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Increasing evidence suggests that infection with Sars-CoV-2 causes neurological deficits in a substantial proportion of affected patients. While these symptoms arise acutely during the course of infection, less is known about the possible long-term consequences for the brain. Severely affected COVID-19 cases experience high levels of proinflammatory cytokines and acute respiratory dysfunction and often require assisted ventilation. All these factors have been suggested to cause cognitive decline. Pathogenetically, this may result from direct negative effects of the immune reaction, acceleration or aggravation of pre-existing cognitive deficits, or de novo induction of a neurodegenerative disease. This article summarizes the current understanding of neurological symptoms of COVID-19 and hypothesizes that affected patients may be at higher risk of developing cognitive decline after overcoming the primary COVID-19 infection. A structured prospective evaluation should analyze the likelihood, time course, and severity of cognitive impairment following the COVID-19 pandemic.

Background Tau stabilizes microtubules; however, in Alzheimer’s disease (AD) and tauopathies, tau becomes hyperphosphorylated, aggregates, and results in neuronal death. Our group recently uncovered a unique interaction between polyamine metabolism and tau fate. Polyamines exert an array of physiological effects that support neuronal function and cognitive processing. Specific stimuli can elicit a polyamine stress response (PSR), resulting in altered central polyamine homeostasis. Evidence suggests that elevations in polyamines following a short-term stressor are beneficial; however, persistent stress and subsequent PSR activation may lead to maladaptive polyamine dysregulation, which is observed in AD, and may contribute to neuropathology and disease progression. Methods Male and female mice harboring tau P301L mutation (rTg4510) were examined for a tau-induced central polyamine stress response (tau-PSR). The direct effect of tau-PSR byproducts on tau fibrillization and oligomerization were measured using a thioflavin T assay and a N2a split superfolder GFP-Tau (N2a-ssGT) cell line, respectively. To therapeutically target the tau-PSR, we bilaterally injected caspase 3-cleaved tau truncated at aspartate 421 (AAV9 Tau ΔD421) into the hippocampus and cortex of spermidine/spermine-N 1-acetyltransferase (SSAT), a key regulator of the tau-PSR, knock out (SSAT-/-), and wild type littermates, and the effects on tau neuropathology, polyamine dysregulation, and behavior were measured. Lastly, cellular models were employed to further examine how SSAT repression impacted tau biology. Results Tau induced a unique tau-PSR signature in rTg4510 mice, notably in the accumulation of acetylated spermidine. In vitro, higher-order polyamines prevented tau fibrillization but acetylated spermidine failed to mimic this effect and even promoted fibrillization and oligomerization. AAV9 Tau ΔD421 also elicited a unique tau-PSR in vivo, and targeted disruption of SSAT prevented the accumulation of acetylated polyamines and impacted several tau phospho-epitopes. Interestingly, SSAT knockout mice presented with altered behavior in the rotarod task, the elevated plus maze, and marble burying task, thus highlighting the impact of polyamine homeostasis within the brain. Conclusion These data represent a novel paradigm linking tau pathology and polyamine dysfunction and that targeting specific arms within the polyamine pathway may serve as new targets to mitigate certain components of the tau phenotype.

Brain myeloid cells, include infiltrating macrophages and resident microglia, play an essential role in responding to and inducing neurodegenerative diseases, such as Alzheimer’s disease (AD). Genome-wide association studies (GWAS) implicate many AD casual and risk genes enriched in brain myeloid cells. Coordinated arginine metabolism through arginase 1 (Arg1) is critical for brain myeloid cells to perform biological functions, whereas dysregulated arginine metabolism disrupts them. Altered arginine metabolism is proposed as a new biomarker pathway for AD. We previously reported Arg1 deficiency in myeloid biased cells using lysozyme M (LysM) promoter-driven deletion worsened amyloidosis-related neuropathology and behavioral impairment. However, it remains unclear how Arg1 deficiency in these cells impacts the whole brain to promote amyloidosis. Herein, we aim to determine how Arg1 deficiency driven by LysM restriction during amyloidosis affects fundamental neurodegenerative pathways at the transcriptome level. By applying several bioinformatic tools and analyses, we found that amyloid-β (Aβ) stimulated transcriptomic signatures in autophagy-related pathways and myeloid cells’ inflammatory response. At the same time, myeloid Arg1 deficiency during amyloidosis promoted gene signatures of lipid metabolism, myelination, and migration of myeloid cells. Focusing on Aβ associated glial transcriptomic signatures, we found myeloid Arg1 deficiency up-regulated glial gene transcripts that positively correlated with Aβ plaque burden. We also observed that Aβ preferentially activated disease-associated microglial signatures to increase phagocytic response, whereas myeloid Arg1 deficiency selectively promoted homeostatic microglial signature that is non-phagocytic. These transcriptomic findings suggest a critical role for proper Arg1 function during normal and pathological challenges associated with amyloidosis. Furthermore, understanding pathways that govern Arg1 metabolism may provide new therapeutic opportunities to rebalance immune function and improve microglia/macrophage fitness.

Alzheimer’s disease (AD) includes several hallmarks comprised of amyloid-β (Aβ) deposition, tau neuropathology, inflammation, and memory impairment. Brain metabolism becomes uncoupled due to aging and other AD risk factors, which ultimately lead to impaired protein clearance and aggregation. Increasing evidence indicates a role of arginine metabolism in AD, where arginases are key enzymes in neurons and glia capable of depleting arginine and producing ornithine and polyamines. However, currently, it remains unknown if the reduction of arginase 1 (Arg1) in myeloid cell impacts amyloidosis. Herein, we produced haploinsufficiency of Arg1 by the hemizygous deletion in myeloid cells using Arg1fl/fl and LysMcreTg/+ mice crossed with APP Tg2576 mice. Our data indicated that Arg1 haploinsufficiency promoted Aβ deposition, exacerbated some behavioral impairment, and decreased components of Ragulator-Rag complex involved in mechanistic target of rapamycin complex 1 (mTORC1) signaling and autophagy. Additionally, Arg1 repression and arginine supplementation both impaired microglial phagocytosis in vitro. These data suggest that proper function of Arg1 and arginine metabolism in myeloid cells remains essential to restrict amyloidosis.

