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

Prostaglandin E2 in the Tumor Microenvironment, a Convoluted Affair Mediated by EP Receptors 2 and 4

The involvement of the prostaglandin E2 (PGE2) system in cancer progression has long been recognized. PGE2 functions as an autocrine and paracrine signaling molecule with pleiotropic effects in the human body. High levels of intratumoral PGE2 and overexpression of the key metabolic enzymes of PGE2 have been observed and suggested to contribute to tumor progression. This has been claimed for different types of solid tumors, including, but not limited to, lung, breast, and colon cancer. PGE2 has direct effects on tumor cells and angiogenesis that are known to promote tumor development. However, one of the main mechanisms behind PGE2 driving cancerogenesis is currently thought to be anchored in suppressed antitumor immunity, thus providing possible therapeutic targets to be used in cancer immunotherapies. EP2 and EP4, two receptors for PGE2, are emerging as being the most relevant for this purpose. This review aims to summarize the known roles of PGE2 in the immune system and its functions within the tumor microenvironment. SIGNIFICANCE STATEMENT: Prostaglandin E2 (PGE2) has long been known to be a signaling molecule in cancer. Its presence in tumors has been repeatedly associated with disease progression. Elucidation of its effects on immunological components of the tumor microenvironment has highlighted the potential of PGE2 receptor antagonists in cancer treatment, particularly in combination with immune checkpoint inhibitor therapeutics. Adjuvant treatment could increase the response rates and the efficacy of immune-based therapies.

Correlation between whole salivary prostaglandin E2 and hemoglobin A1c levels among type-2 diabetic and non-diabetic patients with periodontal inflammation

BACKGROUND

It is hypothesized that whole salivary prostaglandin E2 (PgE2) levels are higher in patients with type-2 diabetes mellitus (type-2 DM) than non-diabetic individuals with periodontal inflammation; and that whole salivary expression of PgE2 is correlated with hemoglobin A1C (HbA1c) levels. The aim of the present study was to compare whole salivary PgE2 levels among patients with type-2 DM and non-diabetic individuals with periodontal inflammation.

METHODS

Sociodemographic data, duration since the diagnosis and management of type-2 DM, most recent hemoglobin A1C (HbA1c level), and any familial history of DM was retrieved from patient's healthcare records. Participants were divided into four groups: Group-1: type-2 diabetics with periodontal inflammation; Group-2: type-2 diabetics without periodontal inflammation; Group-3: non-diabetics with periodontal inflammation; and Group-4: non-diabetics without periodontal inflammation. Plaque and gingival indices (PI and GI), probing depth (PD), clinical attachment loss (CAL) and marginal bone loss (MBL) were measured. Unstimulated whole saliva samples were collected and PgE2 levels were measured. Group-comparisons were done and P < 0.05 were considered statistically significant.

RESULTS

One-hundred-sixty individuals were included. Mean HbA1c levels were higher in Group-1 than groups 2 (P < 0.05), 3 (P < 0.05) and 4 (P < 0.05). The PI (P < 0.05), GI (P < 0.05) and PD (P < 0.05) were higher in Group-1 than groups 2 and 4. The CAL was higher in Group-1 than groups 2 (P < 0.05) and 3 (P < 0.05). The PD (P < 0.05), PI (P < 0.05) and GI (P < 0.05) were higher in Group-3 than Group-4. The MBL was higher in Group-1 than groups 2 (P < 0.05), 3 (P < 0.05) and 4 (P < 0.05). The PgE2 levels were higher in Group-1 than groups 2 (P < 0.05), 3 (P < 0.05) and 4 (P < 0.05).

CONCLUSION

Hyperglycemia in patients with type-2 DM is associated with increased expression of whole salivary PgE2 levels and worsened periodontal inflammation compared with individuals with well-controlled type-2 DM and non-diabetic individuals.

Ginsenoside Rb1 Promotes Hepatic Glycogen Synthesis to Ameliorate T2DM Through 15-PGDH/PGE2/EP4 Signaling Pathway

Purpose

Ginsenoside Rb1 (Rb1), one of the crucial bioactive constituents in Panax ginseng C. A. Mey., possesses anti-type 2 diabetes mellitus (T2DM) property. Nevertheless, the precise mechanism, particularly the impact of Rb1 on hepatic glycogen production, a crucial process in the advancement of T2DM, remains poorly understood. 15-hydroxyprostaglandin dehydrogenase (15-PGDH) is responsible for prostaglandin E2 (PGE2) inactivation. A recent study has reported that inhibition of 15-PGDH promoted hepatic glycogen synthesis and improved T2DM. Therefore, herein, we aimed to investigate whether Rb1 ameliorated T2DM through 15-PGDH/PGE2-regulated hepatic glycogen synthesis.

Methods

By combining streptozotocin with a high-fat diet, we successfully established a mouse model for T2DM. Afterward, these mice were administered Rb1 or metformin for 8 weeks. An insulin-resistant cell model was established by incubating LO2 cells with palmitic acid. Liver glycogen and PGE2 levels, the expression levels of 15-PGDH, serine/threonine kinase AKT (AKT), and glycogen synthase kinase 3 beta (GSK3β) were measured. Molecular docking was used to predict the binding affinity between 15-PGDH and Rb1.

Results

Rb1 administration increased the phosphorylation levels of AKT and GSK3β to enhance glycogen synthesis in the liver of T2DM mice. Molecular docking indicated that Rb1 had a high affinity for 15-PGDH. Moreover, Rb1 treatment resulted in the suppression of elevated 15-PGDH levels and the elevation of decreased PGE2 levels in the liver of T2DM mice. Furthermore, in vitro experiments showed that Rb1 administration might enhance glycogen production by modulating the 15-PGDH/PGE2/PGE2 receptor EP4 pathway.

Conclusion

Our findings indicate that Rb1 may enhance liver glycogen production through a 15-PGDH-dependent pathway to ameliorate T2DM, thereby offering a new explanation for the positive impact of Rb1 on T2DM and supporting its potential as an effective therapeutic approach for T2DM.

