Fat cell size and adipokine expression in relation to gender, depot, and metabolic risk factors in morbidly obese adolescents

Sex- and depot-specific differences in cellular insulin responsiveness during adipose expansion

BACKGROUND

Adipose tissue distribution, metabolism, and expansion capacity exhibit notable sex- and depot-specific differences. Herein, we monitored adipocyte traits related to insulin responsiveness and glucose transport during adipose expansion in visceral and subcutaneous fat from male and female mice.

MATERIALS AND METHODS

Adipocytes were isolated from perigonadal and inguinal adipose tissue of chow-fed female and male C57Bl6/J mice and assessed for adipocyte size distribution using a coulter counter; glucose uptake and cytosolic volume were measured using glucose tracer assays. GLUT1, GLUT4, and IRS-1 protein levels were assessed by western blot. Pharmacological inhibition (BAY876) of GLUT1 and GLUT4 was used to resolve their respective contribution to cellular glucose transport.

KEY FINDINGS

Independent of adiposity or sex, visceral adipocytes were larger and displayed higher glucose transport, cytosolic volume, and GLUT4 levelsthan subcutaneous adipocytes. GLUT1 content was higher in subcutaneous than visceral adipocytes in both sexes. Pharmacological inhibition confirmed that GLUT1 contributes to <10 % of adipocyte glucose uptake, while GLUT4 facilitates most of both basal and insulin-stimulated glucose uptake. Females showed significantly higher basal and insulin-stimulated glucose transport, higher cytosolic volume, and greater GLUT4 and IRS-1 protein levels than males in both adipose depots. Interestingly, insulin responsiveness was preserved in female subcutaneous adipocytes but deteriorated in subcutaneous male adipocytes during adipose expansion.

SIGNIFICANCE

The improved insulin responsiveness, increased glucose transport, and higher levels of GLUT4 and IRS-1 in adipocytes might protect females from the adverse systemic effects linked to obesity. Insulin responsiveness was preserved in female subcutaneous adipocytes during adipose tissue expansion, which could contribute to the reduced risk of females to develop systemic insulin resistance.

Investigating the role of adipose tissue in mobility and aging: design and methods of the Adipose Tissue ancillary to the Study of Muscle, Mobility, and Aging (SOMMA-AT)

BACKGROUND

Age-related changes in adipose tissue affect chronic medical diseases and mobility disability but mechanism remains poorly understood. The goal of this study is to define methods for phenotyping unique characteristics of adipose tissue from older adults.

METHODS

Older adults enrolled in study of muscle, mobility, and aging selected for the adipose tissue ancillary (SOMMA-AT; N = 210, 52.38% women, 76.12 ± 4.37 years) were assessed for regional adiposity by whole-body magnetic resonance (AMRA) and underwent a needle-aspiration biopsy of abdominal subcutaneous adipose tissue (ASAT). ASAT biopsies were flash frozen, fixed, or processed for downstream applications and deposited at the biorepository. Biopsy yields, qualitative features, adipocyte sizes, and concentration of adipokines secreted in ASAT explant conditioned media were measured. Inter-measure Spearman correlations were determined.

RESULTS

Regional, but not total, adiposity differed by sex: women had greater ASAT mass (8.20 ± 2.73 kg, p < .001) and biopsy yield (3.44 ± 1.81 g, p < .001) than men (ASAT = 5.95 ± 2.30 kg, biopsy = 2.30 ± 1.40 g). ASAT mass correlated with leptin (r = 0.54, p < .001) and not resistin (p = .248) and adiponectin (p = .353). Adipocyte area correlated with ASAT mass (r = 0.34, p < .001), BMI (r = 0.33, p < .001), adiponectin (r = -0.22, p = .005) and leptin (r = 0.18, p = .024) but not with resistin (p = .490).

CONCLUSION

In addition to the detailed ASAT biopsy processing in this report, we found that adipocyte area correlated with ASAT mass, and both measures related to some key adipokines in the explant conditioned media. These results, methods, and biological repositories underscore the potential of this unique cohort to impact the understanding of aging adipose biology on disease, disability, and other aging tissues.

Association of adipocyte size and SREBP-1c in visceral and subcutaneous adipose tissue in non-obese type 2 diabetes mellitus

OBJECTIVE

Non-obese type 2 diabetes seems to be common in India; hence the current study tried to understand the pathogenesis of diabetes in this group focusing on the role of adipocytes especially abdominal fat compartment. Comparison was made between non-obese subjects with newly detected diabetes and those without diabetes, in relation to levels of adipogenic factor and adipokines in pre-adipocytes and mature adipocytes respectively.

RESEARCH DESIGN METHODS

Non-obese subjects (BMI-18-25 Kg/m2) were consecutively selected of whom 15 had newly-detected, treatment naïve type 2 diabetes (HbA1% ≥6.5) while 25 were control (HbA1c% ≤5.6). We examined the expression of adipocyte differentiation factor - SREBP-1c from preadipocytes and adipocyte specific adipokines- HMW isoform and total adiponectin, leptin, FABP-4, TNF-α and IL-6 from adipocytesisolated from abdominal visceral and subcutaneous adipose tissues (VAT and SCAT) by RT-PCR and as well as from serum by ELISA. Size of cultured adipocytes was measured in a fully automated imaging system microscope.

RESULT

Both in SCAT and VAT, SREBP-1c and adiponectin had significantly lower expression along with increased mRNA level of inflammatory adipokinesdiabetes.Average adipocyte size and frequency of large(hypertrophied) adipocytes were comparatively higher in T2DM subjects and had significant negative correlation with SREBP-1c. HMW adiponectin level significantly reduced in the secretion from VAT and SCAT of T2DM subjects compared to control.

CONCLUSION

Reduced expression of SREBP-1c in preadipocytes may lead to increased number of hypertrophied adipocytes in T2DM. Therefore, these dysfunctional hypertrophied adipocytes could cause imbalanced expression of insulin resistant and insulin sensitive adipokines.

Adipokines in atopic dermatitis: the link between obesity and atopic dermatitis

Atopic dermatitis (AD) is a chronic skin condition with intense pruritus, eczema, and dry skin. The recurrent intense pruritus and numerous complications in patients with AD can profoundly affect their quality of life. Obesity is one of its comorbidities that has been confirmed to be the hazard factor of AD and also worsen its severity. Nevertheless, the specific mechanisms that explain the connection between obesity and AD remain incompletely recognized. Recent studies have built hopes on various adipokines to explain this connection. Adipokines, which are disturbed by an obese state, may lead to immune system imbalances in people with AD and promote the development of the disease. This review focuses on the abnormal expression patterns of adipokines in patients with AD and their potential regulatory molecular mechanisms associated with AD. The connection between AD and obesity is elucidated through the involvement of adipokines. This conduces to the in-depth exploration of AD pathogenesis and provides a new perspective to develop therapeutic targets.

Adipose Tissue Dysfunction Determines Lipotoxicity and Triggers the Metabolic Syndrome: Current Challenges and Clinical Perspectives

The adipose tissue organ is organised as distinct anatomical depots located all along the body axis, and it is constituted of three different types of adipocytes: white, beige and brown, which are integrated with vascular, immune, neural, and extracellular stroma cells. These distinct adipocytes serve different specialised functions. The main function of white adipocytes is to ensure healthy storage of excess nutrients/energy and its rapid mobilisation to supply the demand of energy imposed by physiological cues in other organs, whereas brown and beige adipocytes are designed for heat production through uncoupling lipid oxidation from energy production. The concerted action of the three types of adipocytes/tissues ensures an optimal metabolic status. However, when one or several of these adipose depots become dysfunctional because of sustained lipid/nutrient overload, then insulin resistance and associated metabolic complications ensue. These metabolic alterations close a vicious cycle that negatively affects the adipose tissue functionality and compromises global metabolic homeostasis. Optimising white adipose tissue expandability and ensuring its functional metabolic flexibility and/or promoting brown/beige mediated thermogenic activity are complementary strategies that counteract obesity and its associated lipotoxic metabolic effects. However, the development of these therapeutic approaches requires a deep understanding of adipose tissue in all broad aspects. In this chapter, we will discuss the characteristics of the different adipose tissue depots with respect to origins and precursors recruitment, plasticity, cellular composition, and expandability capacity potential as well as molecular and metabolic characteristic signatures in both physiological and pathophysiological conditions. Current antilipotoxic strategies for future clinical application are also discussed in this chapter.

