PROTECTIVE EFFECT OF JNK INHIBITION IN RETINAL GANGLION CELLS AND IN RETINAL ISCHEMIA/REPERFUSION INJURY

Purpose: The JNK (cJUN N-terminal kinase) signaling pathway plays an important role in various neuronal pathophysiologies. Using JNK inhibitor SP600125, we examined involvement of the JNK pathway in cultured retinal ganglion cell (RGC) death and in mouse retinal ischemia/reperfusion (I/R) injury. Methods: The in vitro effects of of several JNK inhibitors were evaluated in cultured adult rat retinal cells enriched in RGCs. Cytotoxicity was induced by glutamate or trophic factor withdrawal. Survival of RGCs was assessed by counting Thy-1 postive cells. Retinal I/R was induced in female C57BL/6J mice by raising the intraocular pressure to 120 mmHg for 60 min followed by reperfusion. SP600125 (5, 15, 30 mg/kg) was administered intraperitoneally once daily for 28 days starting at 2 h prior to injury. At various time points after I/R, phosphorylation of JNK and cJun was examined by immunoblotting of retinal proteins. The thickness of retinal layers and cell numbers in ganglion cell layer (GCL) were monitored using H&E stained retinal cross sections, and retinal function was measured by scotopic ERG. Results: SP600125 dose-dependently and significantly (p<0.05) completely protected against glutamate- and trophic factor withdrawal-induced cultured RGC cell death. In the I/R model, phosphorylation of JNK and cJun in retina was significantly (p<0.05) increased at 1 h after injury. I/R injury significantly (p<0.05) decreased the thickness of retinal layers, including whole retina (-23.2 ± 5.7%), inner plexiform layer (-38.0 ± 6.7%), and inner nuclear layer (-25.1 ± 7.4 %) and cell numbers in GCL (-30.0 ± 5.6%). Importantly, administration of all three doses of SP600125 protected against all these degenerative morphological changes (p<0.05). In addition, SP600125 administration also significantly (p<0.05) protected against I/R-induced reduction in b-wave amplitude at 3, 7, 14, 21 and 28 days after injury. Conclusions: Our results demonstrated involvement of the JNK pathway in retinal degeneration in both in vitro and in vivo models and suggest that JNK inhibitors may be a useful therapeutic strategy for neuroprotection in the retina.