15-Hydroxyprostaglandin dehydrogenase inhibitor SW033291 ameliorates hepatic abnormal lipid metabolism, ER stress, and inflammation through PGE2/EP4 in T2DM mice

Type 2 diabetes mellitus (T2DM) is a rapidly growing epidemic that results in increased morbidity, mortality, and soaring medical costs. Prostaglandin E₂ (PGE₂), a vital lipid mediator, has been reported to protect against hepatic steatosis, inflammation, endoplasmic reticulum (ER) stress, and insulin resistance, indicating its potential therapeutic role in T2DM. PGE₂ can be degraded by 15-hydroxyprostaglandin dehydrogenase (15-PGDH). SW033291, an inhibitor of 15-PGDH, has been reported to increase PGE₂ levels, however, the effect of SW033291 in T2DM remains to be explored. This study aims to evaluate whether SW033291 protects against T2DM and explore its potential mechanisms. A T2DM mouse model was established through high-fat diet/streptozotocin injection, while palmitic acid-treated mouse primary hepatocytes were used as insulin-resistant cell models. SW033291 treatment reduced body weight, fat weight, fasting blood glucose, and improved impaired glucose tolerance and insulin resistance in T2DM mice. More importantly, SW033291 alleviated steatosis, inflammation, and ER stress in the liver of T2DM mice. Mechanistically, SW033291 decreased the expressions of SREBP-1c and ACC1, and increased the expression of PPARα in T2DM mice. Additionally, SW033291 inhibited NF-κB and eIF2α/CHOP signaling in T2DM mice. Further, we showed that the protective effects of SW033291 on the above-mentioned pathophysiological processes could be hindered by inhibition of the PGE₂ receptor EP4. Overall, our study reveals a novel role of SW033291 in alleviating T2DM and suggests its potential as a new therapeutic strategy for T2DM.

m 6 A mRNA Methylation in Brown Adipose Tissue Regulates Systemic Insulin Sensitivity via an Inter-Organ Prostaglandin Signaling Axis

Brown adipose tissue (BAT) has the capacity to regulate systemic metabolism through the secretion of signaling lipids. N6-methyladenosine (m 6 A) is the most prevalent and abundant post-transcriptional mRNA modification and has been reported to regulate BAT adipogenesis and energy expenditure. In this study, we demonstrate that the absence of m 6 A methyltransferase-like 14 (METTL14), modifies the BAT secretome to initiate inter-organ communication to improve systemic insulin sensitivity. Importantly, these phenotypes are independent of UCP1-mediated energy expenditure and thermogenesis. Using lipidomics, we identified prostaglandin E2 (PGE2) and prostaglandin F2a (PGF2a) as M14 KO -BAT-secreted insulin sensitizers. Notably, circulatory PGE2 and PGF2a levels are inversely correlated with insulin sensitivity in humans. Furthermore, in vivo administration of PGE2 and PGF2a in high-fat diet-induced insulin-resistant obese mice recapitulates the phenotypes of METTL14 deficient animals. PGE2 or PGF2a improves insulin signaling by suppressing the expression of specific AKT phosphatases. Mechanistically, METTL14-mediated m 6 A installation promotes decay of transcripts encoding prostaglandin synthases and their regulators in human and mouse brown adipocytes in a YTHDF2/3-dependent manner. Taken together, these findings reveal a novel biological mechanism through which m 6 A-dependent regulation of BAT secretome regulates systemic insulin sensitivity in mice and humans.

Highlights

Mettl14 KO -BAT improves systemic insulin sensitivity via inter-organ communication; PGE2 and PGF2a are BAT-secreted insulin sensitizers and browning inducers;PGE2 and PGF2a sensitize insulin responses through PGE2-EP-pAKT and PGF2a-FP-AKT axis; METTL14-mediated m 6 A installation selectively destabilizes prostaglandin synthases and their regulator transcripts; Targeting METTL14 in BAT has therapeutic potential to enhance systemic insulin sensitivity.

Abstract Figure

The 15-hydroxyprostaglandin dehydrogenase inhibitor SW033291 ameliorates abnormal hepatic glucose metabolism through PGE2-EP4 receptor-AKT signaling in a type 2 diabetes mellitus mouse model

Type 2 diabetes mellitus (T2DM) is associated with high rates of morbidity and mortality worldwide. Prostaglandin E₂ (PGE₂) is a lipid signaling molecule that can ameliorate the symptoms of some metabolic diseases, including T2DM, and improve tissue repair and regeneration. Although SW033291 can increase PGE₂ levels through its action as a small molecule inhibitor of the PGE₂-degrading enzyme 15-hydroxyprostaglandin dehydrogenase, its effects on T2DM remain unclear. In the present study, we evaluated whether SW033291 treatment exerts a protective effect against T2DM and explored the underlying mechanisms. A T2DM mouse model was established using a high-fat diet combined with streptozotocin treatment. Palmitic acid-treated LO2 cells were used as an insulin-resistant cell model. SW033291 treatment reduced body weight and fasting blood glucose levels as well as serum triglyceride, total cholesterol, and low-density lipoprotein cholesterol levels in vivo. In addition to ameliorating glucose and insulin tolerance, SW033291 treatment reversed the T2DM-induced decrease in glycogen synthesis and increase in gluconeogenesis in the liver. Furthermore, SW033291 administration increased hepatic glycogen synthase kinase 3 beta (GSK3β) phosphorylation levels to promote glycogen synthesis. SW033291 treatment also inhibited gluconeogenesis by upregulating AKT serine/threonine kinase (AKT) and forkhead box O1 (FOXO1) phosphorylation and reducing glucose-6-phosphatase and phosphoenolpyruvate carboxykinase 1 expression in the livers of T2DM model mice. Additionally, SW033291 treatment improved abnormal hepatic glucose metabolism through the PGE₂-EP4 receptor-AKT-GSK3β/FOXO1 signaling pathway in vitro. These results suggest a novel role of SW033291 in improving T2DM and support its potential as a novel therapeutic agent.

