Tissular T(regs): a unique population of adipose-tissue-resident Foxp3+CD4+ T cells that impacts organismal metabolism

Crosstalk between skin inflammation and adipose tissue-derived products: pathogenic evidence linking psoriasis to increased adiposity

INTRODUCTION

Psoriasis is a chronic skin disorder associated with several comorbid conditions. In psoriasis pathogenesis, the role of some cytokines, including TNF-α and IL-17, has been elucidated. Beside their pro-inflammatory activity, they may also affect glucose and lipid metabolism, possibly promoting insulin resistance and obesity. On the other hand, adipose tissue, secreting adipokines such as chemerin, visfatin, leptin, and adiponectin, not only regulates glucose and lipid metabolism, and endothelial cell function regulation, but it may contribute to inflammation. Areas covered: This review provides an updated 'state-of-the-art' about the reciprocal contribution of a small subset of conventional cytokines and adipokines involved in chronic inflammatory pathways, upregulated in both psoriasis and increased adiposity. A systematic search was conducted using the PubMed Medline database for primary articles. Expert commentary: Because psoriasis is associated with increased adiposity, it would be important to define the contribution of chronic skin inflammation to the onset of obesity and vice versa. Clarifying the pathogenic mechanism underlying this association, a therapeutic strategy having favorable effects on both psoriasis and increased adiposity could be identified.

Notch1 regulated autophagy controls survival and suppressor activity of activated murine T-regulatory cells

Cell survival is one of several processes regulated by the Notch pathway in mammalian cells. Here we report functional outcomes of non-nuclear Notch signaling to activate autophagy, a conserved cellular response to nutrient stress, regulating survival in murine natural T-regulatory cells (Tregs), an immune subset controlling tolerance and inflammation. Induction of autophagy required ligand-dependent, Notch intracellular domain (NIC) activity, which controlled mitochondrial organization and survival of activated Tregs. Consistently, NIC immune-precipitated Beclin and Atg14, constituents of the autophagy initiation complex. Further, ectopic expression of an effector of autophagy (Atg3) or recombinant NIC tagged to a nuclear export signal (NIC-NES), restored autophagy and suppressor function in Notch1(-/-) Tregs. Furthermore, Notch1 deficiency in the Treg lineage resulted in immune hyperactivity, implicating Notch activity in Treg homeostasis. Notch1 integration with autophagy, revealed in these experiments, holds implications for Notch regulated cell-fate decisions governing differentiation.

Role of T-Cell Polarization and Inflammation and Their Modulation by n-3 Fatty Acids in Gestational Diabetes and Macrosomia

Th (T helper) cells are differentiated into either Th1 or Th2 phenotype. It is generally considered that Th1 phenotype is proinflammatory, whereas Th2 phenotype exerts anti-inflammatory or protective effects. Gestational diabetes mellitus (GDM) has been associated with a decreased Th1 phenotype, whereas macrosomia is marked with high expression of Th1 cytokines. Besides, these two pathological situations are marked with high concentrations of inflammatory mediators like tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6), known to play a pivotal role in insulin resistance. Dietary n-3 polyunsaturated fatty acids (n-3 PUFAs) may exert a beneficial effect by shifting Th1/Th2 balance to a Th2 phenotype and increasing insulin sensitivity. In this paper, we shed light on the role of T-cell malfunction that leads to an inflammatory and pathophysiological state, related to insulin resistance in GDM and macrosomia. We will also discuss the nutritional management of these pathologies by dietary n-3 polyunsaturated fatty acids (PUFAs).

Regulation of metabolic health and adipose tissue function by group 2 innate lymphoid cells

Adipose tissue (AT) is home to an abundance of immune cells. With chronic obesity, inflammatory immune cells accumulate and promote insulin resistance and the progression to type 2 diabetes mellitus. In contrast, recent studies have highlighted the regulation and function of immune cells in lean, healthy AT, including those associated with type 2 or "allergic" immunity. Although traditionally activated by infection with multicellular helminthes, AT type 2 immunity is active independently of infection, and promotes tissue homeostasis, AT "browning," and systemic insulin sensitivity, protecting against obesity-induced metabolic dysfunction and type 2 diabetes mellitus. In particular, group 2 innate lymphoid cells (ILC2s) are integral regulators of AT type 2 immunity, producing the cytokines interleukin-5 and IL-13, promoting eosinophils and alternatively activated macrophages, and cooperating with and promoting AT regulatory T (Treg) cells. In this review, we focus on the recent developments in our understanding of group 2 innate lymphoid cell cells and type 2 immunity in AT metabolism and homeostasis.

The role of the local environment and epigenetics in shaping macrophage identity and their effect on tissue homeostasis

Macrophages provide a critical systemic network cells of the innate immune system. Emerging data suggest that in addition, they have important tissue-specific functions that range from clearance of surfactant from the lungs to neuronal pruning and establishment of gut homeostasis. The differentiation and tissue-specific activation of macrophages require precise regulation of gene expression, a process governed by epigenetic mechanisms such as DNA methylation, histone modification and chromatin structure. We argue that epigenetic regulation of macrophages is determined by lineage- and tissue-specific transcription factors controlled by the built-in programming of myeloid development in combination with signaling from the tissue environment. Perturbation of epigenetic mechanisms of tissue macrophage identity can affect normal macrophage tissue function and contribute to pathologies ranging from obesity and autoimmunity to neurodegenerative diseases.

CD4(+), CD25(+), FOXP3 (+) T Regulatory Cell Levels in Obese, Asthmatic, Asthmatic Obese, and Healthy Children

The aim of this prospective case control study is to determine CD4(+), CD25(+), and FoxP3(+) T regulatory cells (Tregs) and T helper cells (Ths) in obese, asthmatic, asthmatic obese, and healthy children. Obese (n = 40), asthmatic (n = 40), asthmatic obese (n = 40), and healthy children (n = 40) were included in this study. Blood samples collected from children were marked with CD4, CD25, ve Foxp3 in order to detect Tregs and Ths by flow cytometric method. Statistical analyses were performed. p ≤ 0.05 was chosen as meaningful threshold. Tregs exhibiting anti-inflammatory nature were significantly lower in obese (0.16 %; p ≤ 0.001), asthmatic (0.25 %; p ≤ 0.01), and asthmatic obese (0.29 %; p ≤ 0.05) groups than control group (0.38 %). Ths were counted higher in asthma group than control (p ≤ 0.01) and obese (p ≤ 0.001) groups. T cell immunity plays important roles in chronic inflammatory diseases such as obesity and asthma pathogeneses. Decreased numbers of Tregs found in obese, asthmatic, and asthmatic obese children might represent a challenge of these cells.

