Figure 1

Diagram of key metabolic pathways (glycolysis, aerobic glycolysis, penthose phosphate pathway (PPP), and Kennedy pathway (KP)), transporters (GLUT1, MCT1), enzymes (lactate dehydrogenase B (LDHB)), and feedback metabolite flow between the RPE and the rods considered in our model. The metabolic pathway blocks represent several enzymatic reactions, and each reaction uses a specific metabolite as substrate to produce another metabolite. The RPE transports glucose from the choroid into the photoreceptors and keeps only a small portion to be converted into pyruvate through glycolysis. The transport is enabled by GLUT1. Once in the photoreceptors, glucose enters the glycolysis pathway from which intermediate metabolites are directed to the PPP and KP. Pyruvate, the end product of glycolysis, is reduced into lactate by aerobic glycolysis in the rods. Lactate is cleared from the rods, and transported to the interphotoreceptor matrix by MCT1, which also transports it into the RPE. Inside the RPE, lactate is converted to pyruvate by LDHB to be oxidized and processed by the tricarboxylic acid cycle, also known as the Krebs cycle.