Sphingosine-1-phosphate (S1P) is an intracellularly generated bioactive lipid essential for development, vascular integrity, and immunity. These functions are mediated by S1P-selective cell surface G-protein coupled receptors. S1P signaling therefore requires extracellular release of this lipid. Several cell types release S1P and evidence for both plasma membrane transporter-mediated and vesicle-dependent secretion has been presented. Platelets are an important source of S1P and can release it in response to agonists generated at sites of vascular injury. S1P release from agonist-stimulated platelets was measured in the presence of a carrier molecule (albumin) using HPLC-MS/MS. The kinetics and agonist-dependence of S1P release were similar to that of other granule cargo e.g. platelet factor IV (PF4). Agonist-stimulated S1P release was defective in platelets from Unc13dJinx (Munc13-4 null) mice demonstrating a critical role for regulated membrane fusion in this process. Consistent with this observation, platelets efficiently converted fluorescent NBD-sphingosine to its phosphorylated derivative which accumulated in granules. Fractionation of platelet organelles revealed the presence of S1P in both the plasma membrane and in α-granules. Resting platelets contained a second pool of constitutively releasable S1P that was more rapidly labeled by exogenously added sphingosine. Our studies indicate that platelets contain two pools of S1P that are released extracellularly: a readily-exchangeable, metabolically active pool of S1P, perhaps in the plasma membrane, and a granular pool that requires platelet activation and regulated exocytosis for release.
|Number of pages||9|
|Journal||Biochimica et Biophysica Acta - Molecular and Cell Biology of Lipids|
|State||Published - Nov 2014|
Bibliographical noteFunding Information:
Funding: This work was supported by Grant HL56652 and HL082193 from the National Heart, Lung, and Blood Institute ( National Institutes of Health ) to S.W.W. and by Grant GM50388 and HL112788 from the National Heart, Lung, and Blood Institute (National Institutes of Health) to A.J.M. The microscopy was performed using facilities of the Molecular Basis of Human Disease COBRE Imaging Core, which is supported by grant P20RR020171 from the National Institutes of Health.
© 2014 Elsevier B.V.
- Platelet activation
ASJC Scopus subject areas
- Molecular Biology
- Cell Biology