Lipopolysaccharide Signaling Research Articles

The effect of low dose lipopolysaccharide on thyroid hormone-regulated actin cytoskeleton modulation and type 2 iodothyronine deiodinase activity in astrocytes

Systemic infection/inflammation can severely interfere with brain development. Lipopolysaccharide (LPS) is a major cell wall component of gram-negative bacteria and commonly used to model the response by infections. Since perinatal exposure to LPS shows neurodevelopmental defects partly similar to those seen in perinatal hypothyroidism, we examined the effect of LPS on thyroxin (T4)-mediated signalings in astrocytes. Initially, C6 rat glioma-derived clonal cells were used, whose biological nature is similar to that of astrocytes. To measure the effects of LPS and T4, actin polymerization and D2 activity assays were carried out. LPS treatment (10 ng/mL) markedly induced actin depolymerization, whereas 10 nM T4 promoted actin polymerization. Furthermore, T4 partly rescued LPS-induced actin depolymerization. LPS treatment (10 ng/mL) increased D2 activity, whereas T4 (10 nM) suppressed this activity. T4 restored LPS-increased D2 activity at 10 nM. LPS-induced actin depolymerization and D2 activity were blocked by p38 MAP kinase inhibitor. Such effects were not seen in T4-mediated changes. Furthermore, similar results were found in the cerebellar primary astrocyte. These results indicate that, although LPS affects T4-regulated cellular events such as actin polymerization and D2 activity, which may induce neurodevelopmental defects similar to those in perinatal hypothyroidism, LPS signaling pathways are independent of T4 signaling pathways.

Propofol Reduces Lipopolysaccharide-Induced, NADPH Oxidase (NOX2) Mediated TNF-αand IL-6 Production in Macrophages

During an infection, lipopolysaccharide (LPS) stimulates the production of reactive oxygen species (ROS), which is mediated, in large part, by nicotinamide adenine dinucleotide phosphate (NADPH) oxidases (NOXs); NOX2 is the major NOX isoform found in the macrophage cell membrane. While the immunomodulatory activity of propofol is highly documented, its effect on the LPS-induced NOX2/ROS/NF-κB signaling pathway in macrophages has not been addressed. In present study, we used murine macrophage cell line RAW264.7 pretreated with propofol and stimulated with LPS. IL-6 and TNF-α expression, ROS production, and NOX activity were determined. Results showed that propofol attenuated LPS-induced TNF-α and IL-6 expression. Moreover, LPS-stimulated phosphorylation of NF-κB and generation of ROS were weakened in response to propofol. Propofol also reduced LPS-induced NOX activity and expression of gp91phox and p47phox. We conclude that propofol modulates LPS signaling in macrophages by reducing NOX-mediated production of TNF-α and IL-6.

Cytoprotection of Perfluorocarbon on PMVECs In Vitro

Lipopolysaccharide (LPS) can activate endothelial cells and induce inflammatory injury. Toll-like receptor-4 (TLR-4) is integrally involved in LPS signaling and has a requisite role in the activation of nuclear factor (NF)-κB. A number of studies have demonstrated the cytoprotective action of perfluorocarbon (PFC) both in vivo and in vitro, but the exact mechanisms have yet to be elucidated. In this study, we examined in an in vitro model the cytoprotective effect of PFC on LPS-stimulated pulmonary vascular endothelial cells (PMVECs). Intercellular adhesion molecule-1 (ICAM-1), tumor necrosis factor-α (TNF-α), and interleukin-8 (IL-8) were significantly increased in the LPS-stimulated PMVECs groups. The expression of TLR-4 mRNA and protein in LPS groups was markedly increased. Meanwhile, NF-κB was activated. There were no significant effects of PFC alone on any of the factors studied while the coculture group showed significant downregulation of the secretion of ICAM-1, TNF-α, and IL-8; the expression of TLR-4 mRNA; and the activity of NF-κB. LPS can induce PMVEC inflammatory injury via the activation of TLR-4 and subsequent activation of NF-κB. PFC is able to protect PMVECs from LPS-induced inflammatory injury by blocking the initiation of the LPS signaling pathway.

