Abstract
Purpose :
Age-related macular degeneration (AMD) is a leading cause of irreversible vision loss in the elderly. A reduction in RPE phagocytosis of the photoreceptor outer segments (POS) has been implicated in the formation of waste deposits observed in the fundus of patients with AMD and in aging. The aim of this study was to investigate how the phagocytic function of the RPE changes with age using the mouse as a model.
Methods :
Using immunohistochemistry and super resolution microscopy, phagocytosis of POS was investigated in murine RPE whole mounts from young (3 months, n=3) and old mice (20-21 months, n=3), which were stained using ZO1 as an RPE marker, rhodopsin for engulfed POS, and cathepsin D for lysosomes. The area of RPE cells, number of nuclei and, number of phagosomes in the basal and apical RPE were quantified in central, mid-peripheral and peripheral eccentricities. Gene expression changes in the RPE phagocytosis pathways were investigated using isolated RPE/choroid from 3 (n=6) and 24 months old (n=6) mice using RNASeq.
Results :
With age, the RPE cell size in the periphery increased significantly. The number of cell nuclei decreased with eccentricity, however, there was no effect of age. The amount of rhodopsin-positive phagosomes per RPE cell area increased at all eccentricities with age and it was associated with an increase in phagosome number in the basal RPE cells but not the apical RPE. However, the proportion of phagolysosomes did not change suggesting undigested POS accumulate in the RPE with age. The expression of genes important for phagocytosis during initiation and engulfment such as MERTK and TYRO3 were significantly downregulated (FDR<0.05). Meanwhile, mRNA expression of PLXNB1 and SEMA4D that are involved in the termination of phagocytosis were upregulated significantly (FDR<0.05).
Conclusions :
Overall, the results of this study suggest a decline of phagocytotic function in the aging murine RPE. More work is required to determine whether the aging changes observed in this study exacerbate pathology in those predisposed to AMD.
This is a 2021 ARVO Annual Meeting abstract.