Reduced serum level of antibodies against amyloid beta peptide is associated with aging in Tg2576 mice

Both active and passive immunization to eliminate amyloid plaques from the brain of patients with Alzheimer's disease (AD) have confirmed that amyloid beta (Abeta) vaccination does not only result in clearance of Abeta plaques but improves behavioral-cognitive deficits in animal models of AD. In the present study, the levels of naturally occurring serum antibodies against Abeta were measured in Tg2576 mice at various ages using ELISA to determine the relationship between aging and the level of anti-Abeta autoantibody. The level of anti-Abeta antibody fell significantly at the age of 9 months, at the age when amyloid plaques started to appear in the brain of Tg2576 mice, and was persistently low thereafter. However, serum immunoglobulin (Ig) level was elevated in older transgenic mice compared with younger transgenic mice suggesting that the reduced level of anti-Abeta autoantibody was not merely due to deterioration of the immune response in aged Tg2576 mice.     

The evolution of A beta peptide burden in the APP23 transgenic mice: implications for A beta deposition in Alzheimer disease.

BACKGROUND: High levels of A beta in the cerebral cortex distinguish demented Alzheimer's disease (AD) from nondemented elderly individuals, suggesting that decreased amyloid-beta (A beta) peptide clearance from the brain is a key precipitating factor in AD. MATERIALS AND METHODS: The levels of A beta in brain and plasma as well as apolipoprotein E (ApoE) in brain were investigated by enzyme-linked immunosorbent assay (ELISA) and Western blotting at various times during the life span of the APP23 transgenic (Tg) and control mice. Histochemistry and immunocytochemistry were used to assess the morphologic characteristics of the brain parenchymal and cerebrovascular amyloid deposits and the intracellular amyloid precursor protein (APP) deposits in the APP23 Tg mice. RESULTS: No significant differences were found in the plasma levels of A beta between the APP23 Tg and control mice from 2-20 months of age. In contrast, soluble A beta levels in the brain were continually elevated, increasing 4-fold at 2 months and 33-fold in the APP23 Tg mice at 20 months of age when compared to the control mice. Soluble A beta42 was about 60% higher than A beta40. In the APP23 Tg mice, insoluble A beta40 remained at basal levels in the brain until 9 months and then rose to 680 microg/g cortex by 20 months. Insoluble A beta40 was negligible in non-Tg mice at all ages. Insoluble A beta42 in APP23 Tg mice rose to 60 microg/g cortex at 20 months, representing 24 times the control A beta42 levels. Elevated levels of ApoE in the brain were observed in the APP23 Tg mice at 2 months of age, becoming substantially higher by 20 months. ApoE colocalized with A beta in the plaques. Beta-amyloid precursor protein (betaAPP) deposits were detected within the neuronal cytoplasm from 4 months of age onward. Amyloid angiopathy in the APP23 Tg mice increased markedly with age, being by far more severe than in the Tg2576 mice. CONCLUSIONS: We suggest that the APP23 Tg mouse may develop an earlier blockage in A beta clearance than the Tg2576 mice, resulting in a more severe accumulation of A beta in the perivascular drainage pathways and in the brain. Both Tg mice reflect decreased A beta elimination and as models for the amyloid cascade they are useful to study AD pathophysiology and therapy.     

In vivo inhibition of Abeta production by memapsin 2 (beta-secretase) inhibitors

We have previously reported structure-based design of memapsin 2 (beta-secretase) inhibitors with high potency. Here we show that two such inhibitors covalently linked to a "carrier peptide" penetrated the plasma membrane in cultured cells and inhibited the production of beta-amyloid (Abeta). Intraperitoneal injection of the conjugated inhibitors in transgenic Alzheimer's mice (Tg2576) resulted in a significant decrease of Abeta level in the plasma and brain. These observations verified that memapsin 2 is a therapeutic target for Abeta reduction and also establish that transgenic mice are suitable in vivo models for the study of memapsin 2 inhibition.     

