RESUMEN
Alzheimer's disease is a learning and memory disorder pathologically characterized by the deposition of beta-amyloid plaques and loss of neurons and synapses in affected areas of the brain. Mutations in presenilin 1 (PS1) lead to the most aggressive form of familial Alzheimer's disease (FAD), and are associated with accelerated plaque deposition. However, since the function of PS1 is pleiotropic, we reasoned that the FAD mutations may alter multiple PS1-mediated pathways, and the combination of which may account for the early onset nature of the disease phenotype. Using the PS1M146V knockin mice in which the M146V mutation was incorporated into the endogenous mouse PS1 gene, we report here that the FAD mutation results in impaired hippocampus-dependent associative learning, as measured by a contextual fear conditioning paradigm, at 3 months of age. This is correlated with reduced adult neurogenesis in the dentate gyrus. However, short-term and long-term synaptic plasticity in both area CA1 and dentate gyrus are not affected. Our results suggest that impaired adult neurogenesis may contribute to the memory deficit associated with FAD.
Asunto(s)
Aprendizaje por Asociación/fisiología , Giro Dentado/citología , Giro Dentado/fisiología , Proteínas de la Membrana/genética , Mutación/genética , Animales , Condicionamiento Psicológico/fisiología , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Presenilina-1RESUMEN
Alzheimer's Disease (AD) is the most common of the senile dementias, the prevalence of which is increasing rapidly, with a projected 14 million affected worldwide by 2025. The signal transduction mechanisms that underlie the learning and memory derangements in AD are poorly understood. beta-Amyloid (Abeta) peptides are elevated in brain tissue of AD patients and are the principal component of amyloid plaques, a major criterion for postmortem diagnosis of the disease. Using acute and organotypic hippocampal slice preparations, we demonstrate that Abeta peptide 1-42 (Abeta42) couples to the mitogen-activated protein kinase (MAPK) cascade via alpha7 nicotinic acetylcholine receptors (nAChRs). In vivo elevation of Abeta, such as that exhibited in an animal model for AD, leads to the upregulation of alpha7 nAChR protein. alpha7 nAChR upregulation occurs concomitantly with the downregulation of the 42 kDa isoform of extracellular signal-regulated kinase (ERK2) MAPK in hippocampi of aged animals. The phosphorylation state of a transcriptional mediator of long-term potentiation and a downstream target of the ERK MAPK cascade, the cAMP-regulatory element binding (CREB) protein, were affected also. These findings support the model that derangement of hippocampus signal transduction cascades in AD arises as a consequence of increased Abeta burden and chronic activation of the ERK MAPK cascade in an alpha7 nAChR-dependent manner that eventually leads to the downregulation of ERK2 MAPK and decreased phosphorylation of CREB protein.
Asunto(s)
Enfermedad de Alzheimer/metabolismo , Péptidos beta-Amiloides/farmacología , Hipocampo/metabolismo , Sistema de Señalización de MAP Quinasas/efectos de los fármacos , Fragmentos de Péptidos/farmacología , Receptores Nicotínicos/metabolismo , Envejecimiento/metabolismo , Enfermedad de Alzheimer/etiología , Animales , Células Cultivadas , Enfermedad Crónica , Proteína de Unión a Elemento de Respuesta al AMP Cíclico/metabolismo , Modelos Animales de Enfermedad , Activación Enzimática/efectos de los fármacos , Activadores de Enzimas/farmacología , Heterocigoto , Hipocampo/citología , Hipocampo/efectos de los fármacos , Técnicas In Vitro , Aprendizaje por Laberinto/efectos de los fármacos , Ratones , Ratones Transgénicos , Proteína Quinasa 1 Activada por Mitógenos/metabolismo , Nicotina/farmacología , Antagonistas Nicotínicos/farmacología , Ratas , Ratas Sprague-Dawley , Receptores Nicotínicos/efectos de los fármacos , Regulación hacia Arriba , Receptor Nicotínico de Acetilcolina alfa 7RESUMEN
Hippocampal long-term potentiation (LTP) is a robust and long-lasting form of synaptic plasticity that is the leading candidate for a cellular mechanism contributing to mammalian learning and memory. Investigations over the past decade have revealed that the biochemistry of LTP induction involves mechanisms of great subtlety and complexity. This review highlights themes that have emerged as a result of our increased knowledge of the signal transduction pathways involved in the induction of NMDA receptor-dependent LTP in area CA1 of the hippocampus. Among these themes are signal amplification, signal integration and signal coordination. Here we use these themes as an organizing context for reviewing the profusion of signaling mechanisms involved in the induction of LTP.
