-Amyloid Deposition and Functional Impairment in the Retina of the APPswe/PS1E9 Transgenic Mouse Model of Alzheimer’s Disease Sylvia E. Perez, 1 Stephen Lumayag, 1,2 Beatrix Kovacs, 1,2 Elliott J. Mufson,* ,1 and Shunbin Xu* ,1,2 PURPOSE. To determine whether -amyloid (A) deposition affects the structure and function of the retina of the APPswe/ PS1E9 transgenic (tg) mouse model of Alzheimer’s disease. METHODS. Retinas from 12- to 19-month old APPswe/PS1E9 tg and age-matched non-transgenic (ntg) littermates were single or double stained with thioflavine-S and antibodies against A, glial fibrilar acidic protein (GFAP), microglial marker F4/80, choline acetyltransferase (ChAT), and syntaxin 1. Quantifica- tion of thioflavine-S positive plaques and retinal layer thickness was analyzed semi-quantitatively, whereas microglial cell size and levels of F4/80 immunoreactivity were evaluated using a densitometry program. Scotopic electroretinogram (ERG) re- cording was used to investigate retinal physiology in these mice. RESULTS. Thioflavine-S positive plaques appeared at 12 months in the retinas of APPswe/PS1E9 tg mice with the majority of plaques in the outer and inner plexiform layers. Plaques were embedded in the inner plexiform layer strata displaying syn- taxin 1 and ChAT. The number and size of the plaques in the retina increased with age. Plaques appeared earlier and in greater numbers in females than in male tg littermate mice. Microglial activity was significantly increased in the retinas of APPswe/PS1E9 tg mice. Although we did not detect neuronal degeneration in the retina, ERG recordings revealed a signifi- cant reduction in the amplitudes of a- and b-waves in aged APPswe/PS1E9 tg compared to ntg littermates. CONCLUSIONS. The present findings suggest that A deposition disrupts retinal structure and may contribute to the visual deficits seen in aged APPswe/PS1E9 tg mice. Whether A is involved in other forms of age-related retinal dysfunction is unclear. (Invest Ophthalmol Vis Sci. 2009;50:793– 800) DOI: 10.1167/iovs.08-2384 A lzheimer’s disease (AD) is a progressive neurodegenerative disorder characterized by loss of memory and cognitive decline, and is neuropathologically associated with an increase in -amyloid (A) plaque deposition, neurofibrillary tangle for- mation (NFT), neuronal loss, and inflammation. 1–3 A peptides (4 kDa), which are the predominant component of plaques, are the result of sequential cleavage of an integral membrane protein, the amyloid precursor protein (APP), via a Bace1 and -secretase complex. 4 Presenilins 1 and 2 (PS1 and PS2) play a central role in -secretase–mediated cleavage of APP. 4,5 Muta- tions in the genes encoding APP, PS1, or PS2 lead to increased production of highly fibrillogenic and pathogenic 42-amino- acid A peptides (A 1– 42 ) causing familial forms of AD (FAD). 4,5 Although these A peptides are thought to be neu- rotoxic, 4,6 the structural and functional consequences of the over-expression of these proteins in vivo remains an active area of research in both the central and peripheral nervous system. In addition to cognitive impairment, people with AD often develop visual anomalies in color discrimination, stereoacuity, contrast sensitivity, and backward masking. 7–10 These visual abnormalities have been attributed, in part, to AD pathology in central visual pathways. 9,11–13 Additionally, retinal dysfunc- tion, such as ganglion cell loss, 14,15 reduction in the thickness of the retinal nerve fiber layer, 16 –19 and optic nerve degener- ation 20 occur in AD. Although A deposition is found in the lens fiber cells in AD and trisomy 21 patients, 21,22 the patho- logic hallmarks of the AD brain (i.e., A plaques or NFTs) have not been observed in AD retinas. 16 In the past several years, transgenic mouse models have been engineered to mimic different aspects of AD neurodegen- eration. 23–26 Most transgenic mice were made to over-express mutant forms of APP and/or PS1 and display an age-dependent onset of brain A deposition, synaptic dysfunction, gliosis, and memory deficits. 26 In particular, APPswe/PS1E9 transgenic (tg) mice, co-expressing the genes for PS1E9 and human APP with mutations (K595N, M596L) linked to Swedish FAD pedi- grees (APPswe) display an earlier and more aggressive onset of neuritic A deposition in the brain, 27–31 as well as motor and memory deficits. 31,32 These findings indicate that elevated lev- els of A peptides are associated with dysfunctional neuronal networks, making APPswe/PS1E9 transgenic mice an ideal model to investigate the pathogenic role(s) that A has on the structure and functions of the nervous system. Therefore, to test whether A deposition alters the physiology of the retina, a neuroectodermal derivative of the forebrain, we examined the eye of middle to aged APPswe/PS1E9 transgenic mice. Here we report, for the first time, age-dependent A plaques, gliosis, and functional deficits in the retina of APPswe/PS1E9 tg mice. These results suggest that A deposition within the retina can contribute to retinal dysfunction and should be further examined in AD. MATERIALS AND METHODS Transgenic Mice We used a total of 31 animals, consisting of 14 middle-aged (12–16 months; 8 male and 9 female) and 2 old (19 –21 months; female) heterozygous tg mice harboring FAD-linked mutant APPswe/ From the Departments of 1 Neurological Sciences and 2 Ophthal- mology, Rush University Medical Center, Chicago, Illinois. Supported by National Institute on Aging Grant AG10668 (EJM), the Shapiro Foundation (EJM), the Lincy Foundation (SX), and the Cornell Foundation (SX). Submitted for publication June 4, 2008; revised August 1 and 27, 2008; accepted October 31, 2008. Disclosure: S.E. Perez, None; S. Lumayag, None; B. Kovacs, None; E.J. Mufson, None; S. Xu, None The publication costs of this article were defrayed in part by page charge payment. This article must therefore be marked “advertise- ment” in accordance with 18 U.S.C. §1734 solely to indicate this fact. *Each of the following is a corresponding author: Shunbin Xu, 1735 W. Harrison St, Chicago, IL 60612; shunbin_xu@rush.edu. Elliott J. Mufson, 1735 W. Harrison St, Chicago, IL 60612; emufson@rush.edu. Investigative Ophthalmology & Visual Science, February 2009, Vol. 50, No. 2 Copyright © Association for Research in Vision and Ophthalmology 793