Heterotrimeric G proteins physically associated with the lipopolysaccharide receptor CD14 modulate both in vivo and in vitro responses to lipopolysaccharide

Medial prefrontal cortex connectivity with the nucleus accumbens is related to HIV serostatus, perceptions of psychological stress, and monocyte expression of TNF-a

Post-menopausal persons living with HIV (PWH) report elevated levels of psychological stress and monocyte activation compared to persons living without HIV (PWOH). Resting state functional connectivity (rsFC) of mesolimbic brain regions underpinning stress and emotion regulation are susceptible to inflammatory insult. Although psychological stress is elevated, rsFC reduced, and CD16+ monocytes overexpressed in the brains of PWH, it is unclear whether the relationships amongst these variables differ compared to PWOH. An ethnically diverse sample of postmenopausal women, 24 PWH and 30 PWOH provided self-report mood surveys and provided peripheral blood specimens to quantify LPS-stimulated CD16+/- expression of TNF-α via flow cytometric analysis. An anatomical and resting state functional MRI scan were used to derive time-series metrics of connectivity between the medial prefrontal cortex (mPFC) and the nucleus accumbens (NAcc) as well as the amygdala. A positive association was observed between levels of perceived stress and CD16+/- TNF-α in both LPS-stimulated and unstimulated cells. PLWH showed lower connectivity between mPFC and NAcc. In turn, lower rsFC between these regions predicted greater psychological stress and proportion of CD16-, but not CD16+, cells expression of TNF-α. Neuroimmune effects of monocyte inflammation on the functional connectivity of mesolimbic regions critical for discrimination of uncertainty-safety and reward signals were observed in an ethnically diverse sample of postmenopausal women living with and without HIV. PWH showed lower mPFC-NAcc functional connectivity, which in turn was associated with greater perceived stress.

Exploration of gut microbiome and inflammation: A review on key signalling pathways

The gut microbiome, a crucial component of the human system, is a diverse collection of microbes that belong to the gut of human beings as well as other animals. These microbial communities continue to coexist harmoniously with their host organisms and perform various functions that affect the host's general health. Each person's gut microbiota has a unique makeup. The gut microbiota is well acknowledged to have a part in the local as well as systemic inflammation that underlies a number of inflammatory disorders (e.g., atherosclerosis, diabetes mellitus, obesity, and inflammatory bowel disease).The gut microbiota's metabolic products, such as short-chain fatty acids (butyrate, propionate, and acetate) inhibit inflammation by preventing immune system cells like macrophages and neutrophils from producing pro-inflammatory factors, which are triggered by the structural elements of bacteria (like lipopolysaccharide). The review's primary goal is to provide comprehensive and compiled data regarding the contribution of gut microbiota to inflammation and the associated signalling pathways.

RGS2 is an innate immune checkpoint for TLR4 and Gαq-mediated IFNγ generation and lung injury

IFNγ, a type II interferon secreted by immune cells, augments tissue responses to injury following pathogenic infections leading to lethal acute lung injury (ALI). Alveolar macrophages (AM) abundantly express Toll-like receptor-4 and represent the primary cell type of the innate immune system in the lungs. A fundamental question remains whether AM generation of IFNg leads to uncontrolled innate response and perpetuated lung injury. LPS induced a sustained increase in IFNg levels and unresolvable inflammatory lung injury in the mice lacking RGS2 but not in RGS2 null chimeric mice receiving WT bone marrow or receiving the RGS2 gene in AM. Thus, indicating RGS2 serves as a gatekeeper of IFNg levels in AM and thereby lung's innate immune response. RGS2 functioned by forming a complex with TLR4 shielding Gaq from inducing IFNg generation and AM inflammatory signaling. Thus, inhibition of Gaq blocked IFNg generation and subverted AM transcriptome from being inflammatory to reparative type in RGS2 null mice, resolving lung injury.

Highlights

RGS2 levels are inversely correlated with IFNγ in ARDS patient's AM.RGS2 in alveolar macrophages regulate the inflammatory lung injury.During pathogenic insult RGS2 functioned by forming a complex with TLR4 shielding Gαq from inducing IFNγ generation and AM inflammatory signaling.

eToc Blurb

Authors demonstrate an essential role of RGS2 in macrophages in airspace to promoting anti-inflammatory function of alveolar macrophages in lung injury. The authors provided new insight into the dynamic control of innate immune response by Gαq and RGS2 axis to prevent ALI.

Interplay between Systemic Glycemia and Neuroprotective Activity of Resveratrol in Modulating Astrocyte SIRT1 Response to Neuroinflammation

The flow of substances between the blood and the central nervous system is precisely regulated by the blood-brain barrier (BBB). Its disruption due to unbalanced blood glucose levels (hyper- and hypoglycemia) occurring in metabolic disorders, such as type 2 diabetes, can lead to neuroinflammation, and increase the risk of developing neurodegenerative diseases. One of the most studied natural anti-diabetic, anti-inflammatory, and neuroprotective compounds is resveratrol (RSV). It activates sirtuin 1 (SIRT1), a key metabolism regulator dependent on cell energy status. The aim of this study was to assess the astrocyte SIRT1 response to neuroinflammation and subsequent RSV treatment, depending on systemic glycemia. For this purpose, we used an optimized in vitro model of the BBB consisting of endothelial cells and astrocytes, representing microvascular and brain compartments (MC and BC), in different glycemic backgrounds. Astrocyte-secreted SIRT1 reached the highest concentration in hypo-, the lowest in normo-, and the lowest in hyperglycemic backgrounds. Lipopolysaccharide (LPS)-induced neuroinflammation caused a substantial decrease in SIRT1 in all glycemic backgrounds, as observed earliest in hyperglycemia. RSV partially counterbalanced the effect of LPS on SIRT1 secretion, most remarkably in normoglycemia. Our results suggest that abnormal glycemic states have a worse prognosis for RSV-therapy effectiveness compared to normoglycemia.

Extraction, Quantification, and Cytokine Inhibitory Response of Bakuchiol in Psoralea coryfolia Linn

(1) Background: The present investigation studies the optimization of extraction, quantification, and cytokine inhibitory effects bakuchiol (BKL) in Psoralea coryfolia Linn. (2) Methods: The seeds of Psoralea coryfolia cleaned, dried, and powdered. Different separation methods maceration, reflux, Soxhlet, and ultrasonic assisted extraction (UAE) were employed for the isolation of BKL by five pure solvents. The quantity of BKL was measured by high-performance liquid chromatography (HPLC) method to determine the highest yield percentage. The effect of optimized BKL was then tested in an animal model of sepsis induced by lipopolysaccharides (LPS). (3) Results: The UAE method was found to be the best among tested separation methods and yielded highest percentage of BKL in petroleum ether extract. Septic rats showed a significant elevation in levels of biochemical markers like AST, ALT, ALP, BIL, SCr, and BUN in plasma. Proinflammatory cytokines (TNF-α and IL-1) levels were also increased in LPS-induced animals. BKL has been found to significantly reverse these elevated levels as compared to the LPS-induced animals. (4) Conclusion: The present results suggest that BKL has positive effects when administered in animals with pathogenic shock by decreasing the circulating levels of biomarkers. Further studies are necessary to explore the clinical implications of such findings.

Impact of CD14 on Reactive Oxygen Species Production from Human Leukocytes Primed by Escherichia coli Lipopolysaccharides

Lipopolysaccharides (LPS) from Gram-negative bacteria prime human polymorphonuclear neutrophils (PMNs) via multicomponent receptor cluster including CD14 and MD-2·TLR4 for the enhanced release of reactive oxygen species (ROS) were triggered by bacterial derived peptide N-formyl-methionyl-leucyl-phenylalanine (fMLP). In this study, we investigated the impact of CD14 on LPS-induced priming of human PMNs for fMLP-triggered ROS generation (respiratory or oxidative) burst. Monoclonal antibodies against human CD14 (mAbs) as well as isotype-matched IgG2a did not influence significantly fMLP-triggered ROS production from LPS-unprimed PMNs. Anti-CD14 mAbs (clone UCHM-1) attenuated LPS-induced priming of PMNs as it had been mirrored by fMLP-triggered decrease of ROS production. Similar priming activity of S-LPS or Re-LPS from Escherichia coli for fMLP-triggered ROS release from PMNs was found. Obtained results suggest that glycosylphosphatidylinositol-anchored CD14 is the key player in LPS-induced PMN priming for fMLP-triggered ROS production. We believe that blockade of CD14 on the cell surface and clinical use of anti-CD14 mAbs or their Fab fragments may diminish the production of ROS and improve outcomes during cardiovascular diseases manifested by LPS-induced inflammation.