The role of PGE2 and EP receptors on lung's immune and structural cells; possibilities for future asthma therapy

Asthma is the most common airway chronic disease with treatments aimed mainly to control the symptoms. Adrenergic receptor agonists, corticosteroids and anti-leukotrienes have been used for decades, and the development of more targeted asthma treatments, known as biological therapies, were only recently established. However, due to the complexity of asthma and the limited efficacy as well as the side effects of available treatments, there is an urgent need for a new generation of asthma therapies. The anti-inflammatory and bronchodilatory effects of prostaglandin E2 in asthma are promising, yet complicated by undesirable side effects, such as cough and airway irritation. In this review, we summarize the most important literature on the role of all four E prostanoid (EP) receptors on the lung's immune and structural cells to further dissect the relevance of EP2/EP4 receptors as potential targets for future asthma therapy.

Association of urinary prostaglandin E2 metabolite and mortality among adults

Prostaglandins play a critical role in inflammatory response. To investigate the association of urinary PGE-M, a stable end-product of prostaglandin E2 (PGE₂) with overall and cause-specific mortality and examine potential effect modifiers, we obtained urinary PGE-M levels of 2927 non-cancerous adults from our previous case-control studies nested in the Shanghai Women's Health Study and Shanghai Men's Health Study, two cohort studies conducted in Shanghai, China. Mortality data and modifiable factors associated with urinary PGE-M were obtained from the parent cohort studies. Using linear regression models, we found that high urinary PGE-M levels were significantly associated with low education, heaving smoking, old age at urine collection, and abdominal obesity. Using Cox proportional hazards models, we found that increase (per standard deviation) of urinary PGE-M levels were significantly associated with overall mortality (adjusted hazard ratio = 1.19, 95% confidence interval: 1.07, 1.33) and particularly deaths from cardiometabolic diseases (adjusted hazard ratio = 1.27, 95% confidence interval: 1.11, 1.44). The increased death risks persisted across different time intervals during the follow-up and were stronger among participants who were younger than 60 (P = 0.0014 for all- cause mortality and P = 0.007 for deaths from cardiometabolic diseases) at urine collection or perhaps among those who had higher education.

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.

SILAC-based quantitative proteomics to investigate the eicosanoid associated inflammatory response in activated macrophages

BACKGROUND

Macrophages play a central role in inflammation by phagocytosing invading pathogens, apoptotic cells and debris, as well as mediating repair of tissues damaged by trauma. In order to do this, these dynamic cells generate a variety of inflammatory mediators including eicosanoids such as prostaglandins, leukotrienes and hydroxyeicosatraenoic acids (HETEs) that are formed through the cyclooxygenase, lipoxygenase and cytochrome P450 pathways. The ability to examine the effects of eicosanoid production at the protein level is therefore critical to understanding the mechanisms associated with macrophage activation.

RESULTS

This study presents a stable isotope labelling with amino acids in cell culture (SILAC) -based proteomics strategy to quantify the changes in macrophage protein abundance following inflammatory stimulation with Kdo2-lipid A and ATP, with a focus on eicosanoid metabolism and regulation. Detailed gene ontology analysis, at the protein level, revealed several key pathways with a decrease in expression in response to macrophage activation, which included a promotion of macrophage polarisation and dynamic changes to energy requirements, transcription and translation. These findings suggest that, whilst there is evidence for the induction of a pro-inflammatory response in the form of prostaglandin secretion, there is also metabolic reprogramming along with a change in cell polarisation towards a reduced pro-inflammatory phenotype.

CONCLUSIONS

Advanced quantitative proteomics in conjunction with functional pathway network analysis is a useful tool to investigate the molecular pathways involved in inflammation.

Metabolic Syndrome and Overactive Bladder Syndrome May Share Common Pathophysiologies

Metabolic syndrome (MetS) is defined by a group of cardiovascular risk factors, including impaired glucose tolerance, central obesity, hypertension, and dyslipidemia. Overactive bladder (OAB) syndrome consists of symptoms such as urinary urgency, frequency, and nocturia with or without urge incontinence. The high prevalences of metabolic syndrome (MetS) and overactive bladder (OAB) worldwide affect quality of life and cause profound negative impacts on the social economy. Accumulated evidence suggests that MetS might contribute to the underlying mechanisms for developing OAB, and MetS-associated OAB could be a subtype of OAB. However, how could these two syndromes interact with each other? Based on results of animal studies and observations in epidemiological studies, we summarized the common pathophysiologies existing between MetS and OAB, including autonomic and peripheral neuropathies, chronic ischemia, proinflammatory status, dysregulation of nutrient-sensing pathways (e.g., insulin resistance at the bladder mucosa and excessive succinate intake), and the probable role of dysbiosis. Since the MetS-associated OAB is a subtype of OAB with distinctive pathophysiologies, the regular and non-specific medications, such as antimuscarinics, beta-3 agonist, and botulinum toxin injection, might lead to unsatisfying results. Understanding the pathophysiologies of MetS-associated OAB might benefit future studies exploring novel biomarkers for diagnosis and therapeutic targets on both MetS and OAB.

Prostaglandin E2 receptor 3 (EP3) promotes M1 macrophages polarization in unexplained recurrent pregnancy loss (uRPL)

Unexplained Recurrent Pregnancy Loss (uRPL) is associated with macrophage polarization, which can be modulated by prostaglandin E2 (PGE2). Our previous study demonstrated that PGE2 receptor 3 (EP3) signaling is induced in the first trimester placentas of uRPL patients compared to its expression in healthy controls. However, whether EP3 plays a role in macrophage polarization at the maternal-fetal interface of uRPL women remains unknown. The positive expression of EP3 in decidual macrophages was confirmed by double immunofluorescence staining in the first trimester placentas collected from uRPL patients and healthy controls. CD68, iNOS and CD163 were used as immunofluorescence marker for decidual macrophages, M1 and M2 macrophages. To clarify the effects of EP3 on macrophage polarization, THP-1 monocyte cells were applied as M0 macrophages after phorbol 12-myristate 13-acetate (PMA) treatment for in vitro study. The mRNA levels of representative M1 markers (interleukin-1β and interleukin-6) and M2 markers (interleukin-10 and arginase-1) were quantified with qPCR in M0 macrophages being stimulated with sulprostone (an EP3 agonist) or L-798, 106 (an EP3 antagonist). We found that EP3 expression was upregulated in the decidual macrophages of first trimester placentas from uRPL patients compared to healthy controls. Furthermore, EP3 expression was increased in M1 macrophages compared to in M2 macrophages in first trimester placentas of uRPL patients. Sulprostone intensified the mRNA levels of IL-6 together with interferon-γ (IFN-γ), while L-798,106 stimulated the mRNA expression of IL-10 and Arg-1 in a dose-dependent manner.

