Contribution of TNF-alpha converting enzyme and proteinase-3 to TNF-alpha processing in human alveolar macrophages

Pseudomonas aeruginosa Alters Critical Lung Epithelial Cell Functions through Activation of ADAM17

Severe epithelial dysfunction is one major hallmark throughout the pathophysiological progress of bacterial pneumonia. Junctional and cellular adhesion molecules (e.g., JAMA-A, ICAM-1), cytokines (e.g., TNFα), and growth factors (e.g., TGFα), controlling proper lung barrier function and leukocyte recruitment, are proteolytically cleaved and released into the extracellular space through a disintegrin and metalloproteinase (ADAM) 17. In cell-based assays, we could show that the protein expression, maturation, and activation of ADAM17 is upregulated upon infection of lung epithelial cells with Pseudomonas aeruginosa and Exotoxin A (ExoA), without any impact of infection by Streptococcus pneumoniae. The characterization of released extracellular vesicles/exosomes and the comparison to heat-inactivated bacteria revealed that this increase occurred in a cell-associated and toxin-dependent manner. Pharmacological targeting and gene silencing of ADAM17 showed that its activation during infection with Pseudomonas aeruginosa was critical for the cleavage of junctional adhesion molecule A (JAM-A) and epithelial cell survival, both modulating barrier integrity, epithelial regeneration, leukocyte adhesion and transepithelial migration. Thus, site-specific targeting of ADAM17 or blockage of the activating toxins may constitute a novel anti-infective therapeutic option in Pseudomonas aeruginosa lung infection preventing severe epithelial and organ dysfunctions and stimulating future translational studies.

Molecular and cellular regulation of psoriatic inflammation

This review highlights the molecular and cellular mechanisms underlying psoriatic inflammation with an emphasis on recent developments which may impact on treatment approaches for this chronic disease. We consider both the skin and the musculoskeletal compartment and how different manifestations of psoriatic inflammation are linked. This review brings a focus to the importance of inflammatory feedback loops that exist in the initiation and chronic stages of the condition, and how close interaction between the epidermis and both innate and adaptive immune compartments drives psoriatic inflammation. Furthermore, we highlight work done on biomarkers to predict the outcome of therapy as well as the transition from psoriasis to psoriatic arthritis.

The role of ADAM17 during liver damage

A disintegrin and metalloprotease (ADAM) 17 is a membrane bound protease, involved in the cleavage and thus regulation of various membrane proteins, which are critical during liver injury. Among ADAM17 substrates are tumor necrosis factor α (TNFα), tumor necrosis factor receptor 1 and 2 (TNFR1, TNFR2), the epidermal growth factor receptor (EGFR) ligands amphiregulin (AR) and heparin-binding-EGF-like growth factor (HB-EGF), the interleukin-6 receptor (IL-6R) and the receptor for a hepatocyte growth factor (HGF), c-Met. TNFα and its binding receptors can promote liver injury by inducing apoptosis and necroptosis in liver cells. Consistently, hepatocyte specific deletion of ADAM17 resulted in increased liver cell damage following CD95 stimulation. IL-6 trans-signaling is critical for liver regeneration and can alleviate liver damage. EGFR ligands can prevent liver damage and deletion of amphiregulin and HB-EGF can result in increased hepatocyte death and reduced proliferation. All of which indicates that ADAM17 has a central role in liver injury and recovery from it. Furthermore, inactive rhomboid proteins (iRhom) are involved in the trafficking and maturation of ADAM17 and have been linked to liver damage. Taken together, ADAM17 can contribute in a complex way to liver damage and injury.

A leukotriene-dependent spleen-liver axis drives TNF production in systemic inflammation

Production of the proinflammatory cytokine tumor necrosis factor (TNF) must be precisely regulated for effective host immunity without the induction of collateral tissue damage. Here, we showed that TNF production was driven by a spleen-liver axis in a rat model of systemic inflammation induced by bacterial lipopolysaccharide (LPS). Analysis of cytokine expression and secretion in combination with splenectomy and hepatectomy revealed that the spleen generated not only TNF but also factors that enhanced TNF production by the liver, the latter of which accounted for nearly half of the TNF secreted into the circulation. Using mass spectrometry-based lipidomics, we identified leukotriene B₄ (LTB₄) as a candidate blood-borne messenger in this spleen-liver axis. LTB₄ was essential for spleen-liver communication in vivo, as well as for humoral signaling between splenic macrophages and Kupffer cells in vitro. LPS stimulated the splenic macrophages to secrete LTB₄, which primed Kupffer cells to secrete more TNF in response to LPS in a manner dependent on LTB₄ receptors. These findings provide a framework to understand how systemic inflammation can be regulated at the level of interorgan communication.

