Regulation of leptin release and lipolysis by PGE2 in rat adipose tissue

Unloading-Induced Skeletal Interoception Alters Hypothalamic Signaling to Promote Bone Loss and Fat Metabolism

Microgravity is the primary factor that affects human physiology in spaceflight, particularly bone loss and disturbances of the central nervous system. However, little is known about the cellular and molecular mechanisms of these effects. Here, it is reported that in mice hindlimb unloading stimulates expression of neuropeptide Y (NPY) and tyrosine hydroxylase (TH) in the hypothalamus, resulting in bone loss and altered fat metabolism. Enhanced expression of TH and NPY in the hypothalamus occurs downstream of a reduced prostaglandin E2 (PGE2)-mediated ascending interoceptive signaling of the skeletal interoception. Sympathetic antagonist propranolol or deletion of Adrb2 in osteocytes rescue bone loss in the unloading model. Moreover, depletion of TH+ sympathetic nerves or inhibition of norepinephrine release ameliorated bone resorption. Stereotactic inhibition of NPY expression in the hypothalamic neurons reduces the food intake with altered energy expenditure with a limited effect on bone, indicating hypothalamic neuroendocrine factor NPY in the facilitation of bone formation by sympathetic TH activity. These findings suggest that reduced PGE2-mediated interoceptive signaling in response to microgravity or unloading has impacts on the skeletal and central nervous systems that are reciprocally regulated.

Lipid droplet deposition in the regenerating liver: A promoter, inhibitor, or bystander?

Liver regeneration (LR) is a complex process involving intricate networks of cellular connections, cytokines, and growth factors. During the early stages of LR, hepatocytes accumulate lipids, primarily triacylglycerol, and cholesterol esters, in the lipid droplets. Although it is widely accepted that this phenomenon contributes to LR, the impact of lipid droplet deposition on LR remains a matter of debate. Some studies have suggested that lipid droplet deposition has no effect or may even be detrimental to LR. This review article focuses on transient regeneration-associated steatosis and its relationship with the liver regenerative response.

The biological actions of prostanoids in adipose tissue in physiological and pathophysiological conditions

Adipose tissue has been established as an endocrine organ that plays an important role in maintaining metabolic homeostasis. Adipose tissue releases several bioactive molecules called adipokines. Inflammation, dysregulation of adipokine synthesis, and secretion are observed in obesity and related diseases and cause adipose tissue dysfunction. Prostanoids, belonging to the eicosanoid family of lipid mediators, can be synthesized in adipose tissue and play a critical role in adipose tissue biology. In this review, we summarized the current knowledge regarding the interaction of prostanoids with adipokines, the expression of prostanoid receptors, and prostanoid synthase enzymes in adipose tissues in health and disease. Furthermore, the involvement of prostanoids in the physiological function or dysfunction of adipose tissue including inflammation, lipolysis, adipogenesis, thermogenesis, browning of adipocytes, and vascular tone regulation was also discussed by examining studies using pharmacological approaches or genetically modified animals for prostanoid receptors/synthase enzymes. Overall, the present review provides a perspective on the evidence from literature regarding the biological effects of prostanoids in adipose tissue. Among prostanoids, prostaglandin E2 (PGE₂) is prominent in regards to its substantial role in both adipose tissue physiology and pathophysiology. Targeting prostanoids may serve as a potential therapeutic strategy for preventing or treating obesity and related diseases.

Prostaglandin 2α Promotes Autophagy and Mitochondrial Energy Production in Fish Hepatocytes