Diminished levels of regulatory T cell subsets (CD8+Foxp3, CD4+Foxp3 and CD4+CD39+Foxp3) but increased Foxp3 expression in adipose tissue from overweight subjects

OBJECTIVES

The aim of this study was to identify regulatory T cell (Treg) subsets residing in adipose tissue, demonstrate their immunosuppressive functions, and assess the possible role of Sirt1 in their function in overweight subjects.

METHODS

Fat samples were obtained by lipoaspiration from healthy overweight (n = 15) and normoweight (n = 11) subjects. We obtained the stromal vascular fraction and then isolated the mononuclear cells by Ficoll-Hypaque sedimentation. The Treg subsets were analyzed by flow cytometry, the expression of Sirt1 and Foxp3 was detected by western blot, and peroxisome proliferator-activated receptor gamma (PPAR-γ) expression was evaluated by qPCR.

RESULTS

We detected low numbers of Treg cell subsets displaying the phenotypes CD4+CD25-Foxp3+, CD8+CD25-Foxp3+, and CD4+CD39+Foxp3+ associated with increased body mass index in overweight subjects. We found lower levels of mRNA SIRT1 expression in adipocytes from overweight subjects than in those from normoweight subjects. In contrast, increased amounts of the Sirt1 and Foxp3 proteins in adipose tissue mononuclear cells from overweight subjects were observed. The immunosuppressive function of CD4+CD25+ Treg cells is higher in cells from obese subject than in those from normoweight subject.

CONCLUSIONS

Low levels of Treg subsets in overweight subjects with a high percentage of inhibition of proliferation could be related to high levels of the Foxp3 protein. Likewise, the low expression of SIRT1 and PPAR-γ mRNA levels and increased concentration of Sirt1 proteins allows adipose tissue mononuclear cells to respond to stimuli dependent on adenosine receptors and sirtuin pathways.

Parasitic helminths and their beneficial impact on type 1 and type 2 diabetes

It is estimated that by the year 2035 almost 600 million people will suffer from diabetes. In the case of type 2 diabetes, the strongest increase of diabetes incidence occurs in developing and newly industrialized countries. This increase correlates not only with a progressing sedentary lifestyle and nutritional changes, but also environmental changes. Similarly, the increase of type 1 diabetes incidence in industrialized countries over the past decades cannot be explained by genetic factors alone, suggesting that environmental changes are also involved. One such environmental change is a reduced exposure to pathogens because of improved hygiene. Parasitic helminths modulate the immune system of their hosts and induce type 2 as well as regulatory immune responses. As pro-inflammatory immune responses are crucial for the onset of both type 1 and type 2 diabetes, helminth-induced immunomodulation may prevent diabetes onset and ameliorate insulin sensitivity. Several epidemiological studies in human and experimental animal models support such a protective effect of helminths for autoimmune diabetes. Recent studies further suggest that helminths may also provide such a beneficial effect for type 2 diabetes. In this review we summarize studies that investigated parasitic helminths and helminth-derived products and their impact on both type 1 and type 2 diabetes highlighting potential protective mechanisms.

Regulatory T Cells in Kidney Transplantation: New Directions?

The contribution of regulatory T cells in the maintenance of kidney graft survival is of major interest. Although many experimental models suggest a role in the induction of graft tolerance, reproducing these findings in clinic is less clear. While modulation of the regulatory T cell response is a promising therapeutic concept in transplantation, a better understanding of function, phenotype and biology is needed to be able to optimally exploit these cells in order to induce graft tolerance. With this in mind, we review here the current understanding of the phenotypic-functional delineation of Tregs and how Tregs can contribute to graft survival. We highlight their potential role in long-term graft survival and kidney operational tolerance. We also discuss the mechanisms needed for the molecular development of regulatory T cells: A combination of FOXP3 molecular partners, epigenetic, metabolic, and posttranslational modifications are necessary to generate well-functioning regulatory T cells and maintain their core identify. We discuss how an improved understanding of these mechanisms will permit the identification of new potent therapeutic strategies to improve kidney graft survival.

Treg Cell Differentiation: From Thymus to Peripheral Tissue

Regulatory T cells (Tregs) are crucial mediators of self-tolerance in the periphery. They differentiate in the thymus, where interactions with thymus-resident antigen-presenting cells, an instructive cytokine milieu, and stimulation of the T cell receptor lead to the selection into the Treg lineage and the induction of Foxp3 gene expression. Once mature, Treg cells leave the thymus and migrate into either the secondary lymphoid tissues, e.g., lymph nodes and spleen, or peripheral nonlymphoid tissues. There is growing evidence that Treg cells go beyond the classical modulation of immune responses and also play important functional roles in nonlymphoid peripheral tissues. In this review, we summarize recent findings about the thymic Treg lineage differentiation as well as the further specialization of Treg cells in the secondary lymphoid and in the peripheral nonlymphoid organs.

Cross talk of the immune system in the adipose tissue and the liver in non-alcoholic steatohepatitis: Pathology and beyond

Non-alcoholic steatohepatitis (NASH) is considered to be the hepatic manifestation of the metabolic syndrome, thus has a tight correlation with systemic metabolic impairment. The complex mechanisms underlying the pathogenesis of NASH involve different organs and systems that cross talk together contributing to the onset of NASH. A crucial role is played by inflammatory mediators, especially those deriving from the adipose tissue and the liver, which are involved in the cascade of inflammation, fibrosis and eventually tumorigenesis. In this setting cytokines and adipokines as well as immunity are emerging drivers of the key features of NASH. The immune system participates in this process with disturbances of the cells constituting both the innate and the adaptive immune systems that have been reported in different organs, such as in the liver and in the adipose tissue, in clinical and preclinical studies. The role of the immune system in NASH is increasingly studied, not only because of its contribution to the pathogenetic mechanisms of NASH but also because of the new potential therapeutic options it offers in this setting. Indeed, novel treatments acting on the immune system could offer new options in the management of NASH and the correlated clinical consequences.

