Dave Morgan

A|[beta]| peptide vaccination prevents memory loss in an animal model of Alzheimer's disease

Vaccinations with amyloid-β peptide (AB) can dramatically reduce amyloid deposition in a transgenic mouse model of Alzheimers disease. To determine if the vaccinations had deleterious or beneficial functional consequences, we tested eight months of Aβ vaccination in a different transgenic model for Alzheimers disease in which mice develop learning deficits as amyloid accumulates . Here we show that vaccination with Aβ protects transgenic mice from the learning and age-related memory deficits that normally occur in this mouse model for Alzheimers disease. During testing for potential deleterious effects of the vaccine, all mice performed superbly on the radial-arm water-maze test of working memory. Later, at an age when untreated transgenic mice show memory deficits, the Aβ-vaccinated transgenic mice showed cognitive performance superior to that of the control transgenic mice and, ultimately, performed as well as nontransgenic mice. The Aβ-vaccinated mice also had a partial reduction in amyloid burden at the end of the study. This therapeutic approach may thus prevent and, possibly, treat Alzheimers dementia.

Passive immunotherapy against Aβ in aged APP-transgenic mice reverses cognitive deficits and depletes parenchymal amyloid deposits in spite of increased vascular amyloid and microhemorrhage

BackgroundAnti-Aβ immunotherapy in transgenic mice reduces both diffuse and compact amyloid deposits, improves memory function and clears early-stage phospho-tau aggregates. As most Alzheimer disease cases occur well past midlife, the current study examined adoptive transfer of anti-Aβ antibodies to 19- and 23-month old APP-transgenic mice.MethodsWe investigated the effects of weekly anti-Aβ antibody treatment on radial-arm water-maze performance, parenchymal and vascular amyloid loads, and the presence of microhemorrhage in the brain. 19-month-old mice were treated for 1, 2 or 3 months while 23-month-old mice were treated for 5 months. Only the 23-month-old mice were subject to radial-arm water-maze testing.ResultsAfter 3 months of weekly injections, this passive immunization protocol completely reversed learning and memory deficits in these mice, a benefit that was undiminished after 5 months of treatment. Dramatic reductions of diffuse Aβ immunostaining and parenchymal Congophilic amyloid deposits were observed after five months, indicating that even well-established amyloid deposits are susceptible to immunotherapy. However, cerebral amyloid angiopathy increased substantially with immunotherapy, and some deposits were associated with microhemorrhage. Reanalysis of results collected from an earlier time-course study demonstrated that these increases in vascular deposits were dependent on the duration of immunotherapy.ConclusionsThe cognitive benefits of passive immunotherapy persist in spite of the presence of vascular amyloid and small hemorrhages. These data suggest that clinical trials evaluating such treatments will require precautions to minimize potential adverse events associated with microhemorrhage.

Behavioral changes in transgenic mice expressing both amyloid precursor protein and presenilin-1 mutations: lack of association with amyloid deposits.

Mutations in the amyloid precursor protein (mAPP) and in presenilin 1 (mPS1) have both been linked to increased production of the β-amyloid peptide (Aβ). Doubly transgenic mice produced by mating of a parental line carrying the “Swedish” (K670N/M671L) APP mutation with a FAD4 (M146L) mutant presenilin 1 line developed numerous fibrillar Aβ deposits by 6 months of age. Prior work demonstrated that mAPP and doubly transgenic (mAPP/mPS1) mice have deficits in Y-maze alternation behavior as early as 3 months of age. Increased activity was also apparent in the mAPP/mPS1 mice at this time point. These changes in Y-maze performance persisted in mAPP/mPS1 mice at 6 and 9 months of age. The mPS1 singly transgenic mice were not impaired on this task at any age. Six- and nine-month-old mice were also tested for spatial navigation behavior in the Morris water maze. In training trials, no differences in escape latency were detected among the four genotypes. In probe trials, no differences were detected in either the time spent in the trained quadrant or the number of platform crossings among the four groups. Histological staining for Aβ amyloid deposits indicates that all doubly transgenic mice have amyloid deposits by 6 months of age (roughly 25 mice examined thus far), yet no 3-month-old mice have been found with deposits. Aβ immunostaining confirmed that the 9-month-old mice tested behaviorally also have Aβ deposits. Thus, doubly transgenic mice exhibited changes in Y-maze performance prior to the formation of amyloid deposits, which are essentially unchanged as the deposits increase in number and size to 9 months of age. Yet these mice fail to reveal impairments in spatial navigation at 6 or 9 months in spite of the increasing plaque burden. These data indicate that Aβ deposits alone are not sufficient to cause robust spatial memory impairment in mice of this mixed background lineage and age.

