Measuring committed preadipocytes in human adipose tissue from severely obese patients by using adipocyte fatty acid binding protein

Regional primary preadipocyte characteristics in humans with obesity and type 2 diabetes mellitus

The excessive accumulation of adipose tissue in obesity appears to result in adipose tissue dysfunction perpetuating the onset of obesity-related diseases, including type 2 diabetes (T2DM). In humans, adipose tissue is stored in several depots including subcutaneous and visceral. These depots contribute to the pathology of obesity differently owing to differences in the tissue microenvironment, a main one being preadipocyte function. In examining adipocyte and preadipocyte characteristics, many have used the 3T3-L1 murine cell lines. Though these cell lines provide valuable mechanistic data, the results remain to be translated to humans. Experiments using primary human preadipocytes has shown that obesity and T2DM impact preadipocyte phenotypes. The objective of this review is to describe the differences in regional characteristics of primary preadipocytes collected from humans with obesity and to discuss how these characteristics might be affected in type 2 diabetes mellitus. In doing so, we will show that the characteristics of regional primary preadipocytes in humans are differentially affected by obesity and the development of T2DM.

The optimized priming effect of FGF-1 and FGF-2 enhances preadipocyte lineage commitment in human adipose-derived mesenchymal stem cells

The cell-assisted lipotransfer technique, integrating adipose-derived mesenchymal stem cells (ADMSCs), has transformed lipofilling, enhancing fat graft viability. However, the multipotent nature of ADMSCs poses challenges. To improve safety and graft vitality and to reduce unwanted lineage differentiation, this study refines the methodology by priming ADMSCs into preadipocytes-unipotent, self-renewing cells. We explored the impact of fibroblast growth factor-1 (FGF-1), fibroblast growth factor-2 (FGF-2), and epidermal growth factor (EGF), either alone or in combination, on primary human ADMSCs during the proliferative phase. FGF-2 emerged as a robust stimulator of cell proliferation, preserving stemness markers, especially when combined with EGF. Conversely, FGF-1, while not significantly affecting cell growth, influenced cell morphology, transitioning cells to a rounded shape with reduced CD34 expression. Furthermore, co-priming with FGF-1 and FGF-2 enhanced adipogenic potential, limiting osteogenic and chondrogenic tendencies, and possibly promoting preadipocyte commitment. These preadipocytes exhibited unique features: rounded morphology, reduced CD34, decreased preadipocyte factor 1 (Pref-1), and elevated C/EBPα and PPARγ, alongside sustained stemness markers (CD73, CD90, CD105). Mechanistically, FGF-1 and FGF-2 activated key adipogenic transcription factors-C/EBPα and PPARγ-while inhibiting GATA3 and Notch3, which are adipogenesis inhibitors. These findings hold the potential to advance innovative strategies for ADMSC-mediated lipofilling procedures.

Maternal obesity and programming of metabolic syndrome in the offspring: searching for mechanisms in the adipocyte progenitor pool

BACKGROUND

It is now understood that it is the quality rather than the absolute amount of adipose tissue that confers risk for obesity-associated disease. Adipose-derived stem cells give rise to adipocytes during the developmental establishment of adipose depots. In adult depots, a reservoir of progenitors serves to replace adipocytes that have reached their lifespan and for recruitment to increase lipid buffering capacity under conditions of positive energy balance. MAIN: The adipose tissue expandability hypothesis posits that a failure in de novo differentiation of adipocytes limits lipid storage capacity and leads to spillover of lipids into the circulation, precipitating the onset of obesity-associated disease. Since adipose progenitors are specified to their fate during late fetal life, perturbations in the intrauterine environment may influence the rapid expansion of adipose depots that occurs in childhood or progenitor function in established adult depots. Neonates born to mothers with obesity or diabetes during pregnancy tend to have excessive adiposity at birth and are at increased risk for childhood adiposity and cardiometabolic disease.

CONCLUSION

In this narrative review, we synthesize current knowledge in the fields of obesity and developmental biology together with literature from the field of the developmental origins of health and disease (DOHaD) to put forth the hypothesis that the intrauterine milieu of pregnancies complicated by maternal metabolic disease disturbs adipogenesis in the fetus, thereby accelerating the trajectory of adipose expansion in early postnatal life and predisposing to impaired adipose plasticity.

Mediation analysis of multiple mediators with incomplete omics data

There is an increasing interest in using multiple types of omics features (e.g., DNA sequences, RNA expressions, methylation, protein expressions, and metabolic profiles) to study how the relationships between phenotypes and genotypes may be mediated by other omics markers. Genotypes and phenotypes are typically available for all subjects in genetic studies, but typically, some omics data will be missing for some subjects, due to limitations such as cost and sample quality. In this article, we propose a powerful approach for mediation analysis that accommodates missing data among multiple mediators and allows for various interaction effects. We formulate the relationships among genetic variants, other omics measurements, and phenotypes through linear regression models. We derive the joint likelihood for models with two mediators, accounting for arbitrary patterns of missing values. Utilizing computationally efficient and stable algorithms, we conduct maximum likelihood estimation. Our methods produce unbiased and statistically efficient estimators. We demonstrate the usefulness of our methods through simulation studies and an application to the Metabolic Syndrome in Men study.

The Effect of Mineralocorticoid Receptor 3 Antagonists on Anti-Inflammatory and Anti-Fatty Acid Transport Profile in Patients with Heart Failure

Epicardial fat thickness is associated with cardiovascular disease. Mineralocorticoid receptor antagonist (MRA), a pharmaceutical treatment for CVD, was found to have an effect on adipose tissue. Our aim was to analyse the main epicardial fat genesis and inflammation-involved cell markers and their regulation by risk factors and MRA. We included blood and epicardial or subcutaneous fat (EAT or SAT) from 71 patients undergoing heart surgery and blood from 66 patients with heart failure. Cell types (transcripts or proteins) were analysed by real-time polymerase chain reaction or immunohistochemistry. Plasma proteins were analysed by Luminex technology or enzyme-linked immunoassay. Our results showed an upregulation of fatty acid transporter levels after aldosterone-induced genesis. The MRA intake was the main factor associated with lower levels in epicardial fat. On the contrary, MRA upregulated the levels and its secretion of the anti-inflammatory marker intelectin 1 and reduced the proliferation of epicardial fibroblasts. Our results have shown the local MRA intake effect on fatty acid transporters and anti-inflammatory marker levels and the proliferation rate on epicardial fat fibroblasts. They suggest the role of MRA on epicardial fat genesis and remodelling in patients with cardiovascular disease. Translational perspective: the knowledge of epicardial fat genesis and its modulation by drugs might be useful for improving the treatments of cardiovascular disease.

Epigenetic regulation by long noncoding RNAs in osteo-/adipogenic differentiation of mesenchymal stromal cells and degenerative bone diseases

Bone is a complex tissue that undergoes constant remodeling to maintain homeostasis, which requires coordinated multilineage differentiation and proper proliferation of mesenchymal stromal cells (MSCs). Mounting evidence indicates that a disturbance of bone homeostasis can trigger degenerative bone diseases, including osteoporosis and osteoarthritis. In addition to conventional genetic modifications, epigenetic modifications (i.e., DNA methylation, histone modifications, and the expression of noncoding RNAs) are considered to be contributing factors that affect bone homeostasis. Long noncoding RNAs (lncRNAs) were previously regarded as 'transcriptional noise' with no biological functions. However, substantial evidence suggests that lncRNAs have roles in the epigenetic regulation of biological processes in MSCs and related diseases. In this review, we summarized the interactions between lncRNAs and epigenetic modifiers associated with osteo-/adipogenic differentiation of MSCs and the pathogenesis of degenerative bone diseases and highlighted promising lncRNA-based diagnostic and therapeutic targets for bone diseases.

