sphingosine-kinase and Asthma

Sphingolipids are amphiphatic molecules ubiquitously expressed in all eukaryotic cell membranes. Initially characterized as structural components of cell membranes, sphingolipids have emerged as sources of important signalling molecules over the past decade. Sphingolipid metabolites, such as ceramide and S1P (sphingosine 1-phosphate), have been demonstrated to have roles as potent bioactive messengers involved in cell differentiation, proliferation, apoptosis, migration and angiogenesis. The importance of SphK (sphingosine kinase) and S1P in inflammation has been demonstrated extensively. The prevalence of asthma is increasing in many developed nations. Consequently, there is an urgent need for the development of new agents for the treatment of asthma, especially for patients who respond poorly to conventional therapy. Recent studies have demonstrated the important role of SphK and S1P in the development of asthma by regulating pro-inflammatory responses. These novel pathways represent exciting potential therapeutic targets in the treatment of asthma and are described in the present review.

Topics: Animals; Anti-Asthmatic Agents; Asthma; Cytokines; Disease Models, Animal; Epithelial Cells; Fingolimod Hydrochloride; Humans; Inflammation; Lung; Lysophospholipids; Mast Cells; Mice; Phosphotransferases (Alcohol Group Acceptor); Propylene Glycols; Receptors, Lysosphingolipid; Signal Transduction; Sphingolipids; Sphingosine

The bioactive lipid sphingosine-1-phosphate (S1P) fulfils manifold tasks in the immune system acting in auto- and/or paracrine fashion. This includes regulation of apoptosis, migration and proliferation. Upon its generation by sphingosine kinases from plasma membrane sphingolipids, S1P can either act as a second messenger within cells or can be released from cells to occupy a family of specific G-protein-coupled receptors (S1P1-5). This diversity is reflected by the impact of S1P on macrophage biology and function. Over the last years it became apparent that the sphingosine kinase/S1P/S1P-receptor signalling axis in macrophages might play a central role in the pathogenesis of inflammatory diseases such as atherosclerosis, asthma, rheumatoid arthritis and cancer. Here, we summarize the current knowledge of the function of S1P in macrophage biology and discuss potential implications for pathology.

Topics: Animals; Arthritis, Rheumatoid; Asthma; Atherosclerosis; Humans; Inflammation; Lysophospholipids; Macrophage Activation; Macrophages; Neoplasms; Phosphotransferases (Alcohol Group Acceptor); Receptors, G-Protein-Coupled; Receptors, Lysosphingolipid; Signal Transduction; Sphingosine

Mast cell activation is a central event in allergic diseases, and investigating the signalling pathways triggered during mast cell activation may lead to the discovery of novel therapeutic targets. Mast cells can be activated by a multitude of stimuli including antibodies/antigen, cytokines/chemokines and neuropeptides, resulting in a variety of responses including the immediate release of potent inflammatory mediators. Moreover, recent data suggest that mast cell-mediated responses are also influenced by the differential sphingolipids/sphingosine to sphingosine-1-phosphate ratio. The importance of sphingolipids as potent biological mediators of both intracellular and extracellular responses is being increasingly recognized and accepted; it is now appreciated that activation of mast cells, via the high-affinity IgE-receptor (FcepsilonRI) leads to the activation of sphingosine kinases (SphK), resulting in increased formation of sphingosine-1-phosphate. Furthermore, FcepsilonRI activates SphK-dependent calcium mobilization in mast cells, leading to degranulation, cytokine, and eicosanoid production, and chemotaxis. In the past two years a critical role for SphK in allergic responses in vivo has emerged. In this review, I focus on the current understanding of the role of sphingosine kinases during mast cell signalling in vitro and their role during hypersensitivity responses in vivo, and discuss the potential of these enzymes as novel therapeutic targets to treat allergic diseases.

