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

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.

Structure, Functions, and Implications of Selected Lipocalins in Human Disease

The lipocalin proteins are a large family of small extracellular proteins that demonstrate significant heterogeneity in sequence similarity and have highly conserved crystal structures. They have a variety of functions, including acting as carrier proteins, transporting retinol, participating in olfaction, and synthesizing prostaglandins. Importantly, they also play a critical role in human diseases, including cancer. Additionally, they are involved in regulating cellular homeostasis and immune response and dispensing various compounds. This comprehensive review provides information on the lipocalin family, including their structure, functions, and implications in various diseases. It focuses on selective important human lipocalin proteins, such as lipocalin 2 (LCN2), retinol binding protein 4 (RBP4), prostaglandin D2 synthase (PTGDS), and α1-microglobulin (A1M).

Targeting the DP2 receptor alleviates muscle atrophy and diet-induced obesity in mice through oxidative myofiber transition

BACKGROUND

Mammalian skeletal muscles consist of two main fibre types: slow-twitch (type I, oxidative) and fast-twitch (type IIa, fast oxidative; type IIb/IIx, fast glycolytic). Muscle fibre composition switch is closely associated with chronic diseases such as muscle atrophy, obesity, type II diabetes and athletic performance. Prostaglandin D₂ (PGD₂ ) is a bioactive lipid derived from arachidonic acid that aggravates muscle damage and wasting during muscle atrophy. This study aimed to investigate the precise mechanisms underlying PGD₂ -mediated muscle homeostasis and myogenesis.

METHODS

Skeletal muscle-specific PGD₂ receptor DP2-deficient mice (DP2^fl/fl HSA^Cre ) and their littermate controls (DP2^fl/fl ) were subjected to exhaustive exercise and fed a high-fat diet (HFD). X-linked muscular dystrophy (MDX) mice and HFD-challenged mice were treated with the selective DP2 inhibitor CAY10471. Exercise tolerance, body weight, glycometabolism and skeletal muscle fibre composition were measured to determine the role of the skeletal muscle PGD₂ /DP2 signalling axis in obesity and muscle disorders. Multiple genetic and pharmacological approaches were also used to investigate the intracellular signalling cascades underlying the PGD₂ /DP2-mediated skeletal muscle fibre transition.

RESULTS

PGD₂ generation and DP2 expression were significantly upregulated in the hindlimb muscles of HFD-fed mice (P < 0.05 or P < 0.01 vs. normal chow diet). Compared with DP2^fl/fl mice, DP2^fl/fl HSA^Cre mice exhibited remarkable glycolytic-to-oxidative fibre-type transition in hindlimb muscles and were fatigue resistant during endurance exercise (154.9 ± 6.0 vs. 124.2 ± 8.1 min, P < 0.05). DP2^fl/fl HSA^Cre mice fed an HFD showed less weight gain (P < 0.05) and hepatic lipid accumulation (P < 0.01), reduced insulin resistance and enhanced energy expenditure (P < 0.05) compared with DP2^fl/fl mice. Mechanistically, DP2 deletion promoted the nuclear translocation of nuclear factor of activated T cells 1 (NFATc1) by suppressing RhoA/Rho-associated kinase 2 (ROCK2) signalling, which led to enhanced oxidative fibre-specific gene transcription in muscle cells. Treatment with CAY10471 enhanced NFATc1 activity in the skeletal muscles and ameliorated HFD-induced obesity (P < 0.05 vs. saline) and insulin resistance in mice. CAY10471 also enhanced exercise tolerance in MDX mice (100.8 ± 8.0 vs. 68.9 ± 11.1 min, P < 0.05 vs. saline) by increasing the oxidative fibre-type ratio in the muscles (45.1 ± 2.3% vs. 32.3 ± 2.6%, P < 0.05 vs. saline).

CONCLUSIONS

DP2 activation suppresses oxidative fibre transition via RhoA/ROCK2/NFATc1 signalling. The inhibition of DP2 may be a potential therapeutic approach against obesity and muscle disorders.

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.

