Role of sphingosine kinase 1 in allergen-induced pulmonary vascular remodeling and hyperresponsiveness

Acid ceramidase gene therapy ameliorates pulmonary arterial hypertension with right heart dysfunction

BACKGROUND

Up-regulation of ceramides in pulmonary hypertension (PH), contributing to perturbations in sphingolipid homeostasis and the transition of cells to a senescence state. We assessed the safety, feasibility, and efficiency of acid ceramidase gene transfer in a rodent PH model.

METHODS

A model of PH was established by the combination of left pneumonectomy and injection of Sugen toxin. Magnetic resonance imaging and right heart catheterization confirmed development of PH. Animals were subjected to intratracheal administration of synthetic adeno-associated viral vector (Anc80L65) carrying the acid ceramidase (Anc80L65.AC), an empty capsid vector, or saline. Therapeutic efficacy was evaluated 8 weeks after gene delivery.

RESULTS

Hemodynamic assessment 4 weeks after PH model the development demonstrated an increase in the mean pulmonary artery pressure to 30.4 ± 2.13 mmHg versus 10.4 ± 1.65 mmHg in sham (p < 0.001), which was consistent with the definition of PH. We documented a significant increase in pulmonary vascular resistance in the saline-treated (6.79 ± 0.85 mm Hg) and empty capsid (6.94 ± 0.47 mm Hg) groups, but not in animals receiving Anc80L65.AC (4.44 ± 0.71 mm Hg, p < 0.001). Morphometric analysis demonstrated an increase in medial wall thickness in control groups in comparison to those treated with acid ceramidase. After acid ceramidase gene delivery, a significant decrease of pro-inflammatory factors, interleukins, and senescence markers was observed.

CONCLUSION

Gene delivery of acid ceramidase provided tropism to pulmonary tissue and ameliorated vascular remodeling with right ventricular dysfunction in pulmonary hypertension.

Endothelin B Receptor Immunodynamics in Pulmonary Arterial Hypertension

Introduction

Inflammation is a major pathological feature of pulmonary arterial hypertension (PAH), particularly in the context of inflammatory conditions such as systemic sclerosis (SSc). The endothelin system and anti-endothelin A receptor (ET_A) autoantibodies have been implicated in the pathogenesis of PAH, and endothelin receptor antagonists are routinely used treatments for PAH. However, immunological functions of the endothelin B receptor (ET_B) remain obscure.

Methods

Serum levels of anti-ET_B receptor autoantibodies were quantified in healthy donors and SSc patients with or without PAH. Age-dependent effects of overexpression of prepro-endothelin-1 or ET_B deficiency on pulmonary inflammation and the cardiovascular system were studied in mice. Rescued ET_B-deficient mice (ET_B^-/-) were used to prevent congenital Hirschsprung disease. The effects of pulmonary T-helper type 2 (Th2) inflammation on PAH-associated pathologies were analyzed in ET_B^-/- mice. Pulmonary vascular hemodynamics were investigated in isolated perfused mouse lungs. Hearts were assessed for right ventricular hypertrophy. Pulmonary inflammation and collagen deposition were assessed via lung microscopy and bronchoalveolar lavage fluid analyses.

Results

Anti-ET_B autoantibody levels were elevated in patients with PAH secondary to SSc. Both overexpression of prepro-endothelin-1 and rescued ET_B deficiency led to pulmonary hypertension, pulmonary vascular hyperresponsiveness, and right ventricular hypertrophy with accompanying lymphocytic alveolitis. Marked perivascular lymphocytic infiltrates were exclusively found in ET_B^-/- mice. Following induction of pulmonary Th2 inflammation, PAH-associated pathologies and perivascular collagen deposition were aggravated in ET_B^-/- mice.

Conclusion

This study provides evidence for an anti-inflammatory role of ET_B. ET_B seems to have protective effects on Th2-evoked pathologies of the cardiovascular system. Anti-ET_B autoantibodies may modulate ET_B-mediated immune homeostasis.

Targeting sphingosine kinase 1 for the treatment of pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH), characterized by high morbidity and mortality, is a serious hazard to human life. Until now, the long-term survival of the PAH patients is still suboptimal. Recently, sphingosine kinase 1 (SPHK1) has drawn more and more attention due to its essential role in the pulmonary vasoconstriction, remodeling of pulmonary blood vessels and right cardiac lesions in PAH patients, and this enzyme is regarded as a new target for the treatment of PAH. Here, we discussed the multifarious functions of SPHK1 in PAH physiology and pathogenesis. Moreover, the structural features of SPHK1 and binding modes with different inhibitors were summarized. Finally, recent advances in the medicinal chemistry research of SPHK1 inhibitors are presented.

