RESUMO
RATIONALE: Increasing evidence indicates that alterations of the cerebral microcirculation may play a role in Alzheimer disease, the leading cause of late-life dementia. The amyloid-ß peptide (Aß), a key pathogenic factor in Alzheimer disease, induces profound alterations in neurovascular regulation through the innate immunity receptor CD36 (cluster of differentiation 36), which, in turn, activates a Nox2-containing NADPH oxidase, leading to cerebrovascular oxidative stress. Brain perivascular macrophages (PVM) located in the perivascular space, a major site of brain Aß collection and clearance, are juxtaposed to the wall of intracerebral resistance vessels and are a powerful source of reactive oxygen species. OBJECTIVE: We tested the hypothesis that PVM are the main source of reactive oxygen species responsible for the cerebrovascular actions of Aß and that CD36 and Nox2 in PVM are the molecular substrates of the effect. METHODS AND RESULTS: Selective depletion of PVM using intracerebroventricular injection of clodronate abrogates the reactive oxygen species production and cerebrovascular dysfunction induced by Aß applied directly to the cerebral cortex, administered intravascularly, or overproduced in the brain of transgenic mice expressing mutated forms of the amyloid precursor protein (Tg2576 mice). In addition, using bone marrow chimeras, we demonstrate that PVM are the cells expressing CD36 and Nox2 responsible for the dysfunction. Thus, deletion of CD36 or Nox2 from PVM abrogates the deleterious vascular effects of Aß, whereas wild-type PVM reconstitute the vascular dysfunction in CD36-null mice. CONCLUSIONS: The data identify PVM as a previously unrecognized effector of the damaging neurovascular actions of Aß and unveil a new mechanism by which brain-resident innate immune cells and their receptors may contribute to the pathobiology of Alzheimer disease.
Assuntos
Doença de Alzheimer/metabolismo , Peptídeos beta-Amiloides/metabolismo , Circulação Cerebrovascular/fisiologia , Macrófagos/metabolismo , Córtex Somatossensorial/irrigação sanguínea , Córtex Somatossensorial/metabolismo , Doença de Alzheimer/patologia , Animais , Encéfalo/irrigação sanguínea , Encéfalo/metabolismo , Encéfalo/patologia , Macrófagos/patologia , Masculino , Camundongos , Camundongos Transgênicos , Distribuição Aleatória , Espécies Reativas de Oxigênio/metabolismoRESUMO
In Alzheimer's disease (AD), the accumulation and deposition of amyloid-ß (Aß) peptides in the brain is a central event. Aß is cleaved from amyloid precursor protein (APP) by ß-secretase and γ-secretase mainly in neurons. Although mutations inAPP,PS1, orPS2cause early-onset familial AD,ABCA7encoding ATP-binding cassette transporter A7 is one of the susceptibility genes for late-onset AD (LOAD), in which itsloss-of-functionvariants increase the disease risk. ABCA7 is homologous to a major lipid transporter ABCA1 and is highly expressed in neurons and microglia in the brain. Here, we show that ABCA7 deficiency altered brain lipid profile and impaired memory in ABCA7 knock-out (Abca7(-/-)) mice. When bred to amyloid model APP/PS1 mice, plaque burden was exacerbated by ABCA7 deficit.In vivomicrodialysis studies indicated that the clearance rate of Aß was unaltered. Interestingly, ABCA7 deletion facilitated the processing of APP to Aß by increasing the levels of ß-site APP cleaving enzyme 1 (BACE1) and sterol regulatory element-binding protein 2 (SREBP2) in primary neurons and mouse brains. Knock-down of ABCA7 expression in neurons caused endoplasmic reticulum stress highlighted by increased level of protein kinase R-like endoplasmic reticulum kinase (PERK) and increased phosphorylation of eukaryotic initiation factor 2α (eIF2α). In the brains of APP/PS1;Abca7(-/-)mice, the level of phosphorylated extracellular regulated kinase (ERK) was also significantly elevated. Together, our results reveal novel pathways underlying the association of ABCA7 dysfunction and LOAD pathogenesis. SIGNIFICANCE STATEMENT: Gene variants inABCA7encoding ATP-binding cassette transporter A7 are associated with the increased risk for late-onset Alzheimer's disease (AD). Importantly, we found the altered brain lipid profile and impaired memory in ABCA7 knock-out mice. The accumulation of amyloid-ß (Aß) peptides cleaved from amyloid precursor protein (APP) in the brain is a key event in AD pathogenesis and we also found that ABCA7 deficit exacerbated brain Aß deposition in amyloid AD model APP/PS1 mice. Mechanistically, we found that ABCA7 deletion facilitated the processing of APP and Aß production by increasing the levels of ß-secretase 1 (BACE1) in primary neurons and mouse brains without affecting the Aß clearance rate in APP/PS1 mice. Our study demonstrates a novel mechanism underlying how dysfunctions of ABCA7 contribute to the risk for AD.