Topics: Anaphylaxis; Asthma; Enzyme Inhibitors; Humans; Hypersensitivity; Mast Cells; Phosphotransferases (Alcohol Group Acceptor); Signal Transduction

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

Topics: Amino Alcohols; Animals; Asthma; Bronchial Hyperreactivity; Bronchoalveolar Lavage Fluid; Cells, Cultured; Chemokine CCL2; Female; Goblet Cells; Humans; Hyperplasia; Immunoglobulin E; Inflammation; Interferon-gamma; Interleukins; Lung; Lysophospholipids; Mast Cells; Methacholine Chloride; Mice; Mice, Inbred C57BL; NF-kappa B; Ovalbumin; Phosphotransferases (Alcohol Group Acceptor); Sphingosine; Tumor Necrosis Factor-alpha

Our previous report showed that inhibition of sphingosine kinase (SphK) ameliorates eosinophilic inflammation and mucin production in a mouse asthmatic model. To clarify the role of SphK in airway mucin production, we utilized the mouse asthmatic model and found that both SphK and MUC5AC expression were increased and co-localized in airway epithelium. Next we cultured normal human bronchial epithelial cells in an air-liquid interface and treated with IL-13 to induce their differentiation into goblet cells. We found that SphK1 and MUC5AC expression was increased by IL-13 treatment at both protein and mRNA levels, whereas SphK2 expression was not changed. N,N-dimethylsphingosine (DMS), a potent SphK inhibitor, decreased MUC5AC expression up-regulated by IL-13 treatment. Furthermore, DMS inhibited IL-13-induced ERK1/2 phosphorylation but neither p38 MAPK nor STAT6 phosphorylation. These results suggest that SphK1 is involved in MUC5AC production induced by IL-13 upstream of ERK1/2 phosphorylation, and independent of STAT6 phosphorylation.

Topics: Animals; Asthma; Bronchi; Interleukin-13; Mice; Mice, Inbred C57BL; Mitogen-Activated Protein Kinase 1; Mitogen-Activated Protein Kinase 3; Mucin 5AC; Phosphorylation; Phosphotransferases (Alcohol Group Acceptor); Sphingosine

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.

Topics: Animals; Antigens; Asthma; Bronchi; Bronchial Hyperreactivity; Bronchoalveolar Lavage Fluid; Immunoglobulin E; Interleukin-13; Interleukin-4; Lysophospholipids; Male; Mice; Mice, Inbred BALB C; Muscle, Smooth; Phosphotransferases (Alcohol Group Acceptor); Sphingosine; Thiazoles

Asthma is an allergic disease characterized by chronic airway eosinophilia and pulmonary infiltration of lymphocytes, particularly of the Th2 subtype, macrophages and mast cells. Previous studies have shown a pivotal role for sphingosine kinase (SphK) on various proinflammatory cells, such as lymphocyte and eosinophil migration and mast cell degranulation. We therefore examined the roles of SphK in a murine model of allergic asthma. In mice previously sensitized to OVA, i.p. administration of N,N-dimethylsphingosine (DMS), a potent SphK inhibitor, significantly reduced the total inflammatory cell infiltrate and eosinophilia and the IL-4, IL-5, and eotaxin levels in bronchoalveolar lavage fluid in response to inhaled OVA challenge. In addition, DMS significantly suppressed OVA-induced inflammatory infiltrates and mucus production in the lungs, and airway hyperresponsiveness to methacholine in a dose-dependent manner. OVA-induced lymphocyte proliferation and IL-4 and IL-5 secretion were reduced in thoracic lymph node cultures from DMS-treated mice. Moreover, similar reduction in inflammatory infiltrates, bronchoalveolar lavage, IL-4, IL-5, eotaxin, and serum OVA-specific IgE levels was observed in mice with SphK1 knock-down via small interfering RNA approach. Together, these data demonstrate the therapeutic potential of SphK modulation in allergic airways disease.

Topics: Airway Resistance; Allergens; Animals; Asthma; Bronchoalveolar Lavage Fluid; Cell Movement; Cells, Cultured; Disease Models, Animal; Enzyme Inhibitors; Eosinophils; Female; Immunosuppressive Agents; Inflammation Mediators; Mice; Mice, Inbred BALB C; Ovalbumin; Phosphotransferases (Alcohol Group Acceptor); RNA, Small Interfering; Sphingosine; Th2 Cells

