The sodium/hydrogen exchanger: a possible mediator of immunity

Activation of microglia depends on Na+/H+ exchange-mediated H+ homeostasis

H(+) extrusion is important for sustained NADPH oxidase activation after "respiratory" burst in macrophage/microglia activation. In this study, we investigated the role of Na(+)/H(+) exchanger isoform 1 (NHE-1) in activation of microglia after lipopolysaccharide (LPS) or oxygen and glucose deprivation and reoxygenation (OGD/REOX) exposure. NHE-1 functioned in maintaining basal pH(i) of immortalized M4T.4 microglia or mouse primary microglia. Pharmacological inhibition of NHE-1 activity with the potent inhibitor cariporide [HOE 642 (4-isopropyl-3-methylsulfonyl-benzoyl-guanidine-methanesulfonate)] abolished pH(i) regulation in microglia under basal conditions. Activation of microglia either by LPS, phorbol myristate acetate, or OGD/REOX accelerated pH(i) regulation and caused pH(i) elevation, which was accompanied with an increase in [Na(+)](i) and [Ca(2+)](i) as well as production of superoxide anion and cytokines. Interestingly, inhibition of NHE-1 not only abolished pH(i) regulation but also reduced production of superoxide anion as well as expression of cytokines and inducible nitric oxide synthase. Together, these results reveal that there was a concurrent activation of NHE-1 in microglia in response to proinflammatory stimuli. The study suggests that NHE-1 functions to maintain microglial pH(i) homeostasis allowing for sustained NADPH oxidase function and "respiratory" burst.

Amphotericin B membrane action: role for two types of ion channels in eliciting cell survival and lethal effects

The formation of aqueous pores by the polyene antibiotic amphotericin B (AmB) is at the basis of its fungicidal and leishmanicidal action. However, other types of nonlethal and dose-dependent biphasic effects that have been associated with the AmB action in different cells, including a variety of survival responses, are difficult to reconcile with the formation of a unique type of ion channel by the antibiotic. In this respect, there is increasing evidence indicating that AmB forms nonaqueous (cation-selective) channels at concentrations below the threshold at which aqueous pores are formed. The main foci of this review will be (1) to provide a summary of the evidence supporting the formation of cation-selective ion channels and aqueous pores by AmB in lipid membrane models and in the membranes of eukaryotic cells; (2) to discuss the influence of membrane parameters such as thickness fluctuations, the type of sterol present and the existence of sterol-rich specialized lipid raft microdomains in the formation process of such channels; and (3) to develop a cell model that serves as a framework for understanding how the intracellular K(+) and Na(+) concentration changes induced by the cation-selective AmB channels enhance multiple survival response pathways before they are overcome by the more sustained ion fluxes, Ca(2+)-dependent apoptotic events and cell lysis effects that are associated with the formation of AmB aqueous pores.

Phosphoinositide 3-kinase-dependent regulation of Na+/H+ exchanger in dendritic cells

Dendritic cells (DCs), antigen-presenting cells that are able to initiate primary immune responses and to establish immunological memory, are activated by exposure to bacterial lipopolysaccharides (LPS), which leads to cell swelling, triggering ROS formation and stimulating migration. The function of DCs is regulated by the phosphoinositide 3 (PI3) kinase pathway. On the other hand, PI3 kinase is an important regulator of diverse transporters including the Na(+)/H(+) exchanger (NHE). The present study was performed to elucidate the role of PI3 kinase in NHE activity, cell volume, ROS formation, and migration. To this end, DCs were isolated from murine bone marrow, cytosolic pH (pH(i)) determined utilizing 2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein fluorescence, Na(+)/H(+) exchanger activity from the Na(+)-dependent realkalinization after an ammonium pulse, cell volume from forward scatter in fluorescence-activated cell sorter analysis, ROS production from 2',7'-dichlorodihydrofluorescein diacetate fluorescence, and migration utilizing transwell migration assays. Exposure of DCs to LPS led within 4 h to a gradual cytosolic acidification paralleled by a transient time- and dose-dependent increase of Na(+)/H(+) exchanger activity, cell swelling, enhanced ROS production, and stimulation of migration. The PI3K inhibitors Wortmannin (1 μM) or LY294002 (10 μM) significantly blunted the effects of LPS on NHE activity, cell volume, ROS production, and migration. The present observations disclose a critical role of PI3K signaling in the regulation of DC function following exposure to LPS.

