Quantification of amyloid-beta in eye tissues of APPswe/PS1ΔE9 mice

Abstract

Purpose : Accumulations of amyloid-beta (Aβ) peptides, particularly as soluble oligomers and higher aggregates, are hallmarks of Alzheimer’s disease (AD). Aβ’s presence in eye tissues (e.g., ref. 1) raises the question of whether Aβ accumulation may promote the progression of age-related macular degeneration and/or other retina and retinal pigment epithelium (RPE) diseases. APPswe/PS1ΔE9 transgenic mice are a widely used model for AD-relevant Aβ studies of hippocampus (2). We determined the amounts of Aβ₄₀ and Aβ₄₂ (prominent Aβ forms; monomeric lengths 40- and 42-amino acids, respectively) in retina and in combined RPE/choroid of these mice. In the AD field, Aβ₄₂ is widely viewed as the more toxic Aβ form.

Methods : Neural retina and RPE/choroid were separately recovered from enucleated eyes (1,3); hippocampus was dissected from the brain. Tissues were homogenized in PBS supplemented with 5 M guanidine HCl (GuHCl), pH 7.4, and 2% (v/v) EDTA-free protease inhibitor, incubated overnight, then centrifuged. After desalting, filtrates were analyzed for Aβ₄₀ and Aβ₄₂ (ELISA) and protein (Bradford) (3). Data were obtained from duplicate samples of pooled tissues from multiple eyes; n values below represent animal numbers.

Results : We observed a wide range in comparative amounts (mean ± SEM of pmol per g protein; pmol/g) of Aβ₄₀ and Aβ₄₂ (Table). Other than for 2-month old males, levels of both Aβ₄₀ and Aβ₄₂ in both retina and RPE/choroid of the transgenic mice were considerably smaller (less than ~55%) than those in hippocampus. Additional data obtained by whole-eye analysis (combined lens, vitreous, retina, and RPE/choroid) yielded (in pmol/g): for 6-month females (n=4), Aβ₄₀ 9.63 ± 0.83 and Aβ₄₂ 4.65 ± 0.43; for 1-year males (n=2), Aβ₄₀ 10.91 ± 0.20 and Aβ₄₂ 4.28 ± 0.16.

Conclusions : The present ELISA results, together with data reported by Gupta et al. (4), encourage larger-scope investigation of Aβ₄₀/Aβ₄₂ abundances in APPswe/PS1ΔE9 retina/RPE in relation to structural and functional properties.

References: (1) Parthasarathy et al. (2015) Exper. Eye Res. 138:134-144. (2) Shen et al. (2017) PLoS One 12:e0174763. (3) Wang et al. (2017) IOVS 58:3574a. (4) Gupta et al. (2016) Neurosci. Lett. 623:52-56.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.