Obesity-associated improvements in metabolic profile through expansion of adipose tissue

Mechanistic Links Between Obesity, Diabetes, and Blood Pressure: Role of Perivascular Adipose Tissue

Obesity is increasingly prevalent and is associated with substantial cardiovascular risk. Adipose tissue distribution and morphology play a key role in determining the degree of adverse effects, and a key factor in the disease process appears to be the inflammatory cell population in adipose tissue. Healthy adipose tissue secretes a number of vasoactive adipokines and anti-inflammatory cytokines, and changes to this secretory profile will contribute to pathogenesis in obesity. In this review, we discuss the links between adipokine dysregulation and the development of hypertension and diabetes and explore the potential for manipulating adipose tissue morphology and its immune cell population to improve cardiovascular health in obesity.

Discrepancies Between BMI and Classic Cardiovascular Risk Factors

BACKGROUND

Obesity is related to increased cardiovascular risk. It is unknown whether increasing levels of obesity also increase levels of cardiovascular risk factors and systemic inflammation. This study describes the relationship between classic cardiovascular risk factors and inflammatory markers with BMI in a group of obese and non-obese subjects.

MATERIALS AND METHODS

Obese subjects (BMI ≥ 30 kg/m²; n = 576; mean ± SD BMI 43.8 ± 7.58 kg/m²) scheduled for bariatric surgery were included. The reference population consisted of non-obese volunteers (BMI < 30 kg/m²; n = 377, BMI 25.0 ± 2.81 kg/m²). The relationship between BMI quintiles and the levels of cardiovascular risk factors was analyzed. Adipose tissue volumetry was performed in 42 obese subjects using abdominal CT scans.

RESULTS

The obese group included more women and subjects with type 2 diabetes mellitus, hypertension, and current smoking behavior. In obese subjects, HDL-C and triglycerides decreased with increasing BMI. Systolic and diastolic blood pressure, total cholesterol, LDL-C, and apoB were not related to BMI in the obese group, in contrast to the non-obese group. Inflammatory markers CRP, leukocyte count, and serum complement C3 increased with increasing BMI in the obese group, while these relations were less clear in the non-obese group. The subcutaneous adipose tissue surface was positively correlated to BMI, while no correlation was observed between BMI and visceral adipose tissue.

CONCLUSIONS

Markers of inflammation are strongest related to BMI in obese subjects, most likely due to increased adipose tissue mass, while cardiovascular risk factors do not seem to deteriorate above a certain BMI level. Limited expansion capacity of visceral adipose tissue may explain these findings.

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

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

Role of Complement and Complement-Related Adipokines in Regulation of Energy Metabolism and Fat Storage

Adipose tissue releases many cytokines and inflammatory factors described as adipokines. In obesity, adipokines released from expanding adipose tissue are implicated in disease progression and metabolic dysfunction. However, mechanisms controlling the progression of adiposity and metabolic complications are not fully understood. It has been suggested that expanding fat mass and sustained release of inflammatory adipokines in adipose tissue lead to hypoxia, oxidative stress, apoptosis, and cellular damage. These changes trigger an immune response involving infiltration of adipose tissue with immune cells, complement activation and generation of factors involved in opsonization and clearance of damaged cells. Abundant evidence now indicates that adipose tissue is an active secretory source of complement and complement-related adipokines that, in addition to their inflammatory role, contribute to the regulation of metabolic function. This article highlights advances in knowledge regarding the role of these adipokines in energy regulation of adipose tissue through modulating lipogenic and lipolytic pathways. Several adipokines will be discussed including adipsin, Factor H, properdin, C3a, Acylation-Stimulating Protein, C1q/TNF-related proteins, and response gene to complement-32 (RGC-32). Interactions between these factors will be described considering their immune-metabolic roles in the adipose tissue microenvironment and their potential contribution to progression of adiposity and metabolic dysfunction. The differential expression and the role of complement factors in gender-related fat partitioning will also be addressed. Identifying lipogenic adipokines and their specific autocrine/paracrine roles may provide means for adipose-tissue-targeted therapeutic interventions that may disrupt the vicious circle of adiposity and disease progression. © 2019 American Physiological Society. Compr Physiol 9:1411-1429, 2019.

Controlling Obesity and Metabolic Diseases by Hydrodynamic Delivery of a Fusion Gene of Exendin-4 and α1 Antitrypsin

Obesity and associated metabolic comorbidities represent a growing public health problem. In this study, we demonstrate the use of a newly created fusion gene of exendin-4 and α1-antitrypsin to control obesity and obesity-associated metabolic disorders including insulin resistance, fatty liver and hyperglycemia. The fusion gene encodes a protein with exendin-4 peptide placed at the N-terminus of human α-1 antitrypsin, and is named EAT. Hydrodynamic transfer of the EAT gene to mice prevents high-fat diet-induced obesity, insulin resistance and fatty liver development. In diet-induced obese mice, expression of EAT gene induces weight loss, improves glucose homeostasis, and attenuates hepatic steatosis. In ob/ob mice, EAT gene transfer suppresses body weight gain, maintains metabolic homeostasis, and completely blocks fatty liver development. Six-month overexpression of the EAT fusion gene in healthy mice does not lead to any detectable toxicity. Mechanistic study reveals that the resulting metabolic benefits are achieved by a reduced food take and down-regulation of transcription of pivotal genes responsible for lipogenesis and lipid droplet formation in the liver and chronic inflammation in visceral fat. These results validate the feasibility of gene therapy in preventing and restoring metabolic homeostasis under diverse pathologic conditions, and provide evidence in support of a new strategy to control obesity and related metabolic diseases.

Adipose tissue loss and lipodystrophy in xylosyltransferase II deficient mice

BACKGROUND/OBJECTIVES

The cellular and extracellular matrix (ECM) interactions that regulate adipose tissue homeostasis are incompletely understood. Proteoglycans (PGs) and their sulfated glycosaminoglycans (GAGs) provide spatial and temporal signals for ECM organization and interactions with resident cells by impacting growth factor and cytokine activity. Therefore, PGs and their GAGs could be significant to adipose tissue homeostasis. The purpose of this study was to determine the role of ECM sulfated GAGs in adipose tissue homeostasis.

METHODS

Adipose tissue and metabolic homeostasis in mice deficient in xylosyltransferase 2 (Xylt2-/-) were examined by histologic analyses, gene expression analyses, whole body fat composition measurements, and glucose tolerance test. Adipose tissue inflammation and adipocyte precursors were characterized by flow cytometry and in vitro culture of mesenchymal stem cells.

RESULTS

Xylt2-/- mice have low body weight due to overall reductions in abdominal fat deposition. Histologically, the adipocytes are reduced in size and number in both gonadal and mesenteric fat depots of Xylt2-/- mice. In addition, these mice are glucose intolerant, insulin resistant, and have increased serum triglycerides as compared to Xylt2 + / + control mice. Furthermore, the adipose tissue niche has increased inflammatory cells and enrichment of proinflammatory factors IL6 and IL1β, and these mice also have a loss of adipose tissue vascular endothelial cells. Lastly, xylosyltransferease-2 (XylT2) deficient mesenchymal stem cells from gonadal adipose tissue and bone marrow exhibit impaired adipogenic differentiation in vitro.

CONCLUSIONS

Decreased GAGs due to the loss of the key GAG assembly enzyme XylT2 causes reduced steady state adipose tissue stores leading to a unique lipodystrophic model. Accumulation of an adipocytic precursor pool of cells is discovered indicating an interruption in differentiation. Therefore, adipose tissue GAGs are important in the homeostasis of adipose tissue by mediating control of adipose precursor development, tissue inflammation, and vascular development.

