Involvement of a cGMP-dependent pathway in the natriuretic peptide-mediated hormone-sensitive lipase phosphorylation in human adipocytes

Cardiac corin and atrial natriuretic peptide regulate liver glycogen metabolism and glucose homeostasis

BACKGROUND

Cardiovascular function and metabolic homeostasis are closely linked, but the underlying mechanisms are not fully understood. Corin is a protease that activates atrial natriuretic peptide (ANP), an essential hormone for normal blood pressure and cardiac function. The goal of this study is to investigate a potential corin and ANP function in regulating liver glycogen metabolism and glucose homeostasis.

METHODS

Liver glycogen and blood glucose levels were analyzed in Corin or Nppa (encoding ANP) knockout (KO) mice. ANP signaling was examined in livers from Corin and Nppa KO mice and in cultured human and mouse hepatocytes by western blotting.

RESULTS

We found that Corin and Nppa KO mice had reduced liver glycogen contents and increased blood glucose levels. By analyzing conditional KO mice lacking either cardiac or renal Corin, we showed that cardiac corin and ANP act in an endocrine manner to enhance cGMP-protein kinase G (PKG)-AKT-GSK3 signaling in hepatocytes. In cultured hepatocytes, ANP treatment stimulated PKG signaling, glucose uptake, and glycogen production, which could be blocked by small molecule PKG and AKT inhibitors.

CONCLUSIONS

Our results indicate that corin and ANP are important regulators in liver glycogen metabolism and glucose homeostasis, suggesting that defects in the corin and ANP pathway may contribute to both cardiovascular and metabolic diseases.

Central activation of catecholamine-independent lipolysis drives the end-stage catabolism of all adipose tissues

Several adipose depots, including constitutive bone marrow adipose tissue (cBMAT), resist conventional lipolytic cues, making them metabolically non-responsive. However, under starvation, wasting, or cachexia, the body can eventually catabolize these stable adipocytes through unknown mechanisms. To study this, we developed a mouse model of brain-evoked depletion of all fat, including cBMAT, independent of food intake. Genetic, surgical, and chemical approaches demonstrated that depletion of stable fat required adipose triglyceride lipase-dependent lipolysis but was independent of local nerves, the sympathetic nervous system, and catecholamines. Instead, concurrent hypoglycemia and hypoinsulinemia activated a potent catabolic state by suppressing lipid storage and increasing catecholamine-independent lipolysis via downregulation of cell-autonomous lipolytic inhibitors Acvr1c, G0s2, and Npr3. This was also sufficient to delipidate classical adipose depots. Overall, this work defines unique adaptations of stable adipocytes to resist lipolysis in healthy states while isolating a potent in vivo neurosystemic pathway by which the body can rapidly catabolize all adipose tissues.

Transcriptional regulation of adipocyte lipolysis by IRF2BP2

Adipocyte lipolysis controls systemic energy levels and metabolic homeostasis. Lipolysis is regulated by post-translational modifications of key lipolytic enzymes. However, less is known about the transcriptional mechanisms that regulate lipolysis. Here, we identify the transcriptional factor interferon regulatory factor-2 binding protein 2 (IRF2BP2) as a repressor of adipocyte lipolysis. Deletion of IRF2BP2 in primary human adipocytes increases lipolysis without affecting glucose uptake, whereas IRF2BP2 overexpression decreases lipolysis. RNA-seq and ChIP-seq analyses reveal that IRF2BP2 directly represses several lipolysis-related genes, including LIPE ( HSL , hormone sensitive lipase), which encodes the rate-limiting enzyme in lipolysis. Adipocyte-selective deletion of Irf2bp2 in mice increases Lipe expression and free fatty acid levels, resulting in elevated adipose tissue inflammation and glucose intolerance. Altogether, these findings demonstrate that IRF2BP2 restrains adipocyte lipolysis and opens new avenues to target lipolysis for the treatment of metabolic disease.

Aging impairs cold-induced beige adipogenesis and adipocyte metabolic reprogramming

The energy-burning capability of beige adipose tissue is a potential therapeutic tool for reducing obesity and metabolic disease, but this capacity is decreased by aging. Here, we evaluate the impact of aging on the profile and activity of adipocyte stem and progenitor cells (ASPCs) and adipocytes during the beiging process in mice. We found that aging increases the expression of Cd9 and other fibro-inflammatory genes in fibroblastic ASPCs and blocks their differentiation into beige adipocytes. Fibroblastic ASPC populations from young and aged mice were equally competent for beige differentiation in vitro, suggesting that environmental factors suppress adipogenesis in vivo. Examination of adipocytes by single nucleus RNA-sequencing identified compositional and transcriptional differences in adipocyte populations with aging and cold exposure. Notably, cold exposure induced an adipocyte population expressing high levels of de novo lipogenesis (DNL) genes, and this response was severely blunted in aged animals. We further identified Npr3, which encodes the natriuretic peptide clearance receptor, as a marker gene for a subset of white adipocytes and an aging-upregulated gene in adipocytes. In summary, this study indicates that aging blocks beige adipogenesis and dysregulates adipocyte responses to cold exposure and provides a resource for identifying cold and aging-regulated pathways in adipose tissue.

Adipose organ dysfunction and type 2 diabetes: Role of nitric oxide

Adipose organ, historically known as specialized lipid-handling tissue serving as the long-term fat depot, is now appreciated as the largest endocrine organ composed of two main compartments, i.e., subcutaneous and visceral adipose tissue (AT), madding up white and beige/brown adipocytes. Adipose organ dysfunction manifested as maldistribution of the compartments, hypertrophic, hypoxic, inflamed, and insulin-resistant AT, contributes to the development of type 2 diabetes (T2D). Here, we highlight the role of nitric oxide (NO·) in AT (dys)function in relation to developing T2D. The key aspects determining lipid and glucose homeostasis in AT depend on the physiological levels of the NO· produced via endothelial NO· synthases (eNOS). In addition to decreased NO· bioavailability (via decreased expression/activity of eNOS or scavenging NO·), excessive NO· produced by inducible NOS (iNOS) in response to hypoxia and AT inflammation may be a critical interfering factor diverting NO· signaling to the formation of reactive oxygen and nitrogen species, resulting in AT and whole-body metabolic dysfunction. Pharmacological approaches boosting AT-NO· availability at physiological levels (by increasing NO· production and its stability), as well as suppression of iNOS-NO· synthesis, are potential candidates for developing NO·-based therapeutics in T2D.

Aging impairs cold-induced beige adipogenesis and adipocyte metabolic reprogramming

The energy-burning capability of beige adipose tissue is a potential therapeutic tool for reducing obesity and metabolic disease, but this capacity is decreased by aging. Here, we evaluate the impact of aging on the profile and activity of adipocyte stem and progenitor cells (ASPCs) and adipocytes during the beiging process. We found that aging increases the expression of Cd9 and other fibro-inflammatory genes in fibroblastic ASPCs and blocks their differentiation into beige adipocytes. Fibroblastic ASPC populations from young and aged mice were equally competent for beige differentiation in vitro, suggesting that environmental factors suppress adipogenesis in vivo. Examination of adipocytes by single nucleus RNA-sequencing identified compositional and transcriptional differences in adipocyte populations with age and cold exposure. Notably, cold exposure induced an adipocyte population expressing high levels of de novo lipogenesis (DNL) genes, and this response was severely blunted in aged animals. We further identified natriuretic peptide clearance receptor Npr3, a beige fat repressor, as a marker gene for a subset of white adipocytes and an aging-upregulated gene in adipocytes. In summary, this study indicates that aging blocks beige adipogenesis and dysregulates adipocyte responses to cold exposure and provides a unique resource for identifying cold and aging-regulated pathways in adipose tissue.

