Selectively knocking down insulin receptor in rods disrupts glucose flux and leads to photoreceptor degeneration

Abstract

Purpose : The retina relies on glucose for energy so derangement of glucose metabolism is a potential cause of photoreceptor degeneration. The aim of this project was to study the effect of disrupting glucose metabolism by selectively knocking down insulin receptor (IR) in rod photoreceptors on the health of the mouse retina.

Methods : Rhodopsin (RHO)-Cre mice were crossed with IR-floxed mice (IR^fl/fl) to selectively knock down IR in rods, with RHO-Cre mice and IR^fl/fl mice serving as controls. Changes in IR expression were studied by immunohistochemistry (IHC) and western blots. Retinal glucose uptake was studied by fluorescent microscopy after oral gavage of a fluorescent glucose analogue (2-NBDG). Fluorescence-labelled peanut agglutinin (PNA) was used to study changes in cone[MOU1] photoreceptor apical processes. We also studied changes in photoreceptor-associated proteins including recoverin and rhodopsin, mitochondrial stress markers including heat-shock proteins (HSPs) and prohibitin1 (PHB1), retinal cell apoptosis and electroretinographic responses after selectively knocking down IR in rods.

Results : IHC and western blots confirmed successful knockdown of IR in the retina of RHO-Cre:IR^fl/fl mice. 2-NBDG was mainly taken up by photoreceptor inner segments in the normal retina. Knocking down IR in rods led to reduced uptake of 2-NBDG in photoreceptor inner segments, accumulation of 2-NBDG in the retinal pigment epithelium (RPE) and loss of PNA-stained photoreceptor apical processes. Knocking down IR in rods also led to reduced expression of recoverin and rhodopsin and increased expression of mitochondrial proteins, including HSP60, HSP90 and PHB1. These changes were accompanied by impaired electroretinographic responses. However, TUNEL staining found no cell apoptosis and western blots revealed no changes in expression of anti-apoptotic protein BCL-XL in the retina of RHO-Cre:IR^fl/fl mice.

Conclusions : Our data provide further evidence that glucose metabolism in rods is important for the maintenance of photoreceptor health. Selective knockdown of IR in rods disrupted glucose flux from the RPE to photoreceptors, leading to mitochondrial stress and cone photoreceptor degeneration.

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