RESUMEN
Amyloid-beta (Abeta) is cleared from the brain by both proteolytic digestion and transport across the blood-brain-barrier into the peripheral circulatory system. To investigate the role peripheral Abeta levels play in regulating Abeta brain clearance, we measured the clearance of [125I]-Abeta(1-40) injected into the brains of liver-ligated rats that allowed peripheral Abeta levels to be maintained at elevated levels for approximately one hour with/without a single peripheral bolus of unlabeled Abeta(1-40). We found that elevating peripheral Abetalevels significantly decreased [125I]-Abeta(1-40) brain clearance, thus supporting the hypothesis that peripheral Abeta levels regulate Abeta clearance from the central nervous system.
Asunto(s)
Péptidos beta-Amiloides/metabolismo , Péptidos beta-Amiloides/farmacocinética , Encéfalo/metabolismo , Fragmentos de Péptidos/metabolismo , Fragmentos de Péptidos/farmacocinética , Análisis de Varianza , Animales , Área Bajo la Curva , Transporte Biológico Activo/fisiología , Encéfalo/efectos de los fármacos , Isótopos de Yodo/farmacocinética , Masculino , Tasa de Depuración Metabólica/fisiología , Ratas , Ratas Sprague-Dawley , Factores de TiempoRESUMEN
Apolipoprotein E (apoE) remains the most important genetic risk factor for the development of Alzheimer's disease (AD). Still elusive, the role of apoE is under intense investigation. We propose that proteolysis of apoE in the brain leads to two major fragments, N- and C-terminal apoE, each of which would drive a different neuropathological pathway. N-terminal fragments of apoE are implicated in neurotoxicity, and C-terminal fragments might play a role in amyloid deposition and plaque formation. The greater risk of AD associated with the E4 isoform might relate to its greater neurotoxicity. Drugs that either directly inhibit the toxic effects of apoE or prevent the production of apoE fragments may provide novel therapeutic approaches to the treatment of AD and other disorders in which apoE is implicated.
Asunto(s)
Enfermedad de Alzheimer/tratamiento farmacológico , Apolipoproteínas E/antagonistas & inhibidores , Encéfalo/efectos de los fármacos , Fármacos Neuroprotectores/farmacología , Fragmentos de Péptidos/antagonistas & inhibidores , Enfermedad de Alzheimer/metabolismo , Enfermedad de Alzheimer/fisiopatología , Apolipoproteínas E/metabolismo , Encéfalo/metabolismo , Encéfalo/fisiopatología , Humanos , Ovillos Neurofibrilares/efectos de los fármacos , Ovillos Neurofibrilares/metabolismo , Fármacos Neuroprotectores/química , Neurotoxinas/antagonistas & inhibidores , Neurotoxinas/metabolismo , Fragmentos de Péptidos/metabolismo , Péptido Hidrolasas/efectos de los fármacos , Péptido Hidrolasas/metabolismo , Placa Amiloide/efectos de los fármacos , Placa Amiloide/metabolismo , Estructura Terciaria de Proteína/efectos de los fármacos , Estructura Terciaria de Proteína/fisiologíaRESUMEN
Apolipoprotein E (apoE) genotype is the single most important genetic risk factor for the most common (sporadic) form of Alzheimer's disease (AD). Increasing evidence supports the hypothesis that the presence of the E4 isoform of this cholesterol-binding protein contributes directly to disease risk, age of onset, and severity of the neuropathology. For example, studies in transgenic mice demonstrate that apoE is necessary for the formation of plaques with neuritic pathology. The precise mechanism by which apoE contributes to the disease remains unknown. However, several lines of investigation from a number of laboratories now point to a role for proteolytic fragments of apoE in the formation of both plaques and tangles, the two pathological hallmarks of the disease. In particular, the C-terminal portion of apoE has been implicated in binding to amyloid and is localized to plaques. The N-terminal domain, on the other hand, is neurotoxic in culture and has been localized to, and implicated in the formation of, neurofibrillary tangles. These results suggest that inhibition of apoE proteolysis is a potential therapeutic strategy for AD. Using human brain homogenates, we have determined that proteolysis of apoE is greatest at acidic pH and can be inhibited by compounds targeting aspartic proteases. The feasibility of screening candidate inhibitors is supported by both ELISA and immunoblotting methods. Future studies will use a combination of in vitro and in vivo assays to test the efficacy of the most effective compounds for their ability to inhibit apoE proteolysis in human brain and apoE transgenic mouse brain tissue.