ADAM17: An Emerging Therapeutic Target for Lung Cancer

Lung cancer is the leading cause of cancer-related mortality, which histologically is classified into small-cell lung cancer (SCLC) and non-small cell lung cancer (NSCLC). NSCLC accounts for approximately 85% of all lung cancer diagnoses, with the majority of patients presenting with lung adenocarcinoma (LAC). KRAS mutations are a major driver of LAC, and are closely related to cigarette smoking, unlike mutations in the epidermal growth factor receptor (EGFR) which arise in never-smokers. Although the past two decades have seen fundamental progress in the treatment and diagnosis of NSCLC, NSCLC still is predominantly diagnosed at an advanced stage when therapeutic interventions are mostly palliative. A disintegrin and metalloproteinase 17 (ADAM17), also known as tumour necrosis factor-α (TNFα)-converting enzyme (TACE), is responsible for the protease-driven shedding of more than 70 membrane-tethered cytokines, growth factors and cell surface receptors. Among these, the soluble interleukin-6 receptor (sIL-6R), which drives pro-inflammatory and pro-tumourigenic IL-6 trans-signaling, along with several EGFR family ligands, are the best characterised. This large repertoire of substrates processed by ADAM17 places it as a pivotal orchestrator of a myriad of physiological and pathological processes associated with the initiation and/or progression of cancer, such as cell proliferation, survival, regeneration, differentiation and inflammation. In this review, we discuss recent research implicating ADAM17 as a key player in the development of LAC, and highlight the potential of ADAM17 inhibition as a promising therapeutic strategy to tackle this deadly malignancy.

Inflammatory cytokine production in tumor cells upon chemotherapy drug exposure or upon selection for drug resistance

Tumor Necrosis Factor alpha (TNF-α) has been shown to be released by tumor cells in response to docetaxel, and lipopolysaccharides (LPS), the latter through activation of toll-like receptor 4 (TLR4). However, it is unclear whether the former involves TLR4 receptor activation through direct binding of the drug to TLR4 at the cell surface. The current study was intended to better understand drug-induced TNF-α production in tumor cells, whether from short-term drug exposure or in cells selected for drug resistance. ELISAs were employed to measure cytokine release from breast and ovarian tumor cells in response to several structurally distinct chemotherapy agents and/or TLR4 agonists or antagonists. Drug uptake and drug sensitivity studies were also performed. We observed that several drugs induced TNF-αrelease from multiple tumor cell lines. Docetaxel-induced cytokine production was distinct from that of LPS in both MyD88-positive (MCF-7) and MyD88-deficient (A2780) cells. The acquisition of docetaxel resistance was accompanied by increased constitutive production of TNF-αand CXCL1, which waned at higher levels of resistance. In docetaxel-resistant MCF-7 and A2780 cell lines, the production of TNF-α could not be significantly augmented by docetaxel without the inhibition of P-gp, a transporter protein that promotes drug efflux from tumor cells. Pretreatment of tumor cells with LPS sensitized MyD88-positive cells (but not MyD88-deficient) to docetaxel cytotoxicity in both drug-naive and drug-resistant cells. Our findings suggest that taxane-induced inflammatory cytokine production from tumor cells depends on the duration of exposure, requires cellular drug-accumulation, and is distinct from the LPS response seen in breast tumor cells. Also, stimulation of the LPS-induced pathway may be an attractive target for treatment of drug-resistant disease.

Apolipoprotein A-I Limits the Negative Effect of Tumor Necrosis Factor on Lymphangiogenesis

OBJECTIVE

Lymphatic endothelial dysfunction underlies the pathogenesis of many chronic inflammatory disorders. The proinflammatory cytokine tumor necrosis factor (TNF) is known for its role in disrupting the function of the lymphatic vasculature. This study investigates the ability of apolipoprotein (apo) A-I, the principal apolipoprotein of high-density lipoproteins, to preserve the normal function of lymphatic endothelial cells treated with TNF.

