Galphai2-mediated signaling events in the endothelium are involved in controlling leukocyte extravasation

Stabilization of Interdomain Interactions in G protein αi Subunits Determines Gαi Subtype Signaling Specificity

Highly homologous members of the Gαi family, Gαi1-3, have distinct tissue distributions and physiological functions, yet the functional properties of these proteins with respect to GDP/GTP binding and regulation of adenylate cyclase are very similar. We recently identified PDZ-RhoGEF (PRG) as a novel Gαi1 effector, however, it is poorly activated by Gαi2. Here, in a proteomic proximity labeling screen we observed a strong preference for Gαi1 relative to Gαi2 with respect to engagement of a broad range of potential targets. We investigated the mechanistic basis for this selectivity using PRG as a representative target. Substitution of either the helical domain (HD) from Gαi1 into Gαi2 or substitution of a single amino acid, A230 in Gαi2 to the corresponding D in Gαi1, largely rescues PRG activation and interactions with other Gαi targets. Molecular dynamics simulations combined with Bayesian network models revealed that in the GTP bound state, dynamic separation at the HD-Ras-like domain (RLD) interface is prevalent in Gαi2 relative to Gαi1 and that mutation of A230s4h3.3 to D in Gαi2 stabilizes HD-RLD interactions through formation of an ionic interaction with R145HD.11 in the HD. These interactions in turn modify the conformation of Switch III. These data support a model where D229s4h3.3 in Gαi1 interacts with R144HD.11 stabilizes a network of interactions between HD and RLD to promote protein target recognition. The corresponding A230 in Gαi2 is unable to form the "ionic lock" to stabilize this network leading to an overall lower efficacy with respect to target interactions. This study reveals distinct mechanistic properties that could underly differential biological and physiological consequences of activation of Gαi1 or Gαi2 by GPCRs.

Gαi protein subunit: A step toward understanding its non-canonical mechanisms

The heterotrimeric G protein family plays essential roles during a varied array of cellular events; thus, its deregulation can seriously alter signaling events and the overall state of the cell. Heterotrimeric G-proteins have three subunits (α, β, γ) and are subdivided into four families, Gαi, Gα12/13, Gαq, and Gαs. These proteins cycle between an inactive Gα-GDP state and active Gα-GTP state, triggered canonically by the G-protein coupled receptor (GPCR) and by other accessory proteins receptors independent also known as AGS (Activators of G-protein Signaling). In this review, we summarize research data specific for the Gαi family. This family has the largest number of individual members, including Gαi1, Gαi2, Gαi3, Gαo, Gαt, Gαg, and Gαz, and constitutes the majority of G proteins α subunits expressed in a tissue or cell. Gαi was initially described by its inhibitory function on adenylyl cyclase activity, decreasing cAMP levels. Interestingly, today Gi family G-protein have been reported to be importantly involved in the immune system function. Here, we discuss the impact of Gαi on non-canonical effector proteins, such as c-Src, ERK1/2, phospholipase-C (PLC), and proteins from the Rho GTPase family members, all of them essential signaling pathways regulating a wide range of physiological processes.

Intravital imaging of eosinophils: Unwrapping the enigma

Eosinophils are traditionally associated with allergic and parasitic inflammation. More recently, eosinophils have also been shown to have roles in diverse processes including development, intestinal health, thymic selection, and B-cell survival with the majority of these insights being derived from murine models and in vitro assays. Despite this, tools to measure the dynamic activity of eosinophils in situ have been lacking. Intravital microscopy is a powerful tool that enables direct visualization of leukocytes and their dynamic behavior in real-time in a wide range of processes in both health and disease. Until recently eosinophil researchers have not been able to take full advantage of this technology due to a lack of tools such as genetically encoded reporter mice. This mini-review examines the history of intravital microscopy with a focus on eosinophils. The development and use of eosinophil-specific Cre (EoCre) mice to create GFP and tdTomato fluorescent reporter animals is also described. Genetically encoded eosinophil reporter mice combined with intravital microscopy provide a powerful tool to add to the toolbox of technologies that will help us unravel the mysteries still surrounding this cell.

Gestational binge alcohol-induced alterations in maternal uterine artery transcriptome

Binge alcohol exposure during pregnancy results in diminished vessel function and altered proteome in the maternal uterine artery. We aimed to utilize high throughput RNA-seq deep-sequencing to characterize specific effects of binge alcohol exposure during pregnancy on the uterine artery transcriptome, and gain insight into mechanisms underlying alcohol-mediated uterine artery dysfunction. Pregnant Sprague-Dawley rats assigned to Pair-Fed Control or Alcohol groups, received a once-daily orogastric gavage in a binge paradigm. RNA-sequencing using Illumina NextSeq 500, identified 13,941 genes; 40 significantly altered genes were altered by log2(fold change) > 2; 27 genes were upregulated and 13 were downregulated in the Alcohol group. Transcripts altered included those which encode for aldehyde dehydrogenases, matrix metalloproteases, and molecules vital for vasodilation and vascular remodeling. Biological pathways that were disproportionally altered by alcohol were proline and citrulline biosynthesis/metabolism. Disruption of these pathways suggests candidate mechanism(s) for alcohol-mediated impairments to the proteome and vascular function.

GNAI1 and GNAI3 Reduce Colitis-Associated Tumorigenesis in Mice by Blocking IL6 Signaling and Down-regulating Expression of GNAI2

BACKGROUND & AIMS

Interleukin 6 (IL6) and tumor necrosis factor contribute to the development of colitis-associated cancer (CAC). We investigated these signaling pathways and the involvement of G protein subunit alpha i1 (GNAI1), GNAI2, and GNAI3 in the development of CAC in mice and humans.

METHODS

B6;129 wild-type (control) or mice with disruption of Gnai1, Gnai2, and/or Gnai3 or conditional disruption of Gnai2 in CD11c+ or epithelial cells were given dextran sulfate sodium (DSS) to induce colitis followed by azoxymethane (AOM) to induce carcinogenesis; some mice were given an antibody against IL6. Feces were collected from mice, and the compositions of microbiomes were analyzed by polymerase chain reactions. Dendritic cells (DCs) and myeloid-derived suppressor cells (MDSCs) isolated from spleen and colon tissues were analyzed by flow cytometry. We performed immunoprecipitation and immunoblot analyses of colon tumor tissues, MDSCs, and mouse embryonic fibroblasts to study the expression levels of GNAI1, GNAI2, and GNAI3 and the interactions of GNAI1 and GNAI3 with proteins in the IL6 signaling pathway. We analyzed the expression of Gnai2 messenger RNA by CD11c+ cells in the colonic lamina propria by PrimeFlow, expression of IL6 in DCs by flow cytometry, and secretion of cytokines in sera and colon tissues by enzyme-linked immunosorbent assay. We obtained colon tumor and matched nontumor tissues from 83 patients with colorectal cancer having surgery in China and 35 patients with CAC in the United States. Mouse and human colon tissues were analyzed by histology, immunoblot, immunohistochemistry, and/or RNA-sequencing analyses.

RESULTS

GNAI1 and GNAI3 (GNAI1;3) double-knockout (DKO) mice developed more severe colitis after administration of DSS and significantly more colonic tumors than control mice after administration of AOM plus DSS. Development of increased tumors in DKO mice was not associated with changes in fecal microbiomes but was associated with activation of nuclear factor (NF) κB and signal transducer and activator of transcription (STAT) 3; increased levels of GNAI2, nitric oxide synthase 2, and IL6; increased numbers of CD4+ DCs and MDSCs; and decreased numbers of CD8+ DCs. IL6 was mainly produced by CD4+/CD11b+, but not CD8+, DCs in DKO mice. Injection of DKO mice with a blocking antibody against IL6 reduced the expansion of MDSCs and the number of tumors that developed after CAC induction. Incubation of MDSCs or mouse embryonic fibroblasts with IL6 induced activation of either NF-κB by a JAK2-TRAF6-TAK1-CHUK/IKKB signaling pathway or STAT3 by JAK2. This activation resulted in expression of GNAI2, IL6 signal transducer (IL6ST, also called GP130) and nitric oxide synthase 2, and expansion of MDSCs; the expression levels of these proteins and expansion of MDSCs were further increased by the absence of GNAI1;3 in cells and mice. Conditional disruption of Gnai2 in CD11c+ cells of DKO mice prevented activation of NF-κB and STAT3 and changes in numbers of DCs and MDSCs. Colon tumor tissues from patients with CAC had reduced levels of GNAI1 and GNAI3 and increased levels of GNAI2 compared with normal tissues. Further analysis of a public human colorectal tumor DNA microarray database (GSE39582) showed that low Gani1 and Gnai3 messenger RNA expression and high Gnai2 messenger RNA expression were significantly associated with decreased relapse-free survival.

