A Novel hAPP/htau Mouse Model of Alzheimer's Disease: Inclusion of APP With Tau Exacerbates Behavioral Deficits and Zinc Administration Heightens Tangle Pathology

Abstract

The brains of those with Alzheimer's disease have amyloid and tau pathology; thus, mice modeling AD should have both markers. In this study, we characterize offspring from the cross of the J20 (hAPP) and rTg4510 (htau) strains (referred to as dual Tg). Behavior was assessed at both 3.5 and 7 months, and biochemical differences were assessed at 8 months. Additionally, mice were placed on zinc (Zn) water or standard lab water in order to determine the role of this essential biometal. Behavioral measures examined cognition, emotion, and aspects of daily living. Transgenic mice (dual Tg and htau) showed significant deficits in spatial memory in the Barnes Maze at both 3.5 and 7 months compared to controls. At 7 months, dual Tg mice performed significantly worse than htau mice (p < 0.01). Open field and elevated zero maze (EZM) data indicated that dual Tg and htau mice displayed behavioral disinhibition compared to control mice at both 3.5 and 7 months (p < 0.001). Transgenic mice showed significant deficits in activities of daily living, including burrowing and nesting, at both 3.5 and 7 months compared to control mice (p < 0.01). Dual Tg mice built very poor nests, indicating that non-cognitive tasks are also impacted by AD. Overall, dual Tg mice demonstrated behavioral deficits earlier than those shown by the htau mice. In the brain, dual Tg mice had significantly less free Zn compared to control mice in both the dentate gyrus and the CA3 of the hippocampus (p < 0.01). Dual Tg mice had increased tangles and plaques in the hippocampus compared to htau mice and the dual Tg mice given Zn water displayed increased tangle pathology in the hippocampus compared to htau mice on Zn water (p < 0.05). The dual Tg mouse described here displays pathology reminiscent of the human AD condition and is impaired early on in both cognitive and non-cognitive behaviors. This new mouse model allows researchers to assess how both amyloid and tau in combination impact behavior and brain pathology.

Keywords: Barnes Maze; Zinc; activities of daily living; amyloid; behavior; mouse models; tau.

Figure 1

Open field percent time spent in the center. Dual Tg and htau mice spent significantly less time in the center of the OF than control mice at both time points (p < 0.001). With increased age, tau (p < 0.01), tTA (p = 0.01), and WT mice (p = 0.001) spent less time in the center of the OF. Bars represent mean ± SEM (***p < 0.001).

Figure 2

(A) Elevated zero maze percent time in the open arms. Dual Tg and htau mice spent significantly more time in the open arms than control animals (p < 0.001). With increased age, dual Tg and htau mice spent significantly more time in the open arms of the EZM (p < 0.001). Bars represent mean ± SEM (***p < 0.001). (B) EZM head dips. Dual Tg and htau mice made significantly more head dips in the EZM at 7 months than at 3.5 months (p < 0.001). At both ages, dual Tg and htau mice made significantly more head dips than control mice did. Bars represent mean ± SEM (*p < 0.05, ***p < 0.001).

Figure 3

(A) Latency to find the escape hole (3.5 months). At 3.5 months, WT mice found the escape hole significantly faster than dual Tg and htau mice (p < 0.001) and tTA mice (p < 0.01). Bars represent mean ± SEM. (B) Latency to find the escape hole (7 months). At 7 months, dual Tg mice took longer to find the escape hole than control (p < 0.001) and tau mice (p = 0.004). Tau mice took longer to find the escape hole than WT mice (p < 0.001), and tTA mice (p < 0.05). Bars represent mean ± SEM.

Figure 4

Barnes maze 24-h probe trial. Dual Tg mice spent less time in the target quadrant on the 7th day probe trial than control mice (p < 0.01) and htau mice spent less time in the target quadrant than tTA (p < 0.01) and WT mice (p < 0.05). Dual Tg mice spent significantly less time in the target quadrant with age (p < 0.01). Bars represent mean ± SEM (*p < 0.05, **p < 0.01, ***p < 0.001) The dotted line represents chance performance (25%).

Figure 5

(A) FST latency to immobility. htau mice spent more time swimming at 7 months compared to 3.5 months (p < 0.01). At 7 months specifically, tTA mice had shorter latencies to become immobile than dual Tg and htau mice (p < 0.05). Bars represent mean ± SEM (*p < 0.05, **p < 0.01). (B) FST time spent immobile. All genetic groups spent less time immobile; dual Tg mice spent significantly less time immobile (increased activity) with increased age (p < 0.05). At 7 months, tTA mice spent more time immobile than dual Tg mice (p < 0.05). Bars represent mean ± SEM (*p < 0.05).

