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Katharine Brown Williams, Eric Pineda, Brandon Taoka, Ken Lin, Dana Nojima, Paul Carrington; LXR agonists promote lipid droplet formation in RPE cells. Invest. Ophthalmol. Vis. Sci. 2020;61(7):3114.
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Drusen, a characteristic phenotype in Age-related Macular Degeneration (AMD), are comprised of lipoprotein particles comprised of phospholipids and cholesterol esters; this content suggests that AMD retinas/retinal pigmented epithelial (RPE) cells have disrupted reverse cholesterol transport through ABCA1-cholesterol efflux. LXR agonists, that upregulate ABCA1 activity, have been proposed as therapies for retinal diseases such as AMD. Here, we characterize an LXR agonist using in vitro RPE models.
ARPE-19 cells, a spontaneously immortalized human RPE cell line, as well as primary RPE cells, were tested as in vitro models. LXR agonism on cells was shown by upregulation of target genes, including ABCA1. Cholesterol efflux was performed by the addition of 25 ug/mL of ApoA1, the acceptor apolipoprotein for ABCA1 efflux activity, and quantified using LC/MS. Lipid droplets were detected in cells using standard Bodipy 493/503 staining and microscopy.
We confirmed an increase in ABCA1 expression by more than 200-fold and cholesterol efflux activity by more than 2-fold in the presence of ApoA1. However, we observed LXR agonism also promotes lipid droplet formation in these cells. Mechanistically, this appears to be due to de novo lipogenesis and triacylglycerol synthesis, as inhibition by FASN inhibitors and DGAT inhibitors prevented lipid droplet formation by nearly 100%.
LXR activity is known to regulate various aspects of cholesterol metabolism and lipid synthesis. Here, we have shown that LXR agonism upregulates ABCA1 expression and cholesterol efflux activity as predicted. However, lipid synthesis is also upregulated, promoting lipid droplet formation. Whether LXR agonism promotes lipid droplet formation in vivo in the RPE layer is an open question, but our results suggest caution if LXR agonists were to be pursued as therapeutics for retinal disease.
This is a 2020 ARVO Annual Meeting abstract.
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