Transgenic Expression of the Amyloid-β Precursor Protein-Intracellular Domain Does Not Induce Alzheimer's Disease–Like Traits In Vivo

BACKGROUND: Regulated intramembranous proteolysis of the amyloid-beta precursor protein by the gamma-secretase yields amyloid-beta, which is the major component of the amyloid plaques found in Alzheimer's disease (AD), and the APP intracellular domain (AID). In vitro studies have involved AID in apoptosis and gene transcription. In vivo studies, which utilize transgenic mice expressing AID in the forebrain, only support a role for AID in apoptosis but not gene transcription. METHODOLOGY/PRINCIPAL FINDINGS: Here, we have further characterized several lines of AID transgenic mice by crossing them with human Tau-bearing mice, to determine whether over-expression of AID in the forebrain provokes AD-like pathologic features in this background. We have found no evidence that AID overexpression induces AD-like characteristics, such as activation of GSK-3beta, hyperphosphorylation of Tau and formation of neurofibrillary pathology. CONCLUSIONS/SIGNIFICANCE: Overall, these data suggest that AID transgenic mice do not represent a model that reproduces the overt biochemical and anatomo-pathologic lesions observed in AD patients. They can still be a valuable tool to understand the role of AID in enhancing the cell sensitivity to apoptotic stimuli, whose pathways still need to be characterized

Tau passive immunotherapy in mutant P301L mice: antibody affinity versus specificity.

The use of antibodies to treat neurodegenerative diseases has undergone rapid development in the past decade. To date, immunotherapeutic approaches to Alzheimer's disease have mostly targeted amyloid beta as it is a secreted protein that can be found in plasma and CSF and is consequently accessible to circulating antibodies. Few recent publications have suggested the utility of treatment of tau pathology with monoclonal antibodies to tau. Our laboratory has begun a systematic study of different classes of tau monoclonal antibodies using mutant P301L mice. Three or seven months old mutant tau mice were inoculated weekly with tau monoclonal antibodies at a dose of 10 mg/Kg, until seven or ten months of age were reached respectively. Our data strongly support the notion that in P301L animals treated with MC1, a conformational monoclonal antibody specific for PHF-tau, the rate of development of tau pathology is effectively reduced, while injecting DA31, a high affinity tau sequence antibody, does not exert such benefit. MC1 appears superior to DA31 in overall effects, suggesting that specificity is more important than affinity in therapeutic applications. Unfortunately the survival rate of the P301L treated mice was not improved when immunizing either with MC1 or PHF1, a high affinity phospho-tau antibody previously reported to be efficacious in reducing pathological tau. These data demonstrate that passive immunotherapy in mutant tau models may be efficacious in reducing the development of tau pathology, but a great deal of work remains to be done to carefully select the tau epitopes to target

Immunohistochemical analysis of AID/hTau mice.

<p>Forebrains were stained with antibodies against total Tau (DA9, A, B, C), pSer202 (CP13; D, E, F), pSer396/404 (PHF1; G, H, I), the neuronal protein NeuN (J, K) and the microglia activation protein Iba1 (L, M). The expressed AID transgene, together with hTau, and mouse are indicated in the panels. Selected samples are representative of the analysis conducted on all AID/hTau transgenics, at all ages. We found no significant difference in the amount and pattern of distribution of total Tau and its phosphorylations, in hippocampal and peri-hippocampal neuronal cellularity and microglia activation between controls and AID expressing mice.</p

Western Blot analysis of GSK3β activation.

<p>Forebrain lysates from different lines of AID/hTau mice, at 4 different ages, were run on PAGE (Column A) and probed with antibodies against total GSK3α and β, the inhibiting phosphorylation pSer9 and the activating phosphorylation pTyrα279/β216. Densitometric quantification over β-Actin only (Column B) and over total GSK3α/β (Column C), shows no clear cut activation or inhibition of GSK3βby AID overexpression, related neither to AID length, mouse line nor age. Experiments were repeated at least 3 times on at least 2 mice/line. Quantifications units are arbitrary. *p<0.05; **p<0.01; ***P<0.001.</p

ELISA analysis of Tau phosphorylation.

<p>Homogenate from forebrains of AID/hTau mice were anaylzed by mean of sandwich ELISA, capturing with the total Tau DA9 antibody, and revealing with antibodies specific for total human Tau (CP27), total mouse and human Tau (TG5), or for several Tau phosphorylations, pSer202 (CP13) (Column A), pThr231 (CP17) (Column B), pSer396/Ser404 (PHF1) (Column C) and conformational modification of human Tau (MC1) (column D). The top 16 panels show scattered differences in the phosphorylation pattern, which do not seem to be related to AID overexpression, length, mouse line or age. The bottom panel (E) shows how levels of total human and murine Tau are maintained in the different mouse lines and ages. Experiments were repeated at least 3 times on at least 2 mice/line. Quantifications units are arbitrary. *p<0.05; **p<0.01; ***P<0.001.</p

CD36 overexpression in human brain correlates with β-amyloid deposition but not with Alzheimer's disease

Scavenger receptors recently have been related to Alzheimer's disease, although it is still unclear whether they contribute to the pathogenesis of the disease or reflect an inflammatory response to the deposition of amyloid β-protein (Aβ). In this study we demonstrate that CD36, a class B scavenger receptor, is highly expressed in the cerebral cortex of Alzheimer's disease patients and cognitively normal aged subjects with diffuse amyloid plaques compared with age-matched amyloid-free control brains. Moreover, in vitro experiments indicated that Aβ is able to induce CD36 expression in neuronal cells after 24 h treatment. The interaction between CD36 and Aβ has been reported to trigger oxidant production by macrophages and microglia. In line with this observation, we found an increased presence of nitrated proteins in brains showing Aβ loads and CD36 overexpression, independent of the occurrence of Alzheimer's disease pathologic features

Endogenous retroviruses are associated with hippocampus-based memory impairment

Retrotransposons compose a staggering 40% of the mammalian genome. Among them, endogenous retroviruses (ERV) represent sequences that closely resemble the proviruses created from exogenous retroviral infection. ERVs make up 8 to 10% of human and mouse genomes and range from evolutionarily ancient sequences to recent acquisitions. Studies in Drosophila have provided a causal link between genomic retroviral elements and cognitive decline; however, in mammals, the role of ERVs in learning and memory remains unclear. Here we studied 2 independent murine models for ERV activation: muMT strain (lacking B cells and antibody production) and intracerebroventricular injection of streptozotocin (ICVI-STZ). We conducted behavioral assessments (contextual fear memory and spatial learning), as well as gene and protein analysis (RNA sequencing, PCR, immunohistochemistry, and western blot assays). Mice lacking mitochondrial antiviral-signaling protein (MAVS) and mice lacking stimulator of IFN genes protein (STING), 2 downstream sensors of ERV activation, provided confirmation of ERV impact. We found that muMT mice and ICVI-STZ mice induced hippocampal ERV activation, as shown by increased gene and protein expression of the Gag sequence of the transposable element intracisternal A-particle. ERV activation was accompanied by significant hippocampus-related memory impairment in both models. Notably, the deficiency of the MAVS pathway was protective against ICVI-STZ-induced cognitive pathology. Overall, our results demonstrate that ERV activation is associated with cognitive impairment in mice. Moreover, they provide a molecular target for strategies aimed at attenuating retroviral element sensing, via MAVS, to treat dementia and neuropsychiatric disorders