Human breast adipocytes express interleukin-6 (IL-6) and its receptor system: increased IL-6 production by beta-adrenergic activation and effects of IL-6 on adipocyte function

Development and characterization of a chicory extract fermented by Akkermansia muciniphila: An in vitro study on its potential to modulate obesity-related inflammation

Obesity, the fifth leading cause of death globally and linked to chronic low-grade inflammation and development of numerous severe pathologies, is a major public health problem. Fermented foods, probiotics, and postbiotics emerge as promising avenues for combating obesity and inflammation. The aim of our study was to develop and characterize phyto-postbiotics corresponding to prebiotic compounds fermented by gut bacteria, which could act on obesity and related-inflammation. Chicory extract fermented by Akkermansia muciniphila (C-Akm) was selected as the most antioxidant of 20 fermented extracts. The identification of metabolites derived from C-Akm extract has enabled us to detect mostly amino acids, acids, and some polyphenols (daidzein and genistein). The anti-inflammatory and anti-obesity activities of C-Akm extract were studied by testing the extract (50 μg/mL) on the polarization of THP-1 into macrophages, the secretion of pro-inflammatory cytokines in LPS-stimulated PBMCs, and the secretion of leptin and adiponectin in adipospheroids derived from human adipose stem cells. Finally, the extract was examined in 3D co-culture model mimicking inflamed obese adipose tissue. We found that C-Akm extract decreased ROS generation, TNF-α and Il-6 gene expression in polarized macrophages, INFγ and IL-17A secretion in LPS-stimulated PBMCs stimulated with LPS. It also decreased leptin expression while increasing adiponectin and HSL expression levels in both adipocytes and co-cultures. In addition, C-Akm extract stimulated adiponectin secretion in the co-culture model. Finally, our in vitro investigations demonstrated the potential benefits of C-Akm extract in the prevention and treatment of obesity-related inflammation.

Fat and inflammation: adipocyte-myeloid cell crosstalk in atherosclerosis

Adipose tissue inflammation has been implicated in various chronic inflammatory diseases and cancer. Perivascular adipose tissue (PVAT) surrounds the aorta as an extra layer and was suggested to contribute to atherosclerosis development. PVAT regulates the function of endothelial and vascular smooth muscle cells in the aorta and represent a reservoir for various immune cells which may participate in aortic inflammation. Recent studies demonstrate that adipocytes also express various cytokine receptors and, therefore, may directly respond to inflammatory stimuli. Here we will summarize current knowledge on immune mechanisms regulating adipocyte activation and the crosstalk between myeloid cells and adipocytes in pathogenesis of atherosclerosis.

SHP2 regulates adipose maintenance and adipocyte-pancreatic cancer cell crosstalk via PDHA1

Adipocytes are the most abundant cell type in the adipose tissue, and their dysfunction is a significant driver of obesity-related pathologies, such as cancer. The mechanisms that (1) drive the maintenance and secretory activity of adipocytes and (2) mediate the cancer cellular response to the adipocyte-derived factors are not fully understood. To address that gap of knowledge, we investigated how alterations in Src homology region 2-containing protein (SHP2) activity affect adipocyte function and tumor crosstalk. We found that phospho-SHP2 levels are elevated in adipose tissue of obese mice, obese patients, and differentiating adipocytes. Immunofluorescence and immunoprecipitation analyses as well as in-silico protein-protein interaction modeling demonstrated that SHP2 associates with PDHA1, and that a positive association promotes a reactive oxygen species (ROS)-driven adipogenic program. Accordingly, this SHP2-PDHA1-ROS regulatory axis was crucial for adipocyte maintenance and secretion of interleukin-6 (IL-6), a key cancer-promoting cytokine. Mature adipocytes treated with an inhibitor for SHP2, PDHA1, or ROS exhibited an increased level of pro-lipolytic and thermogenic proteins, corresponding to an increased glycerol release, but a suppression of secreted IL-6. A functional analysis of adipocyte-cancer cell crosstalk demonstrated a decreased migration, invasion, and a slight suppression of cell cycling, corresponding to a reduced growth of pancreatic cancer cells exposed to conditioned media (CM) from mature adipocytes previously treated with inhibitors for SHP2/PDHA1/ROS. Importantly, PDAC cell growth stimulation in response to adipocyte CM correlated with PDHA1 induction but was suppressed by a PDHA1 inhibitor. The data point to a novel role for (1) SHP2-PDHA1-ROS in adipocyte maintenance and secretory activity and (2) PDHA1 as a regulator of the pancreatic cancer cells response to adipocyte-derived factors.

Association of adipokines with insulin resistance and metabolic syndrome including obesity and diabetes

Adipose tissue (AT) acts as a highly active endocrine organ, which secretes a wide range of adipokine hormones. In the past few years, several adipokines (leptin, adiponectin, resistin etc.) have been discovered showing metabolic consequences in relation to insulin resistance (IR), obesity and diabetes. These adipokines are considered to be an important component playing an important role in the regulation of energy metabolism. They have been shown to be involved in the pathogenesis of metabolic syndrome (MetS) and cardiac diseases. The current article provides a holistic summary of recent knowledge on adipokines and emphasizes their importance in association with IR, obesity, diabetes and MetS. Adipokines such as leptin, adiponectin, resistin and tumor necrosis factor-alpha (TNF-α) have been involved in the regulation of an array of metabolic functions and disease associated with it, e.g. appetite and energy balance of the body, suppression of atherosclerosis and liver fibrosis, obesity with type 2 diabetes (T2D) and IR. An important adipokine, Interleukin-6 (IL-6), also correlates positively with human obesity and IR and also the elevated level of IL-6 predicts development of T2D. All of these hormones have important correlation with energy homeostasis, glucose and lipid metabolism, cardiovascular function and immunity. All the possible connections have extended the biological emphasis of AT secreted adipokines as an investigator in the development of MetS, and are now no longer considered as only an energy storage site.

Interleukin 6 as an energy allocator in muscle tissue

Extensive research has shown that interleukin 6 (IL-6) is a multifunctional molecule that is both proinflammatory and anti-inflammatory, depending on the context. Here, we combine an evolutionary perspective with physiological data to propose that IL-6's context-dependent effects on metabolism reflect its adaptive role for short-term energy allocation. This energy-allocation role is especially salient during physical activity, when skeletal muscle releases large amounts of IL-6. We predict that during bouts of physical activity, myokine IL-6 fulfills the three main characteristics of a short-term energy allocator: it is secreted from muscle in response to an energy deficit, it liberates somatic energy through lipolysis and it enhances muscular energy uptake and transiently downregulates immune function. We then extend this model of energy allocation beyond myokine IL-6 to reinterpret the roles that IL-6 plays in chronic inflammation, as well as during COVID-19-associated hyperinflammation and multiorgan failure.

