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INTRODUCTION: Impaired brain protein synthesis, synaptic plasticity, and memory are major hallmarks of Alzheimer's disease (AD). The ketamine metabolite (2R,6R)-hydroxynorketamine (HNK) has been shown to modulate protein synthesis, but its effects on memory in AD models remain elusive. METHODS: We investigated the effects of HNK on hippocampal protein synthesis, long-term potentiation (LTP), and memory in AD mouse models. RESULTS: HNK activated extracellular signal-regulated kinase 1/2 (ERK1/2), mechanistic target of rapamycin (mTOR), and p70S6 kinase 1 (S6K1)/ribosomal protein S6 signaling pathways. Treatment with HNK rescued hippocampal LTP and memory deficits in amyloid-ß oligomers (AßO)-infused mice in an ERK1/2-dependent manner. Treatment with HNK further corrected aberrant transcription, LTP and memory in aged APP/PS1 mice. DISCUSSION: Our findings demonstrate that HNK induces signaling and transcriptional responses that correct synaptic and memory deficits in AD mice. These results raise the prospect that HNK could serve as a therapeutic approach in AD. HIGHLIGHTS: The ketamine metabolite HNK activates hippocampal ERK/mTOR/S6 signaling pathways. HNK corrects hippocampal synaptic and memory defects in two mouse models of AD. Rescue of synaptic and memory impairments by HNK depends on ERK signaling. HNK corrects aberrant transcriptional signatures in APP/PS1 mice.
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Beta-amyloid (Aß) is thought to play a critical role in Alzheimer's disease (AD), and application of soluble oligomeric forms of Aß produces AD-like impairments in cognition and synaptic plasticity in experimental systems. We found previously that transgenic overexpression of the PP2A methylesterase, PME-1, or the PP2A methyltransferase, LCMT-1, altered the sensitivity of mice to Aß-induced impairments, suggesting that PME-1 inhibition may be an effective approach for preventing or treating these impairments. To explore this possibility, we examined the behavioral and electrophysiological effects of acutely applied synthetic Aß oligomers in male and female mice heterozygous for either a PME-1 KO or an LCMT-1 gene-trap mutation. We found that heterozygous PME-1 KO mice were resistant to Aß-induced impairments in cognition and synaptic plasticity, whereas LCMT-1 gene-trap mice showed increased sensitivity to Aß-induced impairments. The heterozygous PME-1 KO mice produced normal levels of endogenous Aß and exhibited normal electrophysiological responses to picomolar concentrations of Aß, suggesting that reduced PME-1 expression in these animals protects against Aß-induced impairments without impacting normal physiological Aß functions. Together, these data provide additional support for roles for PME-1 and LCMT-1 in regulating sensitivity to Aß-induced impairments, and suggest that inhibition of PME-1 may constitute a viable therapeutic approach for selectively protecting against the pathologic actions of Aß in AD.SIGNIFICANCE STATEMENT Elevated levels of ß-amyloid (Aß) in the brain are thought to contribute to the cognitive impairments observed in Alzheimer's disease patients. Here we show that genetically reducing endogenous levels of the PP2A methylesterase, PME-1, prevents the cognitive and electrophysiological impairments caused by acute exposure to pathologic concentrations of Aß without impairing normal physiological Aß function or endogenous Aß production. Conversely, reducing endogenous levels of the PP2A methyltransferase, LCMT-1, increases sensitivity to Aß-induced impairments. These data offer additional insights into the molecular factors that control sensitivity to Aß-induced impairments, and suggest that inhibiting PME-1 may constitute a viable therapeutic avenue for preventing Aß-related impairments in Alzheimer's disease.
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Peptídeos beta-Amiloides/toxicidade , Hidrolases de Éster Carboxílico/biossíntese , Disfunção Cognitiva/induzido quimicamente , Disfunção Cognitiva/enzimologia , Proteína O-Metiltransferase/biossíntese , Animais , Hidrolases de Éster Carboxílico/genética , Disfunção Cognitiva/fisiopatologia , Fenômenos Eletrofisiológicos/efeitos dos fármacos , Fenômenos Eletrofisiológicos/fisiologia , Feminino , Expressão Gênica , Masculino , Camundongos , Camundongos Knockout , Proteína O-Metiltransferase/genéticaRESUMO
Elevated levels of the ß-amyloid peptide (Aß) are thought to contribute to cognitive and behavioral impairments observed in Alzheimer's disease (AD). Protein phosphatase 2A (PP2A) participates in multiple molecular pathways implicated in AD, and its expression and activity are reduced in postmortem brains of AD patients. PP2A is regulated by protein methylation, and impaired PP2A methylation is thought to contribute to increased AD risk in hyperhomocysteinemic individuals. To examine further the link between PP2A and AD, we generated transgenic mice that overexpress the PP2A methylesterase, protein phosphatase methylesterase-1 (PME-1), or the PP2A methyltransferase, leucine carboxyl methyltransferase-1 (LCMT-1), and examined the sensitivity of these animals to behavioral and electrophysiological impairments caused by exogenous Aß exposure. We found that PME-1 overexpression enhanced these impairments, whereas LCMT-1 overexpression protected against Aß-induced impairments. Neither transgene affected Aß production or the electrophysiological response to low concentrations of Aß, suggesting that these manipulations selectively affect the pathological response to elevated Aß levels. Together these data identify a molecular mechanism linking PP2A to the development of AD-related cognitive impairments that might be therapeutically exploited to target selectively the pathological effects caused by elevated Aß levels in AD patients.
