Stephan A. Kaeser

Exogenous induction of cerebral beta-amyloidogenesis is governed by agent and host

Protein aggregation is an established pathogenic mechanism in Alzheimers disease, but little is known about the initiation of this process in vivo. Intracerebral injection of dilute, amyloid-β (Aβ)–containing brain extracts from humans with Alzheimers disease or β-amyloid precursor protein (APP) transgenic mice induced cerebral β-amyloidosis and associated pathology in APP transgenic mice in a time- and concentration-dependent manner. The seeding activity of brain extracts was reduced or abolished by Aβ immunodepletion, protein denaturation, or by Aβ immunization of the host. The phenotype of the exogenously induced amyloidosis depended on both the host and the source of the agent, suggesting the existence of polymorphic Aβ strains with varying biological activities reminiscent of prion strains.

Aβ42‐driven cerebral amyloidosis in transgenic mice reveals early and robust pathology

We have generated a novel transgenic mouse model on a C57BL/6J genetic background that coexpresses KM670/671NL mutated amyloid precursor protein and L166P mutated presenilin 1 under the control of a neuron‐specific Thy1 promoter element (APPPS1 mice). Cerebral amyloidosis starts at 6–8 weeks and the ratio of human amyloid (A)β42 to Aβ40 is 1.5 and 5 in pre‐depositing and amyloid‐depositing mice, respectively. Consistent with this ratio, extensive congophilic parenchymal amyloid but minimal amyloid angiopathy is observed. Amyloid‐associated pathologies include dystrophic synaptic boutons, hyperphosphorylated tau‐positive neuritic structures and robust gliosis, with neocortical microglia number increasing threefold from 1 to 8 months of age. Global neocortical neuron loss is not apparent up to 8 months of age, but local neuron loss in the dentate gyrus is observed. Because of the early onset of amyloid lesions, the defined genetic background of the model and the facile breeding characteristics, APPPS1 mice are well suited for studying therapeutic strategies and the pathomechanism of amyloidosis by cross‐breeding to other genetically engineered mouse models.

The Alzheimer's Association external quality control program for cerebrospinal fluid biomarkers.

The cerebrospinal fluid (CSF) biomarkers amyloid β (Aβ)‐42, total‐tau (T‐tau), and phosphorylated‐tau (P‐tau) demonstrate good diagnostic accuracy for Alzheimers disease (AD). However, there are large variations in biomarker measurements between studies, and between and within laboratories. The Alzheimers Association has initiated a global quality control program to estimate and monitor variability of measurements, quantify batch‐to‐batch assay variations, and identify sources of variability. In this article, we present the results from the first two rounds of the program.

Peripherally Applied Aβ-Containing Inoculates Induce Cerebral β-Amyloidosis

Infectious Amyloid? Patients with Alzheimers disease have characteristic lesions in the brains associated with masses of polymerized protein called β-amyloid. Recently, evidence from mouse models of Alzheimers disease shows that brain extracts containing β-amyloid can “infect” otherwise healthy animals when injected directly into their brains. Eisele et al. (p. 980, published online 21 October; see the Perspective by Kim and Holtzman) extend these findings to show that when mice are injected in other parts of their bodies with similar brain extracts after several months, they also develop amyloidosis within their brains. Amyloid-containing brain extracts can “infect” susceptible Alzheimer’s disease model animals. The intracerebral injection of β-amyloid–containing brain extracts can induce cerebral β-amyloidosis and associated pathologies in susceptible hosts. We found that intraperitoneal inoculation with β-amyloid–rich extracts induced β-amyloidosis in the brains of β-amyloid precursor protein transgenic mice after prolonged incubation times.

Peripherally applied Abeta-containing inoculates induce cerebral beta-amyloidosis.

