P2X7–Receptor Expression Is Upregulated During Degenerative Ganglion Cell Loss in Retinas of DBA/2J–Mice

Abstract

Abstract: : Purpose: P2X7 receptors have been found on neuronal and non–neuronal cells in the retina. The activation of ATP–sensitive P2X7–receptors leads to multiple downstream events including influx of ions, pore formation and cell death by apoptosis and/or necrosis. The DBA/2J–mouse spontaneously develops ocular hypertension and time–dependent retinal ganglion cell loss. Here, we demonstrate the retinal expression and alterations of P2X7–receptors in DBA/2J–mice during aging. Methods: Retinas were obtained from DBA/2J–mice of different ages (3, 6, 11 months), C57 BL/6–mice were used as age–matched controls. Western Blotting and immunohistochemistry were performed using specific antibodies against P2X7–receptor proteins. Results: P2X7–receptors were prominently expressed on cells in the ganglion cell layer (GCL) of the DBA/2J–mice. A very faint staining was occasionally also found in the inner plexiform layer (IPL) and on cells located in the inner row of the inner nuclear layer (INL). This staining was identical in DBA/2J–mice at the age of 3 and 6 months. As earlier results show, an apoptotic process starts at 4–6 months of age leading to a significant loss of retinal ganglion cells (RGC) in later stages. Despite this intense ganglion cell degeneration immunostaining was conspicuously upregulated in the GCL and in the adjacent sublayer 5 of the IPL. Semiquantitative Western Blot analysis showed that the amount of P2X7–receptor protein expression remained constant during aging in wild type mice and in DBA/2J–mice at 3 and 6 months. The level of P2X7 protein was not reduced in the 11 months old DBA/2J–mice even though most of the receptor carrying ganglion cells had disappeared. Conclusions: Our data show that ganglion cell loss in the DBA/2J–mice is correlated with an upregulation of P2X7–receptor expression in the remaining cells of the GCL. P2X7–receptors may therefore be involved in processes leading to neurodegeneration of the retina.

Keywords: retina: proximal (bipolar, amacrine, and ganglion cells) • receptors • apoptosis/cell death