Role In Adipose Tissue Function Research Articles

A MDM2 inhibitor MX69 inhibits adipocytes adipogenesis and differentiation

Adipose tissue, a key regulator of systemic energy homeostasis, can synthesize and store triglycerides to meet long-term energy demands. In response to nutrient overload, adipose tissue expands by hypertrophy or hyperplasia. As an oncogene, MDM2 has exerted diverse biological activities including human development, tissue regeneration, and inflammation, in addition to major oncogenic activities. Recently, some studies indicated that MDM2 plays an important role in adipose tissue function. However, the role of MX69, a MDM2 inhibitor, in adipose tissue function has not been fully elucidated. Here, we administered MX69 intraperitoneally to high-fat diet-induced obesity (DIO) wild type C57BL/6 mice and found that MX69 could promote the body weight and white adipose tissue weight of DIO mice. Moreover, MX69 had no effects on glucose tolerance and insulin sensitivity in DIO mice. And MX69 treatment decreased the size of adipocytes and fat deposition in adipose tissue and inhibited 3T3-L1 preadipocytes differentiation. Mechanistically, MX69 inhibited the protein levels of MDM2 and the mRNA levels of genes related to adipogenesis and differentiation. In summary, our results indicated that MDM2 has a crucial and complex role in regulating adipose tissue function.

Metabolically Healthy Obesity: Criteria, Epidemiology, Controversies, and Consequences.

To present a comprehensive overview regarding criteria, epidemiology, and controversies that have arisen in the literature about the existence and the natural course of the metabolic healthy phenotype. The concept of metabolically healthy obesity (MHO) implies that a subgroup of obese individuals may be free of the cardio-metabolic risk factors that commonly accompany obese subjects with adipose tissue dysfunction and insulin resistance, known as having metabolic syndrome or the metabolically unhealthy obesity (MUO) phenotype. Individuals with MHO appear to have a better adipose tissue function, and are more insulin sensitive, emphasizing the central role of adipose tissue function in metabolic health. The reported prevalence of MHO varies widely, and this is likely due the lack of universally accepted criteria for the definition of metabolic health and obesity. Also, the natural course and the prognostic value of MHO is hotly debated but it appears that it likely evolves towards MUO, carrying an increased risk for cardiovascular disease and mortality over time. Understanding the pathophysiology and the determinants of metabolic health in obesity will allow a better definition of the MHO phenotype. Furthermore, stratification of obese subjects, based on metabolic health status, will be useful to identify high-risk individuals or subgroups and to optimize prevention and treatment strategies to compact cardio-metabolic diseases.

Toward noninvasive quantification of adipose tissue oxygenation with MRI.

Molecular oxygen (O2) plays a key role in normal and pathological adipose tissue function, yet technologies to measure its role in adipose tissue function are limited. O2 is paramagnetic and, in principle, directly influences the magnetic resonance (MR) 1H longitudinal relaxation rate constant of lipids, R1; thus, we hypothesize that MR imaging (MRI) can directly measure adipose O2 via a simple measure of R1. R1 was measured in a 4.7T preclinical MRI system at discrete oxygen partial pressure (pO2) levels. These measures were made in vitro in an idealized system and in vivo in subcutaneous and visceral white adipose of rodents. pO2 was determined using an invasive fiber-optic oxygen monitor. From the MRI and fiber optic data we determined the "relaxivity" of O2 in lipid, a critical parameter in converting the MRI-based R1 measurement into pO2. We used breathing gas challenge to estimate the changes in lipid pO2 (ΔpO2). The relaxivity of O2 in lipid was determined to be 1.7·10-3 ± 4·10-4 mmHg-1s-1 at 4.7T and 37 °C, and was consistent between in vitro and in vivo adipose tissue. There was a strong, significant correlation between MRI- and gold standard OxyLite-based measurements of lipid ΔpO2 for in vivo visceral and subcutaneous fat depots in rodents. This study lays the foundation for a direct, noninvasive measure of adipose pO2 using MRI and will allow for noninvasive measurement of O2 flux in adipose tissue. The proposed approach would be of particular importance in the interrogation of the pathogenesis of type 2 diabetes, where it has been suggested that adipose tissue hypoxia is an independent driver of insulin resistance pathway.

