Tumor necrosis factor alpha and glucocorticoid synergistically increase leptin production in human adipose tissue: role for p38 mitogen-activated protein kinase

Adipose tissue aging is regulated by an altered immune system

Adipose tissue is a widely distributed organ that plays a critical role in age-related physiological dysfunctions as an important source of chronic sterile low-grade inflammation. Adipose tissue undergoes diverse changes during aging, including fat depot redistribution, brown and beige fat decrease, functional decline of adipose progenitor and stem cells, senescent cell accumulation, and immune cell dysregulation. Specifically, inflammaging is common in aged adipose tissue. Adipose tissue inflammaging reduces adipose plasticity and pathologically contributes to adipocyte hypertrophy, fibrosis, and ultimately, adipose tissue dysfunction. Adipose tissue inflammaging also contributes to age-related diseases, such as diabetes, cardiovascular disease and cancer. There is an increased infiltration of immune cells into adipose tissue, and these infiltrating immune cells secrete proinflammatory cytokines and chemokines. Several important molecular and signaling pathways mediate the process, including JAK/STAT, NFκB and JNK, etc. The roles of immune cells in aging adipose tissue are complex, and the underlying mechanisms remain largely unclear. In this review, we summarize the consequences and causes of inflammaging in adipose tissue. We further outline the cellular/molecular mechanisms of adipose tissue inflammaging and propose potential therapeutic targets to alleviate age-related problems.

Exercise training remodels subcutaneous adipose tissue in adults with obesity even without weight loss

Excessive adipose tissue mass underlies much of the metabolic health complications in obesity. Although exercise training is known to improve metabolic health in individuals with obesity, the effects of exercise training without weight loss on adipose tissue structure and metabolic function remain unclear. Thirty-six adults with obesity (body mass index = 33 ± 3 kg · m^-2 ) were assigned to 12 weeks (4 days week^-1 ) of either moderate-intensity continuous training (MICT; 70% maximal heart rate, 45 min; n = 17) or high-intensity interval training (HIIT; 90% maximal heart rate, 10 × 1 min; n = 19), maintaining their body weight throughout. Abdominal subcutaneous adipose tissue (aSAT) biopsy samples were collected once before and twice after training (1 day after last exercise and again 4 days later). Exercise training modified aSAT morphology (i.e. reduced fat cell size, increased collagen type 5a3, both P ≤ 0.05, increased capillary density, P = 0.05) and altered protein abundance of factors that regulate aSAT remodelling (i.e. reduced matrix metallopeptidase 9; P = 0.02; increased angiopoietin-2; P < 0.01). Exercise training also increased protein abundance of factors that regulate lipid metabolism (e.g. hormone sensitive lipase and fatty acid translocase; P ≤ 0.03) and key proteins involved in the mitogen-activated protein kinase pathway when measured the day after the last exercise session. However, most of these exercise-mediated changes were no longer significant 4 days after exercise. Importantly, MICT and HIIT induced remarkably similar adaptations in aSAT. Collectively, even in the absence of weight loss, 12 weeks of exercise training induced changes in aSAT structure, as well as factors that regulate metabolism and the inflammatory signal pathway in adults with obesity. KEY POINTS: Exercise training is well-known to improve metabolic health in obesity, although how exercise modifies the structure and metabolic function of adipose tissue, in the absence of weight loss, remains unclear. We report that both 12 weeks of moderate-intensity continuous training (MICT) and 12 weeks of high-intensity interval training (HIIT) induced modifications in adipose tissue structure and factors that regulate adipose tissue remodelling, metabolism and the inflammatory signal pathway in adults with obesity, even without weight loss (with no meaningful differences between MICT and HIIT). The modest modifications in adipose tissue structure in response to 12 weeks of MICT or HIIT did not lead to changes in the rate of fatty acid release from adipose tissue. These results expand our understanding about the effects of two commonly used exercise training prescriptions (MICT and HIIT) on adipose tissue remodelling that may lead to advanced strategies for improving metabolic health outcomes in adults with obesity.

Immunometabolic adaptation and immune plasticity in pregnancy and the bi-directional effects of obesity

Mandatory maternal metabolic and immunological changes are essential to pregnancy success. Parallel changes in metabolism and immune function make immunometabolism an attractive mechanism to enable dynamic immune adaptation during pregnancy. Immunometabolism is a burgeoning field with the underlying principle being that cellular metabolism underpins immune cell function. With whole body changes to the metabolism of carbohydrates, protein and lipids well recognised to occur in pregnancy and our growing understanding of immunometabolism as a determinant of immunoinflammatory effector responses, it would seem reasonable to expect immune plasticity during pregnancy to be linked to changes in the availability and handling of multiple nutrient energy sources by immune cells. While studies of immunometabolism in pregnancy are only just beginning, the recognised bi-directional interaction between metabolism and immune function in the metabolic disorder obesity might provide some of the earliest insights into the role of immunometabolism in immune plasticity in pregnancy. Characterised by chronic low-grade inflammation including in pregnant women, obesity is associated with numerous adverse outcomes during pregnancy and beyond for both mother and child. Concurrent changes in metabolism and immunoinflammation are consistently described but any causative link is not well established. Here we provide an overview of the metabolic and immunological changes that occur in pregnancy and how these might contribute to healthy versus adverse pregnancy outcomes with special consideration of possible interactions with obesity.

KRAS Affects Adipogenic Differentiation by Regulating Autophagy and MAPK Activation in 3T3-L1 and C2C12 Cells

Kirsten rat sarcoma 2 viral oncogene homolog (Kras) is a proto-oncogene that encodes the small GTPase transductor protein KRAS, which has previously been found to promote cytokine secretion, cell survival, and chemotaxis. However, its effects on preadipocyte differentiation and lipid accumulation are unclear. In this study, the effects of KRAS inhibition on proliferation, autophagy, and adipogenic differentiation as well as its potential mechanisms were analyzed in the 3T3-L1 and C2C12 cell lines. The results showed that KRAS was localized mainly in the nuclei of 3T3-L1 and C2C12 cells. Inhibition of KRAS altered mammalian target of rapamycin (Mtor), proliferating cell nuclear antigen (Pcna), Myc, peroxisome proliferator-activated receptor γ (PPARγ), CCAAT/enhancer binding protein beta (C/ebp-β), diacylglycerol O-acyltransferase 1 (Dgat1), and stearoyl-coenzyme A desaturase 1 (Scd1) expression, thereby reducing cell proliferation capacity while inducing autophagy, enhancing differentiation of 3T3-L1 and C2C12 cells into mature adipocytes, and increasing adipogenesis and the capacity to store lipids. Moreover, during differentiation, KRAS inhibition reduced the levels of extracellular regulated protein kinases (ERK), c-Jun N-terminal kinase (JNK), p38, and phosphatidylinositol 3 kinase (PI3K) activation. These results show that KRAS has unique regulatory effects on cell proliferation, autophagy, adipogenic differentiation, and lipid accumulation.

