The retinal pigment epithelium of the canine area centralis is uniquely susceptible to mitochondrial toxicant damage

Abstract

Purpose : Mitochondrial dysfunction has been implicated in the ageing process, and may contribute to pathology of the retinal pigment epithelium (RPE) in age-related macular degeneration. The canine retina, unlike that of rodents, has a well-defined cone photoreceptor enriched region known as the area centralis, comparable to the human macula. We tested the hypothesis that the canine area centralis RPE has features that make it more sensitive to toxicity from hydroquinone, a mitochondrial toxicant component of cigarette smoke.

Methods : We harvested and cultured RPE cells from 4 different regions of the eye (area centralis, nasal visual streak, superior and inferior periphery) from young, healthy adult mixed-breed dogs following humane euthanasia. We quantified the individual cellular mitochondrial content in RPE cells immediately after harvest and in confluent culture from different regions using Mitotracker Red staining and ImageJ image analysis tools. Mitochondrial basal activity and response to stressors were measured using a Seahorse XF Mito Stress assay. Cultures were treated with 6h exposures of 0, 25, or 50 μM hydroquinone, every 3 days for a total of 5 times. Cell viability was quantified following exposure. An ANOVA was used to compare values from the area centralis with other regions of the eye.

Results : The basal and maximal mitochondrial respiratory capacity of the area centralis was lower than the superior peripheral retina. There was decreased viability of area centralis cells exposed to hydroquinone compared to other regions. There was a 24.5% increase in cell death compared to control in area centralis cells treated with 50 μM hydroquinone, a concentration which produced no increase in cell death in other regions.

Conclusions : The retinal pigment epithelium of the area centralis has reduced mitochondrial respiratory capacity compared with the superior periphery. When exposed to the mitochondrial toxicant hydroquinone, RPE of the area centralis undergoes a greater amount of cell death. The canine area centralis therefore has the potential to be used to study mechanisms of RPE injury in diseases such as age-related macular degeneration.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.