient microglia was further confirmed in vivo in the cuprizone-induced demyelination model in mice.
  
  
  CONCLUSIONS
  This study is the first to demonstrate the essential contribution of IRF8-mediated transcription to a broad range of microglial phenotype. Microglia are distinct from the bone marrow myeloid lineage with respect to their dependence on IRF8-mediated transcription.
authors.affiliation: Department of Neurology, University of California Davis, School of Medicine, 4860 Y Street, Sacramento, CA 95817, USA.
authors.forename: Makoto
authors.initials: M
authors.lastname: Horiuchi
authors.forename: Kouji
authors.initials: K
authors.lastname: Wakayama
authors.forename: Aki
authors.initials: A
authors.lastname: Itoh
authors.forename: Kumi
authors.initials: K
authors.lastname: Kawai
authors.forename: David
authors.initials: D
authors.lastname: Pleasure
authors.forename: Keiko
authors.initials: K
authors.lastname: Ozato
authors.forename: Takayuki
authors.initials: T
authors.lastname: Itoh
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D015703:Antigens, CD / Q000378:metabolism; D015214:Antigens, Differentiation, Myelomonocytic / Q000378:metabolism; D001921:Brain / Q000166:cytology; D039481:CD11b Antigen / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism; D049109:Cell Proliferation / Q000187:drug effects; D002478:Cells, Cultured; D003471:Cuprizone / Q000633:toxicity; D003711:Demyelinating Diseases / Q000139:chemically induced; D004195:Disease Models, Animal; D005434:Flow Cytometry; D005786:Gene Expression Regulation / Q000187:drug effects / Q000235:genetics; D050835:Interferon Regulatory Factors / Q000172:deficiency / Q000378:metabolism / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008840:Microfilament Proteins / Q000235:genetics / Q000378:metabolism; D017628:Microglia / Q000378:metabolism*; D008996:Monoamine Oxidase Inhibitors / Q000633:toxicity; D009186:Myelin Sheath / Q000473:pathology; D010587:Phagocytosis / Q000235:genetics; D010641:Phenotype; D010671:Phenylurea Compounds / Q000494:pharmacology; D013116:Spinal Cord / Q000378:metabolism / Q000473:pathology; D000099185:Interferon Regulatory Factor-8; D000097382:CD68 Molecule
chemical_list: D015703:Antigens, CD; D015214:Antigens, Differentiation, Myelomonocytic; D039481:CD11b Antigen; D002135:Calcium-Binding Proteins; D003471:Cuprizone; D050835:Interferon Regulatory Factors; D008840:Microfilament Proteins; D008996:Monoamine Oxidase Inhibitors; D010671:Phenylurea Compounds; D000099185:Interferon Regulatory Factor-8; C491049:Aif1 protein, mouse; C067980:CD68 antigen, human; D000097382:CD68 Molecule; C032766:ethylene diurea