GLUT1 is Required for the Anabolic Metabolism of Photoreceptor Cells

Abstract

Purpose : Glucose supports catabolic and anabolic metabolism in the neural retina. It is transported into the retina by the outer (RPE) and inner blood-retinal barrier (BRB) via the glucose transporters GLUT1, encoded by Slc2a1. GLUT1 is highly expressed by Muller glia and photoreceptor cells in the outer retina, while the neurons express GLUT3 in the inner retina. To understand how glucose supports the metabolism and function of the retina, we generated and characterized mouse models with the deletion of the glucose transporter GLUT1 in the neural retina and photoreceptors.

Methods : Mice carrying floxed alleles for Slc2a1 (The Jackson Laboratory, #031871) were crossed with transgenic mice expressing Cre recombinase in the retina (129.B6C3-Tg(Crx-cre)1Tfur), rods Pde6gCre-ERT2 (Tsang lab) and cones (Tg(Opn1mw-cre)1Asw) to generate RetinaΔGlut1, RodΔGlut1, ConeΔGlut1 and GLUT1^Flox/Flox (control). Structure and function were assessed by optical coherence tomography (OCT), confocal scanning laser ophthalmoscopy (cSLO) and electroretinograms (ERGs). Immunofluorescence (IF), in-situ hybridization, qPCR, and GC/MS were used to determine changes in the retinas.

Results : In-situ hybridization, IF, and western blot were done to confirm the deletion of GLUT1 in the neural retinas. RetinaΔGlut1 mice showed loss of GLUT1 as early as P3, but exhibited normal retinal lamination at 1 month of age. We found that Slc2a1 and Slc2a3 are the highest expressed glucose transporters in the neural retina. In-situ hybridization of Slc2a1 showed expression in both inner and outer retinal layers, but Slc2a3 was only seen in the inner retinal layers. Scotopic ERGs from RetinaΔGlut1 and RodΔGlut1 were reduced. Photopic ERGs were reduced in RetinaΔGlut1, but not in ConeΔGlut1. OCT scans of RetinaΔGlut1 and RodΔGlut1 only showed ONL thinning and OS shortening. TUNEL positive cells were detected only in the ONL. There were no changes in cone density in RetinaΔGlut1 and ConeΔGlut1. Rhodopsin transcript and protein were severely reduced when normalized to OS length and ONL thickness, consistent with nutrient deprivation. Metabolic measurements confirmed decreased aerobic glycolysis.

Conclusions : GLUT1 expression in the neural retina is required for visual function and the viability of rods, but not cone photoreceptors. Glucose uptake via GLUT1 is necessary for OS renewal. Genetic deletion of GLUT1 does not cause cell death in the inner retina.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.