ADAM17 activity during human neutrophil activation and apoptosis

Endocytosis of the non-catalytic ADAM23: Recycling and long half-life properties

A Disintegrin And Metalloprotease 23 (ADAM23) is a member of the ADAMs family of transmembrane proteins, mostly expressed in nervous system, and involved in traffic and stabilization of Kv1-potassium channels, synaptic transmission, neurite outgrowth, neuronal morphology and cell adhesion. Also, ADAM23 has been linked to human pathological conditions, such as epilepsy, cancer metastasis and cardiomyopathy. ADAM23 functionality depends on the molecule presence at the cell surface and along the secretory pathway, as expected for a cell surface receptor. Because endocytosis is an important functional regulatory mechanism of plasma membrane receptors and no information is available about the traffic or turnover of non-catalytic ADAMs, we investigated ADAM23 internalization, recycling and half-life properties. Here, we show that ADAM23 undergoes constitutive internalization from the plasma membrane, a process that depends on lipid raft integrity, and is redistributed to intracellular vesicles, especially early and recycling endosomes. Furthermore, we observed that ADAM23 is recycled from intracellular compartments back to the plasma membrane and thus has longer half-life and higher cell surface stability compared with other ADAMs. Our findings suggest that regulation of ADAM23 endocytosis/stability could be exploited therapeutically in diseases in which ADAM23 is directly involved, such as epilepsy, cancer progression and cardiac hypertrophy.

Ectodomain shedding by ADAM17 (a disintegrin and metalloproteinase 17) in canine neutrophils

ADAM17 is a transmembrane protease expressed by most cells in humans and mice that cleaves cell surface substrates primarily in a cis manner, a process referred to as ectodomain shedding. ADAM17 has numerous substrates and plays a broad role in various physiological processes, including as a key regulator of inflammation. At this time, little is known about ADAM17 expression and function in dogs. A well-established ADAM17 substrate is the leukocyte adhesion protein CD62L (L-selectin). We show that a selective inhibitor of ADAM17, but not an inhibitor of its most closely related family member ADAM10, blocks CD62L shedding upon canine neutrophil activation. We also tested several anti-human ADAM17 monoclonal antibodies (mAbs) for staining canine neutrophils. Although most did not recognize canine neutrophils, the mAbs MEDI3622 and D1(A12) did. They also blocked the downregulation of CD62L upon neutrophil activation. MEDI3622 is a human IgG antibody and we found that a canine chimeric version of this mAb also blocked CD62L shedding by canine leukocytes. Taken together, our findings provide the first direct evidence of ADAM17 expression and sheddase activity in dogs, establishing a potential therapeutic target for various inflammatory disorders.

Inactivation of Endothelial ADAM17 Reduces Retinal Ischemia-Reperfusion Induced Neuronal and Vascular Damage

Retinal ischemia contributes to visual impairment in ischemic retinopathies. A disintegrin and metalloproteinase ADAM17 is implicated in multiple vascular pathologies through its ability to regulate inflammatory signaling via ectodomain shedding. We investigated the role of endothelial ADAM17 in neuronal and vascular degeneration associated with retinal ischemia reperfusion (IR) injury using mice with conditional inactivation of ADAM17 in vascular endothelium. ADAM17Cre-flox and control ADAM17flox mice were subjected to 40 min of pressure-induced retinal ischemia, with the contralateral eye serving as control. Albumin extravasation and retinal leukostasis were evaluated 48 h after reperfusion. Retinal morphometric analysis was conducted 7 days after reperfusion. Degenerate capillaries were assessed by elastase digest and visual function was evaluated by optokinetic test 14 and 7 days following ischemia, respectively. Lack of ADAM17 decreased vascular leakage and reduced retinal thinning and ganglion cell loss in ADAM17Cre-flox mice. Further, ADAM17Cre-flox mice exhibited a remarkable reduction in capillary degeneration following IR. Decrease in neurovascular degeneration in ADAM17Cre-flox mice correlated with decreased activation of caspase-3 and was associated with reduction in oxidative stress and retinal leukostasis. In addition, knockdown of ADAM17 resulted in decreased cleavage of p75NTR, the process known to be associated with retinal cell apoptosis. A decline in visual acuity evidenced by decrease in spatial frequency threshold observed in ADAM17flox mice was partially restored in ADAM17-endothelial deficient mice. The obtained results provide evidence that endothelial ADAM17 is an important contributor to IR-induced neurovascular damage in the retina and suggest that interventions directed at regulating ADAM17 activity can be beneficial for alleviating the consequences of retinal ischemia.

Role of Endothelial ADAM17 in Early Vascular Changes Associated with Diabetic Retinopathy

ADAM17, a disintegrin and metalloproteinase 17, is a transmembrane metalloproteinase that regulates bioavailability of multiple membrane-bound proteins via ectodomain shedding. ADAM17 activity was shown to contribute to a number of vascular pathologies, but its role in the context of diabetic retinopathy (DR) is not determined. We found that expression and enzymatic activity of ADAM17 are upregulated in human diabetic postmortem retinas and a mouse model of streptozotocin-induced diabetes. To further investigate the contribution of ADAM17 to vascular alterations associated with DR, we used human retinal endothelial cells (HREC) treated with ADAM17 neutralizing antibodies and exposed to glucidic stress and streptozotocin-induced endothelial ADAM17 knockout mice. Evaluation of vascular permeability, vascular inflammation, and oxidative stress was performed. Loss of ADAM17 in endothelial cells markedly reduced oxidative stress evidenced by decreased levels of superoxide, 3-nitrotyrosine, and 4-hydroxynonenal and decreased leukocyte-endothelium adhesive interactions in vivo and in vitro. Reduced leukostasis was associated with decreased vascular permeability and was accompanied by downregulation of intercellular adhesion molecule-1 expression. Reduction in oxidative stress in HREC was associated with downregulation of NAD(P)H oxidase 4 (Nox4) expression. Our data suggest a role for endothelial ADAM17 in DR pathogenesis and identify ADAM17 as a potential new therapeutic target for DR.

Expression, Role, and Regulation of Neutrophil Fcγ Receptors

Neutrophils are best known for their critical role in host defense, for which they utilize multiple innate immune mechanisms, including microbe-associated pattern recognition, phagocytosis, production of reactive oxygen species, and the release of potent proteases, mediators, antimicrobials, and neutrophil extracellular traps. Beyond their well-established contribution to innate immunity, neutrophils were more recently reported to interact with various other cell types, including cells from the adaptive immune system, thereby enabling neutrophils to tune the overall immune response of the host. Neutrophils express different receptors for IgG antibodies (Fcγ receptors), which facilitate the engulfment of IgG-opsonized microbes and trigger cell activation upon cross-linking of several receptors. Indeed, FcγRs (via IgG antibodies) confer neutrophils with a key feature of the adaptive immunity: an antigen-specific cell response. This review summarizes the expression and function of FcγRs on human neutrophils in health and disease and how they are affected by polymorphisms in the FCGR loci. Additionally, we will discuss the role of neutrophils in providing help to marginal zone B cells for the production of antibodies, which in turn may trigger neutrophil effector functions when engaging FcγRs.

Metalloproteinases TACE and MMP-9 Differentially Regulate Death Factors on Adult and Neonatal Monocytes After Infection with Escherichia coli

Background: Cleaving ligands and receptors of the tumor necrosis factor (TNF) superfamily can critically regulate the induction of apoptosis. Matrix metalloproteinases (MMPs) such as MMP-9 and tumor necrosis factor-α-converting enzyme (TACE) have been shown to cleave CD95-Ligand (CD95L) and TNF/(TNF receptor-1) TNFR1 which induce phagocytosis induced cell death (PICD) in adult monocytes. This process is reduced in neonatal monocytes. Methods: Here we tested in vitro, whether Escherichia coli infection mounts for activation of MMP-9 and TACE in monocytes and whether this process regulates PICD. Results: The surface expression of TACE was most prominent on infected adult monocytes. In contrast, surface presentation of MMP-9 was highest on infected neonatal monocytes. Selective blocking of MMP-9 decreased CD95L secretion, while inhibition of TACE left CD95L secretion unaltered. Blocking of MMP-9 increased surface CD95L (memCD95L) expression on infected neonatal monocytes to levels comparable to infected adult monocytes. Moreover, MMP-9 inhibition raised PICD of infected neonatal monocytes to levels observed for infected adult monocytes. In contrast, TACE inhibition decreased PICD in infected monocytes. Addition of extracellular TNF effectively induced memCD95L presentation and PICD of adult monocytes and less of neonatal monocytes. Conclusion: MMP-9 activity is crucial for downregulating cell-contact dependent PICD in E. coli infected neonatal monocytes. By this mechanism, MMP-9 could contribute to reducing sustained inflammation in neonates.

