Role of microtubules in LPS-induced macrophage inflammatory protein-2 production from rat pneumocytes

NF-κB activation enhances STING signaling by altering microtubule-mediated STING trafficking

It is widely known that stimulator of interferon genes (STING) can trigger nuclear factor κB (NF-κB) signaling. However, whether and how the NF-κB pathway affects STING signaling remains largely unclear. Here, we report that Toll-like receptor (TLR)-, interleukin-1 receptor (IL-1R)-, tumor necrosis factor receptor (TNFR)-, growth factor receptor (GF-R)-, and protein kinase C (PKC)-mediated NF-κB signaling activation dramatically enhances STING-mediated immune responses. Mechanistically, we find that STING interacts with microtubules, which plays a crucial role in STING intracellular trafficking. We further uncover that activation of the canonical NF-κB pathway induces microtubule depolymerization, which inhibits STING trafficking to lysosomes for degradation. This leads to increased levels of activated STING that persist for a longer period of time. The synergy between NF-κB and STING triggers a cascade-amplified interferon response and robust host antiviral defense. In addition, we observe that several gain-of-function mutations of STING abolish the microtubule-STING interaction and cause abnormal STING trafficking and ligand-independent STING autoactivation. Collectively, our data demonstrate that NF-κB activation enhances STING signaling by regulating microtubule-mediated STING trafficking.

Modulation of osteoclastogenesis with macrophage M1- and M2-inducing stimuli

Macrophages are generated through the differentiation of monocytes in tissues and they have important functions in innate and adaptive immunity. In addition to their roles as phagocytes, macrophages can be further differentiated, in the presence of receptor activator of nuclear factor kappa-B ligand (RANKL) and macrophage colony-stimulating factor (M-CSF), into osteoclasts (multinucleated giant cells that are responsible for bone resorption). In this work, we set out to characterize whether various inflammatory stimuli, known to induce macrophage polarization, can alter the type of multinucleated giant cell obtained from RANKL differentiation. Following a four-day differentiation protocol, along with lipopolysaccharide (LPS)/interferon gamma (IFNγ) as one stimulus, and interleukin-4 (IL-4) as the other, three types of multinucleated cells were generated. Using various microscopy techniques (bright field, epifluorescence and scanning electron), functional assays, and western blotting for osteoclast markers, we found that, as expected, RANKL treatment alone resulted in osteoclasts, whereas the addition of LPS/IFNγ to RANKL pre-treated macrophages generated Langhans-type giant cells, while IL-4 led to giant cells resembling foreign body giant cells with osteoclast-like characteristics. Finally, to gain insight into the modulation of osteoclastogenesis, we characterized the formation and morphology of RANKL and LPS/IFNγ-induced multinucleated giant cells.

Depolymerization of Actin Filament by Cytochalasin E Induces Interleukin-8 Production and Up-Regulates CD54 in the HeLa Epithelial Cell Line

We previously reported that the depolymerization of actin filament by cytochalasin E enhances low affinity Fcepsilon receptor II (CD23) expression on the human monocyte-like cell line, U937 (J. Clin. Immunol. 20: 235, 2000). In this study, we found that cytochalasin E strongly induces interleukin-8 through an epithelial cell line, HeLa, in dose- and time-dependent manners as assessed by enzyme-linked immunoassay and reverse transcription-polymerase chain reaction techniques. In addition, interleukin-8 production in the HeLa cells cultured with cytochalasin E was blocked in the presence of protein kinase C inhibitors, Go6976 and H-7. On the other hand, it was found that CD54 (intercellular adhesion molecule-1; ICAM-1) expression on the HeLa cells and the secretion of soluble CD54 were significantly up-regulated after culturing with cytochalasin E, and that these up-regulations of CD54 were also suppressed by Go6976. Taken together, these findings indicate that cytochalasin E activates protein kinase C under the depolymerization of actin filament, leading to the induction of interleukin-8 production and the up-regulation of CD54 in HeLa cells.