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Peptídeos beta-Amiloides/fisiologia , Transtornos Cognitivos/fisiopatologia , Proteína Fosfatase 2/metabolismo , Animais , Comportamento Animal , Metilação , Camundongos , Camundongos TransgênicosRESUMO
Small ubiquitin-related modifiers (SUMOs) conjugated or bound to target proteins can affect protein trafficking, processing and solubility. SUMOylation has been suggested to play a role in the amyloid plaque and neurofibrillary tangle pathology of Alzheimer disease (AD) and related neurodegenerative diseases. The current study examines the impact of SUMO1 on processing of the amyloid precursor protein (APP) leading to the production and deposition of the amyloid-ß (Aß) peptide. An in vivo model of these pathways was developed by the generation of double transgenic mice over-expressing human SUMO1 and a mutant APP. The SUMO1-APP transgenics displayed normal APP processing but, at later ages, exhibited increased insoluble Aß and plaque density accompanied by increased dendritic spine loss, more pronounced synaptic and cognitive deficits. These findings suggest a potential impairment in Aß clearance as opposed to increased amyloid production. Examination of microglia indicated a reduction in the SUMO1-APP transgenics which is a possible mechanism for the SUMO1-mediated increase in amyloid load. These findings suggest an indirect activity of SUMO1 possibly in the removal of Aß plaques rather than a direct impact on amyloid generation.
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Doença de Alzheimer/metabolismo , Doença de Alzheimer/patologia , Encéfalo/metabolismo , Encéfalo/patologia , Proteína SUMO-1/metabolismo , Peptídeos beta-Amiloides/metabolismo , Animais , Modelos Animais de Doenças , Feminino , Humanos , Masculino , Camundongos , Camundongos Transgênicos , Placa Amiloide/metabolismo , Placa Amiloide/patologiaRESUMO
A growing number of studies link dysfunction of macroautophagy/autophagy to the pathogenesis of diseases such as Alzheimer disease (AD). Given the global importance of autophagy for homeostasis, how its dysfunction can lead to specific neurological changes is puzzling. To examine this further, we compared the global deactivation of autophagy in the adult mouse using the atg7iKO with the impact of AD-associated pathogenic changes in autophagic processing of synaptic proteins. Isolated forebrain synaptosomes, rather than total homogenates, from atg7iKO mice demonstrated accumulation of synaptic proteins, suggesting that the synapse might be a vulnerable site for protein homeostasis disruption. Moreover, the deactivation of autophagy resulted in impaired cognitive performance over time, whereas gross locomotor skills remained intact. Despite deactivation of autophagy for 6.5 weeks, changes in cognition were in the absence of cell death or synapse loss. In the symptomatic APP PSEN1 double-transgenic mouse model of AD, we found that the impairment in autophagosome maturation coupled with diminished presence of discrete synaptic proteins in autophagosomes isolated from these mice, leading to the accumulation of one of these proteins in the detergent insoluble protein fraction. This protein, SLC17A7/Vglut, also accumulated in atg7iKO mouse synaptosomes. Taken together, we conclude that synaptic autophagy plays a role in maintaining protein homeostasis, and that while decreasing autophagy interrupts normal cognitive function, the preservation of locomotion suggests that not all circuits are affected similarly. Our data suggest that the disruption of autophagic activity in AD may have relevance for the cognitive impairment in this adult-onset neurodegenerative disease. Abbreviations: 2dRAWM: 2-day radial arm water maze; AD: Alzheimer disease; Aß: amyloid-beta; AIF1/Iba1: allograft inflammatory factor 1; APP: amyloid beta precursor protein; ATG7: autophagy related 7; AV: autophagic vacuole; CCV: cargo capture value; Ctrl: control; DLG4/PSD-95: discs large MAGUK scaffold protein 4; GFAP: glial fibrillary acidic protein; GRIN2B/NMDAR2b: glutamate ionotropic receptor NMDA type subunit 2B; LTD: long-term depression; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; m/o: months-old; PNS: post-nuclear supernatant; PSEN1/PS1: presenilin 1; SHB: sucrose homogenization buffer; SLC32A1/Vgat: solute carrier family 32 member 1; SLC17A7/Vglut1: solute carrier family 17 member 7; SNAP25: synaptosome associated protein 25; SQSTM1/p62: sequestosome 1; SYN1: synapsin I; SYP: synaptophysin ; SYT1: synaptotagmin 1; Tam: tamoxifen; VAMP2: vesicle associated membrane protein 2; VCL: vinculin; wks: weeks.
