APOE Impacts Lipid Trafficking in Retinal Pigment Epithelium Cells

Age-related macular degeneration (AMD) is typified by the formation of lipid-rich drusen under the retinal pigment epithelium (RPE) layer. Apolipoprotein E (APOE) is a known genetic risk factor for AMD and a substantial component of drusen, however, the mechanism by which APOE variants contribute to AMD pathology remains unclear. APOE is the primary cholesterol and lipid transport protein of the central nervous system, as well as a component circulating lipoproteins. To better understand how APOE-dependent lipid transport may impact AMD risk, we generated isogenic APOE iPS-RPE cells expressing each of the common human APOE isoforms, as well as an APOE knockout line. APOE knockout cells showed significant morphological and barrier function deficits, suggesting that APOE is essential for RPE health. Furthermore, we observed that APOE abundance is isoform-dependent in RPE cells and that lipid transport is deficient in APOE knockout RPE cells, as well as in RPE cells expressing APOE2, a variant associated with higher risk of AMD. Contrastingly, cells expressing APOE4 seem to respond strongly to lipid challenges by upregulating APOE to support efficient lipid transport. Our results suggest that disease associated APOE variants may impact lipid transport in RPE, contributing to the formation of drusen and impairing cellular function.