GENE DELIVERY OF GRP78/BIP PROMOTES RETINAL GANGLION CELL SURVIVAL FOLLOWING OPTIC NERVE CRUSH

We delivered GRP78/BiP gene into the mouse eye and promoted retinal ganglion cell survival after optic nerve injury. This study suggests a potential therapeutic target for central nervous system neurodegenerative diseases such as glaucoma and optic nerve trauma. Purpose (a): Optic nerve injury triggers endoplasmic reticulum (ER) stress and activates the unfolded protein response (UPR), leading to retinal ganglion cell (RGC) degeneration. Glucose-regulated protein (GRP78/BiP) is a sensor of ER homeostasis and plays a role in ER stress alleviation. In this study, we evaluated the involvement of GRP78/BiP in RGC degeneration induced by optic nerve crush (ONC) and the neuroprotective effects of gene delivery of GRP78/BiP. Methods (b): ONC was performed unilaterally in adult BALB/cJ mice. The expression of GRP78/BiP was evaluated by real time PCR and fluorescent in situ hybridization (FISH). To evaluate the potential neuroprotective effect of BiP , an AAV2 vector harboring the human BiP gene (AAV2-hBiP) or green fluorescent protein (AAV2-GFP) (2 x 109 P) was intravitreally injected 4 weeks prior to the ONC. Seven and fourteen days after the ONC, RGC survival was determined by RBPMS immunofluorescence staining of retinal flat mounts. Retinal function was assessed using full field flash ERG. Expression of UPR related proteins was evaluated by western blotting. Results (c): Three days after ONC, GRP78/BiP expression was significantly up-regulated in RGCs (p<0.01). Intravitreal administration of AAV2-hBiP significantly reduced RGC loss at 7 and 14 days post-ONC compared to AAV2-GFP injected group (n=5, p<0.01). ERG analysis showed partial protection of pSTR amplitudes in AAV2-hBiP injected eyes (n=5, p<0.05). Retina levels of cleaved ATF6 in AAV2-hBiP injected eyes were much lower than those of AAV2-GFP injected eyes. Conclusions (d): Gene delivery of GRP78/BiP promotes RGC survival and preserves RGC function following optic nerve injury. This study suggests a potential therapeutic target for central nervous system neurodegenerative diseases.