The Role of the Adipokine Leptin in Immune Cell Function in Health and Disease

Leptin is a critical mediator of the immune response to changes in overall nutrition. Leptin is produced by adipocytes in proportion to adipose tissue mass and is therefore increased in obesity. Despite having a well-described role in regulating systemic metabolism and appetite, leptin displays pleiotropic actions, and it is now clear that leptin has a key role in influencing immune cell function. Indeed, many immune cells have been shown to respond to leptin directly via the leptin receptor, resulting in a largely pro-inflammatory phenotype. Understanding the role of adipose-tissue derived mediators in inflammation is critical to determining the pathophysiology of multiple obesity-associated diseases, such as type 2 diabetes, autoimmune disease, and infection. This review, therefore, focuses on the latest data regarding the role of leptin in modulating inflammation.

Uncovering the Role of p38 Family Members in Adipose Tissue Physiology

The complex functions of adipose tissue have been a focus of research interest over the past twenty years. Adipose tissue is not only the main energy storage depot, but also one of the largest endocrine organs in the body and carries out crucial metabolic functions. Moreover, brown and beige adipose depots are major sites of energy expenditure through the activation of adaptive, non-shivering thermogenesis. In recent years, numerous signaling molecules and pathways have emerged as critical regulators of adipose tissue, in both homeostasis and obesity-related disease. Among the best characterized are members of the p38 kinase family. The activity of these kinases has emerged as a key contributor to the biology of the white and brown adipose tissues, and their modulation could provide new therapeutic approaches against obesity. Here, we give an overview of the roles of the distinct p38 family members in adipose tissue, focusing on their actions in adipogenesis, thermogenic activity, and secretory function.

Adrenal Steroids Modulate Fibroblast-Like Synoviocytes Response During B. abortus Infection

Brucella abortus stimulates an inflammatory immune response that stimulates the endocrine system, inducing the secretion of dehydroepiandrosterone (DHEA) and cortisol. In humans, the active disease is generally present as osteoarticular brucellosis. In previous studies we showed that B. abortus infection of synoviocytes creates a proinflammatory microenvironment. We proposed to determine the role of cortisol and DHEA on synoviocytes and infiltrating monocytes during B. abortus infection. Cortisol inhibited IL-6, IL-8, MCP-1, and MMP-2 secretion induced by B. abortus infection in synovial fibroblast. Cortisol-mediated MMP-2 inhibition during B. abortus infection was reversed by IL-6. DHEA inhibited B. abortus-induced RANKL up-regulation in synovial fibroblast through estrogen receptor (ER). B. abortus infection did not modulate glucocorticoid receptor (GR) expression. Cell responses to cortisol also depended on its intracellular bioavailability, according to the activity of the isoenzymes 11β-hydroxysteroid dehydrogenase (HSD) type-1 and 11β-HSD2 (which are involved in cortisone-cortisol interconversion). B. abortus infection did not modify 11β-HSD1 expression and GRα/β ratio in the presence or absence of adrenal steroids. Supernatants from B. abortus-infected monocytes induced 11β-HSD1 in synovial cells. Administration of cortisone was capable of inhibiting the secretion of RANKL by synoviocytes mimicking cortisol's effect. These results go along with previous observations that highlighted the ability of synovial tissue to secrete active steroids, making it an intracrine tissue. This is the first study that contributes to the knowledge of the consequence of adrenal steroids on synoviocytes in the context of a bacterial infection.

Metabolic benefits of inhibition of p38α in white adipose tissue in obesity

p38 has long been known as a central mediator of protein kinase A (PKA) signaling in brown adipocytes, which positively regulate the transcription of uncoupling protein 1 (UCP-1). However, the physiological role of p38 in adipose tissues, especially the white adipose tissue (WAT), is largely unknown. Here, we show that mice lacking p38α in adipose tissues display a lean phenotype, improved metabolism, and resistance to diet-induced obesity. Surprisingly, ablation of p38α causes minimal effects on brown adipose tissue (BAT) in adult mice, as evident from undetectable changes in UCP-1 expression, mitochondrial function, body temperature (BT), and energy expenditure. In contrast, genetic ablation of p38α in adipose tissues not only markedly facilitates the browning in WAT upon cold stress but also prevents diet-induced obesity. Consistently, pharmaceutical inhibition of p38α remarkably enhances the browning of WAT and has metabolic benefits. Furthermore, our data suggest that p38α deficiency promotes white-to-beige adipocyte reprogramming in a cell-autonomous manner. Mechanistically, inhibition of p38α stimulates the UCP-1 transcription through PKA and its downstream cAMP-response element binding protein (CREB), which form a positive feedback loop that functions to reinforce the white-to-beige phenotypic switch during cold exposure. Together, our study reveals that inhibition of p38α is able to promote WAT browning and confer metabolic benefits. Our study also indicates that p38α in WAT represents an exciting pharmacological target to combat obesity and metabolic diseases.

The functional brown adipose tissue (BAT) identified in human adults consists of not only classic brown adipocytes but also brown-like adipocytes (beige adipocytes), both of which are important for energy homeostasis. Due to the same ability to convert fat into heat as brown adipocytes, beige adipocytes have been considered as a novel pharmacological target to combat obesity. Growing evidence suggests that promoting the development and formation of beige adipocytes in white adipose tissue (WAT), also called the browning of WAT, is able to prevent diet-induced obesity and improve metabolism in rodents. Thus, understanding the molecular basis for the regulation of browning in WAT may help us to develop new strategies to counteract obesity and metabolic diseases. In this study, adipocyte-specific p38α knockout (Fp38αKO) mice are generated that display a lean phenotype, improved metabolism, and resistance to diet-induced obesity. Interestingly, we found that adipocyte p38α deficiency facilitates the browning in WAT. Then, we show that pharmaceutical inhibition of p38α enhances the browning in WAT and has metabolic benefits. We propose that inhibiting p38α in WAT, possibly combined with cold exposure, could constitute an exciting pharmacological target to combat obesity and metabolic diseases.

