RESUMO
The activation of the canonical Wnt signaling pathway protects hippocampal neurons against the toxicity of Alzheimer's amyloid-beta-peptide (Abeta), however, the role played by the Wnt receptors Frizzleds, has not been studied. We report here that Frizzled-1 mediates the activation of the canonical Wnt/beta-catenin pathway by Wnt3a in PC12 cells. In addition, the protective effect of Wnt3a against the toxicity of Abeta oligomers was modulated by Frizzled-1 expression levels in both PC12 cells and hippocampal neurons. Over-expression of Frizzled-1 significantly increased cell survival induced by Wnt3a and diminished caspase-3 activation, while knocking-down Frizzled-1 expression by antisense oligonucleotides decreased the Wnt3a protection. Over-expression of wild-type beta-catenin, but not a transcriptionally inactive mutated version, prevented the toxicity of Abeta suggesting that the transcription of Wnt target genes may be involved in these events. This was confirmed by co-transfecting both Frizzled-1 and the inactive form of beta-catenin, which does not elicited protection levels similar to those showed with endogenous beta-catenin. Our results indicate that Wnt3a protects from Abeta-oligomers toxicity by activating the canonical Wnt signaling pathway through the Frizzled-1 receptor, suggesting a therapeutic potential for this signaling pathway in the treatment of Alzheimer's disease.
Assuntos
Peptídeos beta-Amiloides/toxicidade , Receptores Frizzled/metabolismo , Degeneração Neural/metabolismo , Transdução de Sinais/fisiologia , Proteínas Wnt/metabolismo , Animais , Western Blotting , Caspase 3/metabolismo , Linhagem Celular , Sobrevivência Celular/fisiologia , Células Cultivadas , Imunofluorescência , Hipocampo/metabolismo , Hipocampo/patologia , Imuno-Histoquímica , Neurônios/metabolismo , Neurônios/patologia , Ratos , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Transfecção , Proteína Wnt3 , beta Catenina/metabolismoRESUMO
Prion diseases are fatal neurodegenerative disorders associated with the conversion of the cellular prion protein (PrPC) into a pathologic isoform. Although the physiological function of PrPC remains unknown, evidence relates PrPC to copper metabolism and oxidative stress as suggested by its copper-binding properties in the N-terminal octapeptide repeat region. This region also reduces copper ions in vitro, and this reduction ability is associated with the neuroprotection exerted by the octarepeat region against copper in vivo. In addition, the promoter region of the PrPC gene contains putative metal response elements suggesting it may be regulated by heavy metals. Here we address some of the evidence that support a physiological link between PrPC and copper. Also, in vivo experiments suggesting the physiological relevance of PrPC interaction with heparan sulfate proteoglycans are discussed.
Assuntos
Cobre/metabolismo , Estresse Oxidativo/fisiologia , Proteínas PrPC/metabolismo , Animais , Proteoglicanas de Heparan Sulfato/metabolismo , Proteínas PrPC/genética , Doenças Priônicas/metabolismo , Ligação Proteica , RatosRESUMO
Prion diseases are fatal neurodegenerative disorders associated with the conversion of the cellular prion protein (PrPC) into a pathologic isoform. Although the physiological function of PrPC remains unknown, evidence relates PrPC to copper metabolism and oxidative stress as suggested by its copper-binding properties in the N-terminal octapeptide repeat region. This region also reduces copper ions in vitro, and this reduction ability is associated with the neuroprotection exerted by the octarepeat region against copper in vivo. In addition, the promoter region of the PrPC gene contains putative metal response elements suggesting it may be regulated by heavy metals. Here we address some of the evidence that support a physiological link between PrPC and copper. Also, in vivo experiments suggesting the physiological relevance of PrPC interaction with heparan sulfate proteoglycans are discussed.