Interleukin 6 receptor is not directly involved in regulation of body weight in diet-induced obesity with and without physical exercise

High level of interleukin 6 (IL-6), released by adipocytes in an obesity-induced, low grade inflammation state, is a regulator of insulin resistance and glucose tolerance. IL-6 has also regenerative, anti-inflammatory and anti-diabetogenic functions, when secreted as myokine by skeletal muscles during physical exercise. IL-6 mainly activates cells via two different receptor constellations: classic and trans-signalling, in which IL-6 initially binds to membrane-bound receptor (IL-6R) or soluble IL-6 receptor (sIL-6R) before activating signal transducing gp130 receptor. Previously, we generated transgenic soluble IL-6 receptor ^+/+ (sIL-6R^+/+) mice with a strategy that mimics ADAM10/17 hyperactivation, reflecting a situation in which only IL-6 trans-signalling is active, whereas classic signalling is completely abrogated. In this study, we metabolically phenotyped IL-6R deficient mice (IL-6R-KO), sIL-6R^+/+ mice and wild-type littermates fed either a standard chow (SD) or a high-fat diet (HFD) in combination with a 6-weeks treadmill exercise protocol. All mice were subjected to analyses of body weight and body composition, determination of blood glucose and insulin level under fasting conditions, as well as determination of substrate preference by indirect calorimetry. Neither classic IL-6 nor trans-signalling do influence the outcome of diet-induced obesity, insulin sensitivity and glycaemic control. Furthermore, IL-6R deficiency is not impairing the beneficial effect of physical exercise. We conclude that the IL-6R does not play a requisite role in regulation of body weight and glucose metabolism in diet-induced obese mice.

Ketones for Post-exercise Recovery: Potential Applications and Mechanisms

Ketogenic diet has been introduced in therapeutic areas for more than a century, but the role of ketones in exercise performance has only been explored in the past decade. One of the main reasons that allows the investigation of the role of ketones in exercise performance is the emergence of exogenous ketones, allowing athletes to achieve the state of ketosis acutely, and independent of their metabolic states. While there are mixed results showing either exogenous ketones improve exercise performance or no effect, the mechanisms of action are still being heavily researched. Moreover, these early data from exercise physiology studies suggested that exogenous ketones may play a more prominent role in post-exercise recovery, leading to a more pronounced cumulative impact over subsequent exercise performance. This review will look at existing evidence on the role of ketones in recovery and attempt to identify the current best practices and potential mechanisms that drive improved recovery.

Role of Interleukin-6 in Vascular Health and Disease

IL-6 is usually described as a pleiotropic cytokine produced in response to tissue injury or infection. As a pro-inflammatory cytokine, IL-6 activates innate and adaptative immune responses. IL-6 is released in the innate immune response by leukocytes as well as stromal cells upon pattern recognition receptor activation. IL-6 then recruits immune cells and triggers B and T cell response. Dysregulated IL-6 activity is associated with pathologies involving chronic inflammation and autoimmunity, including atherosclerosis. However, IL-6 is also produced and released under beneficial conditions, such as exercise, where IL-6 is associated with the anti-inflammatory and metabolic effects coupled with physical adaptation to intense training. Exercise-associated IL-6 acts on adipose tissue to induce lipogenesis and on arteries to induce adaptative vascular remodeling. These divergent actions could be explained by complex signaling networks. Classical IL-6 signaling involves a membrane-bound IL-6 receptor and glycoprotein 130 (gp130), while trans-signaling relies on a soluble version of IL-6R (sIL-6R) and membrane-bound gp130. Trans-signaling, but not the classical pathway, is regulated by soluble gp130. In this review, we discuss the similarities and differences in IL-6 cytokine and myokine signaling to explain the differential and opposite effects of this protein during inflammation and exercise, with a special focus on the vascular system.

Adipocytes: active facilitators in epithelial ovarian cancer progression?

There is growing evidence that adipocytes play important roles in the progression of multiple cancers. Moreover, in obesity, adipocytes alter their original functions and contribute to the metabolic and inflammatory changes of adipose tissue microenvironment, which can further enhance tumor development. At present, the roles of adipocytes in the pathogenesis of epithelial ovarian cancer (EOC) are far from being fully elucidated. Herein, we summarized the recent advances in understanding the roles of adipocytes in EOC progression. Adipocytes, close neighbors of EOC tissue, promote EOC growth, invasion, metastasis and angiogenesis through adipokine secretion, metabolic remodeling and immune microenvironment modulation. Moreover, adipocytes are important therapeutic targets and may work as useful anticancer drug delivery depot for EOC treatment. Furthermore, adipocytes also act as a therapeutic obstacle for their involvement in EOC treatment resistance. Hence, better characterization of the adipocytes in EOC microenvironment and the crosstalk between adipocytes and EOC cells may provide insights into EOC progression and suggest novel therapeutic opportunities.

Catecholamines suppress fatty acid re-esterification and increase oxidation in white adipocytes via STAT3

Catecholamines stimulate the mobilization of stored triglycerides in adipocytes to provide fatty acids (FAs) for other tissues. However, a large proportion is taken back up and either oxidized or re-esterified. What controls the disposition of these FAs in adipocytes remains unknown. Here, we report that catecholamines redirect FAs for oxidation through the phosphorylation of signal transducer and activator of transcription 3 (STAT3). Adipocyte STAT3 is phosphorylated upon activation of β-adrenergic receptors, and in turn suppresses FA re-esterification to promote FA oxidation. Adipocyte-specific Stat3 KO mice exhibit normal rates of lipolysis, but exhibit defective lipolysis-driven oxidative metabolism, resulting in reduced energy expenditure and increased adiposity when they are on a high-fat diet. This previously unappreciated, non-genomic role of STAT3 explains how sympathetic activation can increase both lipolysis and FA oxidation in adipocytes, revealing a new regulatory axis in metabolism.

The role of interleukin-6 in glucose homeostasis and lipid metabolism

Low-grade inflammation is recognized as an important factor in the development and progression of a multitude of diseases including type 2 diabetes mellitus and cardiovascular disease. The potential of using antibody-based therapies that neutralize key players of low-grade inflammation has gained scientific momentum as a novel therapeutic strategy in metabolic diseases. As interleukin-6 (IL-6) is traditionally considered a key pro-inflammatory factor, the potential of expanding the use of anti-IL-6 therapies to metabolic diseases is intriguing. However, IL-6 is a molecule of a very pleiotropic nature that regulates many aspects of not only inflammation but also metabolism. In this review, we give a brief overview of the pro- and anti-inflammatory aspects of IL-6 and provide an update on its role in metabolic regulation, with a specific focus on glucose homeostasis and adipose tissue metabolism. Finally, we shall discuss the metabolic implications and clinical potential of blocking IL-6 signaling, focusing on glucose homeostasis and lipid metabolism.

An 8-Week Ketogenic Diet Alternated Interleukin-6, Ketolytic and Lipolytic Gene Expression, and Enhanced Exercise Capacity in Mice

Adjusting dietary fat intake is reported to affect mitochondrial biogenesis and fatty acid oxidation (FAO), and thus may enhance exercise capacity. However, a high-fat diet where carbohydrate intake is not limited enough also makes it difficult for athletes to maintain weight, and may fail to force the body to utilize fat. As such, a low-carbohydrate, high-fat, ketogenic diet (KD) may be viable. We have previously reported that an eight-week KD enhances exercise capacity, and suggested the mechanism to be enhanced lipolysis and ketolysis. In the present study, we investigated how an eight-week KD alters mRNA expression during fatty acid mobilization, FAO and ketolysis. We found that an eight-week KD may remodel the lipid metabolism profile, thus contributing to influence exercise capacity. We also found that ketolysis, lipolysis and FAO adaptations may contribute to enhanced exhaustive exercise performance. Along with enhanced FAO capacity during exhaustive exercise, a KD may also alter IL-6 synthesis and secretion profile, thus contribute to fatty acid mobilization, ketolysis, lipolysis and preventing muscle damage. Both the lipid metabolism response and IL-6 secretion appeared to be muscle fiber specific. Taken together, the previous and present results reveal that an eight-week KD may enhance exercise performance by up-regulating ketolysis and FAO ability. Therefore, a KD may have the potential to prevent muscle damage by altering IL-6 secretion profile, indicating that a KD may be a promising dietary approach in endurance athletes, sports, and for injury prevention.