CONCLUSIONS

GNAI1;3 suppresses DSS-plus-AOM-induced colon tumor development in mice, whereas expression of GNAI2 in CD11c+ cells and IL6 in CD4+/CD11b+ DCs appears to promote these effects. Strategies to induce GNAI1;3, or block GNAI2 and IL6, might be developed for the prevention or therapy of CAC in patients.

Regulator of G protein signaling 5 restricts neutrophil chemotaxis and trafficking

Neutrophils are white blood cells that are mobilized to damaged tissues and to sites of pathogen invasion, providing the first line of host defense. Chemokines displayed on the surface of blood vessels promote migration of neutrophils to these sites, and tissue- and pathogen-derived chemoattractant signals, including N-formylmethionylleucylphenylalanine (fMLP), elicit further migration to sites of infection. Although nearly all chemoattractant receptors use heterotrimeric G proteins to transmit signals, many of the mechanisms lying downstream of chemoattractant receptors that either promote or limit neutrophil motility are incompletely defined. Here, we show that regulator of G protein signaling 5 (RGS5), a protein that modulates G protein activity, is expressed in both human and murine neutrophils. We detected significantly more neutrophils in the airways of Rgs5^-/- mice than WT counterparts following acute respiratory virus infection and in the peritoneum in response to injection of thioglycollate, a biochemical proinflammatory stimulus. RGS5-deficient neutrophils responded with increased chemotaxis elicited by the chemokines CXC motif chemokine ligand 1 (CXCL1), CXCL2, and CXCL12 but not fMLP. Moreover, adhesion of these cells was increased in the presence of both CXCL2 and fMLP. In summary, our results indicate that RGS5 deficiency increases chemotaxis and adhesion, leading to more efficient neutrophil mobilization to inflamed tissues in mice. These findings suggest that RGS5 expression and activity in neutrophils determine their migrational patterns in the complex microenvironments characteristic of inflamed tissues.

Regulation of Chemokine Signal Integration by Activator of G-Protein Signaling 4 (AGS4)

Activator of G-protein signaling 4 (AGS4)/G-protein signaling modulator 3 (Gpsm3) contains three G-protein regulatory (GPR) motifs, each of which can bind Gαi-GDP free of Gβγ We previously demonstrated that the AGS4-Gαi interaction is regulated by seven transmembrane-spanning receptors (7-TMR), which may reflect direct coupling of the GPR-Gαi module to the receptor analogous to canonical Gαβγ heterotrimer. We have demonstrated that the AGS4-Gαi complex is regulated by chemokine receptors in an agonist-dependent manner that is receptor-proximal. As an initial approach to investigate the functional role(s) of this regulated interaction in vivo, we analyzed leukocytes, in which AGS4/Gpsm3 is predominantly expressed, from AGS4/Gpsm3-null mice. Loss of AGS4/Gpsm3 resulted in mild but significant neutropenia and leukocytosis. Dendritic cells, T lymphocytes, and neutrophils from AGS4/Gpsm3-null mice also exhibited significant defects in chemoattractant-directed chemotaxis and extracellular signal-regulated kinase activation. An in vivo peritonitis model revealed a dramatic reduction in the ability of AGS4/Gpsm3-null neutrophils to migrate to primary sites of inflammation. Taken together, these data suggest that AGS4/Gpsm3 is required for proper chemokine signal processing in leukocytes and provide further evidence for the importance of the GPR-Gαi module in the regulation of leukocyte function.

Gene-specific sex effects on eosinophil infiltration in leishmaniasis

Background

Sex influences susceptibility to many infectious diseases, including some manifestations of leishmaniasis. The disease is caused by parasites that enter to the skin and can spread to the lymph nodes, spleen, liver, bone marrow, and sometimes lungs. Parasites induce host defenses including cell infiltration, leading to protective or ineffective inflammation. These responses are often influenced by host genotype and sex. We analyzed the role of sex in the impact of specific gene loci on eosinophil infiltration and its functional relevance.

Methods

We studied the genetic control of infiltration of eosinophils into the inguinal lymph nodes after 8 weeks of Leishmania major infection using mouse strains BALB/c, STS, and recombinant congenic strains CcS-1,-3,-4,-5,-7,-9,-11,-12,-15,-16,-18, and -20, each of which contains a different random set of 12.5% genes from the parental “donor” strain STS and 87.5% genes from the “background” strain BALB/c. Numbers of eosinophils were counted in hematoxylin-eosin-stained sections of the inguinal lymph nodes under a light microscope. Parasite load was determined using PCR-ELISA.

Results

The lymph nodes of resistant STS and susceptible BALB/c mice contained very low and intermediate numbers of eosinophils, respectively. Unexpectedly, eosinophil infiltration in strain CcS-9 exceeded that in BALB/c and STS and was higher in males than in females. We searched for genes controlling high eosinophil infiltration in CcS-9 mice by linkage analysis in F₂ hybrids between BALB/c and CcS-9 and detected four loci controlling eosinophil numbers. Lmr14 (chromosome 2) and Lmr25 (chromosome 5) operate independently from other genes (main effects). Lmr14 functions only in males, the effect of Lmr25 is sex independent. Lmr15 (chromosome 11) and Lmr26 (chromosome 9) operate in cooperation (non-additive interaction) with each other. This interaction was significant in males only, but sex-marker interaction was not significant. Eosinophil infiltration was positively correlated with parasite load in lymph nodes of F₂ hybrids in males, but not in females.

Conclusions

We demonstrated a strong influence of sex on numbers of eosinophils in the lymph nodes after L. major infection and present the first identification of sex-dependent autosomal loci controlling eosinophilic infiltration. The positive correlation between eosinophil infiltration and parasite load in males suggests that this sex-dependent eosinophilic infiltration reflects ineffective inflammation.

Pertussis leukocytosis: mechanisms, clinical relevance and treatment

The significant and sometimes dramatic rise in the number of circulating white blood cells (leukocytosis) in infants suffering from pertussis (whooping cough) has been recognized for over a century. Although pertussis is a disease that afflicts people of all ages, it can be particularly severe in young infants, and these are the individuals in whom leukocytosis is most pronounced. Very high levels of leukocytosis are associated with poor outcome in infants hospitalized with pertussis and modern treatments are often aimed at reducing the number of leukocytes. Pertussis leukocytosis is caused by pertussis toxin, a soluble protein toxin released by Bordetella pertussis during infection, but the exact mechanisms by which this occurs are still unclear. In this minireview, I discuss the history of clinical and experimental findings on pertussis leukocytosis, possible contributing mechanisms causing this condition and treatments aimed at reducing leukocytosis in hospitalized infants. Since recent studies have detailed significant associations between specific levels of pertussis leukocytosis and fatal outcome, this is a timely review that may stimulate new thinking on how to understand and combat this problem.

Blunted apoptosis of erythrocytes in mice deficient in the heterotrimeric G-protein subunit Gαi2

Putative functions of the heterotrimeric G-protein subunit Gαi2-dependent signaling include ion channel regulation, cell differentiation, proliferation and apoptosis. Erythrocytes may, similar to apoptosis of nucleated cells, undergo eryptosis, characterized by cell shrinkage and cell membrane scrambling with phosphatidylserine (PS) exposure. Eryptosis may be triggered by increased cytosolic Ca²⁺ activity and ceramide. In the present study, we show that Gαi2 is expressed in both murine and human erythrocytes and further examined the survival of erythrocytes drawn from Gαi2-deficient mice (Gαi2^−/−) and corresponding wild-type mice (Gαi2^+/+). Our data show that plasma erythropoietin levels, erythrocyte maturation markers, erythrocyte counts, hematocrit and hemoglobin concentration were similar in Gαi2^−/− and Gαi2^+/+ mice but the mean corpuscular volume was significantly larger in Gαi2^−/− mice. Spontaneous PS exposure of circulating Gαi2^−/− erythrocytes was significantly lower than that of circulating Gαi2^+/+ erythrocytes. PS exposure was significantly lower in Gαi2^−/− than in Gαi2^+/+ erythrocytes following ex vivo exposure to hyperosmotic shock, bacterial sphingomyelinase or C6 ceramide. Erythrocyte Gαi2 deficiency further attenuated hyperosmotic shock-induced increase of cytosolic Ca²⁺ activity and cell shrinkage. Moreover, Gαi2^−/− erythrocytes were more resistant to osmosensitive hemolysis as compared to Gαi2^+/+ erythrocytes. In conclusion, Gαi2 deficiency in erythrocytes confers partial protection against suicidal cell death.

