Abstract
Purpose :
During geographic atrophy (GA), the cause of the expansion of retinal pigment epithelium (RPE) atrophy is poorly known. We have previously documented the subretinal location and changes over time of pigmented (melanocytic) mottling termed “thickened RPE” (tRPE), a new feature observed in margins of atrophy. Here we characterized by histology the phenotype of RPE cells within and around tRPEs.
Methods :
Donor eyes from healthy (n=5) and GA patients (n=9) were examined. To identify tRPEs spots, reflectance and autofluorescence infrared scanning laser ophthalmoscopy were performed using the Heidelberg SLO on the sample. Nomarski optics enabled to document the redistribution of melanin. On flatmounts of RPE, confocal and spinning disk fluorescence microscopy were performed after phalloidin and anti-RPE65 immunolabelling. RPE cells were segmented and analyzed using an custom software.
Results :
GA areas varied from 0.97 to 10.72 mm2. tRPE spots were identified in all eyes by their hyper NIRAF; they matched hyperpigmented spots seen by Nomarski optics. A variety of RPE phenotypes were identified, yet they always had a polygonal shape of RPE cells; the degree of pigmentation was highly cariable, with hyperîgmented cells adjacent to RPE cells devoid of melanin. tRPE consisted of large, polygonal, thickened, monolayered hyperpigmented RPE65+ cells. Patches of double layered RPE were occasionally seen in which both layers maintained an epithelial phenotype. A mean of 38256 cells were analyzed per sample (range 10159-99466). RPE cells from GA were significantly larger than in controls (p<0.0001), mainly due to a subpopulation of enlarged cells rather than to generalized increase in size. Cell shape varied from regular hexagons to elongated polygons, in particular along margins.The largest RPE cells were observed within tRPE. Actin stress fibers were more common in elongated RPE cells close to the margins.
Conclusions :
In GA eyes, shape, pigmentation and size of RPE cells varied considerably yet RPE65 expression and polygonal epithelial phenotype were preserved. Such changes were seen throughout samples. Our findings suggests that the expression of stress fibers accompanies enlargment of atrophy. As time-lapse imaging showed that tRPE propagate in synchrony with expansion of atrophyt, these findings may be of interest to better understand the process of GA enlargment.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.