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Decades of research have correlated increased levels of amyloid-ß peptide (Aß) with neuropathological progression in Alzheimer's disease (AD) patients and transgenic models. Aß precipitates synaptic and neuronal anomalies by perturbing intracellular signaling, which, in turn, may underlie cognitive impairment. Aß also alters lipid metabolism, notably causing a deficiency of phosphatidylinositol 4,5-bisphosphate [PI(4,5)P(2)], a phospholipid that regulates critical neuronal functions. Haploinsufficiency of the gene encoding synaptojanin 1 (Synj1), a major PI(4,5)P(2) phosphatase in the brain, provided protection against PI(4,5)P(2) breakdown and electrophysiological deficits attributable to Aß. Based on these data, we tested whether reduction of Synj1 could rescue cognitive deficits and Aß-induced morphological alterations of synapses. We found that hemizygous deletion of Synj1 in the context of a mouse model expressing the Swedish mutant of amyloid precursor protein rescues deficits in learning and memory without affecting amyloid load. Synj1 heterozygosity also rescued PI(4,5)P(2) deficiency in a synaptosome-enriched fraction from the brain of Tg2576 mice. Genetic disruption of Synj1 attenuated Aß oligomer-induced changes in dendritic spines of cultured hippocampal neurons, sparing mature spine classes, which corroborates the protective role for Synj1 reduction against Aß insult at the synapse. These results indicate that Synj1 reduction ameliorates AD-associated behavioral and synaptic deficits, providing evidence that Synj1 and, more generally, phosphoinositide metabolism may be promising therapeutic targets. Our work expands on recent studies identifying lipid metabolism and lipid-modifying enzymes as targets of AD-associated synaptic and behavioral impairment.
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Doença de Alzheimer/patologia , Doença de Alzheimer/psicologia , Comportamento Animal/fisiologia , Monoéster Fosfórico Hidrolases/genética , Monoéster Fosfórico Hidrolases/fisiologia , Sinapses/patologia , Peptídeos beta-Amiloides/metabolismo , Animais , Western Blotting , Células Cultivadas , Condicionamento Psicológico/fisiologia , Sinais (Psicologia) , Espinhas Dendríticas/fisiologia , Medo/fisiologia , Feminino , Genótipo , Metabolismo dos Lipídeos/fisiologia , Masculino , Aprendizagem em Labirinto/fisiologia , Memória/fisiologia , Camundongos , Camundongos Endogâmicos , Fosfatidilinositóis/metabolismo , Desempenho Psicomotor/fisiologiaRESUMO
OBJECTIVE: The goal of this study was to investigate the role of endogenous amyloid-ß peptide (Aß) in healthy brain. METHODS: Long-term potentiation (LTP), a type of synaptic plasticity that is thought to be associated with learning and memory, was examined through extracellular field recordings from the CA1 region of hippocampal slices, whereas behavioral techniques were used to assess contextual fear memory and reference memory. Amyloid precursor protein (APP) expression was reduced through small interfering RNA (siRNA) technique. RESULTS: We found that both antirodent Aß antibody and siRNA against murine APP reduced LTP as well as contextual fear memory and reference memory. These effects were rescued by the addition of human Aß42, suggesting that endogenously produced Aß is needed for normal LTP and memory. Furthermore, the effect of endogenous Aß on plasticity and memory was likely due to regulation of transmitter release, activation of α7-containing nicotinic acetylcholine receptors, and Aß42 production. INTERPRETATION: Endogenous Aß42 is a critical player in synaptic plasticity and memory within the normal central nervous system. This needs to be taken into consideration when designing therapies aiming at reducing Aß levels to treat Alzheimer disease.