Paracrine Role of the Endothelium in Metabolic Homeostasis in Health and Nutrient Excess

The vascular endothelium traditionally viewed as a simple physical barrier between the circulation and tissue is now well-established as a key organ mediating whole organism homeostasis by release of a portfolio of anti-inflammatory and pro-inflammatory vasoactive molecules. Healthy endothelium releases anti-inflammatory signaling molecules such as nitric oxide and prostacyclin; in contrast, diseased endothelium secretes pro-inflammatory signals such as reactive oxygen species, endothelin-1 and tumor necrosis factor-alpha (TNFα). Endothelial dysfunction, which has now been identified as a hallmark of different components of the cardiometabolic syndrome including obesity, type 2 diabetes and hypertension, initiates and drives the progression of tissue damage in these disorders. Recently it has become apparent that, in addition to vasoactive molecules, the vascular endothelium has the potential to secrete a diverse range of small molecules and proteins mediating metabolic processes in adipose tissue (AT), liver, skeletal muscle and the pancreas. AT plays a pivotal role in orchestrating whole-body energy homeostasis and AT dysfunction, characterized by local and systemic inflammation, is central to the metabolic complications of obesity. Thus, understanding and targeting the crosstalk between the endothelium and AT may generate novel therapeutic opportunities for the cardiometabolic syndrome. Here, we provide an overview of the role of the endothelial secretome in controlling the function of AT. The endothelial-derived metabolic regulatory factors are grouped and discussed based on their physical properties and their downstream signaling effects. In addition, we focus on the therapeutic potential of these regulatory factors in treating cardiometabolic syndrome, and discuss areas of future study of potential translatable and clinical significance. The vascular endothelium is emerging as an important paracrine/endocrine organ that secretes regulatory factors in response to nutritional and environmental cues. Endothelial dysfunction may result in imbalanced secretion of these regulatory factors and contribute to the progression of AT and whole body metabolic dysfunction. As the vascular endothelium is the first responder to local nutritional changes and adipocyte-derived signals, future work elucidating the changes in the endothelial secretome is crucial to improve our understanding of the pathophysiology of cardiometabolic disease, and in aiding our development of new therapeutic strategies to treat and prevent cardiometabolic syndrome.

Metabolite G-Protein Coupled Receptors in Cardio-Metabolic Diseases

G protein-coupled receptors (GPCRs) have originally been described as a family of receptors activated by hormones, neurotransmitters, and other mediators. However, in recent years GPCRs have shown to bind endogenous metabolites, which serve functions other than as signaling mediators. These receptors respond to fatty acids, mono- and disaccharides, amino acids, or various intermediates and products of metabolism, including ketone bodies, lactate, succinate, or bile acids. Given that many of these metabolic processes are dysregulated under pathological conditions, including diabetes, dyslipidemia, and obesity, receptors of endogenous metabolites have also been recognized as potential drug targets to prevent and/or treat metabolic and cardiovascular diseases. This review describes G protein-coupled receptors activated by endogenous metabolites and summarizes their physiological, pathophysiological, and potential pharmacological roles.

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.

Investigation of candidate genes and mechanisms underlying obesity associated type 2 diabetes mellitus using bioinformatics analysis and screening of small drug molecules

BACKGROUND

Obesity associated type 2 diabetes mellitus is a metabolic disorder ; however, the etiology of obesity associated type 2 diabetes mellitus remains largely unknown. There is an urgent need to further broaden the understanding of the molecular mechanism associated in obesity associated type 2 diabetes mellitus.

METHODS

To screen the differentially expressed genes (DEGs) that might play essential roles in obesity associated type 2 diabetes mellitus, the publicly available expression profiling by high throughput sequencing data (GSE143319) was downloaded and screened for DEGs. Then, Gene Ontology (GO) and REACTOME pathway enrichment analysis were performed. The protein - protein interaction network, miRNA - target genes regulatory network and TF-target gene regulatory network were constructed and analyzed for identification of hub and target genes. The hub genes were validated by receiver operating characteristic (ROC) curve analysis and RT- PCR analysis. Finally, a molecular docking study was performed on over expressed proteins to predict the target small drug molecules.

RESULTS

A total of 820 DEGs were identified between healthy obese and metabolically unhealthy obese, among 409 up regulated and 411 down regulated genes. The GO enrichment analysis results showed that these DEGs were significantly enriched in ion transmembrane transport, intrinsic component of plasma membrane, transferase activity, transferring phosphorus-containing groups, cell adhesion, integral component of plasma membrane and signaling receptor binding, whereas, the REACTOME pathway enrichment analysis results showed that these DEGs were significantly enriched in integration of energy metabolism and extracellular matrix organization. The hub genes CEBPD, TP73, ESR2, TAB1, MAP 3K5, FN1, UBD, RUNX1, PIK3R2 and TNF, which might play an essential role in obesity associated type 2 diabetes mellitus was further screened.

CONCLUSIONS

The present study could deepen the understanding of the molecular mechanism of obesity associated type 2 diabetes mellitus, which could be useful in developing therapeutic targets for obesity associated type 2 diabetes mellitus.

