Direct regulation of lipolysis by interleukin-15 in primary pig adipocytes

We recently provided evidence that interleukin-15 (IL-15) is expressed lowly in the pig adipocyte and that interferon-gamma (IFN-gamma) markedly increases this expression through a pathway regulated in part by protein kinase C. In the present study, we tested the hypothesis that IL-15 acts directly on the adipocyte to regulate lipid accretion by enhancing lipolysis or suppressing lipogenesis. Using recombinant porcine IL-15, we determined that this cytokine stimulates lipolysis in a dose-dependent manner (P < 0.001). Furthermore, comparative studies with other cytokines showed that IL-15 is more potent in its acute stimulation of lipolysis than either TNF-alpha, IL-6, or LPS (P < 0.001). When specific inhibitors of protein kinase A or Janus kinase are present, the lipolytic effect of IL-15 is attenuated (P < 0.01). These data indicate that, in addition to its regulation of muscle protein accretion and T-cell growth and development, IL-15 also targets the adipocyte directly to alter stimulate lipolysis. Thus, when induced by IFN-gamma or other inflammatory mediators, IL-15 may be a significant homeorhetic factor that mobilizes and directs energy away from the adipocyte to other cells during the acute phase of the inflammatory response.     

Glutamine decreases lipopolysaccharide-induced IL-8 production in Caco-2 cells through a non-NF-kappaB p50 mechanism

Glutamine (Gln) supplementation has been shown to decrease production of pro-inflammatory cytokines by the human intestinal mucosa. The mechanism of this is poorly understood. We hypothesize that Gln down-regulates lipopolysaccharide (LPS)-stimulated pro-inflammatory cytokine production in Caco-2 cells by nuclear factor-kappa B (NF-kappaB). Caco-2 cells were incubated with different concentrations of Gln with or without methionine sulfoximine (MS, an inhibitor of glutamine synthetase) before stimulation with LPS. IL-6, IL-8, IL-10 and TNF-alpha protein and mRNA level were determined. NF-kappaB translocation was determined using an ELISA-based kit. IL-8 was the only detectable cytokine/chemokine. The largest amount of IL-8 was secreted by cells in the presence of MS with no Gln in the medium after exposure to LPS. LPS increased IL-8 production, peaking 10h after LPS administration. The addition of Gln (0.5 or 5.0mM) decreased IL-8 peptide and mRNA expression. LPS increased NF-kappaB nuclear translocation in the presence or absence of MS. Neither Gln nor MS altered NF-kappaB nuclear translocation. These results indicate that the lack of glutamine increases IL-8 production by Caco-2 cells after LPS stimulation. However, the glutamine-mediated decrease in LPS-stimulated IL-8 production is not associated with NF-kappaB p50 nuclear binding.     

Regulation of granulocyte-macrophage colony-stimulating factor in human retinal pigment epithelial cells by IL-1beta and IFN-gamma.

GM-CSF production by RPE cells, which form part of the blood-retina barrier, is upregulated by IL-1beta and this increase can be reversed by IFN-gamma. IL-1beta up-regulation is not dependent on PKC but the PKC activator PMA induces low levels of GM-CSF production and acts synergistically with IL-1beta to further increase GM-CSF. Although A23187 and ionomycin stimulated low levels of GM-CSF production, the IL-1beta pathway was cyclosporin A insensitive and did not interact with the calcium pathway. IL-1beta-stimulated GM-CSF mRNA expression and production was strongly dependent on NF-kappaB. IFN-gamma inhibition of the GM-CSF response to IL-1beta acted via NF-kappaB, reducing the translocation of NF-kappaB to the nuclei of RPE cells treated with IL-1beta and IFN-gamma. The results show that IFN-gamma down-regulation acts either directly on NF-kappaB or its activation or by blockade of a pathway upstream of NF-kappaB. However, any such blockade does not involve PKC or intracellular calcium.     

