title: M1 macrophages are required for murine cerebral aneurysm formation.
abstract: BACKGROUND
  Macrophages and neutrophils have been separately implicated in cerebral aneurysm formation. The interactions between different myeloid subsets and the contributions of macrophage phenotypes in these lesions over time are not known. The purpose of the study was to examine macrophage phenotypic changes in cerebral aneurysms.
  
  
  METHODS
  We induced aneurysm formation in C57BL/6 mice and quantified contributions of M1 and M2 macrophages in aneurysm specimens with or without neutrophil blockade. In our aneurysm model, the left common carotid and right renal arteries were ligated, and mice were placed on a hypertensive high fat diet. One week later, stereotactic injection with elastase solution into the basal cisterns was performed. An angiotensin II secreting osmotic pump was implanted. The mice were then treated with anti-CXCL1 antibody or IgG control antibody. Animals were euthanized at 3 days, or 1 or 2 weeks. The circle of Willis was analyzed using immunohistochemistry for M1 and M2 macrophage phenotype contributions.
  
  
  RESULTS
  Proinflammatory M1/M2 ratio increased in cerebral aneurysm formation over time, from 0.56 at 3 days to 1.75 at 2 weeks (p<0.0001). In contrast, anti-CXCL1 antibody blockade led to polarization towards an anti-inflammatory phenotype with an M1/M2 ratio of 0.95 at 2 weeks compared with IgG treated mice (p=0.0007).
  
  
  CONCLUSIONS
  CXCL1 dependent neutrophil inflammation appears to have an important role in macrophage polarization to M1 phenotype in cerebral aneurysm development.
authors.affiliation: Department of Neurosurgery, University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania, USA.
authors.forename: Kamil W
authors.initials: KW
authors.lastname: Nowicki
authors.affiliation: Department of Neurosurgery, University of Florida, Gainesville, Florida, USA.
authors.forename: Koji
authors.initials: K
authors.lastname: Hosaka
authors.affiliation: Department of Neurosurgery, University of Colorado, Denver, Colorado, USA.
authors.forename: Frank J
authors.initials: FJ
authors.lastname: Walch
authors.affiliation: Department of Molecular Genetics and Microbiology, University of Florida, Gainesville, Florida, USA.
authors.forename: Edward W
authors.initials: EW
authors.lastname: Scott
authors.affiliation: Department of Neurosurgery, University of Florida, Gainesville, Florida, USA.
authors.forename: Brian L
authors.initials: BL
authors.lastname: Hoh
mesh_terms: D000818:Animals; D000893:Anti-Inflammatory Agents / Q000008:administration & dosage; D054360:Chemokine CXCL1 / Q000037:antagonists & inhibitors / Q000276:immunology; D005260:Female; D007074:Immunoglobulin G / Q000008:administration & dosage; D016756:Immunoglobulins, Intravenous / Q000008:administration & dosage; D002532:Intracranial Aneurysm / Q000188:drug therapy / Q000276:immunology* / Q000473:pathology*; D008264:Macrophages / Q000187:drug effects / Q000276:immunology* / Q000473:pathology*; D051379:Mice; D008810:Mice, Inbred C57BL; D010641:Phenotype
chemical_list: D000893:Anti-Inflammatory Agents; D054360:Chemokine CXCL1; C475895:Cxcl1 protein, mouse; D007074:Immunoglobulin G; D016756:Immunoglobulins, Intravenous
keywords: Aneurysm; Brain; Inflammation; Inflammatory Response