Donna M. Wilcock

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.

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.

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.

Intrahippocampal LPS injections reduce Aβ load in APP+PS1 transgenic mice

Multiple lines of evidence indicate that inflammatory processes are involved in the pathogenesis of Alzheimers disease. Lipopolysaccharide (LPS) is widely used to induce inflammation in experimental systems. Consequently we injected LPS or saline intrahippocampally in 11 and 16 months old APP+PS1 transgenic mice to induce brain inflammation, then used immunocytochemistry to examine amyloid pathology 7 days later. As expected, LPS activated microglia as indicated by a significant increase in the area covered by major histocompatibility complex-II (MHC-II) immunostaining in the mice injected with LPS compared to the saline injected. Simultaneously, Abeta immunostaining showed an unexpected reduction of the Abeta load in the mice injected with LPS compared to the saline injected. This effect of LPS on the Abeta load in APP+PS1 mice strengthens the hypothesis that moderate amounts of microglial activation may be beneficial in Alzheimers disease, by increasing the clearance of Abeta.

Deglycosylated anti-amyloid-beta antibodies eliminate cognitive deficits and reduce parenchymal amyloid with minimal vascular consequences in aged amyloid precursor protein transgenic mice.

Systemic administration of anti-amyloid-β (Aβ) antibodies results in reduced parenchymal amyloid but increased vascular amyloid and microhemorrhage in amyloid precursor protein (APP) transgenic mice. Here, we evaluate the effects of reducing effector interactions of the antibody via deglycosylation. Mice aged 20 months were treated weekly for 4 months and tested behaviorally before they were killed. APP transgenic mice receiving either anti-Aβ (2H6) or deglycosylated anti-Aβ (de-2H6) showed significant improvement in radial arm water maze performance compared with mice receiving a control antibody. Both groups receiving anti-Aβ antibodies showed significant reductions in total Aβ immunochemistry and Congo red. Significantly fewer vascular amyloid deposits and microhemorrhages were observed in mice administered the de-2H6 antibody compared with those receiving unmodified 2H6 antibody. Deglycosylated anti-Aβ antibodies may be preferable to unmodified IgG because they retain the cognition-enhancing and amyloid-reducing properties of anti-Aβ immunotherapy, while greatly attenuating the increased vascular amyloid deposition and microhemorrhage observed with unmodified IgG.

Dynamic complexity of the microglial activation response in transgenic models of amyloid deposition : Implications for alzheimer therapeutics

The presence of activated microglia in postmortem Alzheimer disease specimens is used to support the argument that inflammation contributes to Alzheimer pathogenesis. Transgenic mice overexpressing the amyloid precursor protein (APP) gene form amyloid plaques that are accompanied by local activation of microglia/macrophages in a manner similar to the human disease. Many markers of microglial activation and inflammation increase in an age-dependent manner in these mice. However, manipulation of these inflammatory reactions can lead to unexpected outcomes with several instances of reduced pathology when microglia/macrophages are activated further. In particular, anti-Aβ immunotherapy in amyloid-depositing transgenic mice causes a complex series of changes in microglial markers, negating the implicit belief that such activation is monotonic and represented equally well by any of several “activation” markers. A survey of the peripheral macrophage literature identifies at least 2 distinct activation states of macrophages with different consequences for the surrounding tissue. These different activation states can often be distinguished by the markers that are expressed. Several markers are identified from studies outside the brain that neuroscientists might consider evaluating when attempting to more definitively describe the activation state of the monocyte-derived cells in the brain.

Vascular contributions to cognitive impairment and dementia including Alzheimer's disease

Scientific evidence continues to demonstrate the linkage of vascular contributions to cognitive impairment and dementia such as Alzheimers disease. In December, 2013, the Alzheimers Association, with scientific input from the National Institute of Neurological Disorders and Stroke and the National Heart, Lung and Blood Institute from the National Institutes of Health, convened scientific experts to discuss the research gaps in our understanding of how vascular factors contribute to Alzheimers disease and related dementia. This manuscript summarizes the meeting and the resultant discussion, including an outline of next steps needed to move this area of research forward.

Two-day radial-arm water maze learning and memory task; robust resolution of amyloid-related memory deficits in transgenic mice

The radial arm water maze (RAWM) contains six swim paths (arms) extending out of an open central area, with an escape platform located at the end of one arm (the goal arm). The goal arm location remains constant for a given mouse. On day 1, mice are trained for 15 trials (spaced over 3 h), with trials alternating between visible and hidden platform. On day 2, mice are trained for 15 trials with the hidden platform. Entry into an incorrect arm is scored as an error. The RAWM has the spatial complexity and performance measurement simplicity of the dry radial arm maze combined with the rapid learning and strong motivation observed in the Morris water maze without requiring foot shock or food deprivation as motivating factors. With two sessions each day, 16 mice can be tested over 2 days.