Valorization of onion peel waste: From trash to treasure

Globally, fruits and vegetables are consumed as raw, processed, or as an additive, accounting for approximately 50% of total food wastage. Among the fruits and vegetables, onion is well known for its potential bioactive components; however, peels of onion are a major concern for the environmental health and food industries. Effective utilization methods for valorizing the onion peel should be needed to develop value-added products, which are more eco-friendly, cost-effective, and sustainable. Therefore, this review attempts to emphasize the conventional and emerging valorization techniques for onion peel waste to generate value-added products. Several vital applications including anticancerous, antiobesity, antimicrobial, and anti-inflammatory activities are thoroughly discussed. The findings showed that the use of advanced technologies like ultrasound-assisted extraction, microwave-assisted extraction, and enzymatic extraction, demonstrated improved extraction efficiency and higher yield of bioactive compounds, which showed the anticancerous, antiobesity, antimicrobial, and anti-inflammatory properties. However, in-depth studies are recommended to elucidate the mechanisms of action and potential synergistic effects of the bioactive compounds derived from onion peel waste, and to promote the sustainable utilization of onion peel waste in the long-term.

Identifying sex differences in predictors of epicardial fat cell morphology

Predictors of overall epicardial adipose tissue deposition have been found to vary between males and females. Whether similar sex differences exist in epicardial fat cell morphology is currently unknown. This study aimed to determine whether epicardial fat cell size is associated with different clinical measurements in males and females. Fat cell sizes were measured from epicardial, paracardial, and appendix adipose tissues of post-mortem cases (N= 118 total, 37 females). Epicardial, extra-pericardial, and visceral fat volumes were measured by computed tomography from a subset of cases (N= 70, 22 females). Correlation analyses and stepwise linear regression were performed to identify predictors of fat cell size in males and females. Median fat cell sizes in all depots did not differ between males and females. Body mass index (BMI) and age were independently predictive of epicardial, paracardial, and appendix fat cell sizes in males, but not in females. Epicardial and appendix fat cell sizes were associated with epicardial and visceral fat volumes, respectively, in males only. In females, paracardial fat cell size was associated with extra-pericardial fat volume, while appendix fat cell size was associated with BMI only. No predictors were associated with epicardial fat cell size in females at the univariable or multivariable levels. To conclude, no clinical measurements were useful surrogates of epicardial fat cell size in females, while BMI, age, and epicardial fat volume were independent, albeit weak, predictors in males only.

Angiogenesis in adipose tissue and obesity

While most tissues exhibit their greatest growth during development, adipose tissue is capable of additional massive expansion in adults. Adipose tissue expandability is advantageous when temporarily storing fuel for use during fasting, but becomes pathological upon continuous food intake, leading to obesity and its many comorbidities. The dense vasculature of adipose tissue provides necessary oxygen and nutrients, and supports delivery of fuel to and from adipocytes under fed or fasting conditions. Moreover, the vasculature of adipose tissue comprises a major niche for multipotent progenitor cells, which give rise to new adipocytes and are necessary for tissue repair. Given the multiple, pivotal roles of the adipose tissue vasculature, impairments in angiogenic capacity may underlie obesity-associated diseases such as diabetes and cardiometabolic disease. Exciting new studies on the single-cell and single-nuclei composition of adipose tissues in mouse and humans are providing new insights into mechanisms of adipose tissue angiogenesis. Moreover, new modes of intercellular communication involving micro vesicle and exosome transfer of proteins, nucleic acids and organelles are also being recognized to play key roles. This review focuses on new insights on the cellular and signaling mechanisms underlying adipose tissue angiogenesis, and on their impact on obesity and its pathophysiological consequences.

Pro-Inflammatory Profile of Adipokines in Obesity Contributes to Pathogenesis, Nutritional Disorders, and Cardiovascular Risk in Chronic Kidney Disease

Obesity is a disease which leads to the development of many other disorders. Excessive accumulation of lipids in adipose tissue (AT) leads to metabolic changes, including hypertrophy of adipocytes, macrophage migration, changes in the composition of immune cells, and impaired secretion of adipokines. Adipokines are cytokines produced by AT and greatly influence human health. Obesity and the pro-inflammatory profile of adipokines lead to the development of chronic kidney disease (CKD) through different mechanisms. In obesity and adipokine profile, there are gender differences that characterize the male gender as more susceptible to metabolic disorders accompanying obesity, including impaired renal function. The relationship between impaired adipokine secretion and renal disease is two-sided. In the developed CKD, the concentration of adipokines in the serum is additionally disturbed due to their insufficient excretion by the excretory system caused by renal pathology. Increased levels of adipokines affect the nutritional status and cardiovascular risk (CVR) of patients with CKD. This article aims to systematize the current knowledge on the influence of obesity, AT, and adipokine secretion disorders on the pathogenesis of CKD and their influence on nutritional status and CVR in patients with CKD.

Fat Cell Size: Measurement Methods, Pathophysiological Origins, and Relationships With Metabolic Dysregulations

The obesity pandemic increasingly causes morbidity and mortality from type 2 diabetes, cardiovascular diseases and many other chronic diseases. Fat cell size (FCS) predicts numerous obesity-related complications such as lipid dysmetabolism, ectopic fat accumulation, insulin resistance, and cardiovascular disorders. Nevertheless, the scarcity of systematic literature reviews on this subject is compounded by the use of different methods by which FCS measurements are determined and reported. In this paper, we provide a systematic review of the current literature on the relationship between adipocyte hypertrophy and obesity-related glucose and lipid dysmetabolism, ectopic fat accumulation, and cardiovascular disorders. We also review the numerous mechanistic origins of adipocyte hypertrophy and its relationship with metabolic dysregulation, including changes in adipogenesis, cell senescence, collagen deposition, systemic inflammation, adipokine secretion, and energy balance. To quantify the effect of different FCS measurement methods, we performed statistical analyses across published data while controlling for body mass index, age, and sex.

Lipocalin-type Prostaglandin D2 Synthase appears to function as a Novel Adipokine Preventing Adipose Dysfunction in response to a High Fat Diet

Adipose dysfunction is the primary defect in obesity that contributes to the development of dyslipidemia, insulin resistance, cardiovascular diseases, type 2 diabetes, non-alcoholic fatty liver disease (NAFLD) and some cancers. Previously, we demonstrated the development of NAFLD in lipocalin-type prostaglandin D₂ synthase (L-PGDS) knockout mice regardless of diet. In the present study, we examined the role of L-PGDS in adipose in response to a high fat diet. We observed decreased expression of L-PGDS in adipose tissue and concomitant lower plasma levels in a dietary model of obesity as well as in insulin resistant 3T3-L1 adipocytes. We show reduced adiponectin expression and phosphorylation of AMPK in white adipose tissue of L-PGDS KO mice after 14 weeks on a high fat diet as compared to control C57BL/6 mice. We also observe an increased fat content in L-PGDS KO mice as demonstrated by adipocyte hypertrophy and increased expression of lipogenenic genes. We confirmed our in vivo findings in in vitro 3T3-L1 adipocytes, using an enzymatic inhibitor of L-PGDS (AT56). Rosiglitazone treatment drastically increased L-PGDS expression in insulin resistant 3T3-L1 adipocytes and increased adiponectin expression and AMPK phosphorylation in AT56 treated 3T3-L1 adipocytes. We conclude that the absence of L-PGDS has a deleterious effect on adipose tissue functioning, which further reduces insulin sensitivity in adipose tissue. Consequently, we propose L-PGDS appears to function as a potential member of the adipokine secretome involved in the regulation of the obesity-associated metabolic syndrome.

