Abstract
Purpose :
RPE65 is the isomerohydrolase, a key enzyme in the visual cycle. RPE65 mutations lead to a lost enzymatic activity, inherited retinal dystrophies and blindness. RPE65 knockout (Rpe65−/−) mice show a disrupted visual cycle and retinal degeneration. It has been shown previously that BALB/c or SV-129 mice carry RPE65-Leu450 variant, which possesses substantially higher RPE65 abundance and retinol isomerase activity and leads to a faster visual cycle compared to RPE65-Met450 as found in C57BL6J mice. The retina function requires high levels of ATP production. Dysregulation of retinal energy metabolism and mitochondrial dysfunction play central roles in ocular diseases. This work investigated how the visual cycle affects retinal energy metabolism.
Methods :
Age-matched male BALB/c mice, SV-129 (S129) mice, albino C57BL/6J (albino C57) mice, C57BL/6J (C57) and Rpe65−/−mice (S129 background) were housed under similar light intensities with a 12:12 light/dark cycle. Animals were euthanized on zeitgeber hour (ZT)3 to ZT4 (the 3rd-4th hours after light onset) by ketamine/xylazine overdose. Mitochondrial respiration was evaluated by oxygen consumption rates (OCR) using a Seahorse analyzer from 1-mm retinal explants with photoreceptor-side up or the INSTECH Oxygen consumption measurement system on the whole retina. The basal glycolysis level was calculated using the extracellular acidification rate (ECAR) from the Seahorse assay.
Results :
Mitochondrial respiration was significantly lower in C57 (RPE65-Met450) retinas relative to S129 and BALB/c retinas (RPE65-Leu450). However, there is no statistical difference in mitochondrial respiration between C57 and albino C57 retinas, suggesting that lower mitochondrial respiration in C57 is not due to the pigmentation. Further, decreased OCR, but not ECAR, was observed in the Rpe65−/− mice relative to the wild-type S129 mice at 1 and 3 months of age. Since Rpe65−/− mice show normal retinal OS structure and ONL thickness before 7 weeks of age, our results suggested that disrupted visual cycle from the RPE65 deficiency decreased retinal mitochondrial respiration.
Conclusions :
RPE65 Met450 variant or RPE65 deficiency decreases retinal mitochondrial respiration, suggesting that the visual cycle regulates retinal energy metabolism.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.