Innate immune activation is a major contributor to Alzheimer's Disease (AD) pathophysiology, although the mechanisms involved are poorly understood. Chemokine C-C motif ligand (CCL) 2 is produced by neurons and glial cells and is upregulated in the AD brain. Transgene expression of CCL2 in mouse models of amyloidosis produces microglia-induced amyloid β oligomerization, a strong indication of the role of these activation pathways in the amyloidogenic processes of AD. We have previously shown that CCL2 polarizes microglia in wild type mice. However, how CCL2 signaling contributes to tau pathogenesis remains unknown. To address this question, CCL2 was delivered via recombinant adeno-associated virus serotype 9 into both cortex and hippocampus of a mouse model with tau pathology (rTg4510). We report that CCL2 overexpression aggravated tau pathology in rTg4510 as shown by the increase in Gallyas stained neurofibrillary tangles as well as phosphorylated tau-positive inclusions. In addition, biochemical analysis showed a reduction in the levels of detergent-soluble tau species followed by increase in the insoluble fraction, indicating a shift toward larger tau aggregates. Indeed, increased levels of high molecular weight species of phosphorylated tau were found in the mice injected with CCL2. We also report that worsening of tau pathology following CCL2 overexpression was accompanied by a distinct inflammatory response. We report an increase in leukocyte common antigen (CD45) and Cluster of differentiation 68 (CD68) expression in the brain of rTg4510 mice without altering the expression levels of a cell-surface protein Transmembrane Protein 119 (Tmem119) and ionized calcium-binding adaptor molecule 1 (Iba-1) in resident microglia. Furthermore, the analysis of cytokines in brain extract showed a significant increase in interleukin (IL)-6 and CCL3, while CCL5 levels were decreased in CCL2 mice. No changes were observed in IL-1α, IL-1β, TNF-α. IL-4, Vascular endothelial growth factor-VEGF, IL-13 and CCL11. Taken together our data report for the first time that overexpression of CCL2 promotes the increase of pathogenic tau species and is associated with glial neuroinflammatory changes that are deleterious. We propose that these events may contribute to the pathogenesis of Alzheimer's disease and other tauopathies.

Abnormal tau hyperphosphorylation and its aggregation into neurofibrillary tangles are a hallmark of tauopathies, neurodegenerative disorders that include Alzheimer’s disease (AD). Active and passive Tau-immunotherapy has been proposed as a therapeutic approach to AD with mixed results. One of the limitations of active immunotherapy may be associated with the mediocre immunogenicity of vaccines that are not inducing therapeutically potent titers of antibodies. The aim of this study was to test the efficacy of an anti-tau vaccine, AV-1980R/A composed of N terminal peptide of this molecule fused with an immunogenic MultiTEP platform and formulated in a strong adjuvant, Advax(CpG) in a Tg4510 mouse model of tauopathy. Experimental mice were immunized with AV-1980R/A and a control group of mice were injected with adjuvant only. Nontransgenic and tetracycline transactivator (tTA) transgenic littermates were included as baseline controls to contrast with the tau phenotype. Active immunization with AV-1980R/A induced very strong anti-tau humoral immune responses in both nontransgenic and transgenic mice with evidence of IgG in brains of AV-1980R/A vaccinated mice. These experimental animals displayed an improvement in short-term memory during a novel object recognition test. However, impairments in other behavioral tasks were not prevented by AV-1980R/A vaccinations. At the same time, high titers of anti-tau antibodies reduced hyperphosphorylated pSer396 tau but did not lower the level of other phosphorylated tau species in the brains of AV-1980R/A vaccinated mice. These data indicate that active immunotherapy with an N-terminal Tau epitope was only partially effective in improving cognition and reducing pathology in the stringent Tg4510 mouse model of tauopathy.

Accumulating evidence increasingly implicates regulation of neuroinflammation as a potential therapeutic target in Alzheimer's disease and other neurodegenerative disorders. Fractalkine (FKN) is a unique chemokine that is expressed and secreted by neurons and reduces expression of pro-inflammatory genes. To further demonstrate the utility of agents that increase FKN signaling throughout the central nervous system as possible therapies for AD, we assessed the impact of soluble FKN (sFKN) over expression on cognition in tau depositing rTg450 mice after the onset of cognitive deficits. Using adeno-associated virus serotype 4, we infected cells lining the ventricular system with soluble FKN to increase FKN signaling over a larger fraction of the brain than achieved with intraparenchymal injections. We found that soluble FKN over expression by cells lining the ventricles significantly improved cognitive performance on the novel mouse recognition and radial arm water maze tasks. These benefits were achieved without detectable reductions in tau hyperphosphorylation, hippocampal atrophy, or microglial CD45 expression. Utilizing qPCR, we report a significant increase in Vegfa expression, indicating an increase in trophic support and possible neovascularization in AAV-sFKN-injected mice. To our knowledge, this is the first demonstration that FKN over expression can rescue cognitive function in a tau depositing mouse line. Graphical Abstract Regulating neuroinflammation is an attractive therapeutic target for Alzheimer's disease. Microglial activation can not only drive pathology but also accelerate cognitive decline. The chemokine fractalkine regulates the microglial phenotype, increasing trophic support of neurons, and significantly improving cognitive functioning in the rTg4510 mouse model of tauopathy.

Inflammation, including microglial activation in the CNS, is an important hallmark in many neurodegenerative diseases. Microglial stimuli not only impact the brain microenvironment by production and release of cytokines and chemokines, but also influence the activity of bone marrow derived cells and blood born macrophage populations. In many diseases including brain disorders and spinal cord injury, researchers have tried to harbor the neuroprotective and repair properties of these subpopulations. Hematopoietic bone marrow derived cells (BMDCs) are of great interest, especially during gene therapy because certain hematopoietic cell subpopulations traffic to the sites of injury and inflammation. The aim of this study was to develop a method of labeling endogenous bone marrow derived cells through intraosseous impregnation of recombinant adeno-associated virus (rAAV) or lentivirus. We utilized rAAV serotype 9 (rAAV-9) or lentivirus for gene delivery of green florescence protein (GFP) to the mouse bone marrow cells. Flow cytometry showed that both viruses were able to efficiently transduce mouse bone marrow cells in vivo. However, the rAAV9-GFP viral construct transduced BMDCs more efficiently than the lentivirus (11.2% vs. 6.8%), as indicated by cellular GFP expression. We also demonstrate that GFP labeled cells correspond to bone marrow cells of myeloid origin using CD11b as a marker. Additionally, we characterized the ability of bone marrow derived, GFP labeled cells to extravasate into the brain parenchyma upon acute and subchronic neuroinflammatory stimuli in the mouse CNS. Viral mediated over expression of chemokine (C-C motif) ligand 2 (CCL2) or intracranial injection of lipopolysaccharide (LPS) recruited GFP labeled BMDCs from the periphery into the brain parenchyma compared to vehicle treated mice. Altogether our findings demonstrate a useful method of labeling endogenous BMDCs via viral transduction and the ability to track subpopulations throughout the body following insult or injury. Alternatively, this method might find utility in delivering therapeutic genes for neuroinflammatory conditions.

