Pronounced adipogenesis and increased insulin sensitivity caused by overproduction of prostaglandin D2 in vivo

Benefit of using interaction effects for the analysis of high-dimensional time-response or dose-response data for two-group comparisons

High throughput RNA sequencing experiments are widely conducted and analyzed to identify differentially expressed genes (DEGs). The statistical models calculated for this task are often not clear to practitioners, and analyses may not be optimally tailored to the research hypothesis. Often, interaction effects (IEs) are the mathematical equivalent of the biological research question but are not considered for different reasons. We fill this gap by explaining and presenting the potential benefit of IEs in the search for DEGs using RNA-Seq data of mice that receive different diets for different time periods. Using an IE model leads to a smaller, but likely more biologically informative set of DEGs compared to a common approach that avoids the calculation of IEs.

Effects of Tylophora yunnanensis Schltr on regulating the gut microbiota and its metabolites in non-alcoholic steatohepatitis rats by inhibiting the activation of NOD-like receptor protein 3

ETHNOPHARMACOLOGICAL RELEVANCE

Tylophora yunnanensis Schltr (TYS) is widely distributed in Yunnan, Guizhou, and other places in China. It is commonly used by folks to treat hepatitis and other liver-related diseases; however, its mechanism of action is still unclear.

AIM OF THE STUDY

This study aimed to determine the effects of TYS on regulating gut microbiota and its metabolites in non-alcoholic steatohepatitis (NASH) rats by inhibiting the activation of NOD-like receptor protein3 (NLRP3).

MATERIAL AND METHODS

An HFD-induced rat model was established to investigate if the intragastric administration of TYS could mediate gut microbiota and their metabolites to ultimately improve the symptoms of NASH. The improving effects of TYS on NASH rats were assessed by measuring their body weight, lipid levels, histopathology, and inflammatory factor levels in the rat models. The regulatory effects of TYS on NLRP3 in the NASH rats were analyzed using real-time quantitative reverse transcription polymerase chain reaction (RT-qPCR) and enzyme-linked immunosorbent assay (ELISA), which determined the levels of NLRP3-related factors. The changes in the composition of the gut microbiota of NASH rats were analyzed using 16S rRNA gene sequencing technology. Meanwhile, the Ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was used for the non-targeted analysis of metabolites in the cecum contents.

RESULTS

The results showed that TYS could improve NASH by decreasing the body weight and levels of lipid, AST, ALT, LPS, FFA, VLDL, IL-1β, IL-6, TNF-α, TGF-β, NLRP3, ASC, and Caspase-1 in the NASH rats. The analysis of gut microbiota showed that TYS could improve the diversity and abundance of gut microbiota and alter their composition by decreasing the Firmicutes/Bacteroidetes (F/B) ratio and relative abundances of Lachnospiraceae, Christensenellaceae, Blautia, etc. while increasing those of Muribaculaceae, Rumiaococcus, Ruminococcaceae, etc. The analysis of metabolites in the cecum contents suggested that the arachidonic acid metabolism, bile secretion, serotonergic synapse, Fc epsilon RI signaling pathway, etc. were regulated by TYS. The metabolites enriched in these pathways mainly included chenodeoxycholic acid, prostaglandin D2, TXB2, 9-OxoODE, and 13(S)-HOTrE.

CONCLUSIONS

These findings suggested that TYS could alleviate the NASH symptoms by decreasing the body weight, regulating the lipid levels, reducing the inflammatory response, and inhibiting the expression levels of NLRP3, ASC, and Caspase-1 in the NASH rats. The changes in the composition of gut microbiota and their metabolic disorder were closely related to the activation of NLRP3. TYS could significantly inhibit the activation of NLRP3 and regulate the composition of gut microbiota and the disorder of metabolites during NASH modeling.

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.

Islet Gene View-a tool to facilitate islet research

Characterization of gene expression in pancreatic islets and its alteration in type 2 diabetes (T2D) are vital in understanding islet function and T2D pathogenesis. We leveraged RNA sequencing and genome-wide genotyping in islets from 188 donors to create the Islet Gene View (IGW) platform to make this information easily accessible to the scientific community. Expression data were related to islet phenotypes, diabetes status, other islet-expressed genes, islet hormone-encoding genes and for expression in insulin target tissues. The IGW web application produces output graphs for a particular gene of interest. In IGW, 284 differentially expressed genes (DEGs) were identified in T2D donor islets compared with controls. Forty percent of DEGs showed cell-type enrichment and a large proportion significantly co-expressed with islet hormone-encoding genes; glucagon (<i>GCG</i>, 56%), amylin (<i>IAPP</i>, 52%), insulin (<i>INS</i>, 44%), and somatostatin (<i>SST</i>, 24%). Inhibition of two DEGs, <i>UNC5D</i> and <i>SERPINE2</i>, impaired glucose-stimulated insulin secretion and impacted cell survival in a human β-cell model. The exploratory use of IGW could help designing more comprehensive functional follow-up studies and serve to identify therapeutic targets in T2D.

Lipid metabolism disorders and lipid mediator changes of mice in response to long-term exposure to high-fat and high sucrose diets and ameliorative effects of mulberry leaves

Mulberry leaves exhibit anti-lipogenic and lipid-lowering effects. However, the lipid biomarkers and underlying mechanisms for the improvement of the action of mulberry leaves on obesity and lipid metabolism disorders have not been sufficiently investigated yet. Herein, biochemical analysis combined with metabolomics targeting serum lipid mediators (oxylipins) were used to explore the efficacy and underlying mechanisms of mulberry leaf water extract (MLWE) in high-fat and high-sucrose diet (HFHSD)-fed mice. Our results showed that MLWE supplementation not only decreased body weight gain, serum total triglycerides, low-density lipoprotein cholesterol, alanine transaminase and aspartate transaminase levels, but also increased the serum level of high-density lipoprotein cholesterol. In addition, MLWE supplementation also ameliorated hepatic steatosis and lipid accumulation. These beneficial effects were associated with down-regulating genes involved in oxidative stress, inflammation, and lipogenesis such as acetyl-CoA carboxylase and fatty acid synthase, and up-regulating genes related to lipolysis that encoded peroxisome proliferator-activated receptor α, adiponectin (ADPN), adiponectin receptor (AdipoR) 1, AdipoR2, adenosine monophosphate-activated protein kinase (AMPK) and hormone-sensitive lipase. Moreover, a total of 54 serum lipid mediators were differentially changed in HFHSD-fed mice, among which 11 lipid mediators from n-3 polyunsaturated fatty acids (PUFAs) were apparently reversed by MLWE. These findings indicated that the ADPN/AMPK pathway, anti-inflammation, anti-oxidation, and n-3 PUFA metabolism played important roles in anti-obesity and improvement of lipid metabolism disorders modulated by MLWE supplementation.

