Characterization of the PD-1 Expression Pattern After Optic Nerve Transection in the Rat

Abstract

Purpose: : Understanding cellular signals that trigger retinal ganglion cell (RGC) death may help guide development of new therapeutic approaches. Programmed cell death-1 (PD-1) is a membrane receptor expressed in rodent RGCs and a subpopulation of amacrine cells. Engagement of PD-1 with its ligand promotes developmental RGC death in mice. We hypothesize that PD-1 ligation could trigger RGC death following optic nerve transection (ONT). This study characterizes retinal PD-1 expression in the setting of optic nerve injury using a rat ONT model.

Methods: : Left optic nerves of adult male Wistar rats (4 animals per group) were transected and fluorogold (FG) retrograde tracer was applied to the transected nerve to identify RGCs; right eyes served as uninjured controls. At 14 days following ONT >95% of RGCs die whereas amacrine cells survive prompting a time course study at 1, 3, 7, and 14 days post-ONT. Vertical retinal sections were stained with anti-PD-1 and serial sections were analyzed using epifluorescent images. All ganglion cell layer (GCL) cells were scored for positivity of PD-1, FG, and RGC morphology by two independent blinded investigators. Statistical analysis was performed using Pearson correlation coefficients and two-tailed p-values.

Results: : At day 1 post-ONT 84% of the FG+ cells are positive for PD-1. At day 14 the majority of FG+ cells resemble activated microglia by morphology and only 52% are positive for PD-1. In comparison to day 1, FG+ RGCs were decreased by 97% at day 14, and 73% of these cells are PD-1 positive. Over the ONT time course, the decrease in PD-1 expression correlates with loss of RGCs (p<0.05), but not with the FG negative GCL cells.

Conclusions: : PD-1 expression changes during the process of ONT-induced RGC death. Additional studies are needed to fully define the role of PD-1 ligation as a trigger for RGC death following injury.

Keywords: ganglion cells • retinal degenerations: cell biology • pathology: experimental