Abstract
(1) Background: Retinal pigment epithelial cells (RPE) cells constitutively secrete vascular endothelial growth factor (VEGF) in the retina, protecting the neuronal cells and the choroid. Increased VEGF secretion, however, can result in neovascularization and edema. Many factors regulate VEGF secretion. In this study, we investigated the effect of external stimuli in relation to diurnal rhythm on constitutive VEGF secretion. (2) Methods: Single-eye RPE cell culture was prepared from porcine eyes. RPE cells were cultured in darkness, treated with daylight or room light, and treated with melatonin at different time frames, either respectively or in combination. Supernatants were collected and VEGF content evaluated using ELISA. Expression of the clock protein BMAL1 was evaluated with Western blot. (3) Results: VEGF secretion of the RPE shows a diurnal rhythm. While the rhythm is not influenced by either light or melatonin, the amount of secreted VEGF can be increased by nocturnal melatonin, especially in combination with morning daylight. These findings disclose another layer of VEGF regulation in the retina.
Highlights
The retinal pigment epithelium (RPE) is an epithelial monolayer situated beneath the neuroretina
24 h into the the supernatant of cultured cells were analysed for different conditions
We investigated whether external light or external melatonin changed the production level and circadian rhythm of BMAL1 protein content in primary, porcine single-eye RPE
Summary
The retinal pigment epithelium (RPE) is an epithelial monolayer situated beneath the neuroretina. It is in close contact and interaction with the photoreceptors and the underlying choroid [1]. The RPE has a plethora of functions in the retina, including phagocytosis of photoreceptor outer segments, recycling the visual pigment, retinal waste disposal, and constituting the outer blood retinal barrier [2]. VEGF has many protective functions in the retina [6] It protects retinal neurons and the RPE, as well as endothelial cells, and keeps up the fenestration of the endothelial cells of the choroid [3,4,10,11,12], which is important for the nutrient supply of the photoreceptors [1]. The expression of VEGF is regulated at many levels in order to uphold the appropriate amount for protection and oxygen supply [20,21,22,23]
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