Fluoxetine-induced hepatic lipid accumulation is mediated by prostaglandin endoperoxide synthase 1 and is linked to elevated 15-deoxy-Δ12,14 PGJ2

Major depressive disorder and other neuropsychiatric disorders are often managed with long-term use of antidepressant medication. Fluoxetine, an SSRI antidepressant, is widely used as a first-line treatment for neuropsychiatric disorders. However, fluoxetine has also been shown to increase the risk of metabolic diseases such as non-alcoholic fatty liver disease. Fluoxetine has been shown to increase hepatic lipid accumulation in vivo and in vitro. In addition, fluoxetine has been shown to alter the production of prostaglandins which have also been implicated in the development of non-alcoholic fatty liver disease. The goal of this study was to assess the effect of fluoxetine exposure on the prostaglandin biosynthetic pathway and lipid accumulation in a hepatic cell line (H4-II-E-C3 cells). Fluoxetine treatment increased mRNA expression of prostaglandin biosynthetic enzymes (Ptgs1, Ptgs2, and Ptgds), PPAR gamma (Pparg), and PPAR gamma downstream targets involved in fatty acid uptake (Cd36, Fatp2, and Fatp5) as well as production of 15-deoxy-Δ^12,14 PGJ₂ a PPAR gamma ligand. The effects of fluoxetine to induce lipid accumulation were attenuated with a PTGS1 specific inhibitor (SC-560), whereas inhibition of PTGS2 had no effect. Moreover, SC-560 attenuated 15-deoxy-Δ^12,14 PGJ₂ production and expression of PPAR gamma downstream target genes. Taken together these results suggest that fluoxetine-induced lipid abnormalities appear to be mediated via PTGS1 and its downstream product 15d-PGJ₂ and suggest a novel therapeutic target to prevent some of the adverse effects of fluoxetine treatment.

Biochemical and Structural Characteristics, Gene Regulation, Physiological, Pathological and Clinical Features of Lipocalin-Type Prostaglandin D2 Synthase as a Multifunctional Lipocalin

Lipocalin-type prostaglandin (PG) D₂ synthase (L-PGDS) catalyzes the isomerization of PGH₂, a common precursor of the two series of PGs, to produce PGD₂. PGD₂ stimulates three distinct types of G protein-coupled receptors: (1) D type of prostanoid (DP) receptors involved in the regulation of sleep, pain, food intake, and others; (2) chemoattractant receptor-homologous molecule expressed on T helper type 2 cells (CRTH2) receptors, in myelination of peripheral nervous system, adipocyte differentiation, inhibition of hair follicle neogenesis, and others; and (3) F type of prostanoid (FP) receptors, in dexamethasone-induced cardioprotection. L-PGDS is the same protein as β-trace, a major protein in human cerebrospinal fluid (CSF). L-PGDS exists in the central nervous system and male genital organs of various mammals, and human heart; and is secreted into the CSF, seminal plasma, and plasma, respectively. L-PGDS binds retinoic acids and retinal with high affinities (Kd < 100 nM) and diverse small lipophilic substances, such as thyroids, gangliosides, bilirubin and biliverdin, heme, NAD(P)H, and PGD₂, acting as an extracellular carrier of these substances. L-PGDS also binds amyloid β peptides, prevents their fibril formation, and disaggregates amyloid β fibrils, acting as a major amyloid β chaperone in human CSF. Here, I summarize the recent progress of the research on PGD₂ and L-PGDS, in terms of its “molecular properties,” “cell culture studies,” “animal experiments,” and “clinical studies,” all of which should help to understand the pathophysiological role of L-PGDS and inspire the future research of this multifunctional lipocalin.

Transcriptional Network Analysis Reveals the Role of miR-223-5p During Diabetic Corneal Epithelial Regeneration

Diabetes mellitus (DM) is a complex metabolic disorder. Long-term hyperglycemia may induce diabetic keratopathy (DK), which is mainly characterized by delayed corneal epithelial regeneration. MicroRNAs (miRNAs) have been reported to play regulatory roles during tissue regeneration. However, the molecular mechanism by which miRNAs influence epithelial regeneration in DK is largely unknown. In this study, we performed miRNA and mRNA sequencing of regenerative corneal epithelium tissue from streptozotocin-induced type 1 diabetic (T1DM) and wild-type mice to screen for differentially expressed miRNAs and mRNAs. Based on regulatory network analysis, miR-223-5p was selected for subsequent experiments and Hpgds was then identified as a direct target gene. MiR-223-5p downregulation significantly promoted diabetic corneal epithelial wound healing and nerve regeneration. However, the beneficial effects of miR-223-5p inhibition were abolished by an Hpgds inhibitor. Furthermore, mechanistic studies demonstrated that miR-223-5p suppression ameliorated inflammation and enhanced cell proliferation signaling in DK. Taken together, our findings revealed that the regulatory role of miR-223-5p in diabetic corneal epithelial and nerve regeneration by mediating inflammatory processes and cell proliferation signaling. And silencing miR-223-5p may contribute to the development of potential therapeutic strategies for DK.

Lipocalin-type Prostaglandin D2 Synthase appears to function as a Novel Adipokine Preventing Adipose Dysfunction in response to a High Fat Diet

Adipose dysfunction is the primary defect in obesity that contributes to the development of dyslipidemia, insulin resistance, cardiovascular diseases, type 2 diabetes, non-alcoholic fatty liver disease (NAFLD) and some cancers. Previously, we demonstrated the development of NAFLD in lipocalin-type prostaglandin D₂ synthase (L-PGDS) knockout mice regardless of diet. In the present study, we examined the role of L-PGDS in adipose in response to a high fat diet. We observed decreased expression of L-PGDS in adipose tissue and concomitant lower plasma levels in a dietary model of obesity as well as in insulin resistant 3T3-L1 adipocytes. We show reduced adiponectin expression and phosphorylation of AMPK in white adipose tissue of L-PGDS KO mice after 14 weeks on a high fat diet as compared to control C57BL/6 mice. We also observe an increased fat content in L-PGDS KO mice as demonstrated by adipocyte hypertrophy and increased expression of lipogenenic genes. We confirmed our in vivo findings in in vitro 3T3-L1 adipocytes, using an enzymatic inhibitor of L-PGDS (AT56). Rosiglitazone treatment drastically increased L-PGDS expression in insulin resistant 3T3-L1 adipocytes and increased adiponectin expression and AMPK phosphorylation in AT56 treated 3T3-L1 adipocytes. We conclude that the absence of L-PGDS has a deleterious effect on adipose tissue functioning, which further reduces insulin sensitivity in adipose tissue. Consequently, we propose L-PGDS appears to function as a potential member of the adipokine secretome involved in the regulation of the obesity-associated metabolic syndrome.

