In vivo expression of neutrophil inhibitory factor via gene transfer prevents lipopolysaccharide-induced lung neutrophil infiltration and injury by a beta2 integrin-dependent mechanism

Ubiquitin ligase CHFR mediated degradation of VE-cadherin through ubiquitylation disrupts endothelial adherens junctions

Vascular endothelial cadherin (VE-cadherin) expressed at endothelial adherens junctions (AJs) is vital for vascular integrity and endothelial homeostasis. Here we identify the requirement of the ubiquitin E3-ligase CHFR as a key mechanism of ubiquitylation-dependent degradation of VE-cadherin. CHFR was essential for disrupting the endothelium through control of the VE-cadherin protein expression at AJs. We observe augmented expression of VE-cadherin in endothelial cell (EC)-restricted Chfr knockout (ChfrΔEC) mice. We also observe abrogation of LPS-induced degradation of VE-cadherin in ChfrΔEC mice, suggesting the pathophysiological relevance of CHFR in regulating the endothelial junctional barrier in inflammation. Lung endothelial barrier breakdown, inflammatory neutrophil extravasation, and mortality induced by LPS were all suppressed in ChfrΔEC mice. We find that the transcription factor FoxO1 is a key upstream regulator of CHFR expression. These findings demonstrate the requisite role of the endothelial cell-expressed E3-ligase CHFR in regulating the expression of VE-cadherin, and thereby endothelial junctional barrier integrity.

Galectin-1 mediates interactions between polymorphonuclear leukocytes and vascular endothelial cells, and promotes their extravasation during lipopolysaccharide-induced acute lung injury

The lung airway epithelial surface is heavily covered with sialic acids as the terminal carbohydrate on most cell surface glycoconjugates and can be removed by microbial neuraminidases or endogenous sialidases. By desialylating the lung epithelial surface, neuraminidase acts as an important virulence factor in many mucosal pathogens, such as influenza and S. pneumoniae. Desialylation exposes the subterminal galactosyl moieties - the binding glycotopes for galectins, a family of carbohydrate-recognition proteins playing important roles in various aspects of immune responses. Galectin-1 and galectin-3 have been extensively studied in their roles related to host immune responses, but some questions about their role(s) in leukocyte recruitment during lung bacterial infection remain unanswered. In this study, we found that both galectin-1 and galectin-3 bind to polymorphonuclear leukocytes (PMNs) and enhance the interaction of endothelial intercellular adhesion molecule-1 (ICAM-1) with PMNs, which is further increased by PMN desialylation. In addition, we observed that in vitro galectin-1 mediates the binding of PMNs, particularly desialylated PMNs, onto the endothelial cells. Finally, in a murine model for LPS-mediated acute lung injury, we observed that galectin-1 modulates PMN infiltration to the lung without altering the expression of chemoattractant cytokines. We conclude that galectins, particularly galectin-1, may function as adhesion molecules that mediate PMN-endothelial cell interactions, and modulate PMN infiltration during acute lung injury.

Interferon regulatory factor 1 (IRF1) inhibits lung endothelial regeneration following inflammation-induced acute lung injury

BACKGROUND

Acute respiratory distress syndrome (ARDS) is a respiratory condition caused by severe endothelial barrier dysfunction within the lung. In ARDS, excessive inflammation, tissue edema, and immune cell influx prevents endothelial cell regeneration that is crucial in repairing the endothelial barrier. However, little is known about the molecular mechanism that underpin endothelial cell regeneration in ARDS.

METHODS

R-based bioinformatics tools were used to analyze microarray-derived transcription profiles in human lung microvascular endothelial cells (HLMVECs) subjected to non-treatment or lipopolysaccharide (LPS) exposure. We generated endothelial cell-specific interferon regulatory factor 1 (Irf1) knockout (Irf1EC-/-) and Irf1fl/fl control mice for use in an endotoxemic murine model of acute lung injury (ALI). In vitro studies (qPCR, immunoblotting, and ChIP-qPCR) were conducted in mouse lung endothelial cells (MLECs) and HLMVECs. Dual-luciferase promoter reporter assays were performed in HLMVECs.

RESULTS

Bioinformatics analyses identified IRF1 as a key up-regulated gene in HLMVECs post-LPS exposure. Endothelial-specific knockout of Irf1 in ALI mice resulted in enhanced regeneration of lung endothelium, while liposomal delivery of endothelial-specific Irf1 to wild-type ALI mice inhibited lung endothelial regeneration in a leukemia inhibitory factor (Lif)-dependent manner. Mechanistically, we demonstrated that LPS-induced Stat1Ser727 phosphorylation promotes Irf1 transactivation, resulting in downstream up-regulation of Lif that inhibits endothelial cell proliferation.

CONCLUSIONS

These results demonstrate the existence of a p-Stat1Ser727-Irf1-Lif axis that inhibits lung endothelial cell regeneration post-LPS injury. Thus, direct inhibition of IRF1 or LIF may be a promising strategy for enhancing endothelial cell regeneration and improving clinical outcomes in ARDS patients.

The role of G protein-coupled receptor in neutrophil dysfunction during sepsis-induced acute respiratory distress syndrome

Sepsis is defined as a life-threatening dysfunction due to a dysregulated host response to infection. It is a common and complex syndrome and is the leading cause of death in intensive care units. The lungs are most vulnerable to the challenge of sepsis, and the incidence of respiratory dysfunction has been reported to be up to 70%, in which neutrophils play a major role. Neutrophils are the first line of defense against infection, and they are regarded as the most responsive cells in sepsis. Normally, neutrophils recognize chemokines including the bacterial product N-formyl-methionyl-leucyl-phenylalanine (fMLP), complement 5a (C5a), and lipid molecules Leukotriene B4 (LTB4) and C-X-C motif chemokine ligand 8 (CXCL8), and enter the site of infection through mobilization, rolling, adhesion, migration, and chemotaxis. However, numerous studies have confirmed that despite the high levels of chemokines in septic patients and mice at the site of infection, the neutrophils cannot migrate to the proper target location, but instead they accumulate in the lungs, releasing histones, DNA, and proteases that mediate tissue damage and induce acute respiratory distress syndrome (ARDS). This is closely related to impaired neutrophil migration in sepsis, but the mechanism involved is still unclear. Many studies have shown that chemokine receptor dysregulation is an important cause of impaired neutrophil migration, and the vast majority of these chemokine receptors belong to the G protein-coupled receptors (GPCRs). In this review, we summarize the signaling pathways by which neutrophil GPCR regulates chemotaxis and the mechanisms by which abnormal GPCR function in sepsis leads to impaired neutrophil chemotaxis, which can further cause ARDS. Several potential targets for intervention are proposed to improve neutrophil chemotaxis, and we hope that this review may provide insights for clinical practitioners.

The Actin-Binding Protein Cortactin Promotes Sepsis Severity by Supporting Excessive Neutrophil Infiltration into the Lung

Sepsis is a systemic infection that can lead to multi-organ failure. It is characterised by an uncontrolled immune response with massive neutrophil influx into peripheral organs. Neutrophil extravasation into tissues depends on actin remodeling and actin-binding proteins such as cortactin, which is expressed ubiquitously, except for neutrophils. Endothelial cortactin is necessary for proper regulation of neutrophil transendothelial migration and recruitment to sites of infection. We therefore hypothesised that cortactin plays a crucial role in sepsis development by regulating neutrophil trafficking. Using a murine model of sepsis induced by cecal ligation and puncture (CLP), we showed that cortactin-deficient (KO) mice survive better due to reduced lung injury. Histopathological analysis of lungs from septic KO mice revealed absence of oedema, reduced vascular congestion and mucus deposition, and better-preserved alveoli compared to septic wild-type (WT) mice. Additionally, sepsis-induced cytokine storm, excessive neutrophil infiltration into the lung and oxidative stress were significantly reduced in KO mice. Neutrophil depletion 12 h after sepsis improved survival in WT mice by averting lung injury, similar to both neutrophil-depleted and non-depleted KO mice. Our findings highlight a critical role of cortactin for lung neutrophil infiltration and sepsis severity.