Gαi2 and Gαi3 Differentially Regulate Arrest from Flow and Chemotaxis in Mouse Neutrophils

Leukocyte recruitment to inflammation sites progresses in a multistep cascade. Chemokines regulate multiple steps of the cascade, including arrest, transmigration, and chemotaxis. The most important chemokine receptor in mouse neutrophils is CXCR2, which couples through Gαi2- and Gαi3-containing heterotrimeric G proteins. Neutrophils arrest in response to CXCR2 stimulation. This is defective in Gαi2-deficient neutrophils. In this study, we show that Gαi3-deficient neutrophils showed reduced transmigration but normal arrest in mice. We also tested Gαi2- or Gαi3-deficient neutrophils in a CXCL1 gradient generated by a microfluidic device. Gαi3-, but not Gαi2-, deficient neutrophils showed significantly reduced migration and directionality. This was confirmed in a model of sterile inflammation in vivo. Gαi2-, but not Gαi3-, deficient neutrophils showed decreased Ca(2+) flux in response to CXCR2 stimulation. Conversely, Gαi3-, but not Gαi2-, deficient neutrophils exhibited reduced AKT phosphorylation upon CXCR2 stimulation. We conclude that Gαi2 controls arrest and Gαi3 controls transmigration and chemotaxis in response to chemokine stimulation of neutrophils.

Red raspberry decreases heart biomarkers of cardiac remodeling associated with oxidative and inflammatory stress in obese diabetic db/db mice

Red raspberries decreased the expression of proteins linked to inflammatory/stress response and cardiac remodeling in hearts of obese diabetic mice.

Regulation of allergic lung inflammation by endothelial cell transglutaminase 2

Tissue transglutaminase 2 (TG2) is an enzyme with multiple functions, including catalysis of serotonin conjugation to proteins (serotonylation). Previous research indicates that TG2 expression is upregulated in human asthma and in the lung endothelium of ovalbumin (OVA)-challenged mice. It is not known whether endothelial cell TG2 is required for allergic inflammation. Therefore, to determine whether endothelial cell TG2 regulates allergic inflammation, mice with an endothelial cell-specific deletion of TG2 were generated, and these mice were sensitized and challenged in the airways with OVA. Deletion of TG2 in endothelial cells blocked OVA-induced serotonylation in lung endothelial cells, but not lung epithelial cells. Interestingly, deletion of endothelial TG2 reduced allergen-induced increases in respiratory system resistance, number of eosinophils in the bronchoalveolar lavage, and number of eosinophils in the lung tissue. Endothelial cell deletion of TG2 did not alter expression of adhesion molecules, cytokines, or chemokines that regulate leukocyte recruitment, consistent with other studies, demonstrating that deletion of endothelial cell signals does not alter lung cytokines and chemokines during allergic inflammation. Taken together, the data indicate that endothelial cell TG2 is required for allergic inflammation by regulating the recruitment of eosinophils into OVA-challenged lungs. In summary, TG2 functions as a critical signal for allergic lung responses. These data identify potential novel targets for intervention in allergy/asthma.

Defective chemokine signal integration in leukocytes lacking activator of G protein signaling 3 (AGS3)

Activator of G-protein signaling 3 (AGS3, gene name G-protein signaling modulator-1, Gpsm1), an accessory protein for G-protein signaling, has functional roles in the kidney and CNS. Here we show that AGS3 is expressed in spleen, thymus, and bone marrow-derived dendritic cells, and is up-regulated upon leukocyte activation. We explored the role of AGS3 in immune cell function by characterizing chemokine receptor signaling in leukocytes from mice lacking AGS3. No obvious differences in lymphocyte subsets were observed. Interestingly, however, AGS3-null B and T lymphocytes and bone marrow-derived dendritic cells exhibited significant chemotactic defects as well as reductions in chemokine-stimulated calcium mobilization and altered ERK and Akt activation. These studies indicate a role for AGS3 in the regulation of G-protein signaling in the immune system, providing unexpected venues for the potential development of therapeutic agents that modulate immune function by targeting these regulatory mechanisms.

G proteins Gαi1/3 are critical targets for Bordetella pertussis toxin-induced vasoactive amine sensitization

Pertussis toxin (PTX) is an AB5-type exotoxin produced by the bacterium Bordetella pertussis, the causative agent of whooping cough. In vivo intoxication with PTX elicits a variety of immunologic and inflammatory responses, including vasoactive amine sensitization (VAAS) to histamine (HA), serotonin (5-HT), and bradykinin (BDK). Previously, by using a forward genetic approach, we identified the HA H1 receptor (Hrh1/H1R) as the gene in mice that controls differential susceptibility to B. pertussis PTX-induced HA sensitization (Bphs). Here we show, by using inbred strains of mice, F1 hybrids, and segregating populations, that, unlike Bphs, PTX-induced 5-HT sensitivity (Bpss) and BDK sensitivity (Bpbs) are recessive traits and are separately controlled by multiple loci unlinked to 5-HT and BDK receptors, respectively. Furthermore, we found that PTX sensitizes mice to HA independently of Toll-like receptor 4, a purported receptor for PTX, and that the VAAS properties of PTX are not dependent upon endothelial caveolae or endothelial nitric oxide synthase. Finally, by using mice deficient in individual Gαi/o G-protein subunits, we demonstrate that Gαi1 and Gαi3 are the critical in vivo targets of ADP-ribosylation underlying VAAS elicited by PTX exposure.

Vitamin E isoforms as modulators of lung inflammation

Asthma and allergic diseases are complex conditions caused by a combination of genetic and environmental factors. Clinical studies suggest a number of protective dietary factors for asthma, including vitamin E. However, studies of vitamin E in allergy commonly result in seemingly conflicting outcomes. Recent work indicates that allergic inflammation is inhibited by supplementation with the purified natural vitamin E isoform α-tocopherol but elevated by the isoform γ-tocopherol when administered at physiological tissue concentrations. In this review, we discuss opposing regulatory effects of α-tocopherol and γ-tocopherol on allergic lung inflammation in clinical trials and in animal studies. A better understanding of the differential regulation of inflammation by isoforms of vitamin E provides a basis towards the design of clinical studies and diets that would effectively modulate inflammatory pathways in lung disease.

Neutrophil swarms require LTB4 and integrins at sites of cell death in vivo

Neutrophil recruitment from blood to extravascular sites of sterile or infectious tissue damage is a hallmark of early innate immune responses, and the molecular events leading to cell exit from the bloodstream have been well defined. Once outside the vessel, individual neutrophils often show extremely coordinated chemotaxis and cluster formation reminiscent of the swarming behaviour of insects. The molecular players that direct this response at the single-cell and population levels within the complexity of an inflamed tissue are unknown. Using two-photon intravital microscopy in mouse models of sterile injury and infection, we show a critical role for intercellular signal relay among neutrophils mediated by the lipid leukotriene B4, which acutely amplifies local cell death signals to enhance the radius of highly directed interstitial neutrophil recruitment. Integrin receptors are dispensable for long-distance migration, but have a previously unappreciated role in maintaining dense cellular clusters when congregating neutrophils rearrange the collagenous fibre network of the dermis to form a collagen-free zone at the wound centre. In this newly formed environment, integrins, in concert with neutrophil-derived leukotriene B4 and other chemoattractants, promote local neutrophil interaction while forming a tight wound seal. This wound seal has borders that cease to grow in kinetic concert with late recruitment of monocytes and macrophages at the edge of the displaced collagen fibres. Together, these data provide an initial molecular map of the factors that contribute to neutrophil swarming in the extravascular space of a damaged tissue. They reveal how local events are propagated over large-range distances, and how auto-signalling produces coordinated, self-organized neutrophil-swarming behaviour that isolates the wound or infectious site from surrounding viable tissue.