Enhanced expression of TACE contributes to elevated levels of sVCAM-1 in endometriosis

STUDY QUESTION

Are increased sVCAM-1 and sICAM-1 levels associated with tumor necrosis factor-alpha-converting enzyme (TACE) activity in endometriosis?

SUMMARY ANSWER

Here we provide the first functional evidence that induced TACE activity in human endometriotic epithelial cells is at least in part responsible for the enhanced release of sVCAM-1 from these cells.

WHAT IS KNOWN ALREADY

We and others have shown that serum-soluble (s)VCAM-1 levels are significantly higher in women with endometriosis, compared to disease-free controls. Experimental evidence exists suggesting a role of sICAM-1 and sVCAM-1 in the pathogenesis of endometriosis. TACE was identified as the protease responsible for phorbol 12-myristate 13-acetate (PMA)-induced VCAM-1 release in murine endothelial cells. Additionally, it has recently been shown that TACE is upregulated in the endometrial luminal epithelium of the mid-secretory phase in infertile women.

STUDY DESIGN, SIZE, DURATION

This study was conducted at the Tertiary Endometriosis Referral Center of the Medical University of Vienna. Samples from a total number of 97 women were collected between July 2013 and September 2014.

PARTICIPANTS/MATERIALS, SETTING, METHODS

After complete surgical exploration of the abdominopelvic cavity, 49 women with histologically proven endometriosis and 48 endometriosis-free control women were enrolled. Each participating woman contributed only one sample of eutopic endometrium and normal peritoneum, and some of the women with endometriosis contributed samples of diverse types of endometriotic lesions (in total 52 ectopic samples). Among the 49 women with endometriosis, 36 matched samples of endometriotic lesions and corresponding eutopic endometrium were collected. In order to detect sVCAM-1 and TACE protein by ELISA, peritoneal fluid (PF) samples were collected from 44 cases and 32 controls during surgery. Expression of TACE mRNA was analyzed by qRT-PCR in 111 endometrium tissue samples (28 eutopic control samples, 33 eutopic samples from women with endometriosis, 50 ectopic samples from lesions) and 37 healthy peritoneum samples. Immunohistochemistry was performed in 123 tissue samples (39 eutopic control samples, 42 eutopic samples from women with endometriosis, 42 ectopic samples from lesions) and the relation between tissue TACE protein levels and sVCAM-1 secretion was examined. PMA-induced sVCAM-1 release, and TACE- and VCAM-1-transcripts or proteins were measured in an immortalized endometriotic epithelial cell line (11Z) pre-incubated either with TACE inhibitors or following TACE siRNA knockdown.

MAIN RESULTS AND THE ROLE OF CHANCE

Here, we demonstrate that TACE protein is overexpressed in epithelium of tissue samples of both eutopic endometrium and ectopic lesions of women with endometriosis compared to disease-free controls (P < 0.001 both) and that the overexpression of the protein in the lesions is due to activation of TACE gene transcription (P < 0.001). Moreover, epithelial TACE protein was significantly higher in ectopic samples than in corresponding eutopic tissue of women with the disease (P < 0.001). High endometrial tissue TACE protein expression correlated with higher serum sVCAM-1 levels (P < 0.05) but not with sICAM-1 levels. Inhibition of TACE either by TACE inhibitors or by TACE siRNA knockdown resulted in decreased PMA-induced shedding of sVCAM-1 in vitro (P < 0.005 or P < 0.01, respectively), but the TACE inhibitors did not affect transcription of TACE or VCAM-1. Additionally, we observed an upregulation of TACE in proliferative endometrial epithelium of infertile (P < 0.005), compared to fertile women. TACE was increased in infertile women with endometriosis (P = 0.051) but not in infertile women without endometriosis.

LIMITATIONS, REASONS FOR CAUTION

Albeit well characterized, our control population included women with other gynecologic diseases, which may have impacted the levels of sVCAM-1 and tissue TACE expression levels, e.g. benign ovarian cysts or uterine fibroids. Thus, the results of our analysis have to be interpreted carefully and in the context of the current experimental settings.

WIDER IMPLICATIONS OF THE FINDINGS

The dysregulation of TACE substrate shedding represents a promising yet relatively unexplored area of endometriosis progression and could serve as a basis for the development of new treatments of the disease.

STUDY FUNDING AND COMPETING INTEREST(S)

This work was supported by the Ingrid Flick Foundation. The authors have no competing interests to declare.

Decoding the enigma of antiviral crisis: Does one target molecule regulate all?

•

IL-6 class switching provides regulation over pro- and anti-inflammatory responses.

•

Unregulated IL-6 trans-signaling promotes uncontrolled pro-inflammatory responses.

•

ADAM-17 regulates class switching between IL-6 trans- and classical-signaling.

•

Selective ADAM-17 blocking restricts overexpression of pro-inflammatory cytokines.

•

ADAM-17 may be an antiviral drug target to reduce immunopathology disease severity.

Disease fatality associated with Ebola, SARS-CoV and dengue infections in humans is attributed to a cytokine storm that is triggered by excessive pro-inflammatory responses. Interleukin (IL)-6 acts as a mediator between pro- and anti-inflammatory reactivity by initiating trans- and classical-signaling, respectively. Hence, IL-6 is assumed to provide a target for a broad range of antiviral agents. Available immunosuppressive antivirals are directed to control an often exaggerated pro-inflammatory response that gives rise to complex clinical conditions such as lymphocytopenia. It is known that IL-6, via its soluble receptor (sIL-6R), initiates a pro-inflammatory response while an anti-inflammatory response is triggered by the membrane-bound IL-6 receptor (IL-6R). Future antivirals should thus aim to target the mechanism that regulates switching between IL-6 trans- and classical-signaling. In this review, we propose that the tumour necrosis factor-α converting enzyme ADAM-17 could be the master molecule involved in regulating IL-6 class switching and through this in controlling pro- and anti-inflammatory responses to viral antigenic stimuli. Therefore, ADAM-17 should be considered as a potential target molecule for novel antiviral drug discovery that would regulate host reactivity to infection and thereby limit or prevent fatal outcomes.

Human neutrophils can mimic myeloid-derived suppressor cells (PMN-MDSC) and suppress microbead or lectin-induced T cell proliferation through artefactual mechanisms

We report that human conventional CD15⁺ neutrophils can be isolated in the peripheral blood mononuclear cell (PBMC) layer during Ficoll gradient separation, and that they can impair T cell proliferation in vitro without concomitant neutrophil activation and killing. This effect was observed in a total of 92 patients with organ transplants, lung cancer or anxiety/depression, and in 18 healthy donors. Although such features are typically associated in the literature with the presence of certain myeloid-derived suppressor cell (PMN-MDSC) populations, we found that commercial centrifuge tubes that contained membranes or gels for PBMC isolation led to up to 70% PBMC contamination by CD15⁺ neutrophils, with subsequent suppressive effects in certain cellular assays. In particular, the suppressive activity of human MDSC should not be evaluated using lectin or microbead stimulation, whereas assays involving soluble or plate-bound antibodies or MLR are unaffected. We conclude that CD15⁺ neutrophil contamination, and associated effects on suppressor assays, can lead to significant artefacts in studies of human PMN-MDSC.

