Steroids do not prevent photoreceptor degeneration in the light-exposed T4R rhodopsin mutant dog retina irrespective of AP-1 inhibition.
OBJECTIVE
AP-1 has been proposed as a key intermediate linking exposure to light and photoreceptor cell death in rodent light-damage models. Inhibition of AP-1 associated with steroid administration also prevents light damage. In this study the role of steroids in inhibiting AP-1 activation and/or in preventing photoreceptor degeneration was examined in the rhodopsin mutant dog model.


METHODS
The dogs were dark adapted overnight, eyes dilated with mydriatics; the right eye was light occluded and the fundus of the left eye photographed ( approximately 15-17 overlapping frames) with a fundus camera. For biochemical studies, the dogs remained in the dark for 1 to 3 hours after exposure. Twenty-four hours before exposure to light, some dogs were treated with systemic dexamethasone or intravitreal/subconjunctival triamcinolone. AP-1 DNA-binding activity was determined by electrophoresis mobility shift assay (EMSA) and phosphorylation of c-Fos and activation of ERK1/2 were determined by immunoblot analyses. The eyes were collected 1 hour and 2 weeks after exposure to light, for histopathology and immunocytochemistry.


RESULTS
Inhibition of AP-1 activation, and phosphorylation of ERK1/2 and c-Fos were found after dexamethasone treatment in light-exposed T4R RHO mutant dog retinas. In contrast, increased AP-1 activity and phosphorylation of c-Fos and ERK1/2 were found in triamcinolone-treated mutant retinas. Similar extensive rod degeneration was found after exposure to light with or without treatment, and areas with surviving photoreceptor nuclei consisted primarily of cones. Only with systemic dexamethasone did the RPE cell layer remain.


CONCLUSIONS
Intraocular or systemic steroids fail to prevent light-induced photoreceptor degeneration in the T4R RHO dog retina. Finding that systemic dexamethasone prevents AP-1 activation, yet does not prevent retinal light damage, further supports the hypothesis that AP-1 is not the critical player in the cell-death signal that occurs in rods.
Gu
Danian
D
Section of Ophthalmology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
Beltran
William A
WA
Pearce-Kelling
Sue
S
Li
Zexiao
Z
Acland
Gregory M
GM
Aguirre
Gustavo D
GD
D000818:Animals; D003623:Dark Adaptation; D003907:Dexamethasone / Q000008:administration & dosage; D004195:Disease Models, Animal; D004283:Dog Diseases / Q000235:genetics / Q000473:pathology / Q000517:prevention & control*; D004285:Dogs; D024202:Electrophoretic Mobility Shift Assay; D019084:Fluorescent Antibody Technique, Indirect; D005938:Glucocorticoids / Q000008:administration & dosage*; D015151:Immunoblotting; D008027:Light / Q000009:adverse effects*; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D009154:Mutation; D015345:Oligonucleotide Probes; D010766:Phosphorylation; D020419:Photoreceptor Cells, Vertebrate / Q000473:pathology / Q000528:radiation effects*; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism; D011833:Radiation Injuries, Experimental / Q000235:genetics / Q000473:pathology / Q000517:prevention & control / Q000662:veterinary*; D012162:Retinal Degeneration / Q000235:genetics / Q000473:pathology / Q000517:prevention & control / Q000662:veterinary*; D012243:Rhodopsin / Q000235:genetics*; D018808:Transcription Factor AP-1 / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D014222:Triamcinolone Acetonide / Q000008:administration & dosage
D005938:Glucocorticoids; D015345:Oligonucleotide Probes; D016760:Proto-Oncogene Proteins c-fos; D018808:Transcription Factor AP-1; D003907:Dexamethasone; D012243:Rhodopsin; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D014222:Triamcinolone Acetonide