Eosinophil adoptive transfer system to directly evaluate pulmonary eosinophil trafficking in vivo

Most in vivo studies of granulocytes draw conclusions about their trafficking based on examination of their steady-state tissue/blood levels, which result from a combination of tissue homing, survival, and egress, rather than direct examination of cellular trafficking. Herein, we developed a unique cell transfer system involving the adoptive transfer of a genetically labeled, bone-marrow-derived unique granulocyte population (eosinophils) into an elicited inflammatory site, the allergic lung. A dual polychromatic FACS-based biomarker-labeling system based on the IL4-eGFP transgene (4get) or Cd45.1 allele was used to track i.v. transferred eosinophils into the airway following allergen or T(H)2-associated stimuli in the lung in multiple mouse strains. The system was amenable to reverse tagging of recipients, thus allowing transfer of nonlabeled eosinophils and competitive tracking of multiple populations of eosinophils in vivo. The half-life of eosinophils in the blood was 3 h, and migration to the lung was dependent upon the dosage of transferred eosinophils, sensitive to pertussis toxin pretreatment, peaked at ∼24 h after adoptive transfer, and revealed a greater than 8-d eosinophil half-life in the lung. Eosinophil migration to the lung was dependent upon recipient IL-5 and IL-13 receptor α1 and donor eosinophil C-C chemokine receptor type 3 (CCR3) and interleukin 1 receptor-like 1 (ST2) in vivo. Taken together, this unique eosinophil transfer system provides an unprecedented opportunity to examine airway eosinophil migration without the need for extensive efforts to acquire donor source and time-consuming genetic crossing and has already been used to identify a long eosinophil half-life in the allergic lung and a definite role for ST2 in regulating eosinophil trafficking.

Isoforms of Vitamin E Differentially Regulate PKC α and Inflammation: A Review

Vitamin E regulation of disease has been extensively studied but most studies focus on the α-tocopherol isoform of vitamin E. These reports indicate contradictory outcomes for anti-inflammatory functions of the α-tocopherol isoform of vitamin E with regards to animal and clinical studies. These seemingly disparate results are consistent with our recent studies demonstrating that purified natural forms of vitamin E have opposing regulatory functions during inflammation. In this review, we discuss that α-tocopherol inhibits whereas γ-tocopherol elevates allergic inflammation, airway hyperresponsiveness, leukocyte transendothelial migration, and endothelial cell adhesion molecule signaling through protein kinase Cα. Moreover, we have demonstrated that α-tocopherol is an antagonist and γ-tocopherol is an agonist of PKCα through direct binding to a regulatory domain of PKCα. In summary, we have determined mechanisms for opposing regulatory functions of α-tocopherol and γ-tocopherol on inflammation. Information from our studies will have significant impact on the design of clinical studies and on vitamin E consumption.

Differential expression of alpha 4 integrins on effector memory T helper cells during Bordetella infections. Delayed responses in Bordetella pertussis

Bordetella pertussis (B. pertussis) is the causative agent of whooping cough, a respiratory disease that is reemerging worldwide. Mechanisms of selective lymphocyte trafficking to the airways are likely to be critical in the immune response to this pathogen. We compared murine infection by B. pertussis, B. parapertussis, and a pertussis toxin-deleted B. pertussis mutant (BpΔPTX) to test the hypothesis that effector memory T-helper cells (emTh) display an altered pattern of trafficking receptor expression in B. pertussis infection due to a defect in imprinting. Increased cell recruitment to the lungs at 5 days post infection (p.i.) with B. parapertussis, and to a lesser extent with BpΔPTX, coincided with an increased frequency of circulating emTh cells expressing the mucosal-associated trafficking receptors α4β7 and α4β1 while a reduced population of these cells was observed in B. pertussis infection. These cells were highly evident in the blood and lungs in B. pertussis infection only at 25 days p.i. when B. parapertussis and BpΔPTX infections were resolved. Although at 5 days p.i., an equally high percentage of lung dendritic cells (DCs) from all infections expressed maturation markers, this expression persisted only in B. pertussis infection at 25 days p.i. Furthermore, at 5 days p.i with B. pertussis, lung DCs migration to draining lymph nodes may be compromised as evidenced by decreased frequency of CCR7(+) DCs, inhibited CCR7-mediated in vitro migration, and fewer DCs in lung draining lymph nodes. Lastly, a reduced frequency of allogeneic CD4(+) cells expressing α4β1 was detected following co-culture with lung DCs from B. pertussis-infected mice, suggesting a defect in DC imprinting in comparison to the other infection groups. The findings in this study suggest that B. pertussis may interfere with imprinting of lung-associated trafficking receptors on T lymphocytes leading to extended survival in the host and a prolonged course of disease.

Gαi2 is the essential Gαi protein in immune complex-induced lung disease

Heterotrimeric G proteins of the Gα(i) family have been implicated in signaling pathways regulating cell migration in immune diseases. The Gα(i)-protein-coupled C5a receptor is a critical regulator of IgG FcR function in experimental models of immune complex (IC)-induced inflammation. By using mice deficient for Gα(i2) or Gα(i3), we show that Gα(i2) is necessary for neutrophil influx in skin and lung Arthus reactions and agonist-induced neutrophilia in the peritoneum, whereas Gα(i3) plays a less critical but variable role. Detailed analyses of the pulmonary IC-induced inflammatory response revealed several shared functions of Gα(i2) and Gα(i3), including mediating C5a anaphylatoxin receptor-induced activation of macrophages, involvement in alveolar production of chemokines, transition of neutrophils from bone marrow into blood, and modulation of CD11b and CD62L expression that account for neutrophil adhesion to endothelial cells. Interestingly, C5a-stimulated endothelial polymorphonuclear neutrophil transmigration, but not chemotaxis, is enhanced versus reduced in the absence of neutrophil Gα(i3) or Gα(i2), respectively, and knockdown of endothelial Gα(i2) caused decreased transmigration of wild-type neutrophils. These data demonstrate that Gα(i2) and Gα(i3) contribute to inflammation by redundant, overlapping, and Gα(i)-isoform-specific mechanisms, with Gα(i2) exhibiting unique functions in both neutrophils and endothelial cells that appear essential for polymorphonuclear neutrophil recruitment in IC disease.

Tight junctions at the blood brain barrier: physiological architecture and disease-associated dysregulation

The Blood–brain barrier (BBB), present at the level of the endothelium of cerebral blood vessels, selectively restricts the blood-to-brain paracellular diffusion of compounds; it is mandatory for cerebral homeostasis and proper neuronal function. The barrier properties of these specialized endothelial cells notably depend on tight junctions (TJs) between adjacent cells: TJs are dynamic structures consisting of a number of transmembrane and membrane-associated cytoplasmic proteins, which are assembled in a multimolecular complex and acting as a platform for intracellular signaling. Although the structural composition of these complexes has been well described in the recent years, our knowledge about their functional regulation still remains fragmentary. Importantly, pericytes, embedded in the vascular basement membrane, and perivascular microglial cells, astrocytes and neurons contribute to the regulation of endothelial TJs and BBB function, altogether constituting the so-called neurovascular unit.

The present review summarizes our current understanding of the structure and functional regulation of endothelial TJs at the BBB. Accumulating evidence points to a correlation between BBB dysfunction, alteration of TJ complexes and progression of a variety of CNS diseases, such as stroke, multiple sclerosis and brain tumors, as well as neurodegenerative diseases like Parkinson’s and Alzheimer’s diseases. Understanding how TJ integrity is controlled may thus help improve drug delivery across the BBB and the design of therapeutic strategies for neurological disorders.

Eliminating or blocking 12/15-lipoxygenase reduces neutrophil recruitment in mouse models of acute lung injury

INTRODUCTION

Acute lung injury (ALI) is a common disease in critically ill patients with a high morbidity and mortality. 12/15-lipoxygenase (12/15-LO) is an enzyme generating 12-hydroxy-eicosatetraenoic acid (12-HETE) and 15-HETE from arachidonic acid. It has been shown that 12/15-LO is involved in the regulation of vascular permeability during ALI.

METHODS

To test whether 12/15-LO participates in leukocyte recruitment into the lung, we investigated the role of 12/15-LO in mouse models of lipopolysaccharide (LPS)-induced pulmonary inflammation and acid-induced ALI, a clinically relevant model of acute lung injury.

RESULTS

The increase in neutrophil recruitment following LPS inhalation was reduced in 12/15-LO-deficient (Alox15(-/-)) mice and in wild-type (WT) mice after the blocking of 12/15-LO with a pharmacological inhibitor. Bone marrow chimeras revealed that 12/15-LO in hematopoietic cells regulates neutrophil accumulation in the interstitial and alveolar compartments, whereas the accumulation of neutrophils in the intravascular compartment is regulated by 12/15-LO in non-hematopoietic and hematopoietic cells. Mechanistically, the increased plasma levels of the chemokine CXCL1 in Alox15(-/-) mice led to a reduced response of the neutrophil chemokine receptor CXCR2 to stimulation with CXCL1, which in turn abrogated neutrophil recruitment. Alox15(-/-) mice also showed decreased edema formation, reduced neutrophil recruitment and improved gas exchange in an acid-induced ALI model.

CONCLUSIONS

Our findings suggest that 12/15-LO modulates neutrophil recruitment into the lung by regulating chemokine/chemokine receptor homeostasis.