Lipopolysaccharide activates an innate immune system response in human adipose tissue in obesity and type 2 diabetes

Type 2 diabetes (T2DM) is associated with chronic low-grade inflammation. Adipose tissue (AT) may represent an important site of inflammation. 3T3-L1 studies have demonstrated that lipopolysaccharide (LPS) activates toll-like receptors (TLRs) to cause inflammation. For this study, we 1) examined activation of TLRs and adipocytokines by LPS in human abdominal subcutaneous (AbdSc) adipocytes, 2) examined blockade of NF-kappaB in human AbdSc adipocytes, 3) examined the innate immune pathway in AbdSc AT from lean, obese, and T2DM subjects, and 4) examined the association of circulating LPS in T2DM subjects. The findings showed that LPS increased TLR-2 protein expression twofold (P<0.05). Treatment of AbdSc adipocytes with LPS caused a significant increase in TNF-alpha and IL-6 secretion (IL-6, Control: 2.7+/-0.5 vs. LPS: 4.8+/-0.3 ng/ml; P<0.001; TNF-alpha, Control: 1.0+/-0.83 vs. LPS: 32.8+/-6.23 pg/ml; P<0.001). NF-kappaB inhibitor reduced IL-6 in AbdSc adipocytes (Control: 2.7+/-0.5 vs. NF-kappaB inhibitor: 2.1+/-0.4 ng/ml; P<0.001). AbdSc AT protein expression for TLR-2, MyD88, TRAF6, and NF-kappaB was increased in T2DM patients (P<0.05), and TLR-2, TRAF-6, and NF-kappaB were increased in LPS-treated adipocytes (P<0.05). Circulating LPS was 76% higher in T2DM subjects compared with matched controls. LPS correlated with insulin in controls (r=0.678, P<0.0001). Rosiglitazone (RSG) significantly reduced both fasting serum insulin levels (reduced by 51%, P=0.0395) and serum LPS (reduced by 35%, P=0.0139) in a subgroup of previously untreated T2DM patients. In summary, our results suggest that T2DM is associated with increased endotoxemia, with AT able to initiate an innate immune response. Thus, increased adiposity may increase proinflammatory cytokines and therefore contribute to the pathogenic risk of T2DM.     

Lipopolysaccharide-induced cytokine cascade and lethality in LT alpha/TNF alpha-deficient mice.

BACKGROUND: Tumor necrosis factor alpha (TNF-alpha) is often considered the main proinflammatory cytokine induced by lipopolysaccharide (LPS) and consequently the critical mediator of the lethality associated with septic shock. MATERIALS AND METHODS: We used mice carrying a deletion of both the lymphotoxin alpha (LT-alpha) and TNF-alpha genes to assess the role of TNF in the cytokine cascade and lethality induced by LPS. RESULTS: Initial production of IL-1 alpha, IL-1 beta, IL-6, and IL-10 is comparable in wild-type and mutant mice. However, at later times, expression of IL-1 alpha, IL-1 beta, and IL-10 is prolonged, whereas that of IL-6 decreases in mutant mice. Expression of IFN-gamma is almost completely abrogated in mutants, which is in agreement with a more significant alteration of the late phase of the cytokine cascade. We measured similar LD50 (600 micrograms) for the intravenous injection of LPS in mice of the three genotypes (+/+, +/-, -/-), demonstrating that the absence of TNF does not confer long-term protection from lethality. However, death occurred much more slowly in mutant mice, who were protected more efficiently from death by CNI 1493, an inhibitor of proinflammatory cytokine production, than were wild-type mice. DISCUSSION: Thus, while TNF-alpha is not required for the induction of these cytokines by LPS, it modulates the kinetics of their expression. The lethality studies simultaneously confirm a role for TNF as a mediator of early lethality and establish that, in the absence of these cytokines, other mediators take over, resulting in the absence of long-term protection from LPS toxicity.     