Transgenic potato expressing Abeta reduce Abeta burden in Alzheimer's disease mouse model

Beta amyloid (Abeta) is believed one of the major pathogens of Alzheimer's disease (AD), and the reduction of Abeta is considered a primary therapeutic target. Immunization with Abeta can reduce Abeta burden and pathological features in transgenic AD model mice. Transgenic potato plants were made using genes encoding 5 tandem repeats of Abeta1-42 peptides with an ER retention signal. Amyloid precursor protein transgenic mice (Tg2576) fed with transgenic potato tubers with adjuvant showed a primary immune response and a partial reduction of Abeta burden in the brain. Thus, Abeta tandem repeats can be expressed in transgenic potato plants to form immunologically functional Abeta, and these potatoes has a potential to be used for the prevention and treatment of AD.     

APP transgenic mice Tg2576 accumulate Abeta peptides that are distinct from the chemically modified and insoluble peptides deposited in Alzheimer's disease senile plaques.

The amyloid (Abeta) peptides generated in Hsiao's APP Tg2576 transgenic (Tg) mice are physically and chemically distinct from those characteristic of Alzheimer's disease (AD). Transgenic mouse Abeta peptides were purified using sequential size-exclusion and reverse-phase chromatographic systems and subjected to amino acid sequencing and mass spectrometry analyses. The mouse Abeta peptides lacked the extensive N-terminal degradations, posttranslational modifications, and cross-linkages abundant in the stable Abeta peptide deposits observed in AD. Truncated Abeta molecules appear to be generated in vivo by hydrolysis at multiple sites rather than by post-mortem C-terminal degradation. In contrast to AD amyloid cores, the Tg mice peptides were soluble in Tris-SDS-EDTA solutions, revealing both monomeric and SDS-stable oligomeric species of Abeta. In contrast to our report on Novartis Pharma APP23 Tg mice [Kuo et al. (2001) J. Biol. Chem. 276, 12991], which maintain high levels of soluble Abeta early on with later development of extensive vascular amyloid, Tg2576 mice exhibited an age-related elevation of soluble Abeta with relatively limited vascular amyloid deposition. The transgenic mouse levels of carboxy-terminal (CT) APP fragments were nearly 10-fold greater than those of human brains, and this condition may contribute to the unique pathology observed in these animals. Immunization of transgenic mice may act to prevent the pathological effects of betaAPP overproduction by binding CT molecules or halting their processing to toxic forms, in addition to having any effects on Abeta itself. Thus, differences in disease evolution and biochemistry must be considered when using transgenic animals to evaluate drugs or therapeutic interventions intended to reduce the Abeta burden in Alzheimer's disease.     

The neuronal adaptor protein X11alpha reduces Abeta levels in the brains of Alzheimer's APPswe Tg2576 transgenic mice

Increased production and deposition of the 40-42-amino acid beta-amyloid peptide (Abeta) is believed to be central to the pathogenesis of Alzheimer's disease. Abeta is derived from the amyloid precursor protein (APP), but the mechanisms that regulate APP processing to produce Abeta are not fully understood. X11alpha (also known as munc-18-interacting protein-1 (Mint1)) is a neuronal adaptor protein that binds APP and modulates APP processing in transfected non-neuronal cells. To investigate the in vivo effect of X11alpha on Abeta production in the brain, we created transgenic mice that overexpress X11alpha and crossed these with transgenics harboring a familial Alzheimer's disease mutant APP that produces increased levels of Abeta (APPswe Tg2576 mice). Analyses of Abeta levels in the offspring generated from two separate X11alpha founder mice revealed a significant, approximate 20% decrease in Abeta(1-40) in double transgenic mice expressing APPswe/X11alpha compared with APPswe mice. At a key time point in Abeta plaque deposition (8 months old), the number of Abeta plaques was also deceased in APPswe/X11alpha mice. Thus, we report here the first demonstration that X11alpha inhibits Abeta production and deposition in vivo in the brain.     