TAK1 is essential for endothelial barrier maintenance and repair after lung vascular injury

TGF–β-activated kinase 1 (TAK1) plays crucial roles in innate and adaptive immune responses and is required for embryonic vascular development. However, TAK1’s role in regulating vascular barrier integrity is not well defined. Here we show that endothelial TAK1 kinase function is required to maintain and repair the injured lung endothelial barrier. We observed that inhibition of TAK1 with 5Z-7-oxozeaenol markedly reduced expression of β-catenin (β-cat) and VE-cadherin at endothelial adherens junctions and augmented protease-activated receptor-1 (PAR-1)- or toll-like receptor-4 (TLR-4)-induced increases in lung vascular permeability. In inducible endothelial cell (EC)-restricted TAK1 knockout (TAK1^i∆EC) mice, we observed that the lung endothelial barrier was compromised and in addition, TAK1^i∆EC mice exhibited heightened sensitivity to septic shock. Consistent with these findings, we observed dramatically reduced β-cat expression in lung ECs of TAK1^i∆EC mice. Further, either inhibition or knockdown of TAK1 blocked PAR-1- or TLR-4-induced inactivation of glycogen synthase kinase 3β (GSK3β), which in turn increased phosphorylation, ubiquitylation, and degradation of β-cat in ECs to destabilize the endothelial barrier. Importantly, we showed that TAK1 inactivates GSK3β through AKT activation in ECs. Thus our findings in this study point to the potential of targeting the TAK1-AKT-GSK3β axis as a therapeutic approach to treat uncontrolled lung vascular leak during sepsis.

Hookworm infections: Reappraising the evidence for a role of Neutrophils in light of NETosis

In Hookworm infection, neutrophils have long had the image of the villain, being recruited to the site of larval migration because of damage but participating themselves in tissue injury. With recent developments in neutrophil biology, there is an increasing body of evidence for the role of neutrophils as effector cells in hookworm immunity. In particular, their ability to release extracellular traps, or neutrophil extracellular traps (NETs), confer neutrophils a larvicidal activity. Here, we review recent evidence in this nascent field and discuss the avenue for future research on NETs/hookworm interactions.

IL-1β suppression of VE-cadherin transcription underlies sepsis-induced inflammatory lung injury

Unchecked inflammation is a hallmark of inflammatory tissue injury in diseases such as acute respiratory distress syndrome (ARDS). Yet the mechanisms of inflammatory lung injury remain largely unknown. Here we showed that bacterial endotoxin lipopolysaccharide (LPS) and cecal ligation and puncture-induced (CLP-induced) polymicrobial sepsis decreased the expression of transcription factor cAMP response element binding (CREB) in lung endothelial cells. We demonstrated that endothelial CREB was crucial for VE-cadherin transcription and the formation of the normal restrictive endothelial adherens junctions. The inflammatory cytokine IL-1β reduced cAMP generation and CREB-mediated transcription of VE-cadherin. Furthermore, endothelial cell-specific deletion of CREB induced lung vascular injury whereas ectopic expression of CREB in the endothelium prevented the injury. We also observed that rolipram, which inhibits type 4 cyclic nucleotide phosphodiesterase-mediated (PDE4-mediated) hydrolysis of cAMP, prevented endotoxemia-induced lung vascular injury since it preserved CREB-mediated VE-cadherin expression. These data demonstrate the fundamental role of the endothelial cAMP-CREB axis in promoting lung vascular integrity and suppressing inflammatory injury. Therefore, strategies aimed at enhancing endothelial CREB-mediated VE-cadherin transcription are potentially useful in preventing sepsis-induced lung vascular injury in ARDS.

Sox17 is required for endothelial regeneration following inflammation-induced vascular injury

Repair of the endothelial cell barrier after inflammatory injury is essential for tissue fluid homeostasis and normalizing leukocyte transmigration. However, the mechanisms of endothelial regeneration remain poorly understood. Here we show that the endothelial and hematopoietic developmental transcription factor Sox17 promotes endothelial regeneration in the endotoxemia model of endothelial injury. Genetic lineage tracing studies demonstrate that the native endothelium itself serves as the primary source of endothelial cells repopulating the vessel wall following injury. We identify Sox17 as a key regulator of endothelial cell regeneration using endothelial-specific deletion and overexpression of Sox17. Endotoxemia upregulates Hypoxia inducible factor 1α, which in turn transcriptionally activates Sox17 expression. We observe that Sox17 increases endothelial cell proliferation via upregulation of Cyclin E1. Furthermore, endothelial-specific upregulation of Sox17 in vivo enhances lung endothelial regeneration. We conclude that endotoxemia adaptively activates Sox17 expression to mediate Cyclin E1-dependent endothelial cell regeneration and restore vascular homeostasis.

In Vivo Calpain Knockdown Using Delivery of siRNA

Calpain is an intracellular Ca²⁺-dependent non-lysosomal cysteine protease expressed ubiquitously in mammals. In endothelial cells, dysregulation of calpain has been shown to be involved in a wide variety of pathological conditions such as angiogenesis, vascular inflammation, and diabetes. Cell- or tissue-targeted in vivo delivery of small interfering RNA (siRNA) is a powerful research tool in the analysis of protein function and has been proposed as an attractive therapeutic modality that is applicable against a large number of human diseases including cancer. In this chapter we describe a method to knockdown calpain 1 in mouse pulmonary vascular endothelium using delivery of siRNA/cationic liposome complex. This technique results in a greater than 80% reduction in calpain 1 protein levels 48 h after a single i.v. injection of calpain 1 siRNA (0.5 mg siRNA/kg)/cationic liposome complex. We also describe confocal imaging to verify the loss of calpain 1 expression in pulmonary microvessel endothelial cells and application of this technique in the mouse model of ventilator-induced lung injury.

Modulation of Host Immunity by Helminths: The Expanding Repertoire of Parasite Effector Molecules

Helminths are extraordinarily successful parasites due to their ability to modulate the host immune response. They have evolved a spectrum of immunomodulatory molecules that are now beginning to be defined, heralding a molecular revolution in parasite immunology. These discoveries have the potential both to transform our understanding of parasite adaptation to the host and to develop possible therapies for immune-mediated disease. In this review we will summarize the current state of the art in parasite immunomodulation and discuss perspectives on future areas for research and discovery.

Deubiquitinase function of A20 maintains and repairs endothelial barrier after lung vascular injury

Vascular endothelial cadherin (VE-cad) expression at endothelial adherens junctions (AJs) regulates vascular homeostasis. Here we show that endothelial A20 is required for VE-cad expression at AJs to maintain and repair the injured endothelial barrier. In endothelial cell (EC)-restricted Tnfaip3 (A20) knockout (A20^∆EC ) mice, LPS challenge caused uncontrolled lung vascular leak and persistent sequestration of polymorphonuclear neutrophil (PMNs). Importantly, A20^∆EC mice exhibited drastically reduced VE-cad expression in lungs compared with wild-type counterparts. Endothelial expression of wild-type A20 but not the deubiquitinase-inactive A20 mutant (A20^C103A) prevented VE-cad ubiquitination, restored VE-cad expression, and suppressed lung vascular leak in A20^∆EC mice. Interestingly, IRAK-M-mediated nuclear factor-κB (NF-κB) signaling downstream of TLR4 was required for A20 expression in ECs. interleukin-1 receptor-associated kinase M (IRAK-M) knockdown suppressed basal and LPS-induced A20 expression in ECs. Further, in vivo silencing of IRAK-M in mouse lung vascular ECs through the CRISPR-Cas9 system prevented expression of A20 and VE-cad while augmenting lung vascular leak. These results suggest that targeting of endothelial A20 is a potential therapeutic strategy to restore endothelial barrier integrity in the setting of acute lung injury.

Neutrophil Activation of Endothelial Cell-Expressed TRPM2 Mediates Transendothelial Neutrophil Migration and Vascular Injury

RATIONALE

TRPM2 (transient receptor potential melastatin-2) expressed in endothelial cells (ECs) is a cation channel mediating Ca²⁺ entry in response to intracellular generation of adenosine diphosphoribose-the TRPM2 ligand.

OBJECTIVE

Because polymorphonuclear neutrophils (PMN) interaction with ECs generates reactive oxygen species, we addressed the possible role of TRPM2 expressed in ECs in the mechanism of transendothelial migration of PMNs.

METHODS AND RESULTS

We observed defective PMN transmigration in response to lipopolysaccharide challenge in adult mice in which the EC expressed TRPM2 is conditionally deleted (Trpm2^iΔEC ). PMN interaction with ECs induced the entry of Ca²⁺ in ECs via the EC-expressed TRPM2. Prevention of generation of adenosine diphosphoribose in ECs significantly reduced Ca²⁺ entry in response to PMN activation of TRPM2 in ECs. PMNs isolated from gp91phox^-/- mice significantly reduced Ca²⁺ entry in ECs via TRPM2 as compared with wild-type PMNs and failed to induce PMN transmigration. Overexpression of the adenosine diphosphoribose insensitive TRPM2 mutant channel (C1008→A) in ECs suppressed the Ca²⁺ entry response. Further, the forced expression of TRPM2 mutant channel (C1008→A) or silencing of poly ADP-ribose polymerase in ECs of mice prevented PMN transmigration.

