Cyclooxygenase-2 deficiency attenuates adipose tissue differentiation and inflammation in mice

Emerging Roles and Therapeutic Applications of Arachidonic Acid Pathways in Cardiometabolic Diseases

Cardiometabolic disease has become a major health burden worldwide, with sharply increasing prevalence but highly limited therapeutic interventions. Emerging evidence has revealed that arachidonic acid derivatives and pathway factors link metabolic disorders to cardiovascular risks and intimately participate in the progression and severity of cardiometabolic diseases. In this review, we systemically summarized and updated the biological functions of arachidonic acid pathways in cardiometabolic diseases, mainly focusing on heart failure, hypertension, atherosclerosis, nonalcoholic fatty liver disease, obesity, and diabetes. We further discussed the cellular and molecular mechanisms of arachidonic acid pathway-mediated regulation of cardiometabolic diseases and highlighted the emerging clinical advances to improve these pathological conditions by targeting arachidonic acid metabolites and pathway factors.

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.

Aspirin attenuates the expression of adhesion molecules, risk of obesity, and adipose tissue inflammation in high-fat diet-induced obese mice

The prevalence of obesity is increasing at an alarming rate and keeps on being one of the significant challenges of this century. Obesity promotes adipose tissue hypertrophy and causes the release of different pro-inflammatory cytokines, playing a significant role in the pathophysiology of metabolic syndrome. Aspirin is known as a potent anti-inflammatory drug, but its role in adipogenesis, adipocyte-specific inflammation, and metabolic syndrome is not well characterized. Thus, in this experiment, we aimed to determine the effect of low-dose aspirin on obesity, obesity-induced inflammation, and metabolic syndrome. High-fat diet-induced obese female mice (Swiss Albino) were used in our study. Mice were fed on a normal diet, a high-fat diet, and a low dose of aspirin (LDA) in the presence of a high-fat diet for 11 weeks. Body weight, lipid profile, adipose tissue size, and inflammatory status were analyzed after that period. The ∆∆CT method was used to calculate the relative mRNA expression of target genes. Treatment with a low dose of aspirin resulted in a significant reduction of body weight, visceral fat mass and serum total cholesterols, serum and adipose tissue triglycerides, and blood glucose levels in high-fat diet-induced obese mice compared to the untreated obese group. Consistent with these biochemical results, a significant reduction in mRNA expression of different genes like PPARγ, GLUT4, IL-6, TNFα, MCP-1, ICAM-I, and VCAM-I associated with adipogenesis and inflammation were noticed. Overall, current study findings indicate that low-dose aspirin reduces obesity, hyperlipidemia, adipocyte-specific inflammation, and metabolic syndrome in high-fat diet-induced obese mice.

COX-2 Deficiency Promotes White Adipogenesis via PGE2-Mediated Paracrine Mechanism and Exacerbates Diet-Induced Obesity

Cyclooxygenase-2 (COX-2) plays a critical role in regulating innate immunity and metabolism by producing prostaglandins (PGs) and other lipid mediators. However, the implication of adipose COX-2 in obesity remains largely unknown. Using adipocyte-specific COX-2 knockout (KO) mice, we showed that depleting COX-2 in adipocytes promoted white adipose tissue development accompanied with increased size and number of adipocytes and predisposed diet-induced adiposity, obesity, and insulin resistance. The increased size and number of adipocytes by COX-2 KO were reversed by the treatment of prostaglandin E2 (PGE2) but not PGI2 and PGD2 during adipocyte differentiation. PGE2 suppresses PPARγ expression through the PKA pathway at the early phase of adipogenesis, and treatment of PGE2 or PKA activator isoproterenol diminished the increased lipid droplets in size and number in COX-2 KO primary adipocytes. Administration of PGE2 attenuated increased fat mass and fat percentage in COX-2 deficient mice. Taken together, our study demonstrated the suppressing effect of adipocyte COX-2 on adipogenesis and reveals that COX-2 restrains adipose tissue expansion via the PGE2-mediated paracrine mechanism and prevents the development of obesity and related metabolic disorders.

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.

Adipocyte-derived PGE2 is required for intermittent fasting-induced Treg proliferation and improvement of insulin sensitivity

The intermittent fasting (IF) diet has profound benefits for diabetes prevention. However, the precise mechanisms underlying IF's beneficial effects remain poorly defined. Here, we show that the expression levels of cyclooxygenase-2 (COX-2), an enzyme that produces prostaglandins, are suppressed in white adipose tissue (WAT) of obese humans. In addition, the expression of COX-2 in WAT is markedly upregulated by IF in obese mice. Adipocyte-specific depletion of COX-2 led to reduced fractions of CD4+Foxp3+ Tregs and a substantial decrease in the frequency of CD206+ macrophages, an increase in the abundance of γδT cells in WAT under normal chow diet conditions, and attenuation of IF-induced antiinflammatory and insulin-sensitizing effects, despite a similar antiobesity effect in obese mice. Mechanistically, adipocyte-derived prostaglandin E2 (PGE2) promoted Treg proliferation through the CaMKII pathway in vitro and rescued Treg populations in adipose tissue in COX-2-deficient mice. Ultimately, inactivation of Tregs by neutralizing anti-CD25 diminished IF-elicited antiinflammatory and insulin-sensitizing effects, and PGE2 restored the beneficial effects of IF in COX-2-KO mice. Collectively, our study reveals that adipocyte COX-2 is a key regulator of Treg proliferation and that adipocyte-derived PGE2 is essential for IF-elicited type 2 immune response and metabolic benefits.

The Multifaceted Actions of Curcumin in Obesity

Obesity remains a pervasive health concern worldwide with concomitant comorbidities such as cardiovascular diseases, diabetes, inflammation, and other metabolic disorders. A wealth of data validates dietary and lifestyle modifications such as restricting caloric intake and increasing physical activity to slow the obesity development. Recently, the advent of phytochemicals such as curcumin, the active ingredient in turmeric, has attracted considerable research interest in tracking down their possible effects in protection against obesity and obesity-related comorbidities. According to the existing literature, curcumin may regulate lipid metabolism and suppress chronic inflammation interacting with white adipose tissue, which plays a central role in the complications associated with obesity. Curcumin also inhibits the differentiation of adipocyte and improves antioxidant properties. In the present review, we sought to deliberate the possible effects of curcumin in downregulating obesity and curtailing the adverse health effects of obesity.

Microsomal Prostaglandin E Synthase-1 (mPGES-1) is involved in the metabolic and cardiovascular alterations associated with obesity

BACKGROUND AND PURPOSE

Microsomal prostaglandin E synthase-1 (mPGES-1) is an inducible isomerase responsible for prostaglandin E₂ production in inflammatory conditions. We evaluated the role of mPGES-1 in obesity development and in the metabolic and cardiovascular alterations associated.