Molecular Crosstalk Between Macrophages and Mesenchymal Stromal Cells

Mesenchymal stromal cells (MSCs) have been widely investigated for regenerative medicine applications, from treating various inflammatory diseases as a cell therapy to generating engineered tissue constructs. Numerous studies have evaluated the potential effects of MSCs following therapeutic administration. By responding to their surrounding microenvironment, MSCs may mediate immunomodulatory effects through various mechanisms that directly (i.e., contact-dependent) or indirectly (i.e., paracrine activity) alter the physiology of endogenous cells in various disease pathologies. More specifically, a pivotal crosstalk between MSCs and tissue-resident macrophages and monocytes (TMφ) has been elucidated using in vitro and in vivo preclinical studies. An improved understanding of this crosstalk could help elucidate potential mechanisms of action (MOAs) of therapeutically administered MSCs. TMφ, by nature of their remarkable functional plasticity and prevalence within the body, are uniquely positioned as critical modulators of the immune system - not only in maintaining homeostasis but also during pathogenesis. This has prompted further exploration into the cellular and molecular alterations to TMφ mediated by MSCs. In vitro assays and in vivo preclinical trials have identified key interactions mediated by MSCs that polarize the responses of TMφ from a pro-inflammatory (i.e., classical activation) to a more anti-inflammatory/reparative (i.e., alternative activation) phenotype and function. In this review, we describe physiological and pathological TMφ functions in response to various stimuli and discuss the evidence that suggest specific mechanisms through which MSCs may modulate TMφ phenotypes and functions, including paracrine interactions (e.g., secretome and extracellular vesicles), nanotube-mediated intercellular exchange, bioenergetics, and engulfment by macrophages. Continued efforts to elucidate this pivotal crosstalk may offer an improved understanding of the immunomodulatory capacity of MSCs and inform the development and testing of potential MOAs to support the therapeutic use of MSCs and MSC-derived products in various diseases.

Metabolic Functions of G Protein-Coupled Receptors in Hepatocytes-Potential Applications for Diabetes and NAFLD

G protein-coupled receptors (GPCRs) are cell surface receptors that mediate the function of extracellular ligands. Understanding how GPCRs work at the molecular level has important therapeutic implications, as 30–40% of the drugs currently in clinical use mediate therapeutic effects by acting on GPCRs. Like many other cell types, liver function is regulated by GPCRs. More than 50 different GPCRs are predicted to be expressed in the mouse liver. However, knowledge of how GPCRs regulate liver metabolism is limited. A better understanding of the metabolic role of GPCRs in hepatocytes, the dominant constituent cells of the liver, could lead to the development of novel drugs that are clinically useful for the treatment of various metabolic diseases, including type 2 diabetes, nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH). In this review, we describe the functions of multiple GPCRs expressed in hepatocytes and their role in metabolic processes.

International Union of Basic and Clinical Pharmacology. CIX. Differences and Similarities between Human and Rodent Prostaglandin E2 Receptors (EP1-4) and Prostacyclin Receptor (IP): Specific Roles in Pathophysiologic Conditions

Prostaglandins are derived from arachidonic acid metabolism through cyclooxygenase activities. Among prostaglandins (PGs), prostacyclin (PGI2) and PGE2 are strongly involved in the regulation of homeostasis and main physiologic functions. In addition, the synthesis of these two prostaglandins is significantly increased during inflammation. PGI2 and PGE2 exert their biologic actions by binding to their respective receptors, namely prostacyclin receptor (IP) and prostaglandin E2 receptor (EP) 1-4, which belong to the family of G-protein-coupled receptors. IP and EP1-4 receptors are widely distributed in the body and thus play various physiologic and pathophysiologic roles. In this review, we discuss the recent advances in studies using pharmacological approaches, genetically modified animals, and genome-wide association studies regarding the roles of IP and EP1-4 receptors in the immune, cardiovascular, nervous, gastrointestinal, respiratory, genitourinary, and musculoskeletal systems. In particular, we highlight similarities and differences between human and rodents in terms of the specific roles of IP and EP1-4 receptors and their downstream signaling pathways, functions, and activities for each biologic system. We also highlight the potential novel therapeutic benefit of targeting IP and EP1-4 receptors in several diseases based on the scientific advances, animal models, and human studies. SIGNIFICANCE STATEMENT: In this review, we present an update of the pathophysiologic role of the prostacyclin receptor, prostaglandin E2 receptor (EP) 1, EP2, EP3, and EP4 receptors when activated by the two main prostaglandins, namely prostacyclin and prostaglandin E2, produced during inflammatory conditions in human and rodents. In addition, this comparison of the published results in each tissue and/or pathology should facilitate the choice of the most appropriate model for the future studies.

Leukotriene A4 hydrolase deficiency protects mice from diet-induced obesity by increasing energy expenditure through neuroendocrine axis

Obesity is a health problem worldwide, and brown adipose tissue (BAT) is important for energy expenditure. Here, we explored the role of leukotriene A₄ hydrolase (LTA₄ H), a key enzyme in the synthesis of the lipid mediator leukotriene B₄ (LTB₄ ), in diet-induced obesity. LTA₄ H-deficient (LTA₄ H-KO) mice fed a high-fat diet (HFD) showed a lean phenotype, and bone-marrow transplantation studies revealed that LTA₄ H-deficiency in non-hematopoietic cells was responsible for this lean phenotype. LTA₄ H-KO mice exhibited greater energy expenditure, but similar food intake and fecal energy loss. LTA₄ H-KO BAT showed higher expression of thermogenesis-related genes. In addition, the plasma thyroid-stimulating hormone and thyroid hormone concentrations, as well as HFD-induced catecholamine secretion, were higher in LTA₄ H-KO mice. In contrast, LTB₄ receptor (BLT1)-deficient mice did not show a lean phenotype, implying that the phenotype of LTA₄ H-KO mice is independent of the LTB₄ /BLT1 axis. These results indicate that LTA₄ H mediates the diet-induced obesity by reducing catecholamine and thyroid hormone secretion.

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.

EP4 signalling is essential for controlling islet inflammation by causing a shift in macrophage polarization in obesity/type 2 diabetes

Activation of the prostaglandin E₂ receptor EP4 alters polarization of adipose tissue macrophages towards the anti-inflammatory M2 phenotype to suppress chronic inflammation. However, the role of EP4 signalling in pancreatic macrophages that affect insulin secretion is unclear. We examined the role of EP4 signalling in islet inflammation in vitro and in vivo. Obese diabetic db/db mice were treated with an EP4-selective agonist or vehicle for 4 weeks. Islet morphology did not significantly differ and glucose-stimulated insulin secretion was increased, whereas the pancreatic M1/M2 ratio was decreased in the EP4 agonist-treated group compared to the vehicle group. Because EP4 activation in MIN6 cells did not affect insulin secretion, we used a MIN6/macrophage co-culture system to evaluate the role of EP4 signalling in islet inflammation and subsequent inhibition of insulin release. Co-culture with M1-polarized macrophages markedly suppressed insulin expression in MIN6 cells; however, modulation of M1 polarization by the EP4 agonist significantly reversed the negative impact of co-cultivation on insulin production. The enhanced expression levels of pro-inflammatory cytokines in co-cultured MIN6 cells were markedly inhibited by EP4 agonist treatment of M1 macrophages. Thus, EP4 activation may suppress islet inflammation and protect β-cell function by altering inflammatory macrophages in the diabetic pancreas.

