RESUMEN
NACP, the precursor of non-A beta component of Alzheimer's disease (AD) amyloid (NAC), is a synaptic protein that could potentially be involved in AD. We studied, by dot-blot, NACP levels in the frontal cortex of AD cases staged according to severity of disease and correlated them with cognitive performance and neuropathological markers. Early AD cases showed one fold higher levels of NACP immunoreactivity (IR) compared to moderate and severe AD. Levels of NACP-IR were correlated with tangle counts (r = -0.305, P = 0.04) and Blessed score (r = -0.356, P = 0.01), but not with plaque counts (r = 0.132, P = 0.39). This study suggests that the abnormal accumulation of NACP during the early stages of AD might play an important role in the mechanisms of neurodegeneration and synaptic damage in AD.
Asunto(s)
Enfermedad de Alzheimer/metabolismo , Amiloide/biosíntesis , Proteínas del Tejido Nervioso , Precursores de Proteínas/biosíntesis , Anciano , Anciano de 80 o más Años , Enfermedad de Alzheimer/patología , Enfermedad de Alzheimer/psicología , Cognición/fisiología , Progresión de la Enfermedad , Femenino , Humanos , Procesamiento de Imagen Asistido por Computador , Immunoblotting , Masculino , Ovillos Neurofibrilares/patología , Corteza Prefrontal/metabolismo , Corteza Prefrontal/patología , SinucleínasRESUMEN
The secreted form (sAPP) of the Alzheimer amyloid beta/A4 protein precursor (APP) has been shown to be involved in the in vitro regulation of fibroblast growth and neurite extension from neuronal cells. The active site of sAPP responsible for these functions is within a small domain just C-terminal to the Kunitz-type protease inhibitor (KPI) insertion site. We report here that a 17-mer peptide, containing this active domain of sAPP, can induce cellular and behavioral changes when infused into rat brains. After 2 weeks of APP 17-mer peptide infusion, the animals were tested for reversal learning and memory retention and were sacrificed for morphological examination of brains. We found that administration of the APP 17-mer peptide resulted in an 18% increase in the number of presynaptic terminals in the frontoparietal cortex. At the behavioral level, 17-mer-infused animals with nonimpaired learning capability showed an increased memory retention that seemed to interfere with reversal learning performance. This APP 17-mer effect on memory retention was not observed in animals with impaired initial learning capacity. These results suggest that APP is involved in memory retention through its effect on synaptic structure.
Asunto(s)
Precursor de Proteína beta-Amiloide/farmacología , Encéfalo/efectos de los fármacos , Fragmentos de Péptidos/farmacología , Retención en Psicología/efectos de los fármacos , Sinapsis/efectos de los fármacos , Secuencia de Aminoácidos , Animales , Conducta Animal , Femenino , Lóbulo Frontal/anatomía & histología , Hipocampo/anatomía & histología , Inmunohistoquímica , Masculino , Datos de Secuencia Molecular , Lóbulo Parietal/anatomía & histología , Ratas , Ratas Endogámicas F344 , Sinaptofisina/aislamiento & purificaciónRESUMEN
The growth of A-1 fibroblasts depends on exogenous amyloid beta/A4 protein precursor (APP), providing a simple bioassay to study the function of APP. Our preliminary study, testing the activity of a series of fragments derived from the secreted form of APP-695 (sAPP-695) on this bioassay, has shown that at least one of the active sites of sAPP-695 was localized within a 40-mer sequence (APP296-335, Kang sequence; Roch, J.-M., I. P. Shapiro, M. P. Sundsmo, D. A. C. Otero, L. M. Refolo, N. K. Robakis, and T. Saitoh. 1992. J. Biol. Chem. 267:2214-2221). In the present study, to further characterize the growth-promoting activity of sAPP-695 on fibroblasts, we applied a battery of synthetic peptides on this bioassay and found that: (a) the sequence of five amino acids, RERMS (APP328-332), was uniquely required for the growth-promoting activity of sAPP-695; (b) the activity was sequence-specific because the reverse-sequence peptide of the active domain had no activity; and (c) the four-amino-acid peptide RMSQ (APP330-333), which partially overlaps the COOH-terminal side of the active sequence RERMS, could antagonize the activity of sAPP-695. Furthermore, a recombinant protein which lacks this active domain (APP20-591 without 306-335) did not promote fibroblast cell growth, suggesting that this domain is the only site of sAPP-695 involved in the growth stimulation. The availability of these biologically active, short peptides and their antagonists should prove to be an essential step for the elucidation of APP involvement in regulation of cellular homeostasis.
Asunto(s)
Precursor de Proteína beta-Amiloide/química , Fibroblastos/citología , Secuencia de Aminoácidos , Precursor de Proteína beta-Amiloide/fisiología , Análisis de Varianza , Secuencia de Bases , División Celular , Línea Celular , ADN , Datos de Secuencia MolecularRESUMEN
The secreted form of Alzheimer amyloid beta/A4 protein precursor (APP) has been shown to be involved in cell growth regulation (Saitoh, T., Sundsmo, M., Roch, J.-M., Kimura, N., Cole, G., Schubert, D., Oltersdorf, T., and Schenk, D.B. (1989) Cell 58, 615-622). Using a strong prokaryotic expression system, we expressed, in Escherichia coli, peptide fragments covering different regions of the secreted form of APP-695. The longest of these fragments (KB75, 572 amino acids from Val-20 to Ile-591), which contained neither the Kunitz-type protease inhibitor (KPI) domain nor the amyloid beta/A4-protein domain, was purified and shown to be biologically active in terms of growth regulation. Two other APP fragments (KB48, 316 amino acids from Val-20 to Met-335; and RB17, 150 amino acids from Thr-296 to Pro-445), overlapping by only 40 amino acids at a close site C-terminal to the KPI insertion site, were also active. Furthermore, a chemically synthesized 40-residue peptide corresponding to this region of overlap also stimulated the growth of A-1 fibroblasts. These results establish the presence of growth-promoting activity in the secreted form of APP-695 and suggest that the site of this activity of APP-695 lies within a 40-amino acid domain next to the KPI insertion site.