Gαi2 Signaling Regulates Inflammasome Priming and Cytokine Production by Biasing Macrophage Phenotype Determination

Macrophages exist as innate immune subsets that exhibit phenotypic heterogeneity and functional plasticity. Their phenotypes are dictated by inputs from the tissue microenvironment. G-protein-coupled receptors are essential in transducing signals from the microenvironment, and heterotrimeric Gα signaling links these receptors to downstream effectors. Several Gα_i-coupled G-protein-coupled receptors have been implicated in macrophage polarization. In this study, we use genetically modified mice to investigate the role of Gα_i2 on inflammasome activity and macrophage polarization. We report that Gα_i2 in murine bone marrow-derived macrophages (BMDMs) regulates IL-1β release after activation of the NLRP3, AIM2, and NLRC4 inflammasomes. We show this regulation stems from the biased polarity of Gα_i2 deficient (Gnai2 ^-/-) and RGS-insensitive Gα_i2 (Gnai2 ^G184S/G184S) BMDMs. We determined that although Gnai2 ^G184S/G184S BMDMs (excess Gα_i2 signaling) have a tendency toward classically activated proinflammatory (M1) phenotype, Gnai2^-/- BMDMs (Gα_i2 deficient) are biased toward alternatively activated anti-inflammatory (M2) phenotype. Finally, we find that Gα_i2-deficient macrophages have increased Akt activation and IFN-β production but defects in ERK1/2 and STAT3 activation after LPS stimulation. Gα_i2-deficient macrophages also exhibit increased STAT6 activation after IL-4 stimulation. In summary, our data indicates that excess Gα_i2 signaling promotes an M1 macrophage phenotype, whereas Gα_i2 signaling deficiency promotes an M2 phenotype. Understanding Gα_i2-mediated effects on macrophage polarization may bring to light insights regarding disease pathogenesis and the reprogramming of macrophages for the development of novel therapeutics.

Lipopolysaccharide-induced inflammation in monocytes/macrophages is blocked by liposomal delivery of Gi-protein inhibitor

Background

Lipopolysaccharide (LPS) is widely recognized as a potent activator of monocytes/macrophages, and its effects include an altered production of key mediators, such as inflammatory cytokines and chemokines. The involvement of G_i protein in mediating LPS effects has been demonstrated in murine macrophages and various cell types of human origin.

Purpose

The aim of the present work was to evaluate the potential of a G_i-protein inhibitor encapsulated in liposomes in reducing the inflammatory effects induced by LPS in monocytes/macrophages.

Materials and methods

Guanosine 5′-O-(2-thiodiphosphate) (GOT), a guanosine diphosphate analog that completely inhibits G-protein activation by guanosine triphosphate and its analogs, was encapsulated into liposomes and tested for anti-inflammatory effects in LPS-activated THP1 monocytes or THP1-derived macrophages. The viability of monocytes/macrophages after incubation with different concentrations of free GOT or liposome-encapsulated GOT was assessed by MTT assay. MAPK activation and production of IL1β, TNFα, IL6, and MCP1 were assessed in LPS-activated monocytes/macrophages in the presence or absence of free or encapsulated GOT. In addition, the effect of free or liposome-encapsulated GOT on LPS-stimulated monocyte adhesion to activated endothelium and on monocyte chemotaxis was evaluated.

Results

We report here that GOT-loaded liposomes inhibited activation of MAPK and blocked the production of the cytokines IL1β, TNFα, IL6, and MCP1 induced by LPS in monocytes and macrophages. Moreover, GOT encapsulated in liposomes reduced monocyte adhesion and chemotaxis. All demonstrated events were in contrast with free GOT, which showed reduced or no effect on monocyte/macrophage activation with LPS.

Conclusion

This study demonstrates the potential of liposomal GOT in blocking LPS proinflammatory effects in monocytes/macrophages.

Proinflammatory switch from Gαs to Gαi signaling by Glucagon-like peptide-1 receptor in murine splenic monocyte following burn injury

OBJECTIVE

Glucagon-like peptide-1 (GLP-1)-based therapy via G protein-coupled receptor (GPCR) GLP-1R, to attenuate hyperglycemia in critical care has attracted great attention. However, the exaggerated inflammation by GLP-1R agonist, Exendin-4, in a mouse model of burn injury was quite unexpected. Recent studies found that GPCR might elicit proinflammatory effects by switching from Gαs to Gαi signaling in the immune system. Thus, we aimed to investigate the possible Gαs to Gαi switch in GLP-1R signaling in monocyte following burn injury.

MATERIALS AND METHODS

Splenic monocytes from sham and burn mice 24 h following burn injury were treated with consecutive doses of Exendin-4 alone or in combination with an inhibitor of Gαi signaling (pertussis toxin, PTX), or a blocker of protein kinase A (H89). Cell viability was assessed by CCK-8, and the supernatant was collected for cytokine measurement by ELISA. Intracellular cAMP level, phosphorylated PKA activity, and nuclear NF-κB p65 were determined by ELISA, ERK1/2 activation was analyzed by Western blot. The expression of GLP-1R downstream molecules, Gαs, Gαi and G-protein coupled receptor kinase 2 (GRK2) were examined by immunofluorescence staining and Western blot.

RESULTS

Exendin-4 could inhibit the viability of monocyte from sham rather than burn mice. Unexpectedly, it could also reduce TNF-α secretion from sham monocyte while increase it from burn monocyte. The increased secretion of TNF-α by Exendin-4 from burn monocyte could be reversed by pretreatment of PTX or H89. Accordingly, Exendin-4 could stimulates cAMP production dose dependently from sham instead of burn monocyte. However, the blunt cAMP production from burn monocyte was further suppressed by pretreatment of PTX or H89 after 6-h incubation. Nevertheless, phosphorylated PKA activity was significantly increased by low dose of Exendin-4 in sham monocyte, by contrast, it was enhanced by high dose of Exendin-4 in burn monocyte after 1-h incubation. Following Exendin-4 treatment for 2 h ex vivo, total nuclear NF-κB and phosphorylated NF-κB activity, as well as cytoplasmic pERK1/2 expressions were reduced in sham monocyte, however, only pERK1/2 was increased by Exendin-4 in burn monocytes. Moreover, reduced expressions of GLP-1R, GRK-2 and Gαs in contrast with increased expression of Gαi were identified in burn monocyte relative to sham monocyte.

CONCLUSIONS

This study presents an unexpected proinflammatory switch from Gαs to Gαi signaling in burn monocyte, which promotes ERK1/2 and NF-κB activation and the downstream TNF-α secretion. This phenomenon is most probably responsible for proinflammatory response evoked by Gαs agonist Exendin-4 following burn injury.

Implication of G i proteins and Src tyrosine kinases in endotoxin-induced signal transduction events and mediator production

Previous studies have suggested that heterotrimeric G proteins and tyrosine kinases may be involved in lipopolysaccharide (LPS) signaling events. Signal transduction pathways activated by LPS were examined in human promonocytic THP-1 cells. We hypothesized that Gi proteins and Src tyrosine kinase differentially affect mitogen-activated protein (MAP) kinases (MAPK) and nuclear factor kappa (NF- B) activation. Post-receptor coupling to G i proteins were examined using pertussis toxin (PTx), which inhibits G i receptor-coupling. The involvement of the Src family of tyrosine kinases was examined using the selective Src tyrosine kinase inhibitor pyrazolopyrimidine-2 (PP2). Pretreatment of THP-1 cells with PTx attenuated LPS-induced activation of c-Jun-N-terminal kinase (JNK) and p38 kinase, and production of tumor necrosis factor-alpha (TNF-) and thromboxane B2 (TxB2). Pretreatment with PP2 inhibited TNF- and TxB2 production, but had no effect on p38 kinase or JNK signaling. Therefore, the G i-coupled signaling pathways and Src tyrosine kinase-coupled signaling pathways are necessary for LPS-induced TNF- and TxB2 production, but differ in their effects on MAPK activation. Neither PTx nor PP2 inhibited LPS-induced activation of interleukin receptor activated kinase (IRAK) or inhibitedtranslocation of NF- B. However, PP2 inhibitedLPS-inducedNF-B transactivation of a luciferase reporter gene construct in a concentration-dependent manner. Thus, LPS induction of Src tyrosine kinases may be essential in downstream NF- B transactivation of genes following DNA binding. PTx had no effect on NF- B activation of the reporter construct. These data suggest upstream divergence in signaling through G i pathways leading to MAPK activation and other signaling events leading to I B degradation and NF- B DNA binding.

