Abstract
Purpose :
Mechanisms leading to RPE dysfunction as seen in AMD are still unknown. Previously we identified the orphan nuclear receptor related 1 (NURR1), from a nuclear receptor atlas of human RPE cells, as a candidate receptor, which may play a role in AMD pathobiology, given its reported function as a regulator of neuroprotection and inflammation. Herein we studied the role of NURR1 in RPE cells in detail.
Methods :
Freshly isolated (n=34, ages=18-94 yrs) and primary cultures (ages=5-93 yrs) of human RPE cells were used. Levels of NURR1 and its binding partners, RXRα and LXRα, following receptor activation were measured using qPCR or western blot analysis. Receptor activity and target gene expression were determined in cells challenged with pro-inflammatory agents (TNFα, LPS and PGE2) and lipids (fatty acids and oxidized low density lipoproteins). Expression of autophagic, endothelial and mesenchymal markers were examined in cells overexpressing NURR1. NURR1 immunoreactivity in retinal sections from dry AMD donor eyes (e.g. drusen, geographic atrophy) was evaluated. In vitro experiments were performed (n>3) and significance determined (student t-test/one-way ANOVA).
Results :
NURR1 expression in human RPE cells decreased with age. When challenged with docosahexanoic acid, receptor activity increased in ‘old’ RPE cells through monomerization with NURR1 not heterodimerization with RXRα. When challenged with pro-inflammatory cytokines, NURR1 and target gene expression increased in ‘young’ RPE cells only. Overexpression of NURR1 in both ‘young’ and ‘old’ RPE cells resulted in a reversal of TNFα induced-stretched morphology to a cuboidal shape, concomitant with decreased cell migration. The acute response to inflammation was increased NURR1 and LC3-II expression. Similarly, LC3-II increased in both ‘young’ and ‘old’ RPE cells overexpressing NURR1. Finally, diffuse NURR1 immunoreactivity was observed in RPE cells overlying drusen in AMD donor tissue and in spheroids within drusen.
Conclusions :
NURR1 is important in regulating RPE cell health against inflammation-induced injury and may therefore have a protective role against AMD, modulating inflammatory responses. The contribution of RXRα and LXRα to NURR1 activity differs in aging and AMD, revealing a novel mechanism for the NURR1 signaling pathway in RPE cells.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.