Enhancement of capillary leakage and restoration of lymphocyte egress by a chiral S1P1 antagonist in vivo

Sphingosine 1-phosphate (S1P, 1) regulates vascular barrier and lymphoid development, as well as lymphocyte egress from lymphoid organs, by activating high-affinity S1P1 receptors. We used reversible chemical probes (i) to gain mechanistic insights into S1P systems organization not accessible through genetic manipulations and (ii) to investigate their potential for therapeutic modulation. Vascular (but not airway) administration of the preferred R enantiomer of an in vivo-active chiral S1P1 receptor antagonist induced loss of capillary integrity in mouse skin and lung. In contrast, the antagonist did not affect the number of constitutive blood lymphocytes. Instead, alteration of lymphocyte trafficking and phenotype required supraphysiological elevation of S1P1 tone and was reversed by the antagonist. In vivo two-photon imaging of lymph nodes confirmed requirements for obligate agonism, and the data were consistent with the presence of a stromal barrier mechanism for gating lymphocyte egress. Thus, chemical modulation reveals differences in S1P-S1P1 'set points' among tissues and highlights both mechanistic advantages (lymphocyte sequestration) and risks (pulmonary edema) of therapeutic intervention.

Chemical modulators of sphingosine-1-phosphate receptors as barrier-oriented therapeutic molecules

Biological barriers regulate the passage of cells, pathogens, fluids, nutrients, ions and signalling molecules between anatomical compartments during homeostasis and disease. Yet strategies that allow for reversible therapeutic modulation of these barriers are still in their infancy. The enhancement or protection of natural barriers is desirable in conditions such as acute respiratory distress syndrome or ischaemia-reperfusion injuries, whereas a temporary disruption could facilitate the penetration of drugs across such barriers. This Review discusses the role of sphingosine-1-phosphate receptors in the regulation and protection of biological barriers, and the potential of therapeutic strategies that target this receptor family.

Neutrophils and macrophages accumulate sequentially following Achilles tendon injury

Structural damage and inflammation occur following tendon injury. The purpose of this study was to determine the time course of inflammatory cell accumulation in two animal models of acute tendinopathy. In the first model, rat Achilles tendons were exposed by blunt dissection, injected with collagenase and sacrificed at 1, 3, 7, 14 and 28 days. In the second model, collagenase was injected percutaneously and rats were sacrificed after 1 and 3 days. Sham animals were sacrificed at 1 and 3 days in both models. Neutrophil and ED1 macrophage populations increased by 46- and 18-fold, respectively, after 1 day in surgically exposed Achilles tendons (EAT) injected with collagenase. Neutrophils dropped by 70% while the concentration of ED1 macrophages remained constant at day 3 post-injury. Neutrophils and ED1+ macrophages returned to control values after 7 and 14 days, respectively. ED2+ macrophages showed a tendency to increase at day 28 although no significant difference was observed relative to ambulatory controls. Collagenase injected percutaneously reduced the extent of inflammation compared with operated animals. Thus, injured tendons exhibited a specific sequence of inflammatory cell accumulation which varied in intensity according to the modality used for collagenase injection.

Increased prevalence of Methanosphaera stadtmanae in inflammatory bowel diseases

Background

The gut microbiota is associated with the modulation of mucosal immunity and the etiology of inflammatory bowel diseases (IBD). Previous studies focused on the impact of bacterial species on IBD but seldom suspected archaea, which can be a major constituent of intestinal microbiota, to be implicated in the diseases. Recent evidence supports that two main archaeal species found in the digestive system of humans, Methanobrevibacter smithii (MBS) and Methanosphaera stadtmanae (MSS) can have differential immunogenic properties in lungs of mice; with MSS but not MBS being a strong inducer of the inflammatory response. We thus aimed at documenting the immunogenic potential of MBS and MSS in humans and to explore their association with IBD.

Methods

To validate the immunogenicity of MBS and MSS in humans, peripheral blood mononuclear cells from healthy subjects were stimulated with these two microorganisms and the production of inflammatory cytokine TNF was measured by ELISA. To verify MBS and MSS prevalence in IBD, stool samples from 29 healthy control subjects and 29 patients suffering from IBD were collected for DNA extraction. Plasma was also collected from these subjects to measure antigen-specific IgGs by ELISA. Quantitative PCR was used for bacteria, methanogens, MBS and MSS quantification.

Results

Mononuclear cells stimulated with MSS produced higher concentrations of TNF (39.5 ng/ml) compared to MBS stimulation (9.1 ng/ml). Bacterial concentrations and frequency of MBS-containing stools were similar in both groups. However, the number of stool samples positive for the inflammatory archaea MSS was higher in patients than in controls (47% vs 20%). Importantly, only IBD patients developed a significant anti-MSS IgG response.

Conclusion

The prevalence of MSS is increased in IBD patients and is associated with an antigen-specific IgG response.