Fatty liver, characterized by excessive lipid droplet (LD) accumulation in hepatocytes, is a common physiological condition in humans and aquaculture species. Lipid mobilization is an important strategy for modulating the number and size of cellular LDs. Cyclooxygenase (COX)-mediated arachidonic acid derivatives are known to improve lipid catabolism in fish; however, the specific derivatives remain unknown. In the present study, we showed that serum starvation induced LD degradation via autophagy, lipolysis, and mitochondrial energy production in zebrafish hepatocytes, accompanied by activation of the COX pathway. The cellular concentration of PGF2α, but not other prostaglandins, was significantly increased. Administration of a COX inhibitor or interference with PGF2α synthase abolished serum deprivation-induced LD suppression, LD–lysosome colocalization, and expression of autophagic genes. Additionally, exogenous PGF2α suppressed the accumulation of LDs, promoted the accumulation of lysosomes with LD and the autophagy marker protein LC3A/B, and augmented the expression of autophagic genes. Moreover, PGF2α enhanced mitochondrial accumulation and ATP production, and increased the transcript levels of β-oxidation- and mitochondrial respiratory chain-related genes. Collectively, these findings demonstrate that the COX pathway is implicated in lipid degradation induced by energy deprivation, and that PGF2α is a key molecule triggering autophagy, lipolysis, and mitochondrial development in zebrafish hepatocytes.

Inflammatory dysregulation in women with an eating disorder: Relationships with altered emotional reactivity

BACKGROUND

Some studies suggest that inflammatory signaling dysregulation may contribute to eating disorder (ED) pathophysiology. However, little is known about the influence of inflammatory response on altered processes seen among patients with ED, such as emotional processing and reactivity.

OBJECTIVES

The objectives were: (a) to investigate the systemic inflammatory response in ED women; and (b) to analyze the role of inflammatory markers in emotional reactivity.

METHOD

Concentrations of several intercellular and intracellular inflammatory mediators (cytokines, prostaglandin by-products and enzymes, TBARS, and MAPK proteins) were quantified in plasma and PBMCs from 68 women with an ED (m = 22.01 years, SD = 9.15) and 35 healthy controls (m = 18.54 years, SD = 4.21). Moreover, emotional reactivity to affective pictures (those without either food or thinness content) was studied using the adult (>18 years old) sample (n = 41).

RESULTS

Between-group differences were revealed for most markers (TNF-α, PGE₂ , COX2, and ratio of activated MAPK proteins), pointing to increased inflammatory response in patients (p < .01). Women with ED showed heightened emotional reactivity, regardless of picture valence. Principal components derived from inflammatory markers showed an explanatory loading on patient's emotional reaction, in terms of valence and arousal.

CONCLUSION

This study corroborates the altered systemic inflammatory response in patients with ED. The inflammatory dysregulation may contribute to ED phenotype, as seen by its relationship with heightened emotional reactivity, even though the inflammatory markers were not evaluated throughout the emotional reactivity protocol.

Skeleton interoception regulates bone and fat metabolism through hypothalamic neuroendocrine NPY

The central nervous system regulates activity of peripheral organs through interoception. In our previous study, we have demonstrated that PGE2/EP4 skeleton interception regulate bone homeostasis. Here, we show that ascending skeleton interoceptive signaling downregulates expression of hypothalamic neuropeptide Y (NPY) and induce lipolysis of adipose tissue for osteoblastic bone formation. Specifically, the ascending skeleton interoceptive signaling induces expression of small heterodimer partner-interacting leucine zipper protein (SMILE) in the hypothalamus. SMILE binds to pCREB as a transcriptional heterodimer on Npy promoters to inhibit NPY expression. Knockout of EP4 in sensory nerve increases expression of NPY causing bone catabolism and fat anabolism. Importantly, inhibition of NPY Y1 receptor (Y1R) accelerated oxidation of free fatty acids in osteoblasts and rescued bone loss in AvilCre:Ptger4fl/fl mice. Thus, downregulation of hypothalamic NPY expression lipolyzes free fatty acids for anabolic bone formation through a neuroendocrine descending interoceptive regulation.