Lipopolysaccharide binds to and activates A1 adenosine receptors on human pulmonary artery endothelial cells

Previously, it was reported that A1 adenosine receptor antagonists prevent endotoxin-inducedacute lung injury and pulmonary arterial endothelial cell damage. In competition radioligand binding experiments in membranes prepared from human pulmonary artery endothelial cells (PAECs), lipopolysaccharides (LPSs) of Escherichia coli, Salmonella typhimurium, Klebsiella pneumoniae, and Pseudomonas aeruginosa displaced the binding of a selective A adenosine receptor antagonist [125I]-BWA844U (IC 50 values: 195 ng/ml, 290 ng/ml, 602 ng/ml, and 6931 ng/ml, respectively)in a dose-dependent, competitive manner. There was no displacement of this radioligand by enterotoxin (≤ 10 μg/ml), diphosphoryl lipid A (≤ 10μg/ml), and glycolipids, monosialoganglioside(≤ 1μg/ml), lactocerebroside (≤ 100μg/ml), or NBD galactocerebroside (≤ 100 μg/ml). Based on calculated IC values, LPS ( E. coli, IC50 111 ng/ml) 50 6 displaced the selective A1 adenosine receptor agonist, [3H]-2-chloro, N -cyclopentyladenosine (CCPA) in human PAECs with a potency profile, CCPA > LPS > 2-phenylaminoadenosine (CV 1808), a selective A2 adenosine receptor agonist. The potency profile for displacement of the selective A μ 2a adenosine receptor agonist [ 3H]-CGS 21680 was CV 1808 > CCPA. LPS ( E. coli 0.1 pg/ml—10 g/ml) did not displace [3H]-CGS 21680 binding. In human PAECs, IL-6 and TXA2 release induced by LPS (0—1 μg/ml) or CCPA (0—1 μM) at high doses was significantly reduced by the selective A1 adenosine receptor antagonist, 8-cyclopentyl-1,3-dipropylxanthine(DPCPX; 1 μM). These data suggest that LPS binds to and activates A1 adenosine receptors on human PAECs to induce the release of IL-6 and TXA 2. Activation of A1 adenosine receptors on human PAECs by LPS, may contribute to the pathophysiology of acute lung injury associated with Gram-negative septicemia and endotoxemia.

Decay-accelerating factor (DAF/CD55) is a functional active element of the LPS receptor complex

Previously, we identified an 80 kDa membrane protein (LMP80) that is capable of binding to LPS and lipid A in the presence of LBP and sCD14. LMP80 could also be detected after immuno-coprecipitation of cell membranes with LPS and lipid A, indicating a physical contact of LMP80 and LPS/lipid A. Further analysis and peptide sequencing revealed that LMP80 is identical to CD55 (decay accelerating factor, DAF), a regulatory molecule of the complement cascade. Transfection of LPS-hyporesponsive Chinese hamster ovary (CHO) cells with human CD55 resulted in the translocation of NF-κB upon stimulation with LPS or lipid A. Our results demonstrate a new functional role of CD55 as a molecule able to mediate LPS-induced activation of cells that may be part of a multimeric LPS receptor complex.

Structure-activity relationship of mastoparan analogs: Effects of the number and positioning of Lys residues on secondary structure, interaction with membrane-mimetic systems and biological activity

In this study, a series of mastoparan analogs were engineered based on the strategies of Ala and Lys scanning in relation to the sequences of classical mastoparans. Ten analog mastoparans, presenting from zero to six Lys residues in their sequences were synthesized and assayed for some typical biological activities for this group of peptide: mast cell degranulation, hemolysis, and antibiosis. In relation to mast cell degranulation, the apparent structural requirement to optimize this activity was the existence of one or two Lys residues at positions 8 and/or 9. In relation to hemolysis, one structural feature that strongly correlated with the potency of this activity was the number of amino acid residues from the C-terminus of each peptide continuously embedded into the zwitterionic membrane of erythrocytes-mimicking liposomes, probably due to the contribution of this structural feature to the membrane perturbation. The antibiotic activity of mastoparan analogs was directly dependent on the apparent extension of their hydrophilic surface, i.e., their molecules must have from four to six Lys residues between positions 4 and 11 of the peptide chain to achieve activities comparable to or higher than the reference antibiotic compounds. The optimization of the antibacterial activity of the mastoparans must consider Lys residues at the positions 4, 5, 7, 8, 9, and 11 of the tetradecapeptide chain, with the other positions occupied by hydrophobic residues, and with the C-terminal residue in the amidated form. These requirements resulted in highly active AMPs with greatly reduced (or no) hemolytic and mast cell degranulating activities.

Gαi1 and Gαi3 regulate macrophage polarization by forming a complex containing CD14 and Gab1

Heterotrimeric G proteins have been implicated in Toll-like receptor 4 (TLR4) signaling in macrophages and endothelial cells. However, whether guanine nucleotide-binding protein G(i) subunit alpha-1 and alpha-3 (Gαi1/3) are required for LPS responses remains unclear, and if so, the underlying mechanisms need to be studied. In this study, we demonstrated that, in response to LPS, Gαi1/3 form complexes containing the pattern recognition receptor (PRR) CD14 and growth factor receptor binding 2 (Grb2)-associated binding protein (Gab1), which are required for activation of PI3K-Akt signaling. Gαi1/3 deficiency decreased LPS-induced TLR4 endocytosis, which was associated with decreased phosphorylation of IFN regulatory factor 3 (IRF3). Gαi1/3 knockdown in bone marrow-derived macrophage cells (Gαi1/3 KD BMDMs) exhibited an M2-like phenotype with significantly suppressed production of TNF-α, IL-6, IL-12, and NO in response to LPS. The altered polarization coincided with decreased Akt activation. Further, Gαi1/3 deficiency caused LPS tolerance in mice. In vitro studies revealed that, in LPS-tolerant macrophages, Gαi1/3 were down-regulated partially by the proteasome pathway. Collectively, the present findings demonstrated that Gαi1/3 can interact with CD14/Gab1, which modulates macrophage polarization in vitro and in vivo.

Caveolin-1 Tyr14 phosphorylation induces interaction with TLR4 in endothelial cells and mediates MyD88-dependent signaling and sepsis-induced lung inflammation

Activation of TLR4 by the endotoxin LPS is a critical event in the pathogenesis of Gram-negative sepsis. Caveolin-1, the signaling protein associated with caveolae, is implicated in regulating the lung inflammatory response to LPS; however, the mechanism is not understood. In this study, we investigated the role of caveolin-1 in regulating TLR4 signaling in endothelial cells. We observed that LPS interaction with CD14 in endothelial cells induced Src-dependent caveolin-1 phosphorylation at Tyr(14). Using a TLR4-MD2-CD14-transfected HEK-293 cell line and caveolin-1-deficient (cav-1(-/-)) mouse lung microvascular endothelial cells, we demonstrated that caveolin-1 phosphorylation at Tyr(14) following LPS exposure induced caveolin-1 and TLR4 interaction and, thereby, TLR4 activation of MyD88, leading to NF-κB activation and generation of proinflammatory cytokines. Exogenous expression of phosphorylation-deficient Y14F caveolin-1 mutant in cav-1(-/-) mouse pulmonary vasculature rendered the mice resistant to LPS compared with reintroduction of wild-type caveolin-1. Thus, caveolin-1 Y14 phosphorylation was required for the interaction with TLR4 and activation of TLR4-MyD88 signaling and sepsis-induced lung inflammation. Inhibiting caveolin-1 Tyr(14) phosphorylation and resultant inactivation of TLR4 signaling in pulmonary vascular endothelial cells represent a novel strategy for preventing sepsis-induced lung inflammation and injury.

Caveolin-1 Tyr14 phosphorylation induces interaction with TLR4 in endothelial cells and mediates MyD88-dependent signaling and sepsis-induced lung inflammation

Activation of TLR4 by the endotoxin LPS is a critical event in the pathogenesis of Gram-negative sepsis. Caveolin-1, the signaling protein associated with caveolae, is implicated in regulating the lung inflammatory response to LPS; however, the mechanism is not understood. In this study, we investigated the role of caveolin-1 in regulating TLR4 signaling in endothelial cells. We observed that LPS interaction with CD14 in endothelial cells induced Src-dependent caveolin-1 phosphorylation at Tyr(14). Using a TLR4-MD2-CD14-transfected HEK-293 cell line and caveolin-1-deficient (cav-1(-/-)) mouse lung microvascular endothelial cells, we demonstrated that caveolin-1 phosphorylation at Tyr(14) following LPS exposure induced caveolin-1 and TLR4 interaction and, thereby, TLR4 activation of MyD88, leading to NF-κB activation and generation of proinflammatory cytokines. Exogenous expression of phosphorylation-deficient Y14F caveolin-1 mutant in cav-1(-/-) mouse pulmonary vasculature rendered the mice resistant to LPS compared with reintroduction of wild-type caveolin-1. Thus, caveolin-1 Y14 phosphorylation was required for the interaction with TLR4 and activation of TLR4-MyD88 signaling and sepsis-induced lung inflammation. Inhibiting caveolin-1 Tyr(14) phosphorylation and resultant inactivation of TLR4 signaling in pulmonary vascular endothelial cells represent a novel strategy for preventing sepsis-induced lung inflammation and injury.

