Thromboxane synthase deficiency improves insulin action and attenuates adipose tissue fibrosis

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.

Metabolic adaptations in severe obesity: Insights from circulating oxylipins before and after weight loss

BACKGROUND

The relationship between lipid mediators and severe obesity remains unclear. Our study investigates the impact of severe obesity on plasma concentrations of oxylipins and fatty acids and explores the consequences of weight loss.

METHODS

In the clinical trial identifier NCT05554224 study, 116 patients with severe obesity and 63 overweight/obese healthy controls matched for age and sex (≈2:1) provided plasma. To assess the effect of surgically induced weight loss, we requested paired plasma samples from 44 patients undergoing laparoscopic sleeve gastrectomy one year after the procedure. Oxylipins were measured using ultra-high-pressure liquid chromatography coupled to a triple quadrupole mass spectrometer via semi-targeted lipidomics. Cytokines and markers of interorgan crosstalk were measured using enzyme-linked immunosorbent assays.

RESULTS

We observed significantly elevated levels of circulating fatty acids and oxylipins in patients with severe obesity compared to their metabolically healthier overweight/obese counterparts. Our findings indicated that sex and liver disease were not confounding factors, but we observed weak correlations in plasma with circulating adipokines, suggesting the influence of adipose tissue. Importantly, while weight loss restored the balance in circulating fatty acids, it did not fully normalize the oxylipin profile. Before surgery, oxylipins derived from lipoxygenase activity, such as 12-HETE, 11-HDoHE, 14-HDoHE, and 12-HEPE, were predominant. However, one year following laparoscopic sleeve gastrectomy, we observed a complex shift in the oxylipin profile, favoring species from the cyclooxygenase pathway, particularly proinflammatory prostanoids like TXB2, PGE2, PGD2, and 12-HHTrE. This transformation appears to be linked to a reduction in adiposity, underscoring the role of lipid turnover in the development of metabolic disorders associated with severe obesity.

CONCLUSIONS

Despite the reduction in fatty acid levels associated with weight loss, the oxylipin profile shifts towards a predominance of more proinflammatory species. These observations underscore the significance of seeking mechanistic approaches to address severe obesity and emphasize the importance of closely monitoring the metabolic adaptations after weight loss.

Effects of Fatty Acid Metabolites on Adipocytes Britening: Role of Thromboxane A2

Obesity is a complex disease highly related to diet and lifestyle and is associated with low amount of thermogenic adipocytes. Therapeutics that regulate brown adipocyte recruitment and activity represent interesting strategies to fight overweight and associated comorbidities. Recent studies suggest a role for several fatty acids and their metabolites, called lipokines, in the control of thermogenesis. The purpose of this work was to analyze the role of several lipokines in the control of brown/brite adipocyte formation. We used a validated human adipocyte model, human multipotent adipose-derived stem cell model (hMADS). In the absence of rosiglitazone, hMADS cells differentiate into white adipocytes, but convert into brite adipocytes upon rosiglitazone or prostacyclin 2 (PGI2) treatment. Gene expression was quantified using RT-qPCR and protein levels were assessed by Western blotting. We show here that lipokines such as 12,13-diHOME, 12-HEPE, 15dPGJ2 and 15dPGJ3 were not able to induce browning of white hMADS adipocytes. However, both fatty acid esters of hydroxy fatty acids (FAHFAs), 9-PAHPA and 9-PAHSA potentiated brown key marker UCP1 mRNA levels. Interestingly, CTA2, the stable analog of thromboxane A2 (TXA2), but not its inactive metabolite TXB2, inhibited the rosiglitazone and PGI2-induced browning of hMADS adipocytes. These results pinpoint TXA2 as a lipokine inhibiting brown adipocyte formation that is antagonized by PGI2. Our data open new horizons in the development of potential therapies based on the control of thromboxane A2/prostacyclin balance to combat obesity and associated metabolic disorders.