ΔFosB Requires Galanin, but not Leptin, to Increase Bone Mass via the Hypothalamus, but both are needed to increase Energy expenditure

Energy metabolism and bone homeostasis share several regulatory pathways. The AP1 transcription factor ΔFosB and leptin both regulate energy metabolism and bone, yet whether their pathways intersect is not known. Transgenic mice overexpressing ΔFosB under the control of the Enolase 2 (ENO2) promoter exhibit high bone mass, high energy expenditure, low fat mass, and low circulating leptin levels. Because leptin is a regulator of bone and ΔFosB acts on leptin-responsive ventral hypothalamic (VHT) neurons to induce bone anabolism, we hypothesized that regulation of leptin may contribute to the central actions of ΔFosB in the VHT. To address this question, we used adeno-associated virus (AAV) expression of ΔFosB in the VHT of leptin-deficient ob/ob mice and genetic crossing of ENO2-ΔFosB with ob/ob mice. In both models, leptin deficiency prevented ΔFosB-triggered reduction in body weight, increase in energy expenditure, increase in glucose utilization, and reduction in pancreatic islet size. In contrast, leptin deficiency failed to prevent ΔFosB-triggered increase in bone mass. Unlike leptin deficiency, galanin deficiency blocked both the metabolic and the bone ΔFosB-induced effects. Overall, our data demonstrate that, while the catabolic energy metabolism effects of ΔFosB require intact leptin and galanin signaling, the bone mass-accruing effects of ΔFosB require galanin but are independent of leptin. © 2019 American Society for Bone and Mineral Research.

The endocrine function of adipose tissues in health and cardiometabolic disease

In addition to their role in glucose and lipid metabolism, adipocytes respond differentially to physiological cues or metabolic stress by releasing endocrine factors that regulate diverse processes, such as energy expenditure, appetite control, glucose homeostasis, insulin sensitivity, inflammation and tissue repair. Both energy-storing white adipocytes and thermogenic brown and beige adipocytes secrete hormones, which can be peptides (adipokines), lipids (lipokines) and exosomal microRNAs. Some of these factors have defined targets; for example, adiponectin and leptin signal through their respective receptors that are expressed in multiple organs. For other adipocyte hormones, receptors are more promiscuous or remain to be identified. Furthermore, many of these hormones are also produced by other organs and tissues, which makes defining the endocrine contribution of adipose tissues a challenge. In this Review, we discuss the functional role of adipose tissue-derived endocrine hormones for metabolic adaptations to the environment and we highlight how these factors contribute to the development of cardiometabolic diseases. We also cover how this knowledge can be translated into human therapies. In addition, we discuss recent findings that emphasize the endocrine role of white versus thermogenic adipocytes in conditions of health and disease.

Changes in Visceral Adipose Tissue Plasma Membrane Lipid Composition in Old Rats Are Associated With Adipocyte Hypertrophy With Aging

Increased adiposity, through adipocyte hypertrophy, and/or hyperplasia, characterizes aging and obesity. Both are leptin-resistant states, associated with disturbed lipid metabolism, reduced insulin sensitivity and inflammation. Nevertheless, fat tissue dysfunction appears earlier in obesity than in normal aging. In contrast, lipodystrophy is accompanied by diabetes, and improving the fat cell capacity to expand rescues the diabetic phenotype. Fat tissue dysfunction is extensively studied in the diet-induced obesity, but remains relatively neglected in the aging-associated obesity. In the Wistar rat, as occurs in humans, early or middle aging is accompanied by an increase in adiposity. Using this experimental model, we describe the molecular mechanisms contributing to the white adipose tissue (WAT) hypertrophy. WAT from middle-old age rats is characterized by decreased basal lipogenesis and lipolysis, increased esterification, as demonstrated by the higher TAG and cholesterol content in visceral WAT, and the maintenance of total ceramide levels within normal values. In addition, we describe alterations in the adipose tissue plasma membrane lipid composition, as increased total ether-phosphatidylcholine, sphingomyelin, and free cholesterol levels that favor an enlarged fat cell size with aging. All these metabolic changes may be regarded as a survival advantage that prevents the aged rats from becoming overtly diabetic.

Impaired metabolic and hepatic functions following subcutaneous lipectomy in adult obese rats

NEW FINDINGS

What is the central question of this study? What is the impact and drawbacks of subcutaneous lipectomy on body metabolism? What is the main finding and its importance? Subcutaneous lipectomy resulted in deterioration of hepatic functions, atherosclerotic lipid profile and disturbed redox state. While the results support lipectomy as an effective treatment for obesity, lipectomy induces unfavourable changes in health.

ABSTRACT

The number of obese older adults is on the rise, but data about proper treatment of obesity in the elderly is controversial. The present study was designed to investigate the effectiveness and consequences of partial subcutaneous lipectomy, as a rapid medical intervention against increased accumulation of body fat, in adult obese rats. The study was conducted on adult (9-12 months) female rats, in which obesity was induced by bilateral surgical ovariectomy. They were randomized into two main groups: short term (5 weeks) and long term (10 weeks). Both groups were subdivided into control, ovariectomized (OVX) and ovariectomized lipectomized groups. Body weight (BW) was measured and body mass index (BMI) calculated. Fasting blood glucose, lipid profile and plasma levels of total proteins, albumin, liver enzymes, malondialdehyde (MDA), leptin and adiponectin were determined. The content of both blood and hepatic tissue of reduced glutathione was estimated. In addition, histological study of the liver, aorta and peri-renal fat was performed. Compared to controls, OVX rats showed significant increase in BW, BMI and plasma levels of liver enzymes, MDA and leptin. Histological study revealed vacuolated ballooned hepatocytes and enlarged irregular visceral adipocytes with atherosclerotic changes in the wall of aorta. Following subcutaneous lipectomy, rats exhibited significant fasting hyperglycaemia, dyslipidaemia, lowered plasma albumin and disturbed redox state with aggravation of the histological changes. The findings indicate that although subcutaneous lipectomy appears to be effective in combating obesity in older females, it has unfavourable effects on both metabolic and hepatic functions.

Kinin B1 Receptor Acts in Adipose Tissue to Control Fat Distribution in a Cell-Nonautonomous Manner

The kinin B₁ receptor (B₁R) plays a role in inflammatory and metabolic processes. B₁R deletion (B₁ ^-/-) protects mice from diet-induced obesity and improves insulin and leptin sensitivity. In contrast, genetic reconstitution of B₁R exclusively in adipose tissue reverses the lean phenotype of B₁ ^-/- mice. To study the cell-nonautonomous nature of these effects, we transplanted epididymal white adipose tissue (eWAT) from wild-type donors (B₁ ^+/+) into B₁ ^-/- mice (B₁ ^+/+→B₁ ^-/-) and compared them with autologous controls (B₁ ^+/+→B₁ ^+/+ or B₁ ^-/-→B₁ ^-/-). We then fed these mice a high-fat diet for 16 weeks and investigated their metabolic phenotypes. B₁ ^+/+→B₁ ^-/- mice became obese but not glucose intolerant or insulin resistant, unlike B₁ ^-/-→B₁ ^-/- mice. Moreover, the endogenous adipose tissue of B₁ ^+/+→B₁ ^-/- mice exhibited higher expression of adipocyte markers (e.g., Fabp4 and Adipoq) and changes in the immune cell pool. These mice also developed fatty liver. Wild-type eWAT transplanted into B₁ ^-/- mice normalized circulating insulin, leptin, and epidermal growth factor levels. In conclusion, we demonstrated that B₁R in adipose tissue controls the response to diet-induced obesity by promoting adipose tissue expansion and hepatic lipid accumulation in cell-nonautonomous manners.

Palmitic acid is an intracellular signaling molecule involved in disease development

Emerging evidence shows that palmitic acid (PA), a common fatty acid in the human diet, serves as a signaling molecule regulating the progression and development of many diseases at the molecular level. In this review, we focus on its regulatory roles in the development of five pathological conditions, namely, metabolic syndrome, cardiovascular diseases, cancer, neurodegenerative diseases, and inflammation. We summarize the clinical and epidemiological studies; and also the mechanistic studies which have identified the molecular targets for PA in these pathological conditions. Activation or inactivation of these molecular targets by PA controls disease development. Therefore, identifying the specific targets and signaling pathways that are regulated by PA can give us a better understanding of how these diseases develop for the design of effective targeted therapeutics.

