Expression and secretion of the atrial natriuretic peptide in human adipose tissue and preadipocytes

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.

Regulatory role of atrial natriuretic peptide in brown adipose tissue: A narrative review

Atrial natriuretic peptide (ANP) has been considered to exert an essential role as a cardiac secretory hormone in the regulation of hemodynamic homeostasis. As the research progresses, the role of ANP in the crosstalk between heart and lipid metabolism has become an interesting topic that is attracting the interest of researchers. The regulation of ANP in lipid metabolism shows favorable effects, particularly the activation of brown adipose tissue (BAT). The complex regulatory network of ANP on BAT has not been fully outlined. This narrative review critically evaluated the existing literature on the regulatory effects of ANP on BAT. In general, we have summarized the expression of ANP and its receptors in various human tissues, analyzed the progress of research on the relationship between the ANP and BAT, and described several potential pathways of ANP to BAT. Exogenous ANP, natriuretic peptide receptor C (NPRC) deficiency, cold exposure, bariatric surgery, and cardiac or renal insufficiency could all contribute to BAT expression by increasing circulating ANP levels.

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.

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.

Role of natriuretic peptides in the cardiovascular-adipose communication: a tale of two organs

Natriuretic peptides have long been known for their cardiovascular function. However, a growing body of evidence emphasizes the role of natriuretic peptides in the energy metabolism of several substrates in humans and animals, thus interrelating the heart, as an endocrine organ, with various insulin-sensitive tissues and organs such as adipose tissue, muscle skeletal, and liver. Adipose tissue dysfunction is associated with altered regulation of the natriuretic peptide system, also indicated as a natriuretic disability. Evidence points to a contribution of this natriuretic disability to the development of obesity, type 2 diabetes mellitus, and cardiometabolic complications; although the causal relationship is not fully understood at present. However, targeting the natriuretic peptide pathway may improve metabolic health in obesity and type 2 diabetes mellitus. This review will focus on the current literature on the metabolic functions of natriuretic peptides with emphasis on lipid metabolism and insulin sensitivity. Natriuretic peptide system alterations could be proposed as one of the linking mechanisms between adipose tissue dysfunction and cardiovascular disease.

Expression and Secretion of an Atrial Natriuretic Peptide in Beige-Like 3T3-L1 Adipocytes

The browning of white adipose tissue (beige adipocytes) stimulates energy expenditure. Omega-3 fatty acids have been shown to induce thermogenic action in adipocytes via G-protein coupled receptor 120 (GPR120). Atrial natriuretic peptide (ANP) is a peptide hormone that plays the role of maintaining normal blood pressure in kidneys to inhibit Na⁺ reuptake. Recently, ANP was found to induce adipocyte browning by binding to NPR1, an ANP receptor. However, the expression of ANP in adipocytes has not yet been studied. Therefore, in this study, we investigate the expression of ANP in beige-like adipocytes induced by docosahexaenoic acids (DHA), T3, or a PPAR agonist, rosiglitazone. First, we found that brown adipocyte-specific genes were upregulated in beige-like adipocytes. DHA promoted ANP expression in beige-like cells, whereas DHA-induced ANP expression was abolished by GPR120 knockout. ANP secretion of beige-like adipocytes was increased via PKC/ERK1/2 signaling in the GPR120 pathway. Furthermore, ANP secreted from beige-like adipocytes acted on HEK-293 cells, the recipient cells, leading to increased cGMP activity. After the NPR1 knockdown of HEK-293 cells, cGMP activity was not changed. Taken together, our findings indicate that beige-like adipocytes induce ANP secretion, which may contribute to improving obesity-associated metabolic disease.

Comparision of secretagogue effects of rosiglitazone and telmisartan on ANP secretion in rats

Peroxisome proliferator-activated receptor-gamma (PPAR-γ), a nuclear transcription factor, is a key regulator of insulin signaling, and glucose and fat metabolism. In this study, we evaluated the direct effect of PPAR-γ ligand on the secretion of atrial natriuretic peptide (ANP). The isolated perfused beating atria were used and rosiglitazone (0.01, 0.3 and 1 μM) or telmisartan was perfused into atria with and without inhibitors. High frequency stimulation caused a decreased atrial contractility by 40% and an increased ANP secretion by 80%. Rosiglitazone augmented high frequency-induced ANP secretion and concentration in a dose-dependent manner. Rosiglitazone-induced ANP secretion was attenuated by the pretreatment with PPAR-γ antagonist (GW 9662), or inhibitor for phosphoinositol 3-kinase (PI3-kinase, wortmannin), Akt (API-2) or nitric oxide synthase (l-NAME). Telmisartan, a partial agonist of PPAR-γ with angiotensin II type 1 receptor (AT1R) blocker, also stimulated ANP secretion, which was more potent than rosiglitazone or losartan. Infusion of rosiglitazone or telmisartan in anesthetized rats tended to decrease mean arterial pressure and to increase pulse pressure without difference. A plasma ANP level was increased by telmisartan more than by rosiglitazone. In diabetic rats, an increased plasma ANP level was more prominent than sham rats. Therefore, we suggest that rosiglitazone stimulates high frequency-induced ANP secretion through the PPAR-γ receptor-PI3-kinase-Akt-eNOS pathway and telmisartan shows synergistic effect on ANP secretion.

