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Roxana A Radu, Zhichun Jiang, Jane Hu, Marcia Lloyd, Steven Nusinowitz, Dean Bok; Characterization of the Cfh-/-Abca4-/- mouse model. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):4655. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Accumulation of vitamin A-derived fluorophores in the retinal pigment epithelium (RPE) is a pathologic feature of recessive Stargardt disease caused by mutations in the ABCA4 gene. Previously, we showed that albino Abca4‑/‑ mice manifest significant dysregulation of the complement system, increased oxidative stress, and late-onset retinal degeneration. In the current study, we evaluated the phenotype of the pigmented Abca4-/- mice that are on a Cfh null background. These mice should provide direct information about the interplay between bisretinoid accumulation, complement activation, and inflammation of the RPE in the absence of oxidative stress.
Age-matched pigmented 129/Sv, Cfh-/-, Abca4-/-, and Abca4-/-Cfh-/- mouse strains were on the Rpe65-Leu450 background without the Rd8 mutation. Retinas and RPE-containing eyecups were collected to measure the negative complement-regulatory protein and oxidative stress levels by qRT-PCR and immunoblotting. Retinoids and bisretinoids were quantified by HPLC. Retina structure was evaluated by optical coherence tomography, fundus photography, and light microscopy. Autofluorescence was quantified by confocal microscopy and Bruch’s membrane thickness was measured by electron microscopy. Functionality of the photoreceptors was determined by electroretinogram (ERG).
Fundus photography depicted subretinal depigmentation in Abca4-/-Cfh-/- mice starting at 8 months. One-year old Abca4-/-Cfh-/- showed significant increase in the lipofuscin deposition compared to the Abca4-/- mice. Bisretinoid levels were similar between the Abca4-/-Cfh-/- and Abca4-/- mice. However, these levels were several-fold higher when compared to the 129/Sv and Cfh-/- mice. Bruch's membrane was significantly thickened in the Abca4-/-Cfh-/- mice compared to age-control groups. By ERG, the a- and b-wave amplitudes were considerably lower in the Abca4-/-Cfh-/- vs controls. These ERG findings were consistent with ~25% decrease in the 11-cis-retinaldehye levels in the Abca4-/-Cfh-/- compared to controls. Reduction in visual chromophore was paralleled by loss of photoreceptor cells by light microscopy.
Our data suggest that a combined loss of Cfh and Abca4 genes leads to age-dependent lipofuscin accumulation in the RPE, increased thickness of Bruch’s membrane, and photoreceptor loss. Longitudinal studies to assess the complement system and oxidative stress levels in this new mouse model are ongoing.
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