Browsing by Author "Bronfman, M"
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- ItemEthanol specifically decreases peroxisome proliferator activated receptor β in B12 oligodendrocyte-like cells(2003) Leisewitz, AV; Jung, JE; Perez-Alzola, P; Fuenzalida, KM; Roth, A; Inestrosa, NC; Bronfman, MPeroxisome proliferator activated receptors (PPARs) are nuclear receptors that control important genes involved in lipid metabolism. Their role in nerve cells is uncertain, although anomalous myelination of the corpus callosum has been described in the PPARbeta-null mouse, and abnormalities of this tissue have been documented in fetal alcohol syndrome in humans. We report here that ethanol treatment of B12 oligodendrocyte-like cells induces a concentration- and time-dependent decrease in the mRNA and protein levels of PPARbeta, with no effect on PPARalpha or PPARgamma. The effect on PPARbeta is seen as an increase in mRNA degradation, as assessed by run-off assays, due to a significant decrease in PPARbeta mRNA half-life, with no observed changes in intracellular localization. Our results suggest a possible link between PPARbeta function and ethanol-induced abnormal myelination in oligodendrocytes.
- ItemHigh-affinity binding of fatty acyl-CoAs and peroxisome proliferator-CoA esters to glutathione S-transferases -: Effect on enzymatic activity(1999) Silva, C; Loyola, G; Valenzuela, R; García-Huidobro, T; Monasterio, O; Bronfman, MAcyl-CoAs an present at high concentrations within the cell, yet are strongly buffered by specific binding proteins in order to maintain a low intracellular unbound acyl-CoA concentration, compatible with their metabolic role? their importance in cell signaling, and as protection from their detergent properties. This intracellular regulation may be disrupted by nonmetabolizables acyl-CoA esters of xenobiotics, such as peroxisome proliferators, which are formed at relatively high concentration within the liver cell. The low molecular mass acyl-CoA binding protein (ACBP) and fatty acyl-CoA binding protein (FABP) have been proposed as the buffering system for fatty acyl-CoAs. Whether these proteins also bind xenobiotic-CoA is not known. Here we have identified new liver cytosolic fatty acyl-CoA and xenobiotic-CoA binding sites as glutathione S-transferase (GST), using fluorescent polarization and a acyl-etheno-CoA derivative of the peroxisome proliferator nafenopin as ligand. Rat liver GST and human liver recombinant GSTA1-1, GSTP1-1 and GSTM1-1 were used. Only class alpha rat liver GST and human GSTA1-1 bind xenobiotic-CoAs and fatty acyl-CoAs, with K-d values ranging from 200 nM to 5 mu M. One mol of acyl-CoA is bound per mol of dimeric enzyme, and no metabolization or hydrolysis was observed. Binding results in strong inhibition of rat Liver GST and human recombinant GSTA1-1 (IC50 at the nanomolar level for palmitoyl-CoA) but not GSTP1-1 and GSTM1-1. Acyl-CoAs do not interact with the GSTA1-1 substrate binding site, but probably with a different domain. Results suggest that under increased acyl-CoA concentration, as occurs after exposure to peroxisome proliferators, acyl-CoA binding to the abundant class alpha GSTs may result in strong inhibition of xenobiotic detoxification, Analysis of the binding properties of GSTs and other acyl-CoA binding proteins suggest that under increased acyl-CoA concentration GSTs would be responsible for xenobiotic-CoA binding whereas ACBP would preferentially bind fatty acyl-CoAs.
- ItemPeroxisome proliferator-activated receptor gamma is expressed in hippocampal neurons and its activation prevents beta-amyloid neurodegeneration: role of Wnt signaling(ELSEVIER INC, 2005) Inestrosa, NC; Godoy, JA; Quintanilla, RA; Koenig, CS; Bronfman, MThe molecular pathogenesis of Alzheimer's disease (AD) involves the participation of the amyloid-beta-peptide (Abeta), which plays a critical role in the neurodegeneration that triggers the disease. Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors, which are members of the nuclear receptor family. We report here that (1) PPARgamma is present in rat hippocampal neurons in culture. (2) Activation of PPAR-gamma by troglitazone and rosiglitazone protects rat hippocampal neurons against Abeta-induced neurodegeneration, as shown by the 3-[4,5 -2yl]-2,5-diphenyltetrazolium bromide (MTT) reduction assay, immunofluorescence using an anti-heavy neurofilament antibody, and quantitative electron microscopy. (3) Hippocampal neurons treated with several PPAR-gamma agonists, including troglitazone, rosiglitazone, and ciglitazone, prevent the excitotoxic Abeta-induced rise in bulk-free Ca2+. (4) PPARgamma activation results in the modulation of Wnt signaling components, including the inhibition of glycogen synthase kinase-3beta (GSK-3beta) and an increase of the cytoplasmic and nuclear beta-catenin levels. We conclude that the activation of PPARgamma prevents Abeta-induced neurodegeneration by a mechanism that may involve a cross talk between neuronal PPAR-y and the Writ signaling pathway. More important, the fact that the activation of PPAR-y attenuated Abeta-dependent neurodegeneration opens the possibility to fight AD from a new therapeutic perspective. (C) 2004 Published by Elsevier Inc.