Early Childhood Fat Tissue Changes-Adipocyte Morphometry, Collagen Deposition, and Expression of CD163+ Cells in Subcutaneous and Visceral Adipose Tissue of Male Children

Childhood obesity is a complex health problem, and not many studies have been done on adipose tissue remodeling in early childhood. The aim of this study was to examine extracellular matrix remodeling in the adipose tissue of healthy male children depending on their weight status. Subcutaneous and visceral adipose tissue was obtained from 45 otherwise healthy male children who underwent elective surgery for hernia repairs or orchidopexy. The children were divided into overweight/obese (n = 17) or normal weight groups (n = 28) depending on their body mass index (BMI) z-score. Serum was obtained for glucose, testosterone, triglyceride, total cholesterol, high-density lipoprotein (HDL), and low-density lipoprotein (LDL) measurements. Sections of adipose tissue were stained with hematoxylin and eosin to determine the adipocytes' surface area, and Masson's trichrome stain was used to detect the adipocytes' collagen content. Immunohistochemistry for CD163⁺ cells was also performed. The results showed that male children in the overweight group had higher serum triglyceride levels, greater adipocyte surface area and collagen content in their subcutaneous adipose tissue, more crown-like structures in fat tissues, and more CD163⁺ cells in their visceral adipose tissue than males in the normal weight group. In conclusion, in male children, obesity can lead to the hypertrophy of adipocytes, increased collagen deposition in subcutaneous adipose tissues, and changes in the polarization and accumulation of macrophages.

Antiretroviral Therapy Initiation Is Associated With Decreased Visceral and Subcutaneous Adipose Tissue Density in People Living With Human Immunodeficiency Virus

BACKGROUND

Adipose tissue (AT) alterations are common in people living with human immunodeficiency virus (PLWH). Decreases in AT density suggest disrupted adipocyte function/hypertrophy. We assessed changes in AT density after antiretroviral therapy (ART) initiation and associations with immunometabolic parameters.

METHODS

In a prospective randomized clinical trial of ART initiation, L4-L5 abdominal CT scans measured subcutaneous AT (SAT) and visceral AT (VAT) area and density in treatment-naive PLWH randomized to tenofovir-emtricitabine plus ritonavir-boosted atazanavir, ritonavir-boosted darunavir, or raltegravir. Linear regression models compared week 0 and week 96 levels, and 96-week changes, in SAT and VAT density (in Hounsfield units [HU]). Spearman correlations assessed relationships between AT density and immunometabolic parameters.

RESULTS

Of the 228 participants, 89% were male and 44% were white non-Hispanic. Median age was 36 years, baseline HIV-1 RNA was 4.6 log10 copies/mL, and CD4+ T-cell count was 344 cells/μL. Over 96 weeks, SAT and VAT HU decreased significantly in all arms. Less dense week 96 SAT and VAT density correlated with higher high-density lipoprotein (HDL) cholesterol and adiponectin (r = 0.19-0.30) levels and lower interleukin 6, non-HDL cholesterol, triglyceride, leptin, and homeostatic model assessment of insulin resistance (r = -0.23 to -0.68) levels at week 96 after adjusting for baseline CD4+ T-cell count, HIV-1 RNA, and baseline AT area.

CONCLUSIONS

Following virologic suppression, lower SAT and VAT density was associated with greater plasma measures of systemic inflammation, lipid disturbances, and insulin resistance independent of AT area, suggesting that changes in AT density with ART may lead to adverse health outcomes independent of AT quantity.

CLINICAL TRIALS REGISTRATION

NCT00851799.

Circadian Melatonin Secretion In Obese Adolescents With Or Without Obstructive Sleep Apnea

Objective — To compare melatonin levels in saliva during a 24-hr day in order to identify the specificities of circadian melatonin secretion in obese adolescents with or without obstructive sleep apnea (OSA). Material and Methods — We examined 18 obese adolescents with OSA, 12 obese adolescents without OSA, and 15 healthy adolescents with a normal body weight, from whom saliva was sampled four time during the 24-hr day. Polysomnography was used to diagnose OSA. Saliva samples (n=180) were subjected to enzyme-linked immunosorbent assay. Results — Obese adolescents with OSA had higher evening melatonin levels than obese adolescents without OSA. For example, this indicator in OSA patients was 5.3 times higher than in participants without OSA, who had the lowest evening melatonin level among all groups. In both obese groups, nighttime melatonin levels were significantly lower than in the control group. A positive correlation was detected between the levels of morning and afternoon melatonin and body mass index only in obese adolescents without OSA (r=0.58; p=0.03 and r=0.68; p=0.01, respectively). It was found that evening melatonin correlated with minimum blood oxygen saturation (SaO2) in the entire sample of adolescents with OSA (r=-0.69; p=0.008), and it also correlated with time with SaO2 <90% in the group with clinical manifestations of OSA (r=0.76; p=0.003). Nighttime melatonin levels negatively correlated with the minimum SaO2 value solely in the group with clinical manifestations of OSA (r=-0.58; p=0.035). Conclusion — The circadian melatonin secretion in obese adolescents differed, depending on the presence or absence of OSA, and correlated with the level of oxygen desaturation in OSA patients, to a greater extent – in the presence of clinical manifestations.

Chronic exposure to methylmercury enhances the anorexigenic effects of leptin in C57BL/6J male mice

Several studies have demonstrated that heavy metals disrupt energy homeostasis. Leptin inhibits food intake and decreases body weight through activation of its receptor in the hypothalamus. The impact of heavy metals on leptin signaling in the hypothalamus is unclear. Here, we show that the environmental pollutant, methylmercury (MeHg), favors an anorexigenic profile in wild-type males. C57BL/6J mice were exposed to MeHg via drinking water (5 ppm) up to 30 days. Our data shows that MeHg exposure was associated with changes in leptin induced activation of Janus kinase 2 (JAK2)/signal transducer and activator of transcription 3 (STAT3) signaling pathway in the hypothalamus. In males, the activation of JAK2/STAT3 signaling pathway was sustained by an increase in SOCS3 protein levels. In females, MeHg-activated STAT3 was inhibited by a concomitant increase in PTP1B. Taken together, our data suggest that MeHg enhanced leptin effects in males, favoring an anorexigenic profile in males, which notably, have been shown to be more sensitive to the neurological effects of this organometal than females. A better understanding of MeHg-induced molecular mechanism alterations in the hypothalamus advances the understanding of its neurotoxicity and provides molecular sites for novel therapies.

Adipose Morphology: a Critical Factor in Regulation of Human Metabolic Diseases and Adipose Tissue Dysfunction

Emerging evidence highlights that dysfunction of adipose tissue contributes to impaired insulin sensitivity and systemic metabolic deterioration in obese state. Of note, adipocyte hypertrophy serves as a critical event which associates closely with adipose dysfunction. An increase in cell size exacerbates hypoxia and inflammation as well as excessive collagen deposition, finally leading to metabolic dysregulation. Specific mechanisms of adipocyte hypertrophy include dysregulated differentiation and maturation of preadipocytes, enlargement of lipid droplets, and abnormal adipocyte osmolarity sensors. Also, weight loss therapies exert profound influence on adipocyte size. Here, we summarize the critical role of adipocyte hypertrophy in the development of metabolic disturbances. Future studies are required to establish a standard criterion of size measurement to better clarify the impact of adipocyte hypertrophy on changes in metabolic homeostasis.

Factors affecting weight loss variability in obesity

Current obesity treatment strategies include diet, exercise, bariatric surgery, and a limited but growing repertoire of medications. Individual weight loss in response to each of these strategies is highly variable. Here we review research into factors potentially contributing to inter-individual variability in response to treatments for obesity, with a focus on studies in humans. Well-recognized factors associated with weight loss capacity include diet adherence, physical activity, sex, age, and specific medications. However, following control for each of these, differences in weight loss appear to persist in response to behavioral, pharmacological and surgical interventions. Adaptation to energy deficit involves complex feedback mechanisms, and inter-individual differences likely to arise from a host of poorly defined genetic factors, as well as differential responses in neurohormonal mechanisms (including gastrointestinal peptides), metabolic efficiency and capacity of tissues, non-exercise activity thermogenesis, thermogenic response to food, and in gut microbiome. A better understanding of the factors involved in inter-individual variability in response to therapies will guide more personalized approaches to the treatment of obesity.