Oxytocin stimulates lipolysis, prostaglandin E2 synthesis, and leptin secretion in 3T3-L1 adipocytes

A model of oxytocin in the regulation of metabolic status has described one of oxytocin synthesis and release from the neurohypophysis in response to leptin, to suppress further leptin release. In addition, a lipogenic role for oxytocin has been suggested, consistent with an insulinergic action. This model, however, may be incorrect. Oxytocin reduces fat mass in the absence of either leptin or leptin receptor signalling, thereby challenging the interdependence between leptin and oxytocin. An oxytocin induced production of the anti-lipolytic prostaglandin E₂ (PGE₂) might account for this. Media from 3T3-L1 differentiated adipocytes treated with oxytocin (0-50 nmol.L^-1) for 24 hrs were assayed for PGE₂, leptin, adiponectin, and glycerol. Harvested cells were analysed for lipid droplet triglyceride and cytosolic free fatty acid (FFA) by flow cytometry, and for altered expression of lipolytic and lipogenic associated gene ontology transcripts by cDNA array. Both PGE₂ and leptin secretion were significantly increased by oxytocin treatment whilst adiponectin secretion was not. A significant increase in cytosolic FFA was detected following oxytocin treatment, similar to that determined following treatment with isoproterenol (positive control). A significant increase in glycerol release to the culture media confirmed a lipolytic effect. No enrichment of lipolytic and lipogenic associated gene ontology transcripts was determined, but significant overrepresentation of chemosensory olfactory transcripts was. In conclusion, oxytocin stimulates lipolysis in 3T3-L1 adipocytes, mediated by autocrine/paracrine actions of PGE₂ and leptin. To confirm that this response is mediated solely by the oxytocin receptor, further experiments would require those effects being blocked by a specific oxytocin antagonist.

A compendium of G-protein-coupled receptors and cyclic nucleotide regulation of adipose tissue metabolism and energy expenditure

With the ever-increasing burden of obesity and Type 2 diabetes, it is generally acknowledged that there remains a need for developing new therapeutics. One potential mechanism to combat obesity is to raise energy expenditure via increasing the amount of uncoupled respiration from the mitochondria-rich brown and beige adipocytes. With the recent appreciation of thermogenic adipocytes in humans, much effort is being made to elucidate the signaling pathways that regulate the browning of adipose tissue. In this review, we focus on the ligand-receptor signaling pathways that influence the cyclic nucleotides, cAMP and cGMP, in adipocytes. We chose to focus on G-protein-coupled receptor (GPCR), guanylyl cyclase and phosphodiesterase regulation of adipocytes because they are the targets of a large proportion of all currently available therapeutics. Furthermore, there is a large overlap in their signaling pathways, as signaling events that raise cAMP or cGMP generally increase adipocyte lipolysis and cause changes that are commonly referred to as browning: increasing mitochondrial biogenesis, uncoupling protein 1 (UCP1) expression and respiration.

Invalidation of Microsomal Prostaglandin E Synthase-1 (mPGES-1) Reduces Diet-Induced Low-Grade Inflammation and Adiposity

Chronic low-grade inflammation is known to be linked to obesity, and to occur in the early stages of the disease. This mechanism is complex and involves numerous organs, cells, and cytokines. In this context, inflammation of white adipose tissue seems to play a key role in the development of obesity. Because of its properties, prostaglandin E2 (PGE2), an emblematic inflammatory mediator, has been proposed as an actor linking inflammation and obesity. Indeed, PGE2 is involved in mechanisms that are dysregulated in obesity such as lipolysis and adipogenesis. Microsomal prostaglandin E synthase-1 (mPGES-1) is an enzyme, which specifically catalyzes the final step of PGE2 biosynthesis. Interestingly, mPGES-1 invalidation dramatically alters the production of PGE2 during inflammation. In the present work, we sought to determine whether mPGES-1 could contribute to inflammation associated with obesity. To this end, we analyzed the energy metabolism of mPGES-1 deficient mice (mPGES-1^-/-) and littermate controls, fed with a high-fat diet. Our data showed that mPGES-1^-/- mice exhibited resistance to diet-induced obesity when compared to wild-type littermates. mPGES-1^-/- mice fed with a high-fat diet, showed a lower body weight gain and a reduced adiposity, which were accompanied by a decrease in adipose tissues inflammation. We also observed an increase in energy expenditures in mPGES-1^-/- mice fed with a high-fat diet without any changes in activity and browning process. Altogether, these data suggest that mPGES-1 inhibition may prevent diet-induced obesity.