Role of 2‑series prostaglandins in the pathogenesis of type 2 diabetes mellitus and non‑alcoholic fatty liver disease (Review)

Nowadays, metabolic syndromes are emerging as global epidemics, whose incidence are increasing annually. However, the efficacy of therapy does not increase proportionately with the increased morbidity. Type 2 diabetes mellitus (T2DM) and non-alcoholic fatty liver disease (NAFLD) are two common metabolic syndromes that are closely associated. The pathogenic mechanisms of T2DM and NAFLD have been studied, and it was revealed that insulin resistance, hyperglycemia, hepatic lipid accumulation and inflammation markedly contribute to the development of these two diseases. The 2-series prostaglandins (PGs), a subgroup of eicosanoids, including PGD₂, PGE₂, PGF_2α and PGI₂, are converted from arachidonic acid catalyzed by the rate-limiting enzymes cyclooxygenases (COXs). Considering their wide distribution in almost every tissue, 2-series PG pathways exert complex and interlinked effects in mediating pancreatic β-cell function and proliferation, insulin sensitivity, fat accumulation and lipolysis, as well as inflammatory processes. Previous studies have revealed that metabolic disturbances, such as hyperglycemia and hyperlipidemia, can be improved by treatment with COX inhibitors. At present, an accumulating number of studies have focused on the roles of 2-series PGs and their metabolites in the pathogenesis of metabolic syndromes, particularly T2DM and NAFLD. In the present review, the role of 2-series PGs in the highly intertwined pathogenic mechanisms of T2DM and NAFLD was discussed, and important therapeutic strategies based on targeting 2-series PG pathways in T2DM and NAFLD treatment were provided.

Fish Oil Improves Pathway-Oriented Profiling of Lipid Mediators for Maintaining Metabolic Homeostasis in Adipose Tissue of Prediabetic Rats

Adipose tissue is now recognized as an active organ with an important homeostatic function in glucose and lipid metabolism and the development of insulin resistance. The present research investigates the role of lipid mediators and lipid profiling for controlling inflammation and the metabolic normal function of white adipose tissue from rats suffering from diet-induced prediabetes. Additionally, the contribution to the adipose lipidome induced by the consumption of marine ω-3 PUFAs as potential regulators of inflammation is addressed. For that, the effects on the inflammatory response triggered by high-fat high-sucrose (HFHS) diets were studied in male Sprague-Dawley rats. Using SPE-LC-MS/MS-based metabolo-lipidomics, a range of eicosanoids, docosanoids and specialized pro-resolving mediators (SPMs) were measured in white adipose tissue. The inflammatory response occurring in prediabetic adipose tissue was associated with the decomposition of ARA epoxides to ARA-dihydroxides, the reduction of oxo-derivatives and the formation of prostaglandins (PGs). In an attempt to control the inflammatory response initiated, LOX and non-enzymatic oxidation shifted toward the production of the less pro-inflammatory EPA and DHA metabolites rather than the high pro-inflammatory ARA hydroxides. Additionally, the change in LOX activity induced the production of intermediate hydroxides precursors of SPMs as protectins (PDs), resolvins (Rvs) and maresins (MaRs). This compensatory mechanism to achieve the restoration of tissue homeostasis was significantly strengthened through supplementation with fish oils. Increasing proportions of ω-3 PUFAs in adipose tissue significantly stimulated the formation of DHA-epoxides by cytochrome P450, the production of non-enzymatic EPA-metabolites and prompted the activity of 12LOX. Finally, protectin PDX was significantly reduced in the adipose tissue of prediabetic rats and highly enhanced through ω-3 PUFAs supplementation. Taken together, these actively coordinated modifications constitute key mechanisms to restore adipose tissue homeostasis with an important role of lipid mediators. This compensatory mechanism is reinforced through the supplementation of the diet with fish oils with high and balanced contents of EPA and DHA. The study highlights new insides on the targets for effective treatment of incipient diet-induced diabetes and the mechanism underlying the potential anti-inflammatory action of marine lipids.

Identification and characterization of adipose surface epitopes

Adipose tissue is a central regulator of metabolism and an important pharmacological target to treat the metabolic consequences of obesity, such as insulin resistance and dyslipidemia. Among the various cellular compartments, the adipocyte cell surface is especially appealing as a drug target as it contains various proteins that when activated or inhibited promote adipocyte health, change its endocrine function and eventually maintain or restore whole-body insulin sensitivity. In addition, cell surface proteins are readily accessible by various drug classes. However, targeting individual cell surface proteins in adipocytes has been difficult due to important functions of these proteins outside adipose tissue, raising various safety concerns. Thus, one of the biggest challenges is the lack of adipose selective surface proteins and/or targeting reagents. Here, we discuss several receptor families with an important function in adipogenesis and mature adipocytes to highlight the complexity at the cell surface and illustrate the problems with identifying adipose selective proteins. We then discuss that, while no unique adipocyte surface protein might exist, how splicing, posttranslational modifications as well as protein/protein interactions can create enormous diversity at the cell surface that vastly expands the space of potentially unique epitopes and how these selective epitopes can be identified and targeted.

Role of Mineralocorticoid Receptor in Adipogenesis and Obesity in Male Mice

Increased visceral adiposity and hyperglycemia, 2 characteristics of metabolic syndrome, are also present in conditions of excess glucocorticoids (GCs). GCs are hormones thought to act primarily via the glucocorticoid receptor (GR). GCs are commonly prescribed for inflammatory disorders, yet their use is limited due to many adverse metabolic side effects. In addition to GR, GCs also bind the mineralocorticoid receptor (MR), but there are many conflicting studies about the exact role of MR in metabolic disease. Using MR knockout mice (MRKO), we find that both white and brown adipose depots form normally when compared with wild-type mice at P5. We created mice with adipocyte-specific deletion of MR (FMRKO) to better understand the role of MR in metabolic dysfunction. Treatment of mice with excess GCs for 4 weeks, via corticosterone in drinking water, induced increased fat mass and glucose intolerance to similar levels in FMRKO and floxed control mice. Separately, when fed a high-fat diet for 16 weeks, FMRKO mice had reduced body weight, fat mass, and hepatic steatosis, relative to floxed control mice. Decreased adiposity likely resulted from increased energy expenditure since food intake was not different. RNA sequencing analysis revealed decreased enrichment of genes associated with adipogenesis in inguinal white adipose of FMRKO mice. Differentiation of mouse embryonic fibroblasts (MEFs) showed modestly impaired adipogenesis in MRKO MEFs compared with wild type, but this was rescued upon the addition of peroxisome proliferator-activated receptor gamma (PPARγ) agonist or PPARγ overexpression. Collectively, these studies provide further evidence supporting the potential value of MR as a therapeutic target for conditions associated with metabolic syndrome.

Loss of Endothelial FTO Antagonizes Obesity-Induced Metabolic and Vascular Dysfunction

RATIONALE

Increasing prevalence of obesity and its associated risk with cardiovascular diseases demands a better understanding of the contribution of different cell types within this complex disease for developing new treatment options. Previous studies could prove a fundamental role of FTO (fat mass and obesity-associated protein) within obesity; however, its functional role within different cell types is less understood.

OBJECTIVES

We identify endothelial FTO as a previously unknown central regulator of both obesity-induced metabolic and vascular alterations.

METHODS AND RESULTS

We generated endothelial Fto-deficient mice and analyzed the impact of obesity on those mice. While the loss of endothelial FTO did not influence the development of obesity and dyslipidemia, it protected mice from high-fat diet-induced glucose intolerance and insulin resistance by increasing AKT (protein kinase B) phosphorylation in endothelial cells and skeletal muscle. Furthermore, loss of endothelial FTO prevented the development of obesity-induced hypertension by preserving myogenic tone in resistance arteries. In Fto-deficient arteries, microarray analysis identified upregulation of L-Pgds with significant increases in prostaglandin D₂ levels. Blockade of prostaglandin D₂ synthesis inhibited the myogenic tone protection in resistance arteries of endothelial Fto-deficient mice on high-fat diet; conversely, direct addition of prostaglandin D₂ rescued myogenic tone in high-fat diet-fed control mice. Myogenic tone was increased in obese human arteries with FTO inhibitors or prostaglandin D₂ application.

