Interleukin-12 P40 induces the expression of TNF-α in microglia and macrophages

Recently, it has been found that overproduction of IL-12 can be dangerous to the host as it is involved in the pathogenesis of a number of autoimmune inflammatory diseases such as multiple sclerosis. It is composed of two different subunits – p40 and p35. Expression of p40 mRNA but not that of p35 mRNA in excessive amount in the CNS of patients with Multiple Sclerosis (MS) suggests that IL-12 p40 may have a role in the pathogenesis of the disease. The present study was undertaken to explore the role of p40 in the expression of TNF-α in microglia. Interestingly, we have found that IL-12 p70, p402 (the p40 homodimer) and p40 (the p40 monomer) dose-dependently induced the production of TNF-α in BV-2 microglial cells. This induction of TNF-α production was accompanied by an induction of TNF-α mRNA. In addition to BV-2 glial cells, p70, p402 and p40 also induced the production of TNF-α in mouse primary microglia and peritoneal macrophages. Since the activation of both NF-κB and C/EBPb is important for the expression of TNF-α in microglial cells, we investigated the effect of p40 on the activation of NF-κB as well as C/EBPb. Activation of NF-κB as well as C/EBPb by p40 and inhibition of p40-induced expression of TNF-α by Dp65, a dominant-negative mutant of p65, and DC/EBPb, a dominant-negative mutant of C/EBPb, suggests that p40 induces the expression of TNF-α through the activation of NF-κB and C/EBPb. This study delineates a novel role of IL-12 p40 in inducing the expression of TNF-α in microglial cells which may participate in the pathogenesis of neuroinflammatory diseases.
Acknowledgements:   This study was supported by NIH grants (NS39940 and AG19487).     

Muscle precursor cells isolated from aged rats exhibit an increased tumor necrosis factor-α response

Improving muscle precursor cell (MPC, muscle-specific stem cells) function during aging has been implicated as a key therapeutic target for improving age-related skeletal muscle loss. MPC dysfunction during aging can be attributed to both the aging MPC population and the changing environment in skeletal muscle. Previous reports have identified elevated levels of tumor necrosis factor-α (TNF-α) in aging, both circulating and locally in skeletal muscle. The purpose of the present study was to determine if age-related differences exist between TNF-α-induced nuclear factor-kappa B (NF-κB) activation and expression of apoptotic gene targets. MPCs isolated from 32-month-old animals exhibited an increased NF-κB activation in response to 1, 5, and 20 ng mL⁻¹ TNF-α, compared to MPCs isolated from 3-month-old animals. No age differences were observed in the rapid canonical signaling events leading to NF-κB activation or in the increase in mRNA levels for TNF receptor 1, TNF receptor 2, TNF receptor-associated factor 2 (TRAF2), or Fas (CD95) observed after 2 h of TNF-α stimulation. Interestingly, mRNA levels for TRAF2 and the cell death-inducing receptor, Fas (CD95), were persistently upregulated in response to 24 h TNF-α treatment in MPCs isolated from 32-month-old animals, compared to 3-month-old animals. Our data indicate that age-related differences may exist in the regulatory mechanisms responsible for NF-κB inactivation, which may have an effect on TNF-α-induced apoptotic signaling. These findings improve our understanding of the interaction between aged MPCs and the changing environment associated with age, which is critical for the development of potential clinical interventions aimed at improving MPC function with age.     

TNF-α reduces the level of Staphylococcus epidermidis internalization by bovine endothelial cells

Staphylococcus epidermidis is an environmental opportunistic pathogen associated with bovine intramammary infections. In bacterial infections, the endothelial tissue plays an important role during inflammation and it is the target of proinflammatory cytokines such as tumor necrosis factor α (TNF-α). Therefore, this work was designed to explore the effect of TNF-α on the interaction of S. epidermidis with bovine endothelial cells (BEC). We show that cell signaling activated by TNF-α caused a marked reduction in the number of intracellular S. epidermidis , suggesting that molecules participating in this pathway were involved in the internalization of this bacterium. We also found that S. epidermidis internalization was not associated with basal levels of nuclear factor kappa B (NF-κB) activity because the intracellular number of bacteria recovered after treating BEC with the NF-κB inhibitors, SN50 or BAY 11–7083, was similar to that of the untreated control. Interestingly, inhibition of the basal activity of JNK with SP600125 and p38 with SB203580 caused a decrease in the number of intracellular S. epidermidis . These results suggest that activation of the signaling pathway initiated by TNF-α could play an important role in the phagocytosis of this bacterium. However, the basal activity of NF-κB was shown not to be important for the internalization process of S. epidermidis .     

