Neuroinflammation and Neuronal Loss Precede Aβ Plaque Deposition in the hAPP-J20 Mouse Model of Alzheimer's Disease

Recent human trials of treatments for Alzheimer's disease (AD) have been largely unsuccessful, raising the idea that treatment may need to be started earlier in the disease, well before cognitive symptoms appear. An early marker of AD pathology is therefore needed and it is debated as to whether amyloid-βAβ? plaque load may serve this purpose. We investigated this in the hAPP-J20 AD mouse model by studying disease pathology at 6, 12, 24 and 36 weeks. Using robust stereological methods, we found there is no neuron loss in the hippocampal CA3 region at any age. However loss of neurons from the hippocampal CA1 region begins as early as 12 weeks of age. The extent of neuron loss increases with age, correlating with the number of activated microglia. Gliosis was also present, but plateaued during aging. Increased hyperactivity and spatial memory deficits occurred at 16 and 24 weeks. Meanwhile, the appearance of plaques and oligomeric Aβ were essentially the last pathological changes, with significant changes only observed at 36 weeks of age. This is surprising given that the hAPP-J20 AD mouse model is engineered to over-expresses Aβ. Our data raises the possibility that plaque load may not be the best marker for early AD and suggests that activated microglia could be a valuable marker to track disease progression. © 2013 Wright et al

Neuroinflammation and Neuronal Loss Precede Aβ Plaque Deposition in the hAPP-J20 Mouse Model of Alzheimer’s Disease

Recent human trials of treatments for Alzheimer's disease (AD) have been largely unsuccessful, raising the idea that treatment may need to be started earlier in the disease, well before cognitive symptoms appear. An early marker of AD pathology is therefore needed and it is debated as to whether amyloid-βAβ? plaque load may serve this purpose. We investigated this in the hAPP-J20 AD mouse model by studying disease pathology at 6, 12, 24 and 36 weeks. Using robust stereological methods, we found there is no neuron loss in the hippocampal CA3 region at any age. However loss of neurons from the hippocampal CA1 region begins as early as 12 weeks of age. The extent of neuron loss increases with age, correlating with the number of activated microglia. Gliosis was also present, but plateaued during aging. Increased hyperactivity and spatial memory deficits occurred at 16 and 24 weeks. Meanwhile, the appearance of plaques and oligomeric Aβ were essentially the last pathological changes, with significant changes only observed at 36 weeks of age. This is surprising given that the hAPP-J20 AD mouse model is engineered to over-expresses Aβ. Our data raises the possibility that plaque load may not be the best marker for early AD and suggests that activated microglia could be a valuable marker to track disease progression.Funding provided by Iain S. Gray Foundation, Stanley and John Roth, Patricia A. Quick foundation, David King, Doug Battersby, Tony and Vivian Howland-Rose, Walter and Edith Sheldon, Gleneagle Securities, Bill Gruy, Geoffrey Towner, Amadeus Energy Ltd., Nick and Melanie Kell, J. O. and J. R. Wicking Trust and the Mason Foundation, the New South Wales Government, through their office for Science and Medical Research, and SpinalCure Australia. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript

Time course of disease progression, as a percentage of hAPP-J20 6-week-old mice.

<p>Mice exhibit 32% loss of neurons in the CA1 region of the hippocampus between 6 weeks and 36 weeks of age. In addition, a 163% increase in the number of CD68-positive microglia and a 62% increase in the number of CA1 GFAP-positive astrocytes occurred between 6 weeks and 36 weeks of age. Total Aβ expression increases by 242% between the ages of 6 weeks and 36 weeks of age. Small arrow represents plaque load in some mice, while larger arrow represents plaque load in all mice.</p

Correlations between CA1 regions (NeuN and GFAP), CD68 cell numbers and total hippocampal Aβ.

*<p><i>p</i><0.05.</p>**<p><i>p</i><0.01.</p

Age-dependent Aβ expression and plaque deposition in the hAPP-J20 mice.

<p>(A) 6E10 immunohistochemistry illustrated increased neuronal Aβ from 6 to 12, 24 and 36-week-old hAPP-J20 mice (quantified in E). (B) Aβ oligomer formation was not apparent until 24 weeks of age and appeared by 36 weeks of age when it appeared to be associated with neuronal processes. (C) Plaques were present by 36 weeks of age, but not earlier (quantified in F). (D and G) A dot plot quantification with the Aβ-oligomer specific antibody, A11, revealed increases in Aβ oligomers through aging in the hAPP-J20 mouse, with a significant increase in 36-week-old hAPP-J20 mice. (H) Quantification of Aβ by ELISA revealed an increase in total Aβ from 6 (p<0.05) and 12 (p<0.05) to 36 weeks of age in the hAPP-J20 mouse. Each value represents the mean ± standard error of the mean (SEM). *<i>p</i><0.05, **<i>p</i><0.01, ***<i>p</i><0.001.</p

Spatial learning and memory deficits in hAPP-J20 mice.

<p>(A) Schematic representation of the radial arm maze. Filled circles represent the baited arms (B) hAPP-J20 mice had significantly impaired spatial reference memory and learning at 16 weeks of age (<i>p</i><0.05) when compared to age-matched WT littermates. (C) 16-week-old hAPP-J20 mice had significant deficits in spatial reference memory and learning retention (<i>p</i><0.05) when compared to age-matched WT littermates. (D) 24-week-old hAPP-J20 mice also showed significantly impaired spatial reference memory and learning (<i>p</i><0.05) when compared to age-matched WT littermates. (E) Spatial reference memory and learning retention was significantly impaired in 24-week-old hAPP-J20 mice (<i>p</i><0.05). Each value represents the mean ± standard error of the mean (SEM). *<i>p</i><0.05, **<i>p</i><0.01.</p

Quantification of GFAP-positive astrocytes in hAPP-J20 mice.

<p>GFAP-positive astrocytes in the hippocampus were observed more often in (B) 36-week-old hAPP-J20 mice compared to age-matched (A) WT littermates. (C) Quantification analysis revealed no differences in GFAP-positive astrocytes in the CA3 at 6 or 12 weeks, however significant increases in cell number were detected at 24 (<i>p</i><0.05) and 36 weeks (<i>p</i><0.05). (D) In the CA1 region of the hippocampus, there was no increase in GFAP-positive astrocytes at 6 and 36 weeks, though significant increases at 12 (<i>p</i><0.05) and 24 weeks (<i>p</i><0.05) were observed when compared to WT controls. In addition, a significant increase occurred between 6 week and 24-week-old hAPP-J20 mice (<i>p</i><0.05). Each value represents the mean ± standard error of the mean (SEM). *<i>p</i><0.05.</p

Contextual fear conditioning is not impaired in hAPP-J20 mice.

<p>(A) No deficits were seen in the percentage of freezing in 28 and 36-week-old hAPP-J20 mice when compared to age-matched WT littermates. (B) A retention test, performed at 40 weeks, also revealed no deficits in the percentage of freezing in 36-week-old hAPP-J20 mice when compared to age-matched controls. Each value represents the mean ± standard error of the mean (SEM).</p