Assuntos
Transportadores de Cassetes de Ligação de ATP/deficiência , Doença de Alzheimer , Peptídeos beta-Amiloides/metabolismo , Encéfalo/metabolismo , Regulação da Expressão Gênica/genética , Transportadores de Cassetes de Ligação de ATP/genética , Transportadores de Cassetes de Ligação de ATP/metabolismo , Doença de Alzheimer/genética , Doença de Alzheimer/metabolismo , Doença de Alzheimer/patologia , Precursor de Proteína beta-Amiloide/genética , Animais , Encéfalo/patologia , Modelos Animais de Doenças , Fator de Iniciação 2 em Eucariotos/metabolismo , Feminino , Humanos , Metabolismo dos Lipídeos/genética , Masculino , Transtornos da Memória/genética , Camundongos , Camundongos Transgênicos , Mutação/genética , Presenilina-1/genética , Transdução de Sinais/genéticaRESUMO
Deposition of amyloid-ß (Aß) in cerebral arteries, known as cerebral amyloid angiopathy (CAA), occurs both in the setting of Alzheimer's disease and independent of it, and can cause cerebrovascular insufficiency and cognitive deficits. The mechanisms leading to CAA have not been established, and no therapeutic targets have been identified. We investigated the role of CD36, an innate immunity receptor involved in Aß trafficking, in the neurovascular dysfunction, cognitive deficits, and amyloid accumulation that occurs in mice expressing the Swedish mutation of the amyloid precursor protein (Tg2576). We found that Tg2576 mice lacking CD36 have a selective reduction in Aß1-40 and CAA. This reduced vascular amyloid deposition was associated with preservation of the Aß vascular clearance receptor LRP-1, and protection from the deleterious effects of Aß on cerebral arterioles. These beneficial vascular effects were reflected by marked improvements in neurovascular regulation and cognitive performance. Our data suggest that CD36 promotes vascular amyloid deposition and the resulting cerebrovascular damage, leading to neurovascular dysfunction and cognitive deficits. These findings identify a previously unrecognized role of CD36 in the mechanisms of vascular amyloid deposition, and suggest that this scavenger receptor is a putative therapeutic target for CAA and related conditions.
Assuntos
Antígenos CD36/imunologia , Angiopatia Amiloide Cerebral/imunologia , Imunidade Inata , Animais , Vasos Sanguíneos/metabolismo , Antígenos CD36/genética , Circulação Cerebrovascular , Imunofluorescência , Aprendizagem em Labirinto , Camundongos , Camundongos Transgênicos , Pericitos/imunologia , Proteína da Zônula de Oclusão-1/metabolismoRESUMO
BACKGROUND: Plasma amyloid-ß (Aß) peptide levels have been examined as a low-cost accessible marker for risk of incident Alzheimer's disease (AD) and dementia, but results have varied between studies. We reassessed these associations in one of the largest, prospective, community-based studies to date. METHODS: A total of 2189 dementia-free, Framingham Study participants aged >60 years (mean age, 72 ± 8 years; 56% women) had plasma Aß1-42 and Aß1-40 measured and were followed prospectively (mean, 7.6 ± 3.0 years) for dementia/AD. RESULTS: Increased plasma Aß1-42 levels were associated with lower risk of dementia (Aß1-42: hazard ratio [HR] = 0.80 [0.71â0.90], P < .001; Aß1-42-to-Aß1-40 ratio: HR = 0.86 [0.76â0.98], P = .027) and AD (Aß1-42: HR = 0.79 [0.69â0.90], P < .001; Aß1-42-to-Aß1-40 ratio: HR = 0.83 [0.72â0.96], P = .012). CONCLUSION: Our results suggest that lower plasma Aß levels are associated with risk of incident AD and dementia. They encourage further evaluation of plasma Aß levels as a biomarker for risk of developing clinical AD and dementia.
Assuntos
Doença de Alzheimer/sangue , Peptídeos beta-Amiloides/sangue , Fragmentos de Peptídeos/sangue , Idoso , Doença de Alzheimer/diagnóstico , Biomarcadores/sangue , Feminino , Humanos , Estudos Longitudinais , Masculino , Pessoa de Meia-Idade , Modelos de Riscos Proporcionais , Estudos Prospectivos , Risco , Análise de SobrevidaRESUMO
Neuronal network hyperexcitability underlies the pathogenesis of seizures and is a component of some degenerative neurological disorders such as Alzheimer's disease (AD). Recently, the microtubule-binding protein tau has been implicated in the regulation of network synchronization. Genetic removal of Mapt, the gene encoding tau, in AD models overexpressing amyloid-ß (Aß) decreases hyperexcitability and normalizes the excitation/inhibition imbalance. Whether this effect of tau removal is specific to Aß mouse models remains to be determined. Here, we examined tau as an excitability modifier in the non-AD nervous system using genetic deletion of tau in mouse and Drosophila models of hyperexcitability. Kcna1(-/-) mice lack Kv1.1-delayed rectifier currents and exhibit severe spontaneous seizures, early lethality, and megencephaly. Young Kcna1(-/-) mice retained wild-type levels of Aß, tau, and tau phospho-Thr(231). Decreasing tau in Kcna1(-/-) mice reduced hyperexcitability and alleviated seizure-related comorbidities. Tau reduction decreased Kcna1(-/-) video-EEG recorded seizure frequency and duration as well as normalized Kcna1(-/-) hippocampal network hyperexcitability in vitro. Additionally, tau reduction increased Kcna1(-/-) survival and prevented megencephaly and hippocampal hypertrophy, as determined by MRI. Bang-sensitive Drosophila mutants display paralysis and seizures in response to mechanical stimulation, providing a complementary excitability assay for epistatic interactions. We found that tau reduction significantly decreased seizure sensitivity in two independent bang-sensitive mutant models, kcc and eas. Our results indicate that tau plays a general role in regulating intrinsic neuronal network hyperexcitability independently of Aß overexpression and suggest that reducing tau function could be a viable target for therapeutic intervention in seizure disorders and antiepileptogenesis.
