Nimodipine inhibits IL-1β release stimulated by amyloid β from microglia

BACKGROUND AND PURPOSE

There is growing evidence that inflammation plays a major role in the pathogenesis of neural damage caused by deposition of amyloid β (Aβ) in the brain. Nimodipine has received attention as a drug that might improve learning and reduce cognitive deficits in Alzheimer's disease, but the mechanism of action is poorly known. In this study, we tested the hypothesis that nimodipine inhibited Aβ-stimulated IL-1β release from microglia.

EXPERIMENTAL APPROACH

Cultures of N13 microglia cells or primary mouse microglia were treated with nimodipine, and intracellular accumulation and release of IL-1β in response to Aβ or to the P2 receptor agonists ATP and benzoyl ATP (BzATP) were measured. Accumulation of IL-1β was measured in vivo after intrahippocampal inoculation of Aβ in the absence or presence of nimodipine. The effect of nimodipine on Aβ-triggered cytotoxicity was also investigated.

KEY RESULTS

We show here that nimodipine dose-dependently inhibited Aβ-stimulated IL-1β synthesis and release from primary microglia and microglia cell lines. Furthermore, nimodipine also inhibited Aβ-induced IL-1βin vivo accumulation at concentrations known to be reached in the CNS. Finally, nimodipine protected microglia from Aβ-dependent cytotoxicity.

CONCLUSION AND IMPLICATIONS

These data suggest that alleviation of symptoms of Alzheimer's disease following nimodipine administration might be due to an anti-inflammatory effect and point to a novel role for nimodipine as a centrally acting anti-inflammatory drug.

P2 purinoceptors in the immune system

Immune cells express plasma membrane receptors for extracellular nucleotides. Both G protein-linked metabotropic and channel-forming ionotropic receptors have been described, although no P2 receptor subtype has been cloned from the immune system thus far. Metabotropic receptors have been described in human B but not T lymphocytes; they have not been found in mouse B and T cells. Ionotropic receptors seem to be ubiquitously expressed in the immune system; however, their functional properties, if not their pharmacology, appear to be different in different immune cells. Human T normal and B leukaemic lymphocytes, human macrophages, mouse B and T lymphocytes, mouse microglial and macrophage cells, and rat mast cells express ionotropic receptors that recognize ATP4- as the preferred ligand, are activated by 3'-O-(4-benzoyl)benzoyl ATP and inhibited by oxidized ATP. The pharmacological profile of ionotropic receptors expressed by different immune cells is similar, but their permeability properties may be different: the pore formed by receptors expressed by macrophages, microglial cells and mast cells is typically permeable to charged molecules of molecular mass up to 900 Da; on the contrary, that expressed by lymphocytes has a molecular cut-off of 200-300 Da. The ionotrpic receptor of immune cells is modulated by inflammatory cytokines (e.g. interleukin [IL]-2 and gamma-interferon) and is also modulated during monocyte to macrophage differentiation. Transient stimulation of the ionotropic receptor of macrophages and microglial cells elicits IL-1 beta release. Sustained activation leads to cell death, either by necrosis or apoptosis, depending on the given cell type.

Modulation of P2X7 receptor functions by polymyxin B: crucial role of the hydrophobic tail of the antibiotic molecule

BACKGROUND AND PURPOSE

P2X7 is a membrane receptor for extracellular ATP which is highly expressed in dendritic cells, macrophages and microglia where it mediates pro-inflammatory responses. The antibiotic polymyxin B, which binds to and neutralizes the toxic residue of bacterial lipopolysaccharide, greatly amplifies cellular responses mediated by the P2X7 receptor. However, the molecular mechanism involved is so far unknown.

EXPERIMENTAL APPROACH

We investigated the effects of polymyxin B and polymyxin B nonapeptide (PMBN) which is the deacylated amino derivative of polymyxin B lacking the N-terminal fatty amino acid 6-methylheptanoic/octanoic-Dab residue, in human macrophages and HEK293 cells stably expressing the human P2X7 receptor (HEK293-hP2X7). Differences between the two antibiotics were assessed by monitoring the following: nucleotide-induced cytoplasmic free Ca2+ concentration changes, plasma membrane permeability changes, lactate dehydrogenase activity, cell morphology changes. Western blot and microscopic analyses of P2X7GFP-expressing cells were also performed.

KEY RESULTS

In contrast to polymyxin B, the polymyxin B nonapeptide was unable to potentiate: a) the ATP-induced Ca2+ increase, b) pore formation and consequently ATP-mediated plasma membrane permeabilization; c) ATP-dependent cytotoxicity. Moreover, in contrast to polymyxin B, polymyxin B nonapeptide did not affect aggregation of the P2X7 receptor subunits and it did not potentiate P2X7-dependent cell fusion.

CONCLUSIONS AND IMPLICATIONS

The effects of polymyxin B depended on the presence of its N-terminal fatty amino acid 6-methylheptanoic/octanoic-Dab residue as deletion of this residue abolished polymyxin B-dependent modulation of ATP-triggered responses. These findings are important in the search for allosteric modulators of the P2X7 receptor.