Full pharmacological efficacy of a novel S1P1 agonist that does not require S1P-like headgroup interactions

Strong evidence exists for interactions of zwitterionic phosphate and amine groups in sphingosine-1 phosphate (S1P) to conserved Arg and Glu residues present at the extracellular face of the third transmembrane domain of S1P receptors. The contribution of Arg(120) and Glu(121) for high-affinity ligand-receptor interactions is essential, because single-point R(120)A or E(121)A S1P(1) mutants neither bind S1P nor transduce S1P function. Because S1P receptors are therapeutically interesting, identifying potent selective agonists with different binding modes and in vivo efficacy is of pharmacological importance. Here we describe a modestly water-soluble highly selective S1P(1) agonist [2-(4-(5-(3,4-diethoxyphenyl)-1,2,4-oxadiazol-3-yl)-2,3-dihydro-1H-inden-1-yl amino) ethanol (CYM-5442)] that does not require Arg(120) or Glu(121) residues for activating S1P(1)-dependent p42/p44 mitogen-activated protein kinase phosphorylation, which defines a new hydrophobic pocket in S1P(1). CYM-5442 is a full agonist in vitro for S1P(1) internalization, phosphorylation, and ubiquitination. It is noteworthy that CYM-5442 was a full agonist for induction and maintenance of S1P(1)-dependent blood lymphopenia, decreasing B lymphocytes by 65% and T lymphocytes by 85% of vehicle. Induction of CYM-5442 lymphopenia was dose- and time-dependent, requiring serum concentrations in the 50 nM range. In vitro measures of S1P(1) activation by CYM-5442 were noncompetitively inhibited by a specific S1P(1) antagonist [(R)-3-amino-(3-hexylphenylamino)-4-oxobutylphosphonic acid (W146)], competitive for S1P, 2-amino-2-(4-octylphenethyl)propane-1,3-diol (FTY720-P), and 5-[4-phenyl-5-(trifluoromethyl)-2-thienyl]-3-[3-(trifluoromethyl)phenyl]-1,2, 4-oxadiazole (SEW2871). In addition, lymphopenia induced by CYM-5442 was reversed by W146 administration or upon pharmacokinetic agonist clearance. Pharmacokinetics in mice also indicated that CYM-5442 partitions significantly in central nervous tissue. These data show that CYM-5442 activates S1P(1)-dependent pathways in vitro and to levels of full efficacy in vivo through a hydrophobic pocket separate from the orthosteric site of S1P binding that is headgroup-dependent.

Nonsteroidal anti-inflammatory drug reduces neutrophil and macrophage accumulation but does not improve tendon regeneration

Whether nonsteroidal anti-inflammatory drugs have a beneficial effect on tendon regeneration is still a matter of debate. Given that inflammatory cells are thought to induce nonspecific damage following an injury, we tested the hypothesis that a 3-day treatment with diclofenac would protect tendons from inflammatory cell injury and would promote healing. Neutrophil and ED1(+) macrophage concentrations were determined in the paratenon and the core of the rat Achilles tendon following collagenase-induced injury. Hydroxyproline content, edema, and mechanical properties were also evaluated at 1, 3, 7, 14, and 28 days post-trauma. Collagenase injections induced a 70% decrease in the ultimate rupture point at Day 3. Diclofenac treatments (1 mg/kg bid) selectively decreased the accumulation of neutrophils and ED1(+) macrophages by 59% and 35%, respectively, in the paratenon, where blood vessels are numerous, but did not reduce the accumulation of neutrophils and ED1(+) macrophages in the core of the tendon. Edema was significantly reduced on Day 3 but persisted during the remodeling phase in the diclofenac-treated group only. The inhibition of leukocyte accumulation by diclofenac did not translate into a reduction of tissue damage or a promotion of tissue healing, because the mechanical properties of injured Achilles tendons were identical in placebo and diclofenac-treated groups. These results indicate that diclofenac reduced both edema and the accumulation of inflammatory cells within the paratenon but provided no biochemical or functional benefits for the Achilles tendon.

Modulating tone: the overture of S1P receptor immunotherapeutics

SUMMARY

Modulation of complex functions within the immune system has proven to be surprisingly sensitive to alterations in the lysophospholipid sphingosine 1-phosphate (S1P) receptor-ligand rheostat. This has become increasingly evident from both chemical and genetic manipulation of the S1P system, with pharmacological effects upon lymphoid cells, dendritic cell function, as well as vascular interfaces. The integrated immune system, perhaps as a result of its relatively recent evolutionary ontogeny, has selected for a number of critical control points regulated by five distinct high affinity G-protein-coupled receptor subtypes with a shared ligand, with receptors distributed on lymphocytes, dendritic cells, and endothelium. All of these cellular components of the axis are capable of modulating immune responses in vivo, with the impact on the immune response being very different from classical immunosuppressants, by virtue of selective spatial and temporal sparing of humoral and myeloid elements of host defense. Pharmacological subversion of the S1P rheostat is proving to be clinically efficacious in multiple sclerosis, and both the scope and limitations of therapeutic modulation of the S1P axis in immunotherapy are becoming clearer as understanding of the integrated chemical physiology of the S1P system emerges.