Guanine nucleotide exchange factor-H1 signaling is involved in lipopolysaccharide-induced endothelial barrier dysfunction

BACKGROUND

Gram-negative bacterial lipopolysaccharide (LPS) leads to the pathologic increase of vascular leakage under septic conditions. However, the mechanisms behind LPS-induced vascular hyperpermeability remain incompletely understood. In this study, we tested hypothesis that guanine nucleotide exchange factor-H1 (GEF-H1) signaling might be a key pathway involved in endothelial cells (ECs) barrier dysfunction.

METHODS

The roles of GEF-H1 signaling pathway in LPS-induced ECs barrier dysfunction were accessed by Evans blue dye-labeled albumin (EB-albumin) leak across the human umbilical vein EC (HUVEC) monolayers and Western blot assays. Furthermore, the effect of GEF-H1 signaling on LPS-induced alteration of cytoskeletal proteins and disruption of cell-cell junctions were analyzed by immunofluorescent analysis and Western blot assays, respectively.

RESULTS

We found that LPS could rapidly activated GEF-H1/RhoA/Rho-associated protein kinase (ROCK) signaling pathway in ECs. The LPS-mediated increase in EB-albumin flux across human HUVECs monolayers could be prevented by GEF-H1 depletion or ROCK inactivation. ECs permeability is controlled by actin filaments and cell-cell contact protein complexes. Actin stress fiber formation and/or cell-cell contact proteins loss cause vascular barrier disruption. Here, GEF-H1 knockdown or ROCK inactivation both not only significantly inhibited LPS-induced actin stress fiber formation, phosphorylation of myosin light chain, and myosin-associated phosphatase type 1, but also suppressed LPS-induced loss of occludin, claudin-1, and vascular endothelial (VE)-cadherin in ECs, which suggested that LPS-induced stress fiber formation and cell-cell junctions disruption were closely associated with GEF-H1/RhoA/ROCK signaling activation.

CONCLUSION

Our findings indicate that GEF-H1/RhoA/ROCK pathway in ECs plays an important role in LPS-mediated alteration of cell morphology and disruption of cell-cell junctions, consequently regulate LPS-induced vascular permeability dysfunction.

Guanine-nucleotide exchange factor H1 mediates lipopolysaccharide-induced interleukin 6 and tumor necrosis factor α expression in endothelial cells via activation of nuclear factor κB

The development of sepsis is multifactorial. Tissue damage and organ dysfunction may be caused not only by the microorganisms but also by the inflammatory mediators released in response to the infection. Interleukin 6 (IL-6) and tumor necrosis factor α (TNF-α) levels in serum are well known to be upregulated in humans with sepsis and can be used to predict outcome. Using human umbilical vein endothelial cells, we analyzed the role of guanine-nucleotide exchange factor H1 (GEF-H1) on lipopolysaccharide (LPS)-dependent IL-6/TNF-α expression in endothelial cells. Lipopolysaccharide upregulated IL-6 secretion in a dose- and time-dependent manner. Specific inactivation of RhoA/Cdc42/Rac1 by Clostridium difficile toxin B-10463 (TcdB-10463) reduced LPS-induced nuclear factor κB (NF-κB) p65 phosphorylation, IL-6/TNF-α messenger RNA (mRNA), and IL-6/TNF-α protein productions. Guanine-nucleotide exchange factor H1 protein expression remained on a high level among 1 to 9 h in response to LPS challenge of endothelial cells. Inhibition of GEF-H1 by specific small interfering RNA or inactivation of Rho-associated kinase with Y-27632 not only significantly reduced LPS-induced p38 and extracellular signal-regulated kinase 1/2 (ERK1/2) activities but also blocked LPS-induced NF-κB translocation and activation, thereby inhibiting IL-6/TNF-α mRNA and protein productions. Furthermore, SB203580 (p38 inhibitor) but not PD98059 (ERK1/2 inhibitor) blocked LPS-induced NF-κB activation; however, both inhibitors significantly suppressed IL-6/TNF-α mRNA and protein expression. In summary, our data suggest that LPS rapidly upregulates GEF-H1 expression. Activated Rho-associated kinase by GEF-H1 subsequently activates p38 and ERK1/2, thereby increasing IL-6/TNF-α expression in endothelial cells. P38 and ERK1/2 regulate LPS-induced IL-6/TNF-α expression through an NF-κB-dependent manner and an NF-κB-independent manner, respectively.