Involvement of Na+/H+ exchanger and respiratory burst enzymes NADPH oxidase and NO synthase, in Cd-induced lipid peroxidation and DNA damage in haemocytes of mussels

This study investigated cadmium-induced oxidative and genotoxic effects, such as lipid peroxidation and disturbance of DNA integrity (DNA damage) in haemocytes of mussel Mytilus galloprovincialis and the possible involvement of Na+/H+ exchanger (NHE), and/or the main enzymes of respiratory burst, NADPH oxidase and nitric oxide (NO) synthase, in the induction of Cd toxic effects. In order to verify the role of either NHE, or NADPH oxidase and NO synthase in Cd-mediated toxicity, inhibitors such as ethyl-N-isopropyl-amiloride (EIPA), diphenyleneiodonium chloride (DPI) and NG-nitro-L-arginine methyl ester (L-NAME) were used in each case. Moreover, phorbol-myristate acetate (PMA), a well-known protein kinase C (PKC)-mediated NADPH oxidase and NO synthase stimulator, as well as hydrogen peroxide (H2O2), a well-known genotoxic agent, was also used for elucidating the modulation of signaling molecules within cells, thus leading to the induction of lipid peroxidation and DNA damage. The results of the present study showed that micromolar concentrations of Cd (0.05-50 microM) could enhance both lipid peroxidation and DNA damage, possible via a PKC-mediated signaling pathway with the involvement of NHE, thus leading to the induction of NADPH oxidase and NO synthase activity, since inhibition of either NHE, or NADPH oxidase and NO synthase activity, significantly attenuates Cd-induced toxic effects in each case.

Effect of canrenone and amiloride on the prooxidative effect induced by aldosterone in human mononuclear leukocytes in vitro

Clinical studies have demonstrated that aldosterone receptor antagonists do improve the survival of patients with chronic heart diseases and in vitro studies have shown that canrenone blocks the proinflammatory effect of aldosterone in mononucler leukocytes (MNL). The aim of the study was to compare, in the model of human MNL, the effect of potassium-sparing diuretics amiloride and canrenone, on the protein expression of p22phox, a NADPH-oxidase system subunit, that is a principal marker of production of superoxide anions. MNL were isolated from 10 informed healthy volunteers (5 males and 5 females, age range 24-36 yr) and the proteins extracted. p22phox protein expression was evaluated by Western blot and quantified using a densitometric semiquantitative analysis. The experiments showed that aldosterone (10(-8) M) enhances the protein expression of p22phox and that its effect is reversed by co-incubation with canrenone (10(-6) M), while incubation with amiloride (10(-6) M) reduced the prooxidative effect of aldosterone at a significantly lower extent than canrenone. Co-incubation with canrenone, amiloride, and aldosterone together produced the same effect as aldosterone plus canrenone. Incubation with cortisol (40(-8) M) was not effective. These data confirm the prooxidative effect of aldosterone in MNL. The addition of aldosterone-receptor antagonist canrenone produced a higher inhibition than sodium channel blocker amiloride on the effect of aldosterone on p22phox protein expression.

Glutathione S-transferase in the white shrimp Litopenaeus vannamei: Characterization and regulation under pH stress

We first expressed a Mu-class GST from white shrimp Litopenaeus vannamei in Escherichia coli, and then characterized the purified recombinant enzyme with respect to the effects of pH, temperature on its catalytic (1-chloro-2, 4-dinitrobenzene-glutathione conjugation) activity. We also analyzed its expression profile in L. vannamei tissues, and assessed changes in Mu-GST expression, GST activity profiles and mortality rates following exposure of white shrimp to low and high pH (5.6 and 9.3, respectively). Realtime-PCR analysis showed that Mu-GST transcripts were expressed in all examined L. vannamei tissues, but were most abundant in the hepatopancreas. At low pH Mu-GST transcript levels in the hepatopancreas were highest after 12 h, and then declined to their original levels after 24 h. After 12 h they were also upregulated in haemocytes, but downregulated in the gills, and unchanged in the stomach following exposure to pH stress. Western blot analyses confirmed that the Mu-GST protein was strongly expressed in the hepatopancreas after 12 h at low pH and remain unchanged in the stomach after exposure to pH stress. pH-Related changes in GST activities in the shrimp hepatopancreas were similar to those displayed by the Mu-GST mRNA and protein profiles. In addition, the mortality of L. vannamei was higher at high pH than at low pH. These results suggest that L. vannamei Mu-GST expression is stimulated by acidic pH and that it may play important roles in detoxification of xenobiotics and antioxidant defenses.