CONCLUSIONS

These data identify endothelial FTO as a previously unknown regulator in the development of obesity-induced metabolic and vascular changes, which is independent of its known function in regulation of obesity.

Effects of prostaglandin E2 and D2 on cell proliferation and osteogenic capacity of human mesenchymal stem cells

The manifestation of periodontitis-related inflammatory reaction is inevitably bound to the production of prostaglandins E₂ and D₂ which have been suggested to mediate osteoclastic and osteogenic effects within the affected tissue. We demonstrated the presence of PGE₂ and PGD₂ receptors on hMSCs on RNA level and with immunofluorescence. For each Prostaglandin, three concentrations were studied: 0.1; 0.5 or 1.0 µg/ml. A lower expression of EP1 and EP4 (PGE₂ receptors 1 and 4) after stimulation with PGE₂ was shown, thus a tendency to compromise osteogenic differentiation and metabolism. PGE₂ induced a higher growth-rate during the first week, while a continuous inflammatory challenge determined a decrease of the proliferation of hMSCs. PGD₂ inhibited cell growth irrespective of the duration of the stimulation. PGE₂ and PGD₂ have also negative effects on calcium deposition osteogenic, thus on differentiation of hMSCs. PGE₂ and PGD₂ seem to induce bone resorption also having indirectly a negative impact on the osteogenic differentiation of hMSCs. Thus, inhibitors of PGE₂ and PGD₂ can be used as adjunct to mechanical periodontal treatment.

L-PGDS-produced PGD2 in premature, but not in mature, adipocytes increases obesity and insulin resistance

Lipocalin-type prostaglandin (PG) D synthase (L-PGDS) is responsible for the production of PGD₂ in adipocytes and is selectively induced by a high-fat diet (HFD) in adipose tissue. In this study, we investigated the effects of HFD on obesity and insulin resistance in two distinct types of adipose-specific L-PGDS gene knockout (KO) mice: fatty acid binding protein 4 (fabp4, aP2)-Cre/L-PGDS^flox/flox and adiponectin (AdipoQ)-Cre/L-PGDS^flox/flox mice. The L-PGDS gene was deleted in adipocytes in the premature stage of the former strain and after maturation of the latter strain. The L-PGDS expression and PGD₂ production levels decreased in white adipose tissue (WAT) under HFD conditions only in the aP2-Cre/L-PGDS^flox/flox mice, but were unchanged in the AdipoQ-Cre/L-PGDS^flox/flox mice. When fed an HFD, aP2-Cre/L-PGDS^flox/flox mice significantly reduced body weight gain, adipocyte size, and serum cholesterol and triglyceride levels. In WAT of the HFD-fed aP2-Cre/L-PGDS^flox/flox mice, the expression levels of the adipogenic, lipogenic, and M1 macrophage marker genes were decreased, whereas those of the lipolytic and M2 macrophage marker genes were enhanced or unchanged. Insulin sensitivity was improved in the HFD-fed aP2-Cre/L-PGDS^flox/flox mice. These results indicate that PGD₂ produced by L-PGDS in premature adipocytes is involved in the regulation of body weight gain and insulin resistance under nutrient-dense conditions.

A gain-of-function study of amelioration of pentylenetetrazole-induced seizures by endogenous prostaglandin D2

We previously showed that knockout mice of hematopoietic prostaglandin (PG) D synthase (H-PGDS) produce less PGD₂ to exacerbate pentylenetetrazole (PTZ)-induced seizures. Here, we adopted a gain-of-function strategy and used transgenic mice that over-express human H-PGDS enzyme, to elucidate the role of overproduction of endogenous PGD₂ in PTZ-induced seizures. H-PGDS-transgenic mice showed the elevated level of a urinary metabolite of PGD₂, tetranor-PGDM, 3.3- and 2.8-fold higher than the wild-type littermates under the basal condition and after the PTZ administration, respectively, without significantly changing the urinary concentration of a PGE₂-metabolite, tetranor-PGE₂. The intensity of PTZ-induced seizures was decreased in H-PGDS-transgenic mice as evident by the increased seizure onset latency, and a decrease in total duration of generalized tonic-clonic seizures and a total number of EEG seizure spikes during the postictal period (84 s, 17 s, and 5.3/min, respectively), as compared to wild-type mice (53 s, 24 s, and 12.6/min, respectively). These results indicate that overproduction of endogenous PGD₂ decreased PTZ-induces seizures.

Obesity-induced changes in lipid mediators persist after weight loss

BACKGROUND

Obesity induces significant changes in lipid mediators, however, the extent to which these changes persist after weight loss has not been investigated.

SUBJECTS/METHODS

We fed C57BL6 mice a high-fat diet to generate obesity and then switched the diet to a lower-fat diet to induce weight loss. We performed a comprehensive metabolic profiling of lipid mediators including oxylipins, endocannabinoids, sphingosines and ceramides in key metabolic tissues (including adipose, liver, muscle and hypothalamus) and plasma.

RESULTS

We found that changes induced by obesity were largely reversible in most metabolic tissues but the adipose tissue retained a persistent obese metabolic signature. Prostaglandin signaling was perturbed in the obese state and lasting increases in PGD2, and downstream metabolites 15-deoxy PGJ2 and delta-12-PGJ2 were observed after weight loss. Furthermore expression of the enzyme responsible for PGD2 synthesis (hematopoietic prostaglandin D synthase, HPGDS) was increased in obese adipose tissues and remained high after weight loss. We found that inhibition of HPGDS over the course of 5 days resulted in decreased food intake in mice. Increased HPGDS expression was also observed in human adipose tissues obtained from obese compared with lean individuals. We then measured circulating levels of PGD2 in obese patients before and after weight loss and found that while elevated relative to lean subjects, levels of this metabolite did not decrease after significant weight loss.

CONCLUSIONS

These results suggest that lasting changes in lipid mediators induced by obesity, still present after weight loss, may play a role in the biological drive to regain weight.