GEF-H1/RhoA signalling pathway mediates lipopolysaccharide-induced intercellular adhesion molecular-1 expression in endothelial cells via activation of p38 and NF-κB

The purpose of study is to investigate the effects of GEF-H1/RhoA pathway in regulating intercellular adhesion molecule-1 (ICAM-1) expression in lipopolysaccharide (LPS)-activated endothelial cells. Exposure of human umbilical vein endothelial cells (HUVECs) to LPS induced GEF-H1 and ICAM-1 expression in dose- and time-dependent up-regulating manners. Pretreatment with Clostridium difficile toxin B-10463 (TcdB-10463), an inhibitor of Rho activity, reduced LPS-related phosphorylation of p65 at Ser 536 in a dose-dependent manner. Inhibition of TLR4 expression significantly blocked LPS-induced RhoA activity, NF-κB transactivation, GEF-H1 and ICAM-1 expression. Coimmunoprecipitation assay indicated that LPS-activated TLR4 and GEF-H1 formed a signalling complex, suggesting that LPS, acting through TLR4, stimulates GEF-H1 expression and RhoA activity, and thereby induces NF-κB transactivation and ICAM-1 gene expression. However, GEF-H1/RhoA regulates LPS-induced NF-κB transactivation and ICAM-1 expression in a MyD88-independent pathway because inhibition of MyD88 expression could not block LPS-induced RhoA activity. Furthermore, pretreatment with Y-27632, an inhibitor of ROCK, significantly reduced LPS-induced p38, ERK1/2 and p65 phosphorylation, indicating that ROCK acts as an upstream effector of p38 and ERK1/2 to promote LPS-induced NF-κB transactivation and ICAM-1 expression. What is more, the p38 inhibitor (SB203580) but not ERK1/2 inhibitor (PD98059) blocked LPS-induce NF-κB transactivation and ICAM-1 expression, which demonstrates that RhoA mediates LPS-induced NF-κB transactivation and ICAM-1 expression dominantly through p38 but not ERK1/2 activation. In summary, our data suggest that LPS-induced ICAM-1 synthesis in HUVECs is regulated by GEF-H1/RhoA-dependent signaling pathway via activation of p38 and NF-κB.

GEF-H1-RhoA signaling pathway mediates LPS-induced NF-κB transactivation and IL-8 synthesis in endothelial cells

Secretion of proinflammatory cytokines by LPS activated endothelial cells contributes substantially to the pathogenesis of sepsis. However, the mechanism involved in this process is not well understood. In the present study, we determined the roles of GEF-H1 (guanine-nucleotide exchange factor-H1)-RhoA signaling in LPS-induced interleukin-8 (IL-8, CXCL8) production in endothelial cells. First, we observed that GEF-H1 expression was upregulated in a dose- and time-dependent manner as consistent with TLR4 (Toll-like receptor 4) expression after LPS stimulation. Afterwards, Clostridium difficile toxin B-10463 (TcdB-10463), an inhibitor of Rho activities, reduced LPS-induced NF-κB phosphorylation. Inhibition of GEF-H1 and RhoA expression reduced LPS-induced NF-κB and p38 phosphorylation. TLR4 knockout blocked LPS-induced activity of RhoA, however, MyD88 knockout did not impair the LPS-induced activity of RhoA. Nevertheless, TLR4 and MyD88 knockout both significantly inhibited transactivation of NF-κB. GEF-H1-RhoA and MyD88 both induced significant changes in NF-κB transactivation and IL-8 synthesis. Co-inhibition of GEF-H1-RhoA and p38 expression produced similar inhibitory effects on LPS-induced NF-κB transactivation and IL-8 synthesis as inhibition of p38 expression alone, thus confirming that activation of p38 was essential for the GEF-H1-RhoA signaling pathway to induce NF-κB transactivation and IL-8 synthesis. Taken together, these results demonstrate that LPS-induced NF-κB activation and IL-8 synthesis in endothelial cells are regulated by the MyD88 pathway and GEF-H1-RhoA pathway.