Nystatin-induced nitric oxide production in mouse macrophage-like cell line RAW264.7

Nystatin is known to deplete lipid rafts from mammalian cell membranes. Lipid rafts have been reported to be necessary for lipopolysaccharide signaling. In this study, it was unexpectedly found that lipopolysaccharide-induced nitric oxide production was not inhibited, but rather increased in the presence of a non-cytotoxic concentration of nystatin. Surprisingly, treatment with nystatin induced only NO production and iNOS expression in RAW264.7 cells. At the concentration used, no changes in the expression of GM1 ganglioside, a lipid raft marker on RAW264.7 cells, was seen. From studies using several kinds of inhibitors for signaling molecules, nystatin-induced NO production seems to occur via the iκB/NF-κB and the PI3 K/Akt pathway. Furthermore, because nystatin is known to activate the Na-K pump, we examined whether the Na-K pump inhibitor amiloride suppresses nystatin-induced NO production. It was found that amiloride significantly inhibited nystatin-induced NO production. The results suggest that a moderate concentration of nystatin induces NO production by Na-pump activation through the PI3 kinase/Akt/NF-κB pathway without affecting the condition of lipid rafts.     

Leuconostoc citreum HJ-P4 (KACC 91035) regulates immunoglobulin E in an ovalbumin-induced allergy model and induces interleukin-12 through nuclear factor-kappa B and p38/c-Jun N-terminal kinases signaling in macrophages

Leuconostoc citreum ( L. citreum ) HJ-P4 (KACC 91035) is one of the major predominant species in kimchi fermentation in Korea. The purpose of the present study was to test the immunomodulatory capacity of L. citreum to modulate the IgE-mediated allergic response and to examine the involvement of NF-κB and MAPK in IL-12 production in macrophages. Balb/c mice were sensitized with OVA/alum and oral administration of L. citreum to the mice began before or after the OVA sensitization. Protein and mRNA expression of Th1 cytokines in splenocytes by L. citreum in vitro was measured. The role of NF-κB and MAPK such as p38, ERK1/2 and JNK in L. citreum -induced IL-12 was investigated in peritoneal macrophages and RAW264.7 cell lines. L. citreum inhibited the serum levels of total IgE, IgG1 and IgG2a altogether and increased OVA-specific IFN-γ production in splenocytes from pre- and post-sensitized animals. However, the downregulation of IL-4 and IL-5 production was observed only in the pre-sensitization group. The ability of L. citreum to stimulate IFN-γ was dependent on its induction of IL-12. NF-κB, p38 and JNK were mainly involved in L. citreum -induced IL-12 production. In conclusion, the current study demonstrated that L. citreum is able to regulate serum IgE generation at the induction and effector phases of allergic response through overall control over antibody production and that its involvement of IL-12 production was mediated through NF-κB and p38/JNK. Taken together, the use of L. citreum can be useful in preventing the development and progression of IgE production.     

Degradation of IkappaBalpha in activated RAW264.7 cells is blocked by the phosphatidylinositol 3-kinase inhibitor LY294002

The mechanism by which lipopolysaccharide (LPS) or phorbol 12-myristate 13-acetate (PMA) induces production of proinflammatory cytokines in murine macrophages, and the role of phosphatidylinositol 3-kinase (PI3-kinase) have not been well investigated. Activation of nuclear factor κB (NF-κB) is initiated by the phosphorylation of the inhibitory subunit, IκB, which targets IκB for degradation and leads to the release of active NF-κB. In this study we demonstrate that 2- (4-morpholinyl)-8-phenylchromone (LY294002), which inhibits PI3-kinase, specifically inhibited degradation of IκBα in RAW264.7 cells stimulated with interferon-γ (IFN-γ) plus LPS or IFN-γ plus PMA. To elucidate the importance of this activity in RAW264.7 cells, we examined tumor necrosis factor-α (TNF-α) and interleukin IL)-6 production in the activated cells. Pretreatment of the cells with LY294002 resulted in the inhibition of TNF-α and IL-6 production in RAW264.7 cells stimulated with IFN-γ plus LPS or IFN-γ plus PMA. Furthermore, LY294002 inhibited the production of nitric oxide NO) in RAW264.7 cells stimulated with IFN-γ plus LPS or IFN-γ plus PMA. LY294002 also inhibited inducible NO synthase (iNOS) mRNA expression in the activated RAW264.7 cells. In conclusion, the present results suggest that PI3-kinase is involved in the signal transduction pathway responsible for LPS- or PMA-mediated TNF-α and IL-6 production, and that LY294002 inhibits NO generation through blocking the degradation of IκBα in activated RAW264.7 cells. This revised version was published online in August 2006 with corrections to the Cover Date.     

Anti-inflammatory activity of a globular adiponectin function on RAW 264 cells stimulated by lipopolysaccharide from Aggregatibacter actinomycetemcomitans

Adiponectin is an adipokine with potent anti-inflammatory properties. We previously reported that a globular adiponectin (gAd) suppresses Aggregatibacter actinomycetemcomitans lipopolysaccharide-induced nuclear factor-κB activity, suggesting an anti-inflammatory effect of gAd. In this study, we investigated whether gAd is able to modulate the effect of A. actinomycetemcomitans lipopolysaccharide on cytokine induction in a murine macrophage cell line (RAW 264). The phosphorylation of p38 mitogen-activated protein kinase, c-Jun N-terminal kinase, extracellular signal-regulated kinase, and IκB kinase α/β and the degradation of IκB, which were induced by A. actinomycetemcomitans lipopolysaccharide intoxication, were clearly reduced in gAd-pretreated RAW 264 cells compared with the untreated cells. Expression levels of tumor necrosis factor (TNF)-α and interleukin-10 (IL-10) mRNA were assessed by real-time PCR. Cell-free supernatants were collected after 12 h of stimulation and analyzed by enzyme-linked immunosorbent assay for TNF-α and IL-10. Pretreatment with gAd significantly inhibited the A. actinomycetemcomitans lipopolysaccharide-induced TNF-α mRNA expression and protein secretion. In contrast, pretreatment with gAd significantly enhanced the A. actinomycetemcomitans lipopolysaccharide-induced IL-10 mRNA expression and protein secretion. These data suggest a mechanism for the anti-inflammatory activity of gAd in local inflammatory lesions, such as periodontitis.     