Sensitive mass spectrometric assay for determination of 15-deoxy-Δ12,14-prostaglandin J2 and its application in human plasma samples of patients with diabetes

The determination of individual prostaglandins (PG) in humans is mainly performed in urine samples. The quantification of PGs in human plasma could improve the understanding of particular PG species under various physiological and pathological conditions. 15-Deoxy-Δ^12,14-prostaglandin J₂ (15d-PGJ₂) is a dehydrated downstream product of PGD₂ and is of high interest due to its recently discovered anti-inflammatory effects. Increasing availability of highly sensitive mass spectrometry allows the quantification of low abundant biomarkers like 15d-PGJ₂ in human plasma samples. Herein, a sensitive LC-MS/MS method for the determination of 15d-PGJ₂ was established. The method was validated according to the guidance of the American Food and Drug Administration and tested in plasma samples from patients with poorly controlled diabetes, considered to be a pro-inflammatory condition. Extraction of 15d-PGJ₂ was achieved with an easy-to-use liquid-liquid extraction by ethyl acetate following a methanol precipitation. The lower limit of quantification was 2.5 pg mL⁻¹ and linearity (R² = 0.998) was guaranteed between 2.5 and 500 pg mL⁻¹ for 15d-PGJ₂. Selectivity was assured by the use of two individual mass transitions (qualifier and quantifier). Precision and accuracy were validated in an inter- and intraday assay with a coefficient of variation below 11.8% (intraday) and 14.7% (interday). In diabetic patients with an HbA_1C > 9%, increased plasma concentrations of 15d-PGJ₂ compared to control plasma were measured. 15d-PGJ₂ correlated negatively with the inflammation marker C-reactive protein. The developed LC-MS/MS method represents a new possibility to quantify 15d-PGJ₂ with high specificity in human plasma samples. This may contribute to a better understanding of the potential anti-inflammatory effects of 15d-PGJ₂ in severe long-term pro-inflammatory disorders like diabetes, cancer, or cardiovascular disease.

Prostaglandin D2 enhances lipid accumulation through suppression of lipolysis via DP2 (CRTH2) receptors in adipocytes

Prostaglandin (PG) D₂ enhanced lipid accumulation in adipocytes. However, its molecular mechanism remains unclear. In this study, we investigated the regulatory mechanisms of PGD₂-elevated lipid accumulation in mouse adipocytic 3T3-L1 cells. The Gi-coupled DP2 (CRTH2) receptors (DP2R), one of the two-types of PGD₂ receptors were dominantly expressed in adipocytes. A DP2R antagonist, CAY10595, but not DP1 receptor antagonist, BWA868C cleared the PGD₂-elevated intracellular triglyceride level. While, a DP2R agonist, 15R-15-methyl PGD₂ (15R) increased the mRNA levels of the adipogenic and lipogenic genes, and decreased the glycerol release level. In addition, the forskolin-mediated increase of cAMP-dependent protein kinase A (PKA) activity and phosphorylation of hormone-sensitive lipase (HSL) was repressed by the co-treatment with 15R. Moreover, the lipolysis was enhanced in the adipocyte-differentiated DP2R gene-knockout mouse embryonic fibroblasts. These results indicate that PGD₂ suppressed the lipolysis by repression of the cAMP-PKA-HSL axis through DP2R in adipocytes.

Mast cell activation disease and the modern epidemic of chronic inflammatory disease

A large and growing portion of the human population, especially in developed countries, suffers 1 or more chronic, often quite burdensome ailments which either are overtly inflammatory in nature or are suspected to be of inflammatory origin, but for which investigations to date have failed to identify specific causes, let alone unifying mechanisms underlying the multiple such ailments that often afflict such patients. Relatively recently described as a non-neoplastic cousin of the rare hematologic disease mastocytosis, mast cell (MC) activation syndrome-suspected to be of greatly heterogeneous, complex acquired clonality in many cases-is a potential underlying/unifying explanation for a diverse assortment of inflammatory ailments. A brief review of MC biology and how aberrant primary MC activation might lead to such a vast range of illness is presented.

Adipocyte Mineralocorticoid Receptor Activation Leads to Metabolic Syndrome and Induction of Prostaglandin D2 Synthase

Metabolic syndrome is a major risk factor for the development of diabetes mellitus and cardiovascular diseases. Pharmacological antagonism of the mineralocorticoid receptor (MR), a ligand-activated transcription factor, limits metabolic syndrome in preclinical models, but mechanistic studies are lacking to delineate the role of MR activation in adipose tissue. In this study, we report that MR expression is increased in visceral adipose tissue in a preclinical mouse model of metabolic syndrome and in obese patients. In vivo conditional upregulation of MR in mouse adipocytes led to increased weight and fat mass, insulin resistance, and metabolic syndrome features without affecting blood pressure. We identified prostaglandin D2 synthase as a novel MR target gene in adipocytes and AT56, a specific inhibitor of prostaglandin D2 synthase enzymatic activity, blunted adipogenic aldosterone effects. Moreover, translational studies showed that expression of MR and prostaglandin D2 synthase is strongly correlated in adipose tissues from obese patients.

Prostaglandin profiling reveals a role for haematopoietic prostaglandin D synthase in adipose tissue macrophage polarisation in mice and humans

BACKGROUND/OBJECTIVES

Obesity has been associated with both changes in adipose tissue lipid metabolism and inflammation. A key class of lipid-derived signalling molecules involved in inflammation are the prostaglandins. In this study, we aimed to determine how obesity affects the levels of prostaglandins within white adipose tissue (WAT) and determine which cells within adipose tissue produce them. To avoid the effects of cellular stress on prostaglandin levels, we developed a multivariate statistical approach in which metabolite concentrations and transcriptomic data were integrated, allowing the assignment of metabolites to cell types.

SUBJECTS/METHODS

Eicosanoids were measured by liquid chromatography-tandem mass spectrometry and mRNA levels using real-time PCR. Eicosanoid levels and transcriptomic data were combined using principal component analysis and hierarchical clustering in order to associate metabolites with cell types. Samples were obtained from C57Bl/6 mice aged 16 weeks. We studied the ob/ob genetically obese mouse model and diet-induced obesity model. We extended our results in mice to a cohort of morbidly obese humans undergoing bariatric surgery.

RESULTS

Using our modelling approach, we determined that prostglandin D₂ (PGD₂) in adipose tissue was predominantly produced in macrophages by the haematopoietic isoform of prostaglandin D synthase (H-Pgds). Analysis of sub-fractionated WAT confirmed that H-Pgds was expressed in adipose tissue macrophages (ATMs). Furthermore, H-Pgds expression in ATMs isolated from lean and obese mice was consistent with it affecting macrophage polarisation. Functionally, we demonstrated that H-PGDS-produced PGD₂ polarised macrophages toward an M2, anti-inflammatory state. In line with a potential anti-inflammatory role, we found that H-PGDS expression in ATMs was positively correlated with both peripheral insulin and adipose tissue insulin sensitivity in humans.

CONCLUSIONS

In this study, we have developed a method to determine the cellular source of metabolites within an organ and used it to identify a new role for PGD₂ in the control of ATM polarisation.

Targeting steroid receptor coactivator 1 with antisense oligonucleotides increases insulin-stimulated skeletal muscle glucose uptake in chow-fed and high-fat-fed male rats

The steroid receptor coactivator 1 (SRC1) regulates key metabolic pathways, including glucose homeostasis. SRC1(-/-) mice have decreased hepatic expression of gluconeogenic enzymes and a reduction in the rate of endogenous glucose production (EGP). We sought to determine whether decreasing hepatic and adipose SRC1 expression in normal adult rats would alter glucose homeostasis and insulin action. Regular chow-fed and high-fat-fed male Sprage-Dawley rats were treated with an antisense oligonucleotide (ASO) against SRC1 or a control ASO for 4 wk, followed by metabolic assessments. SRC1 ASO did not alter basal EGP or expression of gluconeogenic enzymes. Instead, SRC1 ASO increased insulin-stimulated whole body glucose disposal by ~30%, which was attributable largely to an increase in insulin-stimulated muscle glucose uptake. This was associated with an approximately sevenfold increase in adipose expression of lipocalin-type prostaglandin D2 synthase, a previously reported regulator of insulin sensitivity, and an approximately 70% increase in plasma PGD2 concentration. Muscle insulin signaling, AMPK activation, and tissue perfusion were unchanged. Although GLUT4 content was unchanged, SRC1 ASO increased the cleavage of tether-containing UBX domain for GLUT4, a regulator of GLUT4 translocation. These studies point to a novel role of adipose SRC1 as a regulator of insulin-stimulated muscle glucose uptake.

