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Ai Ling Wang, Scott A Nawy; Role of Ca2+-permeable AMPA receptor in retinal ischemia models. Invest. Ophthalmol. Vis. Sci. 2014;55(13):1905.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Recent work has found that expression of the Ca2+-permeable AMPA receptor (CP-AMPAR) is elevated following transient global forebrain ischemia, resulting in increased neuronal death. Retinal ischemia is also associated with neuronal death, particularly the death of retinal ganglion cells, and can lead to blindness. At present, there is no effective treatment against retinal ischemic damage. The purpose of the present study was two fold: 1) We tested the hypothesis that CP-AMPARs are upregulated following ischemic insult, and that Ca2+ influx through these channels contributes to RGC death in retinal ischemia. 2) We investigated the idea that global forebrain ischemia can also damage RGCs through the same mechanisms as retinal ischemia.
Two in vivo animal models were used. One was a transient, global cerebral ischemia (4-VO) model, and the other was a retinal ischemia/reperfusion model. In addition, the oxygen/glucose deprivation (OGD) model was established in cultured primary RGCs. To test for changes in AMPAR expression, we measured levels of GluA2, a subunit that, following Q/R editing by ADAR2, renders AMPARs impermeable to Ca2+. In separate experiments, siRNA was used to knockdown levels of ADAR2 in primary culture to directly test the hypothesis that increased expression of CP-AMPARs contributes to RGCs death.
Using real-time RT-PCR, we found a 75% decrease in GluA2 expression in the retina in the 4-VO model, and a 65% decrease in GluA2 expression in response to increased IOP in the ischemia/reperfusion model at 1 week, suggesting that both forms of ischemia can induce changes in AMPAR composition. We also observed a decrease in GluA2 immunoreactivity in retinal neural cell cultures exposed to OGD. This decrease was confirmed by real-time RT-PCR and western blots. In a second series of experiments, we used Co2+ staining and electrophysiology to confirm that ADAR2 siRNA increased Ca2+ permeability through AMPARs. Importantly, the susceptibility of RGCs to AMPA induced excitotoxicity was dramatically increased in siRNA-treated RGCs compared with control or sham siRNA treated RGCs.
We investigated the function of increased CP-AMPARs levels on RGCs function and viability. Our work suggests that global ischemia can increase expression of CP-AMPARs in RGCs, and that Ca2+ influx into RGCs as a result of increased CP-AMPARs may play a role in the pathogenesis of retinal ischemia.
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