Local not systemic modulation of dendritic cell S1P receptors in lung blunts virus-specific immune responses to influenza

The mechanism by which locally delivered sphingosine analogs regulate host response to localized viral infection has never been addressed. In this report, we show that intratracheal delivery of the chiral sphingosine analog (R)-2-amino-4-(4-heptyloxyphenyl)-2-methylbutanol (AAL-R) or its phosphate ester inhibits the T-cell response to influenza virus infection. In contrast, neither intraperitoneal delivery of AAL-R nor intratracheal instillation of the non-phosphorylatable stereoisomer AAL-S suppressed virus-specific T-cell response, indicating that in vivo phosphorylation of AAL-R and sphingosine 1-phosphate (S1P) receptor modulation in lungs is essential for immunomodulation. Intratracheal delivery of water-soluble S1P(1) receptor agonist at doses sufficient to induce systemic lymphopenia did not inhibit virus-specific T-cell response, indicating that S1P(1) is not involved in the immunosuppressive activities of AAL-R and that immunosuppression acts independently of naive lymphocyte recirculation. Accumulation of dendritic cells (DCs) in draining lymph nodes was inhibited by intratracheal but not intraperitoneal delivery of AAL-R. Direct modulation of DCs is demonstrated by the impaired ability of virus-infected bone marrow-derived DCs treated in vitro with AAL-R to trigger in vivo T-cell response after adoptive transfer to the airways. Thus, our results suggest that locally delivered sphingosine analogs induce immunosuppression by modulating S1P receptors other than S1P(1) or S1P(2) on dendritic cells in the lungs after influenza virus infection.

The endocannabinoid 2-arachidonoyl-glycerol activates human neutrophils: critical role of its hydrolysis and de novo leukotriene B4 biosynthesis

Although endocannabinoids are important players in nociception and obesity, their roles as immunomodulators remain elusive. The main endocannabinoids described to date, namely 2-arachidonoyl-glycerol (2-AG) and arachidonyl-ethanolamide (AEA), induce an intriguing profile of pro- and anti-inflammatory effects. This could relate to cell-specific cannabinoid receptor expression and/or the action of endocannabinoid-derived metabolites. Importantly, 2-AG and AEA comprise a molecule of arachidonic acid (AA) in their structure and are hydrolyzed rapidly. We postulated the following: 1) the released AA from endocannabinoid hydrolysis would be metabolized into eicosanoids; and 2) these eicosanoids would mediate some of the effects of endocannabinoids. To confirm these hypotheses, experiments were performed in which freshly isolated human neutrophils were treated with endocannabinoids. Unlike AEA, 2-AG stimulated myeloperoxidase release, kinase activation, and calcium mobilization by neutrophils. Although 2-AG did not induce the migration of neutrophils, it induced the release of a migrating activity for neutrophils. 2-AG also rapidly (1 min) induced a robust biosynthesis of leukotrienes, similar to that observed with AA. The effects of 2-AG were not mimicked nor prevented by cannabinoid receptor agonists or antagonists, respectively. Finally, the blockade of either 2-AG hydrolysis, leukotriene (LT) B(4) biosynthesis, or LTB(4) receptor 1 activation prevented all the effects of 2-AG on neutrophil functions. In conclusion, we demonstrated that 2-AG potently activates human neutrophils. This is the consequence of 2-AG hydrolysis, de novo LTB(4) biosynthesis, and an autocrine activation loop involving LTB(4) receptor 1.