Termination mechanism of CREB-dependent activation of COX-2 expression in early phase of adipogenesis

We elucidated the molecular mechanism of prostaglandin (PG) E2- and PGF2α-mediated suppression of the early phase of adipogenesis through enhanced COX-2 expression in 3T3-L1 cells. 3-Isobutyl-1-methylxanthine, an inhibitor of phosphodiesterase which catalyzes the conversion of cAMP to AMP, enhanced the activity of protein kinase A (PKA). Dibutyryl cAMP activated PKA and enhanced the phosphorylation of cAMP response element (CRE)-binding protein (CREB). The ability of CREB binding to the CRE of the COX-2 promoter was elevated for enhancement of the expression of the COX-2 gene. CREB siRNA suppressed the expression of the COX-2 gene. Furthermore, okadaic acid, a protein phosphatase (PP) 1/2A inhibitor, suppressed the progression of adipogenesis by preventing PP1/2A-mediated suppression of CREB-dependent COX-2 expression, thus resulting in increased production of anti-adipogenic PGE2 and PGF2α. These results indicate that CREB-dependent expression of COX-2 for the production of anti-adipogenic PGs is critical for the regulation of the early phase of adipogenesis.

Transcriptional regulation in adipogenesis through PPARγ-dependent and -independent mechanisms by prostaglandins

Adipogenesis is controlled by complex mechanisms, and transcription factors are involved in its regulation. PPARγ is a ligand-dependent transcription factor and the most important one for adipogenesis. Although prostaglandin (PG) D2 metabolites have been reported as being the ligands of PPARγ, the endogenous PPARγ ligand in adipocytes remains unclear. Here, we show the methods for the general analysis of adipocyte differentiation and the protocols for promoter analysis, fluorescence EMSA, and chromatin immunoprecipitation assay for the transcriptional regulation of the SREBP-1c-activated lipocalin-type PGD synthase gene in adipocytes. Moreover, we describe that PGD2 and its metabolites are involved in the regulation of adipogenesis through PPARγ-dependent and -independent mechanisms.

Opposing immunomodulatory roles of prostaglandin D2 during the progression of skin inflammation

The effects of PGD2 are extremely context dependent. It can have pro- or anti-inflammatory effects in clinically important pathological conditions. A greater mechanistic insight into the determinants of PGD2 activity during inflammation is thus required. In this study, we investigated the role of PGD2 in croton oil-induced dermatitis using transgenic (TG) mice overexpressing hematopoietic PGD synthase. Administration of croton oil caused tissue swelling and vascular leakage in the mouse ear. Compared with wild-type animals, TG mice produced more PGD2 and showed decreased inflammation in the early phase, but more severe manifestations during the late phase. Data obtained from bone marrow transplantation between wild-type and TG mice indicated that PGD2 produced by tissue resident cells in the TG mice attenuated early-phase inflammation, whereas PGD2 produced from hematopoietic lineage cells exacerbated late-phase inflammation. There are two distinct PGD2 receptors: D-prostanoid receptor (DP) and chemoattractant receptor-homologous molecule expressed on Th2 cells (CRTH2). In TG mice, treatment with a DP antagonist exacerbated inflammation in the early phase, whereas treatment with a CRTH2 antagonist attenuated inflammation during the late phase. In vitro experiments showed that DP agonism enhanced vascular endothelial barrier formation, whereas CRTH2 agonism stimulated neutrophil migration. Collectively, these results show that when hematopoietic PGD synthase is overexpressed, tissue resident cell-derived PGD2 suppresses skin inflammation via DP in the early phase, but hematopoietic lineage cell-derived PGD2 stimulates CRTH2 and promotes inflammation during the late phase. DP-mediated vascular barrier enhancement or CRTH2-mediated neutrophil activation may be responsible for these effects. Thus, PGD2 represents opposite roles in inflammation, depending on the disease phase in vivo.

The beneficial role of vitamin D in obesity: possible genetic and cell signaling mechanisms

The prevalence rates of overweight and obesity are considered an important public issue in the United States, and both of these conditions are increasing among both children and adults. There is evidence of aberrations in the vitamin D-endocrine system in obese subjects. Vitamin D deficiency is highly prevalent in patients with obesity, and many studies have demonstrated the significant effect of calcitriol on adipocytes. Genetic studies have provided an opportunity to determine which proteins link vitamin D to obesity pathology, including the vitamin D receptor, toll-like receptors, the renin-angiotensin system, apolipoprotein E, vascular endothelial growth factor, and poly (ADP-ribose) polymerase-1. Vitamin D also exerts its effect on obesity through cell-signaling mechanisms, including matrix metalloproteinases, mitogen-activated protein kinase pathways, the reduced form of nicotinamide adenine dinucleotide phosphate, prostaglandins, reactive oxygen species, and nitric oxide synthase.

In conclusion, vitamin D may have a role in obesity. The best form of vitamin D for use in the obese individuals is calcitriol because it is the active form of the vitamin D₃ metabolite, its receptors are present in adipocytes, and modulates inflammatory cytokine expression.

The lipocalin-type prostaglandin D2 synthase knockout mouse model of insulin resistance and obesity demonstrates early hypothalamic-pituitary-adrenal axis hyperactivity

Obesity and diabetes are closely associated with hyperactivation of the hypothalamic-pituitary-adrenal (HPA) axis. In this study, the diet-induced obese C57BL/6 mouse was used to test the hypothesis that chronically elevated metabolic parameters associated with the development of obesity such as cholesterol and glucose can aggravate basal HPA axis activity. Because the lipocalin-type prostaglandin D(2) synthase (L-PGDS) knockout (KO) mouse is a model of accelerated insulin resistance, glucose intolerance, and obesity, it was further hypothesized that HPA activity would be greater in this model. Starting at 8 weeks of age, the L-PGDS KO and C57BL/6 mice were maintained on a low-fat or high-fat diet. After 20 or 37 weeks, fasting metabolic parameters and basal HPA axis hormones were measured and compared between genotypes. Correlation analyses were performed to identify associations between obesity-related chronic metabolic changes and changes in the basal activity of the HPA axis. Our results have identified strong positive correlations between total cholesterol, LDL-cholesterol, glucose, and HPA axis hormones that increase with age in the C57BL/6 mice. These data confirm that obesity-related elevations in cholesterol and glucose can heighten basal HPA activity. Additionally, the L-PGDS KO mice show early elevations in HPA activity with no age-related changes relative to the C57BL/6 mice.

