The Impact of Bdnf Gene Deficiency to the Memory Impairment and Brain Pathology of APPswe/PS1dE9 Mouse Model of Alzheimer's Disease

Peer reviewe

Brain-Specific Basal and Novelty-Induced Alternations in PI3K-Akt and MAPK/ERK Signaling in a Middle-Aged AβPP/PS1 Mouse Model of Alzheimer's Disease.

International audienceAlthough it is well established that insulin/IGF and BDNF signaling are dysfunctionally regulated in Alzheimer's disease, there are very few studies documenting changes in major target proteins in different murine models of the disease. We investigated a panel of proteins in the PI3K-Akt and MAPK/ERK cascades in parietal cortex, dentate gyrus and CA1 in 13-month-old AβPP/PS1 transgenic mice to determine whether amyloid pathology is associated with basal dysregulation of these proteins or following exposure to novelty. The most striking effect we found was that there was little common regulation of proteins either by pathology alone or exposure to novelty across the three structures, suggesting dysfunctional mechanisms that occur simultaneously have important structure specificity. CA1 shared certain dysfunctional regulation of proteins in the MAPK/ERK cascade, but shared dysfunctional regulation of the PI3K/Akt cascade with the dentate gyrus. Changes in ERK/CREB in transgenic mice did not result in coordinated dysfunction of the downstream transcription factor, Egr1, as it was overexpressed in a normal manner following exposure to novelty. In the PI3K-Akt cascade, there was a flagrant increase in the levels of proteins associated with inflammation, such as NFκB, and structure specific regulation of proteins associated with autophagy, such as mTOR and FOXO1 and lack of regulation of Beclin-1. Finally, Beclin-1 was increased by novelty in wild-type mice but deficient in transgenic mice. Results are interpreted in terms of structure-specific dysfunctional regulation of signaling mechanisms associated with Alzheimer's disease

Special lipid-based diets alleviate cognitive deficits in the APPswe/PS1dE9 transgenic mouse model of Alzheimer's disease independent of brain amyloid deposition

Abstract Dietary fish oil, providing n3 polyunsaturated fatty acids like eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), associates with reduced dementia risk in epidemiological studies and reduced amyloid accumulation in Alzheimer mouse models. We now studied whether additional nutrients can improve the efficacy of fish oil in alleviating cognitive deficits and amyloid pathology in APPswe/PS1dE9 transgenic and wild-type mice. We compared four isocaloric (5 fat) diets. The fish oil diet differed from the control diet only by substituted fish oil. Besides fish oil, the plant sterol diet was supplemented with phytosterols, while the Fortasyn diet contained as supplements precursors and cofactors for membrane synthesis, viz. uridine-monophosphate; {DHA} and EPA; choline; folate; vitamins B6, B12, C and E; phospholipids and selenium. Mice began the special diets at 5 months and were sacrificed at 14 months after behavioral testing. Transgenic mice, fed with control chow, showed poor spatial learning, hyperactivity in exploring a novel cage and reduced preference to explore novel odors. All fish-oil-containing diets increased exploration of a novel odor over a familiar one. Only the Fortasyn diet alleviated the spatial learning deficit. None of the diets influenced hyperactivity in a new environment. Fish-oil-containing diets strongly inhibited β- and γ-secretase activity, and the plant sterol diet additionally reduced amyloid-β 1–42 levels. These data indicate that beneficial effects of fish oil on cognition in Alzheimer model mice can be enhanced by adding other specific nutrients, but this effect is not necessarily mediated via reduction of amyloid accumulation

BDNF protein accumulates around amyloid plaques in the brains of <b><i>APdE9</i></b> mice.