Integrative genomics reveal a role for MCPIP1 in adipogenesis and adipocyte metabolism

Obesity is considered a serious chronic disease, associated with an increased risk of developing cardiovascular diseases, non-alcoholic fatty liver disease and type 2 diabetes. Monocyte chemoattractant protein-1-induced protein-1 (MCPIP1) is an RNase decreasing stability of transcripts coding for inflammation-related proteins. In addition, MCPIP1 plays an important role in the regulation of adipogenesis in vitro by reducing the expression of key transcription factors, including C/EBPβ. To elucidate the role of MCPIP1 in adipocyte biology, we performed RNA-Seq and proteome analysis in 3T3-L1 adipocytes overexpressing wild-type (WTMCPIP1) and the mutant form of MCPIP1 protein (D141NMCPIP1). Our RNA-Seq analysis followed by confirmatory Q-RT-PCR revealed that elevated MCPIP1 levels in 3T3-L1 adipocytes upregulated transcripts encoding proteins involved in signal transmission and cellular remodeling and downregulated transcripts of factors involved in metabolism. These data are consistent with our proteomic analysis, which showed that MCPIP1 expressing adipocytes exhibit upregulation of proteins involved in cellular organization and movement and decreased levels of proteins involved in lipid and carbohydrate metabolism. Moreover, MCPIP1 adipocytes are characterized by decreased level of insulin receptor, reduced insulin-induced Akt phosphorylation, as well as depleted Glut4 level and impaired glucose uptake. Overexpression of Glut4 in 3T3-L1 cells expressed WTMCPIP1 rescued adipogenesis. Interestingly, we found decreased level of MCPIP1 along with an increase in body mass index in subcutaneous adipose tissue. The presented data show a novel role of MCPIP1 in modulating insulin sensitivity in adipocytes. Overall, our findings demonstrate that MCPIP1 is an important regulator of adipogenesis and adipocyte metabolism.

Chemerin facilitates intervertebral disc degeneration via TLR4 and CMKLR1 and activation of NF-kB signaling pathway

Now days, obesity is a major risk factor for intervertebral disc degeneration (IDD). However, adipokine, such as chemerin is a novel cytokine, which is secreted by adipose tissue, and are thought to be played major roles in various degenerative diseases. Obese individuals are known to have high concentration of serum chemerin. Our purpose was to study whether chemerin acts as a biochemical relationship between obesity, and IDD. In this study, we found that the expression level of chemerin was significantly increased in the human degenerated nucleus pulposus (NP) tissues, and had higher level in the obese people than the normal people. Chemerin significantly increased the inflammatory mediator level, contributing to ECM degradation in nucleus pulposus cells (NPCs). Furthermore, chemerin overexpression aggravates the puncture-induced IVDD progression in rats, while knockdown CMKLR1 reverses IVDD progression. Chemerin activates the NF-kB signaling pathway via its receptors CMKLR1, and TLR4 to release inflammatory mediators, which cause matrix degradation, and cell aging. These findings generally provide novel evidence supporting the causative role of obesity in IDD, which is essentially important to literally develop novel preventative or generally therapeutic treatment in the disc degenerative disorders.

Thigh Adipocyte Size is Inversely Related to Energy Intake and Respiratory Quotient in Healthy Women

OBJECTIVE

The relationship between adipocyte size and ad libitum energy intake has not been previously examined. This study hypothesized an inverse relationship between adipocyte size and daily energy intake (DEI).

METHODS

Seventy healthy adults (39 men and 31 women; BMI 30.0  [SD 6.3]) underwent dual-energy x-ray absorptiometry and subcutaneous fat biopsies from the abdomen and thigh. Osmium-fixed adipocytes were sized with a Coulter counter. Volunteers self-selected food from a vending machine paradigm as the only source of energy intake over 3 days as inpatients. Volunteers also had 24-hour respiratory quotient (RQ) measured in a whole-room indirect calorimeter.

RESULTS

In women, the large cell peak diameter of the thigh depot was greater than that of the abdominal depot (Δ = +15.8 μm; P < 0.0001). In women, thigh peak diameter was inversely associated with DEI (β = -264.7 kcal/d per 10-μm difference; P = 0.03) after adjusting for demographics and body composition. The thigh peak diameter in women was associated with 24-hour RQ (r = -0.47, P = 0.04) after adjusting for demographics, body composition, and 24-hour energy balance. These associations did not extend to men or the abdominal depot.

CONCLUSIONS

In women, thigh adipocyte size was associated with reduced DEI and 24-hour RQ, indicating a special role for thigh fat in women. This depot-specific sexual dimorphism indicates common regulation of energy intake and adipocyte size in the thigh region of women.

miR-196b-5p controls adipocyte differentiation and lipogenesis through regulating mTORC1 and TGF-β signaling

MicroRNAs have been reported to play a role in adipogenesis and obesity. This study was performed to investigate the role of miR-196b-5p in adipogenesis and the mechanism involved. The data revealed that miR-196b-5p expression increased in primary or established marrow stromal progenitor cells after adipogenic treatment. Supplementing miR-196b-5p in the progenitor cells stimulated adipogenic differentiation and lipogenesis, along with the induction of adipogenic and lipogenic factors. Conversely, inhibition of endogenous miR-196b-5p blocked adipogenesis and lipogenesis. Tuberous sclerosis 1 (Tsc1) and transforming growth factor-β receptor 1 (TGFBR1) were demonstrated to be the direct target genes of miR-196b-5p. Supplementing miR-196b-5p activity in progenitor cells reduced the protein level of TSC1 and activated mammalian target of rapamycin complex 1 (mTORC1) signaling. We further demonstrated that the perturbation of TSC1 in progenitor cells altered the trend of adipogenic differentiation and lipogenesis. Overexpression of Tsc1 or inactivation of mTORC1 signaling attenuated the stimulation of adipogenic differentiation and lipogenesis by miR-196b-5p. Overexpression of Tgfbr1 also partially blocked the adipogenic effect of miR-196b-5p. Further investigations demonstrated that zinc finger E-box-binding homeobox 1 (ZEB1) transcriptionally upregulated miR-196b-5p expression. The current study suggests that miR-196b-5p promotes adipogenic differentiation and lipogenesis in progenitor cells through targeting TSC1 and TGFBR1 and therefore regulating mTORC1 and TGF-β signaling.

The omentum of obese girls harbors small adipocytes and browning transcripts

Severe obesity (SO) affects about 6% of youth in the United States, augmenting the risks for cardiovascular disease and type 2 diabetes. Herein, we obtained paired omental adipose tissue (omVAT) and abdominal subcutaneous adipose tissue (SAT) biopsies from girls with SO undergoing sleeve gastrectomy (SG), to test whether differences in cellular and transcriptomic profiles between omVAT and SAT depots affect insulin sensitivity differently. Following weight loss, these analyses were repeated in a subgroup of subjects having a second SAT biopsy. We found that omVAT displayed smaller adipocytes compared with SAT, increased lipolysis through adipose triglyceride lipase phosphorylation, reduced inflammation, and increased expression of browning/beiging markers. Contrary to omVAT, SAT adipocyte diameter correlated with insulin resistance. Following SG, both weight and insulin sensitivity improved markedly in all subjects. SAT adipocytes' size became smaller, showing increased lipolysis through perilipin 1 phosphorylation, decreased inflammation, and increased expression in browning/beiging markers. In summary, in adolescent girls with SO, both omVAT and SAT depots showed distinct cellular and transcriptomic profiles. Following weight loss, the SAT depot changed its cellular morphology and transcriptomic profiles into more favorable ones. These changes in the SAT depot may play a fundamental role in the resolution of insulin resistance.

Associations between adipose tissue volume and small molecules in plasma and urine among asymptomatic subjects from the general population

Obesity is one of the major risk factor for cardiovascular and metabolic diseases. A disproportional accumulation of fat at visceral (VAT) compared to subcutaneous sites (SAT) has been suspected as a key detrimental event. We used non-targeted metabolomics profiling to reveal metabolic pathways associated with higher VAT or SAT amount among subjects free of metabolic diseases to identify possible contributing metabolic pathways. The study population comprised 491 subjects [mean (standard deviation): age 44.6 yrs (13.0), body mass index 25.4 kg/m² (3.6), 60.1% females] without diabetes, hypertension, dyslipidemia, the metabolic syndrome or impaired renal function. We associated MRI-derived fat amounts with mass spectrometry-derived metabolites in plasma and urine using linear regression models adjusting for major confounders. We tested for sex-specific effects using interactions terms and performed sensitivity analyses for the influence of insulin resistance on the results. VAT and SAT were significantly associated with 155 (101 urine) and 49 (29 urine) metabolites, respectively, of which 45 (27 urine) were common to both. Major metabolic pathways were branched-chain amino acid metabolism (partially independent of insulin resistance), surrogate markers of oxidative stress and gut microbial diversity, and cortisol metabolism. We observed a novel positive association between VAT and plasma levels of the potential pharmacological agent piperine. Sex-specific effects were only a few, e.g. the female-specific association between VAT and O-methylascorbate. In brief, higher VAT was associated with an unfavorable metabolite profile in a sample of healthy, mostly non-obese individuals from the general population and only few sex-specific associations became apparent.