Prevention of pathological change and cognitive degeneration of Tg2576 mice by inoculating Aβ1–15 vaccine

This study aims to discuss the effect of preventing pathological changes and cognitive degeneration of Tg2576 mice by inoculating the subunit fragment of Aβ vaccine. Thirty-two Tg2576 mice were randomly divided into four groups, each having eight mice: Group I, the control group, inoculated with adjuvants; Group II, the Aβ42 group, inoculated with Aβ^₄₂ vaccine; Group III, the Aβ_1―15 group, inoculated with Aβ_1―15 vaccine; and Group IV, the Aβ_36―42 group, inoculated with Aβ_36―42 vaccine. The titer of the serum anti-body against Aβ₄₂ (Group II) was significantly higher than that of the control group (Group I), and a low level of antibodies could be detected in the brain homogenate in the three vaccine-inoculated groups. Morris water maze test showed that the Aβ42 group, Aβ_1―15 group and Aβ_36―42 group were obviously im-proved compared with the control group. The cultured splenocytes sampled from each group were induced by Con A or their respective antigens, and the cell proliferation of the three vaccine-inoculated groups was significantly higher than that of the control group. In the Aβ₄₂ group, IL2 and IFN-γ were relatively low and IL4 and IL10 were relatively high. By contrast, IL4 and IL10 were much higher in the Aβ_1―15 group and IL2 and IFN-γ were much higher in the Aβ_36―42 group. The immunohistochemical test showed a large number of senile plaques in the brain cortex and hippocampus of the mice in the con-trol group, no senile plaque in the brain of the Aβ_1―15 group and Aβ₄₂ group mice, and a small number of senile plaques in the brain of the Aβ_36―42 group mice. The results suggest that the subunit fragment of Aβ_1―15 vaccine could prevent not only cognitive and behavioral degeneration but also Aβ deposition and formation of senile plaques in Tg2576 mice.     

Overexpression of Alzheimer's disease amyloid-beta opposes the age-dependent elevations of brain copper and iron

Increased brain metal levels have been associated with normal aging and a variety of diseases, including Alzheimer's disease (AD). Copper and iron levels both show marked increases with age and may adversely interact with the amyloid-beta (Abeta) peptide causing its aggregation and the production of neurotoxic hydrogen peroxide (H(2)O(2)), contributing to the pathogenesis of AD. Amyloid precursor protein (APP) possesses copper/zinc binding sites in its amino-terminal domain and in the Abeta domain. Here we demonstrate that overexpression of the carboxyl-terminal fragment of APP, containing Abeta, results in significantly reduced copper and iron levels in transgenic mouse brain, while overexpression of the APP in Tg2576 transgenic mice results in significantly reduced copper, but not iron, levels prior to the appearance of amyloid neuropathology and throughout the lifespan of the mouse. Concomitant increases in brain manganese levels were observed with both transgenic strains. These findings, complemented by our previous findings of elevated copper levels in APP knock-out mice, support roles for APP and Abeta in physiological metal regulation.     

Progressive cognitive decline in a transgenic mouse model of Alzheimer's disease overexpressing mutant hAPPswe

The possibility of detecting progressive changes in cognitive function reflecting the spatio-temporal pattern of beta-amyloid peptide (Abeta) deposition was investigated in Tg2576 mice overexpressing the human mutant amyloid precursor protein (hAPP). Here, we show that at 7 months of age, Tg2576 mice exhibited a selective deficit in hippocampus-based operations including a defective habituation of object exploration, a lack of reactivity to spatial novelty and a disruption of allothetic orientation in a cross-shaped maze. At 14 months of age, Tg2576 mice displayed a more extended pattern of behavioral abnormalities, because they failed to react to object novelty and exclusively relied on motor-based orientation in the cross-shaped maze. However, an impaired reactivity to spatial and object novelty possibly reflecting age-related attention deficits also emerged in aged wild-type mice. These findings further underline that early cognitive markers of AD can be detected in Tg2576 mice before Abeta deposition occurs and suggest that as in humans, cognitive deterioration progressively evolves from an initial hippocampal syndrome to global dementia because of the combined effect of the neuropathology and aging.     

Behavioral assessment of Alzheimer's transgenic mice following long-term Abeta vaccination: task specificity and correlations between Abeta deposition and spatial memory.

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.     