The molecular mechanism of obesity: The science behind natural exercise yoga and healthy diets in the treatment of obesity

The review centers on the scientific evidence underlying obesity, providing a detailed examination of the role of perilipin in this condition. It explores potential causes of obesity and delves into therapeutic approaches involving exercise, yoga, and herbal treatments. The paper discusses natural sources that can contribute to combating obesity and underscores the importance of exercise in a scientific context for overcoming obesity. Additionally, it includes information on herbal ingredients that aid in reducing obesity. The review also examines the impact of exercise type and intensity at various time intervals on muscle development. It elucidates triglyceride hydrolysis through different enzymes and the deposition of fatty acids in adipose tissue. The mechanisms by which alpha/beta hydrolase domain-containing protein 5 (ABHD5) and hormone-sensitive lipase (HSL) target and activate their functions are detailed. The inflammatory response in obesity is explored, encompassing inflammatory markers, lipid storage diseases, and their classification with molecular mechanisms. Furthermore, the hormonal regulation of lipolysis is elaborated upon in the review.

Association between glomerular filtration rate and plasma N-terminal pro-atrial natriuretic peptide concentration in dogs

OBJECTIVES

To investigate the association between plasma N-terminal pro-atrial natriuretic peptide concentration and glomerular filtration rate in dogs.

MATERIALS AND METHODS

Dogs were classified into four categories by bodyweight. Dogs were divided into four groups (Groups 1 to 4) based on glomerular filtration rate estimates using plasma iohexol clearance per bodyweight category. Generalised linear models were built to explore the relationship between plasma N-terminal pro-atrial natriuretic peptide concentration and glomerular filtration rate and the effect of confounders on plasma N-terminal pro-atrial natriuretic peptide concentration.

RESULTS

Fifty-three dogs were included (Group 1, 25; Group 2, seven; Group 3, five; and Group 4, 16). The medians (interquartile range) N-terminal pro-atrial natriuretic peptide concentrations for Groups 1 to 4 were 7224 pg/mL (4766 to 10,254 mg/dL), 8958 pg/mL (4935 to 11,271 mg/dL), 9280 pg/mL (9195 to 10,384 mg/dL) and 12,683 pg/mL (9133 to 19,217 mg/dL), respectively. Group 4, estimated to have the highest reduction in glomerular filtration rate, had a higher plasma N-terminal pro-atrial natriuretic peptide concentration than Groups 1 to 3. Based on the final generalised linear model, influencing factors for plasma N-terminal pro-atrial natriuretic peptide concentration were plasma iohexol clearance (-0.136; 95% confidence interval, -0.227 to -0.046) and bodyweight (-0.058; 95% confidence interval, -0.098 to -0.018).

CLINICAL SIGNIFICANCE

N-terminal pro-atrial natriuretic peptide concentration is associated with the glomerular filtration rate.

Natriuretic Peptide Signaling in Uterine Biology and Preeclampsia

Endometrial decidualization is a uterine process essential for spiral artery remodeling, embryo implantation, and trophoblast invasion. Defects in endometrial decidualization and spiral artery remodeling are important contributing factors in preeclampsia, a major disorder in pregnancy. Atrial natriuretic peptide (ANP) is a cardiac hormone that regulates blood volume and pressure. ANP is also generated in non-cardiac tissues, such as the uterus and placenta. In recent human genome-wide association studies, multiple loci with genes involved in natriuretic peptide signaling are associated with gestational hypertension and preeclampsia. In cellular experiments and mouse models, uterine ANP has been shown to stimulate endometrial decidualization, increase TNF-related apoptosis-inducing ligand expression and secretion, and enhance apoptosis in arterial smooth muscle cells and endothelial cells. In placental trophoblasts, ANP stimulates adenosine 5'-monophosphate-activated protein kinase and the mammalian target of rapamycin complex 1 signaling, leading to autophagy inhibition and protein kinase N3 upregulation, thereby increasing trophoblast invasiveness. ANP deficiency impairs endometrial decidualization and spiral artery remodeling, causing a preeclampsia-like phenotype in mice. These findings indicate the importance of natriuretic peptide signaling in pregnancy. This review discusses the role of ANP in uterine biology and potential implications of impaired ANP signaling in preeclampsia.

Type II Transmembrane Serine Proteases as Modulators in Adipose Tissue Phenotype and Function

Adipose tissue is a crucial organ in energy metabolism and thermoregulation. Adipose tissue phenotype is controlled by various signaling mechanisms under pathophysiological conditions. Type II transmembrane serine proteases (TTSPs) are a group of trypsin-like enzymes anchoring on the cell surface. These proteases act in diverse tissues to regulate physiological processes, such as food digestion, salt-water balance, iron metabolism, epithelial integrity, and auditory nerve development. More recently, several members of the TTSP family, namely, hepsin, matriptase-2, and corin, have been shown to play a role in regulating lipid metabolism, adipose tissue phenotype, and thermogenesis, via direct growth factor activation or indirect hormonal mechanisms. In mice, hepsin deficiency increases adipose browning and protects from high-fat diet-induced hyperglycemia, hyperlipidemia, and obesity. Similarly, matriptase-2 deficiency increases fat lipolysis and reduces obesity and hepatic steatosis in high-fat diet-fed mice. In contrast, corin deficiency increases white adipose weights and cell sizes, suppresses adipocyte browning and thermogenic responses, and causes cold intolerance in mice. These findings highlight an important role of TTSPs in modifying cellular phenotype and function in adipose tissue. In this review, we provide a brief description about TTSPs and discuss recent findings regarding the role of hepsin, matriptase-2, and corin in regulating adipose tissue phenotype, energy metabolism, and thermogenic responses.

Pharmacologic blockade of the natriuretic peptide clearance receptor promotes weight loss and enhances insulin sensitivity in type 2 diabetes

While natriuretic peptides (NPs) are primarily known for their renal and cardiovascular actions, NPs stimulate lipolysis in adipocytes and induce a thermogenic program in white adipose tissue (WAT) that resembles brown fat. The biologic effects of NPs are negatively regulated by the NP clearance receptor (NPRC), which binds and degrades NPs. Knockout (KO) of NPRC protects against diet induced obesity and improves insulin sensitivity in obese mice. To determine if pharmacologic blockade of NPRC enhanced the beneficial metabolic actions of NPs in type 2 diabetes, we blocked NP clearance in a mouse model of type 2 diabetes using the specific NPRC ligand ANP(4-23). We found that treatment with ANP(4-23) caused a significant decrease in body weight by increasing energy expenditure and reducing fat mass without a change in lean body mass. The decrease in fat mass was associated with a significant improvement in insulin sensitivity and reduced serum insulin levels. These beneficial effects were accompanied by a decrease in infiltrating macrophages in adipose tissue, and reduced expression of inflammatory markers in both serum and WAT. These data suggest that inhibiting NP clearance may be an effective pharmacologic approach to promote weight loss and enhance insulin sensitivity in type 2 diabetes. Optimizing the therapeutic approach may lead to useful therapies for obesity and type 2 diabetes.

Resistance to energy metabolism - targeted therapy of AML cells residual in the bone marrow microenvironment

In response to the changing availability of nutrients and oxygen in the bone marrow microenvironment, acute myeloid leukemia (AML) cells continuously adjust their metabolic state. To meet the biochemical demands of their increased proliferation, AML cells strongly depend on mitochondrial oxidative phosphorylation (OXPHOS). Recent data indicate that a subset of AML cells remains quiescent and survives through metabolic activation of fatty acid oxidation (FAO), which causes uncoupling of mitochondrial OXPHOS and facilitates chemoresistance. For targeting these metabolic vulnerabilities of AML cells, inhibitors of OXPHOS and FAO have been developed and investigated for their therapeutic potential. Recent experimental and clinical evidence has revealed that drug-resistant AML cells and leukemic stem cells rewire metabolic pathways through interaction with BM stromal cells, enabling them to acquire resistance against OXPHOS and FAO inhibitors. These acquired resistance mechanisms compensate for the metabolic targeting by inhibitors. Several chemotherapy/targeted therapy regimens in combination with OXPHOS and FAO inhibitors are under development to target these compensatory pathways.