Gamma-ray activity in the volcanic islands of the Southern Tyrrhenian Sea

Field gamma-ray spectrometry was used for the quantitative assessment of U, Th and K of rocks of Stromboli, Salina, Filicuidi and Panarea (Aeolian arc of the Southern Tyrrhenian, Italy). The air absorbed dose rate was calculated from radioelement concentrations. For some rocks the gamma-ray spectra were analysed with the three photo-peak methods and the response matrix method, which converts the pulse height distribution into the true incident gamma-ray energy spectrum. The higher values of U (8.2-9.8 ppm) coincide with higher Th (20.6-27.8 ppm) concentrations associated with rocks of shoshonitic composition. The spatial variation in radioelement concentration reflects the geochemical differences among the rocks. The air absorbed dose rate varies from 25 to 215 nGy h(-1). The highest values correspond to outcrops located in the eastern part of Stromboli, where the annual effective dose equivalent reaches a value of 264 microSv.

Natural gamma-radiation in the Aeolian volcanic arc

Pulse-height distributions of gamma-rays, obtained with a field NaI(Tl) scintillation spectrometer in numerous sites of the Lipari and Vulcano islands (Aeolian volcanic arc, Italy), were measured to determine the U, Th and K concentrations of the bedrock and the relative values of the air absorbed dose rate. U is spatially related to both Th and K and the Th/U ratio is on average 3.1-3.5. The magmatic evolution is reflected by the concentration of the three radioelements, as they are more abundant within the more felsic units of the volcanic series. The higher values of U (15.7-20.0 ppm) coincide with higher Th (48.3-65.9 ppm) and K (4.9-6.1%) concentrations associated with rhyolitic rocks of the third cycle (< 50 ky). The air absorbed dose rate varies from 20 to 470 nGy h(-1). The highest values (> 350 nGy h(-1)) are observed on outcrops of rhyolitic obsidian lava flows. The cosmic-ray contribution is also evaluated to estimate the total background radiation dose rate.

A defect in glycogen synthesis characterizes insulin resistance in hypertensive patients with type 2 diabetes

A subgroup of patients with type 2 diabetes shows a clustering of abnormalities such as peripheral insulin resistance, hypertension, and microalbuminuria. To evaluate whether these traits reflect intrinsic disorders of cell function rather than in vivo environmental effects, we studied a group of 7 nondiabetic hypertensive subjects with an altered albumin excretion rate (AER) (HyMA+) and 3 groups of patients with type 2 diabetes: 7 with normal blood pressure and normal AER (DH-MA-), 7 with high blood pressure and normal AER (DH+MA-), and 7 with both high blood pressure and altered AER (DH+MA+). Glucose disposal was measured during an hyperinsulinemic clamp (40 mU. m(2)(-1). min(-1)) with primed deuterated [6.6 (2)H(2)] glucose infusion. In the same subjects, a skin biopsy was performed and the following parameters were investigated: glucose transport (as determined by [(3)H]2-deoxyglucose uptake); glycogen synthase activity (as determined by [(14)C] glucose incorporation from UDP-[U-(14)C] glucose into glycogen); glycogen phosphorylase activity (as measured by the incorporation of [U-(14)C]glucose 1-phosphate into glycogen); and total glycogen content. In vivo glucose disposal was significantly reduced in DH+MA- and DH+MA+, with respect to DH-MA-, HyMA+, and controls. Insulin-stimulated glucose transport was similar in the 3 groups of patients with diabetes. A significant reduction of intracellular glycogen content was observed in DH+MA- and DH+MA+ compared with DH-MA- in both basal and insulin-stimulated conditions, probably because of a major impairment of glycogen synthase activity. Glycogen phosphorylase activity did not show differences between the groups. These results suggest that (1) the combination of type 2 diabetes with hypertension and altered AER is associated with impaired insulin sensitivity, and (2) intrinsic, possibly genetic, factors may account for increased peripheral insulin resistance in hypertensive microalbuminuric patients with type 2 diabetes, pointing to the reduction of glycogen synthase activity as a shared common defect.

Nucleotide receptors: an emerging family of regulatory molecules in blood cells

Nucleotides are emerging as an ubiquitous family of extracellular signaling molecules. It has been known for many years that adenosine diphosphate is a potent platelet aggregating factor, but it is now clear that virtually every circulating cell is responsive to nucleotides. Effects as different as proliferation or differentiation, chemotaxis, release of cytokines or lysosomal constituents, and generation of reactive oxygen or nitrogen species are elicited upon stimulation of blood cells with extracellular adenosine triphosphate (ATP). These effects are mediated through a specific class of plasma membrane receptors called purinergic P2 receptors that, according to the molecular structure, are further subdivided into 2 subfamilies: P2Y and P2X. ATP and possibly other nucleotides are released from damaged cells or secreted via nonlytic mechanisms. Thus, during inflammation or vascular damage, nucleotides may provide an important mechanism involved in the activation of leukocytes and platelets. However, the cell physiology of these receptors is still at its dawn, and the precise function of the multiple P2X and P2Y receptor subtypes remains to be understood.