APPROACH AND RESULTS

TNF decreased the ability of lymphatic endothelial cells to form tube-like structures. Preincubation of lymphatic endothelial cells with apoA-I attenuated the TNF-mediated inhibition of tube formation in a concentration-dependent manner. In addition, apoA-I reversed the TNF-mediated suppression of lymphatic endothelial cell migration and lymphatic outgrowth in thoracic duct rings. ApoA-I also abrogated the negative effect of TNF on lymphatic neovascularization in an ATP-binding cassette transporter A1-dependent manner. At the molecular level, this involved downregulation of TNF receptor-1 and the conservation of prospero-related homeobox gene-1 expression, a master regulator of lymphangiogenesis. ApoA-I also re-established the normal phenotype of the lymphatic network in the diaphragms of human TNF transgenic mice.

CONCLUSIONS

ApoA-I restores the neovascularization capacity of the lymphatic system during TNF-mediated inflammation. This study provides a proof-of-concept that high-density lipoprotein-based therapeutic strategies may attenuate chronic inflammation via its action on lymphatic vasculature.

Noncoding RNAs and LRRFIP1 regulate TNF expression

Noncoding RNAs have been implicated in the regulation of expression of numerous genes; however, the mechanism is not fully understood. We identified bidirectional, long noncoding RNAs upstream of the TNF gene using five different methods. They arose in a region where the repressors LRRFIP1, EZH2, and SUZ12 were demonstrated to bind, suggesting a role in repression. The noncoding RNAs were polyadenylated, capped, and chromatin associated. Knockdown of the noncoding RNAs was associated with derepression of TNF mRNA and diminished binding of LRRFIP1 to both RNA targets and chromatin. Overexpression of the noncoding RNAs led to diminished expression of TNF and recruitment of repressor proteins to the locus. One repressor protein, LRRFIP1, bound directly to the noncoding RNAs. These data place the noncoding RNAs upstream of TNF gene as central to the transcriptional regulation. They appear to serve as a platform for the assembly of a repressive complex.

Membrane versus soluble isoforms of TNF-α exert opposing effects on tumor growth and survival of tumor-associated myeloid cells

TNF-α, produced by most malignant cells, orchestrates the interplay between malignant cells and myeloid cells, which have been linked to tumor growth and metastasis. Although TNF-α can exist as one of two isoforms, a 26-kDa membrane tethered form (mTNF-α) or a soluble 17-kDa cytokine (sTNF-α), the vast majority of published studies have only investigated the biologic effects of the soluble form. We show for the first time that membrane and soluble isoforms have diametrically opposing effects on both tumor growth and myeloid content. Mouse lung and melanoma tumor lines expressing mTNF-α generated small tumors devoid of monocytes versus respective control lines or lines expressing sTNF-α. The lack of myeloid cells was due to a direct effect of mTNF-α on myeloid survival via induction of cell necrosis by increasing reactive oxygen species. Human non-small cell lung carcinoma expressed varying levels of both soluble and membrane TNF-α, and gene expression patterns favoring mTNF-α were predictive of improved lung cancer survival. These data suggest that there are significant differences in the role of different TNF-α isoforms in tumor progression and the bioavailability of each isoform may distinctly regulate tumor progression. This insight is critical for effective intervention in cancer therapy with the available TNF-α inhibitors, which can block both TNF-α isoforms.

Neutrophil-mediated inhibition of proinflammatory cytokine responses

Neutrophils (polymorphonuclear neutrophils [PMNs]) play an elaborate role in the innate immune response against invading pathogens. Recent research provided evidence that PMNs can play a modulatory role in inflammation next to their primary role of phagocytosis. In the current study, we investigated whether neutrophils can modulate the innate immune response against Candida albicans. Production of the proinflammatory cytokines IL-1β and TNF-α by human PBMCs in response to C. albicans or LPS was decreased by coculture of PMNs; however, the anti-inflammatory cytokine IL-10 remained unaffected. Using Transwells and cells of patients with chronic granulomatous disease, we show that this downregulation of proinflammatory cytokine production was independent of phagocytosis and reactive oxygen species but was dependent on a soluble factor. We suggest that neutrophil-derived proteases are responsible for the downregulation of IL-1β and TNF-α, as cytokine production could be recovered by addition of α1-antitrypsin, an endogenous inhibitor of serine proteases. PMN lysates and neutrophil elastase could degrade recombinant human IL-1β and TNF-α but not IL-10, and this could be inhibited by addition of α1-antitrypsin. Moreover, we also provide evidence that the dampening effect of PMNs is present in vivo in a murine zymosan-induced arthritis model and a murine experimental endotoxemia model. Altogether, our data show that PMNs can dampen the proinflammatory response to C. albicans by protease-mediated degradation of cytokines. This observation suggest that PMNs might play a important regulatory role in the host defense against C. albicans and can be important for understanding the regulation of inflammation in general.