Silencing of genes involved in Anaplasma marginale-tick interactions affects the pathogen developmental cycle in Dermacentor variabilis

BACKGROUND

The cattle pathogen, Anaplasma marginale, undergoes a developmental cycle in ticks that begins in gut cells. Transmission to cattle occurs from salivary glands during a second tick feeding. At each site of development two forms of A. marginale (reticulated and dense) occur within a parasitophorous vacuole in the host cell cytoplasm. However, the role of tick genes in pathogen development is unknown. Four genes, found in previous studies to be differentially expressed in Dermacentor variabilis ticks in response to infection with A. marginale, were silenced by RNA interference (RNAi) to determine the effect of silencing on the A. marginale developmental cycle. These four genes encoded for putative glutathione S-transferase (GST), salivary selenoprotein M (SelM), H+ transporting lysosomal vacuolar proton pump (vATPase) and subolesin.

RESULTS

The impact of gene knockdown on A. marginale tick infections, both after acquiring infection and after a second transmission feeding, was determined and studied by light microscopy. Silencing of these genes had a different impact on A. marginale development in different tick tissues by affecting infection levels, the densities of colonies containing reticulated or dense forms and tissue morphology. Salivary gland infections were not seen in any of the gene-silenced ticks, raising the question of whether these ticks were able to transmit the pathogen.

CONCLUSION

The results of this RNAi and light microscopic analyses of tick tissues infected with A. marginale after the silencing of genes functionally important for pathogen development suggest a role for these molecules during pathogen life cycle in ticks.

Involvement of Na+/H+ exchanger 1 in advanced glycation end products-induced proliferation of vascular smooth muscle cell

In this present study, we examined the role of Na(+)/H(+) exchanger 1 (NHE1) in the cultured rat vascular smooth muscle cell (VSMC) proliferation induced by advanced glycation end products (AGEs). AGEs significantly increased the [(3)H] thymidine incorporation of VSMC. Cariporide, an NHE1 inhibitor, dose-dependently attenuated the AGEs-induced increase in cell DNA synthesis. Thus the effect of AGEs on NHE1 activity was next examined. The cariporide-dependent intracellular pH (pH(i)) was significantly increased after 24h exposure to AGEs (10mug/ml). The direct AGEs-induced NHE1 activation was measured by the Na(+)-dependent intracellular pH recovery from intracellular acidosis. AGEs can increase the NHE1 activity in a time- and concentration-dependent manner. Inhibition of either the receptor for AGEs (RAGE) by anti-RAGE or mitogen-activated protein kinases (MAPK) by PD98059 reversed the effect of AGEs on NHE1 activity. Reverse transcription (RT)-PCR analysis revealed that AGEs dose-dependently increased NHE1 mRNA at 24h. These findings demonstrate NHE1 is required for in AGEs-induced proliferation of VSMC, and AGEs increase NHE1 activity via the MAPK pathway.

Effect of NHE1 antisense gene transfection on the biological behavior of SGC-7901 human gastric carcinoma cells

AIM: To study the effect of type 1 Na⁺/H⁺ exchanger (NHE1) antisense human gene transfection on the biological behavior of gastric carcinoma cell line SGC-7901.

METHODS: Antisense NHE1 eukaryotic expression on vector pcDNA3.1 was constructed by recombinant DNA technique and transfected into gastric carcinoma cell line SGC-7901 with DOTAP liposome transfection method. Morphological changes of cells were observed with optic and electron microscopes. Changes in cell proliferative capacity, apoptosis, intracellular pH (pH_i), cell cycle, clone formation in two-layer soft agar, and tumorigenicity in nude mice were examined.