A Human 3D Extracellular Matrix-Adipocyte Culture Model for Studying Matrix-Cell Metabolic Crosstalk.

The extracellular matrix (ECM) plays a central role in regulating tissue homeostasis, engaging in crosstalk with cells and regulating multiple aspects of cellular function. The ECM plays a particularly important role in adipose tissue function in obesity, and alterations in adipose tissue ECM deposition and composition are associated with metabolic disease in mice and humans. Tractable in vitro models that permit dissection of the roles of the ECM and cells in contributing to global tissue phenotype are sparse. We describe a novel 3D in vitro model of human ECM-adipocyte culture that permits study of the specific roles of the ECM and adipocytes in regulating adipose tissue metabolic phenotype. Human adipose tissue is decellularized to isolate ECM, which is subsequently repopulated with preadipocytes that are then differentiated within the ECM into mature adipocytes. This method creates ECM-adipocyte constructs that are metabolically active and retain characteristics of the tissues and patients from which they are derived. We have used this system to demonstrate disease-specific ECM-adipocyte crosstalk in human adipose tissue. This culture model provides a tool for dissecting the roles of the ECM and adipocytes in contributing to global adipose tissue metabolic phenotype and permits study of the role of the ECM in regulating adipose tissue homeostasis.

Integrated analysis of long noncoding RNA and mRNA expression profile in children with obesity by microarray analysis

Long noncoding RNAs (lncRNAs) have an important role in adipose tissue function and energy metabolism homeostasis, and abnormalities may lead to obesity. To investigate whether lncRNAs are involved in childhood obesity, we investigated the differential expression profile of lncRNAs in obese children compared with non-obese children. A total number of 1268 differentially expressed lncRNAs and 1085 differentially expressed mRNAs were identified. Gene Ontology (GO) and pathway analysis revealed that these lncRNAs were involved in varied biological processes, including the inflammatory response, lipid metabolic process, osteoclast differentiation and fatty acid metabolism. In addition, the lncRNA-mRNA co-expression network and the protein-protein interaction (PPI) network were constructed to identify hub regulatory lncRNAs and genes based on the microarray expression profiles. This study for the first time identifies an expression profile of differentially expressed lncRNAs in obese children and indicated hub lncRNA RP11-20G13.3 attenuated adipogenesis of preadipocytes, which is conducive to the search for new diagnostic and therapeutic strategies of childhood obesity.

Adipose tissue dysfunction increases fatty liver association with pre diabetes and newly diagnosed type 2 diabetes mellitus.

BackgroundTo evaluate the role of adipose tissue function on the association of fatty liver (FL) with impaired fasting glucose (IFG) or newly diagnosed type 2 diabetes mellitus (nT2D).MethodsIn 1264 subjects, computed tomography was used to evaluate FL and elevated visceral adipose tissue (VAT). Fasting plasma glucose, <5.6, 5.6–6.9 and ≥7 mmol/l, were used to defined normoglycemic (NG), IFG or nT2D, respectively. Elevated free fatty acids, low serum adiponectin levels and adipose tissue insulin resistance (Adipo-IR), were used as markers of adipose tissue dysfunction.ResultsCompared to NG subjects, those with IFG or nT2D had higher prevalence of FL and elevated VAT. FL was found to be independently associated with IFG and nT2D. Adipo-IR increased the association between FL and IFG [OR: 2.46 (95% I.C.: 1.73–3.49) to 5.42 (3.11–9.41)], whereas low adiponectin levels had a higher effect on the FL and nT2D association [OR: 4.26 (2.18–8.34) to 8.53 (2.96–24.55)].ConclusionFatty liver was independently associated with IFG and nT2D. Our results indicate for the first time, that adipose tissue dysfunction increases these associations.Electronic supplementary materialThe online version of this article (doi:10.1186/s13098-016-0189-6) contains supplementary material, which is available to authorized users.

