Abstract
Purpose :
Metabolic changes characterize aging and age-related diseases as age-related macular degeneration (AMD). RPE’s metabolic homeostasis with the retina occurs through its bidirectional filtering of metabolites and daily phagocytosis of photoreceptor outer segments. We previously discovered that orphan nuclear receptor Nur77/NUR77 decreases with age, in mouse and human RPE. Given NUR77’s role in metabolism, inflammation, and mitochondrial homeostasis, herein we investigated NUR77’s impact on metabolic functions in RPE as a function of age.
Methods :
Transient over-expression of NUR77 and its target gene expression were evaluated in primary RPE cells from young (ages15-48; n=4) and old (ages 79-93; n=4) donors using qPCR. Bioenergetic profiles of young, old, and NUR77 overexpressing RPE were generated using Seahorse metabolic assays. Expressions of glycolysis-related and mitochondrial markers were measured by RT-PCR. RPE phagocytosis was measured using pH-sensitive fluorescence assays. Phagocytosis marker genes were examined by qRT-PCR. Full body Nur77−/− mice were randomly divided into groups of 5 and 20 mon. Metabolic analyses of the RPE/choroid/sclera from 5-15 mon old Nur77−/− mice were done on Seahorse XF analyzer. Statistical methods for data analysis included two-tailed Student’s t-test, two-way ANOVA and values at p < 0.05 were considered statistically significant.
Results :
NUR77 overexpression in old RPE results in a metabolic shift towards glycolysis and increased expression of metabolic target genes including GLU4, GLU3 and APOA5. Increased phagocytosis was observed in old RPE overexpressing NUR77. Initial assessments of the ocular morphology of Nur77-/- mice aged 5 mon revealed the presence of hypopigmented regions within the posterior pole, concomitant with differential expression of markers of cellular metabolism (HK1,PKM2,NRF2), inflammation(CCL2,TNF-α) and oxidative stress (HMOX1,SOD1) in the RPE/choroid. Oxygen consumption rate (OCR) and extracellular acidification rate (ECAR) were significantly reduced in 12-mon Nur77−/− mice vs age-matched wild type as measured by Seahorse XF ATP Rate assay.
Conclusions :
Our results indicate an age-dependent role of NUR77 in balancing a metabolic switch towards glycolysis in the aged RPE. Studies are ongoing to further dissect NUR77-mediated signaling pathways in young donors and determine if NUR77 overexpression may serve as potential therapy.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.