Corin Deficiency Alters Adipose Tissue Phenotype and Impairs Thermogenesis in Mice

Atrial natriuretic peptide (ANP) is a key regulator in body fluid balance and cardiovascular biology. In addition to its role in enhancing natriuresis and vasodilation, ANP increases lipolysis and thermogenesis in adipose tissue. Corin is a protease responsible for ANP activation. It remains unknown if corin has a role in regulating adipose tissue function. Here, we examined adipose tissue morphology and function in corin knockout (KO) mice. We observed increased weights and cell sizes in white adipose tissue (WAT), decreased levels of uncoupling protein 1 (Ucp1), a brown adipocyte marker in WAT and brown adipose tissue (BAT), and suppressed thermogenic gene expression in BAT from corin KO mice. At regular room temperature, corin KO and wild-type mice had similar metabolic rates. Upon cold exposure at 4 °C, corin KO mice exhibited impaired thermogenic responses and developed hypothermia. In BAT from corin KO mice, the signaling pathway of p38 mitogen-activated protein kinase, peroxisome proliferator-activated receptor c coactivator 1a, and Ucp1 was impaired. In cell culture, ANP treatment increased Ucp1 expression in BAT-derived adipocytes from corin KO mice. These data indicate that corin mediated-ANP activation is an important hormonal mechanism in regulating adipose tissue function and body temperature upon cold exposure in mice.

Cold exposure induces lipid dynamics and thermogenesis in brown adipose tissue of goats

Background

Adaptive thermogenesis by brown adipose tissue (BAT) is important to the maintenance of temperature in newborn mammals. Cold exposure activates gene expression and lipid metabolism to provide energy for BAT thermogenesis. However, knowledge of BAT metabolism in large animals after cold exposure is still limited.

Results

In this study, we found that cold exposure induced expression of BAT thermogenesis genes and increased the protein levels of UCP1 and PGC1α. Pathway analysis showed that cold exposure activated BAT metabolism, which involved in cGMP-PKG, TCA cycle, fatty acid elongation, and degradation pathways. These were accompanied by decreased triglyceride (TG) content and increased phosphatidylcholine (PC) and phosphatidylethanolamine (PE) content in BAT.

Conclusion

These results demonstrate that cold exposure induces metabolites involved in glycerolipids and glycerophospholipids metabolism in BAT. The present study provides evidence for lipid composition associated with adaptive thermogenesis in goat BAT and metabolism pathways regulated by cold exposure.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08765-5.

Subcutaneous Administration of a Nitric Oxide-Releasing Nanomatrix Gel Ameliorates Obesity and Insulin Resistance in High-Fat Diet-Induced Obese Mice

Nitric oxide (NO) is a gaseous signaling molecule, which plays crucial roles in various biological processes, including inflammatory responses, metabolism, cardiovascular functions, and cognitive function. NO bioavailability is reduced with aging and cardiometabolic disorders in humans and rodents. NO stimulates the metabolic rate by increasing the mitochondrial biogenesis and brown fat activation. Therefore, we propose a novel technology of providing exogenous NO to improve the metabolic rate and cognitive function by promoting the development of brown adipose tissue. In the present study, we demonstrate the effects of the peptide amphiphiles-NO-releasing nanomatrix gel (PANO gel) on high-fat diet-induced obesity, insulin resistance, and cognitive functions. Eight-week-old male C57BL/6 mice were subcutaneously injected in the brown fat area with the PANO gel or vehicle (PA gel) every 2 weeks for 12 weeks. The PANO gel-injected mice gained less body weight, improved glucose tolerance, and decreased fasting serum insulin and leptin levels compared with the PA gel-injected mice. Insulin signaling in the muscle, liver, and epididymal white adipose tissue was improved by the PANO gel injection. The PANO gel reduced inflammation, increased lipolysis in the epididymal white adipose tissue, and decreased serum lipids and liver triglycerides. Interestingly, the PANO gel stimulated uncoupled protein 1 gene expression in the brown and beige fat tissues. Furthermore, the PANO gel increased the cerebral blood flow and improved learning and memory abilities. Our results suggest that using the PANO gel to supply exogenous NO is a novel technology to treat metabolic disorders and cognitive dysfunctions.

Molecular Systems Architecture of Interactome in the Acute Myeloid Leukemia Microenvironment

A molecular systems architecture is presented for acute myeloid leukemia (AML) to provide a framework for organizing the complexity of biomolecular interactions. AML is a multifactorial disease resulting from impaired differentiation and increased proliferation of hematopoietic precursor cells involving genetic mutations, signaling pathways related to the cancer cell genetics, and molecular interactions between the cancer cell and the tumor microenvironment, including endothelial cells, fibroblasts, myeloid-derived suppressor cells, bone marrow stromal cells, and immune cells (e.g., T-regs, T-helper 1 cells, T-helper 17 cells, T-effector cells, natural killer cells, and dendritic cells). This molecular systems architecture provides a layered understanding of intra- and inter-cellular interactions in the AML cancer cell and the cells in the stromal microenvironment. The molecular systems architecture may be utilized for target identification and the discovery of single and combination therapeutics and strategies to treat AML.

The effect of adenosine monophosphate-activated protein kinase on lipolysis in adipose tissue: an historical and comprehensive review

CONTEXT

Lipolysis is one of the most important pathways for energy management, its control in the adipose tissue (AT) is a potential therapeutic target for metabolic diseases. Adenosine Mono Phosphate-activated Protein Kinase (AMPK) is a key regulatory enzyme in lipids metabolism and a potential target for diabetes and obesity treatment.

OBJECTIVE

The aim of this work is to analyse the existing information on the relationship of AMPK and lipolysis in the AT.

METHODS

A thorough search of bibliography was performed in the databases Scopus and Web of Knowledge using the terms lipolysis, adipose tissue, and AMPK, the unrelated publications were excluded, and the documents were analysed.

RESULTS

Sixty-three works were found and classified in 3 categories: inhibitory effects, stimulatory effect, and diverse relationships; remarkably, the newest researches support an upregulating relationship of AMPK over lipolysis.

CONCLUSION

The most probable reality is that the relationship AMPK-lipolysis depends on the experimental conditions.

Endothelin-1 induces lipolysis through activation of the GC/cGMP/Ca2+/ERK/CaMKIII pathway in 3T3-L1 adipocytes

Endothelin-1 (ET-1) is a potent vasoconstrictive peptide produced and secreted mainly by endothelial cells. Recent studies indicate that ET-1 can regulate lipid metabolism, which may increase the risk of insulin resistance. Our previous studies revealed that ET-1 induced lipolysis in adipocytes, but the underlying mechanisms were unclear. 3T3-L1 adipocytes were used to investigate the effect of ET-1 on lipolysis and the underlying mechanisms. Glycerol levels in the incubation medium and hormone-sensitive lipase (HSL) phosphorylation were used as indices for lipolysis. ET-1 significantly increased HSL phosphorylation and lipolysis, which were completely inhibited by ERK inhibitor (PD98059) and guanylyl cyclase (GC) inhibitor (LY83583). LY83583 reduced ET-1-induced ERK phosphorylation. A Ca2+-free medium and PLC inhibitor caused significant decreases in ET-1-induced lipolysis as well as ERK and HSL phosphorylation, and IP3 receptor activator (D-IP3) increased lipolysis. ET-1 increased cGMP production, which was not affected by depletion of extracellular Ca2+. On the other hand, LY83583 diminished the ET-1-induced Ca2+ influx. Transient receptor potential vanilloid-1 (TRPV-1) antagonist and shRNA partially inhibited ET-1-induced lipolysis. ET-1-induced lipolysis was completely suppressed by CaMKIII inhibitor (NH-125). These results indicate that ET-1 stimulates extracellular Ca2+ entry and activates the intracellular PLC/IP3/Ca2+ pathway through a cGMP-dependent pathway. The increased cytosolic Ca2+ that results from ET-1 treatment stimulates ERK and HSL phosphorylation, which subsequently induces lipolysis. ET-1 induces HSL phosphorylation and lipolysis via the GC/cGMP/Ca2+/ERK/CaMKIII signaling pathway in 3T3-L1 adipocytes.