Monocarboxylate Transporter 6-Mediated Interactions with Prostaglandin F2α: In Vitro and In Vivo Evidence Utilizing a Knockout Mouse Model

Monocarboxylate transporter 6 (MCT6; SLC16A5) is a recently studied drug transporter that currently has no annotated endogenous function. Currently, only a handful of compounds have been characterized as substrates for MCT6 (e.g., bumetanide, nateglinide, probenecid, and prostaglandin F_2α (PGF2α)). The objective of our research was to characterize the MCT6-specific transporter kinetic parameters and MCT6-specific in vitro and in vivo interactions of PGF2α. Murine and human MCT6-mediated transport of PGF2α was assessed in MCT6-transfected oocytes. Additionally, endogenous PGF2α and a primary PGF2α metabolite (PGFM) were measured in plasma and urine in Mct6 knockout (Mct6^−/−) and wild-type (Mct6^+/+) mice. Results demonstrated that the affinity was approximately 40.1 and 246 µM respectively, for mouse and human, at pH 7.4. In vivo, plasma PGF2α concentrations in Mct6^−/− mice were significantly decreased, compared to Mct6^+/+ mice (3.3-fold). Mct6^-/- mice demonstrated a significant increase in urinary PGF2α concentrations (1.7-fold). A similar trend was observed with plasma PGFM concentrations. However, overnight fasting resulted in significantly increased plasma PGF2α concentrations, suggesting a diet-dependent role of Mct6 regulation on the homeostasis of systemic PGF2α. Overall, these results are the first to suggest the potential regulatory role of MCT6 in PGF2α homeostasis, and potentially other PGs, in distribution and metabolism.

Correlative Study on Impaired Prostaglandin E2 Regulation in Epicardial Adipose Tissue and its Role in Maladaptive Cardiac Remodeling via EPAC2 and ST2 Signaling in Overweight Cardiovascular Disease Subjects

There is recent evidence that the dysfunctional responses of a peculiar visceral fat deposit known as epicardial adipose tissue (EAT) can directly promote cardiac enlargement in the case of obesity. Here, we observed a newer molecular pattern associated with LV dysfunction mediated by prostaglandin E2 (PGE₂) deregulation in EAT in a cardiovascular disease (CVD) population. A series of 33 overweight CVD males were enrolled and their EAT thickness, LV mass, and volumes were measured by echocardiography. Blood, plasma, EAT, and SAT biopsies were collected for molecular and proteomic assays. Our data show that PGE₂ biosynthetic enzyme (PTGES-2) correlates with echocardiographic parameters of LV enlargement: LV diameters, LV end diastolic volume, and LV masses. Moreover, PTGES-2 is directly associated with EPAC2 gene (r = 0.70, p < 0.0001), known as a molecular inducer of ST2/IL-33 mediators involved in maladaptive heart remodelling. Furthermore, PGE₂ receptor 3 (PTEGER3) results are downregulated and its expression is inversely associated with ST2/IL-33 expression. Contrarily, PGE₂ receptor 4 (PTGER4) is upregulated in EAT and directly correlates with ST2 molecular expression. Our data suggest that excessive body fatness can shift the EAT transcriptome to a pro-tissue remodelling profile, may be driven by PGE₂ deregulation, with consequent promotion of EPAC2 and ST2 signalling.

Prostaglandin E2/EP Signaling in the Tumor Microenvironment of Colorectal Cancer

The number of colorectal cancer (CRC) patients is increasing worldwide. Accumulating evidence has shown that the tumor microenvironment (TME), including macrophages, neutrophils, and fibroblasts, plays an important role in the development and progression of CRC. Although targeting the TME could be a promising therapeutic approach, the mechanisms by which inflammatory cells promote CRC tumorigenesis are not well understood. When inflammation occurs in tissues, prostaglandin E2 (PGE2) is generated from arachidonic acid by the enzyme cyclooxygenase-2 (COX-2). PGE2 regulates multiple functions in various immune cells by binding to the downstream receptors EP1, EP2, EP3, and EP4, and plays an important role in the development of CRC. The current therapies targeting PGE2 using non-steroidal anti-inflammatory drugs (NSAIDs) or COX-2 inhibitors have failed due to the global prostanoid suppression resulting in the severe adverse effects despite the fact they could prevent tumorigenesis. Therefore, therapies targeting the specific downstream molecules of PGE2 signaling could be a promising approach. This review highlights the role of each EP receptor in the TME of CRC tumorigenesis and their therapeutic potential.

Beyond adiponectin and leptin: adipose tissue-derived mediators of inter-organ communication

The breakthrough discoveries of leptin and adiponectin more than two decades ago led to a widespread recognition of adipose tissue as an endocrine organ. Many more adipose tissue-secreted signaling mediators (adipokines) have been identified since then, and much has been learned about how adipose tissue communicates with other organs of the body to maintain systemic homeostasis. Beyond proteins, additional factors, such as lipids, metabolites, noncoding RNAs, and extracellular vesicles (EVs), released by adipose tissue participate in this process. Here, we review the diverse signaling mediators and mechanisms adipose tissue utilizes to relay information to other organs. We discuss recently identified adipokines (proteins, lipids, and metabolites) and briefly outline the contributions of noncoding RNAs and EVs to the ever-increasing complexities of adipose tissue inter-organ communication. We conclude by reflecting on central aspects of adipokine biology, namely, the contribution of distinct adipose tissue depots and cell types to adipokine secretion, the phenomenon of adipokine resistance, and the capacity of adipose tissue to act both as a source and sink of signaling mediators.