Immunogenic properties of archaeal species found in bioaerosols

The etiology of bioaerosol-related pulmonary diseases remains poorly understood. Recently, archaea emerged as prominent airborne components of agricultural environments, but the consequences of airway exposure to archaea remain unknown. Since subcomponents of archaea can be immunogenic, we used a murine model to study the pulmonary immune responses to two archaeal species found in agricultural facilities: Methanobrevibacter smithii (MBS) and Methanosphaera stadtmanae (MSS). Mice were administered intranasally with 6.25, 25 or 100 µg of MBS or MSS, once daily, 3 days a week, for 3 weeks. MSS induced more severe histopathological alterations than MBS with perivascular accumulation of granulocytes, pronounced thickening of the alveolar septa, alveolar macrophages accumulation and increased perivascular mononucleated cell accumulation. Analyses of bronchoalveolar lavage fluids revealed up to 3 times greater leukocyte accumulation with MSS compared to MBS. Instillation of 100 µg of MBS or MSS caused predominant accumulation of monocyte/macrophages (4.5×10(5) and 4.8×10(5) cells/ml respectively) followed by CD4(+) T cells (1.38×10(5) and 1.94×10(5) cells/ml respectively), B cells (0.73×10(5) and 1.28×10(5) cells/ml respectively), and CD8(+) T cells (0.20×10(5) and 0.31×10(5) cells/ml respectively) in the airways. Both archaeal species induced similar titers of antigen-specific IgGs in plasma. MSS but not MBS caused an accumulation of eosinophils and neutrophils in the lungs, which surprisingly, correlated inversely with the size of the inoculum. Stronger immunogenicity of MSS was confirmed by a 3 fold higher accumulation of myeloid dendritic cells in the airways, compared to MBS. Thus, the dose and species of archaea determine the magnitude and nature of the pulmonary immune response. This is the first report of an immunomodulatory role of archaeal species found in bioaerosols.

Monocyte depletion increases local proliferation of macrophage subsets after skeletal muscle injury

Background

Sequential accumulation of M1 and M2 macrophages is critical for skeletal muscle recovery after an acute injury. While M1 accumulation is believed to rely on monocyte infiltration, the mechanisms of M2 accumulation remain controversial, but could involve an infiltrating precursor. Yet, strong depletion of monocytes only partially impairs skeletal muscle healing, supporting the existence of alternative mechanisms to palliate the loss of infiltrating macrophage progenitors. The aims of this study are thus to investigate if proliferation occurs in macrophage subsets within injured skeletal muscles; and to determine if monocyte depletion leads to increased proliferation of macrophages after injury.

Methods

Injury was induced by bupivacaine injection in the tibialis anterior muscle of rats. Blood monocytes were depleted by daily intravenous injections of liposome-encapsulated clodronate, starting 24 h prior to injury. In separate experiments, irradiation of hind limb was also performed to prevent resident cell proliferation. Upon euthanasia, blood and muscles were collected for flow cytometric analyses of macrophage/monocyte subsets.

Results

Clodronate induced a 80%-90% depletion of monocyte but only led to 57% and 41% decrease of M1 and M2 macrophage accumulation, respectively, 2 d following injury. Conversely, the number of M1 macrophages in monocyte-depleted rats was 2.4-fold higher than in non-depleted rats 4 d after injury. This was associated with a 16-fold increase in the number of proliferative M1 macrophages, which was reduced by 46% in irradiated animals. Proliferation of M2 macrophages was increased tenfold by clodronate treatment 4 d post injury. The accumulation of M2 macrophages was partially impaired by irradiation, regardless of monocyte depletion.

Conclusions

M1 and M2 subsets proliferate after skeletal muscle injury and their proliferation is enhanced under condition of monocyte depletion. Our study supports the conclusion that both infiltrating and resident precursors could contribute to M1 or M2 macrophage accumulation in muscle injury.

Three phases of CD8 T cell response in the lung following H1N1 influenza infection and sphingosine 1 phosphate agonist therapy

Influenza-induced lung edema and inflammation are exacerbated by a positive feedback loop of cytokine and chemokine production termed a 'cytokine storm', a hallmark of increased influenza-related morbidity and mortality. Upon infection, an immune response is rapidly initiated in the lungs and draining lymph node, leading to expansion of virus-specific effector cells. Using two-photon microscopy, we imaged the dynamics of dendritic cells (DC) and virus-specific eGFP(+)CD8(+) T cells in the lungs and draining mediastinal lymph nodes during the first two weeks following influenza infection. Three distinct phases of T cell and CD11c(+) DC behavior were revealed: 1) Priming, facilitated by the arrival of lung DCs in the lymph node and characterized by antigen recognition and expansion of antigen-specific CD8(+) T cells; asymmetric T cell division in contact with DCs was frequently observed. 2) Clearance, during which DCs re-populate the lung and T cells leave the draining lymph node and re-enter the lung tissue where enlarged, motile T cells come into contact with DCs and form long-lived interactions. 3) Maintenance, characterized by T-cell scanning of the lung tissue and dissociation from local antigen presenting cells; the T cells spend less time in association with DCs and migrate rapidly on collagen. A single dose of a sphingosine-1-phosphate receptor agonist, AAL-R, sufficient to suppress influenza-induced cytokine-storm, altered T cell and DC behavior during influenza clearance, delaying T cell division, cellular infiltration in the lung, and suppressing T-DC interactions in the lung. Our results provide a detailed description of T cell and DC choreography and dynamics in the lymph node and the lung during influenza infection. In addition, we suggest that phase lags in T cell and DC dynamics induced by targeting S1P receptors in vivo may attenuate the intensity of the immune response and can be manipulated for therapeutic benefit.