Adipocyte Biology from the Perspective of In Vivo Research: Review of Key Transcription Factors

Obesity and type 2 diabetes are both significant contributors to the contemporary pandemic of non-communicable diseases. Both disorders are interconnected and associated with the disruption of normal homeostasis in adipose tissue. Consequently, exploring adipose tissue differentiation and homeostasis is important for the treatment and prevention of metabolic disorders. The aim of this work is to review the consecutive steps in the postnatal development of adipocytes, with a special emphasis on in vivo studies. We gave particular attention to well-known transcription factors that had been thoroughly described in vitro, and showed that the in vivo research of adipogenic differentiation can lead to surprising findings.

Sympathetic nerve-adipocyte interactions in response to acute stress

Psychological stress predisposes our body to several disorders. Understanding the cellular and molecular mechanisms involved in the physiological responses to psychological stress is essential for the success of therapeutic applications. New studies show, by using in vivo inducible Cre/loxP-mediated approaches in combination with pharmacological blockage, that sympathetic nerves, activated by psychological stress, induce brown adipocytes to produce IL-6. Strikingly, this cytokine promotes gluconeogenesis in hepatocytes, that results in the decline of tolerance to inflammatory organ damage. The comprehension arising from this research will be crucial for the handling of many inflammatory diseases. Here, we review recent advances in our comprehension of the sympathetic nerve-adipocyte axis in the tissue microenvironment.

Adipogenesis and therapeutic potentials of antiobesogenic phytochemicals: Insights from preclinical studies

Obesity is one of the most serious public health problems in both developed and developing countries in recent years. While lifestyle and diet modifications are the most important management strategies of obesity, these may be insufficient to ensure long-term weight reduction in certain individuals and alternative strategies including pharmacotherapy need to be considered. However, drugs option remains limited due to low efficacy and adverse effects associated with their use. Hence, identification of safe and effective alternative therapeutic agents remains warranted to combat obesity. In recent years, bioactive phytochemicals are considered as valuable sources for the discovery of new pharmacological agents for the treatment of obesity. Adipocyte hypertrophy and hyperplasia increases with obesity and undergo molecular and cellular alterations that can affect systemic metabolism giving rise to metabolic syndrome and comorbidities such as type 2 diabetes and cardiovascular diseases. Many phytochemicals have been reported to target adipocytes by inhibiting adipogenesis, inducing lipolysis, suppressing the differentiation of preadipocytes to mature adipocytes, reducing energy intake, and boosting energy expenditure mainly in vitro and in animal studies. Nevertheless, further high-quality studies are needed to firmly establish the clinical efficacy of these phytochemicals. This review outlines common pathways involved in adipogenesis and phytochemicals targeting effector molecules of these pathways, the challenges faced and the way forward for the development of phytochemicals as antiobesity agents.

Origins, potency, and heterogeneity of skeletal muscle fibro-adipogenic progenitors-time for new definitions

Striated muscle is a highly plastic and regenerative organ that regulates body movement, temperature, and metabolism-all the functions needed for an individual's health and well-being. The muscle connective tissue's main components are the extracellular matrix and its resident stromal cells, which continuously reshape it in embryonic development, homeostasis, and regeneration. Fibro-adipogenic progenitors are enigmatic and transformative muscle-resident interstitial cells with mesenchymal stem/stromal cell properties. They act as cellular sentinels and physiological hubs for adult muscle homeostasis and regeneration by shaping the microenvironment by secreting a complex cocktail of extracellular matrix components, diffusible cytokines, ligands, and immune-modulatory factors. Fibro-adipogenic progenitors are the lineage precursors of specialized cells, including activated fibroblasts, adipocytes, and osteogenic cells after injury. Here, we discuss current research gaps, potential druggable developments, and outstanding questions about fibro-adipogenic progenitor origins, potency, and heterogeneity. Finally, we took advantage of recent advances in single-cell technologies combined with lineage tracing to unify the diversity of stromal fibro-adipogenic progenitors. Thus, this compelling review provides new cellular and molecular insights in comprehending the origins, definitions, markers, fate, and plasticity of murine and human fibro-adipogenic progenitors in muscle development, homeostasis, regeneration, and repair.

DNA methylation of JAK3/STAT5/PPARγ regulated the changes of lipid levels induced by di (2-ethylhexyl) phthalate and high-fat diet in adolescent rats

Di (2-ethylhexyl) phthalate (DEHP) and high-fat diet (HFD) could induce lipid metabolic disorder. This study was undertaken to identify the effect of DNA methylation of JAK3/STAT5/PPARγ on lipid metabolic disorder induced by DEHP and HFD. Wistar rats were divided into a normal diet (ND) group and HFD group. Each diet group treated with DEHP (0, 5, 50, 500 mg/kg/d) for 8 weeks' gavage. The DNA-methylated levels of PPARγ, JAK3, STAT5a, and STAT5b in rats' livers and adipose were analyzed with MethylTarget. The lipid levels of rats' livers and adipose were detected with ELISA. Results showed in ND group that the DNA methylation levels of PPARγ, JAK3 in livers, and STAT5b in adipose were lower in 500 mg/kg/d group than the control. And the level of total cholesterol (TC) in adipose was higher in 500 mg/kg/d group than the control. In HFD group, the DNA methylation level of JAK3 was the lowest in livers and the highest in adipose in 50 mg/kg/d group. And the level of TC in livers was the lowest in 50 mg/kg/d group. In the 500 mg/kg/d group, the DNA methylation level of STAT5b was lower in livers and higher in adipose in HFD group than that in ND group. And the levels of TC in livers were lower in HFD group than those in ND group. Therefore, DNA methylation of JAK3/STAT5/PPARγ regulated the changes in lipid levels induced by DEHP and HFD in adolescent rats.

Adipose Stromal Cell Expansion and Exhaustion: Mechanisms and Consequences

Adipose tissue (AT) is comprised of a diverse number of cell types, including adipocytes, stromal cells, endothelial cells, and infiltrating leukocytes. Adipose stromal cells (ASCs) are a mixed population containing adipose progenitor cells (APCs) as well as fibro-inflammatory precursors and cells supporting the vasculature. There is growing evidence that the ability of ASCs to renew and undergo adipogenesis into new, healthy adipocytes is a hallmark of healthy fat, preventing disease-inducing adipocyte hypertrophy and the spillover of lipids into other organs, such as the liver and muscles. However, there is building evidence indicating that the ability for ASCs to self-renew is not infinite. With rates of ASC proliferation and adipogenesis tightly controlled by diet and the circadian clock, the capacity to maintain healthy AT via the generation of new, healthy adipocytes appears to be tightly regulated. Here, we review the contributions of ASCs to the maintenance of distinct adipocyte pools as well as pathogenic fibroblasts in cancer and fibrosis. We also discuss aging and diet-induced obesity as factors that might lead to ASC senescence, and the consequences for metabolic health.

Adipose Tissue Gene Expression Associations Reveal Hundreds of Candidate Genes for Cardiometabolic Traits

Genome-wide association studies (GWASs) have identified thousands of genetic loci associated with cardiometabolic traits including type 2 diabetes (T2D), lipid levels, body fat distribution, and adiposity, although most causal genes remain unknown. We used subcutaneous adipose tissue RNA-seq data from 434 Finnish men from the METSIM study to identify 9,687 primary and 2,785 secondary cis-expression quantitative trait loci (eQTL; <1 Mb from TSS, FDR < 1%). Compared to primary eQTL signals, secondary eQTL signals were located further from transcription start sites, had smaller effect sizes, and were less enriched in adipose tissue regulatory elements compared to primary signals. Among 2,843 cardiometabolic GWAS signals, 262 colocalized by LD and conditional analysis with 318 transcripts as primary and conditionally distinct secondary cis-eQTLs, including some across ancestries. Of cardiometabolic traits examined for adipose tissue eQTL colocalizations, waist-hip ratio (WHR) and circulating lipid traits had the highest percentage of colocalized eQTLs (15% and 14%, respectively). Among alleles associated with increased cardiometabolic GWAS risk, approximately half (53%) were associated with decreased gene expression level. Mediation analyses of colocalized genes and cardiometabolic traits within the 434 individuals provided further evidence that gene expression influences variant-trait associations. These results identify hundreds of candidate genes that may act in adipose tissue to influence cardiometabolic traits.