Hydrogen Sulfide, Adipose Tissue and Diabetes Mellitus

Hydrogen sulfide (H₂S) is now increasingly considered to be the third gasotransmitter alongside other gaseous signaling molecules, nitric oxide (NO) and carbon monoxide (CO). H₂S is produced by a variety of endogenous enzymatic and non-enzymatic pathways and acts as a modulator of the physiological and pathological events of the body. Adipocytes express the cystathionine γ lyase (CSE)/H₂S system, which modulates a variety of biological activities in adipose tissue (AT), including inflammation, apoptosis, insulin resistance, adipokine secretion and adipocyte differentiation. Abnormalities in the physiological functions of AT play an important role in the process of diabetes mellitus. Therefore, this review provides an overview of the general aspects of H₂S biochemistry, the effect of H₂S on AT function and diabetes mellitus and its molecular signalling mechanisms as well as the potential application of H₂S in pharmacotherapy.

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.

The Complex Interactions Between Obesity, Metabolism and the Brain

Obesity is increasing at unprecedented levels globally, and the overall impact of obesity on the various organ systems of the body is only beginning to be fully appreciated. Because of the myriad of direct and indirect effects of obesity causing dysfunction of multiple tissues and organs, it is likely that there will be heterogeneity in the presentation of obesity effects in any given population. Taken together, these realities make it increasingly difficult to understand the complex interplay between obesity effects on different organs, including the brain. The focus of this review is to provide a comprehensive view of metabolic disturbances present in obesity, their direct and indirect effects on the different organ systems of the body, and to discuss the interaction of these effects in the context of brain aging and the development of neurodegenerative diseases.

Weight Cycling Increases Longevity Compared with Sustained Obesity in Mice

OBJECTIVE

Despite the known health benefits of weight loss among persons with obesity, observational studies have reported that cycles of weight loss and regain, or weight cycling, are associated with increased mortality. To study whether weight loss must be sustained to achieve health and longevity benefits, we performed a randomized controlled feeding study of weight cycling in mice.

METHODS

In early adult life, obese mice were randomized to ad libitum feeding to sustain obesity, calorie restriction to achieve a "normal" or intermediate body weight, or weight cycling (repeated episodes of calorie restriction and ad libitum refeeding). Body weight, body composition, and food intake were followed longitudinally until death. A subsample of mice was collected from each group for determination of adipose cell size, serum analytes, and gene expression.

RESULTS

Weight loss significantly reduced adipose mass and adipocyte size in both sexes, whereas weight cycling animals regained body fat and cell size during refeeding. Sustained weight loss resulted in a dose-dependent decrease in mortality compared with ad libitum feeding.

CONCLUSIONS

Weight cycling significantly increased life-span relative to remaining with obesity and had a similar benefit to sustained modest weight loss.

1,25-Dihydroxyvitamin D regulates lipid metabolism and glucose utilization in differentiated 3T3-L1 adipocytes

It is well established that adipose tissue can both store and metabolize vitamin D. The active form of vitamin D, 1,25 dihydroxyvitamin D [1,25(OH)₂D], regulates adipocyte differentiation and inflammation, highlighting the multifaceted role that vitamin D plays in adipose tissue physiology. However, there is limited evidence regarding vitamin D regulation of mature adipocyte lipid metabolism. We hypothesize that 1,25(OH)₂D alters lipid and glucose metabolism in differentiated 3T3-L1 adipocytes to reduce triacylglycerol (TAG) accumulation. In this study, 1,25(OH)₂D (10 nmol/L) stimulated a 21% reduction in TAG accumulation in differentiated 3T3-L1 adipocytes after 4 days (P = .01) despite a significant increase in fatty acid uptake (P < .01). Additionally, 1,25(OH)₂D stimulated a 2.5-fold increase in ¹⁴CO₂ production from [1-¹⁴C] palmitic acid (P < .01), indicative of an elevated rate of fatty acid β-oxidation, while stimulating a 9% reduction in de novo fatty acid synthesis (P = .03). Interestingly, d-[U-¹³C]glucose incorporation into fatty acids was reduced by 30% in response to 1,25(OH)₂D (P < .01), indicating a reduced contribution of glucose as a substrate for de novo lipogenesis. Consistent with these findings, mRNA expression of the anaplerotic enzyme pyruvate carboxylase was reduced by 41% (P < .01). In summary, 1,25(OH)₂D stimulated fatty acid oxidation and reduced TAG accumulation in differentiated adipocytes. Furthermore, 1,25(OH)₂D reduced glucose utilization as a substrate for fatty acid synthesis potentially by downregulating pyruvate carboxylase and stimulating glucose disposal as glycerol. Collectively, these 1,25(OH)₂D-induced changes in lipid metabolism and glucose utilization may contribute to the reduction in TAG accumulation and be protective against excessive fat mass accumulation and associated metabolic disorders.

Brown and beige fat: From molecules to physiology and pathophysiology

The adipose organ portrays adipocytes of diverse tones: white, brown and beige, each type with distinct functions. Adipocytes orchestrate their adaptation and expansion to provide storage to excess nutrients, the quick mobilisation of fuel to supply peripheral functional demands, insulation, and, in their thermogenic form, heat generation to maintain core body temperature. Thermogenic adipocytes could be targets for anti-obesity and anti-diabetic therapeutic approaches aiming to restore adipose tissue functionality and increase energy dissipation. However, for thermogenic adipose tissue to become therapeutically relevant, a better understanding of its development and origins, its progenitors and their characteristics and the composition of its niche, is essential. Also crucial is the identification of stimuli and molecules promoting its specific differentiation and activation. Here we highlight the structural/cellular differences between human and rodent brown adipose tissue and discuss how obesity and metabolic complication affects brown and beige cells as well as how they could be targeted to improve their activation and improve global metabolic homeostasis. Finally, we describe the limitations of current research models and the advantages of new emerging approaches.

Anaphylatoxin C5a induces inflammation and reduces insulin sensitivity by activating TLR4/NF-kB/PI3K signaling pathway in 3T3-L1 adipocytes

Obesity closely correlates with metaflammation and characterizes with systemic-chronic-low inflammation. This study aims to evaluate effects of C5a on the inflammatory response and insulin resistance in 3T3-L1 adipocytes. 3T3-L1 pre-adipocytes were induced to the mature 3T3-L1 adipocytes. Then, 3T3-L1 were intervened with anaphylatoxin C5a, lipopolysaccharide (LPS) and C5a + LPS, respectively. Levels of Omentin, Chemerin, Vaspin and Apelin 12 in supernatants of medium were examined using ELISA. C5L2, C5a receptor (C5aR), I kappa B (IkB), IkB kinase (IKK), insulin receptor substrate 1 (IRS-1), IRS-2, PI3 K, p-PI3 K and β-actin were examined using RT-PCR and western blot assay, respectively. C5L2-C5aR colocalization was identified using immunofluorescence double label. NF-kB expression or activity was evaluated using electrophoretic mobility shift assay (EMSA), dual luciferase assay and immunofluorescence assay, respectively. The glucose uptake and insulin sensitivity were also evaluated. Results showed that C5a intervention significantly enhanced inflammatory molecule levels in supernatants of 3T3-L1 adipocytes. IKK inflammatory signaling pathway participated in C5a induced inflammation of 3T3-L1 adipocytes. C5a triggered the colocalization of C5L2 and C5aR and activated the NF-kB inflammatory signaling pathway. C5a intervention in 3T3-L1 adipocytes decreased the glucose uptake and resulted in reduction of insulin sensitivity. Insulin signaling pathway participated in C5a caused insulin sensitivity reduction. C5a intervention triggered the phosphorylation of PI3 K. In conclusion anaphylatoxin C5a induced inflammatory response by activating TLR4/NF-kB signaling pathway and generating C5L2-C5aR dimer, and caused insulin sensitivity reduction by activating PI3 K signaling pathway.