Aspirin Suppresses Hepatic Glucagon Signaling Through Decreasing Production of Thromboxane A2

Excessive hepatic glucose production (HGP) is a major cause of fasting hyperglycemia in diabetes, and antihyperglycemic therapy takes center stage. Nonsteroidal anti-inflammatory drugs, such as acetylsalicylic acid (aspirin), reduce hyperglycemia caused by unrestrained gluconeogenesis in diabetes, but its mechanism is incompletely understood. Here, we reported that aspirin lowers fasting blood glucose and hepatic gluconeogenesis, corresponds with lower thromboxane A2 (TXA2) levels, and the hypoglycemic effect of aspirin could be rescued by TP agonist treatment. On fasting and diabetes stress, the cyclooxygenase (COX)/TXA2/thromboxane A2 receptor (TP) axis was increased in the livers. TP deficiency suppressed starvation-induced hepatic glucose output, thus inhibiting the progression of diabetes, whereas TP activation promoted gluconeogenesis. Aspirin restrains glucagon signaling and gluconeogenic gene expression (phosphoenolpyruvate carboxykinase [PCK1] and glucose-6-phosphatase [G6Pase]) through the TXA2/TP axis. TP mediates hepatic gluconeogenesis by activating PLC/IP3/IP3R signaling, which subsequently enhances CREB phosphorylation via facilitating CRTC2 nuclear translocation. Thus, our findings demonstrate that TXA2/TP plays a crucial role in aspirin's inhibition of hepatic glucose metabolism, and TP may represent a therapeutic target for diabetes.

Ameliorating Inflammation in Insulin-resistant Rat Adipose Tissue with Abdominal Massage Regulates SIRT1/NF-κB Signaling

It was the aim of this study to determine whether abdominal massage reverses high-fat diet-induced insulin resistance compared with RSV treatment. A total of sixty male Sprague-Dawley rats were randomly placed in one of four groups:the non-fat diet (NFD), the high-fat diet (HFD), the HFD with abdominal massage (HFD+ AM), and the HFD plus resveratrol (HFD+ RSV). For eight weeks, rats were fed high-fat diets to create insulin resistance, followed by six weeks of either AM or RSV. Molecular mechanisms of adipogenesis and cytokine production in rats with high-fat diets were investigated. The model rat adipose tissue showed significant improvements in obesity, glucose intolerance, and the accumulation of lipid in the body [the total cholesterol level (TC), triglycerides (TG), high-density lipoprotein cholesterol (HDL-C), and low-density lipoprotein cholesterol (LDL-C)], metabolic effects of glucose [The fasting blood glucose (FBG), Fasting insulin levels (FINS)], inflammatory status [interleukin-6 (IL-6) and tumor necrosis factor (TNF)-α, C-reactive protein (CRP)], and macrophage polarization after AM or RSV treatment. Further, AM increased SIRT1/NF-κB signaling in rat adipose tissue. Accordingly, in rat adipose tissue, our results indicate that AM regulates the secretion of proinflammatory cytokines, blood sugar levels, and related signaling pathways, contributing to improvement of IR, which may serves as a new therapeutic approach for the treatment for IR.

Quantifying the inflammatory secretome of human intermuscular adipose tissue

Adipose tissue secretes an abundance of lipid and protein mediators, and this secretome is depot-specific, with local and systemic effects on metabolic regulation. Intermuscular adipose tissue (IMAT) accumulates within the skeletal muscle compartment in obesity, and is associated with insulin resistance and metabolic disease. While the human IMAT secretome decreases insulin sensitivity in vitro, its composition is entirely unknown. The current study was conducted to investigate the composition of the human IMAT secretome, compared to that of the subcutaneous (SAT) and visceral adipose tissue (VAT) depots. IMAT, SAT, and VAT explants from individuals with obesity were used to generate conditioned media. Proteomics analysis of conditioned media was performed using multiplex proximity extension assays, and eicosanoid analysis using liquid chromatography-tandem mass spectrometry. Compared to SAT and/or VAT, IMAT secreted significantly more cytokines (IL2, IL5, IL10, IL13, IL27, FGF23, IFNγ and CSF1) and chemokines (MCP1, IL8, CCL11, CCL20, CCL25 and CCL27). Adipokines hepatocyte growth factor and resistin were secreted significantly more by IMAT than SAT or VAT. IMAT secreted significantly more eicosanoids (PGE2, TXB2 , 5-HETE, and 12-HETE) compared to SAT and/or VAT. In the context of obesity, IMAT is a distinct adipose tissue with a highly immunogenic and inflammatory secretome, and given its proximity to skeletal muscle, may be critical to glucose regulation and insulin resistance.