P2 purinergic receptors of human eosinophils: characterization and coupling to oxygen radical production

Extracellular nucleotides elicit multiple responses in eosinophils but no information on expression of purinergic receptors in these cells is available so far. In the present study we show that human eosinophils express the following P2Y and P2X subtypes: P2Y(1), P2Y(2), P2Y(4), P2Y(6), P2Y(11), and P2X(1), P2X(4), P2X(7), whose stimulation results in intracellular Ca(2+) increase and production of large amounts of reactive oxygen intermediates. These events are stimulated or inhibited, respectively, by P2 receptor agonists or antagonists.

The P2 purinergic receptors of human dendritic cells: identification and coupling to cytokine release

We investigated the expression of purinoceptors in human dendritic cells, providing functional, pharmacological, and biochemical evidence that immature and mature cells express P2Y and P2X subtypes, coupled to increase in the intracellular Ca(2+), membrane depolarization, and secretion of inflammatory cytokines. The ATP-activated Ca(2+) change was biphasic, with a fast release from intracellular stores and a delayed influx across the plasma membrane. A prolonged exposure to ATP was toxic to dendritic cells that swelled, lost typical dendrites, became phase lucent, detached from the substrate, and eventually died. These changes were highly suggestive of expression of the cytotoxic receptor P2X(7), as confirmed by ability of dendritic cells to become permeant to membrane impermeant dyes such as Lucifer yellow or ethidium bromide. The P2X(7) receptor ligand 2',3'-(4-benzoylbenzoyl)-ATP was a better agonist then ATP for Ca(2+) increase and plasma membrane depolarization. Oxidized ATP, a covalent blocker of P2X receptors, and the selective P2X(7) antagonist KN-62 inhibited both permeabilization and Ca(2+) changes induced by ATP. The following purinoceptors were expressed by immature and mature dendritic cells: P2Y(1), P2Y(2), P2Y(5), P2Y(11) and P2X(1), P2X(4), P2X(7). Finally, stimulation of LPS-matured cells with ATP triggered release of IL-1 beta and TNF-alpha. Purinoceptors may provide a new avenue to modulation of dendritic cells function.

High glucose modulates P2X7 receptor-mediated function in human primary fibroblasts

AIMS/HYPOTHESIS

Purinergic receptors are a family of newly characterized plasma membrane molecules involved in several and as yet only partially known cellular functions such as vascular reactivity, apoptosis and cytokine secretion. Little is known about the effect extracellular microenvironment has on their function. Fibroblasts share several features with smooth muscle cells and are an important constituent of the atherosclerotic plaque. Our aim was to evaluate the effect of high glucose concentration on ATP-mediated responses in human fibroblasts.

METHODS

Fibroblasts were obtained by skin biopsies and grown at two different glucose concentrations. We evaluated receptor expression by RT-PCR and immunoblotting and receptor localization by immunofluorescence. Plasma membrane potential and calcium changes were measured by fluorescent indicators. Apoptosis was determined by ethidium bromide staining and caspase-3 activation.

RESULTS

We show that cells grown in a medium with high glucose concentration underwent great ATP-mediated morphological changes, enhanced apoptosis, caspase 3 activation and interleukin-6 release. We identified P2X7 as the main purinergic receptor involved in these responses. Furthermore, high glucose concentration triggered the assembly of P2X7 into ring-like structures located at the periphery of the cells.

CONCLUSION/INTERPRETATION

Given that ATP is frequently released into the extracellular milieu upon cell and tissue damage, secretory exocytosis or activation of plasma membrane transporters, we hypothesize that ATP receptors participate in the pathogenesis of vascular complications of diabetes.

P2X(7) receptor and polykarion formation

Cell fusion is a central phenomenon during the immune response that leads to formation of large elements called multinucleated giant cells (MGCs) of common occurrence at sites of granulomatous inflammation. We have previously reported on the involvement in this event of a novel receptor expressed to high level by mononuclear phagocytes, the purinergic P2X(7) receptor. Herein, we show that blockade of this receptor by a specific monoclonal antibody prevents fusion in vitro. In contrast, cell fusion is stimulated by addition of enzymes that destroy extracellular ATP (i.e., apyrase or hexokinase). Experiments performed with phagocytes selected for high (P2X(7) hyper) or low (P2X(7) hypo) P2X(7) expression show that fusion only occurs between P2X(7) hyper/P2X(7) hyper and not between P2X(7) hyper/P2X(7) hypo or P2X(7) hypo/P2X(7) hypo. During MGCs formation we detected activation of caspase 3, an enzyme that is powerfully stimulated by P2X(7). Finally, we observed that during MGCs formation, the P2X(7) receptor is preferentially localized at sites of cell-to-cell contact. These findings support the hypothesis originally put forward by our group that the P2X(7) receptor participates in multinucleated giant cell formation.