Lipocalin-Type Prostaglandin D2 Synthase Protein- A Central Player in Metabolism

Lipocalin-type prostaglandin D synthase was previously known as β-trace protein (BTP), a low-molecular-weight glycoprotein that is heavily expressed in human cerebrospinal fluid. Nevertheless, it is also seen to be expressed in numerous other tissues including the kidney, liver, lung, heart, adipose, muscle, and pancreas. Functionally, L-PGDS behaves like a lipocalin type protein where it helps in binding and transportation of small lipophilic substances, such as steroids, retinoids, and other lipophilic ligands. Enzymatically, L-PGDS functions as a prostaglandin synthase where it helps in the production of PGD₂ by catalyzing the isomerization of PGH₂, a common precursor of the two series of prostaglandins. PGD₂ regulates its physiological function through two individual receptors named DP1 and DP2. L-PGDS has been a central player in many diseases, its role in metabolism including diabetes, fatty liver disease, and obesity has gathered a large attention. In this review, we summarize the current state of knowledge about L-PGDS and it's signaling in adipose, hepatic, skeletal muscle, and pancreas tissues, which are core targets for metabolic studies. Modulation of L-PGDS signaling can be considered as a potential future therapeutic target for the treatment of insulin resistance as well as fatty liver disease.

Ramatroban for chemoprophylaxis and treatment of COVID-19: David takes on Goliath

INTRODUCTION

In COVID-19 pneumonia, there is a massive increase in fatty acid levels and lipid mediators with a predominance of cyclooxygenase metabolites, notably TxB2 ≫ PGE2 > PGD2 in the lungs, and 11-dehydro-TxB2, a TxA2 metabolite, in the systemic circulation. While TxA2 stimulates thromboxane prostanoid (TP) receptors, 11-dehydro-TxB2 is a full agonist of DP2 (formerly known as the CRTh2) receptors for PGD2. Anecdotal experience of using ramatroban, a dual receptor antagonist of the TxA2/TP and PGD2/DP2 receptors, demonstrated rapid symptomatic relief from acute respiratory distress and hypoxemia while avoiding hospitalization.

AREAS COVERED

Evidence supporting the role of TxA2/TP receptors and PGD2/DP2 receptors in causing rapidly progressive lung injury associated with hypoxemia, a maladaptive immune response and thromboinflammation is discussed. An innovative perspective on the dual antagonism of TxA2/TP and PGD2/DP2 receptor signaling as a therapeutic approach in COVID-19 is presented. This paper examines ramatroban an anti-platelet, immunomodulator, and antifibrotic agent for acute and long-haul COVID-19.

EXPERT OPINION

Ramatroban, a dual blocker of TP and DP2 receptors, has demonstrated efficacy in animal models of respiratory dysfunction, atherosclerosis, thrombosis, and sepsis, as well as preliminary evidence for rapid relief from dyspnea and hypoxemia in COVID-19 pneumonia. Ramatroban merits investigation as a promising antithrombotic and immunomodulatory agent for chemoprophylaxis and treatment.

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

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

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.

Increased prostaglandin-D2 in male STAT3-deficient hearts shifts cardiac progenitor cells from endothelial to white adipocyte differentiation

