RPE utilizes proline for maturation, metabolic communication with retina and anti-oxidative damage

Abstract

Purpose : We previously reported that retinal pigment epithelium (RPE) prefers proline as a nutrient in primarily cultured human fetal RPE cells. The goal of this study is to investigate the role of proline in RPE maturation, metabolism and its ability to anti-oxidative stress in vitro and in vivo.

Methods : Proline utilization was analyzed in human RPE cells, mouse RPE/choroid explant, and retina explant with mass spectrometry. Proline metabolism in vivo was measured by continuously infusing ¹³C labeled proline through jugular vein for 6 hours in conscious free-moving mice. Oxidative damage in RPE cells was evaluated by ethidium homodimer (EthD) staining of dead cells and lactate dehydrogenase (LDH) activity assay. Customized proline enriched diet and regular amino acid diet was prepared by Envigo. Retinal degeneration model was made by injection with sodium iodate. Visual function was evaluated by electroretinography (ERG).

Results : Proline was consumed only in matured human RPE cells and naïve mouse RPE tissue, but not in RPE cell lines and mouse neural retina. Constantly infusion of ¹³C proline in mice significantly enhanced the flux into mitochondrial intermediates in both RPE and retina through exporting proline-dervied intermediates from RPE to retina. Proline dehydrogease (PRODH) is partially responsible for the high proline uptake. The inhibition of PRODH suppressed glucose metabolism and glutathione production in RPE. Supplementation with proline prevented oxidative damage in human fetal RPE cells through enchancing glycolysis and glutathione. Mice fed with enriched proline diet protected the damage of RPE and improved retinal function in a retinal degeneration model.

Conclusions : Matured RPE switches metabolism to use proline as nutrient substrate. RPE utilizes proline to fule mitochondrial metabolism for both RPE and retina. Utilization of proline enhances glucose metabolism and protects RPE from oxidative damage.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.