Characterization of Yersinia pestis Interactions with Human Neutrophils In vitro

Yersinia pestis is a gram-negative, zoonotic, bacterial pathogen, and the causative agent of plague. The bubonic form of plague occurs subsequent to deposition of bacteria in the skin by the bite of an infected flea. Neutrophils are recruited to the site of infection within the first few hours and interactions between neutrophils and Y. pestis have been demonstrated in vivo. In contrast to macrophages, neutrophils have been considered non-permissive to Y. pestis intracellular survival. Several studies have shown killing of the vast majority of Y. pestis ingested by human neutrophils. However, survival of 10–15% of Y. pestis after phagocytosis by neutrophils is consistently observed. Furthermore, these surviving bacteria eventually replicate within and escape from the neutrophils. We set out to further characterize the interactions between Y. pestis and human neutrophils by (1) determining the effects of known Y. pestis virulence factors on bacterial survival after uptake by neutrophils, (2) examining the mechanisms employed by the neutrophil to kill the majority of intracellular Y. pestis, (3) determining the activation phenotype of Y. pestis-infected neutrophils, and (4) characterizing the Y. pestis-containing phagosome in neutrophils. We infected human neutrophils in vitro with Y. pestis and assayed bacterial survival and uptake. Deletion of the caf1 gene responsible for F1 capsule production resulted in significantly increased uptake of Y. pestis. Surprisingly, while the two-component regulator PhoPQ system is important for survival of Y. pestis within neutrophils, pre-induction of this system prior to infection did not increase bacterial survival. We used an IPTG-inducible mCherry construct to distinguish viable from non-viable intracellular bacteria and determined the association of the Y. pestis-containing phagosome with neutrophil NADPH-oxidase and markers of primary, secondary and tertiary granules. Additionally, we show that inhibition of reactive oxygen species (ROS) production or Src family kinases increased survival of intracellular bacteria indicating that both ROS and granule-phagosome fusion contribute to neutrophil killing of Y. pestis. The data presented here further our understanding of the Y. pestis neutrophil interactions and suggest the existence of still unknown virulence factors involved in Y. pestis survival within neutrophils.

Ectodomain Shedding by ADAM17: Its Role in Neutrophil Recruitment and the Impairment of This Process during Sepsis

Neutrophils are specialized at killing bacteria and are recruited from the blood in a rapid and robust manner during infection. A cascade of adhesion events direct their attachment to the vascular endothelium and migration into the underlying tissue. A disintegrin and metalloproteinase 17 (ADAM17) functions in the cell membrane of neutrophils and endothelial cells by cleaving its substrates, typically in a cis manner, at an extracellular site proximal to the cell membrane. This process is referred to as ectodomain shedding and it results in the downregulation of various adhesion molecules and receptors, and the release of immune regulating factors. ADAM17 sheddase activity is induced upon cell activation and rapidly modulates intravascular adhesion events in response to diverse environmental stimuli. During sepsis, an excessive systemic inflammatory response against infection, neutrophil migration becomes severely impaired. This involves ADAM17 as indicated by increased levels of its cleaved substrates in the blood of septic patients, and that ADAM17 inactivation improves neutrophil recruitment and bacterial clearance in animal models of sepsis. Excessive ADAM17 sheddase activity during sepsis thus appears to undermine in a direct and indirect manner the necessary balance between intravascular adhesion and de-adhesion events that regulate neutrophil migration into sites of infection. This review provides an overview of ADAM17 function and regulation and its potential contribution to neutrophil dysfunction during sepsis.

Semaphorin 4D inhibits neutrophil activation and is involved in the pathogenesis of neutrophil-mediated autoimmune vasculitis

Objectives

Inappropriate activation of neutrophils plays a pathological role in antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV). The aim of this study was to investigate the functions of semaphorin 4D (SEMA4D) in regulation of neutrophil activation, and its involvement in AAV pathogenesis.

Methods

Serum levels of soluble SEMA4D were evaluated by ELISA. Blood cell-surface expression of membrane SEMA4D was evaluated by flow cytometry. To determine the functional interactions between neutrophil membrane SEMA4D and endothelial plexin B2, wild-type and SEMA4D^−/− mice neutrophils were cultured with an endothelial cell line (MS1) stained with SYTOX green, and subjected to neutrophil extracellular trap (NET) formation assays. The efficacy of treating human neutrophils with recombinant plexin B2 was assessed by measuring the kinetic oxidative burst and NET formation assays.

Results

Serum levels of soluble SEMA4D were elevated in patients with AAV and correlated with disease activity scores. Cell-surface expression of SEMA4D was downregulated in neutrophils from patients with AAV, a consequence of proteolytic cleavage of membrane SEMA4D. Soluble SEMA4D exerted pro-inflammatory effects on endothelial cells. Membranous SEMA4D on neutrophils bound to plexin B2 on endothelial cells, and this interaction decreased NET formation. Recombinant plexin B2 suppressed neutrophil Rac1 activation through SEMA4D’s intracellular domain, and inhibited pathogen-induced or ANCA-induced oxidative burst and NET formation.

Conclusions

Neutrophil surface SEMA4D functions as a negative regulator of neutrophil activation. Proteolytic cleavage of SEMA4D as observed in patients with AAV may amplify neutrophil-mediated inflammatory responses. SEMA4D is a promising biomarker and potential therapeutic target for AAV.

Cutting Edge: Helicobacter pylori Induces Nuclear Hypersegmentation and Subtype Differentiation of Human Neutrophils In Vitro

Helicobacter pylori infects the human stomach and causes a spectrum of disease that includes gastritis, peptic ulcers, and gastric adenocarcinoma. A chronic, neutrophil-rich inflammatory response characterizes this infection. It is established that H. pylori stimulates neutrophil chemotaxis and a robust respiratory burst, but other aspects of this interaction are incompletely defined. We demonstrate here that H. pylori induces N1-like subtype differentiation of human neutrophils as indicated by profound nuclear hypersegmentation, a CD62L^dim, CD16^bright, CD11b^bright, CD66b^bright, CD63^bright surface phenotype, proinflammatory cytokine secretion, and cytotoxicity. Hypersegmentation requires direct neutrophil-H. pylori contact as well as transcription and both host and bacterial protein synthesis, but not urease, NapA, VacA, CagA, or CagT. The concept of neutrophil plasticity is new and, to our knowledge, these data are the first evidence that neutrophils can undergo subtype differentiation in vitro in response to bacterial pathogen infection. We hypothesize that these changes favor H. pylori persistence and disease.

Circulating Soluble IL-6R but Not ADAM17 Activation Drives Mononuclear Cell Migration in Tissue Inflammation

Neutrophil and mononuclear cell infiltration during inflammatory processes is highly regulated. The first cells at the site of infection or inflammation are neutrophils, followed by mononuclear cells. IL-6 plays an important role during inflammatory states. It has been shown in several models that the soluble form of IL-6R (sIL-6R) is involved in the recruitment of mononuclear cells by a mechanism called IL-6 trans-signaling. It had been speculated that sIL-6R was generated at the site of inflammation by shedding from neutrophils via activation of the metalloprotease ADAM17. Attempts to genetically delete the floxed ADAM17 gene selectively in myeloid cells infiltrating an air pouch cavity upon injection of carrageenan failed because in transgenic mice, LysM^cre did not lead to appreciable loss of the ADAM17 protein in these cells. We therefore used ADAM17 hypomorphic mice, which only express ∼5% of ADAM17 wild-type levels in all tissues and show virtually no shedding of all tested ADAM17 substrates, to clarify the role of ADAM17 during local inflammation in the murine air pouch model. In the present study, we demonstrate that although IL-6 and the trans-signaling mechanism is mandatory for cellular infiltration in this model, it is not ADAM17-mediated shedding of IL-6R within the pouch that orchestrates this inflammatory process. Instead, we demonstrate that sIL-6R is infiltrating from the circulation in an ADAM17-independent process. Our data suggest that this infiltrating sIL-6R, which is needed for IL-6 trans-signaling, is involved in the controlled resolution of an acute inflammatory episode.

Expression of ADAM17 and ADAM10 in nasal polyps

BACKGROUND

The "a disintegrin and metalloproteases" (ADAMs) are a multifunctional gene family that contribute to the homeostasis of the extracellular matrix, transduction of specific intracellular signals, organogenesis, inflammation, tissue remodeling, adhesion, and cell migration. ADAM17 is the best-characterized of the "sheddases," and its putative substrates are widespread, including various inflammatory modulators. ADAM10 is the most similar to ADAM17 in terms of protein sequence and the structural properties of their catalytic domains. The objective of this work was to assess the roles of ADAM17 and ADAM10 in nasal polyps (NPs) by measuring their expression.

METHODS

The expression of ADAM10 and 17 was investigated in NPs at endonasal sinus surgery (n = 15) and compared with that in inferior turbinate mucosa samples obtained from nonallergic hypertrophic rhinitis patients (n = 15). Tissue samples were analyzed by real-time polymerase chain reaction (PCR), Western blotting, and immunohistochemical staining.