Tissue resident regulatory T cells: novel therapeutic targets for human disease

Over the past decade, the ability of regulatory T cells (Tregs) to suppress multiple types of immune cells has received tremendous attention. Mounting evidence has revealed that tissue resident Tregs control non-immunological processes of their target tissues and contribute to a plethora of human diseases. The identification of novel tissue-specific Tregs has highlighted their heterogeneity and complexity. This review summarizes the recent findings for visceral adipose tissue CD4+Foxp3+ regulatory T cells (VAT Tregs), muscle Tregs, bone Tregs and skin memory Tregs, with a focus on their unique functions in local tissues. This interpretation of the roles of tissue-specific Tregs and of their involvement in disease progression provides new insight into the discovery of potential therapeutic targets of human diseases.

Regulatory effects of resveratrol on glucose metabolism and T-lymphocyte subsets in the development of high-fat diet-induced obesity in C57BL/6 mice

High-fat diet (HFD)-induced obesity is often associated with immune dysfunction. Resveratrol (trans-3,5,4'-trihydroxystilbene), which has well-founded immunity-related beneficial properties, was used to elucidate the regulatory effect on glucose metabolism and T-lymphocyte subsets in the development of HFD-induced obesity. Resveratrol, being associated with decreases of plasma leptin and plasma lipids and the release of oxidative stress, significantly decreased the body weight and fat masses in HF mice after 26 weeks of feeding. Furthermore, resveratrol decreased the fasting blood glucose and fasting plasma insulin and increased the CD3(+)CD4(+)/CD3(+)CD8(+) subsets percentages and the regulatory T cells (Tregs) production after 13 and 26 weeks of feeding. The results indicate that resveratrol, as an effective supplement for HFD, maintained glucose homeostasis by activating the PI3K and SIRT1 signaling pathways. Moreover, resveratrol activated the Nrf2 signaling pathway-mediated antioxidant enzyme expression to alleviate inflammation by protecting against oxidative damage and T-lymphocyte subset-related chronic inflammatory response in the development of HFD-induced obesity.

Metabolic inflammation in inflammatory bowel disease: crosstalk between adipose tissue and bowel

Epidemiological studies show that both the incidence of inflammatory bowel disease (IBD) and the proportion of people with obesity and/or obesity-associated metabolic syndrome increased markedly in developed countries during the past half century. Obesity is also associated with the development of more active IBD and requirement for hospitalization and with a decrease in the time span between diagnosis and surgery. Patients with IBD, especially Crohn's disease, present fat-wrapping or "creeping fat," which corresponds to ectopic adipose tissue extending from the mesenteric attachment and covering the majority of the small and large intestinal surface. Mesenteric adipose tissue in patients with IBD presents several morphological and functional alterations, e.g., it is more infiltrated with immune cells such as macrophages and T cells. All these lines of evidence clearly show an association between obesity, adipose tissue, and functional bowel disorders. In this review, we will show that the mesenteric adipose tissue and creeping fat are not innocent by standers but actively contribute to the intestinal and systemic inflammatory responses in patients with IBD. More specifically, we will review evidence showing that adipose tissue in IBD is associated with major alterations in the secretion of cytokines and adipokines involved in inflammatory process, in adipose tissue mesenchymal stem cells and adipogenesis, and in the interaction between adipose tissue and other intestinal components (immune, lymphatic, neuroendocrine, and intestinal epithelial systems). Collectively, these studies underline the importance of adipose tissue for the identification of novel therapeutic approaches for IBD.

Pioglitazone alters monocyte populations and stimulates recent thymic emigrants in the BBDZR/Wor type 2 diabetes rat model

BACKGROUND

Type 2 diabetes is commonly characterized by insulin deficiency and decreased sensitivity of insulin receptors, leading to a chronic state of hyperglycemia in individuals. Disease progression induces changes in the immune profile that engenders a chronic inflammatory condition. Thiazolidinedione (TDZ) drugs, such as Pioglitazone (Pio), aid in controlling disease symptoms. While the mechanisms by which Pio controls hyperglycemia are beginning to be understood, relatively little is known about the effects of Pio on suppression of the systemic immune phenotype, attributed to visceral adipose tissue and macrophages.

METHODS

Here, we utilize the recently developed BBDZR/Wor type 2 diabetes rat model to test our hypothesis that a selective in vivo growth of CD3(+)T cells in the spleen contributes to the increase in T lymphocytes, including Tregs, independent of visceral adipose tissue. We investigated the systemic effects of Pio on multifactorial aspects of the disease-induced immune phenotype both in vivo and in vitro in normal, non-diabetic animals and in disease.

RESULTS

Our work revealed that Pio reversed the lymphopenic status of diabetic rats, in part by an increase in CD3(+) T lymphocytes and related subsets. Moreover, we found evidence that Pio caused a selective growth of newly differentiated T lymphocytes, based on the presence of recent thymic emigrants in vivo. To investigate effects of Pio on the inflammatory milieu, we examined the production of the signature cytokines TNF-α and IL-1β and found they were reduced by Pio-treatment, while the levels of IL-4, an anti-inflammatory mediator, were significantly increased in a Pio-dependent manner. The increase in IL-4 production, although historically attributed to macrophages from visceral adipose tissue under other conditions, came also from CD3(+) T lymphocytes from the spleen, suggesting splenocytes contribute to the Pio-induced shift towards an anti-inflammatory phenotype.

CONCLUSIONS

We show for the first time that Pio treatment significantly suppresses the systemic inflammatory status in the BBDZR/Wor type 2 diabetes rat model by the selective growth of newly differentiated CD3(+) T cells and by increasing CD3(+)IL-4 production in immigrant spleen lymphocytes.

Regulatory T Cells in Obesity

The current concept of the pathogenesis of obesity relates to the inflammation caused by excess of adipose tissue. Regulatory T cells accumulated in visceral adipose tissue (VAT-resident Tregs) are also involved in this pathogenesis. In the present paper the mechanisms responsible for alterations in the number and function of VAT-resident Tregs T in obesity are described. The role of Tregs in inflammation, insulin resistance, atherogenesis, and also the influence on VAT-resident Tregs of adipocytokines and insulin are reviewed.

