Sex and Age-Related Changes in RPE Morphology and Function in Mice

Abstract

Purpose : While age is the major risk factor for developing AMD, age-matched comparisons found that women have a higher risk of developing wet AMD indicating an additional life-span-independent, sex-dependent risk factor. The primary cellular target of AMD is retinal pigment epithelial cells (RPE), which are post-mitotic and, as they age, undergo a slow degeneration leading to a loss of function. We hypothesize the increased susceptibility of women to AMD is caused, in part, by an age-related RPE degeneration that is more prominent and progresses faster in females than in males.

Methods : Functional and morphological analyses were performed on young (2-4 months) and aged (16-36 months) female (f) and male (m) C57BL/6 mice. Visual function was assessed by ERG a, b, and c- waves and optomotor reflex (OMR), which measured visual acuity and contrast sensitivity. Morphological analyses were performed by immunohistochemical staining of f-actin on RPE/choroid flat mounts. RPE cell density, cell area, and the number and size of RPE lesions (area with amorphic and enlarged cells) were quantified. P2ry12 immunostaining was used to monitor microglia recruitment to the subretinal space.

Results :
As expected, visual function was significantly reduced in aged mice as compared to young mice. However, aging female mice (18 months) displayed a significant decrease in contrast sensitivity vs age-matched males (mean % contrast 25.4 (f) vs 18.2 (m) at 0.267 cycl/deg, p=0.0001). This loss in vision coincided with a functional decline in RPE as shown by a significant reduction in the ERG c-wave (mean amplitudes [µV] 192 (f) vs 229.3 (m) at 24.1 cd.s/m², p=0.0001), while the a- and b-waves were not different. Highly geriatric mice (24-36 months) showed gross PRE morphological anomalies characterized by areas with amorphic and enlarged cells, which were significantly more frequent in females, 77% of RPE/choroid flat mounts (n=10 of 13) with at least 1 or more areas of aberrant RPE, as compared to males with < 10% (n=1 of 15). Interestingly, the loss of RPE morphology and function in female mice coincided with an increased recruitment of microglia to the subretinal space.

Conclusions : We conclude the age-dependent decline in visual function in mice is sex dysmorphic with females showing an accelerated loss of function that coincides with a decline of RPE. Implying RPE dysfunction may account for the AMD sex-dependent risk factor in women.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.