Mangifera indica L. Leaf Extract Induces Adiponectin and Regulates Adipogenesis

Natural bioactive compounds may be used in obese patients because of their ability to impact on various key mechanisms involved in the complex pathophysiological mechanisms of such condition. The aim of this study was to investigate the effect of a Mangifera indica L. leaf extract (MLE) on adipogenic differentiation of murine preadipocyte cells. 3T3-L1 cells were treated during their differentiation with various concentrations of (Mangifera indica L.) leaves extract (MLE) (750, 380, 150, 75 and 35 μg) in order to assess their lipid content, adiponectin production, expression profile of genes involved in lipid metabolism, oxidative stress and inflammation. Our results showed that MLE was particularly enriched in polyphenols (46.30 ± 0.083 mg/g) and that pharmacological treatment of cells resulted in a significant increase of adiponectin levels and reduction of intracellular lipid content. Consistently with these results, MLE resulted in a significant decrease of the expression of genes involved in lipid metabolism (FAS, PPARG, DGAT1, DGAT2, and SCD-1). In conclusion, our results suggest that MLE may represent a possible pharmacological tool for obese or metabolic syndrome patients.

Beneficial Role of HO-1-SIRT1 Axis in Attenuating Angiotensin II-Induced Adipocyte Dysfunction

Background: Angiotensin II (Ang II), released by the renin–angiotensin–aldosterone system (RAAS), contributes to the modulatory role of the RAAS in adipose tissue dysfunction. Investigators have shown that inhibition of AngII improved adipose tissue function and insulin resistance in mice with metabolic syndrome. Heme Oxygenase-1 (HO-1), a potent antioxidant, has been demonstrated to improve oxidative stress and adipocyte phenotype. Molecular effects of high oxidative stress include suppression of sirtuin-1 (SIRT1), which is amenable to redox manipulations. The mechanisms involved, however, in these metabolic effects of the RAAS remain incompletely understood. Hypothesis: We hypothesize that AngII-induced oxidative stress has the potential to suppress adipocyte SIRT1 via down regulation of HO-1. This effect of AngII will, in turn, upregulate mineralocorticoid receptor (MR). The induction of HO-1 will rescue SIRT1, hence improving oxidative stress and adipocyte phenotype. Methods and Results: We examined the effect of AngII on lipid accumulation, oxidative stress, and inflammatory cytokines in mouse pre-adipocytes in the presence and absence of cobalt protoporphyrin (CoPP), HO-1 inducer, tin mesoporphyrin (SnMP), and HO-1 inhibitor. Our results show that treatment of mouse pre-adipocytes with AngII increased lipid accumulation, superoxide levels, inflammatory cytokine levels, interleukin-6 (IL-6) and tumor necrosis factor α (TNFα), and adiponectin levels. This effect was attenuated by HO-1 induction, which was further reversed by SnMP, suggesting HO-1 mediated improvement in adipocyte phenotype. AngII-treated pre-adipocytes also showed upregulated levels of MR and suppressed SIRT1 that was rescued by HO-1. Subsequent treatment with CoPP and SIRT1 siRNA in mouse pre-adipocytes increased lipid accumulation and fatty acid synthase (FAS) levels, suggesting that beneficial effects of HO-1 are mediated via SIRT1. Conclusion: Our study demonstrates for the first time that HO-1 has the ability to restore cellular redox, rescue SIRT1, and prevent AngII-induced impaired effects on adipocytes and the systemic metabolic profile.

Nonalcoholic fatty liver disease in obese adolescent females is associated with multi-tissue insulin resistance and visceral adiposity markers

Objective

Nonalcoholic fatty liver disease (NAFLD) is associated with insulin resistance (IR) and visceral adiposity in adults and boys, but girls with NAFLD are understudied. We sought to evaluate adipose, liver, and skeletal muscle insulin sensitivity in obese adolescent females with or without hepatic steatosis (HS) (intrahepatic triglyceride (IHTG) content >5.5%) along with cardiometabolic components typically associated with IR.

Study design

73 obese adolescent girls at high risk for NAFLD were enrolled. Participants underwent fasting labs, an MRI to measure IHTG and visceral fat, ³¹phosphorous MR spectroscopy for muscle mitochondrial function, ¹H MR spectroscopy for intramyocellular lipid (IMCL), bicycle ergometry to assess VO₂peak and a 4-phase hyperinsulinemic euglycemic clamp with isotope tracers to measure hepatic and peripheral IR. 29 participants had HS [age 15 yrs(13,16), BMI%ile 98.7(97.4,99.0), IHTG 10.4%(8.0,13.5)] and 44 did not [age 15 yrs(13,17), BMI%ile 98.5(96.2,99.0), IHTG 2.0%(1.1,3.0)].

Results

During hyperinsulinemia, participants with HS vs. non-HS had failure to suppress free fatty acids (p = 0.008), endogenous glucose release (p = 0.002), and a lower glucose metabolic rate of disappearance (Rd) (p = 0.012). Girls with NALFD also had higher visceral fat (p < 0.001), systolic blood pressure (p = 0.026), triglycerides (p = 0.02), ALT (p < 0.01) and white blood cell count (p < 0.01), and lower adiponectin (p = 0.02). There was no difference between girls with and without HS in systemic glycerol turnover measured with glycerol release, or in IMCL, mitochondrial function or VO₂peak.

Conclusions

Obese adolescent girls with HS have evidence of multi-tissue IR, visceral adiposity, inflammation and multiple components of the metabolic syndrome, arguing for close cardiometabolic surveillance over time of girls with HS.

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We described tissue specific insulin sensitivity in adolescent girls ± NAFLD.

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Girls with NAFLD have higher hepatic and muscular insulin resistance.

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Intramyocellular lipids and muscle mitochondrial function were not different between groups.

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Adipose tissue insulin resistance was not different between groups.

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Girls with NAFLD have worst metabolic profile than those without.

GABA-stimulated adipose-derived stem cells suppress subcutaneous adipose inflammation in obesity

Accumulating evidence suggests that subcutaneous and visceral adipose tissues are differentially associated with metabolic disorders. In obesity, subcutaneous adipose tissue is beneficial for metabolic homeostasis because of repressed inflammation. However, the underlying mechanism remains unclear. Here, we demonstrate that γ-aminobutyric acid (GABA) sensitivity is crucial in determining fat depot-selective adipose tissue macrophage (ATM) infiltration in obesity. In diet-induced obesity, GABA reduced monocyte migration in subcutaneous inguinal adipose tissue (IAT), but not in visceral epididymal adipose tissue (EAT). Pharmacological modulation of the GABA_B receptor affected the levels of ATM infiltration and adipose tissue inflammation in IAT, but not in EAT, and GABA administration ameliorated systemic insulin resistance and enhanced insulin-dependent glucose uptake in IAT, accompanied by lower inflammatory responses. Intriguingly, compared with adipose-derived stem cells (ADSCs) from EAT, IAT-ADSCs played key roles in mediating GABA responses that repressed ATM infiltration in high-fat diet-fed mice. These data suggest that selective GABA responses in IAT contribute to fat depot-selective suppression of inflammatory responses and protection from insulin resistance in obesity.