Differential activation and functional specialization of miR-146 and miR-155 in innate immune sensing

Many microRNAs (miRNAs) are co-regulated during the same physiological process but the underlying cellular logic is often little understood. The conserved, immunomodulatory miRNAs miR-146 and miR-155, for instance, are co-induced in many cell types in response to microbial lipopolysaccharide (LPS) to feedback-repress LPS signalling through Toll-like receptor TLR4. Here, we report that these seemingly co-induced regulatory RNAs dramatically differ in their induction behaviour under various stimuli strengths and act non-redundantly through functional specialization; although miR-146 expression saturates at sub-inflammatory doses of LPS that do not trigger the messengers of inflammation markers, miR-155 remains tightly associated with the pro-inflammatory transcriptional programmes. Consequently, we found that both miRNAs control distinct mRNA target profiles; although miR-146 targets the messengers of LPS signal transduction components and thus downregulates cellular LPS sensitivity, miR-155 targets the mRNAs of genes pervasively involved in pro-inflammatory transcriptional programmes. Thus, miR-155 acts as a broad limiter of pro-inflammatory gene expression once the miR-146 dependent barrier to LPS triggered inflammation has been breached. Importantly, we also report alternative miR-155 activation by the sensing of bacterial peptidoglycan through cytoplasmic NOD-like receptor, NOD2. We predict that dose-dependent responses to environmental stimuli may involve functional specialization of seemingly co-induced miRNAs in other cellular circuitries as well.

COX-2 IN MYOCARDIAL INJURY AND REMODELLING: ELUCIDATING MECHANISMS OF INDUCTION BY FIBRONECTIN FRAGMENTS INCLUDING EXTRA-DOMAIN A

Cyclooxygenases (COXs) catalyse the rate-limiting step in prostanoid synthesis. COX-2 is essential for cardiovascular homeostasis and cardioprotection. Myocardial COX-2 induction occurs in the interstitial myofibroblast (MF) compartment via two distinct...

Zip14 expression induced by lipopolysaccharides in macrophages attenuates inflammatory response

We investigated the role and regulation of zinc transporters in the activation of the inflammatory response in macrophages. Our exploratory computational study found that Zip14 (SLC39A14) was consistently up-regulated in activated macrophages; we therefore focused subsequently on that gene in the mechanistic study. The expression and function of Zip14 was assessed in primary macrophages obtained by in-vitro differentiation of monocytes from human blood. Primary macrophages were subjected to treatments with lipopolysaccharides, cytokines, chemicals, and pharmacological agents. SLC39A14 and inflammatory cytokine gene expressions were assessed by RT-qPCR. Zip14 siRNA knockdown was performed to explore the gene function. Lipopolysaccharide's inflammatory stimulus was a strong inducer of SLC39A14 mRNA expression in macrophages. This induction was dependent on calcium signaling, GC-rich DNA-binding, and NF-κB down-regulation. Impregnation of lipopolysaccharide-stimulated macrophages with the glucocorticoid dexamethasone further enhanced Zip14 expression while reducing interleukin-6 and tumor necrosis factor-α production. Zip14 knockdown in macrophages attenuated the expression and secretion of cytokines, indicating a buffering function for this zinc transporter. Collectively, our results identified the zinc transporter Zip14 as expressed downstream of lipopolysaccharide signals in macrophages. Zip14 induction had a regulatory function in cytokine production.

TLR Signalling and Adapter Utilization in Primary Human In vitro Differentiated Adipocytes