Dendritic cells and adipose tissue

Visceral adipose tissue inflammation in obesity is an established risk factor for metabolic syndrome, which can include insulin resistance, type 2 diabetes, hypertension and cardiovascular diseases. With obesity and related metabolic disorders reaching epidemic proportions globally, an understanding of the mechanisms of adipose tissue inflammation is crucial. Within the immune cell cohort, dendritic cells (DC) play a key role in balancing tolerance and immunity. Despite decades of research into the characterization of DC in lymphoid and non-lymphoid organs, their role in adipose tissue function is poorly understood. There is now an increasing interest in identification and characterization of DC in adipose tissue and understanding their function in regulating tissue metabolic homeostasis. This review provides an overview of the study of DC in adipose tissue, focusing on possible mechanisms by which DC may contribute to adipose tissue homeostasis.

Obesity, adipose tissue function and the role of vitamin D.

IntroductionObesity is not just a cosmetic problem. Pathological accumulation of body fat can cause many health problems: insulin resistance, impaired glucose tolerance, and diabetes mellitus type 2. It may also increase morbidity and mortality. Adipose tissue plays an important role in body homeostasis by producing and secreting several bioactive proteins known as adipokines: adiponectin, leptin, resistin, visfatin, and apelin, which are involved in the regulation of food intake, glucose and lipid metabolism, and insulin action. There can be observed nutritional deficiencies, despite increased food intake, in morbidly obese people. Data concerning concentrations of serum 25(OH)D3 presented an inverse correlation with obesity parameters like: BMI (body mass index), waist circumference, fat mass or percentage of body fat. Also, higher insulin sensitivity was associated with higher concentrations of vitamin D.ConclusionsStudies published up to now suggest that vitamin D plays an important role in adipose tissue function and could be involved in the synthesis and modulation of adipokine production. This article is a review of the literature on fatty tissue function and the role of vitamin D in obesity.

Proline oxidase–adipose triglyceride lipase pathway restrains adipose cell death and tissue inflammation

The nutrient-sensing lipolytic enzyme adipose triglyceride lipase (ATGL) has a key role in adipose tissue function, and alterations in its activity have been implicated in many age-related metabolic disorders. In adipose tissue reduced blood vessel density is related to hypoxia state, cell death and inflammation. Here we demonstrate that adipocytes of poorly vascularized enlarged visceral adipose tissue (i.e. adipose tissue of old mice) suffer from limited nutrient delivery. In particular, nutrient starvation elicits increased activity of mitochondrial proline oxidase/dehydrogenase (POX/PRODH) that is causal in triggering a ROS-dependent induction of ATGL. We demonstrate that ATGL promotes the expression of genes related to mitochondrial oxidative metabolism (peroxisome proliferator-activated receptor-α, peroxisome proliferator-activated receptor-γ coactivator-1α), thus setting a metabolic switch towards fat utilization that supplies energy to starved adipocytes and prevents cell death, as well as adipose tissue inflammation. Taken together, these results identify ATGL as a stress resistance mediator in adipocytes, restraining visceral adipose tissue dysfunction typical of age-related metabolic disorders.

Body Fat Distribution and Insulin Resistance

The burden of obesity has increased globally over the last few decades and its association with insulin resistance and related cardio-metabolic problems have adversely affected our ability to reduce population morbidity and mortality. Traditionally, adipose tissue in the visceral fat depot has been considered a major culprit in the development of insulin resistance. However, there is a growing body of evidence supporting the role of subcutaneous truncal/abdominal adipose tissue in the development of insulin resistance. There are significant differences in the functional characteristics of subcutaneous abdominal/truncal vs. intraabdominal vs. gluteo-femoral fat depots. More recently, mounting evidence has been supporting the role of adipose tissue function in the development of metabolic complications independent of adipose tissue volume or distribution. Decreased capacity for adipocyte differentiation and angiogenesis along with adipocyte hypertrophy can trigger a vicious cycle of inflammation leading to subcutaneous adipose tissue dysfunction and ectopic fat deposition. Therapeutic lifestyle change continues to be the most important intervention in clinical practice to improve adipose tissue function and avoid development of insulin resistance and related cardio-metabolic complications.