The Macrophage Switch in Obesity Development

Immune cell infiltration in (white) adipose tissue (AT) during obesity is associated with the development of insulin resistance. In AT, the main population of leukocytes are macrophages. Macrophages can be classified into two major populations: M1, classically activated macrophages, and M2, alternatively activated macrophages, although recent studies have identified a broad range of macrophage subsets. During obesity, AT M1 macrophage numbers increase and correlate with AT inflammation and insulin resistance. Upon activation, pro-inflammatory M1 macrophages induce aerobic glycolysis. By contrast, in lean humans and mice, the number of M2 macrophages predominates. M2 macrophages secrete anti-inflammatory cytokines and utilize oxidative metabolism to maintain AT homeostasis. Here, we review the immunologic and metabolic functions of AT macrophages and their different facets in obesity and the metabolic syndrome.

Low-Grade Inflammation, Obesity, and Diabetes

Obesity and its comorbidities are closely related to the inflammatory environment created by expanded adipose tissue. Several mechanisms trigger inflammation in adipose tissue, including excess fatty acids, hypoxia, and activation of the inflammasome. Inflammation is characterized by the abundance of immune cells, particularly M1 macrophages and T lymphocytes, which have increased secretion of proinflammatory cytokines that act to perpetuate systemic inflammation and induce insulin resistance. The gut microbiota is also involved in obesity-induced inflammation via LPS-related endotoxemia that induces cytokine secretion and insulin resistance. Innate lymphoid type 2 cells, regulatory T cells, and interleukine (IL)-10 counteract the inflammation and insulin resistance, establishing classical or metabolically healthy obesity.

Adipose-tissue and intestinal inflammation - visceral obesity and creeping fat

Obesity has become one of the main threats to health worldwide and therefore gained increasing clinical and economic significance as well as scientific attention. General adipose-tissue accumulation in obesity is associated with systemically increased pro-inflammatory mediators and humoral and cellular changes within this compartment. These adipose-tissue changes and their systemic consequences led to the concept of obesity as a chronic inflammatory state. A pathognomonic feature of Crohn’s disease (CD) is creeping fat (CF), a locally restricted hyperplasia of the mesenteric fat adjacent to the inflamed segments of the intestine. The precise role of this adipose-tissue and its mediators remains controversial, and ongoing work will have to define whether this compartment is protecting from or contributing to disease activity. This review aims to outline specific cellular changes within the adipose-tissue, occurring in either obesity or CF. Hence the potential impact of adipocytes and resident immune cells from the innate and adaptive immune system will be discussed for both diseases. The second part focuses on the impact of generalized adipose-tissue accumulation in obesity, respectively on the locally restricted form in CD, on intestinal inflammation and on the closely related integrity of the mucosal barrier.

Adipose tissue-resident regulatory T cells: phenotypic specialization, functions and therapeutic potential

Foxp3(+)  CD4(+) regulatory T (Treg) cells, recognized to be one of the most important defences of the human body against an inappropriate immune response, have recently gained attention from those outside immunology thanks to the compelling evidence for their capability to exert non-canonical immune functions in a variety of tissues in health and disease. The recent discovery of the differences between tissue-resident Treg cells and those derived from lymphoid organs is affecting the mindset of many investigators now questioning the broad applicability of observations originally based on peripheral blood/lymphoid organ cells. So far, the best characterized 'Treg flavour' comes from studies focused on their role in suppressing adipose tissue inflammation and obesity-driven insulin resistance. Adipose tissue derived Treg cells are distinct from their counterparts in lymphoid organs based on their transcriptional profile, T-cell receptor repertoire, and cytokine and chemokine receptor expression pattern. These cells are abundant in visceral adipose tissue of lean mice but their number is greatly reduced in insulin-resistant animal models of obesity. Interestingly, peroxisome-proliferator-activated receptor γ expression by visceral adipose tissue Treg cells is crucial for their accumulation, phenotype and function in the fat and surprisingly necessary for complete restoration of insulin sensitivity in obese mice by the anti-diabetic drug Pioglitazone. This review surveys recent findings relating to the unique phenotype and function of adipose tissue-resident Treg cells, speculates on the nature of their dynamics in lean and obese mouse models, and analyses their potential therapeutic application in the treatment of type 2 diabetes.

T cell-derived IL-22 amplifies IL-1β-driven inflammation in human adipose tissue: relevance to obesity and type 2 diabetes

Proinflammatory cytokines are critically involved in the alteration of adipose tissue biology leading to deterioration of glucose homeostasis in obesity. Here we show a pronounced proinflammatory signature of adipose tissue macrophages in type 2 diabetic obese patients, mainly driven by increased NLRP3-dependent interleukin (IL)-1β production. IL-1β release increased with glycemic deterioration and decreased after gastric bypass surgery. A specific enrichment of IL-17- and IL-22-producing CD4(+) T cells was found in adipose tissue of type 2 diabetic obese patients. Coculture experiments identified the effect of macrophage-derived IL-1β to promote IL-22 and IL-17 production by human adipose tissue CD4(+) T cells. Reciprocally, adipose tissue macrophages express IL-17 and IL-22 receptors, making them sensitive to IL-17 and IL-22. IL-22 increased IL-1β release by inducing pro-IL-1β transcription through activation of C-Jun pathways in macrophages. In sum, these human data identified IL-1β and the T-cell cytokine IL-22 as key players of a paracrine inflammatory pathway previously unidentified in adipose tissue, with a pathological relevance to obesity-induced type 2 diabetes. These results provide an additional rationale for targeting IL-1β in obesity-linked type 2 diabetes and may have important implications for the conception of novel combined anti-IL-1β and anti-IL-22 immunotherapy in human obesity.

MitoNEET-mediated effects on browning of white adipose tissue

MitoNEET is an outer mitochondrial membrane protein that, upon overexpression in white adipose tissue (WAT), exerts a positive impact on tissue expansion and whole-body lipid and carbohydrate homeostasis by altering mitochondrial matrix iron metabolism. Here we determine the key transcriptional events in subcutaneous WAT of mice in response to mitoNEET overexpression and a high-fat diet (HFD). Microarray analyses at key points during weight gain upon body-weight divergence with wild-type mice demonstrate that mitoNEET-enriched sWAT early on upregulates a browning signature program that limits WAT expansion in transgenic mice for a period of up to 12-weeks of HFD. This compensatory browning phenotype is subsequently lost, resulting in rapid WAT expansion and body-weight gain. Exposure to thermoneutral temperatures during HFD prompts weight gain significantly earlier. Similar WAT expansion is achieved upon infection with an adeno-associated virus expressing mitoNEET. Collectively, the mitoNEET enriched fat-pads feature a more vascularized, anti-inflammatory and less fibrotic environment.