Laboratory application of NaI(Tl) gamma-ray spectrometry to studies of natural radioactivity in geophysics

We implemented a laboratory apparatus based on a NaI(TI) gamma-ray spectrometer for the assessment of naturally occurring radioactive materials. This apparatus is devoted to the quantitative determination of U, Th and K in rock and soil samples. We analysed the calibration procedures with particular emphasis to factors which affect accuracy and detection limits. A first series of measurements were compared to those obtained by means of high energy gamma-ray spectrometry. A discussion was made on factors restricting the approach based on scintillation spectrometry, such as secular equilibrium and radon encapsulation.

Increased proliferation rate of lymphoid cells transfected with the P2X(7) ATP receptor

Human leukocytes can express the P2X(7) purinergic receptor, an ionic channel gated by extracellular ATP, for which the physiological role is only partially understood. Transfection of P2X(7) cDNA into lymphoid cells that lack this receptor sustains their proliferation in serum-free medium. Increased proliferation of serum-starved P2X(7) transfectants is abolished by the P2X(7) receptor blocker oxidized ATP or by the ATP hydrolase apyrase. Both wild type and P2X(7)-transfected lymphoid cells release large amounts of ATP into the culture medium. These data suggest the operation of an ATP-based autocrine/paracrine loop that supports lymphoid cell growth in the absence of serum-derived growth factors.

ATP receptors and giant cell formation

We have investigated the role of the purinergic P2X7 receptor in the formation of multinucleated giant cells in human monocyte/macrophage cultures stimulated with either concanavalin A or phytohemagglutinin. Macrophage fusion can be blocked by a P2X7-selective pharmacological antagonist or by a mAb directed against the extracellular P2X7 domain. Furthermore, macrophage cell clones expressing high P2X7 levels spontaneously fuse in culture, whereas macrophage clones lacking P2X7 are unable to fuse. Our findings suggest that the newly identified purinergic P2X7 receptor plays a central role in the complex chain of events leading to generation of macrophage-derived giant cells.

Mouse dendritic cells express the P2X7 purinergic receptor: characterization and possible participation in antigen presentation

Immune cells express P2 purinoceptors of the P2Y and P2X subtypes. In the present work, we show that three dendritic cell (DC) lines, D2SC/1, CB1, and FSDC, representative of immature DCs, express the P2X7 (formerly P2Z) receptor, as judged from RT-PCR amplification, reactivity to a specific antiserum, and pharmacological and functional evidence. Receptor expression is higher in FSDC cells, a cell line that is functionally more mature than D2SC/1 and CB1. From the wild-type DC population, we selected cell clones lacking the P2X7R (P2X7less). We also used a P2XR blocker, oxidized ATP, to irreversibly inhibit the P2X7R. Ability of P2X7less FSDCs or of oxidized ATP-inhibited FSDCs to stimulate Ag-specific TH lymphocytes was severely decreased although Ag endocytosis was minimally affected. During coculture with TH lymphocytes, wild-type FSDC secreted large amounts of IL-1beta. Release of this cytokine was reduced in P2X7less DCs. These data show that DCs express the P2X7 purinoceptor and suggest a correlation between P2X7R expression and Ag-presenting activity.

Human primary fibroblasts in vitro express a purinergic P2X7 receptor coupled to ion fluxes, microvesicle formation and IL-6 release

We have investigated reponses to extracellular ATP in human fibroblasts obtained by skin biopsies. Our data show that these cells express a P2X7 purinergic receptor, as judged by (1) RT-PCR with specific primers, (2) reactivity with a specific anti-P2X7 antiserum, (3) activation by the selective P2X agonist benzoylbenzoylATP and (4) stimulation of transmembrane ion fluxes. Stimulation with benzoylbenzoylATP, and to a lesser extent with ATP, also caused striking morphological changes and increased formation of cytoplasmic microvesicles. These changes were fully reversible upon nucleotide removal. Two known blockers of P2X receptors, oxidised ATP and pyridoxalphosphate-6-azophenyl-2′,4′-disulfonic acid, inhibited the morphological changes fully and the ion fluxes partially. The residual rise in intracellular Ca2+ levels and membrane depolarization observed in the presence of the inhibitors were dependent upon activation of a P2Y-type receptor exhibiting a peculiar pharmacological profile, in that CTP was the preferred agonist. ATP stimulation triggered release of the pro-inflammatory cytokine IL-6 in fibroblasts pre-treated with PMA and bacterial endotoxin. These observations reveal a novel pathway for fibroblast activation and for their recruitment in the inflammatory response.

Tenidap enhances P2Z/P2X7 receptor signalling in macrophages

Tenidap is an anti-inflammatory drug whose mechanism of action is not fully understood. It has been shown to block plasma membrane anion transport and to decrease release of interleukin-1beta, probably via the inhibition of interleukin-1beta converting enzyme. In the present study we showed that: (a) tenidap increases the sensitivity of mouse macrophages to cytotoxic effects mediated by extracellular ATP; (b) tenidap increases lucifer yellow uptake through the macrophage ATP receptor; (c) pretreatment with oxidised ATP, a blocker of the P2Z/P2X7 receptor, inhibits cytotoxicity and lucifer yellow uptake due to the combined effects of ATP and tenidap; (d) macrophages lacking the P2Z/P2X7 receptor are resistant to the synergistic effect of tenidap and ATP. The results suggest that tenidap synergises with extracellular ATP for activation of the P2Z/P2X7 receptor.