Investigating the regulatory role of ORMDL3 in airway barrier dysfunction using in vivo and in vitro models

The airway epithelium (AE) is the main protective barrier between the host and external environmental factors causing asthma. Allergens or pathogens induce AE dysfunction, including epithelial permeability alteration, trans‑epithelial electrical resistance (TEER) reduction, upregulation of inflammatory mediators and downregulation of junctional complex molecules. Orosomucoid‑like protein isoform 3 (ORMDL3), a gene closely associated with childhood onset asthma, is involved in airway inflammation and remodeling. It was hypothesized that ORMDL3 plays an important role in regulating AE barrier function. In vivo [chronic asthma induced by ovalbumin‑respiratory syncytial virus (OVA‑RSV)] in mice) and in vitro (human bronchial epithelial cells and 16HBE cells) models were used to assess ORMDL3's role in AE function regulation, evaluating paracellular permeability, TEER and the expression levels of junctional complex molecules. The effects of ORMDL3 on the extracellular signal‑regulated protein kinase (ERK) pathway were determined. In mice with OVA‑RSV induced chronic asthma, ORMDL3 and sphingosine kinase 1 (SPHK1) were upregulated whereas the junction related proteins Claudin‑18 and E‑cadherin were downregulated. Overexpression of ORMDL3 resulted in decreased TEER, downregulation of junctional complex molecules and induced epithelial permeability. In contrast, ORMDL3 inhibition showed the opposite effects. In 16HBE cells, ORMDL3 overexpression induced SPHK1 distribution and activity, while SPHK1 inhibition resulted in increased TEER upon administration of an ORMDL3 agonist or ORMDL3 overexpression. In addition, ERK activation occurred downstream of SPHK1 activation in 16HBE cells. High levels of ORMDL3 result in damaged AE barrier function by inducing the SPHK1/ERK pathway.

Impact of Fgf10 deficiency on pulmonary vasculature formation in a mouse model of bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD), characterized by alveoli simplification and dysmorphic pulmonary microvasculature, is a chronic lung disease affecting prematurely born infants. Pulmonary hypertension (PH) is an important BPD feature associated with morbidity and mortality. In human BPD, inflammation leads to decreased fibroblast growth factor 10 (FGF10) expression but the impact on the vasculature is so far unknown. We used lungs from Fgf10+/- versus Fgf10+/+ pups to investigate the effect of Fgf10 deficiency on vascular development in normoxia (NOX) and hyperoxia (HOX, BPD mouse model). To assess the role of fibroblast growth factor receptor 2b (Fgfr2b) ligands independently of early developmentaldefects, we used an inducible double transgenic system in mice allowing inhibition of Fgfr2b ligands activity. Using vascular morphometry, we quantified the pathological changes. Finally, we evaluated changes in FGF10, surfactant protein C (SFTPC), platelet endothelial cell adhesion molecule (PECAM) and alpha-smooth muscle actin 2 (α-SMA) expression in human lung samples from patients suffering from BPD. In NOX, no major difference in the lung vasculature between Fgf10+/- and control pups was detected. In HOX, a greater loss of blood vessels in Fgf10+/- lungs is associated with an increase of poorly muscularized vessels. Fgfr2b ligands inhibition postnatally in HOX is sufficient to decrease the number of blood vessels while increasing the level of muscularization, suggesting a PH phenotype. BPD lungs exhibited decreased FGF10, SFTPC and PECAM but increased α-SMA. Fgf10 deficiency-associated vascular defects are enhanced in HOX and could represent an additional cause of morbidity in human patients with BPD.

Blockage of sphingosine-1-phosphate receptor 2 attenuates allergic asthma in mice

BACKGROUND AND PURPOSE

Sphingosine-1-phosphate 2 (S1P₂ ) receptors have been implicated in degranulation of mast cells. However, functions of S1P₂ receptors have not been investigated in an in vivo model of allergic asthma.

EXPERIMENTAL APPROACH

Using an ovalbumin (OVA)-induced asthma model, the function of S1P₂ receptors was evaluated in S1P₂ -deficient mice or in mice treated with JTE-013, a selective S1P₂ antagonist. Bone marrow-derived dendritic cells (BMDCs) were used to investigate the roles of S1P₂ receptors in dendritic cell maturation and migration.

KEY RESULTS

Eosinophil accumulation and elevated Th2 cytokine levels in bronchoalveolar lavage fluid and inflamed lung tissues were strongly inhibited by administration of JTE-013 before OVA sensitization, before OVA challenge, and before both events. In S1P₂ -deficient mice, allergic responses were significantly lower than in wild-type mice. LPS- and OVA-induced maturation of BMDCs was significantly blunted in dendritic cells from S1P₂ -deficient mice and by treatment with JTE-013. Migrations of immature and mature BMDCs were also dependent on S1P₂ receptors. It was found that OVA-challenged mice into which in vitro OVA primed BMDCs from S1P₂ -deficient mice were adoptively transferred, had less severe asthma responses than OVA-challenged mice into which OVA-primed BMDCs from wild-type mice were adoptively transferred.

CONCLUSIONS AND IMPLICATIONS

Pro-allergic functions of S1P₂ receptors were elucidated in a murine asthma model. S1P₂ receptors were involved not only in maturation and migration of dendritic cells in the sensitization phase but also in mast cell degranulation in the challenge phase. These results suggest S1P₂ receptor as a therapeutic target for allergic asthma.