SGLT2 Inhibitors and Ketone Metabolism in Heart Failure

Sodium-glucose cotransporter-2 (SGLT2) inhibitors have emerged as powerful drugs that can be used to treat heart failure (HF) patients, both with preserved and reduced ejection fraction and in the presence or absence of type 2 diabetes. While the mechanisms underlying the salutary effects of SGLT2 inhibitors have not been fully elucidated, there is clear evidence for a beneficial metabolic effect of these drugs. In this review, we discuss the effects of SGLT2 inhibitors on cardiac energy provision secondary to ketone bodies, pathological ventricular remodeling, and inflammation in patients with HF. While the specific contribution of ketone bodies to the pleiotropic cardiovascular benefits of SGLT2 inhibitors requires further clarification, ketone bodies themselves may also be used as a therapy for HF.

NPPA Promoter Hypomethylation Predicts Central Obesity Development: A Prospective Longitudinal Study in Chinese Adults

INTRODUCTION

Atrial natriuretic peptide plays a potential role in obesity with unclear molecular mechanisms. The objective of this study was to examine the association between its coding gene (natriuretic peptide A [NPPA]) methylation and obesity.

METHODS

Peripheral blood DNA methylation of NPPA promoter was quantified at baseline by targeted bisulfite sequencing for 2,497 community members (mean aged 53 years, 38% men) in the Gusu cohort. Obesity was repeatedly assessed by body mass index (BMI) and waist circumference (WC) at baseline and follow-up examinations. The cross-sectional, longitudinal, and prospective associations between NPPA promoter methylation and obesity were examined.

RESULTS

Of the 9 CpG loci assayed, DNA methylation levels at 6 CpGs were significantly lower in participants with central obesity than those without (all p < 0.05 for permutation test). These CpG methylation levels at baseline were also inversely associated with dynamic changes in BMI or WC during follow-up (all p < 0.05 for permutation test). After an average 4 years of follow-up, hypermethylation at the 6 CpGs (CpG2 located at Chr1:11908348, CpG3 located at Chr1:11908299, CpG4 located at Chr1:11908200, CpG5 located at Chr1:11908182, CpG6 located at Chr1:11908178, and CpG8 located at Chr1:11908165) was significantly associated with a lower risk of incident central obesity (all p < 0.05 for permutation test).

CONCLUSIONS

Hypomethylation at NPPA promoter was associated with increased future risk of central obesity in Chinese adults. Aberrant DNA methylation of the NPPA gene may participate in the mechanisms of central obesity.

Receptor Guanylyl Cyclase C and Cyclic GMP in Health and Disease: Perspectives and Therapeutic Opportunities

Receptor Guanylyl Cyclase C (GC-C) was initially characterized as an important regulator of intestinal fluid and ion homeostasis. Recent findings demonstrate that GC-C is also causally linked to intestinal inflammation, dysbiosis, and tumorigenesis. These advances have been fueled in part by identifying mutations or changes in gene expression in GC-C or its ligands, that disrupt the delicate balance of intracellular cGMP levels and are associated with a wide range of clinical phenotypes. In this review, we highlight aspects of the current knowledge of the GC-C signaling pathway in homeostasis and disease, emphasizing recent advances in the field. The review summarizes extra gastrointestinal functions for GC-C signaling, such as appetite control, energy expenditure, visceral nociception, and behavioral processes. Recent research has expanded the homeostatic role of GC-C and implicated it in regulating the ion-microbiome-immune axis, which acts as a mechanistic driver in inflammatory bowel disease. The development of transgenic and knockout mouse models allowed for in-depth studies of GC-C and its relationship to whole-animal physiology. A deeper understanding of the various aspects of GC-C biology and their relationships with pathologies such as inflammatory bowel disease, colorectal cancer, and obesity can be leveraged to devise novel therapeutics.

Effects of different stimulators of cGMP synthesis on lipid content in bovine oocytes matured in vitro

Bovine oocytes and blastocysts produced in vitro are frequently of lower quality and less cryotolerant than those produced in vivo, and greater accumulation of lipids in the cytoplasm has been pointed out as one of the reasons. In human adipocytes cGMP signaling through the activation of PKG appears to be involved in lipid metabolism, and components of this pathway have been detected in bovine cumulus-oocyte complexes (COCs). The aim of this study was to investigate the influence of this pathway on the lipid content in oocytes and expression of PLIN2 (a lipid metabolism-related gene) in cumulus cells. COCs were matured in vitro for 24 h with different stimulators of cGMP synthesis. The activation of soluble guanylyl cyclase (sGC) by Protoporphyrin IX reduced lipid content (22.7 FI) compared to control oocytes (36.45 FI; P <0.05). Stimulation of membrane guanylyl cyclase (mGC) with natriuretic peptides precursors A and C (NPPA and NPPC) had no effect (36.5 FI; P>0.05). When the PKG inhibitor KT5823 was associated with Protoporphyrin IX, its effect was reversed and lipid contents increased (52.71 FI; P<0.05). None of the stimulators of cGMP synthesis affected the expression of PLIN2 in cumulus cells. In conclusion, stimulation of sGC for cGMP synthesis promotes lipolytic activities in bovine oocytes matured in vitro and such effect is mediated by PKG. However, such effect may vary depending on the stimulus received and/or which synthesis enzyme was activated, as stimulation of mGC had no effects.

Inhibiting serotonin signaling through HTR2B in visceral adipose tissue improves obesity-related insulin resistance

Insulin resistance is a cornerstone of obesity-related complications such as type 2 diabetes, metabolic syndrome, and nonalcoholic fatty liver disease. A high rate of lipolysis is known to be associated with insulin resistance, and inhibiting adipose tissue lipolysis improves obesity-related insulin resistance. Here, we demonstrate that inhibition of serotonin (5-hydroxytryptamine [5-HT]) signaling through serotonin receptor 2B (HTR2B) in adipose tissues ameliorates insulin resistance by reducing lipolysis in visceral adipocytes. Chronic high-fat diet (HFD) feeding increased Htr2b expression in epididymal white adipose tissue, resulting in increased HTR2B signaling in visceral white adipose tissue. Moreover, HTR2B expression in white adipose tissue was increased in obese humans and positively correlated with metabolic parameters. We further found that adipocyte-specific Htr2b-knockout mice are resistant to HFD-induced insulin resistance, visceral adipose tissue inflammation, and hepatic steatosis. Enhanced 5-HT signaling through HTR2B directly activated lipolysis through phosphorylation of hormone-sensitive lipase in visceral adipocytes. Moreover, treatment with a selective HTR2B antagonist attenuated HFD-induced insulin resistance, visceral adipose tissue inflammation, and hepatic steatosis. Thus, adipose HTR2B signaling could be a potential therapeutic target for treatment of obesity-related insulin resistance.

Atrial Natriuretic Peptide Inhibited ABCA1/G1-dependent Cholesterol Efflux Related to Low HDL-C in Hypertensive Pregnant Patients

Objective: It has been reported that atrial natriuretic peptide (ANP) regulates lipid metabolism by stimulating adipocyte browning, lipolysis, and lipid oxidation, and by impacting the secretion of adipokines. In our previous study, we found that the plasma ANP concentration of hypertensive disorders of pregnancy (HDP) was significantly increased in comparison to that of normotensive pregnancy patients. Thus, this study’s objective was to investigate the lipid profile in patients with HDP and determine the effects of ANP on the cholesterol efflux in THP-1 macrophages.