RESULTS

The ADAM17 messenger RNA (mRNA) and protein levels were significantly higher in the inferior turbinate than in NPs (p < 0.05). The ADAM10 mRNA and protein levels did not differ significantly between NPs and inferior turbinates (p > 0.05). ADAM10 and ADAM17 were expressed primarily in inflammatory cells, submucosal glandular cells, and lining epithelial cells.

CONCLUSION

ADAM17 may contribute to the development of NPs in contrast to ADAM10, based on their expression patterns. It may be important to discover the role of ADAM17 in the development of NP and helpful to examine the specific mechanism of the development of NPs.

Tumor necrosis factor-α driven inflammation in alpha-1 antitrypsin deficiency: a new model of pathogenesis and treatment

Alpha-1 antitrypsin (AAT) deficiency (AATD) has traditionally been thought of as a genetic disorder characterized by lung destruction and early emphysema in a low AAT, and high neutrophil elastase (NE) environment in the lungs of affected individuals. Recently, a growing body of evidence has emerged to support the hypothesis that tumor necrosis factor alpha (TNF-α) is essential in the pathogenesis of both genetic AATD and non-genetic chronic obstructive pulmonary disease (COPD). Reports have highlighted the importance of TNF-α driven immune cell dysfunction in the development of lung disease in AATD. The authors discuss the role of AAT as a key modulator of TNF-α signaling firstly in the setting of AATD and secondly in other conditions where AAT augmentation therapy has potential utility as a novel therapy.

ADAM17 controls IL-6 signaling by cleavage of the murine IL-6Rα from the cell surface of leukocytes during inflammatory responses

The cytokine IL-6 is part of a regulatory signaling network that controls immune responses. IL-6 binds either to the membrane-bound IL-6 receptor-α (classic signaling) or to the soluble IL-6 receptor-α (trans-signaling) to initiate signal transduction via gp130 activation. Because classic and trans-signaling of IL-6 fulfill different tasks during immune responses, controlled shedding of the membrane-bound IL-6 receptor-α from the surface of immune cells can be considered a central regulator of IL-6 function. The results from cell culture-based experiments have implicated both a disintegrin and metalloprotease 10 and a disintegrin and metalloprotease 17 in IL-6 receptor-α shedding. However, the nature of the protease mediating IL-6 receptor-α release in vivo is not yet known. We used hypomorphic a disintegrin and metalloprotease 17 mice and conditional a disintegrin and metalloprotease 10 knock-out mice to identify the natural protease of the murine IL-6 receptor-α. Circulating homeostatic soluble IL-6 receptor-α levels are not dependent on a disintegrin and metalloprotease 10 or 17 activity. However, during Listeria monocytogenes infection, IL-6 receptor-α cleavage by the α-secretase a disintegrin and metalloprotease 17 is rapidly induced from the surface of different leukocyte populations. In contrast, CD4-Cre-driven a disintegrin and metalloprotease 10 deletion in T cells did not influence IL-6 receptor-α shedding from these cells after L. monocytogenes infection. A disintegrin and metalloprotease 17 was also required for IL-6 receptor-α ectodomain cleavage and release during endotoxemia. These results demonstrate a novel physiologic role for a disintegrin and metalloprotease 17 in regulating murine IL-6 signals during inflammatory processes.

Expression profile of ADAM10 and ADAM17 in allergic rhinitis

BACKGROUND

A disintegrin and metalloprotease (ADAM) is a multifunctional gene family that contributes to the homeostasis of the extracellular matrix, transduction of specific intracellular signals, organogenesis, inflammation, tissue remodeling, adhesion, and cell migration. ADAM17 is the best characterized sheddase, with widespread putative substrates, including various inflammatory modulators. ADAM10 is the most similar ADAM to ADAM17 in terms of both protein sequence and the structural properties of their catalytic domains. The objective of this work was to assess the expression of ADAM10 and ADAM17 in allergic rhinitis to gain insight into their respective roles.

METHODS

The expression of ADAM10 and ADAM17 was investigated in the nasal mucosa under allergic and nonallergic conditions. Tissue samples were evaluated by reverse-transcription polymerase chain reaction (RT-PCR) and Western blotting, and data were analyzed semiquantitatively with densitometry.

RESULTS

The ADAM17 messenger RNA (mRNA) level was significantly (p < 0.001) lower in the allergic nasal mucosa than in the nonallergic nasal mucosa, whereas the ADAM10 mRNA level was significantly (p < 0.001) lower in the nonallergic nasal mucosa. The ADAM17 protein levels were also significantly (p < 0.001) lower in the allergic nasal mucosa, whereas the ADAM10 protein levels were lower in the nonallergic nasal mucosa (p = 0.002).

CONCLUSION

Decreased expression of ADAM17 and increased expression of ADAM10 may contribute to the development of allergic rhinitis through unknown pathways. We suggest that understanding the expression profile of ADAM17 and ADAM10 might help to elucidate the mechanism of allergic rhinitis.

Regulation of CXCR2 expression and function by a disintegrin and metalloprotease-17 (ADAM17)

The chemokine receptor CXCR2 is expressed at high levels on circulating neutrophils and is critical for directing their migration to sites of inflammation. CXCR2 surface levels are rapidly modulated by 2 mechanisms-cell internalization and recycling upon ligand binding-and by a metalloprotease activity following overt neutrophil activation by nonligand stimuli. The latter process has only been described in human neutrophils, and essentially, nothing is known about its functional relevance and the specific protease involved. We show that targeting ADAM17 in mouse and human neutrophils blocks CXCR2 down-regulation induced by nonligand stimuli but not by chemokine ligands. This was determined by use of a selective ADAM17 inhibitor, an ADAM17 function-blocking antibody, and ADAM17 gene-targeted mice. CXCR2 is known to undergo a marked down-regulation during various inflammatory disorders, and this is associated with impaired neutrophil recruitment. We show that blocking ADAM17 activity reduced CXCR2 down-regulation on circulating neutrophils and enhanced their recruitment during acute inflammation, which was reversed by a CXCR2 inhibitor. Taken together, our findings demonstrate that unlike CXCR2 internalization, ADAM17 induction down-regulates the receptor in an irreversible manner and may serve as a master switch in controlling CXCR2 function, but may also contribute to neutrophil dysfunction during excessive inflammation.

ADAM17-mediated shedding of FcγRIIIA on human NK cells: identification of the cleavage site and relationship with activation

FcγRIIIA/CD16A, the low-affinity receptor for the IgG Fc portion expressed on human CD56(dim) NK cells and involved in Ab-dependent cell cytotoxicity, is shed upon NK cell activation. We found that recombinant a disintegrin and metalloprotease (ADAM) 17 cleaved the ectodomain of FcγRIIIA/CD16A and a peptide for which the sequence encompasses aa 191-201 of the FcγRIIIA/CD16A stalk region but not ADAM10. MALDI-TOF analysis revealed that the peptide was cleaved between Ala(195) and Val(196) (i.e., 1 aa upstream of the expected position). This location of the cleavage site was confirmed by the finding that ADAM17 failed to cleave a peptide in which Ala and Val were reversed. ADAM17 was found to be expressed on NK cells, and stimulation with PMA or N-ethyl-maleimide resulted in the shedding of FcγRIIIA/CD16A and CD62L, a specific substrate of ADAM17. Selective inhibition of ADAM17 prevented the shedding of both molecules. Moreover, the shedding of FcγRIIIA/CD16A was strongly correlated with degranulation when a wide range of CD56(dim) NK cell activating receptors were stimulated, whereas both ADAM17-dependent shedding and internalization were involved in FcγRIIIA/CD16A downmodulation when the latter was engaged. Finally, the shedding of FcγRIIIA/CD16A was restricted to activated cells, suggesting that ADAM17 acts mainly, if not exclusively, in cis. Taken together, our results demonstrated for the first time, to our knowledge, at the molecular level that ADAM17 cleaves the stalk region of FcγRIIIA/CD16A and identified its cleavage site. The shedding of FcγRIIIA/CD16A was at least partially ADAM17 dependent, and it may be considered as a marker of FcγRIIIA/CD16A-independent NK cell activation highly correlated with degranulation.