EXPERIMENTAL APPROACH

mPGES-1^+/+ and mPGES-1^-/- mice were fed with normal or high fat diet (HFD, 60% fat). The glycaemic and lipid profile was studied by glucose and insulin tolerance tests and colorimetric assays. Vascular function, structure and mechanics were evaluated by myography. Histological studies, q-RT-PCR and Western Blot analyses were performed in adipose tissue depots and cardiovascular tissues. Gene expression in abdominal fat and perivascular adipose tissue (PVAT) from patients and its correlation with vascular damage was determined.

KEY RESULTS

Male mPGES-1^-/- mice fed with HFD were protected against body weight gain and showed reduced adiposity, better glucose tolerance and insulin sensitivity, lipid levels and less white adipose tissue and PVAT inflammation and fibrosis, compared to mPGES-1^+/+ mice. mPGES-1 knockdown prevented cardiomyocyte hypertrophy, cardiac fibrosis, endothelial dysfunction, aortic insulin resistance, and vascular inflammation and remodeling, induced by HFD. Obesity-induced weight gain and endothelial dysfunction of resistance arteries were ameliorated in female mPGES-1^-/- mice. In humans, we found a positive correlation between mPGES-1 expression in abdominal fat and vascular remodeling, vessel stiffness and systolic blood pressure. In human PVAT, there was a positive correlation between mPGES-1 expression and inflammatory markers.

CONCLUSIONS AND IMPLICATIONS

mPGES-1 inhibition might be a novel therapeutic approach for the management of obesity and the associated cardiovascular and metabolic alterations.

Involvement of prostacyclin synthase in high-fat-diet-induced obesity

Prostacyclin (PGI2) synthase (PGIS) functions downstream of inducible cyclooxygenase COX-2 in the PGI2 biosynthetic pathway. Although COX-2 and PGI2 receptor (IP) are known to be involved in adipogenesis and obesity, the involvement of PGIS has not been fully elucidated. In this study, we examined the role of PGIS in adiposity by using PGIS-deficient mice. Although PGIS deficiency did not affect in vitro adipocyte differentiation, when fed a high-fat diet (HFD), PGIS knockout (KO) mice showed reductions in both body weight gain and epididymal fat mass relative to wild-type (WT) mice. PGIS deficiency might reduce HFD-induced obesity by suppressing PGI2 production. We further found that additional gene deletion of microsomal prostaglandin (PG) E synthase-1 (mPGES-1), one of the other PG terminal synthases that also functions downstream of COX-2, emphasized the metabolic phenotypes of PGIS-deficient mice. More marked reduction in obesity and improved insulin resistance were observed in PGIS/mPGES-1 double KO (DKO) mice. Since an additive increase in PGF2α level in epididymal fat was observed in DKO mice, mPGES-1 deficiency might affect adiposity by enhancing the production of PGF2α. Our immunohistochemical analysis further revealed that in adipose tissues, PGIS was expressed in vascular and stromal cells but not in adipocytes. These results suggested that PGI2 produced from PGIS-expressed stromal tissues might enhance HFD-induced obesity by acting on IP expressed in adipocytes. The balance of expressions of PG terminal synthases and the subsequent production of prostanoids might be critical for adiposity.

Evaluation of cyclooxygenase oxylipins as potential biomarker for obesity-associated adipose tissue inflammation and type 2 diabetes using targeted multiple reaction monitoring mass spectrometry

INTRODUCTION

Obesity is associated with adipose tissue inflammation which in turn drives insulin resistance and the development of type 2 diabetes. Oxylipins are a collection of lipid metabolites, subdivided in different classes, which are involved in inflammatory cascades. They play important roles in regulating adipose tissue homeostasis and inflammation and are therefore putative biomarkers for obesity-associated adipose tissue inflammation and the subsequent risk of type 2 diabetes onset. The objective for this study is to design an assay for a specific oxylipin class and evaluate these as potential prognostic biomarker for obesity-associated adipose tissue inflammation and type 2 diabetes.

METHODS

An optimized workflow was developed to extract oxylipins from plasma using solid-phase extraction followed by analysis using ultra-high performance liquid chromatography coupled to a triple quadrupole mass spectrometer in multiple reaction monitoring mode. This workflow was applied to clinical plasma samples obtained from obese-type 2 diabetes patients and from lean and obese control subjects.

RESULTS

The assay was analytically validated and enabled reproducible analyses of oxylipins extracted from plasma with acceptable sensitivities. Analysis of clinical samples revealed discriminative values for four oxylipins between the type 2 diabetes patients and the lean and obese control subjects, viz. PGF_2α, PGE₂, 15-keto-PGE₂ and 13,14-dihydro-15-keto-PGE₂. The combination of PGF_2α and 15-keto-PGE₂ had the most predictive value to discriminate type 2 diabetic patients from lean and obese controls.

CONCLUSIONS

This proof-of-principle study demonstrates the potential value of oxylipins as biomarkers to discriminate obese individuals from obese-type 2 diabetes patients.

Estrogen exacerbates mammary involution through neutrophil-dependent and -independent mechanism

There is strong evidence that the pro-inflammatory microenvironment during post-partum mammary involution promotes parity-associated breast cancer. Estrogen exposure during mammary involution drives tumor growth through neutrophils’ activity. However, how estrogen and neutrophils influence mammary involution are unknown. Combined analysis of transcriptomic, protein, and immunohistochemical data in BALB/c mice showed that estrogen promotes involution by exacerbating inflammation, cell death and adipocytes repopulation. Remarkably, 88% of estrogen-regulated genes in mammary tissue were mediated through neutrophils, which were recruited through estrogen-induced CXCR2 signalling in an autocrine fashion. While neutrophils mediate estrogen-induced inflammation and adipocytes repopulation, estrogen-induced mammary cell death was via lysosome-mediated programmed cell death through upregulation of cathepsin B, Tnf and Bid in a neutrophil-independent manner. Notably, these multifaceted effects of estrogen are mostly mediated by ERα and unique to the phase of mammary involution. These findings are important for the development of intervention strategies for parity-associated breast cancer.

Lipokines and Thermogenesis

Adaptive thermogenesis is a catabolic process that consumes energy-storing molecules and expends that energy as heat in response to environmental changes. This process occurs primarily in brown and beige adipose tissue. Thermogenesis is regulated by many factors, including lipid derived paracrine and endocrine hormones called lipokines. Recently, technologic advances for identifying new lipid biomarkers of thermogenic activity have shed light on a diverse set of lipokines that act through different pathways to regulate energy expenditure. In this review, we highlight a few examples of lipokines that regulate thermogenesis. The biosynthesis, regulation, and effects of the thermogenic lipokines in several families are reviewed, including oloeylethanolamine, endocannabinoids, prostaglandin E2, and 12,13-diHOME. These thermogenic lipokines present potential therapeutic targets to combat states of excess energy storage, such as obesity and related metabolic disorders.