EP4 receptor-associated protein regulates gluconeogenesis in the liver and is associated with hyperglycemia in diabetic mice

Prostaglandin E₂ receptor 4-associated protein (EPRAP) is a key molecule in suppressing inflammatory responses in macrophages. EPRAP is expressed not only in macrophages but also in hepatocytes; however, the role of EPRAP in hepatocytes has not yet been defined. To examine the physiological role of hepatic EPRAP in mice, we performed the glucose tolerance test and the hyperinsulinemic-euglycemic clamp in high-fat sucrose diet (HFSD)-fed wild-type (WT) and Eprap null mice. We evaluated the contribution of EPRAP to gluconeogenesis by pyruvate tolerance test and primary hepatocyte experiments. Furthermore, lentivirus-expressing Eprap-specific small-hairpin RNA was injected in db/ db mice. HFSD-fed Eprap null mice had significantly lower blood glucose levels than HFSD-fed WT mice. Eprap null mice also had low glucose levels after fasting or pyruvic acid injection. Moreover, primary hepatocytes from Eprap-deficient mice showed decreased glucose production and lower expression of the Phosphoenol pyruvate carboxykinase and Glucose 6-phosphatase genes. Lentivirus-mediated hepatic Eprap suppression decreased glucose levels and the expression of gluconeogenic genes in db/ db mice. We conclude that EPRAP regulates gluconeogenesis in hepatocytes and is associated with hyperglycemia in diabetic mice. Our data suggest that suppression of EPRAP could be a novel strategy for the treatment of diabetes.

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

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

The Eicosanoids, Redox-Regulated Lipid Mediators in Immunometabolic Disorders

SIGNIFICANCE

The oxidation of arachidonic acid via cyclooxygenase (COX) and lipoxygenase (LOX) activity to produce eicosanoids during inflammation is a well-known biosynthetic pathway. These lipid mediators are involved in fever, pain, and thrombosis and are produced from multiple cells as well as cell/cell interactions, for example, immune cells and epithelial/endothelial cells. Metabolic disorders, including hyperlipidemia, hypertension, and diabetes, are linked with chronic low-grade inflammation, impacting the immune system and promoting a variety of chronic diseases. Recent Advances: Multiple studies have corroborated the important function of eicosanoids and their receptors in (non)-inflammatory cells in immunometabolic disorders (e.g., insulin resistance, obesity, and cardiovascular and nonalcoholic fatty liver diseases). In this context, LOX and COX products are involved in both pro- and anti-inflammatory responses. In addition, recent work has elucidated the potent function of specialized proresolving mediators (i.e., lipoxins and resolvins) in resolving inflammation, protecting organs, and stimulating tissue repair and remodeling.

CRITICAL ISSUES

Inhibiting/stimulating selected eicosanoid pathways may result in anti-inflammatory and proresolution responses leading to multiple beneficial effects, including the abrogation of reactive oxygen species production, increased speed of resolution, and overall improvement of diseases related to immunometabolic perturbations.

FUTURE DIRECTIONS

Despite many achievements, it is crucial to understand the molecular and cellular mechanisms underlying immunological/metabolic cross talk to offer substantial therapeutic promise. Antioxid. Redox Signal. 29, 275-296.

Metabolites in visceral fat: useful signals of metabolic syndrome?

Metabolic syndrome comprises a series of health conditions, such as increased blood pressure, high blood sugar, excess abdominal fat, and altered circulating cholesterol or triglyceride levels. A fast growing number of affected individuals are at an increased risk of heart disease, stroke and type-2 diabetes. Obesity, especially build-up of visceral fat, is a recognized major risk factor for the development of metabolic syndrome. However, our understanding of the mechanistic links and biomarkers that associate visceral fat with the development of conditions underlying metabolic syndrome is still inadequate. In a recent paper published in the Biochemical Journal [Biochem. J. (2018) 475, 1019–1035], Candi et al. address this lack of knowledge, performing high-throughput metabolomics analysis of visceral fat isolated from obese individuals, with and without metabolic syndrome, and non-obese healthy controls. The authors identify alterations in metabolic pathways that distinguish pathologically from healthy obese subjects. They identify metabolic cues that point to oxidative and inflammatory burden as the leitmotifs of metabolic syndrome. Of particular interest is the identification of increased metabolism of γ-glutamyl amino acids and plasmalogens in pathological obesity. γ-glutamyl amino acids, generated through the transfer of a γ-glutamyl moiety from glutathione to an amino acid acceptor, are involved in glutathione metabolism and the response to oxidative stress, whereas plasmalogens, a poorly studied class of phospholipids, are known contributors to insulin resistance and hypertension. Both classes of metabolites are intriguing candidate biomarkers that warrant further investigation.

Human umbilical cord mesenchymal stem cells polarize RAW264.7 macrophages to an anti-inflammatory subpopulation

OBJECTIVE

To investigate the effects of human umbilical cord mesenchymal stem cells (hUCMSCs) on the polarization of lipopolysaccharide-stimulated RAW264.7 macrophages.

METHODS

Lipopolysaccharide-stimulated RAW264.7 macrophages were co-cultured with hUCMSCs in a Transwell system for 4 d, and then labelled with anti-F4/80, anti-CD86, and anti-CD206 antibodies for flow cytometry. The co-cultured supernatants were detected by enzyme-linked immunosorbent assay for prostaglandin E2. The co-cultured RAW264.7 macrophages were also lysed to measure the intracellular level of inducible nitric oxide synthase.

RESULTS

There were significantly more F4/80+CD86+CD206+ RAW264.7 macrophages in the hUCMSCs-treated groups than the control group (P<0.001). The secretion of prostaglandin E2 by lipopolysaccharide-stimulated RAW264.7 macrophages was significantly inhibited in a dose-dependent manner with the addition of hUCMSCs (P<0.001). The expression of iNOS, the intracellular marker of M1 cells, was also significantly inhibited by hUCMSCs (P<0.05).