Melatonin, mitochondria, and the metabolic syndrome

A number of risk factors for cardiovascular disease including hyperinsulinemia, glucose intolerance, dyslipidemia, obesity, and elevated blood pressure are collectively known as metabolic syndrome (MS). Since mitochondrial activity is modulated by the availability of energy in cells, the disruption of key regulators of metabolism in MS not only affects the activity of mitochondria but also their dynamics and turnover. Therefore, a link of MS with mitochondrial dysfunction has been suspected since long. As a chronobiotic/cytoprotective agent, melatonin has a special place in prevention and treatment of MS. Melatonin levels are reduced in diseases associated with insulin resistance like MS. Melatonin improves sleep efficiency and has antioxidant and anti-inflammatory properties, partly for its role as a metabolic regulator and mitochondrial protector. We discuss in the present review the several cytoprotective melatonin actions that attenuate inflammatory responses in MS. The clinical data that support the potential therapeutical value of melatonin in human MS are reviewed.

Adipose Tissue Function and Expandability as Determinants of Lipotoxicity and the Metabolic Syndrome

The adipose tissue organ is organised as distinct anatomical depots located all along the body axis and it is constituted of three different types of adipocytes : white, beige and brown which are integrated with vascular, immune, neural and extracellular stroma cells. These distinct adipocytes serve different specialised functions. The main function of white adipocytes is to ensure healthy storage of excess nutrients/energy and its rapid mobilisation to supply the demand of energy imposed by physiological cues in other organs, whereas brown and beige adipocytes are designed for heat production through uncoupling lipid oxidation from energy production. The concert action of the three type of adipocytes/tissues has been reported to ensure an optimal metabolic status in rodents. However, when one or multiple of these adipose depots become dysfunctional as a consequence of sustained lipid/nutrient overload, then insulin resistance and associated metabolic complications ensue. These metabolic alterations negatively affects the adipose tissue functionality and compromises global metabolic homeostasis. Optimising white adipose tissue expandability and its functional metabolic flexibility and/or promoting brown/beige mediated thermogenic activity counteracts obesity and its associated lipotoxic metabolic effects. The development of these therapeutic approaches requires a deep understanding of adipose tissue in all broad aspects. In this chapter we will discuss the characteristics of the different adipose tissue depots with respect to origins and precursors recruitment, plasticity, cellular composition and expandability capacity as well as molecular and metabolic signatures in both physiological and pathophysiological conditions.

Plasminogen Activator Inhibitor-1 is Regulated Through Dietary Fat Intake and Heritability: Studies in Twins

In different pathophysiological conditions plasminogen activator inhibitor-1 (PAI-1) plasma concentrations are elevated. As dietary patterns are considered to influence PAI-1 concentration, we aimed to determine active PAI-1 plasma concentrations and mRNA expression in adipose tissue before and after consumption of a high-fat diet (HFD) and the impact of additive genetic effects herein in humans. For 6 weeks, 46 healthy, non-obese pairs of twins (aged 18–70) received a normal nutritionally balanced diet (ND) followed by an isocaloric HFD for 6 weeks. Active PAI-1 plasma levels and PAI-1 mRNA expression in subcutaneous adipose tissue were assessed after the ND and after 1 and 6 weeks of HFD. Active PAI-1 plasma concentrations and PAI-1 mRNA expression in adipose tissue were significantly increased after both 1 and 6 weeks of HFD when compared to concentrations determined after ND (p< .05), with increases of active PAI-1 being independent of gender, age, or changes of BMI and intrahepatic fat content, respectively. However, analysis of covariance suggests that serum insulin concentration significantly affected the increase of active PAI-1 plasma concentrations. Furthermore, the increase of active PAI-1 plasma concentrations after 6 weeks of HFD was highly heritable (47%). In contrast, changes in PAI-1 mRNA expression in fatty tissue in response to HFD showed no heritability and were independent of all tested covariates. In summary, our data suggest that even an isocaloric exchange of macronutrients — for example, a switch to a fat-rich diet — affects PAI-1 concentrations in humans and that this is highly heritable.

High Thyroid-stimulating Hormone Levels Increase Proinflammatory and Cardiovascular Markers in Patients with Extreme Obesity

BACKGROUND AND AIMS

Obesity is an important health problem worldwide and many studies have suggested a relationship between obesity and thyroid function, with controversial results. Interestingly, high TSH levels have been involved with the presence of inflammatory state and risk for developing cardiovascular diseases in hypothyroid and obese patients. The aim in this work was to determine the prevalence of hypothyroidism in patients with extreme obesity and to determine whether their TSH levels were related to increased serum levels of inflammatory and cardiovascular markers.

METHODS

A cross-sectional study in 101 patients with extreme obesity (BMI ≥40) was performed. Anthropometric (weight, height and waist circumference) and biochemical (fasting glucose, glycosylated hemoglobin, triglycerides, total cholesterol, LDL-C, HDL-C and insulin) parameters were measured. TSH and FT4 levels as well as clinical exploration for diagnosis of hypothyroidism were carried out. Serum concentration of IL-10, IL-6, adiponectin, resistin, leptin, ICAM-1, VCAM-1 and E-selectin were determined.

RESULTS

A high prevalence for diabetes (37.6%), prediabetes (50.5%), dyslipidemia (74.3%), hypertension (61.4%) and hypothyroidism (48.5%) was observed in patients with extreme obesity. The presence of hypothyroidism increased serum concentration of proinflammatory cytokines IL-6 and leptin and decreased the antiinflammatory cytokine adiponectin. In addition, serum TSH levels showed a correlation for waist circumference, weight, BMI, A1c, insulin, IL-6, leptin, ICAM-1 and E-selectin.

CONCLUSION

There is a high prevalence for hypothyroidism in patients with extreme obesity. High levels of TSH contribute to elevate proinflammatory and cardiovascular risk markers, increasing the risk for development of cardiovascular diseases.

Upregulation of Early and Downregulation of Terminal Pathway Complement Genes in Subcutaneous Adipose Tissue and Adipocytes in Acquired Obesity

Inflammation is an important mediator of obesity-related complications such as the metabolic syndrome but its causes and mechanisms are unknown. As the complement system is a key mediator of inflammation, we studied whether it is activated in acquired obesity in subcutaneous adipose tissue (AT) and isolated adipocytes. We used a special study design of genetically matched controls of lean and heavy groups, rare monozygotic twin pairs discordant for body mass index (BMI) [n = 26, within-pair difference (Δ) in body mass index, BMI >3 kg/m²] with as much as 18 kg mean Δweight. Additionally, 14 BMI-concordant (BMI <3 kg/m²) served as a reference group. The detailed measurements included body composition (DEXA), fat distribution (MRI), glucose, insulin, adipokines, C3a and SC5b-9 levels, and the expression of complement and insulin signaling pathway-related genes in AT and adipocytes. In both AT and isolated adipocytes, the classical and alternative pathway genes were upregulated, and the terminal pathway genes downregulated in the heavier co-twins of the BMI-discordant pairs. The upregulated genes included C1q, C1s, C2, ficolin-1, factor H, receptors for C3a and C5a (C5aR1), and the iC3b receptor (CR3). While the terminal pathway components C5 and C6 were downregulated, its inhibitor clusterin was upregulated. Complement gene upregulation in AT and adipocytes correlated positively with adiposity and hyperinsulinemia and negatively with the expression of insulin signaling-related genes. Plasma C3a, but not SC5b-9, levels were elevated in the heavier co-twins. There were no differences between the co-twins in BMI-concordant pairs. Obesity is associated with increased expression of the early, but not late, complement pathway components and of key receptors. The twins with acquired obesity have therefore an inflated inflammatory activity in the AT. The results suggest that complement is likely involved in orchestrating clearance of apoptotic debris and inflammation in the AT.

Interactions of exercise training and high-fat diet on adiponectin forms and muscle receptors in mice

Background

Metabolic syndrome (MetS) is characterized by systemic disturbances that increase cardiovascular risk. Adiponectin (Ad) exhibits a cardioprotective function because of its anti-inflammatory and anti-atherosclerotic properties. In the bloodstream, this adipocytokine circulates on multimers (Ad_mer), among which high molecular weight (HMW) are the most active forms. Because alterations of Ad plasmatic levels, Ad_mer distribution and receptor (AdipoR) expression have been described in murine models and obese patients, strategies that aim to enhance Ad production or its effect on target tissues are the subject of intense investigations. While exercise training is well known to be beneficial for reducing cardiovascular risk, the contribution of Ad is still controversial. Our aim was to evaluate the effect of exercise training on Ad production, Ad_mer distribution and AdipoR muscle expression in a murine model of MetS.