The loss of RGS protein-Gα(i2) interactions results in markedly impaired mouse neutrophil trafficking to inflammatory sites

Neutrophils are first responders rapidly mobilized to inflammatory sites by a tightly regulated, nonredundant hierarchy of chemoattractants. These chemoattractants engage neutrophil cell surface receptors triggering heterotrimeric G-protein Gα(i) subunits to exchange GDP for GTP. By limiting the duration that Gα(i) subunits remain GTP bound, RGS proteins modulate chemoattractant receptor signaling. Here, we show that neutrophils with a genomic knock in of a mutation that disables regulator of G-protein signaling (RGS)-Gα(i2) interactions accumulate in the bone marrow and mobilize poorly to inflammatory sites. These defects are attributable to enhanced sensitivity to background signals, prolonged chemoattractant receptor signaling, and inappropriate CXCR2 downregulation. Intravital imaging revealed a failure of the mutant neutrophils to accumulate at and stabilize sites of sterile inflammation. Furthermore, these mice could not control a nonlethal Staphylococcus aureus infection. Neutrophil RGS proteins establish a threshold for Gα(i) activation, helping to coordinate desensitization mechanisms. Their loss renders neutrophils functionally incompetent.

CXCR2: From Bench to Bedside

Leukocyte recruitment to sites of infection or tissue damage plays a crucial role for the innate immune response. Chemokine-dependent signaling in immune cells is a very important mechanism leading to integrin activation and leukocyte recruitment. CXC chemokine receptor 2 (CXCR2) is a prominent chemokine receptor on neutrophils. During the last years, several studies were performed investigating the role of CXCR2 in different diseases. Until now, many CXCR2 inhibitors are tested in animal models and clinical trials and promising results were obtained. This review gives an overview of the structure of CXCR2 and the signaling pathways that are activated following CXCR2 stimulation. We discuss in detail the role of this chemokine receptor in different disease models including acute lung injury, COPD, sepsis, and ischemia-reperfusion-injury. Furthermore, this review summarizes the results of clinical trials which used CXCR2 inhibitors.

Inhibition of allergic inflammation by supplementation with 5-hydroxytryptophan

Clinical reports indicate that patients with allergy/asthma commonly have associated symptoms of anxiety/depression. Anxiety/depression can be reduced by 5-hydroxytryptophan (5-HTP) supplementation. However, it is not known whether 5-HTP reduces allergic inflammation. Therefore, we determined whether 5-HTP supplementation reduces allergic inflammation. We also determined whether 5-HTP decreases passage of leukocytes through the endothelial barrier by regulating endothelial cell function. For these studies, C57BL/6 mice were supplemented with 5-HTP, treated with ovalbumin fraction V (OVA), house dust mite (HDM) extract, or IL-4, and examined for allergic lung inflammation and OVA-induced airway responsiveness. To determine whether 5-HTP reduces leukocyte or eosinophil transendothelial migration, endothelial cells were pretreated with 5-HTP, washed and then used in an in vitro transendothelial migration assay under laminar flow. Interestingly, 5-HTP reduced allergic lung inflammation by 70-90% and reduced antigen-induced airway responsiveness without affecting body weight, blood eosinophils, cytokines, or chemokines. 5-HTP reduced allergen-induced transglutaminase 2 (TG2) expression and serotonylation (serotonin conjugation to proteins) in lung endothelial cells. Consistent with the regulation of endothelial serotonylation in vivo, in vitro pretreatment of endothelial cells with 5-HTP reduced TNF-α-induced endothelial cell serotonylation and reduced leukocyte transendothelial migration. Furthermore, eosinophil and leukocyte transendothelial migration was reduced by inhibitors of transglutaminase and by inhibition of endothelial cell serotonin synthesis, suggesting that endothelial cell serotonylation is key for leukocyte transendothelial migration. In summary, 5-HTP supplementation inhibits endothelial serotonylation, leukocyte recruitment, and allergic inflammation. These data identify novel potential targets for intervention in allergy/asthma.

Use of inotropes and vasopressor agents in critically ill patients

Inotropes and vasopressors are biologically and clinically important compounds that originate from different pharmacological groups and act at some of the most fundamental receptor and signal transduction systems in the body. More than 20 such agents are in common clinical use, yet few reviews of their pharmacology exist outside of physiology and pharmacology textbooks. Despite widespread use in critically ill patients, understanding of the clinical effects of these drugs in pathological states is poor. The purpose of this article is to describe the pharmacology and clinical applications of inotropic and vasopressor agents in critically ill patients.

Endothelial CD47 promotes vascular endothelial-cadherin tyrosine phosphorylation and participates in T cell recruitment at sites of inflammation in vivo

At sites of inflammation, endothelial adhesion molecules bind leukocytes and transmit signals required for transendothelial migration (TEM). We previously reported that adhesive interactions between endothelial cell CD47 and leukocyte signal regulatory protein γ (SIRPγ) regulate human T cell TEM. The role of endothelial CD47 in T cell TEM in vivo, however, has not been explored. In this study, CD47⁻/⁻ mice showed reduced recruitment of blood T cells as well as neutrophils and monocytes in a dermal air pouch model of TNF-α-induced inflammation. Reconstitution of CD47⁻/⁻ mice with wild-type bone marrow cells did not restore leukocyte recruitment to the air pouch, indicating a role for endothelial CD47. The defect in leukocyte TEM in the CD47⁻/⁻ endothelium was corroborated by intravital microscopy of inflamed cremaster muscle microcirculation in bone marrow chimera mice. In an in vitro human system, CD47 on both HUVEC and T cells was required for TEM. Although previous studies showed CD47-dependent signaling required G(αi)-coupled pathways, this was not the case for endothelial CD47 because pertussis toxin, which inactivates G(αi), had no inhibitory effect, whereas G(αi) was required by the T cell for TEM. We next investigated the endothelial CD47-dependent signaling events that accompany leukocyte TEM. Ab-induced cross-linking of CD47 revealed robust actin cytoskeleton reorganization and Src- and Pyk-2-kinase dependent tyrosine phosphorylation of the vascular endothelial-cadherin cytoplasmic tail. This signaling was pertussis toxin insensitive, suggesting that endothelial CD47 signaling is independent of G(αi). These findings suggest that engagement of endothelial CD47 by its ligands triggers outside-in signals in endothelium that facilitate leukocyte TEM.

Defective macrophage migration in Gαi2- but not Gαi3-deficient mice

Various heterotrimeric G(i) proteins are considered to be involved in cell migration and effector function of immune cells. The underlying mechanisms, how they control the activation of myeloid effector cells, are not well understood. To elucidate isoform-redundant and -specific roles for Gα(i) proteins in these processes, we analyzed mice genetically deficient in Gα(i2) or Gα(i3). First, we show an altered distribution of tissue macrophages and blood monocytes in the absence of Gα(i2) but not Gα(i3). Gα(i2)-deficient but not wild-type or Gα(i3)-deficient mice exhibited reduced recruitment of macrophages in experimental models of thioglycollate-induced peritonitis and LPS-triggered lung injury. In contrast, genetic ablation of Gα(i2) had no effect on Gα(i)-dependent peritoneal cytokine production in vitro and the phagocytosis-promoting function of the Gα(i)-coupled C5a anaphylatoxin receptor by liver macrophages in vivo. Interestingly, actin rearrangement and CCL2- and C5a anaphylatoxin receptor-induced chemotaxis but not macrophage CCR2 and C5a anaphylatoxin receptor expression were reduced in the specific absence of Gα(i2). Furthermore, knockdown of Gα(i2) caused decreased cell migration and motility of RAW 264.7 cells, which was rescued by transfection of Gα(i2) but not Gα(i3). These results indicate that Gα(i2), albeit redundant to Gα(i3) in some macrophage activation processes, clearly exhibits a Gα(i) isoform-specific role in the regulation of macrophage migration.

Guanine nucleotide-binding protein Gαi2: a new partner of claudin-5 that regulates tight junction integrity in human brain endothelial cells

The blood-brain barrier (BBB) selectively controls the exchanges between the blood and the brain: it is formed by tight junctions (TJs) between adjacent microvascular endothelial cells. The transmembrane protein claudin-5 is known as a key TJ protein at the BBB, although, the molecular mechanisms by which it regulates TJ tightness are poorly understood. To identify putative claudin-5 partners that contribute to TJ integrity, claudin-5-enriched membrane microdomains were prepared by cell fractionation, using the human brain endothelial cell line hCMEC/D3 and claudin-5 immunoprecipitates were submitted to tandem mass spectrometry. Because a high concentration of mannitol is known to transiently destabilize TJs, this analysis was performed in basal conditions, after mannitol treatment, and after recovery of TJ integrity. We here demonstrate that the G-protein subunit αi2 (Gαi2) interacts with claudin-5 and that association is correlated with TJ integrity in hCMEC/D3 cells; also, a selective expression of Gαi2 is observed in human brain vasculature in situ. Moreover, small interfering RNA-mediated depletion of Gαi2 or claudin-5 in hCMEC/D3 cells similarly increases their paracellular permeability and delays TJ recovery after mannitol treatment. Altogether, our results identify Gαi2 as a novel claudin-5 partner required for TJ integrity in brain endothelial cells.