C1q/Tumor Necrosis Factor-Related Protein 9: Basics and Therapeutic Potentials

C1q/tumor necrosis factor-related protein 9 (CTRP9) is a newly discovered adipokine that is the closest paralog of adiponectin. Proteolytic cleavage of CTRP9 leads to the release of the globular domain (gCTRP9), which serves as the major circulating subtype. After binding with adiponectin receptor 1 (AdipoR1) and N-cadherin, CTRP9 activates various signaling pathways to regulate glucose and lipid metabolism, vasodilation and cell differentiation. Throughout human development and adult life, CTRP9 controls many biological phenomena. simultaneously, abnormal gene or protein expression of CTRP9 is accompanied by a wide range of human pathological phenomena. In this review, we briefly introduce CTRP9 and its associated signaling pathways and physiological functions, which may be helpful in the understanding of the occurrence of diseases. Moreover, we summarize the broader research prospects of CTRP9 and advances in therapeutic intervention. In recent years, CTRP9 has attracted extensive attention due to its role in the pathogenesis of various diseases, providing further avenues for its exploitation as a potential biomarker or therapeutic target.

C1q/tumour necrosis factor-related protein-9 aggravates lipopolysaccharide-induced inflammation via promoting NLRP3 inflammasome activation

The NLRP3 inflammasome plays a vital role in inflammation by increasing the maturation of interleukin-1β (IL-1β) and promoting pyroptosis. Given that C1q/tumour necrosis factor-related protein-9 (CTRP9) has been shown to be involved in diverse inflammatory diseases, we sought to assess the underlying impact of CTRP9 on NLRP3 inflammasome activation. In vitro, macrophages isolated from murine peritonea were stimulated with exogenous CTRP9, followed by lipopolysaccharide (LPS) and adenosine 5'-triphosphate (ATP). We demonstrated that CTRP9 markedly augmented the activation of the NLRP3 inflammasome, as shown by increased mature IL-1β secretion, triggering ASC speck formation and promoting pyroptosis. Mechanistically, CTRP9 increased the levels of NADPH oxidase 2 (NOX2)-derived reactive oxygen species (ROS). Suppressing ROS with N-acetylcysteine (NAC) or interfering with NOX2 by small interfering RNA weakened the promoting effect of CTRP9 on the NLRP3 inflammasome. Furthermore, NLRP3 inflammasome activation, pyroptosis and secretion of mature IL-1β were significantly decreased in macrophages from CTRP9-KO mice compared to those from WT mice with the same treatment. In vivo, we established a sepsis model by intraperitoneal injection of LPS into WT and CTRP9-KO mice. CTRP9 knockout improved the survival rates of the septic mice and attenuated NLRP3 inflammasome-mediated inflammation. In conclusion, our study indicates that CTRP9 aggravates LPS-induced inflammation by promoting NLRP3 inflammasome activation via the NOX2/ROS pathway. CTRP9 could be a promising target for NLRP3 inflammasome-driven inflammatory diseases.

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.

The Roles of Various Prostaglandins in Fibrosis: A Review

Organ fibrosis is a common pathological result of various chronic diseases with multiple causes. Fibrosis is characterized by the excessive deposition of extracellular matrix and eventually leads to the destruction of the tissue structure and impaired organ function. Prostaglandins are produced by arachidonic acid through cyclooxygenases and various prostaglandin-specific synthases. Prostaglandins bind to homologous receptors on adjacent tissue cells in an autocrine or paracrine manner and participate in the regulation of a series of physiological or pathological processes, including fibrosis. This review summarizes the properties, synthesis, and degradation of various prostaglandins, as well as the roles of these prostaglandins and their receptors in fibrosis in multiple models to reveal the clinical significance of prostaglandins and their receptors in the treatment of fibrosis.