Neuroendocrine Regulation of Energy Metabolism Involving Different Types of Adipose Tissues

Despite tremendous research efforts to identify regulatory factors that control energy metabolism, the prevalence of obesity has been continuously rising, with nearly 40% of US adults being obese. Interactions between secretory factors from adipose tissues and the nervous system innervating adipose tissues play key roles in maintaining energy metabolism and promoting survival in response to metabolic challenges. It is currently accepted that there are three types of adipose tissues, white (WAT), brown (BAT), and beige (BeAT), all of which play essential roles in maintaining energy homeostasis. WAT mainly stores energy under positive energy balance, while it releases fuels under negative energy balance. Thermogenic BAT and BeAT dissipate energy as heat under cold exposure to maintain body temperature. Adipose tissues require neural and endocrine communication with the brain. A number of WAT adipokines and BAT batokines interact with the neural circuits extending from the brain to cooperatively regulate whole-body lipid metabolism and energy homeostasis. We review neuroanatomical, histological, genetic, and pharmacological studies in neuroendocrine regulation of adipose function, including lipid storage and mobilization of WAT, non-shivering thermogenesis of BAT, and browning of BeAT. Recent whole-tissue imaging and transcriptome analysis of differential gene expression in WAT and BAT yield promising findings to better understand the interaction between secretory factors and neural circuits, which represents a novel opportunity to tackle obesity.

Pathobiological mechanisms underlying metabolic syndrome (MetS) in chronic obstructive pulmonary disease (COPD): clinical significance and therapeutic strategies

Chronic obstructive pulmonary disease (COPD) is a major incurable global health burden and is currently the 4th largest cause of death in the world. Importantly, much of the disease burden and health care utilisation in COPD is associated with the management of its comorbidities (e.g. skeletal muscle wasting, ischemic heart disease, cognitive dysfunction) and infective viral and bacterial acute exacerbations (AECOPD). Current pharmacological treatments for COPD are relatively ineffective and the development of effective therapies has been severely hampered by the lack of understanding of the mechanisms and mediators underlying COPD. Since comorbidities have a tremendous impact on the prognosis and severity of COPD, the 2015 American Thoracic Society/European Respiratory Society (ATS/ERS) Research Statement on COPD urgently called for studies to elucidate the pathobiological mechanisms linking COPD to its comorbidities. It is now emerging that up to 50% of COPD patients have metabolic syndrome (MetS) as a comorbidity. It is currently not clear whether metabolic syndrome is an independent co-existing condition or a direct consequence of the progressive lung pathology in COPD patients. As MetS has important clinical implications on COPD outcomes, identification of disease mechanisms linking COPD to MetS is the key to effective therapy. In this comprehensive review, we discuss the potential mechanisms linking MetS to COPD and hence plausible therapeutic strategies to treat this debilitating comorbidity of COPD.

Adiponectin for the treatment of diabetic nephropathy

The metabolic burden caused by hyperglycemia can result in direct and immediate metabolic injuries, such as oxidative stress and tissue inflammation, in the kidney. Furthermore, chronic hyperglycemia can lead to substantial structural changes such as formation of advanced glycation end-products, glomerular and tubular hypertrophy, and tissue fibrosis. Glomerular hypertrophy renders podocytes vulnerable to increased glomerular filtration, leading to podocyte instability and loss. Thus, prevention of glomerular hypertrophy and attenuation of glomerular hyperfiltration may have therapeutic potential for diabetic nephropathy (DN). Adiponectin is an adipokine that improves insulin sensitivity in obesity-related metabolic disorders, including diabetes, but its efficacy is unknown. Moreover, the recently developed adiponectin receptor agonist, AdipoRon, shows therapeutic potential for DN. In this review, we focus on the role of glomerular hypertrophy in the pathogenesis of DN and discuss the role of adiponectin in its prevention.

Metabolic surgery for the treatment of type 2 diabetes in patients with BMI lower than 35 kg/m2 : Why caution is still needed

Bariatric surgery has shifted from being a risky procedure to an evidence-based one, with proven benefits on all-cause mortality, cardiovascular disease, cancer, and diabetes control. The procedure has an overall positive result on type 2 diabetes mellitus (T2DM), with a substantial number of patients achieving disease remission. This has resulted in several studies assessing possible weight-independent effects of bariatric surgery on glycemic improvement, in addition to recommendation of the procedure to patients with class 1 obesity and T2DM, for whom the procedure was classically not indicated, and adoption of a new term, "metabolic surgery," to highlight the overall metabolic benefit of the procedure beyond weight loss. Recently, the Diabetes Surgery Summit (DSS) has included metabolic surgery in its T2DM treatment algorithm. Although the discussion brought by this consensus is highly relevant, the recommendation of metabolic surgery for patients with uncontrolled T2DM and a body mass index of 30 to 35 kg/m² still lacks enough evidence. This article provides an overall view of the metabolic benefits of bariatric/metabolic surgery in patients with class 1 obesity, compares the procedure against clinical treatment, and presents our rationale for defending caution on recommending the procedure to less obese individuals.

Whole-body vibration for patients with nonalcoholic fatty liver disease: a 6-month prospective study

Physical exercise has demonstrated benefits for managing nonalcoholic fatty liver disease (NAFLD). However, in daily life maintaining exercise without help may be difficult. A whole-body vibration device (WBV) has been recently introduced as an exercise modality that may be suitable for patients who have difficulty engaging in exercise. We tested WBV in patients with NAFLD and estimated its effectiveness. We studied the effects of a 6-month WBV program on hepatic steatosis and its underlying pathophysiology in 25 patients with NAFLD. Seventeen patients with NAFLD were designated as a control group. After WBV exercise, body weight in the study group decreased by only 2.5% compared with the control group. However, we found significant increases in muscle area (+2.6%) and strength (+20.5%) and decreases in fat mass (-6.8%). The hepatic (-9.9%) and visceral (-6.2%) fat content also significantly decreased (P < 0.05). There was substantial lowering of hepatic stiffness (-15.7%), along with improvements in the levels of inflammatory markers; tumor necrosis factor alpha (-50.9%), adiponectin (+12.0%), ferritin (-33.2%), and high-sensitivity C-reactive protein (-43.0%) (P < 0.05). These results suggest that WBV is an exercise option for patients with NAFLD that is effective, efficient, and convenient.

A Lipophilic Fucoxanthin-Rich Phaeodactylum tricornutum Extract Ameliorates Effects of Diet-Induced Obesity in C57BL/6J Mice

Phaeodactylum tricornutum (P. tricornutum) comprise several lipophilic constituents with proposed anti-obesity and anti-diabetic properties. We investigated the effect of an ethanolic P. tricornutum extract (PTE) on energy metabolism in obesity-prone mice fed a high fat diet (HFD). Six- to eight-week-old male C57BL/6J mice were switched to HFD and, at the same time, received orally placebo or PTE (100 mg or 300 mg/kg body weight/day). Body weight, body composition, and food intake were monitored. After 26 days, blood and tissue samples were collected for biochemical, morphological, and gene expression analyses. PTE-supplemented mice accumulated fucoxanthin metabolites in adipose tissues and attained lower body weight gain, body fat content, weight of white adipose tissue (WAT) depots, and inguinal WAT adipocyte size than controls, independent of decreased food intake. PTE supplementation was associated with lower expression of Mest (a marker of fat tissue expandability) in WAT depots, lower gene expression related to lipid uptake and turnover in visceral WAT, increased expression of genes key to fatty acid oxidation and thermogenesis (Cpt1, Ucp1) in subcutaneous WAT, and signs of thermogenic activation including enhanced UCP1 protein in interscapular brown adipose tissue. In conclusion, these data show the potential of PTE to ameliorate HFD-induced obesity in vivo.

Resistance to visceral obesity is associated with increased locomotion in mice expressing an endothelial cell-specific fibroblast growth factor 1 transgene

Overdevelopment of visceral adipose is positively correlated with the etiology of obesity-associated pathologies including cardiovascular disease and insulin resistance. However, identification of genetic, molecular, and physiological factors regulating adipose development and function in response to nutritional stress is incomplete. Fibroblast Growth Factor 1 (FGF1) is a cytokine expressed and released by both adipocytes and endothelial cells under hypoxia, thermal, and oxidative stress. Expression of Fibroblast Growth Factor 1 (FGF1) in adipose is required for normal depot development and remodeling. Loss of FGF1 leads to deleterious changes in adipose morphology, metabolism, and insulin resistance. Conversely, diabetic and obese mice injected with recombinant FGF1 display improvements in insulin sensitivity and a reduction in adiposity. We report in this novel, in vivo study that transgenic mice expressing an endothelial-specific FGF1 transgene (FGF1-Tek) are resistant to high-fat diet-induced abdominal adipose accretion and are more glucose-tolerant than wild-type control animals. Metabolic chamber analyses indicate that suppression of the development of visceral adiposity and insulin resistance was not associated with alterations in appetite or resting metabolic rate in the FGF1-Tek strain. Instead, FGF1-Tek mice display increased locomotor activity that likely promotes the utilization of dietary fatty acids before they can accumulate in adipose and liver. This study provides insight into the impact that genetic differences dictating the production of FGF1 has on the risk for developing obesity-related metabolic disease in response to nutritional stress.