Spleen tyrosine kinase inhibition blocks airway constriction and protects from Th2-induced airway inflammation and remodeling

BACKGROUND

Spleen tyrosine kinase (Syk) is an intracellular nonreceptor tyrosine kinase, which has been implicated as central immune modulator promoting allergic airway inflammation. Syk inhibition has been proposed as a new therapeutic approach in asthma. However, the direct effects of Syk inhibition on airway constriction independent of allergen sensitization remain elusive.

METHODS

Spectral confocal microscopy of human and murine lung tissue was performed to localize Syk expression. The effects of prophylactic or therapeutic Syk inhibition on allergic airway inflammation, hyperresponsiveness, and airway remodeling were analyzed in allergen-sensitized and airway-challenged mice. The effects of Syk inhibitors BAY 61-3606 or BI 1002494 on airway function were investigated in isolated lungs of wild-type, PKCα-deficient, mast cell-deficient, or eNOS-deficient mice.

RESULTS

Spleen tyrosine kinase expression was found in human and murine airway smooth muscle cells. Syk inhibition reduced allergic airway inflammation, airway hyperresponsiveness, and pulmonary collagen deposition. In naïve mice, Syk inhibition diminished airway responsiveness independently of mast cells, or PKCα or eNOS expression and rapidly reversed established bronchoconstriction independently of NO. Simultaneous inhibition of Syk and PKC revealed additive dilatory effects, whereas combined inhibition of Syk and rho kinase or Syk and p38 MAPK did not cause additive bronchodilation.

CONCLUSIONS

Spleen tyrosine kinase inhibition directly attenuates airway smooth muscle cell contraction independent of its protective immunomodulatory effects on allergic airway inflammation, hyperresponsiveness, and airway remodeling. Syk mediates bronchoconstriction in a NO-independent manner, presumably via rho kinase and p38 MAPK, and Syk inhibition might present a promising therapeutic approach in chronic asthma as well as acute asthma attacks.

Sphingosine-1-phosphate is involved in the occlusive arteriopathy of pulmonary arterial hypertension

Despite several advances in the pathobiology of pulmonary arterial hypertension (PAH), its pathogenesis is not completely understood. Current therapy improves symptoms but has disappointing effects on survival. Sphingosine-1-phosphate (S1P) is a lysophospholipid synthesized by sphingosine kinase 1 (SphK1) and SphK2. Considering the regulatory roles of S1P in several tissues leading to vasoconstriction, inflammation, proliferation, and fibrosis, we investigated whether S1P plays a role in the pathogenesis of PAH. To test this hypothesis, we used plasma samples and lung tissue from patients with idiopathic PAH (IPAH) and the Sugen5416/hypoxia/normoxia rat model of occlusive PAH. Our study revealed an increase in the plasma concentration of S1P in patients with IPAH and in early and late stages of PAH in rats. We observed increased expression of both SphK1 and SphK2 in the remodeled pulmonary arteries of patients with IPAH and PAH rats. Exogenous S1P stimulated the proliferation of cultured rat pulmonary arterial endothelial and smooth-muscle cells. We also found that 3 weeks of treatment of late-stage PAH rats with an SphK1 inhibitor reduced the increased plasma levels of S1P and the occlusive pulmonary arteriopathy. Although inhibition of SphK1 improved cardiac index and the total pulmonary artery resistance index, it did not reduce right ventricular systolic pressure or right ventricular hypertrophy. Our study supports that S1P is involved in the pathogenesis of occlusive arteriopathy in PAH and provides further evidence that S1P signaling may be a novel therapeutic target.

PKCα Deficiency in Mice Is Associated with Pulmonary Vascular Hyperresponsiveness to Thromboxane A2 and Increased Thromboxane Receptor Expression

Pulmonary vascular hyperresponsiveness is a main characteristic of pulmonary arterial hypertension (PAH). In PAH patients, elevated levels of the vasoconstrictors thromboxane A2 (TXA2), endothelin (ET)-1 and serotonin further contribute to pulmonary hypertension. Protein kinase C (PKC) isozyme alpha (PKCα) is a known modulator of smooth muscle cell contraction. However, the effects of PKCα deficiency on pulmonary vasoconstriction have not yet been investigated. Thus, the role of PKCα in pulmonary vascular responsiveness to the TXA2 analog U46619, ET-1, serotonin and acute hypoxia was investigated in isolated lungs of PKCα-/- mice and corresponding wild-type mice, with or without prior administration of the PKC inhibitor bisindolylmaleimide I or Gö6976. mRNA was quantified from microdissected intrapulmonary arteries. We found that broad-spectrum PKC inhibition reduced pulmonary vascular responsiveness to ET-1 and acute hypoxia and, by trend, to U46619. Analogously, selective inhibition of conventional PKC isozymes or PKCα deficiency reduced ET-1-evoked pulmonary vasoconstriction. The pulmonary vasopressor response to serotonin was unaffected by either broad PKC inhibition or PKCα deficiency. Surprisingly, PKCα-/- mice showed pulmonary vascular hyperresponsiveness to U46619 and increased TXA2 receptor (TP receptor) expression in the intrapulmonary arteries. To conclude, PKCα regulates ET-1-induced pulmonary vasoconstriction. However, PKCα deficiency leads to pulmonary vascular hyperresponsiveness to TXA2, possibly via increased pulmonary arterial TP receptor expression.