Conserved responses to trichostatin A in rodent lungs exposed to endotoxin or stretch

Histone deacetylase (HDAC) isoenzymes have been suggested as possible drug targets in pulmonary cancer and in inflammatory lung diseases such as asthma and COPD. Whether HDAC inhibition is pro- or anti-inflammatory is under debate. To further examine this clinically relevant paradigm, we analyzed 8 genes that are upregulated by two pro-inflammatory stimuli, i.e. endotoxin and mechanical stress (overventilation), in isolated rat and mouse lungs, respectively. We studied the effect of the HDAC inhibitor trichostatin A (TSA) under control conditions, in response to endotoxin and overventilation, and on the effects of the steroid dexamethasone. TSA affected gene expression largely independent of the stimulus (endotoxin, overventilation) and the species (rat, mouse) leading to upregulation of some genes (Tnf, Cxcl2) and downregulation of others (Cxcl10, Timp1, Selp, Il6). At the protein level, TSA reduced the stimulated release of TNF, MIP-2alpha and IL-6, indicating that TSA may affect protein translation independent from gene transcription. In general, the anti-inflammatory effects of TSA on gene expression and protein release were additive to that of dexamethasone, suggesting that both drugs employ different mechanisms. We conclude that pro-inflammatory stimuli induce distinct sets of genes that are regulated by HDAC in a diverse, but consistent manner across two rodent species. The present findings together with previous in vivo studies suggest that the effect of HDAC inhibition in the intact lung is in part anti-inflammatory.

Post-translational inhibition of IP-10 secretion in IEC by probiotic bacteria: impact on chronic inflammation

Background

Clinical and experimental studies suggest that the probiotic mixture VSL#3 has protective activities in the context of inflammatory bowel disease (IBD). The aim of the study was to reveal bacterial strain-specific molecular mechanisms underlying the anti-inflammatory potential of VSL#3 in intestinal epithelial cells (IEC).

Methodology/Principal Findings

VSL#3 inhibited TNF-induced secretion of the T-cell chemokine interferon-inducible protein (IP-10) in Mode-K cells. Lactobacillus casei (L. casei) cell surface proteins were identified as active anti-inflammatory components of VSL#3. Interestingly, L. casei failed to block TNF-induced IP-10 promoter activity or IP-10 gene transcription at the mRNA expression level but completely inhibited IP-10 protein secretion as well as IP-10-mediated T-cell transmigration. Kinetic studies, pulse-chase experiments and the use of a pharmacological inhibitor for the export machinery (brefeldin A) showed that L. casei did not impair initial IP-10 production but decreased intracellular IP-10 protein stability as a result of blocked IP-10 secretion. Although L. casei induced IP-10 ubiquitination, the inhibition of proteasomal or lysosomal degradation did not prevent the loss of intracellular IP-10. Most important for the mechanistic understanding, the inhibition of vesicular trafficking by 3-methyladenine (3-MA) inhibited IP-10 but not IL-6 expression, mimicking the inhibitory effects of L. casei. These findings suggest that L. casei impairs vesicular pathways important for the secretion of IP-10, followed by subsequent degradation of the proinflammatory chemokine. Feeding studies in TNF^ΔARE and IL-10^−/− mice revealed a compartimentalized protection of VSL#3 on the development of cecal but not on ileal or colonic inflammation. Consistent with reduced tissue pathology in IL-10^−/− mice, IP-10 protein expression was reduced in primary epithelial cells.

Conclusions/Significance

We demonstrate segment specific effects of probiotic intervention that correlate with reduced IP-10 protein expression in the native epithelium. Furthermore, we revealed post-translational degradation of IP-10 protein in IEC to be the molecular mechanism underlying the anti-inflammatory effect.

Acute lung injury and cell death: how many ways can cells die?