The role of gastrointestinal hormones in hepatic lipid metabolism

Hepatocellular accumulation of free fatty acids (FFAs) in the form of triglycerides constitutes the metabolic basis for the development of nonalcoholic fatty liver disease (NAFLD). Recent data demonstrate that excess FFA hepatocyte storage is likely to lead to lipotoxicity and hepatocyte apoptosis. Hence, FFA-mediated hepatocyte injury is a key contributor to the pathogenesis of nonalcoholic steatohepatitis (NASH). Nonalcoholic steatohepatitis, obesity, type 2 diabetes, essential hypertension, and other common medical problems together comprise metabolic syndrome. Evidence suggests that peptide hormones from the L cells of the distal small intestine, which comprise the core of the enteroendocrine system (EES), play two key roles, serving either as incretins, or as mediators of appetite and satiety in the central nervous system. Recent data related to glucagon-like peptide-1 (GLP-1) and other known L-cell hormones have accumulated due to the increasing frequency of bariatric surgery, which increase delivery of bile salts to the hindgut. Bile acids are a key stimulus for the TGR5 receptor of the L cells. Enhanced bile-salt flow and subsequent EES stimulation may be central to elimination of hepatic steatosis following bariatric surgery. Although GLP-1 is a clinically relevant pharmacological analogue that drives pancreatic β-cell insulin output, GLP-1 analogues also have independent benefits via their effects on hepatocellular FFA metabolism. The authors also discuss recent data regarding the role of the major peptides released by the EES, which promote satiety and modulate energy homeostasis and utilization, as well as those that control fat absorption and intestinal permeability. Taken together, elucidating novel functions for EES-related peptides and pharmacologic development of peptide analogues offer potential far-ranging treatment for obesity-related human disease.

Adipokines as mediators of endothelial function and atherosclerosis

For many decades, adipose tissue was considered as an inactive body compartment that was only used as an energy store. During the recent years, an increasing amount of data has revealed that adipose tissue is a major endocrine and paracrine organ producing numerous enzymes, hormones and growth factors which are collectively termed as adipokines. Several experimental and clinical studies showed that adipokines modulate insulin sensitivity and have an influence on glucose/fat metabolism and obesity. Apart from these properties, recent research revealed several direct actions of adipokines on endothelial function, vascular homeostasis and atherogenesis which are independent of their effects on glucose and fat metabolism. The present review focuses on the direct effects of adipokines on vascular/endothelial function and atherosclerosis and summarizes the experimental and clinical data which suggest a role for these molecules as potential diagnostic and prognostic cardiovascular markers as well as potential therapeutic target to reduce cardiovascular risk.

Adipose tissue: friend or foe?

The perception of adipose tissue has changed considerably with the dramatic increase in the incidence of obesity and obesity-related comorbidities over the past 3 decades. Excess fat is no longer associated with wealth, but is instead recognized as a risk factor for many diseases. Adipose tissue is increasingly being identified as a vital, complex endocrine organ, and not simply as a fat store. Not all fat is created equal--regional, developmental, structural, and functional variations exist. Epicardial adipose tissue is a metabolically active organ producing a number of factors that modulate cardiac structure and function. The global epidemic of obesity and metabolic syndrome imposes a major disease burden, particularly of cardiovascular disease. In this Review, we describe the various types of adipose tissue--their developmental biology, differentiation, cell heterogeneity, and functional characteristics. We discuss the link between adipose tissue and inflammation, the signaling factors released by adipose tissue, as well as cardiac adiposity and its relevance to cardiovascular diseases. Finally, we review the myocardial regenerative potential of adipose-tissue-derived stem cells. We believe that a thorough understanding of adipose tissue is of great clinical value.