Gαi2 signaling: friend or foe in cardiac injury and heart failure?

Receptors coupled to G proteins have many effects on the heart. Enhanced signaling by Gα(s) and Gα(q) leads to cardiac injury and heart failure, while Gα(i2) signaling in cardiac myocytes can protect against ischemic injury and β-adrenergic-induced heart failure. We asked whether enhanced Gα(i2) signaling in mice could protect against heart failure using a point mutation in Gα(i2) (G184S), which prevents negative regulation by regulators of G protein signaling. Contrary to our expectation, it worsened effects of a genetic dilated cardiomyopathy (DCM) and catecholamine-induced cardiac injury. Gα (i2) (G184S/+) /DCM double heterozygote mice (TG9(+)Gα (i2) (G184S/+)) had substantially decreased survival compared to DCM animals. Furthermore, heart weight/body weight ratios (HW/BW) were significantly greater in TG9(+)Gα (i2) (G184S/+) mice as was expression of natriuretic peptide genes. Catecholamine injury in Gα (i2) (G184S/G184S) mutant mice produced markedly increased isoproterenol-induced fibrosis and collagen III gene expression vs WT mice. Cardiac fibroblasts from Gα (i2) (G184S/G184S) mice also showed a serum-dependent increase in proliferation and ERK phosphorylation, which were blocked by pertussis toxin and a mitogen-activated protein/extracellular signal-regulated kinase kinase inhibitor. Gα(i2) signaling in cardiac myocytes protects against ischemic injury but enhancing Gα(i2) signaling overall may have detrimental effects in heart failure, perhaps through actions on cardiac fibroblasts.

Vascular cell adhesion molecule-1 expression and signaling during disease: regulation by reactive oxygen species and antioxidants

The endothelium is immunoregulatory in that inhibiting the function of vascular adhesion molecules blocks leukocyte recruitment and thus tissue inflammation. The function of endothelial cells during leukocyte recruitment is regulated by reactive oxygen species (ROS) and antioxidants. In inflammatory sites and lymph nodes, the endothelium is stimulated to express adhesion molecules that mediate leukocyte binding. Upon leukocyte binding, these adhesion molecules activate endothelial cell signal transduction that then alters endothelial cell shape for the opening of passageways through which leukocytes can migrate. If the stimulation of this opening is blocked, inflammation is blocked. In this review, we focus on the endothelial cell adhesion molecule, vascular cell adhesion molecule-1 (VCAM-1). Expression of VCAM-1 is induced on endothelial cells during inflammatory diseases by several mediators, including ROS. Then, VCAM-1 on the endothelium functions as both a scaffold for leukocyte migration and a trigger of endothelial signaling through NADPH oxidase-generated ROS. These ROS induce signals for the opening of intercellular passageways through which leukocytes migrate. In several inflammatory diseases, inflammation is blocked by inhibition of leukocyte binding to VCAM-1 or by inhibition of VCAM-1 signal transduction. VCAM-1 signal transduction and VCAM-1-dependent inflammation are blocked by antioxidants. Thus, VCAM-1 signaling is a target for intervention by pharmacological agents and by antioxidants during inflammatory diseases. This review discusses ROS and antioxidant functions during activation of VCAM-1 expression and VCAM-1 signaling in inflammatory diseases.

Phospholipase Cβ3 mediates LH-induced granulosa cell differentiation

Previous studies showed that under certain conditions LH can stimulate not only adenylate cyclase (AC) but also phospholipase Cβ (PLCβ) signaling in target cells; however, the physiological involvement of PLCβ in LH-induced ovarian follicular cell differentiation has not been determined. To address this, ex vivo expression analyses and specific PLCβ targeting were performed in primary bovine granulosa cells. Expression analyses in cells from small (2.0-5.9 mm), medium (6.0-9.9 mm), and ovulatory-size (10.0-13.9 mm) follicles revealed an increase in mRNA and protein levels of heterotrimeric G protein subunits-αs, -αq, -α11, and -αi2 in ovulatory-size follicles, simultaneous with a substantial increase in LH receptor expression. Among the four known PLCβ isoforms, PLCβ3 (PLCB3) was specifically up-regulated in cells from ovulatory-size follicles, in association with a predominantly cytoplasmic location of PLCB3 in these cells and a significant inositol phosphate response to LH stimulation. Furthermore, RNA interference-mediated PLCB3 down-regulation reduced the ability of LH to induce hallmark differentiation responses of granulosa cells, namely transcriptional up-regulation of prostaglandin-endoperoxide synthase 2 and down-regulation of both aromatase expression and estradiol production. Responses to the AC agonist, forskolin, however, were not affected. In addition, PLCB3 down-regulation did not alter cAMP responses to LH in granulosa cells, ruling out a primary involvement of AC in mediating the effects of PLCB3. In summary, we provide evidence of a physiological involvement of PLCβ signaling in ovulatory-size follicles and specifically identify PLCB3 as a mediator of LH-induced differentiation responses of granulosa cells.

Exercise and leukocyte interchange among central circulation, lung, spleen, and muscle

Circulating leukocytes increase rapidly with exercise then quickly decrease when the exercise ends. We tested whether exercise acutely led to bidirectional interchange of leukocytes between the circulation and the lung, spleen, and active skeletal muscle. To accomplish this it was necessary to label a large number of immune cells (granulocytes, monocytes, and lymphocytes) in a way that resulted in minimal perturbation of cell function. Rats were injected intravenously with a single bolus of carboxyfluorescein diacetate succinamidyl ester (CFSE) dye which is rapidly and irreversibly taken up by circulating cells. The time course of the disappearance of labeled cells and their reappearance in the circulation following exercise was determined via flow cytometry. The majority of circulating leukocytes were labeled at 4h. post-injection and this proportion slowly declined out to 120 h. At both 24 and 120 h, running resulted in an increase in the proportion of labeled leukocytes in the circulation. Analysis of the skeletal muscle, spleen and lung indicated that labeled leukocytes had accumulated in those tissues and were mobilized to the circulation in response to exercise. This indicates that there is an ongoing exchange of leukocytes between the circulation and tissues and that exercise can stimulate their redistribution. Exchange was slower with muscle than with spleen and lung, but in all cases, influenced by exercise. Exercise bouts redistribute leukocytes between the circulation and the lung, spleen and muscle. The modulatory effects of exercise on the immune system may be regulated in part by the systemic redistribution of immune cells.

Isoforms of vitamin E differentially regulate inflammation

Vitamin E regulation of disease has been extensively studied in humans, animal models and cell systems. Most of these studies focus on the α-tocopherol isoform of vitamin E. These reports indicate contradictory outcomes for anti-inflammatory functions of the α-tocopherol isoform of vitamin E, especially with regards to clinical studies of asthma and atherosclerosis. These seemingly disparate clinical results are consistent with recently reported unrecognized properties of isoforms of vitamin E. Recently, it has been reported that physiological levels of purified natural forms of vitamin E have opposing regulatory functions during inflammation. These opposing regulatory functions by physiological levels of vitamin E isoforms impact interpretations of previous studies on vitamin E. Moreover, additional recent studies also indicate that the effects of vitamin E isoforms on inflammation are only partially reversible using physiological levels of a vitamin E isoform with opposing immunoregulatory function. Thus, this further influences interpretations of previous studies with vitamin E in which there was inflammation and substantial vitamin E isoforms present before the initiation of the study. In summary, this review will discuss regulation of inflammation by vitamin E, including alternative interpretations of previous studies in the literature with regards to vitamin E isoforms.