Deletion of lysophosphatidylcholine acyltransferase 3 in myeloid cells worsens hepatic steatosis after a high-fat diet

Recent studies have highlighted an important role for lysophosphatidylcholine acyltransferase 3 (LPCAT3) in controlling the PUFA composition of cell membranes in the liver and intestine. In these organs, LPCAT3 critically supports cell-membrane-associated processes such as lipid absorption or lipoprotein secretion. However, the role of LPCAT3 in macrophages remains controversial. Here, we investigated LPCAT3's role in macrophages both in vitro and in vivo in mice with atherosclerosis and obesity. To accomplish this, we used the LysMCre strategy to develop a mouse model with conditional Lpcat3 deficiency in myeloid cells (Lpcat3KOMac). We observed that partial Lpcat3 deficiency (approximately 75% reduction) in macrophages alters the PUFA composition of all phospholipid (PL) subclasses, including phosphatidylinositols and phosphatidylserines. A reduced incorporation of C20 PUFAs (mainly arachidonic acid [AA]) into PLs was associated with a redistribution of these FAs toward other cellular lipids such as cholesteryl esters. Lpcat3 deficiency had no obvious impact on macrophage inflammatory response or endoplasmic reticulum (ER) stress; however, Lpcat3KOMac macrophages exhibited a reduction in cholesterol efflux in vitro. In vivo, myeloid Lpcat3 deficiency did not affect atherosclerosis development in LDL receptor deficient mouse (Ldlr-/-) mice. Lpcat3KOMac mice on a high-fat diet displayed a mild increase in hepatic steatosis associated with alterations in several liver metabolic pathways and in liver eicosanoid composition. We conclude that alterations in AA metabolism along with myeloid Lpcat3 deficiency may secondarily affect AA homeostasis in the whole liver, leading to metabolic disorders and triglyceride accumulation.

New Insights Into Implications of CTRP3 in Obesity, Metabolic Dysfunction, and Cardiovascular Diseases: Potential of Therapeutic Interventions

Adipose tissue, as the largest endocrine organ, secretes many biologically active molecules circulating in the bloodstream, collectively termed adipocytokines, which not only regulate the metabolism but also play a role in pathophysiological processes. C1q tumor necrosis factor (TNF)-related protein 3 (CTRP3) is a member of C1q tumor necrosis factor-related proteins (CTRPs), which is a paralog of adiponectin. CTRP3 has a wide range of effects on glucose/lipid metabolism, inflammation, and contributes to cardiovascular protection. In this review, we comprehensively discussed the latest research on CTRP3 in obesity, diabetes, metabolic syndrome, and cardiovascular diseases.

Late-onset renal hypertrophy and dysfunction in mice lacking CTRP1

Local and systemic factors that influence renal structure and function in aging are not well understood. The secretory protein C1q/TNF-related protein 1 (CTRP1) regulates systemic metabolism and cardiovascular function. We provide evidence here that CTRP1 also modulates renal physiology in an age- and sex-dependent manner. In mice lacking CTRP1, we observed significantly increased kidney weight and glomerular hypertrophy in aged male but not female or young mice. Although glomerular filtration rate, plasma renin and aldosterone levels, and renal response to water restriction did not differ between genotypes, CTRP1-deficient male mice had elevated blood pressure. Echocardiogram and pulse wave velocity measurements indicated normal heart function and vascular stiffness in CTRP1-deficient animals, and increased blood pressure was not due to greater salt retention. Paradoxically, CTRP1-deficient mice had elevated urinary sodium and potassium excretion, partially resulting from reduced expression of genes involved in renal sodium and potassium reabsorption. Despite renal hypertrophy, markers of inflammation, fibrosis, and oxidative stress were reduced in CTRP1-deficient mice. RNA sequencing revealed alterations and enrichments of genes in metabolic processes in CTRP1-deficient animals. These results highlight novel contributions of CTRP1 to aging-associated changes in renal physiology.