CONCLUSIONS

Thus, endotoxin-induced transmigration of PMNs was secondary to TRPM2-activated Ca²⁺ signaling and VE-cadherin phosphorylation resulting in the disassembly of adherens junctions and opening of the paracellular pathways. These results suggest blocking TRPM2 activation in ECs is a potentially important means of therapeutically modifying PMN-mediated vascular inflammation.

Signals of vagal circuits engaging with AKT1 in α7 nAChR+CD11b+ cells lessen E. coli and LPS-induced acute inflammatory injury

Vagal circuits-α7 nAChR (α7 nicotinic acetylcholine receptor, coded by Chrna7) signaling utilizes spleen as a hub to dampen systemic inflammatory responses. Vagal innervations also extend to the distal airways and alveoli. Vagotomy and deficiency of α7 nAChR deteriorate E. coli and lipopolysaccharide (LPS)-induced acute lung inflammatory responses; however, the underlying mechanisms remain elusive. Here, we hypothesized that vagal circuits would limit splenic release and lung recruitment of α7 nAChR⁺CD11b⁺ cells (CD11b is coded by Itgam, a surface marker of monocytes and neutrophils) via phosphorylation of AKT1 and that this process would define the severity of lung injury. Using both E. coli and LPS-induced lung injury mouse models, we found that vagotomy augmented splenic egress and lung recruitment of α7 nAChR⁺CD11b⁺ cells, and consequently worsened lung inflammatory responses. Rescue of vagotomy with an α7 nAChR agonist preserved α7 nAChR⁺CD11b⁺ cells in the spleen, suppressed recruitment of these cells to the lung and attenuated lung inflammatory responses. Vagal signals via α7 nAChR promoted serine473 phosphorylation of AKT1 in α7 nAChR⁺CD11b⁺ cells and stabilized these cells in the spleen. Deletion of Akt1 enhanced splenic egress and lung recruitment of α7 nAChR⁺CD11b⁺ cells, which elicited neutrophil-infiltrated lung inflammation and injury. Vagotomy and double deletion of Chrna7 and Itgam reduced serine473 phosphorylation of AKT1 in the spleen and BAL (bronchoalveolar lavage) Ly6C^intGr1^hi neutrophils and Ly6C^hi monocytes, and they facilitated the recruitment of neutrophils and monocytes to the airspaces of E. coli-injured lungs. Double deletion of Chrna7 and Itgam increased lung recruitment of monocytes and/or neutrophils and deteriorated E. coli and LPS-induced lung injury. Thus, signals of vagal circuits engaging with AKT1 in α7 nAChR⁺CD11b⁺ cells attenuate E. coli and LPS-induced acute lung inflammatory responses. Targeting this signaling pathway could provide novel therapeutic strategies for treating acute lung injury.

Pyk2 phosphorylation of VE-PTP downstream of STIM1-induced Ca2+ entry regulates disassembly of adherens junctions

Vascular endothelial protein tyrosine phosphatase (VE-PTP) stabilizes endothelial adherens junctions (AJs) through constitutive dephosphorylation of VE-cadherin. Here we investigated the role of stromal interaction molecule 1 (STIM1) activation of store-operated Ca²⁺ entry (SOCE) in regulating AJ assembly. We observed that SOCE induced by STIM1 activated Pyk2 in human lung microvascular endothelial cells (ECs) and induced tyrosine phosphorylation of VE-PTP at Y1981. Pyk2-induced tyrosine phosphorylation of VE-PTP promoted Src binding to VE-PTP, Src activation, and subsequent VE-cadherin phosphorylation and thereby increased the endothelial permeability response. The increase in permeability was secondary to disassembly of AJs. Pyk2-mediated responses were blocked in EC-restricted Stim1 knockout mice, indicating the requirement for STIM1 in initiating the signaling cascade. A peptide derived from the Pyk2 phosphorylation site on VE-PTP abolished the STIM1/SOCE-activated permeability response. Thus Pyk2 activation secondary to STIM1-induced SOCE causes tyrosine phosphorylation of VE-PTP, and VE-PTP, in turn, binds to and activates Src, thereby phosphorylating VE-cadherin to increase endothelial permeability through disassembly of AJs. Our results thus identify a novel signaling mechanism by which STIM1-induced Ca²⁺ signaling activates Pyk2 to inhibit the interaction of VE-PTP and VE-cadherin and hence increase endothelial permeability. Therefore, targeting the Pyk2 activation pathway may be a potentially important anti-inflammatory strategy.

A recombinant fusion protein derived from dog hookworm inhibits autoantibody-induced dermal-epidermal separation ex vivo

The proteins secreted by parasitic nematodes are evolutionarily optimized molecules with unique capabilities of suppressing the immune response of the host organism. Neutrophil inhibitory factor (NIF), which is secreted by the dog hookworm Ancylostoma caninum, binds to the β2 integrin CD11b/CD18, which is expressed on human neutrophils, eosinophils, monocytes and macrophages and inhibits neutrophil-dependent lung injury and neutrophil invasion of ischaemic brain tissue. Neutrophils are key players in the pathogenesis of subepidermal autoimmune blistering diseases (sAIBDs), and their pathogenic activities are crucially dependent on β2 integrin functionality. Based on the template of single-stranded, dimerizing antibody derivatives, which are already used in cancer treatment, we designed a novel biologic, NIF-IGHE-CH4, comprising NIF and the dimerizing but otherwise inert constant heavy subdomain 4 (CH4) of human IgE (IGHE). This molecule was evaluated in a variety of in vitro assays, demonstrating its ability to inhibit pathogenically relevant neutrophil functions such as migration, adhesion and spreading, and release of reactive oxygen species. Finally, we confirmed that NIF-IGHE-CH4 inhibits blister formation in an ex vivo assay of sAIBD. These results suggest that NIF-IGHE-CH4 is a novel potential anti-inflammatory drug for the treatment of neutrophil-mediated diseases such as sAIBDs. This study promotes the drugs from bugs concept and encourages further research and development focused on turning parasite proteins into useful anti-inflammatory biologics.

SH2 domain-containing protein tyrosine phosphatase 2 and focal adhesion kinase protein interactions regulate pulmonary endothelium barrier function

Enhanced protein tyrosine phosphorylation is associated with changes in vascular permeability through formation and dissolution of adherens junctions and regulation of stress fiber formation. Inhibition of the protein tyrosine phosphorylase SH2 domain-containing protein tyrosine phosphatase 2 (SHP2) increases tyrosine phosphorylation of vascular endothelial cadherin and β-catenin, resulting in disruption of the endothelial monolayer and edema formation in the pulmonary endothelium. Vascular permeability is a hallmark of acute lung injury (ALI); thus, enhanced SHP2 activity offers potential therapeutic value for the pulmonary vasculature in diseases such as ALI, but this has not been characterized. To assess whether SHP2 activity mediates protection against edema in the endothelium, we assessed the effect of molecular activation of SHP2 on lung endothelial barrier function in response to the edemagenic agents LPS and thrombin. Both LPS and thrombin reduced SHP2 activity, correlated with decreased focal adhesion kinase (FAK) phosphorylation (Y(397) and Y(925)) and diminished SHP2 protein-protein associations with FAK. Overexpression of constitutively active SHP2 (SHP2(D61A)) enhanced baseline endothelial monolayer resistance and completely blocked LPS- and thrombin-induced permeability in vitro and significantly blunted pulmonary edema formation induced by either endotoxin (LPS) or Pseudomonas aeruginosa exposure in vivo. Chemical inhibition of FAK decreased SHP2 protein-protein interactions with FAK concomitant with increased permeability; however, overexpression of SHP2(D61A) rescued the endothelium and maintained FAK activity and FAK-SHP2 protein interactions. Our data suggest that SHP2 activation offers the pulmonary endothelium protection against barrier permeability mediators downstream of the FAK signaling pathway. We postulate that further studies into the promotion of SHP2 activation in the pulmonary endothelium may offer a therapeutic approach for patients suffering from ALI.