New Insights Regarding Genetic Aspects of Childhood Obesity: A Minireview

Introduction: Childhood obesity is occurring at alarming rates in both developed and developing countries. "Obesogenic" environmental factors must be associated with variants of different risk alleles to determine polygenic or common obesity, and their impact depends on different developmental stages.The interaction between obesogenic environment and genetic susceptibility results in the so-called polygenic forms of obesity. In contrast, monogenic and syndromic obesity are not influenced by environmental events. Therefore, this review aimed to underline the roles of some of the most studied genes in the development of monogenic and polygenic obesity in children. Results: Among the most common obesity related genes, we chose the fat mass and obesity-associated (FTO) gene, leptin gene and its receptor, tumor necrosis factor alpha (TNF-α), the melanocortin 4 receptor gene (MC4R), Ectoenzyme nucleotide pyrophosphate phosphodiesterase 1 (ENPP1), and others, such as peroxisome proliferator-activated receptor gamma (PPARG), angiotensin-converting enzyme (ACE), glutathione S-transferase (GST), and interleukin-6 (IL-6) genes. The roles of these genes are complex and interdependent, being linked to different cornerstones in obesity development, such as appetite behavior, control of food intake and energy balance, insulin signaling, lipid and glucose metabolism, metabolic disorders, adipocyte differentiation, and so on. Conclusions: Genetic predisposition is mandatory, but not enough to trigger obesity.Dietary interventions and proper lifestyle changes can prevent obesity development in genetically predisposed children. Further studies are needed to identify the precise role of both genetic and obesogenic factors in the development of childhood obesity in order to design effective preventive methods.

Does road transport influence plasma leptin concentrations in horses? Preliminary study

Transport is one of the most common stressors for horses leading to an increase in cortisol secretion. Cortisol promotes leptin synthesis and release. The aim of the study was to evaluate the effect of short transport on circulating leptin and cortisol concentrations. A total of 16 crossbred naïve horses (7 geldings, 9 mares) aged 2-11 years, and weighing 530-680 kg were included in the study. The horses were transported in a commercial horse-truck to an unknown holding pen for temporary housing. To measure plasma leptin and cortisol concentrations, three blood samples were collected from each horse: before transport, immediately after unloading from the truck, and nine hours after transport at the arrival point. Transport caused a significant increase in mean plasma cortisol concentration determined at unloading, and after nine hours of unloading, in comparison to values obtained before loading. Plasma leptin concentrations did not change during the study. In conclusion, transportation procedures did not influence plasma leptin concentration in horses, despite significantly increased cortisol release.

Dehydroepiandrosterone-enhanced dual specificity protein phosphatase (DDSP) prevents diet-induced and genetic obesity

Dehydroepiandrosterone (DHEA) exerts a wide variety of therapeutic effects against medical disorders, such as diabetes and obesity. However, the molecular basis of DHEA action remains to be clarified. Previously, we reported that DHEA-enhanced dual specificity protein phosphatase, designated DDSP, is one of the target molecules of DHEA. To examine the role of DDSP in DHEA signaling, we generated mice that carry a DDSP transgene in which expression is driven by the CAG promoter (DDSP-Tg). DDSP-Tg mice weighed significantly less than wild-type (WT) control mice when a high fat diet was supplied (p < 0.01). No difference in food-intake or locomotor activity was found between DDSP-Tg and WT mice. Oxygen consumption of DDSP-Tg mice was higher than that of WT mice (p < 0.01), which suggested an increase in basal metabolism in DDSP-Tg mice. To further investigate the role of DDSP in genetic obese mice, DDSP-Tg mice with a db/db background were generated (DDSP-Tg db/db). We observed cancellation of obesity by the db/db mutation and development of a cachexic phenotype in DDSP-Tg db/db mice. In conclusion, our study shows that expression of DDSP leads to prevention of diet-induced and genetic (db/db) obesity. Anti-obese effects of DHEA might be mediated through DDSP, which might be a therapeutic target for intervention of obesity.

High Temporal Resolution Detection of Patient-Specific Glucose Uptake from Human ex Vivo Adipose Tissue On-Chip

Human tissue in vitro models on-chip are highly desirable to dissect the complexity of a physio-pathological in vivo response because of their advantages compared to traditional static culture systems in terms of high control of microenvironmental conditions, including accurate perturbations and high temporal resolution analyses of medium outflow. Human adipose tissue (hAT) is a key player in metabolic disorders, such as Type 2 Diabetes Mellitus (T2DM). It is involved in the overall energy homeostasis not only as passive energy storage but also as an important metabolic regulator. Here, we aim at developing a large scale microfluidic platform for generating high temporal resolution of glucose uptake profiles, and consequently insulin sensitivity, under physio-pathological stimulations in ex vivo adipose tissues from nondiabetic and T2DM individuals. A multiscale mathematical model that integrates fluid dynamics and an intracellular insulin signaling pathway description was used for assisting microfluidic design in order to maximize measurement accuracy of tissue metabolic activity in response to perturbations. An automated microfluidic injection system was included on-chip for performing precise dynamic biochemical stimulations. The temporal evolution of culture conditions could be monitored for days, before and after perturbation, measuring glucose concentration in the outflow with high temporal resolution. As a proof of concept for detection of insulin resistance, we measured insulin-dependent glucose uptake by hAT from nondiabetic and T2DM subjects, mimicking the postprandial response. The system presented thus represents an important tool in dissecting the role of single tissues, such as hAT, in the complex interwoven picture of metabolic diseases.