Toll-like receptors (TLRs) are central to innate immunity and yet their expression is widespread and not restricted to professional inflammatory cells. TLRs have been reported on adipocytes and have been implicated in obesity-associated pathologies such as diabetes. Why TLRs are found on adipocytes is not clear although one hypothesis is that they may coordinate energy utilization for the energy intensive process of an immune response. We have explored TLR signalling in primary human in vitro differentiated adipocytes and investigated the specific adapter molecules that are involved. Only lipopolysaccharide (LPS), poly(I:C), Pam3CSK4 and MALP-2 could induce the production of IL-6, IL-8 and MCP-1 by adipocytes. Poly(I:C) alone caused a strong induction of type I interferons, as assessed by IP-10 production. Using siRNA, it was confirmed that LPS-dependent signalling in adipocytes occurs via TLR4 utilizing the adapter molecules MyD88, Mal and TRIF and caused rapid degradation of IκBα. Pam3CSK4 signalling utilized TLR2, MyD88 and Mal (but not TRIF). However, the response to poly(I:C) observed in these cells appeared not to require TRIF, but MyD88 was required for induction of NFκB-dependent cytokines by Poly(I:C). Despite this, IκBα degradation could not be detected in poly(I:C) stimulated adipocytes at any time-point up to 4 h. Indeed, IL-6 transcription was not induced until 8-16 h after exposure. These data suggest that Pam3CSK4 and LPS signal via the expected routes in human adipocytes, whereas poly(I:C)/TLR3 signalling may act via a TRIF-independent, MyD88-dependent route.

Induction of nuclear factor‐κB responses by the S100A9 protein is Toll‐like receptor‐4‐dependent

Interactions between danger-associated molecular patterns (DAMP) and pathogen-associated molecular patterns (PAMP) and pattern recognition receptors such as Toll-like receptors (TLRs) are critical for the regulation of the inflammatory process via activation of nuclear factor-κB (NF-κB) and cytokine secretion. In this report, we investigated the capacity of lipopolysaccharide (LPS) -free S100A9 (DAMP) protein to activate human and mouse cells compared with lipoprotein-free LPS (PAMP). First, we showed that LPS and S100A9 were able to increase NF-κB activity followed by increased cytokine and nitric oxide (NO) secretion both in human THP-1 cells and in mouse bone marrow-derived dendritic cells. Surprisingly, although S100A9 triggered a weaker cytokine response than LPS, we found that S100A9 more potently induced IκBα degradation and hence NF-κB activation. Both the S100A9-induced response and the LPS-induced response were completely absent in TLR4 knockout mice, whereas it was only slightly affected in RAGE knockout mice. Also, we showed that LPS and S100A9 NF-κB induction were strongly reduced in the presence of specific inhibitors of TLR-signalling. Chloroquine reduced S100A9 but not LPS signalling, indicating that S100A9 may need to be internalized to be fully active as a TLR4 inducer. This was confirmed using A488-labelled S100A9 that was internalized in THP-1 cells, showing a raise in fluorescence after 30 min at 37°. Chloroquine treatment significantly reduced the fluorescence. In summary, our data indicate that both human and mouse S100A9 are TLR4 agonists. Importantly, S100A9 induced stronger NF-κB activation albeit weaker cytokine secretion than LPS, suggesting that S100A9 and LPS activated NF-κB in a qualitatively distinct manner.

Gut-Derived Lipopolysaccharide Promotes T-Cell–Mediated Hepatitis in Mice through Toll-Like Receptor 4

Robust clinical and epidemiologic data support the role of inflammation as a key player in hepatocellular carcinoma (HCC) development. Our previous data showed that gut-derived lipopolysaccharide (LPS) promote HCC development by activating Toll-like receptor 4 (TLR4) expressed on myeloid-derived cells. However, the effects of gut-derived LPS on other types of liver injury models are yet to be studied. The purpose of this study was to determine the importance of gut-derived LPS and TLR4 signaling in a T-cell-mediated hepatitis-Con A-induced hepatitis model, which mimic the viral hepatitis. Reduction of endotoxin using antibiotics regimen or genetic ablation of TLR4 in mice significantly alleviate Con A-induced liver injury by inhibiting the infiltration of T lymphocytes into the liver and the activation of CD4(+) T lymphocytes as well as the production of T helper 1 cytokines; in contrast, exogenous LPS can promote Con A-induced hepatitis and CD4(+) T cells activation in vivo and in vitro. Reconstitution of TLR4-expressing myeloid cells in TLR4-deficient mice restored Con A-induced liver injury and inflammation, indicating the major cell target of LPS. In addition, TLR4 may positively regulate the target hepatocellular apoptosis via the perforin/granzyme B pathway. These data suggest that gut-derived LPS and TLR4 play important positive roles in Con A-induced hepatitis and modulation of the gut microbiotia may represent a new avenue for therapeutic intervention to treat acute hepatitis induced by hepatitis virus infection, thus to prevent hepatocellular carcinoma.

