| Co-Investigator(Kenkyū-buntansha) |
QI Rounei Faculty of Medicine, Yamanashi Med. Univ., Assistant professor, 医学部, 助手 (30303423)
SATOH Kaneo Faculty of Medicine, Yamanashi Med. Univ., Research Assistant, 医学部, 教務職員 (20242662)
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| Budget Amount *help |
¥2,800,000 (Direct Cost: ¥2,800,000)
Fiscal Year 2001: ¥1,300,000 (Direct Cost: ¥1,300,000)
Fiscal Year 2000: ¥1,500,000 (Direct Cost: ¥1,500,000)
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| Research Abstract |
The serum-borne lysophospholipid mediators sphingosine 1-phosphate. (Sph-1-P) and lysophosphatidic acid (LPA) have been shown to be released from activated platelets and to act on endothelial cells. In this study, we employed the repeated lipid extraction (under alkaline and acidic conditions), capable of detecting Sph-1-P, LPA, and possibly structurally-similar lysophospholipids ; a marked formation of [<32>^P]Sph-1-P, but not [32P]LPA, was observed in [<32>^P]orthophosphate-labeled platelets. Platelet Sph-1-P release, possibly mediated by protein kinase C, was greatly enhanced in the presence of albumin, which formed a complex with Sph-1-P. This suggests that platelet Sph-1-P may become accessible to depletion by albumin when its transbilayer movement (flipping) across the plasma membrane is enhanced by protein kinase C. Although human umbilical vein endothelial cells (HUVECs) expressed receptors for both Sph-1-P and LPA, Sph-1-P acted much more potently than LPA on HUVECs, in terms of intracellular Ca^<2+> mobilization, cytoskeletal reorganization, and migration. In HUVECs stimulated with Sph-1-P, I) cytoskeletal signalings may be separable into Gi-mediated signaling pathways (involving Cas) and Rho-mediated ones (involving FAK) and ii) coordinated signalings from both pathways are required for Sph-1 -P-enhanced HUVEC motility. Our results suggest that Sph-l-P, rather than LPA, is a major bioactive lysophospholipid which is released from platelets and interacts with endothelial cells, under the conditions in which critical platelet-endothelial interactions (including thrombosis, angiogenesis, and atherosclerosis) occur. Furthermore, albumin-bound Sph-l-P may account for at least some of the serum biological activities on endothelial cells, which have been ascribed to the effects of albumin-bound LPA based on the similarities between LPA and serum effects.
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