The Dualistic Effect of COX-2-Mediated Signaling in Obesity and Insulin Resistance

Obesity and insulin resistance are two major risk factors for the development of metabolic syndrome, type 2 diabetes and associated cardiovascular diseases (CVDs). Cyclooxygenase (COX), a rate-limiting enzyme responsible for the biosynthesis of prostaglandins (PGs), exists in two isoforms: COX-1, the constitutive form, and COX-2, mainly the inducible form. COX-2 is the key enzyme in eicosanoid metabolism that converts eicosanoids into a number of PGs, including PGD₂, PGE₂, PGF_2α, and prostacyclin (PGI₂), all of which exert diverse hormone-like effects via autocrine or paracrine mechanisms. The COX-2 gene and immunoreactive proteins have been documented to be highly expressed and elevated in adipose tissue (AT) under morbid obesity conditions. On the other hand, the environmental stress-induced expression and constitutive over-expression of COX-2 have been reported to play distinctive roles under different pathological and physiological conditions; i.e., over-expression of the COX-2 gene in white AT (WAT) has been shown to induce de novo brown AT (BAT) recruitment in WAT and then facilitate systemic energy expenditure to protect mice against high-fat diet-induced obesity. Hepatic COX-2 expression was found to protect against diet-induced steatosis, obesity, and insulin resistance. However, COX-2 activation in the epidydimal AT is strongly correlated with the development of AT inflammation, insulin resistance, and fatty liver in high-fat-diet-induced obese rats. This review will provide updated information regarding the role of COX-2-derived signals in the regulation of energy metabolism and the pathogenesis of obesity and MS.

Overexpression of cyclooxygenase-2 in adipocytes reduces fat accumulation in inguinal white adipose tissue and hepatic steatosis in high-fat fed mice

Cyclooxygenases are known as important regulators of metabolism and immune processes via conversion of C20 fatty acids into various regulatory lipid mediators, and cyclooxygenase activity has been implicated in browning of white adipose tissues. We generated transgenic (TG) C57BL/6 mice expressing the Ptgs2 gene encoding cyclooxygenase-2 (COX-2) in mature adipocytes. TG mice fed a high-fat diet displayed marginally lower weight gain with less hepatic steatosis and a slight improvement in insulin sensitivity, but no difference in glucose tolerance. Compared to littermate wildtype mice, TG mice selectively reduced inguinal white adipose tissue (iWAT) mass and fat cell size, whereas the epididymal (eWAT) fat depot remained unchanged. The changes in iWAT were accompanied by increased levels of specific COX-derived lipid mediators and increased mRNA levels of interleukin-33, interleukin-4 and arginase-1, but not increased expression of uncoupling protein 1 or increased energy expenditure. Epididymal WAT (eWAT) in TG mice exhibited few changes except from increased infiltration with eosinophils. Our findings suggest a role for COX-2-derived lipid mediators from adipocytes in mediating type 2 immunity cues in subcutaneous WAT associated with decreased hepatic steatosis, but with no accompanying induction of browning and increased energy expenditure.

Diet Supplementation in ω3 Polyunsaturated Fatty Acid Favors an Anti-Inflammatory Basal Environment in Mouse Adipose Tissue

Oxylipins are metabolized from dietary ω3 and ω6 polyunsaturated fatty acids and are involved in an inflammatory response. Adipose tissue inflammatory background is a key factor of metabolic disorders and it is accepted that dietary fatty acids, in terms of quality and quantity, modulate oxylipin synthesis in this tissue. Moreover, it has been reported that diet supplementation in ω3 polyunsaturated fatty acids resolves some inflammatory situations. Thus, it is crucial to assess the influence of dietary polyunsaturated fatty acids on oxylipin synthesis and their impact on adipose tissue inflammation. To this end, mice fed an ω6- or ω3-enriched standard diet (ω6/ω3 ratio of 30 and 3.75, respectively) were analyzed for inflammatory phenotype and adipose tissue oxylipin content. Diet enrichment with an ω3 polyunsaturated fatty acid induced an increase in the oxylipins derived from ω6 linoleic acid, ω3 eicosapentaenoic, and ω3 docosahexaenoic acids in brown and white adipose tissues. Among these, the level of pro-resolving mediator intermediates, as well as anti-inflammatory metabolites, were augmented. Concomitantly, expressions of M2 macrophage markers were increased without affecting inflammatory cytokine contents. In vitro, these metabolites did not activate macrophages but participated in macrophage polarization by inflammatory stimuli. In conclusion, we demonstrated that an ω3-enriched diet, in non-obesogenic non-inflammatory conditions, induced synthesis of oxylipins which were involved in an anti-inflammatory response as well as enhancement of the M2 macrophage molecular signature, without affecting inflammatory cytokine secretion.

Casein glycomacropeptide hydrolysates inhibit PGE2 production and COX2 expression in LPS-stimulated RAW 264.7 macrophage cells via Akt mediated NF-κB and MAPK pathways

A casein glycomacropeptide hydrolysate (GMPH) was found to possess inhibitory activity against lipopolysaccharide (LPS)-induced inflammatory response in our previous study. In the current study, the inhibitory effect and the underlying molecular mechanism of GMPH on inflammatory response in LPS-stimulated RAW264.7 macrophages were further investigated. Results showed that GMPH significantly suppressed LPS-induced intracellular reactive oxygen species (ROS) and malondialdehyde (MDA) production. GMPH reduced the production of prostaglandin E2 (PEG2) and the expression of cyclooxygenase-2 (COX-2) and cytosolic phospholipase A2 (cPLA2) in LPS-stimulated macrophages. GMPH also attenuated LPS-induced phosphorylation of MAPK (c-Jun NH2-terminal kinase (JNK), extracellular signal-regulated kinase (ERK) and p38) and protein kinase B (Akt). Furthermore, GMPH inhibited nuclear transcription factor kappa-B (NF-κB) activation by suppressing the nuclear translocation of NF-κB p65, which was markedly reversed by LY294002, an Akt inhibitor. These results demonstrated that GMPH exerts anti-inflammatory functions through the inactivation of MAPK and Akt in LPS-stimulated RAW264.7 macrophages, therefore may hold potential to ameliorate inflammation-related metabolic disorders.

Mast cells participate in chronic low-grade inflammation within adipose tissue

Obesity is reckoned as one of the civilization diseases, posing a considerable global health issue. Evidence points towards a contribution of multitude immune cell populations in obesity pathomechanism and the development of chronic low-grade inflammation in the expanded adipose tissue. Notably, adipose tissue is a reservoir of mast cells which number in individuals with obesity particularly increased. Some of them tend to degranulation what generate secretion of strong pro-inflammatory and regulatory mediators, as well as cytokines/chemokines. Several lines of evidence suggest that mast cells are strictly associated with pro-inflammatory status in adipose tissue by their indirect impact on immune cell attraction and activation. Furthermore, mast cells affect adipose tissue remodelling and fibrosis by adipocyte differentiation, fibroblast proliferation and enhancing extracellular matrix proteins expression. This review will summarize current knowledge on mast cell features and their role in the development of chronic low-grade inflammation within adipose tissue.