Association between acetylcholinesterase and beta-amyloid peptide in Alzheimer's cerebrospinal fluid

The altered expression of acetylcholinesterase (AChE) in the brains of patients with Alzheimer's disease (AD) has raised much interest of late. Despite an overall decrease in the AD brain, the activity of AChE increases around beta-amyloid plaques and indeed, the beta-amyloid peptide (Abeta) can influence AChE levels. Such evidence stimulated our interest in the possibility that the levels of AChE and amyloid might vary together in AD. We previously found that the different AChE forms present in both the brain and in the cerebrospinal fluid (CSF) of AD patients varied in conjunction with abnormal glycosylation. Thus, the alterations in glycosylation are correlated with the accumulation of a minor subspecies of AChE monomers. We also recently analysed whether long-term exposure to the cholinesterase inhibitor (ChE-I) donepezil influences the AChE species found in AD CSF. The marked increase in CSF-AChE activity in AD patients following long-term treatment with donepezil was not paralleled by a rise in this subset of light variants. Hence, the correlation with the levels of CSF-Abeta is unique to these AChE species in patients receiving such treatment. The aim of this report is to review the links between AChE and beta-amyloid, and to discuss the significance of the responses of the distinct AChE species to ChE-I during the treatment of AD.     

Effect of PPF and ALCAR on the induction of NGF- and p75-mRNA and on APP processing in Tg2576 brain

Amyloidogenic processing of beta-amyloid precursor protein (APP) leading to Abeta accumulation is critical in Alzheimer's disease (AD). Abeta leads to pre-synaptic molecular changes in hippocampus of the AD mutant transgenic mouse model Tg2576 prior to plaque formation. Since NGF is critical to neuronal growth and is involved in regulating APP processing, we tested the hypothesis that NGF expression is altered early in this model of AD. We measured APP products and mRNAs for NGF and its low-affinity receptor p75 in 10-month-old Tg2576 whole brain after dietary propentofylline (PPF) or acetyl-L-carnitine (ALCAR) for 4 weeks to induce NGF- or p75-expression, respectively. The results (all P<0.0002) show that compared to wild-type or littermate controls, the transgene leads to decreases of 44% in NGF-mRNA, 25% in p75-mRNA, 64% in sAPPalpha, and 21-fold increases in Abeta40/42. PPF increased NGF-mRNA by 20% and sAPPalpha by 42% while decreasing Abeta40/42 by 45/48%, with no effect on p75-mRNA in Tg animals. ALCAR increased p75-mRNA by 16% and decreased Abeta40/42 by 46/26% with no significant effect on sAPPalpha or NGF-mRNA in Tg animals. The results indicate that NGF expression is reduced early in the Tg brain, that this reduction potentiates further Abeta formation in a vicious cycle, and that inducing NGF shifts the balance toward secretory processing of APP. To a lesser extent, p75 decreases Abeta peptides, possibly via peptidases since sAPPalpha level is not changed.     

The neuronal adaptor protein X11beta reduces amyloid beta-protein levels and amyloid plaque formation in the brains of transgenic mice

Accumulation of cerebral amyloid beta-protein (Abeta) is believed to be part of the pathogenic process in Alzheimer's disease. Abeta is derived by proteolytic cleavage from a precursor protein, the amyloid precursor protein (APP). APP is a type-1 membrane-spanning protein, and its carboxyl-terminal intracellular domain binds to X11beta, a neuronal adaptor protein. X11beta has been shown to inhibit the production of Abeta in transfected non-neuronal cells in culture. However, whether this is also the case in vivo in the brain and whether X11beta can also inhibit the deposition of Abeta as amyloid plaques is not known. Here we show that transgenic overexpression of X11beta in neurons leads to a decrease in cerebral Abeta levels in transgenic APPswe Tg2576 mice that are a model of the amyloid pathology of Alzheimer's disease. Moreover, overexpression of X11beta retards amyloid plaque formation in these APPswe mice. Our findings suggest that modulation of X11beta function may represent a novel therapeutic approach for preventing the amyloid pathology of Alzheimer's disease.     