Apoptosis has been considered as an underlying mechanism in acute lung injury/acute respiratory distress syndrome and multiorgan dysfunction syndrome. Recently, several alternative pathways for cell death (such as caspase-independent cell death, oncosis, and autophagy) have been discovered. Evidence of these pathways in the pathogenesis of acute lung injury has also come into light. In this article, we briefly introduce cell death pathways and then focus on studies related to lung injury. The different types of cell death that occur and the underlying mechanisms utilized depend on both experimental and clinical conditions. Lipopolysaccharide-induced acute lung injury is associated with apoptosis via Fas/Fas ligand mechanisms. Hyperoxia and ischemia-reperfusion injury generate reactive oxidative species, which induce complex cell death patterns composed of apoptosis, oncosis, and necrosis. Prolonged overexpression of inflammatory mediators results in increased production and activation of proteases, especially cathepsins. Activation and resistance to death of neutrophils also plays an important role in promoting parenchymal cell death. Knowledge of the coexisting multiple cell death pathways and awareness of the pharmacological inhibitors targeting different proteases critical to cell death may lead to the development of novel therapies for acute lung injury.

Long pentraxin 3 in pulmonary infection and acute lung injury

Long pentraxin 3 (PTX3) is a newly discovered acute phase protein produced at the sites of infection and inflammation by tissue cells, macrophages, monocytes, and dendritic cells. PTX3 plays an important role in preventing infection of certain fungi, bacteria, and viruses in the lung. Recombinant PTX3 has been proposed as a potential antifungal molecule for therapy. However, under certain experimental conditions, such as intestinal ischemia-reperfusion, high volume mechanical ventilation, or severe bacterial infection, increased expression of PTX3 is associated with more severe lung injury. Therefore, it is necessary to further explore the sources of PTX3 in the lung and the regulatory mechanisms of its expression. It is also essential to further determine how PTX3 binds to pathogens, complement, and apoptotic cells, and to determine whether PTX3 has a specific receptor in targeted cells. These studies will provide insight into the pathological processes of pulmonary infection and acute lung injury and provide potential novel therapeutic strategies to control pulmonary infections without severe lung injury.

Expression of CINC-2beta is related to the state of differentiation of alveolar epithelial cells

Alveolar epithelial cells are among the first cells to encounter inhaled particles or organisms. These cells likely participate in the initiation and modulation of the inflammatory response by production of chemokines. However, there is little information on the extent or regulation of chemokine production by these cells. Rat type II cells were studied under differentiated and dedifferentiated conditions to determine their ability to express and secrete CXC chemokines. Both differentiated and dedifferentiated type II cells secreted MIP-2, MCP-1, and CINC-2 in response to a cytokine mixture of IL-1beta, TNF-alpha, and IFN-gamma or to IL-1beta alone. The cytokine mixture also induced iNOS expression and nitrite secretion. Both differentiated and dedifferentiated type II cells expressed CINC-1 (GRO), CINC-2alpha, CINC-3 (MIP-2), and MCP-1 mRNA, and their expression was increased by the cytokine mixture or by IL-1beta alone. However, CINC-2beta, a splice variant of CINC-2, was only expressed under differentiated conditions stimulated by KGF and was not increased by the cytokine mixture or by IL-1beta. In situ hybridization of normal lung and lung instilled with Ad-KGF demonstrated that CINC-2beta was expressed by alveolar and bronchiolar epithelial cells in vivo. We conclude that CINC-2beta is regulated differently from most other chemokines and that its expression is related to the state of alveolar type II cell differentiation.

Calprotectin release from human neutrophils is induced by Porphyromonas gingivalis lipopolysaccharide via the CD-14-Toll-like receptor-nuclear factor kappaB pathway

OBJECTIVES

Calprotectin is a cytosolic protein with antibacterial action in leukocytes and its level increases in some inflammatory diseases, including periodontal diseases, rheumatoid arthritis and ulcerative colitis. Recently, we found that the lipopolysaccharide of Porphyromonas gingivalis (P-LPS) induced calprotectin release from human neutrophils. P-LPS, a major virulence factor of periodontal pathogens, is known to induce the production and release of inflammatory cytokines through CD14, Toll-like receptor (TLR) and nuclear factor kappaB (NF-kappaB). In the present study, we investigated whether calprotectin release by P-LPS is induced via the CD14-TLR-NF-kappaB pathway and the cellular mechanism of calprotectin release in human neutrophils.