- ItemPeroxisome 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, MPeroxisome 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.
- ItemProtein kinase C inhibits amyloid β-peptide neurotoxicity by acting on members of the Wnt pathway(2002) Garrido, JL; Godoy, J; Alvarez, A; Bronfman, M; Inestrosa, NCCurrent evidence supports the notion that the amyloid beta-peptide (Abeta) plays a major role in the neurotoxicity observed in the brain in Alzheimer's disease. However, the signal transduction mechanisms involved still remain unknown. In the present work, we analyzed the effect of protein kinase C (PKC) on some members of the Writ signaling pathway and its implications for Abeta neurotoxicity. Activation of PKC by phorbol 12-myristate 13-acetate protected rat hippocampal neurons from A(3 toxicity. This effect was accomplished by inhibition of glycogen synthase kinase-3beta (GSK-3beta) activity, which led to the accumulation of cytoplasmic beta-catenin and transcriptional activation via beta-catenin/T-cell factor/lymphoid enhancer factor-1 (TCF/LEF-1) of Writ target genes, which in the present study were engrailed-1 (en-1) and cyclin D1 (cycD1). In contrast, inhibition of Ca2+-dependent PKC isoforms activated GSK-3beta and offered no protection from Abeta neurotoxicity. Wnt-3a and lithium salts, classical activators of the Writ pathway, mimicked PKC activation. Our results suggest that regulation of members of the Writ signaling pathway by Ca2+-dependent PKC isoforms may be important in controlling the neurotoxic process induced by Abeta.
- ItemThe hypolipidemic drug metabolites nafenopin-CoA and ciprofibroyl-CoA are competitive P2Y1 receptor antagonists(2003) Coddou, C; Loyola, G; Boyer, JL; Bronfman, M; Huidobro-Toro, JPCoenzyme A (CoA-SH), endogenous and drug-derived CoA-derivatives were tested as putative antagonists of P2Y receptors expressed in Xenopus laevis oocytes, a method used to determine calcium-activated chloride current, an indicator of the activation of these receptors. CoA-SH antagonized reversibly and in a concentration-dependent manner the ATP-gated currents evoked by the human P2Y(1) but not the P2Y(2) receptor. Palmitoyl-CoA was four-fold more potent than CoASH as an antagonist while palmitoyl-carnitine was inactive, highlighting the role of the CoA-SH moiety in the antagonism. The CoA derivatives of nafenopin and ciprofibrate, two clinically relevant hypolipidemic drugs, increased 13 and three-fold the potency of CoA-SH, respectively. The K(B)s of nafenopin-CoA and ciprofibroyl-CoA were 58 and 148 nM, respectively; the slopes of the Schild plots were unitary. Neither 100 muM nafenopin nor ciprofibrate alone altered the P2Y, receptor activity. Neither CoA-SH nor ciprofibroyl-CoA antagonized the rat P2X(2) or the P2X(4) nucleotide receptors nor interacted with the 5-HT2A/C receptors. The bulky drug CoA-SH derivatives identify a hydrophobic pocket, which may serve as a potential target for novel selective P2Y(1) antagonists. (C) 2003 Published by Elsevier Science B.V. on behalf of the Federation of European Biochemical Societies.
- ItemWnt signaling involvement in β-amyloid-dependent neurodegeneration(2002) Inestrosa, NC; De Ferrari, GV; Garrido, JL; Alvarez, A; Olivares, GH; Barría, MI; Bronfman, M; Chacón, MAAlzheimer's disease (AD) is a progressive dementia paralleled by selective neuronal death, which is probably caused by the cytotoxic effects of the amyloid-p peptide (Abeta). We have observed that Abeta-dependent neurotoxicity induces a loss of function of Wnt signaling components and that activation of this signaling cascade prevent such cytotoxic effects. Therefore we propose that compounds which mimic this signaling cascade may be candidates for therapeutic intervention in Alzheimer's patients. (C) 2002 Elsevier Science Ltd. All rights reserved.