1,720,997 research outputs found
Metabotropic purinergic receptors in lipid membrane microdomains
No full textThere is broad evidence that association of transmembrane receptors and signalling molecules with lipid rafts/caveolae provides an enriched environment for protein-protein interactions necessary for signal transduction, and a mechanism for the modulation of neurotransmitter and/or growth factor receptor function. Several receptors translocate into submembrane compartments after ligand binding, while others move in the opposite direction. The role of such a dynamic localization and functional facilitation is signalling modulation and receptor desensitization or internalization. Purine and pyrimidine nucleotides have been viewed as primordial precursors in the evolution of all forms of intercellular communication, and they are now regarded as fundamental extracellular signalling molecules. They propagate the purinergic signalling by binding to ionotropic and metabotropic receptors expressed on the plasma membrane of almost all cell types, tissues and organs. Here, we have illustrated the localization in lipid rafts/caveolae of G protein-coupled P1 receptors for adenosine and P2Y receptors for nucleoside tri- and di-phosphates. We have highlighted that microdomain partitioning of these purinergic GPCRs is cell-specific, as is the overall expression levels of these same receptors. Moreover, we have described that disruption of submembrane compartments can shift the purinergic receptors from raft/caveolar to non-raft/non-caveolar fractions, and then abolish their ability to activate lipid signalling pathways and to integrate with additional lipid-controlled signalling events. This modulates the biological response to purinergic ligands and most of all indicates that the topology of the various purinergic components at the cell surface not only organizes the signal transduction machinery, but also controls the final cellular response
Commentary: Multifactoriality of amytrophic lateral sclerosis: linking unfolded proteins to oxidative stress in microglia
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Protein disulfide isomerase in ALS mouse glia links protein misfolding with NADPH oxidase-catalyzed superoxide production
P2X3 receptor localizes into lipid rafts in neuronal cells
No full textP2X receptors are a family of seven(P2X(1-7)) cation channels gated by extracellular ATP, widely expressed in neurons and nonneuronal cells. Lipid rafts are cholesterol/sphingolipid-rich membrane domains, involved in many cellular processes, including transmembrane receptor signaling, vesicle traffic, and protein sorting. We provide direct biochemical evidence that P2X(3) receptor localizes into lipid rafts, in primary cultures of cerebellar granule neurons as well as in brain and dorsal root ganglia extracts. We show that P2X(3) exhibits all the characteristics distinctive of a protein associated with lipid rafts. These characteristics include resistance to detergent extraction at 4degreesC, solubility after extraction of cholesterol from membranes with either saponin or methyl-beta-cyclodextrin, and partitioning to low buoyant density fractions after sucrose gradient centrifugation in both detergent-containing and detergent-free conditions. Furthermore, P2X(3) localizes in raft-containing fractions in transiently transfected SH-SY5Y neuroblastorna cells. The present finding contributes to the characterization of the functional localization of P2X(3) in neurons and provides a novel potential mechanism for correct targeting and dynamic activation of this receptor. (C) 2004 Wiley-Liss, Inc
Drug Repurposing: A Network-based Approach to Amyotrophic Lateral Sclerosis
Full text linkThe continuous adherence to the conventional “one target, one drug” paradigm has failed so far to provide effective therapeutic solutions for heterogeneous and multifactorial diseases as amyotrophic lateral sclerosis (ALS), a rare progressive and chronic, debilitating neurological disease for which no cure is available. The present study is aimed at finding innovative solutions and paradigms for therapy in ALS pathogenesis, by exploiting new insights from Network Medicine and drug repurposing strategies. To identify new drug-ALS disease associations, we exploited SAveRUNNER, a recently developed network-based algorithm for drug repurposing, which quantifies the proximity of disease-associated genes to drug targets in the human interactome. We prioritized 403 SAveRUNNER-predicted drugs according to decreasing values of network similarity with ALS. Among catecholamine, dopamine, serotonin, histamine, and GABA receptor modulators, as well as angiotensin-converting enzymes, cyclooxygenase isozymes, and serotonin transporter inhibitors, we found some interesting no customary ALS drugs, including amoxapine, clomipramine, mianserin, and modafinil. Furthermore, we strengthened the SAveRUNNER predictions by a gene set enrichment analysis that confirmed modafinil as a drug with the highest score among the 121 identified drugs with a score > 0. Our results contribute to gathering further proofs of innovative solutions for therapy in ALS pathogenesis
Synthesis and content of a DNA-binding protein with lactic dehydrogenase activity are reduced by nerve growth factor in the neoplastic cell line PC12