RESULTS: Antisense eukaryotic expressing vectors were successfully constructed and transfected into SGC-7901. The transfectant obtained named 7901-antisense (7901-AS) stablely produced antisense NHE1. There was a significant difference between the pH_i of 7901-AS cells (6.77 ± 0.05) and that of 7901-zeo cells and SGC-7901 cells (7.24 ± 0.03 and 7.26 ± 0.03, P < 0.01). Compared with SGC-7901 and 7901-zeo cells, 7901-AS cells mostly showed cell proliferation inhibition, G₁/G₀ phase arrest, increased cell apoptotic rate, recovery of contact inhibition, and density contact. The tumorigenicity in nude mice and cloning efficiency in the two-layer soft agar were clearly inhibited.

CONCLUSION: NHE1 antisense gene significantly restrains the malignant behavior of human gastric carcinoma cells, suppresses cell growth and induces cell apoptosis, and partially reverses the malignant phenotypes of SGC-7901. These results suggest a potential role for human tumor gene therapy.

Role of NHE1 in calcium signaling and cell proliferation in human CNS pericytes

The central nervous system (CNS) pericytes play an important role in brain microcirculation. Na(+)/H(+) exchanger isoform 1 (NHE1) has been suggested to regulate the proliferation of nonvascular cells through the regulation of intracellular pH, Na(+), and cell volume; however, the relationship between NHE1 and intracellular Ca(2+), an essential signal of cell growth, is still not known. The aim of the present study was to elucidate the role of NHE1 in Ca(2+) signaling and the proliferation of human CNS pericytes. The intracellular Ca(2+) concentration was measured by fura 2 in cultured human CNS pericytes. The cells showed spontaneous Ca(2+) oscillation under quasi-physiological ionic conditions. A decrease in extracellular pH or Na(+) evoked a transient Ca(2+) rise followed by Ca(2+) oscillation, whereas an increase in pH or Na(+) did not induce the Ca(2+) responses. The Ca(2+) oscillation was inhibited by an inhibitor of NHE in a dose-dependent manner and by knockdown of NHE1 by using RNA interference. The Ca(2+) oscillation was completely abolished by thapsigargin. The proliferation of pericytes was attenuated by inhibition of NHE1. These results demonstrate that NHE1 regulates Ca(2+) signaling via the modulation of Ca(2+) release from the endoplasmic reticulum, thus contributing to the regulation of proliferation in CNS pericytes.

Involvement of Na+/H+exchangers in induction of cyclooxygenase-2 by vacuolar-type (H+)-ATPase inhibitors in RAW 264 cells

In the mouse macrophage-like cell line RAW 264, vacuolar-type (H(+))-ATPase (V-ATPase) inhibitors, bafilomycin A(1) and concanamycin A, increased the level of cyclooxygenase (COX)-2 protein and its mRNA. The V-ATPase inhibitor-induced expression of COX-2 was suppressed by inhibitors of c-jun N-terminal kinase (JNK) and nuclear factor-kappaB, and by inhibitors of Na(+)/H(+) exchangers (NHEs). The bafilomycin A(1)-induced activation of JNK but not degradation of IkappaB-alpha was suppressed by NHE inhibitors and by an inhibitor of Na(+)/Ca(2+) exchanger SN-6. These results suggested that V-ATPase inhibitors induce the expression of COX-2 via NHE-dependent and -independent pathways.

Interlinking interleukin-7

The signaling processes that maintain the homeostatic proliferation of peripheral T-cells and result in their self-renewal largely remain to be elucidated. Much focus has been placed on the anti-apoptotic function of the cytokine, interleukin-7 (IL-7), during T-cell development. But a more critical role has been ascribed to IL-7 as a mediator of peripheral T-cell maintenance. The biological effects responsive to IL-7 signaling are transduced through only a few well-known pathways. In this review we will focus on the signals transduced by IL-7 and similar cytokines, examining how proliferative signals originate from cytokine receptors, are amplified and eventually alter gene expression. In this regard we will highlight the crosstalk between pathways that promote survival, drive cell cycle progression and most importantly provide the needed energy to sustain these critical cellular activities. Though this review showcases much of what has been learned about IL-7 proliferative signaling, it also reveals the significant gaps in our knowledge about cytokine signaling in the very relevant context of peripheral T-cell homeostasis.