BACE1 deficiency rescues memory deficits and cholinergic dysfunction in a mouse model of Alzheimer's disease

beta-site APP cleaving enzyme 1 (BACE1) is the beta-secretase enzyme required for generating pathogenic beta-amyloid (Abeta) peptides in Alzheimer's disease (AD). BACE1 knockout mice lack Abeta and are phenotypically normal, suggesting that therapeutic inhibition of BACE1 may be free of mechanism-based side effects. However, direct evidence that BACE1 inhibition would improve cognition is lacking. Here we show that BACE1 null mice engineered to overexpress human APP (BACE1(-/-).Tg2576(+)) are rescued from Abeta-dependent hippocampal memory deficits. Moreover, impaired hippocampal cholinergic regulation of neuronal excitability found in the Tg2576 AD model is ameliorated in BACE1(-/-).Tg2576(+) bigenic mice. The behavioral and electrophysiological rescue of deficits in BACE1(-/-).Tg2576(+) mice is correlated with a dramatic reduction of cerebral Abeta40 and Abeta42 levels and occurs before amyloid deposition in Tg2576 mice. Our gene-based approach demonstrates that lower Abeta levels are beneficial for AD-associated memory impairments, validating BACE1 as a therapeutic target for AD.     

Early-onset amyloid deposition and cognitive deficits in transgenic mice expressing a double mutant form of amyloid precursor protein 695

We have created early-onset transgenic (Tg) models by exploiting the synergistic effects of familial Alzheimer's disease mutations on amyloid beta-peptide (Abeta) biogenesis. TgCRND8 mice encode a double mutant form of amyloid precursor protein 695 (KM670/671NL+V717F) under the control of the PrP gene promoter. Thioflavine S-positive Abeta amyloid deposits are present at 3 months, with dense-cored plaques and neuritic pathology evident from 5 months of age. TgCRND8 mice exhibit 3,200-4,600 pmol of Abeta42 per g brain at age 6 months, with an excess of Abeta42 over Abeta40. High level production of the pathogenic Abeta42 form of Abeta peptide was associated with an early impairment in TgCRND8 mice in acquisition and learning reversal in the reference memory version of the Morris water maze, present by 3 months of age. Notably, learning impairment in young mice was offset by immunization against Abeta42 (Janus, C., Pearson, J., McLaurin, J., Mathews, P. M., Jiang, Y., Schmidt, S. D., Chishti, M. A., Horne, P., Heslin, D., French, J., Mount, H. T. J., Nixon, R. A., Mercken, M., Bergeron, C., Fraser, P. E., St. George-Hyslop, P., and Westaway, D. (2000) Nature 408, 979-982). Amyloid deposition in TgCRND8 mice was enhanced by the expression of presenilin 1 transgenes including familial Alzheimer's disease mutations; for mice also expressing a M146L+L286V presenilin 1 transgene, amyloid deposits were apparent by 1 month of age. The Tg mice described here suggest a potential to investigate aspects of Alzheimer's disease pathogenesis, prophylaxis, and therapy within short time frames.     

Vitamin E reduces amyloidosis and improves cognitive function in Tg2576 mice following repetitive concussive brain injury

Traumatic brain injury is a well-recognized environmental risk factor for developing Alzheimer's disease. Repetitive concussive brain injury (RCBI) exacerbates brain lipid peroxidation, accelerates amyloid (Abeta) formation and deposition, as well as cognitive impairments in Tg2576 mice. This study evaluated the effects of vitamin E on these four parameters in Tg2576 mice following RCBI. Eleven-month-old mice were randomized to receive either regular chow or chow-supplemented with vitamin E for 4 weeks, and subjected to RCBI (two injuries, 24 h apart) using a modified controlled cortical impact model of closed head injury. The same dietary regimens were maintained up to 8 weeks post-injury, when the animals were killed for biochemical and immunohistochemical analyses after behavioral evaluation. Vitamin E-treated animals showed a significant increase in brain vitamin E levels and a significant decrease in brain lipid peroxidation levels. After RBCI, compared with the group on regular chow, animals receiving vitamin E did not show the increase in Abeta peptides, and had a significant attenuation of learning deficits. This study suggests that the exacerbation of brain oxidative stress following RCBI plays a mechanistic role in accelerating Alphabeta accumulation and behavioral impairments in the Tg2576 mice.     