Asunto(s)
Hipocampo/fisiología , Potenciación a Largo Plazo/fisiología , Animales , Calcio/fisiología , Retroalimentación , Hipocampo/metabolismo , Modelos Neurológicos , Receptores AMPA/fisiología , Receptores de N-Metil-D-Aspartato/fisiología , Transducción de SeñalRESUMEN
The mitogen-activated protein kinase ERK has recently become a focus of studies of synaptic plasticity and learning and memory. Due to the prominent role of potassium channels in regulating the electrical properties of membranes, modulation of these channels by ERK could play an important role in mediating learning-related synaptic plasticity in the CNS. Kv4.2 is a Shal-type potassium channel that passes an A-type current and is localized to dendrites and cell bodies in the hippocampus. The sequence of Kv4.2 contains several consensus sites for ERK phosphorylation. In the present studies, we tested the hypothesis that Kv4.2 is an ERK substrate. We determined that the Kv4.2 C-terminal cytoplasmic domain is an effective ERK2 substrate, and that it is phosphorylated at three sites: Thr(602), Thr(607), and Ser(616). We used this information to develop antibodies that recognize Kv4.2 phosphorylated by ERK2. One of our phospho-site-selective antibodies was generated using a triply phosphorylated peptide as the antigen. We determined that this antibody recognizes ERK-phosphorylated Kv4.2 in COS-7 cells transfected with Kv4.2 and native ERK-phosphorylated Kv4.2 in the rat hippocampus. These observations indicate that Kv4.2 is a substrate for ERK in vitro and in vivo, and suggest that ERK may regulate potassium-channel function by direct phosphorylation of the pore-forming alpha subunit.
Asunto(s)
Proteína Quinasa 1 Activada por Mitógenos/metabolismo , Canales de Potasio con Entrada de Voltaje , Canales de Potasio/metabolismo , Secuencia de Aminoácidos , Animales , Anticuerpos/metabolismo , Especificidad de Anticuerpos , Sitios de Unión/efectos de los fármacos , Western Blotting , Células COS , Hipocampo/citología , Hipocampo/metabolismo , Inmunohistoquímica , Técnicas In Vitro , Proteína Quinasa 1 Activada por Mitógenos/farmacología , Datos de Secuencia Molecular , Fosforilación/efectos de los fármacos , Canales de Potasio/química , Estructura Terciaria de Proteína/efectos de los fármacos , Ratas , Canales de Potasio ShalRESUMEN
Transient transfection has not been a successful method to express the alpha7 nicotinic acetylcholine receptor such that these receptors are detected on the cell surface. This is not the case for all ligand-gated ion channels. Transient transfection with the 5-hydroxytryptamine type 3 subunit cDNA results in detectable surface receptor expression. Cell lines stably expressing the alpha7 nicotinic acetylcholine receptor produce detectable, albeit variable, levels of surface receptor expression. alpha7 nicotinic acetylcholine receptor surface expression is dependent, at least in part, on cell-specific factors. In addition to factors provided by the cells used for receptor expression, we hypothesize that the surface expression level in transfected cells is an intrinsic property of the receptor protein under study. Employing a set of alpha7-5-hydroxytryptamine type 3 chimeric receptor subunit cDNAs, we expressed these constructs in a transient transfection system and quantified surface receptor expression. We have identified amino acids that control receptor distribution between surface and intracellular pools; surface receptor expression can be manipulated without affecting the total number of receptors. These determinants function independently of the cell line used for expression and the transfection method employed. How these surface expression determinants in the alpha7 nicotinic acetylcholine receptor might influence synaptic efficacy is discussed.
Asunto(s)
Aminoácidos , Receptores Nicotínicos/genética , Secuencia de Aminoácidos , Sustitución de Aminoácidos , Animales , Secuencia de Bases , Transporte Biológico , Células COS , Membrana Celular/metabolismo , ADN Complementario/genética , Datos de Secuencia Molecular , Receptores Nicotínicos/biosíntesis , TransfecciónRESUMEN
Participation of the neuronal nicotinic receptor subunit alpha6 in a physiologically relevant receptor has yet to be demonstrated, but its high degree of expression in catecholaminergic nuclei has attracted considerable interest. To investigate the pattern of expression of the alpha6 protein, a subunit specific antibody against the alpha6 subunit was used to immunohistochemically label sections of the adult rat brain. Alpha6 immunoreactivity was found to be present in the substantia nigra, the ventral tegmental area, the locus coeruleus and the medial habenula, and double-labeling for tyrosine hydroxylase demonstrated that the alpha6 protein is present on dopaminergic neurons of the midbrain. A possible role for the alpha6 subunit in nicotinic modulation of dopaminergic transmission is therefore proposed.