An increase in the Akkermansia spp. population induced by metformin treatment improves glucose homeostasis in diet-induced obese mice

BACKGROUND

Recent evidence indicates that the composition of the gut microbiota contributes to the development of metabolic disorders by affecting the physiology and metabolism of the host. Metformin is one of the most widely prescribed type 2 diabetes (T2D) therapeutic agents.

OBJECTIVE

To determine whether the antidiabetic effect of metformin is related to alterations of intestinal microbial composition.

DESIGN

C57BL/6 mice, fed either a normal-chow diet or a high-fat diet (HFD), were treated with metformin for 6 weeks. The effect of metformin on the composition of the gut microbiota was assessed by analysing 16S rRNA gene sequences with 454 pyrosequencing. Adipose tissue inflammation was examined by flow cytometric analysis of the immune cells present in visceral adipose tissue (VAT).

RESULTS

Metformin treatment significantly improved the glycaemic profile of HFD-fed mice. HFD-fed mice treated with metformin showed a higher abundance of the mucin-degrading bacterium Akkermansia than HFD-fed control mice. In addition, the number of mucin-producing goblet cells was significantly increased by metformin treatment (p<0.0001). Oral administration of Akkermansia muciniphila to HFD-fed mice without metformin significantly enhanced glucose tolerance and attenuated adipose tissue inflammation by inducing Foxp3 regulatory T cells (Tregs) in the VAT.

CONCLUSIONS

Modulation of the gut microbiota (by an increase in the Akkermansia spp. population) may contribute to the antidiabetic effects of metformin, thereby providing a new mechanism for the therapeutic effect of metformin in patients with T2D. This suggests that pharmacological manipulation of the gut microbiota in favour of Akkermansia may be a potential treatment for T2D.

Once a Treg, always a Treg?

Regulatory T cells (Tregs) prevail as a specialized cell lineage that has a central role in the dominant control of immunological tolerance and maintenance of immune homeostasis. Thymus-derived Tregs (tTregs) and their peripherally induced counterparts (pTregs) are imprinted with unique Forkhead box protein 3 (Foxp3)-dependent and independent transcriptional and epigenetic characteristics that bestows on them the ability to suppress disparate immunological and non-immunological challenges. Thus, unidirectional commitment and the predominant stability of this regulatory lineage is essential for their unwavering and robust suppressor function and has clinical implications for the use of Tregs as cellular therapy for various immune pathologies. However, recent studies have revealed considerable heterogeneity or plasticity in the Treg lineage, acquisition of alternative effector or hybrid fates, and promotion rather than suppression of inflammation in extreme contexts. In addition, the absolute stability of Tregs under all circumstances has been questioned. Since these observations challenge the safety and efficacy of human Treg therapy, the issue of Treg stability versus plasticity continues to be enthusiastically debated. In this review, we assess our current understanding of the defining features of Foxp3(+) Tregs, the intrinsic and extrinsic cues that guide development and commitment to the Treg lineage, and the phenotypic and functional heterogeneity that shapes the plasticity and stability of this critical regulatory population in inflammatory contexts.

Human adipose-derived stromal/stem cells induce functional CD4+CD25+FoxP3+CD127- regulatory T cells under low oxygen culture conditions

Human adipose tissue stromal/stem cells (ASCs) are known to induce proliferation of resting T cells under ambient (21%) O2 conditions; however, ASCs exist physiologically under lower oxygen (5% O2) conditions in adipose tissue. The effects of low oxygen levels on ASC immunomodulation of T cells are unknown. In this study, we show that ASCs stimulated proliferation of naive CD4(+) T cells and the percentage of CD25(+) T cells was significantly increased under both low and ambient O2. Forkhead box P3 (FoxP3) and transforming growth factor beta (TGF-β) mRNA expression were significantly increased when ASCs were cocultured with CD4(+) T cells under low compared with ambient O2 conditions. The low O2-induced regulatory T cells (iTregs) exhibited functionality when added to mixed lymphocyte reactions as demonstrated by inhibition of peripheral blood mononuclear cell proliferation, and by >300-fold increase in FoxP3 mRNA, and >2-fold increase in TGF-β mRNA expression. These results demonstrate that under physiologically relevant low O2 conditions, direct contact of human ASCs with naive CD4(+) T cells induced functional iTregs.

RBP4 activates antigen-presenting cells, leading to adipose tissue inflammation and systemic insulin resistance

Insulin resistance is a major cause of diabetes and is highly associated with adipose tissue (AT) inflammation in obesity. RBP4, a retinol transporter, is elevated in insulin resistance and contributes to increased diabetes risk. We aimed to determine the mechanisms for RBP4-induced insulin resistance. Here we show that RBP4 elevation causes AT inflammation by activating innate immunity that elicits an adaptive immune response. RBP4-overexpressing mice (RBP4-Ox) are insulin resistant and glucose intolerant and have increased AT macrophage and CD4 T cell infiltration. In RBP4-Ox, AT CD206(+) macrophages express proinflammatory markers and activate CD4 T cells while maintaining alternatively activated macrophage markers. These effects result from direct activation of AT antigen-presenting cells (APCs) by RBP4 through a JNK-dependent pathway. Transfer of RBP4-activated APCs into normal mice is sufficient to induce AT inflammation, insulin resistance, and glucose intolerance. Thus, RBP4 causes insulin resistance, at least partly, by activating AT APCs that induce CD4 T cell Th1 polarization and AT inflammation.

Pro-inflammatory macrophages increase in skeletal muscle of high fat-fed mice and correlate with metabolic risk markers in humans

OBJECTIVE

In obesity, immune cells infiltrate adipose tissue. Skeletal muscle is the major tissue of insulin-dependent glucose disposal, and indices of muscle inflammation arise during obesity, but whether and which immune cells increase in muscle remain unclear.

METHODS

Immune cell presence in quadriceps muscle of wild type mice fed high-fat diet (HFD) was studied for 3 days to 10 weeks, in CCL2-KO mice fed HFD for 1 week, and in human muscle. Leukocyte presence was assessed by gene expression of lineage markers, cyto/chemokines and receptors; immunohistochemistry; and flow cytometry.