Cytolytic P2X purinoceptors

Anecdoctal evidence accumulated over almost 20 years has shown that many different cell types are killed by sustained exposure to high concentrations of extracellular ATP. The plasma membrane receptors involved have been pharmacologically characterized and cloned during the last 3 years, and named purinergic P2X. P2X receptors share an intriguing structural relatedness with Caenorhabditis elegans degenerins and mammalian amiloride-sensitive Na channels (ENaCs). Depending on the ATP dose, length of stimulation and receptor subtype, P2X receptor stimulation may cause necrosis or apoptosis. The intracellular pathways activated are poorly known, but the perturbation in intracellular ion homeostasis clearly plays a major role. ICE proteases (caspases) are also triggered, nonetheless their activation is not requested for ATP-dependent cell death. The physiological meaning of P2X receptor-dependent cytotoxicity is not understood, but an involvement in immune-mediated reactions is postulated.

ATP-mediated cytotoxicity in microglial cells

Microglial cells are known to express purinergic receptors for extracellular ATP of both the P2Y and P2X subtypes. Functional studies have shown that both primary mouse microglial cells and the N9 and N13 microglial cell lines express the pore-forming P2Z/P2X7 receptor. Here we identify the presence of this receptor in N9 and N13 cells with a specific polyclonal Ab and show that microglial cells expressing the P2Z/P2X7 receptor are exquisitively sensitive to ATP-mediated cytotoxicity while clones selected for the lack of this receptor are resistant. Transfection of HEK293 cells with P2X7 (but not P2X2) receptor cDNA confers susceptibility to ATP-mediated cytotoxicity. Morphological and biochemical analysis suggests that ATP-dependent cell death in microglial cells occurs by apoptosis. Finally, microglial cells release ATP via a non-lytic mechanism when activated by bacterial endotoxin, thus suggesting the operation of a purinergic autocrine/paracrine loop.

Spontaneous cell fusion in macrophage cultures expressing high levels of the P2Z/P2X7 receptor

Mouse and human macrophages express a plasma membrane receptor for extracellular ATP named P2Z/P2X7. This molecule, recently cloned, is endowed with the intriguing property of forming an aqueous pore that allows transmembrane fluxes of hydrophylic molecules of molecular weight below 900. The physiological function of this receptor is unknown. In a previous study we reported experiments suggesting that the P2Z/P2X7 receptor is involved in the formation of macrophage-derived multinucleated giant cells (MGCs; Falzoni, S., M. Munerati, D. Ferrari, S. Spisani, S. Moretti, and F. Di Virgilio. 1995. J. Clin. Invest. 95:1207- 1216). We have selected several clones of mouse J774 macrophages that are characterized by either high or low expression of the P2Z/P2X7 receptor and named these clones P2Zhyper or P2Zhypo, respectively. P2Zhyper, but not P2Zhypo, cells grown to confluence in culture spontaneously fuse to form MGCs. As previously shown for human macrophages, fusion is inhibited by the P2Z/P2X7 blocker oxidized ATP. MGCs die shortly after fusion through a dramatic process of cytoplasmic sepimentation followed by fragmentation. These observations support our previous hypothesis that the P2Z/P2X7 receptor is involved in macrophage fusion.

Extracellular ATP triggers IL-1 beta release by activating the purinergic P2Z receptor of human macrophages

Extracellular ATP (ATPe) is known to cause release of processed IL-1 beta from LPS-treated macrophages and microglial cells. IL-1 beta release is fast and thought to be associated with cell death. We have reinvestigated this process to identify 1) the purinergic receptor involved; 2) the relationship to cell death; and 3) pharmacologic agonists or antagonists able to modulate IL-1 beta release. Our data confirm that ATPe is a powerful stimulus for IL-1 beta release from LPS-treated human macrophages; however, we also show that IL-1 beta release is not necessarily associated with cell death, as it occurs at lower ATP concentrations and much earlier than leakage of cytoplasmic markers. The selective purinergic P2Z receptor agonist benzoylbenzoyl ATP was at least one order of magnitude more powerful than ATP, but also had a strong cytotoxic effect. 2-Methylthio-ATP was equipotent as ATPe at the optimal concentration of 1 mM, but markedly inhibitory at higher concentrations. The irreversible P2Z blocker-oxidized ATP completely inhibited ATPe-induced IL-1 beta release. IL-1 beta release also was inhibited by increasing the K+ concentration of the incubation medium. These data suggest that ATPe triggers IL-1 beta via the purinergic P2Z receptor recently shown to be expressed by human macrophages and identified as a new member of the P2X family (P2X7), and provide pharmacologic tools for the modulation of IL-1 beta release in vitro and, possibly, in vivo.