Calorie restriction (CR) was shown previously to improve cognition and decrease pathology in transgenic mouse models with Alzheimer-like amyloid deposition. In the present study, we investigated the effects of CR on the Tg4510 model of tau deposition. Mice in the calorie restriction group had food intake gradually decreased until they reached an average of 35% body weight reduction. Body weight and food intake were monitored throughout the study. After being on their respective diets for 3 months, all animals were submitted to behavioral testing. Tg4510 mice fed ad libitum showed lower body weight than nontransgenic littermates despite their increased food intake. Additionally, Tg4510 showed increased locomotor activity in the open field regardless of diet. Calorie restricted Tg4510 mice performed significantly better than ad libitum fed mice in the novel object recognition test, suggesting improved short-term memory. CR Tg4510 mice also performed significantly better in contextual fear conditioning than mice fed ad libitum. However, in a modified version of the novelty test that allows for interaction with other mice instead of inanimate objects, CR was not able to rescue the deficit found in Tg4510 mice in this ethologically more salient version of the task. No treatment differences in motor performance or spatial memory were observed in the rotarod or radial arm water maze tests, respectively. Histopathological and biochemical assessments showed no diet-induced changes in total or phospho-tau levels. Moreover, increased activation of both astrocytes and microglia in Tg4510 mice was not rescued by calorie restriction. Taken together, our data suggests that, despite an apparent rescue of associative memory, CR had no consistent effects on pathological outcomes of a mouse model of tau deposition.

The roles of microglia and macrophages during neuroinflammation and neurodegenerative diseases remain controversial. To date, at least 2 activations states have been suggested, consisting of a classical response (M1) and the alternative response (M2). Identifying selective biomarkers of microglia that representative their functional activation states may help elucidate disease course and enable a better understanding of repair mechanisms. Two cocktails containing either tumor necrosis factor (TNF)-α, interleukin (IL)-12, and IL-1β (referred to as CKT-1) or IL-13 and IL-4 (referred to CKT-2) were injections into the hippocampus of mice aged 6, 12, or 24 months. Microarray analysis was performed on hippocampal tissue 3 days postinjection. Gene transcripts were compared between CKT-1 versus CKT-2 stimulator cocktails. Several selective transcripts expressed for the CKT-1 included CXCL13, haptoglobin, MARCO, and calgranulin B, whereas a smaller subset of genes was selectively induced by the CKT-2 and consisted of FIZZ1, IGF-1, and EAR 11. Importantly, selective transcripts were induced at all ages by CKT-1, whereas selective gene transcripts induced by CKT-2 decreased with age suggesting an age-related reduction in the IL-4/ IL-13 signaling pathway.

The inflammation hypothesis of Alzheimer's pathogenesis has directed much scientific effort towards ameliorating this disease. The development of mouse models of amyloid deposition permitted direct tests of the proposal that amyloid-activated microglia could cause neurodegeneration in vivo. Many approaches to manipulating microglial activation have been applied to these mouse models, and are the subject of this review. In general, these results do not support a direct neuricidal action of microglia in mouse amyloid models under any activation state. Some of the manipulations cause both a reduction in pathology and a reduction in microglial activation. However, at least for agents like ibuprofen, this outcome may result from a direct action on amyloid production, and a reduction in the microglial-provoking amyloid deposits, rather than from reduced microglial activation leading to a decline in amyloid deposition. Instead, a surprising number of the experimental manipulations which increase microglial activation lead to enhanced clearance of the amyloid deposits. Both the literature and new data presented here suggest that either classical or alternative activation of microglia can lead to enhanced amyloid clearance. However, a limited number of studies comparing the same treatments in amyloid-depositing vs. tau-depositing mice find the opposite effects. Treatments that benefit amyloid pathology accelerate tau pathology. This observation argues strongly that potential treatments be tested for impact on both amyloid and tau pathology before consideration of testing in humans.

Why certain diseases primarily affect one specific neuronal subtype rather than another is a puzzle whose solution underlies the development of specific therapies. Selective basal forebrain cholinergic (BFC) neurodegeneration participates in cognitive impairment in Alzheimer’s disease (AD), yet the underlying mechanism remains elusive. Here, we report the first recapitulation of the selective BFC neuronal loss that is typical of human AD in a mouse model termed GAP. We created GAP mice by crossing Tg2576 mice that over-express the Swedish mutant human β-amyloid precursor protein gene with G protein-coupled receptor kinase-5 (GRK5) knockout mice. This doubly defective mouse displayed significant BFC neuronal loss at 18 months of age, which was not observed in either of the singly defective parent strains or in the wild type. Along with other supporting evidence, we propose that GRK5 deficiency selectively renders BFC neurons more vulnerable to degeneration.

One vexing issue in biomedical research is the failure of many therapies to translate from success in animal models to effective treatment of human disease. One significant difference between the animal models and the human disease is the age of the subject. Cancer, stroke and Alzheimer's occur mainly in humans beyond the 75% mean survival age, while most mouse models use juvenile or young adult animals. Here we compare two mouse models of amyloid deposition, the Tg2576 APP model and the more aggressive APP+PS1 model in which a mutant presenilin1 gene is overexpressed with Tg2576. Middle-aged APP+PS1 mice and aged APP mice have similar degrees of amyloid pathology with a few differences that may partially explain some of the differences between the two age cohorts. The first study evaluated production of microhemorrhage by a monoclonal anti-Aβ antibody. We found that in spite of greater amyloid clearance in middle-aged APP+PS1 mice than aged APP mice, the microhemorrhage only developed in old animals. This argues that preclinical studies of immunotherapy in young or middle-aged mice may not predict this potential liability in clinical trials. A second study evaluated the infiltration of systemically injected GFP labeled monocytes into the CNS. Here we find that infiltration is greater in aged mice than middle-aged mice, in spite of greater total Aß staining in the middle-aged animals. We conclude that preclinical studies should be conducted in aged animal models as well as young mice to better prepare for unintended consequences in the human trial.