RESULTS

After 1 week HFD, concomitantly with glucose intolerance, muscle gene expression of Ly6b, Emr1 (F4/80), Tnf, Ccl2, and Ccr2 rose, as did pro- and anti-inflammatory markers Itgax (CD11c) and Mgl2. CD11c+ proinflammatory macrophages in muscle increased by 76%. After 10 weeks HFD, macrophages in muscle increased by 47%. Quadriceps from CCL2-KO mice on HFD did not gain macrophages and maintained insulin sensitivity. Muscle of obese, glucose-intolerant humans showed elevated CD68 (macrophage marker) and ITGAX, correlating with poor glucose disposal and adiposity.

CONCLUSION

Mouse and human skeletal muscles gain a distinct population of inflammatory macrophages upon HFD or obesity, linked to insulin resistance in humans and CCL2 availability in mice.

Morphological and inflammatory changes in visceral adipose tissue during obesity

Obesity is a major health burden worldwide and is a major factor in the development of insulin resistance and metabolic complications such as type II diabetes. Chronic nutrient excess leads to visceral adipose tissue (VAT) expansion and dysfunction in an active process that involves the adipocytes, their supporting matrix, and immune cell infiltrates. These changes contribute to adipose tissue hypoxia, adipocyte cell stress, and ultimately cell death. Accumulation of lymphocytes, macrophages, and other immune cells around dying adipocytes forms the so-called "crown-like structure", a histological hallmark of VAT in obesity. Cross talk between immune cells in adipose tissue dictates the overall inflammatory response, ultimately leading to the production of pro-inflammatory mediators which directly induce insulin resistance in VAT. In this review, we summarize recent studies demonstrating the dramatic changes that occur in visceral adipose tissue during obesity leading to low-grade chronic inflammation and metabolic disease.

A special population of regulatory T cells potentiates muscle repair

Long recognized to be potent suppressors of immune responses, Foxp3(+)CD4(+) regulatory T (Treg) cells are being rediscovered as regulators of nonimmunological processes. We describe a phenotypically and functionally distinct population of Treg cells that rapidly accumulated in the acutely injured skeletal muscle of mice, just as invading myeloid-lineage cells switched from a proinflammatory to a proregenerative state. A Treg population of similar phenotype accumulated in muscles of genetically dystrophic mice. Punctual depletion of Treg cells during the repair process prolonged the proinflammatory infiltrate and impaired muscle repair, while treatments that increased or decreased Treg activities diminished or enhanced (respectively) muscle damage in a dystrophy model. Muscle Treg cells expressed the growth factor Amphiregulin, which acted directly on muscle satellite cells in vitro and improved muscle repair in vivo. Thus, Treg cells and their products may provide new therapeutic opportunities for wound repair and muscular dystrophies.

Role of "Western diet" in inflammatory autoimmune diseases

Developed societies, although having successfully reduced the burden of infectious disease, constitute an environment where metabolic, cardiovascular, and autoimmune diseases thrive. Living in westernized countries has not fundamentally changed the genetic basis on which these diseases emerge, but has strong impact on lifestyle and pathogen exposure. In particular, nutritional patterns collectively termed the "Western diet", including high-fat and cholesterol, high-protein, high-sugar, and excess salt intake, as well as frequent consumption of processed and 'fast foods', promote obesity, metabolic syndrome, and cardiovascular disease. These factors have also gained high interest as possible promoters of autoimmune diseases. Underlying metabolic and immunologic mechanisms are currently being intensively explored. This review discusses the current knowledge relative to the association of "Western diet" with autoimmunity, and highlights the role of T cells as central players linking dietary influences to autoimmune pathology.

Linking obesity with type 2 diabetes: the role of T-bet

Obesity is a major predisposing factor for the development of type 2 diabetes (T2D) and is an escalating public health issue around the world. The transition from obesity to T2D is preceded by the induction of a state of insulin resistance, which occurs in response to genetic factors and environmental influences, such as diet. Recent advances have implicated inflammatory immune cells and cytokines as critical pathogenic mediators of insulin resistance and T2D. In particular proinflammatory T helper (Th)1 cells and M1 macrophages are recruited to adipose tissue in response to high fat diet and directly promote the development of insulin resistance. The function of these two cell types is linked by the actions of the cytokine interferon (IFN)γ and one of its major transcriptional regulators T-bet. Recent studies in animal models of T2D demonstrate that T-bet is critical for the development of insulin resistance in response to high fat diet as T-bet-deficient animals are protected from the development of insulin resistance. These data indicate that T-bet and type 1 immunity may constitute novel sites of therapeutic intervention for the treatment of insulin resistance and T2D, in obese human patients.

Modulation of adipose tissue inflammation by FOXP3+ Treg cells, IL-10, and TGF-β in metabolically healthy class III obese individuals

OBJECTIVE

The objective of this study was to compare the profiles of proinflammatory (interleukin [IL]-6 and tumor necrosis factor [TNF]) and anti-inflammatory (IL-10 and transforming growth factor [TGF]-β) adipokines in the blood, subcutaneous adipose tissue (SAT), and visceral adipose tissue (VAT) of metabolically healthy class III obese individuals and normal-weight controls.

METHODS

The serum concentrations (enzyme-linked immunosorbent assay [ELISA]), mRNA expression levels (reverse transcriptase polymerase chain reaction), and adipose tissue secretion (ELISA) of IL-6, TNF, IL-10, and TGF-β were analyzed, as were the mRNA expression of FOXP3 (present in regulatory T cells) and the secretion (Western blotting) of matrix metalloproteinases in the adipose tissue.

RESULTS

There were no differences in the circulating levels, expression, or secretion of IL-6 and TNF between the groups or tissues. The expression and circulating levels of IL-10 were higher in obese individuals, especially in the SAT. Although the blood concentration of TGF-β was similar between the groups, its expression and secretion levels were higher in the adipose tissues of obese individuals compared with controls. FOXP3 and MMP expression levels were higher in the SAT and VAT of obese individuals, respectively, compared with the controls.

CONCLUSION

Metabolically healthy, extremely obese individuals have effective immunoregulation to counter chronic obesity-related inflammation through the increased production of the anti-inflammatory cytokines IL-10 and TGF-β in adipose tissue, especially SAT; the increased presence of FOXP3-positive regulatory T cells; and increases in angiogenesis and adipogenesis induced by TGF-β and MMPs. These regulatory mechanisms could be important in the delayed onset of metabolic complications, even in extremely obese individuals.

