Abstract
Purpose :
Rod photoreceptors metabolize glucose to lactate via aerobic glycolysis to meet their metabolic needs despite abundant oxygen. Known as the Warburg effect, this phenomenon has been well studied in cancer, where lactate derived from aerobic glycolysis acts as a signaling molecule via Hydroxycarboxylic Acid Receptor 1 (HCAR1/GPR81). This receptor has been reported in the neural retina, but its expression in the RPE has not been studied. We wished to study whether GPR81 was present in the RPE.
Methods :
C57/BL/6 mice were sacrificed at P30, P60, or P200, and whole globes were fixed in 4% paraformaldehyde, embedded for cryosectioning and subject to immunohistochemistry for GPR81. RPE lysates were subject to western blotting, and GPR81 expression was normalized to β-Actin. Formalin-fixed paraffin-embedded human globes obtained at autopsy with and without histopathologic features of AMD were identified by the Ocular Pathology Division at Wilmer Eye Institute after IRB approval, stained for GPR81, and semi-quantitatively evaluated by H scoring (labeling intensity x percentage of cells with positive labeling; range: 0-300).
Results :
Immunohistochemistry for GPR81 was performed on cryosections from C57/BL/6 mice at P30, P60, and P200. RPE showed GPR81 staining at all ages, although it was more intense at P200. Western blots showed an increase of 24% in GPR81 protein (p=0.0117) from P30 to P200.Immunohistochemistry for GPR81 in sections of human donor ocular tissue again demonstrated consistent RPE labeling. Interestingly, RPE from eyes with features of AMD had significantly lower GPR81 labeling scores (p=0.0088 n = 22 non-AMD and 21 AMD eyes). Although total retina GPR81 labeling scores was not different between eyes with and without AMD, GPR81 was significantly increased in the inner retina of eyes with AMD pathology (p=0.0157).
Conclusions :
We show expression of GPR81 in RPE, and that GPR81 expression is altered in the retina and RPE of eyes with AMD pathology. This suggests that RPE may respond to lactate signals from aerobic glycolysis, and there may be a change in this signaling pathway in AMD that merits further study.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.