IL-17 promotes neutrophil entry into tumor-draining lymph nodes following induction of sterile inflammation

Blood-borne neutrophils are excluded from entering lymph nodes across vascular portals termed high endothelial venules (HEVs) because of lack of expression of the CCR7 homeostatic chemokine receptor. Induction of sterile inflammation increases neutrophil entry into tumor-draining lymph nodes (TDLNs), which is critical for induction of antitumor adaptive immunity following treatments such as photodynamic therapy (PDT). However, the mechanisms controlling neutrophil entry into TDLNs remain unclear. Prior evidence that IL-17 promotes neutrophil emigration to sites of infection via induction of CXCL2 and CXCL1 inflammatory chemokines raised the question of whether IL-17 contributes to chemokine-dependent trafficking in TDLNs. In this article, we demonstrate rapid accumulation of IL-17-producing Th17 cells in the TDLNs following induction of sterile inflammation by PDT. We further report that nonhematopoietic expression of IL-17RA regulates neutrophil accumulation in TDLNs following induction of sterile inflammation by PDT. We show that HEVs are the major route of entry of blood-borne neutrophils into TDLNs through interactions of l-selectin with HEV-expressed peripheral lymph node addressin and by preferential interactions between CXCR2 and CXCL2 but not CXCL1. CXCL2 induction in TDLNs was mapped in a linear pathway downstream of IL-17RA-dependent induction of IL-1β. These results define a novel IL-17-dependent mechanism promoting neutrophil delivery across HEVs in TDLNs during acute inflammatory responses.

Hydrogen sulfide reduces neutrophil recruitment in hind-limb ischemia-reperfusion injury in an L-selectin and ADAM-17-dependent manner

BACKGROUND

Reperfusion following ischemia leads to neutrophil recruitment into injured tissue. Selectins and β2-integrins regulate neutrophil interaction with the endothelium during neutrophil rolling and firm adhesion. Excessive neutrophil infiltration into tissue is thought to contribute to ischemia-reperfusion injury damage. Hydrogen sulfide mitigates the damage caused by ischemia-reperfusion injury. This study's objective was to determine the effect of hydrogen sulfide on neutrophil adhesion receptor expression.

METHODS

Human neutrophils were either left untreated or incubated in 20 μM hydrogen sulfide and/or 50 μg/ml pharmacologic ADAM-17 inhibitor TAPI-0; activated by interleukin-8, fMLP, or TNF-α; and labeled against P-selectin glycoprotein ligand-1, leukocyte function associated antigen-1, Mac-1 α, L-selectin, and β2-integrin epitopes CBRM1/5 or KIM127 for flow cytometry. Cohorts of three C57BL/6 mice received an intravenous dose of saline vehicle or 20 μM hydrogen sulfide with or without 50 μg/ml TAPI-0 before unilateral tourniquet-induced hind-limb ischemia for 3 hours followed by 3 hours of reperfusion. Bilateral gastrocnemius muscles were processed for histology before neutrophil infiltration quantification.

RESULTS

Hydrogen sulfide treatment significantly increased L-selectin shedding from human neutrophils following activation by fMLP and interleukin-8 in an ADAM-17-dependent manner. Mice treated with hydrogen sulfide to raise bloodstream concentration by 20 μM before ischemia or reperfusion showed a significant reduction in neutrophil recruitment into skeletal muscle tissue following tourniquet-induced hind-limb ischemia-reperfusion injury.

CONCLUSIONS

Hydrogen sulfide administration results in the down-regulation of L-selectin expression in activated human neutrophils. This leads to a reduction in neutrophil extravasation and tissue infiltration and may partially account for the protective effects of hydrogen sulfide seen in the setting of ischemia-reperfusion injury.

ADAM17 cleaves CD16b (FcγRIIIb) in human neutrophils

CD16b (FcγRIIIb) is exclusively expressed by human neutrophils and binds IgG in immune complexes. Cell surface CD16b undergoes efficient ectodomain shedding upon neutrophil activation and apoptosis. Indeed, soluble CD16b is present at high levels in the plasma of healthy individuals, which appears to be maintained by the daily turnover of apoptotic neutrophils. At this time, the principal protease responsible for CD16b shedding is not known. We show that CD16b plasma levels were significantly decreased in patients administered a selective inhibitor targeting the metalloproteases ADAM10 and ADAM17. Additional analysis with inhibitors selective for ADAM10 or ADAM17 revealed that only inhibition of ADAM17 significantly blocked the cleavage of CD16b following neutrophil activation and apoptosis. CD16b shedding by ADAM17 was further demonstrated using a unique ADAM17 function-blocking mAb and a cell-based ADAM17 reconstitution assay. Unlike human CD16, however, mouse CD16 did not undergo efficient ectodomain shedding upon neutrophil stimulation or apoptosis, indicating that this mechanism cannot be modeled in normal mice. Taken together, our findings are the first to directly demonstrate that ADAM17 cleaves CD16 in human leukocytes.

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.

Pharmacological inhibition of caspase and calpain proteases: a novel strategy to enhance the homing responses of cord blood HSPCs during expansion

Background

Expansion of hematopoietic stem/progenitor cells (HSPCs) is a well-known strategy employed to facilitate the transplantation outcome. We have previously shown that the prevention of apoptosis by the inhibition of cysteine proteases, caspase and calpain played an important role in the expansion and engraftment of cord blood (CB) derived HSPCs. We hypothesize that these protease inhibitors might have maneuvered the adhesive and migratory properties of the cells rendering them to be retained in the bone marrow for sustained engraftment. The current study was aimed to investigate the mechanism of the homing responses of CB cells during expansion.

Methodology/Principal Findings

CB derived CD34⁺ cells were expanded using a combination of growth factors with and without Caspase inhibitor -zVADfmk or Calpain 1 inhibitor- zLLYfmk. The cells were analyzed for the expression of homing-related molecules. In vitro adhesive/migratory interactions and actin polymerization dynamics of HSPCs were assessed. In vivo homing assays were carried out in NOD/SCID mice to corroborate these observations. We observed that the presence of zVADfmk or zLLYfmk (inhibitors) caused the functional up regulation of CXCR4, integrins, and adhesion molecules, reflecting in a higher migration and adhesive interactions in vitro. The enhanced actin polymerization and the RhoGTPase protein expression complemented these observations. Furthermore, in vivo experiments showed a significantly enhanced homing to the bone marrow of NOD/SCID mice.

Conclusion/Significance

Our present study reveals another novel aspect of the regulation of caspase and calpain proteases in the biology of HSPCs. The priming of the homing responses of the inhibitor-cultured HSPCs compared to the cytokine-graft suggests that the modulation of these proteases may help in overcoming the major homing defects prevalent in the expansion cultures thereby facilitating the manipulation of cells for transplant procedures.

Attenuated, oncolytic, but not wild-type measles virus infection has pleiotropic effects on human neutrophil function

We previously showed that neutrophils play a role in regression of human tumor xenografts in immunodeficient mice following oncolytic vaccine measles virus (MV-Vac) treatment. In this study, we sought, using normal human neutrophils, to identify potential neutrophil-mediated mechanisms for the attenuated MV-Vac induced effects seen in vivo, by comparison with those consequent on wild-type (WT-MV) infection. Both MV-Vac and WT-MV infected and replicated within neutrophils, despite lack of SLAM expression. In both cases, neutrophils survived longer ex vivo postinfection. Furthermore, MV-Vac (but not WT-MV) infection activated neutrophils and stimulated secretion of several specific antitumor cytokines (IL-8, TNF-α, MCP-1, and IFN-α) via induction of de novo RNA and protein synthesis. In addition, MV-Vac (but not WT-MV) infection caused TRAIL secretion in the absence of de novo synthesis by triggering release of prefabricated TRAIL, via a direct effect upon degranulation. The differences between the outcome of infection by MV-Vac and WT-MV were not entirely explained by differential infection and replication of the viruses within neutrophils. To our knowledge, this is the first demonstration of potential mechanisms of oncolytic activity of an attenuated MV as compared with its WT parent. Furthermore, our study suggests that neutrophils have an important role to play in the antitumor effects of oncolytic MV.

