Abstract
Purpose :
Age-related macular degeneration (AMD) is a progressive disease of the macula that at advanced stages leads to blindness in the elderly population. While the neovascular form is characterized by choroidal blood vessels invading the retina, the dry form leads to atrophy of the retinal pigment epithelium (RPE) and degeneration of photoreceptors. Genes involved in lipid metabolism, including ATP-binding cassette transporter A1 (ABCA1) were associated with AMD through genome-wide association studies. ABCA1 is strongly expressed in the RPE and required for lipid metabolism and export. AMD-associated genetic variants near the ABCA1 gene were shown to modulate its expression in patient-derived lymphoblastoid cell lines, suggesting that these variants may lead to disturbed lipid transport in the human RPE.
Methods :
Patient induced pluripotent stem cells (iPSC) harboring homozygous ABCA1 genotypes for increased (rs1883025:C and rs2740488:A) or decreased (rs1883025:T and rs2740488:C) risk for AMD were differentiated into RPE. These iPSC-RPE cells were analyzed for ABCA1 gene and protein expression, their ability to phagocytize photoreceptor outer segments (POS) and the efficiency of cholesterol efflux. Experiments were conducted under normoxic and hypoxic (4% O2) conditions to mimic the physiological conditions in the ageing eye. Furthermore, ABCA1 expression and function was also examined after Liver X receptor (LXR) agonist treatment, a regulator of cholesterol homeostasis.
Results :
iPSC-derived RPE cells showed similar gene expression and morphological characteristics of RPE cells in vivo. Interestingly, hypoxia-treated RPE cells exhibited reduced ABCA1 expression and dysregulation of several hypoxia-associated genes (e.g. PDK1 and ADM). Diminished ABCA1 expression was also observed in increased risk genotype-bearing iPSC-RPE cells treated with an LXR agonist compared to iPSC-RPE cells carrying the reduced risk ABCA1 genotype. Subsequently, the lack of ABCA1 expression hampered cholesterol efflux, leading to lipid accumulation in iPSC-RPE cells.
Conclusions :
In conclusion, this study points towards a functional effect of AMD-associated genetic variants in ABCA1 on cholesterol efflux in iPSC-RPE cells and suggests that this model system may be used to study the mechanism of altered lipid metabolism in the development of AMD.
This is a 2021 ARVO Annual Meeting abstract.