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IL-17 Regulates Adipogenesis, Glucose Homeostasis, and Obesity
Abstract
Inflammatory mediators have the potential to impact a surprising range of diseases, including obesity and its associated metabolic syndrome. In this paper, we show that the proinflammatory cytokine IL-17 inhibits adipogenesis, moderates adipose tissue (AT) accumulation, and regulates glucose metabolism in mice. IL-17 deficiency enhances diet-induced obesity in mice and accelerates AT accumulation even in mice fed a low-fat diet. In addition to potential systemic effects, IL-17 is expressed locally in AT by leukocytes, predominantly by γδ T cells. IL-17 suppresses adipocyte differentiation from mouse-derived 3T3-L1 preadipocytes in vitro, and inhibits expression of genes encoding proadipogenic transcription factors, adipokines, and molecules involved in lipid and glucose metabolism. IL-17 also acts on differentiated adipocytes, impairing glucose uptake, and young IL-17-deficient mice show enhanced glucose tolerance and insulin sensitivity. Our findings implicate IL-17 as a negative regulator of adipogenesis and glucose metabolism in mice, and show that it delays the development of obesity.
... IL-17 deficiency may be also related to increased rate of glucose metabolism disturbances in Bcc infected group. In vivo and in vitro studies suggest that IL-17 cytokines contribute significantly to the homeostatic regulation of glucose metabolism (Zuñiga et al., 2010;Bechara et al., 2021). In vitro, IL-17 inhibited insulin-induced glucose uptake by adipocytes (Zuñiga et al., 2010). ...
... In vivo and in vitro studies suggest that IL-17 cytokines contribute significantly to the homeostatic regulation of glucose metabolism (Zuñiga et al., 2010;Bechara et al., 2021). In vitro, IL-17 inhibited insulin-induced glucose uptake by adipocytes (Zuñiga et al., 2010). In vivo, IL-17 deficiency enhanced glucose tolerance and insulin sensitivity in young mice, but simultaneously promoted adipocyte differentiation, leading to the increased accumulation of adipose tissue mass, the onset of obesity and the metabolic syndrome development. ...
... In vivo, IL-17 deficiency enhanced glucose tolerance and insulin sensitivity in young mice, but simultaneously promoted adipocyte differentiation, leading to the increased accumulation of adipose tissue mass, the onset of obesity and the metabolic syndrome development. Even lean IL-17 deficient mice have found to demonstrate modest fasting hyperglycemia and reduced basal insulin levels suggesting that control of basal insulin secretion may also be affected (Zuñiga et al., 2010). In CF, insulin production is initially compromised due to basic defect. ...
Background
In current literature there are only scarce data on the host inflammatory response during Burkholderia cepacia complex (Bcc) persistence. The primary objective of the present research was to carry out cross-sectional analyses of biomarkers and evaluate disease progression in cystic fibrosis (CF) patients with chronic Bcc infection and pathogen-free ones. The secondary aim was to assess prospectively overall survival of the study participants during up to 8 years of follow-up.
Methods
The study included 116 paediatric patients with CF; 47 CF patients were chronically infected with Bcc, and 69 individuals were Bcc free. Plasma and sputum biomarkers (neutrophil elastase, MMP-8, MMP-9, MMP-12, IL-2, IL-4, IL-6, IL-8, IL-10, IL-18, IL-22, IL-23, IL-17, IFN-γ, TGFβ1, TNF-α) were analysed using commercially available kits. Besides, inhibitory effect of dexamethasone on proliferative response of PHA-stimulated peripheral blood lymphocytes had been assessed.
Results
Bcc infected patients did not differ from Bcc free ones in demographic and clinical parameters, but demonstrated an increased rate of glucose metabolism disturbances and survival disadvantage during prolong follow-up period. Biomarkers analyses revealed elevated TNF-α and reduced IL-17F levels in sputum samples of Bcc infected patients. These patients also demonstrated improvement of peripheral blood lymphocyte sensitivity to steroid treatment and reduction in plasma pro-inflammatory (IL-17F and IL-18) and anti-inflammatory (TGFβ1 and IL-10) cytokine concentrations.
Conclusions
Reduction in IL-17F levels may have several important consequences including increase in steroid sensitivity and glycemic control disturbances. Further investigations are needed to clarify the role of IL-17 cytokines in CF complication development. Low plasma TGFβ1 and IL-10 levels in Bcc infected group may be a sign of subverted activity of regulatory T cells. Such immune alterations may be one of the factors contributing to the development of the cepacia syndrome.
... Gamma-delta (γδ) T cells γδ T cells are a class of tissue-resident lymphocytes present in both mice and humans with primary roles in defending against pathogens in epithelial tissues such as the skin, gut, and lungs (72). γδ T cells are also present in AT, comprising~4 to 11% of CD3 + T cells in mice (73). γδ T cells are unique in that they respond to antigen presentation similar to conventional T cells but also respond to cytokines, bridging a gap between innate and adaptive immunity. ...
... γδ T cells are unique in that they respond to antigen presentation similar to conventional T cells but also respond to cytokines, bridging a gap between innate and adaptive immunity. In mice, γδ T cells in AT have been shown to increase in obesity and are noted to secrete cytokines IL-17 (73,74) and TNF-α (75). IL-17 released by γδ T cells may limit adipogenesis (73), increase M1-like (CD11c + CD206-) macrophages (75), and limit glucose tolerance (73,75). ...
... In mice, γδ T cells in AT have been shown to increase in obesity and are noted to secrete cytokines IL-17 (73,74) and TNF-α (75). IL-17 released by γδ T cells may limit adipogenesis (73), increase M1-like (CD11c + CD206-) macrophages (75), and limit glucose tolerance (73,75). In humans, circulating γδ T cells are decreased with obesity (76), yet omental AT γδ T cells are increased (77). ...
Obesity-associated inflammation is a systemic process that affects all metabolic organs. Prominent among these is adipose tissue, where cells of the innate and adaptive immune system are markedly changed in obesity, implicating these cells in a range of processes linking immune memory to metabolic regulation. Furthermore, weight loss and weight cycling have unexpected effects on adipose tissue immune populations. Here, we review the current literature on the roles of various immune cells in lean and obese adipose tissue. Within this context, we discuss pharmacological and nonpharmacological approaches to obesity treatment and their impact on systemic inflammation.
... 28 Therefore, adipogenesis is suppressed by IL-17 due to the combined action of transcription factors that govern adipocyte differentiation. [28][29][30] Reports have also suggested that IL-17 acts as a negative regulator of adipogenesis and glucose metabolism and delays the onset of obesity. 29 Therefore, we assumed that IL-31 may act as an effector via IL-17 signaling during the anti-adipogenesis process. ...
... [28][29][30] Reports have also suggested that IL-17 acts as a negative regulator of adipogenesis and glucose metabolism and delays the onset of obesity. 29 Therefore, we assumed that IL-31 may act as an effector via IL-17 signaling during the anti-adipogenesis process. Further research is needed to clarify the exact role of IL-31 in the anti-adipogenic properties of metabolic syndrome. ...
Psoriasis is recognized not only as a skin disease but also as a systemic disorder. Interleukin-31 (IL-31) may be associated with psoriasis and systemic inflammation. We aimed to quantify serum IL-31 levels in patients with psoriasis and explore their associations with specific clinical manifestations. 30 patients with psoriasis and 30 healthy controls were included in this study. Demographic information and clinical characteristics were obtained through physical examination and medical history review. Serum IL-31 levels were measured using an enzyme-linked immunosorbent assay. IL-31 concentration was significantly higher in patients with psoriasis than in the control group (p<0.001). Patients with psoriasis vulgaris, psoriasis erythroderma, and pustular psoriasis had significantly higher serum IL-31 levels than healthy controls. Additionally, serum IL-31 levels were associated with itch numerical rating scale (NRS) scores and body mass index (BMI) but not with disease severity as measured by the Psoriasis Area and Severity Index (PASI). In patients with psoriasis, increased serum IL-31 levels correlated with itch severity but not with PASI. This suggests that IL-31 may play a critical role in the pathogenesis of psoriasis and could be a valuable target for further studies and therapeutic interventions.
... Although the function of Th17 cells in obesity is not fully elucidated, there is growing evidence indicating that Th17 cell serve as negative regulator of adipogenesis and can play a pivotal role in preventing obesity 43 . This notion is supported by the observation that IL-17-deficient mice exhibit increased susceptibility to obesity, glucose intolerance, and insulin resistance 43 . ...
... Although the function of Th17 cells in obesity is not fully elucidated, there is growing evidence indicating that Th17 cell serve as negative regulator of adipogenesis and can play a pivotal role in preventing obesity 43 . This notion is supported by the observation that IL-17-deficient mice exhibit increased susceptibility to obesity, glucose intolerance, and insulin resistance 43 . Moreover, the intestinal transfer of Th17 cells into obese mice has been shown to contribute to intestinal microbiota homeostasis, thereby aiding in the reduction of obesity and metabolic disorders 39 . ...
Obesity is a growing healthcare problem globally. In Saudi Arabia, 24% of adults aged 15 years and above have been living with Obesity. It is considered a chronic inflammatory condition that is linked to a wide range of disorders including type 2 diabetes mellitus, insulin resistance and cardiovascular diseases. In this study, we aimed to assess the influence of obesity on the proportion of Th17 cells among healthy, overweight, and obese women in Saudi Arabia. Additionally, we aimed to explore potential ligands targeting the master transcription factor of Th17 cells: RORγt. A cross-sectional study was conducted, wherein their body mass index (BMI) and waist circumference (WC) were measured. The proportion of peripheral Th17 cells was determined using flow cytometry. We found a decrease in the proportion of peripheral Th17 among women with central obesity, though this was observed among overweight and obese participants. Interestingly, both BMI and WC were inversely correlated with the proportion of peripheral Th17 cells in women experiencing overweight or obesity, while no change was observed among healthy participants. Notably, the analysis revealed a significant moderate negative correlation between the proportion of Th17 cells and HbA1c levels, observed only among the overweight and obese participants. In this study, we identified three potential binding sites on RORγt molecules of Th17 cells, bound to 58 chemical ligands. The majority of the chemical structures (72.4%) were targeted binding pocket 1 of the RORγt molecule. These findings could provide a new insight to develop new pharmaceutical molecules targeting immune cells to combat obesity and related metabolic disorders.
Supplementary Information
The online version contains supplementary material available at 10.1038/s41598-024-81070-1.
... It has been reported that competitive binding of an IL1 receptor (IL1R) antagonist with the IL1R diminishes basal-fed plasma glucose levels in type 2 diabetic Goto-Kakizaki rats [15]. Moreover, IL17 treatment hinders glucose uptake in 3T3-L1 adipocytes in vitro, and young IL17-deficient mice display increased glucose tolerance and insulin sensitivity, indicating that the inflammatory cytokine IL17 acts as a negative regulator of glucose metabolism in vivo [16]. Given the incomplete understanding of the immunoregulatory role of chromatin remodeling factor SRG3 in the adipose tissue, we hypothesized that SRG3 expression facilitates immune homeostasis in adipose tissues. ...
... Moreover, previous studies have provided evidence that neutrophil-derived IL1β is required for IL17 production by γδ T cells in the injured central nervous system during EAE pathogenesis and, conversely, γδ T cell-derived IL17 drives the recruitment of IL1β-producing neutrophils [25]. Based on previous reports showing that IL17 and IL1β both worsen glucose intolerance [16,19], together with our findings that IL17-producing γδ T cells and IL1β-producing neutrophils are dramatically reduced in the adipose tissues of SRG3 β-actin B10.PL mice, it will be interesting to investigate how crosstalk between γδ T cells and neutrophils (i.e., γδ T cell-neutrophil axis) contributes to regulating immune responses in adipose tissues. ...