Neu1 sialidase and matrix metalloproteinase-9 cross-talk regulates nucleic acid-induced endosomal TOLL-like receptor-7 and -9 activation, cellular signaling and pro-inflammatory responses

The precise mechanism(s) by which intracellular TOLL-like receptors (TLRs) become activated by their ligands remains unclear. Here, we report a molecular organizational G-protein coupled receptor (GPCR) signaling platform to potentiate a novel mammalian neuraminidase-1 (Neu1) and matrix metalloproteinase-9 (MMP-9) cross-talk in alliance with neuromedin B GPCR, all of which form a tripartite complex with TLR-7 and -9. siRNA silencing Neu1, MMP-9 and neuromedin-B GPCR in RAW-blue macrophage cells significantly reduced TLR7 imiquimod- and TLR9 ODN1826-induced NF-κB (NF-κB-pSer(536)) activity. Tamiflu, specific MMP-9 inhibitor, neuromedin B receptor specific antagonist BIM23127, and the selective inhibitor of whole heterotrimeric G-protein complex BIM-46174 significantly block nucleic acid-induced TLR-7 and -9 MyD88 recruitment, NF-κB activation and proinflammatory TNFα and MCP-1 cytokine responses. For the first time, Neu1 clearly plays a central role in mediating nucleic acid-induced intracellular TLR activation, and the interactions involving NMBR-MMP9-Neu1 cross-talk constitute a novel intracellular TLR signaling platform that is essential for NF-κB activation and pro-inflammatory responses.

Toll-like receptor-induced inflammatory cytokines are suppressed by gain of function or overexpression of Gα(i2) protein

Previous studies have implicated a role of Gα(i) proteins as co-regulators of Toll-like receptor (TLR) activation. These studies largely derived from examining the effect of Gα(i) protein inhibitors or genetic deletion of Gα(i) proteins. However, the effect of increased Gα(i) protein function or Gα(i) protein expression on TLR activation has not been investigated. We hypothesized that gain of function or increased expression of Gα(i) proteins suppresses TLR2- and TLR4-induced inflammatory cytokines. Novel transgenic mice with genomic "knock-in" of a regulator of G protein signaling (RGS)-insensitive Gnai2 allele (Gα(i2)(G184S/G184S) ; GS/GS) were employed. These mice express essentially normal levels of Gα(i2) protein; however, the Gα(i2) is insensitive to its negative regulator RGS thus rendering more sustained Gα(i2) protein activation following ligand/receptor binding. In subsequent studies, we generated Raw 264.7 cells that stably overexpress Gα(i2) protein (Raw Gα(i2)). Peritoneal macrophages, splenocytes, and mouse embryonic fibroblasts (MEF) were isolated from WT and GS/GS mice and were stimulated with LPS, Pam3CSK4, or Poly (I:C). We also subjected WT and GS/GS mice to endotoxic shock (LPS, 25 mg/kg i.p.) and plasma tumor necrosis factor alpha (TNF-α) and interleukin (IL)-6 production were determined. We found that in vitro LPS and Pam3CSK4-induced TNF-α, and IL-6 production are decreased in macrophages from GS/GS mice compared with WT mice (p < 0.05). In vitro, LPS and Pam3CSK4 induced IL-6 production in splenocytes, and in vivo, LPS-induced IL-6 were suppressed in GS/GS mice. Poly (I:C)-induced TNF-α, and IL-6 in vitro demonstrated no difference between GS/GS mice and WT mice. LPS-induced IL-6 production was inhibited in MEFs from GS/GS mice similarly to macrophage and splenocytes. In parallel studies, Raw Gα(i2) cells also exhibit decreased TNF-α and IL-6 production in response to LPS and Pam3CSK4. These studies support our hypothesis that Gα(i2) proteins are novel negative regulators of TLR activation.

Tuning innate immune activation by surface texturing of polymer microparticles: the role of shape in inflammasome activation

Polymeric microparticles have been widely investigated as platforms for delivery of drugs, vaccines, and imaging contrast agents and are increasingly used in a variety of clinical applications. Microparticles activate the inflammasome complex and induce the processing and secretion of IL-1β, a key innate immune cytokine. Recent work suggests that although receptors are clearly important for particle phagocytosis, other physical characteristics, especially shape, play an important role in the way microparticles activate cells. We examined the role of particle surface texturing not only on uptake efficiency but also on the subsequent immune cell activation of the inflammasome. Using a method based on emulsion processing of amphiphilic block copolymers, we prepared microparticles with similar overall sizes and surface chemistries but having either smooth or highly microtextured surfaces. In vivo, textured (budding) particles induced more rapid neutrophil recruitment to the injection site. In vitro, budding particles were more readily phagocytosed than smooth particles and induced more lipid raft recruitment to the phagosome. Remarkably, budding particles also induced stronger IL-1β secretion than smooth particles through activation of the NLRP3 inflammasome. These findings demonstrate a pronounced role of particle surface topography in immune cell activation, suggesting that shape is a major determinant of inflammasome activation.

Regulation of Toll-like receptor 4-mediated immune responses through Pasteurella multocida toxin-induced G protein signalling

Background

Lipopolysaccharide (LPS)-triggered Toll-like receptor (TLR) 4-signalling belongs to the key innate defence mechanisms upon infection with Gram-negative bacteria and triggers the subsequent activation of adaptive immunity. There is an active crosstalk between TLR4-mediated and other signalling cascades to secure an effective immune response, but also to prevent excessive inflammation. Many pathogens induce signalling cascades via secreted factors that interfere with TLR signalling to modify and presumably escape the host response. In this context heterotrimeric G proteins and their coupled receptors have been recognized as major cellular targets. Toxigenic strains of Gram-negative Pasteurella multocida produce a toxin (PMT) that constitutively activates the heterotrimeric G proteins Gα_q, Gα₁₃ and Gα_i independently of G protein-coupled receptors through deamidation. PMT is known to induce signalling events involved in cell proliferation, cell survival and cytoskeleton rearrangement.

Results

Here we show that the activation of heterotrimeric G proteins through PMT suppresses LPS-stimulated IL-12p40 production and eventually impairs the T cell-activating ability of LPS-treated monocytes. This inhibition of TLR4-induced IL-12p40 expression is mediated by Gα_i-triggered signalling as well as by Gβγ-dependent activation of PI3kinase and JNK.

Taken together we propose the following model: LPS stimulates TLR4-mediated activation of the NFĸB-pathway and thereby the production of TNF-α, IL-6 and IL-12p40. PMT inhibits the production of IL-12p40 by Gα_i-mediated inhibition of adenylate cyclase and cAMP accumulation and by Gβγ-mediated activation of PI3kinase and JNK activation.

Conclusions

On the basis of the experiments with PMT this study gives an example of a pathogen-induced interaction between G protein-mediated and TLR4-triggered signalling and illustrates how a bacterial toxin is able to interfere with the host’s immune response.

Beneficial effect of a CXCR4 agonist in murine models of systemic inflammation

The chemokine CXC receptor 4 (CXCR4) is activated by stromal cell-derived factor (SDF-1α). CXCR4 may be part of a lipopolysaccharide (LPS) sensing co-clustering complex that modulates TLR4 activation and evidence suggest that SDF-1α can activate anti-inflammatory signaling pathways and suppress inflammation. In the present study we examined the hypothesis that the SDF-1α peptide analog and CXCR4 agonist CTCE-0214 is anti-inflammatory in three distinct models of murine systemic inflammation. Our findings demonstrate that CTCE-0214 in vivo significantly suppressed plasma tumor necrosis factor alpha (TNF-α) increases in acute endotoxemia and following zymosan-induced multiple organ dysfunction syndrome (MODS). In both models, CTCE-0214 did not suppress plasma increases in the anti-inflammatory cytokine interleukin (IL)-10. CTCE-0214 improved survival without antibiotics in a model of severe sepsis induced by cecal ligation and puncture (CLP). CTCE-0214 also decreased plasma increases in IL-6 but not TNF-α and IL-10 in response to CLP-induced inflammation. We demonstrated in a moderately severe model of CLP (one puncture) that IL-6 levels at 24 h were similar to sham controls. However in severe CLP (two punctures) plasma IL-6 levels were markedly elevated. Plasma SDF-1α levels varied inversely with the plasma IL-6. In addition to the beneficial effect of CTCE-0214 in these models of systemic inflammation in vivo, we also demonstrated that the analog dose dependently suppressed LPS-induced IL-6 production in bone marrow-derived macrophages. CTCE-0214 therefore may be beneficial in controlling inflammation sepsis and systemic inflammatory syndromes.