Prostaglandin E2 receptor EP3 regulates both adipogenesis and lipolysis in mouse white adipose tissue

Among the four prostaglandin E2 receptors, EP3 receptor is the one most abundantly expressed in white adipose tissue (WAT). The mouse EP3 gene gives rise to three isoforms, namely EP3α, EP3β, and EP3γ, which differ only at their C-terminal tails. To date, functions of EP3 receptor and its isoforms in WAT remain incompletely characterized. In this study, we found that the expression of all EP3 isoforms were downregulated in WAT of both db/db and high-fat diet-induced obese mice. Genetic ablation of three EP3 receptor isoforms (EP3^-/- mice) or EP3α and EP3γ isoforms with EP3β intact (EP3β mice) led to an obese phenotype with increased food intake, decreased motor activity, reduced insulin sensitivity, and elevated serum triglycerides. Since the differentiation of preadipocytes and mouse embryonic fibroblasts to adipocytes was markedly facilitated by either pharmacological blockade or genetic deletion/inhibition of EP3 receptor via the cAMP/PKA/PPARγ pathway, increased adipogenesis may contribute to obesity in EP3^-/- and EP3β mice. Moreover, both EP3^-/- and EP3β mice had increased lipolysis in WAT mainly due to the activated cAMP/PKA/hormone-sensitive lipase pathway. Taken together, our findings suggest that EP3 receptor and its α and γ isoforms are involved in both adipogenesis and lipolysis and influence food intake, serum lipid levels, and insulin sensitivity.

Characterization of Eicosanoids Produced by Adipocyte Lipolysis: IMPLICATION OF CYCLOOXYGENASE-2 IN ADIPOSE INFLAMMATION

Excessive adipocyte lipolysis generates lipid mediators and triggers inflammation in adipose tissue. However, the specific roles of lipolysis-generated mediators in adipose inflammation remain to be elucidated. In the present study, cultured 3T3-L1 adipocytes were treated with isoproterenol to activate lipolysis and the fatty acyl lipidome of released lipids was determined by using LC-MS/MS. We observed that β-adrenergic activation elevated levels of approximately fifty lipid species, including metabolites of cyclooxygenases, lipoxygenases, epoxygenases, and other sources. Moreover, we found that β-adrenergic activation induced cyclooxygenase 2 (COX-2), not COX-1, expression in a manner that depended on activation of hormone-sensitive lipase (HSL) in cultured adipocytes and in the epididymal white adipose tissue (EWAT) of C57BL/6 mice. We found that lipolysis activates the JNK/NFκB signaling pathway and inhibition of the JNK/NFκB axis abrogated the lipolysis-stimulated COX-2 expression. In addition, pharmacological inhibition of COX-2 activity diminished levels of COX-2 metabolites during lipolytic activation. Inhibition of COX-2 abrogated the induction of CCL2/MCP-1 expression by β-adrenergic activation and prevented recruitment of macrophage/monocyte to adipose tissue. Collectively, our data indicate that excessive adipocyte lipolysis activates the JNK/NFκB pathway leading to the up-regulation of COX-2 expression and recruitment of inflammatory macrophages.

The Prostaglandin E2 Receptor EP4 Regulates Obesity-Related Inflammation and Insulin Sensitivity