Membrane metallo-endopeptidase (Neprilysin) regulates inflammatory response and insulin signaling in white preadipocytes

OBJECTIVE

Accumulation of visceral white adipose tissue (WAT) associates with insulin resistance, adipose tissue inflammation, and metabolic syndrome, whereas accumulation of subcutaneous WAT may be protective. We aimed to identify molecular mechanisms that might provide mechanistic insights underlying the phenotypic differences in these tissues. Membrane Metallo-Endopeptidase (MME/Neprislyin) is an extracellular, membrane-bound protease enriched in subcutaneous WAT that can target degradation of a variety of peptides, including insulin, IL6, and β-amyloids. We hypothesized that MME contributes to adipose depot-specific metabolic properties.

METHODS

We performed RNA sequencing on human subcutaneous and visceral preadipocytes and array gene expression profiling in murine subcutaneous and visceral preadipocytes. We conducted several insulin signaling and inflammatory response experiments on different cellular states of MME expression.

RESULTS

MME in white preadipocytes is expressed at a higher level in subcutaneous compared to visceral WAT and favors insulin signaling and a low inflammatory response. Thus, knockdown of MME in subcutaneous preadipocytes increased the inflammatory response to substance P and amyloid β aggregates. This associated with increased basal insulin signaling and decreased insulin-stimulated signaling. Moreover, MME differentially regulates the internalization and turnover of the α/β subunits of the insulin receptor.

CONCLUSION

MME is a novel regulator of the insulin receptor in adipose tissue. Given the clinical significance of both chronic inflammation and insulin sensitivity in metabolic disease, these results show a potentially new target to increase insulin sensitivity and decrease inflammatory susceptibility.

Adipose-derived stromal/stem cells from different adipose depots in obesity development

The increasing prevalence of obesity is alarming because it is a risk factor for cardiovascular and metabolic diseases (such as type 2 diabetes). The occurrence of these comorbidities in obese patients can arise from white adipose tissue (WAT) dysfunctions, which affect metabolism, insulin sensitivity and promote local and systemic inflammation. In mammals, WAT depots at different anatomical locations (subcutaneous, preperitoneal and visceral) are highly heterogeneous in their morpho-phenotypic profiles and contribute differently to homeostasis and obesity development, depending on their ability to trigger and modulate WAT inflammation. This heterogeneity is likely due to the differential behavior of cells from each depot. Numerous studies suggest that adipose-derived stem/stromal cells (ASC; referred to as adipose progenitor cells, in vivo) with depot-specific gene expression profiles and adipogenic and immunomodulatory potentials are keys for the establishment of the morpho-functional heterogeneity between WAT depots, as well as for the development of depot-specific responses to metabolic challenges. In this review, we discuss depot-specific ASC properties and how they can contribute to the pathophysiology of obesity and metabolic disorders, to provide guidance for researchers and clinicians in the development of ASC-based therapeutic approaches.

Distinct Fractions of an Artemisia scoparia Extract Contain Compounds With Novel Adipogenic Bioactivity

Adipocytes are important players in metabolic health and disease, and disruption of adipocyte development or function contributes to metabolic dysregulation. Hence, adipocytes are significant targets for therapeutic intervention in obesity and metabolic syndrome. Plants have long been sources for bioactive compounds and drugs. In previous studies, we screened botanical extracts for effects on adipogenesis in vitro and discovered that an ethanolic extract of Artemisia scoparia (SCO) could promote adipocyte differentiation. To follow up on these studies, we have used various separation methods to identify the compound(s) responsible for SCO's adipogenic properties. Fractions and subfractions of SCO were tested for effects on lipid accumulation and adipogenic gene expression in differentiating 3T3-L1 adipocytes. Fractions were also analyzed by Ultra Performance Liquid Chromatography- Mass Spectrometry (UPLC-MS), and resulting peaks were putatively identified through high resolution, high mass accuracy mass spectrometry, literature data, and available natural products databases. The inactive fractions contained mostly quercetin derivatives and chlorogenates, including chlorogenic acid and 3,5-dicaffeoylquinic acid, which had no effects on adipogenesis when tested individually, thus ruling them out as pro-adipogenic bioactives in SCO. Based on these studies we have putatively identified the principal constituents in SCO fractions and subfractions that promoted adipocyte development and fat cell gene expression as prenylated coumaric acids, coumarin monoterpene ethers, 6-demethoxycapillarisin and two polymethoxyflavones.

Beneficial Effects of Adiponectin on Glucose and Lipid Metabolism and Atherosclerotic Progression: Mechanisms and Perspectives

Circulating adiponectin concentrations are reduced in obese individuals, and this reduction has been proposed to have a crucial role in the pathogenesis of atherosclerosis and cardiovascular diseases associated with obesity and the metabolic syndrome. We focus on the effects of adiponectin on glucose and lipid metabolism and on the molecular anti-atherosclerotic properties of adiponectin and also discuss the factors that increase the circulating levels of adiponectin. Adiponectin reduces inflammatory cytokines and oxidative stress, which leads to an improvement of insulin resistance. Adiponectin-induced improvement of insulin resistance and adiponectin itself reduce hepatic glucose production and increase the utilization of glucose and fatty acids by skeletal muscles, lowering blood glucose levels. Adiponectin has also β cell protective effects and may prevent the development of diabetes. Adiponectin concentration has been found to be correlated with lipoprotein metabolism; especially, it is associated with the metabolism of high-density lipoprotein (HDL) and triglyceride (TG). Adiponectin appears to increase HDL and decrease TG. Adiponectin increases ATP-binding cassette transporter A1 and lipoprotein lipase (LPL) and decreases hepatic lipase, which may elevate HDL. Increased LPL mass/activity and very low density lipoprotein (VLDL) receptor and reduced apo-CIII may increase VLDL catabolism and result in the reduction of serum TG. Further, adiponectin has various molecular anti-atherosclerotic properties, such as reduction of scavenger receptors in macrophages and increase of cholesterol efflux. These findings suggest that high levels of circulating adiponectin can protect against atherosclerosis. Weight loss, exercise, nutritional factors, anti-diabetic drugs, lipid-lowering drugs, and anti-hypertensive drugs have been associated with an increase of serum adiponectin level.

The Effects of Graded Levels of Calorie Restriction: X. Transcriptomic Responses of Epididymal Adipose Tissue

Calorie restriction (CR) leads to a remarkable decrease in adipose tissue mass and increases longevity in many taxa. Since the discovery of leptin, the secretory abilities of adipose tissue have gained prominence in the responses to CR. We quantified transcripts of epididymal white adipose tissue of male C57BL/6 mice exposed to graded levels of CR (0–40% CR) for 3 months. The numbers of differentially expressed genes (DEGs) involved in NF-κB, HIF1-α, and p53 signaling increased with increasing levels of CR. These pathways were all significantly downregulated at 40% CR relative to 12 h ad libitum feeding. In addition, graded CR had a substantial impact on DEGs associated with pathways involved in angiogenesis. Of the 497 genes differentially expressed with graded CR, 155 of these genes included a signal peptide motif. These putative signaling proteins were involved in the response to ketones, TGF-β signaling, negative regulation of insulin secretion, and inflammation. This accords with the previously established effects of graded CR on glucose homeostasis in the same mice. Overall these data suggest reduced levels of adipose tissue under CR may contribute to the protective impact of CR in multiple ways linked to changes in a large population of secreted proteins.

