sphingosine-1-phosphate and Dermatitis--Contact

Sphingosine 1-phosphate (S1P) regulates lymphocyte trafficking via type-1 S1P receptor (S1P(1)) and participates in many pathological conditions. We developed a novel type S1P(1)-selective antagonist, TASP0251078, which is structurally unrelated to S1P. This competitive antagonist inhibited binding of S1P to S1P(1) resulting in reduced signaling downstream of S1P(1), including GTPγS-binding and cAMP formation. TASP0251078 also inhibited S1P-induced cellular responses such as chemotaxis and receptor-internalization. Furthermore, when administered in vivo, TASP0251078 induced lymphopenia in blood, which is different from previously reported effects of other S1P(1)-antagonists. In a mouse contact hypersensitivity model, TASP0251078 effectively suppressed ear swelling, leukocyte infiltration, and hyperplasia. These findings provide the chemical evidence that S1P(1) antagonism is responsible for lymphocyte sequestration from the blood, and suggest that the effect of S1P(1) agonists on lymphocyte sequestration results from their functional antagonism.

Topics: Animals; Chemotaxis; CHO Cells; Cricetinae; Cricetulus; Cyclic AMP; Dermatitis, Contact; Ear; Edema; Female; Guanosine 5'-O-(3-Thiotriphosphate); HEK293 Cells; Humans; Hyperplasia; Leukocytes; Lymphopenia; Lysophospholipids; Male; Mice; Mice, Inbred BALB C; Molecular Structure; Protein Binding; Rats; Rats, Inbred Lew; Receptors, Lysosphingolipid; Sphingosine; Sulfonamides; Triazoles

Dendritic cells (DCs) play a pivotal role in the development of cutaneous contact hypersensitivity (CHS) and atopic dermatitis as they capture and process antigen and present it to T lymphocytes in the lymphoid organs. Recently, it has been indicated that a topical application of the sphingolipid sphingosine 1-phosphate (S1P) prevents the inflammatory response in CHS, but the molecular mechanism is not fully elucidated. Here we indicate that treatment of mice with S1P is connected with an impaired antigen uptake by Langerhans cells (LCs), the initial step of CHS. Most of the known actions of S1P are mediated by a family of five specific G protein-coupled receptors. Our results indicate that S1P inhibits macropinocytosis of the murine LC line XS52 via S1P(2) receptor stimulation followed by a reduced phosphatidylinositol 3-kinase (PI3K) activity. As down-regulation of S1P(2) not only diminished S1P-mediated action but also enhanced the basal activity of LCs on antigen capture, an autocrine action of S1P has been assumed. Actually, S1P is continuously produced by LCs and secreted via the ATP binding cassette transporter ABCC1 to the extracellular environment. Consequently, inhibition of ABCC1, which decreased extracellular S1P levels, markedly increased the antigen uptake by LCs. Moreover, stimulation of sphingosine kinase activity, the crucial enzyme for S1P formation, is connected not only with enhanced S1P levels but also with diminished antigen capture. These results indicate that S1P is essential in LC homeostasis and influences skin immunity. This is of importance as previous reports suggested an alteration of S1P levels in atopic skin lesions.

Topics: Administration, Topical; Animals; Antigens; Cells, Cultured; Dermatitis, Contact; Endocytosis; Female; Homeostasis; Langerhans Cells; Lysophospholipids; Mice; Mice, Inbred BALB C; Phosphatidylinositol 3-Kinase; Phosphorylation; Proto-Oncogene Proteins c-akt; Receptors, Lysosphingolipid; Skin; Sphingosine