Dysregulation of alveolar macrophages unleashes dendritic cell-mediated mechanisms of allergic airway inflammation

Allergic asthma is a chronic inflammatory disorder characterized by eosinophilia and T helper type 2 (Th2) cell activation. However, little information is available on the mechanisms leading to this pathology. We previously showed that alveolar macrophages (AM) from rats with experimental asthma lose their ability to prevent asthma symptoms. To understand the implication of AM in lung immunity, we investigated the influence of AM sensitization status on lung dendritic cell (DC) activation induced by allergen challenge in vivo. Rat sensitized to ovalbumin developed airway inflammation (eosinophils and Th2 cells) and demonstrated myeloid DC (mDC) activation following allergen exposure. The replacement of AM of sensitized animals by AM from naive animals did not affect allergen-triggered eosinophilia but completely abolished lung mDC allergen capture and migration to the lymph nodes, as well as Th2 cell polarization. Moreover, immunosuppressive functions of naive AM occurred in conjunction with low engulfment of allergens but without variation of major histocompatibility complex II and CD23 expression. Interestingly, sensitized AM that were withdrawn from the inflammatory environment regained their immunosuppressive functions when transferred to sensitized rats. Thus, these are the first in vivo evidences showing that dysregulation of AM functions is sufficient to induce DC-triggered allergic response.

Loss of OcaB Prevents Age-Induced Fat Accretion and Insulin Resistance by Altering B-Lymphocyte Transition and Promoting Energy Expenditure

The current demographic shift toward an aging population has led to a robust increase in the prevalence of age-associated metabolic disorders. Recent studies have demonstrated that the etiology of obesity-related insulin resistance that develops with aging differs from that induced by high-calorie diets. Whereas the role of adaptive immunity in changes in energy metabolism driven by nutritional challenges has recently gained attention, its impact on aging remains mostly unknown. Here we found that the number of follicular B2 lymphocytes and expression of the B-cell-specific transcriptional coactivator OcaB increase with age in spleen and in intra-abdominal epididymal white adipose tissue (eWAT), concomitantly with higher circulating levels of IgG and impaired glucose homeostasis. Reduction of B-cell maturation and Ig production-especially that of IgG2c-by ablation of OcaB prevented age-induced glucose intolerance and insulin resistance and promoted energy expenditure by stimulating fatty acid utilization in eWAT and brown adipose tissue. Transfer of wild-type bone marrow in OcaB^-/- mice replenished the eWAT B2-cell population and IgG levels, which diminished glucose tolerance, insulin sensitivity, and energy expenditure while increasing body weight gain in aged mice. Thus these findings demonstrate that upon aging, modifications in B-cell-driven adaptive immunity contribute to glucose intolerance and fat accretion.

Pulmonary CD103 expression regulates airway inflammation in asthma

Although CD103(+) cells recently emerged as key regulatory cells in the gut, the role of CD103 ubiquitous expression in the lung and development of allergic airway disease has never been studied. To answer this important question, we evaluated the response of Cd103(-/-) mice in two separate well-described mouse models of asthma (ovalbumin and house dust mite extract). Pulmonary inflammation was assessed by analysis of bronchoalveolar lavage content, histology, and cytokine response. CD103 expression was analyzed on lung dendritic cells and T cell subsets by flow cytometry. Cd103(-/-) mice exposed to antigens developed exacerbated lung inflammation, characterized by increased eosinophilic infiltration, severe tissue inflammation, and altered cytokine response. In wild-type mice exposed to house dust mite, CD103(+) dendritic cells are increased in the lung and an important subset of CD4(+) T cells, CD8(+) T cells, and T regulatory cells express CD103. Importantly, Cd103(-/-) mice presented a deficiency in the resolution phase of inflammation, which supports an important role for this molecule in the control of inflammation severity. These results suggest an important role for CD103 in the control of airway inflammation in asthma.

Treatment with a sphingosine analog does not alter the outcome of a persistent virus infection

There is no known antiviral drug treatment that routinely terminates persistent virus infections. A recent provocative report indicated that low dosage of the sphingosine analog FTY720 caused lymphopenia in mice persistently infected with lymphocytic choriomeningitis virus (LCMV)-clone 13 (Cl 13) and induced viral clearance within 30 days post-treatment (Premenko-Lanier et al., 2008). However, we find that low dosage of FTY720 fails to purge LCMV-Cl 13 infection and does not induce lymphopenia in LCMV-Cl 13-infected mice. In fact, infection with non-persistent LCMV-Arm53b or with persistent LCMV-Cl 13 induces an equivalent lymphopenia, demonstrating that the quantity of circulating cells has little bearing on viral persistence. In addition, treatment with FTY720 or the sphingosine-1-phosphate receptor 1 (S1P1)-specific agonist, AUY954, does not alleviate T cell exhaustion and exacerbates disruption of the CD8(+) T cells response following LCMV-Cl 13 infection. Therefore, treatment with a sphingosine analog does not ameliorate persistent LCMV-Cl 13 infection.