IL-6-mediated cross-talk between human preadipocytes and ductal carcinoma in situ in breast cancer progression

Background

The function of preadipocytes in the progression of early stage breast cancer has not been fully elucidated at the molecular level. To delineate the role of preadipocytes in breast cancer progression, we investigated the cross-talk between human breast ductal carcinoma in situ (DCIS) cells and preadipocytes with both an in vitro culture and xenograft tumor model.

Methods

GFP or RFP was transduced into human DCIS cell line MCF10DCIS.com cells or preadipocytes using lentivirus. Cell sorter was used to separate pure, viable populations of GFP- or RFP-transduced cells. Cell viability and proliferation was assessed by crystal violet assays and cell migration and invasion capability was assayed by the transwell strategy. Gene and protein levels were measured by western blot, RT-PCR and immunostaining. Adipokines and cytokines were quantified using ELISA. Human tumor xenografts in a nude mice model were used. Ultrasound imaging of tumors was performed to evaluate the therapeutic potential of a IL-6 neutralizing antibody.

Results

In the co-culture system with the MCF10DCIS.com and preadipocytes, MCF10DCIS.com proliferation, migration and invasion were enhanced by preadipocytes. Preadipocytes exhibited in an increased IL-6 secretion and cancer-associated fibroblast markers expression, FSP1 and α-SMC in co-culture with MCF10DCIS.com or in MCF10DCIS.com conditioned media, whereas the adipocyte differentiation capacity was suppressed by co-culture with MCF10DCIS.com. A neutralizing antibody of IL-6 or IL-6R suppressed the promotion of MCF10DCIS.com proliferation and migration by co-culture with preadipocytes. In the xenograft tumor model, the tumor growth of MCF10DCIS.com was enhanced by the co-injection of preadipocytes, and the administration of IL-6 neutralizing antibodies resulted in potent effects on tumor inhibition.

Conclusions

Our findings suggest that IL-6-mediated cross-talk between preadipocytes and breast DCIS cells can promote the progression of early stage breast cancer. Therefore, blocking IL-6 signaling might be a potential therapeutic strategy for breast DCIS characterized by pathological IL-6 overproduction.

Electronic supplementary material

The online version of this article (10.1186/s13046-018-0867-3) contains supplementary material, which is available to authorized users.

Multifaceted Roles of Interleukin-6 in Adipocyte-Breast Cancer Cell Interaction

Breast cancer is the most common malignancy in women worldwide, with a developmental process spanning decades. The malignant cells recruit a variety of cells including fibroblasts, endothelial cells, immune cells, and adipocytes, creating the tumor microenvironment. The tumor microenvironment has emerged as active participants in breast cancer progression and response to treatment through autocrine and paracrine interaction with the malignant cells. Adipose tissue is abundant in the breast cancer microenvironment; interactions with cancer cells create cancer-associated adipocytes which produce a variety of adipokines that influence breast cancer initiation, metastasis, angiogenesis, and cachexia. Interleukin (IL)-6 has emerged as key compound significantly produced by breast cancer cells and adipocytes, with the potential of inducing proliferation, epithelial-mesenchymal phenotype, stem cell phenotype, angiogenesis, cachexia, and therapeutic resistance in breast cancer cells. Our aim is to present a brief knowledge of IL-6’s role in breast cancer. This review summarizes our current understanding of the breast microenvironment, with emphasis on adipocytes as key players in breast cancer tumorigenesis. The effects of key adipocytes such as leptin, adipokines, TGF-b, and IL-6 are discussed. Finally, we discuss the role of IL-6 in various aspects of cancer progression.

The brain and immune system prompt energy shortage in chronic inflammation and ageing

Sequelae frequently seen in patients with chronic inflammatory diseases, such as fatigue, depressed mood, sleep alterations, loss of appetite, muscle wasting, cachectic obesity, bone loss and hypertension, can be the result of energy shortages caused by an overactive immune system. These sequelae can also be found in patients with chronic inflammatory diseases that are in remission and in ageing individuals, despite the immune system being less active in these situations. This Perspectives article proposes a new way of understanding situations of chronic inflammation (such as rheumatic diseases) and ageing based on the principles of evolutionary medicine, energy regulation and neuroendocrine-immune crosstalk. A conceptual framework is provided to enable physicians and scientists to better understand the signs and symptoms of chronic inflammatory diseases and long-term disease consequences resulting from physical and mental inactivity.

In Vivo Effects of Lipopolysaccharide on Peroxisome Proliferator-Activated Receptor Expression in Juvenile Gilthead Seabream (Sparus Aurata)

Fish are constantly exposed to microorganisms in the aquatic environment, many of which are bacterial pathogens. Bacterial pathogens activate the innate immune response in fish involving the production of pro-inflammatory molecules that, in addition to their immune-related role, can affect non-immune tissues. In the present study, we aimed at investigating how inflammatory responses can affect metabolic homeostasis in the gilthead seabream (Sparus aurata), a teleost of considerable economic importance in Southern European countries. Specifically, we mimicked a bacterial infection by in vivo administration of lipopolysaccharide (LPS, 6 mg/kg body weight) and measured metabolic parameters in the blood and, importantly, the mRNA expression levels of the three isotypes of peroxisome proliferator activated receptors (PPARα, β, and γ) in metabolically-relevant tissues in seabream. PPARs are nuclear receptors that are important for lipid and carbohydrate metabolism in mammals and that act as biological sensors of altered lipid metabolism. We show here that LPS-induced inflammatory responses result in the modulation of triglyceride plasma levels that are accompanied most notably by a decrease in the hepatic mRNA expression levels of PPARα, β, and γ and by the up-regulation of PPARγ expression only in adipose tissue and the anterior intestine. In addition, LPS-induced inflammation results in an increase in the hepatic mRNA expression and protein activity levels of members of the mitogen-activated protein kinase (MAPK) family, known in mammals to regulate the transcription and activity of PPARs. Our results provide evidence for the involvement of PPARs in the metabolic response to inflammatory stimuli in seabream and offer insights into the molecular mechanisms underlying the redirection of metabolic activities under inflammatory conditions in vertebrates.

Cocktail supplement with rosiglitazone: a novel inducer for chicken preadipocyte differentiation in vitro

Chicken preadipocytes cultured in cocktail supplement with rosiglitazone resulted in a marked increase in lipid droplet accumulation, glycerol-3-phosphate dehydrogenase (GPDH) activity and mRNA expression of adipocyte fatty acid-binding protein (aP2), G₀/G₁ switch gene 2 (G0S2), peroxisome proliferator-activated receptor γ (PPARγ) and lipolysis. The present study provides a novel induction method for in vitro chicken preadipocyte differentiation.

The preadipocyte differentiation biological process involves a cascade of transcriptional events that culminates in the expression of peroxisome proliferator-activated receptor (PPAR) γ. The differentiation cocktail [insulin (INS), dexamethasone (DEX) and isobutylmethylxanthine (IBMX)] can induce preadipocyte differentiation in mammals, but it is insufficient for chicken (Gallus gallus) adipogenesis. Oleate can induce chicken preadipocyte differentiation, but these differentiated preadipocytes may not be fully functional. The objective of the current study was to evaluate whether chicken preadipocytes can be induced to mature adipocytes by a novel induction method using differentiation cocktail supplemented with PPARγ agonist(s). Chicken preadipocytes cultured in cocktail supplemented with rosiglitazone or troglitazone resulted in a marked increase in lipid droplet accumulation (P<0.05), glycerol-3-phosphate dehydrogenase (GPDH) activity (P<0.05), mRNA expression level of adipocyte fatty acid-binding protein (aP2; P<0.05), G₀/G₁ switch gene 2 (G0S2; P<0.05) and lipolysis (P<0.05). In addition, supplementation of the cocktail with rosiglitazone promoted PPARγ mRNA expression (P<0.05). In conclusion, our data indicated that chicken preadipocytes can be induced to mature adipocytes using differentiation cocktail supplemented with rosiglitazone. The results of the present study provide a novel induction method for in vitro chicken preadipocyte differentiation.