Methods: A total of 265 HDP patients and 178 normotensive women as the control group were recruited. Clinical demographic characteristics and laboratory profile data were collected. Plasma total triglycerides (TGs), total cholesterol (TC), low-density cholesterol (LDL-C), and high-density cholesterol (HDL-C) were compared between the two groups. THP-1 monocytes were incubated with different concentrations of ANP. ATP-binding cassette transporter A1 (ABCA1) and ATP-binding cassette transporter G1 (ABCG1) mRNA and protein were evaluated. ABCA1- and ABCG1-mediated cholesterol efflux to apolipoprotein A-Ⅰ (apoA-Ⅰ) and HDL, respectively, were measured by green fluorescent labeled NBD cholesterol. Natriuretic peptide receptor A (NPR-A) siRNA and specific agonists of the peroxisome proliferator–activated receptor-γ (PPAR-γ) and liver X receptor α (LXRα) were studied to investigate the mechanism involved.

Results: Plasma TG, TC, LDL-C, and LDL-C/HDL-C were significantly increased, and HDL-C was significantly decreased in the HDP group in comparison to the control (all p < 0.001). ANP inhibited the expression of ABCA1 and ABCG1 at both the mRNA and protein levels in a dose-dependent manner. The functions of ABCA1- and ABCG1-mediated cholesterol efflux to apoA-I and HDL were significantly decreased. NPR-A siRNA further confirmed that ANP binding to its receptor inhibited ABCA1/G1 expression through the PPAR-γ/LXRα pathway.

Conclusions: ABCA1/G1 was inhibited by the stimulation of ANP when combined with NPR-A through the PPAR-γ/LXRα pathway in THP-1 macrophages. The ABCA1/G1-mediated cholesterol efflux was also impaired by the stimulation of ANP. This may provide a new explanation for the decreased level of HDL-C in HDP patients.

Redox Regulation of Lipid Mobilization in Adipose Tissues

Lipid mobilization in adipose tissues, which includes lipogenesis and lipolysis, is a paramount process in regulating systemic energy metabolism. Reactive oxygen and nitrogen species (ROS and RNS) are byproducts of cellular metabolism that exert signaling functions in several cellular processes, including lipolysis and lipogenesis. During lipolysis, the adipose tissue generates ROS and RNS and thus requires a robust antioxidant response to maintain tight regulation of redox signaling. This review will discuss the production of ROS and RNS within the adipose tissue, their role in regulating lipolysis and lipogenesis, and the implications of antioxidants on lipid mobilization.

Atrial Natriuretic Peptide Orchestrates a Coordinated Physiological Response to Fuel Non-shivering Thermogenesis

Atrial natriuretic peptide (ANP) is a cardiac hormone controlling blood volume and pressure in mammals. It is still unclear whether ANP controls cold-induced thermogenesis in vivo. Here, we show that acute cold exposure induces cardiac ANP secretion in mice and humans. Genetic inactivation of ANP promotes cold intolerance and suppresses half of cold-induced brown adipose tissue (BAT) activation in mice. While white adipocytes are resistant to ANP-mediated lipolysis at thermoneutral temperature in mice, cold exposure renders white adipocytes fully responsive to ANP to activate lipolysis and a thermogenic program, a physiological response that is dramatically suppressed in ANP null mice. ANP deficiency also blunts liver triglycerides and glycogen metabolism, thus impairing fuel availability for BAT thermogenesis. ANP directly increases mitochondrial uncoupling and thermogenic gene expression in human white and brown adipocytes. Together, these results indicate that ANP is a major physiological trigger of BAT thermogenesis upon cold exposure in mammals.

Natriuretic Peptides as Predictors of Protein-Energy Wasting in Hemodialysis Population

OBJECTIVE

Imbalance between anabolism and catabolism is linked to cachexia and protein-energy wasting (PEW), especially in frail populations such as patients with chronic kidney disease. PEW is responsible of poor outcomes with increased morbidity and mortality. Several causes are involved in PEW such as insulin resistance, acidosis, or hyperparathyroidism. Natriuretic peptides (NPs) have recently been described as activators of resting energy expenditure through the induction of browning of white adipose tissue in rodents with chronic kidney disease. The present study was therefore implemented to investigate whether NPs could be associated with PEW criteria and predict clinical outcomes.

METHODS

We quantified serum N-terminal pro-B-type natriuretic peptide (NT-proBNP) in a prospective cohort of 231 patients undergoing maintenance hemodialysis and atrial natriuretic peptide in a subgroup of 35 patients. Body composition parameters were measured with bioimpedance spectroscopy.

RESULTS

NT-proBNP was inversely associated with serum albumin, prealbumin, and body mass index and, conversely, positively associated with age and C-reactive protein. NT-proBNP as well as atrial natriuretic peptide were significantly higher in patients with PEW criteria. NT-proBNP was negatively associated with body fat mass. In multiple linear regression, NT-proBNP remained associated with body mass index. Kaplan-Meier analysis revealed a significant correlation between serum NT-proBNP concentrations and all-cause mortality and cardiovascular events. This association remained significant after multivariable Cox regression models adjusted for demographic factors and cardiovascular risk factors.

CONCLUSION

Accumulation of NPs seems to be associated with poor nutritional status and reduced survival among hemodialysis patients. Further studies are needed to confirm this association using resting energy expenditure measurement and adipose tissue biopsy.

CD10 marks non-canonical PPARγ-independent adipocyte maturation and browning potential of adipose-derived stem cells

BACKGROUND

Effective stem cell therapy is dependent on the stem cell quality that is determined by their differentiation potential, impairment of which leads to poor engraftment and survival into the target cells. However, limitations in our understanding and the lack of reliable markers that can predict their maturation efficacies have hindered the development of stem cells as an effective therapeutic strategy. Our previous study identified CD10, a pro-adipogenic, depot-specific prospective cell surface marker of human adipose-derived stem cells (ASCs). Here, we aim to determine if CD10 can be used as a prospective marker to predict mature adipocyte quality and play a direct role in adipocyte maturation.

METHODS

We first generated 14 primary human subject-derived ASCs and stable immortalized CD10 knockdown and overexpression lines for 4 subjects by the lentiviral transduction system. To evaluate the role of CD10 in adipogenesis, the adipogenic potential of the human subject samples were scored against their respective CD10 transcript levels. Assessment of UCP1 expression levels was performed to correlate CD10 levels to the browning potential of mature ASCs. Quantitative polymerase chain reaction (qPCR) and Western blot analysis were performed to determine CD10-dependent regulation of various targets. Seahorse analysis of oxidative metabolism and lipolysis assay were studied. Lastly, as a proof-of-concept study, we used CD10 as a prospective marker for screening nuclear receptor ligands library.

RESULTS

We identified intrinsic CD10 levels as a positive determinant of adipocyte maturation as well as browning potential of ASCs. Interestingly, CD10 regulates ASC's adipogenic maturation non-canonically by modulating endogenous lipolysis without affecting the classical peroxisome proliferator-activated receptor gamma (PPARγ)-dependent adipogenic pathways. Furthermore, our CD10-mediated screening analysis identified dexamethasone and retinoic acid as stimulator and inhibitor of adipogenesis, respectively, indicating CD10 as a useful biomarker for pro-adipogenic drug screening.

CONCLUSION

Overall, we establish CD10 as a functionally relevant ASC biomarker, which may be a prerequisite to identify high-quality cell populations for improving metabolic diseases.