Impact of glucocorticoid hormones on adipokine secretion and human adipose tissue metabolism

The glucocorticoid hormones alter the metabolism of the adipose tissue after an approximately 2-h lag period. The effects are mediated through the nuclear receptors that alter the expression of a wide variety of genes through the mechanisms that are similar to those seen in the other cells. There are many direct metabolic effects of the glucocorticoids on the adipose tissue metabolism, and every year, new effects are added to the list of proteins whose expression is influenced by the glucocorticoids. Furthermore, some enzymatic processes are affected by these hormones only in the presence of the other hormones such as growth hormone (GH) or insulin. Most of the effects of the glucocorticoids are on the gene transcription, and the effects on the mRNA are reflected in the altered levels of the target proteins. The glucocorticoids enhance the leptin release, while reducing that of the inflammatory adipokines and stimulating that of the lipoprotein lipase (LPL) in the presence of insulin. The activity of 11β-hydroxysteroid dehydrogenase type 1 (HSD1) is enhanced by the glucocorticoids along with that of α1 glycoprotein 1 and serum amyloid A release by the adipose tissue. In contrast, the tumor necrosis factor α (TNF)-stimulated lipolysis in the adipose tissue is blocked by the glucocorticoids. It is still unclear which, if any, of these effects account for the insulin resistance due to the glucocorticoids in the adipose tissue. However, recent work suggests that, at least in mice, the reduction in the osteocalcin release by the osteoblasts in the presence of the glucocorticoids accounts for much of the in vivo insulin resistance. In summary, there are multiple direct effects of the glucocorticoids, both anti-inflammatory and proinflammatory, on the adipose tissue.

Environment, leptin sensitivity, and hypothalamic plasticity

Regulation of feeding behavior has been a crucial step in the interplay between leptin and the arcuate nucleus of the hypothalamus (ARC). On one hand, the basic mechanisms regulating central and peripheral action of leptin are becoming increasingly clear. On the other hand, knowledge on how brain sensitivity to leptin can be modulated is only beginning to accumulate. This point is of paramount importance if one considers that pathologically obese subjects have high levels of plasmatic leptin. A possible strategy for exploring neural plasticity in the ARC is to act on environmental stimuli. This can be achieved with various protocols, namely, physical exercise, high-fat diet, caloric restriction, and environmental enrichment. Use of these protocols can, in turn, be exploited to isolate key molecules with translational potential. In the present review, we summarize present knowledge about the mechanisms of plasticity induced by the environment in the ARC. In addition, we also address the role of leptin in extrahypothalamic plasticity, in order to propose an integrated view of how a single diffusible factor can regulate diverse brain functions.

Mesenchymal stem cells: a revolution in therapeutic strategies of age-related diseases

The great evolutionary biologist Theodosius Dobzhansky once said: "Nothing in biology makes sense except in the light of evolution". Aging is a complex biological phenomenon and the factors governing the process of aging and age-related diseases are only beginning to be understood, oxidative stress, telomere shortening in DNA components and genetic changes were shown to be the mainly regulating mechanisms during the recent decades. Although a considerable amount of both animal and clinical data that demonstrate the extensive and safe use of mesenchymal stromal cells (MSCs) is available, the precise summarization and identification of MSCs in age-related diseases remains a challenge. Along this line, this review discussed several typical age-related diseases for which MSCs have been proved to confer protection and put forward a hypothesis for the association among MSCs and age-related diseases from an evolutionary perspective. Above all, we hope further and more research efforts could be aroused to elucidate the role and mechanisms that MSCs involved in the age-related diseases.

Ligand-independent phosphorylation of the glucocorticoid receptor integrates cellular stress pathways with nuclear receptor signaling

Glucocorticoids are stress hormones that maintain homeostasis through gene regulation mediated by nuclear receptors. We have discovered that other cellular stressors are integrated with glucocorticoid signaling through a new hormone-independent phosphorylation site, Ser134, on the human glucocorticoid receptor (GR). Ser134 phosphorylation is induced by a variety of stress-activating stimuli in a p38 mitogen-activated protein kinase (MAPK)-dependent manner. Cells expressing a mutant glucocorticoid receptor incapable of phosphorylation at Ser134 (S134A-GR) had significantly altered hormone-dependent genome-wide transcriptional responses and associated hormone-mediated cellular functions. The phosphorylation of Ser134 significantly increased the association of the GR with the zeta isoform of the 14-3-3 class of signaling proteins (14-3-3zeta) on chromatin promoter regions, resulting in a blunted hormone-dependent transcriptional response of select genes. These data argue that the phosphorylation of Ser134 acts as a molecular sensor on the GR, monitoring the level of cellular stress to redirect glucocorticoid-regulated signaling through altered 14-3-3zeta cofactor binding and promoter recruitment. This posttranslational modification allows prior cellular stress signals to dictate the transcriptional response to glucocorticoids.

Association of TNF-α promoter gene G-308A polymorphism with metabolic syndrome, insulin resistance, serum TNF-α and leptin levels in Indian adult women

BACKGROUND

Tumour necrosis factor alpha is a multifunctional proinflammatory cytokine involved in the pathogenesis of metabolic syndrome, insulin resistance, and obesity. Aim of this study is to investigate in a North Indian female population the impact of the G-308A TNF-α variant on various components of the metabolic syndrome, Insulin Resistance, serum TNF-α and Leptin levels.

METHODS

The G-308A TNF-α polymorphism has been studied in 269 females with metabolic syndrome (NCEP ATP III criteria) (age 31.91±6.05) and 272 healthy females without metabolic syndrome (age 30.96±7.01). The G-308A variant was detected by PCR amplification and Nco-1 digestion.

RESULTS

Homozygous mutant genotype (AA) (p=<0.001: OR=3.24: 95% CI=2.15-4.89) and mutant allele (A) (p=<0.001: OR=3.04: 95% CI=2.08-4.43) of TNF-α was significantly less frequently observed in the control population as compared to study group. Furthermore, on dividing the subjects into two groups according to the absence (TNF-1 allele) or presence of the mutant A (TNF-2) allele, significant results were obtained in most of the metabolic risk factors.

CONCLUSIONS

Our results suggest that the G-308A polymorphism of the TNF-α gene may be independently associated with hypertension, leptin level and hypercholesterolemia leading to metabolic syndrome independent of Insulin resistance and hyperglycemia.