The SWItch3-related gene (SRG3) is a core component of ATP-dependent SWI/SNF complexes, which are crucial for regulating immune cell development and function (e.g., macrophages and CD4⁺ T cells), embryonic development, and non-immune cell differentiation. Notably, SRG3 overexpression has been shown to polarize macrophages in the central nervous system toward an anti-inflammatory M2 phenotype, thereby protecting against the development of experimental autoimmune encephalomyelitis in mice. However, the effect of SRG3 on immune responses in adipose tissues remains unclear. To address this issue, we examined the cellularity and inflammatory status of adipose tissue in B10.PL mice overexpressing the SRG3 gene under the ubiquitous β-actin promoter (SRG3β-actin). Interestingly, SRG3 overexpression significantly reduced adipocyte size in both white and brown adipose tissues, without affecting the overall adipose tissue weight. Such phenotypic effects might be associated with the improved glucose tolerance observed in SRG3β-actin B10.PL mice. Moreover, we found that SRG3 overexpression down-regulates IL1β-expressing M1 macrophages, leading to a significant decrease in the M1/M2 macrophage ratio. Additionally, SRG3β-actin B10.PL mice showed a dramatic reduction in neutrophils as well as IL1β- and IL17-producing T cells in adipose tissues. Taken together, our results indicate that SRG3 plays a vital role in maintaining immune homeostasis within adipose tissues.
... The chronic inflammation in T2DM leads to insulin resistance which is a key factor that results in impaired glucose metabolism [15]. The altered pro-inflammatory cytokines level for example higher IL-17 level plays a significant role in the suppression of preadipocyte differentiation which might reduces adipsin expression in adipocyte [16]. Zhou et al. [11], showed that acute insulin response (AIR) and HOMA-B were positively correlated with serum adipsin levels, which suggested that serum adipsin levels were closely linked to first-phase insulin secretion. ...
... TNFα and IL-6 are proinflammatory cytokines that can induce expression of IL-17 which promotes inflammation through stimulating NF-κB and other pathways [22]. Zúñiga et al. [16], found that IL-17 could diminish the expression of adipsin. Mathews et al. [23], found that adipsin mRNA in lung tissue is significantly inversely correlated with IL-17 mRNA in obese mice. ...
Adipsin is an anti-inflammatory adipokines and its altered level was seen in obesity and type II DM. Our study investigated the clinical significance of serum adipsin levels as a risk marker for type 2 diabetes and its relationships with insulin resistance and various adipo-cytokines. The study included 110 treatment-naïve T2DM cases and 100 controls of similar age and gender from northern India. Clinical, biochemical, and anthropometric characteristics were all profiled. Serum adipo-cytokines were measured using ELISA methods. Adipsin was significantly inversely correlated with body mass index (BMI), waist circumference, fasting plasma glucose, glycated haemoglobin (HbA1C), total cholesterol (TC), triglyceride (TG), homeostasis model assessment-estimated insulin resistance (HOMA-IR), tumour necrosis factor- α (TNF-α) and interleulin-6 (IL-6) and positively correlated with high-density lipoprotein cholesterol (HDL-C) and homeostasis model assessment of β-cell function (HOMA-B) (P < 0.05). T2DM occurrence decreased with increasing concentration of adipsin with an odds ratio (OR) of 0.68 (95% CI = 0.58–0.79), P < 0.001. The area under curve (95% CI) for adipsin was 0.70 (0.63 to 0.76) with P < 0.001. The best cutoff value for adipsin to predict T2DM was < 5.50 µg/ml with 47.27% sensitivity and 82.00% specificity. FPG and WC were both independent predictors of serum adipsin levels. Our findings showed that high adipsin levels reduced the likelihood of T2DM and emerged as a potential risk marker in the prediction of T2DM.Graphical Abstract
... A study demonstrated that DIO is predisposed to an increased Th17 bias [111]. Similarly, an increased number of Th17 cells and levels of IL-17 were also observed in adipose tissue and liver tissue in mice with DIO [112][113][114]. However, interesting findings were observed in the gut of obese mice fed an HFD, which demonstrated that number of Th17 cells and levels of IL-17 were decreased [115,116], suggesting different functions of Th17 cells in intestines, which will be discussed in the intestinal immune section below. ...
In recent decades, the global prevalence of metabolic syndrome has surged, posing a significant public health challenge. Metabolic disorders, encompassing diabetes, obesity, nonalcoholic fatty liver disease, and polycystic ovarian syndrome, have been linked to alterations in the gut microbiota. Nonetheless, the connection between gut microbiota and host metabolic diseases warrants further investigation. In this review, we delve into the associations between various metabolic disorders and the gut microbiota, focusing on immune responses and bile acid (BA) metabolism. Notably, T helper cells, innate lymphoid cells, macrophages, and dendritic cells have been shown to modulate host metabolism through interactions with intestinal microorganisms and the release of cytokines. Furthermore, secondary BA metabolites, derived from the microbiota, are involved in the pathogenesis of metabolic diseases via the farnesoid X receptor and Takeda G protein-coupled receptor 5. By covering both aspects of this immune system-microorganism axis, we present a comprehensive overview of the roles played by the gut microbiota, microbiota-derived BA metabolites, and immune responses in metabolic diseases, as well as the interplay between these systems.
... These cytokines disrupt normal insulin signaling in target cells [50]. Moreover, IL-17 can directly interfere with the insulin signaling pathway, particularly by acting on differentiated adipocytes, leading to impaired cellular responsiveness to insulin and reduced glucose uptake [51]. ...
Gestational diabetes mellitus (GDM) is a common pregnancy complication characterized by hyperglycemia and insulin resistance, with unclear genetic mechanisms. The specific involvement of proinflammatory cytokines, including IL-17A, and the immuno-tolerogenic HLA-G remains poorly understood in GDM. We aimed to explore the associations of three polymorphisms, IL-17A -197G>A (rs2275913), IL-17RA -947A>G (rs4819554), and HLA-G 14-bp insertion/deletion (indel), with GDM risk in a Brazilian population. We conducted a case-control study (79 GDM cases and 79 controls). Genetic polymorphisms were analyzed using PCR–RFLP, with DNA extracted using the Salting-out procedure. Significant associations were identified between -197G>A rs2275913 and HLA-G 14-bp indel polymorphisms in both codominant and recessive models. The IL-17A rs2275913 AA genotype was associated with a nearly ten-fold increased risk of GDM in both the codominant (p = 0.021, OR 9.89, 95% CI: 1.63–59.92) and recessive models (p = 0.006, OR 9.33, 95% CI: 1.57–55.38). Similarly, the HLA-G 14-bp Ins/Ins genotype was associated with an increased risk in both the codominant (p = 0.026, OR 3.34, 95% CI: 0.98–11.41) and recessive models (p = 0.010, OR 4.20, 95% CI: 1.36–12.96). IL-17RA polymorphism showed no significant associations. The study findings highlight the potential genetic and immune factors associated with GDM, particularly the -197G>A rs2275913 and HLA-G 14-bp indel polymorphisms. Further functional characterization is warranted to uncover the mechanism of genotype–phenotype association.
... Furthermore, SARS-CoV-2 infection may exacerbate pre-existing metabolic dysregulation, leading to hypertriglyceridemia. This aligns with reports of altered adipokine levels (e.g., increased leptin) in post-COVID-19 patients, further supporting the role of an immune-metabolic interface in these outcomes [32,33]. ...
Dysfunctions in the immune system and alterations in the microbiome composition following SARS-CoV-2 infection contribute to persistent neurological issues observed in long COVID-19 survivors. We hypothesize that alterations in the gut microbiome composition and peripheral inflammatory profile following COVID-19 may play pivotal roles in behavior changes among individuals experiencing long-term illness. This cross-sectional study included a sample of post-COVID-19 and non-COVID-19 subjects. We assessed the presence of psychiatric conditions utilizing standardized diagnostic criteria, Hamilton Rating Scale for Anxiety (HAM-A), Hamilton Rating Scale for Depression (HAM-D), Biological Rhythms in Neuropsychiatry Assessment Interview (BRIAN), and Functional Assessment Short Test (FAST). Plasma samples were analyzed to examine lipid and inflammatory profiles. Fecal samples were evaluated by 16S rRNA sequencing to identify the gut microbiome composition. Noteworthy findings include a significant increase in the myeloid progenitor inhibitory factor 1 (MPIF-1), interleukin (IL)-17, and triglyceride among post-COVID-19 individuals. While α-diversity in the gut microbiome composition showed no significant differences, β-diversity demonstrated a notable distinction between the healthy control and post-COVID-19 groups. Post-COVID-19 individuals exhibited a decreased abundance of phylum, class, and order of Verrucomicrobia, family, and genus of Akkermansia, a short-chain fatty acid producer and microbial group significantly associated with intestinal barrier homeostasis and the amelioration of metabolic diseases. No difference was found between the behavioral and clinical data. In post-COVID-19 individuals, there were elevated IL-17 and MPIF-1 levels, compared to non-COVID-19 individuals. Additionally, there were notable alterations in gut microbiome composition, as evidenced by changes in β-diversity and a decrease of Verrucomicrobia, family, and Akkermansia genus abundance.
... Among the different factors that play a role in inflammation, TNF-α, IL-6, IL-17, and IL-10 are cytokines that orchestrate both PsO and MetS. The IL-17 family participates in the complex interplay between inflammation and metabolism, with systemic effects on glucose homeostasis and a negative regulatory role in adipogenesis and adipocyte function [26]. Moreover, obesity has been shown to promote the expansion of IL-17-producing T cells in adipose tissue, inducing a vicious cycle in which IL-17 promotes inflammation through a positive feedback mechanism. ...
Psoriasis (PsO) is a chronic inflammatory dermatosis that often presents with erythematous, sharply demarcated lesions. Although psoriasis is primarily a dermatological disease, its immune-mediated pathogenesis produces systemic effects and is closely associated with various comorbid conditions such as cardiovascular disease (CVD), metabolic syndrome (MetS), and diabetes mellitus type II (DMII). Apremilast, an oral phosphodiesterase 4 (PDE-4) inhibitor, has shown promise in treating moderate-to-severe psoriasis and is associated with potential cardiometabolic benefits. In a 12-month prospective observational study involving 137 patients with moderate-to-severe psoriasis, we assessed changes in psoriasis clinimetric scores and metabolic profiles from baseline (T0) to 52 weeks (T1) to evaluate the efficacy of apremilast. After 52 weeks of apremilast treatment, we documented a statistically significant decrease in low-density lipoprotein (LDL) and total cholesterol, triglycerides, and glucose levels. Our findings even suggest a potential synergistic effect among patients treated with apremilast, alongside concomitant statin and/or insulin therapy. Although the results of our study must be validated on a larger scale, the use of apremilast in the treatment of psoriatic patients with cardio-metabolic comorbidities yields promising results.
... Importantly, RORγt + pTregs and Th17 homeostasis were not affected by 4 weeks of HFD feeding nor FOS supplementation in other metabolic organs such as the liver (Fig. S3A) and the perigonadal adipose tissue (Fig. S3B). Thus, 4 weeks of HFD were not sufficient to increase Th17 cells in the adipose tissue and liver, which is known to have a detrimental impact on metabolic pathology after longer period of HFD feeding (superior to 12 weeks) [29][30][31][32][33] . Hence, altered RORγt + T cells homeostasis seems restrained to the intestine after 4 weeks of HFD. ...
Diet composition impacts metabolic health and is now recognized to shape the immune system, especially in the intestinal tract. Nutritional imbalance and increased caloric intake are induced by high-fat diet (HFD) in which lipids are enriched at the expense of dietary fibers. Such nutritional challenge alters glucose homeostasis as well as intestinal immunity. Here, we observed that short-term HFD induced dysbiosis, glucose intolerance and decreased intestinal RORγt⁺ CD4 T cells, including peripherally-induced Tregs and IL17-producing (Th17) T cells. However, supplementation of HFD-fed male mice with the fermentable dietary fiber fructooligosaccharides (FOS) was sufficient to maintain RORγt⁺ CD4 T cell subsets and microbial species known to induce them, alongside having a beneficial impact on glucose tolerance. FOS-mediated normalization of Th17 cells and amelioration of glucose handling required the cDC2 dendritic cell subset in HFD-fed animals, while IL-17 neutralization limited FOS impact on glucose tolerance. Overall, we uncover a pivotal role of cDC2 in the control of the immune and metabolic effects of FOS in the context of HFD feeding.