Hormone-sensitive lipase: sixty years later

Hormone-sensitive lipase (HSL) was initially characterized as the hormonally regulated neutral lipase activity responsible for the breakdown of triacylglycerols into fatty acids in adipose tissue. This review aims at providing up-to-date information on structural properties, regulation of expression, activity and function as well as therapeutic potential. The lipase is expressed as different isoforms produced from tissue-specific alternative promoters. All isoforms are composed of an N-terminal domain and a C-terminal catalytic domain within which a regulatory domain containing the phosphorylation sites is embedded. Some isoforms possess additional N-terminal regions. The catalytic domain shares similarities with bacteria, fungus and vascular plant proteins but not with other mammalian lipases. HSL singularity is provided by regulatory and N-terminal domains sharing no homology with other proteins. HSL has a broad substrate specificity compared to other neutral lipases. It hydrolyzes acylglycerols, cholesteryl and retinyl esters among other substrates. A novel role of HSL, independent of its enzymatic function, has recently been described in adipocytes. Clinical studies revealed dysregulations of HSL expression and activity in disorders, such as lipodystrophy, obesity, type 2 diabetes and cancer-associated cachexia. Development of specific inhibitors positions HSL as a pharmacological target for the treatment of metabolic complications.

CD47 differentially regulates white and brown fat function

Mechanisms that enhance energy expenditure are attractive therapeutic targets for obesity. Previously we have demonstrated that mice lacking cd47 are leaner, exhibit increased energy expenditure, and are protected against diet-induced obesity. In this study, we further defined the physiological role of cd47 deficiency in regulating mitochondrial function and energy expenditure in both white and brown adipose tissue. We observed that cd47 deficient mice (under normal chow diet) had comparable amount of white fat mass but reduced white adipocyte size as compared to wild-type mice. Subsequent ex vivo and in vitro studies suggest enhanced lipolysis, and not impaired lipogenesis or energy utilization, contributes to this phenotype. In contrast to white adipose tissue, there were no obvious morphological differences in brown adipose tissue between wild-type and knockout mice. However, mitochondria isolated from brown fat of cd47 deficient mice had significantly higher rates of free fatty acid-mediated uncoupling. This suggests that enhanced fuel availability via white adipose tissue lipolysis may perpetuate elevated brown adipose tissue energy expenditure and contributes to the lean phenotype observed in cd47 deficient mice.

Adipocyte lipolysis: from molecular mechanisms of regulation to disease and therapeutics

Fatty acids (FAs) are stored safely in the form of triacylglycerol (TAG) in lipid droplet (LD) organelles by professional storage cells called adipocytes. These lipids are mobilized during adipocyte lipolysis, the fundamental process of hydrolyzing TAG to FAs for internal or systemic energy use. Our understanding of adipocyte lipolysis has greatly increased over the past 50 years from a basic enzymatic process to a dynamic regulatory one, involving the assembly and disassembly of protein complexes on the surface of LDs. These dynamic interactions are regulated by hormonal signals such as catecholamines and insulin which have opposing effects on lipolysis. Upon stimulation, patatin-like phospholipase domain containing 2 (PNPLA2)/adipocyte triglyceride lipase (ATGL), the rate limiting enzyme for TAG hydrolysis, is activated by the interaction with its co-activator, alpha/beta hydrolase domain-containing protein 5 (ABHD5), which is normally bound to perilipin 1 (PLIN1). Recently identified negative regulators of lipolysis include G0/G1 switch gene 2 (G0S2) and PNPLA3 which interact with PNPLA2 and ABHD5, respectively. This review focuses on the dynamic protein-protein interactions involved in lipolysis and discusses some of the emerging concepts in the control of lipolysis that include allosteric regulation and protein turnover. Furthermore, recent research demonstrates that many of the proteins involved in adipocyte lipolysis are multifunctional enzymes and that lipolysis can mediate homeostatic metabolic signals at both the cellular and whole-body level to promote inter-organ communication. Finally, adipocyte lipolysis is involved in various diseases such as cancer, type 2 diabetes and fatty liver disease, and targeting adipocyte lipolysis is of therapeutic interest.

Adipocytes: active facilitators in epithelial ovarian cancer progression?

There is growing evidence that adipocytes play important roles in the progression of multiple cancers. Moreover, in obesity, adipocytes alter their original functions and contribute to the metabolic and inflammatory changes of adipose tissue microenvironment, which can further enhance tumor development. At present, the roles of adipocytes in the pathogenesis of epithelial ovarian cancer (EOC) are far from being fully elucidated. Herein, we summarized the recent advances in understanding the roles of adipocytes in EOC progression. Adipocytes, close neighbors of EOC tissue, promote EOC growth, invasion, metastasis and angiogenesis through adipokine secretion, metabolic remodeling and immune microenvironment modulation. Moreover, adipocytes are important therapeutic targets and may work as useful anticancer drug delivery depot for EOC treatment. Furthermore, adipocytes also act as a therapeutic obstacle for their involvement in EOC treatment resistance. Hence, better characterization of the adipocytes in EOC microenvironment and the crosstalk between adipocytes and EOC cells may provide insights into EOC progression and suggest novel therapeutic opportunities.

Lemon Extract Reduces Angiotensin Converting Enzyme (ACE) Expression and Activity and Increases Insulin Sensitivity and Lipolysis in Mouse Adipocytes

Obesity is associated with insulin resistance and cardiovascular complications. In this paper, we examine the possible beneficial role of lemon juice in dieting. Lemon extract (LE) has been proposed to improve serum insulin levels and decrease angiotensin converting enzyme (ACE) activity in mouse models. ACE is also a biomarker for sustained weight loss and ACE inhibitors improve insulin sensitivity in humans. Here, we show that LE impacts adipose tissue metabolism directly. In 3T3-L1 differentiated adipocyte cells, LE improved insulin sensitivity as evidenced by a 3.74 ± 0.54-fold increase in both pAKT and GLUT4 levels. LE also induced lipolysis as demonstrated by a 16.6 ± 1.2 fold-change in pHSL protein expression levels. ACE gene expression increased 12.0 ± 0.1 fold during differentiation of 3T3-L1 cells in the absence of LE, and treatment with LE decreased ACE gene expression by 80.1 ± 0.5% and protein expression by 55 ± 0.37%. We conclude that LE's reduction of ACE expression causes increased insulin sensitivity and breakdown of lipids in adipocytes.

Low-density lipoprotein receptor-related protein 1 deficiency in cardiomyocytes reduces susceptibility to insulin resistance and obesity

BACKGROUND

Low-density lipoprotein receptor-related protein 1 (LRP1) plays a key role in fatty acid metabolism and glucose homeostasis. In the context of dyslipemia, LRP1 is upregulated in the heart. Our aim was to evaluate the impact of cardiomyocyte LRP1 deficiency on high fat diet (HFD)-induced cardiac and metabolic alterations, and to explore the potential mechanisms involved.

METHODS

We used TnT-iCre transgenic mice with thoroughly tested suitability to delete genes exclusively in cardiomyocytes to generate an experimental mouse model with conditional Lrp1 deficiency in cardiomyocytes (TNT-iCre⁺-LRP1^flox/flox).

FINDINGS

Mice with Lrp1-deficient cardiomyocytes (cm-Lrp1^-/-) have a normal cardiac function combined with a favorable metabolic phenotype against HFD-induced glucose intolerance and obesity. Glucose intolerance protection was linked to higher hepatic fatty acid oxidation (FAO), lower liver steatosis and increased whole-body energy expenditure. Proteomic studies of the heart revealed decreased levels of cardiac pro-atrial natriuretic peptide (pro-ANP), which was parallel to higher ANP circulating levels. cm-Lrp1^-/- mice showed ANP signaling activation that was linked to increased fatty acid (FA) uptake and increased AMPK/ ACC phosphorylation in the liver. Natriuretic peptide receptor A (NPR-A) antagonist completely abolished ANP signaling and metabolic protection in cm-Lrp1^-/- mice.

