Browsing by Author "Bronfman, Miguel"

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    A PPARs cross-talk concertedly commits C6 glioma cells to oligodendrocytes and induces enzymes involved in myelin synthesis
    (WILEY, 2008) Leisewitz, Andrea V.; Urrutia, Carolina R.; Martinez, Gabriela R.; Loyola, Gloria; Bronfman, Miguel
    Peroxisome proliferator activated receptors (PPARs, alpha, beta/delta, gamma) control lipid homeostasis and differentiation in various tissues and tumor cells. PPAR beta and PPAR gamma increase oligodendrocyte maturation in glial mixed populations and spinal cord oligodendrocytes, respectively, and PPAR beta is known to modulate the activity of other PPARs. To assess a possible interaction between PPARs in glial cell differentiation we used the undifferentiated C6 glioma cell line as model. These cells express all three PPARs, but only PPAR gamma shows transcriptional activity in agonist-based reporter gene assay. Agonist-activated PPAR gamma up-regulates oligodendrocyte markers, down-regulates an astrocyte marker, and increases alkyl-dihydroxyacetone phosphate synthase, enzyme involved in the synthesis of myelin-rich plasmalogens. Similar effects are induced in PPAR gamma overexpressing cells, which in addition show PPAR beta up-regulation. PPAR beta or PPAR alpha agonists show no effect. Nevertheless, PPAR beta overexpression up-regulates PPAR gamma and commits C6 cells to oligodendrocytes: effect that is abrogated by a PPAR gamma antagonist or PPAR gamma interference RNA. Moreover, PPAR beta overexpression also induces PPAR alpha and its target genes, including acyl-CoA oxidase, enzyme involved in very long chain fatty acid recycling, and in the synthesis of myelin components such as docosahexaenoic acid. These results indicate for the first time, that PPARs concertedly cooperate in C6 glioma cell differentiation to oligodendrocytes. Further, they suggest that active PPAR beta might be essential for increasing oligodendrocyte distinctive markers and enzymes required for myelin synthesis in C6 glioma cells through up-regulation of PPAR gamma and PPAR alpha.
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    Inhibition of nuclear factor-kappa B enhances the capacity of immature dendritic cells to induce antigen-specific tolerance in experimental autoimmune encephalomyelitis
    (AMER SOC PHARMACOLOGY EXPERIMENTAL THERAPEUTICS, 2006) Iruretagoyena, Mirentxu I.; Sepulveda, Sofia E.; Lezana, J. Pablo; Hermoso, Marcela; Bronfman, Miguel; Gutierrez, Miguel A.; Jacobelli, Sergio H.; Kalergis, Alexis M.
    Autoimmune disorders develop as a result of deregulated immune responses that target self-antigens and cause destruction of healthy host tissues. Because dendritic cells (DCs) play an important role in the maintenance of peripheral immune tolerance, we are interested in identifying means of enhancing their therapeutic potential in autoimmune diseases. It is thought that during steady state, DCs are able to anergize potentially harmful T cells bearing T cell receptors that recognize self-peptide-major histocompatibility complexes. The tolerogenic capacity of DCs requires an immature phenotype, which is characterized by a reduced expression of costimulatory molecules. On the contrary, activation of antigen-specific naive T cells is enhanced by DC maturation, a process that involves expression of genes controlled by the transcription factor nuclear factor (NF)-kappa B. We evaluated the capacity of drugs that inhibit NF-kappa B to enhance the tolerogenic properties of immature DCs in the experimental autoimmune encephalomyelitis (EAE) model. We show that andrographolide, a bicyclic diterpenoid lactone, and rosiglitazone, a peroxisome proliferator-activated receptor gamma agonist, were able to interfere with NF-kappa B activation in murine DCs. As a result, treated DCs showed impaired maturation and a reduced capacity to activate antigen-specific T cells. Furthermore, NF-kappa B-blocked DCs had an enhanced tolerogenic capacity and were able to prevent EAE development in mice. The tolerogenic feature was specific for myelin antigens and involved the expansion of regulatory T cells. These data suggest that NF-kappa B blockade is a potential pharmacological approach that can be used to enhance the tolerogenic ability of immature DCs to prevent detrimental autoimmune responses.
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    Megalin/LRP2 Expression Is Induced by Peroxisome Proliferator-Activated Receptor -Alpha and -Gamma: Implications for PPARs' Roles in Renal Function
    (PUBLIC LIBRARY SCIENCE, 2011) Cabezas, Felipe; Lagos, Jonathan; Cespedes, Carlos; Vio, Carlos P.; Bronfman, Miguel; Marzolo, Maria Paz
    Background: Megalin is a large endocytic receptor with relevant functions during development and adult life. It is expressed at the apical surface of several epithelial cell types, including proximal tubule cells (PTCs) in the kidney, where it internalizes apolipoproteins, vitamins and hormones with their corresponding carrier proteins and signaling molecules. Despite the important physiological roles of megalin little is known about the regulation of its expression. By analyzing the human megalin promoter, we found three response elements for the peroxisomal proliferator-activated receptor (PPAR). The objective of this study was to test whether megalin expression is regulated by the PPARs.
