Involvement of P2X7 receptors in retinal ganglion cell death after optic nerve crush injury in rats

We investigated whether P2X(7) antagonists rescue retinal ganglion cells (RGCs) in culture and after optic nerve crush (ONC) injury. Rats were sacrificed 7 days after retrograde labeling of RGCs with 4',6-diamidino-2-phenylindole (DAPI), and the retinas were enzymatically dissociated in vitro and incubated with P2X(7) antagonists or agonists for 3 days. Adenosine triphosphate (ATP) and benzoylbenzoyl ATP were used as P2X(7) agonists, and oxidized ATP and brilliant blue G were used as P2X(7) antagonists. DAPI-positive and calcein-positive RGCs were counted to determine the number of living cells. We observed that RGCs were preserved when treated with P2X(7) antagonists, as compared with the controls. In contrast, P2X(7) agonists significantly decreased the number of viable RGCs. In vivo, P2X(7) antagonists at various doses were injected into the vitreous body immediately after ONC injuries in rats. Surviving RGCs were stained with anti-neuron-specific beta-tubulin antibody in flat-mounted retinas. RGCs were observed to decrease to 61% of baseline 7 days after ONC injury, whereas RGCs were significantly preserved when P2X(7) antagonists were applied. When P2X(7) receptor expression was examined immunohistochemically in rat retinas after ONC, the retinal expression of the P2X(7) receptors was observed to be upregulated after ONC and peaked on day 3. Meanwhile, P2X(7) antagonists suppressed this upregulation. Collectively, these results suggest that P2X(7) antagonists prevent loss of RGCs after ONC, and that this protective effect is possibly mediated through suppressing the upregulation of retinal P2X(7) expression. (C) 2012 Elsevier Ireland Ltd. All rights reserved.