RESUMEN
Intracellular amyloid-beta peptide (Abeta) has been implicated in neuronal death associated with Alzheimer's disease. Although Abeta is predominantly secreted into the extracellular space, mechanisms of Abeta transport at the level of the neuronal cell membrane remain to be fully elucidated. We demonstrate that receptor for advanced glycation end products (RAGE) contributes to transport of Abeta from the cell surface to the intracellular space. Mouse cortical neurons exposed to extracellular human Abeta subsequently showed detectable peptide intracellularly in the cytosol and mitochondria by confocal microscope and immunogold electron microscopy. Pretreatment of cultured neurons from wild-type mice with neutralizing antibody to RAGE, and neurons from RAGE knockout mice displayed decreased uptake of Abeta and protection from Abeta-mediated mitochondrial dysfunction. Abeta activated p38 MAPK, but not SAPK/JNK, and then stimulated intracellular uptake of Abeta-RAGE complex. Similar intraneuronal co-localization of Abeta and RAGE was observed in the hippocampus of transgenic mice overexpressing mutant amyloid precursor protein. These findings indicate that RAGE contributes to mechanisms involved in the translocation of Abeta from the extracellular to the intracellular space, thereby enhancing Abeta cytotoxicity.
Asunto(s)
Péptidos beta-Amiloides/metabolismo , Proteínas Quinasas Activadas por Mitógenos/metabolismo , Neuronas/metabolismo , Transducción de Señal/fisiología , Péptidos beta-Amiloides/genética , Animales , Transporte Biológico/fisiología , Encéfalo/anatomía & histología , Encéfalo/metabolismo , Células Cultivadas , Activación Enzimática , Humanos , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Ratones Transgénicos , Mitocondrias/metabolismo , Proteínas Quinasas Activadas por Mitógenos/genética , Neuronas/citología , Proteínas Quinasas p38 Activadas por Mitógenos/metabolismoRESUMEN
In Alzheimer's disease (AD), the expression of matrix metalloproteases (MMPs), which are capable of degrading extracellular matrix proteins, is increased in the brain. Previous studies with cultured glial cells have demonstrated that amyloid beta (Abeta) protein can induce the expression of MMPs, which could be involved in the degradation of Abeta. In the present study, we investigated the role of MMP-2 and MMP-9 in cognitive impairment induced by the injection of Abeta in mice. The intracerebroventricular injection of Abeta25-35, Abeta1-40, and Abeta1-42, but not Abeta40-1, transiently increased MMP-9, but not MMP-2, activity and protein expression in the hippocampus. Immunohistochemistry revealed the expression of MMP-9 to be increased in both neurons and glial cells in the hippocampus after Abeta treatment. The Abeta-induced cognitive impairment in vivo as well as neurotoxicity in vitro was significantly alleviated in MMP-9 homozygous knockout mice and by treatment with MMP inhibitors. These results suggest the increase in MMP-9 expression in the hippocampus to be involved in the development of cognitive impairment induced by Abeta1-40. Thus, specific inhibitors of MMP-9 may have therapeutic potential for the treatment of AD. Our findings suggest that, as opposed to expectations based on previous findings, MMP-9 plays a causal role in Abeta-induced cognitive impairment and neurotoxicity.
Asunto(s)
Péptidos beta-Amiloides/toxicidad , Trastornos del Conocimiento/enzimología , Trastornos del Conocimiento/prevención & control , Inhibidores de la Metaloproteinasa de la Matriz , Inhibidores de Proteasas/farmacología , Animales , Células Cultivadas , Trastornos del Conocimiento/inducido químicamente , Masculino , Metaloproteinasa 9 de la Matriz/fisiología , Ratones , Ratones Endogámicos ICR , Ratones Noqueados , Inhibidores de Proteasas/uso terapéuticoRESUMEN
Ovarian hormone decline after menopause may influence cognitive performance and increase the risk for Alzheimer's disease (AD) in women. Amyloid-beta peptide (Abeta) has been proposed to be the primary cause of AD. In this study, we examined whether ovariectomy (OVX) could affect the levels of cofactors Abeta-binding alcohol dehydrogenase (ABAD) and receptor for advanced glycation endproducts (RAGE), which have been reported to potentiate Abeta-mediated neuronal perturbation, in mouse hippocampus, correlating with estrogen and Abeta levels. Female ICR mice were randomly divided into ovariectomized or sham-operated groups, and biochemical analyses were carried out at 5 weeks after the operation. OVX for 5 weeks significantly decreased hippocampal 17beta-estradiol level, while it tended to reduce the hormone level in serum, compared with the sham-operated control. In contrast, OVX did not affect hippocampal Abeta(1-40) level, although it significantly increased serum Abeta(1-40) level. Furthermore, we demonstrated that OVX increased hippocampal ABAD level in neurons, but not astrocytes, while it did not affect RAGE level. These findings suggest that the expression of neuronal ABAD depends on estrogen level in the hippocampus and the increase in serum Abeta and hippocampal ABAD induced by ovarian hormone decline may be associated with pre-stage of memory deficit in postmenopausal women and Abeta-mediated AD pathology.
Asunto(s)
Alcohol Deshidrogenasa/metabolismo , Péptidos beta-Amiloides/metabolismo , Hipocampo/metabolismo , Neuronas/metabolismo , Ovariectomía , Animales , Astrocitos/metabolismo , Western Blotting , Proteínas de Unión al ADN , Estradiol/farmacología , Femenino , Proteína Ácida Fibrilar de la Glía/metabolismo , Hipocampo/citología , Hipocampo/enzimología , Ratones , Ratones Endogámicos ICR , Proteínas del Tejido Nervioso/metabolismo , Proteínas Nucleares/metabolismo , Receptor para Productos Finales de Glicación Avanzada , Receptores Inmunológicos/metabolismoRESUMEN
Ovarian hormone decline after menopause may influence cognitive performance and increase the risk for Alzheimer's disease (AD) in women. We have recently demonstrated that a combination of ovariectomy and chronic stress (OVX/stress) causes hippocampus-associated cognitive dysfunction in mice. In this study, we examined whether OVX/stress could affect the levels of AD-related molecules in the mouse hippocampus. Female ICR mice were ovariectomized or sham-operated, and then randomly divided into a daily restraint stress (21 days, 6 h/day) or non-stress group. Although OVX or stress alone did not affect beta-site amyloid precursor protein (APP)-cleaving enzyme-1 (BACE1) activity, OVX/stress increased activity in hippocampal CA1 and CA3 regions, compared with other groups. In contrast, OVX/stress did not affect gamma-secretase activity, Abeta(1-40), and phosphorylated-tau levels in the hippocampus. These findings suggest that a stressful life after menopause can influence the levels of AD-related molecules and that BACE1 is the most sensitive molecule for such a situation.