Assuntos
Epilepsia/metabolismo , Epilepsia/fisiopatologia , Rede Nervosa/fisiopatologia , Proteínas tau/metabolismo , Animais , Western Blotting , Modelos Animais de Doenças , Drosophila , Eletroencefalografia , Ensaio de Imunoadsorção Enzimática , Epilepsia/genética , Feminino , Hipocampo/metabolismo , Hipocampo/fisiopatologia , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Rede Nervosa/metabolismo , Técnicas de Cultura de Órgãos , Técnicas de Patch-ClampRESUMO
Increasing evidence indicates that cerebrovascular dysfunction plays a pathogenic role in Alzheimer's dementia (AD). Amyloid-ß (Aß), a peptide central to the pathogenesis of AD, has profound vascular effects mediated, for the most part, by reactive oxygen species produced by the enzyme NADPH oxidase. The mechanisms linking Aß to NADPH oxidase-dependent vascular oxidative stress have not been identified, however. We report that the scavenger receptor CD36, a membrane glycoprotein that binds Aß, is essential for the vascular oxidative stress and neurovascular dysfunction induced by Aß1-40. Thus, topical application of Aß1-40 onto the somatosensory cortex attenuates the increase in cerebral blood flow elicited by neural activity or by endothelium-dependent vasodilators in WT mice but not in CD36-null mice (CD36(0/0)). The cerebrovascular effects of infusion of Aß1-40 into cerebral arteries are not observed in mice pretreated with CD36 blocking antibodies or in CD36(0/0) mice. Furthermore, CD36 deficiency prevents the neurovascular dysfunction observed in transgenic mice overexpressing the Swedish mutation of the amyloid precursor protein Tg2576 despite elevated levels of brain Aß1-40. CD36 is also required for the vascular oxidative stress induced by exogenous Aß1-40 or observed in Tg2576 mice. These observations establish CD36 as a key link between Aß1-40 and the NADPH oxidase-dependent vascular oxidative stress underlying the neurovascular dysfunction and suggest that CD36 is a potential therapeutical target to counteract the cerebrovascular dysfunction associated with Aß.
Assuntos
Doença de Alzheimer/metabolismo , Peptídeos beta-Amiloides/metabolismo , Antígenos CD36/metabolismo , Transtornos Cerebrovasculares/metabolismo , Estresse Oxidativo , Fragmentos de Peptídeos/metabolismo , Doença de Alzheimer/genética , Doença de Alzheimer/fisiopatologia , Peptídeos beta-Amiloides/genética , Animais , Anticorpos Neutralizantes/farmacologia , Antígenos CD36/genética , Circulação Cerebrovascular/efeitos dos fármacos , Circulação Cerebrovascular/genética , Transtornos Cerebrovasculares/genética , Transtornos Cerebrovasculares/fisiopatologia , Feminino , Humanos , Masculino , Camundongos , Camundongos Transgênicos , Mutação , NADPH Oxidases/genética , NADPH Oxidases/metabolismo , Fragmentos de Peptídeos/genética , Ligação Proteica , Córtex Somatossensorial/metabolismo , Córtex Somatossensorial/fisiopatologiaRESUMO
Alterations in cerebrovascular regulation related to vascular oxidative stress have been implicated in the mechanisms of Alzheimer's disease (AD), but their role in the amyloid deposition and cognitive impairment associated with AD remains unclear. We used mice overexpressing the Swedish mutation of the amyloid precursor protein (Tg2576) as a model of AD to examine the role of reactive oxygen species produced by NADPH oxidase in the cerebrovascular alterations, amyloid deposition, and behavioral deficits observed in these mice. We found that 12- to 15-month-old Tg2576 mice lacking the catalytic subunit Nox2 of NADPH oxidase do not develop oxidative stress, cerebrovascular dysfunction, or behavioral deficits. These improvements occurred without reductions in brain amyloid-beta peptide (Abeta) levels or amyloid plaques. The findings unveil a previously unrecognized role of Nox2-derived radicals in the behavioral deficits of Tg2576 mice and provide a link between the neurovascular dysfunction and cognitive decline associated with amyloid pathology.