Inhibition of the transcription factor c-Jun by the MAPK family, and not the NF-κB pathway, suggests that peanut extract has anti-inflammatory properties

BACKGROUND

Tumor necrosis factor-α (TNF-α) is involved in inflammatory responses in atherosclerosis. We propose an in vitro cellular assay to evaluate the anti-inflammatory mechanisms of potential modifiers such as food extracts. In the current model we assessed an anti-inflammatory effect of polyphenol-rich peanut extract in lipopolysaccharide (LPS)-induced THP-1 monocytes.

METHODS

THP-1 monocytes were incubated with peanut extract (5, 25, 50 and 100 μg/mL) consisting of 39% flavonols, 37% flavanols and 24% phenolic acid (or BAY 11-7082 (5 μM) as experiment control) for 1 h and then stimulated with LPS (500 ng/mL) for 4 h. Cytotoxicity was measured as lactate dehydrogenase (LDH) activity release. NF-κB and MAPK family were determined by TransAm kit while TNF-α mRNA levels and its mRNA stability by RT-PCR. Intra- and extracellular TNF-α protein was measured by ELISA, and TNF-α converting enzyme (TACE) activity by a fluorimetric assay.

RESULTS

Peanut extract inhibited the maximal LPS-induced extracellular TNF-α protein secretion by 18%, 29% and 47% at 25, 50 and 100 μg/mL, respectively (P<0.05). LPS stimulation revealed that 85% of TNF-α was released extracellularly while 15% remained intracellular. Peanut extract did not modify NF-κB but, instead, reduced c-Jun transcription factor activity (P<0.05), decreased TNF-α mRNA (albeit non-significantly) and had no effect on mRNA stability and TACE activity.

CONCLUSION

Polyphenol-rich peanut extract reduces extracellular TNF-α protein by inhibiting c-Jun transcription factor from MAPK family, suggesting an anti-inflammatory effect. The proposed THP-1 monocyte model could be used to assess food extract impact (site and size effects) on the inflammation pathway.

Lung endothelial ADAM17 regulates the acute inflammatory response to lipopolysaccharide

Acute lung injury (ALI) is associated with increased vascular permeability, leukocyte recruitment, and pro-inflammatory mediator release. We investigated the role of the metalloproteinase ADAM17 in endotoxin-induced ALI with focus on endothelial ADAM17. In vitro, endotoxin-mediated induction of endothelial permeability and IL-8-induced transmigration of neutrophils through human microvascular endothelial cells required ADAM17 as shown by inhibition with GW280264X or shRNA-mediated knockdown. In vivo, ALI was induced by intranasal endotoxin-challenge combined with GW280264X treatment or endothelial adam17-knockout. Endotoxin-triggered upregulation of ADAM17 mRNA in the lung was abrogated in knockout mice and associated with reduced ectodomain shedding of the junctional adhesion molecule JAM-A and the transmembrane chemokine CX3CL1. Induced vascular permeability, oedema formation, release of TNF-α and IL-6 and pulmonary leukocyte recruitment were all markedly reduced by GW280264X or endothelial adam17-knockout. Intranasal application of TNF-α could not restore leukocyte recruitment and oedema formation in endothelial adam17-knockout animals. Thus, activation of endothelial ADAM17 promotes acute pulmonary inflammation in response to endotoxin by multiple endothelial shedding events most likely independently of endothelial TNF-α release leading to enhanced vascular permeability and leukocyte recruitment.