Interleukin-6 induces impairment in human subcutaneous adipogenesis in obesity-associated insulin resistance

AIMS/HYPOTHESIS

A subset of obese individuals remains insulin sensitive by mechanisms as yet unclear. The hypothesis that maintenance of normal subcutaneous (SC) adipogenesis accounts, at least partially, for this protective phenotype and whether it can be abrogated by chronic exposure to IL-6 was investigated.

METHODS

Adipose tissue biopsies were collected from insulin-sensitive (IS) and insulin-resistant (IR) individuals undergoing weight-reduction surgery. Adipocyte size, pre-adipocyte proportion of stromal vascular fraction (SVF)-derived cells, adipogenic capacity and gene expression profiles of isolated pre-adipocytes were determined, along with local in vitro IL-6 secretion. Adipogenic capacity was further assessed in response to exogenous IL-6 application.

RESULTS

Despite being equally obese, IR individuals had significantly lower plasma leptin and adiponectin levels and higher IL-6 levels compared with age-matched IS counterparts. Elevated systemic IL-6 in IR individuals was associated with hyperplasia of adipose tissue-derived SVF cells, despite higher frequency of hypertrophied adipocytes. SC pre-adipocytes from these tissues exhibited lower adipogenic capacity accompanied by downregulation of PPARγ (also known as PPARG) and CEBPα (also known as CEBPA) and upregulation of GATA3 expression. Impaired adipogenesis in IR individuals was further associated with increased adipose secretion of IL-6. Treatment of IS-derived SC pre-adipocytes with IL-6 reduced their adipogenic capacity to levels of the IR group.

CONCLUSIONS/INTERPRETATION

Obesity-associated insulin resistance is marked by impaired SC adipogenesis, mediated, at least in a subset of individuals, by elevated local levels of IL-6. Understanding the molecular mechanisms underlying reduced adipogenic capacity in IR individuals could help target appropriate therapeutic strategies aimed at those at greatest risk of insulin resistance and type 2 diabetes mellitus.

CXCL3 positively regulates adipogenic differentiation

Chemokines are a family of cytokines inducing cell migration and inflammation. Recent reports have implicated the roles of chemokines in cell differentiation. However, little is known about the functional roles of chemokines in adipocytes. Here, we explored gene expression levels of chemokines and chemokine receptors during adipogenic differentiation. We have found that two chemokines, chemokine (C-X-C motif) ligand 3 (CXCL3) and CXCL13, as well as CXC chemokine receptor 2 (CXCR2), a CXCL3 receptor, are highly expressed in mature adipocytes. When 3T3-L1 cells and ST2 cells were induced to differentiate, both the number of lipid droplets and the expression levels of adipogenic markers were significantly promoted by the addition of CXCL3, but not CXCL13. Conversely, gene knockdown of either CXCL3 or CXCR2 by specific siRNA effectively inhibited the course of adipogenic differentiation. CXCL3 treatment of 3T3-L1 cells significantly induced the phosphorylation of ERK and c-jun N-terminal kinase (JNK). Furthermore, CXCL3-induced CCAAT-enhancer binding protein (C/EBP)β and δ expression was suppressed by both ERK and JNK-specific inhibitors. Furthermore, chromatin immunoprecipitation assay revealed functional binding of PPARγ2 within the cxcl3 promoter region. Taken together, these results have indicated that CXCL3 is a novel adipokine that facilitates adipogenesis in an autocrine and/or a paracrine manner through induction of c/ebpb and c/ebpd.

Post-menopausal Women Exhibit Greater Interleukin-6 Responses to Mental Stress Than Older Men

BACKGROUND

Acute stress triggers innate immune responses and elevation in circulating cytokines including interleukin-6 (IL-6). The effect of sex on IL-6 responses remains unclear due to important limitations of previous studies.

PURPOSE

The purpose of this study was to examine sex differences in IL-6 responses to mental stress in a healthy, older (post-menopausal) sample accounting for several moderating factors.

METHODS

Five hundred six participants (62.9 ± 5.60 years, 55 % male) underwent 10 min of mental stress consisting of mirror tracing and Stroop task. Blood was sampled at baseline, after stress, and 45 and 75 min post-stress, and assayed using a high sensitivity kit. IL-6 reactivity was computed as the mean difference between baseline and 45 min and between baseline and 75 min post-stress. Main effects and interactions were examined using ANCOVA models.

RESULTS

There was a main effect of time for the IL-6 response (F 3,1512 = 201.57, p = <.0001) and a sex by time interaction (F 3,1512 = 17.07, p = <.001). In multivariate adjusted analyses, IL-6 reactivity was significantly greater in females at 45 min (M = 0.37 ± 0.04 vs. 0.20 ± 0.03 pg/mL, p = .01) and at 75 min (M = 0.57 ± 0.05 vs. 0.31 ± 0.05 pg/mL, p = .004) post-stress compared to males. Results were independent of age, adiposity, socioeconomic position, depression, smoking and alcohol consumption, physical activity, statin use, testing time, task appraisals, hormone replacement, and baseline IL-6. Other significant predictors of IL-6 reactivity were lower household wealth, afternoon testing, and baseline IL-6.

CONCLUSIONS

Healthy, post-menopausal females exhibit substantially greater IL-6 responses to acute stress. Inflammatory responses if sustained over time may have clinical implications for the development and maintenance of inflammatory-related conditions prevalent in older women.

Obesity and inflammation: reduced cytokine expression due to resveratrol in a human in vitro model of inflamed adipose tissue

Obesity is associated with an inflammatory status and linked with a number of pathophysiological complications among them cardiovascular disease, type 2 diabetes mellitus, or the metabolic syndrome. Resveratrol was proposed to improve obesity-related inflammatory problems, but the effect of resveratrol on cytokine expression in obesity is not completely understood. In this study, we used an in vitro model of human adipose tissue inflammation to examine the effects of resveratrol on the production of the inflammatory cytokines interleukin 6 (IL-6), IL-8, and monocyte chemoattractant protein 1 (MCP-1). We found that resveratrol reduced IL-6, IL-8, and MCP-1 levels in a concentration-dependent manner in adipocytes under inflammatory conditions. Further experiments showed that the action of resveratrol was mainly due to its NFκB inhibitory potential. Thus, our data support the concept that resveratrol can alleviate obesity-induced up-regulation of inflammatory cytokines providing a new insight toward novel treatment options in obesity.