... Although cytokines are traditionally studied concerning immune responses, many findings have recognized their role in modulating lipid metabolism in cancer and metabolic disorders. Numerous inflammatory cytokines including IL-17A, IL-6, IL-4, TNF-a, IL-15, IL-1, IL-32, and IL-33 have been implicated in modulating the levels of lipolysis (Fuster et al., 2011), lipogenesis (Tsao et al., 2014;Zúñiga et al., 2010), FAO (Carey et al., 2006;Stienstra et al., 2010), cholesterol accumulation (Isoda et al., 2005;Xu et al., 2017), and triglyceride storage (Kralisch et al., 2005) to either promote or inhibit the development of several metabolic diseases. Likewise, specific cytokines such as IL-6, TNF-a, IL-15, and IL-1 have been postulated to promote or inhibit cancer cachexia and prostate cancer by affecting several aspects of lipid metabolism (Batista et al., 2012;Han et al., 2018;Rohena-Rivera et al., 2017). ...
Context-dependent physiological remodeling of the extracellular matrix (ECM) is essential for development and organ homeostasis. On the other hand, consumption of high-caloric diet leverages ECM remodeling to create pathological conditions that impede the functionality of different organs, including the heart. However, the mechanistic basis of high caloric diet–induced ECM remodeling has yet to be elucidated. Employing in vivo molecular genetic analyses in Drosophila, we demonstrate that high dietary sugar triggers ROS-independent activation of JNK signaling to promote fatty acid oxidation (FAO) in the pericardial cells (nephrocytes). An elevated level of FAO, in turn, induces histone acetylation–dependent transcriptional upregulation of the cytokine Unpaired 3 (Upd3). Release of pericardial Upd3 augments fat body-specific expression of the cardiac ECM protein Pericardin, leading to progressive cardiac fibrosis. Importantly, this pathway is quite distinct from the ROS-Ask1-JNK/p38 axis that regulates Upd3 expression under normal physiological conditions. Our results unravel an unknown physiological role of FAO in cytokine-dependent ECM remodeling, bearing implications in diabetic fibrosis.
... The MAPK signalling pathway regulates adipocyte differentiation and has been shown to downregulate the expression of C/EBPα and PPAR-γ, thereby regulating adipocyte differentiation [31,32]. IL-17 is a cytokine that plays a regulatory role in the formation of adipocytes and the growth of adipose tissue in the body [33]. In the GO analysis, there were many DEGs involved in cell proliferation, including TBX2, FGF12, GLI1, LIF and MAP3K7. ...
Simple Summary
Fat deposition is essential for the productivity of livestock farming and is also of considerable importance for maintaining human health. Previous studies have provided a clue to explore the involvement of adenosine deaminase acting on RNA 1 (ADAR1) in adipogenesis. In this study, we confirmed that ADAR1 enhances the proliferation and suppresses the differentiation and apoptosis of porcine preadipocytes through over-expression and knockdown approaches. We also identify the genes and pathways that ADAR1 may affect in the regulation of preadipocyte proliferation. The findings provide novel insights that shed light on the molecular mechanisms underlying lipid accumulation.
Abstract
Recent research has identified ADAR1 as a participant in the regulation of lipid accumulation in mice. However, there are no reports on the roles of ADAR1 in proliferation, apoptosis and differentiation of porcine preadipocytes. In this study, we investigated the role of ADAR1 in differentiation, proliferation and apoptosis of porcine preadipocytes using CCK-8, EdU staining, cell cycle detection, RT-qPCR, Western blot, a triglyceride assay and Oil Red O staining. The over-expression of ADAR1 significantly promoted proliferation but inhibited the differentiation and apoptosis of porcine preadipocytes. The inhibition of ADAR1 had the opposite effect on the proliferation, differentiation and apoptosis of porcine preadipocytes with over-expressed ADAR1. Then, the regulation mechanisms of ADAR1 on preadipocyte proliferation were identified using RNA-seq, and 197 DEGs in response to ADAR1 knockdown were identified. The MAPK signaling pathway is significantly enriched, indicating its importance in mediating fat accumulation regulated by ADAR1. The study’s findings will aid in uncovering the mechanisms that regulate fat accumulation through ADAR1.
... Following on, several studies investigated other adipose tissue-resident immune cells. Those cells traditionally considered proinflammatoryincluding dendritic cells (DCs), neutrophils, natural killer cells, innate lymphoid cells (ILCs), Th1 and Th17 cells, γδ T cells, and B cellswere able to promote inflammation and IR ( Figure 2) [41,[46][47][48][49][50][51]. Conversely, immune cells that were traditionally viewed as anti-inflammatory cellssuch as eosinophils, ILC2, and regulatory B cellsinhibited obesity-induced inflammation and IR [11,52,53]. ...
Obesity is a worldwide pandemic and major risk factor for the development of metabolic syndrome (MetS) and type 2 diabetes (T2D). T2D requires lifelong medical support to limit complications and is defined by impaired glucose tolerance, insulin resistance (IR), and chronic low-level systemic inflammation initiating from adipose tissue. The current preventative strategies include a healthy diet,
controlled physical activity, and medication targeting hyperglycemia, with underexplored underlying inflammation. Studies suggest a protective role for helminth infection in the prevention of T2D. The mechanisms may involve induction of modified type 2 and regulatory immune responses that suppress inflammation and promote insulin sensitivity. In this review, the roles of helminths in counteracting MetS, and prospects for harnessing these protective mechanisms for the development of novel anti-diabetes drugs are discussed.
... Although several studies in mice indicate that Th1 cells may be driving inflammation in type 2 diabetes, recent work indicates that Th17 cells may be the most central T cell subset in human type 2 diabetes [78][79][80][81]. Indeed, mice lacking the IL-17 gene exhibit increased insulin sensitivity but decreased tolerance to glucose when compared to the control group [82]. Furthermore, the introduction of an anti-IL-17 antibody to insulin-resistant mice induced by angiotensin II resulted in enhanced insulin sensitivity and reduced glucose intolerance [83]. ...
Around 285 million people worldwide currently have type 2 diabetes and it is projected that this number will be surpassed by 2030. Therefore, it is of the utmost importance to enhance our comprehension of the disease’s development. The regulation of diet, obesity, and inflammation in type 2 diabetes is believed to play a crucial role in enhancing insulin sensitivity and reducing the risk of onset diabetes. Obesity leads to an increase in visceral adipose tissue, which is a prominent site of inflammation in type 2 diabetes. Dyslipidemia, on the other hand, plays a significant role in attracting activated immune cells such as macrophages, dendritic cells, T cells, NK cells, and B cells to visceral adipose tissue. These immune cells are a primary source of pro-inflammatory cytokines that are believed to promote insulin resistance. This review delves into the influence of elevated dietary free saturated fatty acids and examines the cellular and molecular factors associated with insulin resistance in the initiation of inflammation induced by obesity. Furthermore, it explores novel concepts related to diet-induced inflammation and its relationship with type 2 diabetes.
... However, their localization in peripheral tissues indicates physiological roles in maintaining tissue homeostasis beyond host protection (Johnson et al., 2020;Giri and Lal, 2021;Ribot et al., 2021). γδ T cells are uniquely enriched in adipose tissues (Kohlgruber et al., 2018) and have been identified as regulators of adipogenesis, thermogenesis, and sympathetic innervation (Zuniga et al., 2010;Kohlgruber et al., 2018;Hu et al., 2020). Research using diet-induced obesity models have provided evidence for a deleterious role of γδ T cells in driving obesity-induced inflammation and metabolic dysfunction (Mehta et al., 2015). ...
γδ T cells are resident in visceral adipose tissue (VAT) where they show an age-associated increase in numbers and contribute to local and systemic chronic inflammation. However, regulation of this population and mechanisms for the age-dependent accumulation are not known. In this study, we identified a progressive trend of γδ T cell accumulation in VAT over the lifespan in mice and explored physiological mechanisms contributing to accumulation. Using isochronic parabiotic pairs of wild-type (WT) and T cell receptor delta knockout (TCRδ KO) mice at young and old age, we confirmed that VAT γδ T cells are predominately a tissue-resident population which is sustained in aging. Migration of peripheral γδ T cells into VAT was observed at less than 10%, with a decreasing trend by aging, suggesting a minor contribution of recruitment to γδ T cell accumulation with aging. Since tissue-resident T cell numbers are tightly regulated by a balance between proliferation and programmed cell death, we further explored these processes. Using in vivo EdU incorporation and the proliferation marker Ki67, we found that the absolute number of proliferating γδ T cells in VAT is significantly higher in the aged compared to young and middle-aged mice, despite a decline in the proportion of proliferating to non-proliferating cells by age. Analysis of apoptosis via caspase 3/7 activation revealed that VAT γδ T cells show reduced apoptosis starting at middle age and continuing into old age. Further, induction of apoptosis using pharmacological inhibitors of Bcl2 family proteins revealed that VAT γδ T cells at middle age are uniquely protected from apoptosis via a mechanism independent of traditional anti-apoptotic Bcl2-family proteins. Collectively, these data indicate that protection from apoptosis at middle age increases survival of tissue-resident γδ T cells resulting in an increased number of proliferative cells from middle age onward, and leading to the age-associated accumulation of γδ T cells in VAT. These findings are important to better understand how adipose tissue dysfunction and related changes in the immune profile contribute to inflammaging among the elderly.
... An HFD is responsible for a decrease in Th17 cells, which are crucial for the maintenance of the mucosal barrier structure and function [146]. IL-17 cytokine production by TH17 cells inhibits the pro-adipogenic transcription factor and modulates glucose metabolism in an obesity model induced by an HFD [147]. ...
Lactoferrin (LF) is a glycoprotein that binds to iron ions (Fe²⁺) and other metallic ions, such as Mg²⁺, Zn²⁺, and Cu²⁺, and has antibacterial and immunomodulatory properties. The antibacterial properties of LF are due to its ability to sequester iron. The immunomodulatory capability of LF promotes homeostasis in the enteric environment, acting directly on the beneficial microbiota. LF can modulate antigen-presenting cell (APC) biology, including migration and cell activation. Nonetheless, some gut microbiota strains produce toxic metabolites, and APCs are responsible for initiating the process that inhibits the inflammatory response against them. Thus, eliminating harmful strains lowers the risk of inducing chronic inflammation, and consequently, metabolic disease, which can progress to type 2 diabetes mellitus (T2DM). LF and retinoic acid (RA) exhibit immunomodulatory properties such as decreasing cytokine production, thus modifying the inflammatory response. Their activities have been observed both in vitro and in vivo. The combined, simultaneous effect of these molecules has not been studied; however, the synergistic effect of LF and RA may be employed for enhancing the secretion of humoral factors, such as IgA. We speculate that the combination of LF and RA could be a potential prophylactic alternative for the treatment of metabolic dysregulations such as T2DM. The present review focuses on the importance of a healthy diet for a balanced gut and describes how probiotics and prebiotics with immunomodulatory activity as well as inductors of differentiation and cell proliferation could be acquired directly from the diet or indirectly through the oral administration of formulations aimed to maintain gut health or restore a eubiotic state in an intestinal environment that has been dysregulated by external factors such as stress and a high-fat diet.
... The source of inflammatory cytokines was initially considered to be adipocytes, whereas immune cells in adipose tissue (AT), such as αβ T, NK, macrophage cells, and innate-like γδ T cells, in the case of obesity, could also trigger inflammation and aggravate insulin resistance [21][22][23][24][25]. Blocking pro-inflammatory activity reduces the expression of cytokines (TNF, IL-6, IL-1β, IFN-γ, and IL-17) and ameliorates insulin resistance [17,26,27]. After a long-term high-fat diet, tissue residual γδ T cells are the major source of IL-17a, which regulates adipogenesis and glucose metabolism in AT [28]. These findings suggest that targeting the inflammatory signaling pathway of γδ T cells might be a potential way to reverse insulin resistance. ...
Background: Chronic inflammation caused by immune cells is the central link between obesity and insulin resistance. Targeting the inflammatory process is a highly promising method for reversing systemic insulin resistance.
Methods: Blood samples were prospectively collected from 68 patients with type 2 diabetes. C57BL/6J mice were fed either a high-fat diet (HFD) or normal chow (NC). We performed phenotypical and functional analyses of immune cells using flow cytometry. Vitamin D receptor (VDR) knockout γδ T cells were constructed using Cas9-gRNA targeted approaches to identify 1α,25(OH)2D3/VDR signaling pathway-mediated transcriptional regulation of fructose-1,6-bisphosphatase (FBP1) in γδ T cells.