Investigation of the role of TNF-α converting enzyme (TACE) in the inhibition of cell surface and soluble TNF-α production by acute ethanol exposure

Toll-like receptors (TLRs) play a fundamental role in the immune system by detecting pathogen associated molecular patterns (PAMPs) to sense host infection. Ethanol at doses relevant for humans inhibits the pathogen induced cytokine response mediated through TLRs. The current study was designed to investigate the mechanisms of this effect by determining whether ethanol inhibits TLR3 and TLR4 mediated TNF-α secretion through inhibition of transcription factor activation or post-transcriptional effects. In NF-κB reporter mice, activation of NF-κB in vivo by LPS was inhibited by ethanol (LPS alone yielded 170,000±35,300 arbitrary units of light emission; LPS plus ethanol yielded 56,120±16880, p = 0.04). Inhibition of protein synthesis by cycloheximide revealed that poly I:C- or LPS-induced secreted TNF-α is synthesized de novo, not released from cellular stores. Using real time RT-PCR, we found inhibition of LPS and poly I:C induced TNF-α gene transcription by ethanol. Using an inhibitor of tumor necrosis factor alpha converting enzyme (TACE), we found that shedding caused by TACE is a prerequisite for TNF-α release after pathogen challenge. Flow cytometry was used to investigate if ethanol decreases TNF-α secretion by inhibition of TACE. In cells treated with LPS, ethanol decreased both TNF-α cell surface expression and secretion. For example, 4.69±0.60% of untreated cells were positive for cell surface TNF-α, LPS increased this to 25.18±0.85%, which was inhibited by ethanol (86.8 mM) to 14.29±0.39% and increased by a TACE inhibitor to 57.88±0.62%. In contrast, cells treated with poly I:C had decreased secretion of TNF-α but not cell surface expression. There was some evidence for inhibition of TACE by ethanol in the case of LPS, but decreased TNF-α gene expression seems to be the major mechanism of ethanol action in this system.

Reactive oxygen species and p38 mitogen-activated protein kinase mediate tumor necrosis factor α-converting enzyme (TACE/ADAM-17) activation in primary human monocytes

Tumor necrosis factor α-converting enzyme (TACE) is responsible for the shedding of cell surface TNF. Studies suggest that reactive oxygen species (ROS) mediate up-regulation of TACE activity by direct oxidization or modification of the protein. However, these investigations have been largely based upon nonphysiological stimulation of promonocytic cell lines which may respond and process TACE differently from primary cells. Furthermore, investigators have relied upon TACE substrate shedding as a surrogate for activity quantification. We addressed these concerns, employing a direct, cell-based fluorometric assay to investigate the regulation of TACE catalytic activity on freshly isolated primary human monocytes during LPS stimulation. We hypothesized that ROS mediate up-regulation of TACE activity indirectly, by activation of intracellular signaling pathways. LPS up-regulated TACE activity rapidly (within 30 min) without changing cell surface TACE expression. Scavenging of ROS or inhibiting their production by flavoprotein oxidoreductases significantly attenuated LPS-induced TACE activity up-regulation. Exogenous ROS (H(2)O(2)) also up-regulated TACE activity with similar kinetics and magnitude as LPS. H(2)O(2)- and LPS-induced TACE activity up-regulation were effectively abolished by a variety of selective p38 MAPK inhibitors. Activation of p38 was redox-sensitive as H(2)O(2) caused p38 phosphorylation, and ROS scavenging significantly reduced LPS-induced phospho-p38 expression. Inhibition of the p38 substrate, MAPK-activated protein kinase 2, completely attenuated TACE activity up-regulation, whereas inhibition of ERK had little effect. Lastly, inhibition of cell surface oxidoreductases prevented TACE activity up-regulation distal to p38 activation. In conclusion, our data indicate that in primary human monocytes, ROS mediate LPS-induced up-regulation of TACE activity indirectly through activation of the p38 signaling pathway.

Studies on the role of acid sphingomyelinase and ceramide in the regulation of tumor necrosis factor alpha (TNFalpha)-converting enzyme activity and TNFalpha secretion in macrophages

Acid sphingomyelinase (ASMase) has been proposed to mediate lipopolysaccharide (LPS) signaling in various cell types. This study shows that ASMase is a negative regulator of LPS-induced tumor necrosis factor alpha (TNFalpha) secretion in macrophages. ASMase-deficient (asm(-/-)) mice and isolated peritoneal macrophages produce severalfold more TNFalpha than their wild-type (asm(+/+)) counterparts when stimulated with LPS, whereas the addition of exogenous ceramides or sphingomyelinase reduces the differences. The underlying mechanism for these effects is not transcriptional but post-translational. The TNFalpha-converting enzyme (TACE) catalyzes the maturation of the 26-kDa precursor (pro-TNFalpha) to an active 17-kDa form (soluble (s)TNFalpha). In mouse peritoneal macrophages, the activity of TACE was the rate-limiting factor regulating TNFalpha production. A substantial portion of the translated pro-TNFalpha was not processed to sTNFalpha; instead, it was rapidly internalized and degraded in the lysosomes. TACE activity was 2-3-fold higher in asm(-/-) macrophages as compared with asm(+/+) macrophages and was suppressed when cells were treated with exogenous ceramide and sphingomyelinase. Indirect immunofluorescence analyses revealed distinct TNFalpha-positive structures in the close vicinity of the plasma membrane in asm(-/-) but not in asm(+/+) macrophages. asm(-/-) cells also had a higher number of early endosomal antigen 1-positive early endosomes. Experiments that involved inhibitors of TACE, endocytosis, and lysosomal proteolysis suggest that in the asm(-/-) cells a significant portion of pro-TNFalpha was sequestered within the early endosomes, and instead of undergoing lysosomal proteolysis, it was recycled to the plasma membrane and processed to sTNFalpha.