Insulin Controls Triacylglycerol Synthesis through Control of Glycerol Metabolism and Despite Increased Lipogenesis

Under normoxic conditions, adipocytes in primary culture convert huge amounts of glucose to lactate and glycerol. This “wasting” of glucose may help to diminish hyperglycemia. Given the importance of insulin in the metabolism, we have studied how it affects adipocyte response to varying glucose levels, and whether the high basal conversion of glucose to 3-carbon fragments is affected by insulin. Rat fat cells were incubated for 24 h in the presence or absence of 175 nM insulin and 3.5, 7, or 14 mM glucose; half of the wells contained ¹⁴C-glucose. We analyzed glucose label fate, medium metabolites, and the expression of key genes controlling glucose and lipid metabolism. Insulin increased both glucose uptake and the flow of carbon through glycolysis and lipogenesis. Lactate excretion was related to medium glucose levels, which agrees with the purported role of disposing excess (circulating) glucose. When medium glucose was low, most basal glycerol came from lipolysis, but when glucose was high, release of glycerol via breakup of glycerol-3P was predominant. Although insulin promotes lipogenesis, it also limited the synthesis of glycerol-3P from glucose and its incorporation into acyl-glycerols. We assume that this is a mechanism of adipose tissue defense to avoid crippling fat accumulation which has not yet been described.

Circadian rhythms of hormone secretion and obesity

The adipose tissue homeostasis is profoundly affected by circadian rhythms of corticosteroid secretion and chronic loss of hormonal oscillations is associated with obesity. How adipose tissue differentially responds to pulsatile vs continuous presence of glucocorticoids is poorly defined. To address this question, Bahrami-Nejad et al studied differentiation of pre-adipocytes, containing endogenously tagged CCAAT/enhancer binding protein and peroxisome proliferator-activated receptor (PPAR) γ (key regulators of adipocyte differentiation), in response to corticosteroids that were delivered either in an oscillatory fashion or continuously. The authors show that the bi-stable state of differentiation of pre-adipocytes and adipocytes was regulated by a combination of fast and slow positive feedback networks, that determined unique threshold of PPARγ in these cells. Evidently, pre-adipocytes used the fast feedback loop to reject differentiation cues of oscillating pulses of glucocorticoids and failed to differentiate into fat cells. In contrast, when glucocorticoids were delivered continuously, precursor cells exploited the slow feedback loop to embark on a path of maximal differentiation. This differential differentiation response of pre-adipocytes to pulsatile vs continuous exposure to glucocorticoids was corroborated in vivo. Thus, mice receiving non-oscillating doses of exogenous glucocorticoids, for 21 d, elicited excessive accumulation of visceral and subcutaneous fat. These data shed new light on the mechanisms of obesity caused by putative misalignment of circadian secretion of glucocorticoids or their persistently high levels due to chronic stress or Cushing’s disease.

Effect of a 9-week exercise training regimen on expression of developmental genes related to growth-dependent fat expansion in juvenile rats

This study examined the association between changes in mRNA expression of development-related genes including those of the homeobox (Hox) family and growth-dependent increases in inguinal, mesenteric, and epididymal white adipose tissue (WAT) at 4, 6, 10, and 14 weeks of age in rats. We also examined the effects of a 9-week exercise training regimen starting at 5 weeks of age on the mRNA levels of the genes of interest. HoxC8, HoxC9, Gpc4, Bmpr1a, Pparγ, Pgc1α, Adrb3, Hsl, leptin, and adiponectin in each type of WAT - except HoxA5, Gpc4, and Pgc1α in epididymal - showed a positive association between WAT weights and WAT mRNA levels; however, the slope of the regression lines exhibited fat depot-specific differences. HoxA5 showed no significant association, and Gpc4 and Pgc1α showed a negative association in epididymal WAT. After exercise training, the mean HoxA5, HoxC8, HoxC9, HoxC10, Gpc4, Pparγ, and Pgc1α mRNA levels in inguinal WAT were outliers on the regression line between mean mRNA level and WAT weight in control rats - that is, mean HoxA5 and Pgc1α mRNA level was higher, whereas HoxC8, HoxC9, HoxC10, Gpc4, and Ppar levels were lower in exercise-trained rats than in same-age controls. Pparγγ and adiponectin levels were upregulated in epididymal WAT, while HoxA5 was downregulated, but HoxC9, Gpc4, Pparγ, and adiponectin levels were upregulated in mesenteric WAT. These results suggest that some of the developmental genes tested may have fat depot-specific roles in the growth-dependent expansion of WAT, and that Hox genes that are activated in response to exercise training also vary among different WAT types.

A Transcriptional Circuit Filters Oscillating Circadian Hormonal Inputs to Regulate Fat Cell Differentiation

Glucocorticoid and other adipogenic hormones are secreted in mammals in circadian oscillations. Loss of this circadian oscillation pattern correlates with obesity in humans, raising the intriguing question of how hormone secretion dynamics affect adipocyte differentiation. Using live, single-cell imaging of the key adipogenic transcription factors CEBPB and PPARG, endogenously tagged with fluorescent proteins, we show that pulsatile circadian hormone stimuli are rejected by the adipocyte differentiation control system. In striking contrast, equally strong persistent signals trigger maximal differentiation. We identify the mechanism of how hormone oscillations are filtered as a combination of slow and fast positive feedback centered on PPARG. Furthermore, we confirm in mice that flattening of daily glucocorticoid oscillations significantly increases the mass of subcutaneous and visceral fat pads. Together, our study provides a molecular mechanism for why stress, Cushing's disease, and other conditions for which glucocorticoid secretion loses its pulsatility may lead to obesity.

Differential response of adipose tissue gene and protein expressions to 4- and 8-week administration of β-guanidinopropionic acid in mice

β-Guanidinopropionic acid (β-GPA) feeding inhibits growth-associated gain of body mass. It remains unknown, however, whether and how β-GPA feeding affects growth-associated increase in white adipose tissue (WAT) mass. We examined the effects of 4- and 8-week β-GPA feeding on serum myostatin levels and expression of genes and proteins related to adipogenesis, lipolysis, and liposynthesis in epididymal WAT (eWAT) and brown adipose tissue (BAT) in 3-week-old, juvenile male mice. Body, eWAT, and muscle weights were significantly lower in β-GPA-fed mice than in controls after feeding. Four- but not 8-week-β-GPA feeding increased the serum myostatin level. Incubation of C2C12 myotubes with β-GPA (1 mM) significantly promoted myostatin mRNA expression. The protein expression of peroxisome proliferator-activated receptor gamma coactivator 1 α (PGC-1α) and peroxisome proliferator-activated receptor α (PPARα) was up-regulated in GPAF eWAT at week 4, but down-regulated at week 8. There was no significant difference in the protein expression of adipocyte triglyceride lipase (ATGL), hormone-sensitive lipase (HSL), fatty acid synthase (FAS), and acetyl-CoA carboxylase (ACC) between groups in eWAT. In BAT, no significant difference was found in the protein expression of PGC-1α, PPARα, ATGL, and HSL between β-GPA-fed and control mice, whereas that of FAS and ACC was significantly lower in β-GPA-fed mice at week 8. Uncoupling protein 1 was expressed higher in β-GPA-fed mice both at weeks 4 and 8 than that in controls. Thus, the mechanism by which β-GPA feeding in early juvenile mice inhibits growth-associated increase in eWAT mass may differ between early and later periods of growth.