Trichomonas vaginalis inhibits proinflammatory cytokine production in macrophages by suppressing NF-kappaB activation

Activation of NF-kappaB leads to the production of proinflammatory cytokines such as IL-12 and TNF-alpha that are involved in innate and adaptive immunity. We determined whether T. vaginalis-induced inflammatory response in macrophages associated with NF-kappaB. T. vaginalis adhesion led to transient NF-kappaB activation at 6 h but activation declined dramatically by 8 h. Super-shift assays showed that the gel-shifted complexes consisted of p65 (Rel A) and p50 (NF-kappaB1). NF-kappaB activation was accompanied by IkappaB-alpha degradation, and was inhibited by blocking T. vaginalis adhesion, indicating that the early NF-kappaB activation by T. vaginalis depends on IkappaB-alpha degradation. Quantitative real-time RT-PCR analyses revealed that the expression of TNF-alpha and IL-12 mRNA in T. vaginalis-adhesive cells was rapidly suppressed in comparison with LPS stimulation. We also observed that the parasite inhibited the nuclear translocation of NF-kappaB at 8 h, and diminished IL-12 and TNF-alpha production in response to LPS. In addition, inhibition of IkappaB-alpha degradation by MG-132 resulted in apoptosis. These results demonstrate that effects of T. vaginalis on NF-kappaB regulation are critical for cytokine production and the survival of macrophages. We suggest that there exist inhibitory mechanisms induced by T. vaginalis to evade host immunity.     

Alveolar macrophage activation after trauma-hemorrhage and sepsis is dependent on NF-kappaB and MAPK/ERK mechanisms

The acute respiratory distress syndrome (ARDS) is a major cause of morbidity after injury. We hypothesized that alveolar macrophage (AMPhi) chemokine and cytokine release after hemorrhage and sepsis is regulated by NF-kappaB and MAPK. Adult male rats underwent soft tissue trauma and hemorrhagic shock (~90 min) followed by crystalloid resuscitation. Sepsis was induced by cecal ligation and puncture (CLP) 20 h after resuscitation. AMPhi were harvested, and TNF-alpha, IL-6, and macrophage inflammatory protein (MIP)-2 release and serum IL-6 and TNF-alpha levels were measured at 5 h after HCLP. Lung tissues were analyzed for activation of NF-kappaB, myeloperoxidase activity, and wet/dry weight ratio. In control animals, AMPhi were stimulated with LPS with or without inhibitors of NF-kappaB and MAPK. Serum TNF-alpha and IL-6 levels and spontaneous AMPhi TNF-alpha and MIP-2 release were elevated (P < 0.05) after HCLP, concomitantly with the development of lung edema and leukocyte activation. Activation of NF-kappaB increased in lungs from the hemorrhage and CLP group compared with shams. Inhibition of NF-kappaB or the upstream MAPK significantly decreased LPS-stimulated AMPhi activation. Because enhanced release of inflammatory mediators by AMPhi may contribute to ARDS after severe trauma, inhibition of intracellular signaling pathways represents a target to attenuate organ injury under those conditions.     

Immunostimulatory activities of polysaccharides from liquid culture of pine-mushroom Tricholoma matsutake

Mushrooms are regarded as one of the well-known foods and biopharmaceutical materials with a great deal of interest. Polysaccharide beta-glucan is the major component of mushrooms that displays various biological activities such as antidiabetic, anticancer, and antihyperlipidemic effects. In this study, we compared the immunostimulatory potency of polysaccharide fractions, prepared from liquid culture of pinemushroom Tricholoma matsutake, with a potent immunogen lipopolysaccharide (LPS), and their molecular mechanisms on the functional activation of macrophages. We found that fraction II (TMF-II) was able to comparably upregulate or highly enhance the phenotypic functions of macrophages such NO production and cytokine (IL-1beta, IL-6, IL-12, and TNF-alpha) expression, to LPS. TMF-II triggered the phosphorylation of IkappaBalpha, a critical step for NF-kappaB activation and translocation. Of the upstream signaling enzymes tested, Src and Akt were thought to be the responsible upstream signaling components in induction of NO production, although TMF-II strongly upregulated the phosphorylation of all MAPK pathways. Therefore, our data suggest that T. matsutake-derived beta-glucan may exert its immunostimulating activities with similar potency to LPS via activation of multiple signaling pathways linked to NF-kappaB activation.     