Ceramide Signaling and Metabolism in Pathophysiological States of the Lung

Following the discovery of ceramide as the central signaling and metabolic relay among sphingolipids, studies of its involvement in lung health and pathophysiology have exponentially increased. In this review, we highlight key studies in the context of recent progress in metabolomics and translational research methodologies. Evidence points toward an important role for the ceramide/sphingosine-1-phosphate rheostat in maintaining lung cell survival, vascular barrier function, and proper host response to airway microbial infections. Sphingosine kinase 1 has emerged as an important determinant of sphingosine-1-phosphate lung levels, which, when aberrantly high, contribute to lung fibrosis, maladaptive vascular remodeling, and allergic asthma. New sphingolipid metabolites have been discovered as potential biomarkers of several lung diseases. Although multiple acute and chronic lung pathological conditions involve perturbations in sphingolipid signaling and metabolism, there are specific patterns, unique sphingolipid species, enzymes, metabolites, and receptors, which have emerged that deepen our understanding of lung pathophysiology and inform the development of new therapies for lung diseases.

Sphingosine kinase 1/sphingosine 1-phosphate signalling pathway as a potential therapeutic target of pulmonary hypertension

Pulmonary hypertension is characterized by extensive vascular remodelling, leading to increased pulmonary vascular resistance and eventual death due to right heart failure. The pathogenesis of pulmonary hypertension involves vascular endothelial dysfunction and disordered vascular smooth muscle cell (VSMC) proliferation and migration, but the exact processes remain unknown. Sphingosine 1-phosphate (S1P) is a bioactive lysophospholipid involved in a wide spectrum of biological processes. S1P has been shown to regulate VSMC proliferation and migration and vascular tension via a family of five S1P G-protein-coupled receptors (S1P1-SIP5). S1P has been shown to have both a vasoconstrictive and vasodilating effect. The S1P receptors S1P1 and S1P3 promote, while S1P2 inhibits VSMC proliferation and migration in vitro in response to S1P. Moreover, it has been reported recently that sphingosine kinase 1 and S1P2 inhibitors might be useful therapeutic agents in the treatment of empirical pulmonary hypertension. The sphingosine kinase 1/S1P signalling pathways may play a role in the pathogenesis of pulmonary hypertension. Modulation of this pathway may offer novel therapeutic strategies.

Spinster 2, a sphingosine-1-phosphate transporter, plays a critical role in inflammatory and autoimmune diseases

Sphingosine 1-phosphate (S1P) is a pleiotropic bioactive sphingolipid metabolite that regulates numerous processes important for immune responses. S1P is made within cells and must be transported out of cells to exert its effects through activation of 5 specific cell surface GPCRs in an autocrine or paracrine fashion. Spinster 2 (Spns2) transports S1P out of cells, and its deletion in mice reduces circulating levels of S1P, alters immune cell trafficking, and induces lymphopenia. Here we examined the effects of Spns2 deletion on adaptive immune responses and in autoimmune disease models. Airway inflammation and hypersensitivity as well as delayed-type contact hypersensitivity were attenuated in Spns2(-/-) mice. Similarly, Spns2 deletion reduced dextran sodium sulfate- and oxazolone-induced colitis. Intriguingly, Spns2(-/-) mice were protected from the development of experimental autoimmune encephalopathy, a model of the autoimmune disease multiple sclerosis. Deletion of Spns2 also strongly alleviated disease development in collagen-induced arthritis. These results point to a broad role for Spns2-mediated S1P transport in the initiation and development of adaptive immune related disorders.

CFTR and sphingolipids mediate hypoxic pulmonary vasoconstriction

Hypoxic pulmonary vasoconstriction (HPV) optimizes pulmonary ventilation-perfusion matching in regional hypoxia, but promotes pulmonary hypertension in global hypoxia. Ventilation-perfusion mismatch is a major cause of hypoxemia in cystic fibrosis. We hypothesized that cystic fibrosis transmembrane conductance regulator (CFTR) may be critical in HPV, potentially by modulating the response to sphingolipids as mediators of HPV. HPV and ventilation-perfusion mismatch were analyzed in isolated mouse lungs or in vivo. Ca(2+) mobilization and transient receptor potential canonical 6 (TRPC6) translocation were studied in human pulmonary (PASMCs) or coronary (CASMCs) artery smooth muscle cells. CFTR inhibition or deficiency diminished HPV and aggravated ventilation-perfusion mismatch. In PASMCs, hypoxia caused CFTR to interact with TRPC6, whereas CFTR inhibition attenuated hypoxia-induced TRPC6 translocation to caveolae and Ca(2+) mobilization. Ca(2+) mobilization by sphingosine-1-phosphate (S1P) was also attenuated by CFTR inhibition in PASMCs, but amplified in CASMCs. Inhibition of neutral sphingomyelinase (nSMase) blocked HPV, whereas exogenous nSMase caused TRPC6 translocation and vasoconstriction that were blocked by CFTR inhibition. nSMase- and hypoxia-induced vasoconstriction, yet not TRPC6 translocation, were blocked by inhibition or deficiency of sphingosine kinase 1 (SphK1) or antagonism of S1P receptors 2 and 4 (S1P2/4). S1P and nSMase had synergistic effects on pulmonary vasoconstriction that involved TRPC6, phospholipase C, and rho kinase. Our findings demonstrate a central role of CFTR and sphingolipids in HPV. Upon hypoxia, nSMase triggers TRPC6 translocation, which requires its interaction with CFTR. Concomitant SphK1-dependent formation of S1P and activation of S1P2/4 result in phospholipase C-mediated TRPC6 and rho kinase activation, which conjointly trigger vasoconstriction.