Carbon monoxide down-modulates Toll-like receptor 4/MD2 expression on innate immune cells and reduces endotoxic shock susceptibility

Carbon monoxide (CO) has been recently reported as the main anti-inflammatory mediator of the haem-degrading enzyme haem-oxygenase 1 (HO-1). It has been shown that either HO-1 induction or CO treatment reduces the ability of monocytes to respond to inflammatory stimuli, such as lipopolysaccharide (LPS), due to an inhibition of the signalling pathways leading to nuclear factor-κB, mitogen-activated protein kinases and interferon regulatory factor 3 activation. Hence, it has been suggested that CO impairs the stimulation of the Toll-like receptor 4 (TLR4)/myeloid differentiation factor-2 (MD2) complex located on the surface of immune cells. However, whether CO can negatively modulate the surface expression of the TLR4/MD2 complex in immune cells remains unknown. Here we report that either HO-1 induction or treatment with CO decreases the surface expression of TLR4/MD2 in dendritic cells (DC) and neutrophils. In addition, in a septic shock model of mice intraperitoneally injected with lipopolysaccharide (LPS), prophylactic treatment with CO protected animals from hypothermia, weight loss, mobility loss and death. Further, mice pre-treated with CO and challenged with LPS showed reduced recruitment of DC and neutrophils to peripheral blood, suggesting that this gas causes a systemic tolerance to endotoxin challenge. No differences in the amount of innate cells in lymphoid tissues were observed in CO-treated mice. Our results suggest that CO treatment reduces the expression of the TLR4/MD2 complex on the surface of myeloid cells, which renders them resistant to LPS priming in vitro, as well as in vivo in a model of endotoxic shock.

Protective effects of Radix Astragali injection on multiple organs of rats with obstructive jaundice

OBJECTIVE

To investigate the protective effects and mechanisms of Radix Astragali Injection on multiple organs of rats with obstructive jaundice (OJ).

METHODS

A total of 180 rats were randomly divided into the sham-operated, model control and treated groups (60 in each group). On 7, 14, 21 and 28 days after operation, the serum contents of alanine aminotransferase (ALT), aspartate aminotransferase (AST), r-glutamyl transpeptidase (r-GT), total bilirubin (TBil), direct bilirubin (DBil), blood urine nitrogen (BUN), and creatinine (CREA) were determined. And the pathological changes of livers, kidneys and lungs, and protein expressions of toll-like receptor-4 (TLR-4) of livers, intercellular adhesion molecule-1 (ICAM-1) of lungs, Bax and nuclear factor-kappa B (NF-κB), as well as apoptotic indexes of multiple organs were observed, respectively.

RESULTS

The pathological severity scores of multiple organs (including livers on 7, 14, 21 and 28 days, kidneys on 14 and 28 days, and lungs on 14 days), serum contents of ALT (14 and 21 days), AST (14 days), TBil (7, 14, 21 and 28 days), DBil (14 and 21 days), BUN (28 days), protein expressions of TLR-4 (in livers, 28 days), Bax (in livers and kidneys, 21 days), and apoptotic indexes in livers (7 and 21 days) in the treated group were significantly lower than those in the model control group (P<0.05 or P<0.01).

CONCLUSION

Radix Astragali Injection exerts protective effects on multiple organs of OJ rats by improving the pathological changes of lung, liver and kidney, decreasing the serum index of hepatic and renal function as well as inhibiting the protein expression of TLR-4 and Bax in the livers and Bax in the kidneys.

p18, a novel adaptor protein, regulates pulmonary endothelial barrier function via enhanced endocytic recycling of VE-cadherin

Vascular permeability is a hallmark of several disease states including acute lung injury (ALI). Endocytosis of VE-cadherin, away from the interendothelial junction (IEJ), causes acute endothelial barrier permeability. A novel protein, p18, anchors to the endosome membrane and plays a role in late endosomal signaling via MAPK and mammalian target of rapamycin. However, the fate of the VE-cadherin-positive endosome has yet to be elucidated. We sought to elucidate a role for p18 in VE-cadherin trafficking and thus endothelial barrier function, in settings of ALI. Endothelial cell (EC) resistance, whole-cell ELISA, and filtration coefficient were studied in mice or lung ECs overexpressing wild-type or nonendosomal-binding mutant p18, using green fluorescent protein as a control. We demonstrate a protective role for the endocytic protein p18 in endothelial barrier function in settings of ALI in vitro and in vivo, through enhanced recycling of VE-cadherin-positive early endosomes to the IEJ. In settings of LPS-induced ALI, we show that Src tethered to the endosome tyrosine phosphorylates p18 concomitantly with VE-cadherin internalization and pulmonary edema formation. We conclude that p18 regulates pulmonary endothelial barrier function in vitro and in vivo, by enhancing recycling of VE-cadherin-positive endosomes to the IEJ.

Vagus nerve through α7 nAChR modulates lung infection and inflammation: models, cells, and signals

Cholinergic anti-inflammatory pathway (CAP) bridges immune and nervous systems and plays pleiotropic roles in modulating inflammation in animal models by targeting different immune, proinflammatory, epithelial, endothelial, stem, and progenitor cells and signaling pathways. Acute lung injury (ALI) is a devastating inflammatory disease. It is pathogenically heterogeneous and involves many cells and signaling pathways. Here, we emphasized the research regarding the modulatory effects of CAP on animal models, cell population, and signaling pathways that involved in the pathogenesis of ALI. By comparing the differential effects of CAP on systemic and pulmonary inflammation, we postulated that a pulmonary parasympathetic inflammatory reflex is formed to sense and respond to pathogens in the lung. Work targeting the formation and function of pulmonary parasympathetic inflammatory reflex would extend our understanding of how vagus nerve senses, recognizes, and fights with pathogens and inflammatory responses.

NF-κB-to-AP-1 switch: a mechanism regulating transition from endothelial barrier injury to repair in endotoxemic mice

Endothelial barrier disruption is a hallmark of multiple organ injury (MOI). However, mechanisms governing the restoration of endothelial barrier function are poorly understood. Here, we uncovered an NF-κB-to-AP-1 switch that regulates the transition from barrier injury to repair following endotoxemic MOI. Endothelial NF-κB mediates barrier repair by inhibiting endothelial cell (EC) apoptosis. Blockade of endothelial NF-κB pathway activated the activator protein (AP)-1 pathway (NF-κB-to-AP-1 switch), which compensated for the anti-apoptotic and barrier-repair functions of NF-κB. The NF-κB-to-AP-1 switch occurred at 24 hours (injury to repair transition phase), but not at 48 hours (repair phase) post-LPS, and required an inflammatory signal within the endothelium. In the absence of an inflammatory signal, the NF-κB-to-AP-1 switch failed, resulting in enhanced EC apoptosis, augmented endothelial permeability, and impeded transition from barrier injury to recovery. The NF-κB-to-AP-1 switch is a protective mechanism to ensure timely transition from endothelial barrier injury to repair, accelerating barrier restoration following MOI.

The transcription factor DREAM represses the deubiquitinase A20 and mediates inflammation

Here we show that the transcription-repressor DREAM binds to the A20 promoter to repress the expression of A20, the deubiquitinase suppressing inflammatory NF-κB signaling. DREAM-deficient (Dream^−/−) mice displayed persistent and unchecked A20 expression in response to endotoxin. DREAM functioned by transcriptionally repressing A20 through binding to downstream regulatory elements (DREs). In contrast, USF1 binding to the DRE-associated E-box domain activated A20 expression in response to inflammatory stimuli. These studies define the critical opposing functions of DREAM and USF1 in inhibiting and inducing A20 expression, respectively, and thereby the strength of NF-κB signaling. Targeting of DREAM to induce USF1-mediated A20 expression is therefore a potential anti-inflammatory strategy in diseases such as acute lung injury associated with unconstrained NF-κB activity.

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

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

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

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

TRPV1 ablation aggravates inflammatory responses and organ damage during endotoxic shock

To test the hypothesis that ablation of transient receptor potential vanilloid type 1 (TRPV1) channels leads to exacerbated inflammatory responses and organ damage during endotoxic shock, lipopolysaccharide (LPS; 5 million endotoxin units/kg of body weight) was injected intraperitoneally (i.p.) into wild-type (WT) and TRPV1-null mutant (TRPV1(-/-)) mice. Mean arterial pressure and heart rate, determined by radiotelemetry, were severely depressed after LPS injection into WT and TRPV1(-/-) mice, with no distinction between the two strains. At 24 h after LPS injection, renal glomerular hypercellularity and hepatocellular injury were observed in both strains, accompanying further elevated serum levels of creatinine and alanine aminotransferase in TRPV1(-/-) mice compared to those in WT mice. At 6 or 24 h after LPS injection, neutrophil recruitment into kidneys and livers, serum cytokine (tumor necrosis factor alpha [TNF-α], interleukin 1β [IL-1β], IL-6) and renal chemokine (KC, macrophage inflammatory protein 2 [MIP-2]) levels, and renal VCAM-1 and ICAM-1 expression were greater in TRPV1(-/-) mice than WT mice. In addition, increased plasma calcitonin gene-related peptide (CGRP) levels observed in WT mice 6 h after LPS injection were absent in TRPV1(-/-) mice. Thus, TRPV1 ablation aggravates inflammatory responses, including neutrophil infiltration, proinflammatory cytokine production, and adhesion molecule expression, leading to intensified organ damage during endotoxic shock in the absence of worsened circulatory failure. The data indicate that TRPV1 activation may attenuate endotoxin-induced organ damage, possibly via its anti-inflammatory action rather than alteration of hemodynamics.