Immunostimulating activity by polysaccharides isolated from fruiting body of <Emphasis Type="Italic">Inonotus obliquus</Emphasis>

In this study, we investigated the immunostimulating activity of polysaccharides isolated from fruiting body of Inonotus obliquus (PFIO). Additionally, the signaling pathway of PFIO-mediated macrophage activation was investigated in RAW264.7 macrophage cells. We found that PFIO was capable of promoting NO/ROS production, TNF-α secretion and phagocytic uptake in macrophages, as well as cell proliferation, comitogenic effect and IFN-γ/IL-4 secretion in mouse splenocytes. PFIO was able to induce the phosphorylation of three MAPKs as well as the nuclear translocation of NF-κB, resulting in activation of RAW264.7 macrophages. PFIO also induced the inhibition of TNF-α secretion by anti-TLR2 mAb, consequently, PFIO might be involved in TNF-α secretion via the TLR2 receptor. In addition, our results showed that oral administration of PFIO suppressed in vivo growth of melanoma tumor in tumorbearing mice. In conclusion, our experiments presented that PFIO effectively promotes macrophage activation through the MAPK and NF-κB signaling pathways, suggesting that PFIO may potentially regulate the immune response.     

Inhibitory action of telithromycin against Shiga toxin and endotoxin

Shiga toxin (Stx)-producing Escherichia coli (STEC) is associated with hemolytic uremic syndrome (HUS). High inflammatory cytokine [interleukin (IL)-6 and IL-8] levels and low anti-inflammatory cytokine (IL-10) levels are indicators of a high risk for developing HUS in STEC-infected children. In this study, we investigated inhibitory action of telithromycin, a ketolide, against STEC and against Stx and lipopolysaccharide (LPS). Telithromycin inhibited in vitro STEC growth without inducing Stx phage, in marked contrast to norfloxacin. Stx markedly induced inflammatory (but not anti-inflammatory) cytokine production in human peripheral blood monocytes, while LPS induced both inflammatory and anti-inflammatory cytokine production. Telithromycin selectively inhibited the IL-6 and IL-8 production from Stx-stimulated (but not LPS-stimulated) monocytes. The drug did not significantly inhibit IL-10 production. Our data suggest that Stx plays a crucial role in the stimulation of inflammatory cytokines and such inflammatory response is inhibited by telithromycin, an anti-bacterial agent.     

ChlaDub1 of Chlamydia trachomatis suppresses NF-kappaB activation and inhibits IkappaBalpha ubiquitination and degradation

Chlamydia trachomatis is an obligate intracellular bacterial pathogen that causes various human diseases, including blindness caused by ocular infection and sexually transmitted diseases resulting from urogenital infection. After infecting host cells, Chlamydiae avoid alarming the host's immune system. Among the immune evasion mechanisms, Chlamydiae can inhibit NF-κB activation, a crucial pathway for host inflammatory responses. In this study, we show that Chla Dub1, a deubiquitinating and deNeddylating protease from C. trachomatis , is expressed in infected cells. In transfection experiments, Chla Dub1 suppresses NF-κB activation induced by several pro-inflammatory stimuli and binds the NF-κB inhibitory subunit IκBα, impairing its ubiquitination and degradation. Thus, we provide further insight into the mechanism by which C. trachomatis may evade the host inflammatory response by demonstrating that Chla Dub1, a protease produced by this microorganism, is capable of inhibiting IκBα degradation and blocking NF-κB activation.     

Differential regulation of c-Jun N-terminal kinase and NF-kappaB pathway by caffeic acid phenethyl ester in astroglial and monocytic cells

Caffeic acid phenethyl ester (CAPE), an active component of propolis extracts, has been known for its specific inhibition of nuclear factor κB (NF-κB) and subsequent anti-inflammatory activity. In this study, we report that (i) CAPE exerts its anti-inflammatory action (inhibition of tumor necrosis factor-induced expression of intercellular adhesion molecule-1 and CC chemokine ligand-2) via NF-κB inhibition by two distinct molecular mechanisms in a cell-specific manner: CAPE inhibited downstream pathways of inhibitor κB (IκB) degradation in monocytic cells, while activation of upstream IκB kinase was suppressed by CAPE pre-treatment in astroglial cells; and (ii) CAPE paradoxically activates the c-Jun N-terminal kinase (JNK) pathway, which might be responsible for its pro-apoptotic action and divergent regulation of proinflammatory mediators such as CXC chemokine ligand-8.