Results: Serum vitamin D deficiency aggravates inflammation in circulating γδ T cells in type 2 diabetes patients. We defined a critical role for 1α,25(OH)2D3 in regulating glycolysis metabolism, protecting against inflammation, and alleviating insulin resistance. Mechanistically, 1α,25(OH)2D3-VDR promoted FBP1 expression to suppress glycolysis in γδ T cells, thereby inhibiting Akt/p38 MAPK phosphorylation and reducing inflammatory cytokine production. Notably, therapeutic administration of 1α,25(OH)2D3 restrained inflammation in γδ T cells and ameliorated systemic insulin resistance in obese mice.
Conclusions: Collectively, these findings show that 1α,25(OH)2D3 plays an important role in maintaining γδ T cell homeostasis by orchestrating metabolic programs, and is a highly promising target for preventing obesity, inflammation, and insulin resistance.
... An antiadipogenic role was revealed for IL-17. IL-17 suppresses adipocyte differentiation in vivo and in vitro, and moderates adipose tissue accumulation; therefore, it contributes to inhibiting obesity in mice [48,49]. IL-17A promotes the transdifferentiation of C2C12, mouse myoblast cells, into adipocytes via increasing the expression of PPARγ [50]. ...
Simple Summary
Fat accumulation is important for both livestock production and human health. Previous studies provide a clue to the involvement of Homeobox C8 (HOXC8) in adipogenesis. Here, we make clear that porcine HOXC8 promotes the proliferation and differentiation of preadipocytes through gain- and loss-of-function approaches. Furthermore, the genes and pathways affected by HOXC8 during the regulation of preadipocyte proliferation and differentiation are identified. The results provide new data for the clarification of mechanisms underlying fat accumulation, which is the basis for controlling fat contents in mammals.
Abstract
Transcription factor Homeobox C8 (HOXC8) is identified as a white adipose gene as revealed by expression profile analysis in fat tissues. However, the specific role of HOXC8 in fat accumulation remains to be identified. This study was designed to reveal the effects of HOXC8 on preadipocyte proliferation and differentiation. We first make clear that the expression of HOXC8 is associated with fat contents in muscles, highlighting a role of HOXC8 in fat accumulation. Next, it is demonstrated that HOXC8 promotes the proliferation and differentiation of preadipocytes through gain- and loss-of-function assays in primary cultured porcine preadipocytes. Then, mechanisms underlying the regulation of HOXC8 on preadipocyte proliferation and differentiation are identified with RNA sequencing, and a number of differentially expressed genes (DEGs) in response to HOXC8 knockdown are identified. The top GO (Gene Ontology) terms enriched by DEGs involved in proliferation and differentiation, respectively, are identical. IL-17 signaling pathway is the common one significantly enriched by DEGs involved in preadipocyte proliferation and differentiation, respectively, indicating its importance in mediating fat accumulation regulated by HOXC8. Additionally, we find that the inhibition of proliferation is one of the main processes during preadipocyte differentiation. The results will contribue to further revealing the mechanisms underlying fat accumulation regulated by HOXC8.
... For instance, adipocytes respond to Il-17 by inhibiting adipogenesis and moderating lipid and glucose uptake. 53 In the CNS, particularly in the hypothalamus, Il-17 receptors are expressed on both POMC and AgRP neurons of the arcuate nucleus. Food intake increases Il-17 production in the gut followed by increases in circulating Il-17 levels, and its action in the arcuate nucleus increases POMC expression and feeling of satiety. ...
The choroid plexus (CP) is a source of trophic factors for the developing and mature brain. Insulin is produced in epithelial cells of the CP (EChPs), and its secretion is stimulated by Htr2c-mediated signaling. We modulated insulin expression in EChPs with intracerebroventricular injections of AAV5. Insulin overexpression in CP decelerates food intake, whereas its knockdown has the opposite effect. Insulin overexpression also results in reduced anxious behavior. Transcriptomic changes in the hypothalamus, especially in synapse-related processes, are also seen in mice overexpressing insulin in CP. Last, activation of Gq signaling in CP leads to acute Akt phosphorylation in neurons of the arcuate nucleus, indicating a direct action of CP-derived insulin on the hypothalamus. Taken together, our findings signify that CP is a relevant source of insulin in the central nervous system and that CP-derived insulin should be taken into consideration in future work pertaining to insulin actions in the brain.
... In the top 20 KEGG results, IL-17 and TNF which are closely related to adipogenesis, were significantly enriched. Here, IL-17 is associated with adipogenesis and adipocyte metabolism, where it inhibits the expression of genes related to adipogenesis (PPARG, CEBPA, adipsin, etc.) and lipid metabolism (FABP4, perilipin, ATGL, etc) [47,48]. Similarly, TNF-α inhibits lipogenesis by inhibiting the expression of the adipokines PPARG and CEBPA [49]. ...
Intramuscular fat content is closely related to the quality of beef, where the forkhead box protein O1 (FOXO1) is involved in adipocyte differentiation and lipid metabolism, but the specific mechanism of its involvement is still unclear. In this study, interfering with FOXO1 promoted the G1/S transformation of bovine adipocytes by enhancing the expression of proliferation marker genes PCNA, CDK1, CDK2, CCNA2, CCNB1, and CCNE2, thereby positively regulating the proliferation of bovine adipocytes. Additionally, interfering with FOXO1 negatively regulated the expression of adipogenic differentiation marker genes PPARG and CEBPA, as well as lipid anabolism marker genes ACC, FASN, SCD1, SREBP1, FABP4, ACSL1, LPL, and DGAT1, thus reducing triglyceride (TG) content and inhibiting the generation of lipid droplets in bovine adipocytes. A combination of transcriptomic and metabolomics analyses revealed that FOXO1 could regulate the lipogenesis of cattle by influencing the AMPK and PI3K/AKT pathways. Importantly, chromatin immunoprecipitation (ChIP) and site-directed mutagenesis revealed that FOXO1 could regulate bovine lipogenesis by binding to the promoter regions of the CD36 and STEAP4 genes and affecting their transcriptional activities. These results provide a foundation for studying the role and molecular mechanism of FOXO1 in the bovine adipogenesis.
... T H 17 cells are known to expand in the liver of obese humans and mice [145], and multiple rodent models of NAFLD show increased IL-17A signaling through the IL-17A receptor (IL-17RA) [146,147]. The development of NAFLD leads to increased infiltration of nonconventional CXCR3 + T H 17 cells, which can co-express IFNγ. ...
The liver performs a multitude of bodily functions, whilst retaining the ability to regenerate damaged tissue. In this review, we discuss sex steroid biology, regulation of mammalian liver physiology and the development of new model systems to improve our understanding of liver biology in health and disease. A major risk factor for the development of liver disease is hepatic fibrosis. Key drivers of this process are metabolic dysfunction and pathologic activation of the immune system. Although non-alcoholic fatty liver disease (NAFLD) is largely regarded as benign, it does progress to non-alcoholic steatohepatitis in a subset of patients, increasing their risk of developing cirrhosis and hepatocellular carcinoma. NAFLD susceptibility varies across the population, with obesity and insulin resistance playing a strong role in the disease development. Additionally, sex and age have been identified as important risk factors. In addition to the regulation of liver biochemistry, sex hormones also regulate the immune system, with sexual dimorphism described for both innate and adaptive immune responses. Therefore, sex differences in liver metabolism, immunity and their interplay are important factors to consider when designing, studying and developing therapeutic strategies to treat human liver disease. The purpose of this review is to provide the reader with a general overview of sex steroid biology and their regulation of mammalian liver physiology.
... The physiological and pathological effects of IL-17 family members are summarized in Table 1. [51] Induces the production of bradykinin in the epithelial cells of the tubules of the kidneys in acute injury [52] Participation in the regulation of glucose and lipid metabolism [53] Development of inflammatory arthritis [35] Possible link between depression and increased levels of IL-17 [54] Key role in the pathogenesis of spondyloarthritis [55] Injurious role in ischemic stroke [56] Involvement in the progression of neurocognitive disorders [57] The key link in the pathogenesis of psoriasis [58] The role in the development of liver fibrosis is being studied [59] IL-17B ...
Spondyloarthritis (SpA) encompasses a group of chronic inflammatory rheumatic diseases with a predilection for the spinal and sacroiliac joints, which include axial spondyloarthritis, psoriatic arthritis, reactive arthritis, arthritis associated with chronic inflammatory bowel disease, and undifferentiated spondyloarthritis. The prevalence of SpA in the population varies from 0.5 to 2%, most commonly affecting young people. Spondyloarthritis pathogenesis is related to the hyperproduction of proinflammatory cytokines (TNFα, IL-17А, IL-23, etc.). IL-17A plays a key role in the pathogenesis of spondyloarthritis (inflammation maintenance, syndesmophites formation and radiographic progression, enthesites and anterior uveitis development, etc.). Targeted anti-IL17 therapies have established themselves as the most efficient therapies in SpA treatment. The present review summarizes literature data on the role of the IL-17 family in the pathogenesis of SpA and analyzes existing therapeutic strategies for IL-17 suppression with monoclonal antibodies and Janus kinase inhibitors. We also consider alternative targeted strategies, such as the use of other small-molecule inhibitors, therapeutic nucleic acids, or affibodies. We discuss advantages and pitfalls of these approaches and the future prospects of each method.
... Studies have shown that although IL-17 is a pro-inflammatory factor, The IL-17 pathway may also function in a negative-feedback fashion to inhibit the production of excess adipose tissue 46 . The inflammatory factor IL-17 can inhibit adipose formation, regulate adipose tissue accumulation, and regulate glucose metabolism in mice 47 , and IL-17 antibody can reduce obesity by reducing the accumulation of macrophages in adipose tissue and reducing inflammation 48 . Down-regulated inflammatory factors include IL-34, which has been shown to enhance fat accumulation and inhibit the stimulating effect of insulin on glucose transport, which is related to insulin resistance 49 . ...
Objective:
Obesity and overweight are risk factors for chronic disease worldwide. The purpose of this study was to compare the transcriptome of exercise-induced fat mobilization in obese people, and to explore the effect of different exercise intensity on the correlation of immune microenvironment remodeling and lipolysis in adipose tissue.
Materials and methods:
Microarray datasets of adipose tissue before and after exercise were downloaded from the Gene Expression Omnibus. Then, we used gene-enrichment analysis and PPI-network construction to elucidate the function and enrichment pathways of the differentially expressed genes (DEGs) and to identify the central genes. A network of protein-protein interactions was obtained using STRING and visualized with Cytoscape.
Results:
A total of 929 DEGs were identified between 40 pre-exercise (BX) samples and 65 post-exercise (AX) samples from GSE58559, GSE116801, and GSE43471. Among these DEGs, adipose tissue-expressed genes were duly recognized. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses indicated that DEGs were mostly enriched in lipid metabolism. Studies have found that mitogen-activated protein kinase (MAPK) signaling pathway and forkhead box O (FOXO) signaling pathway are up-regulated, while Ribosome, coronavirus disease (COVID-19) and IGF-1 gene are down-regulated. Although we found the up-regulated genes that noted IL-1 among others, and the down-regulated gene was IL-34. The increase of inflammatory factors leads to changes in cellular immune microenvironment, and high-intensity exercise leads to increased expression of inflammatory factors in adipose tissue, leading to inflammatory responses.
Conclusions:
Exercise at different intensities leads to the degradation of adipose and is accompanied by changes in the immune microenvironment within adipose tissue. High intensity exercise can cause the imbalance of immune microenvironment of adipose tissue while causing fat degradation. Therefore, moderate intensity and below exercise is the best way for the general population to reduce fat and weight.
