RESUMO
Incorporation of Alzheimer's disease amyloid beta-proteins (AbetaPs) across natural and artificial bilayer membranes leads to the formation of cation-selective channels. To study the peptide-membrane interactions involved in channel formation, we used cation reporter dyes to measure AbetaP-induced influx of Na+, Ca2+, and K+ into liposomes formed from phosphatidylserine (PS), phosphatidylinositol (PI) and phosphatidylcholine (PC). We found that Abeta40, but not Abeta40-1 or Abeta28, caused a dose-dependent increase in the concentration of each cation in the lumen of liposomes formed from the acidic phospholipids PS and PI. The Abeta40-induced changes in cation concentration, which we attribute to ion entry through Abeta40 channels, were not observed when using liposomes formed from the neutral phospholipid PC. Using mixtures of phospholipids, the magnitude of the AbetaP40-induced ion entry increased with the acidic phospholipid content of the liposomes, with entry being observed with as little as 5% PS or PI. Thus, while negatively charged phospholipids are required for formation of cation-permeable channels by Abeta40, a small amount is sufficient to support the process. These results have implications for the mechanisms of AbetaP cytotoxicity, suggesting that even a small amount of externalized negative charge could render cells susceptible to the deleterious effects of unregulated ion influx through AbetaP channels.
Assuntos
Doença de Alzheimer/metabolismo , Peptídeos beta-Amiloides/metabolismo , Canais Iônicos/metabolismo , Lipossomos/metabolismo , Fragmentos de Peptídeos/metabolismo , Fosfolipídeos/fisiologia , Peptídeos beta-Amiloides/fisiologia , Peptídeos beta-Amiloides/toxicidade , Ânions/metabolismo , Cálcio/metabolismo , Humanos , Concentração de Íons de Hidrogênio , Fragmentos de Peptídeos/fisiologia , Fragmentos de Peptídeos/toxicidade , Fosfatidilcolinas/fisiologia , Fosfatidilinositóis/fisiologia , Fosfatidilserinas/fisiologia , Sódio/metabolismo , Espectrometria de FluorescênciaRESUMO
Apoptosis is the most common phenotype observed when cells die through programmed cell death. The morphologic and biochemical changes that characterize apoptotic cells depend on the activation of a diverse set of genes. Apoptosis is essential for multicellular organisms since their development and homeostasis are dependent on extensive cell renewal. In fact, there is strong evidence for the correlation between the emergence of multicellular organisms and apoptosis during evolution. On the other hand, no obvious advantages can be envisaged for unicellular organisms to carry the complex machinery required for programmed cell death. However, accumulating evidence shows that free-living and parasitic protozoa as well as yeasts display apoptotic markers. This phenomenon has been related to altruistic behavior, when a subpopulation of protozoa or yeasts dies by apoptosis, with clear benefits for the entire population. Recently, phosphatidylserine (PS) exposure and its recognition by a specific receptor (PSR) were implicated in the infectivity of amastigote forms of Leishmania, an obligatory vertebrate intramacrophagic parasite, showing for the first time that unicellular organisms use apoptotic features for the establishment and/or maintenance of infection. Here we focus on PS exposure in the outer leaflet of the plasma membrane--an early hallmark of apoptosis--and how it modulates the inflammatory activity of phagocytic cells. We also discuss the possible mechanisms by which PS exposure can define Leishmania survival inside host cells and the evolutionary implications of apoptosis at the unicellular level.
Assuntos
Apoptose/fisiologia , Leishmania/fisiologia , Fosfatidilserinas/fisiologia , Animais , Apoptose/imunologia , Arginase/metabolismo , Interações Hospedeiro-Parasita/imunologia , Interações Hospedeiro-Parasita/fisiologia , Sistema Imunitário/fisiologia , Leishmania/imunologia , Macrófagos/fisiologia , Fosfatidilserinas/imunologiaRESUMO
Enveloped viruses always gain entry into the cytoplasm by fusion of their lipid envelope with a cell membrane. Some enveloped viruses fuse directly with the host cell plasma membrane after virus binding to the cell receptor. Other enveloped viruses enter the cells by the endocytic pathway, and fusion depends on the acidification of the endosomal compartment. In both cases, virus-induced membrane fusion is triggered by conformational changes in viral envelope glycoproteins. Two different classes of viral fusion proteins have been described on the basis of their molecular architecture. Several structural data permitted the elucidation of the mechanisms of membrane fusion mediated by class I and class II fusion proteins. In this article, we review a number of results obtained by our laboratory and by others that suggest that the mechanisms involved in rhabdovirus fusion are different from those used by the two well-studied classes of viral glycoproteins. We focus our discussion on the electrostatic nature of virus binding and interaction with membranes, especially through phosphatidylserine, and on the reversibility of the conformational changes of the rhabdovirus glycoprotein involved in fusion. Taken together, these data suggest the existence of a third class of fusion proteins and support the idea that new insights should emerge from studies of membrane fusion mediated by the G protein of rhabdoviruses. In particular, the elucidation of the three-dimensional structure of the G protein or even of the fusion peptide at different pH's might provide valuable information for understanding the fusion mechanism of this new class of fusion proteins.