Lipopolysaccharide-induced cytokine expression in alveolar epithelial cells: role of PKCζ-mediated p47phox phosphorylation

Chronic inflammation incited by bacteria in the saccular lung of premature infants contributes to the pathogenesis of bronchopulmonary dysplasia (BPD). LPS-mediated type II alveolar epithelial cell (AEC) injury induces the expression of pro-inflammatory cytokines that trigger pulmonary neutrophil influx, alveolar matrix degradation and lung remodeling. We hypothesized that NADPH oxidase (Nox)-dependent mechanisms mediate LPS-induced cytokine expression in AEC. We examined the role of p47phox in mediating LPS-dependent inflammatory cytokine expression in A549 cells (which exhibit phenotypic features characteristic of type II AEC) and elucidated the proximal signaling events by which Nox is activated by LPS. LPS-induced ICAM-1 and IL-8 expression was associated with increased superoxide formation in AEC. LPS-mediated oxidative stress and cytokine expression was inhibited by apocynin and augmented by PMA demonstrating that Nox-dependent redox signaling regulates LPS-dependent pro-inflammatory signaling in AEC. In LPS-treated cells, p47phox translocated from the cytoplasm to the perinuclear region and co-localized with gp91phox. LPS also induced a temporal increase in p47phox serine304 phosphorylation in AEC. While inhibition of classical PKC and novel PKC with calphostin and rottlerin did not inhibit ICAM-1 or IL-8 expression, the myristolyated PKCζ pseudosubstrate peptide (a specific inhibitor of PKCζ) inhibited LPS-induced cytokine expression in AEC. Inhibition of PKCζ also attenuated LPS-mediated p47phox phosphorylation and perinuclear translocation in AEC. Consistent with these data, LPS activated PKCζ in AEC as evidenced by increased threonine410 phophorylation. We conclude that PKCζ-mediated p47phox activation regulates LPS-dependent cytokine expression in AEC. Selective inhibition of PKCζ or p47phox might attenuate LPS-mediated inflammation and alveolar remodeling in BPD.     

Modulation of innate and acquired immune responses by Escherichia coli heat-labile toxin: distinct pro- and anti-inflammatory effects of the nontoxic AB complex and the enzyme activity

We have examined the roles of enzyme activity and the nontoxic AB complex of heat-labile toxin (LT) from Escherichia coli on its adjuvant and immunomodulatory properties. LTK63, an LT mutant that is completely devoid of enzyme activity, enhanced Th1 responses to coinjected Ags at low adjuvant dose. In contrast, LTR72, a partially detoxified mutant, enhanced Th2 responses and when administered intranasally to mice before infection with Bordetella pertussis suppressed Th1 responses and delayed bacterial clearance from the lungs. LTR72 or wild-type LT inhibited Ag-induced IFN-gamma production by Th1 cells, and LT enhanced IL-5 production by Th2 cells in vitro. Each of the toxins enhanced B7-1 expression on macrophages, but enhancement of B7-2 expression was dependent on enzyme activity. We also observed distinct effects of the nontoxic AB complex and enzyme activity on inflammatory cytokine production. LT and LTR72 suppressed LPS and IFN-gamma induced TNF-alpha and IL-12 production, but enhanced IL-10 secretion by macrophages in vitro and suppressed IL-12 production in vivo in a murine model of LPS-induced shock. In contrast, LTK63 augmented the production of IL-12 and TNF-alpha. Furthermore, LTK63 enhanced NF-kappaB translocation, whereas low doses of LTR72 or LT failed to activate NF-kappaB, but stimulated cAMP production. Thus, E. coli LT appears to be capable of suppressing Th1 responses and enhancing Th2 responses through the modulatory effects of enzyme activity on NF-kappaB activation and IL-12 production. In contrast, the nontoxic AB complex can stimulate acquired immune responses by activating components of the innate immune system.     