Neu1 sialidase and matrix metalloproteinase-9 cross-talk is essential for Toll-like receptor activation and cellular signaling

The signaling pathways of mammalian Toll-like receptors (TLRs) are well characterized, but the precise mechanism(s) by which TLRs are activated upon ligand binding remains poorly defined. Recently, we reported a novel membrane sialidase-controlling mechanism that depends on ligand binding to its TLR to induce mammalian neuraminidase-1 (Neu1) activity, to influence receptor desialylation, and subsequently to induce TLR receptor activation and the production of nitric oxide and proinflammatory cytokines in dendritic and macrophage cells. The α-2,3-sialyl residue of TLR was identified as the specific target for hydrolysis by Neu1. Here, we report a membrane signaling paradigm initiated by endotoxin lipopolysaccharide (LPS) binding to TLR4 to potentiate G protein-coupled receptor (GPCR) signaling via membrane Gα(i) subunit proteins and matrix metalloproteinase-9 (MMP9) activation to induce Neu1. Central to this process is that a Neu1-MMP9 complex is bound to TLR4 on the cell surface of naive macrophage cells. Specific inhibition of MMP9 and GPCR Gα(i)-signaling proteins blocks LPS-induced Neu1 activity and NFκB activation. Silencing MMP9 mRNA using lentivirus MMP9 shRNA transduction or siRNA transfection of macrophage cells and MMP9 knock-out primary macrophage cells significantly reduced Neu1 activity and NFκB activation associated with LPS-treated cells. These findings uncover a molecular organizational signaling platform of a novel Neu1 and MMP9 cross-talk in alliance with TLR4 on the cell surface that is essential for ligand activation of TLRs and subsequent cellular signaling.

Heterotrimeric Gα(i) proteins are regulated by lipopolysaccharide and are anti-inflammatory in endotoxemia and polymicrobial sepsis

Previous studies have implicated a role of heterotrimeric Gα(i) proteins in lipopolysaccharide (LPS)-induced inflammatory responses. We hypothesized that Toll-like receptor (TLR) signaling regulates Gα(i) proteins, which are anti-inflammatory in endotoxemia and polymicrobial sepsis. RAW 264.7 cells were stimulated with LPS and the Gα(i)-GTP protein complex was immunoprecipitated with a Gα(i) protein activation assay. In subsequent in vivo studies, the Gα(i) protein inhibitor pertussis toxin (PTx) or G(i) protein agonist mastoparan (MP-7) were administrated prior to endotoxemia. LPS-induced pro-inflammatory cytokines and mortality were determined. To examine the role of Gα(i2) in sepsis, Gα(i2) (-/-) and wildtype (WT) mice were subjected to cecal ligation and puncture (CLP) and monitored every 24 h for 120 h. Other mice were sacrificed 24 h after CLP. Peritoneal fluid, blood, and tissue samples were collected. Plasma pro-inflammatory cytokine production, bacterial load in peritoneal fluid, blood and lung tissue, myeloperoxidase (MPO) activity in lung and liver and different immune cell populations in spleen were studied. We found that Gα(i) proteins are rapidly activated by LPS followed by rapid inactivation. These studies provide the first direct evidence that Gα(i) proteins are modulated by TLR signaling. In following studies, PTx augmented LPS-induced plasma TNFα, IL-6, whereas MP-7 suppressed LPS-induced TNFα and decreased LPS-induced mortality. In sepsis studies, the survival rate post-CLP was significantly decreased in the Gα(i2) (-/-) mice compared to WT mice. CLP-induced plasma TNFα, IL-6, bacterial load in peritoneal fluid, blood and lung tissue and lung and liver MPO activity were significantly increased in Gα(i2) (-/-) compared to WT mice. Gα(i2) (-/-) mice also exhibited increased Th1 and Th2 responses compared to WT mice. Taken together, Gα(i) proteins are activated by LPS and negatively regulate endotoxemia and sepsis. Understanding the role of Gα(i2) protein in regulation of the inflammatory response in sepsis may provide novel targets for treatment of sepsis.

Heterotrimeric G protein signaling outside the realm of seven transmembrane domain receptors

Heterotrimeric G proteins, consisting of the guanine nucleotide-binding Galpha subunits with GTPase activity and the closely associated Gbeta and Ggamma subunits, are important signaling components for receptors with seven transmembrane domains (7TMRs). These receptors, also termed G protein-coupled receptors (GPCRs), act as guanine nucleotide exchange factors upon agonist stimulation. There is now accumulating evidence for noncanonical functions of heterotrimeric G proteins independent of 7TMR coupling. Galpha proteins belonging to all 4 subfamilies, including G(s), G(i), G(q), and G(12) are found to play important roles in receptor tyrosine kinase signaling, regulation of oxidant production, development, and cell migration, through physical and functional interaction with proteins other than 7TMRs. Association of Galpha with non-7TMR proteins also facilitates presentation of these G proteins to specific cellular microdomains. This Minireview aims to summarize our current understanding of the noncanonical roles of Galpha proteins in cell signaling and to discuss unresolved issues including regulation of Galpha activation by proteins other than the 7TMRs.

Association of CD14 variant with prostate cancer in African American men

BACKGROUND

African American men have the highest rates of prostate cancer worldwide, and immunogenetic studies suggest that people of African descent have increased susceptibility to diseases of inflammation. Since genetic susceptibility is an etiological factor in prostate cancer, we hypothesize that sequence variants in the promoter region of the CD14 gene that regulate inflammation may modify individual susceptibility to this disease.

METHODS

The CD14 promoter was screened for single-nucleotide polymorphisms (SNPs) using dHPLC. One variant, -260 C>T (rs2569190), was genotyped via restriction digest in all study participants (264 cases and 188 controls). The association of disease status and the polymorphism was analyzed by unconditional logistic regression. Odds ratios with 95% confidence intervals were calculated, stratifying by ethnicity and adjusting for age. Two-sided P-values of < or =0.05 were considered as statistically significant.

RESULTS

Eleven variants (four novel) were identified in the promoter region of CD14. A marginal association between the C genotypes (C/C + C/T) and prostate cancer was found (P = 0.07). When stratified by age, among men > or =55 years of age, the C genotypes were significantly associated with prostate cancer (P < 0.05). When stratified by self-reported ethnicity, African American males who had the C genotypes were at a higher risk for prostate cancer (P < 0.05).

CONCLUSIONS

This is the first study to show an association between the C genotypes of the CD14 (-260) variant and prostate cancer which supports the hypothesis that genetic variation in the inflammatory process can contribute to prostate cancer susceptibility in African American men.

TLR accessory molecules

Accessory molecules are required for microbial recognition by Toll-like receptor (TLR), subsequent signaling, and regulation of ensuing immune responses. Accessory molecules regulate TLRs on the cell surface (MD-2 and RP105), or in the endoplasmic reticulum (ER) (Unc93B, PRAT4A, and gp96). Other types of accessory molecules modulate TLR responses by acting directly on TLR ligands (CD14, CD36, HMGB1, and the antimicrobial peptide LL37). These molecules cooperate with TLR, inducing appropriate defense mechanisms. It is important to understand how TLR signaling is controlled by these accessory molecules. These accessory molecules could be promising targets for therapeutic intervention in infectious disease and immune disorders.

Physiology of the prion protein

Prion diseases are transmissible spongiform encephalopathies (TSEs), attributed to conformational conversion of the cellular prion protein (PrP(C)) into an abnormal conformer that accumulates in the brain. Understanding the pathogenesis of TSEs requires the identification of functional properties of PrP(C). Here we examine the physiological functions of PrP(C) at the systemic, cellular, and molecular level. Current data show that both the expression and the engagement of PrP(C) with a variety of ligands modulate the following: 1) functions of the nervous and immune systems, including memory and inflammatory reactions; 2) cell proliferation, differentiation, and sensitivity to programmed cell death both in the nervous and immune systems, as well as in various cell lines; 3) the activity of numerous signal transduction pathways, including cAMP/protein kinase A, mitogen-activated protein kinase, phosphatidylinositol 3-kinase/Akt pathways, as well as soluble non-receptor tyrosine kinases; and 4) trafficking of PrP(C) both laterally among distinct plasma membrane domains, and along endocytic pathways, on top of continuous, rapid recycling. A unified view of these functional properties indicates that the prion protein is a dynamic cell surface platform for the assembly of signaling modules, based on which selective interactions with many ligands and transmembrane signaling pathways translate into wide-range consequences upon both physiology and behavior.