IL-6 and epinephrine have divergent fiber type effects on intramuscular lipolysis

IL-6 is an exercise-regulated myokine that has been suggested to increase lipolysis in fast-twitch skeletal muscle. However, it is not known if a similar effect is present in slow-twitch muscle. Furthermore, epinephrine increases IL-6 secretion from skeletal muscle, suggesting that IL-6 could play a role in mediating the lipolytic effects of catecholamines. The purpose of this study was to determine whether IL-6 stimulates skeletal muscle lipolysis in a fiber type dependent manner and is required for epinephrine-stimulated lipolysis in murine skeletal muscle. Soleus and extensor digitorum longus (EDL) muscles from male C57BL/6J wild-type and IL-6(-/-) mice were incubated with 1 μM (183 ng/ml) epinephrine or 75 ng/ml recombinant IL-6 (rIL-6) for 60 min. IL-6 treatment increased 5'-AMP-activated protein kinase and signal transducer and activator of transcription 3 phosphorylation and glycerol release in isolated EDL but not soleus muscles from C57BL/6J mice. Conversely, epinephrine increased glycerol release in soleus but not EDL muscles from C57BL/6J mice. Basal lipolysis was elevated in soleus muscle from IL-6(-/-) mice, and this was associated with increases in adipose triglyceride lipase (ATGL) and its coactivator comparative gene identification-58 (CGI-58). The increase in ATGL content does not appear to be due to a loss of IL-6's direct effects, because ex vivo treatment with IL-6 failed to alter the expression of ATGL mRNA in soleus muscle. In summary, IL-6 stimulates lipolysis in glycolytic but not oxidative muscle, whereas the opposite fiber type effect is seen with epinephrine. The absence of IL-6 indirectly upregulates lipolysis, and this is associated with increases in ATGL and its coactivator CGI-58.

Differentiation of human adipocytes at physiological oxygen levels results in increased adiponectin secretion and isoproterenol-stimulated lipolysis

Adipose tissue (AT) hypoxia occurs in obese humans and mice. Acute hypoxia in adipocytes causes dysregulation of adipokine secretion with an increase in inflammatory factors and diminished adiponectin release. O₂ levels in humans range between 3 and 11% revealing that conventional in vitro culturing at ambient air and acute hypoxia treatment (1% O₂) are performed under non-physiological conditions. In this study, we mimicked physiological conditions by differentiating human primary adipocytes under 10% or 5% O₂ in comparison to 21% O₂. Induction of differentiation markers was comparable between all three conditions. Adipokine release by adipocytes differentiated at lower oxygen levels was altered, with a marked upregulation of adiponectin, IL-6 and DPP4 secretion, and reduced leptin levels compared with adipocytes differentiated at 21% O₂. Isoproterenol-induced lipolysis was significantly elevated in adipocytes differentiated at 10% and 5% compared with 21% O₂. This effect was accompanied by increased protein expression of β-1 and -2 adrenergic receptor, HSL and perilipin. Conditioned medium (CM) of adipocytes differentiated at the three different conditions was generated for stimulation of human skeletal muscle cells (SkMC) or smooth muscle cells (SMC). CM-induced insulin resistance in SkMC was comparable for the different CMs. However, the SMC proliferative effect of CM from adipocytes differentiated at 10% O₂ was significantly reduced compared with 21% O₂. This study demonstrates that oxygen levels during adipogenesis are important factors altering adipocyte functionality such as adipokine release, in particular adiponectin secretion, as well as the hormone-induced lipolytic pathway.

Dopamine receptors in human adipocytes: expression and functions

Introduction

Dopamine (DA) binds to five receptors (DAR), classified by their ability to increase (D1R-like) or decrease (D2R-like) cAMP. In humans, most DA circulates as dopamine sulfate (DA-S), which can be de-conjugated to bioactive DA by arylsulfatase A (ARSA). The objective was to examine expression of DAR and ARSA in human adipose tissue and determine whether DA regulates prolactin (PRL) and adipokine expression and release.

Methods

DAR were analyzed by RT-PCR and Western blotting in explants, primary adipocytes and two human adipocyte cell lines, LS14 and SW872. ARSA expression and activity were determined by qPCR and enzymatic assay. PRL expression and release were determined by luciferase reporter and Nb2 bioassay. Analysis of cAMP, cGMP, leptin, adiponectin and interleukin 6 (IL-6) was done by ELISA. Activation of MAPK and PI3 kinase/Akt was determined by Western blotting.

Results

DAR are variably expressed at the mRNA and protein levels in adipose tissue and adipocytes during adipogenesis. ARSA activity in adipocyte increases after differentiation. DA at nM concentrations suppresses cAMP, stimulates cGMP, and activates MAPK in adipocytes. Acting via D2R-like receptors, DA and DA-S inhibit PRL gene expression and release. Acting via D1R/D5R receptors, DA suppresses leptin and stimulates adiponectin and IL-6 release.

Conclusions

This is the first report that human adipocytes express functional DAR and ARSA, suggesting a regulatory role for peripheral DA in adipose functions. We speculate that the propensity of some DAR-activating antipsychotics to increase weight and alter metabolic homeostasis is due, in part, to their direct action on adipose tissue.

Activation of peroxisome proliferator-activated receptor-β/-δ (PPAR-β/-δ) ameliorates insulin signaling and reduces SOCS3 levels by inhibiting STAT3 in interleukin-6-stimulated adipocytes

OBJECTIVE

It has been suggested that interleukin (IL)-6 is one of the mediators linking obesity-derived chronic inflammation with insulin resistance through activation of STAT3, with subsequent upregulation of suppressor of cytokine signaling 3 (SOCS3). We evaluated whether peroxisome proliferator-activated receptor (PPAR)-β/-δ prevented activation of the IL-6-STAT3-SOCS3 pathway and insulin resistance in adipocytes.

RESEARCH DESIGN AND METHODS

Adipocytes and white adipose tissue from wild-type and PPAR-β/-δ-null mice were used to evaluate the effect of PPAR-β/-δ on the IL-6-STAT3-SOCS3 pathway.

RESULTS

First, we observed that the PPAR-β/-δ agonist GW501516 prevented both IL-6-dependent reduction in insulin-stimulated Akt phosphorylation and glucose uptake in adipocytes. In addition, this drug treatment abolished IL-6-induced SOCS3 expression in differentiated 3T3-L1 adipocytes. This effect was associated with the capacity of the drug to prevent IL-6-induced STAT3 phosphorylation on Tyr(705) and Ser(727) residues in vitro and in vivo. Moreover, GW501516 prevented IL-6-dependent induction of extracellular signal-related kinase (ERK)1/2, a serine-threonine-protein kinase involved in serine STAT3 phosphorylation. Furthermore, in white adipose tissue from PPAR-β/-δ-null mice, STAT3 phosphorylation (Tyr(705) and Ser(727)), STAT3 DNA-binding activity, and SOCS3 protein levels were higher than in wild-type mice. Several steps in STAT3 activation require its association with heat shock protein 90 (Hsp90), which was prevented by GW501516 as revealed in immunoprecipitation studies. Consistent with this finding, the STAT3-Hsp90 association was enhanced in white adipose tissue from PPAR-β/-δ-null mice compared with wild-type mice.

CONCLUSIONS

Collectively, our findings indicate that PPAR-β/-δ activation prevents IL-6-induced STAT3 activation by inhibiting ERK1/2 and preventing the STAT3-Hsp90 association, an effect that may contribute to the prevention of cytokine-induced insulin resistance in adipocytes.

PGE2 induces IL-6 in orbital fibroblasts through EP2 receptors and increased gene promoter activity: implications to thyroid-associated ophthalmopathy

Background

IL-6 plays an important role in the pathogenesis of Graves' disease and its orbital component, thyroid-associated ophthalmopathy (TAO). Orbital tissues become inflamed in TAO, a process in which prostanoids have been implicated. Orbital fibroblasts both generate and respond to PGE₂, underlying the inflammatory phenotype of these cells.