Extracellular ATP triggers IL-1 beta release by activating the purinergic P2Z receptor of human macrophages

Extracellular ATP (ATPe) is known to cause release of processed IL-1 beta from LPS-treated macrophages and microglial cells. IL-1 beta release is fast and thought to be associated with cell death. We have reinvestigated this process to identify 1) the purinergic receptor involved; 2) the relationship to cell death; and 3) pharmacologic agonists or antagonists able to modulate IL-1 beta release. Our data confirm that ATPe is a powerful stimulus for IL-1 beta release from LPS-treated human macrophages; however, we also show that IL-1 beta release is not necessarily associated with cell death, as it occurs at lower ATP concentrations and much earlier than leakage of cytoplasmic markers. The selective purinergic P2Z receptor agonist benzoylbenzoyl ATP was at least one order of magnitude more powerful than ATP, but also had a strong cytotoxic effect. 2-Methylthio-ATP was equipotent as ATPe at the optimal concentration of 1 mM, but markedly inhibitory at higher concentrations. The irreversible P2Z blocker-oxidized ATP completely inhibited ATPe-induced IL-1 beta release. IL-1 beta release also was inhibited by increasing the K+ concentration of the incubation medium. These data suggest that ATPe triggers IL-1 beta via the purinergic P2Z receptor recently shown to be expressed by human macrophages and identified as a new member of the P2X family (P2X7), and provide pharmacologic tools for the modulation of IL-1 beta release in vitro and, possibly, in vivo.

Purinergic modulation of interleukin-1 beta release from microglial cells stimulated with bacterial endotoxin

Microglial cells express a peculiar plasma membrane receptor for extracellular ATP, named P2Z/P2X7 purinergic receptor, that triggers massive transmembrane ion fluxes and a reversible permeabilization of the plasma membrane to hydrophylic molecules of up to 900 dalton molecule weight and eventual cell death (Di Virgilio, F. 1995. Immunol. Today, 16:524-528). The physiological role of this newly cloned (Surprenant, A., F. Rassendren, E. Kawashima, R. A. North and G. Buell, 1996. Science (Wash. DC). 272:735-737) cytolytic receptor is unknown. In vitro and in vivo activation of the macrophage and microglial cell P2Z/P2X7 receptor by exogenous ATP causes a large and rapid release of mature IL-1 beta. In the present report we investigated the role of microglial P2Z/P2X7 receptor in IL-1 beta release triggered by LPS. Our data suggest that LPS-dependent IL-1 beta release involves activation of this purinergic receptor as it is inhibited by the selective P2Z/P2X7 blocker oxidized ATP and modulated by ATP-hydrolyzing enzymes such as apyrase or hexokinase. Furthermore, microglial cells release ATP when stimulated with LPS. LPS-dependent release of ATP is also observed in monocyte-derived human macrophages. It is suggested that bacterial endotoxin activates an autocrine/paracrine loop that drives ATP-dependent IL-1 beta secretion.

Mechanism of human sperm activation by extracellular ATP

We have identified the mechanism whereby extracellular ATP (ATPe) triggers the acrosome reaction in human spermatozoa. This nucleotide opens a ligand-gated ion channel expressed on the sperm plasma membrane. ATPe threshold and 50% effective concentration calculated on the total added ATPe are 0.1 and 2 mM, respectively, corresponding to a free ATP concentration (ATP4-) of 3 and 200 microM, respectively. The ATPe-gated channel is selective for monovalent cations (Na+, choline, and methylglucamine), whereas on the contrary, permeability to Ca2+ is negligible. Isosmolar replacement of extracellular Na+ with sucrose fully blocked ATPe-dependent sperm activation, thus suggesting a mandatory role for Na+ influx. These results show that human sperm express an ATPe-gated Na+ channel that might have an important role in sperm activation before egg fertilization.

Mouse microglial cells express a plasma membrane pore gated by extracellular ATP

We have investigated responses to extracellular ATP (ATPe) in the microglial cell lines N9 and N13 and in freshly isolated mouse microglial cells. Upon stimulation with this nucleotide, N9 and N13 cells underwent an increase in the cytoplasmic free Ca2+ concentration ([Ca2+]i), a sustained depolarization of the plasma membrane, and an uptake of extracellular markers such as ethidium bromide and lucifer yellow; increases in plasma membrane permeability were paralleled by striking morphologic changes. ATPe, as well as other nucleotides, activated a spiking Ca2+ release from intracellular stores; however, only ATPe was also able to cause a massive transmembrane Ca2+ influx. The ATP analogue 2'- and 3'-O-(4-benzoylbenzoyl)-ATP (BzATP) triggered a sustained Ca2+ influx accompanied by little release from stores. The ATP derivative oxidized ATP (oATP) strongly inhibited Ca2+ influx, minimally affecting Ca2+ release. From ATPe-sensitive microglial cell lines, we selected several ATPe-resistant clones that showed complete lack of ATPe-mediated plasma membrane permeability changes, although they retained the Ca2+ mobilization response from intracellular stores. ATPe-dependent plasma membrane permeability changes were also greatly reduced in growth-arrested microglial cells. Finally, ATPe triggered IL-1 beta release from wild-type but not ATPe-resistant microglial cells. These results show that microglial cells express at least two purinergic receptor subtypes, metabotropic (P2Y) and ionotropic (P2Z), and that the latter is modulated during cell cycle and coupled to IL-1 beta release.

