Abstract
Purpose :
In cultured retinal pigment epithelial (RPE) cells, iron can oxidize bisretinoids such as A2E and potentiate its toxicity. To test their synergistic toxicity in vivo, mice with high RPE iron levels (hepcidin: Hepc KO) plus high bisretinoid levels (ATP-binding cassette sub-family A member 4: Abca4 KO) were generated. Triple knockout (with retinol dehydrogenase 8 (Rdh8) KO) with even higher levels of bisretinoid were also studied.
Methods :
Male and female mice had Hepc knocked out of the liver using the lox-cre system and were crossed with Abca4 and Rdh8 KO mice. In vivo images of the retina were taken every month using a confocal scanning laser ophthalmoscope (cSLO) and optical coherence tomography (OCT) system. Once the mice were eleven months old, they were euthanized and further analyses were done on the retina using histology and electron microscopy. Serum and liver iron levels were also tested in the Hepc KO mice.
Results :
Knocking out Hepc in the liver caused an increase in systemic iron by 11 months of age. Mice that had only Hepc knocked out showed an increase in retinal blue autofluorescence (488 nm) in the superior and peripapillary RPE beginning at 5 months, progressing further until almost all of the retina was highly autofluorescent by 11 months. Hepc/Rdh8 DKO mice showed phenotypes similar to Hepc single-knockout mice. Mice that had both Hepc and Abca4 knocked out developed hypoautofluorescent spots on infrared autofluorescent (790 nm) imaging that were not observed in either of the single knockouts. Light microscopy showed depigmented RPE cells. TKO mice that had Hepc, Abca4, and Rdh8 knocked out had more severe retinal damage than any single or double knockout.
Conclusions :
High iron plus high bisretinoid levels cause RPE depigmentation. This work supports the concept that iron and bisretinoids such as A2E can potentiate each other’s toxicity. Mice with even higher levels of bisretinoid had more severe degeneration. These studies suggest that recessive Stargardts disease (STGD1) can be exacerbated by iron.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.