Adipokines and Aging

Dysregulation of adipose tissue-derived bioactive molecules, termed adipokines, is recognized as common ground for insulin resistance and metabolic syndrome associated with obesity. However, adipokine dysregulation is paradoxically associated with lipodystrophy and lipoatrophy with aging. In familial partial lipodystrophic syndromes and Hutchinson-Gilford progeria syndrome, both of which are caused by mutations in the LMNA gene, loss of adipose tissue is associated with adipokine dysregulation, insulin resistance, and atherosclerosis, suggesting a critical role of adipose tissue function in controlling whole body energy metabolism, age-related pathologies, and longevity. Centenarians, a model of healthy aging and longevity, are reported to exhibit preserved insulin sensitivity as well as favorable adipokine profiles, particularly high levels of circulating adiponectin. Furthermore, adipose tissue dysfunction indicated by dysregulation of leptin, tumor necrosis factor-α, and adiponectin is associated with poor prognosis in centenarians. In contrast to results obtained for obesity, adipokine dysregulation in centenarians is associated with very low leptin levels, suggesting that age-related lipoatrophy is the major factor for adipose tissue dysfunction at an advanced age. These observations suggest that adipose tissue excess as well as its aging is implicated in the regulation of adipokines, insulin sensitivity, and lifespan in humans.

Tenomodulin Is Highly Expressed in Adipose Tissue, Increased in Obesity, and Down-Regulated during Diet-Induced Weight Loss

Tenomodulin (TNMD), a putative angiogenesis inhibitor, is expressed in hypovascular connective tissues. Global gene expression scans show that the TNMD gene also is expressed in human adipose tissue and that its expression is regulated in response to weight reduction; however, more detailed information is lacking. The aim of this study was to investigate TNMD tissue distribution and TNMD gene expression in human adipose tissue in relation to obesity and metabolic disease. TNMD gene expression, tissue distribution, and TNMD gene expression in adipose tissue from different depots, from lean and obese subjects, and during diet-induced weight reduction were analyzed by DNA microarray and real-time PCR. We primarily measured TNMD gene expression. The TNMD gene was predominantly expressed in sc adipose tissue. TNMD gene expression was higher in sc than omental adipose tissue both in lean (P = 0.002) and obese subjects (P = 0.014). In both women and men, TNMD gene expression was significantly higher in the obese subjects compared to the lean subjects (P = 1.1 x 10(-26) and P = 0.010, respectively). In a multiple linear regression analysis, BMI was a significant independent predictor of TNMD gene expression. TNMD gene expression was down-regulated during diet-induced weight loss, with a 65% decrease after 18 wk of diet (P < 0.0001). We conclude that human adipose tissue TNMD gene expression is highly affected by obesity, adipose tissue location, and weight loss, indicating that TNMD may play a role in adipose tissue function.

Metabolism of methylamine by semicarbazide-sensitive amine oxidase in white and brown adipose tissue of the rat

The metabolism of [ 14C]methylamine (MA) by amine oxidase activity in rat white and brown adipose tissue homogenates, and in mature adipocytes from these tissues has been studied. Oxidation of MA was completely inhibited by 0.1–1 mM semicarbazide, without being affected by the monoamine oxidase (MAO) inhibitor, pargyline (1 mM), indicating that MA is metabolized by semicarbazide-sensitive amine oxidase (SSAO) and not by MAO. The mean K m for MA deamination in all of these sources was around 250–300 μM. SSAO activity towards MA was also demonstrated in white and brown pre-adipocytes, transformed to the adipose phenotype by treatment in culture for 7 days with lipogenic agents. These results are similar to previous findings that SSAO in vascular smooth muscle is able to metabolize aliphatic amines such as MA, and furthermore suggest that SSAO may play a role in adipose tissue function and/or maturation.