Memory deficiency, cerebral amyloid angiopathy, and amyloid-β plaques in APP+PS1 double transgenic rat model of Alzheimer's disease

Abstract

Transgenic rat models of Alzheimer's disease were used to examine differences in memory and brain histology. Double transgenic female rats (APP+PS1) over-expressing human amyloid precursor protein (APP) and presenilin 1 (PS1) and single transgenic rats (APP21) over-expressing human APP were compared with wild type Fischer rats (WT). The Barnes maze assessed learning and memory and showed that both APP21 and APP+PS1 rats made significantly more errors than the WT rats during the acquisition phase, signifying slower learning. Additionally, the APP+PS1 rats made significantly more errors following a retention interval, indicating impaired memory compared to both the APP21 and WT rats. Immunohistochemistry using an antibody against amyloid-β (Aβ) showed extensive and mostly diffuse Aβ plaques in the hippocampus and dense plaques that contained tau in the cortex of the brains of the APP+PS1 rats. Furthermore, the APP+PS1 rats also showed vascular changes, including cerebral amyloid angiopathy with extensive Aβ deposits in cortical and leptomeningeal blood vessel walls and venous collagenosis. In addition to the Aβ accumulation observed in arterial, venous, and capillary walls, APP+PS1 rats also displayed enlarged blood vessels and perivascular space. Overall, the brain histopathology and behavioral assessment showed that the APP+PS1 rats demonstrated behavioral characteristics and vascular changes similar to those commonly observed in patients with Alzheimer's disease.

Fig 1. Barnes maze results.

(A) Overall error and latency performance by genotype collapsed over age and training days for each phase; (B) Acquisition training errors by age; (C) Retention training errors by age; (D) Reversal training errors by age; (E) Acquisition training latency by age; (F) Retention training latency by age; (G) Reversal training latency by age. Letters indicate significant differences between groups (P<0.05).

Fig 2

Immunohistochemistry of the hippocampus and the cortex of an APP+PS1 (A), APP21 (B) and WT (C) rat using 6E10 monoclonal antibody raised against Aβ. Brown staining indicates the presence of Aβ. A. APP+PS1 rat with extensive, mostly diffuse Aβ plaques (arrow heads) under alveolus hippocampus (Alv), above CA1 pyramidal layer of hippocampus, as well as subiculum (S). In addition, several dense plaques (arrow heads) were present under the CA1 pyramidal layer and the hippocampal fissure (hif). Leptomeninges, leptomeningeal blood vessels, and cortex blood vessels stained dark brown indicate Aβ accumulation (clear arrows). APP21 and WT rats did not have Aβ deposits in their hippocampus, brain cortex, or blood vessel walls.

Fig 3. Amyloid-β plaques in the hippocampus of APP+PS1 rats.

(A) Immunohistochemistry using 6E10 antibody against Aβ showing various sizes of dense Aβ plaques (white arrow heads); (B) Adjacent brain section that was used for immunohistochemistry using an antibody against Tau showing dense Aβ plaques also contained Tau (arrow heads). Necrotic neurons that were stained dark blue were not Aβ or Tau positive (arrows); (C) The presence of Aβ plaques under the alveolus hippocampus (Alv) and hippocampal fissure (arrow heads).

Fig 4. APP+PS1 rat leptomeningeal blood vessel walls contained Aβ deposits.

Panels A, B and C show adjacent serial sections of an enlarged leptomeningeal vein and D, E and F show adjacent serial sections of a leptomeningeal artery. (A) Immunohistochemical staining for Aβ showing severe Aβ deposition in all layers of a leptomeningeal vein; (B) Trichrome staining resulted in a blue color in all layers of a vein indicating the presence of collagen related to the amyloid deposits; (C) Elastin staining showing minimal elastic fibers in veins; (D) Adventia and media of a leptomeningeal artery with strong Aβ staining and no Aβ staining of intima. (E) Trichrome staining resulted in a blue color in the adventia and media of an artery corresponding to Aβ deposits; (F) Elastin staining of a leptomeningeal artery with elastic fibers in intima (arrow).

Fig 5. Immunohistochemical staining for Aβ of leptomeninges, leptomeningeal, and cortical blood vessels.

(A) Extensive Aβ deposition in leptomeninges and leptomeningeal blood vessels and their distal branches; APP21 (B) and WT (C) rats did not have Aβ deposits in leptomeningeal or cortical blood vessels. (D, E, F and G) APP+PS1 cortex with cortical and leptomeningeal blood vessels with Aβ deposition; (E) Higher power image of cortical capillaries with Aβ deposits; (F and G) Leptomeningeal artery with Aβ deposits, dense and diffuse cortical Aβ plaques, and smaller cortical artery with Aβ positive content.

Fig 6. Vascular changes in APP+PS1 rats.

Trichrome staining of the frontal cortex from APP+PS1, APP21, and WT rats showing enlarged blood vessels and enlarged perivascular area (black arrows) in an APP+PS1 rat (A) compared with APP21 (B) and WT (C) rats. Immunohistochemistry of an adjacent section to panel A stained with Aβ (D) and tau (E) antibodies showing venous collagenous stenosis which also contains Aβ and tau (black arrow heads). Panel D shows an APP+PS1 rat with cortical Aβ plaque (white arrow head) and CAA in cortical and leptomeningeal blood vessels (clear arrows); (F) Venous collagenosis containing Aβ in the cerebellum of an APP+PS1 rat. Vascular (G), perivascular (H), and collagenous vascular (I) areas which were expressed as a percent of total frontal cortex area were greater in APP+PS1 rats. (J) APP+PS1 rats (A+P) had the largest number of necrotic neuros, followed by APP21 rats. Letters a and b indicate significant differences (P<0.05).