Assuntos
Precursor de Proteína beta-Amiloide/genética , Sintomas Comportamentais/fisiopatologia , Encéfalo/irrigação sanguínea , Encéfalo/fisiopatologia , Radicais Livres/metabolismo , Hiperemia , Glicoproteínas de Membrana/genética , Glicoproteínas de Membrana/metabolismo , NADPH Oxidases/genética , NADPH Oxidases/metabolismo , Sequência de Aminoácidos , Precursor de Proteína beta-Amiloide/biossíntese , Animais , Sintomas Comportamentais/genética , Sintomas Comportamentais/metabolismo , Encéfalo/metabolismo , Circulação Cerebrovascular/genética , Modelos Animais de Doenças , Feminino , Radicais Livres/efeitos adversos , Humanos , Hiperemia/genética , Hiperemia/metabolismo , Hiperemia/fisiopatologia , Masculino , Aprendizagem em Labirinto/fisiologia , Glicoproteínas de Membrana/antagonistas & inibidores , Glicoproteínas de Membrana/biossíntese , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Camundongos Transgênicos , Dados de Sequência Molecular , NADPH Oxidase 2 , NADPH Oxidases/antagonistas & inibidores , NADPH Oxidases/biossínteseRESUMO
CONTEXT: Lower plasma ß-amyloid 42 and 42/40 levels have been associated with incident dementia, but results are conflicting and few have investigated cognitive decline among elders without dementia. OBJECTIVE: To determine if plasma ß-amyloid is associated with cognitive decline and if this association is modified by measures of cognitive reserve. DESIGN, SETTING, AND PARTICIPANTS: We studied 997 black and white community-dwelling older adults from Memphis, Tennessee, and Pittsburgh, Pennsylvania, who were enrolled in the Health ABC Study, a prospective observational study begun in 1997-1998 with 10-year follow-up in 2006-2007. Participant mean age was 74.0 (SD, 3.0) years; 55.2% (n = 550) were female; and 54.0% (n = 538) were black. MAIN OUTCOME MEASURES: Association of near-baseline plasma ß-amyloid levels (42 and 42/40 measured in 2010) and repeatedly measured Modified Mini-Mental State Examination (3MS) results. RESULTS: Low ß-amyloid 42/40 level was associated with greater 9-year 3MS cognitive decline (lowest ß-amyloid tertile: mean change in 3MS score, -6.59 [95% confidence interval [CI], -5.21 to -7.67] points; middle tertile: -6.16 [95% CI, -4.92 to -7.32] points; and highest tertile: -3.60 [95% CI, -2.27 to -4.73] points; P < .001). Results were similar after multivariate adjustment for age, race, education, diabetes, smoking, and apolipoprotein E [APOE ] e4 status and after excluding the 72 participants with incident dementia. Measures of cognitive reserve modified this association whereby among those with high reserve (at least a high school diploma, higher than sixth-grade literacy, or no APOE e4 allele), ß-amyloid 42/40 was less associated with multivariate adjusted 9-year decline. For example, among participants with less than a high school diploma, the 3MS score decline was -8.94 (95% CI, -6.94 to -10.94) for the lowest tertile compared with -4.45 (95% CI, -2.31 to -6.59) for the highest tertile, but for those with at least a high school diploma, 3MS score decline was -4.60 (95% CI,-3.07 to -6.13) for the lowest tertile and -2.88 (95% CI,-1.41 to -4.35) for the highest tertile (P = .004 for interaction). Interactions were also observed for literacy (P = .005) and for APOE e4 allele (P = .02). CONCLUSION: Lower plasma ß-amyloid 42/40 is associated with greater cognitive decline among elderly persons without dementia over 9 years, and this association is stronger among those with low measures of cognitive reserve.
Assuntos
Peptídeos beta-Amiloides/sangue , Transtornos Cognitivos/sangue , Reserva Cognitiva , Idoso , Apolipoproteína E4/genética , Biomarcadores/sangue , População Negra/genética , Feminino , Seguimentos , Humanos , Masculino , Pennsylvania , Fragmentos de Peptídeos/sangue , TennesseeRESUMO
Non-steroidal anti-inflammatory agents (NSAIDs) are associated with a marked reduction in the risk of developing Alzheimer's disease, a form of dementia characterized by the accumulation of amyloid plaques containing the amyloid-beta protein (Abeta). Studies of the effects of NSAIDs upon the inflammatory response surrounding amyloid plaques and upon the generation of Abeta from the amyloid precursor protein (APP) have led to two proposed mechanisms by which NSAIDs may protect against Alzheimer's disease: one, the selective lowering of Abeta42 by a subset of NSAIDs; and two, the reduction of inflammation. Although Alzheimer's disease is a disorder of brain and synaptic function, the effects of NSAIDs on Abeta-mediated suppression of synaptic plasticity and memory function have never been reported. We therefore investigated how three different NSAIDs, chosen for their distinct effects on Abeta42 production and the inhibition of the cyclooxygenase (COX) isoenzymes, COX-1 and COX-2, affect memory function and synaptic plasticity. By focusing upon brain and synapse function, we made novel observations about the effects of NSAIDs on Abeta-mediated neural processes. Here we report that the selective inhibition of COX-2, but not COX-1, acutely prevented the suppression of hippocampal long-term plasticity (LTP) by Abeta. The non-selective NSAIDs, ibuprofen and naproxen, and a selective COX-2 inhibitor, MF-tricyclic, each restored memory function in Tg2576 mice over-expressing APP, and also blocked Abeta-mediated inhibition of LTP. There was no advantage of ibuprofen, a selective Abeta42-lowering agent (SALA), over the non-SALAs, naproxen and MF-tricyclic. The beneficial effects on memory did not depend upon lowered levels of Abeta42 or the inflammatory cytokines, tumour necrosis factor alpha (TNF-alpha) and interleukin 1beta (IL-1beta). Intriguingly, improved memory function was inversely related to prostaglandin E2 (PGE2) levels. Conversely, exogenous PGE2 prevented the restorative effects of COX-2 inhibitors on LTP. The data indicate that the inhibition of COX-2 blocks Abeta-mediated suppression of LTP and memory function, and that this block occurs independently of reductions in Abeta42 or decreases in inflammation. The results lead us to propose a third possible mechanism by which NSAIDs may protect against Alzheimer's disease, involving the blockade of a COX-2-mediated PGE2 response at synapses.
