Obesity results from chronic energy surplus and excess lipid storage in white adipose tissue (WAT). In contrast, brown adipose tissue (BAT) efficiently burns lipids through adaptive thermogenesis. Studying mouse models, we show that cyclooxygenase (COX)-2, a rate-limiting enzyme in prostaglandin (PG) synthesis, is a downstream effector of beta-adrenergic signaling in WAT and is required for the induction of BAT in WAT depots. PG shifted the differentiation of defined mesenchymal progenitors toward a brown adipocyte phenotype. Overexpression of COX-2 in WAT induced de novo BAT recruitment in WAT, increased systemic energy expenditure, and protected mice against high-fat diet-induced obesity. Thus, COX-2 appears integral to de novo BAT recruitment, which suggests that the PG pathway regulates systemic energy homeostasis.

To gain insight into the roles of cyclooxygenase (COX)-1 and -2 in human kidney, we analyzed their expressions and localization in adult and fetal normal kidney. Immunohistology showed expression of COX-1 in collecting duct cells, interstitial cells, endothelial cells, and smooth muscle cells of pre- and postglomerular vessels. Expression of COX-2 immunoreactive protein could be localized to endothelial and smooth muscle cells of arteries and veins and intraglomerularly in podocytes. In contrast to the rat, COX isoforms were not detected in the macula densa. These data were confirmed by in situ mRNA analysis using digoxigenin-labeled riboprobes. In fetal kidney, COX-1 was primarily expressed in podocytes and collecting duct cells. Expression levels of COX-1 in both cell types increased markedly from subcapsular to juxtamedullary cortex. Glomerular staining of COX-2 was detectable in podocytes only at the endstage of renal development. In summary, the localization of COX-2 suggests that this enzyme may be primarily involved in the regulation of renal perfusion and glomerular hemodynamics. The expression of COX-1 in podocytes of the fetal kidney and its absence in adult glomeruli suggests that this isoform might be involved in glomerulogenesis.

Nicotinic acid (niacin) has long been used as an antidyslipidemic drug. Its special profile of actions, especially the rise in HDL-cholesterol levels induced by nicotinic acid, is unique among the currently available pharmacological tools to treat lipid disorders. Recently, a G-protein-coupled receptor, termed GPR109A (HM74A in humans, PUMA-G in mice), was described and shown to mediate the nicotinic acid-induced antilipolytic effects in adipocytes. One of the major problems of the pharmacotherapeutical use of nicotinic acid is a strong flushing response. This side effect, although harmless, strongly affects patient compliance. In the present study, we show that mice lacking PUMA-G did not show nicotinic acid-induced flushing. In addition, flushing in response to nicotinic acid was also abrogated in the absence of cyclooxygenase type 1, and mice lacking prostaglandin D 2 (PGD 2 ) and prostaglandin E 2 (PGE 2 ) receptors had reduced flushing responses. The mouse orthologue of GPR109A, PUMA-G, is highly expressed in macrophages and other immune cells, and transplantation of wild-type bone marrow into irradiated PUMA-G-deficient mice restored the nicotinic acid-induced flushing response. Our data clearly indicate that GPR109A mediates nicotinic acid-induced flushing and that this effect involves release of PGE 2 and PGD 2 , most likely from immune cells of the skin.

Artificial mechanical ventilation represents a major cause of iatrogenic lung damage in intensive care. It is largely unknown which mediators, if any, contribute to the onset of such complications. We investigated whether stress caused by artificial mechanical ventilation leads to induction, synthesis, and release of cytokines or eicosanoids from lung tissue. We used the isolated perfused and ventilated mouse lung where frequent perfusate sampling allows determination of mediator release into the perfusate. Hyperventilation was executed with either negative (NPV) or positive pressure ventilation (PPV) at a transpulmonary pressure that was increased 2.5-fold above normal. Both modes of hyperventilation resulted in an approximately 1.75-fold increased expression of tumor necrosis factor alpha (TNFalpha) and interleukin-6 (IL-6) mRNA, but not of cyclooxygenase-2 mRNA. After switching to hyperventilation, prostacyclin release into the perfusate increased almost instantaneously from 19 +/- 17 pg/min to 230 +/- 160 pg/min (PPV) or 115 +/- 87 pg/min (NPV). The enhancement in TNFalpha and IL-6 production developed more slowly. In control lungs after 150 min of perfusion and ventilation, TNFalpha and IL-6 production was 23 +/- 20 pg/min and 330 +/- 210 pg/min, respectively. In lungs hyperventilated for 150 min, TNFalpha and IL-6 production were increased to 287 +/- 180 pg/min and more than 1,000 pg/min, respectively. We conclude that artificial ventilation might cause pulmonary and systemic adverse reactions by inducing the release of mediators into the circulation.

