Light-induced retinal ganglion cell damage in vivo involves Dexras1.

PURPOSE

Light-induced retinal degeneration is a vision-threatening retinal disease. Light can damage not only photoreceptor cells but also retinal ganglion cells (RGCs). This study was aimed to observe the spatiotemporal expression of dexamethasone-induced Ras protein 1 (Dexras1) and document the effect of Dexras1 on RGC damage after light exposure.

METHODS

Adult Sprague-Dawley rats were exposed to bright white light for 2 h. Reverse transcriptase-PCR (RT-PCR) and western blot analysis were used to analyze mRNA and protein expression of Dexras1. The spatial distribution of Dexras1 and outer nuclear layer (ONL) thickness were evaluated by immunohistochemistry. Immunofluorescence was performed to observe the colocalization of Dexras1. In addition, cell apoptosis in this model was measured using terminal deoxynucleotidyl transferase deoxyuridine triphosphate (dUTP) nick end labeling (TUNEL). Finally, the effect of systemic administration of nitric oxide synthase (NOS) inhibitor on the retina was investigated by western blot analysis and immunofluorescence.

RESULTS

Dexras1 expression increased at 6 h and reached the peak at 1 day, gradually recovering to the baseline level at 7 days after light exposure. Dexras1 immunoreactivity was detected in RGCs and colabeled with cleaved caspase-3 after light exposure, whereas cleaved caspase-3 immunoreactivity was undetectable in the ONL. However, immunohistochemistry demonstrated that the ONL thickness decreased after light exposure and TUNEL revealed that photoreceptor cell apoptosis also occurred. In addition, the ternary complex of Dexras1, neuronal NOS (nNOS), and the C-terminal PSD95/DLG/ZO-1 ligand of nNOS was observed in RGCs. Administration of NOS inhibitor decreased the expression of cleaved caspase-3 and Dexras1.

CONCLUSIONS

Exposure to light caused the transient high expression of Dexras1, which was colabeled with apoptotic marker, nNOS, and the C-terminal PSD95/DLG/ZO-1 ligand of nNOS in RGCs. Administration of the NOS inhibitor prevented RGC apoptosis by decreasing cleaved caspase-3 and Dexras1 expression. Dexras1-mediated RGC damage appears to act through activation of nNOS in this model.