The bioactive lysophospholipid mediator sphingosine-1-phosphate (S1P) promotes the egress of newly formed T cells from the thymus and the release of immature B cells from the bone marrow. It has remained unclear, however, where and how S1P is released. Here, we show that in mice, the S1P transporter spinster homolog 2 (Spns2) is responsible for the egress of mature T cells and immature B cells from the thymus and bone marrow, respectively. Global Spns2-KO mice exhibited marked accumulation of mature T cells in thymi and decreased numbers of peripheral T cells in blood and secondary lymphoid organs. Mature recirculating B cells were reduced in frequency in the bone marrow as well as in blood and secondary lymphoid organs. Bone marrow reconstitution studies revealed that Spns2 was not involved in S1P release from blood cells and suggested a role for Spns2 in other cells. Consistent with these data, endothelia-specific deletion of Spns2 resulted in defects of lymphocyte egress similar to those observed in the global Spns2-KO mice. These data suggest that Spns2 functions in ECs to establish the S1P gradient required for T and B cells to egress from their respective primary lymphoid organs. Furthermore, Spns2 could be a therapeutic target for a broad array of inflammatory and autoimmune diseases.

APJ is a G-protein-coupled receptor with seven transmembrane domains, and its endogenous ligand, apelin, was identified recently. They are highly expressed in the cardiovascular system, suggesting that APJ is important in the regulation of blood pressure. To investigate the physiological functions of APJ, we have generated mice lacking the gene encoding APJ. The base-line blood pressure of APJ-deficient mice is equivalent to that of wild-type mice in the steady state. The administration of apelin transiently decreased the blood pressure of wild-type mice and a hypertensive model animal, a spontaneously hypertensive rat. On the other hand, this hypotensive response to apelin was abolished in APJ-deficient mice. This apelininduced response was inhibited by pretreatment with a nitric-oxide synthase inhibitor, and apelin-induced phosphorylation of endothelial nitric-oxide synthase in lung endothelial cells from APJ-deficient mice disappeared. In addition, APJ-deficient mice showed an increased vasopressor response to the most potent vasoconstrictor angiotensin II, and the base-line blood pressure of double mutant mice homozygous for both APJ and angiotensin-type 1a receptor was significantly elevated compared with that of angiotensintype 1a receptor-deficient mice. These results demonstrate that APJ exerts the hypotensive effect in vivo and plays a counterregulatory role against the pressor action of angiotensin II.A family of G protein-coupled receptors bind a large variety of ligands and plays an essential role for physiological functions in vivo including the maintenance of homeostasis in the cardiovascular system. APJ (a putative receptor protein related to the angiotensin-type 1 receptor (AT1)) 1 is a G protein-coupled receptor that was isolated from human genomic DNA using the polymerase chain reaction (1). The APJ has a 31% amino acid sequence homology with the AT1, but APJ does not display specific binding for angiotensin II, which is the ligand of AT1 and exerts a pressor action in the blood pressure regulation (1). Recently, the endogenous ligand of APJ was identified from bovine stomach, and this peptide was named apelin (for APJ endogenous ligand) (2). APJ and apelin are expressed in several tissues including the cardiovascular and the central nervous systems (3-6), and the structure of APJ and apelin is highly conserved among species, suggesting its important physiological roles.Intravenous administration of apelin suggested a hypotensive effect in rat (5, 7-9). On the other hand, apelin potently contracts human saphenous vein smooth muscle cells in vitro (10), indicating that apelin is a potent vasoconstrictor. Thus, at this moment, the action of apelin in blood pressure regulation is controversial, and it is still unclear whether these actions of apelin are really through APJ because of the absence of specific receptor blocker to clarify the in vivo functions of APJ. Therefore, in this study, by using animal models such as APJ-deficient mice, APJ/AT1a double knock-out mice, and spontaneously hypertens...

Bile acid homeostasis is tightly controlled by the feedback mechanism in which an atypical orphan nuclear receptor (NR) small heterodimer partner (SHP) inactivates several NRs such as liver receptor homologue-1 and hepatocyte nuclear factor 4. Although NRs have been implicated in the transcriptional regulation of gluconeogenic genes, the effect of bile acids on gluconeogenic gene expression remained unknown. Here, we report that bile acids inhibit the expression of gluconeogenic genes, including glucose-6-phosphatase (G6Pase), phosphoenolpyruvate carboxykinase, and fructose 1,6-bis phosphatase in an SHP-dependent fashion. Cholic acid diet decreased the mRNA levels of these gluconeogenic enzymes, whereas those of SHP were increased. Reporter assays demonstrated that the promoter activity of phosphoenolpyruvate carboxykinase and fructose 1,6-bis phosphatase via hepatocyte nuclear factor 4, or that of G6Pase via the forkhead transcription factor Foxo1, was down-regulated by treatment with chenodeoxicholic acid and with transfected SHP. Remarkably, Foxo1 interacted with SHP in vivo and in vitro, which led to the repression of Foxo1-mediated G6Pase transcription by competition with a coactivator cAMP response element-binding proteinbinding protein. These findings reveal a novel mechanism by which bile acids regulate gluconeogenic gene expression via an SHP-dependent regulatory pathway.