A Co-expression Analysis of the Placental Transcriptome in Association With Maternal Pre-pregnancy BMI and Newborn Birth Weight

Maternal body mass index (BMI) before pregnancy is known to affect both fetal growth and later-life health of the newborn, yet the implicated molecular mechanisms remain largely unknown. As the master regulator of the fetal environment, the placenta is a valuable resource for the investigation of processes involved in the developmental programming of metabolic health. We conducted a genome-wide placental transcriptome study aiming at the identification of functional pathways representing the molecular link between maternal BMI and fetal growth. We used RNA microarray (Agilent 8 × 60 K), medical records, and questionnaire data from 183 mother-newborn pairs from the ENVIRONAGE birth cohort study (Flanders, Belgium). Using a weighted gene co-expression network analysis, we identified 17 correlated gene modules. Three of these modules were associated with both maternal pre-pregnancy BMI and newborn birth weight. A gene cluster enriched for genes involved in immune response and myeloid cell differentiation was positively associated with maternal BMI and negatively with low birth weight. Two other gene modules, upregulated in association with maternal BMI as well as birth weight, were involved in processes related to organ and tissue development, with blood vessel morphogenesis and extracellular matrix structure as top Gene Ontology terms. In line with this, erythrocyte-, angiogenesis-, and extracellular matrix-related genes were among the identified hub genes. The association between maternal BMI and newborn weight was significantly mediated by gene expression for 5 of the hub genes (FZD4, COL15A1, GPR124, COL6A1, and COL1A1). As some of the identified hub genes have been linked to obesity in adults, our observation in placental tissue suggests that biological processes may be affected from prenatal life onwards, thereby identifying new molecular processes linking maternal BMI and fetal metabolic programming.

C1q/TNF-Related Protein 3 (CTRP3) Function and Regulation

As the largest endocrine organ, adipose tissue secretes many bioactive molecules that circulate in blood, collectively termed adipokines. Efforts to identify such metabolic regulators have led to the discovery of a family of secreted proteins, designated as C1q tumor necrosis factor (TNF)-related proteins (CTRPs). The CTRP proteins, adiponectin, TNF-alpha, as well as other proteins with the distinct C1q domain are collectively grouped together as the C1q/TNF superfamily. Reflecting profound biological potency, the initial characterization of these adipose tissue-derived CTRP factors finds wide-ranging effects upon metabolism, inflammation, and survival-signaling in multiple tissue types. CTRP3 (also known as CORS26, cartducin, or cartonectin) is a unique member of this adipokine family. In this review we provide a comprehensive overview of the research concerning the expression, regulation, and physiological function of CTRP3. © 2017 American Physiological Society. Compr Physiol 7:863-878, 2017.

CTRP7 deletion attenuates obesity-linked glucose intolerance, adipose tissue inflammation, and hepatic stress

Chronic low-grade inflammation and cellular stress are important contributors to obesity-linked metabolic dysfunction. Here, we uncover an immune-metabolic role for C1q/TNF-related protein 7 (CTRP7), a secretory protein of the C1q family with previously unknown function. In obese humans, circulating CTRP7 levels were markedly elevated and positively correlated with body mass index, glucose, insulin, insulin resistance index, hemoglobin A1c, and triglyceride levels. Expression of CTRP7 in liver was also significantly upregulated in obese humans and positively correlated with gluconeogenic genes. In mice, Ctrp7 expression was differentially modulated in various tissues by fasting and refeeding and by diet-induced obesity. A genetic loss-of-function mouse model was used to determine the requirement of CTRP7 for metabolic homeostasis. When fed a control low-fat diet, male or female mice lacking CTRP7 were indistinguishable from wild-type littermates. In obese male mice consuming a high-fat diet, however, CTRP7 deficiency attenuated insulin resistance and enhanced glucose tolerance, effects that were independent of body weight, metabolic rate, and physical activity level. Improved glucose metabolism in CTRP7-deficient mice was associated with reduced adipose tissue inflammation, as well as decreased liver fibrosis and cellular oxidative and endoplasmic reticulum stress. These results provide a link between elevated CTRP7 levels and impaired glucose metabolism, frequently associated with obesity. Inhibiting CTRP7 action may confer beneficial metabolic outcomes in the setting of obesity and diabetes.