Assuntos
Peptídeos beta-Amiloides/antagonistas & inibidores , Inibidores de Ciclo-Oxigenase 2/farmacologia , Memória/efeitos dos fármacos , Plasticidade Neuronal/efeitos dos fármacos , Peptídeos beta-Amiloides/farmacologia , Animais , Ciclo-Oxigenase 2/metabolismo , Inibidores de Ciclo-Oxigenase 2/uso terapêutico , Inibidores de Ciclo-Oxigenase/farmacologia , Inibidores de Ciclo-Oxigenase/uso terapêutico , Dinoprostona/fisiologia , Furanos/farmacologia , Furanos/uso terapêutico , Hipocampo/efeitos dos fármacos , Hipocampo/metabolismo , Ibuprofeno/farmacologia , Ibuprofeno/uso terapêutico , Mediadores da Inflamação/metabolismo , Interleucina-1beta/metabolismo , Masculino , Transtornos da Memória/tratamento farmacológico , Transtornos da Memória/metabolismo , Transtornos da Memória/prevenção & controle , Camundongos , Camundongos Endogâmicos C57BL , Naproxeno/farmacologia , Naproxeno/uso terapêutico , Fragmentos de Peptídeos/farmacologia , Ratos , Sinapses/fisiologia , Fator de Necrose Tumoral alfa/metabolismoRESUMO
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.
Assuntos
Doença de Alzheimer/fisiopatologia , Doença de Alzheimer/psicologia , Ácido Aspártico Endopeptidases/deficiência , Fibras Colinérgicas , Hipocampo/fisiopatologia , Transtornos da Memória/psicologia , Doença de Alzheimer/metabolismo , Secretases da Proteína Precursora do Amiloide , Peptídeos beta-Amiloides/antagonistas & inibidores , Precursor de Proteína beta-Amiloide/metabolismo , Animais , Encéfalo/metabolismo , Endopeptidases , Humanos , Transtornos da Memória/etiologia , Camundongos , Camundongos Knockout , Camundongos TransgênicosRESUMO
BACKGROUND: To develop preventive therapy for Alzheimer disease (AD), it is essential to develop AD-related biomarkers that identify at-risk individuals in the same way that cholesterol levels identify persons at risk for heart disease. OBJECTIVE: To determine whether plasma levels of amyloid beta protein (Abeta40 and Abeta42) are useful for identifying cognitively normal elderly white subjects at increased risk for mild cognitive impairment (MCI) and AD. DESIGN: Using well-established sandwich enzyme-linked immunosorbent assays, plasma Abeta40 and Abeta42 levels were analyzed at baseline in a prospective, elderly white cohort followed up for 2 to 12 (median, 3.7) years to detect incident cases of MCI or AD. SETTING: Cognitively normal, community-based white volunteers recruited from primary care settings into the Mayo Rochester Alzheimer Disease Patient Registry. Patients We followed up 563 cognitively normal white volunteers (median age, 78 years; 62% female) who had at least 1 follow-up visit after measurement of baseline plasma Abeta levels. MAIN OUTCOME MEASURES: The primary outcome was time to development of MCI or AD. The secondary outcome was the annualized rate of cognitive change in patients for whom we had 2 Mattis Dementia Rating Scale evaluations 3 to 7 years apart. RESULTS: During follow-up, 53 subjects developed MCI or AD. Subjects with plasma Abeta42/Abeta40 ratios in the lower quartiles showed significantly greater risk of MCI or AD (P = .04, adjusted for age and apolipoprotein E genotype). Comparison of subjects with plasma Abeta42/Abeta40 ratios in the lowest vs the highest quartile gave a relative risk of 3.1 (95% confidence interval, 1.1-8.3). After adjusting for age and apolipoprotein E genotype, regression analysis using annualized changes in the Dementia Rating Scale scores as an outcome variable showed that participants with lower Abeta42/Abeta40 ratios had greater cognitive decline (P = .02). CONCLUSION: The plasma Abeta42/Abeta40 ratio may be a useful premorbid biomarker for identifying cognitively normal elderly white subjects who are at increased risk for developing MCI or AD.
Assuntos
Doença de Alzheimer/sangue , Peptídeos beta-Amiloides/sangue , Transtornos Cognitivos/sangue , Fragmentos de Peptídeos/sangue , Risco , Idoso , Idoso de 80 Anos ou mais , Ensaio de Imunoadsorção Enzimática/métodos , Feminino , Avaliação Geriátrica , Humanos , Estudos Longitudinais , Masculino , Pessoa de Meia-Idade , Modelos de Riscos Proporcionais , Características de Residência , Estudos RetrospectivosRESUMO
Epidemiological studies suggest that individuals with greater education or more cognitively demanding occupations have diminished risk of developing dementia. We wanted to test whether this effect could be recapitulated in rodents using environmental enrichment, a paradigm well documented to attenuate behavioral deficits induced by various pathological insults. Here, we demonstrate that learning and memory deficits observed in a transgenic mouse model of Alzheimer's disease can be ameliorated by enrichment. Female transgenic mice overexpressing amyloid precursor protein and/or presenilin-1 and nontransgenic controls were placed into enriched or standard cages at 2 months of age and tested for cognitive behavior after 6 months of differential housing. Enrichment significantly improved performance of all genotypes in the radial water maze and in the classic and repeated-reversal versions of the Morris water maze. However, enrichment did not benefit all genotypes equally. Mice overproducing amyloid-beta (Abeta), particularly those with amyloid deposits, showed weaker memory for the platform location in the classic Morris water maze and learned new platform positions in the repeated-reversals task less quickly than their nontransgenic cagemates. Nonetheless, enrichment normalized the performance of Abeta-overproducing mice to the level of standard-housed nontransgenic mice. Moreover, this functional preservation occurred despite increased neuritic plaque burden in the hippocampus of double-transgenic animals and elevated steady-state Abeta levels, because both endogenous and transgene-derived Abeta are increased in enriched animals. These results demonstrate that the generation of Abeta in vivo and its impact on the function of the nervous system can be strongly modulated by environmental factors.