25-hydroxvitamin D3 promotes the long-term effect of specific immunotherapy in a murine allergy model

Calcitriol (1α,25-dihydroxyvitamin D3) is the active vitamin D metabolite and mediates immunological functions, which are relevant in allergy. Its therapeutic use is limited by hypercalcaemic toxicity. We have previously shown that the activation of the vitamin D receptor inhibits IgE production and that B cells can synthesize calcitriol from its precursor 25-hydroxyvitamin D3 (inactive precursor) [25(OH)D] upon antigenic stimulation. In this study, we address the impact of 25(OH)D on the development of type I sensitization and determine its role in allergen-specific immunotherapy. BALB/c mice were sensitized to OVA, under 25(OH)D-deficient or sufficient conditions. The humoral immune response over time was measured by ELISA. OVA-specific immunotherapy was established and studied in a murine model of allergic airway inflammation using lung histology, pulmonary cytokine expression analysis, and functional parameters in isolated and perfused mouse lungs. In 25(OH)D-deficient mice, OVA-specific IgE and IgG1 serum concentrations were increased compared with control mice. OVA-specific immunotherapy reduced the humoral immune reaction after OVA recall dose-dependently. Coadministration of 25(OH)D in the context of OVA-specific immunotherapy reduced the allergic airway inflammation and responsiveness upon OVA challenge. These findings were paralleled by reduced Th2 cytokine expression in the lungs. In conclusion, 25(OH)D deficiency promotes the development of type I sensitization and correction of its serum concentrations enhances the benefit of specific immunotherapy.

A specific sphingosine kinase 1 inhibitor attenuates airway hyperresponsiveness and inflammation in a mast cell-dependent murine model of allergic asthma

BACKGROUND

Sphingosine-1-phosphate (S1P), which is produced by 2 sphingosine kinase (SphK) isoenzymes, SphK1 and SphK2, has been implicated in IgE-mediated mast cell responses. However, studies of allergic inflammation in isotype-specific SphK knockout mice have not clarified their contribution, and the role that S1P plays in vivo in a mast cell- and IgE-dependent murine model of allergic asthma has not yet been examined.

OBJECTIVE

We used an isoenzyme-specific SphK1 inhibitor, SK1-I, to investigate the contributions of S1P and SphK1 to mast cell-dependent airway hyperresponsiveness (AHR) and airway inflammation in mice.

METHODS

Allergic airway inflammation and AHR were examined in a mast cell-dependent murine model of ovalbumin (OVA)-induced asthma. C57BL/6 mice received intranasal delivery of SK1-I before sensitization and challenge with OVA or only before challenge.

RESULTS

SK1-I inhibited antigen-dependent activation of human and murine mast cells and suppressed activation of nuclear factor κB (NF-κB), a master transcription factor that regulates the expression of proinflammatory cytokines. SK1-I treatment of mice sensitized to OVA in the absence of adjuvant, in which mast cell-dependent allergic inflammation develops, significantly reduced OVA-induced AHR to methacholine; decreased numbers of eosinophils and levels of the cytokines IL-4, IL-5, IL-6, IL-13, IFN-γ, and TNF-α and the chemokines eotaxin and CCL2 in bronchoalveolar lavage fluid; and decreased pulmonary inflammation, as well as activation of NF-κB in the lungs.

CONCLUSION

S1P and SphK1 play important roles in mast cell-dependent, OVA-induced allergic inflammation and AHR, in part by regulating the NF-κB pathway.

Sphingosine-1-phosphate-induced airway hyper-reactivity in rodents is mediated by the sphingosine-1-phosphate type 3 receptor