With increasing body weight, macrophages accumulate in adipose tissue. There, activated macrophages secrete numerous proinflammatory cytokines and chemokines, giving rise to chronic inflammation and insulin resistance. Prostaglandin E₂ suppresses macrophage activation via EP4; however, the role of EP4 signaling in insulin resistance and type 2 diabetes mellitus remains unknown. In this study, we treated db/db mice with an EP4-selective agonist, ONO-AE1-329, for 4 weeks to explore the role of EP4 signaling in obesity-related inflammation in vivo. Administration of the EP4 agonist did not affect body weight gain or food intake; however, in the EP4 agonist–treated group, glucose tolerance and insulin resistance were significantly improved over that of the vehicle–treated group. Additionally, administration of the EP4 agonist inhibited the accumulation of F4/80-positive macrophages and the formation of crown-like structures in white adipose tissue, and the adipocytes were significantly smaller. The treatment of the EP4 agonist increased the number of anti-inflammatory M2 macrophages, and in the stromal vascular fraction of white adipose tissue, which includes macrophages, it markedly decreased the levels of proinflammatory cytokines and chemokines. Further, EP4 activation increased the expression of adiponectin and peroxidase proliferator–activated receptors in white adipose tissue. Next, we examined in vitro M1/M2 polarization assay to investigate the impact of EP4 signaling on determining the functional phenotypes of macrophages. Treatment with EP4 agonist enhanced M2 polarization in wild-type peritoneal macrophages, whereas EP4-deficient macrophages were less susceptible to M2 polarization. Notably, antagonizing peroxidase proliferator–activated receptor δ activity suppressed EP4 signaling-mediated shift toward M2 macrophage polarization. Thus, our results demonstrate that EP4 signaling plays a critical role in obesity-related adipose tissue inflammation and insulin resistance by regulating macrophage recruitment and polarization. The activation of EP4 signaling holds promise for treating obesity and type 2 diabetes mellitus.

Hypoxia and adipose tissue function and dysfunction in obesity

The rise in the incidence of obesity has led to a major interest in the biology of white adipose tissue. The tissue is a major endocrine and signaling organ, with adipocytes, the characteristic cell type, secreting a multiplicity of protein factors, the adipokines. Increases in the secretion of a number of adipokines occur in obesity, underpinning inflammation in white adipose tissue and the development of obesity-associated diseases. There is substantial evidence, particularly from animal studies, that hypoxia develops in adipose tissue as the tissue mass expands, and the reduction in Po(2) is considered to underlie the inflammatory response. Exposure of white adipocytes to hypoxic conditions in culture induces changes in the expression of >1,000 genes. The secretion of a number of inflammation-related adipokines is upregulated by hypoxia, and there is a switch from oxidative metabolism to anaerobic glycolysis. Glucose utilization is increased in hypoxic adipocytes with corresponding increases in lactate production. Importantly, hypoxia induces insulin resistance in fat cells and leads to the development of adipose tissue fibrosis. Many of the responses of adipocytes to hypoxia are initiated at Po(2) levels above the normal physiological range for adipose tissue. The other cell types within the tissue also respond to hypoxia, with the differentiation of preadipocytes to adipocytes being inhibited and preadipocytes being transformed into leptin-secreting cells. Overall, hypoxia has pervasive effects on the function of adipocytes and appears to be a key factor in adipose tissue dysfunction in obesity.

Secreted proteins from adipose tissue and skeletal muscle - adipokines, myokines and adipose/muscle cross-talk

White adipose tissue and skeletal muscle are the largest organs in the body and both are composed of distinct cell types. The signature cell of adipose tissue is the adipocyte while myocytes are the defining cell of skeletal muscle. White adipocytes are major secretory cells and this is increasingly apparent also for myocytes. Both cells secrete a range of bioactive proteins, generally termed adipokines in the case of adipocytes and myokines for muscle cells. There has, however, been some confusion over nomenclature and we suggest that the name myokine is restricted to a protein that is secreted from myocytes, while the term adipokine should be used to describe all proteins secreted from any type of adipocyte (white, brown or brite). These definitions specifically exclude proteins secreted from other cells within adipose tissue and muscle, including macrophages. There is some commonality between the myokines and adipokines in that both groups include inflammation-related proteins - for example, IL-6, Il-8 and MCP-1. Adipokines and myokines appear to be involved in local autocrine/paracrine interactions within adipose tissue and muscle, respectively. They are also involved in an endocrine cross-talk with other tissues, including between adipose tissue and skeletal muscle, and this may be bi-directional. For example, IL-6, secreted from myocytes may stimulate lipolysis in adipose tissue, while adipocyte-derived IL-6 may induce insulin resistance in muscle.