Adipose tissue (AT) is the primary energy reservoir organ, and thereby plays a critical role in energy homeostasis and regulation of metabolism. AT expands in response to chronic overnutrition or aging and becomes a major source of inflammation that has marked influence on systemic metabolism. The chronic, sterile inflammation that occurs in the AT during the development of obesity or in aging contributes to onset of devastating diseases such as insulin resistance, diabetes, and cardiovascular pathologies. Numerous studies have shown that inflammation in the visceral AT of humans and animals is a critical trigger for the development of metabolic syndrome. This work underscores the well‐supported conclusion that the inflammatory immune response and metabolic pathways in the AT are tightly interwoven by multiple layers of relatively conserved mechanisms. During the development of diet‐induced obesity or age‐associated adiposity, cells of the innate and the adaptive immune systems infiltrate and proliferate in the AT. Macrophages, which dominate AT‐associated immune cells in mouse models of obesity, but are less dominant in obese people, have been studied extensively. However, cells of the adaptive immune system, including T cells and B cells, contribute significantly to AT inflammation, perhaps more in humans than in mice. Lymphocytes regulate recruitment of innate immune cells into AT, and produce cytokines that influence the helpful‐to‐harmful inflammatory balance that, in turn, regulates organismal metabolism. This review describes inflammation, or more precisely, metabolic inflammation (metaflammation) with an eye toward the AT and the roles lymphocytes play in regulation of systemic metabolism during obesity and aging. © 2017 American Physiological Society. Compr Physiol 7:1307‐1337, 2017.
The different types of adipose tissues fulfill a wide range of biological functions—from energy storage to hormone secretion and thermogenesis—many of which show pronounced variations over the course of the day. Such 24‐h rhythms in physiology and behavior are coordinated by endogenous circadian clocks found in all tissues and cells, including adipocytes. At the molecular level, these clocks are based on interlocked transcriptional‐translational feedback loops comprised of a set of clock genes/proteins. Tissue‐specific clock‐controlled transcriptional programs translate time‐of‐day information into physiologically relevant signals. In adipose tissues, clock gene control has been documented for adipocyte proliferation and differentiation, lipid metabolism as well as endocrine function and other adipose oscillations are under control of systemic signals tied to endocrine, neuronal, or behavioral rhythms. Circadian rhythm disruption, for example, by night shift work or through genetic alterations, is associated with changes in adipocyte metabolism and hormone secretion. At the same time, adipose metabolic state feeds back to central and peripheral clocks, adjusting behavioral and physiological rhythms. In this overview article, we summarize our current knowledge about the crosstalk between circadian clocks and energy metabolism with a focus on adipose physiology. © 2017 American Physiological Society. Compr Physiol 7:383‐427, 2017.
Hypertension is associated with vascular injury characterized by vascular dysfunction, remodeling, and stiffening, which contributes to end-organ damage leading to cardiovascular events and potentially death. Innate (macrophages and dendritic cells), innate-like (γδ T cells) and adaptive immune cells (T and B cells) play a role in hypertension and vascular injury. Perivascular adipose tissue that is the fourth layer of the blood vessel wall is an important homeostatic regulator of vascular tone. Increased infiltration of immune cells in perivascular adipose tissue in hypertension results in generation of oxidative stress and production of cytokines that may cause vascular injury. This review presents an overview of the role of the different immune cells that infiltrate the perivascular adipose tissue and are involved in the pathophysiology of hypertension.
The aim of this study was to determine the association of serum soluble IL-2 receptor α (sIL-2RA) with T2DM-related characteristics and complications.
Serum sIL-2RA levels were determined in 156 T2DM patients, and the association with T2DM-related characteristics and complications was evaluated.
Serum sIL-2RA levels were significantly increased in T2DM patients with diabetic kidney disease (DKD) (median, IQR, 1434.9, 958.1–1896.0, pg/ml), in comparison with those without DKD (median, IQR, 851.2, 660.2-1089.9, pg/ml)(P < 0.001). The ROC analysis revealed good performance of sIL-2RA for identifying DKD, with the areas under the curve of 0.789 (95%CI of 0.711–0.867, P < 0.001). The correlation analyses showed significantly positive correlations of serum sIL-2RA with urea (r = 0.458, P < 0.001), creatinine (r = 0.508, P < 0.001) and uACR (r = 0.469, P < 0.001), and negative correlation with eGFR (r=-0.561, P < 0.001). The multivariate analyses showed that serum sIL-2RA was independently associated with the increased risks of DKD (OR, 95%CI, 6.539, 1.401–30.529, P = 0.017) and DR (OR, 95%CI, 3.606, 1.073–12.114, P = 0.038). Additionally, serum sIL-2RA was significantly associated with inflammatory indicators in DKD patients, and with metablic indicators in non-DKD patients (all P < 0.05).
Serum sIL-2RA may be closely associated with inflammation, glucose and lipid metabolisms, DKD and DR risks in T2DM. Furthermore, it may be a potential biomarker for T2DM-related micro-vascular complications.
Hyperglycemia, a hallmark of diabetes and various metabolic disorders, has profound implications for immune cell function. The relationship between elevated blood glucose levels and immune cell function is a topic of significant medical interest. In this review, we aim to comprehensively review effects of hyperglycemia on various immune cell types and its clinical implications, particularly T cells, macrophages, natural killer cells, and neutrophils. It aims to consolidate current knowledge on the subject, with a focus on both type 1 and type 2 diabetes, as well as other pathological states where hyperglycemia is a concern. A comprehensive examination of recent studies and clinical data was conducted to assess effects of hyperglycemia on immune cell function. Evidence indicates that hyperglycemia can significantly alter immune cell function, with different diabetic conditions showing varied responses. Roles of key metabolic hormones in regulating T cell function highlight potential therapeutic targets for restoring immune balance. In addition, reprogramming of innate immune cells such as macrophages and natural killer cells under hyperglycemic conditions suggests a complex metabolic–immunological interface. This review will contribute to a better understanding of the link between diabetes, other metabolic disorders, and immune function. By examining recent research and clinical findings, this review will enhance our comprehension of the mechanisms at play and guide future medical strategies for managing and treating conditions associated with hyperglycemia.
Numerous genes including sarcospan (SSPN) have been designated as obesity-susceptibility genes by human genome-wide association studies. Variants in the SSPN locus have been linked with sex-dependent obesity-associated traits, however this association has not been investigated in vivo. To delineate the role SSPN plays in regulating metabolism with potential to impact cardiac function we subjected young and aged global SSPN-deficient (SSPN -/- ) male and female mice to obesogenic conditions (60% fat diet). We hypothesized that loss of SSPN combined with metabolic stress would increase susceptibility of mice to cardiometabolic disease. Baseline and endpoint assessments of several anthropometric parameters were performed including weight, glucose tolerance, and fat distribution of mice fed control (CD) and high fat diet (HFD). Doppler echocardiography was used to monitor cardiac function. White adipose and cardiac tissues were assessed for inflammation utilizing histological, gene expression and cytokine analysis. Overall, SSPN deficiency protected both sexes and ages from diet-induced obesity with a greater effect in females. While SSPN -/- HFD mice gained less weight than WT cohorts, SSPN -/- CD groups increased weight. Furthermore, aged SSPN -/- mice developed glucose intolerance regardless of diet. Echocardiography showed preserved systolic function for all groups, however aged SSPN -/- males (CD) exhibited significant increases in LVmass and (HFD) signs of diastolic dysfunction. Cytokine analysis revealed significantly increased IL-1α and IL-17A in white adipose tissue from young SSPN -/- male mice that may be protective from diet-induced obesity. Overall, these studies suggest several sex-dependent mechanisms influence the role SSPN plays in metabolic responses that become evident with age.
Metabolic dysfunction-associated steatotic liver disease (MASLD) comprises a spectrum of liver diseases that span simple steatosis, metabolic dysfunction-associated steatohepatitis (MASH) and fibrosis and may progress to cirrhosis and cancer. The pathogenesis of MASLD is multifactorial and is driven by environmental, genetic, metabolic and immune factors. This review will focus on the role of the type 3 cytokines IL-17 and IL-22 in MASLD pathogenesis and progression. IL-17 and IL-22 are produced by similar adaptive and innate immune cells such as Th17 and innate lymphoid cells, respectively. IL-17-related signaling is upregulated during MASLD resulting in increased chemokines and proinflammatory cytokines in the liver microenvironment, enhanced recruitment of myeloid cells and T cells leading to exacerbation of inflammation and liver disease progression. IL-17 may also act directly by activating hepatic stellate cells resulting in increased fibrosis. In contrast, IL-22 is a pleiotropic cytokine with a dominantly protective signature in MASLD and is currently being tested as a therapeutic strategy. IL-22 also exhibits beneficial metabolic effects and abrogates MASH-related inflammation and fibrosis development via inducing the production of anti-oxidants and anti-apoptotic factors. A sex-dependent effect has been attributed to both cytokines, most importantly to IL-22 in MASLD or related conditions. Altogether, IL-17 and IL-22 are key effectors in MASLD pathogenesis and progression. We will review the role of these two cytokines and cells that produce them in the development of MASLD, their interaction with host factors driving MASLD including sexual dimorphism, and their potential therapeutic benefits.
Acute ischemic stroke (AIS) remains a major cause of mortality and long-term disability worldwide, driven by complex and multifaceted etiological factors. Metabolic dysregulation, gastrointestinal microbiome alterations, and systemic inflammation are emerging as significant contributors to AIS pathogenesis. This review addresses the critical need to understand how these factors interact to influence AIS risk and outcomes. We aim to elucidate the roles of dysregulated adipokines in obesity, the impact of gut microbiota disruptions, and the neuroinflammatory cascade initiated by lipopolysaccharides (LPS) in AIS. Dysregulated adipokines in obesity exacerbate inflammatory responses, increasing AIS risk and severity. Disruptions in the gut microbiota and subsequent LPS-induced neuroinflammation further link systemic inflammation to AIS. Advances in neuroimaging and biomarker development have improved diagnostic precision. Here, we highlight the need for a multifaceted approach to AIS management, integrating metabolic, microbiota, and inflammatory insights. Potential therapeutic strategies targeting these pathways could significantly improve AIS prevention and treatment. Future research should focus on further elucidating these pathways and developing targeted interventions to mitigate the impacts of metabolic dysregulation, microbiome imbalances, and inflammation on AIS.
Adipose tissue in the obese state can lead to low‐grade chronic inflammation while inducing or exacerbating obesity‐related metabolic diseases and impairing overall health.T cells, which are essential immune cells similar to macrophages, are widely distributed in adipose tissue and perform their immunomodulatory function; they also cross‐talk with other cells in the vascular stromal fraction. Based on a large number of studies, it has been found that N6 methyl adenine (m6A) is one of the most representative of epigenetic modifications, which affects the crosstalk between T cells, as well as other immune cells, in several ways and plays an important role in the development of adipose tissue inflammation and related metabolic diseases. In this review, we first provide an overview of the widespread presence of T cells in adipose tissue and summarize the key role of T cells in adipose tissue inflammation. Next, we explored the effects of m6A modifications on T cells in adipose tissue from the perspective of adipose tissue inflammation. Finally, we discuss the impact of m6a‐regulated crosstalk between T cells and immune cells on the prospects for improving adipose tissue inflammation research, providing additional new ideas for the treatment of obesity.
White adipose tissue is not only a highly heterogeneous organ containing various cells, such as adipocytes, adipose stem and progenitor cells, and immune cells, but also an endocrine organ that is highly important for regulating metabolic and immune homeostasis. In individuals with obesity, dynamic cellular changes in adipose tissue result in phenotypic switching and adipose tissue dysfunction, including pathological expansion, WAT fibrosis, immune cell infiltration, endoplasmic reticulum stress, and ectopic lipid accumulation, ultimately leading to chronic low‐grade inflammation and insulin resistance. Recently, many distinct subpopulations of adipose tissue have been identified, providing new insights into the potential mechanisms of adipose dysfunction in individuals with obesity. Therefore, targeting white adipose tissue as a therapeutic agent for treating obesity and obesity‐related metabolic diseases is of great scientific interest. Here, we provide an overview of white adipose tissue remodeling in individuals with obesity including cellular changes and discuss the underlying regulatory mechanisms of white adipose tissue metabolic dysfunction. Currently, various studies have uncovered promising targets and strategies for obesity treatment. We also outline the potential therapeutic signaling pathways of targeting adipose tissue and summarize existing therapeutic strategies for antiobesity treatment including pharmacological approaches, lifestyle interventions, and novel therapies.