<p><b>A)</b> Amyloid-β selective antibody W02 detects a robust accumulation of amyloid-β in the brain of a 13-month-old <i>APdE9</i> mouse. <b>B)</b> BDNF antibody reveals significant anti-BDNF immunoreactivity in the cortex and hippocampus but not in the thalamus of aged <i>APdE9</i> mouse, thus matching the regional pattern of Amyloid-β accumulation. <b>C)</b> A magnified view of the framed area demonstrating doughnut-shaped anti-BDNF immunopositivity around amyloid plaques. <b>D)</b> The same BDNF antibody dilution that was used to identify BDNF accumulation in the Amyloid-β plaques in <i>APdE9</i> mouse brain did not show notable anti-BDNF immunoreactivity in a wild-type mouse brain. A close-up of a single amyloid plaque in a <i>APdE9</i> mouse stained for (<b>E</b>) anti-BDNF, (<b>F</b>) anti-NGF, (<b>G</b>) anti-CDNF and (<b>H</b>) GFAP to visualize activated astroglia. Only BDNF shows a donut-like staining pattern. Small arrows indicate plaque boundaries. (<b>E–H</b>) Scale bar = 50 µm. Th = thalamus, HC = hippocampus, Ctx = cerebral cortex.</p

Mature BDNF protein levels are specifically increased in 13 month-old female <i>APdE9</i> mouse cortex.

<p>Western blot analysis of mature-BDNF protein levels in the cortex of wild-type mice and mice carrying <i>APdE9</i> and/or <i>Bdnf</i>^+/− mutations. Two-Way ANOVA followed with Tukey-Kramer <i>post hoc</i> test was performed for statistical analysis. *p<0.05, ***p<0.001 compared to the respective wt, ###p<0.001 compared to wt/wt.</p

Impact of <i>Bdnf</i> gene deficiency on BDNF induction in 13-month-old female <i>APdE9</i> mouse cortex.

<p><b>A)</b><b> </b> BDNF protein levels in the temporal cortex of wild-type mice and mice carrying <i>APdE9</i> and/or <i>Bdnf</i>^+/− mutations. <b>B)</b> BDNF protein levels in the hippocampus of wild-type mice and mice carrying <i>APdE9</i> and/or <i>Bdnf</i>^+/− mutations. Two-Way ANOVA followed with Tukey-Kramer <i>post hoc</i> test was performed for statistical analysis. *p<0.05, ***p<0.001 compared to the respective wt, ###p<0.001 compared to wt/wt.</p

Correlation between hippocampal (HC) and cortical (Ctx) BDNF protein levels and key behavioral test parameters in 13-month-old female mice.

<p>All four genotypes are pooled, with n = 29-31 in all correlations. Values are Spearman rho correlation coefficients.</p>*<p>p = 0.01, p>0.10 for all other correlations.</p

Age-dependent increase of BDNF protein in the brains of <i>APdE9</i> mice.

<p><b>A)</b> BDNF protein levels (measured with ELISA) in the hippocampus, frontal cortex, parietal cortex and temporal cortex of 12-month-old female <i>APdE9</i> mice. <b>B)</b> BDNF protein levels (measured with ELISA) in the hippocampus, frontal cortex, parietal cortex and temporal cortex of 15-month-old female <i>APdE9</i> mice. <b>C)</b> NGF protein levels (measured with ELISA) in the temporal cortex of 12-month-old female <i>APdE9</i> mice. <b>D)</b> Total <i>Bdnf</i> mRNA (measured with RT-PCR) in temporal cortex of 12-month-old female <i>APdE9</i> mice. <b>E)</b> Age-dependent BDNF protein levels (measured with ELISA) in the temporal cortex of wild-type and <i>APdE9</i> female mice. <b>F)</b> Age-dependent BDNF protein levels (measured with ELISA) in the temporal cortex of wild-type and <i>APdE9</i> male mice. A t-test was performed between wild-type and mutant animals; *p<0.05, ** p<0.01, *** p<0.001.</p

The number of <i>APdE9</i> (A+) and wild-type (Aw) animals in the aging study on BDNF and NGF protein and TrkB phosphorylation levels.

<p>Abbreviations: BDNF = brain-derived neurotrophic factor; ELISA = enzyme-linked immunosorbent assay; HC = hippocampus; NGF = nerve growth factor; PCR = polymerase chain reaction; WB = western blot; pTrkB = phosphorylated TrkB.</p