Figure 6

Burrow assessment: 2 h. Dual Tg and htau mice burrowed significantly less pea-gravel at the 2-h measurement mark compared to control mice at both 3.5 (p < 0.01) and 7 (p < 0.001) months. Control mice burrowed significantly more at the 2 h period at 7 months compared to 3.5 months. Transgenic mice showed a virtual inability to burrow early on (Higher values on the figure refer to amount left in the tube, thus less burrowed/removed).

Figure 7

(A) Nesting. Dual Tg and htau mice built significantly poorer nests than control mice (***p < 0.001) at both 3.5 and 7 months. With age, tTA mice built significantly worse nests (p < 0.05) and at 7 months built significantly worse nests than WT mice (^#p < 0.05). Nesting score: 1 (poorest nest; no nest constructed), 2 (attempt was made at constructing a nest), and 3 (nest was made). (B). Representative nests at 7 months. Dual Tg and htau mice constructed the worst nests compared to control mice (p < 0.001). 3.5 months: dual Tg: $\overline{X}$ = 1.3816, SD = 0.496, htau: $\overline{X}$ = 1.7826, SD = 0.751, tTA: $\overline{X}$ = 2.5937, SD = 0.471, Wildtype: $\overline{X}$ = 2.6667, SD = 0.604; 7 months: dual Tg: $\overline{X}$ = 1.3947, SD = 0.488, htau: $\overline{X}$ = 1.4783, SD = 0.612, tTA: $\overline{X}$ = 2.3438, SD = 0.729, Wildtype: 2.8214, SD = 0.264.

Figure 8

(A) Zinpyr-1 fluorescence in the hippocampus. In the dentate gyrus, WT mice (n = 6) had significantly more fluorescence (more free Zn²⁺) compared to dual Tg mice (n = 7) (p < 0.001) and htau mice (n = 5) (p < 0.01). tTA (n = 6) mice also had significantly greater fluorescence than dual Tg mice in the DG (p < 0.01). This same pattern was seen in the CA3 region of the hippocampus as well. Bars represent mean ± SEM (**p < 0.01, ***p < 0.001) in arbitrary fluorescence units (AFUs). (B) Representative ZP-1 fluorescence. Representative histological sections stained for free Zn using Zinpyr-1.

Figure 9

(A) GFAP western blots. Dual Tg and htau mice had significantly greater GFAP values than tTA mice (*p < 0.05). Representative western blot shows monoclonal GFAP bands and GAPDH loading control: Dual Tg (Lanes 1–2, n = 8), htau (Lanes 3–4, n = 8), tTA (Lanes 5–6, n = 8), and WT (Lanes 7–8, n = 6) dual Tg: $\overline{X}$ = 1.8368, SD = 0.781, htau: $\overline{X}$ = 1.7609, SD = 0.663, tTA: $\overline{X}$ = 0.8437, SD = 0.293, Wildtype: 1.1165, SD = 0.281. (B) Total tau western blots. Dual Tg (n = 8) and htau mice (n = 8) had significantly greater amounts of total than control mice [tTA (n = 8), WT (n = 6)] (***p < 0.001). htau mice had significantly greater amounts of total tau expression than dual Tg mice (*p < 0.05). (C) Phosphorylated tau (AT8) western blots and representative blots. No significant differences were seen between dual Tg (n = 8) and htau mice (n = 8) in amount of AT8 (phosphorylated tau at sites Ser202/Thr205) detected. Control mice had no detectable signal. Representative western blots show AT8 bands, total tau, and GAPDH loading control. Dual Tg (Lanes 1–2, n = 8), htau (Lanes 3–4, n = 8), tTA (Lanes 5–6, n = 8), and WT (Lane 7, n = 6).

Figure 10

(A) Tangle pathology in the HP. Mice given Zn water (n = 7) had more tangle pathology detected by Thioflavin-S staining than those given lab water (n = 9) (*p < 0.05). Dual Tg mice on Zn water (n = 3) had increased tangle pathology compared to htau mice given Zn water (n = 4) (*p < 0.05). There was a trending difference (p = 0.054) between dual Tg and htau mice where dual Tg mice had more tangles in than did htau mice. Bars represent mean ± SEM. (B) Representative tangle pathology. Representative histological sections illustrating Thioflavin-S staining in the HP for dual Tg and htau mice given lab vs. zinc water.

Figure 11

Congo red amyloid plaques. Representative histological sections illustrating Congo Red staining in the HP for dual Tg mice given Zn and lab water at eight months. Images on the left are higher magnifications of the images on the right.