Metabolically healthy versus metabolically unhealthy obesity

Obesity-related disease complications reduce life quality and expectancy and increase health-care costs. Some studies have suggested that obesity not always entails metabolic abnormalities and increased risk of cardiometabolic complications. Because of the lack of universally accepted criteria to identify metabolically healthy obesity (MHO), its prevalence varies widely among studies. Moreover, the prognostic value of MHO is hotly debated, mainly because it likely shifts gradually towards metabolically unhealthy obesity (MUO). In this review, we outline the differential factors contributing to the metabolic heterogeneity of obesity by discussing the behavioral, genetic, phenotypical, and biological aspects associated with each of the two metabolic phenotypes (MHO and MUO) of obesity and their clinical implications. Particular emphasis will be laid on the role of adipose tissue biology and function, including genetic determinants of body fat distribution, depot-specific fat metabolism, adipose tissue plasticity and, particularly, adipogenesis. Finally, the emerging role of gut microbiota in obesity and adipose tissue dysfunction as well as the search for novel biomarkers for the obesity-related metabolic traits and associated diseases will be briefly presented. A better understanding of the main determinants of a healthy metabolic status in obesity would allow promotion of this favorable condition by targeting the relevant pathways.

Metabolic Messengers: Adiponectin

Adiponectin is one of the most widely studied adipokines to date. First described in the mid-1990's, studying its regulation, biogenesis and physiological effects has proven to be extremely insightful and improved our understanding of the mechanisms that ensure systemic metabolic homeostasis. Here, we provide a brief overview of the current state of the field with respect to adiponectin, its history, sites and mechanisms of action, and the critical questions that will need to be addressed in the future.

Mechanisms of obesity-induced metabolic and vascular dysfunctions

Obesity has reached epidemic proportions and its prevalence is climbing. Obesity is characterized by hypertrophied adipocytes with a dysregulated adipokine secretion profile, increased recruitment of inflammatory cells, and impaired metabolic homeostasis that eventually results in the development of systemic insulin resistance, a phenotype of type 2 diabetes. Nitric oxide synthase (NOS) is an enzyme that converts L-arginine to nitric oxide (NO), which functions to maintain vascular and adipocyte homeostasis. Arginase is a ureohydrolase enzyme that competes with NOS for L-arginine. Arginase activity/expression is upregulated in obesity, which results in diminished bioavailability of NO, impairing both adipocyte and vascular endothelial cell function. Given the emerging role of NO in the regulation of adipocyte physiology and metabolic capacity, this review explores the interplay between arginase and NO, and their effect on the development of metabolic disorders, cardiovascular diseases, and mitochondrial dysfunction in obesity. A comprehensive understanding of the mechanisms involved in the development of obesity-induced metabolic and vascular dysfunction is necessary for the identification of more effective and tailored therapeutic avenues for their prevention and treatment.

The obese adipose tissue microenvironment in cancer development and progression

Obesity is associated with both increased cancer incidence and progression in multiple tumour types, and is estimated to contribute to up to 20% of cancer-related deaths. These associations are driven, in part, by metabolic and inflammatory changes in adipose tissue that disrupt physiological homeostasis both within local tissues and systemically. However, the mechanisms underlying the obesity-cancer relationship are poorly understood. In this Review, we describe how the adipose tissue microenvironment (ATME) evolves during body-weight gain, and how these changes might influence tumour initiation and progression. We focus on multiple facets of ATME physiology, including inflammation, vascularity and fibrosis, and discuss therapeutic interventions that have the potential to normalize the ATME, which might be translationally relevant for cancer prevention and therapy. Given that the prevalence of obesity is increasing on an international scale, translational research initiatives are urgently needed to provide mechanistic explanations for the obesity-cancer relationship, and how to best identify high-risk individuals without relying on crude measures, such as BMI.

Adipose Tissue Expansion by Overfeeding Healthy Men Alters Iron Gene Expression

CONTEXT

Iron overload has been associated with greater adipose tissue (AT) depots. We retrospectively studied the potential interactions between iron and AT during an experimental overfeeding in participants without obesity.

METHODS

Twenty-six participants (mean body mass index ± SD, 24.7 ± 3.1 kg/m2) underwent a 56-day overfeeding (+760 kcal/d). Serum iron biomarkers (ELISA), subcutaneous AT (SAT) gene expression, and abdominal AT distribution assessed by MRI were analyzed at the beginning and the end of the intervention.

RESULTS

Before intervention: SAT mRNA expression of the iron transporter transferrin (Tf) was positively correlated with the expression of genes related to lipogenesis (lipin 1, ACSL1) and lipid storage (SCD). SAT expression of the ferritin light chain (FTL) gene, encoding ferritin (FT), an intracellular iron storage protein, was negatively correlated to SREBF1, a gene related to lipogenesis. Serum FT (mean, 92 ± 57 ng/mL) was negatively correlated with the expression of SAT genes linked to lipid storage (SCD, DGAT2) and to lipogenesis (SREBF1, ACSL1). After intervention: Overfeeding led to a 2.3 ± 1.3-kg weight gain. In parallel to increased expression of lipid storage-related genes (mitoNEET, SCD, DGAT2, SREBF1), SAT Tf, SLC40A1 (encoding ferroportin 1, a membrane iron export channel) and hephaestin mRNA levels increased, whereas SAT FTL mRNA decreased, suggesting increased AT iron requirement. Serum FT decreased to 67 ± 43 ng/mL. However, no significant associations between serum iron biomarkers and AT distribution or expansion were observed.

CONCLUSION

In healthy men, iron metabolism gene expression in SAT is associated with lipid storage and lipogenesis genes expression and is modulated during a 56-day overfeeding diet.

Adiponectin is associated with cardio-metabolic traits in Mexican children

The adipocyte-derived adiponectin hormone bridges obesity and its cardio-metabolic complications. Genetic variants at the ADIPOQ locus, in ADIPOR1, and ADIPOR2 have been associated with adiponectin concentrations and cardio-metabolic complications in diverse ethnicities. However, no studies have examined these associations in Mexican children. We recruited 1 457 Mexican children from Mexico City. Six genetic variants in or near ADIPOQ (rs182052, rs2241766, rs266729, rs822393), ADIPOR1 (rs10920533), and ADIPOR2 (rs11061971) were genotyped. Associations between serum adiponectin, genetic variants, and cardio-metabolic traits were assessed using linear and logistic regressions adjusted for age, sex, and recruitment center. Serum adiponectin concentration was negatively associated with body mass index, waist to hip ratio, low-density lipoprotein cholesterol, total cholesterol, triglycerides, fasting glucose, fasting insulin, homeostatic model assessment of insulin resistance, dyslipidemia and overweight/obesity status (7.76 × 10⁻⁴⁰ ≤ p ≤ 3.00 × 10⁻³). No significant associations between genetic variants in ADIPOQ, ADIPOR1, and ADIPOR2 and serum adiponectin concentration were identified (all p ≥ 0.30). No significant associations between the six genetic variants and cardio-metabolic traits were observed after Bonferroni correction (all p < 6.9 × 10⁻⁴). Our study suggests strong associations between circulating adiponectin concentration and cardio-metabolic traits in Mexican children.