Assuntos
Doença de Alzheimer/complicações , Transtornos Cognitivos/etiologia , Meio Ambiente , Fatores Etários , Peptídeos beta-Amiloides/genética , Precursor de Proteína beta-Amiloide/genética , Precursor de Proteína beta-Amiloide/metabolismo , Análise de Variância , Animais , Comportamento Animal , Modelos Animais de Doenças , Ensaio de Imunoadsorção Enzimática/métodos , Feminino , Hipocampo/metabolismo , Humanos , Imuno-Histoquímica/métodos , Aprendizagem em Labirinto/fisiologia , Proteínas de Membrana/genética , Proteínas de Membrana/metabolismo , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Presenilina-1 , Fatores de TempoRESUMO
To investigate lipid rafts as a site where amyloid beta protein (Abeta) oligomers might accumulate and cause toxicity in Alzheimer's disease (AD), we analyzed Abeta in the Tg2576 transgenic mouse model of AD. Abeta was highly concentrated in lipid rafts, which comprise a small fraction of brain volume but contain 27% of brain Abeta42 and 24% of Abeta40 in young mice. In the Tg2576 model, memory impairment begins at 6 months before amyloid plaques are visible. Here we show that Abeta dimers appear in lipid rafts at 6 months and that raft Abeta, which is primarily dimeric, rapidly accumulates reaching levels >500x those in young mice by 24-28 months. A similar large accumulation of dimeric Abeta was observed in lipid rafts from AD brain. In contrast to extracellular amyloid fibrils, which are SDS-insoluble, virtually all Abeta in lipid rafts is SDS soluble. Coupled with recent studies showing that synthetic and naturally occurring Abeta oligomers can inhibit hippocampal long-term potentiation, the in vivo age-dependent accumulation of SDS-soluble Abeta dimers in lipid rafts at the time when memory impairment begins in Tg2576 mice provides strong evidence linking Abeta oligomers to memory impairment. After dimeric Abeta began to accumulate in lipid rafts of the Tg2576 brain, apolipoprotein E (ApoE) and then phosphorylated tau accumulated. A similar increase in ApoE and a large increase in phosphorylated tau was observed in lipid rafts from AD brain. These findings suggest that lipid rafts may be an important site for interaction between dimeric Abeta, ApoE, and tau.
Assuntos
Doença de Alzheimer/metabolismo , Peptídeos beta-Amiloides/metabolismo , Apolipoproteínas E/metabolismo , Microdomínios da Membrana/metabolismo , Proteínas tau/metabolismo , Fatores Etários , Idoso , Idoso de 80 Anos ou mais , Doença de Alzheimer/patologia , Peptídeos beta-Amiloides/química , Animais , Apolipoproteínas E/química , Dimerização , Modelos Animais de Doenças , Progressão da Doença , Humanos , Microdomínios da Membrana/química , Microdomínios da Membrana/ultraestrutura , Camundongos , Camundongos Transgênicos , Fragmentos de Peptídeos/química , Fragmentos de Peptídeos/metabolismo , Fosforilação , Proteínas tau/químicaRESUMO
Transgenic mice expressing mutant amyloid precursor proteins (APPs) have provided important new information about the pathogenesis of Alzheimer's disease (AD) histopathology. However, the molecular basis of memory loss in these mice is poorly understood. One of the major impediments has been the difficulty of distinguishing between age-dependent and age-independent behavioral changes. To address this issue we studied in parallel two lines of APP transgenic mice expressing comparable levels of mutant and wild-type human APP. This enabled us to identify age-independent behavioral deficits that were not specifically related to mutant APP expression. When mice with age-independent deficits were eliminated, we detected memory loss in transgenic mice expressing mutant APP (Tg2576 mice) starting at approximately 6 months, which coincided with the appearance of detergent-insoluble Abeta aggregates (Abeta(insol)). Genetically accelerating the formation of Abeta(insol) resulted in an earlier onset of memory decline. A facile interpretation of these results, namely that memory loss and Abeta(insol) were closely connected, was rejected when we extended our analysis to include older mice. No obvious correspondence between memory and Abeta(insol) was apparent in a combined group of old and young mice unless the mice were stratified by age, whereupon inverse correlations between memory and Abeta(insol) became evident. These results suggested that Abeta(insol) is a surrogate marker for small assemblies of Abeta that disrupt cognition and occur as intermediates during Abeta(insol) formation, and they are the first descriptive in vivo data supporting their role in impairing memory. These studies also provide a methodological framework within which to investigate these Abeta assemblies in vivo.