Mutations in the presenilin-1 (PS1) gene are independent causes of familial Alzheimer's disease (AD). AD patients have dysregulated immunity, and PS1 mutant mice exhibit abnormal systemic immune responses. To test whether immune function abnormality caused by a mutant human PS1 gene (mhPS1) could modify AD-like pathology, we reconstituted immune systems of AD model mice carrying a mutant human amyloid precursor protein gene (mhAPP; Tg2576 mice) or both mhAPP and mhPS1 genes (PSAPP mice) with allo-geneic bone marrow cells. Here, we report a marked reduction in amyloid-β (Aβ) levels, β-amyloid plaques and brain inflammatory responses in PSAPP mice following strain-matched wild-type PS1 bone marrow reconstitution. These effects occurred with immune switching from pro-inflammatory T helper (Th) 1 to anti-inflammatory Th2 immune responses in the periphery and in the brain, which likely instructed microglia to phagocytose and clear Aβ in an ex vivo assay. Conversely, Tg2576 mice displayed accelerated AD-like pathology when reconstituted with mhPS1 bone marrow. These data show that haematopoietic cells bearing the mhPS1 transgene exacerbate AD-like pathology, suggesting a novel therapeutic strategy for AD based on targeting PS1 in peripheral immune cells.

In the year 1999, a vaccine approach was found to reduce amyloid deposits in transgenic mice overproducing the amyloid precursor protein. This was followed closely by demonstrations that vaccines or passive immunotherapy could rescue memory deficits in these mice. Initial human clinical trials revealed apparent autoimmune reactions in a subset of patients, but also some cases of cognitive benefit and amyloid clearance. Further work with passive immunotherapy in mouse models confirmed exceptional clearing abilities of anti-amyloid antibodies even in older mice. However, in parallel with parenchymal amyloid clearance was the appearance of microhaemorrhages and increased vascular amyloid deposition. Additional clinical trials with passive immunotherapy confirmed occasional appearance of microhaemorrhage and occurrence of vasogenic oedema in some patients, particularly those with the apolipoprotein E4 genotype. Recent data with positron emission tomography demonstrates trial participants passively immunized with anti-As antibodies have reduced signals with amyloid binding ligands after 18 months of therapy. Several anti-As immunotherapies have reached phase 3 testing, and immunotherapy is likely to be the first test of the amyloid hypothesis of Alzheimer's disease. Identifying antibody variants that retain amyloid clearance with fewer adverse reactions remains a major focus of translational research in this area.

The use of recombinant adeno-associated viral (rAAV) vectors as a means of gene delivery to the central nervous system has emerged as a potentially viable method for the treatment of several types of degenerative brain diseases. However, a limitation of typical intracranial injections into the adult brain parenchyma is the relatively restricted distribution of the delivered gene to large brain regions such as the cortex, presumably due to confined dispersion of the injected particles. Optimizing the administration techniques to maximize gene distribution and gene expression is an important step in developing gene therapy studies. Here, we have found additive increases in distribution when 3 methods to increase brain distribution of rAAV were combined. The convection enhanced delivery (CED) method with the step-design cannula was used to deliver rAAV vector serotypes 5, 8 and 9 encoding GFP into the hippocampus of the mouse brain. While the CED method improved distribution of all 3 serotypes, the combination of rAAV9 and CED was particularly effective. Systemic mannitol administration, which reduces intracranial pressure, also further expanded distribution of GFP expression, in particular, increased expression on the contralateral hippocampi. These data suggest that combining advanced injection techniques with newer rAAV serotypes greatly improves viral vector distribution, which could have significant benefits for implementation of gene therapy strategies.

Immunotherapy has emerged as a leading new approach to the reduction of amyloid deposits in the brains of Alzheimer patients. At least 4 distinct actions of anti-Abeta antibodies have been proposed as contributing to the inhibition of amyloid deposition and its clearance. Critically, each of these proposed mechanisms may be acting simultaneously, and it is feasible that different antibodies may utilize each mechanism to a different extent. One of these proposed mechanisms involves the activation of microglia and the phagocytosis of Abeta peptide. In general this is assumed to proceed through the Fcgamma-receptor binding by antibody opsonized Abeta aggregates, however modifying the microglial phenotype into one with a greater propensity for phagocytosing Abeta is also feasible, as microglia avidly phagocytose Abeta in vitro without antibody present. Evidence is presented supporting arguments that microglial activation does play a role in amyloid removal, particularly compacted amyloid deposits, under certain conditions. In addition to the specific antibody used, other considerations in comparing different reports of antibody action in APP mice include the age of the mice, the extent of pre-existing amyloid when therapy is initiated, the time point when the effects of the therapy are examined and the route of antibody administration. Future questions will consider the source of the activated microglia near the plaques after antibody administration (resident or peripheral) and the extent to which shifts in the microglial phenotype mediate some of the amyloid lowering actions of immunotherapy.

Oligomeric assemblies of amyloid-beta (Abeta) are suggested to be central in the pathogenesis of Alzheimer's disease because levels of soluble Abeta correlate much better with the extent of cognitive dysfunctions than do senile plaque counts. Moreover, such Abeta species have been shown to be neurotoxic, to interfere with learned behavior and to inhibit the maintenance of hippocampal long-term potentiation. The tg-ArcSwe model (i.e. transgenic mice with the Arctic and Swedish Alzheimer mutations) expresses elevated levels of Abeta protofibrils in the brain, making tg-ArcSwe a highly suitable model for investigating the pathogenic role of these Abeta assemblies. In the present study, we estimated Abeta protofibril levels in the brain and cerebrospinal fluid of tg-ArcSwe mice, and also assessed their role with respect to cognitive functions. Protofibril levels, specifically measured with a sandwich ELISA, were found to be elevated in young tg-ArcSwe mice compared to several transgenic models lacking the Arctic mutation. In aged tg-ArcSwe mice with considerable plaque deposition, Abeta protofibrils were approximately 50% higher than in younger mice, whereas levels of total Abeta were exponentially increased. Young tg-ArcSwe mice showed deficits in spatial learning, and individual performances in the Morris water maze were correlated inversely with levels of Abeta protofibrils, but not with total Abeta levels. We conclude that Abeta protofibrils accumulate in an age-dependent manner in tg-ArcSwe mice, although to a far lesser extent than total Abeta. Our findings suggest that increased levels of Abeta protofibrils could result in spatial learning impairment.

Anti-Abeta antibody administration to amyloid-depositing transgenic mice can reverse amyloid pathology and restore memory function. However, in old mice, these treatments also increase vascular leakage and promote formation of vascular amyloid deposits. Deglycosylated antibodies with reduced affinity for Fcgamma receptors and complement are associated with reduced vascular amyloid and microhemorrhage while retaining amyloid-clearing and memory-enhancing properties of native intact antibodies. In the current experiment, we investigated the effect of 3, 10, or 30 mg/kg of deglycosylated antibody (D-2H6) on amyloid pathology and cognitive behavior in old Tg2576 mice. We found that low doses of deglycosylated antibody appear more efficacious than higher doses in reducing pathology and memory loss in amyloid precursor protein (APP) transgenic mice. These data suggest that excess antibody unbound to antigen can interfere with antibody-mediated Abeta clearance, possibly by saturating the FcRn antibody transporter.

