The genetic modifier Rpe65Leu(450): effect on light damage susceptibility in c-Fos-deficient mice.
OBJECTIVE
To test whether introduction of the Rpe65Leu(450) variant can overcome protection against light-induced photoreceptor apoptosis in mice without the activator protein (AP)-1 constituent c-Fos.


METHODS
c-Fos-deficient mice (c-fos(-/-)) carrying the Leu(450) variant of RPE65 were compared with c-fos(-/-) mice with Rpe65Met(450). Expression of RPE65 was analyzed by Western blot analysis. Rhodopsin regeneration was determined by measuring rhodopsin after different times in darkness after bleaching. Susceptibility to light-induced damage was tested by exposure to white light and subsequent morphologic analysis. Activation of AP-1 and its complex composition was analyzed by electromobility shift assay (EMSA) and antibody interference. The contribution of AP-1 to apoptosis was tested by pharmacological inhibition of AP-1, using dexamethasone.


RESULTS
Compared with RPE65Met(450), introduction of the RPE65Leu(450) variant led to increased levels of RPE65 protein, accelerated rhodopsin regeneration, loss of protection against light-induced damage, and AP-1 responsiveness to toxic light doses, despite the absence of c-Fos. c-Fos was mainly replaced by Fra-2. Application of dexamethasone restored resistance to light-induced damage.


CONCLUSIONS
Increasing retinal photon catch capacity by introducing the Rpe65Leu(450) variant overcomes light damage resistance provided by c-fos deficiency. Thus, a variation of RPE65 at position 450 is a strong genetic modifier of susceptibility to light-induced damage in mice. Under conditions of high rhodopsin availability during exposure to light, Fra-2 and, to a minor degree, FosB substitute for c-Fos and enable light-induced AP-1 activity and thus photoreceptor apoptosis. Regardless of the AP-1 complex's composition, glucocorticoid receptor activation inhibits AP-1 and prevents apoptosis. Thus, not the absence of c-Fos per se, but rather impairment of AP-1 DNA binding is protective against light-induced damage. This impairment may result from the absence of c-Fos or glucocorticoid receptor-mediated transrepression.
Wenzel
Andreas
A
Laboratory for Retinal Cell Biology, Eye Clinic, University Hospital Zurich, Zurich, Switzerland. awenzel@opht.unizh.ch
Grimm
Christian
C
Samardzija
Marijana
M
Remé
Charlotte E
CE
D000818:Animals; D015153:Blotting, Western; D002352:Carrier Proteins; D004268:DNA-Binding Proteins / Q000378:metabolism; D003907:Dexamethasone / Q000494:pharmacology; D004198:Disease Susceptibility; D024202:Electrophoretic Mobility Shift Assay; D005136:Eye Proteins; D051921:Fos-Related Antigen-2; D005938:Glucocorticoids / Q000494:pharmacology; D007930:Leucine; D008027:Light; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D016760:Proto-Oncogene Proteins c-fos / Q000172:deficiency*; D011833:Radiation Injuries, Experimental / Q000209:etiology* / Q000378:metabolism / Q000473:pathology; D012160:Retina / Q000378:metabolism / Q000528:radiation effects*; D012162:Retinal Degeneration / Q000209:etiology* / Q000378:metabolism / Q000473:pathology; D012243:Rhodopsin / Q000502:physiology; D018808:Transcription Factor AP-1 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism; D019745:cis-trans-Isomerases; D000099178:Retinoid Isomerohydrolase
D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D003907:Dexamethasone; D005136:Eye Proteins; D051921:Fos-Related Antigen-2; D005938:Glucocorticoids; D007930:Leucine; D011506:Proteins; D016760:Proto-Oncogene Proteins c-fos; D012243:Rhodopsin; D018808:Transcription Factor AP-1; D014157:Transcription Factors; D019745:cis-trans-Isomerases; D000099178:Retinoid Isomerohydrolase; C497873:Fosl2 protein, mouse