Assuntos
Doença de Alzheimer/fisiopatologia , Precursor de Proteína beta-Amiloide/genética , Transtornos da Memória/fisiopatologia , Fatores Etários , Envelhecimento , Doença de Alzheimer/complicações , Doença de Alzheimer/genética , Substituição de Aminoácidos , Peptídeos beta-Amiloides/química , Peptídeos beta-Amiloides/genética , Peptídeos beta-Amiloides/metabolismo , Animais , Comportamento Animal , Biomarcadores/análise , Detergentes/química , Modelos Animais de Doenças , Progressão da Doença , Humanos , Substâncias Macromoleculares , Aprendizagem em Labirinto , Proteínas de Membrana/biossíntese , Proteínas de Membrana/genética , Transtornos da Memória/etiologia , Transtornos da Memória/patologia , Camundongos , Camundongos Transgênicos , Mutação , Presenilina-1 , Solubilidade , Fatores de TempoRESUMO
Alzheimer's disease (AD) is a neurodegenerative condition, believed to be irreversible, characterized by inexorable deterioration of memory and intellect, with neuronal loss accompanying amyloid plaques and neurofibrillary tangles. In an amyloid precursor protein transgenic mouse model, Tg2576, little or no neuronal loss accompanies age-related memory impairment or the accumulation of Abeta, a 40-42 aa polypeptide found in plaques. Recently, we have shown inverse correlations between brain Abeta and memory in Tg2576 mice stratified by age (Westerman et al., 2002). Broadening the age range examined obscured this relationship, leading us to propose that small, soluble assemblies of Abeta disrupt cognitive function in these mice. Here we show that memory loss can be fully reversed in Tg2576 mice using intraperitoneally administered BAM-10, a monoclonal antibody recognizing the N terminus of Abeta. The beneficial effect of BAM-10 was not associated with a significant Abeta reduction, but instead eliminated the inverse relationship between brain Abeta and memory. We postulate that BAM-10 acts by neutralizing Abeta assemblies in the brain that impair cognitive function. Our results indicate that a substantial portion of memory loss in Tg2576 mice is not permanent. If these Abeta assemblies contribute significantly to memory loss in AD, then successfully targeting them might improve memory in some AD patients.
Assuntos
Doença de Alzheimer/fisiopatologia , Transtornos da Memória/fisiopatologia , Envelhecimento/metabolismo , Doença de Alzheimer/complicações , Peptídeos beta-Amiloides/análise , Peptídeos beta-Amiloides/antagonistas & inibidores , Peptídeos beta-Amiloides/metabolismo , Precursor de Proteína beta-Amiloide/genética , Animais , Anticorpos Monoclonais/farmacologia , Comportamento Animal/efeitos dos fármacos , Química Encefálica , Cognição/efeitos dos fármacos , Modelos Animais de Doenças , Feminino , Imunização Passiva/métodos , Injeções Intraperitoneais , Masculino , Memória/efeitos dos fármacos , Transtornos da Memória/complicações , Transtornos da Memória/tratamento farmacológico , Camundongos , Camundongos Transgênicos , Indução de Remissão/métodos , Comportamento Espacial/efeitos dos fármacosRESUMO
BACKGROUND: The proteases (secretases) that cleave amyloid-beta (Abeta) peptide from the amyloid precursor protein (APP) have been the focus of considerable investigation in the development of treatments for Alzheimer disease. The prediction has been that reducing Abeta production in the brain, even after the onset of clinical symptoms and the development of associated pathology, will facilitate the repair of damaged tissue and removal of amyloid lesions. However, no long-term studies using animal models of amyloid pathology have yet been performed to test this hypothesis. METHODS AND FINDINGS: We have generated a transgenic mouse model that genetically mimics the arrest of Abeta production expected from treatment with secretase inhibitors. These mice overexpress mutant APP from a vector that can be regulated by doxycycline. Under normal conditions, high-level expression of APP quickly induces fulminant amyloid pathology. We show that doxycycline administration inhibits transgenic APP expression by greater than 95% and reduces Abeta production to levels found in nontransgenic mice. Suppression of transgenic Abeta synthesis in this model abruptly halts the progression of amyloid pathology. However, formation and disaggregation of amyloid deposits appear to be in disequilibrium as the plaques require far longer to disperse than to assemble. Mice in which APP synthesis was suppressed for as long as 6 mo after the formation of Abeta deposits retain a considerable amyloid load, with little sign of active clearance. CONCLUSION: This study demonstrates that amyloid lesions in transgenic mice are highly stable structures in vivo that are slow to disaggregate. Our findings suggest that arresting Abeta production in patients with Alzheimer disease should halt the progression of pathology, but that early treatment may be imperative, as it appears that amyloid deposits, once formed, will require additional intervention to clear.
Assuntos
Doença de Alzheimer/fisiopatologia , Peptídeos beta-Amiloides/fisiologia , Precursor de Proteína beta-Amiloide/metabolismo , Precursor de Proteína beta-Amiloide/biossíntese , Animais , Perfilação da Expressão Gênica , Humanos , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Placa AmiloideRESUMO
Current mouse models of Alzheimer's disease show brain pathology that correlates to a degree with memory impairment, but underlying molecular mechanisms remained unknown. Here we report studies with three lines of transgenic mice: animals that doubly express mutated human amyloid precursor protein (APPswe) and human acetylcholinesterase (hAChE); and animals transgenic for only the APPswe or the hAChE. Among these genotypes, variations were observed in expression of mRNA for presenilin-1, which was highest in singly transgenic hAChE mice, and the stress-inducible form of AChE, which was elevated when both transgenes were present. At the age of nine months, both double and single transgenic mice displayed working memory impairment in a radial arm water maze. However, as compared with mice expressing amyloid alone, the double transgenic animals exhibited more numerous plaques and greater amyloid burden in brain (both by histochemistry and by ELISA of amyloid protein). Moreover, the amyloid burden in double transgenics was tightly correlated with memory impairment as measured by total maze errors (r2= 0.78, p = .002). This correlation was markedly stronger than observed in mice with amyloid alone. These new findings support the notion of cholinergic-amyloid interrelationships and highlight the double transgenic mice as a promising alternative for testing Alzheimer's therapies.