The Role of Phospholipase A(2)-derived Mediators in Obesity

Obesity has become an epidemic and its prevalence is increasing exponentially. A great deal of focus has been given to understanding the molecular processes that regulate obesity. The characterization of phospholipase A(2)s, especially adipose-specific PLA(2), have lead to a proposed role of their downstream products in the progression of obesity and obesity related disorders. This review summarizes recent developments in the role of PLA(2) and their downstream effects in the development of metabolic disorders.

Association analysis between the prostaglandin E synthase 2 R298H polymorphism and body mass index in 8079 participants of the KORA study cohort

CONTEXT

The H-allele of the R298H polymorphism in the prostaglandin E synthase 2 (PTGES2) gene was associated with lower risk of diabetes type 2.

AIM

To explore the association between the PTGES2 R298H SNP and body mass index (BMI).

METHODS

We analyzed the R298H SNP (rs13283456) and three haplotype single-nucleotide polymorphisms (rs884115, rs10987883, and rs4837240) covering a 20 kb gene region in population-based surveys of the Kooperative Gesundheitsforschung in der Region Augsburg study cohort with 8079 participants.

RESULTS

A statistically significant difference in BMI between the heterozygous PTGES2 R298H genotype and the homozygous R/R genotype was found in males but not in females. Males with the R/H genotype showed a decrease in BMI of -0.30 BMI units (95% CI: -0.55, -0.04, p = 0.02) in comparison to R/R males. A haplotype comprising the minor allele of PTGES2 R298H showed a significant decrease of -0.23 BMI units in males (-0.45, -0.02; p = 0.04) but not in females. Other haplotypes and haplotype single-nucleotide polymorphisms were not significantly associated with BMI.

CONCLUSION

We found a marginal but significant influence of the PTGES2 298H SNP on BMI in a large population-based study.

Influence of a type 2 diabetes associated prostaglandin E synthase 2 polymorphism on blood prostaglandin E2 levels

In this study we tested whether the type 2 diabetes mellitus associated prostaglandin E synthase 2 arginine to histidine polymorphism at position 298 (R298H) influences prostaglandin E2 levels in humans. Fasting prostaglandin E2 was determined in the blood of subjects carrying different genotypes of the R298H polymorphism. Subjects were matched by sex, age, and body mass index. No differences in prostaglandin E2 levels were found with respect to genotypes when considering the whole group. Male homozygous histidine carriers showed elevated prostaglandin E2 levels compared to heterozygous carriers and homozygous arginine carriers (188.2+/-42.4 vs. 80.4+/-26.5pg/ml, p=0.021; and vs. 92.9+/-15.3pg/ml, p=0.11). These differences were not evident in female subjects. In contrast, 6-keto-prostaglandin F1alpha levels as independent marker of arachidonic acid metabolism showed ambiguous results. Nevertheless, preliminary evidence of the prostaglandin E synthase 2 R298H polymorphism possibly influencing prostaglandin E2 blood levels in a gender-specific manner was obtained.

The role of dietary fat in adipose tissue metabolism

Energy intake and expenditure tend on average to remain adjusted to each other in order to maintain a stable body weight, which is only likely to be sustained if the fuel mix oxidised is equivalent to the nutrient content of the diet. Whereas protein and carbohydrate degradation and oxidation are closely adjusted to their intakes, fat balance regulation is less precise and that fat is more likely to be stored than oxidised. It has been demonstrated that dietary fatty acids have an influence not only on the fatty acid composition of membrane phospholipids, thus modulating several metabolic processes that take place in the adipocyte, but also on the composition and the quantity of different fatty acids in adipose tissue. Moreover, dietary fatty acids also modulate eicosanoid presence, which have hormone-like activities in lipid metabolism regulation in adipose tissue. Until recently, the adipocyte has been considered to be no more than a passive tissue for storage of excess energy. However, there is now compelling evidence that adipocytes have a role as endocrine secretory cells. Some of the adipokines produced by adipose tissue, such as leptin and adiponectin, act on adipose tissue in an autocrine/paracrine manner to regulate adipocyte metabolism. Furthermore, dietary fatty acids may influence the expression of adipokines. The nutrients are among the most influential of the environmental factors that determine the way adipose tissue genes are expressed by functioning as regulators of gene transcription. Therefore, not only dietary fat amount but also dietary fat composition influence adipose tissue metabolism.

