Adenosine protects zebrafish photoreceptors from apoptosis and damage in a light-induced retinal degeneration model of age-related macular degeneration

Abstract

Purpose : Adenosine has been shown to be neuroprotective in the CNS and in the inner retina. However, the neuroprotective effects of adenosine on the outer retina are unknown. Adenosine has been shown to inhibit photoreceptor excitability by suppressing Ca²⁺ influx through voltage-gated Ca²⁺ channels, which could lead to cell death. The purpose of this study was to see if adenosine would reduce photoreceptor damage and death in a light-induced retinal degeneration (LIRD) model of age-related macular degeneration in pigmented zebrafish.

Methods : Adult wild-type and Tg(nrd:GFP) zebrafish were dark-adapted for 24 hours, followed by intravitreal injections of ~ 0.5 ml of 0.1 mM, 1 mM, or 5 mM of adenosine in both eyes. Controls were injected with saline in both eyes. All zebrafish were exposed to full spectrum high-intensity light for 4 days and collected at 0 and 96 hours post dark-adaptation. Immunohistochemical analysis was performed on vertical retinal sections in order to visualize cones, rods, and the outer nuclear layer of the retina. Retinal damage was assessed using confocal microscopy with a TUNEL assay and cell specific markers.

Results : Photoreceptors in control retinas collected at 96 hours exhibited severe truncation or loss of the outer segments, and swelling of the cell body. Additionally, there was an increase in TUNEL-positive cells and a significant decrease in rod and cone photoreceptors in the control retinas. Photoreceptors from retinas treated with higher concentrations of adenosine (1 mM and 5 mM) lacked swelling, exhibited less cell death, reduced truncation of the outer segments, and had cell morphology similar to retinas collected prior to light exposure. Photoreceptors from retinas treated with 0.1 mM adenosine exhibited no significant differences in cell death in comparison to control retinas at 96 hours, and had similar levels of outer segment truncation and cell body morphology. However, there was a significant reduction in the number of cones and rods lost in the 0.1 mM adenosine-treated retinas at 96 hours in comparison to control retinas at 96 hours.

Conclusions : These findings show that adenosine can prevent light-induced structural damage to rod and cone photoreceptors, prevent photoreceptor death and loss, and provide evidence of a potential novel therapeutic target for the treatment of the “dry” form of AMD.

This is a 2020 ARVO Annual Meeting abstract.