Loss of GLUT1 in the retinal pigment epithelium does not diminish its function, differentiation or polarity.

Abstract

Purpose : The retina is one of the most metabolically active tissues in the body and normal visual function is dependent on a continuous supply of glucose and oxygen. Glucose is transported from the choroid blood supply to the outer retina by GLUT1 transporters expressed in the basolateral and apical membranes of the RPE. In this study, we assessed the impact of conditional deletion of GLUT1 in mouse RPE on the integrity of the outer blood retinal barrier and visual function.

Methods : GLUT1 was conditionally inactivated in the RPE by crossing Glut1^Flox/Flox mice with the VMD-2-cre mouse to create the Tg-VMD-2-cre:Glut1^Flox/Flox conditional knockout mouse. The expression of GLUT1 and retinal structure in GLUT1^Flox/Flox, Tg-VMD-2-cre and Tg-VMD-2-cre:Glut1^Flox/Flox mice were compared by optical coherence tomography (OCT), immunohistochemistry and western blot. Retinal and RPE function was assessed by dark-adapted and light-adapted strobe flash electroretinography as well as by direct current-coupled electroretinography.

Results : The expression of GLUT1 in Tg-VMD-2-cre:Glut1^Flox/Flox mice was found to be patchy with GLUT1 positive cells adjacent to GLUT1 negative cells. The GLUT1 negative RPE did not exhibit changes in expression and polarity of RPE specific genes. No changes in the thickness of the outer nuclear layer were detected and the density of cones did not differ between retinal areas overlying GLUT1 positive or GLUT1 negative RPE cells. No significant differences were found in the dark-adapted strobe flash electroretinogram (ERG), light adapted ERG or direct current-coupled ERG of mice lacking GLUT1 in the RPE.

Conclusions : The reduction of GLUT1 expression in the RPE of the Tg-VMD-2-cre:Glut1^Flox/Flox mice did not cause changes in visual activity. This suggests that the mosaic pattern of the Cre expression allows sufficient glucose to be transported into the retina to support photoreceptor cell function. The integrity of the barrier properties of the RPE supports the hypothesis that they oxidize lactate and fatty acids, sparing glucose for the outer retina.

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