The role of ADAM-mediated shedding in vascular biology

Within the vasculature the disintegrins and metalloproteinases (ADAMs) 8, 9, 10, 12, 15, 17, 19, 28 and 33 are expressed on endothelial cells, smooth muscle cells and on leukocytes. As surface-expressed proteases they mediate cleavage of vascular surface molecules at an extracellular site close to the membrane. This process is termed shedding and leads to the release of a soluble substrate ectodomain thereby critically modulating the biological function of the substrate. In the vasculature several surface molecules undergo ADAM-mediated shedding including tumour necrosis factor (TNF) α, interleukin (IL) 6 receptor α, L-selectin, vascular endothelial (VE)-cadherin, the transmembrane CX3C-chemokine ligand (CX3CL) 1, Notch, transforming growth factor (TGF) and heparin-binding epidermal growth factor (HB-EGF). These substrates play distinct roles in vascular biology by promoting inflammation, permeability changes, leukocyte recruitment, resolution of inflammation, regeneration and/or neovascularisation. Especially ADAM17 and ADAM10 are capable of cleaving many substrates with diverse function within the vasculature, whereas other ADAMs have a more restricted substrate range. Therefore, targeting ADAM17 or ADAM10 by pharmacologic inhibition or gene knockout not only attenuates the inflammatory response in animal models but also affects tissue regeneration and neovascularisation. Recent discoveries indicate that other ADAMs (e.g. ADAM8 and 9) also play important roles in vascular biology but appear to have more selective effects on vascular responses (e.g. on neovascularisation only). Although, targeting of ADAM17 and ADAM10 in inflammatory diseases is still a promising approach, temporal and spatial as well as substrate-specific inhibition approaches are required to minimise undesired side effects on vascular cells.

Different signaling pathways stimulate a disintegrin and metalloprotease-17 (ADAM17) in neutrophils during apoptosis and activation

ADAM17 is a membrane-associated metalloprotease that cleaves proteins from the surface of neutrophils and modulates the density of various receptors and adhesion molecules. The protease activity of ADAM17 is highly inducible and occurs upon neutrophil activation as well as apoptosis. At this time, little is known about the signal transduction pathway that promotes ADAM17 activity in neutrophils upon the induction of apoptosis. We show that caspase-8 activation, Bid cleavage, and the release of mitochondrial reactive oxygen species are sequential transduction components of the Fas signaling cascade that induces ADAM17. This is different from ADAM17 stimulation upon overt neutrophil activation, which requires MAPK p38 or ERK, but not caspases and reactive oxygen species. ADAM17 activity in apoptotic neutrophils may serve to inactivate select effector molecules that promote the pro-inflammatory activity of recruited neutrophils. For instance, TNFα receptors TNF-RI and TNF-RII are substrates of ADAM17, and we show that they are shed during apoptosis, decreasing neutrophil sensitivity to TNFα. Altogether, our findings provide significant new insights into the signal transduction pathway that stimulates ADAM17 during induced neutrophil apoptosis. ADAM17 induction during apoptosis may rapidly diminish neutrophil sensitivity to the inflammatory environment, complementing other anti-inflammatory activities by these cells during inflammation resolution.

The soluble Interleukin 6 receptor: generation and role in inflammation and cancer

Soluble cytokine receptors are frequently found in human serum, most of them possessing antagonistic properties. The Interleukin 6 receptor (IL-6R) is found as a transmembrane protein on hepatocytes and subsets of leukocytes, but soluble isoforms of the IL-6R (sIL-6R) are generated by alternative splicing or by limited proteolysis of the ADisintegrin And Metalloproteinases (ADAM) gene family members ADAM10 and ADAM17. Importantly, the sIL-6R in complex with its ligand Interleukin 6 (IL-6) has agonistic functions and requires cells expressing the signal transducing ß-receptor gp130 but not the membrane-bound IL-6R. We have called this process IL-6 trans-signaling. Naturally occurring isoforms of soluble gp130 (sgp130), which are generated by alternative splicing, are natural inhibitors of IL-6 trans-signaling, leaving IL-6 classic signaling via the membrane-bound IL-6R unaffected. We used recombinant sgp130Fc protein and recently generated transgenic mice expressing high levels of sgp130Fc to discriminate between classic and trans-signaling in vivo, and demonstrated that IL-6 trans-signaling is critically involved in generation and maintenance of several inflammatory and autoimmune diseases including chronic inflammatory bowel disease, rheumatoid arthritis, peritonitis and asthma, as well as inflammation-induced colon cancer.

ADAM17 activity and other mechanisms of soluble L-selectin production during death receptor-induced leukocyte apoptosis

L-selectin is an adhesion molecule expressed by neutrophils that broadly directs their infiltration in to sites of inflammation. It is also present at relatively high levels in the serum of normal individuals. It is well established that L-selectin is efficiently shed from the surface of neutrophils upon their activation, a process that regulates its density and binding activity. Neutrophil programmed cell death is critical for the resolution of inflammation, and L-selectin downregulation is induced during this process as well. The mechanisms underpinning this latter process are much less understood, and were investigated in this study. Using a disintegrin and metalloprotease (ADAM)-17 radiation chimeric mice, we demonstrate for the first time that during early events of death receptor-mediated neutrophil apoptosis, L-selectin downregulation occurs primarily by ADAM17-mediated shedding. This was observed as well upon using shRNA to knock down ADAM17 expression in Jurkat cells, a well-studied cell line in terms of the molecular processes involved in the induction of apoptosis. These findings directly reveal that ADAM17 activity occurs during programmed cell death. Hence, the cleavage of particular ADAM17 substrates may be an additional component of the anti-inflammatory program initiated by apoptotic neutrophils. Of interest was that during later stages of induced leukocyte apoptosis, soluble L-selectin production occurred independent of ADAM17, as well as membrane events, such as blebbing and microparticle production. This process may provide an explanation for the lack of diminished serum L-selectin levels in ADAM17-null mice, and suggests a mechanism for the homeostatic maintenance of soluble L-selectin levels in the blood of healthy individuals.

In vivo role of leukocyte ADAM17 in the inflammatory and host responses during E. coli-mediated peritonitis

Inflammation is the body's initial response to infection, which is harmful when excessive, as exemplified in sepsis inflammatory syndromes. Ectodomain shedding by the membrane metalloprotease ADAM17 is an emerging regulator of inflammation, as it directs the activity of various inflammatory modulators. At this time, however, little is known about the in vivo function of ADAM17. Here, we show that ADAM17-deficient leukocytes afforded mice a survival benefit following Escherichia coli-mediated peritoneal sepsis, which was associated with a reduction in systemic proinflammatory cytokine levels and bacterial burden. A more rapid yet transitory neutrophil infiltration into the peritoneal cavity of conditional ADAM17 knockout mice was observed when compared with control mice, suggesting a mechanism for their enhanced clearance of bacteria. Preventing the shedding of L-selectin augments neutrophil recruitment, and we show that L-selectin shedding by peritoneal neutrophils in conditional ADAM17 knockout mice was impaired. Moreover, their peritoneal TNF-alpha levels were markedly lower than control mice following E. coli challenge. These events indicate key molecular processes involved in the altered time course of neutrophil recruitment in conditional ADAM17 knockout mice. Overall, our study provides novel in vivo evidence of the instrumental role of ADAM17 in modulating inflammation and host resistance during Gram-negative bacterial infection.

Effects of TNF-alpha-converting enzyme inhibition on acute lung injury induced by endotoxin in the rat

We studied the effects of TNF-converting enzyme inhibition with Y-41654, which down-regulates the production of soluble TNF-alpha (sTNF-alpha), on acute lung injury induced by intratracheal administration of LPS. We first verified in vitro that pretreatment of isolated alveolar macrophages from Sprague-Dawley male rats with 20 microL of 0.1-mM Y-41654, decreased significantly (P < 0.05) the concentration of sTNF-alpha in cell supernatants induced by 10 microg/mL of LPS. We then studied four groups of rats (each n = 10) including 1) a control group, 2) an LPS group (300 microg /kg, instilled intratracheally), 3) a Y-41654 group, and 4) a treatment group treated with Y-41654 after LPS instillation. Y-41654, 10 mg/kg in 0.7 mL of phosphate-buffered saline, was administered (i.v.), 15 min before and 0.5, 1.5, 2.5, and 3.5 h after saline or LPS instillation. The animals were observed for 4 h. In the animals treated with Y-41654, the concentrations of sTNF-alpha and protein in bronchoalveolar lavage fluid, and the number of neutrophils in lung tissue and bronchoalveolar lavage fluid were significantly lower at 4 h than in the LPS group (P < 0.05). In conclusion, sTNF-alpha plays an important role in the development of acute lung injury induced by intratracheal administration of LPS, in part modulating neutrophil kinetics.