CONCLUSIONS

These results indicate that an ANP-dependent axis controlled by cardiac LRP1 levels modulates AMPK activity in the liver, energy homeostasis and whole-body metabolism.

cGMP manipulation in cardiometabolic disease: chances and challenges

PURPOSE OF REVIEW

Cardiovascular and metabolic diseases are closely linked and commonly occur in the same patients. This review focuses on the cyclic guanosine monophosphate (cGMP) system and its crosstalk between metabolism and the cardiovascular system.

RECENT FINDINGS

Recent studies suggest that cGMP, which serves as second messenger for nitric oxide and for natriuretic peptides, improves oxidative metabolism and insulin signaling. The clinical evidence is particularly strong for the natriuretic peptide branch of the cGMP system. Clinical trials suggested improvements in insulin sensitivity and reductions in the risk of progressing to type 2 diabetes mellitus. However, further studies are needed.

SUMMARY

Enhancing cGMP signaling through nonpharmacological or pharmacological means may improve glucose metabolism in addition to affecting the cardiovascular system. However, excessive cGMP production could have significant unwanted cardiovascular and metabolic effects.

Fatty Acid Metabolism, Bone Marrow Adipocytes, and AML

Acute myeloid leukemia (AML) cells modulate their metabolic state continuously as a result of bone marrow (BM) microenvironment stimuli and/or nutrient availability. Adipocytes are prevalent in the BM stroma and increase in number with age. AML in elderly patients induces remodeling and lipolysis of BM adipocytes, which may promote AML cell survival through metabolic activation of fatty acid oxidation (FAO). FAO reactions generate acetyl-CoA from fatty acids under aerobic conditions and, under certain conditions, it can cause uncoupling of mitochondrial oxidative phosphorylation. Recent experimental evidence indicates that FAO is associated with quiescence and drug-resistance in leukemia stem cells. In this review, we highlight recent progress in our understanding of fatty acid metabolism in AML cells in the adipocyte-rich BM microenvironment, and discuss the therapeutic potential of combinatorial regimens with various FAO inhibitors, which target metabolic vulnerabilities of BM-resident, chemoresistant leukemia cells.

Therapeutic Progress and Knowledge Basis on the Natriuretic Peptide System in Heart Failure

Notwithstanding substantial improvements in diagnosis and treatment, Heart Failure (HF) remains a major disease burden with high prevalence and poor outcomes worldwide. Natriuretic Peptides (NPs) modulate whole cardiovascular system and exhibit multiple cardio-protective effects, including the counteraction of the Renin-Angiotensin-Aldosterone System (RAAS) and Sympathetic Nervous System (SNS), promotion of vasodilatation and natriuresis, and inhibition of hypertrophy and fibrosis. Novel pharmacological therapies based on NPs may achieve a valuable shift in managing patients with HF from inhibiting RAAS and SNS to a reversal of neurohormonal imbalance. Enhancing NP bioavailability through exogenous NP administration and inhibiting Neutral Endopeptidase (NEP) denotes valuable therapeutic strategies for HF. On the one hand, NEP-resistant NPs may be more specific as therapeutic choices in patients with HF. On the other hand, NEP Inhibitors (NEPIs) combined with RAAS inhibitors have proved to exert beneficial effects and reduce adverse events in patients with HF. Highly effective and potentially safe Angiotensin Receptor Blocker Neprilysin Inhibitors (ARNIs) have been developed after the failure of NEPIs and Vasopeptidase Inhibitors (VPIs) due to lacking efficacy and safety. Therapeutic progress and knowledge basis on the NP system in HF are summarized in the current review.

Naringenin Increases Insulin Sensitivity and Metabolic Rate: A Case Study

Our studies in primary human adipocytes show that naringenin, a citrus flavonoid, increases oxygen consumption rate and gene expression of uncoupling protein 1 (UCP1), glucose transporter type 4, and carnitine palmitoyltransferase 1β (CPT1β). We investigated the safety of naringenin, its effects on metabolic rate, and blood glucose and insulin responses in a single female subject with diabetes. The subject ingested 150 mg naringenin from an extract of whole oranges standardized to 28% naringenin three times/day for 8 weeks, and maintained her usual food intake. Body weight, resting metabolic rate, respiratory quotient, and blood chemistry panel including glucose, insulin, and safety markers were measured at baseline and after 8 weeks. Adverse events were evaluated every 2 weeks. We also examined the involvement of peroxisome proliferator-activated receptor α (PPARα), peroxisome proliferator-activated receptor γ (PPARγ), protein kinase A (PKA), and protein kinase G (PKG) in the response of human adipocytes to naringenin treatment. Compared to baseline, the body weight decreased by 2.3 kg. The metabolic rate peaked at 3.5% above baseline at 1 h, but there was no change in the respiratory quotient. Compared to baseline, insulin decreased by 18%, but the change in glucose was not clinically significant. Other blood safety markers were within their reference ranges, and there were no adverse events. UCP1 and CPT1β mRNA expression was reduced by inhibitors of PPARα and PPARγ, but there was no effect of PKA or PKG inhibition. We conclude that naringenin supplementation is safe in humans, reduces body weight and insulin resistance, and increases metabolic rate by PPARα and PPARγ activation. The effects of naringenin on energy expenditure and insulin sensitivity warrant investigation in a randomized controlled clinical trial.

Activation of NPRs and UCP1-independent pathway following CB1R antagonist treatment is associated with adipose tissue beiging in fat-fed male dogs

CB1 receptor (CB1R) antagonism improves the deleterious effects of a high-fat diet (HFD) by reducing body fat mass and adipocyte cell size. Previous studies demonstrated that the beneficial effects of the CB1R antagonist rimonabant (RIM) in white adipose tissue (WAT) are partially due to an increase of mitochondria numbers and upregulation thermogenesis markers, suggesting an induction of WAT beiging. However, the molecular mechanism by which CB1R antagonism induces weight loss and WAT beiging is unclear. In this study, we probed for genes associated with beiging and explored longitudinal molecular mechanisms by which the beiging process occurs. HFD dogs received either RIM (HFD+RIM) or placebo (PL) (HFD+PL) for 16 wk. Several genes involved in beiging were increased in HFD+RIM compared with pre-fat, HFD, and HFD+PL. We evaluated lipolysis and its regulators including natriuretic peptide (NP) and its receptors (NPRs), β-1 and β-3 adrenergic receptor (β1R, β3R) genes. These genes were increased in WAT depots, accompanied by an increase in lipolysis in HFD+RIM. In addition, RIM decreased markers of inflammation and increased adiponectin receptors in WAT. We observed a small but significant increase in UCP1; therefore, we evaluated the newly discovered UCP1-independent thermogenesis pathway. We confirmed that SERCA2b and RYR2, the two key genes involved in this pathway, were upregulated in the WAT. Our data suggest that the upregulation of NPRs, β-1R and β-3R, lipolysis, and SERCA2b and RYR2 may be one of the mechanisms by which RIM promotes beiging and overall the improvement of metabolic homeostasis induced by RIM.

Adipose tissue browning in mice and humans

In the midst of an obesity epidemic, the promotion of brown adipose tissue (BAT) function and the browning of white adipose tissue (WAT) have emerged as promising therapeutic targets to increase energy expenditure and counteract weight gain. Despite the fact that the thermogenic potential of bone fide BAT in rodents is several orders of magnitudes higher than white fat containing brite/beige adipocytes, WAT browning represents a particularly intriguing concept in humans given the extreme amount of excess WAT in obese individuals. In addition, the clear distinction between classic brown and beige fat that has been proposed in mice does not exist in humans. In fact, studies of human BAT biopsies found controversial results suggesting both classic brown and beige characteristics. Irrespective of the true ‘color’, accumulating evidence suggests the induction of thermogenic adipocytes in human WAT depots in response to specific stimuli, highlighting that WAT browning may occur in both, mice and humans. These observations also emphasize the great plasticity of human fat depots and raise important questions about the metabolic properties of thermogenically active adipose tissue in humans and the potential therapeutic implications. We will first review the cellular and molecular aspects of selected adipose tissue browning concepts that have been identified in mouse models with emphasis on neuronal factors, the microbiome, immune cells and several hormones. We will also summarize the evidence for adipose tissue browning in humans including some experimental pharmacologic approaches.