Loss of CTRP1 disrupts glucose and lipid homeostasis

C1q/TNF-related protein 1 (CTRP1) is a conserved plasma protein of the C1q family with notable metabolic and cardiovascular functions. We have previously shown that CTRP1 infusion lowers blood glucose and that transgenic mice with elevated circulating CTRP1 are protected from diet-induced obesity and insulin resistance. Here, we used a genetic loss-of-function mouse model to address the requirement of CTRP1 for metabolic homeostasis. Despite similar body weight, food intake, and energy expenditure, Ctrp1 knockout (KO) mice fed a low-fat diet developed insulin resistance and hepatic steatosis. Impaired glucose metabolism in Ctrp1 KO mice was associated with increased hepatic gluconeogenic gene expression and decreased skeletal muscle glucose transporter glucose transporter 4 levels and AMP-activated protein kinase activation. Loss of CTRP1 enhanced the clearance of orally administered lipids but did not affect intestinal lipid absorption, hepatic VLDL-triglyceride export, or lipoprotein lipase activity. In contrast to triglycerides, hepatic cholesterol levels were reduced in Ctrp1 KO mice, paralleling the reduced expression of cholesterol synthesis genes. Contrary to expectations, when challenged with a high-fat diet to induce obesity, Ctrp1 KO mice had increased physical activity and reduced body weight, adiposity, and expression of lipid synthesis and fibrotic genes in adipose tissue; these phenotypes were linked to elevated FGF-21 levels. Due in part to increased hepatic AMP-activated protein kinase activation and reduced expression of lipid synthesis genes, Ctrp1 KO mice fed a high-fat diet also had reduced liver and serum triglyceride and cholesterol levels. Taken together, these results provide genetic evidence to establish the significance of CTRP1 to systemic energy metabolism in different metabolic and dietary contexts.

CTRP3 deficiency reduces liver size and alters IL-6 and TGFβ levels in obese mice

C1q/TNF-related protein 3 (CTRP3) is a secreted metabolic regulator whose circulating levels are reduced in human and rodent models of obesity and diabetes. Previously, we showed that CTRP3 infusion lowers blood glucose by suppressing gluconeogenesis and that transgenic overexpression of CTRP3 protects mice against diet-induced hepatic steatosis. Here, we used a genetic loss-of-function mouse model to further address whether CTRP3 is indeed required for metabolic homeostasis under normal and obese states. Both male and female mice lacking CTRP3 had similar weight gain when fed a control low-fat (LFD) or high-fat diet (HFD). Regardless of diet, no differences were observed in adiposity, food intake, metabolic rate, energy expenditure, or physical activity levels between wild-type (WT) and Ctrp3-knockout (KO) animals of either sex. Contrary to expectations, loss of CTRP3 in LFD- or HFD-fed male and female mice also had minimal or no impact on whole body glucose metabolism, insulin sensitivity, and fasting-induced hepatic gluconeogenesis. Unexpectedly, the liver sizes of HFD-fed Ctrp3-KO male mice were markedly reduced despite a modest increase in triglyceride content. Furthermore, liver expression of fat oxidation genes was upregulated in the Ctrp3-KO mice. Whereas the liver and adipose expression of profibrotic TGFβ1, as well as its serum levels, was suppressed in HFD-fed KO mice, circulating proinflammatory IL-6 levels were markedly increased; these changes, however, were insufficient to affect systemic metabolic outcome. We conclude that, although it is dispensable for physiological control of energy balance, CTRP3 plays a previously unsuspected role in modulating liver size and circulating cytokine levels in response to obesity.