Soluble ST2 protein inhibits LPS stimulation on monocyte-derived dendritic cells

ST2 protein is a soluble splicing variant of ST2L protein, which is the receptor for interleukin-33 (IL-33). Previously, we reported that soluble ST2 suppressed the signal transduction of lipopolysaccharide (LPS) and cytokine production in monocytic cells. To investigate whether or not this inhibitory effect occurs in dendritic cells, which are the key players in innate and adaptive immunity, human monocyte-derived dendritic cells were pre-treated with soluble ST2 protein before LPS stimulation. Although soluble ST2 did not attenuate the LPS-induced maturation of dendritic cells, pre-treatment with soluble ST2 suppressed cytokine production and inhibited LPS signaling. Moreover, the proliferation of naive T cells was inhibited significantly by soluble ST2 pre-treatment. IL-33 had little effect on the cytokine production of immature monocyte-derived dendritic cells. Furthermore, soluble ST2 protein was internalized into dendritic cells, suggesting that soluble ST2 protein acts by a noncanonical mechanism other than the sequestration of IL-33.

The Toll Interleukin-1 Receptor (IL-1R) 8/Single Ig Domain IL-1R-Related Molecule Modulates the Renal Response to Bacterial Infection

Our immune system has to constantly strike a balance between activation and inhibition of an inflammatory response to combat invading pathogens and avoid inflammation-induced collateral tissue damage. Toll interleukin-1 receptor 8 (IL-1R-8)/single Ig domain IL-1R-related molecule (TIR8/SIGIRR) is an inhibitor of Toll-like receptor (TLR)/IL-1R signaling, which is predominantly expressed in the kidney. The biological role of renal TIR8 during infection is, however, unknown. We therefore evaluated renal TIR8 expression during Escherichia coli pyelonephritis and explored its role in host defense using TIR8(-/-) versus TIR8(+/+) mice. We found that TIR8 protein is abundantly present in the majority of cortical tubular epithelial cells. Pyelonephritis resulted in a significant downregulation of TIR8 mRNA in kidneys of TIR8(+/+) mice. TIR8 inhibited an effective host response against E. coli, as indicated by diminished renal bacterial outgrowth and dysfunction in TIR8(-/-) mice. This correlated with increased amounts of circulating and intrarenal neutrophils at the early phase of infection. TIR8(-/-) tubular epithelial cells had increased cytokine/chemokine production when stimulated with lipopolysaccharide (LPS) or heat-killed E. coli, suggesting that TIR8 played an anti-inflammatory role during pathogen stimulation by inhibiting LPS signaling. These data suggest that TIR8 is an important negative regulator of an LPS-mediated inflammatory response in tubular epithelial cells and dampens an effective antibacterial host response during pyelonephritis caused by uropathogenic E. coli.

Innate Immune Dysfunction in Trauma Patients

Innate Immune Dysfunction in Trauma Patients

Prediction of Novel Genes Associated with Negative Regulators of Toll-like Receptors-Induced Inflammation Based on Endotoxin Tolerance

Prior exposure of innate immune cells to lipopolysaccharide (LPS) has caused them to be refractory to further endotoxin stimulation, also termed endotoxin tolerance (ET). Bacterial LPS signals through Toll-like receptor (TLR) 4, which was thought to enable the innate immune system to deal with invasive pathogens and to restrain systemic inflammation efficiently. We established a robust model of ET and determined the level of TNF-α and IL-6 in cultured human monocytes. Then, microarray assay was applied to assess gene expression in this model. The results showed that 356 non-tolerizable genes were differentially expressed at a high level in tolerant monocytes. The genes selected were classified into several categories based on gene ontology (GO) and KEGG pathway database. And then literature annotations, protein-protein interaction (PPI) network, and functional consistency were applied to analyze the non-tolerizable genes. Finally, the microarray results were verified by quantitative real-time PCR of seven representative genes, including the two candidate genes, Spry2 and Smurf2, which were supposed to play a critical role in TLRs-induced inflammation based on literature retrieval. Our results would provide useful information for further analysis of regulating TLRs-induced inflammation, and would facilitate the study of associated mechanisms.