Methodology/Principal Findings

Using cultured orbital and dermal fibroblasts, we characterized the effects of PGE₂ on IL-6 expression. We found that the prostanoid provokes substantially greater cytokine synthesis in orbital fibroblasts, effects that are mediated through cell-surface EP₂ receptors and increased steady-state IL-6 mRNA levels. The pre-translational up-regulation of IL-6 results from increased gene promoter activity and can be reproduced with the PKA agonist, Sp-cAMP and blocked by interrupting the PKA pathway. PGE₂-induced production of cAMP in orbital fibroblasts was far greater than that in dermal fibroblasts, resulting from higher levels of adenylate cyclase. PGE₂ provokes CREB phosphorylation, increases the pCREB/CREB ratio, and initiates nuclear localization of the pCREB/CREB binding protein/p300 complex (CBP) preferentially in orbital fibroblasts. Transfection with siRNAs targeting either CREB or CBP blunts the induction of IL-6 gene expression. PGE₂ promotes the binding of pCREB to its target DNA sequence which is substantially greater in orbital fibroblasts.

Conclusion/Significance

These results identify the mechanism underlying the exaggerated induction of IL-6 in orbital fibroblasts and tie together two proinflammatory pathways involved in the pathogenesis of TAO. Moreover, they might therefore define an attractive therapeutic target for the treatment of TAO.

A stimulatory thyrotropin receptor antibody (M22) and thyrotropin increase interleukin-6 expression and secretion in Graves' orbital preadipocyte fibroblasts

BACKGROUND

Patients with Graves' ophthalmopathy (GO) have circulating autoantibodies directed against the thyrotropin receptor (TSHR) and elevated levels of the proinflammatory cytokine interleukin-6 (IL-6) in both serum and orbital tissues. We hypothesized that these autoantibodies might increase IL-6 expression and secretion in preadipocyte fibroblasts and adipocytes from patients with GO, and thus directly impact the clinical activity of the disease.

METHODS

IL-6 mRNA levels were measured in cultures of GO orbital preadipocytes (n = 3) treated during adipocyte differentiation with a monoclonal stimulatory TSHR antibody (M22; 10 ng/mL), IL-6 (1 ng/mL), or TSH (10 U/L). Additionally, levels of IL-6 protein secretion were assessed after adipocyte differentiation in orbital cultures exposed to TSH or M22 for 24 or 48 hours (n = 8). IL-6 mRNA levels were also measured in orbital adipose tissue specimens from well-characterized GO patients (n = 9) and normal individuals (n = 9).

RESULTS

Treatment of GO orbital preadipocyte cultures with IL-6, TSH, or M22 during adipocyte differentiation resulted in increased IL-6 mRNA levels (3.1-fold, 2.9-fold, and 2.7-fold, respectively; p < 0.05). Treatment of orbital cultures with M22 or TSH after adipocyte differentiation enhanced the release of IL-6 protein into the medium at both 24 and 48 hours for TSH (mean 1.9- and 2.3-fold; p = 0.002 and 0.015, respectively) and at 48 hours for M22 (mean 2.0-fold; p = 0.005). In addition, we found mean IL-6 mRNA levels to be significantly increased in GO orbital adipose tissue specimens (10-fold; p < 0.01), primarily attributable to high levels in three of the four patients with clinical activity scores >or=5.

CONCLUSIONS

Both TSH and M22 increase IL-6 expression in orbital preadipocyte fibroblasts and IL-6 secretion by mature adipocytes. These results suggest that circulating TSHR autoantibodies in GO might play a direct role in the clinical activity of the disease.

Signaling pathways mediating beta3-adrenergic receptor-induced production of interleukin-6 in adipocytes

The beta(3)-adrenergic receptor (beta(3)AR) is an essential regulator of metabolic and endocrine functions. A major cellular and clinically significant consequence of beta(3)AR activation is the substantial elevation in interleukin-6 (IL-6) levels. Although the beta(3)AR-dependent regulation of IL-6 expression is well established, the cellular pathways underlying this regulation have not been characterized. Using a novel method of homogenous reporters, we assessed the pattern of activation of 43 transcription factors in response to the specific beta(3)AR agonist CL316243 in adipocytes, cells that exhibit the highest expression of beta(3)ARs. We observed a unique and robust activation of the CRE-response element, suggesting that IL-6 transcription is regulated via the G(s)-protein/cAMP/protein kinase A (PKA) but not nuclear factor kappa B (NF-kappaB) pathway. However, pretreatment of adipocytes with pharmacologic inhibitors of PKA pathway failed to block beta(3)AR-mediated IL-6 up-regulation. Additionally, stimulation of adipocytes with the exchange protein directly activated by cAMP (Epac) agonist did not induce IL-6 expression. Instead, the beta(3)AR-mediated transcription of IL-6 required activation of both the p38 and PKC pathways. Western blot analysis further showed that transcription factors CREB and ATF-2 but not ATF-1 were activated in a p38- and PKC-dependent manner. Collectively, our results suggest that while stimulation of the beta(3)AR leads to a specific activation of CRE-dependent transcription, there are several independent cellular pathways that converge at the level of CRE-response element activation, and in the case of IL-6 this activation is mediated by p38 and PKC but not PKA pathways.

Insulin stimulates interleukin-6 expression and release in LS14 human adipocytes through multiple signaling pathways

IL-6 is an important cytokine that regulates both immune and metabolic functions. Within adipose tissue, preadipocytes produce significant amounts of IL-6, but little is known about the factors or mechanisms that regulate IL-6 production in these cells. Using LS14, a newly developed human adipocyte cell line, our objective was to determine the mechanisms by which insulin stimulates IL-6 production and release in preadipocytes. Insulin increased IL-6 gene expression and secretion in a time- and dose-dependent manner. Insulin decreased cyclic AMP (cAMP) but increased cyclic GMP (cGMP) levels, and IL-6 expression/release was stimulated by a cGMP analog. The stimulatory effect of insulin and cGMP was abrogated by a specific inhibitor of protein kinase G (cyclic GMP-dependent protein kinase). Both insulin and cGMP rapidly induced phosphorylation of cAMP response element binding protein. Insulin also activated the MAPK signaling pathway, and its blockade prevented the insulin-stimulated increases in IL-6 cell content and release, but not IL-6 gene expression. Although inhibition of the proteosome increased IL-6 cell content and release, proteosome activity was unaffected by insulin. These data suggest that the stimulatory effects of insulin on IL-6 release involve several interrelated components: transcription, intracellular releasable pool, and secretion, which are differentially regulated and, thus, determine the size of the releasable pool of IL-6. Insulin-induced IL-6 gene expression is mediated by cGMP/cyclic GMP-dependent protein kinase/cAMP response element binding protein, whereas MAPK is involved in the insulin-stimulated IL-6 synthesis/release.

Interleukin-6 stimulates lipolysis in porcine adipocytes

Interleukin (IL)-6 stimulates lipolysis in human and rodents adipocytes. However, the mechanism regulating this process is little known. In this study, we demonstrated that IL-6 increased lipolysis in differentiated porcine adipocytes by activation of extracellular signal-related kinase (ERK), which was inhibited by specific ERK inhibitor PD98059. IL-6 treatment did not elevate intracellular cAMP and specific PKA inhibitor H89 did not affect IL-6-induced lipolysis, which suggested that protein kinase A (PKA) pathway was not involved in IL-6-induced lipolysis. Also, the expressions of perilipin A and PPARgamma2 were significantly reduced in response to IL-6 treatment, but the expressions of peroxisome proliferators-activated receptor gamma coactivator-1 alpha (PGC-1alpha), carnitinepalmitoyl-transferase-1 (CPT-1), and uncoupling protein 2 (UCP2) were significantly elevated. In conclusion, these results suggested that chronic high dose of IL-6 directly stimulated lipolysis in porcine adipocytes through activation of ERK, subsequently repressing perilipin A and promoting PGC-1alpha expression.