There is a need to better understand the mechanism of airway hyper-reactivity, a key feature of asthma. Evidence suggests that sphingosine-1-phosphate (S1P) could be a major player in this phenomenon. The purpose of this work was to define the S1P receptor responsible for this phenomenon. We have studied, in the rat, the effect of two S1P synthetic receptor ligands, 2-amino-2-[2-(4-octylphenyl)ethyl]propane-1,3-diol (FTY720) (which in its phosphorylated form is a potent agonist at each S1P receptor except S1P(2)) and 3-[[2-[4-phenyl-3-(trifluoromethyl)phenyl]-1-benzothiophen-5-yl]methylamino]propanoic acid (AUY954) (a selective S1P(1) agonist) on lung function in vivo. This was complemented by in vitro studies using isolated trachea from the rat, the S1P(3) receptor-deficient mouse, and its wild-type counterpart. After oral administration, FTY720 induced a generalized airway hyper-reactivity to a range of contractile stimuli. This was observed as early as 1 h postdosing, lasted for at least 24 h, and was not subject to desensitization. In both rat and wild-type mouse isolated trachea, preincubation with the active phosphorylated metabolite of FTY720 induced hyper-responsiveness to 5-hydroxytryptamine. This effect was not seen in the isolated tracheas from S1P(3) receptor-deficient mice. AUY954, did not mimic the effect of FTY720 either in vivo or in vitro. Our data are consistent with activation of the S1P pathway inducing a generalized airway hyper-reactivity in rats and mice that is mediated by the S1P(3) receptor. S1P(3) receptor antagonists might prove to be useful as new therapeutic strategies aimed at blocking the airway hyper-reactivity observed in asthma.

Perspectives on immunomodulation early in life

The immune system early in life is characterized by immature activation and function of immune cells and a preponderance of Th2 cytokines. Together with other factors such as genetics and epigenetics, these immature immune responses might prone newborns susceptible to severe infections as well as allergic diseases. Immunomodulation therapy may have potential as therapeutic strategy against those disorders and might have implication in early-life interventions in the future. In this review, we will focus on two immunomodulatory substance classes, Toll-like receptor (TLR) ligands and sphingolipids, which are the focus of extensive research to date. Both TLRs and sphingolipid receptors have a very distinct distribution pattern and function on immune cells. Therefore, they can potentially modulate and balance immune responses, which might be in particular beneficial for the immaturity of the immune response early in life.

Sphingosine-1-phosphate augments agonist-mediated contraction in the bronchial smooth muscles of mice

The effects of sphingosine-1-phosphate (S1P) on bronchial smooth muscle (BSM) contractility were investigated in naive mice. S1P had no effect on the basal tone of the isolated BSM tissues. However, in the presence of S1P (10(-6) M), the BSM contractions induced by acetylcholine (ACh) and endothelin-1 (ET-1) were significantly augmented: both the ACh and ET-1 concentration-response curves were significantly shifted to the left. In contrast, the pretreatment with S1P had no effect on the contractions induced by high K(+) depolarization. It is thus possible that S1P augments BSM contraction induced by the activation of G protein-coupled receptors.

Expression profile of the sphingosine kinase signalling system in the lung of patients with chronic obstructive pulmonary disease

AIMS

Chronic obstructive pulmonary disease (COPD) is a leading cause of death worldwide. Despite its importance, treatment methods are limited and restricted to symptomatic care, highlighting the urgent need for new treatment options. Tissue damage in COPD is thought to result from an inability of the normal repair processes with accumulation of apoptotic material and impaired clearance of this material by macrophages in the airways. Lung inflammation involves the bioactive sphingolipid sphingosine 1-phosphate (S1P).

MAIN METHODS

We investigated lung tissue samples from 55 patients (25 with COPD) undergoing lobectomies for management of cancer. We analysed the sphingosine-kinase (SphK) mRNA expression profile, SphK enzyme activity as well as the localisation and expression of individual proteins related to the SphK-signalling system.

KEY FINDINGS

We show in this study for the first time a comprehensive expression profile of all synthesising enzymes, receptors and degrading enzymes of the SphK-signalling system in the human lung. Multivariate ANOVA showed that the relative mRNA expression of S1P receptor (S1PR) subtype 5 was reduced in COPD. There were strong positive correlations between the mRNA expression of S1PR5 and S1PR1 and S1PR3, and between S1PR3 and S1PR2. A significant negative correlation was found between S1PR1 and SphK protein activity.

SIGNIFICANCE

The correlations between expression levels of receptors and enzymes involved in the sphingosine kinase signalling system in the lung suggest common regulatory mechanisms. Our findings of reduced S1PR5 in COPD and the correlation with other S1P receptors in COPD identify S1PR5 as a possible novel target for pharmacotherapy.

Sphingosine-1-phospate receptor 4 (S1P₄) deficiency profoundly affects dendritic cell function and TH17-cell differentiation in a murine model

Although predominantly expressed on lymphocytic and hematopoietic cells, the role of sphingosine-1-phospate receptor 4 (S1P(4)) in immune homeostasis is still poorly understood. In this report, we used a S1P(4)-deficient murine model to characterize the biological role of S1P(4)-mediated S1P signaling in the immune system. S1p(4)(-/-) animals showed normal peripheral lymphocyte numbers and a regular architecture of secondary lymphoid organs. Interestingly, S1P(4) only marginally affects T-cell function in vivo. In contrast, dendritic cell (DC) migration and cytokine secretion are profoundly affected by S1P(4) deficiency. Lack of S1P(4) expression on DCs significantly reduces T(H)17 differentiation of T(H) cells. Furthermore, in various in vivo models of T(H)1- or T(H)2-dominated immune reactions, S1P(4) deficiency consistently increased the amplitude of T(H)2-dominated immune responses, while those depending on T(H)1-dominated mechanisms were diminished. Finally, S1p(4)(-/-) mice showed decreased pathology in a model of dextran sulfate sodium-induced colitis. In summary, for the first time, we show that S1P(4) signaling is involved in the regulation of DC function and T(H)17 T-cell differentiation. S1P(4)-mediated S1P signaling also modifies the course of various immune diseases in a murine model. We propose that S1P(4) may constitute an interesting target to influence the course of various autoimmune pathologies.