Assuntos
Animais , Ratos , Cobre/metabolismo , Estresse Oxidativo/fisiologia , Proteínas PrPC/metabolismo , Proteoglicanas de Heparan Sulfato/metabolismo , Ligação Proteica , Proteínas PrPC/genética , Doenças Priônicas/metabolismoRESUMO
It is generally accepted that human Alzheimer's disease (AD) neuropathology markers are completely absent in rodent brains. We report here that an aged wild-type South American rodent, Octodon degu, expresses neuronal beta-amyloid precursor protein (beta-APP695) displaying both intracellular and extracellular deposits of amyloid-beta-peptide (Abeta), intracellular accumulations of tau-protein and ubiquitin, a strong astrocytic response and acetylcholinesterase (AChE)-rich pyramidal neurons. The high amino acid homology (97.5%) between deguAbeta and humanAbeta sequences is probably a major factor in the appearance of AD markers in this aged rodent. Our results indicate that aged O. degu constitutes the first wild-type rodent model for neurodegenerative processes associated to AD.
Assuntos
Envelhecimento/fisiologia , Doença de Alzheimer/metabolismo , Peptídeos beta-Amiloides/metabolismo , Octodon/metabolismo , Acetilcolinesterase/metabolismo , Doença de Alzheimer/patologia , Sequência de Aminoácidos , Peptídeos beta-Amiloides/genética , Animais , Astrócitos/metabolismo , Northern Blotting/métodos , Encéfalo/citologia , Encéfalo/metabolismo , Modelos Animais de Doenças , Regulação da Expressão Gênica/fisiologia , Proteína Glial Fibrilar Ácida/metabolismo , Humanos , Imuno-Histoquímica/métodos , Neurônios/metabolismo , RNA Mensageiro/biossíntese , Ratos , Reação em Cadeia da Polimerase Via Transcriptase Reversa/métodos , Ubiquitina/metabolismo , Proteínas tau/metabolismoRESUMO
The amyloid precursor protein (APP) contains a Cu binding domain (CuBD) localized between amino acids 135 and 156 (APP135-156), which can reduce Cu2+ to Cu1+ in vitro. The physiological function of this APP domain has not yet being established; nevertheless several studies support the notion that the CuBD of APP is involved in Cu homeostasis. We used APP synthetic peptides to evaluate their protective properties against Cu2+ neurotoxicity in a bilateral intra-hippocampal injection model. We found that human APP135-156 protects against Cu2+-induced neurotoxic effects, such as, impairment of spatial memory, neuronal cell loss, and astrogliosis. APP135-156 lacking two histidine residues showed protection against Cu2+; however, APP135-156 mutated in cysteine 144, a key residue in the reduction of Cu2+ to Cu1+, did not protect against Cu2+ neurotoxicity. In accordance with recent reports, the CuBD of the Caenorhabditis elegans, APL-1, protected against Cu2+ neurotoxicity in vivo. We also found that Cu2+ neurotoxicity is associated with an increase in nitrotyrosine immunofluorescence as well as with a decrease in Cu2+ uptake. The CuBD of APP therefore may play a role in the detoxification of brain Cu.
Assuntos
Precursor de Proteína beta-Amiloide/química , Precursor de Proteína beta-Amiloide/fisiologia , Cobre/metabolismo , Cobre/toxicidade , Tirosina/análogos & derivados , Precursor de Proteína beta-Amiloide/uso terapêutico , Animais , Sítios de Ligação , Proteínas de Caenorhabditis elegans/química , Cobre/antagonistas & inibidores , Cisteína/química , Gliose/induzido quimicamente , Gliose/prevenção & controle , Humanos , Transporte de Íons , Proteínas de Membrana/química , Memória/efeitos dos fármacos , Neurônios/citologia , Síndromes Neurotóxicas/prevenção & controle , Peptídeos/química , Peptídeos/uso terapêutico , Estrutura Terciária de Proteína , Proteínas/química , Ratos , Tirosina/análiseRESUMO
Neuropathological changes generated by human amyloid-beta peptide (Abeta) fibrils and Abeta-acetylcholinesterase (Abeta-AChE) complexes were compared in rat hippocampus in vivo. Results showed that Abeta-AChE complexes trigger a more dramatic response in situ than Abeta fibrils alone as characterized by the following features observed 8 weeks after treatment: 1). amyloid deposits were larger than those produced in the absence of AChE. In fact, AChE strongly stimulates rat Abeta aggregation in vitro as shown by turbidity measurements, Congo Red binding, as well as electron microscopy, suggesting that Abeta-AChE deposits observed in vivo probably recruited endogenous Abeta peptide; 2). the appearance of laminin expressing neurons surrounding Abeta-AChE deposits (such deposits are resistant to disaggregation by laminin in vitro); 3). an extensive astrocytosis revealed by both glial fibrillary acidic protein immunoreactivity and number counting of reactive hypertrophic astrocytes; and 4). a stronger neuronal cell loss in comparison with Abeta-injected animals. We conclude that the hippocampal injection of Abeta-AChE complexes results in the appearance of some features reminiscent of Alzheimer-like lesions in rat brain. Our studies are consistent with the notion that Abeta-AChE complexes are more toxic than Abeta fibrils and that AChE triggered some of the neurodegenerative changes observed in Alzheimer's disease brains.