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.

Gene deletion reveals roles for annexin A1 in the regulation of lipolysis and IL-6 release in epididymal adipose tissue

In this study, epididymal adipose tissue from male annexin 1 (ANXA1)-null and wild-type control mice were used to explore the potential role of ANXA1 in adipocyte biology. ANXA1 was detected by Western blot analysis in wild-type tissue and localized predominantly to the stromal-vascular compartment. Epididymal fat pad mass was reduced by ANXA1 gene deletion, but adipocyte size was unchanged, suggesting that ANXA1 is required for the maintenance of adipocyte and/or preadipocyte cell number. Epididymal tissue from wild-type mice responded in vitro to noradrenaline and isoprenaline with increased glycerol release, reduced IL-6 release, and increased cAMP accumulation. Qualitatively similar but significantly attenuated responses to the catecholamines were observed in tissue from ANXA1-null mice, an effect that was not associated with changes in beta-adrenoceptor mRNA expression. Lipopolysaccharide (LPS) also stimulated lipolysis in vitro, but its effects were muted by ANXA1 gene deletion. By contrast, LPS failed to influence IL-6 release from wild-type tissue but stimulated the release of the cytokine from tissue from ANXA1-null mice. ANXA1 gene deletion did not affect glucocorticoid receptor expression or the ability of dexamethasone to suppress catecholamine-induced lipolysis. It did, however, augment IL-6 expression and modify the inhibitory effects of glucocorticoids on IL-6 release. Collectively, these studies suggest that ANXA1 supports aspects of adipose tissue mass and alters the sensitivity of epididymal adipose tissue to catecholamines, glucocorticoids, and LPS, thereby modulating lipolysis and IL-6 release.

Interleukin-6 release from human abdominal adipose cells is regulated by thyroid-stimulating hormone: effect of adipocyte differentiation and anatomic depot

Adipose cells are extrathyroidal targets of thyroid-stimulating hormone (TSH). TSH stimulates interleukin-6 (IL-6) release from adipocytes. We examined TSH responsiveness as a function of stage of differentiation or adipose tissue depot in cultured adipose cells and determined the effect of TSH on extrathyroidal IL-6 production in vivo. Stromal preadipocytes, isolated from human abdominal subcutaneous or omental adipose tissue, and their differentiated counterparts were studied. IL-6 protein concentration in the medium was measured after TSH stimulation. Basal IL-6 release was greater for preadipocytes than differentiated adipocytes, whether derived from subcutaneous or omental fat depots. A depot-dependent effect (omental > subcutaneous) on basal IL-6 release was observed for preadipocytes (1.6-fold, P < 0.05); a similar trend for differentiated adipocytes was not significant (6.2-fold, P > 0.05). IL-6 responsiveness to TSH was observed upon differentiation, but only for subcutaneous adipocytes (1.9-fold over basal, P < 0.001). To determine if TSH could stimulate IL-6 release from extrathyroidal tissues in vivo, we measured serum IL-6 levels from five thyroidectomized patients who received recombinant human (rh) TSH and found that levels increased by threefold on days 3 and 4 (P < 0.05) after its administration. Our data demonstrate that stage of differentiation and fat depot origin affect basal and TSH-stimulated IL-6 release from adipose cells in culture. Furthermore, rhTSH elevates serum IL-6 response in thyroidectomized patients, indicating an extrathyroidal site of TSH action.

Prevention of Cancer Cachexia by a Novel Nuclear Factor κB Inhibitor in Prostate Cancer

PURPOSE

To investigate the association between serum interleukin-6 (IL-6) and cachexia in patients with prostate cancer and the inhibitory effect of a new nuclear factor kappaB (NF-kappaB) inhibitor, dehydroxymethylepoxyquinomicin (DHMEQ), on IL-6 production and cachexia in an animal model of hormone-refractory prostate cancer.

EXPERIMENTAL DESIGN

The association between serum IL-6 levels and variables of cachexia was evaluated in 98 patients with prostate cancer. The inhibitory effects of DHMEQ on IL-6 secretion and cachexia were investigated in in vitro and in vivo studies using JCA-1 cells derived from human prostate cancer.

RESULTS

Serum IL-6 levels were significantly elevated and cachexia developed in JCA-1 tumor-bearing mice as well as in prostate cancer patients with progressive disease. IL-6 secretion was significantly inhibited in JCA-1 cells exposed to DHMEQ. Intraperitoneal administration of DHMEQ (8 mg/kg) to tumor-bearing mice produced a significant amelioration of the reduction in body weight, epididymal fat weight, gastrocnemius muscle weight, hematocrit, and serum levels of triglyceride and albumin when compared with administration of DMSO or no treatment. DHMEQ caused a significant decrease of serum IL-6 level in JCA-1 tumor-bearing mice (all P < 0.05).

CONCLUSIONS

These results suggested an association between serum IL-6 and cachexia in patients with prostate cancer and in JCA-1 tumor-bearing mice and that a new NF-kappaB inhibitor, DHMEQ, could prevent the development of cachexia in JCA-1 tumor-bearing mice presumably through the inhibition of IL-6 secretion. DHMEQ seems to show promise as a novel and unique anticachectic agent in hormone-refractory prostate cancer.

Hormone-sensitive lipase is reduced in the adipose tissue of patients with type 2 diabetes mellitus: influence of IL-6 infusion

AIMS/HYPOTHESIS

Type 2 diabetes mellitus is characterised by increased plasma NEFA and IL-6 concentrations, and IL-6 increases lipolysis in healthy men. We assessed the adipose tissue hormone-sensitive lipase (HSL) mRNA expression, protein expression and HSL activity in patients with type 2 diabetes mellitus, and determined the effect of IL-6 administration on these measures.

METHODS

Seven patients with type 2 diabetes mellitus (age 67+/-4 years, weight 87+/-7 kg) and six age- and weight-matched individuals visited the laboratory on two occasions. Subcutaneous adipose tissue biopsies and blood samples were obtained prior to and during 3 h of either saline or recombinant human IL-6 infusion.

RESULTS

HSL mRNA was reduced (p<0.05) by approximately 40% in type 2 diabetes mellitus relative to control subjects, while HSL protein expression showed a tendency to be decreased (35%, p=0.09). HSL activity averaged 8.87+/-1.25 and 6.91+/-1.20 nmol min(-1) mg(-1) protein for control and type 2 diabetic subjects respectively (p<0.05). IL-6 administration increased (p<0.05) HSL mRNA 2-fold at 60 min in both groups, whereas HSL protein and activity were unaffected by IL-6. Plasma insulin was elevated (p<0.05) in patients with type 2 diabetes mellitus at rest and was blunted (p<0.05) during IL-6 infusion in both groups. Plasma glucagon and cortisol were elevated (p<0.05) by IL-6 in both groups.

CONCLUSIONS/INTERPRETATION

Our data demonstrate that basal HSL is decreased in patients with type 2 diabetes mellitus, and this may be a consequence of elevated plasma insulin levels. We have also shown that IL-6 administration increases HSL gene expression, although it exerted no effect on HSL protein and activity. This disparity between mRNA, protein and enzyme activity may be a function either of the marked alterations in the hormonal milieu induced by IL-6 administration and/or of post-transcriptional events.