Protection of LPS-induced murine acute lung injury by sphingosine-1-phosphate lyase suppression

A defining feature of acute lung injury (ALI) is the increased lung vascular permeability and alveolar flooding, which leads to associated morbidity and mortality. Specific therapies to alleviate the unremitting vascular leak in ALI are not currently clinically available; however, our prior studies indicate a protective role for sphingosine-1-phosphate (S1P) in animal models of ALI with reductions in lung edema. As S1P levels are tightly regulated by synthesis and degradation, we tested the hypothesis that inhibition of S1P lyase (S1PL), the enzyme that irreversibly degrades S1P via cleavage, could ameliorate ALI. Intratracheal instillation of LPS to mice enhanced S1PL expression, decreased S1P levels in lung tissue, and induced lung inflammation and injury. LPS challenge of wild-type mice receiving 2-acetyl-4(5)-[1(R),2(S),3(R),4-tetrahydroxybutyl]-imidazole to inhibit S1PL or S1PL(+/-) mice resulted in increased S1P levels in lung tissue and bronchoalveolar lavage fluids and reduced lung injury and inflammation. Moreover, down-regulation of S1PL expression by short interfering RNA (siRNA) in primary human lung microvascular endothelial cells increased S1P levels, and attenuated LPS-mediated phosphorylation of p38 mitogen-activated protein kinase and I-κB, IL-6 secretion, and endothelial barrier disruption via Rac1 activation. These results identify a novel role for intracellularly generated S1P in protection against ALI and suggest S1PL as a potential therapeutic target.

Sphingosine 1-phosphate, a key mediator of the cytokine network: juxtacrine signaling

Sphingosine 1-phosphate (S1P) is a sphingolipid metabolite, which has emerged as an important signaling mediator participating in the regulation of multiple cellular processes. The discovery of a family of S1P receptors, together with the more recently identified intracellular targets, has provided fundamental understanding of the multi-faceted actions of S1P. Evidence from both in vitro and in vivo studies has implicated the S1P signaling system in the control of immunity, inflammation and many associated diseases. Enigmatically, S1P appears to have both pro- and anti-inflammatory effects depending on the cell context. Here, we review this emerging area and argue for a pivotal role for S1P, as a key mediator of the cytokine network, acting through juxtacrine signaling in the immune system.

SKI-II, an inhibitor of sphingosine kinase, ameliorates antigen-induced bronchial smooth muscle hyperresponsiveness, but not airway inflammation, in mice

To determine if endogenously generated sphingosine-1-phosphate (S1P) is involved in the development of allergic bronchial asthma, the effects of systemic treatments with SKI-II, a specific inhibitor of sphingosine kinase, on antigen-induced bronchial smooth muscle (BSM) hyperresponsiveness and airway inflammation were examined in mice. Male BALB/c mice were actively sensitized with ovalbumin (OA) antigen and were repeatedly challenged with aerosolized antigen. Animals also received intraperitoneal injections with SKI-II (50 mg/kg) 1 h prior to each antigen challenge. The acetylcholine (ACh)-induced contraction of BSM isolated from the repeatedly antigen-challenged mice was significantly augmented, that is, BSM hyperresponsiveness, as compared with that from the control animals (P < 0.05). The BSM hyperresponsiveness induced by antigen exposure was ameliorated by the systemic treatment with SKI-II, whereas the treatments had no effect on BSM responsiveness to ACh in control animals. On the other hand, the systemic treatments with SKI-II had no effect on antigen-induced inflammatory signs, such as increase in cell counts in bronchoalveolar lavage fluids (BALFs) and change in airway histology; upregulation of BALF cytokines, such as interleukin-4 (IL-4) and IL-13; and elevation of total and OA-specific immunoglobulin E (IgE) in sera. These findings suggest that sphingosine kinase inhibitors such as SKI-II have an ability to prevent the development of BSM hyperresponsiveness, but not of allergic airway inflammation. The endogenously generated S1P might be one of the exacerbating factors for the airway hyperresponsiveness, one of the characteristic features of allergic bronchial asthma.

The leukocyte activation antigen CD69 limits allergic asthma and skin contact hypersensitivity

BACKGROUND

Allergic diseases have a major health care impact in industrialized countries. The development of these diseases is influenced by exposure to allergen and to immunological and genetic factors. However, the molecular mechanisms underlying the inflammatory response that triggers allergy are not well defined.

OBJECTIVE

We have investigated the role of the leukocyte activation antigen CD69 in the regulation of two allergic diseases, asthma and contact dermatitis.

METHODS

Analysis of two models of allergic diseases in CD69 knockout and wild-type mice: ovalbumin-induced allergic airway inflammation (BALB/c genetic background) and contact hypersensitivity to oxazolone (C57BL/6J genetic background).