Genetic disruption of protein kinase Cδ reduces endotoxin-induced lung injury

The pathogenesis of acute lung injury and acute respiratory distress syndrome is characterized by sequestration of leukocytes in lung tissue, disruption of capillary integrity, and pulmonary edema. PKCδ plays a critical role in RhoA-mediated endothelial barrier function and inflammatory responses. We used mice with genetic deletion of PKCδ (PKCδ(-/-)) to assess the role of PKCδ in susceptibility to LPS-induced lung injury and pulmonary edema. Under baseline conditions or in settings of increased capillary hydrostatic pressures, no differences were noted in the filtration coefficients (k(f)) or wet-to-dry weight ratios between PKCδ(+/+) and PKCδ(-/-) mice. However, at 24 h after exposure to LPS, the k(f) values were significantly higher in lungs isolated from PKCδ(+/+) than PKCδ(-/-) mice. In addition, bronchoalveolar lavage fluid obtained from LPS-exposed PKCδ(+/+) mice displayed increased protein and cell content compared with LPS-exposed PKCδ(-/-) mice, but similar changes in inflammatory cytokines were measured. Histology indicated elevated LPS-induced cellularity and inflammation within PKCδ(+/+) mouse lung parenchyma relative to PKCδ(-/-) mouse lungs. Transient overexpression of catalytically inactive PKCδ cDNA in the endothelium significantly attenuated LPS-induced endothelial barrier dysfunction in vitro and increased k(f) lung values in PKCδ(+/+) mice. However, transient overexpression of wild-type PKCδ cDNA in PKCδ(-/-) mouse lung vasculature did not alter the protective effects of PKCδ deficiency against LPS-induced acute lung injury. We conclude that PKCδ plays a role in the pathological progression of endotoxin-induced lung injury, likely mediated through modulation of inflammatory signaling and pulmonary vascular barrier function.

Leucocyte recruitment in inflammation and novel endogenous negative regulators thereof

BACKGROUND

The process of extravasation of leucocytes from the vasculature into an infected, inflamed or injured tissue, designated the leucocyte adhesion cascade, is a major process in innate and adaptive immunity. In every immune process, both agonists and inhibitors, that is, positive and negative regulators, exist.

MATERIALS AND METHODS

It was only recently that endogenous inhibitors of the leucocyte adhesion cascade were identified, whereas many selectin, integrin and immunoglobulin superfamily adhesion receptors as well as chemokines and chemokine receptors promoting leucocyte recruitment have been described over the last three decades. Endogenous negative regulators include for instance pentraxin-3 (PTX-3) that blocks selectin-dependent leucocyte rolling, or the endothelium-derived developmental endothelial locus-1 (Del-1) that antagonizes beta2-integrin-mediated firm adhesion of leucocytes to the endothelium.

CONCLUSIONS

As leucocyte infiltration is a major therapeutic target in inflammatory and autoimmune disease, it becomes obvious that such endogenous anti-adhesive and anti-inflammatory agents may represent an attractive novel therapeutic platform for inflammatory and immune disorders. This review focuses on these novel endogenous inhibitors of leucocyte recruitment.

Disintegrins from hematophagous sources

Bloodsucking arthropods are a rich source of salivary molecules (sialogenins) which inhibit platelet aggregation, neutrophil function and angiogenesis. Here we review the literature on salivary disintegrins and their targets. Disintegrins were first discovered in snake venoms, and were instrumental in our understanding of integrin function and also for the development of anti-thrombotic drugs. In hematophagous animals, most disintegrins described so far have been discovered in the salivary gland of ticks and leeches. A limited number have also been found in hookworms and horseflies, and none identified in mosquitoes or sand flies. The vast majority of salivary disintegrins reported display a RGD motif and were described as platelet aggregation inhibitors, and few others as negative modulator of neutrophil or endothelial cell functions. This notably low number of reported disintegrins is certainly an underestimation of the actual complexity of this family of proteins in hematophagous secretions. Therefore an algorithm was created in order to identify the tripeptide motifs RGD, KGD, VGD, MLD, KTS, RTS, WGD, or RED (flanked by cysteines) in sialogenins deposited in GenBank database. The search included sequences from various blood-sucking animals such as ticks (e.g., Ixodes sp., Argas sp., Rhipicephalus sp., Amblyommasp.), tabanids (e.g., Tabanus sp.), bugs (e.g., Triatoma sp., Rhodnius prolixus), mosquitoes (e.g., Anopheles sp., Aedes sp., Culex sp.), sand flies (e.g., Lutzomyia sp., Phlebotomus sp.), leeches (e.g., Macrobdella sp., Placobdella sp.) and worms (e.g., Ancylostoma sp.). This approach allowed the identification of a remarkably high number of novel putative sialogenins with tripeptide motifs typical of disintegrins (>450 sequences) whose biological activity remains to be verified. This database is accessible online as a hyperlinked worksheet and displays biochemical, taxonomic, and gene ontology aspects for each putative disintegrin. It is also freely available for download (right click with the mouse) at links http://exon.niaid.nih.gov/transcriptome/RGD/RGD-Peps-WEB.xlsx (web version) and http://exon.niaid.nih.gov/transcriptome/RGD/RGD-sialogenins.zip (stand alone version).

Protection against LPS-induced pulmonary edema through the attenuation of protein tyrosine phosphatase-1B oxidation

One hallmark of acute lung injury is the disruption of the pulmonary endothelial barrier. Such disruption correlates with increased endothelial permeability, partly through the disruption of cell-cell contacts. Protein tyrosine phosphatases (PTPs) are known to affect the stability of both cell-extracellular matrix adhesions and intercellular adherens junctions (AJs). However, evidence for the role of select PTPs in regulating endothelial permeability is limited. Our investigations noted that the inhibition of PTP1B in cultured pulmonary endothelial cells (ECs), as well as in the vasculature of intact murine lungs via the transient overexpression of a catalytically inactive PTP1B, decreased the baseline resistance of cultured EC monolayers and increased the formation of edema in murine lungs, respectively. In addition, we observed that the overexpression of wild-type PTP1B enhanced basal barrier function in vitro. Immunohistochemical analyses of pulmonary ECs and the coimmunoprecipitation of murine lung homogenates demonstrated the association of PTP1B with the AJ proteins β-catenin, p120-catenin, and VE-cadherin both in vitro and ex vivo. Using LPS in a model of sepsis-induced acute lung injury, we showed that reactive oxygen species were generated in response to LPS, which correlated with enhanced PTP1B oxidation, inhibited phosphatase activity, and attenuation of the interactions between PTP1B and β-catenin, as well as enhanced β-catenin tyrosine phosphorylation. Finally, the overexpression of a cytosolic PTP1B fragment, shown to be resistant to nicotinamide adenine dinucleotide phosphate-reduced oxidase-4 (Nox4)-mediated oxidation, significantly attenuated LPS-induced endothelial barrier dysfunction and the formation of lung edema, and preserved the associations of PTP1B with AJ protein components, independent of PTP1B phosphatase activity. We conclude that PTP1B plays an important role in maintaining the pulmonary endothelial barrier, and PTP1B oxidation appears to contribute to sepsis-induced pulmonary vascular dysfunction, possibly through the disruption of AJs.

Novel neutrophil inhibitory factor homologue in the buccal gland secretion of Lampetra japonica

Abstract To identify the functional gene fragment, a neutrophil inhibitory factor (NIF) like protein was found in the buccal gland of Lampetra japonica, suggesting that this related lamprey protein represents a novel class of integrin receptor antagonists. The recombinant Lampetra japonica-NIF like (rLj-NIF) was identified by SDS-PAGE and purified by using His·Bind affinity chromatography. Effect of rLj-NIF on neutrophil migration suggested that rLj-NIF can act as a neutrophil inhibitory factor. Besides that, oxidative burst activity of neutriphil was tested by flow cytometry using dihydrorhodamine (DHR123) as a fluorogenic substrate, and the data suggested that the mean fluorescence intensity significantly decreased compared with positive controls (p<0.01). All above results indicated that rLj-NIF could also prevent the binding of β2 integrins to the surface of PMN and its FITC-labeled monoclonal antibodies (p<0.05). These data suggest that Lampetra japonica-NIF like protein is secreted by the stage of the parasite at the site of attachment. rLj-NIF plays an essential role in physiological reaction of neutrophil by a novel class of β2 integrin receptor antagonists. The activity of immunosuppressant of L. japonica-NIF could have potential medicinal value in anti-inflammation and therapy of autoimmune diseases.