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Peptídeos beta-Amiloides/metabolismo , Hipocampo/fisiologia , Potenciação de Longa Duração/fisiologia , Memória/fisiologia , Peptídeos beta-Amiloides/genética , Peptídeos beta-Amiloides/imunologia , Precursor de Proteína beta-Amiloide/genética , Precursor de Proteína beta-Amiloide/metabolismo , Animais , Anticorpos/farmacologia , Comportamento Animal/efeitos dos fármacos , Biofísica/métodos , Estimulação Elétrica/métodos , Ensaio de Imunoadsorção Enzimática/métodos , Regulação da Expressão Gênica/fisiologia , Hipocampo/efeitos dos fármacos , Humanos , Potenciação de Longa Duração/efeitos dos fármacos , Masculino , Aprendizagem em Labirinto/efeitos dos fármacos , Memória/efeitos dos fármacos , Camundongos , Camundongos Endogâmicos C57BL , Fragmentos de Peptídeos/metabolismo , RNA Interferente Pequeno/farmacologiaRESUMO
Introduction: Alzheimer's disease (AD) is characterized by neurotoxic immuno-inflammation concomitant with cytotoxic oligomerization of amyloid beta (Aß) and tau, culminating in concurrent, interdependent immunopathic and proteopathic pathogeneses. Methods: We performed a comprehensive series of in silico, in vitro, and in vivo studies explicitly evaluating the atomistic-molecular mechanisms of cytokine-mediated and Aß-mediated neurotoxicities in AD. Next, 471 new chemical entities were designed and synthesized to probe the pathways identified by these molecular mechanism studies and to provide prototypic starting points in the development of small-molecule therapeutics for AD. Results: In response to various stimuli (e.g., infection, trauma, ischemia, air pollution, depression), Aß is released as an early responder immunopeptide triggering an innate immunity cascade in which Aß exhibits both immunomodulatory and antimicrobial properties (whether bacteria are present, or not), resulting in a misdirected attack upon "self" neurons, arising from analogous electronegative surface topologies between neurons and bacteria, and rendering them similarly susceptible to membrane-penetrating attack by antimicrobial peptides (AMPs) such as Aß. After this self-attack, the resulting necrotic (but not apoptotic) neuronal breakdown products diffuse to adjacent neurons eliciting further release of Aß, leading to a chronic self-perpetuating autoimmune cycle. AD thus emerges as a brain-centric autoimmune disorder of innate immunity. Based upon the hypothesis that autoimmune processes are susceptible to endogenous regulatory processes, a subsequent comprehensive screening program of 1137 small molecules normally present in human brain identified tryptophan metabolism as a regulator of brain innate immunity and a source of potential endogenous anti-AD molecules capable of chemical modification into multi-site therapeutic modulators targeting AD's complex immunopathic-proteopathic pathogenesis. Discussion: Conceptualizing AD as an autoimmune disease, identifying endogenous regulators of this autoimmunity, and designing small molecule drug-like analogues of these endogenous regulators represents a novel therapeutic approach for AD.
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Growing evidence implicates aberrant lipid signaling in Alzheimer's disease (AD). While phospholipases A2 and C have been recently shown to mediate key actions of amyloid ß-peptide (Aß) through a dysregulation of arachidonic acid and phosphatidylinositol-4,5-bisphosphate metabolism, respectively, the role of phospholipase D (PLD) has so far remained elusive. PLD produces phosphatidic acid (PA), a bioactive lipid involved in multiple aspects of cell physiology, including signaling and membrane trafficking processes. Here we show that oligomeric Aß enhances PLD activity in cultured neurons and that this stimulatory effect does not occur upon ablation of PLD2 via gene targeting. Aß fails to suppress long-term potentiation in PLD2-deficient hippocampal slices, suggesting that PLD2 is required for the synaptotoxic action of this peptide. In vivo PLD activity, as assessed by detection of phosphatidylethanol levels using mass spectrometry (MS) following ethanol injection, is also increased in the brain of a transgenic mouse model of AD (SwAPP). Furthermore, Pld2 ablation rescues memory deficits and confers synaptic protection in SwAPP mice despite a significant Aß load. MS-based lipid analysis of Pld2 mutant brains in the presence or absence of the SwAPP transgene unmasks striking crosstalks between different PA species. This lipid analysis shows an exquisite acyl chain specificity and plasticity in the perturbation of PA metabolism. Collectively, our results point to specific molecular species of PA as key modulators of AD pathogenesis and identify PLD2 as a novel potential target for therapeutics.