Mouse microglial cells express a plasma membrane pore gated by extracellular ATP

We have investigated responses to extracellular ATP (ATPe) in the microglial cell lines N9 and N13 and in freshly isolated mouse microglial cells. Upon stimulation with this nucleotide, N9 and N13 cells underwent an increase in the cytoplasmic free Ca2+ concentration ([Ca2+]i), a sustained depolarization of the plasma membrane, and an uptake of extracellular markers such as ethidium bromide and lucifer yellow; increases in plasma membrane permeability were paralleled by striking morphologic changes. ATPe, as well as other nucleotides, activated a spiking Ca2+ release from intracellular stores; however, only ATPe was also able to cause a massive transmembrane Ca2+ influx. The ATP analogue 2'- and 3'-O-(4-benzoylbenzoyl)-ATP (BzATP) triggered a sustained Ca2+ influx accompanied by little release from stores. The ATP derivative oxidized ATP (oATP) strongly inhibited Ca2+ influx, minimally affecting Ca2+ release. From ATPe-sensitive microglial cell lines, we selected several ATPe-resistant clones that showed complete lack of ATPe-mediated plasma membrane permeability changes, although they retained the Ca2+ mobilization response from intracellular stores. ATPe-dependent plasma membrane permeability changes were also greatly reduced in growth-arrested microglial cells. Finally, ATPe triggered IL-1 beta release from wild-type but not ATPe-resistant microglial cells. These results show that microglial cells express at least two purinergic receptor subtypes, metabotropic (P2Y) and ionotropic (P2Z), and that the latter is modulated during cell cycle and coupled to IL-1 beta release.

An ATP-activated channel is involved in mitogenic stimulation of human T lymphocytes

We investigated the effect of pharmacologic modulation of the ATP receptor on intracellular ion changes and proliferative response of human peripheral blood lymphocytes (PBLs) and purified T lymphocytes. Extracellular ATP (ATPe) triggered in these cells an increase in the cytoplasmic Ca2+ concentration ([Ca2+]i) and plasma membrane depolarization. Whereas both Ca2+ release from intracellular stores and influx across the plasma membrane were detected in the whole PBL population, only Ca2+ influx was observed in T cells. In the presence of near physiologic extracellular Na+ concentrations (125 mmol/L), Ca2+ permeability through the ATPe-gated channel was very low, suggesting a higher selectivity for monovalent over divalent cations. The selective P2Z agonist benzoylbenzoic ATP (BzATP) increased [Ca2+]i in the presence but not the absence of extracellular Ca2+ and also caused plasma membrane depolarization. The covalent blocker oxidized ATP (oATP), an inhibitor of P2X and P2Z receptors, prevented Ca2+ influx and plasma membrane depolarization, but had no effect on Ca2+ release from stores. Stimulation with ATPe alone had no significant effects on PBL 3H-thymidine incorporation. On the contrary, ATPe or BzATP had a synergistic effect on DNA synthesis stimulated by selective T-cell mitogens such as phytohemagglutinin, anti-CD3 monoclonal antibody, or allogenic PBLs (mixed lymphocyte cultures). Treatment with oATP inhibited mitogenic stimulation by these receptor-directed agents but not by the combined application of the Ca2+ ionophore ionomycin and phorbol myristate acetate. Interleukin-2 partially relieved inhibition by oATP. These results suggest that human T lymphocytes express a plasma membrane channel gated by ATPe that is involved in mitogenic stimulation.

Role of the purinergic P2Z receptor in spontaneous cell death in J774 macrophage cultures

J774 mouse macrophages express an ionotropic receptor gated by extracellular ATP. Activation of this receptor, currently named purinergic P2Z, causes transmembrane ion fluxes, plasma membrane depolarization, cell swelling and eventual cell death. The physiological role of this receptor is as yet unknown. In the present report we show that macrophage cell clones that hypo-express the P2Z receptor showed a very low degree of spontaneous cell death in culture, while hyper-expressing clones were exceedingly susceptible to cell death. To further support a role for ATP receptors in spontaneous cell death, addition to the macrophage cell cultures of oxidized ATP, a selective inhibitor of ionotropic purinergic receptors, or the ATP-hydrolysing enzyme apyrase, also reduced spontaneous death.

Identification of the domain recognized by anti-(ryanodine receptor) antibodies which affect Ca(2+)-induced Ca2+ release

In the present paper we have defined putative functional domains of the ryanodine receptor Ca2+ channel. cDNA fragments of the skeletal muscle ryanodine receptor were fused in-frame with the Escherichia coli trpe protein and the resulting fusion proteins were evaluated for their ability to react with anti-(ryanodine receptor) antibodies, which are known to block Ca(2+)-dependent activation of the Ca(2+)-release channel. Anti-(ryanodine receptor) antibodies react with epitopes lying within a 245-amino-acid-long polypeptide which is located in a region (residues 4380-4625) encompassing most of myoplasmic loop 2, the predicted transmembrane segment M5 and part of the next lumenal loop (45 residues). Purification of the anti-(ryanodine receptor) antibodies by affinity chromatography led to the isolation of a population of antibodies which was capable of decreasing (by > 30%) the doxorubicin-induced Ca2+ release from isolated terminal cisternae. Polyclonal antibodies raised against a ryanodine receptor fusion encompassing part (198 out of 245 residues) of the immunopositive polypeptide decreased by 2-fold the first-order rate constant of Ca(2+)-induced 45Ca2+ efflux from isolated terminal cisternae. These results suggest strongly that the Ca(2+)-activating domain of the skeletal muscle Ca(2+)-release channel is close to, or associated with, myoplasmic loop 2.

