Mutations in the amyloid precursor protein (APP) gene cause early-onset familial Alzheimer disease (AD) by affecting the formation of the amyloid ␤ (A␤) peptide, the major constituent of AD plaques. We expressed human APP 751 containing these mutations in the brains of transgenic mice. Two transgenic mouse lines develop pathological features reminiscent of AD. The degree of pathology depends on expression levels and specific mutations. A 2-fold overexpression of human APP with the Swedish double mutation at positions 670͞671 combined with the V717I mutation causes A␤ deposition in neocortex and hippocampus of 18-month-old transgenic mice. The deposits are mostly of the diffuse type; however, some congophilic plaques can be detected. In mice with 7-fold overexpression of human APP harboring the Swedish mutation alone, typical plaques appear at 6 months, which increase with age and are Congo Red-positive at first detection. These congophilic plaques are accompanied by neuritic changes and dystrophic cholinergic fibers. Furthermore, inf lammatory processes indicated by a massive glial reaction are apparent. Most notably, plaques are immunoreactive for hyperphosphorylated tau, reminiscent of early tau pathology. The immunoreactivity is exclusively found in congophilic senile plaques of both lines. In the higher expressing line, elevated tau phosphorylation can be demonstrated biochemically in 6-month-old animals and increases with age. These mice resemble major features of AD pathology and suggest a central role of A␤ in the pathogenesis of the disease.

Mutations of the presenilin-1 gene are a major cause of familial early-onset Alzheimer's disease. Presenilin-1 can associate with members of the catenin family of signalling proteins, but the significance of this association is unknown. Here we show that presenilin-1 forms a complex with beta-catenin in vivo that increases beta-catenin stability. Pathogenic mutations in the presenilin-1 gene reduce the ability of presenilin-1 to stabilize beta-catenin, and lead to increased degradation of beta-catenin in the brains of transgenic mice. Moreover, beta-catenin levels are markedly reduced in the brains of Alzheimer's disease patients with presenilin-1 mutations. Loss of beta-catenin signalling increases neuronal vulnerability to apoptosis induced by amyloid-beta protein. Thus, mutations in presenilin-1 may increase neuronal apoptosis by altering the stability of beta-catenin, predisposing individuals to early-onset Alzheimer's disease.

The E693Q mutation in the amyloid beta precursor protein (APP) leads to cerebral amyloid angiopathy (CAA), with recurrent cerebral hemorrhagic strokes and dementia. In contrast to Alzheimer disease (AD), the brains of those affected by hereditary cerebral hemorrhage with amyloidosis-Dutch type (HCHWA-D) show few parenchymal amyloid plaques. We found that neuronal overexpression of human E693Q APP in mice (APPDutch mice) caused extensive CAA, smooth muscle cell degeneration, hemorrhages and neuroinflammation. In contrast, overexpression of human wild-type APP (APPwt mice) resulted in predominantly parenchymal amyloidosis, similar to that seen in AD. In APPDutch mice and HCHWA-D human brain, the ratio of the amyloid-beta40 peptide (Abeta40) to Abeta42 was significantly higher than that seen in APPwt mice or AD human brain. Genetically shifting the ratio of AbetaDutch40/AbetaDutch42 toward AbetaDutch42 by crossing APPDutch mice with transgenic mice producing mutated presenilin-1 redistributed the amyloid pathology from the vasculature to the parenchyma. The understanding that different Abeta species can drive amyloid pathology in different cerebral compartments has implications for current anti-amyloid therapeutic strategies. This HCHWA-D mouse model is the first to develop robust CAA in the absence of parenchymal amyloid, highlighting the key role of neuronally produced Abeta to vascular amyloid pathology and emphasizing the differing roles of Abeta40 and Abeta42 in vascular and parenchymal amyloid pathology.

Transgenic mice that overexpress mutant human amyloid precursor protein (APP) exhibit one hallmark of Alzheimer's disease pathology, namely the extracellular deposition of amyloid plaques. Here, we describe significant deposition of amyloid ␤ (A␤) in the cerebral vasculature [cerebral amyloid angiopathy (CAA)] in aging APP23 mice that had striking similarities to that observed in human aging and Alzheimer's disease. Amyloid deposition occurred preferentially in arterioles and capillaries and within individual vessels showed a wide heterogeneity (ranging from a thin ring of amyloid in the vessel wall to large plaque-like extrusions into the neuropil). CAA was associated with local neuron loss, synaptic abnormalities, microglial activation, and microhemorrhage. Although several factors may contribute to CAA in humans, the neuronal origin of transgenic APP, high levels of A␤ in cerebrospinal fluid, and regional localization of CAA in APP23 mice suggest transport and drainage pathways rather than local production or blood uptake of A␤ as a primary mechanism underlying cerebrovascular amyloid formation. APP23 mice on an App-null background developed a similar degree of both plaques and CAA, providing further evidence that a neuronal source of APP͞A␤ is sufficient to induce cerebrovascular amyloid and associated neurodegeneration.