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Doença de Alzheimer/complicações , Transtornos Cognitivos/etiologia , Transtornos Cognitivos/patologia , Fosfolipase D/deficiência , Sinapses/genética , Fatores Etários , Doença de Alzheimer/genética , Peptídeos beta-Amiloides/farmacologia , Precursor de Proteína beta-Amiloide/genética , Animais , Comportamento Animal , Linhagem Celular Transformada , Transtornos Cognitivos/genética , Condicionamento Psicológico/fisiologia , Modelos Animais de Doenças , Interações Medicamentosas , Inibidores Enzimáticos/farmacologia , Ensaio de Imunoadsorção Enzimática/métodos , Estrenos/farmacologia , Potenciais Pós-Sinápticos Excitadores/efeitos dos fármacos , Potenciais Pós-Sinápticos Excitadores/genética , Medo/fisiologia , Regulação da Expressão Gênica/efeitos dos fármacos , Regulação da Expressão Gênica/genética , Proteínas de Fluorescência Verde/genética , Hipocampo/citologia , Humanos , Técnicas In Vitro , Potenciação de Longa Duração/efeitos dos fármacos , Potenciação de Longa Duração/genética , Espectrometria de Massas/métodos , Aprendizagem em Labirinto/fisiologia , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Mutação/genética , Neurônios/efeitos dos fármacos , Neurônios/metabolismo , Neurônios/patologia , Células PC12/efeitos dos fármacos , Fragmentos de Peptídeos/farmacologia , Fosfolipase D/genética , Pirrolidinonas/farmacologia , Ratos , Fatores de TempoRESUMO
Although deficiencies in the retromer sorting pathway have been linked to late-onset Alzheimer's disease, whether these deficiencies underlie the disease remains unknown. Here we characterized two genetically modified animal models to test separate but related questions about the effects that retromer deficiency has on the brain. First, testing for cognitive defects, we investigated retromer-deficient mice and found that they develop hippocampal-dependent memory and synaptic dysfunction, which was associated with elevations in endogenous Abeta peptide. Second, testing for neurodegeneration and amyloid deposits, we investigated retromer-deficient flies expressing human wild-type amyloid precursor protein (APP) and human beta-site APP-cleaving enzyme (BACE) and found that they develop neuronal loss and human Abeta aggregates. By recapitulating features of the disease, these animal models suggest that retromer deficiency observed in late-onset Alzheimer's disease can contribute to disease pathogenesis.
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Doença de Alzheimer/patologia , Peptídeos beta-Amiloides/química , Hipocampo/patologia , Doenças Neurodegenerativas/patologia , Doença de Alzheimer/metabolismo , Animais , Encéfalo/metabolismo , Modelos Animais de Doenças , Drosophila/metabolismo , Eletrofisiologia , Heterozigoto , Hipocampo/metabolismo , Humanos , Camundongos , Camundongos Knockout , Modelos Biológicos , Doenças Neurodegenerativas/metabolismoRESUMO
BACKGROUND: The serine/threonine protein phosphatase, PP2A, is thought to play a central role in the molecular pathogenesis of Alzheimer's disease (AD), and the activity and substrate specificity of PP2A is regulated, in part, through methylation and demethylation of its catalytic subunit. Previously, we found that transgenic overexpression of the PP2A methyltransferase, LCMT-1, or the PP2A methylesterase, PME-1, altered the sensitivity of mice to impairments caused by acute exposure to synthetic oligomeric amyloid-ß (Aß). OBJECTIVE: Here we sought to test the possibility that these molecules also controlled sensitivity to impairments caused by chronically elevated levels of Aß produced in vivo. METHODS: To do this, we examined the effects of transgenic LCMT-1, or PME-1 overexpression on cognitive and electrophysiological impairments caused by chronic overexpression of mutant human APP in Tg2576 mice. RESULTS: We found that LCMT-1 overexpression prevented impairments in short-term spatial memory and synaptic plasticity in Tg2576 mice, without altering APP expression or soluble Aß levels. While the magnitude of the effects of PME-1 overexpression in Tg2576 mice was small and potentially confounded by the emergence of non-cognitive impairments, Tg2576 mice that overexpressed PME-1 showed a trend toward earlier onset and/or increased severity of cognitive and electrophysiological impairments. CONCLUSION: These data suggest that the PP2A methyltransferase, LCMT-1, and the PP2A methylesterase, PME-1, may participate in the molecular pathogenesis of AD by regulating sensitivity to the pathogenic effects of chronically elevated levels of Aß.
