Browsing by Author "Bronfman, FC"

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    Amyloid precursor protein fragment and acetylcholinesterase increase with cell confluence and differentiation in a neuronal cell line
    (1996) Bronfman, FC; Fernandez, HL; Inestrosa, NC
    This study addresses the developmental regulation of amyloid precursor protein (APP) fragments comprising the amyloid-beta peptide (A beta) and the amyloid-promoting factor acetylcholinesterase (AChE) in a mouse neuronal cell line (Neuro-2a). Results indicate that a 35-kDa amyloidogenic fragment of APP and the major molecular forms of AChE (G(1) and G(4)) in Neuro-2a cells significantly increase with increasing levels of cell confluence. The foregoing molecules undergo further increases when neuroblastoma cells differentiate in the presence of dibutyryl cAMP. In contrast, a 17-kDa fragment of APP and butyrylcholinesterase mere not affected by cell confluence or differentiation. These findings are the first to indicate that a selective A beta-containing fragment of APP is subject to developmental regulation. Moreover, our data show that the 35-kDa fragment and AChE forms respond in parallel to the same developmental stimuli, i.e., cell confluence and differentiation. This points to the existence of a functional relationship between both molecules, a notion that is consistent with the potential role that has been ascribed to AChE in both APP processing and the formation of amyloid deposits in Alzheimer's brains. (C) 1996 Academic Press, Inc.
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    Extracellular matrix regulates the amount of the beta-amyloid precursor protein and its amyloidogenic fragments
    (1996) Bronfman, FC; Soto, C; Tapia, L; Tapia, V; Inestrosa, NC
    We have studied the influence of the extracellular matrix (ECM) on the amount of beta-amyloid precursor protein (APP) and C-terminal amyloid-bearing fragments in 3T3 fibroblasts. After incubation with ECM components, the cellular APP content of 3T3 cells changed. Besides, different substrata including collagen, fibronectin, laminin, vitronectin, and heparin, determined changes in the amount of a C-terminal 22 kDa-fragment. The regulation of amyloidogenic fragments by the ECM was transient; in fact, when 3T3 cells were plated on tissue culture dishes coated with collagen or vitronectin, maximal levels of the 22 kDa fragment were observed 12 h after plating; in the presence of fibronectin, the maximum level of the amyloidogenic fragment was obtained 36 h after plating. These results indicate that the ECM modulates in a transient way the generation of APP-derived polypeptides containing the amyloid-beta-peptide (A beta). The ECM does not have a generalized effect on 3T3 fibroblasts, because no significant differences in cell attachment, growth rate, whole-cell polypeptide pattern, beta(1) integrin and a-tubulin levels were observed on cells grown on various matrix proteins. Laminin, collagen, and heparin also influence the level of an amyloidogenic fragment of 35 kDa in Neuro 2A neuronal cells, without a significant change in the neuronal marker acetylcholinesterase. In this case, however, a long-lasting response to ECM molecules was observed. These observations provide evidence that ECM molecules influence APP biogenesis, including the generation of amyloidogenic fragments containing the A beta peptide. Our studies might prove significant to understand the localized increment of beta-amyloid deposition in selected areas of the brain of Alzheimer's patients. (C) 1996 Wiley-Liss, Inc.
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    Laminin blocks the assembly of wild type Aβ and the Dutch variant peptide into Alzheimer's fibrils
    (1998) Bronfman, FC; Alvarez, A; Morgan, C; Inestrosa, NC
    Amyloid fibril formation is believed to be a nucleation-dependent polymerization process which may be influenced by various other factors with important consequences for the development, prevention or treatment of amyloidosis. We have previously shown that laminin inhibits A beta peptide fibril formation in vitro. Here we present a kinetic study that indicates laminin to be a potent anti-amyloidosis factor, as it not only inhibited alpha beta(1-40) fibril aggregation, but also inhibited the aggregation of the Dutch A beta(1-40) variant, a peptide with a higher capacity to aggregate than the wild-type A beta(1-40). The inhibitory effect of laminin on amyloid fibril formation was not overcome by the addition of pre-formed A beta fibrils, suggesting that laminin inhibits the fibril elongation process. At the present time, however, we cannot rule out the possibility that laminin also affects the initial nucleation process of A beta fibril formation. On other hand, laminin was not able to counteract the amyloid fibril formation promoted by acetylcholinesterase (AChE), another component of the amyloid deposits found in AD brains. The effect of laminin may bet important as an inhibitor of A beta amyloidogenesis in vivo, specifically at the level of cerebral blood vessels.
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    Laminin inhibits amyloid-beta-peptide fibrillation
    (1996) Bronfman, FC; Garrido, J; Alvarez, A; Morgan, C; Inestrosa, NC
    Laminin, an important extracellular matrix component is induced by brain injury and colocalizes with amyloid-beta-peptide (A beta) deposits in Alzheimer brains. We report here that laminin inhibits amyloid fibril formation as determined by thioflavin T fluorescence spectroscopy and electron microscopic examination. The inhibition of amyloid formation by laminin was concentration dependent and was observed at a laminin concentration of 300 nM, corresponding to a laminin/A beta protein molar ratio of 1:800. The potential effect of laminin, may prove important to inhibit AP fibrillogenesis in vivo, specifically at the level of cerebral blood vessels.
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    Peroxisome proliferator-activated receptor γ is a novel target of the nerve growth factor signaling pathway in PC12 cells
    (2005) Fuenzalida, KM; Aguilera, MC; Piderit, DG; Ramos, PC; Contador, D; Quiñones, V; Rigotti, A; Bronfman, FC; Bronfman, M
    Peroxisome proliferator- activated receptor gamma ( PPARgamma), a member of the nuclear receptor superfamily, is subject to considerable interest because of its role in adipocyte differentiation, metabolic control, and anti- inflammatory action. PPARgamma research in brain cells is presently focused on glial PPARgamma because of its potential as a pharmacological target in the treatment of neurodegenerative diseases with an inflammatory component. In neurons PPARgamma function is far from clear, and PPARgamma agonist-dependent and -independent effects on cell survival or differentiation have been reported. We used PC12 cells, widely used to study neuronal signaling, such as nerve growth factor (NGF)-induced differentiation and survival or epidermal growth factor-dependent cell proliferation to dissect the possible involvement of PPARgamma in these pathways. We show that NGF but not epidermal growth factor increases the transcriptional activity of PPARgamma, and modulates the expression of this transcription factor. Because NGF signals through the tyrosine kinase (TrkA) NGF receptor and/ or the p75(NTR) receptor, we used rescue experiments with a PC12 cell mutant lacking TrkA to show that NGF- induced PPARgamma activation is dependent on TrkA activation. Our results point out PPARgamma as a novel target of the TrkA-mediated neuronal cell survival and differentiating pathway and suggest a potential new inflammatory-independent therapeutic approach for pharmacological intervention in neurological disorders.