Blueberry Supplementation Enhances Signaling and Prevents Behavioral Deficits in an Alzheimer Disease Model

Abstract Previously, we showed that blueberry (BB) supplementation reversed the deleterious effects of aging on motor behavior and neuronal signaling in senescent rodents. We now report that BB-fed (from 4 months of age) APP+PS1 transgenic mice showed no deficits in Y-maze performance (at 12 months of age) with no alterations in amyloid beta burden. It appeared that the protective mechanisms are derived from BB-induced enhancement of memory-associated neuronal signaling (e.g. extracellular signal-regulated kinase) and alterations in neutral sphingomyelin-specific phospholipase C activity. Thus, our data indicate for the first time that it may be possible to overcome genetic predispositions to Alzheimer disease through diet.

Progressive, age-related behavioral impairments in transgenic mice carrying both mutant amyloid precursor protein and presenilin-1 transgenes.

This study provides a comprehensive behavioral characterization during aging of transgenic mice bearing both presenilin-1 (PS1) and amyloid precursor protein (APP(670,671)) mutations. Doubly transgenic mice and non-transgenic controls were evaluated at ages wherein beta-amyloid (Abeta) neuropathology in APP+PS1 mice is low (5-7 months) or very extensive (15-17 months). Progressive cognitive impairment was observed in transgenic mice for both water maze acquisition and radial arm water maze working memory. However, transgenicity did not affect Y-maze alternations, circular platform performance, standard water maze retention, or visible platform recognition at either age, nor did transgenicity affect anxiety levels in elevated plus-maze testing. In sensorimotor tasks, transgenic mice showed a progressive increase in open field activity, a progressive impairment in string agility, and an early-onset impairment in balance beam. None of these sensorimotor changes appeared to be contributory to any cognitive impairments observed, however. Non-transgenic mice showed no progressive behavioral change in any measure evaluated. Given the age-related cognitive impairments presently observed in APP+PS1 transgenic mice and their progressive Abeta deposition/neuroinflammation, Abeta neuropathology could be involved in these progressive cognitive impairments. As such, the APP+PS1 transgenic mouse offers unique opportunities to develop therapeutics to treat or prevent Alzheimers Disease through modulation of Abeta deposition/neuroinflammation.

Passive Amyloid Immunotherapy Clears Amyloid and Transiently Activates Microglia in a Transgenic Mouse Model of Amyloid Deposition

The role of microglia in the removal of amyloid deposits after systemically administered anti-Aβ antibodies remains unclear. In the current study, we injected Tg2576 APP transgenic mice weekly with an anti-Aβ antibody for 1, 2, or 3 months such that all mice were 22 months at the end of the study. In mice immunized for 3 months, we found an improvement in alternation performance in the Y maze. Histologically, we were able to detect mouse IgG bound to congophilic amyloid deposits in those mice treated with the anti-Aβ antibody but not in those treated with a control antibody. We found that Fcγ receptor expression on microglia was increased after 1 month of treatment, whereas CD45 was increased after 2 months of treatment. Associated with these microglial changes was a reduction in both diffuse and compact amyloid deposits after 2 months of treatment. Interestingly, the microglia markers were reduced to control levels after 3 months of treatment, whereas amyloid levels remained reduced. Serum Aβ levels and anti-Aβ antibody levels were elevated to similar levels at all three survival times in mice given anti-Aβ injections rather than control antibody injections. These data show that the antibody is able to enter the brain and bind to the amyloid deposits, likely opsonizing the Aβ and resulting in Fcγ receptor-mediated phagocytosis. Together with our earlier work, our data argue that all proposed mechanisms of anti-Aβ antibody-mediated amyloid removal can be simultaneously active.

