title: Brief report: Granulocyte-macrophage colony-stimulating factor drives monosodium urate monohydrate crystal-induced inflammatory macrophage differentiation and NLRP3 inflammasome up-regulation in an in vivo mouse model.
abstract: OBJECTIVE
  To determine the role of granulocyte-macrophage colony-stimulating factor (GM-CSF) in the differentiation of inflammatory macrophages in an in vivo model of monosodium urate monohydrate (MSU) crystal-induced inflammation.
  
  
  METHODS
  C57BL/6J mice were treated with either clodronate liposomes to deplete peritoneal macrophages or GM-CSF antibody and were then challenged by intraperitoneal injection of MSU crystals. Peritoneal lavage fluid was collected, and cellular infiltration was determined by flow cytometry. Purified resident and MSU crystal-recruited monocyte/macrophages were stimulated ex vivo with MSU crystals. The interleukin-1β (IL-1β) levels in lavage fluids and ex vivo assay supernatants were measured. GM-CSF-derived and macrophage colony-stimulating factor (M-CSF)-derived macrophages were generated in vitro from bone marrow cells. Protein expression of IL-1β, caspase 1, NLRP3, and ASC by in vitro- and in vivo-generated monocyte/macrophages was analyzed by Western blotting.
  
  
  RESULTS
  Depletion of resident macrophages lowered MSU crystal-induced IL-1β and GM-CSF levels in vivo as well as IL-1β production by MSU crystal-recruited monocytes stimulated ex vivo. GM-CSF neutralization in vivo decreased MSU crystal-induced IL-1β levels and neutrophil infiltration. MSU crystal-recruited monocyte/macrophages from GM-CSF-neutralized mice expressed lower levels of the macrophage marker CD115 and produced less IL-1β following ex vivo stimulation. These monocytes exhibited decreased expression of NLRP3, pro/active IL-1β, and pro/active caspase 1. In vitro-derived GM-CSF-differentiated macrophages expressed higher levels of NLRP3, pro/active IL-1β, and pro/active caspase 1 compared to M-CSF-differentiated macrophages.
  
  
  CONCLUSIONS
  GM-CSF plays a key role in the differentiation of MSU crystal-recruited monocytes into proinflammatory macrophages. GM-CSF production may therefore contribute to the exacerbation of inflammation in gout.
authors.affiliation: Malaghan Institute of Medical Research, Wellington, New Zealand.
authors.forename: Odette M
authors.initials: OM
authors.lastname: Shaw
authors.forename: Stefanie
authors.initials: S
authors.lastname: Steiger
authors.forename: Xiao
authors.initials: X
authors.lastname: Liu
authors.forename: John A
authors.initials: JA
authors.lastname: Hamilton
authors.forename: Jacquie L
authors.initials: JL
authors.lastname: Harper
mesh_terms: D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology*; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000378:metabolism*; D017737:Macrophages, Peritoneal / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D000071199:NLR Family, Pyrin Domain-Containing 3 Protein; D015854:Up-Regulation / Q000187:drug effects / Q000502:physiology*; D014527:Uric Acid / Q000494:pharmacology*
chemical_list: D002352:Carrier Proteins; D000071199:NLR Family, Pyrin Domain-Containing 3 Protein; C492716:Nlrp3 protein, mouse; D014527:Uric Acid; D016178:Granulocyte-Macrophage Colony-Stimulating Factor