Assuntos
Acetilcolinesterase/toxicidade , Precursor de Proteína beta-Amiloide/toxicidade , Astrócitos/patologia , Gliose/patologia , Hipocampo/patologia , Laminina/genética , Neurônios/patologia , Animais , Astrócitos/efeitos dos fármacos , Bovinos , Sobrevivência Celular/efeitos dos fármacos , Proteína Glial Fibrilar Ácida/análise , Gliose/induzido quimicamente , Hipocampo/efeitos dos fármacos , Humanos , Processamento de Imagem Assistida por Computador , Neurônios/efeitos dos fármacos , Ratos , Ratos Sprague-Dawley , Espectrometria de FluorescênciaRESUMO
Previous studies have demonstrated that acetylcholinesterase (AChE) promotes the assembly of amyloid-beta-peptides into neurotoxic amyloid fibrils and is toxic for chick retina neuronal cultures and neuroblastoma cells. Moreover, AChE is present in senile plaques in Alzheimer's disease (AD) brains. Here we have studied the effect of AChE on astrocytes and hippocampal neurons in vivo. Morphological as well as behavioral disturbances were analyzed after intrahippocampal injection of AChE. Rats were trained in the Morris water maze and assayed for behavioral parameters. Neuronal cell loss was found in the upper leaf of the dentate gyrus in rats injected with AChE in comparison with control animals. Glial fibrillary acidic protein immunoreactivity showed astrocytic hypertrophy and the magnitude of the response was associated with neuronal cell loss. Behavioral results show that injection of AChE produces cognitive impairment demonstrated by an altered water maze performance including (i) a higher escape latency score, (ii) a decreased spatial acuity and (iii) a shorter time of swimming in the platform quadrant. These findings indicate that a local increment in neuronal AChE concentration at the mammalian hippocampus, such as those present in amyloid deposits, may play a role in triggering neuropathological and behavioral changes such as those observed in AD brains.
Assuntos
Acetilcolinesterase/farmacologia , Astrócitos/efeitos dos fármacos , Hipocampo/efeitos dos fármacos , Hipocampo/fisiopatologia , Neurônios/efeitos dos fármacos , Animais , Astrócitos/metabolismo , Astrócitos/patologia , Comportamento Animal/efeitos dos fármacos , Bovinos , Vias de Administração de Medicamentos , Proteína Glial Fibrilar Ácida/biossíntese , Hipocampo/patologia , Masculino , Aprendizagem em Labirinto/efeitos dos fármacos , Neurônios/patologia , Ratos , Ratos Sprague-Dawley , Tempo de Reação/efeitos dos fármacosRESUMO
Alzheimer's disease (AD) is a progressive dementia paralleled by selective neuronal death, which is probably caused by the cytotoxic effects of the amyloid-beta peptide (Abeta). We have observed that Abeta-dependent neurotoxicity induces a loss of function of Wnt signaling components and that activation of this signaling cascade prevent such cytotoxic effects. Therefore we propose that compounds which mimic this signaling cascade may be candidates for therapeutic intervention in Alzheimer's patients.