Signaling pathways involved in LPS induced TNFalpha production in human adipocytes

Background

The development of obesity has been linked to an inflammatory process, and the role of adipose tissue in the secretion of pro-inflammatory molecules such as IL-6 or TNFalpha has now been largely confirmed. Although TNFalpha secretion by adipose cells is probably induced, most notably by TLR ligands, the activation and secretion pathways of this cytokine are not yet entirely understood. Moreover, given that macrophagic infiltration is a characteristic of obesity, it is difficult to clearly establish the level of involvement of the different cellular types present within the adipose tissue during inflammation.

Methods

Primary cultures of human adipocytes and human peripheral blood mononuclear cells were used. Cells were treated with a pathogen-associated molecular pattern: LPS, with and without several kinase inhibitors. Western blot for p38 MAP Kinase was performed on cell lysates. TNFalpha mRNA was detected in cells by RT-PCR and TNFalpha protein was detected in supernatants by ELISA assays.

Results

We show for the first time that the production of TNFalpha in mature human adipocytes is mainly dependent upon two pathways: NFkappaB and p38 MAP Kinase. Moreover, we demonstrate that the PI3Kinase pathway is clearly involved in the first step of the LPS-pathway. Lastly, we show that adipocytes are able to secrete a large amount of TNFalpha compared to macrophages.

Conclusion

This study clearly demonstrates that the LPS induced activation pathway is an integral part of the inflammatory process linked to obesity, and that adipocytes are responsible for most of the secreted TNFalpha in inflamed adipose tissue, through TLR4 activation.

Tumour necrosis factor-alpha processing in interstitial lung disease: a potential role for exogenous proteinase-3

Tumour necrosis factor (TNF) blockade has become an important immunomodulatory therapy, particularly in patients refractory to conventional immunosuppression, but responses can be unpredictable. Understanding the complex biology of TNF processing may be key to predicting such responses and reduce unwanted side effects. TNF bioavailability is regulated partly by TNF-alpha converting enzyme (TACE) cleavage; however, it can also be cleaved by proteinase-3 (PR-3). We have demonstrated this mechanism previously in healthy human alveolar macrophages (AM), leading us to hypothesize that PR-3-mediated TNF processing may be an important mechanism in inflammatory lung disease. Furthermore, this may be more apparent in diseases with a neutrophil component typical of usual interstitial pneumonia (UIP), compared with sarcoidosis, where lymphocytes predominate. We isolated AM from patients with UIP and sarcoidosis and healthy subjects. We found increased TACE expression on AM in sarcoidosis. In contrast, TACE was not increased in UIP; we found increased cleavage of glutathione S-transferase-proTNF) substrate, relative to both sarcoidosis and healthy controls. Furthermore, cleavage was subject to inhibition by serine protease inhibitor, rather than a TACE inhibitor BB-3103. Cleavage was proportional to the number of neutrophils isolated from bronchoalveolar lavage, whereas there was an inverse relationship between neutrophils and BB-3103 inhibition. There was also increased PR-3 on the AM surface in UIP relative to healthy controls. These data provide evidence for PR-3-mediated cleavage in UIP, which may have implications for future therapeutic targeting of TACE.

