title: In vivo imaging of microglia turnover in the mouse retina after ionizing radiation and dexamethasone treatment.
abstract: OBJECTIVE
  Gamma irradiation and bone marrow transplantation (BMT) are established clinical procedures for the treatment of hematologic malignancies. The radiation targets cells in the bone marrow, but injury to other tissues, including the central nervous system (CNS), have been reported. Here, we examine if anti-inflammatory treatment can mitigate the radiation-induced turnover of retinal microglia and the replacement by bone marrow-derived cells (BMDCs).
  
  
  METHODS
  Two-color chimeric mice were generated by lethal irradiation of heterozygous CX3CR1-GFP mice that express GFP in microglial cells and bone marrow transplantation from universal DsRed donor mice. Mice were treated with the corticosteroid dexamethasone; a control group received no dexamethasone treatment. The populations of resident microglia (GFP+) and BMDCs (DsRed+) were quantified by serial in vivo imaging for 10 weeks after irradiation with a confocal scanning laser ophthalmoscope that we custom-built specifically for multicolor imaging of the murine retina.
  
  
  RESULTS
  Ionizing radiation resulted in loss of 75% of the resident retinal microglia population after 70 days. Recruitment of BMDCs was delayed with respect to the microglia loss, resulting in a transient depletion of the total immune cell number in the retina. With dexamethasone treatment, both the loss of the resident microglia and the infiltration of BMDCs were suppressed by at least 50%.
  
  
  CONCLUSIONS
  Anti-inflammatory treatment with the corticosteroidal agent dexamethasone preserves resident microglia and minimizes recruitment of BMDCs after ionizing radiation exposure and BMT.
authors.affiliation: Advanced Microscopy Program, Center for Systems Biology and Wellman Center for Photomedicine, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, United States.
authors.forename: Clemens
authors.initials: C
authors.lastname: Alt
authors.affiliation: Advanced Microscopy Program, Center for Systems Biology and Wellman Center for Photomedicine, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, United States.
authors.forename: Judith M
authors.initials: JM
authors.lastname: Runnels
authors.affiliation: Advanced Microscopy Program, Center for Systems Biology and Wellman Center for Photomedicine, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, United States.
authors.forename: Luke J
authors.initials: LJ
authors.lastname: Mortensen
authors.affiliation: Advanced Microscopy Program, Center for Systems Biology and Wellman Center for Photomedicine, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, United States.
authors.forename: Walid
authors.initials: W
authors.lastname: Zaher
authors.affiliation: Advanced Microscopy Program, Center for Systems Biology and Wellman Center for Photomedicine, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, United States.
authors.forename: Charles P
authors.initials: CP
authors.lastname: Lin
mesh_terms: D000818:Animals; D000893:Anti-Inflammatory Agents / Q000494:pharmacology*; D001854:Bone Marrow Cells / Q000187:drug effects / Q000473:pathology / Q000528:radiation effects; D003907:Dexamethasone / Q000494:pharmacology*; D004195:Disease Models, Animal; D049452:Green Fluorescent Proteins / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D017628:Microglia / Q000187:drug effects* / Q000378:metabolism / Q000528:radiation effects*; D012160:Retina / Q000187:drug effects / Q000528:radiation effects
chemical_list: D000893:Anti-Inflammatory Agents; D049452:Green Fluorescent Proteins; D003907:Dexamethasone
keywords: anti-inflammatory agents; bone marrow–derived cells; microglia; radiation damage; scanning laser ophthalmoscopy