Invariant natural killer T cells in adipose tissue: novel regulators of immune-mediated metabolic disease

Adipose tissue (AT) represents a microenvironment where intersection takes place between immune processes and metabolic pathways. A variety of immune cells have been characterized in AT over the past decades, with the most recent addition of invariant natural killer T (iNKT) cells. As members of the T cell family, iNKT cells represent a subset that exhibits both innate and adaptive characteristics and directs ensuing immune responses. In disease conditions, iNKT cells have established roles that include disorders in the autoimmune spectrum in malignancies and infectious diseases. Recent work supports a role for iNKT cells in the maintenance of AT homeostasis through both immune and metabolic pathways. The deficiency of iNKT cells can result in AT metabolic disruptions and insulin resistance. In this review, we summarize recent work on iNKT cells in immune regulation, with an emphasis on AT-resident iNKT cells, and identify the potential mechanisms by which adipocytes can mediate iNKT cell activity.

Metabolic syndrome and insulin resistance: underlying causes and modification by exercise training

Metabolic syndrome (MS) is a collection of cardiometabolic risk factors that includes obesity, insulin resistance, hypertension, and dyslipidemia. Although there has been significant debate regarding the criteria and concept of the syndrome, this clustering of risk factors is unequivocally linked to an increased risk of developing type 2 diabetes and cardiovascular disease. Regardless of the true definition, based on current population estimates, nearly 100 million have MS. It is often characterized by insulin resistance, which some have suggested is a major underpinning link between physical inactivity and MS. The purpose of this review is to: (i) provide an overview of the history, causes and clinical aspects of MS, (ii) review the molecular mechanisms of insulin action and the causes of insulin resistance, and (iii) discuss the epidemiological and intervention data on the effects of exercise on MS and insulin sensitivity.

Immunological mechanisms in the pathophysiology of non-alcoholic steatohepatitis

Non-alcoholic steatohepatitis (NASH) is characterized by the presence of steatosis, inflammation and hepatocyte injury and constitutes hepatic manifestation of the metabolic syndrome. The pathogenesis of NASH is complex and implicates cross-talk between different metabolically active sites, such as liver and adipose tissue. Obesity is considered a chronic low-grade inflammatory state and the liver has been recognized as being an "immunological organ". The complex role of the immune system in the pathogenesis of NASH is currently raising great interest, also in view of the possible therapeutic potential of immunotherapy in NASH. This review focuses on the disturbances of the cells constituting the innate and adaptive immune system in the liver and in adipose tissue.

Immune regulation in obesity-associated adipose inflammation

Adipose tissue inflammation is often a consequence of obesity and is characterized by infiltration and activation of immune cells that overproduce cytokines and chemokines. This apparent loss of immune regulation in obese adipose tissue contributes to the ongoing chronic inflammation that is thought to promote the degradation of metabolic parameters in obesity. Much recent work has sought to identify the immune cell subsets that are involved in adipose tissue inflammation, understand the mechanisms by which adipose tissue inflammation develops, and develop immunotherapeutic strategies to reverse this process. In this review, we describe the known mechanisms that underlie the loss of immune regulation in obesity-associated adipose tissue inflammation and set the stage for the development of novel therapeutic approaches.

Peripherally induced tregs - role in immune homeostasis and autoimmunity

Thymically derived Foxp3(+) regulatory T cells (tTregs) constitute a unique T cell lineage that is essential for maintaining immune tolerance to self and immune homeostasis. However, Foxp3 can also be turned on in conventional T cells as a consequence of antigen exposure in the periphery, under both non-inflammatory and inflammatory conditions. These so-called peripheral Tregs (pTregs) participate in the control of immunity at sites of inflammation, especially at the mucosal surfaces. Although numerous studies have assessed in vitro generated Tregs (termed induced or iTregs), these cells most often do not recapitulate the functional or phenotypic characteristics of in vivo generated pTregs. Thus, there are still many unanswered questions regarding the T cell receptor (TCR) repertoire and function of pTregs as well as conditions under which they are generated in vivo, and the degree to which these characteristics identify specialized features of pTregs versus features that are shared with tTregs. In this review, we summarize the current state of our understanding of pTregs and their relationship to the tTreg subset. We describe the recent discovery of unique cell surface markers and transcription factors (including Neuropilin-1 and Helios) that can be used to distinguish tTreg and pTreg subsets in vivo. Additionally, we discuss how the improved ability to distinguish these subsets provided new insights into the biology of tTregs versus pTregs and suggested differences in their function and TCR repertoire, consistent with a unique role of pTregs in certain inflammatory settings. Finally, these recent advances will be used to speculate on the role of individual Treg subsets in both tolerance and autoimmunity.

Regulation of adipose tissue T cell subsets by Stat3 is crucial for diet-induced obesity and insulin resistance

Dysregulated inflammation in adipose tissue, marked by increased proinflammatory T-cell accumulation and reduced regulatory T cells (Tregs), contributes to obesity-associated insulin resistance. The molecular mechanisms underlying T-cell-mediated inflammation in adipose tissue remain largely unknown, however. Here we show a crucial role for signal transducer and activator of transcription 3 (Stat3) in T cells in skewing adaptive immunity in visceral adipose tissue (VAT), thereby contributing to diet-induced obesity (DIO) and insulin resistance. Stat3 activity is elevated in obese VAT and in VAT-resident T cells. Functional ablation of Stat3 in T cells reduces DIO, improves insulin sensitivity and glucose tolerance, and suppresses VAT inflammation. Importantly, Stat3 ablation reverses the high Th1/Treg ratio in VAT of DIO mice that is likely secondary to elevated IL-6 production, leading in turn to suppression of Tregs. In addition, Stat3 in T cells in DIO mice affects adipose tissue macrophage accumulation and M2 phenotype. Our study identifies Stat3 in VAT-resident T cells as an important mediator and direct target for regulating adipose tissue inflammation, DIO, and its associated metabolic dysfunctions.

Human T regulatory cells: on the way to cognition

Forkhead box P3 (Foxp3)(+) T regulatory (Treg) cells are powerful controllers of the immune response and their role in the human immune system is indispensable. Since a number of revolutionary and very convincing results were brought to light, Foxp3 has unquestionably been thought to be the "master regulator" of Treg lineage commitment. Herein, we depict the revised view on the role of Foxp3 transcription factor, challenging this theory, as well as the growing significance of Runt-related transcription factor (RUNX) family proteins for Treg lineage. The review presents the current notion of Treg cell heterogeneity, molecular characteristics and their mechanisms of action.