Cross talk between cAMP and p38 MAPK pathways in the induction of leptin by hCG in human placental syncytiotrophoblasts

Leptin produced by the placental syncytiotrophoblasts participates in a number of processes in pregnancy including implantation, proliferation of the cytotrophoblasts, and nutrient transfer across the placenta. Despite the functional significance of leptin in pregnancy, the regulation of leptin synthesis is poorly understood in human placental syncytiotrophoblasts. In this study, we investigated the role of endogenous human chorionic gonadotropin (hCG) in the regulation of leptin production as well as the underlying mechanism involving the cross talk between cAMP and p38 mitogen-activated protein kinase (MAPK) pathways. We found that neutralization of endogenous hCG with its antibody dose dependently decreased leptin mRNA level and secretion, whereas exogenous hCG increased leptin mRNA level and secretion. Activation of the cAMP pathway with dibutyryl cAMP (db cAMP) or forskolin recapitulated the stimulatory effect of hCG on leptin expression. Inhibition of protein kinase A with H89 not only reduced the basal leptin expression but also attenuated the induced leptin expression by hCG. Treatment of the syncytiotrophoblasts with db cAMP and hCG phosphorylated p38 MAPK. Inhibition of p38 MAPK with SB203580 not only reduced the basal leptin production but also attenuated the leptin-induced production by both hCG and db cAMP. These data suggest that endogenous hCG plays a significant role in maintaining leptin production in human placental syncytiotrophoblasts, and this effect involves a cross talk between cAMP and p38 MAPK pathways.

Expression of 11β-hydroxysteroid dehydrogenase type 1 in visceral and subcutaneous adipose tissues of patients with polycystic ovary syndrome is associated with adiposity

Polycystic ovary syndrome (PCOS) is characterized by insulin resistance (IR) and central obesity. The impact of adipose tissue cortisol reactivation by 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) on markers of obesity and IR was assessed in PCOS patients. Eighty-five PCOS patients and 43 controls were enrolled for subcutaneous adipose tissue biopsy; 25/85 patients and 29/43 controls underwent also visceral adipose tissue biopsy. HSD11B1 gene expression and expression of lipid metabolism genes were measured in subcutaneous and visceral adipose tissues. Anthropometric and biochemical markers of IR and PCOS were also assessed. HSD11B1 expression in visceral and subcutaneous adipose tissue was increased in PCOS patients compared to controls (p<0.05). After BMI adjustment, the difference was no longer significant. In PCOS patients, visceral HSD11B1 expression correlated positively with waist circumference (p=0.001), BMI (p=0.002), plasma insulin (p<0.05), systolic blood pressure (p=0.003), and lipoprotein lipase (LPL), hormone-sensitive lipase (LIPE) and peroxisome-proliferator activated receptor γ gene expression. Subcutaneous HSD11B1 expression correlated positively with BMI, waist circumference (p<0.001 for both) and HOMA-IR (p=0.003), and negatively with LPL, LIPE, adiponectin and glucose transporter GLUT4 gene expression. HSD11B1 expression in both depots showed a negative correlation with plasma HDL-cholesterol (p<0.03) and a positive one with C-reactive protein (p<0.001). In multiple regression analysis, HSD11B1 expression in visceral adipose tissue was most prominently associated with waist circumference, and that in subcutaneous adipose tissue with BMI (p<0.001 for both). Our results show that PCOS is not associated with increased HSD11B1 expression once adiposity is controlled for. Increased expression of this gene correlates with markers of adiposity and predicts IR and an unfavorable metabolic profile, independently of PCOS.

Leptin and amylin act in an additive manner to activate overlapping signaling pathways in peripheral tissues: in vitro and ex vivo studies in humans

OBJECTIVE

Amylin interacts with leptin to alter metabolism. We evaluated, for the first time, amylin- and/or leptin-activated signaling pathways in human peripheral tissues (hPTs).

RESEARCH DESIGN AND METHODS

Leptin and amylin signaling studies were performed in vitro in human primary adipocytes (hPAs) and human peripheral blood mononuclear cells (hPBMCs) and ex vivo in human adipose tissue (hAT) from male versus female subjects, obese versus lean subjects, and subjects with subcutaneous versus omental adipose tissue.

RESULTS

The long form of leptin receptor was expressed in human tissues and cells studied in ex vivo and in vitro, respectively. Leptin and amylin alone and in combination activate signal transducer and activator of transcription 3 (STAT3), AMP-activated protein kinase, Akt, and extracellular signal-regulated kinase signaling pathways in hAT ex vivo and hPAs and hPBMCs in vitro; all phosphorylation events were saturable at leptin and amylin concentrations of ∼50 and ∼20 ng/ml, respectively. The effects of leptin and amylin on STAT3 phosphorylation in hPAs and hPBMCs in vitro were totally abolished under endoplasmic reticulum stress and/or in the presence of a STAT3 inhibitor. Results similar to those in the in vitro studies were observed in hAT studied ex vivo.

CONCLUSIONS

Leptin and amylin activate overlapping intracellular signaling pathways in humans and have additive, but not synergistic, effects in signaling pathways studied in hPTs in vitro and ex vivo.

The autocrine and paracrine roles of adipokines

Obesity, defined by an excess of adipose tissue, is often associated with the development of various metabolic diseases. The increased and inappropriate deposition of this tissue contributes to hyperglycemia, hyperlipidemia, insulin resistance, endothelial dysfunction and chronic inflammation. Recent evidence suggests that factors expressed and secreted by the adipose tissue, adipokines, may contribute to the development of these abnormalities by mechanisms including inhibition of adipogenesis, adipocyte hypertrophy and death, immune cell infiltration and disruption of tissue metabolism. The presence of adipokine receptors in adipocytes renders these cells available to autocrine and paracrine effects of adipokines. In this review the reported local effects of adipokines on adipose tissue structure, inflammation and regulation of metabolic functions, in the face of over-nutrition and consequent obesity, are outlined. Elucidating the local regulation of white adipocyte development and function could help in the design of effective, tissue-specific therapies for obesity-associated diseases.

Synergistic induction of local glucocorticoid generation by inflammatory cytokines and glucocorticoids: implications for inflammation associated bone loss

Objectives

Synovial fibroblasts and osteoblasts generate active glucocorticoids by means of the 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) enzyme. This activity increases in response to proinflammatory cytokines or glucocorticoids. During inflammatory arthritis synovium and bone are exposed to both these factors. This study hypothesised that glucocorticoids magnify the effects of inflammatory cytokines on local glucocorticoid production in both synovium and bone.