Cardiac levels of the signal transducer and activator of transcription factor-3 (STAT3) decline with age, and male but not female mice with a cardiomyocyte-specific STAT3 deficiency conditional knockout (CKO) display premature age-related heart failure associated with reduced cardiac capillary density. In the present study, isolated male and female CKO-cardiomyocytes exhibit increased prostaglandin (PG)-generating cyclooxygenase-2 (COX-2) expression. The PG-degrading hydroxyprostaglandin-dehydrogenase-15 (HPGD) expression is only reduced in male cardiomyocytes, which is associated with increased prostaglandin D₂ (PGD₂) secretion from isolated male but not female CKO-cardiomyocytes. Reduced HPGD expression in male cardiomyocytes derive from impaired androgen receptor (AR)–signaling due to loss of its cofactor STAT3. Elevated PGD₂ secretion in males is associated with increased white adipocyte accumulation in aged male but not female hearts. Adipocyte differentiation is enhanced in isolated stem cell antigen-1 (SCA-1)⁺ cardiac progenitor cells (CPC) from young male CKO-mice compared with the adipocyte differentiation of male wild-type (WT)-CPC and CPC isolated from female mice. Epigenetic analysis in freshly isolated male CKO-CPC display hypermethylation in pro-angiogenic genes (Fgfr2, Epas1) and hypomethylation in the white adipocyte differentiation gene Zfp423 associated with up-regulated ZFP423 expression and a shift from endothelial to white adipocyte differentiation compared with WT-CPC. The expression of the histone-methyltransferase EZH2 is reduced in male CKO-CPC compared with male WT-CPC, whereas no differences in the EZH2 expression in female CPC were observed. Clonally expanded CPC can differentiate into endothelial cells or into adipocytes depending on the differentiation conditions. ZFP423 overexpression is sufficient to induce white adipocyte differentiation of clonal CPC. In isolated WT-CPC, PGD₂ stimulation reduces the expression of EZH2, thereby up-regulating ZFP423 expression and promoting white adipocyte differentiation. The treatment of young male CKO mice with the COX inhibitor Ibuprofen or the PGD₂ receptor (DP)2 receptor antagonist BAY-u 3405 in vivo increased EZH2 expression and reduced ZFP423 expression and adipocyte differentiation in CKO-CPC. Thus, cardiomyocyte STAT3 deficiency leads to age-related and sex-specific cardiac remodeling and failure in part due to sex-specific alterations in PGD₂ secretion and subsequent epigenetic impairment of the differentiation potential of CPC. Causally involved is the impaired AR signaling in absence of STAT3, which reduces the expression of the PG-degrading enzyme HPGD.

Impaired androgen-receptor-signaling due to STAT3-deficiency promotes increased prostaglandin-D2-secretion from male but not female cardiomyocytes; this induces an epigenetic switch in cardiac progenitor cells from endothelial to white adipocyte differentiation, associated with reduced cardiac capillary density, increased cardiac white fat deposits and heart failure in aged male but not female mice.

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.

Rewiring of Lipid Metabolism in Adipose Tissue Macrophages in Obesity: Impact on Insulin Resistance and Type 2 Diabetes

Obesity and its two major comorbidities, insulin resistance and type 2 diabetes, represent worldwide health issues whose incidence is predicted to steadily rise in the coming years. Obesity is characterized by an accumulation of fat in metabolic tissues resulting in chronic inflammation. It is now largely accepted that adipose tissue inflammation underlies the etiology of these disorders. Adipose tissue macrophages (ATMs) represent the most enriched immune fraction in hypertrophic, chronically inflamed adipose tissue, and these cells play a key role in diet-induced type 2 diabetes and insulin resistance. ATMs are triggered by the continuous influx of dietary lipids, among other stimuli; however, how these lipids metabolically activate ATM depends on their nature, composition and localization. This review will discuss the fate and molecular programs elicited within obese ATMs by both exogenous and endogenous lipids, as they mediate the inflammatory response and promote or hamper the development of obesity-associated insulin resistance and type 2 diabetes.

Limonoid 7-Deacetoxy-7-oxogedunin from Andiroba, Carapa guianensis, Meliaceae, Decreased Body Weight Gain, Improved Insulin Sensitivity, and Activated Brown Adipose Tissue in High-Fat-Diet-Fed Mice

We examined the antiobesity effect of a limonoid 7-deacetoxy-7-oxogedunin, named CG-1, purified from the seeds of Carapa guianensis, Meliaceae, known as andiroba in high-fat-diet (HFD)-fed mice. C57BL/6 mice were fed a low-fat diet or an HFD and orally administered CG-1 (20 mg/kg) for 7 weeks. CG-1 lowered the body weight gain and improved the serum triglyceride level and insulin sensitivity in HFD-fed mice. The expression level of the adipogenesis-related genes was lowered by CG-1 in the visceral white adipose tissue (vWAT). The mRNA expression level of the macrophage-related genes decreased in vWAT following the administration of CG-1 to HFD-fed mice. It is noteworthy that CG-1 activated the brown adipose tissue (BAT) with enhanced expression of uncoupling protein 1 and increased the rectal temperature in HFD-fed mice. These results indicate that the limonoid CG-1 decreased body weight gain and ameliorated hypertriglyceridemia and insulin resistance with the activation of BAT in HFD-fed mice.