Short-term infusion of interleukin-6 does not induce insulin resistance in vivo or impair insulin signalling in rats

AIMS/HYPOTHESIS

Interleukin-6 has been implicated in the insulin resistance associated with obesity and impaired glucose tolerance. Previous studies in vitro have shown that IL-6 rapidly (1-2 h) impairs cellular insulin signalling and action through an increased expression of suppressor of cytokine signalling (SOCS)-3. In the present study, IL-6 or saline was infused in rats that were simultaneously in a state of hyperinsulinaemia. Muscle, liver and adipose tissue were excised after 2 h to examine potential effects on insulin signalling or gene expression.

METHODS

The rats were infused with IL-6 or saline during a euglycaemic-hyperinsulinaemic clamp and the glucose infusion rate was measured after 90 to 120 min. Signal transducer and activator of transcription (STAT)3 phosphorylation and insulin-stimulated tyrosine phosphorylation of the insulin receptors and IRS were measured with immunoblotting and gene expression through real-time PCR.

RESULTS

No inhibitory effect of IL-6 on insulin-stimulated whole-body glucose uptake was seen in spite of high circulating levels of IL-6 (0.85+/-0.08 nmol/l). Tyrosine phosphorylation of the insulin receptors and IRS was also unchanged in the liver, skeletal muscles and adipose tissue. However, tyrosine phosphorylation of STAT3 was increased in all tissues, showing that IL-6 signalling was activated. IL-6 mRNA tended to increase, while GLUT4, peroxisome proliferator-activated receptor-gamma coactivator-1 (PGC-1) and adiponectin gene expression were unchanged.

CONCLUSIONS/INTERPRETATION

Infusion of IL-6 for 120 min in rats during euglycaemic-hyperinsulinaemic conditions did not alter the effect of insulin on whole-body glucose homeostasis, plasma adiponectin levels or insulin signalling in target tissues. Thus, the acute effects of IL-6, associated with SOCS-3 induction, do not lead to whole-body insulin resistance. These data further underscore the importance of the chronic, and potentially tissue-specific effects of IL-6 on insulin signalling and action.

Conjugated linoleic acid induces human adipocyte delipidation: autocrine/paracrine regulation of MEK/ERK signaling by adipocytokines

Dietary conjugated linoleic acid (CLA) reduces body fat in animals and some humans. Here we show that trans-10, cis-12 CLA, but not cis-9, trans-11 CLA, when added to cultures of stromal vascular cells containing newly differentiated human adipocytes, caused a time-dependent decrease in triglyceride content, insulin-stimulated glucose and fatty acid uptake, incorporation into lipid, and oxidation compared with controls. In parallel, gene expression of peroxisome proliferator-activated receptor-gamma and many of its downstream targets were diminished by trans-10, cis-12 CLA, whereas leptin gene expression was increased. Prior to changes in gene expression and metabolism, trans-10, cis-12 CLA caused a robust and sustained activation of mitogen-activated protein kinase kinase/extracellular signal-related kinase (MEK/ERK) signaling. Furthermore, the trans-10, cis-12 CLA-mediated activation of MEK/ERK could be attenuated by pretreatment with U0126 and pertussis toxin. In parallel, pretreatment with U0126 blocked the ability of trans-10, cis-12 CLA to alter gene expression and attenuate glucose and fatty acid uptake of the cultures. Intriguingly, the induction by CLA of MEK/ERK signaling was linked to hypersecretion of adipocytokines interleukin-6 and interleukin-8. Collectively, these data demonstrate for the first time that trans-10, cis-12 CLA decreases the triglyceride content of newly differentiated human adipocytes by inducing MEK/ERK signaling through the autocrine/paracrine actions of interleukins-6 and 8.

Regulation of adipocytokines and insulin resistance

It has long been known that obesity and insulin resistance are linked. Recently, it has been shown that adipocytes secrete several proteins including tumour necrosis factor-alpha, interleukin-6, resistin, and adiponectin. Since several of these so-called adipocytokines influence insulin sensitivity and glucose metabolism profoundly, they might provide a molecular link between increased adiposity and impaired insulin sensitivity. Thiazolidinediones which decrease insulin resistance and are used in the treatment of Type 2 diabetes seem to mediate part of their insulin-sensitising effects via modulation of adipocytokine expression. Furthermore, hormones such as beta-adrenergic agonists, insulin, glucocorticoids, and growth hormone might impair insulin sensitivity at least in part via up-regulation or down-regulation of adipocytokine synthesis. We summarise the current knowledge on how major adipocyte-secreted proteins are regulated by hormones and drugs influencing insulin sensitivity and discuss its implications for insulin resistance and obesity.

Searching for the exercise factor: is IL-6 a candidate?

For years the search for the stimulus that initiates and maintains the change of excitability or sensibility of the regulating centers in exercise has been progressing. For lack of more precise knowledge, it has been called the 'work stimulus', 'the work factor' or 'the exercise factor'. In other terms, one big challenge for muscle and exercise physiologists has been to determine how muscles signal to central and peripheral organs. Here we discuss the possibility that interleukin-6 (IL-6) could mediate some of the health beneficial effects of exercise. In resting muscle, the IL-6 gene is silent, but it is rapidly activated by contractions. The transcription rate is very fast and the fold changes of IL-6 mRNA is marked. IL-6 is released from working muscles into the circulation in high amounts. The IL-6 production is modulated by the glycogen content in muscles, and IL-6 thus works as an energy sensor. IL-6 exerts its effect on adipose tissue, inducing lipolysis and gene transcription in abdominal subcutaneous fat and increases whole body lipid oxidation. Furthermore, IL-6 inhibits low-grade TNF-alpha-production and may thereby inhibit TNF-alpha-induced insulin resistance and atherosclerosis development. We propose that IL-6 and other cytokines, which are produced and released by skeletal muscles, exerting their effects in other organs of the body, should be named 'myokines'.

IL-6 gene expression in human adipose tissue in response to exercise--effect of carbohydrate ingestion

Interleukin-6 (IL-6) is a cytokine involved in a number of immunological processes, but it is also linked to exercise and possibly energy status. During exercise, muscle IL-6 mRNA levels and plasma IL-6 levels are increased and further augmented when intramuscular glycogen levels are low. In contrast, the increase in plasma IL-6 is blunted if carbohydrate is administered, indicating a substrate-regulated induction of IL-6 in human skeletal muscle. Recent studies have demonstrated that IL-6 is also released from adipose tissue in response to an exercise bout. Furthermore, IL-6 has been demonstrated to have a lipolytic effect, thus possibly playing a role in mobilisation of energy as free fatty acids (FFA) in response to exercise. The purpose of the present study was to investigate the gene expression pattern of IL-6 in adipose tissue in response to exercise, and to determine whether gene expression was affected by the ingestion of carbohydrate. Eight male subjects performed 3 h of bicycling with ingestion of a carbohydrate drink or placebo. Fat biopsy samples and blood samples were obtained before, during and in the recovery phase of exercise. Both plasma IL-6 and adipose IL-6 mRNA levels increased in response to exercise. IL-6 gene expression was lower (P<0.05) in the CHO trial (1.98-fold increase, confidence interval (CI) 1.16-3.83) compared with the control (6.49-fold increase, CI 3.57-13.91) at end of exercise. Furthermore, CHO ingestion blunted the increase in plasma IL-6 levels (P<0.05) at end of exercise (26.0+/-3.7 pg ml(-1) in the control vs. 15.6+/-2.4 pg ml(-1) in the CHO trial). In conclusion, exercise results in an increase in IL-6 gene expression in adipose tissue in response to exercise, an effect that is significantly blunted by ingestion of carbohydrate.