Infectious Amyloid? Patients with Alzheimers disease have characteristic lesions in the brains associated with masses of polymerized protein called β-amyloid. Recently, evidence from mouse models of Alzheimers disease shows that brain extracts containing β-amyloid can “infect” otherwise healthy animals when injected directly into their brains. Eisele et al. (p. 980, published online 21 October; see the Perspective by Kim and Holtzman) extend these findings to show that when mice are injected in other parts of their bodies with similar brain extracts after several months, they also develop amyloidosis within their brains. Amyloid-containing brain extracts can “infect” susceptible Alzheimer’s disease model animals. The intracerebral injection of β-amyloid–containing brain extracts can induce cerebral β-amyloidosis and associated pathologies in susceptible hosts. We found that intraperitoneal inoculation with β-amyloid–rich extracts induced β-amyloidosis in the brains of β-amyloid precursor protein transgenic mice after prolonged incubation times.

Cystatin C modulates cerebral |[beta]|-amyloidosis

The CST3 Thr25 allele of CST3, which encodes cystatin C, leads to reduced cystatin C secretion and conveys susceptibility to Alzheimers disease. Here we show that overexpression of human cystatin C in brains of APP-transgenic mice reduces cerebral amyloid-β deposition and that cystatin C binds amyloid-β and inhibits its fibril formation. Our results suggest that cystatin C concentrations modulate cerebral amyloidosis risk and provide an opportunity for genetic risk assessment and therapeutic interventions.

Seeded strain-like transmission of β-amyloid morphotypes in APP transgenic mice.

The polymorphic β‐amyloid lesions present in individuals with Alzheimers disease are collectively known as cerebral β‐amyloidosis. Amyloid precursor protein (APP) transgenic mouse models similarly develop β‐amyloid depositions that differ in morphology, binding of amyloid conformation‐sensitive dyes, and Aβ40/Aβ42 peptide ratio. To determine the nature of such β‐amyloid morphotypes, β‐amyloid‐containing brain extracts from either aged APP23 brains or aged APPPS1 brains were intracerebrally injected into the hippocampus of young APP23 or APPPS1 transgenic mice. APPPS1 brain extract injected into young APP23 mice induced β‐amyloid deposition with the morphological, conformational, and Aβ40/Aβ42 ratio characteristics of β‐amyloid deposits in aged APPPS1 mice, whereas APP23 brain extract injected into young APP23 mice induced β‐amyloid deposits with the characteristics of β‐amyloid deposits in aged APP23 mice. Injecting the two extracts into the APPPS1 host revealed a similar difference between the induced β‐amyloid deposits, although less prominent, and the induced deposits were similar to the β‐amyloid deposits found in aged APPPS1 hosts. These results indicate that the molecular composition and conformation of aggregated Aβ in APP transgenic mice can be maintained by seeded conversion.

Changes in Amyloid-β and Tau in the Cerebrospinal Fluid of Transgenic Mice Overexpressing Amyloid Precursor Protein