Constitutive endocytosis of the chemokine CX3CL1 prevents its degradation by cell surface metalloproteases

CX(3)CL1, a chemokine with transmembrane and soluble species, plays a key role in inflammation by acting as both chemoattractant and adhesion molecule. CX(3)CL1 is the only chemokine known to undergo constitutive internalization, raising the possibility that dynamic equilibrium between the endocytic compartment and the plasma membrane critically regulates the availability and processing of CX(3)CL1 at the cell surface. We therefore investigated how transmembrane CX(3)CL1 is internalized. Inhibition of dynamin using a nonfunctional allele or of clathrin using specific small interfering RNA prevented endocytosis of the chemokine in CX(3)CL1-expressing human ECV-304 cells. Perusal of the cytoplasmic domain of CX(3)CL1 revealed two putative adaptor protein-2 (AP-2)-binding motifs. Accordingly, CX(3)CL1 co-localized with AP-2 at the plasma membrane. We generated a mutant allele of CX(3)CL1 lacking the cytoplasmic tail. Deletion of the cytosolic tail precluded internalization of the chemokine. We used site-directed mutagenesis to disrupt AP-2-binding motifs, singly or in combination, which resulted in diminished internalization of CX(3)CL1. Although CX(3)CL1 was present in both superficial and endomembrane compartments, ADAM10 (a disintegrin and metalloprotease 10) and tumor necrosis factor-converting enzyme, the two metalloproteases that cleave CX(3)CL1, localized predominantly to the plasmalemma. Inhibition of endocytosis using the dynamin inhibitor, Dynasore, promoted rapid metalloprotease-dependent shedding of CX(3)CL1 from the cell surface into the surrounding medium. These findings indicate that the cytoplasmic tail of CX(3)CL1 facilitates its constitutive clathrin-mediated endocytosis. Such regulation enables intracellular storage of a sizable pool of presynthesized CX(3)CL1 that protects the chemokine from degradation by metalloproteases at the plasma membrane.

Neutrophil apoptosis and the resolution of infection

Polymorphonuclear leukocytes (PMNs) are the most abundant white cell in humans and an essential component of the innate immune system. PMNs are typically the first type of leukocyte recruited to sites of infection or areas of inflammation. Ingestion of microorganisms triggers production of reactive oxygen species and fusion of cytoplasmic granules with forming phagosomes, leading to effective killing of ingested microbes. Phagocytosis of bacteria typically accelerates neutrophil apoptosis, which ultimately promotes the resolution of infection. However, some bacterial pathogens alter PMN apoptosis to survive and thereby cause disease. Herein, we review PMN apoptosis and the ability of microorganisms to alter this important process.

Differential expression and regulation of ADAM17 and TIMP3 in acute inflamed intestinal epithelia

The acute phase of Crohn's disease (CD) is characterized by a large afflux of polymorphonuclear leukocytes (PMNL) into the mucosa and by the release of TNF-alpha. Conversion of inactive TNF-alpha into an active form requires the cleavage of a transmembrane TNF-alpha precursor by the TNF-alpha-converting enzyme (ADAM17), a protease mainly regulated by the tissue inhibitor of metalloproteinase 3 (TIMP3). The aim of the present study was to investigate in an in vitro model of PMNL transepithelial migration and in the intestinal mucosa of patients with CD the expression and regulation of ADAM17 and TIMP3 in intestinal epithelial cells (IEC). ADAM17 and TIMP3 expression was analyzed by Western blotting, RT-PCR, confocal microscopy, and immunohistochemistry by using the T84 model and digestive biopsies. ADAM17 expression in IEC was increased at a posttranscriptional level during the early phase (from 2 to 4 h) of PMNL transepithelial migration whereas TIMP3 was only increased 24 h later. TNF-alpha induced an early upregulation of ADAM17 in T84 cells, whereas PMNL adhesion, H(2)O(2), or epithelial tight junction opening alone did not affect the amount of ADAM17. Immunohistochemistry of intestinal biopsies revealed that strong expression of ADAM17 was associated with a high activity of CD. In contrast, TIMP3 was very poorly expressed in these biopsies. ADAM17 and TIMP3 profiling did not correlated with the NOD2/CARD15 status. The ADAM17 activity was higher both in the early phase of PMNL transepithelial migration and in active CD. These results showed early posttranscriptional upregulation of ADAM17 in IEC linked to PMNL transepithelial migration and a high activity of CD.

Trovafloxacin enhances the inflammatory response to a Gram-negative or a Gram-positive bacterial stimulus, resulting in neutrophil-dependent liver injury in mice

Trovafloxacin (TVX), a fluoroquinolone antibiotic, has been strongly linked with several cases of idiosyncratic hepatotoxicity in humans. Previous studies showed that a modest inflammatory stress induced by a Gram-negative bacterial stimulus [i.e., lipopolysaccharide (LPS)] rendered nontoxic doses of TVX hepatotoxic in mice. This study compared the interaction of TVX with Gram-negative and Gram-positive stimuli. Mice were given TVX 3 h before LPS (Gram-negative stimulus) or a peptidoglycan-lipoteichoic acid (PGN-LTA) mixture isolated from Staphylococcus aureus (Gram-positive stimulus). Administration of TVX, LPS, or PGN-LTA alone was nonhepatotoxic. However, TVX administration before PGN-LTA or LPS resulted in significant liver injury that occurred with similar time courses. TVX/PGN-LTA-induced hepatocellular necrosis was primarily localized to centrilobular regions, whereas that caused by TVX/LPS was predominantly midzonal. Administration of either LPS or PGN-LTA alone led to increased plasma concentrations of several cytokines and chemokines at a time near the onset of liver injury. TVX administration before LPS enhanced the concentrations of all of these cytokines, whereas TVX treatment before PGN-LTA increased all of the cytokines except tumor necrosis factor (TNF)-alpha and interferon-gamma. Liver injury was reduced in TVX/LPS- and TVX/PGN-LTA-treated mice given an antibody to CD18 and also in mice deficient in neutrophil [polymorphonuclear neutrophil (PMN)] elastase. Hepatic PMN accumulation and TNF-alpha production after TVX/PGN-LTA-, but not after TVX/LPS-coexposure, was CD18-dependent. In summary, TVX significantly enhanced the murine inflammatory response to either a Gram-negative or a Gram-positive stimulus and caused hepatotoxicity that developed similarly and was dependent on PMN activation in mice but that differed in lesion location and cytokine profile.

Regulation of mature ADAM17 by redox agents for L-selectin shedding

L-selectin is constitutively expressed by neutrophils and plays a key role in directing these cells to sites of inflammation. Upon neutrophil activation, L-selectin is rapidly and efficiently down-regulated from the cell surface by ectodomain shedding. We have directly shown that A disintegrin and metalloprotease 17 (ADAM17) is a primary and nonredundant sheddase of L-selection by activated neutrophils in vivo. Following cell activation, intracellular signals lead to the induction of ADAM17's enzymatic activity; however, the target of this inducer mechanism remains unclear. Our study provides evidence of an activation mechanism that involves the extracellular region of the mature form of cell surface ADAM17 and not its intracellular region. We demonstrate that the catalytic activity of purified ADAM17 lacking a prodomain and its intracellular region is diminished under mild reducing conditions by DTT and enhanced by H(2)O(2) oxidation. Moreover, H(2)O(2) reversed ADAM17 inhibition by DTT. The treatment of neutrophils with H(2)O(2) also induced L-selectin shedding in an ADAM17-dependent manner. These findings suggest that thiol-disulfide conversion occurring in the extracellular region of ADAM17 may be involved in its activation. An analysis of ADAM17 revealed that within its disintegrin/cysteine-rich region are two highly conserved, vicinal cysteine sulfhydryl motifs (cysteine-X-X-cysteine), which are well-characterized targets for thiol-disulfide exchange in various other proteins. Using a cell-based ADAM17 reconstitution assay, we demonstrate that the cysteine-X-X-cysteine motifs are critical for L-selectin cleavage. Taken together, our findings suggest that reduction-oxidation modifications of cysteinyl sulfhydryl groups in mature ADAM17 may serve as a mechanism for regulating the shedding of L-selectin following neutrophil stimulation.