Impact of dietary ω3 polyunsaturated fatty acid supplementation on brown and brite adipocyte function

The recent characterization of functional brown adipose tissue in adult humans has opened new perspectives for regulation of energy expenditure with respect to obesity and diabetes. Furthermore, dietary recommendations have taken into account the insufficient dietary intake of ω3 PUFAs and the concomitant excessive intake of ω6 PUFA associated with the occurrence of overweight/obesity. We aimed to study whether ω3 PUFAs could play a role in the recruitment and function of energy-dissipating brown/brite adipocytes. We show that ω3 PUFA supplementation has a beneficial effect on the thermogenic function of adipocytes. In vivo, a low dietary ω6:ω3 ratio improved the thermogenic response of brown and white adipose tissues to β3-adrenergic stimulation. This effect was recapitulated in vitro by PUFA treatment of hMADS adipocytes. We pinpointed the ω6-derived eicosanoid prostaglandin (PG)F2α as the molecular origin because the effects were mimicked with a specific PGF2α receptor agonist. PGF2α level in hMADS adipocytes was reduced in response to ω3 PUFA supplementation. The recruitment of thermogenic adipocytes is influenced by the local quantity of individual oxylipins, which is controlled by the ω6:ω3 ratio of available lipids. In human nutrition, energy homeostasis may thus benefit from the implementation of a more balanced dietary ω6:ω3 ratio.

Genomic and lipidomic analyses differentiate the compensatory roles of two COX isoforms during systemic inflammation in mice

Both cyclooxygenase (COX)-1 and COX-2, encoded by Ptgs1 and Ptgs2, function coordinately during inflammation. But the relative contributions and compensations of COX-1 and COX-2 to inflammatory responses remain unanswered. We used three engineered mouse lines where the Ptgs1 and Ptgs2 genes substitute for one another to discriminate the distinct roles and interchangeability of COX isoforms during systemic inflammation. In macrophages, kidneys, and lungs, "flipped" Ptgs genes generate a "reversed" COX expression pattern, where the knock-in COX-2 is expressed constitutively and the knock-in COX-1 is lipopolysaccharide inducible. A panel of eicosanoids detected in serum and kidney demonstrates that prostaglandin (PG) biosynthesis requires native COX-1 and cannot be rescued by the knock-in COX-2. Our data further reveal preferential compensation of COX isoforms for prostanoid production in macrophages and throughout the body, as reflected by urinary PG metabolites. NanoString analysis indicates that inflammatory networks can be maintained by isoform substitution in inflamed macrophages. However, COX-1>COX-2 macrophages show reduced activation of inflammatory signaling pathways, indicating that COX-1 may be replaced by COX-2 within this complex milieu, but not vice versa. Collectively, each COX isoform plays a distinct role subject to subcellular environment and tissue/cell-specific conditions, leading to subtle compensatory differences during systemic inflammation.

Over-expression of PPARα in obese mice adipose tissue improves insulin sensitivity

Peroxisome proliferator-activated receptor α (PPARα) is important in the regulation of lipid metabolism and expressed at high levels in the liver. Although PPARα is also expressed in adipose tissue, little is known about the relationship between its activation and the regulation of glucose metabolism. In this study, we developed adipose tissue specific PPARα over-expression (OE) mice. Metabolomics and insulin tolerance tests showed that OE induces branched-chain amino acid (BCAA) profile and improvement of insulin sensitivity. Furthermore, LC-MS and PCR analyses revealed that OE changes free fatty acid (FFA) profile and reduces obesity-induced inflammation. These findings suggested that PPARα activation in adipose tissue contributes to the improvement of glucose metabolism disorders via the enhancement of BCAA and FFA metabolism.

Ellagic acid inhibits the proliferation of human pancreatic carcinoma PANC-1 cells in vitro and in vivo

Ellagic aicd (EA), a dietary polyphenolic compound found in plants and fruits, possesses various pharmacological activities. This study investigated the effect of EA on human pancreatic carcinoma PANC-1 cells both in vitro and in vivo; and defined the associated molecular mechanisms. In vitro, the cell growth and repairing ability were assessed by CCK-8 assay and wound healing assay. The cell migration and invasion activity was evaluated by Tanswell assay. In vivo, PANC-1 cell tumor-bearing mice were treated with different concentrations of EA. We found that EA significantly inhibited cell growth, cell repairing activity, and cell migration and invasion in a dose-dependent manner. Treatment of PANC-1 xenografted mice with EA resulted in significant inhibition in tumor growth and prolong mice survival rate. Furthermore, flow cytometric analysis showed that EA increased the percentage of cells in the G1 phase of cell cycle. Western blot analysis revealed that EA inhibited the expression of COX-2 and NF-κB. In addition, EA reversed epithelial to mesenchymal transition by up-regulating E-cadherin and down-regulating Vimentin. In summary, the present study demonstrated that EA inhibited cell growth, cell repairing activity, cell migration and invasion in a dose-dependent manner. EA also effectively inhibit human pancreatic cancer growth in mice. The anti-tumor effect of EA might be related to cell cycle arrest, down-regulating the expression of COX-2 and NF-κB, reversing epithelial to mesenchymal transition by up-regulating E-cadherin and down-regulating Vimentin. Our findings suggest that the use of EA would be beneficial for the management of pancreatic cancer.

Deuterium-reinforced polyunsaturated fatty acids protect against atherosclerosis by lowering lipid peroxidation and hypercholesterolemia

BACKGROUND AND AIMS

Oxidative modification of lipoproteins is a crucial step in atherosclerosis development. Isotopic-reinforced polyunsaturated fatty acids (D-PUFAs) are more resistant to reactive oxygen species-initiated chain reaction of lipid peroxidation than regular hydrogenated (H-)PUFAs. We aimed at investigating the effect of D-PUFA treatment on lipid peroxidation, hypercholesterolemia and atherosclerosis development.

METHODS

Transgenic APOE*3-Leiden.CETP mice, a well-established model for human-like lipoprotein metabolism, were pre-treated with D-PUFAs or control H-PUFAs-containing diet (1.2%, w/w) for 4 weeks. Thereafter, mice were fed a Western-type diet (containing 0.15% cholesterol, w/w) for another 12 weeks, while continuing the D-/H-PUFA treatment.

RESULTS

D-PUFA treatment markedly decreased hepatic and plasma F₂-isoprostanes (approx. -80%) and prostaglandin F₂α (approx. -40%) as compared to H-PUFA treatment. Moreover, D-PUFAs reduced body weight gain during the study (-54%) by decreasing body fat mass gain (-87%) without altering lean mass. D-PUFAs consistently reduced plasma total cholesterol levels (approx. -25%), as reflected in reduced plasma non-HDL-cholesterol (-28%). Additional analyses of hepatic cholesterol metabolism indicated that D-PUFAs reduced the hepatic cholesterol content (-21%). Sterol markers of intestinal cholesterol absorption and cholesterol breakdown were decreased. Markers of cholesterol synthesis were increased. Finally, D-PUFAs reduced atherosclerotic lesion area formation throughout the aortic root of the heart (-26%).

