Morphometric analysis of inner retinal layer in a mouse model of Alzheimer's disease

Abstract

Reduction of retinal thickness has been reported in patients with mild cognitive impairment and Alzheimer’s disease. Recent studies reported Aβ accumulation, increase of TUNEL positive apoptotic bodies in the retinal ganglion cell layer and even delayed latency of electroretinal potential conduction in APP/PS1 mice. Detailed morphometric analysis of retinal ganglion cell number, size and inner retinal thickness may further characterize the pathological process of retinal changes. Eyes from 24-month-old transgenic mice expressing a mutant form (KM670/671NL) of human amyloid precursor protein (APP) were compared with eyes from wild-type background controls. Eyes were cut horizontally after fixation in 4% paraformaldehyde and then divided into superior and inferior eyecups. Retinal sections with intact optic nerve from the superior half were stained by hematoxylin and eosin for measurements of inner nuclear layer (INL) thickness, size and number of RGC in a masked manner. All measurements and counting were conducted by StereoInvestigator®. The inferior half of the retina was flat-mounted with the RGC facing up and then stained with cresyl violet. Each slide was coded and numbered and the subsequent RGC counting was conducted in a blinded manner. The INL thickness and number of RGC were compared using Student’s t-test (SigmaStat, Statistical significance is noted as *p<0.05). Compared with age-matched wild-type control, there were significant decrease in the mean thickness of INL and the average number of RGCs in both central and peripheral retinal sections in APPswe mice. The number of RGCs per 60 μm2 in the central and peripheral retinal regions of APPswe Tg mice were 52.60% and 41.59% less than the wild-type control, respectively. RGC counting in the flat-mount retinas confirmed the findings from the retinal sections. The APPswe mutant gene triggered quantitative neuronal loss in the inner retina (both the RGC and INL). This system can be used as an evaluation platform for drug intervention on AD progression in vivo.