A non-transgenic mouse model (icv-STZ mouse) of Alzheimer's disease: similarities to and differences from the transgenic model (3xTg-AD mouse)

Abstract

Alzheimer's disease (AD) can be divided into sporadic AD (SAD) and familial AD (FAD). Most AD cases are sporadic and result from multiple etiologic factors, including environmental, genetic, and metabolic factors, whereas FAD is caused by mutations in the presenilins or amyloid-β (Aβ) precursor protein (APP) genes. A commonly used animal model for AD is the 3xTg-AD transgenic mouse model, which harbors mutated presenilin 1, APP, and tau genes and thus represents a model of FAD. There is an unmet need in the field to characterize animal models representing different AD mechanisms, so that potential drugs for SAD can be evaluated preclinically in these animal models. A mouse model generated by intracerebroventricular (icv) administration of streptozocin (STZ), the icv-STZ mouse, shows many aspects of SAD. In this study, we compared the non-cognitive and cognitive behaviors as well as biochemical and immunohistochemical alterations between the icv-STZ mouse and the 3xTg-AD mouse. We found that both mouse models showed increased exploratory activity as well as impaired learning and spatial memory. Both models also demonstrated neuroinflammation, altered synaptic proteins and insulin/IGF-1 (insulin-like growth factor-1) signaling, and increased hyperphosphorylated tau in the brain. The most prominent brain abnormality in the icv-STZ mouse was neuroinflammation, and in the 3xTg-AD mouse it was elevation of hyperphosphorylated tau. These observations demonstrate the behavioral and neuropathological similarities and differences between the icv-STZ mouse and the 3xTg-AD mouse models and will help guide future studies using these two mouse models for the development of AD drugs.

Fig. 1

Animal study design (a) and general behavioral characterization (b–f). The body weight of mice after icv injection was monitored once a week (b). Motor coordination and balance were evaluated using accelerating rotarod (c). Spontaneous locomotor and exploratory activity was assessed in an open field (d). Anxiety-like behaviors were evaluated in an elevated plus maze, and the time spent in the open arms over the total time spent in the maze (open plus close arms) is shown (e). Data are reported as mean ± SEM. *, p< 0.05 vs. control mice. ^#, p< 0.05 vs. icv-STZ mice

Fig. 2

Behavioral tests of mice using one-trial object recognition task and Morris water maze. One-trial object recognition task was carried out in an open field. Time spent exploring two identical objects during sample phase are shown as percentage of object exploring time (a). Object discrimination during test phase is presented by the discrimination index (time exploring the novel object/total time for exploring) (b). Spatial memory of the mice was tested in the Morris water maze (c–f). The average swim speed in the whole tests (c), the distances traveled to the hidden platform during training (d), the number of the platform site crossings during the probe trial (e), and the percentage of distance traveled in the target, opposite (Opp), adjacent right (AR) and adjacent left (AL) quandrants during probe trial (f) are shown. Data are reported as mean ± SEM. *, p< 0.05 vs. control mice

Fig. 3

Neuroinflammation markers in the brains of icv-STZ mice and 3xTg-AD mice. (a) Hippocampi from control, icv-STZ and 3xTg-AD mice were analyzed by Western blots developed with antibodies against GFAP, Iba1 and, as a loading control, GAPDH. (b) Densitometric quantifications (mean ± SEM) of the blots after being normalized with the GAPDH levels. *, p< 0.05 vs. control mice. ^#, p< 0.05 vs. icv-STZ mice. (c) Representative DAB staining images of frozen brain sections of the mice (magnification: 20x)

Fig. 4

Synaptic proteins in icv-STZ mice and 3xTg-AD mice. (a) Hippocampi from control, icv-STZ and 3xTg-AD mice were analyzed by Western blots developed with antibodies indicated on the left of the blots. (b) Densitometric quantifications (mean ± SEM) of the blots after being normalized with the GAPDH levels. *, p< 0.05 vs. control mice. ^#, p< 0.05 vs. icv-STZ mice. (c) Representative DAB staining images of frozen brain sections of the mice (magnification: 20x)

Fig. 5

Brain insulin signaling pathway in icv-STZ and 3xTg-AD mice. (a) Hippocampi from control, icv-STZ and 3xTg-AD mice were analyzed by Western blots developed with antibodies indicated on the left of the blots. (b,c) Densitometric quantifications (mean ± SEM) of the blots after being normalized with the GAPDH levels (b) or with the levels of the corresponding total protein (c). *, p< 0.05 vs. control mice. ^#, p< 0.05 vs. icv-STZ mice

Fig. 6

Level and phosphorylation of tau in icv-STZ mice and 3xTg-AD mice. (a) Hippocampi from control, icv-STZ and 3xTg-AD mice were analyzed by Western blots developed with antibody R134d against total tau and several phosphorylation-dependent and site-specific tau antibodies, as indicated on the left of the blots. (b,c) Densitometric quantifications (mean ± SEM) of the blots after being normalized with the total tau level (b) or with the GAPDH levels (c). *, p< 0.05 vs. control mice