MATERIAL AND METHODS

Human neutrophils were isolated from the peripheral blood of healthy donors and pre-incubated in medium containing antibodies against CD14, TLR2 and TLR4, or several inhibitors of NF-kappaB, microtubules and microfilaments, and then incubated with P-LPS. The calprotectin amount in the culture medium was determined using ELISA, and the nuclear extracts from cells were used for the examination of NF-kappaB binding activity using electrophoretic mobility shift assays.

RESULTS

P-LPS increased calprotectin release from neutrophils and its induction was inhibited by anti-CD14 and anti-TLR2 antibodies, but not by two anti-TLR4 antibodies. NF-kappaB inhibitors suppressed P-LPS-induced NF-kappaB binding activity and calprotectin release. The inhibitors of microtubule and microfilament polymerization significantly decreased P-LPS-induced calprotectin release.

CONCLUSION

These results suggest that calprotectin release is induced by P-LPS via the CD14-TLR2-NF-kappaB signal pathway in human neutrophils and may be dependent on microtubule and microfilament systems.

Cellular biomechanics in the lung

Mechanical forces affect both the function and phenotype of cells in the lung. In this symposium, recent studies were presented that examined several aspects of biomechanics in lung cells and their relationship to disease. Wound healing and recovery from injury in the airways involve epithelial cell spreading and migration on a substrate that undergoes cyclic mechanical deformation; enhanced green fluorescent protein-actin was used in a stable cell line to examine cytoskeletal changes in airway epithelial cells during wound healing. Eosinophils migrate into the airways during asthmatic attacks and can also be exposed to cyclic mechanical deformation; cyclic mechanical stretch caused a decrease in leukotriene C(4) synthesis that may be dependent on mechanotransduction mechanisms involving the production of reactive oxygen species. Recent studies have suggested that proinflammatory cytokines are increased in ventilator-induced lung injury and may be elevated by overdistention of the lung tissue; microarray analysis of human lung epithelial cells demonstrated that cyclic mechanical stretch alone profoundly affects gene expression. Finally, airway hyperresponsiveness is a basic feature of asthma, but the relationship between airway hyperresponsiveness and changes in airway smooth muscle (ASM) function remain unclear. New analysis of the behavior of the ASM cytoskeleton (CSK) suggests, however, that the CSK may behave as a glassy material and that glassy behavior may account for the extensive ASM plasticity and remodeling that contribute to airway hyperresponsiveness. Together, the presentations at this symposium demonstrated the remarkable and varied roles that mechanical forces may play in both normal lung physiology as well as pathophysiology.

Role of LPS-induced microfilament depolymerization in MIP-2 production from rat pneumocytes

We have previously demonstrated that lipopolysaccharide (LPS) induces production of macrophage inflammatory protein-2 (MIP-2), a C-X-C chemokine for neutrophil recruitment and activation, in primary cultured rat lung alveolar epithelial cells. We have also demonstrated that LPS depolymerizes microfilaments in rat alveolar epithelial cells. To determine whether the polymerization status of microfilaments affects LPS-induced MIP-2 production, we treated rat alveolar epithelial cells with cytochalasin D (CytoD), a microfilament-disrupting agent, before and during LPS stimulation. A lower concentration (0.1 microM) of CytoD inhibited LPS-induced MIP-2 production without affecting microfilament polymerization. In contrast, LPS-induced MIP-2 production was enhanced by a higher concentration (10 microM) of CytoD, which disrupted the filamentous structure of actin. Jasplakinolide (1 nM to 1 microM), a polymerizing agent for microfilaments, decreased LPS-induced MIP-2 secretion. Jasplakinolide (1 microM) also blocked LPS-induced depolymerization of microfilaments. These results suggest that, in alveolar epithelial cells, LPS-induced MIP-2 production is at least partially regulated by microfilament depolymerization.