Amyloid-β (Aβ) immunization efficiently reduces amyloid plaque load and memory impairment in transgenic mouse models of Alzheimer’s disease (AD) (Schenk et al., 1999; Morgan et al., 2000). Active Aβ immunization has also yielded favorable results in a subset of AD patients (Hock et al., 2003). However, a small percentage of patients developed severe aseptic meningoencephalitis associated with brain inflammation and infiltration of T-cells (Nicoll et al., 2003; Orgogozo et al., 2003). We and others have shown that blocking the CD40-CD40 ligand (L) interaction mitigates Aβ-induced inflammatory responses and enhances Aβ clearance (Tan et al., 2002b; Townsend et al., 2005). Here, we utilized genetic and pharmacologic approaches to test whether CD40-CD40L blockade could enhance the efficacy of Aβ1–42 immunization, while limiting potentially damaging inflammatory responses. We show that genetic or pharmacologic interruption of CD40-CD40L interaction enhanced Aβ1–42 immunization efficacy to reduce cerebral amyloidosis in the PSAPP and Tg2576 mouse models of AD. Potentially deleterious pro-inflammatory immune responses, cerebral amyloid angiopathy (CAA) and cerebral microhemorrhage were reduced or absent in these combined approaches. Pharmacologic blockade of CD40L decreased T-cell neurotoxicity to Aβ-producing neurons. Further reduction of cerebral amyloidosis in Aβ-immunized PSAPP mice completely deficient for CD40 occurred in the absence of Aβ immunoglobulin G (IgG) antibodies or efflux of Aβ from brain to blood, but was rather correlated with anti-inflammatory cytokine profiles and reduced plasma soluble CD40L. These results suggest CD40-CD40L blockade promotes anti-inflammatory cellular immune responses, likely resulting in promotion of microglial phagocytic activity and Aβ clearance while precluding generation of neurotoxic Aβ-reactive T-cells. Thus, combined approaches of Aβ immunotherapy and CD40-CD40L blockade may provide for safer and more effective Aβ vaccine.

Inflammation has been argued to play a fundamental role in the pathogenesis of Alzheimer's disease. Mice transgenic for mutant human amyloid precursor protein (APP) develop progressive amyloid deposition, gliosis, and cognitive impairment. Paradoxically, intracranial administration of lipopolysaccharide (LPS) to promote neuroinflammation results in a reduction in amyloid-beta peptide (Abeta) burden concurrent with the inflammatory response. To determine whether microglia mediate Abeta clearance after LPS, we used dexamethasone to inhibit the microglial response. Amyloid precursor protein mice were injected intrahippocampally with either LPS or saline and were allowed to survive for 7 days with or without dexamethasone cotreatment. Brain tissue was then analyzed by immunohistochemistry. Hippocampal Abeta burden was reduced 7 days after LPS injection, and this was prevented by cotreatment with dexamethasone. Markers of microglial activation [CD45, complement receptor 3 (CR3), and macrosialin (CD68)] were increased by LPS, and these increases were attenuated by dexamethasone. Dexamethasone failed to block LPS-induced increases in all microglial markers, and Fcgamma receptors II/III and scavenger receptor A were increased by LPS but were unaffected by dexamethasone cotreatment. These results indicate a complex response by microglia to acute LPS treatment, with only some responses sensitive to steroidal anti-inflammatory drug treatment. Nonetheless, microglial activation was necessary to remove Abeta in this model of neuroinflammation.

Vaccination with Aβ1–42 and treatment with NCX-2216, a novel nitric oxide releasing flurbiprofen derivative, have each been shown separately to reduce amyloid deposition in transgenic mice and have been suggested as potential therapies for Alzheimer’s disease. In the current study we treated doubly transgenic amyloid precursor protein and presenilin-1 (APP+PS1) mice with Aβ1–42 vaccination, NCX-2216 or both drugs simultaneously for 9 months. We found that all treatments reduced amyloid deposition, both compact and diffuse, to the same extent while only vaccinated animals, with or without non-steroidal anti-inflammatory drug (NSAID) treatment, showed increased microglial activation associated with the remaining amyloid deposits. We also found that active Aβ vaccination resulted in significantly increased cerebral amyloid angiopathy and associated microhemorrhages, while NCX-2216 did not, in spite of similar reductions in parenchymal amyloid. Co-administration of NCX-2216 did not attenuate this effect of the vaccine. This is the first report showing that active immunization can result in increased vascular amyloid and microhemorrhage, as has been observed with passive immunization. Co-administration of an NSAID agent with Aβ vaccination does not substantially modify the effects of Aβ immunotherapy. The difference between these treatments with respect to vascular amyloid development may reflect the clearance-promoting actions of the vaccine as opposed to the production-modifying effects proposed for flurbiprofen.

Abeta-induced neurodegeneration is limited in APP and APP+PS1 transgenic mice. In middle-aged APP + PS1 transgenic mice, we found significantly increased Bcl-2 expression. The increase in Bcl-2 is restricted to amyloid-containing brain regions and is not found at young ages, suggesting that Abeta deposition is the stimulus for increased Bcl-2. Western blot results were confirmed with immunohistochemistry and qRT-PCR. In addition, we found that APP transgenic mice were protected from neurotoxicity caused by an injection of bak BH3 fusion peptides, known to induce apoptosis by antagonizing bcl protein activity. Nissl and fluorojade-stained slides showed that the active bak BH3 peptide caused substantial neuronal loss in the dentate gyrus and CA3 regions of nontransgenic, but not APP mice. The inactive mutant bak BH3 peptide did not cause degeneration in any mice. These data demonstrate that the increased Bcl-2 expression in brain regions containing Abeta deposits is associated with neuroprotection.

Weight loss and food intake disturbances that often precede cognitive decline and diagnosis have been extensively reported in Alzheimer’s disease patients. Previously, we observed that transgenic mice overexpressing tau seemed to eat more food, yet weigh less than non-transgenic littermates. Thus the present longitudinal study measured the time course of changes in metabolic state over the lifespan of the tau depositing Tg4510 mouse model of tau deposition. Although body weight was comparable to non-transgenic littermates at 2 months of age, Tg4510 mice weighed less at older ages. This was accompanied by the accumulation of tau pathology and by dramatically increased activity in all phases of the 24-hour cycle. Resting metabolic rate was also increased at 7 months of age. At 12 months near the end of the Tg4510 lifespan, there was a wasting phase, with a considerable decrease of resting metabolic rate, although hyperactivity was maintained. These diverse changes in metabolism in a mouse model of tau deposition are discussed in the context of known changes in energy metabolism in Alzheimer’s disease.