Trypsin inhibits lipopolysaccharide signaling in macrophages via toll-like receptor 4 accessory molecules

AimsTo examine the role of trypsin in the immune response of macrophages and to determine whether protease-activated receptors (PARs) are involved in the effects of trypsin. Main methodsWe used RAW264.7 cells and peritoneal macrophages isolated from C57BL/6 wild-type mice, PAR2 knockout mice, and ddY mice. Macrophages were stimulated with lipopolysaccharide (LPS) in the presence or absence of trypsin, thrombin, and PAR subtype-specific agonists (PARs-AP). Activation of macrophages was quantified by nitric oxide production and expression of inflammatory mediators, such as inducible nitric oxide synthase, interleukin-1β, and interleukin-6. To clarify the effect of trypsin on LPS receptors, we also investigated the expression of toll-like receptor 4 (TLR4), soluble MD-2 (sMD-2), membrane-bound MD-2 (mMD-2), soluble CD14 (sCD14), and membrane-bound CD14 (mCD14). To directly investigate the effect of trypsin on CD14 protein, we expressed recombinant CD14 protein. Key findingsTrypsin inhibited LPS-induced nitric oxide production and expression of inducible nitric oxide synthase, interleukin-1β, and interleukin-6. The same inhibitory effects of trypsin were observed in wild-type macrophages and in PAR2 knockout macrophages. Furthermore, the other PAR agonists, thrombin, PAR1-AP, PAR2-AP, and PAR4-AP, did not mimic the effect of trypsin. Although trypsin did not affect TLR4 or mMD-2 expression, sCD14, mCD14, and sMD-2 expressions were decreased by trypsin. Furthermore, trypsin also degraded recombinant CD14 protein. SignificanceTrypsin inhibited LPS signaling PAR-independently via degradation of TLR4 accessory molecules. This observation provides a better understanding of the complicated immune response in acute pancreatitis.

DOK3 Negatively Regulates LPS Responses and Endotoxin Tolerance

Innate immune activation via Toll-like receptors (TLRs), although critical for host defense against infection, must be regulated to prevent sustained cell activation that can lead to cell death. Cells repeatedly stimulated with lipopolysaccharide (LPS) develop endotoxin tolerance making the cells hypo-responsive to additional TLR stimulation. We show here that DOK3 is a negative regulator of TLR signaling by limiting LPS-induced ERK activation and cytokine responses in macrophages. LPS induces ubiquitin-mediated degradation of DOK3 leading to SOS1 degradation and inhibition of ERK activation. DOK3 mice are hypersensitive to sublethal doses of LPS and have altered cytokine responses in vivo. During endotoxin tolerance, DOK3 expression remains stable, and it negatively regulates the expression of SHIP1, IRAK-M, SOCS1, and SOS1. As such, DOK3-deficient macrophages are more sensitive to LPS-induced tolerance becoming tolerant at lower levels of LPS than wild type cells. Taken together, the absence of DOK3 increases LPS signaling, contributing to LPS-induced tolerance. Thus, DOK3 plays a role in TLR signaling during both naïve and endotoxin-induced tolerant conditions.

Molecular mechanisms of anti-inflammatory action of the flavonoid, tricin from Njavara rice (Oryza sativa L.) in human peripheral blood mononuclear cells: Possible role in the inflammatory signaling