Molecular cloning, functional expression and tissue distribution of the cDNA encoding frog skeletal muscle calsequestrin

We have cloned, sequenced and expressed the cDNA encoding frog skeletal muscle calsequestrin. The processed frog calsequestrin is 398 residues long, with an Mr of 45941 (unglycosylated form), and exhibits 77% sequence similarity with its rabbit counterpart. Consensus sequences for glycosylation and phosphorylation of the protein were conserved. Compared with rabbit calsequestrin, the mature amphibian protein has peculiar structural properties, which include (i) a higher content of negatively charged residues (142 versus 109), and (ii) a striking repeat sequence at the C-terminal region of 44 aspartic acid residues. Furthermore, this is the first report on the expression of calsequestrin cDNA in COS-1 cells; the expressed protein exhibited an Mr and antigenic properties which were indistinguishable from those of the native protein. In addition, it was capable of binding 45Ca in a ligand overlay. Northern blot analysis of frog skeletal muscle, liver, heart and brain RNA showed that the protein is mainly expressed in skeletal muscle. The high density of negative charges at the C-terminus might constitute high-capacity low-affinity Ca(2+)-binding sites, which may account for the higher Ca(2+)-binding capacity of frog calsequestrin compared with other members of the calsequestrin family (56 mol/mol versus 40-44 mol/mol of protein).

Frog brain expresses a 60 KDa Ca2+ binding protein similar to mammalian calreticulin

The present report was undertaken in an effort to characterize the nature of Ca2+ binding protein(s) in the central nervous system of less evolved vertebrates. In particular we investigated whether the brain microsomal fraction of Rana esculenta expresses calsequestrin, calreticulin and/or other related Ca2+ binding protein(s). We found that a 60 KDa protein having an NH2-terminal amino acid sequence similar to mammalian calreticulin is the major microsomal Ca2(+)-binding protein.

Interaction of erythrocyte transglutaminase with calcium ions

We have investigated the interaction between calcium ions and erythrocyte transglutaminase and the enzyme activation. The binding involves both high and low affinity sites, but only the former ones are relevant for activation. The binding of calcium and the activation are modified by treatment with NBD-Cl and with PLP suggesting the presence of cysteine and lysine residues at the high affinity binding sites. The interaction of the enzyme with calcium is not calmodulin dependent and is easily detected as a shift in electrophoretic mobility in the presence of SDS.

Evidence for a factor promoting the conversion of VWF from low and intermediate to high molecular mass polymers on the platelet membrane

On the membrane surface of resting platelets exists a factor capable of promoting the conversion of plasma von Willebrand factor from low and intermediate molecular mass to high molecular mass polymers. The process is accompanied by a parallel increase in the von Willebrand factor activity. This could be a regulatory system for the molecular mass distribution of von Willebrand factor during its lifetime in plasma. Glycoprotein Ib of the platelet membrane appears not to be involved in the process.

Lymphocytes treated with natural alfa-interferon produce a chemotactic factor for human neutrophils

Lymphocytes stimulated with alfa-interferon released a chemotactic factor for neutrophils. The process was not inhibited by cycloheximide, whereas mepacrine completely inhibited release of the chemotactic activity. The chemotactic factor was resistant to storage, heat treatment and proteolysis. Recombinant alfa-interferon did not stimulate lymphocytes to release a neutrophil chemotactic factor.

Photoexcitation of the methionine-iron bond in iron(III) cytochrome c: bimolecular reaction with NADH

When iron(III) cytochrome c aqueous solutions containing NADH are irradiated with polychromatic light (wavelength greater than 280 nm), iron(II) cytochrome c and NAD+ in the stoichiometric ratio 2/1 are observed to be the principal reaction products, independently of the presence of oxygen; in addition, a minor process due to direct photodegradation of the nucleotide is observed. The selection of monochromatic 290 nm irradiation light (at which NADH has an absorbance minimum) and an adequate reactant concentration allowed parallel reactions to be minimized and new information to be obtained on the mechanism of the photoredox process. The experimental results are consistent with a reaction mechanism whereby NADH donates one electron to a "reactive intermediate" of the hemoprotein formed from the light-induced methionine-to-iron charge transfer excited state. In this process an NAD. radical is formed which, in deaerated solution, immediately reduces another molecule of the hemoprotein, and is itself oxidized to NAD+. In aerated solution, the NAD. radical rapidly reacts with oxygen to give NAD+ and superoxide O2- anion radical which, in turn, reduces the second iron(III) cytochrome c molecule.