Sphingosine 1-phosphate (S1P) produced by sphingosine kinase (SPHK) is implicated in acute immunoresponses, however, mechanisms of SPHK/S1P signaling in the pathogenesis of bronchial asthma are poorly understood. In this study, we hypothesized that SPHK inhibition could ameliorate lung inflammation in ovalbumin (OVA)-challenged mouse lungs. Six- to eight-week-old C57BL/6J mice were sensitized and exposed to OVA for 3 consecutive days. Twenty-four hours later, mice lungs and bronchoalveolar lavage (BAL) fluid were analyzed. For an inhibitory effect, either of the two different SPHK inhibitors, N,N-dimethylsphingosine (DMS) or SPHK inhibitor [SK-I; 2-(p-hydroxyanilino)-4-(p-chlorophenyl) thiazole], was nebulized for 30 min before OVA inhalation. OVA inhalation caused S1P release into BAL fluid and high expression of SPHK1 around bronchial epithelial walls and inflammatory areas. DMS or SK-I inhalation resulted in a decrease in S1P amounts in BAL fluid to basal levels, accompanied by decreased eosinophil infiltration and peroxidase activity. The extent of inhibition caused by DMS inhalation was higher than that caused by SK-I. Like T helper 2 (Th2) cytokine release, OVA inhalation-induced increase in eotaxin expression was significantly suppressed by DMS pretreatment both at protein level in BAL fluid and at mRNA level in lung homogenates. Moreover, bronchial hyperresponsiveness to inhaled methacholine and goblet cell hyperplasia were improved by SPHK inhibitors. These data suggest that the inhibition of SPHK affected acute eosinophilic inflammation induced in antigen-challenged mouse model and that targeting SPHK may provide a novel therapeutic tool to treat bronchial asthma.

Topics: Administration, Inhalation; Aniline Compounds; Animals; Asthma; Bronchoalveolar Lavage Fluid; Cells, Cultured; Chemokines, CC; Disease Models, Animal; Enzyme Inhibitors; Goblet Cells; Humans; Hyperplasia; Interleukins; Lysophospholipids; Mice; Mice, Inbred C57BL; Ovalbumin; Phosphotransferases (Alcohol Group Acceptor); Respiratory Mucosa; Sphingosine; Thiazoles

Cytosolic phospholipase A(2)alpha (cPLA(2)alpha) activation is a regulatory step in the control of arachidonic acid (AA) liberation for eicosanoid formation. Sphingosine 1-phosphate (S1P) is a bioactive lipid mediator involved in the regulation of many important proinflammatory processes and has been found in the airways of asthmatic subjects. We investigated the mechanism of S1P-induced AA release and determined the involvement of cPLA(2)alpha in these events in A549 human lung epithelial cells. S1P induced AA release rapidly within 5 min in a dose- and time-dependent manner. S1P-induced AA release was inhibited by the cPLA(2)alpha inhibitors methyl arachidonyl fluorophosphonate (MAFP) and pyrrolidine derivative, by small interfering RNA-mediated downregulation of cPLA(2)alpha, and by inhibition of S1P-induced calcium flux, suggesting a significant role of cPLA(2)alpha in S1P-mediated AA release. Knockdown of the S1P3 receptor, the major S1P receptor expressed on A549 cells, inhibited S1P-induced calcium flux and AA release. The S1P-induced calcium flux and AA release was associated with sphingosine kinase 1 (Sphk1) expression and activity. Furthermore, Rho-associated kinase, downstream of S1P3, was crucial for S1P-induced cPLA(2)alpha activation. Our data suggest that S1P acting through S1P3, calcium flux, and Rho kinase activates cPLA(2)alpha and releases AA in lung epithelial cells. An understanding of S1P-induced cPLA(2)alpha activation mechanisms in epithelial cells may provide potential targets to control inflammatory processes in the lung.

Topics: Animals; Arachidonic Acid; Arachidonic Acids; Asthma; Calcium; Calcium Signaling; Cell Line; Eicosanoids; Enzyme Activation; Enzyme Inhibitors; Gene Expression Regulation, Enzymologic; Group IV Phospholipases A2; Humans; Lung; Lysophospholipids; Organophosphonates; Phosphotransferases (Alcohol Group Acceptor); Receptors, Lysosphingolipid; Respiratory Mucosa; rho-Associated Kinases; RNA, Small Interfering; Sphingosine