Association of prostaglandin E synthase 2 (PTGES2) Arg298His polymorphism with type 2 diabetes in two German study populations

CONTEXT

On the basis of its chromosomal localization and its role in the synthesis of the antilipolytic compound prostaglandin E(2), the prostaglandin E synthase 2 (PTGES2) is a candidate gene for type 2 diabetes.

OBJECTIVE

The aim of the present study was to investigate whether genetic variants in the PTGES2 gene are associated with type 2 diabetes.

RESULTS

Sequencing of the PTGES2 gene revealed one nonsynonymous coding single-nucleotide polymorphism (SNP) (Arg298His, rs13283456) and a previously unknown promoter SNP g.-417G>T. Both SNPs and additional haplotype tagging SNPs (rs884115, rs10987883, rs4837240) were genotyped in a nested case-control study of 192 incident type 2 diabetes subjects and 384 controls (European Prospective Investigation into Cancer and Nutrition-Potsdam). Carriers of the minor allele of Arg298His had a lower risk to develop the disease [odds ratio (OR) 0.63, 95% confidence interval (CI) 0.41-0.97, P = 0.04], compared with homozygous individuals with the common allele. The PTGES2 Arg298His polymorphism was reinvestigated in a population-based cross-sectional study (Cooperative Health Research in the Augsburg Region) consisting of 239 individuals with impaired glucose tolerance, 226 with type 2 diabetes, and 863 normoglycemic controls. In this study population, the Arg298His polymorphism was significantly associated with impaired glucose tolerance (OR 0.68, 95% CI 0.50-0.93, P = 0.007) and type 2 diabetes (OR 0.61, 95% CI 0.43-0.86, P = 0.004). A pooled analysis of data from both study populations revealed reduced risk of type 2 diabetes (OR 0.62, 95% CI 0.47-0.81, P = 0.0005) in PTGES2 298His allele carriers.

CONCLUSION

We obtained evidence from two Caucasian study populations that the His298-allele of PTGES2 Arg298His confers to reduced risk of type 2 diabetes.

Night eating and obesity in the EP3R-deficient mouse

Adult mice carrying a null mutation of the prostanoid receptor EP3R (EP3R(-/-) mice) exhibit increased frequency of feeding during the light cycle of the day and develop an obese phenotype under a normal fat diet fed ad libitum. EP3R(-/-) mice show increased motor activity, which is not sufficient to offset the increased feeding leading to increased body weight. Altered "nocturnal" activity and feeding behavior is present from a very early age and does not seem to require age-dependent factors for the development of obesity. Obesity in EP3R(-/-) mice is characterized by elevated leptin and insulin levels and >20% higher body weight compared with WT littermates. Abdominal and subcutaneous fat and increased liver weight account for the weight increase in EP3R(-/-) mice. These observations expand the roles of prostaglandin E(2) signaling in metabolic regulation beyond the reported stimulation of leptin release from adipose tissue to involve actions mediated by EP3R in the regulation of sleep architecture and feeding behavior. The findings add to the growing literature on links between inflammatory signaling and obesity.

Prostaglandin D2 and J2-series (PGJ2, Delta12-PGJ2) prostaglandins stimulate IL-6 and MCP-1, but inhibit leptin, expression and secretion by 3T3-L1 adipocytes