Castor oil is one of the oldest drugs. When given orally, it has a laxative effect and induces labor in pregnant females. The effects of castor oil are mediated by ricinoleic acid, a hydroxylated fatty acid released from castor oil by intestinal lipases. Despite the wide-spread use of castor oil in conventional and folk medicine, the molecular mechanism by which ricinoleic acid acts remains unknown. Here we show that the EP 3 prostanoid receptor is specifically activated by ricinoleic acid and that it mediates the pharmacological effects of castor oil. In mice lacking EP 3 receptors, the laxative effect and the uterus contraction induced via ricinoleic acid are absent. Although a conditional deletion of the EP 3 receptor gene in intestinal epithelial cells did not affect castor oil-induced diarrhea, mice lacking EP 3 receptors only in smooth-muscle cells were unresponsive to this drug. Thus, the castor oil metabolite ricinoleic acid activates intestinal and uterine smooth-muscle cells via EP 3 prostanoid receptors. These findings identify the cellular and molecular mechanism underlying the pharmacological effects of castor oil and indicate a role of the EP 3 receptor as a target to induce laxative effects.G-protein coupled receptor | peristalsis | Ricinus communis | PGE 2

Summary. Background: Platelets release the immune-modulating lipid sphingosine-1-phosphate (S1P). However, the mechanisms of platelet S1P secretion are not fully understood.Objectives: The present study investigates the function of thromboxane (TX) for platelet S1P secretion during platelet activation and the consequences for monocyte chemotaxis. Methods: S1P was detected using thin-layer chromatography in [ 3 H]sphingosine-labeled platelets and by mass spectrometry. Monocyte migration was measured in modified Boyden chamber chemotaxis assays. Results: Release of S1P from platelets was stimulated with protease-activated receptor-1-activating peptide (PAR-1-AP, 100 lM). Acetylsalicylic acid (ASA) and two structurally unrelated reversible cyclooxygenase inhibitors diclofenac and ibuprofen suppressed S1P release. Oral ASA (500-mg single dose or 100 mg over 3 days) attenuated S1P release from platelets in healthy human volunteers ex vivo. This was paralleled by inhibition of TX formation. S1P release was increased by the TX receptor (TP) agonist U-46619, and inhibited by the TP antagonist ramatroban and by inhibitors of ABC-transport. Furthermore, thrombin-induced release of S1P was attenuated in platelets from TP-deficient mice. Supernatants from PAR-1-AP-stimulated human platelets increased the chemotactic capacity of human peripheral monocytes in a S1P-dependent manner via S1P receptors-1 and -3. These effects were inhibited by ASA-pretreatment of platelets. Conclusions: TX synthesis and TP activation mediate S1P release after thrombin receptor activation. Inhibition of this pathway may contribute to the anti-inflammatory actions of ASA, for example by affecting activity of monocytes at sites of vascular injury.

