Differential susceptibility of retinal ganglion cells to reactive oxygen species

PURPOSE. Retinal light exposure is a source of oxidative stress, and retina l cells contain molecules that scavenge or inactivate reactive oxygen speci es (ROS). Yet, ROS also play a role in signal transduction, and some retina l cells (e.g., neurotrophin-dependent retinal ganglion cells, RGCs) may use ROS as parr of the signaling process for cell death. RGCs might therefore have specialized mechanisms for regulating ROS levels. The hypothesis that RGCs might regulate ROS differently from other retinal cells was tested by studying their differential response to oxidative stress in vitro. METHODS. RGCs were retrogradely labeled by injecting the fluorescent tracer DiI into the superior colliculi of postnatal day 2 through 4 Long-Evans ra ts. At postnatal daps 7 through 9 the retinas were dissociated with papain and cultured with and without specific ROS-generating systems and/or scaven gers. RGCs were identified by their DiI positivity using rhodamine filters. Living cells, determined by metabolism of calcein-A viewed with fluorescei n filters, were counted in triplicate. Degenerate reverse transcription-pol ymerase chain reaction (RT-PCR) using primers specific to peroxidase homolo gy regions was used to survey for novel peroxidases expressed within normal retinas. RESULTS. Compared with other retinal cells, RGCs were remarkably resistant to cell death induced by superoxide anion, hydrogen peroxide, or hydroxyl r adical. Catalase counteracted the effect of each ROS-generating system on r etinal cells, consistent with damage occurring via a hydrogen peroxide inte rmediate. Aminotriazole, L-buthionine sulfoximine, and sodium azide partly abrogated the RGC resistance to oxidative stress, suggesting that this resi stance may be mediated by catalase and/or glutathione peroxidase. A limited expression survey within the retina using degenerate RT-PCR did not demons trate novel peroxidases, CONCLUSIONS. These data suggest a role for one or more endogenous peroxidas es within RGCs, which could possibly be protective under conditions of axon al damage. Exploration of the unique characteristics of RGC resistance and susceptibility to injury may help in better understanding the pathophysiolo gy of diseases associated with primary axonal damage.