Abstract
Purpose: :
The retina is crucial for visual transduction and is actively supported by the retinal pigment epithelium (RPE). The RPE maintains retinal ionic homeostasis, and renews the photoreceptor disc membrane through daily phagocytosis and re-isomerization of retinol. RPE phagocytosis is under circadian regulation suggesting active retina-RPE cross-talk. It has been previously reported that the neuropeptide oxytocin localizes to the posterior retina and that its level in the retina shows circadian regulation. We sought to determine if the oxytocin receptor is also present in the retina.
Methods: :
Donor eyes within 12 hrs of death were procured from the Lions Eye Bank of Wisconsin. Macaca mulatta eyes were obtained from the Wisconsin National Primate Research Center (Madison, USA) within 30 minutes of euthanization. After removing the anterior segment, the retina was carefully separated and the RPE cells were isolated by enzymatic digestion. Tissue was snap-frozen in liquid nitrogen and was processed using the RNeasy Mini Kit (Qiagen, USA). The isolated RNA was transcribed with Superscript III kit (Invitrogen, CA, USA). Standard PCR was carried out using Immomix PCR mix (Bioline, MA, USA). Results were resolved using agarose gel electrophoresis.
Results: :
A 256 bp PCR product was detected in human RPE, retina and muscle samples. Appropriate controls showed no amplification of the oxytocin receptor (OXTR) mRNA. These results were confirmed using three independent sets of non-human primate samples. To further ascertain the integrity of our results, hBest1 was detected in the RPE and to a lesser extent in retina, but not in the muscle sample.
Conclusions: :
Although the neuropeptide hormone oxytocin has been shown to be expressed in the eye, the localization of the oxytocin receptor within the RPE is a novel finding. The observation that OXTR is expressed in retina suggests that it plays an important role in the cellular signaling function of the retina.
Keywords: retina • gene/expression • circadian rhythms