Retinal Vascular Physiology Biomarkers in a 5XFAD Mouse Model of Alzheimer's Disease

Abstract

Background: Alzheimer's disease (AD) is a neurodegenerative disorder that affects the brain and retina and lacks reliable biomarkers for early diagnosis. As amyloid beta (Aβ) manifestations emerge prior to clinical symptoms and plaques of amyloid may cause vascular damage, identification of retinal vascular biomarkers may improve knowledge of AD pathophysiology and potentially serve as therapeutic targets. The purpose of the current study was to test the hypothesis that retinal hemodynamic and oxygen metrics are altered in 5XFAD mice.

Methods: Thirty-two male mice were evaluated at 3 months of age: sixteen 5XFAD transgenic and sixteen wild-type mice. Spectral-domain optical coherence tomography, vascular oxygen tension, and blood flow imaging were performed in one eye of each mouse. After imaging, the imaged and fellow retinal tissues were submitted for histological sectioning and amyloid protein analysis, respectively. Protein analysis was also performed on the brain tissues.

Results: Retinal physiological changes in venous diameter and blood velocity, arterial and venous oxygen contents, coupled with anatomical alterations in the thickness of retinal cell layers were detected in 5XFAD mice. Moreover, an increase in Aβ42 levels in both the retina and brain tissues was observed in 5XFAD mice. Significant changes in retinal oxygen delivery, metabolism, or extraction fraction were not detected. Based on compiled data from both groups, arterial oxygen content was inversely related to venous blood velocity and nerve fiber/ganglion cell layer thickness.

Conclusions: Concurrent alterations in retinal hemodynamic and oxygen metrics, thickness, and tissue Aβ42 protein levels in 5XFAD mice at 3 months of age corresponded to previously reported findings in human AD. Overall, these results suggest that this mouse model can be utilized for studying pathophysiology of AD and evaluating potential therapies.

Keywords: 5XFAD; Alzheimer’s disease; amyloid β; retinal vascular physiology biomarkers.

Figure 1

Outline for study design. Diagram showing imaging protocol, tissue collection, and protein analysis for wild-type (WT) and five-familial Alzheimer’s disease (5XFAD) groups.

Figure 2

Retinal vessel diameter, venous blood velocity, and total retinal blood flow (TRBF) in wild-type (WT) and five-familial Alzheimer’s disease (5XFAD) mice. (A) Retinal arterial diameter, (B) venous diameter, (C) venous velocity, and (D) TRBF in WT and 5XFAD groups. The data are presented as mean ± SD. * p < 0.05.

Figure 3

Vascular oxygen contents in wild-type (WT) and five-familial Alzheimer’s disease (5XFAD) mice. (A) Retinal arterial oxygen content (O_2A), (B) venous oxygen content (O_2V), and (C) arteriovenous oxygen content difference (O_2AV) in WT and 5XFAD groups. The data are presented as mean ± SD. * p < 0.05.

Figure 4

Measurements of total and retinal layer thickness in wild-type (WT) and five-familial Alzheimer’s disease (5XFAD) mice. (A) Region of imaging and representative optical coherence tomography image of the retina. (B) Total retinal thickness measured by spectral domain optical coherence tomography. (C) Representative retinal layer thicknesses measured from histological sections. (D) Thickness measurements of nerve fiber layer/retinal ganglion cell (NFL/RGCL), inner plexiform layer (IPL), inner nuclear layer (INL), outer plexiform layer (OPL), outer nuclear layer (ONL), and photoreceptor layer (PRL). The data are presented as mean ± SD. * p < 0.05.

Figure 5

Amyloid-beta (Aβ) protein levels in retinas and brains of wild-type (WT) and five-familial Alzheimer’s disease (5XFAD) mice. Aβ42 levels in the (A) retina and (B) brain. Aβ40 levels in the (C) retina and (D) brain. The data are presented as mean ± SD. * p < 0.05.

Figure 6

(A) Representative H&E-stained transverse retinal section and yellow arrow highlighting area of interest. Amyloid angiopathy is presented in transverse retinal sections of wild-type (WT) and five-familial Alzheimer’s disease (5XFAD) mice (B). Amyloid-beta 42 (Aβ42) is presented in red, endothelial cells in green, and nuclei in blue. Scale bar, 20 μm.

Figure 7

Based on compiled data from wild-type (WT) and five-familial Alzheimer’s disease (5XFAD) mice: (A) relationship between venous velocity (V_V) and arterial oxygen content (O_2A). (B) and (C) The relationships of nerve fiber layer/retinal ganglion cell (NFL/RGCL) thickness to O_2A and venous oxygen content (O_2V), respectively.