Innate immune function of the adherens junction protein p120-catenin in endothelial response to endotoxin

Sepsis-induced acute lung injury is a common clinical disorder in critically ill patients that is associated with high mortality. In this study, we investigated the role of p120-catenin (p120), a constituent of endothelial adherens junctions, in regulating the innate immune function of lungs. In mice in which acute lung injury was induced by i.p. administration of LPS, we observed a rapid decrease in the expression of p120 in lungs. The p120 protein expression was correlated inversely with severity of inflammation. Suppression of p120 expression in lung endothelial cells in mice using small interfering RNA resulted in high sensitivity to endotoxin and greatly increased the mortality compared with controls. Knockdown of p120 also increased the expression of ICAM-1, neutrophil recruitment, production of cytokines TNF-α and IL-6, pulmonary transvascular protein permeability, and lung water content in response to LPS. We demonstrated that endothelial p120 modulates lung innate immune function by interfering with the association of TLR4 with its adaptor MyD88 to block TLR4 signaling and NF-κB activation in endothelial cells. In conclusion, these studies have uncovered a novel innate immune function of endothelial p120 in downregulating the lung inflammatory response to endotoxin through the suppression of TLR4 signaling.

Protective effects of a bacterially expressed NIF-KGF fusion protein against bleomycin-induced acute lung injury in mice

Current evidence suggests that the keratinocyte growth factor (KGF) and the polymorphonuclear leukocyte may play key roles in the development of lung fibrosis. Here we describe the construction, expression, purification, and identification of a novel NIF (neutrophil inhibitory factor)-KGF mutant fusion protein (NKM). The fusion gene was ligated via a flexible octapeptide hinge and expressed as an insoluble protein in Escherichia coli BL21 (DE3). The fusion protein retained the activities of KGF and NIF, as it inhibited both fibroblast proliferation and leukocyte adhesion. Next, the effects of NKM on bleomycin-induced lung fibrosis in mice were examined. The mice were divided into the following four groups: (i) saline group; (ii) bleomycin group (instilled with 5 mg/kg bleomycin intratracheally); (iii) bleomycin plus dexamethasone (Dex) group (Dex was given intraperitoneally (i.p.) at 1 mg/kg/day 2 days prior to bleomycin instillation and daily after bleomycin instillation until the end of the treatment); and (iv) bleomycin plus NKM group (NKM was given i.p. at 2 mg/kg/day using the same protocol as the Dex group). NKM significantly improved the survival rates of mice exposed to bleomycin. The marked morphological changes and increased hydroxyproline levels resulted from the instillation of bleomycin (on Day 17) in the lungs were significantly inhibited by NKM. These results revealed that NKM can attenuate bleomycin-induced lung fibrosis, suggesting that NKM could be used to prevent bleomycin-induced lung damage or other interstitial pulmonary fibrosis.

A novel function of sphingosine kinase 1 suppression of JNK activity in preventing inflammation and injury

The mechanism underlying the protective effect of sphingosine kinase 1 (SphK1) in inflammatory injury is not clear. We demonstrated using SphK1-null mice (SphK1(-/-)) the crucial role of SphK1 in suppressing lipopolysaccharide-induced neutrophil oxidant production and sequestration in lungs and mitigating lung inflammatory injury. This effect of SphK1 was independent of the production of sphingosine 1-phosphate, the product of SphK1 activity. The anti-inflammatory effect of SphK1 in the lipopolysaccharide model was mediated through SphK1 interaction with JNK. SphK1 stabilization of JNK in turn inhibited JNK binding to the JNK-interacting protein 3 (JIP3) and thus abrogated the activation of NADPH oxidase and oxidant generation and resultant NF-kappaB activation. Therefore, SphK1-mediated down-regulation of JNK activity serves to dampen inflammation and tissue injury.

Hydrogen sulfide promotes transient receptor potential vanilloid 1-mediated neurogenic inflammation in polymicrobial sepsis

OBJECTIVE

To investigate the interaction and involvement of hydrogen sulfide and transient receptor potential vanilloid type 1 in the pathogenesis of sepsis. Hydrogen sulfide has been demonstrated to be involved in many inflammatory states including sepsis. Its contribution in neurogenic inflammation has been suggested in normal airways and urinary bladder. However, whether endogenous hydrogen sulfide would induce transient receptor potential vanilloid type 1-mediated neurogenic inflammation in sepsis remains unknown.

DESIGN

Prospective, experimental study.

SETTING

Research laboratory.

SUBJECT

Male Swiss mice.

INTERVENTIONS

Mice were subjected to cecal ligation and puncture-induced sepsis and treated with transient receptor potential vanilloid type 1 antagonist capsazepine (15 mg/kg subcutaneous) 30 mins before cecal ligation and puncture. To investigate hydrogen sulfide-mediated neurogenic inflammation in sepsis, DL-propargylglycine (50 mg/kg intraperitoneal), an inhibitor of hydrogen sulfide formation was administrated 1 hr before or 1 hr after the induction of sepsis, whereas sodium hydrosulfide (10 mg/kg intraperitoneal), a hydrogen sulfide donor, was given at the same time as cecal ligation and puncture. Lung and liver myeloperoxidase activities, liver cystathionine-gamma-lyase activity, plasma hydrogen sulfide level, histopathological examination, and survival studies were determined after induction of sepsis.

MEASUREMENTS AND MAIN RESULTS

Capsazepine treatment attenuates significantly systemic inflammation and multiple organ damage caused by sepsis, and protects against sepsis-induced mortality. Similarly, administration of sodium hydrosulfide exacerbates but capsazepine reverses these deleterious effects. In the presence of DL-propargylglycine, capsazepine causes no significant changes to the attenuation of sepsis-associated systemic inflammation, multiple organ damage, and mortality. In addition, capsazepine has no effect on endogenous generation of hydrogen sulfide, suggesting that hydrogen sulfide is located upstream of transient receptor potential vanilloid type 1 activation, and may play a critical role in regulating the production and release of sensory neuropeptides in sepsis.

CONCLUSIONS

The present study shows that hydrogen sulfide induces systemic inflammation and multiple organ damage characteristic of sepsis via transient receptor potential vanilloid type 1-mediated neurogenic inflammation.

Novel aspects in the regulation of the leukocyte adhesion cascade

Leukocyte recruitment plays a major role in the immune response to infectious pathogens and during inflammatory and autoimmune disorders. The process of leukocyte extravasation from the blood into the inflamed tissue requires a complex cascade of adhesive events between the leukocytes and the endothelium including leukocyte rolling, adhesion and transendothelial migration. Leukocyte-endothelial interactions are mediated by tightly regulated binding interactions between adhesion receptors on both cells. In this regard, leukocyte adhesion onto the endothelium is governed by leukocyte integrins and their endothelial counter-receptors of the immunoglobulin superfamily. The present review will focus on novel aspects with respect to the modulation of the leukocyte adhesion cascade.

Phosphorylation of caveolin-1 regulates oxidant-induced pulmonary vascular permeability via paracellular and transcellular pathways

RATIONALE

Oxidants are important signaling molecules known to increase endothelial permeability, although the mechanisms underlying permeability regulation are not clear.

OBJECTIVE

To define the role of caveolin-1 in the mechanism of oxidant-induced pulmonary vascular hyperpermeability and edema formation.

METHODS AND RESULTS

Using genetic approaches, we show that phosphorylation of caveolin-1 Tyr14 is required for increased pulmonary microvessel permeability induced by hydrogen peroxide (H(2)O(2)). Caveolin-1-deficient mice (cav-1(-/-)) were resistant to H(2)O(2)-induced pulmonary vascular albumin hyperpermeability and edema formation. Furthermore, the vascular hyperpermeability response to H(2)O(2) was completely rescued by expression of caveolin-1 in cav-1(-/-) mouse lung microvessels but was not restored by the phosphorylation-defective caveolin-1 mutant. The increase in caveolin-1 phosphorylation induced by H(2)O(2) was dose-dependently coupled to both increased (125)I-albumin transcytosis and decreased transendothelial electric resistance in pulmonary endothelial cells. Phosphorylation of caveolin-1 following H(2)O(2) exposure resulted in the dissociation of vascular endothelial cadherin/beta-catenin complexes and resultant endothelial barrier disruption.