Anti-inflammatory effect of palmitoylethanolamide on human adipocytes

Obesity leads to the appearance of an inflammatory process, which can be initiated even with a moderate weight gain. Palmitoylethanolamide (PEA) is an endogenous lipid, secreted by human adipocytes, that possesses numerous anti-inflammatory properties. The main purpose of this study was to investigate the anti-inflammatory effect of PEA on human adipocytes, as well as in a murine model. The production of tumor necrosis factor-alpha (TNF-alpha) by lipopolysaccharide (LPS)-treated human subcutaneous adipocytes in primary culture and CF-1 mice was investigated by enzyme-linked immunosorbent assay. The effects of PEA on adipocyte TNF-alpha secretion were explored as well as some suspected PEA anti-inflammatory pathways: nuclear factor-kappaB (NF-kappaB) pathway, peroxisome proliferator-activated receptor-alpha (PPAR-alpha) gene expression, and TNF-alpha-converting enzyme (TACE) activity. The effects of PEA on the TNF-alpha serum concentration in intraperitoneally LPS-treated mice were also studied. We demonstrate that the LPS induced secretion of TNF-alpha by human adipocytes is inhibited by PEA. This action is neither linked to a reduction in TNF-alpha gene transcription nor to the inhibition of TACE activity. Moreover, PPAR-alpha is not implicated in this anti-inflammatory activity. Lastly, PEA exhibits a wide-reaching anti-inflammatory action as the molecule is able to completely inhibit the strong increase in TNF-alpha levels in the serum of mice treated with high doses of LPS. In view of its virtual lack of toxicity, PEA might become a potentially interesting candidate molecule in the prevention of obesity-associated insulin resistance.

Inflammatory processes in preterm and term parturition

A role for the pro-inflammatory cytokines interleukin (IL)-1beta, IL-6, IL-8 and tumor necrosis factor alpha (TNF-alpha) is evident in term and preterm delivery, and this is independent of the presence of infection. All uterine tissues progress through a staged transformation near the end of pregnancy that leads from relative uterine quiescence and maintenance of pregnancy to the activation of the uterus that prepares it for the work of labour and production of stimulatory molecules that trigger the onset of labour and delivery. The uterus is activated by pro-inflammatory cytokines through stimulation of the expression and production of uterine activation proteins (UAPs). One of these actions is the stimulation of prostaglandin (PG) synthesis. Particularly important for labour is PGF(2alpha) and its receptor, PTGFR. In addition, pro-inflammatory cytokines are able to increase the synthesis of matrix metalloproteinases (MMPs), vascular endothelial growth factor (VEGF) and the progesterone receptor C isoform, which leads to decreased tissue progesterone responsiveness. Some of these effects are replicated by PGF(2alpha), suggesting that it may act via its receptor to amplify the direct actions of cytokines. In turn, VEGF may enhance leukocyte recruitment to the uterus, and MMP-9 may promote activation of inactive pro-form cytokines. Pro-inflammatory cytokines also decrease the activity of 11beta-hydroxysteroid dehydrogenase, which likely increases intrauterine cortisol concentrations. In turn, cortisol may drive PG synthesis. Together these feed-forward mechanisms activate the uterus, trigger the production of uterine contractile stimulants and lead to labour and delivery.

Leukocyte cell surface proteinases: regulation of expression, functions, and mechanisms of surface localization

A number of proteinases are expressed on the surface of leukocytes including members of the serine, metallo-, and cysteine proteinase superfamilies. Some proteinases are anchored to the plasma membrane of leukocytes by a transmembrane domain or a glycosyl phosphatidyl inositol (GPI) anchor. Other proteinases bind with high affinity to classical receptors, or with lower affinity to integrins, proteoglycans, or other leukocyte surface molecules. Leukocyte surface levels of proteinases are regulated by: (1) cytokines, chemokines, bacterial products, and growth factors which stimulate synthesis and/or release of proteinases by cells; (2) the availability of surface binding sites for proteinases; and/or (3) internalization or shedding of surface-bound proteinases. The binding of proteinases to leukocyte surfaces serves many functions including: (1) concentrating the activity of proteinases to the immediate pericellular environment; (2) facilitating pro-enzyme activation; (3) increasing proteinase stability and retention in the extracellular space; (4) regulating leukocyte function by proteinases signaling through cell surface binding sites or other surface proteins; and (5) protecting proteinases from inhibition by extracellular proteinase inhibitors. There is strong evidence that membrane-associated proteinases on leukocytes play critical roles in wound healing, inflammation, extracellular matrix remodeling, fibrinolysis, and coagulation. This review will outline the biology of membrane-associated proteinases expressed by leukocytes and their roles in physiologic and pathologic processes.