No full textWe have previously demonstrated that synthesis of a 34 kD protein having specific, high affinity for single-stranded DNA (34kD-ssb protein), is markedly inhibited by nerve growth factor (NGF) in the neoplastic clonal cell line PC12. We report here that total content as well as mRNA for this protein are progressively reduced in PC12 cells undergoing mitotic arrest and morphological differentiation induced by NGF. It is also shown that binding of the 34K-ssb protein to ssDNA is fully inhibited by NADH but not by NAD+ or by several other nucleotides. Enzymatic tests on the possible NADH/NAD+-dependent dehydrogenase activity of the 34K-ssb protein have demonstrated that it has lactic dehydrogenase activity (LDH) with a specific activity comparable to that of rabbit muscle. Furthermore, the 34K-ssb protein has the same peptide mapping as LDH purified from rat muscle. Antibodies directed against the 34K-ssb protein cross-react with the rabbit muscle enzyme and, vice versa, antibodies raised against rabbit LDH cross-react with the 34K-ssb protein. It is concluded that the 34K-ssb protein is identifiable with the type M of LDH, although possible differences in primary structure of the two proteins may have escaped the present studies. We hypothesize that interaction of the PC12 lactic dehydrogenase with ssDNA occurs also in vivo, as indicated by the findings reported in the accompanying paper, and may be modulated by the cellular content of NADH which, in turn, is related to energy metabolism
Extracellular ATP and nerve growth factor intensify hypoglycemia-induced cell death in primary neurons: Role of P2 and NGFRp75 receptors
No full textIn this study, we monitored the direct expression of P2 receptors for extracellular ATP in cerebellar granule neurons undergoing metabolism impairment. Glucose deprivation for 30-60 min inhibited P2Y1 receptor protein, only weakly modulated P2X1, P2X2 and P2X3, and up-regulated by about two-fold P2X4, P2X7 and P2Y4. The P2X/Y antagonist basilen blue, protecting cerebellar neurons from hypoglycemic cell death, maintained within basal levels only the expression of P2X7 and P2Y4 proteins, but not P2X4 or P2Y1. Glucose starvation transiently increased (up to three-fold) the expression of NGFRp75 receptor protein and strongly stimulated the extracellular release of nerve growth factor (NGF; about 10-fold). Exogenously added NGF then augmented hypoglycemic neuronal death by about 60%, increasing the percentage of Höechst-positive nuclei (from approximately 62 to 95%), reducing lactate dehydrogenase (LDH) release (from about 50 to 14%) and significantly overstimulating the hypoglycemia-induced expression of P2X7 and P2Y4. Conversely, extracellular ATP augmented hypoglycemic neuronal death by about 80%, reducing the number of Höechst-positive nuclei (from approximately 62% to 14%), augmenting LDH outflow (by about 30%) and further increasing the hypoglycemia-induced expression of NGFRp75. Our results indicate that P2 and NGFRp75 receptors are modulated during glucose starvation and that extracellular ATP and NGF drive features of, respectively, necrotic and apoptotic hypoglycemic cell death, aggravating the consequences of metabolism impairment in cerebellar primary neurons
Role of the metabotropic P2Y(4) receptor during hypoglycemia: cross talk with the ionotropic NMDAR1 receptor
No full textIt is well established that both extracellular ATP and glutamate exert a critical role during metabolic impairment, that several P2 receptor subunits are directly involved in this action and that a strong relationship exists between glutamatergic and purinergic signals. Therefore, here we studied the molecular behavior of the purinergic metabotropic P2Y4 and the glutamatergic ionotropic NMDAR1 receptors during hypoglycemic cell death. We find that these proteins are oppositely modulated during glucose starvation (P2Y4 is induced, whereas NMDAR1 is inhibited) and that both P2 and NMDA antagonists can restore basal protein expression levels. Moreover, double immunofluorescence experiments with confocal laser microscopy reveal co-localization at the membrane level between the P2Y4 and NMDAR1 receptors, in both homologous (cerebellar granule neurons) and heterologous (Hek-293) cellular systems. This is furthermore confirmed by co-immunoprecipitation experiments. Finally, when we express the P2Y4 receptor in the heterologous SH-SY5Y neuronal cell line, hypoglycemia then causes severe cell death and simultaneous downregulation of the NMDAR1 protein. In summary, our work establishes a potential molecular interplay between P2Y4 and NMDAR1 receptors during glucose deprivation and the causative role of the P2Y 4 during cell death. © 2004 Elsevier Inc. All rights reserved
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Purinergic signalling at the plasma membrane: a multipurpose and multidirectional mode to deal with amyotrophic lateral sclerosis and multiple sclerosis
No full textATP is a widespread and multipurpose signalling molecule copiously released in the extracellular environment of the whole nervous system upon cell activation, stress, or damage. Extracellular ATP is also a multidirectional information molecule, given the concurrent presence at the plasma membrane of various targets for ATP. These include ectonucleotidases (metabolizing ATP down to adenosine), ATP/adenosine transporters, P2 receptors for purine/pyrimidine nucleotides (ligand-gated ion channels P2X receptors and G-protein-coupled P2Y receptors), in addition to metabotropic P1 receptors for nucleosides. All these targets rarely operate as single units, rather they associate with each other at the plasma membrane as multi-protein complexes. Altogether, they control the duration, magnitude and/or direction of the signals triggered and propagated by purine/pyrimidine ligands, and the impact that each single ligand has on a variety of short- and long-term functions. A strict control system allows assorted, even divergent, biological outcomes. Among these, we enumerate cell-to-cell communication, tropic, trophic, but also noxious actions causing the insurgence/progression of pathological conditions. Here, we show that purinergic signalling in the nervous system can be instrumental for instance to neurodegenerative and neuroinflammatory diseases such as amyotrophic lateral sclerosis and multiple sclerosis
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