Store-operated calcium entry mediates intracellular alkalinization, ERK1/2, and Akt/PKB phosphorylation in bovine neutrophils

Neutrophil's responses to G protein-coupled chemoattractants are highly dependent on store-operated calcium (Ca(2+)) entry (SOCE). Platelet-activating factor (PAF), a primary chemoattractant, simultaneously increases cytosolic-free Ca(2+), intracellular pH (pH(i)), ERK1/2, and Akt/protein kinase B (PKB) phosphorylation. In this study, we looked at the efficacy of several putative SOCE inhibitors and whether SOCE mediates intracellular alkalinization, ERK1/2, and Akt/PKB phosphorylation in bovine neutrophils. We demonstrated that the absence of external Ca(2+) and the presence of EGTA reduced the intracellular alkalinization and ERK1/2 phosphorylation induced by PAF, apparently via SOCE influx inhibition. Next, we tested the efficacy of several putative SOCE inhibitors such as 2-aminoethoxydiphenyl borate (2-APB), capsaicin, flufenamic acid, 1-{beta-[3-(4-methoxy-phenyl)propoxy]-4-methoxyphenethyl}-1H-imidazole hydrochloride (SK&F 96365), and N-(4-[3,5-bis(trifluoromethyl)-1H-pyrazol-1-yl]phenyl)-4-methyl-1,2,3-thiadiazole-5-carboxamide (BTP2) on Ca(2+) entry induced by PAF or thapsigargin. 2-APB was the most potent SOCE inhibitor, followed by capsaicin and flufenamic acid. Conversely, SK&F 96365 reduced an intracellular calcium ([Ca(2+)](i)) peak but SOCE partially. BTP2 did not show an inhibitory effect on [Ca(2+)](i) following PAF stimuli. 2-APB strongly reduced the pH(i) recovery, whereas the effect of flufenamic acid and SK&F 96365 was partial. Capsaicin and BTP2 did not affect the pH(i) changes induced by PAF. Finally, we observed that 2-APB reduced the ERK1/2 and Akt phosphorylation completely, whereas the inhibition with flufenamic acid was partial. The results suggest that 2-APB is the most potent SOCE inhibitor and support a key role of SOCE in pH alkalinization and PI-3K-ERK1/2 pathway control. Finally, 2-APB could be an important tool to characterize Ca(2+) signaling in neutrophils.

Role of histamine H3 and H4 receptors in mechanical hyperalgesia following peripheral nerve injury

OBJECTIVE

Histamine is a chemical mediator that acts at four known types of histamine receptors and has been widely implicated in the development of nociception and neuropathic pain. Blocking histamine H(1) and H(2) receptors has been shown to reduce hyperalgesia following nerve injury, but the role of histamine H(3) and H(4) receptors in neuropathic pain has not been studied. Here, we used blockers of histamine H(3) and H(4) receptors to assess their effects on neuropathic pain behavior and mast cell numbers following peripheral nerve injury. In addition, we assessed the effect of activating H(4) receptors on neuropathic pain behavior.

METHODS

Rats were subjected to a partial ligation of the sciatic nerve, a model of neuropathic pain, and were treated either systemically or locally (hindpaw) with the H(3)/H(4) receptor inverse agonist thioperamide, the specific H(4) receptor antagonist JNJ 7777120, or the H(4) receptor agonist VUF 8430. Measurements of mechanical hyperalgesia were carried out by Randall-Selitto test for 1-3 weeks, and sciatic nerve tissues were analyzed for numbers of intact mast cells by histology at 9 h after surgery.

RESULTS

Rats treated with thioperamide or JNJ 7777120 showed significantly enhanced mechanical hyperalgesia after partial ligation of the sciatic nerve. The number of intact mast cells in the injured nerve of these rats was higher than in control rats suggesting reduced mast cell degranulation, but was still significantly lower than in intact nerves. Rats treated with VUF 8430 showed significantly reduced mechanical hyperalgesia.

CONCLUSION

We propose that the increase in mechanical hyperalgesia produced by thioperamide and JNJ 7777120 and the decrease in mechanical hyperalgesia produced by VUF 8430 may represent a direct effect of these agents on mechanospecific primary afferents, or an indirect effect of these agents via injury-induced inflammation.