Intranasal application of the melanocortin 4 receptor agonist MSH/ACTH(4-10) in humans causes lipolysis in white adipose tissue

OBJECTIVE

The melanocortin system has a highly significant role in the hypothalamic regulation of body weight and energy expenditure. In animals, intracerebroventricular infusion of melanocortin receptor 4 (MCR-4) agonists increases basal metabolic rate through activation of the sympathetic nervous system and subsequently reduces food intake. In humans, direct access of MCR-4 agonists to the central nervous system can be achieved by a transnasal route, which leads to weight loss with chronic administration. In the present study, we aimed at investigating the effects of intranasally administered MC4-R agonist MSH/ACTH(4-10) on lipolysis and sympathetic nervous system activity in healthy humans.

DESIGN

Healthy normal weight, male volunteers (n=10) received either 10 mg MSH/ACTH(4-10) or placebo intranasally in a double-blinded randomized crossover design. Interstitial glycerol release was assessed by microdialysis in abdominal white adipose tissue (WAT) and in skeletal muscle (SM) of the forearm. Local blood flow, systemic blood pressure, heart rate and muscle sympathetic nerve activity (MSNA) within the superficial peroneal nerve were recorded at rest and after nitroprusside infusion.

RESULTS

At 45 min after MSH/ACTH(4-10) administration WAT glycerol concentrations increased by 53.4±19.3% compared with baseline conditions (P<0.05) and remained significantly higher throughout the experiment when compared with placebo (P<0.05) while local glycerol release in SM was not significantly affected. Resting MSNA was not altered by MSH/ACTH(4-10) administration; however, sympathoexcitation by intravenous nitroprusside was markedly elevated (MSH/ACTH(4-10) 569±69% increase to baseline; placebo: 315±64%; P<0.01).

CONCLUSION

Intranasally administered MCR-4 agonist MSH/ACTH 4-10 increases both subcutaneous WAT lipolysis and MSNA, which suggests a direct central nervous peptide effect in humans on key factors of human energy metabolism.

Adipose tissue, metabolic syndrome and polycystic ovary syndrome: from pathophysiology to treatment

In the last few years, polycystic ovary syndrome (PCOS) has deserved major attention because it is linked to the same cluster of events that promote the metabolic syndrome. This review will point out the relationships between fat excess, insulin resistance and the metabolic syndrome. Adipocytes are actually considered as endocrine cells that synthesize and release molecules (adipokines) that play an endocrine/paracrine role, such as adiponectin, atrial natriuretic peptide, leptin, resistin, tumour necrosis factor alpha (TNFalpha). Metabolic syndrome is a chronic low-grade inflammatory condition in which adipokines play a major role. Isolated adipocytes from women with PCOS express higher mRNA concentrations of some adipokines involved in cardiovascular risk and insulin resistance. However, environmental factors and lifestyle play a major role in determining the appearance of the phenotypes of PCOS. In morbid obese women with PCOS, bariatric surgery decreases bodyweight and fat excess and reverses hyperandrogenism and sterility. In lean or overweight women with PCOS, changes in lifestyle in combination with drugs reducing visceral fat and insulin resistance reverse the symptoms and signs of PCOS. Promising treatments for PCOS seem to be insulin sensitizers such as metformin and glitazones.

Genetic inversion in mast cell-deficient (Wsh) mice interrupts corin and manifests as hematopoietic and cardiac aberrancy

Mast cells participate in pathophysiological processes that range from antimicrobial defense to anaphylaxis and inflammatory arthritis. Much of the groundwork for the understanding of mast cells was established in mice that lacked mast cells through defects in either stem cell factor or its receptor, Kit. Among available strains, C57BL/6-Kit(W-sh) (W(sh)) mice are experimentally advantageous because of their background strain and fertility. However, the genetic inversion responsible for the W(sh) phenotype remains poorly defined, and its effects beyond the mast cell have been incompletely characterized. We report that W(sh) animals exhibit splenomegaly with expanded myeloid and megakaryocyte populations. Hematopoietic abnormalities extend to the bone marrow and are reflected by neutrophilia and thrombocytosis. In contrast, mast cell-deficient WBB6F1-Kit(W)/Kit(W-v) (W/W(v)) mice display mild neutropenia, but no changes in circulating platelet numbers. To help define the basis for the W(sh) phenotype, a "DNA walking" strategy was used to identify the precise location of the 3' breakpoint, which was found to reside 67.5 kb upstream of Kit. The 5' breakpoint disrupts corin, a cardiac protease responsible for the activation of atrial natriuretic peptide. Consistent with this result, transcription of full-length corin is ablated and W(sh) mice develop symptoms of cardiomegaly. Studies performed using mast cell-deficient strains must consider the capacity of associated abnormalities to either expose or compensate for the missing mast cell lineage.