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Timothy William Corson, Sheik Pran Babu Sardar Pasha, Trupti Shetty, Deepa Mathew, Kamakshi Sishtla, Neeta Patwari, Nathan A Lambert-Cheatham, Ashay D Bhatwadekar; Retinal phenotyping of ferrochelatase mutant mice. Invest. Ophthalmol. Vis. Sci. 2020;61(7):5129.
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© ARVO (1962-2015); The Authors (2016-present)
Ferrochelatase, the terminal enzyme in heme biosynthesis, plays an important role in angiogenesis. It is upregulated in retinal and choroidal neovascularization in mice and humans, and chemical inhibition of ferrochelatase blocks neovascularization in vitro and in vivo. The Fechm1Pas mouse has a partial loss-of-function point mutation in the Fech gene and shows reduced retinal and choroidal neovascularization in disease models. These mice also have a systemic protoporphyria due to buildup of the ferrochelatase substrate, protoporphyrin IX (PPIX). The retinal phenotype of these mice under normal conditions has not previously been investigated in detail. Thus, the purpose of this study was to comprehensively phenotype the retinas of Fechm1Pas mice.
The eyes of juvenile (2-week-old) and adult (8-week-old) Fechm1Pas homozygotes and heterozygotes and their wild-type littermates on a C57BL/6 background were assessed by funduscopy, fluorescein angiography (FA), PPIX fluorescence (excitation = 403 nm, emission = 628 nm), and optical coherence tomography (OCT). Visual function was evaluated by electroretinogram (ERG) and optomotor response (OMR). Ex vivo, isolectin B4 staining of retinal wholemounts, plus VEGF-induced choroidal and retinal sprouting assays were performed.
Adult Fechm1Pas mice had normal fundi, venous width, arterial tortuosity, and retinal structure in vivo, without vascular leakage. However, endogenous PPIX buildup was strongly detected in homozygotes’ retinas, notably in the blood vessels, even in pups. Intriguingly, both retinal and choroidal sprouting ex vivo assays revealed a decrease in sprouting in the mutants, with homozygotes having a more pronounced reduction than heterozygotes. ERG parameters and OMR did not differ significantly between the three genotypes.
Despite a pronounced buildup of retinal PPIX, Fechm1Pas mutant retinal structure and function are largely normal. Importantly, stimulus-induced, ex vivo angiogenesis in choroidal and retinal sprouting assays was reduced in the mutants, consistent with the blunted pathological angiogenesis previously observed in these animals in vivo. Thus, the Fechm1Pas mouse provides a useful model to dissect the inhibition of neovascularization associated with ferrochelatase blockade.
This is a 2020 ARVO Annual Meeting abstract.
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