Tau accumulation remains one of the closest correlates of neuronal loss in Alzheimer's disease. In addition, tau associates with several other neurodegenerative diseases, collectively known as tauopathies, in which clinical phenotypes manifest as cognitive impairment, behavioral disturbances, and motor impairment. Polyamines act as bivalent regulators of cellular function and are involved in numerous biological processes. The regulation of the polyamines system can become dysfunctional during disease states. Arginase 1 (Arg1) and nitric oxide synthases compete forl-arginine to produce either polyamines or nitric oxide, respectively. Herein, we show that overexpression of Arg1 using adeno-associated virus (AAV) in the CNS of rTg4510 tau transgenic mice significantly reduced phospho-tau species and tangle pathology. Sustained Arg1 overexpression decreased several kinases capable of phosphorylating tau, decreased inflammation, and modulated changes in the mammalian target of rapamycin and related proteins, suggesting activation of autophagy. Arg1 overexpression also mitigated hippocampal atrophy in tau transgenic mice. Conversely, conditional deletion of Arg1 in myeloid cells resulted in increased tau accumulation relative to Arg1-sufficient mice after transduction with a recombinant AAV–tau construct. These data suggest that Arg1 and the polyamine pathway may offer novel therapeutic targets for tauopathies.

Immunotherapy directed against tau is a promising treatment strategy for Alzheimer’s Disease (AD) and tauopathies. We review initial studies on tau-directed immunotherapy, and present data from our laboratory testing antibodies using the rTg4510 mouse model, which deposits tau in forebrain neurons. Numerous antibodies have been tested for their efficacy in treating both pathology and cognitive function, in different mouse models, by different routes of administration, and at different ages or durations. We report, here, that the conformation-specific antibody MC-1 produces some degree of improvement to both cognition and pathology in rTg4510. Pathological improvements as measured by Gallyas staining for fully formed tangles and phosphorylated tau appeared four days after intracranial injection into the hippocampus. We also examined markers for microglial activation, which did not appear impacted from treatment. Behavioral effects were noted after continuous infusion of antibodies into the lateral ventricle for approximately 2 weeks. We examined basic motor skills, which were not impacted by treatment, but did note cognitive improvements with both novel object and radial arm water maze testing. Our results support earlier reports in the initial review presented here, and collectively show promise for this strategy of treatment. The general absence of extracellular tau deposits may avoid the opsonization and phagocytosis mechanisms activated by antibodies against amyloid, and make anti tau approaches a safer method of immunotherapy for Alzheimer’s disease.

Increasing evidence suggests that Alzheimer's disease pathogenesis is not restricted to the neuronal compartment but strongly interacts with immunological mechanisms in the brain. Misfolded and aggregated proteins bind to pattern recognition receptors on micro- and astroglia and trigger an innate immune response, characterized by the release of inflammatory mediators, which contribute to disease progression and severity. Genome wide analysis suggests that several genes, which increase the risk for sporadic Alzheimer's disease en-code for factors that regulate glial clearance of misfolded proteins and the inflammatory reaction. External factors, including systemic inflammation and obesity are likely to interfere with the immunological processes of the brain and further promote disease progression. This re-view provides an overview on the current knowledge and focuses on the most recent and exciting findings. Modulation of risk factors and intervention with the described immune mechanisms are likely to lead to future preventive or therapeutic strategies for Alzheimer's disease.

A primary goal of research on Alzheimer's disease is to develop disease modifying therapeutics. The amyloid cascade hypothesis has focused the initial efforts on methods to reduce amyloid. One surprising approach that has shown considerable success in mouse models and has hinted at benefits in human trials is anti-Abeta immunotherapy. Schenk first showed the amyloid reducing potential of active immunization in 1999. This prompted our group and that of St. George-Hyslop to investigate whether active immunization would similarly retard the memory deficits that develop in amyloid depositing transgenic mice. Contrary to our initial predictions of premature memory dysfunction due to inflammation, vaccination protected amyloid depositing mice from developing memory deficits. Subsequent studies found that passive immunization could reverse memory deficits, even when administered for short periods. These encouraging findings led to a trial of an Abeta vaccination in Alzheimer patients. The trial was cut short due to meningoencephalitic symptoms in 6% of patients, yet, in a subset of patients, those developing brain reactive antibodies benefited from slower rates of cognitive decline. These observations have accelerated the development of passive immunization protocols and safer vaccines. At this time, anti-amyloid immunotherapy stands poised to be the first test of the amyloid hypothesis in the treatment of Alzheimer disease.

Alzheimer’s disease is a major health problem with limited available medical treatment options. Immunotherapy is one approach with the potential to slow or reverse the disease process. In transgenic mouse models of amyloid deposition, anti-Aβ immunotherapy is remarkably effective at diminishing the amyloid burden and reversing the memory deficiency phenotype present in these mice. Three distinct mechanisms of antibody action have been proposed to mediate these benefits of anti-Aβ immunotherapy. The first is a catalytic dissolution of the Aβ fibrils, proposed by Beka Solomon and colleagues. A second mechanism is opsonization of the amyloid by the antibody and subsequent phagocytosis by macrophages proposed by Dale Schenk and the Elan group. A third mechanism proposed by DeMattos, Holtzman and colleagues is the peripheral sink hypothesis, arguing that circulating antibodies sequester Aβ and favor efflux of Aβ from the CNS over influx to the CNS. None of these mechanisms are mutually exclusive. Our research group has evaluated these mechanisms using intracranial injection and systemic administration of anti-Aβ antibodies. We found evidence supporting all three mechanisms, and suggest they may act synergistically to achieve the large effect size of the immunotherapeutic approach. However, in aged amyloid precursor protein transgenic mice administered anti-Aβ antibodies systemically, there is a redistribution of the amyloid from the parenchyma to vascular elements. This increase in congophilic angiopathy is associated with increased risk of microhemorrhage. Thus, although we favor continued testing of the immunotherapy to treat Alzheimer’s disease, we believe caution should be taken to minimize the risk of vascular leakage.

