title: Vascular endothelium as a contributor of plasma sphingosine 1-phosphate.
abstract: Sphingosine 1-phosphate (S1P), an abundant lipid mediator in plasma, regulates vascular and immune cells by activating S1P receptors. In this report, we investigated the mechanisms by which high plasma S1P levels are maintained in mice. We found that plasma S1P turns over rapidly with a half-life of approximately 15 minutes, suggesting the existence of a high-capacity biosynthetic source(s). Transplantation of bone marrow from wild-type to Sphk1(-/-)Sphk2(+/-) mice restored plasma S1P levels, suggesting that hematopoietic cells are capable of secreting S1P into plasma. However, plasma S1P levels were not appreciably altered in mice that were thrombocytopenic, anemic, or leukopenic. Surprisingly, reconstitution of Sphk1(-/-)Sphk2(+/-) bone marrow cells into wild-type hosts failed to reduce plasma S1P, suggesting the existence of an additional, nonhematopoietic source for plasma S1P. Adenoviral expression of Sphk1 in the liver of Sphk1(-/-) mice restored plasma S1P levels. In vitro, vascular endothelial cells, but not hepatocytes, secreted S1P in a constitutive manner. Interestingly, laminar shear stress downregulated the expression of S1P lyase (Sgpl) and S1P phosphatase-1 (Sgpp1) while concomitantly stimulating S1P release from endothelial cells in vitro. Modulation of expression of endothelial S1P lyase with small interfering RNA and adenoviral expression altered S1P secretion, suggesting an important role played by this enzyme. These data suggest that the vascular endothelium, in addition to the hematopoietic system, is a major contributor of plasma S1P.
authors.affiliation: Center for Vascular Biology, Department of Cell Biology, University of Connecticut Health Center, Farmington, CT 06030, USA.
authors.forename: Krishnan
authors.initials: K
authors.lastname: Venkataraman
authors.forename: Yong-Moon
authors.initials: YM
authors.lastname: Lee
authors.forename: Jason
authors.initials: J
authors.lastname: Michaud
authors.forename: Shobha
authors.initials: S
authors.lastname: Thangada
authors.forename: Youxi
authors.initials: Y
authors.lastname: Ai
authors.forename: Herbert L
authors.initials: HL
authors.lastname: Bonkovsky
authors.forename: Nehal S
authors.initials: NS
authors.lastname: Parikh
authors.forename: Cheryl
authors.initials: C
authors.lastname: Habrukowich
authors.forename: Timothy
authors.initials: T
authors.lastname: Hla
mesh_terms: D000256:Adenoviridae / Q000235:genetics; D000446:Aldehyde-Lyases / Q000235:genetics / Q000378:metabolism; D000740:Anemia / Q000097:blood / Q000139:chemically induced; D000818:Animals; D000911:Antibodies, Monoclonal; D001854:Bone Marrow Cells / Q000201:enzymology / Q000378:metabolism* / Q000528:radiation effects; D016026:Bone Marrow Transplantation; D002460:Cell Line; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D004195:Disease Models, Animal; D042783:Endothelial Cells / Q000201:enzymology / Q000378:metabolism*; D004730:Endothelium, Vascular / Q000201:enzymology / Q000378:metabolism*; D005822:Genetic Vectors; D006207:Half-Life; D006801:Humans; D007970:Leukopenia / Q000097:blood; D008099:Liver / Q000201:enzymology / Q000378:metabolism; D008246:Lysophospholipids / Q000097:blood / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D010659:Phenylhydrazines; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D019038:Platelet Glycoprotein GPIb-IX Complex / Q000276:immunology; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism; D013110:Sphingosine / Q000031:analogs & derivatives* / Q000097:blood / Q000378:metabolism; D013314:Stress, Mechanical; D013921:Thrombocytopenia / Q000097:blood / Q000276:immunology; D013997:Time Factors; D014161:Transduction, Genetic; D014916:Whole-Body Irradiation; D000099157:Sphingosine Kinase
chemical_list: D000446:Aldehyde-Lyases; D000911:Antibodies, Monoclonal; D008246:Lysophospholipids; D008565:Membrane Proteins; D010659:Phenylhydrazines; D010744:Phosphoric Monoester Hydrolases; D017853:Phosphotransferases (Alcohol Group Acceptor); D019038:Platelet Glycoprotein GPIb-IX Complex; D034741:RNA, Small Interfering; D013110:Sphingosine; D000099157:Sphingosine Kinase; C030299:phenylhydrazine; C060506:sphingosine 1-phosphate; C401298:sphingosine-1-phosphate phosphatase; C022649:sphingosine 1-phosphate lyase (aldolase)