Methods

The effects of inflammatory cytokines (IL-1β/tumour necrosis factor alpha; TNFα) and glucocorticoids, alone or combined, were assessed on the expression and activity of 11β-HSD1 in primary synovial fibroblasts, primary human osteoblasts and MG-63 osteosarcoma cells. A range of other target genes and cell types were used to examine the specificity of effects. Functional consequences were assessed using IL-6 ELISA.

Results

In synovial fibroblasts and osteoblasts, treatment with cytokines or glucocorticoids in isolation induced 11β-HSD1 expression and activity. However, in combination, 11β-HSD1 expression, activity and functional consequences were induced synergistically to a level not seen with isolated treatments. This effect was seen in normal skin fibroblasts but not foreskin fibroblasts or adipocytes and was only seen for the 11β-HSD1 gene. Synergistic induction had functional consequences on IL-6 production.

Conclusions

Combined treatment with inflammatory cytokines and glucocorticoids synergistically induces 11β-HSD1 expression and activity in synovial fibroblasts and osteoblasts, providing a mechanism by which synovium and bone can interact to enhance anti-inflammatory responses by increasing localised glucocorticoid levels. However, the synergistic induction of 11β-HSD1 might also cause detrimental glucocorticoid accumulation in bone or surrounding tissues.

Integration of hormonal and nutrient signals that regulate leptin synthesis and secretion

This review summarizes recent advances in our understanding of the pre- and posttranscriptional mechanisms that regulate leptin production and secretion in adipocytes. Basal leptin production is proportional to the status of energy stores, i.e., fat cell size, and this is mainly regulated by alterations in leptin mRNA levels. Leptin mRNA levels are regulated by hormones, including glucocorticoids and catecholamines, but little is known about the transcriptional mechanisms involved. Leptin synthesis and secretion is also acutely modulated in response to hormones such as insulin and the availability of metabolic fuels. Acute variations in leptin production over a time course of minutes to hours are mediated at the levels of both translation and secretion. Increases in amino acids and insulin after a meal activate the mammalian target of rapamycin (mTOR) pathway, leading to an increase in specific rates of leptin biosynthesis. Cross-talk among mTOR, PKA, and AMP-activated protein kinase pathways appears to integrate hormonal and nutrient signals that regulate leptin mRNA translation, at least in part through mechanisms involving its 5'- and 3'-untranslated regions. In addition, the rate of leptin secretion from preformed stores in response to hormonal cues is also regulated. Insulin stimulates, and adrenergic agonists inhibit, leptin secretion, and this likely contributes to variations in the magnitude of nutrition-related leptin excursions and oscillations. Overall, the study of leptin production has contributed to a deepening understanding of leptin biology and, more broadly, to our understanding of the cellular and molecular mechanisms by which the adipocyte integrates hormonal and nutrient signals to regulate adipokine production.

Glucocorticoids and tumor necrosis factor-alpha synergize to induce absorption by the epithelial sodium channel in the colon

BACKGROUND & AIMS

The epithelial sodium channel (ENaC) mediates electrogenic sodium absorption in distal colon. In patients with inflammatory bowel disease (IBD), ENaC induction is impaired, mainly through transcriptional suppression by proinflammatory cytokines such as tumor necrosis factor (TNF)-alpha. Glucocorticoid therapy rapidly increases sodium absorption; we investigated the molecular mechanisms underlying the interaction among TNF-alpha, glucocorticoids, and ENaC induction.

METHODS

ENaC-mediated sodium transport in glucocorticoid receptor (GR)-expressing HT-29/B6 cells and rat distal colon, under the influence of the synthetic glucocorticoid dexamethasone and TNF-alpha, was quantified in Ussing chambers. ENaC messenger RNA (mRNA) levels were monitored by real-time polymerase chain reaction. GR transactivation and expression were investigated by gene reporter, immunoblot, and confocal immunofluorescence microscopy analyses. The GR mRNA half-life was determined. Signaling pathways were characterized using mitogen-activated protein kinase inhibitors.

RESULTS

Dexamethasone not only prevented TNF-alpha-mediated ENaC suppression but caused synergistic induction of ENaC-dependent sodium absorption in HT-29/B6-GR cells and rat distal colon. This synergy resulted from TNF-alpha-mediated increases in GR protein levels because of GR mRNA stabilization and subsequent GR transactivation by dexamethasone. As a consequence, transcription of the ENaC beta- and gamma-subunits was up-regulated, increasing ENaC-dependent sodium absorption. p38 Mitogen-activated protein kinase is required for this synergistic effect: p38 inhibition blocked the increase in GR protein expression and ENaC-dependent sodium absorption.

CONCLUSIONS

TNF-alpha and dexamethasone induce ENaC, explaining the rapid and intense proabsorptive effect of glucocorticoid therapies.

Exercise and adrenaline increase PGC-1{alpha} mRNA expression in rat adipose tissue

The purpose of the present investigation was to explore the effects of exercise and adrenaline on the mRNA expression of PGC-1alpha, a master regulator of mitochondrial biogenesis, in rat abdominal adipose tissue. We hypothesized that (1) exercise training would increase PGC-1alpha mRNA expression in association with increases in mitochondrial marker enzymes, (2) adrenaline would increase PGC-1alpha mRNA expression and (3) the effect of exercise on PGC-1alpha mRNA expression in white adipose tissue would be attenuated by a beta-blocker. Two hours of daily swim training for 4 weeks led to increases in mitochondrial marker proteins and PGC-1alpha mRNA expression in epididymal and retroperitoneal fat depots. Additionally, a single 2 h bout of exercise led to increases in PGC-1alpha mRNA expression immediately following exercise cessation. Adrenaline treatment of adipose tissue organ cultures led to dose-dependent increases in PGC-1alpha mRNA expression. A supra-physiological concentration of adrenaline increased PGC-1alpha mRNA expression in epididymal but not retroperitoneal adipose tissue. beta-Blockade attenuated the effects of an acute bout of exercise on PGC-1alpha mRNA expression in epididymal but not retroperitoneal fat pads. In summary, this is the first investigation to demonstrate that exercise training, an acute bout of exercise and adrenaline all increase PGC-1alpha mRNA expression in rat white adipose tissue. Furthermore it would appear that increases in circulating catecholamine levels may be one potential mechanism mediating exercise induced increases in PGC-1alpha mRNA expression in rat abdominal adipose tissue.

