sphingosine-kinase and Anaphylaxis

Pharmacological interference with sphingolipid metabolizing enzymes promises to provide novel ways to modulate cellular pathways relevant in multiple diseases. In this review, we focus on two sphingolipid signaling molecules, sphingosine-1-phosphate (S1P) and ceramide, as they are involved in cell fate decisions (survival vs. apoptosis) and in a wide range of pathophysiological processes. For S1P, we will discuss sphingosine kinases and S1P lyase as the enzymes which are crucial for its production and degradation, respectively, emphasizing the potential therapeutic usefulness of inhibitors of these enzymes. For ceramide, we will concentrate on acid sphingomyelinase, and critically review the substantial literature which implicates this enzyme as a worthwhile target for pharmacological inhibitors. It will become clear that the task to validate these enzymes as drug targets is not finished and many questions regarding the therapeutic usefulness of their inhibitors remain unanswered. Still this approach holds promise for a number of totally new therapies, and, on the way, detailed insight into sphingolipid signaling pathways can be gained.

Topics: Aldehyde-Lyases; Anaphylaxis; Animals; Apoptosis; Atherosclerosis; Bacterial Infections; Ceramides; Cyclooxygenase 2; Dendritic Cells; Drug Design; Enzyme Inhibitors; Humans; Immunologic Factors; Leukocytes; Lysophospholipids; Macrophages; Mast Cells; Neoplasms; Neovascularization, Pathologic; Phosphotransferases (Alcohol Group Acceptor); RNA, Small Interfering; Sphingolipids; Sphingomyelin Phosphodiesterase; 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) is a lipid mediator involved in diverse biological processes, from vascular and neural development to the regulation of lymphocyte trafficking. Many of its functions are regulated by five widely expressed S1P G-protein-coupled receptors (S1P(1-5)). S1P is produced mostly intracellularly, thus, much of its potential as an autocrine and paracrine mediator depends on how, when, and where it is generated or secreted out of the cells. However, S1P can also have intracellular activity independent of its receptors, adding to the complexity of S1P function. The mast cell, a major effector cell during an allergic response, has proven instrumental towards understanding the complex regulation and function of S1P. Antigen (Ag) engagement of the IgE receptor in mast cells stimulates sphingosine kinases, which generate S1P and are involved in the activation of calcium fluxes critical for mast cell responses. In addition, mast cells secrete considerable amounts of S1P upon activation, thus affecting the surrounding tissues and recruiting inflammatory cells. Export of S1P is also involved in the autocrine transactivation of S1P receptors present in mast cells. The in vivo response of mast cells, however, is not strictly dependent on their ability to generate S1P, but they are also affected by changes in S1P in the environment previous to Ag challenge. This review will discuss the recent advances towards understanding the intricacies of S1P generation, secretion and regulation in mast cells. In addition, how S1P receptors are activated and their involvement in mast cell functions will also be covered, including new insights on the role of S1P in the mast cell-mediated allergic response of systemic anaphylaxis.

Topics: Anaphylaxis; Animals; Humans; Lysophospholipids; Mast Cells; Models, Biological; Phosphotransferases (Alcohol Group Acceptor); Receptors, Lysosphingolipid; Sphingosine

Sphingosine kinase 1 (SphK1) and SphK2 are ubiquitous enzymes that generate sphingosine-1-phosphate (S1P), a ligand for a family of G protein-coupled receptors (S1PR1-S1PR5) with important functions in the vascular and immune systems. Here we explore the role of these kinases and receptors in recovery from anaphylaxis in mice. We found that Sphk2-/- mice had a rapid recovery from anaphylaxis. In contrast, Sphk1-/- mice showed poor recovery from anaphylaxis and delayed histamine clearance. Injection of S1P into Sphk1-/- mice increased histamine clearance and promoted recovery from anaphylaxis. Adoptive cell transfer experiments demonstrated that SphK1 activity was required in both the hematopoietic and nonhematopoietic compartments for recovery from anaphylaxis. Mice lacking the S1P receptor S1PR2 also showed a delay in plasma histamine clearance and a poor recovery from anaphylaxis. However, S1P did not promote the recovery of S1pr2-/- mice from anaphylaxis, whereas S1pr2+/- mice showed partial recovery. Unlike Sphk2-/- mice, Sphk1-/- and S1pr2-/- mice had severe hypotension during anaphylaxis. Thus, SphK1-produced S1P regulates blood pressure, histamine clearance, and recovery from anaphylaxis in a manner that involves S1PR2. This suggests that specific S1PR2 agonists may serve to counteract the vasodilation associated with anaphylactic shock.

