Characterization of a mouse model of metabolism in age-related macular degeneration, the Slc16a8^MAD/MAD mouse

Abstract

Purpose : The identification of the molecular or cellular defect associated with risk alleles for age-related macular degeneration (AMD) identified by genome wild association studies is a difficult task. We have selected the SLC16A8 gene since it encodes for a lactate transporter, MTC3, expressed specifically at the basal side of the retinal pigment epithelium (RPE). MCT3 is involved in the outer retina efflux of lactate produced by photoreceptors through aerobic glycolysis. We have constructed a mouse model of a rare splicing allele found in AMD patients and characterized this model of metabolism in AMD (MAD).

Methods : The human rs77968014 allele was introduced into the mouse genome by gene editing to generate the Slc16a8^MAD mouse. The expression of MCT3 was tested on RPE samples by RT-PCR, western blotting and immunohistochemistry. The concentration of lactate in the RPE and neural retina was measured using an enzymatic assay. The visual phenotype of groups of Slc16a8^MAD/MAD and controls mice was recorded by optokinetic head tracking (OKT), and by electroretinography (ERG) for scotopic, photopic and flicker analysis. Rods photoreceptors survival was quantified using optical coherence tomography (OCT). The cone density was measured using an automatic counting (e-conome). Finally, the inflammation was analyzed by anti-IBA1 immunohistochemistry and fluorescence-activated cell sorting (FACS).

Results : The MAD allele induces intron retention of the Slc16a8 mRNA that triggers the expression of a N-terminal truncated and non-functional MTC3 protein. The absence of MCT3 generates an increased concentration of lactate in the RPE (3.7-fold) and the neural retina (2.5-fold) of the Slc16a8^MAD/MAD mice. As shown by OCT, rod function is altered in these mice and their survival is decreased at six months of age. Cone function is statistically reduced as shown by OKT measurement and photopic and flicker ERG. Cone density is also reduced (1.5-fold). We observed an inflammatory response in the eye of the Slc16a8^MAD/MAD mice that could be attributed to local microglial activation.

Conclusions : Even if the genetic association of the rs77968014 with AMD is not firmly established, the Slc16a8^MAD/MAD mouse is a model of AMD that will be used to explore therapies of this age-related binding disease.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.