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Doença de Alzheimer/metabolismo , Peptídeos beta-Amiloides/metabolismo , Hidrolases de Éster Carboxílico/metabolismo , Proteína O-Metiltransferase/metabolismo , Doença de Alzheimer/complicações , Peptídeos beta-Amiloides/genética , Animais , Disfunção Cognitiva/etiologia , Modelos Animais de Doenças , Humanos , Camundongos , Camundongos TransgênicosRESUMO
Memory loss, synaptic dysfunction, and accumulation of amyloid beta-peptides (A beta) are major hallmarks of Alzheimer's disease (AD). Downregulation of the nitric oxide/cGMP/cGMP-dependent protein kinase/c-AMP responsive element-binding protein (CREB) cascade has been linked to the synaptic deficits after A beta elevation. Here, we report that the phosphodiesterase 5 inhibitor (PDE5) sildenafil (Viagra), a molecule that enhances phosphorylation of CREB, a molecule involved in memory, through elevation of cGMP levels, is beneficial against the AD phenotype in a mouse model of amyloid deposition. We demonstrate that the inhibitor produces an immediate and long-lasting amelioration of synaptic function, CREB phosphorylation, and memory. This effect is also associated with a long-lasting reduction of A beta levels. Given that side effects of PDE5 inhibitors are widely known and do not preclude their administration to a senile population, these drugs have potential for the treatment of AD and other diseases associated with elevated A beta levels.
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Doença de Alzheimer/tratamento farmacológico , Peptídeos beta-Amiloides/metabolismo , Memória/efeitos dos fármacos , Inibidores da Fosfodiesterase 5 , Inibidores de Fosfodiesterase/farmacologia , Piperazinas/farmacologia , Sulfonas/farmacologia , Transmissão Sináptica/efeitos dos fármacos , Doença de Alzheimer/metabolismo , Doença de Alzheimer/psicologia , Precursor de Proteína beta-Amiloide/genética , Análise de Variância , Animais , Condicionamento Clássico/efeitos dos fármacos , Proteína de Ligação ao Elemento de Resposta ao AMP Cíclico/metabolismo , GMP Cíclico/metabolismo , Modelos Animais de Doenças , Imuno-Histoquímica , Injeções Intraperitoneais , Camundongos , Camundongos Transgênicos , Mutação , Testes Neuropsicológicos , Inibidores de Fosfodiesterase/administração & dosagem , Inibidores de Fosfodiesterase/farmacocinética , Fosforilação/efeitos dos fármacos , Piperazinas/administração & dosagem , Piperazinas/farmacocinética , Reação em Cadeia da Polimerase , Desempenho Psicomotor , Purinas/administração & dosagem , Purinas/farmacocinética , Purinas/farmacologia , Citrato de Sildenafila , Comportamento Espacial/efeitos dos fármacos , Sulfonas/administração & dosagem , Sulfonas/farmacocinética , Fatores de Tempo , Resultado do TratamentoRESUMO
The amyloid hypothesis posits that the amyloid-beta (Aß) protein precedes and requires microtubule-associated protein tau in a sort of trigger-bullet mechanism leading to Alzheimer's disease (AD) pathology. This sequence of events has become dogmatic in the AD field and is used to explain clinical trial failures due to a late start of the intervention when Aß already activated tau. Here, using a multidisciplinary approach combining molecular biological, biochemical, histopathological, electrophysiological, and behavioral methods, we demonstrated that tau suppression did not protect against Aß-induced damage of long-term synaptic plasticity and memory, or from amyloid deposition. Tau suppression could even unravel a defect in basal synaptic transmission in a mouse model of amyloid deposition. Similarly, tau suppression did not protect against exogenous oligomeric tau-induced impairment of long-term synaptic plasticity and memory. The protective effect of tau suppression was, in turn, confined to short-term plasticity and memory. Taken together, our data suggest that therapies downstream of Aß and tau together are more suitable to combat AD than therapies against one or the other alone.
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Doença de Alzheimer/metabolismo , Peptídeos beta-Amiloides/metabolismo , Potenciação de Longa Duração , Sinapses/metabolismo , Transmissão Sináptica , Proteínas tau/metabolismo , Doença de Alzheimer/genética , Doença de Alzheimer/patologia , Peptídeos beta-Amiloides/genética , Animais , Camundongos , Camundongos Knockout , Sinapses/genética , Sinapses/patologia , Proteínas tau/genéticaRESUMO
Amyloid-beta (Abeta) peptides are produced in high amounts during Alzheimer's disease, causing synaptic and memory dysfunction. However, they are also released in lower amounts in normal brains throughout life during synaptic activity. Here we show that low picomolar concentrations of a preparation containing both Abeta(42) monomers and oligomers cause a marked increase of hippocampal long-term potentiation, whereas high nanomolar concentrations lead to the well established reduction of potentiation. Picomolar levels of Abeta(42) also produce a pronounced enhancement of both reference and contextual fear memory. The mechanism of action of picomolar Abeta(42) on both synaptic plasticity and memory involves alpha7-containing nicotinic acetylcholine receptors. These findings strongly support a model for Abeta effects in which low concentrations play a novel positive, modulatory role on neurotransmission and memory, whereas high concentrations play the well known detrimental effect culminating in dementia.