CONCLUSION

hUCMSCs significantly polarize the lipopolysaccharide-stimulated RAW264.7 macrophages from a pro-inflammatory M1 subpopulation to an intermediate subpopulation of anti-inflammatory M2 macrophages, which are associated with a gradual decrease of iNOS and PGE₂ levels.

Mesenchymal stem cells maintain the microenvironment of central nervous system by regulating the polarization of macrophages/microglia after traumatic brain injury

Mesenchymal stem cells (MSCs), which are regarded as promising candidates for cell replacement therapies, are able to regulate immune responses after traumatic brain injury (TBI). Secondary immune response following the mechanical injury is the essential factor leading to the necrosis and apoptosis of neural cells during and after the cerebral edema has subsided and there is lack of efficient agent that can mitigate such neuroinflammation in the clinical application. By means of three molecular pathways (prostaglandin E2 (PGE2), tumor-necrosis-factor-inducible gene 6 protein (TSG-6), and progesterone receptor (PR) and glucocorticoid receptors (GR)), MSCs induce the activation of macrophages/microglia and drive them polarize into the M2 phenotypes, which inhibits the release of pro-inflammatory cytokines and promotes tissue repair and nerve regeneration. The regulation of MSCs and the polarization of macrophages/microglia are dynamically changing based on the inflammatory environment. Under the stimulation of platelet lysate (PL), MSCs also promote the release of pro-inflammatory cytokines. Meanwhile, the statue of macrophages/microglia exerts significant effects on the survival, proliferation, differentiation and activation of MSCs by changing the niche of cells. They form positive feedback loops in maintaining the homeostasis after TBI to relieving the secondary injury and promoting tissue repair. MSC therapies have obtained great achievements in several central nervous system disease clinical trials, which will accelerate the application of MSCs in TBI treatment.

Regulation of pancreatic β-cell function and mass dynamics by prostaglandin signaling

Prostaglandins (PGs) are signaling lipids derived from arachidonic acid (AA), which is metabolized by cyclooxygenase (COX)-1 or 2 and class-specific synthases to generate PGD₂, PGE₂, PGF_2α, PGI₂ (prostacyclin), and thromboxane A₂. PGs signal through G-protein coupled receptors (GPCRs) and are important modulators of an array of physiological functions, including systemic inflammation and insulin secretion from pancreatic islets. The role of PGs in β-cell function has been an active area of interest, beginning in the 1970s. Early studies demonstrated that PGE₂ inhibits glucose-stimulated insulin secretion (GSIS), although more recent studies have questioned this inhibitory action of PGE₂. The PGE₂ receptor EP3 and one of the G-proteins that couples to EP3, Gα_Z, have been identified as negative regulators of β-cell proliferation and survival. Conversely, PGI₂ and its receptor, IP, play a positive role in the β-cell by enhancing GSIS and preserving β-cell mass in response to the β-cell toxin streptozotocin (STZ). In comparison to PGE₂ and PGI₂, little is known about the function of the remaining PGs within islets. In this review, we discuss the roles of PGs, particularly PGE₂ and PGI₂, PG receptors, and downstream signaling events that alter β-cell function and regulation of β-cell mass.

mTORC2 signalling regulates M2 macrophage differentiation in response to helminth infection and adaptive thermogenesis

Alternatively activated macrophages (M2) have an important function in innate immune responses to parasitic helminths, and emerging evidence also indicates these cells are regulators of systemic metabolism. Here we show a critical role for mTORC2 signalling in the generation of M2 macrophages. Abrogation of mTORC2 signalling in macrophages by selective conditional deletion of the adaptor molecule Rictor inhibits the generation of M2 macrophages while leaving the generation of classically activated macrophages (M1) intact. Selective deletion of Rictor in macrophages prevents M2 differentiation and clearance of a parasitic helminth infection in mice, and also abrogates the ability of mice to regulate brown fat and maintain core body temperature. Our findings define a role for mTORC2 in macrophages in integrating signals from the immune microenvironment to promote innate type 2 immunity, and also to integrate systemic metabolic and thermogenic responses.

Augmented oxidative stress and preserved vasoconstriction induced by hydrogen peroxide in coronary arteries in obesity: role of COX-2

BACKGROUND AND PURPOSE

Oxidative stress plays a key role in the vascular and metabolic abnormalities associated with obesity. Herein, we assessed whether obesity can increase coronary vasoconstriction induced by hydrogen peroxide (H₂ O₂ ) and the signalling pathways involving COX-2 and superoxide (O₂^.- ) generation.

EXPERIMENTAL APPROACH

Contractile responses to H₂ O₂ and O₂^.- generation were measured in coronary arteries from genetically obese Zucker rats (OZR) and compared to lean Zucker rats (LZR).

KEY RESULTS

Both basal and H₂ O₂ -stimulated O₂^.- production were enhanced in coronary arteries from OZR, but H₂ O₂ -induced vasoconstriction was unchanged. The selective COX-2 inhibitor NS398 significantly reduced H₂ O₂ -induced contractions in endothelium-denuded arteries from LZR and OZR, but only in endothelium-intact arteries from LZR. PGI₂ (IP) receptor antagonism modestly reduced the vasoconstrictor action of H₂ O₂ while antagonism of the PGE₂ receptor 4 (EP₄ ) enhanced H₂ O₂ contractions in arteries from OZR but not LZR. Basal release of COX-2-derived PGE₂ was higher in coronary arteries from OZR where the selective agonist of EP₄ receptors TCS 2519 evoked potent relaxations. COX-2 was up-regulated after acute exposure to H₂ O₂ in coronary endothelium and vascular smooth muscle (VSM) and inhibition of COX-2 markedly reduced H₂ O₂ -elicited O₂^.- generation in coronary arteries and myocardium. Expression of Nox subunits in VSM and NADPH-stimulated O₂^.- generation was enhanced and contributed to H₂ O₂ vasoconstriction in arteries from obese rats.

CONCLUSION AND IMPLICATIONS

COX-2 contributes to cardiac oxidative stress and to the endothelium-independent O₂^.- -mediated coronary vasoconstriction induced by H₂ O₂ in obesity, which is offset by the release of COX-2-derived endothelial PGE₂ acting on EP₄ vasodilator receptors.