Asunto(s)
Enfermedad de Alzheimer/tratamiento farmacológico , Enfermedad de Alzheimer/enzimología , Apolipoproteínas E/metabolismo , Encéfalo/efectos de los fármacos , Encéfalo/enzimología , Péptido Hidrolasas/efectos de los fármacos , Enfermedad de Alzheimer/genética , Animales , Apolipoproteínas E/genética , Encéfalo/fisiopatología , Evaluación Preclínica de Medicamentos , Inhibidores Enzimáticos/farmacología , Inhibidores Enzimáticos/uso terapéutico , Humanos , Ovillos Neurofibrilares/enzimología , Ovillos Neurofibrilares/genética , Fragmentos de Péptidos/antagonistas & inhibidores , Fragmentos de Péptidos/toxicidad , Péptido Hidrolasas/metabolismo , Placa Amiloide/enzimología , Placa Amiloide/genéticaRESUMEN
Glutamate transporters regulate normal synaptic network interactions and prevent neurotoxicity by rapidly clearing extracellular glutamate. GLT-1, the dominant glutamate transporter in the cerebral cortex and hippocampus, is significantly reduced in Alzheimer's disease (AD). However, the role GLT-1 loss plays in the cognitive dysfunction and pathology of AD is unknown. To determine the significance of GLT-1 dysfunction on AD-related pathological processes, mice lacking one allele for GLT-1(+/-) were crossed with transgenic mice expressing mutations of the amyloid-ß protein precursor and presenilin-1 (AßPPswe/PS1ΔE9) and investigated at 6 or 9 months of age. Partial loss of GLT-1 unmasked spatial memory deficits in 6-month-old mice expressing AßPPswe/PS1ΔE9, with these mice also exhibiting an increase in the ratio of detergent-insoluble Aß42/Aß40. At 9 months both behavioral performance and insoluble Aß42/Aß40 ratios among GLT-1(+/+)/AßPPswe/PS1ΔE9 and GLT-1(+/-)/AßPPswe/PS1ΔE9 mice were comparable. These results suggest that deficits in glutamate transporter function compound the effects of familial AD AßPP/PS1 mutant transgenes in younger animals and thus may contribute to early occurring pathogenic processes associated with AD.
Asunto(s)
Enfermedad de Alzheimer/metabolismo , Trastornos del Conocimiento/metabolismo , Transportador 2 de Aminoácidos Excitadores/metabolismo , Envejecimiento/psicología , Enfermedad de Alzheimer/genética , Péptidos beta-Amiloides/genética , Péptidos beta-Amiloides/metabolismo , Precursor de Proteína beta-Amiloide/genética , Precursor de Proteína beta-Amiloide/metabolismo , Animales , Conducta Animal/fisiología , Western Blotting , Química Encefálica , Trastornos del Conocimiento/genética , Estudios de Cohortes , Ensayo de Inmunoadsorción Enzimática , Transportador 2 de Aminoácidos Excitadores/genética , Aprendizaje por Laberinto , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Mutación , Presenilina-1/genéticaRESUMEN
Apolipoprotein E (apoE) has been genetically linked to late-onset Alzheimer's disease (AD). The role of this lipid-transport protein in AD remains to be established. One hypothesis is that apoE, particularly the apoE4 isoform, may have neurotoxic effects as demonstrated using apoE-related synthetic peptides and the N-terminal fragment of apoE. ApoE is a heparan-sulfate binding protein, and apoE peptide neurotoxicity can be blocked by heparin and prevented by degrading heparan sulfate or inhibiting its biosynthesis. The possibility that heparin inhibition of toxicity is mediated by a specific oligosaccharide sequence was investigated using a bioassay to determine the inhibition of apoE peptide toxicity by glycosaminoglycans and purified glycosaminoglycan oligosaccharides. Studies on modified heparins showed that the presence of N-sulfo groups and either 2- or 6-O sulfo groups were required for inhibition of toxicity. Heparin oligosaccharides with eight or more saccharide residues with seven O-sulfo groups and four N-sulfo groups exhibited potent inhibition. Larger oligosaccharides, and heparin and heparan sulfate polymers, afforded comparable, or somewhat better, protective effects but also caused clumping and detachment of cells when administrated alone.