Methods

At 6 weeks of age, mice were submitted to a standard (SF) or high-fat high-sugar (HF) diet for 10 weeks. After 2 weeks, the SF- and HF-fed animals were randomly assigned to a training program (SFT, HFT) or not (SFC, HFC). The trained groups were submitted to sessions of running on a treadmill 5 days a week.

Results and conclusions

The HF mice presented the key problems associated with MetS (increased caloric intake, body weight, glycemia and fat mass), a change in Ad_mer distribution in favor of the less-active forms and increased AdipoR2 expression in muscle. In contrast, exercise training reversed some of the adverse effects of a HF diet (increased glucose tolerance, better caloric intake control) without any modifications in Ad production and Ad_mer distribution. However, increased AdipoR1 muscle expression was observed in trained mice, but this effect was hampered by HF diet. These data corroborate a recent hypothesis suggesting a functional divergence between AdipoR1 and AdipoR2, with AdipoR1 having the predominant protective action on metabolic function.

Electronic supplementary material

The online version of this article (doi:10.1186/s12986-016-0138-2) contains supplementary material, which is available to authorized users.

Adipose tissue plasticity: how fat depots respond differently to pathophysiological cues

White adipose tissue (WAT) has key metabolic and endocrine functions and plays a role in regulating energy homeostasis and insulin sensitivity. WAT is characterised by its capacity to adapt and expand in response to surplus energy through processes of adipocyte hypertrophy and/or recruitment and proliferation of precursor cells in combination with vascular and extracellular matrix remodelling. However, in the context of sustained obesity, WAT undergoes fibro-inflammation, which compromises its functionality, contributing to increased risk of type 2 diabetes and cardiovascular diseases. Conversely, brown adipose tissue (BAT) and browning of WAT represent potential therapeutic approaches, since dysfunctional white adipocyte-induced lipid overspill can be halted by BAT/browning-mediated oxidative anti-lipotoxic effects. Better understanding of the cellular and molecular pathophysiological mechanisms regulating adipocyte size, number and depot-dependent expansion has become a focus of interest over recent decades. Here, we summarise the mechanisms contributing to adipose tissue (AT) plasticity and function including characteristics and cellular complexity of the various adipose depots and we discuss recent insights into AT origins, identification of adipose precursors, pathophysiological regulation of adipogenesis and its relation to WAT/BAT expandability in obesity and its associated comorbidities.

Adipose Tissue Depots and Their Cross-Sectional Associations With Circulating Biomarkers of Metabolic Regulation

BACKGROUND

Visceral adipose tissue (VAT) and fatty liver differ in their associations with cardiovascular risk compared with subcutaneous adipose tissue (SAT). Several biomarkers have been linked to metabolic derangements and may contribute to the pathogenicity of fat depots. We examined the association between fat depots on multidetector computed tomography and metabolic regulatory biomarkers.

METHODS AND RESULTS

Participants from the Framingham Heart Study (n=1583, 47% women) underwent assessment of SAT, VAT, and liver attenuation. We measured circulating biomarkers secreted by adipose tissue or liver (adiponectin, leptin, leptin receptor, fatty acid binding protein 4, fetuin-A, and retinol binding protein 4). Using multivariable linear regression models, we examined relations of fat depots with biomarkers. Higher levels of fat depots were positively associated with leptin and fatty acid binding protein 4 but negatively associated with adiponectin (all P<0.001). Associations with leptin receptor, fetuin-A, and retinol binding protein 4 varied according to fat depot type or sex. When comparing the associations of SAT and VAT with biomarkers, VAT was the stronger correlate of adiponectin (β=-0.28 [women]; β=-0.30 [men]; both P<0.001), whereas SAT was the stronger correlate of leptin (β=0.62 [women]; β=0.49 [men]; both P<0.001; P<0.001 for comparing VAT versus SAT). Although fetuin-A and retinol binding protein 4 are secreted by the liver in addition to adipose tissue, associations of liver attenuation with these biomarkers was not stronger than that of SAT or VAT.

CONCLUSIONS

SAT, VAT, and liver attenuation are associated with metabolic regulatory biomarkers with differences in the associations by fat depot type and sex. These findings support the possibility of biological differences between fat depots.

Cross-Sectional Associations of Computed Tomography (CT)-Derived Adipose Tissue Density and Adipokines: The Framingham Heart Study

Background

Excess accumulation of abdominal subcutaneous (SAT) and visceral adipose tissue (VAT) is associated with adverse levels of adipokines and cardiovascular disease risk. Whether fat quality is associated with adipokines has not been firmly established. This study examined the association between abdominal SAT and VAT density, an indirect measure of fat quality, with a panel of metabolic regulatory biomarkers secreted by adipose tissue or the liver independently of absolute fat volumes.

Methods and Results

We evaluated 1829 Framingham Heart Study participants (44.9% women). Abdominal SAT and VAT density was estimated indirectly by adipose tissue attenuation using computed tomography. Adipokines included adiponectin, leptin receptor, leptin, fatty acid‐binding protein 4 (FABP‐4), retinol‐binding protein 4 (RBP‐4), and fetuin‐A. Fat density was associated with all the biomarkers evaluated, except fetuin‐A. Lower fat density (ie, more‐negative fat attenuation) was associated with lower adiponectin and leptin receptor, but higher leptin and FABP‐4 levels (all P<0.0001). SAT density was inversely associated with RPB‐4 in both sexes, whereas the association between VAT density and RPB‐4 was only observed in men (P<0.0001). In women, after additional adjustment for respective fat volume, SAT density retained the significant associations with adiponectin, leptin, FABP‐4, and RBP‐4; and VAT density with adiponectin only (all P<0.0001). In men, significant associations were maintained upon additional adjustment for respective fat volume (P<0.005).

Conclusions

Lower abdominal fat density was associated with a profile of biomarkers suggestive of greater cardiometabolic risk. These observations support that fat density may be a valid biomarker of cardiometabolic risk.

Adverse Fat Depots and Marrow Adiposity Are Associated With Skeletal Deficits and Insulin Resistance in Long-Term Survivors of Pediatric Hematopoietic Stem Cell Transplantation

Allogeneic hematopoietic stem-cell transplantation (alloHSCT) survivors treated with total body irradiation (TBI) exhibit bone deficits and excess adiposity, potentially related to altered mesenchymal stem cell differentiation into osteoblasts or adipocytes. We examined associations among fat distribution, bone microarchitecture, and insulin resistance in alloHSCT survivors after TBI. This was a cross-sectional observational study of 25 alloHSCT survivors (aged 12 to 25 years) a median of 9.7 (4.3 to 19.3) years after alloHSCT compared to 25 age-, race-, and sex-matched healthy controls. Vertebral MR spectroscopic imaging and tibia micro-MRI were used to quantify marrow adipose tissue (MAT) and trabecular microarchitecture. Additional measures included DXA whole-body fat mass (WB-FM), leg lean mass (Leg-LM), trunk visceral adipose tissue (VAT), and CT calf muscle density. Insulin resistance in alloHSCT survivors was estimated by HOMA-IR. AlloHSCT survivors had lower Leg-LM (p < 0.001) and greater VAT (p < 0.01), MAT (p < 0.001), and fat infiltration of muscle (p = 0.04) independent of WB-FM, versus matched controls; BMI did not differ. Survivors had lower bone volume fraction and abnormal microarchitecture including greater erosion and more rod-like structure versus controls (all p = 0.04); 14 had vertebral deformities and two had compression fractures. Greater WB-FM, VAT, MAT, and muscle fat infiltration were associated with abnormal trabecular microarchitecture (p < 0.04 for all). AlloHSCT HOMA-IR was elevated, associated with younger age at transplantation (p < 0.01), and positively correlated with WB-FM and VAT (both p < 0.01). In conclusion, the markedly increased marrow adiposity, abnormal bone microarchitecture, and abnormal fat distribution highlight the risks of long-term treatment-related morbidity and mortality in alloHSCT recipients after TBI. Trabecular deterioration was associated with marrow and visceral adiposity. Furthermore, long-term survivors demonstrated sarcopenic obesity, insulin resistance, and vertebral deformities. Future studies are needed to identify strategies to prevent and treat metabolic and skeletal complications in this growing population of childhood alloHSCT survivors.

