Abstract
Purpose :
The retinal pigment epithelium (RPE) secretes significant quantities of apolipoprotein E (apoE), which is a prominent, potentially nucleating, component of the pathologic extracellular lipid-rich deposits, termed drusen and reticular pseudodrusen (RPD), that presage RPE stress and loss in age-related macular degeneration (AMD). ApoE has prominent roles in lipid handling, and the RPE is known to both ingest and secrete lipid as part of its normal physiology. Thus, apoE secreted from the RPE may play a critical role in the buildup of drusen and RPD in AMD. Therefore, understanding the trafficking and regulatory mechanisms of apoE in the RPE will aid in understanding drusen and RPD biogenesis. As the RPE is a polarized cell, it secretes proteins differentially to the apical and basolateral sides. We hypothesize that apoE secretion polarity is modified under stress, which explain why RPD, located apically, predominates in certain AMD eyes. Here, we aim to define the trafficking and secretion mechanisms of RPE apoE. Further, we test whether certain AMD-relevant stressors that trigger the change of polarized secretion of apoE, which would provide a direct correlation between clinical and bench-science observations.
Methods :
We apply sub-lethal AMD-related stressors such as hypoxia, age, and oxidative stress to highly differentiated primary human RPE, then assay the polarization of secreted apoE with western blot. We then use a variety of pharmacological tools to modulate the synthesis, endocytosis, and degradation processes that play a putative role in the life cycle of apoE and identify which are indeed most critical for the extracellular apoE in both normal and diseased states.
Results :
A variety of sub-lethal AMD-related stressors causes an apically shifted polarized secretion phenotype. In the case of hypoxia, which mimics conditions consistent with choroidal insufficiency in AMD, this apical shift may explain why these eyes favor the formation of RPD. We also reveal the role of degradation, synthesis, and recycling processes in determining apoE secretion polarity in normal and diseased states.
Conclusions :
Our studies provide insights into the normal and diseased regulation and trafficking of apoE in the retinal pigment epithelium, a protein implicated in the formation of drusen and RPD in AMD.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.