CONCLUSIONS

D-PUFAs reduce body weight gain, improve cholesterol handling and reduce atherosclerosis development by reducing lipid peroxidation and plasma cholesterol levels. D-PUFAs, therefore, represent a promising new strategy to broadly reduce rates of lipid peroxidation, and combat hypercholesterolemia and cardiovascular diseases.

Obesity: An overview of possible role(s) of gut hormones, lipid sensing and gut microbiota

Obesity is one of the major challenges for public health in 21st century, with 1.9 billion people being considered as overweight and 600 million as obese. There are certain diseases such as type 2 diabetes, hypertension, cardiovascular disease, and several forms of cancer which were found to be associated with obesity. Therefore, understanding the key molecular mechanisms involved in the pathogenesis of obesity could be beneficial for the development of a therapeutic approach. Hormones such as ghrelin, glucagon like peptide 1 (GLP-1) peptide YY (PYY), pancreatic polypeptide (PP), cholecystokinin (CCK) secreted by an endocrine organ gut, have an intense impact on energy balance and maintenance of homeostasis by inducing satiety and meal termination. Glucose and energy homeostasis are also affected by lipid sensing in which different organs respond in different ways. However, there is one common mechanism i.e. formation of esterified lipids (long chain fatty acyl CoAs) and the activation of protein kinase C δ (PKC δ) involved in all these organs. The possible role of gut microbiota and obesity has been addressed by several researchers in recent years, indicating the possible therapeutic approach toward the management of obesity by the introduction of an external living system such as a probiotic. The proposed mechanism behind this activity is attributed by metabolites produced by gut microbial organisms. Thus, this review summarizes the role of various physiological factors such as gut hormone and lipid sensing involved in various tissues and organ and most important by the role of gut microbiota in weight management.

Redox modulation of adipocyte differentiation: hypothesis of "Redox Chain" and novel insights into intervention of adipogenesis and obesity

In view of the global prevalence of obesity and obesity-associated disorders, it is important to clearly understand how adipose tissue forms. Accumulating data from various laboratories implicate that redox status is closely associated with energy metabolism. Thus, biochemical regulation of the redox system may be an attractive alternative for the treatment of obesity-related disorders. In this work, we will review the current data detailing the role of the redox system in adipocyte differentiation, as well as identifying areas for further research. The redox system affects adipogenic differentiation in an extensive way. We propose that there is a complex and interactive "redox chain," consisting of a "ROS-generating enzyme chain," "combined antioxidant chain," and "transcription factor chain," which contributes to fine-tune the regulation of ROS level and subsequent biological consequences. The roles of the redox system in adipocyte differentiation are paradoxical. The redox system exerts a "tridimensional" mechanism in the regulation of adipocyte differentiation, including transcriptional, epigenetic, and posttranslational modulations. We suggest that redoxomic techniques should be extensively applied to understand the biological effects of redox alterations in a more integrated way. A stable and standardized "redox index" is urgently needed for the evaluation of the general redox status. Therefore, more effort should be made to establish and maintain a general redox balance rather than to conduct simple prooxidant or antioxidant interventions, which have comprehensive implications.

The impact of obesity towards prostate diseases

Evidence has supported obesity as a risk factor for both benign prostate hyperplasia (BPH) and prostate cancer (PCa). Obesity causes several mechanisms including increased intra-abdominal pressure, altered endocrine status, increased sympathetic nervous activity, increased inflammation process, and oxidative stress, all of which are favorable in the development of BPH. In PCa, there are several different mechanisms, such as decreased serum testosterone, peripheral aromatization of androgens, insulin resistance, and altered adipokine secretion caused by inflammation, which may precipitate the development of and even cause high-grade PCa. The role of obesity in prostatitis still remains unclear. A greater understanding of the pathogenesis of prostate disease and adiposity could allow the development of new therapeutic markers, prognostic indicators, and drug targets. This review was made to help better understanding of the association between central obesity and prostate diseases, such as prostatitis, BPH, and PCa.

Hematopoietic cyclooxygenase-2 deficiency increases adipose tissue inflammation and adiposity in obesity

OBJECTIVE

Adipose tissue (AT) macrophages mediate AT inflammation in obesity, and cyclooxygenase-2 (COX-2) is a major inflammatory gene. It was hypothesized that deletion of hematopoietic COX-2 will inhibit AT inflammation in obesity.

METHODS

Lethally irradiated wild-type (WT) mice were injected with bone marrow (BM) cells collected from WT or COX-2 knock-out (COX-2-/-) donor mice and fed a high-fat diet for 16 weeks.

RESULTS

The mice that received BM cells from COX-2-/- mice (BM-COX-2-/-) gained increased body weight, fat mass, and visceral AT (VAT) mass. These mice exhibited reduced inflammatory markers in the VAT stromal vascular cells (SVC). However, the inflammatory markers were increased in adipocyte fraction and/or whole VAT. The activation of ERK1/2 MAPK, a pro-inflammatory signaling pathway, was increased in BM-COX-2-/- mice. The molecular markers of adipogenesis were increased in the VAT or adipocyte fraction. Wnt signaling markers which inhibit adipogenesis, including Wnt3A and DVL3, were reduced, and Wnt5a/b which promotes inflammation was increased in the VAT and/or adipocytes. Finally, an increase in hepatic triglyceride levels in BM-COX-2-/- mice was noted.

CONCLUSIONS

The data suggest that COX-2 deletion in hematopoietic cells reduces SVC inflammation but increases VAT inflammation and promotes adiposity likely via altered Wnt signaling.

The Tpl2 Kinase Regulates the COX-2/Prostaglandin E2 Axis in Adipocytes in Inflammatory Conditions

Bioactive lipid mediators such as prostaglandin E2 (PGE2) have emerged as potent regulator of obese adipocyte inflammation and functions. PGE2 is produced by cyclooxygenases (COXs) from arachidonic acid, but inflammatory signaling pathways controlling COX-2 expression and PGE2 production in adipocytes remain ill-defined. Here, we demonstrated that the MAP kinase kinase kinase tumor progression locus 2 (Tpl2) controls COX-2 expression and PGE2 secretion in adipocytes in response to different inflammatory mediators. We found that pharmacological- or small interfering RNA-mediated Tpl2 inhibition in 3T3-L1 adipocytes decreased by 50% COX-2 induction in response to IL-1β, TNF-α, or a mix of the 2 cytokines. PGE2 secretion induced by the cytokine mix was also markedly blunted. At the molecular level, nuclear factor κB was required for Tpl2-induced COX-2 expression in response to IL-1β but was inhibitory for the TNF-α or cytokine mix response. In a coculture between adipocytes and macrophages, COX-2 was mainly increased in adipocytes and pharmacological inhibition of Tpl2 or its silencing in adipocytes markedly reduced COX-2 expression and PGE2 secretion. Further, Tpl2 inhibition in adipocytes reduces by 60% COX-2 expression induced by a conditioned medium from lipopolysaccharide (LPS)-treated macrophages. Importantly, LPS was less efficient to induce COX-2 mRNA in adipose tissue explants of Tpl2 null mice compared with wild-type and Tpl2 null mice displayed low COX-2 mRNA induction in adipose tissue in response to LPS injection. Collectively, these data established that activation of Tpl2 by inflammatory stimuli in adipocytes and adipose tissue contributes to increase COX-2 expression and production of PGE2 that could participate in the modulation of adipose tissue inflammation during obesity.