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    P450CYP2C epoxygenase and CYP4A omega-hydroxylase mediate ciprofibrate-induced PPAR alpha-dependent peroxisomal proliferation
    (AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC, 2007) Gatica, Arnaldo; Aguilera, Mauricio C.; Contador, David; Loyola, Gloria; Pinto, Claudio O.; Amigo, Ludwig; Tichauer, Juan E.; Zanlungo, Silvana; Bronfman, Miguel
    Peroxisomal proliferators, such as ciprofibrate, are used extensively as effective hypolipidemic drugs. The effects of these compounds on lipid metabolism require ligand binding activation of the peroxisome proliferator-activated receptor (PPAR) alpha subtype of nuclear receptors and involve transcriptional activation of the metabolic pathways involved in lipid oxidative metabolism, transport, and disposition. omega-Hydroxylated-eicosatrienoic acids (HEETs), products of the sequential metabolism of arachidonic acid (AA) by the cytochrome P450 CYP2C epoxygenase and CYP4A omega-hydroxylase gene subfamilies, have been identified as potent and high-affinity ligands of PPAR alpha in vitro and as PPAR alpha activators in transient transfection assays. Using isolated rat hepatocytes in culture, we demonstrate that specific inhibition of either the CYP2C epoxygenase or the CYP4A omega-hydroxylase abrogates ciprofibrate-induced peroxisomal proliferation, whereas inhibition of other eicosanoid-synthesizing pathways had no effect. Conversely, overexpression of the rat liver CYP2C11 epoxygenase leads to spontaneous peroxisomal proliferation, an effect that is reversed by a CYP inhibitor. Based on these results, we propose that HEETs may serve as endogenous PPAR alpha ligands and that the P450 AA monooxygenases participate in ciprofibrate-induced peroxisomal proliferation and the activation of PPAR alpha downstream targets.
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    Peroxisome proliferator-activated receptor gamma up-regulates the Bcl-2 anti-apoptotic protein in neurons and induces mitochondrial stabilization and protection against oxidative stress and apoptosis
    (AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC, 2007) Fuenzalida, Karen; Quintanilla, Rodrigo; Ramos, Patricio; Piderit, Daniela; Fuentealba, Rodrigo A.; Martinez, Gabriela; Inestrosa, Nibaldo C.; Bronfman, Miguel
    Peroxisome proliferator-activated receptor gamma(PPAR gamma) has been proposed as a therapeutic target for neurodegenerative diseases because of its anti-inflammatory action in glial cells. However, PPAR gamma agonists prevent beta-amyloid (A beta)-induced neurodegeneration in hippocampal neurons, and PPAR gamma is activated by the nerve growth factor (NGF) survival pathway, suggesting a neuroprotective anti-inflammatory independent action. Here we show that the PPAR gamma agonist rosiglitazone (RGZ) protects hippocampal and dorsal root ganglion neurons against A beta-induced mitochondrial damage and NGF deprivation-induced apoptosis, respectively, and promotes PC12 cell survival. In neurons and in PC12 cells RGZ protective effects are associated with increased expression of the Bcl-2 anti-apoptotic protein. NGF-differentiated PC12 neuronal cells constitutively overexpressing PPAR gamma are resistant to A beta-induced apoptosis and morphological changes and show functionally intact mitochondria and no increase in reactive oxygen species when challenged with up to 50 mu M H2O2. Conversely, cells expressing a dominant negative mutant of PPAR gamma show increased A beta-induced apoptosis and disruption of neuronal-like morphology and are highly sensitive to oxidative stress-induced impairment of mitochondrial function. Cells overexpressing PPAR gamma present a 4-to 5-fold increase in Bcl-2 protein content, whereas in dominant negative PPAR gamma-expressing cells, Bcl-2 is barely detected. Bcl-2 knockdown by small interfering RNA in cells overexpressing PPAR gamma results in increased sensitivity to A beta and oxidative stress, further suggesting that Bcl-2 up-regulation mediates PPAR gamma protective effects. PPAR gamma prosurvival action is independent of the signal-regulated MAPK or the Akt prosurvival pathways. Altogether, these data suggest that PPAR gamma supports survival in neurons in part through a mechanism involving increased expression of Bcl-2.