Non-invasive Brain Delivery and Efficacy of BDNF in APP/PS1 Transgenic Mice as a Model of Alzheimer's Disease

Abstract

Neurotrophic factors such as brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF) have been demonstrated for their potential as a neuroregenerative treatment of Alzheimer's disease (AD). Unfortunately, most proteins cannot be effectively delivered into the brain from the blood stream due to the presence of the blood-brain barrier (BBB). In this study, we delivered BDNF using ADTC5 as BBB modulator (BBBM) into the brains of transgenic APP/PS1 mice, a mouse model for AD. As controls, two groups of APP/PS1 mice were treated with BDNF alone and vehicle, respectively. All three groups were subjected to behavioral/cognitive assessments in Y-maze and novel object recognition (NOR) tests as well as evaluation of the brain markers activated by BDNF. The results showed that BDNF + ADTC5 group performed significantly better in both the Y-maze and NOR assessments compared to mice that received BDNF alone or vehicle. In addition, significant upregulations of NG2 receptors as well as EGR1 and ARC mRNA transcripts were observed in the brain cortex of mice treated with BDNF + ADTC5, further indicating the efficacy of delivered BDNF in the brain. There were high plaque loads in all groups of mice, suggesting no influence of BDNF on the plaque formation. In summary, ADTC5 can deliver BDNF into the brains of APP/PS1 mice and the activity of BDNF in improving cognitive function was likely due to improvement in synaptic plasticity via NG2 glia cells and not by reducing the plaque load.

Keywords: APP/PS1 mice; Alzheimer’s Diseas; BBB modulation; BDNF; Blood-Brain Barrier; Brain delivery; neuroregeneration.

Figure 1.

Y-maze cognitive assessment of transgenic APP/PS1 mice, an AD animal model after eight injections of BDNF (5.71 nmol/kg) + ADTC5 (10 μmol/kg), BDNF alone (5.71 nmol/kg), or vehicle. (A) The percent of total time spent in the novel arm or third arm of the Y-maze. (B) The total number of entries made into the third arm of the Y-maze. *p < 0.05; one-way ANOVA (95% confidence, n =5).

Figure 2.

Novel object recognition (NOR) cognitive assessment of transgenic APP/PS1 mice after eight injections with BDNF (5.71 nmol/kg) + ADTC5 (10 μmol/kg), BDNF alone (5.71 nmol/kg), or vehicle on. (A) The percent of total time spent interacting with the novel object. (B) The total amount of time mice spent interacting with either object. *p < 0.05; one-way ANOVA (95% confidence, n =5); NS = No Significant Difference.

Figure 3.

The effect of eight injections of BDNF (5.71 nmol/kg) + ADTC5 (10 μmol/kg), BDNF alone (5.71 nmol/kg), or vehicle in APP/PS1 mice on amyloid plaque loads at the hippocampal region as determined using Congo red staining. The is no significant difference (NS) in all three groups.

Figure 4.

The effect of multiple treatments of APP/PS1 mice with BDNF (5.71 nmol/kg) + ADTC5 (10 μmol/kg), BDNF alone (5.71 nmol/kg), or vehicle on the expression of NG2 receptors in the cortex as stained by DAB. (A) Color photomicrograph of anti-NG2 staining (brown) taken under identical conditions from the cortex of mice treated with BDNF + ADTC5, BDNF alone, and vehicle; slides from BDNF + ADTC5-treated mice showed dense regions of activated NG2-glia. (B) Quantitative NG2 density comparison among the APP/PS1 mice treated with BDNF + ADTC5, BDNF alone, and vehicle; Scale bar = 100 μm; **p ≤ 0.01; NS = No Significant Difference; one-way ANOVA (95% confidence; n = 5).

Figure 5.

The effects of BDNF (5.71 nmol/kg) + ADTC5 (10 μmol/kg), BDNF alone (5.71 nmol/kg), or vehicle treatments on mRNA expression of MAPK1, EGR1, and ARC in the CA1 region of the brain hippocampus from treated APP/PS1 mice. (A) Photomicrograph of DAPI (grey), EGR1 (green), ARC (red), MAPK (cyan) and composite images taken of the hippocampus of APP/PS1 mice treated with BDNF + ADTC5, BDNF alone, or vehicle. (B) Quantitative comparison using fluorescence intensities of MAPK1 EGR1, and ARC mRNA transcript expressions after multiple treatments with BDNF + ADTC5, BDNF alone, or vehicle. Scale bar = 100 μm; p* ≤ 0.05; ** and ***p ≤ 0.001; one-way ANOVA (99% confidence; n = 4); NS = No significant difference. Contrast and brightness of images were adjusted only for display purposes.

Figure 5.

The effects of BDNF (5.71 nmol/kg) + ADTC5 (10 μmol/kg), BDNF alone (5.71 nmol/kg), or vehicle treatments on mRNA expression of MAPK1, EGR1, and ARC in the CA1 region of the brain hippocampus from treated APP/PS1 mice. (A) Photomicrograph of DAPI (grey), EGR1 (green), ARC (red), MAPK (cyan) and composite images taken of the hippocampus of APP/PS1 mice treated with BDNF + ADTC5, BDNF alone, or vehicle. (B) Quantitative comparison using fluorescence intensities of MAPK1 EGR1, and ARC mRNA transcript expressions after multiple treatments with BDNF + ADTC5, BDNF alone, or vehicle. Scale bar = 100 μm; p* ≤ 0.05; ** and ***p ≤ 0.001; one-way ANOVA (99% confidence; n = 4); NS = No significant difference. Contrast and brightness of images were adjusted only for display purposes.