Supplemental and highly elevated tocopherol doses differentially regulate allergic inflammation: reversibility of α-tocopherol and γ-tocopherol's effects

We have reported that supplemental doses of the α- and γ-tocopherol isoforms of vitamin E decrease and increase, respectively, allergic lung inflammation. We have now assessed whether these effects of tocopherols are reversible. For these studies, mice were treated with Ag and supplemental tocopherols in a first phase of treatment followed by a 4-wk clearance phase, and then the mice received a second phase of Ag and tocopherol treatments. The proinflammatory effects of supplemental levels of γ-tocopherol in phase 1 were only partially reversed by supplemental α-tocopherol in phase 2, but were completely reversed by raising α-tocopherol levels 10-fold in phase 2. When γ-tocopherol levels were increased 10-fold (highly elevated tocopherol) so that the lung tissue γ-tocopherol levels were equal to the lung tissue levels of supplemental α-tocopherol, γ-tocopherol reduced leukocyte numbers in the lung lavage fluid. In contrast to the lung lavage fluid, highly elevated levels of γ-tocopherol increased inflammation in the lung tissue. These regulatory effects of highly elevated tocopherols on tissue inflammation and lung lavage fluid were reversible in a second phase of Ag challenge without tocopherols. In summary, the proinflammatory effects of supplemental γ-tocopherol on lung inflammation were partially reversed by supplemental levels of α-tocopherol but were completely reversed by highly elevated levels of α-tocopherol. Also, highly elevated levels of γ-tocopherol were inhibitory and reversible in lung lavage but, importantly, were proinflammatory in lung tissue sections. These results have implications for future studies with tocopherols and provide a new context in which to review vitamin E studies in the literature.

Pertussis toxin and adenylate cyclase toxin: key virulence factors of Bordetella pertussis and cell biology tools

Pertussis toxin and adenylate cyclase toxin are two important virulence factors of Bordetella pertussis, the bacterial cause of the respiratory disease pertussis or whooping cough. In addition to studies on the structure, function and role in pathogenesis of these two toxins, they are both used as cell biology tools for a variety of applications owing to their ability to enter mammalian cells, perform enzymatic activities and modify cell signaling events. In this article, recent data from the research literature that enhance our understanding of the nature of these two toxins, their role in the pathogenesis of B. pertussis infection and disease, particularly in modulating host immune responses, and their use as tools for other areas of research will be outlined.

Interleukin-13 directly promotes oesophagus production of CCL11 and CCL24 and the migration of eosinophils

BACKGROUND

Eosinophilic oesophagitis (EE) is a clinico-pathologically defined oesophageal disorder that is characterized by eosinophil migration into oesophageal tissues. There is growing support for EE being an allergic disease and for a contribution of T-helper type 2 (Th2)-associated cytokines in disease pathogenesis. The respiratory system has been shown to be critical in driving the development of EE in animal models. However, the mechanisms underlying the recruitment of eosinophils into the oesophagus remain unclear.

OBJECTIVE

We sought to investigate the influence of Th2-associated cytokines on the production of eosinophil-specific chemokines from the oesophagus directly.

METHODS

In order to eliminate the potential involvement of the lung, we utilized isolated oesophageal rings. These were treated in vitro with IL-4 or IL-13 and the expression and production of CCL11 and CCL24 were determined.

RESULTS

Our data demonstrate that IL-13 is a potent and direct inducer of both CCL11 and CCL24 production from the oesophagus, as is IL-4 also. The expression of CCL11 precedes CCL24 by several hours but then diminishes over time, as well as at high concentrations of IL-13. We demonstrate that there is an up-regulation of the inhibitory IL-13 receptor, IL-13Ralpha2 but that IL-13Ralpha1 remains unaltered. Oesophagus rings isolated from STAT6(-/-) mice were unable to produce CCL11 or CCL24 upon IL-13 treatment. Lastly, we demonstrate that oesophageal production of CCL11 and CCL24 upon IL-13 stimulation is sufficient to promote eosinophil migration.

CONCLUSIONS

IL-13 is capable of directly stimulating oesophageal tissue to produce eosinophil-attracting chemokines and drive eosinophil migration.

Eosinophils utilize multiple chemokine receptors for chemotaxis to the parasitic nematode Strongyloides stercoralis

Protective innate immunity to the nematode Strongyloides stercoralis requires eosinophils in the parasite killing process. Experiments were performed to determine if an extract of S. stercoralis would trigger eosinophil chemotaxis, and to then compare the chemotactic migration response, including second messenger signals and receptors, to those mechanisms triggered by host chemoattractants. Eosinophils undergo both chemotaxis and chemokinesis to soluble parasite extract in transwell plates. Pretreatment of eosinophils with pertussis toxin, a G protein-coupled receptor inhibitor, inhibited migration of the eosinophils to the parasite extract. Likewise, blocking PI3K, tyrosine kinase, p38 and p44/42 inhibited eosinophil chemotaxis to parasite extract. Furthermore, CCR3, CXCR4 or CXCR2 antagonists significantly inhibited eosinophil chemotaxis to the parasite extract. Molecular weight fractionation of parasite extract revealed that molecules attracting eosinophils were present in several fractions, with molecules greater than 30 kDa being the most potent. Treating the extract with proteinase K or chitinase significantly inhibited its ability to induce chemotaxis, thereby demonstrating that the chemoattractants were both protein and chitin. Therefore, chemoattractants derived from parasites and host species stimulate similar receptors and second messenger signals to induce eosinophil chemotaxis. Parasite extract stimulates multiple receptors on the eosinophil surface, which ensures a robust innate immune response to the parasite.

Isoforms of vitamin E have opposing immunoregulatory functions during inflammation by regulating leukocyte recruitment

Reports indicate contradictory outcomes for anti-inflammatory functions of the alpha-tocopherol isoform of vitamin E in clinical studies of asthma and atherosclerosis. These seemingly disparate clinical results are consistent with novel unrecognized properties of isoforms of vitamin E reported in this study. We demonstrate that the isoform d-gamma-tocopherol elevates inflammation in experimental asthma. Moreover, d-gamma-tocopherol, at as little as 10% the concentration of d-alpha-tocopherol, ablates the anti-inflammatory benefit of the d-alpha-tocopherol isoform. A mechanism for these opposing immunoregulatory functions of purified tocopherols at physiological concentrations is not through modulation of expression of several cytokines, chemokines, or adhesion molecules, but is, at least in part, by regulation of endothelial cell signals during leukocyte recruitment. These opposing regulatory functions of vitamin E isoforms have impact on interpretations of vitamin E studies. In summary, our studies with purified tocopherol isoforms alter our understanding of vitamin E regulation of vascular function and asthma.

Allergic pulmonary inflammation promotes the recruitment of circulating tumor cells to the lung

Allergen-induced respiratory inflammation facilitates and/or elicits the extravasation of proinflammatory leukocytes by well-understood mechanisms that mediate the movement of multiple cell types. The nonspecific character of these pathways led us to hypothesize that circulating cancer cells use similar mechanisms, promoting secondary tumor formation at distal sites. To test this hypothesis, the frequency of metastasis to the lung as a function of allergic pulmonary inflammation was assessed following the i.v. injection of B16-F10 melanoma cells in mice. These studies showed that allergen-induced pulmonary inflammation resulted in a >3-fold increase in lung metastases. This increase was dependent on CD4(+) T-cell activities; however, it occurred independent of the induced eosinophilia associated with allergen provocation. Interventional strategies showed that existing therapeutic modalities for asthma, such as inhaled corticosteroids, were sufficient to block the enhanced pulmonary recruitment of cancer cells from circulation. Additional mechanistic studies further suggested that the ability of circulating cancer cells to extravasate to surrounding lung tissues was linked to the activation of the vascular endothelium via one or more Galpha(i)-coupled receptors. Interestingly, a survey of a clinical breast cancer surgical database showed that the incidence of asthma was higher among patients with lung metastases. Thus, our data show that allergic respiratory inflammation may represent a risk factor for the development of lung metastases and suggest that amelioration of the pulmonary inflammation associated with asthma will have a direct and immediate benefit to the 7% to 8% of breast cancer patients with this lung disease.

Post-translational tyrosine nitration of eosinophil granule toxins mediated by eosinophil peroxidase

Nitration of tyrosine residues has been observed during various acute and chronic inflammatory diseases. However, the mechanism of tyrosine nitration and the nature of the proteins that become tyrosine nitrated during inflammation remain unclear. Here we show that eosinophils but not other cell types including neutrophils contain nitrotyrosine-positive proteins in specific granules. Furthermore, we demonstrate that the human eosinophil toxins, eosinophil peroxidase (EPO), major basic protein, eosinophil-derived neurotoxin (EDN) and eosinophil cationic protein (ECP), and the respective murine toxins, are post-translationally modified by nitration at tyrosine residues during cell maturation. High resolution affinity-mass spectrometry identified specific single nitration sites at Tyr349 in EPO and Tyr33 in both ECP and EDN. ECP and EDN crystal structures revealed and EPO structure modeling suggested that the nitrated tyrosine residues in the toxins are surface exposed. Studies in EPO(-/-), gp91phox(-/-), and NOS(-/-) mice revealed that tyrosine nitration of these toxins is mediated by EPO in the presence of hydrogen peroxide and minute amounts of NOx. Tyrosine nitration of eosinophil granule toxins occurs during maturation of eosinophils, independent of inflammation. These results provide evidence that post-translational tyrosine nitration is unique to eosinophils.