Adipokines in health and disease

Obesity increases the risk for metabolic, cardiovascular, chronic inflammatory, and several malignant diseases and, therefore, may contribute to shortened lifespan. Adipokines are peptides that signal the functional status of adipose tissue to targets in the brain, liver, pancreas, immune system, vasculature, muscle, and other tissues. Secretion of adipokines, including leptin, adiponectin, fibroblast growth factor 21 (FGF21), retinol-binding protein 4 (RBP4), dipeptidyl peptidase 4 (DPP-4), bone morphogenetic protein (BMP)-4, BMP-7, vaspin, apelin, and progranulin, is altered in adipose tissue dysfunction and may contribute to a spectrum of obesity-associated diseases. Adipokines are promising candidates both for novel pharmacological treatment strategies and as diagnostic tools, provided that we can develop a better understanding of the function and molecular targets of the more recently discovered adipokines.

Evidence of early alterations in adipose tissue biology and function and its association with obesity-related inflammation and insulin resistance in children

Accumulation of fat mass in obesity may result from hypertrophy and/or hyperplasia and is frequently associated with adipose tissue (AT) dysfunction in adults. Here we assessed early alterations in AT biology and function by comprehensive experimental and clinical characterization of 171 AT samples from lean and obese children aged 0 to 18 years. We show an increase in adipocyte size and number in obese compared with lean children beginning in early childhood. These alterations in AT composition in obese children were accompanied by decreased basal lipolytic activity and significantly enhanced stromal vascular cell proliferation in vitro, potentially underlying the hypertrophy and hyperplasia seen in obese children, respectively. Furthermore, macrophage infiltration, including the formation of crown-like structures, was increased in AT of obese children from 6 years on and was associated with higher hs-CRP serum levels. Clinically, adipocyte hypertrophy was not only associated with leptin serum levels but was highly and independently correlated with HOMA-IR as a marker of insulin resistance in children. In summary, we show that adipocyte hypertrophy is linked to increased inflammation in AT in obese children, thereby providing evidence that obesity-associated AT dysfunction develops in early childhood and is related to insulin resistance.

Role of developmental transcription factors in white, brown and beige adipose tissues

In this review we discuss the role of developmental transcription factors in adipose tissue biology with a focus on how these developmental genes may contribute to regional variation in adipose tissue distribution and function. Regional, depot-specific, differences in lipid handling and signalling (lipolysis, lipid storage and adipokine/lipokine signalling) are important determinants of metabolic health. At a cellular level, preadipocytes removed from their original depot and cultured in vitro retain depot-specific functional properties, implying that these are intrinsic to the cells and not a function of their environment in situ. High throughput screening has identified a number of developmental transcription factors involved in embryological development, including members of the Homeobox and T-Box gene families, that are strongly differentially expressed between regional white adipose tissue depots and also between brown and white adipose tissue. However, the significance of depot-specific developmental signatures remains unclear. Developmental transcription factors determine body patterning during embryogenesis. The divergent developmental origins of regional adipose tissue depots may explain their differing functional characteristics. There is evidence from human genetics that developmental genes determine adipose tissue distribution: in GWAS studies a number of developmental genes have been identified as being correlated with anthropometric measures of adiposity and fat distribution. Additionally, compelling functional studies have recently implicated developmental genes in both white adipogenesis and the so-called 'browning' of white adipose tissue. Understanding the genetic and developmental pathways in adipose tissue may help uncover novel ways to intervene with the function of adipose tissue in order to promote health.

Adiponectin as a potential biomarker of vascular disease

The increasing prevalence of diabetes and its complications heralds an alarming situation worldwide. Obesity-associated changes in circulating adiponectin concentrations have the capacity to predict insulin sensitivity and are a link between obesity and a number of vascular diseases. One obvious consequence of obesity is a decrease in circulating levels of adiponectin, which are associated with cardiovascular disorders and associated vascular comorbidities. Human and animal studies have demonstrated decreased adiponectin to be an independent risk factor for cardiovascular disease. However, in animal studies, increased circulating adiponectin alleviates obesity-induced endothelial dysfunction and hypertension, and also prevents atherosclerosis, myocardial infarction, and diabetic cardiac tissue disorders. Further, metabolism of a number of foods and medications are affected by induction of adiponectin. Adiponectin has beneficial effects on cardiovascular cells via its antidiabetic, anti-inflammatory, antioxidant, antiapoptotic, antiatherogenic, vasodilatory, and antithrombotic activity, and consequently has a favorable effect on cardiac and vascular health. Understanding the molecular mechanisms underlying the regulation of adiponectin secretion and signaling is critical for designing new therapeutic strategies. This review summarizes the recent evidence for the physiological role and clinical significance of adiponectin in vascular health, identification of the receptor and post-receptor signaling events related to the protective effects of the adiponectin system on vascular compartments, and its potential use as a target for therapeutic intervention in vascular disease.

Intermuscular and intramuscular adipose tissues: Bad vs. good adipose tissues

Human studies of the influence of aging and other factors on intermuscular fat (INTMF) were reviewed. Intermuscular fat increased with weight loss, weight gain, or with no weight change with age in humans. An increase in INTMF represents a similar threat to type 2 diabetes and insulin resistance as does visceral adipose tissue (VAT). Studies of INTMF in animals covered topics such as quantitative deposition and genetic relationships with other fat depots. The relationship between leanness and higher proportions of INTMF fat in pigs was not observed in human studies and was not corroborated by other pig studies. In humans, changes in muscle mass, strength and quality are associated with INTMF accretion with aging. Gene expression profiling and intrinsic methylation differences in pigs demonstrated that INTMF and VAT are primarily associated with inflammatory and immune processes. It seems that in the pig and humans, INTMF and VAT share a similar pattern of distribution and a similar association of components dictating insulin sensitivity. Studies on intramuscular (IM) adipocyte development in meat animals were reviewed. Gene expression analysis and genetic analysis have identified candidate genes involved in IM adipocyte development. Intramuscular (IM) adipocyte development in human muscle is only seen during aging and some pathological circumstance. Several genetic links between human and meat animal adipogenesis have been identified. In pigs, the Lipin1 and Lipin 2 gene have strong genetic effects on IM accumulation. Lipin1 deficiency results in immature adipocyte development in human lipodystrophy. In humans, overexpression of Perilipin 2 (PLIN2) facilitates intramyocellular lipid accretion whereas in pigs PLIN2 gene expression is associated with IM deposition. Lipins and perilipins may influence intramuscular lipid regardless of species.

White adipose tissue resilience to insulin deprivation and replacement

Introduction

Adipocyte size and body fat distribution are strongly linked to the metabolic complications of obesity. The aim of the present study was to test the plasticity of white adipose tissue in response to insulin deprivation and replacement. We have characterized the changes of adipose cell size repartition and gene expressions in type 1 diabetes Sprague-Dawley rats and type 1 diabetic supplemented with insulin.

Methods

Using streptozotocin (STZ)-induced diabetes, we induced rapid changes in rat adipose tissue weights to study the changes in the distribution of adipose cell sizes in retroperitoneal (rWAT), epididymal (eWAT) and subcutaneous adipose tissues (scWAT). Adipose tissue weights of type 1 diabetic rats were then rapidly restored by insulin supplementation. Cell size distributions were analyzed using multisizer IV (Beckman Coulter). Cell size changes were correlated to transcriptional regulation of genes coding for proteins involved in lipid and glucose metabolisms and adipocytokines.

Results

The initial body weight of the rats was 465±5.2 g. Insulin privation was stopped when rats lost 100 g which induced reductions in fat mass of 68% for rWAT, 42% for eWAT and 59% for scWAT corresponding to decreased mode cell diameters by 31.1%, 20%, 25.3%, respectively. The most affected size distribution by insulin deprivation was observed in rWAT. The bimodal distribution of adipose cell sizes disappeared in response to insulin deprivation in rWAT and scWAT. The most important observation is that cell size distribution returned close to control values in response to insulin treatment. mRNAs coding for adiponectin, leptin and apelin were more stimulated in scWAT compared to other depots in diabetic plus insulin group.

Conclusion

Fat depots have specific responses to insulin deprivation and supplementation. The results show that insulin is a major determinant of bimodal cell repartition in adipose tissues.