The Endocannabinoid Metabolite Prostaglandin E2 (PGE2)-Glycerol Inhibits Human Neutrophil Functions: Involvement of Its Hydrolysis into PGE2 and EP Receptors

The endocannabinoids 2-arachidonoyl-glycerol and N-arachidonoyl-ethanolamine mediate an array of pro- and anti-inflammatory effects. These effects are related, in part, to their metabolism by eicosanoid biosynthetic enzymes. For example, N-arachidonoyl-ethanolamine and 2-arachidonoyl-glycerol can be metabolized by cyclooxygenase-2 into PG-ethanolamide (PG-EA) and PG-glycerol (PG-G), respectively. Although PGE₂ is a recognized suppressor of neutrophil functions, the impact of cyclooxygenase-derived endocannabinoids such as PGE₂-EA or PGE₂-G on neutrophils is unknown. This study's aim was to define the effects of these mediators on neutrophil functions and the underlying cellular mechanisms involved. We show that PGE₂-G, but not PGE₂-EA, inhibits leukotriene B₄ biosynthesis, superoxide production, migration, and antimicrobial peptide release. The effects of PGE₂-G were prevented by EP₁/EP₂ receptor antagonist AH-6809 but not the EP₄ antagonist ONO-AE2-227. The effects of PGE₂-G required its hydrolysis into PGE₂, were not observed with the non-hydrolyzable PGE₂-serinol amide, and were completely prevented by methyl-arachidonoyl-fluorophosphate and palmostatin B, and partially prevented by JZL184 and WWL113. Although we could detect six of the documented PG-G hydrolases in neutrophils by quantitative PCR, only ABHD12 and ABHD16A were detected by immunoblot. Our pharmacological data, combined with our protein expression data, did not allow us to pinpoint one PGE₂-G lipase, and rather support the involvement of an uncharacterized lipase and/or of multiple hydrolases. In conclusion, we show that PGE₂-G inhibits human neutrophil functions through its hydrolysis into PGE₂, and by activating the EP₂ receptor. This also indicates that neutrophils could regulate inflammation by altering the balance between PG-G and PG levels in vivo.

Macrophages, not neutrophils, infiltrate skeletal muscle in mice deficient in P/E selectins after mechanical reloading

Our objective was to test the hypothesis that endothelial selectins, P and E selectins, are necessary for leukocyte migration after muscle injury from unloading/reloading. Mice hindlimbs were suspended for 10 days followed by reloading periods of 6 or 24 h after which the soleus muscle was dissected. Light microscopic observations showed that macrophages, but not neutrophils, were able to invade soleus muscles in mice deficient in P/E selectins (P/E-/-) during reloading periods. The recruitment efficiency of neutrophils after 6 and 24 h of reloading was minimal in P/E-/- mice relative to unloaded animals. The recruitment of macrophages in the soleus muscle was preserved in P/E-/- mice. The concentration of macrophages increased by 8.1-fold compared with unloaded muscles in double-mutant mice after 24 h of reloading. The accumulation of macrophages in reloaded muscles did not lead to fiber necrosis. Together, these findings indicate that macrophages can invade skeletal muscle through cellular mechanisms that do not involve P/E selectins during skeletal muscle reloading.

Modulation of chemokines and allergic airway inflammation by selective local sphingosine-1-phosphate receptor 1 agonism in lungs

Sphingosine-1-phosphate and its receptors have emerged as important modulators of the immune response. The sphingosine-1-phosphate prodrug 2-amino-2-(2-[4-octylphenyl]ethyl)-1,3-propanediol (FTY720) can alleviate experimental allergic airway inflammation. Nevertheless, the role of individual sphingosine-1-phosphate receptors in the regulation of allergic airway inflammation remains undefined. Using a newly characterized potent and selective sphingosine-1-phosphate receptor 1 (S1P₁) agonist with physical properties allowing airway delivery, we studied the contribution of S1P₁ signaling to eosinophilic airway inflammation induced in ovalbumin-immunized mice by airway challenges with ovalbumin. Airway delivery of receptor-nonselective sphingosine-1-phosphate prodrug significantly inhibits the sequential accumulation of antigen-presenting dendritic cells and CD4+ T cells in draining lymph nodes. This in turn suppressed by >80% the accumulation of CD4+ T cells and eosinophils in the airways. Systemic delivery of sphingosine-1-phosphate prodrug or of an S1P)₁-specific agonist at doses sufficient to induce lymphopenia did not inhibit eosinophil accumulation in the airways. In contrast, local airway delivery of S1P₁-specific agonist inhibited airways release of endogenous CCL5 and CCL17 chemokines, and significantly suppressed accumulation of activated T cells and eosinophils in the lungs. Specific S1P₁ agonism in lungs contributes significantly to anti-inflammatory activities of sphingosine-1-phosphate therapeutics by suppressing chemokine release in the airways, and may be of clinical relevance.

