Mutations in the genes for amyloid precursor protein (APP) and presenilins (PS1, PS2) increase production of β-amyloid 42 (Aβ42) and cause familial Alzheimer's disease (FAD). Transgenic mice that express FAD mutant APP and PS1 overproduce Aβ42 and exhibit amyloid plaque pathology similar to that found in AD, but most transgenic models develop plaques slowly. To accelerate plaque development and investigate the effects of very high cerebral Aβ42 levels, we generated APP/PS1 double transgenic mice that coexpress five FAD mutations (5XFAD mice) and additively increase Aβ42 production. 5XFAD mice generate Aβ42 almost exclusively and rapidly accumulate massive cerebral Aβ42 levels. Amyloid deposition (and gliosis) begins at 2 months and reaches a very large burden, especially in subiculum and deep cortical layers. Intraneuronal Aβ42 accumulates in 5XFAD brain starting at 1.5 months of age (before plaques form), is aggregated (as determined by thioflavin S staining), and occurs within neuron soma and neurites. Some amyloid deposits originate within morphologically abnormal neuron soma that contain intraneuronal Aβ. Synaptic markers synaptophysin, syntaxin, and postsynaptic density-95 decrease with age in 5XFAD brain, and large pyramidal neurons in cortical layer 5 and subiculum are lost. In addition, levels of the activation subunit of cyclin-dependent kinase 5, p25, are elevated significantly at 9 months in 5XFAD brain, although an upward trend is observed by 3 months of age, before significant neurodegeneration or neuron loss. Finally, 5XFAD mice have impaired memory in the Y-maze. Thus, 5XFAD mice rapidly recapitulate major features of AD amyloid pathology and may be useful models of intraneuronal Aβ42-induced neurodegeneration and amyloid plaque formation.

Intraneuronal beta-amyloid aggregates, neurodegeneration, and neuron loss in transgenic mice with five familial Alzheimer's disease mutations: potential factors in amyloid plaque formation.

Amyloid plaques are a neuropathological hallmark of Alzheimer's disease (AD), but their relationship to neurodegeneration and dementia remains controversial. In contrast, there is a good correlation in AD between cognitive decline and loss of synaptophysin-immunoreactive (SYN-IR) presynaptic terminals in specific brain regions. We used expression-matched transgenic mouse lines to compare the effects of different human amyloid protein precursors (hAPP) and their products on plaque formation and SYN-IR presynaptic terminals. Four distinct minigenes were generated encoding wild-type hAPP or hAPP carrying mutations that alter the production of amyloidogenic Aβ peptides. The platelet-derived growth factor β chain promoter was used to express these constructs in neurons. hAPP mutations associated with familial AD (FAD) increased cerebral Aβ1–42 levels, whereas an experimental mutation of the β-secretase cleavage site (671M→I) eliminated production of human Aβ. High levels of Aβ1–42 resulted in age-dependent formation of amyloid plaques in FAD-mutant hAPP mice but not in expression-matched wild-type hAPP mice. Yet, significant decreases in the density of SYN-IR presynaptic terminals were found in both groups of mice. Across mice from different transgenic lines, the density of SYN-IR presynaptic terminals correlated inversely with Aβ levels but not with hAPP levels or plaque load. We conclude that Aβ is synaptotoxic even in the absence of plaques and that high levels of Aβ1–42are insufficient to induce plaque formation in mice expressing wild-type hAPP. Our results support the emerging view that plaque-independent Aβ toxicity plays an important role in the development of synaptic deficits in AD and related conditions.

https://www.jneurosci.org/content/jneuro/20/11/4050.full.pdf

High-level neuronal expression of abeta 1-42 in wild-type human amyloid protein precursor transgenic mice: synaptotoxicity without plaque formation.

Since the discovery of organic azides by Peter Griess more than 140 years ago, numerous syntheses of these energy-rich molecules have been developed. In more recent times in particular, completely new perspectives have been developed for their use in peptide chemistry, combinatorial chemistry, and heterocyclic synthesis. Organic azides have assumed an important position at the interface between chemistry, biology, medicine, and materials science. In this Review, the fundamental characteristics of azide chemistry and current developments are presented. The focus will be placed on cycloadditions (Huisgen reaction), aza ylide chemistry, and the synthesis of heterocycles. Further reactions such as the aza-Wittig reaction, the Sundberg rearrangement, the Staudinger ligation, the Boyer and Boyer-Aube rearrangements, the Curtius rearrangement, the Schmidt rearrangement, and the Hemetsberger rearrangement bear witness to the versatility of modern azide chemistry.

Organic Azides: An Exploding Diversity of a Unique Class of Compounds

Studies of the molecular basis of Alzheimer's disease exemplify the increasingly blurred distinction between basic and applied biomedical research.The four genes so far implicated in familial Alzheimer's disease have each been shown to elevate brain levels of the self-aggregating amyloid-β protein, leading gradually to profound neuronal and glial alteration, synaptic loss and dementia. Progress in understanding this cascade has helped to identify specific therapeutic targets and provides a model for elucidating other neurodegenerative disorders.

/pdf/translating-cell-biology-into-therapeutic-advances-in-4kg1ob8m3l.pdf

Translating cell biology into therapeutic advances in Alzheimer's disease

Dendritic Function of Tau Mediates Amyloid-β Toxicity in Alzheimer's Disease Mouse Models

Mutations in the amyloid precursor protein (APP) gene cause early-onset familial Alzheimer disease (AD) by affecting the formation of the amyloid β (Aβ) peptide, the major constituent of AD plaques. We expressed human APP751 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 670/671 combined with the V717I mutation causes Aβ 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, inflammatory 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 Aβ in the pathogenesis of the disease.

https://www.pnas.org/content/pnas/94/24/13287.full.pdf

Caroline Waridel

Papers

Two amyloid precursor protein transgenic mouse models with Alzheimer disease-like pathology

Combined Fmoc-Alloc strategy for a general SPPS of phosphoserine peptides; preparation of phosphorylation-dependent tau antisera.