Morphometric Analysis of Retinal Pigment Epithelial Cells From C57BL/6J Mice During Aging

Abstract

Purpose To quantitatively evaluate the changes in orientation and morphometric features of mouse retinal pigment epithelial (RPE) cells in different regions of the eye during aging. Methods We segmented individual RPE cells from whole RPE flatmount images of C57BL/6J mice (postnatal days 30 to 720) using a machine-learning method and evaluated changes in morphometric features, including our newly developed metric combining alignment and shape of RPE cells during aging. Results Mainly, the anterior part of the RPE sheet grows during aging, while the posterior part remains constant. Changes in size and shape of the peripheral RPE cells are prominent with aging as cells become larger, elongated, and concave. Conversely, the central RPE cells maintain relatively constant size and numbers with aging. Cell count in the central area and the overall cell count (approximately 50,000) were relatively constant over different age groups. RPE cells also present a specific orientation concordance that matches the shape of the specific region of the eyeball. Those cells near the optic disc or equator have a circumferential orientation to cover the round shape of the eyeball, whereas those cells in the periphery have a radial orientation and corresponding radial elongation, the extent of which increases with aging and matches with axial elongation of the eyeball. Conclusions These results suggest that the fluid RPE morphology reflects various growth rates of underlying eyeball, and RPE cells could be classified into four regional classes (near the optic disc, central, equatorial, and peripheral) according to their morphometric features.

An inducible Cre mouse for studying roles of the RPE in retinal physiology and disease

“…The total surface area of the adult mouse retina was estimated to be approximately 17.8 mm 2 , which is consistent with prior literature values ( 71 ). Therefore, we calculated that there are approximately 52,000 RPE cells per mouse retina, consistent with prior estimates ( 72 , 73 ). To avoid counting cells in the far periphery that had been damaged by removal of the anterior segment, only the inner 17 mm 2 of the retina was used for analysis of recombination efficiency and tamoxifen-independent Cre activity.…”

Single-cell–resolution map of human retinal pigment epithelium helps discover subpopulations with differential disease sensitivity

“…Another potential explanation for the presence of P4 could be that the geometry of the eyeball requires RPE cells to be small around the equator of the eye. In mice, RPE cells at the equator appear to be different from neighboring cells—oriented circumferentially instead of radially ( 53 ). Another possibility is that P4 consists of a pool of RPE cells that retain the capacity to enter cell cycle to replenish dying RPE cells.…”

Impact of cell size on morphogen gradient precision

“…MACAs in the postnatal (P1-P21) cochlea are 15-55 µm 2 (Etournay et al;2010). In adult mouse retinal pigment epithelial (mRPE) cells, the MACAs exceed 200 µm 2 in young mice (P30) and increase to > 400 µm 2 in old mice (P720) (Kim et al;2021). In the Drosophila embryo AP (dEAP), the MACA is ≈ 46 µm 2 and in the embryo trunk (dET) ≈ 35 µm 2 ; no GBP was reported (Rupprecht et al;.…”