Time course of high-fat diet-induced reductions in adipose tissue mitochondrial proteins: potential mechanisms and the relationship to glucose intolerance

Increasing evidence suggests that reduced adipose tissue mitochondrial content is associated with the pathogenesis of type 2 diabetes. These investigations have utilized severely insulin-resistant rodent models. Thus, it is difficult to ascertain the potential mechanisms that initiate these changes and whether reductions in adipose mitochondria are an initiating event in the development of impaired glucose homeostasis. Thus, we sought to determine the time course of high-fat diet-induced reductions of mitochondrial content in epididymal adipose tissue in relation to changes in purported mediators of mitochondrial biogenesis and the development of impaired glucose homeostasis. Male Wistar rats were fed a high-fat diet ( approximately 59% of kcals from fat) for 2, 4, or 6 wk. Six weeks of high-fat feeding resulted in reductions in CORE I, COX IV, cytochrome c, HSP60, relative mtDNA copy number, and PGC-1alpha expression. These changes were not associated with decreases in eNOS and AMPK or increases in markers of oxidative stress. Interestingly, ex vivo treatment of adipose tissue cultures with palmitate led to decreases in PGC-1alpha expression and COX IV and CORE I protein content as observed in vivo. Thus, the high-fat diet-induced reductions in adipose tissue mitochondrial proteins may be mediated by increases in plasma fatty acids. Importantly, reductions in adipose tissue mitochondrial content occurred after the development of impaired glucose homeostasis. Thus, reductions in adipose tissue mitochondrial proteins are most likely not a causal event in the development of impaired glucose homeostasis.

Expression and regulation of transcript for the novel transmembrane protein Tmem182 in the adipocyte and muscle lineage

Background

White adipose tissue is not only an energy storage organ; it also functions as an endocrine organ. The coordination and integration of numerous gene expression events is required to establish and maintain the adipocyte phenotype.

Findings

We previously observed a 45-fold upregulation for a transcript encoding a novel predicted transmembrane protein, Tmem182, upon brown preadipocyte to adipocyte conversion. Here we use real-time PCR analysis to further characterize Tmem182 transcript expression in the adipocyte lineage. Analysis across a panel of 10 murine tissues revealed highest Tmem182 transcript expression in white adipose tissues (WAT), with 10-fold to 20-fold higher levels than in brown adipose tissue (BAT). Tmem182 transcript expression is ~3-fold upregulated in BAT of genetically obese (ob/ob) mice vs. wild type C57BL/6. Analysis of three in vitro models of white adipogenesis indicates markedly enriched expression of Tmem182 transcript in adipocytes vs. preadipocytes. Compared to 3T3-L1 preadipocytes, a 157-fold higher level of Tmem182 transcript is detected at 3 day post-induction of adipogenesis and an ~2500-fold higher level in mature 3T3-L1 adipocytes. TNFα treatment of 3T3-L1 adipocytes resulted in a ~90% decrease in Tmem182 transcript level. As skeletal muscle and heart were also found to express Tmem182 transcript, we assessed expression in C2C12 myogenesis and observed a ~770-fold upregulation upon conversion of myoblasts to myocytes.

Conclusion

WAT is the most prominent site of Tmem182 transcript expression and levels of transcript for Tmem182 are altered in adipose tissues of ob/ob mice and upon exposure of 3T3-L1 adipocytes to the proinflammatory cytokine TNFα. The dramatic upregulation of Tmem182 transcript during in vitro adipogenesis and myogenesis suggests Tmem182 may function in intracellular pathways important in these two cell types.

Wdnm1-like, a new adipokine with a role in MMP-2 activation

White adipose tissue functions in energy storage and as an endocrine organ. DNA microarray analysis led us to identify Wdnm1-like, a distant member of the whey acidic protein/four-disulfide core (WAP/4-DSC) family, as a differentiation-dependent gene in white and brown adipogenesis. Wdnm1-like is a novel 6.8-kDa protein, and Western blot analysis reveals secretion into culture media. Wdnm1-like transcript is selectively expressed in adipose tissue and liver and is enriched approximately 500-fold in white adipose depots vs. brown. Cellular fractionation of WAT demonstrates Wdnm1-like transcript expression is restricted to the adipocyte population. Studies in 3T3-L1 preadipocytes, an in vitro model of white adipogenesis, indicate Wdnm1-like transcript increases within 6 h of adipogenic induction with an approximately 17,000-fold increase by day 7. Dramatic upregulation of Wdnm1-like also accompanies white adipogenesis of ScAP-23 preadipocytes and primary preadipocytes. TNF-alpha treatment of 3T3-L1 adipocytes increased Wdnm1-like transcript level 2.4-fold and was attenuated by pretreatment with the p38 MAP kinase inhibitor SB203580. A number of WAP/4-DSC family proteins function as protease inhibitors. This, taken with the role of extracellular remodeling in adipogenesis, led us to address effects of Wdnm1-like on matrix metalloproteinase (MMP) activity. Gelatin zymography of HT1080 fibrosarcoma cells transfected with a Wdnm1-like expression construct revealed markedly increased levels of active MMP-2. Our findings identify a new member of the adipocyte "secretome" that functions to enhance MMP-2 activity. We postulate that Wdnm1-like may play roles in remodeling of the extracellular milieu in adipogenesis, as well as in tumor microenvironments where adipocytes are key stromal components.

Depot-specific regulation of the conversion of cortisone to cortisol in human adipose tissue

OBJECTIVE

Our main objective was to compare the regulation of cortisol production within omental (Om) and abdominal subcutaneous (Abd sc) human adipose tissue.

METHODS AND PROCEDURES

Om and Abd sc adipose tissue were obtained at surgery from subjects with a wide range of BMI. Hydroxysteroid dehydrogenase (HSD) activity ((3)H-cortisone and (3)H-cortisol interconversion) and expression were measured before and after organ culture with insulin and/or dexamethasone.