Prostaglandins as PPARγ Modulators in Adipogenesis

Adipocytes and fat cells play critical roles in the regulation of energy homeostasis. Adipogenesis (adipocyte differentiation) is regulated via a complex process including coordinated changes in hormone sensitivity and gene expression. PPARγ is a ligand-dependent transcription factor and important in adipogenesis, as it enhances the expression of numerous adipogenic and lipogenic genes in adipocytes. Prostaglandins (PGs), which are lipid mediators, are associated with the regulation of PPARγ function in adipocytes. Prostacyclin promotes the differentiation of adipocyte-precursor cells to adipose cells via activation of the expression of C/EBPβ and δ. These proteins are important transcription factors in the activation of the early phase of adipogenesis, and they activate the expression of PPARγ, which event precedes the maturation of adipocytes. PGE₂ and PGF_2α strongly suppress the early phase of adipocyte differentiation by enhancing their own production via receptor-mediated elevation of the expression of cycloxygenase-2, and they also suppress the function of PPARγ. In contrast, PGD₂ and its non-enzymatic metabolite, Δ¹²-PGJ₂, activate the middle-late phase of adipocyte differentiation through both DP2 receptors and PPARγ. This paper focuses on potential roles of PGs as PPARγ modulators in adipogenesis and regulators of obesity.

Depressed levels of prostaglandin F2α in mice lacking Akr1b7 increase basal adiposity and predispose to diet-induced obesity

Negative regulators of white adipose tissue (WAT) expansion are poorly documented in vivo. Prostaglandin F(2α) (PGF(2α)) is a potent antiadipogenic factor in cultured preadipocytes, but evidence for its involvement in physiological context is lacking. We previously reported that Akr1b7, an aldo-keto reductase enriched in adipose stromal vascular fraction but absent from mature adipocytes, has antiadipogenic properties possibly supported by PGF(2α) synthase activity. To test whether lack of Akr1b7 could influence WAT homeostasis in vivo, we generated Akr1b7(-/-) mice in 129/Sv background. Akr1b7(-/-) mice displayed excessive basal adiposity resulting from adipocyte hyperplasia/hypertrophy and exhibited greater sensitivity to diet-induced obesity. Following adipose enlargement and irrespective of the diet, they developed liver steatosis and progressive insulin resistance. Akr1b7 loss was associated with decreased PGF(2α) WAT contents. Cloprostenol (PGF(2α) agonist) administration to Akr1b7(-/-) mice normalized WAT expansion by affecting both de novo adipocyte differentiation and size. Treatment of 3T3-L1 adipocytes and Akr1b7(-/-) mice with cloprostenol suggested that decreased adipocyte size resulted from inhibition of lipogenic gene expression. Hence, Akr1b7 is a major regulator of WAT development through at least two PGF(2α)-dependent mechanisms: inhibition of adipogenesis and lipogenesis. These findings provide molecular rationale to explore the status of aldo-keto reductases in dysregulations of adipose tissue homeostasis.

Synergistic suppression of early phase of adipogenesis by microsomal PGE synthase-1 (PTGES1)-produced PGE2 and aldo-keto reductase 1B3-produced PGF2α

We recently reported that aldo-keto reductase 1B3-produced prostaglandin (PG) F_2α suppressed the early phase of adipogenesis. PGE₂ is also known to suppress adipogenesis. In this study, we found that microsomal PGE₂ synthase (PGES)-1 (mPGES-1; PTGES1) acted as the PGES in adipocytes and that PGE₂ and PGF_2α synergistically suppressed the early phase of adipogenesis. PGE₂ production was detected in preadipocytes and transiently enhanced at 3 h after the initiation of adipogenesis of mouse adipocytic 3T3-L1 cells, followed by a quick decrease; and its production profile was similar to the expression of the cyclooxygenase-2 (PTGS2) gene. When 3T3-L1 cells were transfected with siRNAs for any one of the three major PTGESs, i.e., PTGES1, PTGES2 (mPGES-2), and PTGES3 (cytosolic PGES), only PTGES1 siRNA suppressed PGE₂ production and enhanced the expression of adipogenic genes. AE1-329, a PTGER4 (EP4) receptor agonist, increased the expression of the Ptgs2 gene with a peak at 1 h after the initiation of adipogenesis. PGE₂-mediated enhancement of the PTGS2 expression was suppressed by the co-treatment with L-161982, a PTGER4 receptor antagonist. Moreover, AE1-329 enhanced the expression of the Ptgs2 gene by binding of the cyclic AMP response element (CRE)-binding protein to the CRE of the Ptgs2 promoter; and its binding was suppressed by co-treatment with L-161982, which was demonstrated by promoter luciferase and chromatin immunoprecipitation assays. Furthermore, when 3T3-L1 cells were caused to differentiate into adipocytes in medium containing both PGE₂ and PGF_2α, the expression of the adipogenic genes and the intracellular triglyceride level were decreased to a greater extent than in medium containing either of them, revealing that PGE₂ and PGF_2α independently suppressed adipogenesis. These results indicate that PGE₂ was synthesized by PTGES1 in adipocytes and synergistically suppressed the early phase of adipogenesis of 3T3-L1 cells in cooperation with PGF_2α through receptor-mediated activation of PTGS2 expression.

Aldo-Keto Reductases 1B in Endocrinology and Metabolism

The aldose reductase (AR; human AKR1B1/mouse Akr1b3) has been the focus of many research because of its role in diabetic complications. The starting point of these alterations is the massive entry of glucose in polyol pathway where it is converted into sorbitol by this enzyme. However, the issue of AR function in non-diabetic condition remains unresolved. AR-like enzymes (AKR1B10, Akr1b7, and Akr1b8) are highly related isoforms often co-expressed with bona fide AR, making functional analysis of one or the other isoform a challenging task. AKR1B/Akr1b members share at least 65% protein identity and the general ability to reduce many redundant substrates such as aldehydes provided from lipid peroxidation, steroids and their by-products, and xenobiotics in vitro. Based on these properties, AKR1B/Akr1b are generally considered as detoxifying enzymes. Considering that divergences should be more informative than similarities to help understanding their physiological functions, we chose to review specific hallmarks of each human/mouse isoforms by focusing on tissue distribution and specific mechanisms of gene regulation. Indeed, although the AR shows ubiquitous expression, AR-like proteins exhibit tissue-specific patterns of expression. We focused on three organs where certain isoforms are enriched, the adrenal gland, enterohepatic, and adipose tissues and tried to connect recent enzymatic and regulation data with endocrine and metabolic functions of these organs. We presented recent mouse models showing unsuspected physiological functions in the regulation of glucido-lipidic metabolism and adipose tissue homeostasis. Beyond the widely accepted idea that AKR1B/Akr1b are detoxification enzymes, these recent reports provide growing evidences that they are able to modify or generate signal molecules. This conceptually shifts this class of enzymes from unenviable status of scavenger to upper class of messengers.