Sex Differences in Inflammatory Responses to Adipose Tissue Lipolysis in Diet-Induced Obesity

Males are known to have profound adipose tissue macrophage (ATM) accumulation in gonadal white adipose tissue (GWAT) during obesity, whereas females are protected from such an inflammatory response even with increased adiposity. The inflammatory tone in males is linked to insulin resistance and might be the underlying cause for sex differences in metabolic disease. Factors regulating the meta-inflammatory response remain unclear but enhanced lipid storage in females may explain the reduced inflammatory response to high-fat diets. In this study, we evaluated lean and obese females with stimulated lipolysis to understand whether a stress release of free fatty acids (FFAs) could induce female ATMs. We demonstrate that in both lean and obese females, GWAT CD11c- resident ATMs accumulate with β-3 adrenergic receptor-stimulated lipolysis. Lipolysis elevated serum FFA, triglyceride, and IL-6 levels in females that corresponded to significant phosphorylated hormone-sensitive lipase and adipose triglyceride lipase protein expression in obese female GWAT compared with males. Increased lipolytic response in obese females was associated with crown-like structures and induced Il6, Mcp1, Arg1, and Mgl1 expression in obese female GWAT, suggesting an environment of lipid clearance and adipose remodeling. With this finding we next investigated whether lipid storage and lipolytic mediators differed by sex. Diacylglycerol, ceramides, phospholipids, and certain fatty acid species associated with inflammation were elevated in male GWAT compared with obese female GWAT. Overall, our data demonstrate a role for GWAT lipid storage and lipolytic metabolites to induce inflammation in males and induce remodeling in females that might explain sex differences in overall metabolic health.

The many secret lives of adipocytes: implications for diabetes

Adipose tissue remains a cryptic organ. The ubiquitous presence of adipocytes, the different fat pads in distinct anatomical locations, the many different types of fat, in each case with their distinct precursor populations, and the ability to interchange into other types of fat cells or even de-differentiate altogether, offers a staggering amount of complexity to the adipose tissue organ as a whole. Adipose tissue holds the key to improving our understanding of systemic metabolic homeostasis. As such, understanding adipose tissue physiology offers the basis for a mechanistic understanding of the pathophysiology of diabetes. This review presents some of the lesser known aspects of this fascinating tissue, which consistently still offers much opportunity for the discovery of novel targets for pharmacological intervention.

TRPC5 ion channel permeation promotes weight gain in hypercholesterolaemic mice

Transient Receptor Potential Canonical 5 (TRPC5) is a subunit of a Ca²⁺-permeable non-selective cationic channel which negatively regulates adiponectin but not leptin in mice fed chow diet. Adiponectin is a major anti-inflammatory mediator and so we hypothesized an effect of TRPC5 on the inflammatory condition of atherosclerosis. Atherosclerosis was studied in aorta of ApoE^−/− mice fed western-style diet. Inhibition of TRPC5 ion permeation was achieved by conditional transgenic expression of a dominant negative ion pore mutant of TRPC5 (DNT5). Gene expression analysis in adipose tissue suggested that DNT5 increases transcript expression for adiponectin while decreasing transcript expression of the inflammatory mediator Tnfα and potentially decreasing Il6, Il1β and Ccl2. Despite these differences there was mild or no reduction in plaque coverage in the aorta. Unexpectedly DNT5 caused highly significant reduction in body weight gain and reduced adipocyte size after 6 and 12 weeks of western-style diet. Steatosis and circulating lipids were unaffected but mild effects on regulators of lipogenesis could not be excluded, as indicated by small reductions in the expression of Srebp1c, Acaca, Scd1. The data suggest that TRPC5 ion channel permeation has little or no effect on atherosclerosis or steatosis but an unexpected major effect on weight gain.

Impaired Adipogenesis and Dysfunctional Adipose Tissue in Human Hypertrophic Obesity

The subcutaneous adipose tissue (SAT) is the largest and best storage site for excess lipids. However, it has a limited ability to expand by recruiting and/or differentiating available precursor cells. When inadequate, this leads to a hypertrophic expansion of the cells with increased inflammation, insulin resistance, and a dysfunctional prolipolytic tissue. Epi-/genetic factors regulate SAT adipogenesis and genetic predisposition for type 2 diabetes is associated with markers of an impaired SAT adipogenesis and development of hypertrophic obesity also in nonobese individuals. We here review mechanisms for the adipose precursor cells to enter adipogenesis, emphasizing the role of bone morphogenetic protein-4 (BMP-4) and its endogenous antagonist gremlin-1, which is increased in hypertrophic SAT in humans. Gremlin-1 is a secreted and a likely important mechanism for the impaired SAT adipogenesis in hypertrophic obesity. Transiently increasing BMP-4 enhances adipogenic commitment of the precursor cells while maintained BMP-4 signaling during differentiation induces a beige/brown oxidative phenotype in both human and murine adipose cells. Adipose tissue growth and development also requires increased angiogenesis, and BMP-4, as a proangiogenic molecule, may also be an important feedback regulator of this. Hypertrophic obesity is also associated with increased lipolysis. Reduced lipid storage and increased release of FFA by hypertrophic SAT are important mechanisms for the accumulation of ectopic fat in the liver and other places promoting insulin resistance. Taken together, the limited expansion and storage capacity of SAT is a major driver of the obesity-associated metabolic complications.

Irisin: A Hope in Understanding and Managing Obesity and Metabolic Syndrome

White adipose tissue (WAT) is an endocrine organ highly integrated in homeostasis and capable of establishing ways of communicating and influencing multiple metabolic processes. Brown adipose tissue promotes energy expenditure by incorporating the uncoupling protein 1 (UCP1), also known as thermogenin, which decouples cellular respiration and heat production, in the mitochondrial membranes. Recent data suggest the presence of a thermogenic cell formation from white adipocytes (beige or brite cells) with a potential role in preventing obesity and metabolic syndrome. The formation of these cells is influenced by physical exertion that induces expression of PPARγ coactivator-1 (PGC1) and downstream membrane protein, fibronectin type III domain-containing protein 5 (FNDC5) in skeletal muscle. Irisin, a thermogenic adipomyokine produced by FNDC5 cleavage is involved in the browning of adipose tissue. While animal studies are congruent with regard to the relationship between physical exertion and irisin release, the results from human studies are less than clear. Therefore, this review focuses on recent advances in our understanding of muscle and adipose tissue thermogenesis. Further, it describes the molecular mechanisms by which irisin impacts exercise, glucose homeostasis and obesity. Finally, the review discusses current gaps and controversies related to irisin release, its mode of action and its future potential as a therapeutic tool in managing obesity and metabolic syndrome.

The Impact of Aging on Adipose Function and Adipokine Synthesis

During the last 40 years, there has been a world-wide increase in both the prevalence of obesity and an increase in the number of persons over the age of 60 due to a decline in deaths from infectious disease and the nutrition transition in low and middle income nations. While the increase in the elderly population indicates improvements in global public health, this population may experience a diminished quality of life due to the negative impacts of obesity on age-associated inflammation. Aging alters adipose tissue composition and function resulting in insulin resistance and ectopic lipid storage. A reduction in brown adipose tissue activity, declining sex hormones levels, and abdominal adipose tissue expansion occur with advancing years through the redistribution of lipids from the subcutaneous to the visceral fat compartment. These changes in adipose tissue function and distribution influence the secretion of adipose tissue derived hormones, or adipokines, that promote a chronic state of low-grade systemic inflammation. Ultimately, obesity accelerates aging by enhancing inflammation and increasing the risk of age-associated diseases. The focus of this review is the impact of aging on adipose tissue distribution and function and how these effects influence the elaboration of pro and anti-inflammatory adipokines.