The role of microglia in the removal of amyloid deposits after systemically administered anti-Abeta antibodies remains unclear. In the current study, we injected Tg2576 APP transgenic mice weekly with an anti-Abeta 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-Abeta antibody but not in those treated with a control antibody. We found that Fcgamma 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 Abeta levels and anti-Abeta antibody levels were elevated to similar levels at all three survival times in mice given anti-Abeta 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 Abeta and resulting in Fcgamma receptor-mediated phagocytosis. Together with our earlier work, our data argue that all proposed mechanisms of anti-Abeta antibody-mediated amyloid removal can be simultaneously active.

Antibodies against Abeta have been suggested as potential therapeutic strategies for the treatment of Alzheimer disease (AD) for nearly 8 years. Animal studies have been very encouraging in that both active and passive immunization of transgenic mice can reduce amyloid load and reverse memory deficits found in these mice. Three mechanisms have been proposed to explain these results: (a). catalytic conversion of fibrillar Abeta to less toxic forms, (b). opsonization of Abeta deposits leading to microglial phagocytosis, or (c). promote the efflux of Abeta from the brain to the circulation. Evidence exists supporting all three mechanisms, which, it should be noted, are not mutually exclusive. Phase 2 clinical trials of active immunization with vaccines against human Abeta1-42 were halted due to an unacceptable incidence of meningoencephalitic reactions (6% of patients treated). However, a recent report from a fraction of the patients in this trial found that those patients developing antibodies which reacted with brain amyloid deposits had a significantly slower progression of cognitive loss over a period of 12 months. This supports the continued cautious testing of passive immunization and, possibly even active immunization against the Abeta peptide using preparations less likely to cause autoimmune reactions in the central nervous system.

The mechanisms by which anti-Abeta antibodies clear amyloid plaques in Abeta depositing transgenic mice are unclear. In the current study, we demonstrate that inhibition of anti-Abeta antibody-induced microglial activation with anti-inflammatory drugs, such as dexamethasone, inhibits removal of fibrillar amyloid deposits. We also show that anti-Abeta F(ab')(2) fragments fail to activate microglia and are less efficient in removing fibrillar amyloid than the corresponding complete IgG. Diffuse Abeta deposits are cleared by antibodies under all circumstances. These data suggest that microglial activation is necessary for efficient removal of compact amyloid deposits with immunotherapy. Inhibition of this activation may result in an impaired clinical response to vaccination against Abeta.

To determine the eiects of the recessive retinal degeneration (rd) gene on behavioral performance, three Alzheimer’s transgenic lines (APPsw, P30lL, APPsw + P301L) and non-transgenic littermates were evaluated in a comprehensive behavioral battery between 5 and 8.5 months of age. For all four genotypes collectively, rd homozygosity resulted in profound impairment in spatial cognitive tasks requiring visual acuity (Morris maze, platform recognition, and radial arm water maze). Non-transgenic and P301L mutant tau mice contributed most to this rd eiect since heterozygous and wild type mice performed well. By contrast, spatial cognitive performance of both APPsw-expressing lines was often impaired, irrespective of rd status. Sensorimotor performance was unaiected by rd homozygosity, while rd eiects on anxiety were genotype-dependent (less anxiety in NT, APPsw; more anxiety in P301L, APPsw + P301L). Our results strongly encourage rd screening of genetically manipulated mouse lines produced from rd-carrying strain backgrounds to avoid serious potential confounds in the interpretation of spatially based cognitive performance. NeuroReport 15:73^77 � c 2004 Lippincott Williams &W ilkins.

One increasingly dominant hypothesis regarding the pathogenesis of Alzheimer dementia is the inflammationhypothesis. In brief, this hypothesis argues that at least some of the neurodegeneration found in this disease issecondary to excessive activation of microglia and astrocytes, resulting in secretion of pro-inflammatory mediators,activation of the complement cascade and degeneration of synapses and neurons. The APP+PS1 transgenic mouse isa model of As amyloid deposition that results in a phenotype resembling some but not all aspects of Alzheimer's. Ourgroup has evaluated a number of manipulations designed to both exacerbate and ameliorate the microglial activationin this transgenic model, ranging from LPS injections, administration of anti-As antibodies and treatment with anti-inflammatory drugs. Contrary to our original predictions that microglial activation should exacerbate the Alzheimerphenotype in these mice, we find that treatments that cause microglial activation are associated with reduced amyloidloads. These data are discussed in the context of differences between the murine and human immune systems andqualitative differences in the As deposits found in these mouse models compared to human specimens.

Several different transgenic APP mice develop learning and memory deficits. In some cases the mice have deficits very early in life, while in other instances the mice exhibit deficits only after they have aged and amyloid deposits have accumulated. In many cases, there is a correlation in individual mice of the same age and genotype between the extent of learning and memory deficits and the amounts of deposited amyloid found in the central nervous system. While superficially this might imply that the deposited material is somehow toxic to cognition, it is likely that deposited amyloid is also an index of the overall rate of amyloid production in each mouse. Rate of production would be expected to modify not only the amounts of deposited amyloid, but also other amyloid pools, including soluble, oligomeric, conjugated (e.g. ADDLs) and intracellular. Thus, the deposited material may be an integrated reflection of total As production, in addition to indicating the amounts in fibrillar forms. As such, it is conceivable that other As pools may be more directly linked to memory deficits. Thus far, the one manipulation found to mitigate the learning and memory deficits in APP transgenic mice is immunotherapy for As, either using active or passive immunization against the peptide. These data together with other findings are leading to a conclusion that the fibrillar As deposits are not directly linked to the memory deficits in mice, and that some other As pool, more readily diminished by immunotherapy, is more directly linked to the mechanisms leading to poor performance in learning and memory tasks.

Human C1q when injected directly into hippocampus and cortex of doubly transgenic APP+PS1 mice results in the increase of Congo red-positive fibrillar deposits. Although there was no significant change in overall area stained for Aβ total, qualitatively it appeared that there was less diffuse Aβ in C1q-treated mice versus vehicle. There was no apparent change in astroglial or microglial activation caused by injection of C1q with respect to vehicle injections. These effects of C1q were only found in 50% BUB/BnJ mice, a strain with higher serum complement activity than other mouse lines. These in vivo data were consistent with the effects of C1q to increase fibrillogenesis of Aβ in vitro. In conclusion, complement protein C1q, believed to be involved in the pathogenesis of Alzheimer's disease in humans, can cause increased fibrillogenesis in the APP+PS1 mouse model of amyloid deposition.