Preclinical In vivo Imaging for Fat Tissue Identification, Quantification, and Functional Characterization

Localization, differentiation, and quantitative assessment of fat tissues have always collected the interest of researchers. Nowadays, these topics are even more relevant as obesity (the excess of fat tissue) is considered a real pathology requiring in some cases pharmacological and surgical approaches. Several weight loss medications, acting either on the metabolism or on the central nervous system, are currently under preclinical or clinical investigation. Animal models of obesity have been developed and are widely used in pharmaceutical research. The assessment of candidate drugs in animal models requires non-invasive methods for longitudinal assessment of efficacy, the main outcome being the amount of body fat. Fat tissues can be either quantified in the entire animal or localized and measured in selected organs/regions of the body. Fat tissues are characterized by peculiar contrast in several imaging modalities as for example Magnetic Resonance Imaging (MRI) that can distinguish between fat and water protons thank to their different magnetic resonance properties. Since fat tissues have higher carbon/hydrogen content than other soft tissues and bones, they can be easily assessed by Computed Tomography (CT) as well. Interestingly, MRI also discriminates between white and brown adipose tissue (BAT); the latter has long been regarded as a potential target for anti-obesity drugs because of its ability to enhance energy consumption through increased thermogenesis. Positron Emission Tomography (PET) performed with 18F-FDG as glucose analog radiotracer reflects well the metabolic rate in body tissues and consequently is the technique of choice for studies of BAT metabolism. This review will focus on the main, non-invasive imaging techniques (MRI, CT, and PET) that are fundamental for the assessment, quantification and functional characterization of fat deposits in small laboratory animals. The contribution of optical techniques, which are currently regarded with increasing interest, will be also briefly described. For each technique the physical principles of signal detection will be overviewed and some relevant studies will be summarized. Far from being exhaustive, this review has the purpose to highlight some strategies that can be adopted for the in vivo identification, quantification, and functional characterization of adipose tissues mainly from the point of view of biophysics and physiology.

Vitamin D decreases adipocyte lipid storage and increases NAD-SIRT1 pathway in 3T3-L1 adipocytes

OBJECTIVE

Previous studies suggest that low vitamin D status is associated with obesity characterized by excess lipid storage in adipocytes. The aim of the present study was to determine the effects of the most hormonally active form of vitamin D 1,25-dihydroxyvitamin D [1,25(OH)2D] on adipocyte fat storage and lipid metabolism in mature 3T3-L1 cells.

METHODS

Differentiated 3T3-L1 cells were treated with various concentrations of 1,25(OH)2D. 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide cell proliferation, intracellular lipid content, and basal and isoproterenol-stimulated lipolysis were measured to investigate the regulatory role of 1,25(OH)2D in adipocyte lipid metabolism. Reverse transcription polymerase chain reaction was performed to determine the effects of 1,25(OH)2D on adipogenesis-related markers, fatty acid oxidation-associated genes, and lipolytic enzymes. Sirtulin 1 (SIRT1) activity, nicotinamide adenine dinucleotide (NAD) and NADH were measured.

RESULTS

1,25(OH)2D treatment (24 h, 100 nmol/L) induced a decrease in intracellular fat accumulation and an increase of basal and isoproterenol-stimulated lipolysis without cell toxicity in adipocytes. Adipogenic gene levels were decreased. In contrast, mRNA levels of β-oxidation-related genes, lipolytic enzymes, and vitamin D responsive gene were elevated by 1,25(OH)2D. Additionally, significant incremental changes in NAD levels, the ratio of NAD to NADH, and SIRT1 expression and activity were noted in 1,25(OH)2D-treated 3T3-L1 adipocytes.

CONCLUSIONS

The observed potent inhibitory effect of 1,25(OH)2D on adipocyte fat storage in mature 3T3-L1 cells suggests that vitamin D might improve adipocyte metabolic function and protect against obesity. Increased NAD concentrations and SIRT1 ​activity may play a role in the mechanism of 1,25(OH)2D action.

Inflammation and the depot-specific secretome of human preadipocytes

OBJECTIVE

Visceral white adipose tissue (WAT) expansion and macrophage accumulation are associated with metabolic dysfunction. Visceral WAT typically shows greater macrophage infiltration. Preadipocytes show varying proinflammatory expression profiles among WAT depots. The objective was to examine the secretomes and chemoattractive properties of preadipocytes from visceral and subcutaneous WAT.

METHODS

A label-free quantitative proteomics approach was applied to study secretomes of subcutaneous and omental preadipocytes from obese subjects. Enzyme-linked immunosorbent assays and chemotaxis assays were used to confirm proinflammatory chemokine secretion between depots.

RESULTS

Preadipocyte secretomes showed greater variation between depots than did intracellular protein expression. Chemokines were the most differentially secreted proteins. Omental preadipocytes induced chemoattraction of macrophages and monocytes. Neutralizing antibodies to the identified chemokines reduced macrophage/monocyte chemoattraction. Subcutaneous preadipocytes treated with interleukin-6 (IL-6) resembled omental preadipocytes in terms of chemokine secretion and macrophage/monocyte chemoattraction. Janus-activated kinase (JAK1/2) protein expression, which transduces IL-6 signaling, was higher in omental than subcutaneous preadipocytes and WAT. Inhibiting JAK in omental preadipocytes decreased chemokine secretion and macrophage/monocyte chemoattraction to levels closer to that observed in subcutaneous preadipocytes.

CONCLUSIONS

Secretomes of omental and subcutaneous preadipocytes are distinct, with the former inducing more macrophage/monocyte chemoattraction, in part through IL-6/JAK-mediated signaling.

Secretion of adipocytes and macrophages under conditions of inflammation and/or insulin resistance and effect of adipocytes on preadipocytes under these conditions

The purpose of the present study was to examine changes in preadipocytes following the coculture of preadipocytes and adipocytes and the effects on the secretion of adipocytes and macrophages following induction of inflammation and insulin resistance. Mature adipocytes and RAW264.7 macrophages were treated with lipopolysaccharide and insulin to establish models of inflammation and insulin resistance, respectively. The mRNA expression levels of IL-6, MCP-1, and TNF-α in all adipocyte treatment groups were significantly greater compared with the control, and that of adiponectin was less (P<0.05). In the RAW264.7 macrophages, the mRNA expression levels of IL-6 and TNF-α were greater than those in the control group (P<0.05). Moreover, the results of this study confirmed that adipocytes and macrophages increased the secretion of inflammatory factors under conditions of induced inflammation and insulin resistance. In addition, 3T3-L1 adipocytes inhibited the proliferation and differentiation of preadipocytes when cocultured with adipocytes under conditions of inflammation and/or insulin resistance, and the phenotype of preadipocytes did not change.

Using SRM-MS to quantify nuclear protein abundance differences between adipose tissue depots of insulin-resistant mice

Insulin resistance (IR) underlies metabolic disease. Visceral, but not subcutaneous, white adipose tissue (WAT) has been linked to the development of IR, potentially due to differences in regulatory protein abundance. Here we investigate how protein levels are changed in IR in different WAT depots by developing a targeted proteomics approach to quantitatively compare the abundance of 42 nuclear proteins in subcutaneous and visceral WAT from a commonly used insulin-resistant mouse model, Lepr(db/db), and from C57BL/6J control mice. The most differentially expressed proteins were important in adipogenesis, as confirmed by siRNA-mediated depletion experiments, suggesting a defect in adipogenesis in visceral, but not subcutaneous, insulin-resistant WAT. Furthermore, differentiation of visceral, but not subcutaneous, insulin-resistant stromal vascular cells (SVCs) was impaired. In an in vitro approach to understand the cause of this impaired differentiation, we compared insulin-resistant visceral SVCs to preadipocyte cell culture models made insulin resistant by different stimuli. The insulin-resistant visceral SVC protein abundance profile correlated most with preadipocyte cell culture cells treated with both palmitate and TNFα. Together, our study introduces a method to simultaneously measure and quantitatively compare nuclear protein expression patterns in primary adipose tissue and adipocyte cell cultures, which we show can reveal relationships between differentiation and disease states of different adipocyte tissue types.