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Peptídeos beta-Amiloides/farmacologia , Memória/efeitos dos fármacos , Plasticidade Neuronal/efeitos dos fármacos , Fragmentos de Peptídeos/farmacologia , Sinapses/efeitos dos fármacos , 2-Amino-5-fosfonovalerato/farmacologia , Análise de Variância , Animais , Bungarotoxinas/farmacologia , Relação Dose-Resposta a Droga , Estimulação Elétrica/métodos , Antagonistas de Aminoácidos Excitatórios/farmacologia , Potenciais Pós-Sinápticos Excitadores/efeitos dos fármacos , Potenciais Pós-Sinápticos Excitadores/genética , Hipocampo/citologia , Humanos , Técnicas In Vitro , Masculino , Aprendizagem em Labirinto/efeitos dos fármacos , Mecamilamina/farmacologia , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Plasticidade Neuronal/genética , Antagonistas Nicotínicos/farmacologia , Técnicas de Patch-Clamp , Receptores Nicotínicos/deficiência , Receptor Nicotínico de Acetilcolina alfa7RESUMO
BACKGROUND: Soluble aggregates of oligomeric forms of tau protein (oTau) have been associated with impairment of synaptic plasticity and memory in Alzheimer's disease. However, the molecular mechanisms underlying the synaptic and memory dysfunction induced by elevation of oTau are still unknown. METHODS: This work used a combination of biochemical, electrophysiological and behavioral techniques. Biochemical methods included analysis of phosphorylation of the cAMP-responsive element binding (CREB) protein, a transcriptional factor involved in memory, histone acetylation, and expression immediate early genes c-Fos and Arc. Electrophysiological methods included assessment of long-term potentiation (LTP), a type of synaptic plasticity thought to underlie memory formation. Behavioral studies investigated both short-term spatial memory and associative memory. These phenomena were examined following oTau elevation. RESULTS: Levels of phospho-CREB, histone 3 acetylation at lysine 27, and immediate early genes c-Fos and Arc, were found to be reduced after oTau elevation during memory formation. These findings led us to explore whether up-regulation of various components of the nitric oxide (NO) signaling pathway impinging onto CREB is capable of rescuing oTau-induced impairment of plasticity, memory, and CREB phosphorylation. The increase of NO levels protected against oTau-induced impairment of LTP through activation of soluble guanylyl cyclase. Similarly, the elevation of cGMP levels and stimulation of the cGMP-dependent protein kinases (PKG) re-established normal LTP after exposure to oTau. Pharmacological inhibition of cGMP degradation through inhibition of phosphodiesterase 5 (PDE5), rescued oTau-induced LTP reduction. These findings could be extrapolated to memory because PKG activation and PDE5 inhibition rescued oTau-induced memory impairment. Finally, PDE5 inhibition re-established normal elevation of CREB phosphorylation and cGMP levels after memory induction in the presence of oTau. CONCLUSIONS: Up-regulation of CREB activation through agents acting on the NO cascade might be beneficial against tau-induced synaptic and memory dysfunctions.
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Doença de Alzheimer/metabolismo , Potenciação de Longa Duração/fisiologia , Plasticidade Neuronal/fisiologia , Óxido Nítrico/metabolismo , Proteínas tau/metabolismo , Peptídeos beta-Amiloides/metabolismo , Animais , Feminino , Masculino , Memória/fisiologia , Transtornos da Memória/metabolismo , Camundongos Endogâmicos C57BL , Neurônios/metabolismoRESUMO
Defective brain hormonal signaling has been associated with Alzheimer's disease (AD), a disorder characterized by synapse and memory failure. Irisin is an exercise-induced myokine released on cleavage of the membrane-bound precursor protein fibronectin type III domain-containing protein 5 (FNDC5), also expressed in the hippocampus. Here we show that FNDC5/irisin levels are reduced in AD hippocampi and cerebrospinal fluid, and in experimental AD models. Knockdown of brain FNDC5/irisin impairs long-term potentiation and novel object recognition memory in mice. Conversely, boosting brain levels of FNDC5/irisin rescues synaptic plasticity and memory in AD mouse models. Peripheral overexpression of FNDC5/irisin rescues memory impairment, whereas blockade of either peripheral or brain FNDC5/irisin attenuates the neuroprotective actions of physical exercise on synaptic plasticity and memory in AD mice. By showing that FNDC5/irisin is an important mediator of the beneficial effects of exercise in AD models, our findings place FNDC5/irisin as a novel agent capable of opposing synapse failure and memory impairment in AD.
