Assaying the role of complement factor D on retinal pigment epithelial cell pathology in a mouse model of Stargardt disease
Date
2024
Authors
Xie, Xiaoya
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Abstract
Stargardt disease (STGD) is a macular dystrophy caused by mutations in ABCA4. ABCA4 loss-of-function leads to the accumulation of bisretinoids, known as lipofuscin, in the retinal pigment epithelial (RPE) cells in the retina. When photoxidized, lipofuscin can become toxic and cause RPE cell damage as well as activating the complement system of innate immunity. Complement factor D (CFD) is necessary for activating a branch of the complement system called the alternative pathway (AP) and is hypothesized to compromise normal RPE homeostasis which in turns promotes RPE lipofuscin accumulation and photoreceptor degeneration in Stargardt disease. This study examined the process of lipofuscin accumulation over time and how the loss of CFD affects STGD development in 6-month and 12-month Abca4-/- mice by quantifying (i) 488 nm RPE autofluorescence as a measure of the accumulation of lipofuscin in paraffin-embedded eye sections, and (ii) the immunofluorescence level of C3 (a critical protein in complement system activation) in the RPE. My results showed that the 488 nm autofluorescence level increased between 6-month and 12-month Abca4-/- mice, and between the 12-month Abca4-/- and the age-matched wildtype mice. However, the autofluorescence levels were unchanged among the 6-month experimental genotypes. The C3 immunofluorescence level in most of the 6-month experimental genotypes was unchanged. Due to the absence of the disease phenotype (i.e., elevated 488 nm autofluorescence) in the 6-month experimental samples, the role of CFD in STGD progression could not be assessed. Since the results of the autofluorescence assay on paraffin-embedded sections in this study are consistent with what has been observed by others in the Chow lab on flat-mounted RPE, cross-section tissue slides may be used as an alternative for examining the progression of STGD.