Prostaglandin D(2) and its derivatives PGJ(2) and Delta(12)-PGJ(2) strongly stimulate the synthesis and secretion by white adipocytes of the neurotrophin NGF. Here we have explored whether PGD(2) and the J(2)-series prostaglandins have pervasive effects on adipokine production. The influence of these prostaglandins on the production of the adipocyte hormones leptin and adiponectin, and the inflammatory factors IL-6 and monocyte chemoattractant protein 1 (MCP-1), were examined in 3T3-L1 adipocytes. PGD(2) induced a reduction in adiponectin and leptin mRNA, and the secretion of these adipokines was also inhibited, the effect being greater with leptin (up to 10-fold) than with adiponectin (twofold). In contrast, PGD(2) induced a marked stimulation of IL-6 and MCP-1 expression; with IL-6, this was rapid, the mRNA level increasing by >50-fold by 1 h. The rise in mRNA was accompanied by an increase in IL-6 and MCP-1 release (up to 100- and 6.5-fold, respectively). The effects of PGD(2) were generally mirrored by PGJ(2) and Delta(12)-PGJ(2); Delta(12)-PGJ(2) was a particularly strong stimulator of IL-6 production. These results indicate that PGD(2) and the J(2)-series prostaglandins PGJ(2) and Delta(12)-PGJ(2) can have major effects on the synthesis and release of key adipokines. Such effects could be important in the inflammatory response in adipose tissue.

The effect of carbonic anhydrase inhibition on leptin secretion by rat adipose tissue

It is well known that the role of leptin in the body is to regulate food intake and energy expenditure but the process of leptin secretion by adipose tissue and the components involved in this process are still obscure. Carbonic anhydrase III (CA III) is the most abundant protein of the rat adipose tissue and its amount decreases with obesity. The effect of the inhibition of CA III on leptin secretion by rat epididymal adipose tissue was examined. Dorzolamide, a CA inhibitor, caused a decrease in dexamethasone and insulin-induced leptin secretion suggesting a possible role for CA III in the mechanism of leptin secretion.

Regulation of leptin release by insulin, glucocorticoids, G(i)-coupled receptor agonists, and pertussis toxin in adipocytes and adipose tissue explants from obese humans in primary culture

The basal release of leptin by adipocytes from massively obese human subjects incubated for 48 hours in serum-free suspension culture was comparable to that by explants of subcutaneous adipose tissue from the same obese individuals. There was no stimulation due to dexamethasone or insulin alone of leptin release by adipocytes. However, the combination of insulin and dexamethasone doubled leptin release by adipocytes. The release of leptin was also stimulated by agonists of G(i)-coupled receptors (prostaglandin E(2) [PGE(2)], brimonidine [an alpha(2) catecholamine agonist] and cyclopentyladenosine [CPA]) in the presence of dexamethasone. Leptin release by these agents was further enhanced by insulin in both adipocytes and adipose tissue. Pertussis toxin, which irreversibly inactivates G(i) heterotrimers, inhibited leptin release and abolished the stimulatory effects of G(i)-coupled receptor agonists. However, pertussis toxin did not block the stimulation of leptin release by insulin in either adipose tissue or adipocytes. These data indicate that the release of leptin by human adipocytes cultured for 48 hours in a serum-free medium is comparable to that by explants of adipose tissue except that dexamethasone stimulation of leptin release requires the presence of insulin.

Obesity is induced in mice heterozygous for cyclooxygenase-2

In mice heterozygous for the cyclooxygenase-2 gene (COX-2+/-) the body weight was enhanced by 33% as compared to homozygous COX-2-/- mice. The weights of the gonadal fat pads in COX-2+/- mice were enhanced by 3.5 to 4.7 fold as compared to COX-2-/- mice and by 1.5 to 3.5 fold as compared to wild-type controls+/+ Serum leptin levels and leptin release by cultured adipose tissue of COX-2+/- mice were both elevated as compared to either control or COX-2-/- animals. The basal release of PGE2 or 6 keto PGF1alpha per fat pad over a 24 h incubation of adipose tissue was reduced by 80% and 95% respectively in tissue from COX-2-/- mice. NS-398, a specific COX-2 inhibitor, inhibited leptin release by 27% in adipose tissue from control mice, 31% in tissue from COX-1-/- mice and by 23% in tissue from COX-2+/- mice while having no effect on leptin release by adipose tissue from COX-2-/- mice. These data indicate that heterozygous COX-2 mice develop obesity which is not secondary to a defect in leptin release by adipose tissue.