CONCLUSIONS

Caveolin-1 phosphorylation-dependent signaling plays a crucial role in oxidative stress-induced pulmonary vascular hyperpermeability via transcellular and paracellular pathways. Thus, caveolin-1 phosphorylation may be an important therapeutic target for limiting oxidant-mediated vascular hyperpermeability, protein-rich edema formation, and acute lung injury.

Absence of Smad3 induces neutrophil migration after cutaneous irradiation: possible contribution to subsequent radioprotection

Our previous work showed that 6 weeks after cutaneous irradiation, mice null (knockout, KO) for Smad3, a cytoplasmic downstream mediator of transforming growth factor-beta, demonstrate less epidermal acanthosis and dermal inflammation than wild-type (WT) Smad3 mice. Analysis of the kinetics of inflammation showed that 6 to 8 hours after skin irradiation, there was a transient sevenfold increase in neutrophil influx in Smad3 KO mice compared with WT. Herein we describe bone marrow transplantation and skin grafting between WT and KO mice to assess the contribution of the neutrophil genotype compared with that of irradiated skin to the induction of neutrophil migration after irradiation. Results from bone marrow transplantation showed that WT marrow transplanted into KO mice enhanced neutrophil migration 6 to 8 hours after irradiation by 3.2-fold compared with KO marrow in WT mice. KO skin grafted onto either WT or KO animals showed a sixfold elevation of neutrophils after irradiation compared with grafted WT skin. These results suggest that the genotype of the irradiated skin, rather than the inflammatory cell, controls neutrophil influx. Circulating neutrophils, increased in WT mice after injection of granulocyte colony-stimulating factor, resulted in increased neutrophil migration to the skin 6 to 8 hours after irradiation and less skin damage 6 weeks after irradiation compared with untreated WT mice. Thus, early responses, including enhanced neutrophil influx, appear to contribute to subsequent cutaneous radioprotection.

E3 ubiquitin ligase Cblb regulates the acute inflammatory response underlying lung injury

The E3 ubiquitin ligase Cblb has a crucial role in the prevention of chronic inflammation and autoimmunity. Here we show that Cblb also has an unexpected function in acute lung inflammation. Cblb attenuates the sequestration of inflammatory cells in the lungs after administration of lipopolysaccharide (LPS). In a model of polymicrobial sepsis in which acute lung inflammation depends on the LPS receptor (Toll-like receptor 4, TLR-4), the loss of Cblb expression accentuates acute lung inflammation and reduces survival. Loss of Cblb significantly increases sepsis-induced release of inflammatory cytokines and chemokines. Cblb controls the association between TLR4 and the intracellular adaptor MyD88. Expression of wild-type Cblb, but not expression of a Cblb mutant that lacks E3 ubiquitin ligase function, prevents the activity of a reporter gene for the transcription factor nuclear factor-kappaB (NF-kappaB) in monocytes that have been challenged with LPS. The downregulation of TLR4 expression on the cell surface of neutrophils is impaired in the absence of Cblb. Our data reveal that Cblb regulates the TLR4-mediated acute inflammatory response that is induced by sepsis.

Electroporation-mediated gene transfer of the Na+,K+ -ATPase rescues endotoxin-induced lung injury

RATIONALE

Acute lung injury and acute respiratory distress syndrome are common clinical syndromes resulting largely from the accumulation of and inability to clear pulmonary edema, due to injury to the alveolar epithelium. Gene therapy may represent an important alternative for the treatment and prevention of these diseases by restoring alveolar epithelial function. We have recently developed an electroporation strategy to transfer genes to the lungs of mice, with high efficiency and low inflammation.

OBJECTIVES

We asked whether electroporation-mediated transfer of genes encoding subunits of the Na+,K+ -ATPase could protect from LPS-induced lung injury or be used to treat already injured lungs by up-regulating mechanisms of pulmonary edema clearance.

METHODS

Plasmids were delivered to the lungs of mice using transthoracic electroporation. Lung injury was induced by intratracheal administration of LPS (4 mg/kg body weight). Biochemical, cellular, and physiologic measurements were taken to assess gene transfer and lung injury.

MEASUREMENTS AND MAIN RESULTS

Improvements in wet-to-dry ratios, pulmonary effusions, bronchoalveolar lavage protein levels and cellularity, alveolar fluid clearance, and respiratory mechanics were seen after delivery of plasmids expressing Na+,K+ -ATPase subunits, but not control plasmids, in LPS-injured lungs. Delivery of plasmids expressing Na+,K+ -ATPase subunits both protected from subsequent lung injury and partially reversed existing lung injury by these measures.

CONCLUSIONS

These results demonstrate that electroporation can be used effectively in healthy and injured lungs to facilitate gene delivery and expression. To our knowledge, this is the first successful use of gene delivery to treat existing lung injury, and may have future clinical potential.

Neutrophils in development of multiple organ failure in sepsis

Multiple organ failure is a major threat to the survival of patients with sepsis and systemic inflammation. In the UK and in the USA, mortality rates are currently comparable with and projected to exceed those from myocardial infarction. The immune system combats microbial infections but, in severe sepsis, its untoward activity seems to contribute to organ dysfunction. In this Review we propose that an inappropriate activation and positioning of neutrophils within the microvasculature contributes to the pathological manifestations of multiple organ failure. We further suggest that targeting neutrophils and their interactions with blood vessel walls could be a worthwhile therapeutic strategy for sepsis.

Cdc42 regulates adherens junction stability and endothelial permeability by inducing alpha-catenin interaction with the vascular endothelial cadherin complex

The endothelial adherens junctions (AJs) consist of trans-oligomers of membrane spanning vascular endothelial (VE)-cadherin proteins, which bind beta-catenin through their cytoplasmic domain. beta-Catenin in turn binds alpha-catenin and connects the AJ complex with the actin cytoskeleton. We addressed the in vivo effects of loss of VE-cadherin interactions on lung vascular endothelial permeability and the role of specific Rho GTPase effectors in regulating the increase in permeability induced by AJ destabilization. We used cationic liposomes encapsulating the mutant of VE-cadherin lacking the extracellular domain (DeltaEXD) to interfere with AJ assembly in mouse lung endothelial cells. We observed that lung vascular permeability (quantified as microvessel filtration coefficient [K(f,c)]) was increased 5-fold in lungs expressing DeltaEXD. This did not occur to the same degree on expression of the VE-cadherin mutant, DeltaEXDDeltabeta, lacking the beta-catenin-binding site. The increased vascular permeability was the result of destabilization of VE-cadherin homotypic interaction induced by a shift in the binding of beta-catenin from wild-type VE-cadherin to the expressed DeltaEXD mutant. Because DeltaEXD expression in endothelial cells activated the Rho GTPase Cdc42, we addressed its role in the mechanism of increased endothelial permeability induced by AJ destabilization. Coexpression of dominant-negative Cdc42 (N17Cdc42) prevented the increase in K(f,c) induced by DeltaEXD. This was attributed to inhibition of the association of alpha-catenin with the DeltaEXD-beta-catenin complex. The results demonstrate that Cdc42 regulates AJ permeability by controlling the binding of alpha-catenin with beta-catenin and the consequent interaction of the VE-cadherin/catenin complex with the actin cytoskeleton.

Suppression of RhoA activity by focal adhesion kinase-induced activation of p190RhoGAP: role in regulation of endothelial permeability

The interaction of endothelial cells with extracellular matrix proteins at focal adhesions sites contributes to the integrity of vascular endothelial barrier. Although focal adhesion kinase (FAK) activation is required for the recovery of the barrier function after increased endothelial junctional permeability, the basis for the recovery remains unclear. We tested the hypothesis that FAK activates p190RhoGAP and, thus, negatively regulates RhoA activity and promotes endothelial barrier restoration in response to the permeability-increasing mediator thrombin. We observed that thrombin caused a transient activation of RhoA but a more prolonged FAK activation temporally coupled to the recovery of barrier function. Thrombin also induced tyrosine phosphorylation of p190RhoGAP, which coincided with decrease in RhoA activity. We further showed that FAK was associated with p190RhoGAP, and importantly, recombinant FAK phosphorylated p190RhoGAP in vitro. Inhibition of FAK by adenoviral expression of FRNK (a dominant negative FAK construct) in monolayers prevented p190RhoGAP phosphorylation, increased RhoA activity, induced actin stress fiber formation, and produced an irreversible increase in endothelial permeability in response to thrombin. We also observed that p190RhoGAP was unable to attenuate RhoA activation in the absence of FAK activation induced by FRNK. The inhibition of RhoA by the C3 toxin (Clostridium botulinum toxin) restored endothelial barrier function in the FRNK-expressing cells. These findings in endothelial cells were recapitulated in the lung microcirculation in which FRNK expression in microvessel endothelia increased vascular permeability. Our studies demonstrate that FAK-induced down-modulation of RhoA activity via p190RhoGAP is a crucial step in signaling endothelial barrier restoration after increased endothelial permeability.