Topics: Anaphylaxis; Animals; Bone Marrow Transplantation; Gene Expression Regulation, Enzymologic; Glomerular Filtration Rate; Hematopoietic Stem Cells; Histamine; Kidney; Mice; Mice, Inbred C57BL; Mice, Transgenic; Models, Biological; Permeability; Phosphotransferases (Alcohol Group Acceptor); Receptors, Lysosphingolipid

Mast cell degranulation is pivotal to allergic diseases; investigating novel pathways triggering mast cell degranulation would undoubtedly have important therapeutic potential. FcepsilonRI-mediated degranulation has contradictorily been shown to require SphK1 or SphK2, depending on the reports. We investigated the in vitro and in vivo specific role(s) of SphK1 and SphK2 in FcepsilonRI-mediated responses, using specific small interfering RNA-gene silencing. The small interfering RNA-knockdown of SphK1 in mast cells inhibited several signaling mechanisms and effector functions, triggered by FcepsilonRI stimulation including: Ca(2+) signals, NFkappaB activation, degranulation, cytokine/chemokine, and eicosanoid production, whereas silencing SphK2 had no effect at all. Moreover, silencing SPHK1 in vivo, in different strains of mice, strongly inhibited mast cell-mediated anaphylaxis, including inhibition of vascular permeability, tissue mast cell degranulation, changes in temperature, and serum histamine and cytokine levels, whereas silencing SPHK2 had no effect and the mice developed anaphylaxis. Our data differ from a recent report using SPHK1(-/-) and SPHK2(-/-) mice, which showed that SphK2 was required for FcepsilonRI-mediated mast cell responses. We performed experiments in mast cells derived from SPHK1(-/-) and SPHK2(-/-) mice and show that the calcium response and degranulation, triggered by FcepsilonRI-cross-linking, is not different from that triggered in wild-type cells. Moreover, IgE-mediated anaphylaxis in the knockout mice showed similar levels in temperature changes and serum histamine to that from wild-type mice, indicating that there was no protection from anaphylaxis for either knockout mice. Thus, our data strongly suggest a previously unrecognized compensatory mechanism in the knockout mice, and establishes a role for SphK1 in IgE-mediated mast cell responses.

Topics: Anaphylaxis; Animals; Cell Degranulation; Cells, Cultured; Cross-Linking Reagents; Gene Silencing; Isoenzymes; Male; Mast Cells; Mice; Mice, Inbred BALB C; Mice, Inbred C57BL; Mice, Knockout; Phosphotransferases (Alcohol Group Acceptor); Protein Transport; Receptors, IgE; RNA Interference; Signal Transduction

Sphingosine-1-phosphate, a key mediator in immune cell trafficking, is elevated in the lungs of asthmatic patients and regulates pulmonary epithelium permeability. Stimulation of mast cells by allergens induces two mammalian sphingosine kinases (Sphk1 and Sphk2) to produce sphingosine-1-phosphate (S1P). Little is known about the individual role of these kinases in regulating immune cell function. Here we show that in mast cells, Sphk2 is required for production of S1P, for calcium influx, for activation of protein kinase C, and for cytokine production and degranulation. However, susceptibility to in vivo anaphylaxis is determined both by S1P within the mast cell compartment and by circulating S1P generated by Sphk1 predominantly from a non-mast cell source(s). Thus, sphingosine kinases are determinants of mast cell responsiveness, demonstrating a previously unrecognized relationship with anaphylaxis.

Topics: Anaphylaxis; Animals; Biomarkers; Lysophospholipids; Mast Cells; Mice; Mice, Mutant Strains; Phosphotransferases (Alcohol Group Acceptor); Sphingosine