Chemokine receptor 4 (CXCR4) is part of the lipopolysaccharide "sensing apparatus"

Recognition of bacterial lipopolysaccharide (LPS) by the innate immune system involves at least three receptor molecules: CD14, TLR4 and MD-2. Additional receptor components such as heat shock proteins, chemokine receptor 4 (CXCR4), or CD55 have been suggested to be part of this activation cluster; possibly acting as additional LPS transfer molecules. Our group has previously identified CXCR4 as a component of the "LPS-sensing apparatus". In this study we aimed to elucidate the role that CXCR4 plays in innate immune responses to LPS. Here we demonstrate that CXCR4 transfection results in responsiveness to LPS. Fluorescence correlation spectroscopy experiments further showed that LPS directly interacts with CXCR4. Our data suggest that CXCR4 is not only involved in LPS binding but is also responsible for triggering signalling, especially mitogen-activated protein kinases in response to LPS. Finally, co-clustering of CXCR4 with other LPS receptors seems to be crucial for LPS signalling, thus suggesting that CXCR4 is a functional part of the multimeric LPS "sensing apparatus".

beta-Arrestin 2: a Negative Regulator of Inflammatory Responses in Polymorphonuclear Leukocytes

Heterotrimeric Gi proteins have been previously implicated in signaling leading to inflammatory mediator production induced by bacterial lipopolysaccharide (LPS). beta-arrestins are ubiquitously expressed proteins that alter G-protein-coupled receptors signaling. beta-arrestin 2 plays a multifaceted role as a scaffold protein in regulating cellular inflammatory responses. Polymorphonuclear leukocytes (PMNs) activated by LPS induce inflammatory responses resulting in organ injury during sepsis. We hypothesized that beta-arrestin 2 is a critical modulator of inflammatory responses in PMNs. To examine the potential role of beta-arrestin 2 in LPS-induced cellular activation, we studied homozygous beta-arrestin 2 (-/-), heterozygous (+/-), and wildtype (+/+) mice. PMNs were stimulated with LPS for 16h. There was increased basal TNFalpha and IL-6 production in the beta-arrestin 2 (-/-) compared to both beta-arrestin 2 (+/-) and (+/+) cells. LPS failed to stimulate TNFalpha production in the beta-arrestin 2 (-/-) PMNs. However, LPS stimulated IL-6 production was increased in the beta-arrestin 2 (-/-) cells compared to (+/+) cells. In subsequent studies, peritoneal PMN recruitment was increased 81% in the beta-arrestin 2 (-/-) mice compared to (+/+) mice (p<0.05). beta-arrestin 2 deficiency resulted in an augmented expression of CD18 and CD62L (p<0.05). In subsequent studies, beta-arrestin 2 (-/-) and (+/+) mice were subjected to cecal ligation and puncture (CLP) and lung was collected and analyzed for myeloperoxidase activity (MPO) as index of PMNs infiltrate. CLP-induced MPO activity was significantly increased (p<0.05) in the beta-arrestin 2 (-/-) compared to (+/+) mice. These studies demonstrate that beta-arrestin 2 is a negative regulator of PMN activation and pulmomary leukosequestration in response to polymicrobial sepsis.

Differential regulation of lipopolysaccharide and Gram-positive bacteria induced cytokine and chemokine production in macrophages by Galpha(i) proteins

Heterotrimeric G(i) proteins play a role in signalling activated by lipopolysaccharide (LPS), Staphylococcus aureus (SA) and group B streptococci (GBS), leading to production of inflammatory mediators. We hypothesized that genetic deletion of G(i) proteins would alter cytokine and chemokine production induced by LPS, SA and GBS stimulation. LPS-induced, heat-killed SA-induced and heat-killed GBS-induced cytokine and chemokine production in peritoneal macrophages from wild-type (WT), Galpha(i2) (-/-) or Galpha(i1/3) (-/-) mice were investigated. LPS induced production of tumour necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6), IL-10 and interferon-gamma-inducible protein-10 (IP-10); SA induced TNF-alpha, and IL-1beta production; and GBS induced TNF-alpha, IL-6, IL-1beta, macrophage inflammatory protein-1alpha (MIP-1alpha) and keratinocyte chemoattract (KC) production were all decreased (P < 0.05) in Galpha(i2) (-/-) or Galpha(i1/3) (-/-) mice compared with WT mice. In contrast to the role of G(i) proteins as a positive regulator of mediators, LPS-induced production of MIP-1alpha and granulocyte-macrophage colony-stimulating factor (GM-CSF) were increased in macrophages from Galpha(i1/3) (-/-) mice, and SA-induced MIP-1alpha production was increased in both groups of Galpha(i) protein-depleted mice. LPS-induced production of KC and IL-1beta, SA-induced production of GM-CSF, KC and IP-10, and GBS-induced production of IL-10, GM-CSF and IP-10 were unchanged in macrophages from Galpha(i2) (-/-) or Galpha(i1/3) (-/-) mice compared with WT mice. These data suggest that G(i2) and G(i1/3) proteins are both involved and differentially regulate murine inflammatory cytokine and chemokine production in response to both LPS and Gram-positive microbial stimuli.

Beta-arrestins 1 and 2 differentially regulate LPS-induced signaling and pro-inflammatory gene expression

Toll like receptors, the critical receptor family in innate immunity, have been shown to signal via both ERK 1/2 and transcription factor NFkappaB. beta-Arrestins 1 and 2 have recently been implicated in modulation of NFkappaB signaling and ERK 1/2 activation. Using a number of approaches: mouse embryonic fibroblasts (MEF) from wild-type (WT), beta-arrestins knockouts (KO), beta-arrestins 1 and 2 double KO, and MEFs with reconstituted WT beta-arrestins in the double KO cells, RNA interference (siRNA) specific knockdown of beta-arrestins, and overexpression of WT beta-arrestins, it was demonstrated that beta-arrestin 2 positively regulates LPS-induced ERK 1/2 activation and both beta-arrestins 1 and 2 negatively regulate LPS-induced NFkappaB activation. Also beta-arrestin 2 positively regulate LPS-induced IL-6 production and both beta-arrestins 1 and 2 positively regulate LPS-induced IL-8 production. The specific ERK1/2 inhibitor PD98059 significantly decreased LPS-induced IL-6 and IL-8 production suggesting that IL-6 and IL-8 production is, in part, mediated by ERK 1/2 activation. Over expression of wild type beta-arrestins 1 and 2 had no effect on LPS-induced ERK1/2 activation and LPS-induced IL-8 production suggesting that endogenous beta-arrestins 1 and 2 are sufficient to mediate maximum ERK 1/2 activity and IL-8 production. beta-Arrestins thus not only negatively regulate LPS-induced NFkappaB activation but also positively regulate ERK 1/2 activation and specific pro-inflammatory gene expression. Understanding the role of beta-arrestins in regulation of TLR signaling pathways may provide novel insights into control mechanisms for inflammatory gene expression.

Phosphatidyl inositol-3-phosphate kinase mediates CD14 dependent signaling

Lipopolysaccharide (LPS), a component of the cell wall of Gram-negative bacteria, is an important mediator of innate immunity and septic shock, but the exact mechanisms mediating cellular LPS recognition and the subsequent translation to inflammatory gene expression remain incompletely understood. CD14 has been established as a receptor that confers high sensitivity to LPS in cells of the myeloid lineage, probably by presenting LPS to Toll receptors. We use an anti CD14 blocking antibody to define a LPS stimulus that activates only this high affinity component of the LPS receptor and then examine CD14 dependent signaling events that are activated in response to LPS stimulation. We describe a novel LPS activated signaling pathway in human PBMC that leads to cytokine production and is mediated by PI3 kinase through Ras and the MEK/ERK cassette. Moreover, we show the PI3 kinase effectors PKB and PKC(zeta) are also activated by PI3 kinase in a CD14 dependent manner in LPS stimulated human PBMC. Thus, PI3 kinase appears to be an essential component in LPS signal transduction.

Protective effects of nafamostat mesilate on liver injury induced by lipopolysaccharide in rats: possible involvement of CD14 and TLR-4 downregulation on Kupffer cells

Nafamostat mesilate (NM) is a synthetic protease inhibitor with various biological effects. To determine its effect on liver injury related to sepsis, we investigated the effects of NM on lipopolysaccharide (LPS)-induced liver injury. Wistar rats were allocated into two groups; the NM group underwent intraperitoneal NM administration 30 min before LPS administration, and the control group underwent PBS administration. Serum AST and ALT levels were significantly decreased in NM-treated rats. Reduced levels of TNF-alpha, IL-1beta, and IFN-gamma were observed after LPS administration in NM-treated rats. No significant differences were observed in IL-6 levels between the NM and the control group. In contrast, HGF levels were significantly increased only in control rats. NM treatment decreased protein and mRNA levels of TLR-4 and CD14. Our data suggest that NM treatment has protective effects against LPS-induced hepatotoxicity through downregulation of TLR4 and CD14 in liver, which decreased TNF-alpha, IL-1beta, and IFN-gammaproduction in liver.