Changes in Aβ and Tau in the CSF of APP transgenic mice mirror the temporal sequence and magnitude of changes in these proteins in the CSF of Alzheimer’s disease patients. From Bedside Back to Bench The pathology of Alzheimer’s disease (AD) is thought to start 10 to 20 years before the onset of the first clinical symptoms in both sporadic and familial forms of the disease. Thus, disease-modifying drugs will most likely be effective when given at a preclinical stage of disease before neurodegeneration has become severe enough to induce clinical symptoms. Amyloid-β (Aβ) peptide and Tau protein, the constituents of the pathological hallmarks of AD, amyloid plaques and neurofibrillary tangles, respectively, have shown promise as markers in cerebrospinal fluid (CSF) of early, preclinical AD. Transgenic mice overexpressing human amyloid precursor protein (APP) have been used to model Aβ pathology, but CSF markers have not been investigated. To this end, Maia et al. optimized methods for collecting mouse CSF and validated sensitive assays for detecting Aβ peptides and total Tau in mouse CSF. They then used these assays to measure Aβ peptides and total Tau in the CSF of two different APP transgenic mouse models, with different ages of onset and progression of Aβ pathology. They found that the Aβ42 concentration in mouse CSF decreased as Aβ deposition started and that CSF t-Tau increased when amyloid plaques in mouse brain became prominent. Mechanistically, these results suggest that Aβ deposition in the brain may be the driving force for changes in Aβ and Tau in the CSF of AD patients. They also suggest the translational value of APP mouse models for understanding events in human disease. Altered concentrations of amyloid-β (Aβ) peptide and Tau protein in the cerebrospinal fluid (CSF) are thought to be predictive markers for Alzheimer’s disease (AD). Transgenic mice overexpressing human amyloid precursor protein (APP) have been used to model Aβ pathology, but concomitant changes in Aβ and Tau in CSF have been less well studied. We measured Aβ and Tau in the brains and CSF of two well-characterized transgenic mouse models of AD: one expressing human APP carrying the Swedish mutation (APP23) and the other expressing mutant human APP and mutant human presenilin-1 (APPPS1). Both mouse models exhibit Aβ deposition in the brain, but with different onset and progression trajectories. We found an age-related 50 to 80% decrease in Aβ42 peptide in mouse CSF and a smaller decrease in Aβ40, both inversely correlated with the brain Aβ load. Surprisingly, the same mice showed a threefold increase in total endogenous murine Tau in CSF at the stages when Aβ pathology became prominent. The results mirror the temporal sequence and magnitude of Aβ and Tau changes in the CSF of patients with sporadic and dominantly inherited AD. This observation indicates that APP transgenic mice may be useful as a translational tool for predicting changes in Aβ and Tau markers in the CSF of AD patients. These findings also suggest that APP transgenic mouse models may be useful in the search for new disease markers for AD.

Neocortical synaptic bouton number is maintained despite robust amyloid deposition in APP23 transgenic mice

Major pathological findings in Alzheimers disease (AD) brain include the deposition of amyloid-beta and synapse loss. Synaptic loss has been shown to correlate with the cognitive decline in AD patients, but the relationship between cerebral amyloidosis and synapse loss is complicated by the presence of neurofibrillary tangles and other lesions in AD brain. With the use of the APP23 transgenic mouse model that overexpresses human amyloid precursor protein (APP) with the Swedish double mutation, we investigated whether the development of cortical amyloid deposition was accompanied by synaptic bouton loss. With stereological methods, we show that despite robust age-related cortical amyloid deposition with associated synaptic degeneration, the total number of cortical synaptophysin-positive presynaptic terminals is not changed in 24-month-old animals compared with 3-, 8-, and 15-month-old APP23 mice. Wild-type mice also do not show an age-related loss of presynaptic boutons in the neocortex and are not significantly different from APP23 mice. Synaptophysin Western blotting revealed no significant difference between APP23 mice and wild-type controls at 3 and 25 months of age. Our results suggest that cerebral amyloidosis is not sufficient to account for the global synapse loss in AD. Alternatively, a putative trophic effect of APP may prevent, compensate, or delay a loss of synapses in this mouse model.

Modeling familial Danish dementia in mice supports the concept of the amyloid hypothesis of Alzheimer's disease

Familial Danish dementia (FDD) is a progressive neurodegenerative disease with cerebral deposition of Dan-amyloid (ADan), neuroinflammation, and neurofibrillary tangles, hallmark characteristics remarkably similar to those in Alzheimers disease (AD). We have generated transgenic (tg) mouse models of familial Danish dementia that exhibit the age-dependent deposition of ADan throughout the brain with associated amyloid angiopathy, microhemorrhage, neuritic dystrophy, and neuroinflammation. Tg mice are impaired in the Morris water maze and exhibit increased anxiety in the open field. When crossed with TauP301S tg mice, ADan accumulation promotes neurofibrillary lesions, in all aspects similar to the Tau lesions observed in crosses between β-amyloid (Aβ)-depositing tg mice and TauP301S tg mice. Although these observations argue for shared mechanisms of downstream pathophysiology for the sequence-unrelated ADan and Aβ peptides, the lack of codeposition of the two peptides in crosses between ADan- and Aβ-depositing mice points also to distinguishing properties of the peptides. Our results support the concept of the amyloid hypothesis for AD and related dementias, and suggest that different proteins prone to amyloid formation can drive strikingly similar pathogenic pathways in the brain.