Children With Metabolically Healthy Obesity: A Review

Children with "metabolically healthy obesity" (MHO) are a distinct subgroup of youth with obesity, who are less prone to the clustering of cardiometabolic risk factors. Although this phenotype, frequently defined by the absence of metabolic syndrome components or insulin resistance, was first described during the early 1980s, a consensus-based definition of pediatric MHO was introduced only recently, in 2018. The purpose of this review was to concisely summarize current knowledge regarding the MHO phenomenon in youth. The prevalence of MHO in children varies from 3 to 87%, depending on the definition used and the parameters evaluated, as well as the ethnicity and the pubertal status of the sample. The most consistent predictors of MHO in youth include younger age, lower body mass index, lower waist circumference, and lower body fat measurements. Various hypotheses have been proposed to elucidate the underlying factors maintaining the favorable MHO phenotype. While preserved insulin sensitivity and lack of inflammation were previously considered to be the main etiological factors, the most recent findings have implicated adipokine levels, the number of inflammatory immune cells in the adipose tissue, and the reduction of visceral adiposity due to adipose tissue expandability. Physical activity and genetic factors also contribute to the MHO phenotype. Obesity constitutes a continuum-increased risk for cardiometabolic complications, which is less evident in children with MHO. However, some findings have highlighted the emergence of hepatic steatosis, increased carotid intima-media thickness and inflammatory biomarkers in the MHO group compared to peers without obesity. Screening should be directed at those more likely to develop clustering of cardiometabolic risk factors. Lifestyle modifications should include behavioral changes focusing on sleep duration, screen time, diet, physical activity, and tobacco smoke exposure. Weight loss has also been associated with the improvement of insulin sensitivity and inflammation. Further investigative efforts are needed in order to elucidate the mechanisms which protect against the clustering of cardiometabolic risk factors in pediatric obesity, to provide more efficient, targeted treatment approaches for children with obesity, and to identify the protective factors preserving the MHO profile, avoiding the crossover of MHO to the phenotype with metabolically unhealthy obesity.

Knockdown of Ant2 Reduces Adipocyte Hypoxia And Improves Insulin Resistance in Obesity

Decreased adipose tissue oxygen tension and increased HIF-1α expression can trigger adipose tissue inflammation and dysfunction in obesity. Our current understanding of obesity-associated decreased adipose tissue oxygen tension is mainly focused on changes in oxygen supply and angiogenesis. Here, we demonstrate that increased adipocyte O2 demand, mediated by ANT2 activity, is the dominant cause of adipocyte hypoxia. Deletion of adipocyte Ant2 improves obesity-induced intracellular adipocyte hypoxia by decreasing obesity-induced adipocyte oxygen demand, without effects on mitochondrial number or mass, or oligomycin-sensitive respiration. This led to decreased adipose tissue HIF-1α expression and inflammation with improved glucose tolerance and insulin resistance in both a preventative or therapeutic setting. Our results suggest that ANT2 may be a target for the development of insulin sensitizing drugs and that ANT2 inhibition might have clinical utility.

The Gα12/13-coupled receptor LPA4 limits proper adipose tissue expansion and remodeling in diet-induced obesity

White adipose tissue (WAT) can dynamically expand and remodel through adipocyte hypertrophy and hyperplasia. The relative contribution of these 2 mechanisms to WAT expansion is a critical determinant of WAT function and dysfunction in obesity. However, little is known about the signaling systems that determine the mechanisms of WAT expansion. Here, we show that the GPCR LPA4 selectively activates Gα12/13 proteins in adipocytes and limits continuous remodeling and healthy expansion of WAT. LPA4-KO mice showed enhanced expression of mitochondrial and adipogenesis genes and reduced levels of inhibitory phosphorylation of PPARγ in WAT, along with increased production of adiponectin. Furthermore, LPA4-KO mice showed metabolically healthy obese phenotypes in a diet-induced obesity model, with continuous WAT expansion, as well as protection from WAT inflammation, hepatosteatosis, and insulin resistance. These findings unravel a potentially new signaling system that underlies WAT plasticity and expandability, providing a promising therapeutic approach for obesity-related metabolic disorders.

Contribution of Adipose Tissue Inflammation to the Development of Type 2 Diabetes Mellitus

The objective of this comprehensive review is to summarize and discuss the available evidence of how adipose tissue inflammation affects insulin sensitivity and glucose tolerance. Low-grade, chronic adipose tissue inflammation is characterized by infiltration of macrophages and other immune cell populations into adipose tissue, and a shift toward more proinflammatory subtypes of leukocytes. The infiltration of proinflammatory cells in adipose tissue is associated with an increased production of key chemokines such as C-C motif chemokine ligand 2, proinflammatory cytokines including tumor necrosis factor α and interleukins 1β and 6 as well as reduced expression of the key insulin-sensitizing adipokine, adiponectin. In both rodent models and humans, adipose tissue inflammation is consistently associated with excess fat mass and insulin resistance. In humans, associations with insulin resistance are stronger and more consistent for inflammation in visceral as opposed to subcutaneous fat. Further, genetic alterations in mouse models of obesity that reduce adipose tissue inflammation are-almost without exception-associated with improved insulin sensitivity. However, a dissociation between adipose tissue inflammation and insulin resistance can be observed in very few rodent models of obesity as well as in humans following bariatric surgery- or low-calorie-diet-induced weight loss, illustrating that the etiology of insulin resistance is multifactorial. Taken together, adipose tissue inflammation is a key factor in the development of insulin resistance and type 2 diabetes in obesity, along with other factors that likely include inflammation and fat accumulation in other metabolically active tissues. © 2019 American Physiological Society. Compr Physiol 9:1-58, 2019.

Women with COPD by biomass show different serum profile of adipokines, incretins, and peptide hormones than smokers

Background

The main causes of COPD are tobacco smoking (COPD-TS) and biomass smoke exposure (COPD-BS). COPD-TS is known to induce changes in adipokines, incretins, and peptide hormones, frequent biomarkers of inflammation; however, it is unknown if similar changes occur in COPD-BS.

Methods

Clinical and physiological characteristics, and serum concentration of C-peptide, ghrelin, GIP, GLP-1, glucagon, insulin, leptin, PAI-1, resistin, and visfatin were measured in women with COPD-BS, COPD-TS, and healthy controls.

Data were compared with one-way ANOVA and Tukey’s post hoc test; nonparametric were expressed as median (interquartile ranges), with Kruskal-Wallis and Dunn’s post-hoc test. Multivariate analysis, age, BMI, MS, and FEV₁% pred with levels of inflammatory mediators in COPD women.

Results

FEV1% pred, FVC% pred, and FEV1/FVC ratio were decremented in COPD. In COPD-TS increased C-peptide, ghrelin, GIP, GLP-1, and leptin, and reduced glucagon, PAI-1, resistin, and visfatin. In COPD-BS enlarged ghrelin, insulin, leptin, and PAI-1 comparatively with COPD-TS and control, while C-peptide and GLP-1 relatively with controls; conversely, glucagon, and resistin were reduced. Multivariate analysis showed association of ghrelin, insulin, PAI-1, and visfatin with BS exposure.

Conclusions

women with COPD-BS have a distinct profile of adipokines, incretins, and peptide hormones, and specifically with ghrelin, insulin, PAI-1, and visfatin related to BS exposure.

miR-30a Remodels Subcutaneous Adipose Tissue Inflammation to Improve Insulin Sensitivity in Obesity

Chronic inflammation accompanies obesity and limits subcutaneous white adipose tissue (WAT) expandability, accelerating the development of insulin resistance and type 2 diabetes mellitus. MicroRNAs (miRNAs) influence expression of many metabolic genes in fat cells, but physiological roles in WAT remain poorly characterized. Here, we report that expression of the miRNA miR-30a in subcutaneous WAT corresponds with insulin sensitivity in obese mice and humans. To examine the hypothesis that restoration of miR-30a expression in WAT improves insulin sensitivity, we injected adenovirus (Adv) expressing miR-30a into the subcutaneous fat pad of diabetic mice. Exogenous miR-30a expression in the subcutaneous WAT depot of obese mice coupled improved insulin sensitivity and increased energy expenditure with decreased ectopic fat deposition in the liver and reduced WAT inflammation. High-throughput proteomic profiling and RNA-Seq suggested that miR-30a targets the transcription factor STAT1 to limit the actions of the proinflammatory cytokine interferon-γ (IFN-γ) that would otherwise restrict WAT expansion and decrease insulin sensitivity. We further demonstrated that miR-30a opposes the actions of IFN-γ, suggesting an important role for miR-30a in defending adipocytes against proinflammatory cytokines that reduce peripheral insulin sensitivity. Together, our data identify a critical molecular signaling axis, elements of which are involved in uncoupling obesity from metabolic dysfunction.