Involvement Of Fra-1 In Retinal Ganglion Cell Apoptosis In Rat Light Induced Retina Damage Model

Objective:To observe the mRNA and protein expression patterns of Fra-1 after retinal light damage,as well as to discuss its potential biological roles in the retinal ganglion cell(RGC)damage after light exposure(LE).Methods: Ten-week old Sprague–Dawley rats were exposed to bright light(16 000 Lux)as the model of retinal light damage model.Western blot was used to identify Fra-1,active caspase-3,cyclin D1,p38 and phosphorylated p38(p-p38)expression in retina after LE.Quantitative real-time PCR(qRT-PCR)was used to determine Fra-1 mRNA level at different time point after LE.Immunohistochemistry,immunofluorescence,and TUNEL were performed to observe Fra-1 expression and distribution,cellular localization and cellular apoptosis in the retinal ganglion cell layer after LE.Finally,the rats were intravitreally injected with 10 nmol SB203580,a highly selective inhibitor of p38 mitogen activated protein kinases(p38 MAPKs),and were sacrificed to verify again that MAPK signal pathway and Fra-1 were associated with RGC apoptosis after LE.Results: Fra-1 protein expression increased at 1 d and reached the peak at 3 d and then gradually recovered to the baseline level at 7 d after LE.Immunohistochemistry demonstrated Fra-1 expression in the retinal ganglion cell layer was significantly increased after light exposure.Immunofluorescence double labeling showed that Fra-1,Brn3B(a kind of ganglion cellular marker),and active caspase-3(a kind of apoptotic marker)were co-localized in the RGCs.TUNEL staining demonstrated that apoptosis of RGC was occurred after LE,and Fra-1 was co-localized with the TUNEL positive RGCs.In addition,we found that cell cycle associated protein,cyclin D1,was up-regulated after LE.Fra-1 expression increased in parallel with cyclin D1 and phosphorylated mitogen-activated protein kinase p38(p-p38)expression in retina after LE.Furthermore,Fra-1,cyclin D1 and active caspase-3 protein expression decreased by intravitreal injection of SB203580,a highly selective inhibitor of p38 MAPK.Conclusions: RGC apoptosis after retinal light damage may be associated with the up-regulation of Fra-1 expression regulated by p38 MAPK through cell cycle re-entry mechanism after LE.