title: Histamine modulates microglia function.
abstract: BACKGROUND
  Histamine is commonly acknowledged as an inflammatory mediator in peripheral tissues, leaving its role in brain immune responses scarcely studied. Therefore, our aim was to uncover the cellular and molecular mechanisms elicited by this molecule and its receptors in microglia-induced inflammation by evaluating cell migration and inflammatory mediator release.
  
  
  METHODS
  Firstly, we detected the expression of all known histamine receptor subtypes (H1R, H2R, H3R and H4R), using a murine microglial cell line and primary microglia cell cultures from rat cortex, by real-time PCR analysis, immunocytochemistry and Western blotting. Then, we evaluated the role of histamine in microglial cell motility by performing scratch wound assays. Results were further confirmed using murine cortex explants. Finally, interleukin-1beta (IL-1β) and tumor necrosis factor-alpha (TNF-α) levels were evaluated by ELISA measurements to determine the role of histamine on the release of these inflammatory mediators.
  
  
  RESULTS
  After 12 h of treatment, 100 μM histamine and 10 μg/ml histamine-loaded poly (lactic-co-glycolic acid) microparticles significantly stimulated microglia motility via H4R activation. In addition, migration involves α5β1 integrins, and p38 and Akt signaling pathways. Migration of microglial cells was also enhanced in the presence of lipopolysaccharide (LPS, 100 ng/ml), used as a positive control. Importantly, histamine inhibited LPS-stimulated migration via H4R activation. Histamine or H4R agonist also inhibited LPS-induced IL-1β release in both N9 microglia cell line and hippocampal organotypic slice cultures.
  
  
  CONCLUSIONS
  To our knowledge, we are the first to show a dual role of histamine in the modulation of microglial inflammatory responses. Altogether, our data suggest that histamine per se triggers microglia motility, whereas histamine impedes LPS-induced microglia migration and IL-1β release. This last datum assigns a new putative anti-inflammatory role for histamine, acting via H4R to restrain exacerbated microglial responses under inflammatory challenge, which could have strong repercussions in the treatment of CNS disorders accompanied by microglia-derived inflammation.
authors.affiliation: CNC - Center for Neuroscience and Cell Biology, University of Coimbra, Coimbra, Portugal.
authors.forename: Raquel
authors.initials: R
authors.lastname: Ferreira
authors.forename: Tiago
authors.initials: T
authors.lastname: Santos
authors.forename: Joana
authors.initials: J
authors.lastname: Gonçalves
authors.forename: Graça
authors.initials: G
authors.lastname: Baltazar
authors.forename: Lino
authors.initials: L
authors.lastname: Ferreira
authors.forename: Fabienne
authors.initials: F
authors.lastname: Agasse
authors.forename: Liliana
authors.initials: L
authors.lastname: Bernardino
mesh_terms: D000818:Animals; D002460:Cell Line; D002465:Cell Movement / Q000502:physiology; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000378:metabolism / Q000502:physiology; D006624:Hippocampus / Q000378:metabolism / Q000473:pathology; D006632:Histamine / Q000494:pharmacology / Q000502:physiology*; D018836:Inflammation Mediators / Q000378:metabolism / Q000502:physiology*; D053583:Interleukin-1beta / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000502:physiology; D008070:Lipopolysaccharides / Q000494:pharmacology / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D017628:Microglia / Q000378:metabolism / Q000502:physiology*; D009924:Organ Culture Techniques; D051381:Rats; D043562:Receptors, G-Protein-Coupled / Q000819:agonists / Q000502:physiology*; D011968:Receptors, Histamine / Q000502:physiology*; D000074040:Receptors, Histamine H4
chemical_list: C498829:Hrh4 protein, mouse; D018836:Inflammation Mediators; D053583:Interleukin-1beta; D008070:Lipopolysaccharides; D043562:Receptors, G-Protein-Coupled; D011968:Receptors, Histamine; D000074040:Receptors, Histamine H4; D006632:Histamine