Amplification of Adipogenic Commitment by VSTM2A

Despite progress in our comprehension of the mechanisms regulating adipose tissue development, the nature of the factors that functionally characterize adipose precursors is still elusive. Defining the early steps regulating adipocyte development is needed for the generation of tools to control adipose tissue size and function. Here, we report the discovery of V-set and transmembrane domain containing 2A (VSTM2A) as a protein expressed and secreted by committed preadipocytes. VSTM2A expression is elevated in the early phases of adipogenesis in vitro and adipose tissue development in vivo. We show that VSTM2A-producing cells associate with the vasculature and express the common surface markers of adipocyte progenitors. Overexpression of VSTM2A induces adipogenesis, whereas its depletion impairs this process. VSTM2A controls preadipocyte determination at least in part by modulating BMP signaling and PPARγ2 activation. We propose a model in which VSTM2A is produced to preserve and amplify the adipogenic capability of adipose precursors.

Inflammatory cells do not decrease the ultimate tensile strength of intact tendons in vivo and in vitro: protective role of mechanical loading

Although inflammatory cells and their products are involved in various pathological processes, a possible role in tendon dysfunction has never been convincingly confirmed and extensively investigated. The goal of this study was to determine whether or not an acute inflammatory process deprived of mechanical trauma can induce nonspecific damages to intact collagen fibers. To induce leukocyte accumulation, carrageenan was injected into rat Achilles tendons. We first tested the effect of leukocyte recruitment on the concentrations or activities of matrix metalloproteinases and tissue inhibitors of matrix metalloproteinases. Second, we analyzed at the biochemical, histological, and biomechanical levels the impact of leukocyte invasion on tendons. Finally, collagen bundles isolated from rat-tail tendons were exposed in vitro to mechanical stress and/or inflammatory cells to determine if mechanical loading could protect tendons from the leukocyte proteolytic activity. Carrageenan-induced leukocyte accumulation was associated with an increased matrix metalloproteinase activity and a decreased content of tissue inhibitors of matrix metalloproteinases. However, hydroxyproline content and load to failure did not change significantly in these tendons. Interestingly, mechanical stress, when applied in vitro, protected collagen bundles from inflammatory cell-induced deterioration. Together, our results suggest that acute inflammation does not induce damages to intact and mechanically stressed collagen fibers. This protective effect would not rely on increased tissue inhibitors of matrix metalloproteinases content but would rather be conferred to the intrinsic resistance of mechanically loaded collagen fibers to proteolytic degradation.

Methanosphaera stadtmanae induces a type IV hypersensitivity response in a mouse model of airway inflammation

Despite improved awareness of work‐related diseases and preventive measures, many workers are still at high risk of developing occupational hypersensitivity airway diseases. This stems from a lack of knowledge of bioaerosol composition and their potential effects on human health. Recently, archaea species were identified in bioaerosols, raising the possibility that they play a major role in exposure‐related pathology. Specifically, Methanosphaera stadtmanae (MSS) and Methanobrevibacter smithii (MBS) are found in high concentrations in agricultural environments and respiratory exposure to crude extract demonstrates immunomodulatory activity in mice. Nevertheless, our knowledge of the specific impact of methanogens exposure on airway immunity and their potential to induce airway hypersensitivity responses in workers remains scant. Analysis of the lung mucosal response to methanogen crude extracts in mice demonstrated that MSS and MBS predominantly induced T_H17 airway inflammation, typical of a type IV hypersensitivity response. Furthermore, the response to MSS was associated with antigen‐specific IgG₁ and IgG_2a production. However, despite the presence of eosinophils after MSS exposure, only a weak T_H2 response and no airway hyperresponsiveness were observed. Finally, using eosinophil and mast cell‐deficient mice, we confirmed that these cells are dispensable for the T_H17 response to MSS, although eosinophils likely contribute to the exacerbation of inflammatory processes induced by MSS crude extract exposure. We conclude that, as MSS induces a clear type IV hypersensitivity lung response, it has the potential to be harmful to workers frequently exposed to this methanogen, and that preventive measures should be taken to avoid chronic hypersensitivity disease development in workers.