Emerging pathways of communication between the heart and non-cardiac organs

The breakthrough discovery of cardiac natriuretic peptides provided the first direct demonstration of the connection between the heart and the kidneys for the maintenance of sodium and volume homeostasis in health and disease. Yet, little is still known about how the heart and other organs cross-talk. Here, we review three physiological mechanisms of communication linking the heart to other organs through: i) cardiac natriuretic peptides, ii) the microRNA-208a/mediator complex subunit-13 axis and iii) the matrix metalloproteinase-2 (MMP-2)/C-C motif chemokine ligand-7/cardiac secreted phospholipase A2 (sPLA2) axis – a pathway which likely applies to the many cytokines, which are cleaved and regulated by MMP-2. We also suggest experimental strategies to answer still open questions on the latter pathway. In short, we review evidence showing how the cardiac secretome influences the metabolic and inflammatory status of non-cardiac organs as well as the heart.

Prognostication of clinical outcomes in diabetes mellitus: Emerging role of cardiac biomarkers

Type 2 diabetes mellitus (T2DM) remains substantial health problem and one of the most prevalent metabolic diseases worldwide. The impact of T2DM on CV mortality and morbidity is embedded through a nature evolution of the disease and is modulated by numerous risk factors, such as hypertension, obesity, dyslipidemia. There is large body of evidence regarding use of the cardiac biomarkers to risk stratification at higher CV risk individuals who belongs to general population and cohort with established CV disease. Although T2DM patients have higher incidence of cardiac and vascular complications than the general population, whether cardiac biomarkers would be effective to risk stratification of the T2DM is not fully understood. The aim of the review is to summarize our knowledge regarding clinical implementation of cardiac biomarkers in risk assessment for T2DM patients. The role of natriuretic peptides, soluble ST2, galectin-3, growth differentiation factor-15, and cardiac troponins are widely discussed.

High doses of ANP and BNP exacerbate lipolysis in humans and the lipolytic effect of BNP is associated with cardiac triglyceride content in pigs

Drugs facilitating the cardioprotective effects of natriuretic peptides are introduced in heart failure treatment. ANP and BNP also stimulate lipolysis and increase circulating concentrations of free fatty acids (FFAs); an aspect, however, thought to be confined to primates. We examined the lipolytic effect of natriuretic peptide infusion in healthy young men and evaluated the effect in a porcine model of myocardial ischemia and reperfusion. Six young healthy normotensive men underwent infusion with ANP, BNP, or CNP for 20 min. Blood samples were collected before, during, and after infusion for measurement of FFAs. In a porcine model of myocardial ischemia and reperfusion, animals were infused for 3 h with either BNP (n = 7) or saline (n = 5). Blood samples were collected throughout the infusion period, and cardiac tissue was obtained after infusion for lipid analysis. In humans, ANP infusion dose-dependently increased the FFA concentration in plasma 2.5-10-fold (baseline vs. 0.05 μg/kg/min P < 0.002) and with BNP 1.6-3.5-fold (P = 0.001, baseline vs. 0.02 μg/kg/min) 30 min after initiation of infusion. Infusion of CNP did not affect plasma FFA. In pigs, BNP infusion induced a 3.5-fold increase in plasma FFA (P < 0.0001), which remained elevated throughout the infusion period. Triglyceride content in porcine right cardiac ventricle tissue increased ∼5.5 fold in animals infused with BNP (P = 0.02). Natriuretic peptide infusion has similar lipolytic activity in human and pig. Our data suggest that short-term infusion increases the cardiac lipid content, and that the pig is a suitable model for studies of long-term effects mediated by natriuretic peptides.

Update on the synergistic effect of HSL and insulin in the treatment of metabolic disorders

Hormone-sensitive lipase (HSL) is one of the three lipases in adipose tissue present during periods of energy demand. HSL is tightly controlled by insulin regulation via the central and peripheral systems. The suppressive effects of insulin on HSL are also associated with complex crosstalk with other pathways in the metabolic network. Because impaired insulin action is the driving force behind the pathogenesis of diabetes and other metabolic complications, elucidation of the intricate relationships between HSL and insulin may provide an in-depth understanding of these pandemic diseases and potentially identify strategies to inhibit disease development. Insulin not only differentially regulates HSL isoform transcription but also post-transcriptionally affects HSL phosphorylation by stimulating PKA and endothelin (ET-1), and controls its expression indirectly via regulating the activity of growth hormone (GH). In addition, a rapid elevation of HSL levels was detected after insulin injection in patients, which suggests that the inhibitory effects of insulin on HSL can be overridden by insulin-induced hypoglycemia. Conversely, individuals with hereditary HSL deficiency, and animals with experimental HSL deletion, showed major disruptions in mRNA/protein expression in insulin signaling pathways, ultimately leading to insulin resistance, diabetes, and fatty liver. Notably, HSL inactivation could cause insulin-independent fatty liver, while insulin resistance induced by HSL deficiency may further aggravate disease progression. The common beliefs that HSL is the overall rate-limiting enzyme in lipolysis and that insulin is an inhibitor of HSL have been challenged by recent discoveries; therefore, a renewed examination of their relationships is required. In this review, by analyzing current data related to the role of, and mutual regulation between, HSL and insulin and discussing unanswered questions and disparities in different lines of studies, the authors intend to shed light on our understanding of lipid metabolism and provide a rational basis for future research in drug development.

Exercise-induced 'browning' of adipose tissues

Global rates of obesity continue to rise and are necessarily the consequence of a long-term imbalance between energy intake and energy expenditure. This is the result of an expansion of adipose tissue due to both the hypertrophy of existing adipocytes and hyperplasia of adipocyte pre-cursors. Exercise elicits numerous physiological benefits on adipose tissue, which are likely to contribute to the associated cardiometabolic benefits. More recently it has been demonstrated that exercise, through a range of mechanisms, induces a phenotypic switch in adipose tissue from energy storing white adipocytes to thermogenic beige adipocytes. This has generated the hypothesis that the process of adipocyte 'browning' may partially underlie the improved cardiometabolic health in physically active populations. Interestingly, 'browning' also occurs in response to various stressors and could represent an adaptive response. In the context of exercise, it is not clear whether the appearance of beige adipocytes is metabolically beneficial or whether they occur as a transient adaptive process to exercise-induced stresses. The present review discusses the various mechanisms (e.g. fatty acid oxidation during exercise, decreased thermal insulation, stressors and angiogenesis) by which the exercise-induced 'browning' process may occur.

Cardiomyokines from the heart

The heart is regarded as an endocrine organ as well as a pump for circulation, since atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) were discovered in cardiomyocytes to be secreted as hormones. Both ANP and BNP bind to their receptors expressed on remote organs, such as kidneys and blood vessels; therefore, the heart controls the circulation by pumping blood and by secreting endocrine peptides. Cardiomyocytes secrete other peptides besides natriuretic peptides. Although most of such cardiomyocyte-derived peptides act on the heart in autocrine/paracrine fashions, several peptides target remote organs. In this review, to overview current knowledge of endocrine properties of the heart, we focus on cardiomyocyte-derived peptides (cardiomyokines) that act on the remote organs as well as the heart. Cardiomyokines act on remote organs to regulate cardiovascular homeostasis, systemic metabolism, and inflammation. Therefore, through its endocrine function, the heart can maintain physiological conditions and prevent organ damage under pathological conditions.