RESULTS

CD69 deficiency dramatically enhanced the inflammatory response in the ovalbumin-induced asthma model of antigen-induced airway allergy. CD69 knockout mice showed exacerbated pulmonary eosinophil recruitment, high vascular cell adhesion molecule 1 expression levels in lung vasculature, and enhanced T(H)2 and T(H)17 cytokines in the bronchoalveolar space and lung tissue. In the hapten-induced cutaneous contact hypersensitivity model, both CD69 deficiency and treatment with anti-CD69 mAb increased inflammation. Treatment with contact allergens induced enhanced T(H)1 and T(H)17 responses in CD69 deficient mice, and neutralizing anti-IL-17 antibodies reduced skin inflammation. In both experimental systems, adoptive transfer of lymph node cells from CD69 knockout mice increased the inflammatory response in recipient mice.

CONCLUSION

These results demonstrate that the early activation receptor CD69 is an intrinsic modulator of immune allergic processes through the negative regulation of allergen-induced T-cell effector responses.

Sphingosine-1-phosphate aggravates antigen-induced airway inflammation in mice

Recent investigations suggest an involvement of sphingosine-1-phosphate (S1P) in the pathogenesis of allergic bronchial asthma. However, the role of S1P in the development of asthma is still controversial. Our aim was to investigate the effects of intranasal application of S1P on antigen-induced airway inflammation in a mouse model of allergic bronchial asthma.

METHODOLOGY

Male BALB/c mice were actively sensitized with ovalbumin antigen, and were repeatedly challenged with aerosolized antigen. Animals also received an intranasal administration of S1P (10-5 M, 20 µL) or its vehicle (1% methanol in sterile PBS, 20 µL) 30 min prior to each antigen challenge. Histological examinations of the lungs and determination of cell number in the bronchoalveolar lavage fluids (BALFs) were studied.

RESULTS

The airway inflammation induced by antigen exposure was significantly augmented by the intranasal administration of S1P: the cell number in BALFs of the S1P-treated, antigen-challenged mice (S1P-Challenged, 48.9±4.8 x 10(4)/mL BALF) was significantly increased as compared with those of the vehicle-treated, antigen-challenged ones (Vehicle-Challenged, 26.3±5.7 x 10(4)/mL BALF, P<0.01).

CONCLUSION

In mice, the intranasal administration of S1P might aggravate the antigen-induced airway inflammation.

Role of Rho kinase in sphingosine 1-phosphate-mediated endothelial and smooth muscle cell migration and differentiation

The role of sphingosine 1-phosphate (S1P)-induced Rho kinase (ROCK) activation in the angiogenic responses of pulmonary artery-derived endothelial cells (PAEC) and smooth muscle cells (PASMC) was examined. S1P, a biologically active phospholipid that regulates angiogenesis, promoted PAEC chemotaxis and capillary morphogenesis; furthermore, this activity was unaltered by pretreatment with the pharmacological inhibitor of ROCK, H1152. In contrast, S1P (500 nM) significantly inhibited spontaneous PASMC chemotaxis and differentiation; however, this inhibition was eradicated upon H1152 pretreatment. Similarly, PASMCs transfected with ROCK II siRNA diminished S1P-induced inhibition of the development of multi-cellular structures. Analysis by RT-PCR identified the presence of S1P(1) and S1P(3) receptors on both PAECs and PASMCs, while S1P(2) receptor expression was confined to only PASMCs. Consistent with this observation, the S1P(1) and S1P(3) receptor antagonist, VPC23019, virtually abolished the S1P-initiated PAEC differentiation but did not impede the S1P-induced inhibition of PASMC differentiation. However, the S1P(2) receptor antagonist, JTE013, had no effect on S1P-mediated differentiation of PAECs but abolished the S1P-induced inhibition of PASMC function. Co-cultured endothelial and smooth muscle cells differentiated into "neovascular-like" networks, which were significantly inhibited by S1P. The inhibition of co-culture differentiation in both PAECs and PASMCs was negated by H1152 pretreatment. However, when smooth muscle cells were added to S1P-initiated endothelial cell networks, additional S1P treatment did not inhibit the cellular networks generated by these cells. In conclusion, S1P-induced PAEC angiogenic responses are regulated by S1P(1) and/or S1P(3) receptors independent of Rho kinase activation, whereas S1P(2) receptor-mediated curtailment of PASMC function by S1P.

Key advances in mechanisms of asthma, allergy, and immunology in 2009

The year 2009 was marked by rapid progress in understanding cellular and chemical mechanisms in the pathogenesis of asthma and other allergic disorders. Studies published in the Journal of Allergy and Clinical Immunology described advances in our knowledge of signaling molecules and pathways, cytokines, and activation and tolerance in asthma and murine models of this disease; food allergy; anaphylaxis and immediate hypersensitivity; mast cells and their disorders; atopic dermatitis; allergic conjunctivitis; nasal polyposis; and hypereosinophilic syndromes. Additional studies provided novel information about the induction and regulation of allergic inflammation and the genetic determinants of asthma and responsiveness to asthma therapy. Critical features of these studies and their potential effect on human atopic disorders are summarized here.