3-4-(2-Fluoro-α-methyl-[1,1′-biphenyl]-4-acetyloxy)-3-methoxyphenyl]-2-propenoic acid 4-nitrooxy butyl ester (NCX-2216), a nitric oxide (NO)-releasing derivative of the cyclooxygenase-1-preferring nonsteroidal anti-inflammatory drug (NSAID) flurbiprofen, dramatically reduced both β-amyloid (Aβ) loads and Congo red staining in doubly transgenic (Tg) amyloid precursor protein plus presenilin-1 mice when administered at 375 ppm in diet between 7 and 12 months of age. This reduction was associated with a dramatic increase in the number of microglia expressing major histocompatibility complex-II antigen, a marker for microglial activation. In contrast, ibuprofen at 375 ppm in diet caused modest reductions in Aβ load but not Congo red staining, suggesting that the effects of this nonselective NSAID were restricted primarily to nonfibrillar deposits. We detected no effects of the cyclooxygenase-2-selective NSAID celecoxib at 175 ppm on amyloid deposition. In short-term studies of 12-month-old Tg mice, we found that the microglia-activating properties of NCX-2216 (7.5 mg · kg−1 · d−1, s.c.) were present after 2 weeks of treatment. Microglia were not activated by NCX-2216 in non-Tg mice lacking Aβ deposits, nor were microglia activated in Tg animals by flurbiprofen (5 mg · kg−1 · d−1) alone. These data are consistent with the argument that activated microglia can clear Aβ deposits. We conclude that the NO-generating component of NCX-2216 confers biological actions that go beyond those of typical NSAIDs. In conclusion, NCX-2216 is more efficacious than ibuprofen or celecoxib in clearing Aβ deposits from the brains of Tg mice, implying potential benefit in the treatment of Alzheimer's dementia.

Protein aggregation is involved in a variety of diseases. Alteration of the aggregation pathway, either to produce less toxic structures or to increase aggregate clearance, is a promising therapeutic route. Both active and passive immunization has been used for this purpose. However, the mechanism of action of antibodies on protein aggregates is not completely clear especially given poor ability of antibodies to cross blood–brain barrier. Here, we have shown that antibodies can interfere with protein aggregation at substoichiometric concentrations (as low as 1:1000 antibody to protein ratio). This is an indication that antibodies interact with aggregation intermediates in chaperone-like manner altering the aggregation pathways at very low antibody levels. This observation supports earlier suggestions that antibodies can inhibit aggregation by interaction with low abundance aggregation intermediates.

Background Abnormal tau hyperphosphorylation and its accumulation into intra-neuronal neurofibrillary tangles are linked to neurodegeneration in Alzheimer’s disease and similar tauopathies. One strategy to reduce accumulation is through immunization, but the most immunogenic tau epitopes have so far remained unknown. To fill this gap, we immunized mice with recombinant tau to build a map of the most immunogenic tau epitopes. Methods Non-transgenic and rTg4510 tau transgenic mice aged 5 months were immunized with either human wild-type tau (Wt, 4R0N) or P301L tau (4R0N). Each protein was formulated in Quil A adjuvant. Sera and splenocytes of vaccinated mice were collected to assess the humoral and cellular immune responses to tau. We employed a peptide array assay to identify the most effective epitopes. Brain histology was utilized to measure the effects of vaccination on tau pathology and inflammation. Results Humoral immune responses following immunization demonstrated robust antibody titers (up to 1:80,000 endpoint titers) to each tau species in both mice models. The number of IFN-γ producing T cells and their proliferation were also increased in splenocytes from immunized mice, indicating an increased cellular immune response, and tau levels and neuroinflammation were both reduced. We identified five immunogenic motifs within either the N-terminal (9-15 and 21-27 amino acids), proline rich (168-174 and 220-228 amino acids), or the C-terminal regions (427-438 amino acids) of the wild-type and P301L tau protein sequence. Conclusions Our study identifies five previously unknown immunogenic motifs of wild-type and mutated (P301L) tau protein. Immunization with both proteins resulted in reduced tau pathology and neuroinflammation in a tau transgenic model, supporting the efficacy of tau immunotherapy in tauopathy. Electronic supplementary material The online version of this article (doi:10.1186/s12974-014-0152-0) contains supplementary material, which is available to authorized users.

Long-term vaccinations with human beta-amyloid peptide 1-42 (Abeta1-42) have recently been shown to prevent or markedly reduce Abeta deposition in the PDAPP transgenic model of Alzheimer's disease (AD). Using a similar protocol to vaccinate 7.5-month-old APP (Tg2576) and APP+PS1 transgenic mice over an 8-month period, we previously reported modest reductions in brain Abeta deposition at 16 months. In these same mice, Abeta vaccinations had no deleterious behavioral effects and, in fact, benefited the mice by providing partial protection from age-related deficits in spatial working memory in the radial arm water maze task (RAWM) at 15.5 months. By contrast, control-vaccinated transgenic mice exhibited impaired performance throughout the entire RAWM test period at 15.5 months. The present study expands on our initial report by presenting additional behavioral results following long-term Abeta vaccination, as well as correlational analyses between cognitive performance and Abeta deposition in vaccinated animals. We report that 8 months of Abeta vaccinations did not reverse an early-onset balance beam impairment in transgenic mice. Additionally, in Y-maze testing at 16 months, all mice showed comparable spontaneous alternation irrespective of genotype or vaccination status. Strong correlations were nonetheless present between RAWM performance and extent of "compact" Abeta deposition in both the hippocampus and the frontal cortex of vaccinated APP+PS1 mice. Our results suggest that the behavioral protection of long-term Abeta vaccinations is task specific, with preservation of hippocampal-associated working memory tasks most likely to occur. In view of the early short-term memory deficits exhibited by AD patients, Abeta vaccination of presymptomatic AD patients could be an effective therapeutic to protect against such cognitive impairments.

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.

Alpha(1)-antichymotrypsin (ACT), an acute-phase inflammatory protein, is an integral component of the amyloid deposits in Alzheimer's disease (AD) and has been shown to catalyze amyloid beta-peptide polymerization in vitro. We have investigated the impact of ACT on amyloid deposition in vivo by generating transgenic GFAP-ACT-expressing mice and crossing them with the PDGF-hAPP/V717F mice, which deposit amyloid in an age-dependent manner. The number of amyloid deposits measured by Congo Red birefringence was increased in the double ACT/amyloid precursor protein (APP) transgenic mice compared with transgenic mice that only expressed APP, particularly in the hippocampus where ACT expression was highest, and the increase was preceded by elevated total amyloid beta-peptide levels at an early age. Our data demonstrate that ACT promotes amyloid deposition and provide a specific mechanism by which inflammation and the subsequent upregulation of astrocytic ACT expression in AD brain contributes to AD pathogenesis.