Thermal facilitation of lymphocyte trafficking involves temporal induction of intravascular ICAM-1

OBJECTIVE

Fever is associated with improved survival, although its beneficial mechanisms are poorly understood. Previous studies indicate that the thermal element of fever augments lymphocyte migration across high endothelial venules (HEVs) of lymphoid organs by increasing the intravascular display of a gatekeeper trafficking molecule, intercellular adhesion molecule-1 (ICAM-1). Here, we evaluated the spatio-temporal relationship between the thermal induction of intravascular ICAM-1 and lymphocyte trafficking.

METHODS

Intravascular ICAM-1 density was quantified by immunofluorescence staining in mice exposed to fever-range whole-body hyperthermia (39.5+/-0.5 degrees C). ICAM-1-dependent lymphocyte trafficking was measured in short-term homing assays.

RESULTS

A linear relationship was observed between the duration of heat treatment and intravascular ICAM-1 density in HEVs with maximal responses requiring sustained (i.e., five hours) thermal stress. Circulating lymphocytes were found to sense incremental changes in ICAM-1 on HEVs, such that trafficking is proportional to the intravascular density of ICAM-1. We further identified a hydroxamate-sensitive shedding mechanism that restores ICAM-1 expression to homeostatic levels following the cessation of thermal stress.

CONCLUSIONS

The time-dependent response to thermal stress indicates that ICAM-1 density governs the efficiency of lymphocyte interactions with HEVs in vivo. These studies highlight the dynamic role of the microcirculation in promoting immune surveillance during febrile inflammatory responses.

Acidic mammalian chitinase is secreted via an ADAM17/epidermal growth factor receptor-dependent pathway and stimulates chemokine production by pulmonary epithelial cells

Acidic mammalian chitinase (AMCase) is expressed in an exaggerated fashion in epithelial cells at sites of pulmonary T helper cell type 2 inflammation and plays important roles in the pathogenesis of anti-parasite and asthma-like responses. However, the mechanisms that control epithelial cell AMCase secretion and its effector responses have not been adequately defined. To address these issues, we used in vivo and in vitro experimental systems to define the pathways of epithelial AMCase secretion and its epithelial regulatory effects. Here we demonstrate that, in murine T helper cell type 2 modeling systems, AMCase colocalizes with the epidermal growth factor receptor (EGFR) and ADAM17 (a membrane disintegrin and metallopeptidase 17) in lung epithelial cells. In vitro cotransfection experiments in A549 cells demonstrated that AMCase and EGFR physically interact with each other. Cotransfection of AMCase and EGFR also increased, whereas EGFR inhibition decreased AMCase secretion. Interestingly, AMCase secretion was not significantly altered by treatment with EGF but was significantly decreased when the upstream EGFR transactivator ADAM17 was inhibited. AMCase secretion was also decreased when the EGFR-downstream Ras was blocked. Transfected and recombinant AMCase induced epithelial cell production of CCL2, CCL17, and CXCL8. These studies demonstrate that lung epithelial cells secrete AMCase via an EGFR-dependent pathway that is activated by ADAM17 and mediates its effects via Ras. They also demonstrate that the AMCase that is secreted feeds back in an autocrine and/or paracrine fashion to stimulate pulmonary epithelial cell chemokine production.

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.

Immunology

The concept of forbidden foods that should not be eaten goes back to the Garden of Eden and apart from its religious meanings it may also have foreshadowed the concept of foods that can provoke adverse reactions. Thus we could say that allergic diseases have plagued mankind since the beginning of life on earth. The prophet Job was affected by a condition that following the rare symptoms described by the Holy Bible might be identified as a severe form of atopic dermatitis (AD). The earliest record of an apparently allergic reaction is 2621 B.C., when death from stinging insects was first described by hieroglyphics carved into the walls of the tomb of Pharaoh Menes depicting his death following the sting of a wasp. In 79 A.D., the death of the Roman admiral Pliny the Elder was ascribed to the SO₂-rich gases emanating from the eruption of Mount Vesuvius. Hippocrates (460–377 B.C.) was probably the first to describe how cow’s milk (CM) could cause gastric upset and hives, proposing dietetic measures including both treatment and prevention for CM allergy.

TNF trafficking to human mast cell granules: mature chain-dependent endocytosis

Mast cells play a crucial role at the early stages of immune response against bacteria and parasites where their functionality is based on their capability of releasing highly bioactive compounds, among them TNF. Mast cells are considered the only cells storing preformed TNF, which allows for the immediate release of this cytokine upon contact with pathogens. We approached the question of mechanisms and amino acid motifs directing newly synthesized TNF for storage in cytoplasmic granules by analyzing the trafficking of a series of TNF-enhanced GFP fusion proteins in human mast cell lines HMC-1 and LAD2. Protein covering the full TNF sequence was successfully sorted into secretory granules in a process involving transient exposure on the outer membrane and re-endocytosis. In human cells, contrary to results previously obtained in a rodent model, TNF seems not to be glycosylated and, thus, trafficking is carbohydrate independent. In an effort to localize the amino acid motif responsible for granule targeting, we constructed additional fusion proteins and analyzed their trafficking, concluding that granule-targeting sequences are localized in the mature chain of TNF and that the cytoplasmic tail is expendable for endocytotic sorting of this cytokine, thus excluding direct interactions with intracellular adaptor proteins.

Apoptosis is a natural stimulus of IL6R shedding and contributes to the proinflammatory trans-signaling function of neutrophils

Interleukin 6 (IL6) trans-signaling has emerged as a prominent regulator of immune responses during both innate and acquired immunity. Regulation of IL6 trans-signaling is reliant upon the release of soluble IL6 receptor (sIL6R), which binds IL6 to create an agonistic IL6/sIL6R complex capable of activating cell types that would not normally respond to IL6 itself. Here we show that intrinsic and extrinsic apoptotic stimulation by DNA damage, cytokine deprivation, and Fas stimulation promotes shedding of sIL6R. Apoptosis-induced shedding of the IL6R was caspase dependent but PKC independent, with inhibition of ADAM17 preventing IL6R shedding. Such insight is relevant to the control of acute inflammation, where transition from the initial neutrophil infiltration to a more sustained population of mononuclear cells is essential for the resolution of the inflammatory process. This transitional event is governed by IL6 trans-signaling. This study demonstrates that IL6R is shed from apoptotic human neutrophils. In vivo studies in a murine inflammation model showed that neutrophil depletion resulted in reduced local sIL6R levels and a concomitant decrease in mononuclear cells, suggesting that apoptosis-induced IL6R shedding from neutrophils promotes IL6 trans-signaling and regulates the attraction of monocytic cells involved in the clearance of apoptotic neutrophils.

ADAM17 deficiency by mature neutrophils has differential effects on L-selectin shedding

L-selectin directs neutrophils to sites of inflammation, and upon their activation, surface expression of the receptor is rapidly down-regulated by ectodomain shedding. Tumor necrosis factor-alpha-converting enzyme (TACE, or ADAM17) is a sheddase of L-selectin; however, Adam17 gene targeting (ADAM17(DeltaZn/DeltaZn)) in mice is perinatal lethal and its role in L-selectin shedding by mature neutrophils has not been determined. This was addressed here by using radiation-chimeric mice reconstituted with ADAM17(DeltaZn/DeltaZn) fetal liver cells. ADAM17-deficient neutrophils, monocytes, and lymphocytes failed to shed L-selectin in response to PMA, as did neutrophils infiltrating the inflamed peritoneum. In addition, the absence of functional ADAM17 resulted in significantly increased levels of L-selectin surface expression by peripheral-blood leukocytes, indicating the sheddase also plays a role in the constitutive cleavage of L-selectin. Interestingly, not all manners of L-selectin turnover required ADAM17. Plasma L-selectin levels were similar between ADAM17(DeltaZn/DeltaZn)-chimeric and control mice, as was the shedding of L-selectin by neutrophils undergoing spontaneous apoptosis. The latter process, however, was diminished by a metalloprotease inhibitor, indicating the role of a sheddase other than ADAM17. Together, our data reveal that L-selectin's surface density on neutrophils is regulated by ADAM17, but homeostatic L-selectin cleavage is not.