Thromboxane synthase deficiency improves insulin action and attenuates adipose tissue fibrosis

Thromboxane A2, an arachidonic acid-derived eicosanoid generated by thromboxane synthase (TBXAS), plays critical roles in hemostasis and inflammation. However, the contribution of thromboxane A2 to obesity-linked metabolic dysfunction remains incompletely understood. Here, we used in vitro and mouse models to better define the role of TBXAS in metabolic homeostasis. We found that adipose expression of Tbxas and thromboxane A2 receptor (Tbxa2r) was significantly upregulated in genetic and dietary mouse models of obesity and diabetes. Expression of Tbxas and Tbxa2r was detected in adipose stromal cells, including macrophages. Furthermore, stimulation of macrophages with interferon-γ or resistin factors known to be upregulated in obesity induced Tbxas and Tbxa2r expression. Mice lacking Tbxas had similar weight gain, food intake, and energy expenditure. However, loss of Tbxas markedly enhanced insulin sensitivity in mice fed a low-fat diet. Improvement in glucose homeostasis was correlated with the upregulated expression of multiple secreted metabolic regulators (Ctrp3, Ctrp9, and Ctrp12) in the visceral fat depot. Following a challenge with a high-fat diet, Tbxas deficiency led to attenuated adipose tissue fibrosis and reduced circulating IL-6 levels without adipose tissue macrophages being affected; however, these changes were not sufficient to improve whole body insulin action. Together, our results highlight a novel, diet-dependent role for thromboxane A2 in modulating peripheral tissue insulin sensitivity and adipose tissue fibrosis.

Cyclooxygenase-2 regulates NLRP3 inflammasome-derived IL-1β production

The NLR family, pyrin domain-containing 3 (NLRP3) inflammasome is a reactive oxygen species-sensitive multiprotein complex that regulates IL-1β maturation via caspase-1. It also plays an important role in the pathogenesis of inflammation-related disease. Cyclooxygenase-2 (COX-2) is induced by inflammatory stimuli and contributes to the pathogenesis of inflammation-related diseases. However, there is currently little known about the relationship between COX-2 and the NLRP3 inflammasome. Here, we describe a novel role for COX-2 in regulating the activation of the NLRP3 inflammasome. NLRP3 inflammasome-derived IL-1β secretion and pyroptosis in macrophages were reduced by pharmaceutical inhibition or genetic knockdown of COX-2. COX-2 catalyzes the synthesis of prostaglandin E2 and increases IL-1β secretion. Conversely, pharmaceutical inhibition or genetic knockdown of prostaglandin E2 receptor 3 reduced IL-1β secretion. The underlying mechanisms for the COX-2-mediated increase in NLRP3 inflammasome activation were determined to be the following: (1) enhancement of lipopolysaccharide-induced proIL-1β and NLRP3 expression by increasing NF-κB activation and (2) enhancement of the caspase-1 activation by increasing damaged mitochondria, mitochondrial reactive oxygen species production and release of mitochondrial DNA into cytosol. Furthermore, inhibition of COX-2 in mice in vivo with celecoxib reduced serum levels of IL-1β and caspase-1 activity in the spleen and liver in response to lipopolysaccharide (LPS) challenge. These findings provide new insights into how COX-2 regulates the activation of the NLRP3 inflammasome and suggest that it may be a new potential therapeutic target in NLRP3 inflammasome-related diseases.

Activation of prostaglandin E2-EP4 signaling reduces chemokine production in adipose tissue

Inflammation of adipose tissue induces metabolic derangements associated with obesity. Thus, determining ways to control or inhibit inflammation in adipose tissue is of clinical interest. The present study tested the hypothesis that in mouse adipose tissue, endogenous prostaglandin E2 (PGE2) negatively regulates inflammation via activation of prostaglandin E receptor 4 (EP4). PGE2 (5-500 nM) attenuated lipopolysaccharide-induced mRNA and protein expression of chemokines, including interferon-γ-inducible protein 10 and macrophage-inflammatory protein-1α in mouse adipose tissue. A selective EP4 antagonist (L161,982) reversed, and two structurally different selective EP4 agonists [CAY10580 and CAY10598] mimicked these actions of PGE2. Adipose tissue derived from EP4-deficient mice did not display this response. These findings establish the involvement of EP4 receptors in this anti-inflammatory response. Experiments performed on adipose tissue from high-fat-fed mice demonstrated EP4-dependent attenuation of chemokine production during diet-induced obesity. The anti-inflammatory actions of EP4 became more important on a high-fat diet, in that EP4 activation suppressed a greater variety of chemokines. Furthermore, adipose tissue and systemic inflammation was enhanced in high-fat-fed EP4-deficient mice compared with wild-type littermates, and in high-fat-fed untreated C57BL/6 mice compared with mice treated with EP4 agonist. These findings provide in vivo evidence that PGE2-EP4 signaling limits inflammation. In conclusion, PGE2, via activation of EP4 receptors, functions as an endogenous anti-inflammatory mediator in mouse adipose tissue, and targeting EP4 may mitigate adipose tissue inflammation.

Prenatal polycyclic aromatic hydrocarbon, adiposity, peroxisome proliferator-activated receptor (PPAR) γ methylation in offspring, grand-offspring mice

Rationale

Greater levels of prenatal exposure to polycyclic aromatic hydrocarbon (PAH) have been associated with childhood obesity in epidemiological studies. However, the underlying mechanisms are unclear.

Objectives

We hypothesized that prenatal PAH over-exposure during gestation would lead to weight gain and increased fat mass in offspring and grand-offspring mice. Further, we hypothesized that altered adipose gene expression and DNA methylation in genes important to adipocyte differentiation would be affected.

Materials and Methods

Pregnant dams were exposed to a nebulized PAH mixture versus negative control aerosol 5 days a week, for 3 weeks. Body weight was recorded from postnatal day (PND) 21 through PND60. Body composition, adipose cell size, gene expression of peroxisome proliferator-activated receptor (PPAR) γ, CCAAT/enhancer-binding proteins (C/EBP) α, cyclooxygenase (Cox)-2, fatty acid synthase (FAS) and adiponectin, and DNA methylation of PPAR γ, were assayed in both the offspring and grand-offspring adipose tissue.