Keratinocyte growth factor therapy in murine oleic acid-induced acute lung injury

Alveolar type II (ATII) cell proliferation and differentiation are important mechanisms in repair following injury to the alveolar epithelium. KGF is a potent ATII cell mitogen, which has been demonstrated to be protective in a number of animal models of lung injury. We have assessed the effect of recombinant human KGF (rhKGF) and liposome-mediated KGF gene delivery in vivo and evaluated the potential of KGF as a therapy for acute lung injury in mice. rhKGF was administered intratracheally in male BALB/c mice to assess dose response and time course of proliferation. SP-B immunohistochemistry demonstrated significant increases in ATII cell numbers at all rhKGF doses compared with control animals and peaked 2 days following administration of 10 mg/kg rhKGF. Protein therapy in general is very expensive, and gene therapy has been suggested as a cheaper alternative for many protein replacement therapies. We evaluated the effect of topical and systemic liposome-mediated KGF-gene delivery on ATII cell proliferation. SP-B immunohistochemistry showed only modest increases in ATII cell numbers following gene delivery, and these approaches were therefore not believed to be capable of reaching therapeutic levels. The effect of rhKGF was evaluated in a murine model of OA-induced lung injury. This model was found to be associated with significant alveolar damage leading to severe impairment of gas exchange and lung compliance. Pretreatment with rhKGF 2 days before intravenous OA challenge resulted in significant improvements in PO2, PCO2, and lung compliance. This study suggests the feasibility of KGF as a therapy for acute lung injury.

Protective role of angiopoietin-1 in endotoxic shock

BACKGROUND

Angiopoietin-1 (Ang1) plays an essential role in embryonic vasculature development, protects the adult peripheral vasculature from leakage, and has antiinflammatory properties. Because endotoxin-induced shock is a condition with microvascular leakage resulting from inflammation, we examined the potential therapeutic benefit of Ang1 in a murine model of lipopolysaccharide (LPS)-induced endotoxic shock.

METHODS AND RESULTS

To induce endotoxic shock, LPS was injected intraperitoneally into C57BL/6 mice. Half of the mice received an intravenous application of 1.0x10(9) plaque-forming units of an adenoviral construct expressing human Ang1 (AdhAng1); in the other half an identical vector expressing green fluorescent protein (AdGFP) was injected as a control. In the AdhAng1-treated mice, hepatic transfection and high expression of circulating Ang1 protein were observed. Whereas in LPS-treated control mice, hemodynamic function was severely depressed 12 hours after LPS injection (decrease of blood pressure from 91+/-3 to 49+/-7 mm Hg, dP/dt(max) from 7284+/-550 to 2699+/-233 mm Hg/s, cardiac output from 11.3+/-1.2 to 2.8+/-0.8 mL/min; P<0.0005), in LPS-treated AdhAng1 mice blood pressure fell only to 76+/-3 mm Hg, dP/dt(max) to 5091+/-489 mm Hg/s, and cardiac output to 6.7+/-1.4 mL/min (P<0.05). This resistance to LPS-induced hemodynamic changes was reflected by an improved Kaplan-Meier survival rate of the AdhAng1 mice. Histological analysis revealed that lung injury after LPS injection was markedly attenuated in AdhAng1 mice. In addition, LPS-induced increase in lung water content and pulmonary myeloperoxidase activity was significantly reduced. Furthermore, LPS-induced increases in the expression level of vascular cell adhesion molecule-1, intracellular adhesion molecule-1, and E-selectin protein in the lungs were markedly lower in AdhAng1 mice than in control mice. Finally, in the mice overexpressing Ang1, pulmonary endothelial NO synthase (eNOS) expression and activity remained preserved after LPS challenge, providing evidence that the beneficial effect of Ang1 in endotoxic shock is mediated by eNOS-derived NO.

CONCLUSIONS

Our study demonstrates an improved mortality rate in mice with endotoxic shock pretreated with an adenoviral construct encoding Ang1. The enhanced survival rate induced by Ang1 was accompanied by an improvement in hemodynamic function, reduced lung injury, a lower expression of inflammatory adhesion molecules, and preserved eNOS activity in the lung tissue. Ang1 may therefore have utility as an adjunctive agent for the treatment of septic shock condition.

Endothelial Lipase Modulates Monocyte Adhesion to the Vessel Wall

Endothelial lipase (EL), a new member of the lipoprotein lipase gene family, plays a central role in high density lipoprotein metabolism. Previous studies indicated that EL is expressed in endothelial cells, macrophages, and smooth muscle cells in atherosclerotic lesions in human coronary arteries. However, the functional role of EL in the local vessel wall remains obscure. In this study, we evaluated the ability of EL to modulate monocyte adhesion to the endothelial cell surface. EL mRNA and protein levels were markedly increased in tissues of the mouse model of inflammation induced by lipopolysaccharide injection. Adhesion assays in vitro revealed that overexpression of EL in COS7 or Pro5 cells enhanced monocyte bindings to the EL-expression cells. Heparin or heparinase treatment inhibited EL-mediated increases of monocyte adhesion in a dose-dependent manner. Moreover, ex vivo adhesion assays revealed that the number of adherent monocytes on aortic strips was significantly increased in EL transgenic mice and decreased in EL knock-out mice as compared with wild-type mice. These results suggest that EL on the endothelial cell surface can promote monocyte adhesion to the vascular endothelium through the interaction with heparan sulfate proteoglycans. Thus, the up-regulation of EL by inflammatory stimuli may be involved in the progression of inflammation.

E. coli pneumonia induces CD18-independent airway neutrophil migration in the absence of increased lung vascular permeability

We examined the relationship between neutrophil [polymorphonuclear leukocyte (PMN)] influx and lung vascular injury in response to Escherichia coli pneumonia. We assessed lung tissue PMN uptake by measuring myeloperoxidase and transvascular PMN migration by determining PMN counts in lung interstitium and bronchoalveolar lavage fluid (BALF) in mice challenged intratracheally with E. coli. Lung vascular injury was quantified by determining microvessel filtration coefficient (Kf,c), a measure of vascular permeability. We addressed the role of CD18 integrin in the mechanism of PMN migration and lung vascular injury by inducing the expression of neutrophil inhibitory factor, a CD11/CD18 antagonist. In control animals, we observed a time-dependent sixfold increase in PMN uptake, a fivefold increase in airway PMN migration, and a 20-fold increase in interstitial PMN uptake at 6 h after challenge. Interestingly, Kf,c increased minimally during this period of PMN extravasation. CD11/CD18 blockade reduced lung tissue PMN uptake consistent with the role of CD18 in mediating PMN adhesion to the endothelium but failed to alter PMN migration in the tissue. Moreover, CD11/CD18 blockade did not affect Kf,c. Analysis of BALF leukocytes demonstrated diminished oxidative burst compared with leukocytes from bacteremic mice, suggesting a basis for lack of vascular injury. The massive CD11/CD18-independent airway PMN influx occurring in the absence of lung vascular injury is indicative of an efficient host-defense response elicited by E. coli pneumonia.

Inhibition of Mg2+-dependent Adhesion of Polymorphonuclear Leukocytes by Serum Hemopexin: Differences in Divalent-Cation Dependency of Cell Adhesion in the Presence and Absence of Serum

Circulating and nonadherent polymorphonuclear leukocytes (PMNs) become activated to attain adhesive state in an integrin-dependent manner by various stimuli, and perform a variety of microbicidal functions such as phagocytosis and superoxide production. We found that, in the absence of serum, a physiological concentration of hemopexin has a strong inhibitory action on Mg(2+)-dependent adhesion of PMA-activated PMNs to fibrinogen- and serum-coated surfaces. Under these conditions, Ca(2+) had no effect on Mg(2+)-dependent adhesion or the adhesion-inhibitory activity of hemopexin. In contrast, PMNs suspended in serum containing sufficient amounts of hemopexin to inhibit adhesion showed marked adherence, which was inhibited by EGTA. Next, we prepared a small-molecule fraction of serum by ultrafiltration followed by boiling. PMA-activated PMNs was found to adhere in the presence of both hemopexin and the small-molecule fraction, and the adhesion was enhanced by exogenous Ca(2+). EGTA abolished the effect of the small molecule fraction. The data suggest that serum contains adhesion-promoting factor(s) which allows PMNs to adhere despite the presence of hemopexin and that Ca(2+) is required for adhesion-promoting activity. Further study of hemopexin may provide clues for new therapeutic strategies aimed at interfering with PMN adhesion to control inflammation and tissue injury.