RESULTS

Type 1 HSD (HSD1) mRNA and reductase activity were mainly expressed within adipocytes and tightly correlated with adipocyte size within both depots. There was no depot difference in HSD1 expression or reductase activity, while cortisol inactivation and HSD2 mRNA expression (expressed in stromal cells) were higher in Om suggesting higher cortisol turnover in this depot. Culture with insulin decreased HSD reductase activity in both depots. Culture with dexamethasone plus insulin compared to insulin alone increased HSD reductase activity only in the Om depot. This depot-specific increase in reductase activity could not be explained by an alteration in HSD1 mRNA or protein, which was paradoxically decreased. However, in Om only, hexose-6-phosphate dehydrogenase (H6PDH) mRNA levels were increased by culture with dexamethasone plus insulin compared to insulin alone, suggesting that higher nicotinamide adenine dinucleotide phosphate-oxidase (NADPH) production within the endoplasmic reticulum (ER) contributed to the higher HSD reductase activity.

DISCUSSION

We conclude that in the presence of insulin, glucocorticoids cause a depot-specific increase in the activation of cortisone within Om adipose tissue, and that this mechanism may contribute to adipocyte hypertrophy and visceral obesity.

TNF-alpha and adipocyte biology

Dyslipidemia and insulin resistance are commonly associated with catabolic or lipodystrophic conditions (such as cancer and sepsis) and with pathological states of nutritional overload (such as obesity-related type 2 diabetes). Two common features of these metabolic disorders are adipose tissue dysfunction and elevated levels of tumour necrosis factor-alpha (TNF-alpha). Herein, we review the multiple actions of this pro-inflammatory adipokine on adipose tissue biology. These include inhibition of carbohydrate metabolism, lipogenesis, adipogenesis and thermogenesis and stimulation of lipolysis. TNF-alpha can also impact the endocrine functions of adipose tissue. Taken together, TNF-alpha contributes to metabolic dysregulation by impairing both adipose tissue function and its ability to store excess fuel. The molecular mechanisms that underlie these actions are discussed.

Improvement of chronic heart failure by dexamethasone is not associated with downregulation of leptin in rats

AIM

To demonstrate the hypothesis that dexamethasone (Dex) could improve chronic heart failure (CHF) by inhibiting the downstream signaling transduction of leptin but had no influence on the upregulation of leptin and its receptor in myocardium.

METHODS

CHF was induced by left coronary artery ligation for 6 weeks. CHF rats were treated with Dex 50 mg.kg/d. Hemodynamics, histology, reactive oxygen species (ROS)-related parameters, and leptin concentrations in serum were measured. The mRNA expression of matrix metalloproteinases (MMP)2/9, tissue inhibitor of metalloproteinases (TIMP)1/2, tumor necrosis factor (TNF)-alpha, and OB-Rb were measured by RT-PCR.

RESULTS

In the CHF rats, hemodynamic functions were deteriorated, which was accompanied with myocardium remodeling and histological changes. CHF rats showed hyperleptinemia and excessive ROS in the serum, and the upregulation of MMP-2/9, TNF-alpha, and leptin receptor mRNA and downregulation of TIMP-1/2 mRNA in the myocardium compared with the sham operation group. Dex treatment significantly ameliorated CHF in association with the reversion of the abnormalities of MMP-2/9, TIMP-1/2, TNF-alpha, and ROS. But Dex had no influence on the hyperleptinemia and the upregulated leptin and its receptor in the myocardium during CHF.

CONCLUSION

Dex improves CHF by inhibiting TNF-alpha, MMP-2, MMP-9, and ROS. Dex had no effects on upregulated leptin and its receptor expression and hyperleptinemia induced by CHF.

Adipose tissue-derived factors: impact on health and disease

The endocrine functions of the adipose organ are widely studied at this stage. The adipose organ, and in particular adipocytes, communicate with almost all other organs. Although some adipose tissue pads assume the functions as distinct "miniorgans," adipocytes can also be present in smaller numbers interspersed with other cell types. Although fat pads have the potential to have a significant systemic impact, adipocytes may also affect neighboring tissues through paracrine interactions. These local or systemic effects are mediated through lipid and protein factors. The protein factors are commonly referred to as adipokines. Their expression and posttranslational modifications can undergo dramatic changes under different metabolic conditions. Due to the fact that none of the mutations that affect adipose tissue trigger embryonic lethality, the study of adipose tissue physiology lends itself to genetic analysis in mice. In fact, life in the complete absence of adipose tissue is possible in a laboratory setting, making even the most extreme adipose tissue phenotypes genetically amenable to be analyzed by disruption of specific genes or overexpression of others. Here, we briefly discuss some basic aspects of adipocyte physiology and the systemic impact of adipocyte-derived factors on energy homeostasis.

Les lipodystrophies secondaires aux traitements antirétroviraux de l’infection par le VIH

HIV infection requires the continuous administration of antiretroviral molecules. Individual molecules belonging to the two main classes, protease inhibitors (PIs) and nucleoside analogues inhibitors of the viral reverse transcriptase (NRTIs) have been shown to be involved in deleterious side effects collectively called the lipodystrophy syndrome. This syndrome associates altered body fat repartition (peripheral lipoatrophy and visceral fat hypertrophy) and metabolic alterations (dyslipidemia, insulin resistance and diabetes). The pathophysiology of these alterations is complex but different studies argue for adipose tissue being a target of some PIs and NRTIs acting through different mechanisms. NRTIs are able to induce mitochondrial dysfonction and to modify adipocyte phenotype and adipose tissue pattern of secretion of cytokines (TNFalpha, IL-6) and other adipokines (adiponectin, leptin) probably through the production of reactive oxygen species. Some PIs also act on adipocyte, alter its differentiation and insulin sensitivity and also the pattern of secretion of adipokines by adipose tissue. These hypotheses could explain the loss of adipose tissue, while the mechanisms of visceral fat hypertrophy remain speculative. Since some adipokines and the free fatty acids released by adipocytes play a major role in the control of liver and muscles insulin sensitivity, these alterations are probably involved in the metabolic alterations seen in the patients. In addition, lipodystrophic adipose tissue could be involved in the increased lesions of atherogenesis and steatohepatitis presented by these patients. The treatment of lipodystrophy remains difficult and, at present, privileges the switch of the more deleterious drugs towards new molecules less aggressive for adipose tissue.