At present, diabetes mellitus (DM) has been one of the most endangering healthy diseases. Current therapies contain controlling high blood sugar, reducing risk factors like obesity, hypertension, and so on; however, DM patients inevitably and eventually progress into different types of diabetes complications, resulting in poor quality of life. Unfortunately, the clear etiology and pathogenesis of diabetes complications have not been elucidated owing to intricate whole‐body systems. The immune system was responsible to regulate homeostasis by triggering or resolving inflammatory response, indicating it may be necessary to diabetes complications. In fact, previous studies have been shown inflammation plays multifunctional roles in the pathogenesis of diabetes complications and is attracting attention to be the meaningful therapeutic strategy. To this end, this review systematically concluded the current studies over the relationships of susceptible diabetes complications (e.g., diabetic cardiomyopathy, diabetic retinopathy, diabetic peripheral neuropathy, and diabetic nephropathy) and inflammation, ranging from immune cell response, cytokines interaction to pathomechanism of organ injury. Besides, we also summarized various therapeutic strategies to improve diabetes complications by target inflammation from special remedies to conventional lifestyle changes. This review will offer a panoramic insight into the mechanisms of diabetes complications from an inflammatory perspective and also discuss contemporary clinical interventions.
Immune cell–derived IL-17A is one of the key pathogenic cytokines in psoriasis, an immunometabolic disorder. Although IL-17A is an established regulator of cutaneous immune cell biology, its functional and metabolic effects on nonimmune cells of the skin, particularly keratinocytes, have not been comprehensively explored. Using multiomics profiling and systems biology–based approaches, we systematically uncover significant roles for IL-17A in the metabolic reprogramming of human primary keratinocytes (HPKs). High-throughput liquid chromatography–tandem mass spectrometry and nuclear magnetic resonance spectroscopy revealed IL-17A–dependent regulation of multiple HPK proteins and metabolites of carbohydrate and lipid metabolism. Systems-level MitoCore modeling using flux-balance analysis identified IL-17A–mediated increases in HPK glycolysis, glutaminolysis, and lipid uptake, which were validated using biochemical cell-based assays and stable isotope-resolved metabolomics. IL-17A treatment triggered downstream mitochondrial reactive oxygen species and HIF1α expression and resultant HPK proliferation, consistent with the observed elevation of these downstream effectors in the epidermis of patients with psoriasis. Pharmacological inhibition of HIF1α or reactive oxygen species reversed IL-17A–mediated glycolysis, glutaminolysis, lipid uptake, and HPK hyperproliferation. These results identify keratinocytes as important target cells of IL-17A and reveal its involvement in multiple downstream metabolic reprogramming pathways in human skin.
In the skin, Trypanosoma brucei colonises the subcutaneous white adipose tissue, and is proposed to be competent for forward transmission. The interaction between parasites, adipose tissue, and the local immune system is likely to drive the adipose tissue wasting and weight loss observed in cattle and humans infected with T. brucei. However, mechanistically, events leading to subcutaneous white adipose tissue wasting are not fully understood. Here, using several complementary approaches, including mass cytometry by time of flight, bulk and single cell transcriptomics, and in vivo genetic models, we show that T. brucei infection drives local expansion of several IL-17A-producing cells in the murine WAT, including TH17 and Vγ6⁺ cells. We also show that global IL-17 deficiency, or deletion of the adipocyte IL-17 receptor protect from infection-induced WAT wasting and weight loss. Unexpectedly, we find that abrogation of adipocyte IL-17 signalling results in a significant accumulation of Dpp4⁺Pi16⁺ interstitial preadipocytes and increased extravascular parasites in the WAT, highlighting a critical role for IL-17 signalling in controlling preadipocyte fate, subcutaneous WAT dynamics, and local parasite burden. Taken together, our study highlights the central role of adipocyte IL-17 signalling in controlling WAT responses to infection, suggesting that adipocytes are critical coordinators of tissue dynamics and immune responses to T. brucei infection.
Interleukin‐17 s (IL‐17s) are well‐known proinflammatory cytokines, and their antagonists perform excellently in the treatment of inflammatory skin diseases such as psoriasis. However, their physiological functions have not been given sufficient attention by clinicians. IL‐17s can protect the host from extracellular pathogens, maintain epithelial integrity, regulate cognitive processes and modulate adipocyte activity through distinct mechanisms. Here, we present a systematic review concerning the physiological functions of IL‐17s. Our goal is not to negate the therapeutic effect of IL‐17 antagonists, but to ensure their safe use and reasonably explain the possible adverse events that may occur in their application.
The effectiveness and safety of biological agents for treating psoriasis have been confirmed; however, their effects on glucose metabolism biomarkers in psoriasis patients remain unclear. A systematic review and meta‐analysis were performed according to PRISMA guidelines. The final analysis enrolled 12 studies, including eight randomized controlled trial (RCT) ( n = 5628 patients) and four observational cohort studies (OBSs) ( n = 393 patients). The meta‐analysis comprising nine studies (six RCTs and three OBSs) revealed a slight reduction in the levels of HOMA‐IR associated with the use of biological therapies in OBS (biological therapies vs. traditional therapies: WMD = −0.2, CI = −0.10 to 0.50, p = 0.02). Although a considerable number of studies were analysed, our review did not show a significant alteration in HOMA‐IR levels among patients treated with biological therapies such as IL‐17 inhibitors and IL‐12/23 inhibitors at weeks 12–16 in RCTs. We also did not observe remarkable alterations in the fasting plasma glucose levels of patients in both OBS and RCT. Additional RCT on a larger scale and duration is required to provide more conclusive evidence regarding the effect of biological agents on glycogen metabolism in psoriasis.
With the increase of population aging, the prevalence of type 2 diabetes (T2D) is also rising. Aging affects the tissues and organs of the whole body, which is the result of various physiological and pathological processes. Adipose tissue has a high degree of plasticity and changes with aging. Aging changes the distribution of adipose tissue, affects adipogenesis, browning characteristics, inflammatory status and adipokine secretion, and increases lipotoxicity. These age-dependent changes in adipose tissue are an important cause of insulin resistance and T2D. Understanding adipose tissue changes can help promote healthy aging process. This review summarizes changes in adipose tissue ascribable to aging, with a focus on the role of aging adipose tissue in insulin resistance and T2D.
Psoriatic arthritis is an inflammatory arthritis that significantly impairs patient quality of life and affects multiple domains of life. Lifestyle modification has the potential to improve disease activity and quality of life. We review the cellular pathophysiology of psoriatic arthritis to better understand why lifestyle interventions can make a positive impact on disease, and we discuss the interventions that can be made to treat psoriatic arthritis, including weight loss and dietary changes, exercise, improvements in sleep, alcohol moderation, smoking cessation, and psychologic interventions.
Background
Multiple sclerosis (MS) is a neurodegenerative disorder. Individuals with MS frequently present symptoms such as functional disability, obesity, and anxiety and depression. Axonal demyelination can be observed and implies alterations in mitochondrial activity and increased inflammation associated with disruptions in glutamate neurotransmitter activity. In this context, the ketogenic diet (KD), which promotes the production of ketone bodies in the blood [mainly β-hydroxybutyrate (βHB)], is a non-pharmacological therapeutic alternative that has shown promising results in peripheral obesity reduction and central inflammation reduction. However, the association of this type of diet with emotional symptoms through the modulation of glutamate activity in MS individuals remains unknown.
Aim
To provide an update on the topic and discuss the potential impact of KD on anxiety and depression through the modulation of glutamate activity in subjects with MS.
Discussion
The main findings suggest that the KD, as a source of ketone bodies in the blood, improves glutamate activity by reducing obesity, which is associated with insulin resistance and dyslipidemia, promoting central inflammation (particularly through an increase in interleukins IL-1β, IL-6, and IL-17). This improvement would imply a decrease in extrasynaptic glutamate activity, which has been linked to functional disability and the presence of emotional disorders such as anxiety and depression.
It is well established that patients with altered metabolism manifesting as obesity, metabolic syndrome and chronic inflammation have an increased incidence of cancer; indicating a crucial relationship between host metabolic system and cancer growth. However, the impact of the systemic metabolic system in the host on the local onco-sphere has not been deeply studied especially on how the host dysregulated metabolism could affect the drug absorption and excertion to have significant effect on tumor has not been studied in detail. Interestingly, more research is now supporting the idea that metabolic states and disorders linked to obesity affect not only the number of people who get cancer but also how well they respond to treatments like radiation and chemotherapy. Therefore, in this chapter, we discuss on the host metabolic diseases and how these changes therapeutic efficacy of cancer-related drugs, and the underlying mechanism which might be responsible to this phenomenon. This chapter details the importance of host metabolic changes in cancer progression.
In mammals, interleukin (IL)-17 cytokines are produced by innate and adaptive lymphocytes. However, the IL-17 family has widespread expression throughout evolution, dating as far back as cnidaria, molluscs and worms, which predate lymphocytes. The evolutionary conservation of IL-17 suggests that it is involved in innate defence strategies, but also that this cytokine family has a fundamental role beyond typical host defence. Throughout evolution, IL-17 seems to have a major function in homeostatic maintenance at barrier sites. Most recently, a pivotal role has been identified for IL-17 in regulating cellular metabolism, neuroimmunology and tissue physiology, particularly in adipose tissue. Here we review the emerging role of IL-17 signalling in regulating metabolic processes, which may shine a light on the evolutionary role of IL-17 beyond typical immune responses. We propose that IL-17 helps to coordinate the cross-talk among the nervous, endocrine and immune systems for whole-body energy homeostasis as a key player in neuroimmunometabolism.
This study conducted a high-throughput sequencing analysis of the T- and B- repertoires in the newly diagnosed GDM patients and evaluated the association between abnormal adaptive immunity and GDM. The unique TCR CDR3 clonotypes were mildly decreased in GDM patients, and the similarity of TCR V-J distributions was higher in the GDM group. Moreover, the usages of the V gene and V-J pair and the frequency distributions of some CDR3 amino acids (AAs) both in BCR and TCR were significantly different between groups. Moreover, the cytokines including IL-4, IL-6, IFN-γ and IL-17A were synchronously elevated in the GDM cases. Our findings provide a comprehensive view of BCR and TCR repertoires at newly diagnosed GDM patients, revealing the mild reduction in unique TCRB CDR3 sequences and slight alteration of the V gene, V-J combination and CDR3 (AA) usages of BCR and TCR. This work provides deep insight into the mechanism of maternal adaptive immunity in GDM and provides novel diagnostic biomarkers and potential immunotherapy targets for GDM.
T cells with variable region Vδ1 γδ T cell receptors (TCRs) are distributed throughout the human intestinal epithelium and may function as sentinels that
respond to self antigens. The expression of a major histocompatibility complex (MHC) class I–related molecule, MICA, matches
this localization. MICA and the closely related MICB were recognized by intestinal epithelial T cells expressing diverse Vδ1 γδ TCRs. These interactions involved the α1α2 domains of MICA and MICB but were independent of antigen processing. With
intestinal epithelial cell lines, the expression and recognition of MICA and MICB could be stress-induced. Thus, these molecules
may broadly regulate protective responses by the Vδ1 γδ T cells in the epithelium of the intestinal tract.
Adipocyte differentiation is an important component of obesity and other metabolic diseases. This process is strongly inhibited
by many mitogens and oncogenes. Several growth factors that inhibit fat cell differentiation caused mitogen-activated protein
(MAP) kinase-mediated phosphorylation of the dominant adipogenic transcription factor peroxisome proliferator-activated receptor
γ (PPARγ) and reduction of its transcriptional activity. Expression of PPARγ with a nonphosphorylatable mutation at this site
(serine-112) yielded cells with increased sensitivity to ligand-induced adipogenesis and resistance to inhibition of differentiation
by mitogens. These results indicate that covalent modification of PPARγ by serum and growth factors is a major regulator of
the balance between cell growth and differentiation in the adipose cell lineage.