Cell-autonomous heterogeneity of nutrient uptake in white adipose tissue of rhesus macaques

Phenotypic diversity may play an adaptive role by providing graded biological responses to fluctuations in environmental stimuli. We used single-cell imaging of the metabolizable fluorescent fatty acid analog 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY)-C12 and fluorescent 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl) amino]-2-deoxy-D-glucose (2-NBDG) to explore cellular heterogeneity in nutrient uptake in white adipose tissue (WAT) explants of rhesus macaques. Surprisingly, WAT displayed a striking cell size-independent mosaic pattern, in that adjacent adipocytes varied with respect to insulin-stimulated BODIPY-C12 and 2-NBDG uptake. Relative free fatty acid (FFA) transport activity correlated with the cellular levels of FFA transporter protein-1 and the scavenger receptor CD36 in individual adipocytes. In vitro incubation of WAT explants for 24 hours caused partial desynchronization of cellular responses, suggesting that adipocytes may slowly alter their differential nutrient uptake activity. In vitro-differentiated human adipocytes also exhibited a mosaic pattern of BODIPY-C12 uptake. WAT from animals containing a homogeneous population of large adipocytes was nonmosaic, in that every adipocyte exhibited a similar level of BODIPY-C12 fluorescence, suggesting that the development of obesity is associated with the loss of heterogeneity in WAT. Hence, for the first time, we demonstrate an intrinsic heterogeneity in FFA and glucose transport activity in WAT.

Maintenance of white adipose tissue in man

Obesity is increasing in an epidemic manner in most countries and constitutes a public health problem by enhancing the risk for diseases such as diabetes, fatty liver disease and atherosclerosis. Together these diseases form a cluster referred to as the metabolic syndrome. Despite the negative health consequences associated with excess adipose tissue, very little is known about the origin and maintenance of white adipose tissue in man. In this review we discuss what is known about the turnover of adult human adipocytes and their precursors, as well as adipose tissue heterogeneity, plasticity and developmental origins. The focus of this review is human tissue, however in many cases human data are missing and are inferred from animal studies. As such, reference to animal studies are made where human data is not available. This article is part of a directed issue entitled: Regenerative Medicine: the challenge of translation.

Controlling low rates of cell differentiation through noise and ultrahigh feedback

Mammalian tissue size is maintained by slow replacement of de-differentiating and dying cells. For adipocytes, key regulators of glucose and lipid metabolism, the renewal rate is only 10% per year. We used computational modeling, quantitative mass spectrometry, and single-cell microscopy to show that cell-to-cell variability, or noise, in protein abundance acts within a network of more than six positive feedbacks to permit pre-adipocytes to differentiate at very low rates. This reconciles two fundamental opposing requirements: High cell-to-cell signal variability is needed to generate very low differentiation rates, whereas low signal variability is needed to prevent differentiated cells from de-differentiating. Higher eukaryotes can thus control low rates of near irreversible cell fate decisions through a balancing act between noise and ultrahigh feedback connectivity.

Adipose tissue: cell heterogeneity and functional diversity

There are two types of adipose tissue in the body whose function appears to be clearly differentiated. White adipose tissue stores energy reserves as fat, whereas the metabolic function of brown adipose tissue is lipid oxidation to produce heat. A good balance between them is important to maintain energy homeostasis. The concept of white adipose tissue has radically changed in the past decades, and is now considered as an endocrine organ that secretes many factors with autocrine, paracrine, and endocrine functions. In addition, we can no longer consider white adipose tissue as a single tissue, because it shows different metabolic profiles in its different locations, with also different implications. Although the characteristic cell of adipose tissue is the adipocyte, this is not the only cell type present in adipose tissue, neither the most abundant. Other cell types in adipose tissue described include stem cells, preadipocytes, macrophages, neutrophils, lymphocytes, and endothelial cells. The balance between these different cell types and their expression profile is closely related to maintenance of energy homeostasis. Increases in adipocyte size, number and type of lymphocytes, and infiltrated macrophages are closely related to the metabolic syndrome diseases. The study of regulation of proliferation and differentiation of preadipocytes and stem cells, and understanding of the interrelationship between the different cell types will provide new targets for action against these diseases.

miR-133a regulates adipocyte browning in vivo

Prdm16 determines the bidirectional fate switch of skeletal muscle/brown adipose tissue (BAT) and regulates the thermogenic gene program of subcutaneous white adipose tissue (SAT) in mice. Here we show that miR-133a, a microRNA that is expressed in both BAT and SATs, directly targets the 3′ UTR of Prdm16. The expression of miR-133a dramatically decreases along the commitment and differentiation of brown preadipocytes, accompanied by the upregulation of Prdm16. Overexpression of miR-133a in BAT and SAT cells significantly inhibits, and conversely inhibition of miR-133a upregulates, Prdm16 and brown adipogenesis. More importantly, double knockout of miR-133a1 and miR-133a2 in mice leads to elevations of the brown and thermogenic gene programs in SAT. Even 75% deletion of miR-133a (a1^−/−a2^+/−) genes results in browning of SAT, manifested by the appearance of numerous multilocular UCP1-expressing adipocytes within SAT. Additionally, compared to wildtype mice, miR-133a1^−/−a2^+/− mice exhibit increased insulin sensitivity and glucose tolerance, and activate the thermogenic gene program more robustly upon cold exposure. These results together elucidate a crucial role of miR-133a in the regulation of adipocyte browning in vivo.

Global obesity and associated health issues have raised the significance of adipocyte biology. Adipose tissues are classified as brown and white adipose. White adipose tissues store lipids, leading to overweight, obesity, insulin resistance and Type2 diabetes. In contrast, brown adipose tissues use lipid storage to generate heat, increase insulin sensitivity, and are negatively correlated with the incidence of Type2 diabetes. Recent studies indicate that white adipose is plastic and contains an intermediate type of adaptive adipocytes (so-called beige/brite adipocytes) that have the energy-dissipating properties of brown adipocytes. Prdm16 is a key molecule that determines the development of both brown and beige adipocytes. Thus, Prdm16 represents a novel molecular switch that expands brown/beige adipocytes and increases energy expenditures. However, how Prdm16 is regulated has been unclear. Here we report that the microRNA miR-133a specifically targets Prdm16 at the posttranscriptional level. Inhibition or knockout of miR-133a significantly increases Prdm16 expression and the thermogenic gene program in white adipose tissues, resulting in dramatically enhanced insulin sensitivity in animals. Our results suggest that miR-133a represents a potential drug target against obesity and Type2 diabetes.

Adipose tissue: cell heterogeneity and functional diversity

There are two types of adipose tissue in the body whose function appears to be clearly differentiated. White adipose tissue stores energy reserves as fat, whereas the metabolic function of brown adipose tissue is lipid oxidation to produce heat. A good balance between them is important to maintain energy homeostasis. The concept of white adipose tissue has radically changed in the past decades, and is now considered as an endocrine organ that secretes many factors with autocrine, paracrine, and endocrine functions. In addition, we can no longer consider white adipose tissue as a single tissue, because it shows different metabolic profiles in its different locations, with also different implications. Although the characteristic cell of adipose tissue is the adipocyte, this is not the only cell type present in adipose tissue, neither the most abundant. Other cell types in adipose tissue described include stem cells, preadipocytes, macrophages, neutrophils, lymphocytes, and endothelial cells. The balance between these different cell types and their expression profile is closely related to maintenance of energy homeostasis. Increases in adipocyte size, number and type of lymphocytes, and infiltrated macrophages are closely related to the metabolic syndrome diseases. The study of regulation of proliferation and differentiation of preadipocytes and stem cells, and understanding of the interrelationship between the different cell types will provide new targets for action against these diseases.