Intracranially Administered Anti-Αβ Antibodies Reduce β-Amyloid Deposition by Mechanisms Both Independent of and Associated with Microglial Activation

Active immunization against the β-amyloid peptide (Αβ) with vaccines or passive immunization with systemic monoclonal anti-Aβ antibodies reduces amyloid deposition and improves cognition in APP transgenic mice. In this report, intracranial administration of anti-Αβ antibodies into frontal cortex and hippocampus of Tg2576 transgenic APP mice is described. The antibody injection resulted initially in a broad distribution of staining for the antibody, which diminished over 7 d. Although no loss of immunostaining for deposited Aβ was apparent at 4 hr, a dramatic reduction in the Αβ load was discernible at 24 hr and was maintained at 3 and 7 d. A reduction in the thioflavine-S-positive compact plaque load was delayed until 3 d, at which time microglial activation also became apparent. At 1 week after the injection, microglial activation returned to control levels, whereas Αβ and thioflavine-S staining remained reduced. The results from this study suggest a two-phase mechanism of anti-Αβ antibody action. The first phase occurs between 4 and 24 hr, clears primarily diffuse Αβ deposits, and is not associated with observable microglial activation. The second phase occurs between 1 and 3 d, is responsible for clearance of compact amyloid deposits, and is associated with microglial activation. The results are discussed in the context of other studies identifying coincident microglial activation and amyloid removal in APP transgenic animals.

Immunotherapy for Alzheimer's disease.

Morgan D. (Alzheimer’s Institute, University of South Florida, Tampa, FL, USA) Immunotherapy for Alzheimer’s Disease (Key Symposium). J Intern Med 2011; 269: 54–63.

Time course of the development of Alzheimer-like pathology in the doubly transgenic PS1+APP mouse.

Doubly transgenic mice expressing both a mutated amyloid precursor protein and a mutated presenilin-1 protein accumulate A(beta) deposits as they age. The early A(beta) deposits were found to be primarily composed of fibrillar A(beta) and resembled compact amyloid plaques. As the mice aged, nonfibrillar A(beta) deposits increased in number and spread to regions not typically associated with amyloid plaques in Alzheimers disease. The fibrillar, amyloid-containing deposits remained restricted to cortical and hippocampal structures and did not increase substantially beyond the 12-month time point. Even at early time points, the fibrillar deposits were associated with dystrophic neurites and activated astrocytes expressing elevated levels of glial fibrillary acidic protein. Microglia similarly demonstrated increased staining for complement receptor-3 in the vicinity of A(beta) deposits at early time points. However, when MHC-II staining was used to assess the degree of microglial activation, full activation was not detected until mice were 12 months or older. Overall, the regional pattern of A(beta) staining resembles that found in Alzheimer disease; however, a progression from diffuse A(beta) to more compact amyloid deposits is not observed in the mouse model. It is noted that the activation of microglia at 12 months is coincident with the apparent stabilization of fibrillar A(beta) deposits, raising the possibility that activated microglia might clear fibrillar A(beta) deposits at a rate similar to their rate of formation, thereby establishing a relatively steady-state level of amyloid-containing deposits.

Correlation between cognitive deficits and Aβ deposits in transgenic APP+PS1 mice

Doubly transgenic mAPP+mPS1 mice (15-16 months) had impaired cognitive function in a spatial learning and memory task that combined features of a water maze and a radial arm maze. Nontransgenic mice learned a new platform location each day during 4 consecutive acquisition trials, and exhibited memory for this location in a retention trial administered 30 min later. In contrast, transgenic mice were, on average, unable to improve their performance in finding the hidden platform over trials. The cognitive performance of individual mice within the transgenic group were inversely related to the amount of Abeta deposited in the frontal cortex and hippocampus. These findings imply that mAPP+mPS1 transgenic mice develop deficits in cognitive ability as Abeta deposits increase. These data argue that radial arm water maze testing of doubly transgenic mice may be a useful behavioral endpoint in evaluating the functional consequences of potential AD therapies, especially those designed to reduce Abeta load.