Assuntos
Acetilcolinesterase/genética , Precursor de Proteína beta-Amiloide/genética , Amiloide/metabolismo , DNA Recombinante , Transtornos da Memória/genética , Transtornos da Memória/metabolismo , Mutação , Animais , Sequência de Bases , Encéfalo/metabolismo , Encéfalo/patologia , Ensaio de Imunoadsorção Enzimática , Variação Genética , Masculino , Aprendizagem em Labirinto , Proteínas de Membrana/metabolismo , Transtornos da Memória/patologia , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Dados de Sequência Molecular , Neurônios/metabolismo , Placa Amiloide , Presenilina-1 , RNA Mensageiro/metabolismo , NataçãoRESUMO
BACKGROUND: Alzheimer's disease is a neurodegenerative disorder in which extracellular deposition of ß-amyloid (Aß) oligomers causes synaptic injury resulting in early memory loss, altered homeostasis, accumulation of hyperphosphorylated tau and cell death. Since proteins in the SNAP (Soluble N-ethylmaleimide-sensitive factor Attachment Protein) REceptors (SNARE) complex are essential for neuronal Aß release at pre-synaptic terminals, we hypothesized that genetically controlled SNARE expression could alter neuronal Aß release at the synapse and hence play an early role in Alzheimer's pathophysiology. RESULTS: Here we report 5 polymorphisms in Vesicle-Associated Membrane Protein 1 (VAMP1), a gene encoding a member of the SNARE complex, associated with bidirectionally altered cerebellar VAMP1 transcript levels (all p<0.05). At the functional level, we demonstrated that control of VAMP1 expression by heterogeneous knockdown in mice resulted in up to 74% reduction in neuronal Aß exocytosis (p<0.001). We performed a case-control association study of the 5 VAMP1 expression regulating polymorphisms in 4,667 Alzheimer's disease patients and 6,175 controls to determine their contribution to Alzheimer's disease risk. We found that polymorphisms associated with increased brain VAMP1 transcript levels conferred higher risk for Alzheimer's disease than those associated with lower VAMP1 transcript levels (p=0.03). Moreover, we also report a modest protective association for a common VAMP1 polymorphism with Alzheimer's disease risk (OR=0.88, p=0.03). This polymorphism was associated with decreased VAMP1 transcript levels (p=0.02) and was functionally active in a dual luciferase reporter gene assay (p<0.01). CONCLUSIONS: Genetically regulated VAMP1 expression in the brain may modify both Alzheimer's disease risk and may contribute to Alzheimer's pathophysiology.
Assuntos
Doença de Alzheimer/genética , Predisposição Genética para Doença , Proteína 1 Associada à Membrana da Vesícula/genética , Doença de Alzheimer/fisiopatologia , Peptídeos beta-Amiloides/genética , Peptídeos beta-Amiloides/metabolismo , Animais , Testes Genéticos , Humanos , Camundongos , Sinapses/metabolismo , Proteína 1 Associada à Membrana da Vesícula/metabolismoRESUMO
Following publication of this work, we noticed that we inadvertently failed to include Dr Ferenc Deák in the author list. The author list has now been corrected and the amended authors' contributions section has been modified accordingly below.
RESUMO
Risk for late onset Alzheimer disease (LOAD) and plasma amyloid beta levels (Abeta42; encoded by APP), an intermediate phenotype for LOAD, show linkage to chromosome 10q. Several strong candidate genes (VR22, PLAU, IDE) lie within the 1-lod support interval for linkage. Others have independently identified haplotypes in the chromosome 10q region harboring IDE that show highly significant association with intermediate AD phenotypes and with risk for AD. To pursue these associations, we analyzed the same haplotypes for association with plasma Abeta42 in 24 extended LOAD families and for association with LOAD in two independent case-control series. One series (MCR, 188 age-matched case-control pairs) did not show association (p=0.64) with the six haplotypes in the 276-kb region spanning three genes (IDE, KNSL1, and HHEX) previously shown to associate with LOAD. The other series (MCJ, 109 age-matched case-control pairs) showed significant (p=0.003) association with these haplotypes. In the MCJ series, the H4 (odds ratio [OR]=5.1, p=0.003) and H2(H7) haplotypes (OR=0.60, p=0.04) had the same effects previously reported. In this series, the H8 haplotype (OR=2.7, p=0.098) also had an effect similar as in one previous case control series but not in others. In the extended families, the H8 haplotype was associated with significantly elevated plasma Abeta42 (p=0.02). In addition, the H5(H10) haplotype, which is associated with reduced risk for AD in the other study is associated with reduced plasma Abeta42 (p=0.007) in our family series. These results provide strong evidence for pathogenic variant(s) in the 276-kb region harboring IDE that influence intermediate AD phenotypes and risk for AD.