Neutrophil serine proteases fine-tune the inflammatory response

Neutrophil serine proteases are granule-associated enzymes known mainly for their function in the intracellular killing of pathogens. Their extracellular release upon neutrophil activation is traditionally regarded as the primary reason for tissue damage at the sites of inflammation. However, studies over the past several years indicate that neutrophil serine proteases may also be key regulators of the inflammatory response. Neutrophil serine proteases specifically process and release chemokines, cytokines, and growth factors, thus modulating their biological activity. In addition, neutrophil serine proteases activate and shed specific cell surface receptors, which can ultimately prolong or terminate cytokine-induced responses. Moreover, it has been proposed that these proteases can impact cell viability through their caspase-like activity and initiate the adaptive immune response by directly activating lymphocytes. In summary, these studies point to neutrophil serine proteases as versatile mediators that fine-tune the local immune response and identify them as potential targets for therapeutic interventions.

Inhibition of matrix metalloproteinases increases PPAR-alpha and IL-6 and prevents dietary-induced hepatic steatosis and injury in a murine model

Steatosis is a prominent feature of nonalcoholic fatty liver disease and a potential promoter of inflammation. Injury leading to cirrhosis is partly mediated by dysregulation of matrix protein turnover. Matrix metalloproteinase (MMP) inhibitors protect mice from lethal TNF-alpha induced liver injury. We hypothesized that Marimastat, a broad-spectrum MMP and TNF-alpha converting enzyme (TACE) inhibitor, might modulate this injury through interruption of inflammatory pathways. Triglyceride and phospholipid levels (liver, serum) and fatty acid profiles were used to assess essential fatty acid status and de novo lipogenesis as mechanisms for hepatic steatosis. Mice receiving a fat-free, high-carbohydrate diet (HCD) for 19 days developed severe fatty liver infiltration, demonstrated by histology, magnetic resonance spectroscopy, and elevated liver function tests. Animals receiving HCD plus Marimastat (HCD+MAR) were comparable to control animals. Increased tissue levels of peroxisome proliferator activated receptor-alpha (PPAR-alpha), higher levels of serum IL-6, and decreased levels of serum TNF-alpha receptor II were also seen in the HCD+MAR group compared with HCD-only. In addition, there was increased phosphorylation, and likely activation, of PPAR-alpha in the HCD+MAR group. PPAR-alpha is a transcription factor involved in beta-oxidation of fatty acids, and IL-6 is a hepatoprotective cytokine. Liver triglyceride levels were higher and serum triglyceride and phospholipid levels lower with HCD-only but improved with Marimastat treatment. HCD-only and HCD+MAR groups were essential fatty acid deficient and had elevated rates of de novo lipogenesis. We therefore conclude that Marimastat reduces liver triglyceride accumulation by increasing fat oxidation and/or liver clearance of triglycerides. This may be related to increased expression and activation of PPAR-alpha or IL-6, respectively.

Serglycin is the major secreted proteoglycan in macrophages and has a role in the regulation of macrophage tumor necrosis factor-alpha secretion in response to lipopolysaccharide

It has recently been shown that serglycin is essential for maturation of mast cell secretory granules. However, serglycin is expressed also by other cell types, and in this study we addressed the role of serglycin in macrophages. Adherent cells were prepared from murine peritoneal cell populations and from spleens, and analyzed for proteoglycan synthesis by biosynthetic labeling with [35S]sulfate. Conditioned media from serglycin-/- peritoneal macrophages and adherent spleen cells displayed a 65-80% reduction of 35S-labeled proteoglycans, compared with corresponding material from serglycin+/+ cells, indicating that serglycin is the dominant secretory proteoglycan in macrophages of these origins. In contrast, the levels of intracellular proteoglycans were similar in serglycin+/+ and serglycin-/- cells, suggesting that serglycin is not stored intracellularly to a major extent in macrophages. This is in contrast to mast cells, in which serglycin is predominantly stored intracellularly. Transmission electron microscopy revealed that the absence of serglycin did not cause any major morphological effects on peritoneal macrophages, in contrast to dramatic defects in intracellular storage vesicles in peritoneal mast cells. Several secretory products were not found to be affected by the lack of serglycin. However, the secretion of tumor necrosis factor-alpha in response to lipopolysaccharide stimulation was markedly higher in serglycin-/- cultures than in those of serglycin+/+. The present report thus demonstrates that serglycin is the major proteoglycan secreted by peritoneal macrophages and suggests that the macrophage serglycin may have a role in regulating secretion of tumor necrosis factor-alpha.