Synergism of α-linolenic acid, conjugated linoleic acid and calcium in decreasing adipocyte and increasing osteoblast cell growth

Whole fat milk and dairy products (although providing more energy compared to low- or non-fat products), are good sources of α-linolenic acid (ALA), conjugated linoleic acid (CLA) and calcium, which may be favorable in modulating bone and adipose tissue metabolism. We examined individual and/or synergistic effects of ALA, CLA and calcium (at levels similar to those in whole milk/dairy products) in regulating bone and adipose cell growth. ST2 stromal, MC3T3-L1 adipocyte-like and MC3T3-E1 osteoblast-like cells were treated with: (a) linoleic acid (LNA):ALA ratios = 1-5:1; (b) individual/combined 80-90 % c9, t11 (9,11) and 5-10 % t10, c12 (10,12) CLA isomers; (c) 0.5-3.0 mM calcium; (d) combinations of (a), (b), (c); and (e) control. Local mediators, including eicosanoids and growth factors, were measured. (a) The optimal effect was found at the 4:1 LNA:ALA ratio where insulin-like growth factor-1 (IGF-1) and IGF binding protein-3 (IGFBP-3) production was the lowest in MC3T3-L1 cells. (b) All CLA isomer blends decreased MC3T3-L1 and increased MC3T3-E1 cell differentiation. (c) 1.5-2.5 mM calcium increased ST2 and MC3T3-E1, and decreased MC3T3-L1 cell proliferation. (d) Combination of 4:1 LNA:ALA + 90:10 % CLA + 2.0 mM calcium lowered MC3T3-L1 and increased MC3T3-E1 cell differentiation. Overall, the optimal LNA:ALA ratio to enhance osteoblastogenesis and inhibit adipogenesis was 4:1. This effect was enhanced by 90:10 % CLA + 2.0 mM calcium, indicating possible synergism of these dietary factors in promoting osteoblast and inhibiting adipocyte differentiation in cell cultures.

Pathophysiology of human visceral obesity: an update

Excess intra-abdominal adipose tissue accumulation, often termed visceral obesity, is part of a phenotype including dysfunctional subcutaneous adipose tissue expansion and ectopic triglyceride storage closely related to clustering cardiometabolic risk factors. Hypertriglyceridemia; increased free fatty acid availability; adipose tissue release of proinflammatory cytokines; liver insulin resistance and inflammation; increased liver VLDL synthesis and secretion; reduced clearance of triglyceride-rich lipoproteins; presence of small, dense LDL particles; and reduced HDL cholesterol levels are among the many metabolic alterations closely related to this condition. Age, gender, genetics, and ethnicity are broad etiological factors contributing to variation in visceral adipose tissue accumulation. Specific mechanisms responsible for proportionally increased visceral fat storage when facing positive energy balance and weight gain may involve sex hormones, local cortisol production in abdominal adipose tissues, endocannabinoids, growth hormone, and dietary fructose. Physiological characteristics of abdominal adipose tissues such as adipocyte size and number, lipolytic responsiveness, lipid storage capacity, and inflammatory cytokine production are significant correlates and even possible determinants of the increased cardiometabolic risk associated with visceral obesity. Thiazolidinediones, estrogen replacement in postmenopausal women, and testosterone replacement in androgen-deficient men have been shown to favorably modulate body fat distribution and cardiometabolic risk to various degrees. However, some of these therapies must now be considered in the context of their serious side effects. Lifestyle interventions leading to weight loss generally induce preferential mobilization of visceral fat. In clinical practice, measuring waist circumference in addition to the body mass index could be helpful for the identification and management of a subgroup of overweight or obese patients at high cardiometabolic risk.

Fatty acid binding protein 4 expression marks a population of adipocyte progenitors in white and brown adipose tissues

Adipose tissues regulate metabolism, reproduction, and life span. The development and growth of adipose tissue are due to increases of both adipocyte cell size and cell number; the latter is mediated by adipocyte progenitors. Various markers have been used to identify either adipocyte progenitors or mature adipocytes. The fatty acid binding protein 4 (FABP4), commonly known as adipocyte protein 2 (aP2), has been extensively used as a marker for differentiated adipocytes. However, whether aP2 is expressed in adipogenic progenitors is controversial. Using Cre/LoxP-based cell lineage tracing in mice, we have identified a population of aP2-expressing progenitors in the stromal vascular fraction (SVF) of both white and brown adipose tissues. The aP2-lineage progenitors reside in the adipose stem cell niche and express adipocyte progenitor markers, including CD34, Sca1, Dlk1, and PDGFRα. When isolated and grown in culture, the aP2-expressing SVF cells proliferate and differentiate into adipocytes upon induction. Conversely, ablation of the aP2 lineage greatly reduces the adipogenic potential of SVF cells. When grafted into wild-type mice, the aP2-lineage progenitors give rise to adipose depots in recipient mice. Therefore, the expression of aP2 is not limited to mature adipocytes, but also marks a pool of undifferentiated progenitors associated with the vasculature of adipose tissues. Our finding adds to the repertoire of adipose progenitor markers and points to a new regulator of adipose plasticity.

In vivo adipogenesis in rats measured by cell kinetics in adipocytes and plastic-adherent stroma-vascular cells in response to high-fat diet and thiazolidinedione

Impairment of adipogenesis contributes to the development of obesity-related insulin resistance. The current in vitro approaches for its assessment represent crude estimates of the adipogenic potential because of the disruption of the in vivo microenvironment. A novel assessment of in vivo adipogenesis using the incorporation of the stable isotope deuterium ((2)H) into the DNA of isolated adipocytes and stroma-vascular fraction from adipose tissue has been developed. In the current study, we have refined this technique by purifying the adipocytes via a negative immune selection and sorting the plastic adherent stroma-vascular (aSV) subfraction (using 3 h culture) that contains mostly adipocyte progenitor cells and ∼10% of small adipocytes. Using a 3-week 8% (2)H(2)O ingestion with a high-fat diet (HFD) or HFD plus pioglitazone (HFD-P), we demonstrate that the fractions of new aSV cells (f(aSV)) and immunopurified adipocytes (f(AD)) (the ratio of their (2)H-enrichment of DNA to the maximal (2)H-enrichment of DNA of bone marrow reference cells) recapitulate the known hyperplastic mechanism of weight gain with pioglitazone treatment. We conclude that f(aSV) and f(AD) are reliable indices of in vivo adipogenesis. The proposed method represents a valuable tool for studying the effect of interventions (drugs, diets, and exercise) on in vivo adipogenesis.

Intramuscular adipose is derived from a non-Pax3 lineage and required for efficient regeneration of skeletal muscles

Ectopic accumulation of adipose in the skeletal muscle is associated with muscle wasting, insulin resistance and diabetes. However, the developmental origin of postnatal intramuscular adipose and its interaction with muscle tissue are unclear. We report here that compared to the fast EDL muscles, slow SOL muscles are more enriched with adipogenic progenitors and have higher propensity to form adipose. Using Cre/LoxP mediated lineage tracing in mice, we show that intramuscular adipose in both EDL and SOL muscles is exclusively derived from a Pax3(-) non-myogenic lineage. In contrast, inter-scapular brown adipose is derived from the Pax3(+) lineage. To dissect the interaction between adipose and skeletal muscle tissues, we used Myf5-Cre and aP2-Cre mice in combination with ROSA26-iDTR mice to genetically ablate myogenic and adipogenic cell lineages, respectively. Whereas ablation of the myogenic cell lineage facilitated adipogenic differentiation, ablation of the adipogenic cell lineage surprisingly impaired the regeneration of acutely injured skeletal muscles. These results reveal striking heterogeneity of tissue-specific adipose and a previously unappreciated role of intramuscular adipose in skeletal muscle regeneration.