Differential regulation of lipopolysaccharide and Gram-positive bacteria induced cytokine and chemokine production in splenocytes by Galphai proteins

Heterotrimeric Gi proteins play a role in lipopolysaccharide (LPS) and Staphylococcus aureus (SA) activated signaling leading to inflammatory mediator production. We hypothesized that genetic deletion of Gi proteins would alter cytokine and chemokine production induced by LPS and SA. LPS- and heat killed SA-induced cytokine and chemokine production in splenocytes from wild type (WT), Galpha(i2) (-/-) or Galpha(i1/3) (-/-) mice were investigated. LPS- or SA-induced production of TNFalpha, IL-6, IFNgamma, IL-12, IL-17, GM-CSF, MIP-1alpha, MCP-1, MIG and IP-10 were significantly increased (1.2 to 33 fold, p<0.05) in splenocytes harvested from Galpha(i2)(-/-) mice compared with WT mice. The effect of Galpha(i) protein depletion was remarkably isoform specific. In splenocytes from Galpha(i1/3) (-/-) mice relative to WT mice, SA-induced IL-6, IFNgamma, GM-CSF, and IP-10 levels were decreased (59% to 86%, p<0.05), whereas other LPS- or SA-stimulated cytokines and chemokines were not different relative to WT mice. LPS- and SA-induced production of KC were unchanged in both groups of the genetic deficient mice. Splenocytes from both Galpha(i2) (-/-) and Galpha(i1/3) (-/-) mice did not exhibit changes in TLR2 and TLR4 expression. Also analysis of splenic cellular composition by flow cytometry demonstrated an increase in splenic macrophages and reduced CD4 T cells in both Galpha(i2) (-/-) and Galpha(i1/3) (-/-) mice relative to WT mice. The disparate response of splenocytes from the Galpha(i2) (-/-) relative to Galpha(i1/3) (-/-) mice therefore cannot be attributed to major differences in spleen cellular composition. These data demonstrate that G(i2) and G(i1/3) proteins are both involved and differentially regulate splenocyte inflammatory cytokine and chemokine production in a highly Gi isoform specific manner in response to LPS and Gram-positive microbial stimuli.

Toxoplasma gondiitriggers Gi-dependent PI 3-kinase signaling required for inhibition of host cell apoptosis

Infection with the intracellular parasite Toxoplasma gondii renders cells resistant to multiple pro-apoptotic signals, but underlying mechanisms have not been delineated. The phosphoinositide 3-kinase (PI 3-kinase) pathway and the immediate downstream effector protein kinase B (PKB/Akt) play important roles in cell survival and apoptosis inhibition. Here, we show that Toxoplasma infection of mouse macrophages activates PKB/Akt in vivo and in vitro. In a mixed population of infected and non-infected macrophages, activation is only observed in parasite-infected cells. The PI 3-kinase inhibitors wortmannin and LY294002 block parasite-induced PKB phosphorylation. PKB activation occurs independently of Toll-like receptor adaptor protein MyD88 but uncoupling of Gi-protein-mediated signaling with pertussis toxin prevents PKB phosphorylation. Moreover, in the presence of PI 3-kinase inhibitors or pertussis toxin, not only PKB activation but also ERK1/2 activation during T. gondii infection is defective. Most importantly, the parasite's ability to induce macrophage resistance to pro-apoptotic signaling is prevented by incubation with PI 3-kinase inhibitors. This study demonstrates that T. gondii exploits host Gi-protein-dependent PI 3-kinase signaling to prevent induction of apoptosis in infected macrophages.

CD14: chaperone or matchmaker?

In this issue of Immunity, describe a physical and functional relationship between Toll-like receptor 3 (TLR3) and the pattern recognition protein CD14. In the presence of CD14, TLR3-mediated signal transduction events are amplified.

T-cadherin mediates low-density lipoprotein-initiated cell proliferation via the Ca(2+)-tyrosine kinase-Erk1/2 pathway

The GPI-anchored protein T-cadherin was found to be an atypical LDL binding site that is expressed in various types of cells, including endothelial cells, smooth muscle cells, and neurons. Notably, the expression of T-cadherin was reduced in numerous types of cancers, although it was up-regulated in tumor-penetrating blood vessels, atherosclerotic lesions, and during neointima formation. Despite these intriguing findings, our knowledge of the physiological role and the signal transduction pathways associated with this protein is limited. Therefore, T-cadherin was overexpressed in the human umbilical vein-derived endothelial cell line EA.hy926, the human embryonic kidney cell line HEK293, and LDL-initiated signal transduction, and its consequences were elucidated. Our data revealed that T-cadherin serves as a receptor specifically for LDL. Following LDL binding to T-cadherin, mitogenic signal transduction was initiated that involved activation of PLC and IP3 formation, which subsequently yielded intracellular Ca2+ mobilization. Downstream to these early phenomena, activation of tyrosine kinase(s) Erk 1/2 kinase, and the translocation of NF kappa B toward the nucleus were found. Finally, overexpression of T-cadherin in HEK293 cells resulted in accelerated cell proliferation in an LDL-dependent manner, although cell viability was not influenced. Because LDL uptake was not facilitated by T-cadherin, our data suggest that T-cadherin serves as a signaling receptor for LDL that facilitates an LDL-dependent mitogenic signal in the vasculature.

A synthesized cationic tetradecapeptide from hornet venom kills bacteria and neutralizes lipopolysaccharide in vivo and in vitro

Sepsis is a complex clinical syndrome that results from a harmful host response to infection, in which foreign bacteria and lipopolysaccharide (LPS) are potent activators of different immune cells, including monocytes and macrophages. To date, there are currently few effective adjuvant therapies in clinical use except activated protein C focusing on the coagulation system. Mastoparans (MPs) are wasp venom cationic amphiphilic tetradecapeptides; these are capable of modulating various cellular activities, including stimulation of GTP-binding protein, phospholipase C and can bind to a phospholipid bilayer. Masroparan-1 (MP-1, INLKAIAALAKKLL-NH2), a tetradecapeptide toxin isolated from hornet venom, was synthesized chemically. In this study, Escherichia coli 25922 (E. coli 25922) and LPS were used to induce sepsis in an animal model. We found that MP-1 treatment at 3 mg/kg protected mice from otherwise lethal bacteria and LPS challenges. MP-1 has antibacterial capabilities against Gram-negative and Gram-positive bacteria. Its antibacterial action against E. coli may result from the destruction of bacterial membrane structures. In addition, treatment of murine peritoneal macrophages with MP-1 potently inhibited the respiratory burst. This effect maybe related to an inhibition of NADPH oxidase in the membrane. Furthermore, MP-1, bound with high-affinity to LPS and lipid A with dissociation equilibrium constants of 484 and 456 nM, respectively, and neutralized LPS in a dose-dependent manner. MP-1 also significantly reduced the expression of TLR4, TNF-alpha and IL-6 mRNA and the release of cytokines in LPS-stimulated murine peritoneal macrophages. Our results shows that the MP-1-mediated protection of mice from lethal challenge by live bacteria and LPS was associated with its bactericidal action and inhibition of inflammatory responses by macrophages to both bacteria and LPS (the release of cytokines and reactive oxygen species).

Structure and thermotropic phase behaviour of detergent-resistant membrane raft fractions isolated from human and ruminant erythrocytes

Detergent-resistant membrane raft fractions have been prepared from human, goat, and sheep erythrocyte ghosts using Triton X-100. The structure and thermotropic phase behaviour of the fractions have been examined by freeze-fracture electron microscopy and synchrotron X-ray diffraction methods. The raft fractions are found to consist of vesicles and multilamellar structures indicating considerable rearrangement of the original ghost membrane. Few membrane-associated particles typical of freeze-fracture replicas of intact erythrocyte membranes are observed in the fracture planes. Synchrotron X-ray diffraction studies during heating and cooling scans showed that multilamellar structures formed by stacks of raft membranes from all three species have d-spacings of about 6.5 nm. These structures can be distinguished from peaks corresponding to d-spacings of about 5.5 nm, which were assigned to scattering from single bilayer vesicles on the basis of the temperature dependence of their d-spacings compared with the multilamellar arrangements. The spacings obtained from multilamellar stacks and vesicular suspensions of raft membranes were, on average, more than 0.5 nm greater than corresponding arrangements of erythrocyte ghost membranes from which they were derived. The trypsinization of human erythrocyte ghosts results in a small decrease in lamellar d-spacing, but rafts prepared from trypsinized ghosts exhibit an additional lamellar repeat 0.4 nm less than a lamellar repeat coinciding with rafts prepared from untreated ghosts. The trypsinization of sheep erythrocyte ghosts results in the phase separation of two lamellar repeat structures (d=6.00; 5.77 nm), but rafts from trypsinized ghosts produce a diffraction band almost identical to rafts from untreated ghosts. An examination of the structure and thermotropic phase behaviour of the dispersions of total polar lipid extracts of sheep detergent-resistant membrane preparations showed that a reversible phase separation of an inverted hexagonal structure from coexisting lamellar phase takes place upon heating above about 30 degrees C. Non-lamellar phases are not observed in erythrocytes or detergent-resistant membrane preparations heated up to 55 degrees C, suggesting that the lamellar arrangement is imposed on these membrane lipids by interaction with non-lipid components of rafts and/or that the topology of lipids in the erythrocyte membrane survives detergent treatment.