Inflammation is increasingly regarded as a key process underlying metabolic diseases in obese individuals. In particular, obese adipose tissue shows features characteristic of active local inflammation. At present, however, little is known about the sequence of events that comprises the inflammatory cascade or the mechanism by which inflammation develops. We found that large numbers of CD8(+) effector T cells infiltrated obese epididymal adipose tissue in mice fed a high-fat diet, whereas the numbers of CD4(+) helper and regulatory T cells were diminished. The infiltration by CD8(+) T cells preceded the accumulation of macrophages, and immunological and genetic depletion of CD8(+) T cells lowered macrophage infiltration and adipose tissue inflammation and ameliorated systemic insulin resistance. Conversely, adoptive transfer of CD8(+) T cells to CD8-deficient mice aggravated adipose inflammation. Coculture and other in vitro experiments revealed a vicious cycle of interactions between CD8(+) T cells, macrophages and adipose tissue. Our findings suggest that obese adipose tissue activates CD8(+) T cells, which, in turn, promote the recruitment and activation of macrophages in this tissue. These results support the notion that CD8(+) T cells have an essential role in the initiation and propagation of adipose inflammation.
Obesity and its associated metabolic syndromes represent a growing global challenge, yet mechanistic understanding of this pathology and current therapeutics are unsatisfactory. We discovered that CD4(+) T lymphocytes, resident in visceral adipose tissue (VAT), control insulin resistance in mice with diet-induced obesity (DIO). Analyses of human tissue suggest that a similar process may also occur in humans. DIO VAT-associated T cells show severely biased T cell receptor V(alpha) repertoires, suggesting antigen-specific expansion. CD4(+) T lymphocyte control of glucose homeostasis is compromised in DIO progression, when VAT accumulates pathogenic interferon-gamma (IFN-gamma)-secreting T helper type 1 (T(H)1) cells, overwhelming static numbers of T(H)2 (CD4(+)GATA-binding protein-3 (GATA-3)(+)) and regulatory forkhead box P3 (Foxp3)(+) T cells. CD4(+) (but not CD8(+)) T cell transfer into lymphocyte-free Rag1-null DIO mice reversed weight gain and insulin resistance, predominantly through T(H)2 cells. In obese WT and ob/ob (leptin-deficient) mice, brief treatment with CD3-specific antibody or its F(ab')(2) fragment, reduces the predominance of T(H)1 cells over Foxp3(+) cells, reversing insulin resistance for months, despite continuation of a high-fat diet. Our data suggest that the progression of obesity-associated metabolic abnormalities is under the pathophysiological control of CD4(+) T cells. The eventual failure of this control, with expanding adiposity and pathogenic VAT T cells, can successfully be reversed by immunotherapy.
Obesity is accompanied by chronic, low-grade inflammation of adipose tissue, which promotes insulin resistance and type-2 diabetes. These findings raise the question of how fat inflammation can escape the powerful armamentarium of cells and molecules normally responsible for guarding against a runaway immune response. CD4(+) Foxp3(+) T regulatory (T(reg)) cells with a unique phenotype were highly enriched in the abdominal fat of normal mice, but their numbers were strikingly and specifically reduced at this site in insulin-resistant models of obesity. Loss-of-function and gain-of-function experiments revealed that these T(reg) cells influenced the inflammatory state of adipose tissue and, thus, insulin resistance. Cytokines differentially synthesized by fat-resident regulatory and conventional T cells directly affected the synthesis of inflammatory mediators and glucose uptake by cultured adipocytes. These observations suggest that harnessing the anti-inflammatory properties of T(reg) cells to inhibit elements of the metabolic syndrome may have therapeutic potential.
To compare the concentrations of cytokines belonging to Th17 axis (interleukin (IL)-17 and IL-23) and Th1 axis (IL-12 and interferon (IFN)-gamma) in obese and lean women, and to investigate their relationships with the proinflammatory adipokine leptin, proinflammatory cytokine macrophage migration inhibitory factor (MIF) and anthropometric and metabolic parameters of obesity.
Cross-sectional study.
Twenty-six obese women (age 20-52 years, body mass index (BMI): 30-48 kg/m(2)) and 20 healthy lean women (age 23-46 years, BMI: 18-25 kg/m(2)).
Plasma levels of cytokines and leptin, BMI, waist circumference (WC) and insulin resistance index HOMA (homeostatic model assessment).
Blood concentrations of IL-17, IL-23, MIF and leptin, but not IL-12 or IFN-gamma, were higher in obese compared with lean women (P=0.002, 0.046, 0.006 and 0.002, respectively). There was a positive correlation between IL-17 and IL-23 (r(s)=0.530), which was at the border of statistical significance (P=0.065). Neither IL-17 nor IL-23 correlated with leptin or MIF, and there was no association between IL-17 and IL-23 levels with BMI, WC or HOMA index.
Interleukin-23/IL-17 axis is stimulated in obese women independently of the increase in abdominal fat, insulin resistance, leptin and MIF levels.
The "metabolic syndrome" (MetS) is a clustering of components that reflect overnutrition, sedentary lifestyles, and resultant excess adiposity. The MetS includes the clustering of abdominal obesity, insulin resistance, dyslipidemia, and elevated blood pressure and is associated with other comorbidities including the prothrombotic state, proinflammatory state, nonalcoholic fatty liver disease, and reproductive disorders. Because the MetS is a cluster of different conditions, and not a single disease, the development of multiple concurrent definitions has resulted. The prevalence of the MetS is increasing to epidemic proportions not only in the United States and the remainder of the urbanized world but also in developing nations. Most studies show that the MetS is associated with an approximate doubling of cardiovascular disease risk and a 5-fold increased risk for incident type 2 diabetes mellitus. Although it is unclear whether there is a unifying pathophysiological mechanism resulting in the MetS, abdominal adiposity and insulin resistance appear to be central to the MetS and its individual components. Lifestyle modification and weight loss should, therefore, be at the core of treating or preventing the MetS and its components. In addition, there is a general consensus that other cardiac risk factors should be aggressively managed in individuals with the MetS. Finally, in 2008 the MetS is an evolving concept that continues to be data driven and evidence based with revisions forthcoming.
T cells with variable region Vdelta1 gammadelta T cell receptors (TCRs) are distributed throughout the human intestinal epithelium and may function as sentinels that respond to self antigens. The expression of a major histocompatibility complex (MHC) class I-related molecule, MICA, matches this localization. MICA and the closely related MICB were recognized by intestinal epithelial T cells expressing diverse Vdelta1 gammadelta TCRs. These interactions involved the alpha1alpha2 domains of MICA and MICB but were independent of antigen processing. With intestinal epithelial cell lines, the expression and recognition of MICA and MICB could be stress-induced. Thus, these molecules may broadly regulate protective responses by the Vdelta1 gammadelta T cells in the epithelium of the intestinal tract.
Prolonged treatment (12–24 h) of adipocytes with tumor necrosis factor α (TNFα) stimulates lipolysis. We have investigated
the hypothesis that TNFα stimulates lipolysis by blocking the action of endogenous adenosine. Adipocytes were incubated for
48 h with TNFα, and lipolysis was measured in the absence or presence of adenosine deaminase. Without adenosine deaminase,
the rate of glycerol release was 2–3-fold higher in the TNFα-treated cells, but with adenosine deaminase lipolysis increased
in the controls to approximately that in the TNFα-treated cells. This suggests that TNFα blocks adenosine release or prevents
its antilipolytic effect. Both N6
-phenylisopropyl adenosine and nicotinic acid were less potent and efficacious inhibitors of lipolysis in treated cells. A
decrease in the concentration of α-subunits of all three Gi subtypes was detected by Western blotting without a change in Gsproteins or β-subunits. Gi2α was about 50% of control, whereas Gi1α and Gi3α were about 20 and 40% of control values, respectively. The time course of Gidown-regulation correlated with the stimulation of lipolysis. Furthermore, down-regulation of Gi by an alternative approach (prolonged incubation withN6
-phenylisopropyl adenosine) stimulated lipolysis. These findings indicate that TNFα stimulates lipolysis by blunting endogenous
inhibition of lipolysis. The mechanism appears to be a Gi protein down-regulation.
Whereas truncal (central) adiposity is strongly associated with the insulin resistant metabolic syndrome, it is uncertain whether this is accounted for principally by visceral adiposity (VAT). Several recent studies find as strong or stronger association between subcutaneous abdominal adiposity (SAT) and insulin resistance. To reexamine the issue of truncal adipose tissue depots, we performed cross-sectional abdominal computed tomography, and we undertook the novel approach of partitioning SAT into the plane superficial to the fascia within subcutaneous adipose tissue (superficial SAT) and that below this fascia (deep SAT), as well as measurement of VAT. Among 47 lean and obese glucose-tolerant men and women, insulin-stimulated glucose utilization, measured by euglycemic clamp, was strongly correlated with both VAT and deep SAT (r = -0.61 and -0.64, respectively; both P < 0.001), but not with superficial SAT (r = -0.29, not significant). Also, VAT and deep SAT followed a highly congruent pattern of associations with glucose and insulin area under the curve (75-g oral glucose tolerance test), mean arterial blood pressure, apoprotein-B, high-density lipoprotein cholesterol, and triglyceride. Superficial SAT had markedly weaker association with all these parameters and instead followed the pattern observed for thigh subcutaneous adiposity. We conclude that there are two functionally distinct compartments of adipose tissue within abdominal subcutaneous fat and that the deep SAT has a strong relation to insulin resistance.
Diabetes mellitus is a chronic disease that leads to complications including heart disease, stroke, kidney failure, blindness and nerve damage. Type 2 diabetes, characterized by target-tissue resistance to insulin, is epidemic in industrialized societies and is strongly associated with obesity; however, the mechanism by which increased adiposity causes insulin resistance is unclear. Here we show that adipocytes secrete a unique signalling molecule, which we have named resistin (for resistance to insulin). Circulating resistin levels are decreased by the anti-diabetic drug rosiglitazone, and increased in diet-induced and genetic forms of obesity. Administration of anti-resistin antibody improves blood sugar and insulin action in mice with diet-induced obesity. Moreover, treatment of normal mice with recombinant resistin impairs glucose tolerance and insulin action. Insulin-stimulated glucose uptake by adipocytes is enhanced by neutralization of resistin and is reduced by resistin treatment. Resistin is thus a hormone that potentially links obesity to diabetes.
The immune-modulating cytokine interleukin-6 (IL-6) is expressed both in adipose tissue and centrally in hypothalamic nuclei that regulate body composition. We investigated the impact of loss of IL-6 on body composition in mice lacking the gene encoding IL-6 (Il6-/- mice) and found that they developed mature-onset obesity that was partly reversed by IL-6 replacement. The obese Il6-/- mice had disturbed carbohydrate and lipid metabolism, increased leptin levels and decreased responsiveness to leptin treatment. To investigate the possible mechanism and site of action of the anti-obesity effect of IL-6, we injected rats centrally and peripherally with IL-6 at low doses. Intracerebroventricular, but not intraperitoneal IL-6 treatment increased energy expenditure. In conclusion, centrally acting IL-6 exerts anti-obesity effects in rodents.
The transition between cell proliferation and cell differentiation taking place during adipocyte differentiation is a tightly regulated process where both cell cycle regulators and differentiating factors interact, creating a cascade of events leading to the commitment of the cells into the adipocyte phenotype. Based on in-vitro cell models of adipocyte differentiation, the different stages of adipogenesis have been established, each of them with a particular pattern of gene expression. Re-entry into the cell cycle of growth-arrested preadipocytes is known as the clonal expansion phase. Growth-arrested preadipocytes undergo several rounds of cell cycle before terminally differentiating into adipocytes, suggesting that a cross-talk might exist between the cell cycle or the cell proliferation machinery and the factors controlling cell differentiation. I will focus this review on the influence of the proliferative phase of preadipocytes in the adipocyte differentiation process.