Minireview: PPARγ as the target of obesogens

The peroxisome proliferator-activated receptor gamma (PPARγ) is a key regulator of adipogenesis and is medically important for its connections to obesity and the treatment of type II diabetes. Activation of this receptor by certain natural or xenobiotic compounds has been shown to stimulate adipogenesis in vitro and in vivo. Obesogens are chemicals that ultimately increase obesity through a variety of potential mechanisms, including activation of PPARγ. The first obesogen for which a definitive mechanism of action has been elucidated is the PPARγ and RXR activator tributyltin; however, not all chemicals that activate PPARγ are adipogenic or correlated with obesity in humans. There are multiple mechanisms through which obesogens can target PPARγ that may not involve direct activation of the receptor. Ligand-independent mechanisms could act through obesogen-mediated post-translational modification of PPARγ which cause receptor de-repression or activation. PPARγ is active in multipotent stem cells committing to the adipocyte fate during fat cell development. By modifying chromatin structure early in development, obesogens have the opportunity to influence the promoter activity of PPARγ, or the ability of PPARγ to bind to its target genes, ultimately biasing the progenitor pool towards the fat lineage. Obesogens that act by directly or indirectly activating PPARγ, by increasing the levels of PPARγ protein, or enhancing its recruitment to promoters of key genes in the adipogenic pathway may ultimately play an important role in adipogenesis and obesity.

Storage of circulating free fatty acid in adipose tissue of postabsorptive humans: quantitative measures and implications for body fat distribution

OBJECTIVE

Preferential upper-body fat gain, a typical male pattern, is associated with a greater cardiometabolic risk. Regional differences in lipolysis and meal fat storage cannot explain sex differences in body fat distribution. We examined the potential role of the novel free fatty acid (FFA) storage pathway in determining body fat distribution in postabsorptive humans and whether adipocyte lipogenic proteins (CD36, acyl-CoA synthetases, and diacylglycerol acyltransferase) predict differences in FFA storage.

RESEARCH DESIGN AND METHODS

Rates of postabsorptive FFA (palmitate) storage into upper-body subcutaneous (UBSQ) and lower-body subcutaneous (LBSQ) fat were measured in 28 men and 53 premenopausal women. Stable and radiolabeled palmitate tracers were intravenously infused followed by subcutaneous fat biopsies. Body composition was assessed with a combination of dual-energy X-ray absorptiometry and computed tomography.

RESULTS

Women had greater FFA (palmitate) storage than men in both UBSQ (0.37 ± 0.15 vs. 0.27 ± 0.18 μmol · kg(-1) · min(-1), P = 0.0001) and LBSQ (0.42 ± 0.19 vs. 0.22 ± 0.11 μmol · kg(-1) · min(-1), P < 0.0001) fat. Palmitate storage rates were significantly greater in LBSQ than UBSQ fat in women, whereas the opposite was true in men. Plasma palmitate concentration positively predicted palmitate storage in both depots and sexes. Adipocyte CD36 content predicted UBSQ palmitate storage and sex-predicted storage in LBSQ fat. Palmitate storage rates per kilogram fat did not decrease as a function of fat mass, whereas lipolysis did.

CONCLUSIONS

The FFA storage pathway, which had remained undetected in postabsorptive humans until recently, can have considerable, long-term, and sex-specific effects on body fat distribution. It can also offer a way of protecting the body from excessive circulating FFA in obesity.

Sex- and depot-dependent differences in adipogenesis in normal-weight humans

To elucidate cellular mechanisms of sex-related differences in fat distribution, we determined body fat distribution (dual-energy X-ray absorptiometry and single-slice abdominal computed tomography (CT)), adipocyte size, adipocyte number, and proportion of early-differentiated adipocytes (aP2(+)CD68(-)) in the stromovascular fraction (SVF) in the upper and lower body of normal-weight healthy men (n = 12) and premenopausal women (n = 20) (age: 18-49 years, BMI: 18-26 kg/m(2)). Women had more subcutaneous and less visceral fat than men. The proportion of early differentiated adipocytes in the subcutaneous adipose tissue SVF of women was greater than in men (P = 0.01), especially in the femoral depot, although in vitro adipogenesis, as assessed by peroxisome proliferator activated receptor-γ (PPARγ) expression, was not increased in femoral preadipocytes cultured from women compared with men. In women, differentiation of femoral preadipocytes was less than that of abdominal subcutaneous preadipocytes (P = 0.04), and femoral subcutaneous preadipocytes tended to be more resistant to tumor necrosis factor-α (TNFα)-induced apoptosis (P = 0.06). Thus, turnover and utilization of the preadipocyte pool may be reduced in lower vs. the upper-body fat in women. Collectively, these data indicate that the microenvironment, rather than differences in inherent properties of preadipocytes between genders, may explain the gynoid obesity phenotype and higher percent body fat in women compared to men.

n-6 Fatty acids and cardiovascular health: a review of the evidence for dietary intake recommendations

n-6 PUFA are well known for their critical role in many physiological functions and seem to reduce risks of CHD. However, some argue that excessive consumption of n-6 PUFA may lead to adverse effects on health and therefore recommend reducing dietary n-6 PUFA intake or fixing an upper limit. In this context, the present work aimed to review evidence on the link between n-6 PUFA and risks of CVD. Epidemiological studies show that n-6 PUFA dietary intake significantly lowers blood LDL-cholesterol levels. In addition, n-6 PUFA intake does not increase several CVD risk factors such as blood pressure, inflammatory markers, haemostatic parameters and obesity. Data from prospective cohort and interventional studies converge towards a specific protective role of dietary n-6 PUFA intake, in particular linoleic acid, against CVD. n-6 PUFA benefits are even increased when SFA intake is also reduced. In regards to studies examined in this narrative review, recommendation for n-6 PUFA intake above 5 %, and ideally about 10 %, of total energy appears justified.

Prenatal exposure to the environmental obesogen tributyltin predisposes multipotent stem cells to become adipocytes

The environmental obesogen hypothesis proposes that pre- and postnatal exposure to environmental chemicals contributes to adipogenesis and the development of obesity. Tributyltin (TBT) is an agonist of both retinoid X receptor (RXR) and peroxisome proliferator-activated receptor gamma (PPARgamma). Activation of these receptors can elevate adipose mass in adult mice exposed to the chemical in utero. Here we show that TBT sensitizes human and mouse multipotent stromal stem cells derived from white adipose tissue [adipose-derived stromal stem cells (ADSCs)] to undergo adipogenesis. In vitro exposure to TBT, or the PPARgamma activator rosiglitazone increases adipogenesis, cellular lipid content, and expression of adipogenic genes. The adipogenic effects of TBT and rosiglitazone were blocked by the addition of PPARgamma antagonists, suggesting that activation of PPARgamma mediates the effect of both compounds on adipogenesis. ADSCs from mice exposed to TBT in utero showed increased adipogenic capacity and reduced osteogenic capacity with enhanced lipid accumulation in response to adipogenic induction. ADSCs retrieved from animals exposed to TBT in utero showed increased expression of PPARgamma target genes such as the early adipogenic differentiation gene marker fatty acid-binding protein 4 and hypomethylation of the promoter/enhancer region of the fatty acid-binding protein 4 locus. Hence, TBT alters the stem cell compartment by sensitizing multipotent stromal stem cells to differentiate into adipocytes, an effect that could likely increase adipose mass over time.