Pertussis toxin inhibits early chemokine production to delay neutrophil recruitment in response to Bordetella pertussis respiratory tract infection in mice

Pertussis is an acute respiratory disease of humans caused by the bacterium Bordetella pertussis. Pertussis toxin (PT) plays a major role in the virulence of this pathogen, including important effects that it has soon after inoculation. Studies in our laboratory and other laboratories have indicated that PT inhibits early neutrophil influx to the lungs and airways in response to B. pertussis respiratory tract infection in mice. Previous in vitro and in vivo studies have shown that PT can affect neutrophils directly by ADP ribosylating G(i) proteins associated with surface chemokine receptors, thereby inhibiting neutrophil migration in response to chemokines. However, in this study, by comparing responses to wild-type (WT) and PT-deficient strains, we found that PT has an indirect inhibitory effect on neutrophil recruitment to the airways in response to infection. Analysis of lung chemokine expression indicated that PT suppresses early neutrophil recruitment by inhibiting chemokine upregulation in alveolar macrophages and other lung cells in response to B. pertussis infection. Enhancement of early neutrophil recruitment to the airways in response to WT infection by addition of exogenous keratinocyte-derived chemokine, one of the dominant neutrophil-attracting chemokines in mice, further revealed an indirect effect of PT on neutrophil chemotaxis. Additionally, we showed that intranasal administration of PT inhibits lipopolysaccharide-induced chemokine gene expression and neutrophil recruitment to the airways, presumably by modulation of signaling through Toll-like receptor 4. Collectively, these results demonstrate how PT inhibits early inflammatory responses in the respiratory tract, which reduces neutrophil influx in response to B. pertussis infection, potentially providing an advantage to the pathogen in this interaction.

Regulation of endothelial junctional permeability

The endothelium is a semi-permeable barrier that regulates the flux of liquid and solutes, including plasma proteins, between the blood and surrounding tissue. The permeability of the vascular barrier can be modified in response to specific stimuli acting on endothelial cells. Transport across the endothelium can occur via two different pathways: through the endothelial cell (transcellular) or between adjacent cells, through interendothelial junctions (paracellular). This review focuses on the regulation of the paracellular pathway. The paracellular pathway is composed of adhesive junctions between endothelial cells, both tight junctions and adherens junctions. The actin cytoskeleton is bound to each junction and controls the integrity of each through actin remodeling. These interendothelial junctions can be disassembled or assembled to either increase or decrease paracellular permeability. Mediators, such as thrombin, TNF-alpha, and LPS, stimulate their respective receptor on endothelial cells to initiate signaling that increases cytosolic Ca2+ and activates myosin light chain kinase (MLCK), as well as monomeric GTPases RhoA, Rac1, and Cdc42. Ca2+ activation of MLCK and RhoA disrupts junctions, whereas Rac1 and Cdc42 promote junctional assembly. Increased endothelial permeability can be reversed with "barrier stabilizing agents," such as sphingosine-1-phosphate and cyclic adenosine monophosphate (cAMP). This review provides an overview of the mechanisms that regulate paracellular permeability.

The endothelium in acute lung injury/acute respiratory distress syndrome

PURPOSE OF REVIEW

Since pulmonary edema from increased endothelial permeability is the hallmark of acute lung injury, a frequently encountered entity in critical care medicine, the study of endothelial responses in this setting is crucial to the development of effective endothelial-targeted treatments.

RECENT FINDINGS

From the enormous amount of research in the field of endothelial pathophysiology, we have focused on work delineating endothelial alterations elicited by noxious stimuli implicated in acute lung injury. The bulk of the material covered deals with molecular and cellular aspects of the pathogenesis, reflecting current trends in the published literature. We initially discuss pathways of endothelial dysfunction in acute lung injury and then cover the mechanisms of endothelial protection. Several experimental treatments in animal models are presented, which aid in the understanding of the disease pathogenesis and provide evidence for potentially useful therapies.

SUMMARY

Mechanistic studies have delivered several interventions, which are effective in preventing and treating experimental acute lung injury and have thus provided objectives for translational studies. Some of these modalities may evolve into clinically useful tools in the treatment of this devastating illness.

Mechanisms of eosinophilia in the pathogenesis of hypereosinophilic disorders

The increased numbers of activated eosinophils in the blood and tissues that typically accompany hypereosinophilic disorders result from a variety of mechanisms. Exciting advances in translating discoveries achieved from mouse models and molecular strategies to the clinic have led to a flurry of new therapeutics specifically designed to target eosinophil-associated diseases. So far, this form of hypothesis testing in humans in vivo through pharmacology generally has supported the paradigms generated in vitro and in animal models, raising hopes that a spectrum of novel therapies soon may become available to help those who have eosinophil-associated diseases.

Mechanisms and consequences of neutrophil interaction with the endothelium

Leukocyte recruitment into inflamed tissue proceeds in a cascade-like fashion. The first contact of neutrophils with the endothelium is mediated by selectins and their counterreceptors, followed by rolling of neutrophils along the endothelial wall of postcapillary venules and integrin-mediated arrest. While rolling, neutrophils collect different inflammatory signals that can activate several pathways. In addition to activation of neutrophils by ligation of G-protein-coupled receptors with chemokines and other chemoattractants, integrins and selectin ligands are also able to signal into the cell, where they initiate neutrophil extravasation, promote cytoskeletal rearrangement, and ultimately induce superoxide production and degranulation. These signaling pathways may be targeted by therapeutic interventions to inhibit specific functions of neutrophils without affecting others. This Review is focused on the signaling events during the interaction of neutrophils with the endothelium.

Identification of an alternative G{alpha}q-dependent chemokine receptor signal transduction pathway in dendritic cells and granulocytes

CD38 controls the chemotaxis of leukocytes to some, but not all, chemokines, suggesting that chemokine receptor signaling in leukocytes is more diverse than previously appreciated. To determine the basis for this signaling heterogeneity, we examined the chemokine receptors that signal in a CD38-dependent manner and identified a novel "alternative" chemokine receptor signaling pathway. Similar to the "classical" signaling pathway, the alternative chemokine receptor pathway is activated by Galpha(i2)-containing Gi proteins. However, unlike the classical pathway, the alternative pathway is also dependent on the Gq class of G proteins. We show that Galpha(q)-deficient neutrophils and dendritic cells (DCs) make defective calcium and chemotactic responses upon stimulation with N-formyl methionyl leucyl phenylalanine and CC chemokine ligand (CCL) 3 (neutrophils), or upon stimulation with CCL2, CCL19, CCL21, and CXC chemokine ligand (CXCL) 12 (DCs). In contrast, Galpha(q)-deficient T cell responses to CXCL12 and CCL19 remain intact. Thus, the alternative chemokine receptor pathway controls the migration of only a subset of cells. Regardless, the novel alternative chemokine receptor signaling pathway appears to be critically important for the initiation of inflammatory responses, as Galpha(q) is required for the migration of DCs from the skin to draining lymph nodes after fluorescein isothiocyanate sensitization and the emigration of monocytes from the bone marrow into inflamed skin after contact sensitization.

Galphai2 is required for chemokine-induced neutrophil arrest

Chemokines, including CXCL1, participate in neutrophil recruitment by triggering the activation of integrins, which leads to arrest from rolling. The downstream signaling pathways which lead to integrin activation and neutophil arrest following G-protein-coupled receptor engagement are incompletely understood. To test whether Galpha(i2) is involved, mouse neutrophils in their native whole blood were investigated in mouse cremaster postcapillary venules and in flow chambers coated with P-selectin, ICAM-1, and CXCL1. Gnai2(-/-) neutrophils showed significantly reduced CXCL1-induced arrest in vitro and in vivo. Similar results were obtained with leukotriene B(4) (LTB(4)). Lethally irradiated mice reconstituted with Gnai2(-/-) bone marrow showed a similar defect in chemoattractant-induced arrest as that of Gnai2(-/-) mice. In thioglycollate-induced peritonitis and lipopolysaccaride (LPS)-induced lung inflammation, chimeric mice lacking Galpha(i2) in hematopoietic cells showed about 50% reduced neutrophil recruitment similar to that seen in Gnai2(-/-) mice. These data show that neutrophil Galpha(i2) is necessary for chemokine-induced arrest, which is relevant for neutrophil recruitment to sites of acute inflammation.