Flavonoids are a group of natural substances that are located in sources of vegetal origin and are able to regulate acute and chronic inflammatory responses. The anti-oxidant and anti-inflammatory effects corroborate with the preferential use of Njavara, a rice variety in indigenous medicine and the phytochemical investigations revealed the occurrence of a flavonoid, tricin at significantly higher levels compared to staple varieties. This study describes the new aspects of inflammatory suppression by the Njavara rice by evaluating the role of active constituent, tricin in the regulation of production of various pro‐inflammatory markers by human peripheral blood mononuclear cells stimulated with lipopolysaccharide. Treatment with tricin resulted in significant down‐regulation of LPS-elicited production of TNF-α, IL-6, PGE2 and NO. Tricin was found to be a potential blocker of the expression of isoforms of nitric oxide synthase, cyclooxygenase and matrix metalloproteinases. Modulation of the cascade of molecular events in lipopolysaccharide signaling also includes inhibition of transcription factor NF-κB evidenced by the detection of enhanced p65 subunit in the nuclear extracts on tricin supplementation. The present study summarizes the role of the flavonoid, tricin in the modulation of the expression of different inflammatory mediators and revealed that the inhibitory effects on cell signaling pathways are responsible for its anti-inflammatory activity.

Peroxiredoxin-1, a possible target in modulating inflammatory cytokine production in macrophage like cell line RAW264.7

Peroxiredoxin (PRX), a scavenger of H(2) O(2) and alkyl hydroperoxides in living organisms, protects cells from oxidative stress. Contrary to its known anti-oxidant roles, the involvement of PRX-1 in the regulation of lipopolysaccharide (LPS) signaling is poorly understood, possible immunological functions of PRX-1 having been uncovered only recently. In the present study, it was discovered that the PRX-1 deficient macrophage like cell line (RAW264.7) has anti-inflammatory activity when stimulated by LPS. Treatment with LPS for 3 hrs resulted in increased gene expression of an anti-inflammatory cytokine, interleukin-10 (IL-10), in PRX-1 knock down RAW264.7 cells. Gene expression of pro-inflammatory cytokines IL-1β and tumor necrosis factor- α (TNF-α) did not show notable changes under the same conditions. However, production of these cytokines significantly decreased in PRX-1 knock down RAW264.7 cells with 12 hrs of stimulation. Production of IL-10 was also increased in PRX-1 knock down RAW264.7 cells with 12 hrs of stimulation. We predicted that higher concentrations of IL-10 would result in decreased expression of IL-1β and TNF-α in PRX-1 knock-down cells. This was confirmed by blocking IL-10, which reestablished IL-1β and TNF-α secretion. We also observed that increased concentrations of IL-10 do not affect the NF-κB pathway. Interestingly, STAT3 phosphorylation by LPS stimulation was significantly increased in PRX-1 knockdown RAW264.7 cells. Up-regulation of IL-10 in PRX-1 knockdown cells and the resulting downregulation of proinflammatory cytokine production seem to involve the STAT3 pathway in macrophages. Thus, down-regulation of PRX-1 may contribute to the suppression of adverse effects caused by excessive activation of macrophages through affecting the STAT3 signaling pathway.

Chaperone gp96-independent Inhibition of Endotoxin Response by Chaperone-based Peptide Inhibitors

HSP90 chaperones a large number of proteins, and it plays essential roles in multiple signaling pathways to maintain protein homeostasis in the cytosol. In addition, HSP90 has been implicated in mediating recognition of lipopolysaccharide (LPS). However, no pharmacologic agents have been developed to interrogate this pathway. Herein we demonstrate that a peptide-based inhibitor that was previously reported to inhibit the master Toll-like receptor-chaperone gp96, an endoplasmic reticulum paralog of HSP90, in fact blocks HSP90-LPS interaction. It inhibited the binding of LPS to the cell surface of both wild type and gp96-null cells and thereby abrogated the cellular response to LPS but not to other Toll-like receptor ligands. We also generated a series of peptide derivatives (named peptide inhibitors of endotoxin responsiveness (PIERs)) from the N-terminal helix structure of HSP90 and demonstrated their effectiveness in blocking LPS activity. PIER inhibition of LPS signaling was partially reversed by CD14 expression. Moreover, we found that a cell-permeable PIER abrogated HSP90 function and caused degradation of multiple known HSP90 client proteins in cancer cells. Thus, targeting HSP90 is a promising modality for treatment of both LPS-mediated pathology and cancer.

