HYPERTHERMIA AND HYPOXIA INCREASE TOLERANCE OF RETINAL GANGLION-CELLSTO ANOXIA AND EXCITOTOXICITY

Purpose. Knowledge of the mechanisms by which retinal ganglion cells a re damaged may provide information required to develop novel treatment s for diseases that cause retinal ganglion cell death. The authors inv estigated whether the expression of the 72-kDa heat shock protein in c ultured rat retinal ganglion cells increases tolerance to hypoxic and excitotoxic injury. Methods. Hyperthermia (42 degrees C for 1 hour) an d sublethal hypoxia (9% O-2 for 6 hours) were used to inaaduce synthes is of the 72-kDa heat shock protein in cultured rat retinal ganglion c ells and cultured retinal Muller cells. Induction of the 72-kDa heat s hock protein was detected with immunocytochemical and immunoblot techn iques. Survival of cultured retinal ganglion cells after exposure to a noxia (<1% O-2 for 6 hours) and glutamate (200 mu m for 6 hours) was m easured and compared to control cultures stressed previously by hypert hermia or sublethal hypoxia. The effect of quercetin, a blocker of hea t shock protein synthesis, was evaluated in parallel experiments. Resu lts. Heat shock protein immunoreactivir was expressed in cultured reti nal ganglion cells and Miiller cells after hyperthermia and sublethal hypoxia. The mean (+/-standard deviation) retinal ganglion cell suniva l rates after exposure to anoxia (expressed as a percentage of untreat ed control cultures) in cells pretreated with sublelhal hypoxia (83%+/ -17%) and hyperthermia (82%+/-19%) were significantly greater than for cells that had no pretreatment (50%+/-18%, P <0.001). The mean (+/-st andard deviation) retinal ganglion cell survival rate after exposure t o glutamate in cells pretreated with sublethal hypoxia (82%+/-19%) and hyperthermia (86%+/-17%) were significantly greater than for cells th at had no pretreatment (56%+/-17%, P <0.001). Inhibition of heat shock protein synthesis with quercetin abolished the protective effects of sublethal hypoxia and hyperthermia on cell sunival after anoxia and gl utamate exposure. Conclusions. The neuroprotective effect of hyperther mia and sublethal hypoxia suggests that heat shock proteins confer pro tection against ischemic and excitotoxic retinal ganglion cell death.