Findings

Offspring of dams exposed to greater PAH during gestation had increased weight, fat mass, as well as higher gene expression of PPAR γ, C/EBP α, Cox2, FAS and adiponectin and lower DNA methylation of PPAR γ. Similar differences in phenotype and DNA methylation extended through the grand-offspring mice.

Conclusions

Greater prenatal PAH exposure was associated with increased weight, fat mass, adipose gene expression and epigenetic changes in progeny.

Lipid signaling in adipose tissue: Connecting inflammation & metabolism

Obesity-associated low-grade inflammation of white adipose tissue (WAT) contributes to development of insulin resistance and other disorders. Accumulation of immune cells, especially macrophages, and macrophage polarization from M2 to M1 state, affect intrinsic WAT signaling, namely anti-inflammatory and proinflammatory cytokines, fatty acids (FA), and lipid mediators derived from both n-6 and n-3 long-chain PUFA such as (i) arachidonic acid (AA)-derived eicosanoids and endocannabinoids, and (ii) specialized pro-resolving lipid mediators including resolvins derived from both eicosapentaenoic (EPA) and docosahexaenoic acid (DHA), lipoxins (AA metabolites), protectins and maresins (DHA metabolites). In this respect, potential differences in modulating adipocyte metabolism by various lipid mediators formed by inflammatory M1 macrophages typical of obese state, and non-inflammatory M2 macrophages typical of lean state remain to be established. Studies in mice suggest that (i) transient accumulation of M2 macrophages could be essential for the control of tissue FA levels during activation of lipolysis, (ii) currently unidentified M2 macrophage-borne signaling molecule(s) could inhibit lipolysis and re-esterification of lipolyzed FA back to triacylglycerols (TAG/FA cycle), and (iii) the egress of M2 macrophages from rebuilt WAT and removal of the negative feedback regulation could allow for a full unmasking of metabolic activities of adipocytes. Thus, M2 macrophages could support remodeling of WAT to a tissue containing metabolically flexible adipocytes endowed with a high capacity of both TAG/FA cycling and oxidative phosphorylation. This situation could be exemplified by a combined intervention using mild calorie restriction and dietary supplementation with EPA/DHA, which enhances the formation of "healthy" adipocytes. This article is part of a Special Issue entitled Oxygenated metabolism of PUFA: analysis and biological relevance."

2,4,5-trimethoxybenzaldehyde, a bitter principle in plants, suppresses adipogenesis through the regulation of ERK1

Because of the prevalence of obesity, there is particular interest in finding potential therapeutic targets. In a previous study, we demonstrated that 2,4,5-trimethoxybenzaldehyde (2,4,5-TMBA), a bitter principle in plants and a natural cyclooxygenase II (COX-2) inhibitor, suppressed the differentiation of preadipocyts into adipocytes at the concentration of 0.5 mM. In this current study, we aimed to investigate the stage during adipogenesis that is critically affected by 2,4,5-TMBA and the effects of 2,4,5-TMBA on the time-course expression of signaling molecules MAP kinase kinase (MAPKK, represented by MEK) and extracellular signal-regulated kinase (ERK), transcription factors CCAAT/enhancer binding protein (C/EBP)α, β, and δ and peroxisome proliferator-activated receptor (PPAR)γ, lipogenic enzymes acetyl-CoA carboxylase (ACC) and fatty acid synthase (FAS), and lipid droplet-coating protein perilipin A. When preadipocytes were co-cultured with 2,4,5-TMBA (0.5 mM) specifically at post-induction days 0-2, 2-4, 4-6, or 6-8 only, relative lipid accumulation was decreased by 67.93, 34.65, 49.56, and 34.32%, respectively. A time-course study showed that treatment of 2,4,5-TMBA suppressed the phosphorylation of ERK1 at the initial stage of adipogenesis but upregulated the phosphorylation at the late stage, which is opposite to the conditions required for the differentiation process. The overall expression of C/EBPα, β, and δ, PPARγ2, ACC, FAS, and perilipin A in preadipocytes was downregulated by the treatment of 2,4,5-TMBA. Taken together, our findings suggest that 2,4,5-TMBA suppresses adipogenesis through the regulation of ERK1 phosphorylation. Although results from in vitro studies cannot be directly extrapolated into clinical effects, our study will help to elucidate the anti-adipogenic potential of 2,4,5-TMBA.

Functional characterization of cytochrome P450-derived epoxyeicosatrienoic acids in adipogenesis and obesity

Adipogenesis plays a critical role in the initiation and progression of obesity. Although cytochrome P450 (CYP)-derived epoxyeicosatrienoic acids (EETs) have emerged as a potential therapeutic target for cardiometabolic disease, the functional contribution of EETs to adipogenesis and the pathogenesis of obesity remain poorly understood. Our studies demonstrated that induction of adipogenesis in differentiated 3T3-L1 cells (in vitro) and obesity-associated adipose expansion in high-fat diet (HFD)-fed mice (in vivo) significantly dysregulate the CYP epoxygenase pathway and evoke a marked suppression of adipose-derived EET levels. Subsequent in vitro experiments demonstrated that exogenous EET analog administration elicits potent anti-adipogenic effects via inhibition of the early phase of adipogenesis. Furthermore, EET analog administration to mice significantly mitigated HFD-induced weight gain, adipose tissue expansion, pro-adipogenic gene expression, and glucose intolerance. Collectively, these findings suggest that suppression of EET bioavailability in adipose tissue is a key pathological consequence of obesity, and strategies that promote the protective effects of EETs in adipose tissue offer enormous therapeutic potential for obesity and its downstream pathological consequences.

Prostaglandin E2 signals white-to-brown adipogenic differentiation

The formation of new adipocytes from precursor cells is a crucial aspect of normal adipose tissue function. During the adipogenic process, adipocytes differentiated from mesenchymal stem cells give rise to two main types of fat: white adipose tissue (WAT) characterized by the presence of adipocytes containing large unilocular lipid droplets, and brown adipose tissue (BAT) composed by multilocular brown adipocytes packed with mitochondria. WAT is not only important for energy storage but also as an endocrine organ regulating whole body homeostasis by secreting adipokines and other mediators, which directly impact metabolic functions in obesity. By contrast, BAT is specialized in dissipating energy in form of heat and has salutary effects in combating obesity and associated disorders. Unfortunately, WAT is the predominant fat type, whereas BAT is scarce and located in discrete pockets in adult humans. Luckily, another type of brown adipocytes, called beige or brite (brown-in-white) adipocytes, with similar functions to those of "classical" brown adipocytes has recently been identified in WAT. In this review, a close look is given into the role of bioactive lipid mediators in the regulation of adipogenesis, with a special emphasis on the role of the microsomal prostaglandin E (PGE) synthase-1, a terminal enzyme in PGE2 biosynthesis, as a key regulator of white-to-brown adipogenesis in WAT.