Macrophages are important in the activation of innate immune responses and in a tissue-specific manner in the maintenance of organ homeostasis. Testicular macrophages (TM), which reside in the testicular interstitial space, comprise the largest leukocyte population in the testes and are assumed to play a relevant function in maintaining testicular immune privilege. Numerous studies have indicated that the interstitial fluid (IF) surrounding the TM has immunosuppressive properties, which may influence the phenotype of TM. However, the identity of the immunosuppressive molecules present in the IF is poorly characterized. We show that the rat testicular IF shifted GM-CSF–induced M1 toward the M2 macrophage phenotype. IF-polarized M2 macrophages mimic the properties of TM, such as increased expression of CD163, high secretion of IL-10, and low secretion of TNF-α. In addition, IF-polarized macrophages display immunoregulatory functions by inducing expansion of immunosuppressive regulatory T cells. We further found that corticosterone was the principal immunosuppressive molecule present in the IF and that the glucocorticoid receptor is needed for induction of the testis-specific phenotype of TM. In addition, TM locally produce small amounts of corticosterone, which suppresses the basal expression of inflammatory genes as a means to render TM refractory to inflammatory stimuli. Taken together, these results suggest that the corticosterone present in the testicular environment shapes the immunosuppressive function and phenotype of TM and that this steroid may play an important role in the establishment and sustenance of the immune privilege of the testis.

Abstract-The present experiments were designed to test the hypothesis that prostaglandin (PG) E 2 causes vasodilatation through activation of endothelial NO synthase (eNOS). Aortic rings from mice with targeted deletion of eNOS and E-prostanoid (EP) receptors were used for contraction studies. Blood pressure changes in response to PGE 2 were measured in conscious mice. Single doses of PGE 2 caused concentration-dependent relaxations during contractions to phenylephrine (EC 50 ϭ5*10 Ϫ8 mol/L). Relaxation after PGE 2 was absent in rings without endothelium and in rings from eNOS Ϫ/Ϫ mice and was abolished by N G -nitro-L-arginine methyl ester and the soluble guanylate cyclase inhibitor 1H 1,2,4 -oxadiazolo-[4,3-a]quinoxalin-1-one. In PGE 2 -relaxed aortic rings, the cGMP content increased significantly. PGE 2 -induced relaxations were abolished by the EP4 receptor antagonist AE3-208 (10 Ϫ8 mol/L) and mimicked by an EP4 agonist 10 Ϫ7 mol/L) in the presence of endothelium and eNOS only. Relaxations were attenuated significantly in rings from EP4 Ϫ/Ϫ mice but normal in EP2 Ϫ/Ϫ . Inhibitors of the cAMP-protein kinase A pathway attenuated, whereas the inhibitor of protein phosphatase 1C, calyculin (10 Ϫ8 mol/L), abolished the PGE 2 -mediated relaxation. In aortic rings, PGE 2 dephosphorylated eNOS at Thr 495 . Chronically catheterized eNOS Ϫ/Ϫ mice were hypertensive (137Ϯ3.6 mm Hg, nϭ13, versus 101Ϯ3.9 mm Hg, nϭ9) and exhibited a lower sensitivity of blood pressure reduction in response to PGE 2 compared with wild-type mice. There was no difference in the blood pressure response to nifedipine. These findings show that PGE 2 elicits EP4 receptor-mediated, endothelium-dependent stimulation of eNOS activity by dephosphorylation at Thr 495 resulting in guanylyl cyclase-dependent vasorelaxation and accumulation of cGMP in aortic rings. Key Words: cyclooxygenase Ⅲ cGMP Ⅲ hypertension Ⅲ phosphorylation Ⅲ thromboxane P rostaglandin (PG) E 2 is a physiologically important vasodilator in several vascular beds. 1 PGE 2 can bind to and stimulate a family of specific E-prostanoid (EP) receptors with Ն4 distinct subtypes, EP1 to EP4. Of those, the EP2 and EP4 receptors are functionally associated with vasodilatation. 1 EP2 receptors are less abundant than EP4 in most tissues but are involved in the systemic vasodepressor response to PGE 2 infusion, and targeted deletion of EP2 results in salt-sensitive hypertension. 2,3 PGE 2 signaling through the EP4 receptor contributes to the systemic vasodepressor response to PGE 2 in mice, 4,5 attenuates ischemia-reperfusion injury in the heart, 6 and maintains the patency of the ductus arteriosus in fetal life. 7 Experiments with inhibitors of NO synthase have provided data to suggest that NO is an extracellullar mediator for PGE 2 -mediated vasodilatation in various vascular beds. 8,9 Local infusion of cyclooxygenase inhibitors or NO synthase inhibitors in the renal medulla precipitates hypertension, which would be compatible with a serial coupling between the pathways also at this site. 10,...