Lipopolysaccharide- and gram-positive bacteria-induced cellular inflammatory responses: role of heterotrimeric Galpha(i) proteins

Heterotrimeric G(i) proteins may play a role in lipopolysaccharide (LPS)-activated signaling through Toll-like receptor 4 (TLR4), leading to inflammatory mediator production. Although LPS is a TLR4 ligand, the gram-positive bacterium Staphylococcus aureus (SA) is a TLR2 ligand, and group B streptococci (GBS) are neither TLR2 nor TLR4 ligands but are MyD88 dependent. We hypothesized that genetic deletion of G(i) proteins would alter mediator production induced by LPS and gram-positive bacterial stimulation. We examined genetic deletion of Galpha(i2) or Galpha(i1/3) protein in Galpha(i2)-knockout (Galpha(i2)-/-) or Galpha(i1/3)-knockout (Galpha(i1/3)-/-) mice. LPS-, heat-killed SA-, or GBS-induced mediator production in splenocytes or peritoneal macrophages (MPhi) was investigated. There were significant increases in LPS-, SA-, and GBS-induced production of TNF-alpha and IFN-gamma in splenocytes from Galpha(i2)-/- mice compared with wild-type (WT) mice. Also, LPS-induced TNF-alpha was increased in splenocytes from Galpha(i1/3)-/- mice. In contrast to splenocytes, LPS-, SA-, and GBS-induced TNF-alpha, IL-10, and thromboxane B(2) (TxB(2)) production was decreased in MPhi harvested from Galpha(i2)-/- mice. Also, LPS-induced production of IL-10 and TxB(2) was decreased in MPhi from Galpha(i1/3)-/- mice. In subsequent in vivo studies, TNF-alpha levels after LPS challenge were significantly greater in Galpha(i2)-/- mice than in WT mice. Also, myeloperoxidase activity, a marker of tissue neutrophil infiltration, was significantly increased in the gut and lung of LPS-treated Galpha(i2)-/- mice compared with WT mice. These data suggest that G(i) proteins differentially regulate murine TLR-mediated inflammatory cytokine production in a cell-specific manner in response to both LPS and gram-positive microbial stimuli.

Mastoparan, a G Protein Agonist Peptide, Differentially Modulates TLR4- and TLR2-Mediated Signaling in Human Endothelial Cells and Murine Macrophages

Previous studies have implicated a role for heterotrimeric G protein-coupled signaling in B cells, monocytes, and macrophages stimulated with LPS and have shown that G proteins coimmunoprecipitate with membrane-bound CD14. In this study, we have extended these observations in human dermal microvessel endothelial cells (HMEC) that lack membrane-bound CD14 and in murine macrophages to define further the role of heterotrimeric G proteins in TLR signaling. Using the wasp venom-derived peptide, mastoparan, to disrupt G protein-coupled signaling, we identified a G protein-dependent signaling pathway in HMEC stimulated with TLR4 agonists that is necessary for the activation of p38 phosphorylation and kinase activity, NF-kappaB and IL-6 transactivation, and IL-6 secretion. In contrast, HMEC activation by TLR2 agonists, TNF-alpha, or IL-1beta was insensitive to mastoparan. In the murine macrophage cell line, RAW 264.7, and in primary murine macrophages, G protein dysregulation by mastoparan resulted in significant inhibition of LPS-induced signaling leading to both MyD88-dependent and MyD88-independent gene expression, while TLR2-mediated gene expression was not significantly inhibited. In addition to inhibition of TLR4-mediated MAPK phosphorylation in macrophages, mastoparan blunted IL-1R-associated kinase-1 kinase activity induced by LPS, but not by TLR2 agonists, yet failed to affect phosphorylation of Akt by phosphoinositol-3-kinase induced by either TLR2- or TLR4-mediated signaling. These data confirm the importance of heterotrimeric G proteins in TLR4-mediated responses in cells that use either soluble or membrane-associated CD14 and reveal a level of TLR and signaling pathway specificity not previously appreciated.

Comparative lipid analysis and structure of detergent-resistant membrane raft fractions isolated from human and ruminant erythrocytes

The lipid composition and structure of detergent-resistant membrane rafts from human, goat, and sheep erythrocytes is investigated. While the sphingomyelin:cholesterol ratio varied from about 1:5 in human to 1:1 in sheep erythrocytes a ratio of 1:1 was found in all raft preparations insoluble in Triton X-100 at 4 degrees C. Excess cholesterol is excluded from rafts and saturated molecular species of sphingomyelin assayed by gas chromatography-mass spectrometry determines the solubility of cholesterol in the detergent. Freeze-fracture electron microscopy shows that vesicles and multilamellar structures formed by membrane rafts have undergone considerable rearrangement from the original membrane. No membrane-associated particles are observed. Synchrotron X-ray diffraction studies showed that d spacings of vesicle preparations of rafts cannot be distinguished from ghost membranes from which they are derived. Dispersions of total polar lipid extracts of sheep rafts show phase separation of inverted hexagonal structure upon heating and this phase coexists with multilamellar structures at 37 degrees C.

Failure of the gut barrier system enhances liver injury in rats: protection of hepatocytes by gut-derived hepatocyte growth factor

OBJECTIVE

Clinical and experimental studies suggest that impairment of the mucosal barrier system increases gut-derived endotoxin in the portal blood, which causes liver injury. The aim of this study was to elucidate the mechanism of liver injury caused by gut defence failure.

DESIGN

Wistar rats were administered either enteral lipopolysaccharide (LPS) or LPS via the portal vein.

METHODS

Blood samples were collected via the inferior vena cava at necropsy. Serum aspartate transaminase (AST) and alanine transaminase (ALT) were analysed by standard enzymatic procedures and cytokines [tumour necrosis factor-alpha, interleukin (IL)-1beta, interferon-gamma, IL-6 and hepatocyte growth factor (HGF)] were measured by enzyme-linked immunosorbent assay. Livers were removed and snap-frozen in liquid nitrogen. CD14, CD68, Toll-like receptor (TLR) 2, TLR4 and Fas ligand (FasL) were analysed immunohistochemically. Expression of TLR2, TLR4 and CD14 mRNA was determined by reverse transcriptase-polymerase chain reaction.

RESULTS

In enterally-treated rats, AST and ALT were not increased and cytokine levels were under the limits of detection in the absence of a rise in HGF. Enteral administration of LPS increased HGF dose-dependently. Injection of LPS in the portal vein resulted in significant increases in AST, ALT, tumour necrosis factor-alpha, IL-1beta, interferon-gamma and IL-6 levels, but no change in HGF levels. Immunohistochemical analysis revealed that intraportal LPS administration increased CD14, TLR4, CD68 and FasL. Reverse transcriptase-polymerase chain reaction analysis demonstrated that TLR4 mRNA expression was upregulated 0.5 h after intraportal LPS administration.

CONCLUSION

s Our data suggest that Kupffer cell activation mediated by intraportal LPS via TLR4 is involved in liver injury, possibly through both tumour necrosis factor-alpha/IL-1beta and FasL, and that lack of HGF activity in the impaired gut could not counteract liver injury.

TOLL-LIKE RECEPTOR 4 COUPLED GI PROTEIN SIGNALING PATHWAYS REGULATE EXTRACELLULAR SIGNAL-REGULATED KINASE PHOSPHORYLATION AND AP-1 ACTIVATION INDEPENDENT OF NFκB ACTIVATION

Previous studies have implicated heterotrimeric Gi proteins in signaling leading to inflammatory mediator production induced by lipopolysaccharide (LPS). TLR4 has recently been shown to play a central role in response to LPS activation. We hypothesized that Gi proteins are coupled to TLR4 activation of signaling pathways. To inhibit Gi protein function, human embryonic kidney (HEK) 293 cells or RAW 264.7 cells were pretreated with pertussis toxin (PTx), an inhibitor of receptor-Galphai interaction, or transfected with dominant negative Galphai3 (Galphai3dn) or Galphai2 minigene (an inhibitory carboxyl terminus of Galphai2) plasmid. The cells were subsequently transfected with constitutively active TLR4 (TLR4ca) plasmid or TLR4ca together with an NFkappaB or AP-1 reporter construct. TLR4ca transfection induced ERK 1/2 activation (157 +/- 14%, P < 0.01), AP-1 activation (4.0 +/- 0.2-fold, P < 0.01), and NFkappaB activation (8.1 +/- 0.4-fold, P < 0.01) compared with empty vector controls. Pretreatment with PTx inhibited TLR4ca-induced ERK 1/2 phosphorylation (30 +/- 7%, P < 0.05) and AP-1 activation (36 +/- 3%, P < 0.05) but did not inhibit NFkappaB activation. Cotransfection of TLR4ca with Galphai3dn or Galphai2 minigene also reduced TLR4ca-induced ERK 1/2 phosphorylation (34 +/- 10% and 33 +/- 5%, respectively, P < 0.05). Constitutively active Galphai2 and Galphai3 plasmids potentiated TLR4ca-induced ERK 1/2 phosphorylation (27 +/- 3% and 41 +/- 6%, respectively, P < 0.05). betaARK-ct plasmid, which inhibits the function of betagamma subunit of G protein, has no effect on TLR4ca-induced ERK 1/2 phosphorylation. These data support our hypothesis and provide the first evidence that Galphai-coupled signaling pathways are activated by TLR4. The TLR4-activated Galphai signaling pathway activates ERK 1/2 phosphorylation and AP-1 activation independently of TLR4-mediated signaling to NFkappaB activation.