The role of the PGE2-aromatase pathway in obesity-associated breast inflammation

Subbaramaiah and colleagues present the first evidence indicating that a cyclooxygenase-2-prostaglandin E(2)-aromatase pathway promotes obesity-associated inflammation in women's breast tissues. Their findings shed new light on obesity-associated inflammation in general and provide a rationale for developing effective chemopreventive and therapeutic strategies targeting this pathway for obese women with breast inflammation and patients with hormone-dependent breast cancer.

New candidate loci identified by array-CGH in a cohort of 100 children presenting with syndromic obesity

Syndromic obesity is defined by the association of obesity with one or more feature(s) including developmental delay, dysmorphic traits, and/or congenital malformations. Over 25 syndromic forms of obesity have been identified. However, most cases remain of unknown etiology. The aim of this study was to identify new candidate loci associated with syndromic obesity to find new candidate genes and to better understand molecular mechanisms involved in this pathology. We performed oligonucleotide microarray-based comparative genomic hybridization in a cohort of 100 children presenting with syndromic obesity of unknown etiology, after exhaustive clinical, biological, and molecular studies. Chromosomal copy number variations were detected in 42% of the children in our cohort, with 23% of patients with potentially pathogenic copy number variants. Our results support that chromosomal rearrangements are frequently associated with syndromic obesity with a variety of contributory genes having relevance to either obesity or developmental delay. A list of inherited or apparently de novo duplications and deletions including their enclosed genes and not previously linked to syndromic obesity was established. Proteins encoded by several of these genes are involved in lipid metabolism (ACOXL, MSMO1, MVD, and PDZK1) linked with nervous system function (BDH1 and LINGO2), neutral lipid storage (PLIN2), energy homeostasis and metabolic processes (CDH13, CNTNAP2, CPPED1, NDUFA4, PTGS2, and SOCS6).

Indomethacin treatment prevents high fat diet-induced obesity and insulin resistance but not glucose intolerance in C57BL/6J mice

Chronic low grade inflammation is closely linked to obesity-associated insulin resistance. To examine how administration of the anti-inflammatory compound indomethacin, a general cyclooxygenase inhibitor, affected obesity development and insulin sensitivity, we fed obesity-prone male C57BL/6J mice a high fat/high sucrose (HF/HS) diet or a regular diet supplemented or not with indomethacin (±INDO) for 7 weeks. Development of obesity, insulin resistance, and glucose intolerance was monitored, and the effect of indomethacin on glucose-stimulated insulin secretion (GSIS) was measured in vivo and in vitro using MIN6 β-cells. We found that supplementation with indomethacin prevented HF/HS-induced obesity and diet-induced changes in systemic insulin sensitivity. Thus, HF/HS+INDO-fed mice remained insulin-sensitive. However, mice fed HF/HS+INDO exhibited pronounced glucose intolerance. Hepatic glucose output was significantly increased. Indomethacin had no effect on adipose tissue mass, glucose tolerance, or GSIS when included in a regular diet. Indomethacin administration to obese mice did not reduce adipose tissue mass, and the compensatory increase in GSIS observed in obese mice was not affected by treatment with indomethacin. We demonstrate that indomethacin did not inhibit GSIS per se, but activation of GPR40 in the presence of indomethacin inhibited glucose-dependent insulin secretion in MIN6 cells. We conclude that constitutive high hepatic glucose output combined with impaired GSIS in response to activation of GPR40-dependent signaling in the HF/HS+INDO-fed mice contributed to the impaired glucose clearance during a glucose challenge and that the resulting lower levels of plasma insulin prevented the obesogenic action of the HF/HS diet.

Brown fat determination and development from muscle precursor cells by novel action of bone morphogenetic protein 6

Brown adipose tissue (BAT) plays a pivotal role in promoting energy expenditure by the virtue of uncoupling protein-1 (UCP-1) that differentiates BAT from its energy storing white adipose tissue (WAT) counterpart. The clinical implication of “classical” BAT (originates from Myf5 positive myoblastic lineage) or the “beige” fat (originates through trans-differentiation of WAT) activation in improving metabolic parameters is now becoming apparent. However, the inducers and endogenous molecular determinants that govern the lineage commitment and differentiation of classical BAT remain obscure. We report here that in the absence of any forced gene expression, stimulation with bone morphogenetic protein 6 (BMP6) induces brown fat differentiation from skeletal muscle precursor cells of murine and human origins. Through a comprehensive transcriptional profiling approach, we have discovered that two days of BMP6 stimulation in C2C12 myoblast cells is sufficient to induce genes characteristic of brown preadipocytes. This developmental switch is modulated in part by newly identified regulators, Optineurin (Optn) and Cyclooxygenase-2 (Cox2). Furthermore, pathway analyses using the Causal Reasoning Engine (CRE) identified additional potential causal drivers of this BMP6 induced commitment switch. Subsequent analyses to decipher key pathway that facilitates terminal differentiation of these BMP6 primed cells identified a key role for Insulin Like Growth Factor-1 Receptor (IGF-1R). Collectively these data highlight a therapeutically innovative role for BMP6 by providing a means to enhance the amount of myogenic lineage derived brown fat.

Dietary cocoa reduces metabolic endotoxemia and adipose tissue inflammation in high-fat fed mice

In diet-induced obesity, adipose tissue (AT) is in a chronic state of inflammation predisposing the development of metabolic syndrome. Cocoa (Theobroma cacao) is a polyphenol-rich food with putative anti-inflammatory activities. Here, we examined the impact and underlying mechanisms of action of cocoa on AT inflammation in high fat-fed mice. In the present study, male C57BL/6 J mice were fed a high fat diet (HF), a HF diet with 8% (w/w) unsweetened cocoa powder (HFC), or a low-fat diet (LF) for 18 weeks. Cocoa supplementation decreased AT mRNA levels of tumor necrosis factor-α, interleukin-6, inducible nitric oxide synthase, and EGF-like module-containing mucin-like hormone receptor-like 1 by 40-60% compared to HF group, and this was accompanied by decreased nuclear protein levels of nuclear factor-κB. Cocoa treatment reduced the levels of arachidonic acid in the AT by 33% compared to HF controls. Moreover, cocoa treatment also reduced protein levels of the eicosanoid-generating enzymes, adipose-specific phospholipase A2 and cyclooxygenase-2 by 53% and 55%, respectively, compared to HF-fed mice. Finally, cocoa treatment ameliorated metabolic endotoxemia (40% reduction in plasma endotoxin) and improved gut barrier function (as measured by increased plasma levels of glucagon-like peptide-2). In conclusion, the present study has shown for the first time that long-term cocoa supplementation can reduce AT inflammation in part by modulating eicosanoid metabolism and metabolic endotoxemia.