Chronic nicotine treatment reduces beta-amyloidosis in the brain of a mouse model of Alzheimer's disease (APPsw)

Alzheimer's disease neuropathology is characterised by beta-amyloid plaques and neurofibrillary tangles. Inhibition of beta-amyloid accumulation may be essential for effective therapy in Alzheimer's disease. In this study we have treated transgenic mice carrying the Swedish mutation of human amyloid precursor protein [Tg(Hu.APP695.K670N-M671L)2576], which develop brain beta-amyloid deposits, with nicotine in drinking fluid (200 microg/mL) from 9-14.5 months of age (5.5 months). A significant reduction in amyloid beta peptide 1-42 positive plaques by more than 80% (p < 0.03) was observed in the brains of nicotine treated compared to sucrose treated transgenic mice. In addition, there was a selective reduction in extractable amyloid beta peptides in nicotine treated mice; cortical insoluble 1-40 and 1-42 peptide levels were lower by 48 and 60%, respectively (p < 0.005), whilst there was no significant change in soluble 1-40 or 1-42 levels. The expression of glial fibrillary acidic protein was not affected by nicotine treatment. These results indicate that nicotine may effectively reduce amyloid beta peptide aggregation in brain and that nicotinic drug treatment may be a novel protective therapy in Alzheimer's disease.     

Amelioration of amyloid load by anti-Abeta single-chain antibody in Alzheimer mouse model

Parenteral immunization of transgenic mouse models of Alzheimer disease (AD) with synthetic amyloid beta-peptide (Abeta) prevented or reduced Abeta deposits and attenuated their memory and learning deficits. A clinical trial of immunization with synthetic Abeta, however, was halted due to brain inflammation, presumably induced by a toxic Abeta, T-cell- and/or Fc-mediated immune response. Another issue relating to such immunizations is that some AD patients may not be able to raise an adequate immune response to Abeta vaccination due to immunological tolerance or age-associated decline. Because peripheral administration of antibodies against Abeta also induced clearance of amyloid plaques in the model mice, injection of humanized Abeta antibodies has been proposed as a possible therapy for AD. By screening a human single-chain antibody (scFv) library for Abeta immunoreactivity, we have isolated a scFv that specifically reacts with oligomeric Abeta as well as amyloid plaques in the brain. The scFv inhibited Abeta amyloid fibril formation and Abeta-mediated cytotoxicity in vitro. We have tested the efficacy of the human scFv in a mouse model of AD (Tg2576 mice). Relative to control mice, injections of the scFv into the brain of Tg2576 mice reduced Abeta deposits. Because scFvs lack the Fc portion of the immunoglobulin molecule, human scFvs against Abeta may be useful to treat AD patients without eliciting brain inflammation.     

Blocking TGF-beta-Smad2/3 innate immune signaling mitigates Alzheimer-like pathology

Alzheimer's disease is the most common dementia and is pathologically characterized by deposition of amyloid-beta peptide (Abeta) into beta-amyloid plaques, neuronal injury and low-level, chronic activation of brain immunity. Transforming growth factor-betas (TGF-betas) are pleiotropic cytokines that have key roles in immune cell activation, inflammation and repair after injury. We genetically interrupted TGF-beta and downstream Smad2/3 signaling (TGF-beta-Smad2/3) in innate immune cells by inducing expression of CD11c promoter-driven dominant-negative TGF-beta receptor type II in C57BL/6 mice (CD11c-DNR), crossed these mice with mice overexpressing mutant human amyloid precursor protein, the Tg2576 Alzheimer's disease mouse model, and evaluated Alzheimer's disease-like pathology. Aged double-transgenic mice showed complete mitigation of Tg2576-associated hyperactivity and partial mitigation of defective spatial working memory. Brain parenchymal and cerebrovascular beta-amyloid deposits and Abeta abundance were markedly (up to 90%) attenuated in Tg2576-CD11c-DNR mice. This was associated with increased infiltration of Abeta-containing peripheral macrophages around cerebral vessels and beta-amyloid plaques. In vitro, cultures of peripheral macrophages, but not microglia, from CD11c-DNR mice showed blockade of classical TGF-beta-activated Smad2/3 but also showed hyperactivation of alternative bone morphogenic protein-activated Smad1/5/8 signaling and increased Abeta phagocytosis. Similar effects were noted after pharmacological inhibition of activin-like kinase-5, a type I TGF-beta receptor. Taken together, our results suggest that blockade of TGF-beta-Smad2/3 signaling in peripheral macrophages represents a new therapeutic target for Alzheimer's disease.