PGD synthase and PGD2 in immune resposne

PGD₂ is formed from arachidonic acid by successive enzyme reactions: oxygenation of arachidonic acid to PGH₂, a common precursor of various prostanoids, catalyzed by cyclooxygenase, and isomerization of PGH₂ to PGD₂ by PGD synthases (PGDSs). PGD₂ can be either pro- or anti-inflammatory depending on disease process and etiology. The anti-inflammatory and immunomodulatory attributes of PGDS/PGD₂ provide opportunities for development of novel therapeutic approaches for resistant infections and refractory inflammatory diseases. This paper highlights the role of PGD synthases and PGD2 in immune inflammatory response.

Activation of adipogenesis by lipocalin-type prostaglandin D synthase-generated Δ¹²-PGJ₂ acting through PPARγ-dependent and independent pathways

Lipocalin-type prostaglandin (PG) D synthase (L-PGDS)-produced PGD(2) accelerates adipogenesis. In this study, we investigated the molecular mechanism of PGD(2)-mediated activation of adipogenesis in mouse adipocytic 3T3-L1 cells. LC/MS analysis showed that Δ(12)-PGJ(2), one of the PGD(2) metabolites, was predominantly produced in the differentiated 3T3-L1 cells. Δ(12)-PGJ(2) enhanced the expression of adipogenic genes in a Δ(12)-PGJ(2)-concentration-dependent manner. Suppression of the expression of the adipogenic genes by L-PGDS siRNA or AT-56, an L-PGDS inhibitor, was cleared by the addition of Δ(12)-PGJ(2). Moreover, the production of adiponectin and leptin was increased by treatment with Δ(12)-PGJ(2). Furthermore, the results of a mammalian two-hybrid assay demonstrated that Δ(12)-PGJ(2) enhanced the PPARγ-mediated transcription activity. However, Δ(12)-PGJ(2)-activated expression of adipogenic genes such as fatty acid binding protein 4 (aP2) and stearoyl-CoA desaturase was inhibited only at 38% and 42%, respectively, by treatment with GW9662, a PPARγ antagonist in 3T3-L1 cells, although Troglitazone-mediated activation of the expression of these adipogenic genes was completely suppressed by GW9662, suggesting the existence of a PPARγ-independent mechanism for Δ(12)-PGJ(2)-activated adipogenesis. These results, taken together, indicate that Δ(12)-PGJ(2) is a dominant metabolite of L-PGDS-produced PGD(2) during adipogenesis and acts as an activator for adipogenesis through both PPARγ-dependent and -independent mechanisms in 3T3-L1 cells.

Essential fatty acids and their metabolites as modulators of stem cell biology with reference to inflammation, cancer, and metastasis

Stem cells are pluripotent and expected to be of benefit in the management of coronary heart disease, stroke, diabetes mellitus, cancer, and Alzheimer's disease in which pro-inflammatory cytokines are increased. Identifying endogenous bioactive molecules that have a regulatory role in stem cell survival, proliferation, and differentiation may aid in the use of stem cells in various diseases including cancer. Essential fatty acids form precursors to both pro- and anti-inflammatory molecules have been shown to regulate gene expression, enzyme activity, modulate inflammation and immune response, gluconeogenesis via direct and indirect pathways, function directly as agonists of a number of G protein-coupled receptors, activate phosphatidylinositol 3-kinase/Akt and p44/42 mitogen-activated protein kinases, and stimulate cell proliferation via Ca(2+), phospholipase C/protein kinase, events that are also necessary for stem cell survival, proliferation, and differentiation. Hence, it is likely that bioactive lipids play a significant role in various diseases by modulating the proliferation and differentiation of embryonic stem cells in addition to their capacity to suppress inflammation. Ephrin Bs and reelin, adhesion molecules, and microRNAs regulate neuronal migration and cancer cell metastasis. Polyunsaturated fatty acids and their products seem to modulate the expression of ephrin Bs and reelin and several adhesion molecules and microRNAs suggesting that bioactive lipids participate in neuronal regeneration and stem cell proliferation, migration, and cancer cell metastasis. Thus, there appears to be a close interaction among essential fatty acids, their bioactive products, and inflammation and cancer growth and its metastasis.

Extended release niacin-laropiprant in patients with hypercholesterolemia or mixed dyslipidemias improves clinical parameters

The progression of atherosclerosis remains a major cause of morbidity and mortality. Plaque formation is an immunological response driven by a number of risk factors, and reduction of risk is the primary goal of treatment. The role of LDL-C is well established and statins have proved effective drugs, although the relative risk reduction is only around 30%. The importance of other factors-notably low HDL-C and high TGs-has become increasingly clear and the search for alternative strategies continues. Niacin is particularly effective in achieving normalization of HDL-C but is clinically underutilized due to the side effect of cutaneous flushing. The discovery that flushing is mediated by mechanisms distinct from the lipid-lowering effects has led to the development of combination drugs with reduced side effects. This review considers the evidence regarding the clinical efficacy of extended-release niacin and the DP1 antagonist laropiprant in the treatment of hypercholesterolemia and mixed dyslipidemias.

Central nervous system lipocalin-type prostaglandin D2-synthase is correlated with orexigenic neuropeptides, visceral adiposity and markers of the hypothalamic-pituitary-adrenal axis in obese humans

Lipocalin-type prostaglandin D2-synthase (L-PGDS) is the main producer of prostaglandin D2 (PGD2) in the central nervous system (CNS). Animal data suggest effects of central nervous L-PGDS in the regulation of food intake and obesity. No human data are available. We hypothesised that a role for CNS L-PGDS in metabolic function in humans would be reflected by correlations with known orexigenic neuropeptides. Cerebrospinal fluid (CSF) and serum samples were retrieved from 26 subjects in a weight loss study, comprising a 3-week dietary lead-in followed by 12-weeks of leptin or placebo treatment. At baseline, CSF L-PGDS was positively correlated with neuropeptide Y (NPY) (ρ = 0.695, P < 0.001, n = 26) and galanin (ρ = 0.651, P < 0.001) as well as visceral adipose tissue (ρ = 0.415, P = 0.035). Furthermore, CSF L-PGDS was inversely correlated with CSF leptin (ρ = -0.529, P = 0.005) and tended to correlate inversely with s.c. adipose tissue (ρ = -0.346, P = 0.084). As reported earlier, leptin treatment had no effect on weight loss and did not affect CSF L-PGDS or NPY levels compared to placebo. After weight loss, the change of CSF L-PGDS was significantly correlated with the change of CSF NPY levels (ρ = 0.604, P = 0.004, n = 21). Because of the correlation between baseline CSF L-PGDS levels and visceral adipose tissue, we examined associations with hypothalamic-pituitary-adrenal (HPA) axis components. Baseline CSF L-PGDS was correlated with corticotrophin-releasing hormone (ρ = 0.764, P < 0.001) and β-endorphin (ρ = 0.491, P < 0.001). By contrast, serum L-PGDS was not correlated with any of the measured variables either at baseline or after treatment. In summary, CSF L-PGDS was correlated with orexigenic neuropeptides, visceral fat distribution and central HPA axis mediators. The importance of these findings is unclear but could suggest a role for CSF L-PGDS in the regulation of visceral obesity by interaction with the neuroendocrine circuits regulating appetite and fat distribution. Further interventional studies will be needed to characterise these interactions in more detail.