Adiponectin is an anti-diabetic adipokine. Its receptors possess a seven-transmembrane topology with the amino terminus located intracellularly, which is the opposite of G-protein-coupled receptors. Here we provide evidence that adiponectin induces extracellular Ca(2+) influx by adiponectin receptor 1 (AdipoR1), which was necessary for subsequent activation of Ca(2+)/calmodulin-dependent protein kinase kinase beta (CaMKKbeta), AMPK and SIRT1, increased expression and decreased acetylation of peroxisome proliferator-activated receptor gamma coactivator-1alpha (PGC-1alpha), and increased mitochondria in myocytes. Moreover, muscle-specific disruption of AdipoR1 suppressed the adiponectin-mediated increase in intracellular Ca(2+) concentration, and decreased the activation of CaMKK, AMPK and SIRT1 by adiponectin. Suppression of AdipoR1 also resulted in decreased PGC-1alpha expression and deacetylation, decreased mitochondrial content and enzymes, decreased oxidative type I myofibres, and decreased oxidative stress-detoxifying enzymes in skeletal muscle, which were associated with insulin resistance and decreased exercise endurance. Decreased levels of adiponectin and AdipoR1 in obesity may have causal roles in mitochondrial dysfunction and insulin resistance seen in diabetes.

Phospholipase A2 (PLA2) comprises a superfamily of enzymes that hydrolyse the ester bond of phospholipids at the sn-2 position. Among the members of this superfamily, cytosolic PLA2 has attracted attention because it preferentially hydrolyses arachidonoyl phospholipids and is activated by submicromolar concentrations of Ca2+ ions and by phosphorylation by mitogen-activated protein kinases (MAP kinases). Here we investigate the function of cytosolic PLA2 in vivo by using homologous recombination to generate mice deficient in this enzyme. These mice showed a marked decrease in their production of eicosanoids and platelet-activating factor in peritoneal macrophages. Their ovalbumin-induced anaphylactic responses were significantly reduced, as was their bronchial reactivity to methacholine. Female mutant mice failed to deliver offspring, but these could be rescued by administration of a progesterone-receptor antagonist to the mother at term. Considered together with previous findings, our results indicate that cytosolic PLA2 plays a non-redundant role in allergic responses and reproductive physiology.

Lysophosphatidic acid (LPA) is a bioactive lipid mediator with diverse physiological and pathological actions on many types of cells. LPA has been widely considered to elicit its biological functions through three types of G protein-coupled receptors, Edg-2 (endothelial cell differentiation gene-2)/LPA 1 /vzg-1 (ventricular zone gene-1), Edg-4/LPA 2 , and Edg-7/LPA 3 . We identified an orphan G protein-coupled receptor, p2y 9 /GPR23, as the fourth LPA receptor (LPA 4 ). Membrane fractions of RH7777 cells transiently expressing p2y 9 /GPR23 displayed a specific binding for 1-oleoyl-LPA with a K d value of around 45 nM. Competition binding and reporter gene assays showed that p2y 9 /GPR23 preferred structural analogs of LPA with a rank order of 1-oleoyl-> 1-stearoyl-> 1-palmitoyl-> 1-myristoyl-> 1-alkyl-> 1-alkenyl-LPA. In Chinese hamster ovary cells expressing p2y 9 /GPR23, 1-oleoyl-LPA induced an increase in intracellular Ca 2؉ concentration and stimulated adenylyl cyclase activity. Quantitative real-time PCR demonstrated that mRNA of p2y 9 /GPR23 was significantly abundant in ovary compared with other tissues. Interestingly, p2y 9 /GPR23 shares only 20 -24% amino acid identities with Edg-2/LPA 1 , Edg-4/LPA 2 , and Edg-7/LPA 3 , and phylogenetic analysis also shows that p2y 9 /GPR23 is far distant from the Edg family. These facts suggest that p2y 9 /GPR23 has evolved from different ancestor sequences from the Edg family.

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