Assuntos
Glicoproteínas/fisiologia , Fusão de Membrana/fisiologia , Rhabdoviridae/fisiologia , Proteínas Virais de Fusão/fisiologia , Animais , Proteínas de Ligação ao GTP/fisiologia , Histidina/fisiologia , Humanos , Glicoproteínas de Membrana/fisiologia , Fosfatidilserinas/fisiologiaRESUMO
Enveloped viruses always gain entry into the cytoplasm by fusion of their lipid envelope with a cell membrane. Some enveloped viruses fuse directly with the host cell plasma membrane after virus binding to the cell receptor. Other enveloped viruses enter the cells by the endocytic pathway, and fusion depends on the acidification of the endosomal compartment. In both cases, virus-induced membrane fusion is triggered by conformational changes in viral envelope glycoproteins. Two different classes of viral fusion proteins have been described on the basis of their molecular architecture. Several structural data permitted the elucidation of the mechanisms of membrane fusion mediated by class I and class II fusion proteins. In this article, we review a number of results obtained by our laboratory and by others that suggest that the mechanisms involved in rhabdovirus fusion are different from those used by the two well-studied classes of viral glycoproteins. We focus our discussion on the electrostatic nature of virus binding and interaction with membranes, especially through phosphatidylserine, and on the reversibility of the conformational changes of the rhabdovirus glycoprotein involved in fusion. Taken together, these data suggest the existence of a third class of fusion proteins and support the idea that new insights should emerge from studies of membrane fusion mediated by the G protein of rhabdoviruses. In particular, the elucidation of the three-dimensional structure of the G protein or even of the fusion peptide at different pH's might provide valuable information for understanding the fusion mechanism of this new class of fusion proteins.
Assuntos
Animais , Humanos , Glicoproteínas/fisiologia , Fusão de Membrana/fisiologia , Rhabdoviridae/fisiologia , Proteínas Virais de Fusão/fisiologia , Proteínas de Ligação ao GTP/fisiologia , Histidina/fisiologia , Glicoproteínas de Membrana/fisiologia , Fosfatidilserinas/fisiologiaRESUMO
Apoptosis is the most common phenotype observed when cells die through programmed cell death. The morphologic and biochemical changes that characterize apoptotic cells depend on the activation of a diverse set of genes. Apoptosis is essential for multicellular organisms since their development and homeostasis are dependent on extensive cell renewal. In fact, there is strong evidence for the correlation between the emergence of multicellular organisms and apoptosis during evolution. On the other hand, no obvious advantages can be envisaged for unicellular organisms to carry the complex machinery required for programmed cell death. However, accumulating evidence shows that free-living and parasitic protozoa as well as yeasts display apoptotic markers. This phenomenon has been related to altruistic behavior, when a subpopulation of protozoa or yeasts dies by apoptosis, with clear benefits for the entire population. Recently, phosphatidylserine (PS) exposure and its recognition by a specific receptor (PSR) were implicated in the infectivity of amastigote forms of Leishmania, an obligatory vertebrate intramacrophagic parasite, showing for the first time that unicellular organisms use apoptotic features for the establishment and/or maintenance of infection. Here we focus on PS exposure in the outer leaflet of the plasma membrane - an early hallmark of apoptosis - and how it modulates the inflammatory activity of phagocytic cells. We also discuss the possible mechanisms by which PS exposure can define Leishmania survival inside host cells and the evolutionary implications of apoptosis at the unicellular level.
Assuntos
Animais , Apoptose/fisiologia , Leishmania/fisiologia , Fosfatidilserinas/fisiologia , Apoptose/imunologia , Arginase/metabolismo , Interações Hospedeiro-Parasita/imunologia , Interações Hospedeiro-Parasita/fisiologia , Sistema Imunitário/fisiologia , Leishmania/imunologia , Macrófagos/fisiologia , Fosfatidilserinas/imunologiaRESUMO
Cell death by apoptosis is characterized by specific biochemical changes, including the exposure of multiple ligands, expected to tag the dying cell for prompt recognition by phagocytes. In non-pathological conditions, an efficient clearance is assured by the redundant interaction between apoptotic cell ligands and multiple receptor molecules present on the engulfing cell surface. This review concentrates on the molecular interactions operating in mammalian and non-mammalian systems for apoptotic cell recognition, as well as on the consequences of their signaling. Furthermore, some cellular models where the exposure of the phosphatidylserine (PS) phospholipid, a classical hallmark of the apoptotic phenotype, is not followed by cell death will be discussed.
Assuntos
Apoptose/fisiologia , Fagócitos/fisiologia , Fagocitose/fisiologia , Animais , Membrana Celular/fisiologia , Fosfatidilserinas/fisiologia , Transdução de Sinais/fisiologiaRESUMO
In the present study, the effects of phosphatidylserine (BC-PS) on hippocampal synaptic transmission were evaluated. Extracellular potentials evoked by low-frequency stimulation (0.2 Hz) of the perforant path (PP) were recorded from the granule cell layer of the dentate gyrus in 400 microns hippocampal slices. Slices were perfused with either BC-PS alone (10 microM) or BC-PS in combination with DL-2-amino-5-phosphonovaleric acid (APV, 20 microM), or after previous perfusion with dizocilpine (MK-801, 10 microM). BC-PS significantly potentiated PP-evoked responses (mean percent increase +/- SEM, 108 +/- 18%), an effect that was blocked by perfusion of MK-801, but not APV. The increase in hippocampal synaptic efficacy produced by BC-PS is discussed in terms of N-methyl-D-aspartate receptors (NMDA) and the associated channels.