Assuntos
Doença de Alzheimer/metabolismo , Doença de Alzheimer/fisiopatologia , Fibronectinas/metabolismo , Transtornos da Memória/complicações , Transtornos da Memória/fisiopatologia , Plasticidade Neuronal , Condicionamento Físico Animal , Adolescente , Adulto , Idoso , Doença de Alzheimer/líquido cefalorraquidiano , Doença de Alzheimer/genética , Animais , Encéfalo/metabolismo , Encéfalo/patologia , Modelos Animais de Doenças , Regulação para Baixo , Feminino , Fibronectinas/líquido cefalorraquidiano , Fibronectinas/genética , Humanos , Potenciação de Longa Duração , Masculino , Camundongos Endogâmicos C57BL , Pessoa de Meia-Idade , Fármacos Neuroprotetores/farmacologia , Fármacos Neuroprotetores/uso terapêutico , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Proteínas Recombinantes/farmacologia , Proteínas Recombinantes/uso terapêutico , Transdução de SinaisRESUMO
Oligomerization of soluble tau protein is attracting the attention of an increasingly larger number of scientists involved in research on Alzheimer's disease and other tauopathies. A variety of methods have been developed for the purification of proteins from biological tissues and bacterial cells. Various types of high performance liquid chromatography (HPLC) and affinity tags represent the most common techniques for isolating proteins. Here, we describe a procedure for extracting recombinant tau protein from bacterial cells, utilizing a 6×His affinity tag, or endogenous tau from brain cortices using acid extraction followed by fast protein liquid chromatography (FPLC). Additionally, we introduce a method for oligomerization based on reduction and oxidation of cysteine residues. Our preparation assures high yield of tau protein, while preserving its physiological function.
Assuntos
Bactérias/metabolismo , Encéfalo/metabolismo , Proteínas tau/química , Proteínas tau/isolamento & purificação , Doença de Alzheimer/metabolismo , Animais , Autopsia , Bactérias/genética , Cromatografia de Afinidade , Cromatografia Líquida de Alta Pressão , Cisteína/química , Humanos , Camundongos , Oxirredução , Multimerização Proteica , Proteínas Recombinantes/química , Proteínas Recombinantes/isolamento & purificação , Proteínas tau/genéticaRESUMO
INTRODUCTION: Translational inhibition of amyloid precursor protein (APP) by Posiphen has been shown to reduce APP and its fragments in cell culture, animal models, and mildly cognitively impaired patients, making it a promising drug candidate for the treatment of Alzheimer's disease. METHODS: We used a mouse model of Alzheimer's disease (APP/presenilin-1) to examine Posiphen's efficacy, pharmacodynamics, and pharmacokinetics. RESULTS: Posiphen treatment normalized impairments in spatial working memory, contextual fear learning, and synaptic function in APP/presenilin-1 mice, without affecting their visual acuity, motor skills, or motivation and without affecting wild-type mice. Posiphen had a prolonged effect in reducing APP and all related peptides for at least 9 hours after the last dose. Its concentration was higher in the brain than in plasma, and the most abundant metabolite was N8-norPosiphen. DISCUSSION: This is the first study demonstrating the therapeutic efficacy of inhibiting the translation of APP and its fragments in an Alzheimer's disease model.
RESUMO
Soluble forms of oligomeric beta-amyloid (Aß) are thought to play a central role in Alzheimer's disease (AD). Transgenic manipulation of methylation of the serine/threonine protein phosphatase, PP2A, was recently shown to alter the sensitivity of mice to AD-related impairments resulting from acute exposure to elevated levels of Aß. In addition, eicosanoyl-5-hydroxytryptamide (EHT), a naturally occurring component from coffee beans that modulates PP2A methylation, was shown to confer therapeutic benefits in rodent models of AD and Parkinson's disease. Here, we tested the hypothesis that EHT protects animals from the pathological effects of exposure to elevated levels of soluble oligomeric Aß. We treated mice with EHT-containing food at two different doses and assessed the sensitivity of these animals to Aß-induced behavioral and electrophysiological impairments. We found that EHT administration protected animals from Aß-induced cognitive impairments in both a radial-arm water maze and contextual fear conditioning task. We also found that both chronic and acute EHT administration prevented Aß-induced impairments in long-term potentiation. These data add to the accumulating evidence suggesting that interventions with pharmacological agents, such as EHT, that target PP2A activity may be therapeutically beneficial for AD and other neurological conditions.