Immunoregulatory Protein Profiles of Necrotizing Enterocolitis versus Spontaneous Intestinal Perforation in Preterm Infants

Necrotizing enterocolitis (NEC) and spontaneous intestinal perforation (SIP) are the most common acute surgical emergencies associated with high morbidity and mortality in preterm infants. We aimed to compare the profiles of immunoregulatory proteins and identify novel mediators in plasma of NEC and SIP infants. We also investigated the expression of target genes in resected intestinal tissues and an enterocyte cell line. Using Cytokine Antibody Array assay, we reported the first comparative profiles of immunoregulatory proteins in plasma of NEC and SIP infants, and showed that dysregulated proteins belonged to functionally diversified categories, including pro- and anti-inflammation, angiogenesis, cell growth, wound healing, anti-apoptosis, cell adhesion and extracellular matrix reorganization. Validation by ELISA confirmed significantly higher concentrations of interleukin (IL)-6, angiopoietin (Ang)-2, soluble type II interleukin-1 receptor (sIL-1RII), and soluble urokinase-type plasminogen activator receptor (suPAR) in NEC infants compared with gestational age-matched control, and a lower level of an epidermal growth factor receptor, secreted form of receptor tyrosine-protein kinase ErbB3 (sErbB3), compared with SIP infants. mRNA expressions of IL1-RII and uPAR were up-regulated in resected bowel tissues from NEC infants, indicating that immunoregulation also occurred at the cellular level. In FHs-74 Int cells, Ang-2, IL1-RII and uPAR mRNA expressions were significantly induced by the combined treatment with lipopolysaccharide (LPS) and platelet activating factor (PAF). Our study provided plasmatic signatures of immunoregulatory proteins in NEC and SIP infants, and demonstrated involvement of multiple functional pathways. The magnitude of changes in these proteins was significantly more extensive in NEC infants, reflecting the different nature of injury and/or severity of inflammation. We speculate that dysregulation of IL-6, Ang-2, IL-1RII and uPAR occurred at both systemic and cellular levels, and probably mediated via LPS and endogeneous PAF signals. Such exaggerated immunologic responses may account for the high morbidity and mortality in NEC compared with SIP patients.

Evidence From In Vitro and In Vivo Studies Showing that Nuclear Factor‐Kappa B Within the Pituitary Folliculostellate Cells and Corticotrophs Regulates Adrenocorticotrophic Hormone Secretion in Experimental Endotoxaemia

The hypothalamic-pituitary-adrenocortical (HPA) responses to bacterial infection are mediated, in part, by the actions of lipopolysaccharide (LPS) on pituitary folliculostellate (FS) cells that release pro-inflammatory cytokines [e.g. interleukin (IL)-6] and thereby facilitate adrenocorticotrophic hormone (ACTH) release from neighbouring corticotrophs. In the present study, two murine pituitary cell lines [TtT/GF (FS cells) and AtT20 D16:16 (corticotrophs)], alone and in co-culture, and an in vivo model of endotoxaemia were used to examine the potential role of nuclear factor-kappa B (NF-κB) in mediating LPS-induced ACTH secretion. Both cell lines expressed mRNAs for the key components of the LPS signalling system. LPS stimulated IL-6 release from TtT/GF cells via a glucocorticoid-sensitive, NF-κB-dependent mechanism; it also activated NF-κB in AtT20 cells, as did corticotrophin-releasing hormone (CRH). IL-6 potentiated (but LPS reduced) the stimulatory effects of CRH on ACTH release from AtT20 cells, whereas blockade of NF-κB (SC-514) increased the ACTH release induced by CRH in the presence or absence of LPS. In co-cultures, CRH and LPS acted synergistically to induce release of both IL-6 and ACTH. However, although SC-514 suppressed the release of IL-6 evoked by CRH and LPS, it potentiated the concomitant increase in ACTH release. In vivo both immunological (LPS) and psychological (restraint) stress increased intrapituitary NF-κB, whereas an NF-κB inhibitor (PHA781535E) attenuated the LPS-induced release of ACTH and abolished the HPA response to restraint stress. The results obtained in the present study support the premise that NF-κB plays an important role in mediating LPS signalling in the anterior pituitary gland, particularly in relation to IL-6 and ACTH secretion, and provide novel evidence that NF-κB blockade in vivo compromises stress-induced ACTH release.