The immune system's involvement in obesity-driven type 2 diabetes

Type 2 diabetes is now a worldwide epidemic, strongly correlated with an elevated incidence of obesity. Obesity-associated adipose tissue inflammation is a major cause of the decreased insulin sensitivity seen in type 2 diabetes. Recent studies have shed light on the cross-talk between the immune system and organismal metabolism. This review discusses the connection between inflammation in adipose tissue and systemic insulin resistance, focusing on the roles of innate and adaptive immune cell subsets in the pathogenesis of this metabolic disease.

Generation of functional T-regulatory cells in children with metabolic syndrome

Recent research implies a role of decreased number and/or function of T-regulatory cells (Tregs) in low-grade inflammation associated with obesity and atherosclerosis. The enhancement of atheroprotective immunity by the expansion of Tregs could serve as a therapeutic strategy in obesity-related immunological disturbances. The aim of our study was an attempt to generate Treg cells in children with risk factors for the development of cardiovascular disease and to compare the results to those obtained in healthy subjects. The study group consisted of 30 children with metabolic syndrome (MS) and 30 controls. Conventional CD4(+)CD25(-) cells separated from the peripheral blood were converted into Treg cells with the use of CD3/CD28 antibodies and interleukin (IL)-2/transforming growth factor (TGF)-β stimulation. The expression of critical Treg molecules and cytokines was assessed at mRNA and protein levels. The percentages of Treg cells in the peripheral blood were significantly lower in the children with MS compared to the healthy subjects. After the culture with CD3/CD28 and IL-2/TGF-β we detected a significant increase in the expression of Tregs marker transcription factor FoxP3. The Tregs induced from the children with MS varied from the ones obtained in the controls in the expression of some molecules at mRNA level (e.g. IL-27, LGAL, KLF10 and NRP1) yet not in proliferation studies. For the first time, we have demonstrated the possibility of generating functional Treg cells in children with MS. The results of our study could be used in the design of therapeutic interventions in obesity associated immunologic disturbances.

Lymphocytes in obesity-related adipose tissue inflammation

Inflammation in the white adipose tissue (WAT) is considered a major player in the development of insulin resistance. The role of macrophages accumulating in the WAT during obesity, promoting WAT inflammation and insulin resistance is well established. In contrast, less is known about the role of lymphocytes. Recent studies have implicated different lymphocyte subsets in WAT inflammation. For instance, cytotoxic CD8(+) T cells infiltrating the WAT may contribute to the recruitment, differentiation and activation of macrophages. On the other hand, a differential role for CD4(+) Th1 and CD4(+) Th2 cells has been suggested. Levels of WAT regulatory T cells decrease during the course of obesity and may represent a crucial factor for the maintenance of insulin sensitivity. Moreover, activation of natural killer T cells, an innate-like T cell population, which recognises lipid antigens, promotes insulin resistance and WAT inflammation. Finally, B cells may infiltrate WAT very early in response to high-fat feeding and worsen glucose metabolism through modulation of T cells and the production of pathogenic antibodies. These interesting new findings however bear controversies and introduce novel, yet unanswered, questions. Here, we review and discuss the impact of the different lymphocyte subsets in obesity-related WAT inflammation and attempt to identify the open questions to be answered by future studies.

Identification of adipose tissue dendritic cells correlated with obesity-associated insulin-resistance and inducing Th17 responses in mice and patients

T-cell regulation in adipose tissue provides a link between inflammation and insulin resistance. Because of alterations in adipose tissue T-cell composition in obesity, we aimed to identify the antigen-presenting cells in adipose tissue of obese mice and patients with insulin resistance. Dendritic cells (DCs) and T cells were studied in mice and in two cohorts of obese patients. In lean mice, only CD11c(+) DCs were detected in adipose tissue. Adoptive transfer of naive CD4(+) T cells in Rag1(-/-) mice led to a predominant Th1 response in adipose tissue. In contrast, during obesity DCs (human CD11c(+)CD1c(+) and mouse CD11c(high)F4/80(low)) accumulated in adipose tissue. CD11c(high)F4/80(low) DCs from obese mice induced Th17 differentiation. In patients, the presence of CD11c(+)CD1c(+) DCs correlated with the BMI and with an elevation in Th17 cells. In addition, these DCs led to ex vivo Th17 differentiation. CD1c gene expression further correlated with homeostatic model assessment-insulin resistance in the subcutaneous adipose tissue of obese patients. We show for the first time the presence and accumulation of specific DCs in adipose tissue in mouse and human obesity. These DCs were functional and could be important regulators of adipose tissue inflammation by regulating the switch toward Th17 cell responses in obesity-associated insulin resistance.

Influence of dietary components on regulatory T cells

Common dietary components including vitamins A and D, omega-3 and probiotics are now widely accepted to be essential to protect against many diseases with an inflammatory nature. On the other hand, high-fat diets are documented to exert multiple deleterious effects, including fatty liver diseases. Here we discuss the effect of dietary components on regulatory T cell (Treg) homeostasis, a central element of the immune system to prevent chronic tissue inflammation. Accordingly, evidence on the impact of dietary components on diseases in which Tregs play an influential role will be discussed. We will review chronic tissue-specific autoimmune and inflammatory conditions such as inflammatory bowel disease, type 1 diabetes mellitus, multiple sclerosis, rheumatoid arthritis and allergies among chronic diseases where dietary factors could have a direct influence via modulation of Tregs homeostasis and functions.

Autologous stromal vascular fraction therapy for rheumatoid arthritis: rationale and clinical safety

Advancements in rheumatoid arthritis (RA) treatment protocols and introduction of targeted biological therapies have markedly improved patient outcomes, despite this, up to 50% of patients still fail to achieve a significant clinical response. In veterinary medicine, stem cell therapy in the form of autologous stromal vascular fraction (SVF) is an accepted therapeutic modality for degenerative conditions with 80% improvement and no serious treatment associated adverse events reported. Clinical translation of SVF therapy relies on confirmation of veterinary findings in targeted patient populations. Here we describe the rationale and preclinical data supporting the use of autologous SVF in treatment of RA, as well as provide 1, 3, 6, and 13 month safety outcomes in 13 RA patients treated with this approach.