Lung CD200 Receptor Activation Abrogates Airway Hyperresponsiveness in Experimental Asthma

In allergic asthma, homeostatic pathways are dysregulated, which leads to an immune response toward normally innocuous antigens. The CD200-CD200 receptor pathway is a central regulator of inflammation, and CD200 expression was recently found to be down-regulated in circulating leukocytes of patients with asthma. Given the antiinflammatory properties of CD200, we investigated whether local delivery of recombinant CD200 (rCD200) could reinstate lung homeostasis in an experimental model of asthma. Brown Norway rats were sensitized with ovalbumin (OVA) and alum. rCD200 was intratracheally administered 24 hours before OVA challenge, and airway responsiveness to methacholine was measured 24 hours after the allergen challenge. Inflammation was also assessed by measuring cell recruitment and cytokine levels in bronchoalveolar lavages, as well as lung and draining lymph node accumulation of dendritic cells (DCs) and T cells. In sensitized rats, rCD200 abolished airway hyperresponsiveness, whereas the sham treatment had no effect. In addition, rCD200 strongly reduced OVA-induced lung accumulation of myeloid DCs, CD4(+) T cells, and T helper type 2 cells. This was associated with a strong reduction of OVA-induced IL-13 level and with an increase of IL-10 in supernatants of bronchoalveolar lavages. Lung eosinophilia and draining lymph node accumulation of myeloid DCs and T cells were not affected by rCD200. Overall, these data reveal that rCD200 can inhibit airway hyperresponsiveness in a model of asthma by a multistep mechanism associated with local alterations of the T cell response and the cytokine milieu.

Pifithrin-alpha, an inhibitor of p53 transactivation, alters the inflammatory process and delays tendon healing following acute injury

Transcription factor p53, which was initially associated with cancer, has now emerged as an important regulator of inflammation and extracellular matrix homeostasis, two processes highly relevant to tendon repair. The goal of this study was to evaluate the effect of a p53 transactivation inhibitor, namely, pifithrin-alpha, on the pathophysiological sequence following collagenase-induced tendon injury. Administration of pifithrin-alpha during the inflammatory phase reduced the accumulation of neutrophils and macrophages by 30 and 40%, respectively, on day 3 postinjury. Pifithrin-alpha failed to reduce the percentage of apoptotic cells following collagenase injection but delayed functional recovery. In uninjured Achilles tendons, pifithrin-alpha increased metalloprotease activity 2.4-fold. Accordingly, pifithrin-alpha reduced the collagen content in intact tendons as well as in injured tendons 7 days posttrauma compared with placebo. The effect of pifithrin-alpha on load to failure and stiffness was also evaluated. The administration of pifithrin-alpha during the inflammatory phase did not significantly decrease the functional deficit 3 days posttrauma. More importantly, load to failure and stiffness were significantly decreased in the pifithrin-alpha group from day 7 to day 28 compared with placebo. Overall, our results suggest that administration of pifithrin-alpha alters the inflammatory process and delays tendon healing. The present findings also support the concept that p53 can regulate extracellular matrix homeostasis in vivo.

Treatment with a sphingosine analog after the inception of house dust mite-induced airway inflammation alleviates key features of experimental asthma

Background

In vivo phosphorylation of sphingosine analogs with their ensuing binding and activation of their cell-surface sphingosine-1-phosphate receptors is regarded as the main immunomodulatory mechanism of this new class of drugs. Prophylactic treatment with sphingosine analogs interferes with experimental asthma by impeding the migration of dendritic cells to draining lymph nodes. However, whether these drugs can also alleviate allergic airway inflammation after its onset remains to be determined. Herein, we investigated to which extent and by which mechanisms the sphingosine analog AAL-R interferes with key features of asthma in a murine model during ongoing allergic inflammation induced by Dermatophagoides pteronyssinus.

Methods

BALB/c mice were exposed to either D. pteronyssinus or saline, intranasally, once-daily for 10 consecutive days. Mice were treated intratracheally with either AAL-R, its pre-phosphorylated form AFD-R, or the vehicle before every allergen challenge over the last four days, i.e. after the onset of allergic airway inflammation. On day 11, airway responsiveness to methacholine was measured; inflammatory cells and cytokines were quantified in the airways; and the numbers and/or viability of T cells, B cells and dendritic cells were assessed in the lungs and draining lymph nodes.

Results

AAL-R decreased airway hyperresponsiveness induced by D. pteronyssinus by nearly 70%. This was associated with a strong reduction of IL-5 and IL-13 levels in the airways and with a decreased eosinophilic response. Notably, the lung CD4⁺ T cells were almost entirely eliminated by AAL-R, which concurred with enhanced apoptosis/necrosis in that cell population. This inhibition occurred in the absence of dendritic cell number modulation in draining lymph nodes. On the other hand, the pre-phosphorylated form AFD-R, which preferentially acts on cell-surface sphingosine-1-phosphate receptors, was relatively impotent at enhancing cell death, which led to a less efficient control of T cell and eosinophil responses in the lungs.

Conclusion

Airway delivery of the non-phosphorylated sphingosine analog, but not its pre-phosphorylated counterpart, is highly efficient at controlling the local T cell response after the onset of allergic airway inflammation. The mechanism appears to involve local induction of lymphocyte apoptosis/necrosis, while mildly affecting dendritic cell and T cell accumulation in draining lymph nodes.