Adipose tissue, inflammation and atherosclerosis

Metabolic syndrome is associated with dysfunctional adipose tissue that is most likely a consequence of the enlargement of adipocytes and infiltration of macrophages into adipose tissue. Obesity and ectopic lipid deposition are major risk factors for diseases ranging from insulin resistance to type 2 diabetes and atherosclerosis. Enlargement of adipocytes, due to impaired adipocyte differentiation, leads to a chronic state of inflammation in the adipocytes and adipose tissue with a reduction in the secretion of adiponectin and increase in the secretion of proinflammatory cytokines such as interleukin (IL)-6, IL-8 and monocyte chemoattractant protein (MCP)-1. The secretion of cytokines like tumour necrosis factor (TNF)- alpha, mainly from macrophages, enhances local inflammation. These proinflammatory cytokines might also substantially affect cardiovascular function and morphology. Furthermore, a proinflammatory state in adipose tissue can lead to local insulin resistance with an impaired inhibitory effect of insulin on the release of FFAs and endothelial dysfunction that clearly promotes cardiovascular diseases and type 2 diabetes. The underlying mechanisms of ectopic fat accumulation in various tissues and the impact on metabolic syndrome and its association with insulin resistance are discussed.

Role of WNT-5a in the determination of human mesenchymal stem cells into preadipocytes

Increasing adipocyte size as well as numbers is important in the development of obesity and type 2 diabetes, with adipocytes being generated from mesenchymal precursor cells. This process includes the determination of mesenchymal stem cells (MSC) into preadipocytes (PA) and the differentiation of PA into mature fat cells. Although the process of differentiation has been highly investigated, the determination in humans is poorly understood. In this study, we compared human MSC and human committed PA on a cellular and molecular level to gain further insights into the regulatory mechanisms in the determination process. Both cell types showed similar morphology and expression patterns of common mesenchymal and hematopoietic surface markers. However, although MSC were able to differentiate into adipocytes and osteocytes, PA were only able to undergo adipogenesis, indicating that PA lost their multipotency during determination. WNT-5a expression showed significantly higher levels in MSC compared with PA suggesting that WNT-5a down-regulation might be important in the determination process. Indeed, incubation of human MSC in medium containing neutralizing WNT-5a antibodies abolished their ability to undergo osteogenesis, although adipogenesis was still possible. An opposite effect was achieved using recombinant WNT-5a protein. On a molecular level, WNT-5a was found to promote c-Jun N-terminal kinase-dependent intracellular signaling in MSC. Activation of this noncanonical pathway resulted in the induction of osteopontin expression further indicating pro-osteogenic effects of WNT-5a. Our data suggest that WNT-5a is necessary to maintain osteogenic potential of MSC and that inhibition of WNT-5a signaling therefore plays a role in their determination into PA in humans.

Forced catch-up growth after fetal protein restriction alters the adipose tissue gene expression program leading to obesity in adult mice

A mismatch between fetal and postnatal environment can permanently alter the body structure and physiology and therefore contribute later to obesity and related disorders, as revealed by epidemiological studies. Early programming of adipose tissue might be central in this observation. Moreover, adipose tissue secretes adipokines that provide a molecular link between obesity and its related disorders. Therefore, our aim was to investigate whether a protein restriction during fetal life, followed by catch-up growth could lead to obesity in 9-mo-old male mice and could alter the adipose tissue gene expression profile. Dams were fed a low-protein (LP) or an isocaloric control (C) diet during gestation. Postnatal catch-up growth was induced in LP offspring by feeding dams with control diet and by culling LP litters to four pups instead of eight in the C group. At weaning, male mice were fed by lab chow alone (C) or supplemented with a hypercaloric diet (HC), to induce obesity (C-C, C-HC, LP-C, and LP-HC groups). At 9 mo, LP offspring featured increased relative fat mass, hyperglycemia, hypercholesterolemia, and hyperleptinemia. Using a microarray designed to study the expression of 89 genes involved in adipose tissue differentiation/function, we demonstrated that the expression profile of several genes were dependent upon the maternal diet. Among the diverse genes showing altered expression, we could identify genes encoding several enzymes involved in lipid metabolism. These results indicated that offspring submitted to early mismatched nutrition exhibited alterations in adipose tissue gene expression that probably increases their susceptibility to overweight when challenged after weaning with a HC diet.

Adipose-specific disruption of signal transducer and activator of transcription 3 increases body weight and adiposity

To determine the role of STAT3 in adipose tissue, we used Cre-loxP DNA recombination to create mice with an adipocyte-specific disruption of the STAT3 gene (ASKO mice). aP2-Cre-driven disappearance of STAT3 expression occurred on d 6 of adipogenesis, a time point when preadipocytes have already undergone conversion to adipocytes. Thus, this knockout model examined the role of STAT3 in mature but not differentiating adipocytes. Beginning at 9 wk of age, ASKO mice weighed more than their littermate controls and had increased adipose tissue mass, associated with adipocyte hypertrophy, but not adipocyte hyperplasia, hyperphagia, or reduced energy expenditure. Leptin-induced, but not isoproterenol-induced, lipolysis was impaired in ASKO adipocytes, which may partially explain the increased cell size. Despite reduced adiponectin and increased liver triacylglycerol, ASKO mice displayed normal glucose tolerance. Overall, these findings demonstrate that adipocyte STAT3 regulates body weight homeostasis in part through direct effects of leptin on adipocytes.

Chromatin and chromatin-modifying proteins in adipogenesis

Long considered scarcely more than an uninteresting energy depot, adipose tissue has recently achieved star status. Far from being mere fat droplets, the adipocytes secrete a number of hormones and bioactive peptides, collectively known as adipokines, which participate in the regulation of a variety of functions, from haemostasis to angiogenesis to energy balance. Adipose tissue constitutes a bona-fide endocrine organ whose main dysfunctions, obesity and lipodystrophy, are related to the development of diabetes, hypertension, or dyslipidemia. The renewed interest in this tissue has prompted an escalation in the number of studies focusing on every aspect of the biology of the adipose cell, in the belief that a detailed knowledge of the mechanisms involved in the differentiation and function of adipocytes may contribute new therapeutical approaches to the treatment of such alarming medical problems. Adipogenesis is the result of an intertwined network of transcription factors and coregulators with chromatin-modifying activities that together, are responsible for the establishment of the gene expression pattern of mature adipocytes. Although the exquisitely regulated transcription factor cascade controlling adipogenesis has been extensively studied, the role of chromatin and chromatin-modifying proteins has become apparent only in recent times.

Adipogenic human adenovirus Ad-36 induces commitment, differentiation, and lipid accumulation in human adipose-derived stem cells

Human adenovirus Ad-36 is causatively and correlatively linked with animal and human obesity, respectively. Ad-36 enhances differentiation of rodent preadipocytes, but its effect on adipogenesis in humans is unknown. To indirectly assess the role of Ad-36-induced adipogenesis in human obesity, the effect of the virus on commitment, differentiation, and lipid accumulation was investigated in vitro in primary human adipose-derived stem/stromal cells (hASC). Ad-36 infected hASC in a time- and dose-dependent manner. Even in the presence of osteogenic media, Ad-36-infected hASC showed significantly greater lipid accumulation, suggestive of their commitment to the adipocyte lineage. Even in the absence of adipogenic inducers, Ad-36 significantly increased hASC differentiation, as indicated by a time-dependent expression of genes within the adipogenic cascade-CCAAT/Enhancer binding protein-beta, peroxisome proliferator-activated receptor-gamma, and fatty acid-binding protein-and consequentially increased lipid accumulation in a time- and viral dose-dependent manner. Induction of hASC to the adipocyte state by Ad-36 was further supported by increased expression of lipoprotein lipase and the accumulation of its extracellular fraction. hASC from subjects harboring Ad-36 DNA in their adipose tissue due to natural infection had significantly greater ability to differentiate compared with Ad-36 DNA-negative counterparts, which offers a proof of concept. Thus, Ad-36 has the potential to induce adipogenesis in hASC, which may contribute to adiposity induced by the virus.