Hepcidin and hemojuvelin gene expression in rat liver damage: in vivo and in vitro studies

In this work, we used two rat models, partial hepatectomy (PH) and CCl(4) administration, to study the changes in iron pathways in response to hepatic damage. Liver injury induced changes in the hepatic gene expression of hepcidin, hemojuvelin (Hjv), several other proteins of iron metabolism, and several cytokines such as IL-1beta, IL-6, TNF-alpha, and IFN-gamma. Hepcidin gene expression was upregulated between 4 and 8 h with a maximum up to 16 h after surgery. However, Hjv gene expression was downregulated at the same time. An early upregulation of hepcidin (3 h) and downregulation of Hjv gene expression was found after CCl(4) administration. Transferrin receptor 1 and ferritin H gene expression was upregulated, whereas ferroportin 1 gene expression was downregulated. Hepatic IL-6 gene expression was upregulated early after PH and reached maximum 8 h after the PH. In CCl(4)-induced liver injury, IL-6, IL-1beta, TNF-alpha, and IFN-gamma upregulation were found at the maximum 12 h after the administration of the toxin. Treatment of isolated rat hepatocytes with IL-6 and, to a lesser extent, with IL-1beta but not with TNF-alpha or IFN-gamma dose dependently upregulated hepcidin and downregulated Hjv gene expression. In hepatic damage, changes of the hepatic gene expression of the main proteins involved in iron metabolism may be induced by locally synthesized mediators.     

Regulation of lipopolysaccharide-induced NO synthase expression in the major organs in a mouse model. The roles of endogenous interferon-gamma, tumor necrosis factor-alpha and interleukin-10

Elevated NO production mediated by activation of the enzyme iNOS is thought to play a central role in the development of tissue damage observed during septic shock. IFN-gamma, TNF-alpha and IL-10 have been shown to be involved in the regulation of LPS-induced serum levels of the NO-oxidation products nitrate and nitrite. Therefore, in the present study, we investigated the role of endogenous IFN-gamma, TNF-alpha and IL-10 in the regulation of LPS-induced tissue iNOS expression in the major organs. To this end, mice were pre-treated with anti-IFN-gamma, anti-TNF-alpha, anti-IL-10 monoclonal antibodies, or combinations of these, two hours before intraperitoneal LPS-challenge. Immunohistochemical staining for iNOS and determination of iNOS activity indicated that iNOS expression was mainly upregulated in the small intestine, lung and heart, and that IFN-gamma, TNF-alpha as well as IL-10 are involved in the regulation of iNOS expression and enzyme activity. Whereas blocking either IFN-gamma or TNF-alpha did not affect iNOS expression, iNOS enzymatic activity seems to be inhibited. In contrast, blocking both mediators nearly completely prevents iNOS expression after LPS challenge, suggesting that the presence of either IFN-gamma or TNF-alpha is essential for LPS-induced iNOS expression in these organs. Combined treatment of these monoclonal antibodies revealed that whereas on the one hand IL-10 inhibits LPS-induced iNOS expression, on the other hand IL-10 or an IL-10 inducible factor is also involved in the upregulation of iNOS expression after LPS challenge.     

Regulation of surfactant proteins by LPS and proinflammatory cytokines in fetal and newborn lung

Intra-amniotic lipopolysaccharide (LPS) and cytokines may decrease respiratory distress syndrome (RDS) and increase chronic lung disease in the newborn. The aim was to identify the primary inflammatory mediators regulating the expression of surfactant proteins (SP) in explants from immature (22-day-old fetus) and mature (30-day term fetus and 2-day-old newborn) rabbits. In immature lung, interleukin (IL)-1alpha and IL-1beta upregulated the expression of SP-A and SP-B. These effects of IL-1 were diminished, and SP-C mRNA was suppressed additively in the presence of tumor necrosis factor (TNF)-alpha and either LPS or interferon (IFN)-gamma. LPS, TNF-alpha, or IFN-gamma had no effect alone. In explants from the term fetus and the newborn, LPS, IL-1alpha, and TNF-alpha additively suppressed the SPs. LPS acutely induced IL-1alpha in alveolar macrophages in mature lung but not in the immature lung. IFN-gamma that generally has low expression in intrauterine infection decreased the age dependence of the other agonists' effects on SPs. The present study serves to explain the variation of the pulmonary outcome after an inflammatory insult. We propose that IL-1 from extrapulmonary sources induces the SPs in premature lung and is responsible for the decreased risk of RDS in intra-amniotic infection.