title: Early focal expression of the chemokine Ccl2 by Müller cells during exposure to damage-inducing bright continuous light.
abstract: OBJECTIVE
  To investigate the time course and localization of Ccl2 expression and recruitment of inflammatory cells associated with light-induced photoreceptor degeneration.
  
  
  METHODS
  Sprague-Dawley (SD) rats were exposed to 1000 lux light for up to 24 hours, after which some animals were allowed to recover in dim light (5 lux) for 3 or 7 days. During and after exposure to light, the animals were euthanatized and the retinas processed. Ccl2 expression was assessed by qPCR, immunohistochemistry, and in situ hybridization at each time point. Counts were made of perivascular monocytes/microglia immunolabeled with ED1, and photoreceptor apoptosis was assessed with TUNEL.
  
  
  RESULTS
  Upregulation of Ccl2 expression was evident in the retina by 12 hours of exposure and correlated with increased photoreceptor death. Ccl2 expression reached its maximum at 24 hours, coinciding with peak cell death. Immunohistochemistry and in situ hybridization showed that Ccl2 is expressed by Müller cells from 12 hours of exposure, most intensely in the superior retina, in the region of the incipient light-induced lesion. After the Müller cell-driven expression of Ccl2, there was a substantial recruitment of monocytes to the local retina and choroidal vasculature. This coincided spatially with the expression of Ccl2 in the superior retina. Peak monocyte infiltration followed maximum Ccl2 expression by up to 3 days. Furthermore, Ccl2 immunoreactivity was observed in many infiltrating monocytes after a 24-hour exposure.
  
  
  CONCLUSIONS
  The data indicate that photoreceptor death promotes region-specific expression of Ccl2 by Müller cells, which facilitates targeting of monocytes to sites of injury. The data suggest that recruitment of monocytes to developing lesions is secondary to signaling events in the retina.
authors.affiliation: Research School of Biology, The Australian National University, Canberra ACT 0200, Australia. matt.rutar@rsbs.anu.edu.au
authors.forename: Matt
authors.initials: M
authors.lastname: Rutar
authors.forename: Riccardo
authors.initials: R
authors.lastname: Natoli
authors.forename: Krisztina
authors.initials: K
authors.lastname: Valter
authors.forename: Jan M
authors.initials: JM
authors.lastname: Provis
mesh_terms: D000818:Animals; D017209:Apoptosis; D002452:Cell Count; D018932:Chemokine CCL2 / Q000378:metabolism*; D019084:Fluorescent Antibody Technique, Indirect; D005904:Glial Fibrillary Acidic Protein / Q000378:metabolism; D017403:In Situ Hybridization; D020287:In Situ Nick-End Labeling; D008027:Light; D017628:Microglia / Q000378:metabolism*; D009000:Monocytes / Q000502:physiology; D020419:Photoreceptor Cells, Vertebrate / Q000473:pathology; D011833:Radiation Injuries, Experimental / Q000209:etiology / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012160:Retina / Q000528:radiation effects*; D012162:Retinal Degeneration / Q000209:etiology / Q000378:metabolism*; D013997:Time Factors
chemical_list: D018932:Chemokine CCL2; D005904:Glial Fibrillary Acidic Protein