Abstract
Purpose :
The eyecup consists of retinal pigment epithelium (RPE), choroid, and sclera. RPE metabolism is assumed to be dominant in eyecup preparations, but this has yet to be proven rigorously. In this study we probe the contribution of retinal pigment epithelial cells to eyecup metabolism. We approach this question by determining metabolic flux in eyecup tissue from control and mice injected with the selective RPE cell toxin sodium iodate (NaIO3).
Methods :
We injected C57BL/6J mice with a single intraperitoneal dose of saline or 50 mg/kg NaIO3. Seven days later we sacrificed mice via cervical dislocation and dissected eyecup tissue into Krebs-ringer bicarbonate buffer supplemented with either labeled or unlabeled 5 mM glucose. We quantified extracellular flux of glucose and lactate using spectrophotometric assays and intracellular flux of 1,2-13C2-glucose using gas chromatography-mass spectrometry. We compared glucose flux in saline-injected control eyecups to eyecups from NaIO3-injected mice.
Results :
NaIO3 treated eyecups released 42% less lactate from media than controls (p<0.05), despite negligible glucose consumption. Surprisingly most glycolytic and TCA cycle metabolite levels were unchanged by NaIO3 injection. NaIO3 treatment did however significantly decrease levels of lactate and the TCA cycle metabolites malate and fumarate. 13C flux from 1,2-13C2-glucose to lactate and malate was also decreased by NaIO3 treatment.
Conclusions :
Our results suggest that glycolytic flux and lactate export in the eyecup is partly due to retinal pigment epithelium metabolism. However, metabolite levels and flux were partly maintained, implying that RPE metabolism may not be dominant in the eyecup. The remaining glucose metabolism could be due to contributions from endothelial cells, or microglial cells recruited to the eyecup after NaIO3 treatment. Further analysis is required to fully understand the role of RPE metabolism in the eyecup.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.