Nature © Macmillan Publishers Ltd 1998 NATURE | VOL 395 | 22 OCTOBER 1998 | www.nature.com 755 Neuron loss in APP transgenic mice scientific correspondence F Fi ig gu ur re e 1 1 Distribution of amyloid plaques in a 14-month-old APP23 transgenic mouse (B6,D2-TgN(Thy1-APP K670N/M671L )). Immunostaining with the NT-11 Aȋ antibody 1 shows amyloid plaques most frequently in neocortex and hippocampus. Insets, adjacent sections stained for Aȋ (bottom left) and Congo red (top right).The plaque load in this mouse was 15% for the neocortex and 12% for area CA1 of the hippocampus, approximately the mean of all transgenic animals analysed. Nature

The Cu-binding ␤-amyloid precursor protein (APP), and the amyloid A␤ peptide have been proposed to play a role in physiological metal regulation. There is accumulating evidence of an unbalanced Cu homeostasis with a causative or diagnostic link to Alzheimer's disease. Whereas elevated Cu levels are observed in APP knockout mice, APP overexpression results in reduced Cu in transgenic mouse brain. Moreover, Cu induces a decrease in A␤ levels in APP-transfected cells in vitro. To investigate the influence of bioavailable Cu, transgenic APP23 mice received an oral treatment with Cu-supplemented sucrose-sweetened drinking water (1). Chronic APP overexpression per se reduced superoxide dismutase 1 activity in transgenic mouse brain, which could be restored to normal levels after Cu treatment (2). A significant increase of brain Cu indicated its bioavailability on Cu treatment in APP23 mice, whereas Cu levels remained unaffected in littermate controls (3). Cu treatment lowered endogenous CNS A␤ before a detectable reduction of amyloid plaques. Thus, APP23 mice reveal APP-induced alterations linked to Cu homeostasis, which can be reversed by addition of dietary Cu.

We have undertaken an integrated chemical and morphological comparison of the amyloid-␤ (A␤) molecules and the amyloid plaques present in the brains of APP23 transgenic (tg) mice and human Alzheimer's disease (AD) patients. Despite an apparent overall structural resemblance to AD pathology, our detailed chemical analyses revealed that although the amyloid plaques characteristic of AD contain cores that are highly resistant to chemical and physical disruption, the tg mice produced amyloid cores that were completely soluble in buffers containing SDS. A␤ chemical alterations account for the extreme stability of AD plaque core amyloid. The corresponding lack of post-translational modifications such as N-terminal degradation, isomerization, racemization, pyroglutamyl formation, oxidation, and covalently linked dimers in tg mouse A␤ provides an explanation for the differences in solubility between human AD and the APP23 tg mouse plaques. We hypothesize either that insufficient time is available for A␤ structural modifications or that the complex species-specific environment of the human disease is not precisely replicated in the tg mice. The appraisal of therapeutic agents or protocols in these animal models must be judged in the context of the lack of complete equivalence between the transgenic mouse plaques and the human AD lesions. Alzheimer's disease (AD)1 is a progressive neurodegenerative disorder characterized by the presence of extracellular amyloid plaques composed principally of amyloid-␤ (A␤) surrounded by dystrophic neurites (1). This association and the realization that the basis of certain early-onset familial forms of AD seems to be the enhanced production of one or more A␤ peptides have led to the hypothesis that A␤ is intimately involved in the AD pathogenic process (2). A promising experimental approach to unraveling the role(s) of A␤ in AD pathology has been the construction and characterization of transgenic mice that overexpress the amyloid precursor protein (APP) (3-12). Several transgenic mouse lines have been described that produce A␤ deposits that accumulate in an agedependent fashion and morphologically resemble the senile plaques characteristic of human AD (3,6,8,12,37,38).The APP23 transgenic (tg) mice contain an APP751 cDNA with the Swedish familial AD mutation under the control of the neuron-specific Thy-1 promoter and express this human gene at levels 7-fold greater than endogenous murine APP (12). Longitudinal studies of these mice have revealed that extracellular amyloid deposits become evident as the APP23 tg mice age. These deposits exhibit, at their earliest appearance, the Congo red birefringence characteristic of the dense core plaques of human AD (12). A gradual progression from a diffuse deposit to a dense plaque is not a feature of the APP23 tg mouse pathology, paralleling our previous finding (13) that the diffuse amyloid deposits of AD do not represent a precursor developmental stage of senile plaques.A transgenic mouse model system that faithfully mimics every aspect of AD h...

Amyloid beta protein (Abeta) deposition in the brain is a hallmark of Alzheimer's disease (AD). The fibrillar form of Abeta is neurotoxic, although the mechanism of its toxicity is unknown. We showed that conversion of Abeta to the fibrillar form markedly increased binding to specific neuronal membrane proteins, including amyloid precursor protein (APP). Nanomolar concentrations of fibrillar Abeta bound cell-surface holo-APP in cortical neurons. Reduced vulnerability of cultured APP-null neurons to Abeta neurotoxicity suggested that Abeta neurotoxicity involves APP. Thus Abeta toxicity may be mediated by the interaction of fibrillar Abeta with neuronal membrane proteins, notably APP. An Abeta-APP interaction reminiscent of the pathogenic mechanism of prions may thus contribute to neuronal degeneration in AD.