Several studies have shown a relationship between interleukin (IL) 6 levels and insulin resistance. We here show that human subcutaneous adipose cells, like 3T3-L1 cells, are target cells for IL-6. To examine putative mechanisms and cross-talk with insulin, 3T3-L1 adipocytes were cultured for different times with IL-6 and tumor necrosis factor alpha (TNF-alpha). IL-6, in contrast to TNF-alpha, did not increase pS-307 of insulin-receptor substrate (IRS)-1 or JNK activation. However, IL-6, like TNF-alpha exerted long term inhibitory effects on the gene transcription of IRS-1, GLUT-4, and peroxisome proliferator-activated receptor gamma. This effect of IL-6 was accompanied by a marked reduction in IRS-1, but not IRS-2, protein expression, and insulin-stimulated tyrosine phosphorylation, whereas no inhibitory effect was seen on the insulin receptor tyrosine phosphorylation. Consistent with the reduced GLUT-4 mRNA, insulin-stimulated glucose transport was also significantly reduced by IL-6. An important interaction with TNF-alpha was found because TNF-alpha markedly increased IL-6 mRNA and protein secretion. These results show that IL-6, through effects on gene transcription, is capable of impairing insulin signaling and action but, in contrast to TNF-alpha, IL-6 does not increase pS-307 (or pS-612) of IRS-1. The link between IL-6 and insulin resistance in man was further corroborated by the finding that the expression of IL-6, like that of TNF-alpha and IL-8, was markedly increased ( approximately 15-fold) in human fat cells from insulin-resistant individuals. We conclude that IL-6 can play an important role in insulin resistance in man and, furthermore, that it may act in concert with other cytokines that also are up-regulated in adipose cells in insulin resistance.
Obesity alters adipose tissue metabolic and endocrine function and leads to an increased release of fatty acids, hormones, and proinflammatory molecules that contribute to obesity associated complications. To further characterize the changes that occur in adipose tissue with increasing adiposity, we profiled transcript expression in perigonadal adipose tissue from groups of mice in which adiposity varied due to sex, diet, and the obesity-related mutations agouti (Ay) and obese (Lepob). We found that the expression of 1,304 transcripts correlated significantly with body mass. Of the 100 most significantly correlated genes, 30% encoded proteins that are characteristic of macrophages and are positively correlated with body mass. Immunohistochemical analysis of perigonadal, perirenal, mesenteric, and subcutaneous adipose tissue revealed that the percentage of cells expressing the macrophage marker F4/80 (F4/80+) was significantly and positively correlated with both adipocyte size and body mass. Similar relationships were found in human subcutaneous adipose tissue stained for the macrophage antigen CD68. Bone marrow transplant studies and quantitation of macrophage number in adipose tissue from macrophage-deficient (Csf1op/op) mice suggest that these F4/80+ cells are CSF-1 dependent, bone marrow-derived adipose tissue macrophages. Expression analysis of macrophage and nonmacrophage cell populations isolated from adipose tissue demonstrates that adipose tissue macrophages are responsible for almost all adipose tissue TNF-alpha expression and significant amounts of iNOS and IL-6 expression. Adipose tissue macrophage numbers increase in obesity and participate in inflammatory pathways that are activated in adipose tissues of obese individuals.
The contribution of visceral adipose tissue (VAT) to insulin resistance is well-established; however, the role of subcutaneous abdominal adipose tissue (SAT) in insulin resistance remains controversial. Sex may determine which of these two components of abdominal obesity is more strongly related to insulin resistance and its consequences. The aim of this study was to determine whether both VAT and SAT contribute to insulin resistance in African Americans and to examine the effects of sex on this relationship.
This was a cross-sectional study of 78 nondiabetic African-American volunteers (44 men, 35 women; age 33.8 +/- 7.3 years; BMI 30.9 +/- 7.4 kg/m2). VAT and SAT volumes were measured using serial computerized tomography slices from the dome of the diaphragm to the iliac crest. The insulin sensitivity index (SI) was determined from the minimal model using data obtained from the frequently sampled intravenous glucose tolerance test.
In men, both VAT and SAT were negatively correlated with SI (r for both correlations = -0.57; p < 0.01). In women, the correlation coefficient between VAT and SI was -0.50 (p < 0.01) and between SAT and SI was -0.67 (p < 0.01). In women, the correlation coefficient for SI with SAT was significantly greater than the correlation coefficient with VAT (p = 0.02).
Both SAT and VAT are strongly correlated with insulin resistance in African Americans. For African-American women, SAT may have a greater effect than VAT on insulin resistance.
The ERK, p38 and JNK mitogen activated protein kinases (MAPKs) are intracellular signalling pathways that play a pivotal role in many essential cellular processes such as proliferation and differentiation. MAPKs are activated by a large variety of stimuli and one of their major functions is to connect cell surface receptors to transcription factors in the nucleus, which consequently triggers long-term cellular responses. This review focuses on their in vitro and in vivo roles in adipocyte differentiation and obesity. Hyperplasia of adipose tissue is a critical event for the development of obesity. Several studies have analysed the role of MAPKs in vitro in adipocyte differentiation of preadipocyte established cell lines. In the case of ERK, although the first data appeared contradictory, a consensus scenario arises: ERK would be necessary to initiate the preadipocyte into the differentiation process and, thereafter, this signal transduction pathway needs to be shut-off to proceed with adipocyte maturation. The limitation of these cellular models is that only terminal adipocyte differentiation can be analysed, eluding the early proliferative steps of adipogenesis. New insights are now emerging by investigations conducted either in vitro with the use of embryonic stem (ES) cells or in vivo with mice where these genes are invalidated. These studies not only confirm and/or precise the various functions of MAPKs in adipogenesis but, importantly, reveal unsuspected roles, for example JNK in obesity or ERK in adipogenesis of ES cells, and, for a given pathway, assign specific functions to each isoform. It appears now that a fine tuning of the MAPKs regulates both normal and pathological adipogenesis. The precise understanding of the cascade of these molecular events and the way to regulate them will be certainly crucial in order to efficiently fight obesity.
The molecular basis of gammadelta T cell receptor (TCR) recognition is poorly understood. Here, we analyze the TCR sequences of a natural gammadelta T cell population specific for the major histocompatibility complex class Ib molecule T22. We find that T22 recognition correlates strongly with a somatically recombined TCRdelta complementarity-determining region 3 (CDR3) motif derived from germ line-encoded residues. Sequence diversity around these residues modulates TCR ligand-binding affinities, whereas V gene usage correlates mainly with tissue origin. These results show how an antigen-specific gammadelta TCR repertoire can be generated at a high frequency and suggest that gammadelta T cells recognize a limited number of antigens.
A unique population of T lymphocytes, designated dendritic epidermal T cells (DETC), homes to the murine epidermis during fetal development. DETC express a canonical gammadelta TCR, Vgamma3/Vdelta1, which recognizes Ag expressed on damaged, stressed, or transformed keratinocytes. Recently, DETC were shown to play a key role in the complex process of wound repair. To examine the role of the DETC TCR in DETC localization to the epidermis, maintenance in the skin, and activation in vivo, we analyzed DETC in the TCRdelta(-/-) mouse. Unlike previous reports in which the TCRdelta(-/-) skin was found to be devoid of any DETC, we discovered that TCRdelta(-/-) mice have alphabeta TCR-expressing DETC with a polyclonal Vbeta chain repertoire. The alphabeta DETC are not retained over the life of the animal, suggesting that the gammadelta TCR is critical for the maintenance of DETC in the skin. Although the alphabeta DETC can be activated in response to direct stimulation, they do not respond to keratinocyte damage. Our results suggest that a keratinocyte-responsive TCR is necessary for DETC activation in response to keratinocyte damage and for DETC maintenance in the epidermis.
Macrophage infiltration of white adipose tissue (WAT) is implicated in the metabolic complications of obesity. The precipitating event(s) and function(s) of macrophage infiltration into WAT are unknown. We demonstrate that >90% of all macrophages in WAT of obese mice and humans are localized to dead adipocytes, where they fuse to form syncytia that sequester and scavenge the residual “free” adipocyte lipid droplet and ultimately form multinucleate giant cells, a hallmark of chronic inflammation. Adipocyte death increases in obese (db/db) mice (30-fold) and humans and exhibits ultrastructural features of necrosis (but not apoptosis). These observations identify necrotic-like adipocyte death as a pathologic hallmark of obesity and suggest that scavenging of adipocyte debris is an important function of WAT macrophages in obese individuals. The frequency of adipocyte death is positively correlated with increased adipocyte size in obese mice and humans and in hormone-sensitive lipase-deficient (HSL−/−) mice, a model of adipocyte hypertrophy without increased adipose mass. WAT of HSL−/− mice exhibited a 15-fold increase in necrotic-like adipocyte death and formation of macrophage syncytia, coincident with increased tumor necrosis factor-α gene expression.
These results provide a novel framework for understanding macrophage recruitment, function, and persistence in WAT of obese individuals.
The C-C motif chemokine receptor-2 (CCR2) regulates monocyte and macrophage recruitment and is necessary for macrophage-dependent inflammatory responses and the development of atherosclerosis. Although adipose tissue expression and circulating concentrations of CCL2 (also known as MCP1), a high-affinity ligand for CCR2, are elevated in obesity, the role of CCR2 in metabolic disorders, including insulin resistance, hepatic steatosis, and inflammation associated with obesity, has not been studied. To determine what role CCR2 plays in the development of metabolic phenotypes, we studied the effects of Ccr2 genotype on the development of obesity and its associated phenotypes. Genetic deficiency in Ccr2 reduced food intake and attenuated the development of obesity in mice fed a high-fat diet. In obese mice matched for adiposity, Ccr2 deficiency reduced macrophage content and the inflammatory profile of adipose tissue, increased adiponectin expression, ameliorated hepatic steatosis, and improved systemic glucose homeostasis and insulin sensitivity. In mice with established obesity, short-term treatment with a pharmacological antagonist of CCR2 lowered macrophage content of adipose tissue and improved insulin sensitivity without significantly altering body mass or improving hepatic steatosis. These data suggest that CCR2 influences the development of obesity and associated adipose tissue inflammation and systemic insulin resistance and plays a role in the maintenance of adipose tissue macrophages and insulin resistance once obesity and its metabolic consequences are established.
Whereas the vast majority of T cells express a T-cell receptor (TCR) composed of alphabeta heterodimers, a smaller population expresses a gammadelta TCR. In contrast to alphabeta T cells, gammadelta T cells show less TCR diversity, are particularly enriched at epithelial surfaces and appear to respond to self-molecules that signal potential danger or cellular stress. In addition, various subsets of gammadelta T cells have shown antitumor and immunoregulatory activities. This review considers what has been discovered about the important cutaneous functions of gammadelta T cells through the study of mutant mice and offers perspectives on the roles of gammadelta T cells in human disease.
Tumor necrosis factor (TNF) is implicated in wasting syndromes and insulin resistance in chronic infection and obese-linked diabetes. TNF (10 ng/ml) inhibited adipocyte differentiation of 3T3-L1 cells, and in these TNF treated cells little insulin-stimulated glucose uptake was observed. Treatment of 3T3-L1 cells with troglitazone (1-10 microM) partially prevented this inhibitory effect of TNF on adipogenesis, and enhanced expression of C/EBP alpha and GLUT4, even in the presence of TNF. Troglitazone also prevented the inhibitory effects of interleukin-1, interleukin-6, and leukemia inhibitory factor, but not of transforming growth factor beta on adipocyte differentiation of 3T3-L1 cells. These effects might contribute to the antidiabetic effect of troglitazone in obese diabetic animals.
The C-C motif chemokine receptor–2 (CCR2) regulates monocyte and macrophage recruitment and is necessary for macrophage-dependent inflammatory responses and the development of atherosclerosis. Although adipose tissue expression and circulating concentrations of CCL2 (also known as MCP1), a high-affinity ligand for CCR2, are elevated in obesity, the role of CCR2 in metabolic disorders, including insulin resistance, hepatic steatosis, and inflammation associated with obesity, has not been studied. To determine what role CCR2 plays in the development of metabolic phenotypes, we studied the effects of Ccr2 genotype on the development of obesity and its associated phenotypes. Genetic deficiency in Ccr2 reduced food intake and attenuated the development of obesity in mice fed a high-fat diet. In obese mice matched for adiposity, Ccr2 deficiency reduced macrophage content and the inflammatory profile of adipose tissue, increased adiponectin expression, ameliorated hepatic steatosis, and improved systemic glucose homeostasis and insulin sensitivity. In mice with established obesity, short-term treatment with a pharmacological antagonist of CCR2 lowered macrophage content of adipose tissue and improved insulin sensitivity without significantly altering body mass or improving hepatic steatosis. These data suggest that CCR2 influences the development of obesity and associated adipose tissue inflammation and systemic insulin resistance and plays a role in the maintenance of adipose tissue macrophages and insulin resistance once obesity and its metabolic consequences are established.
Experts on psoriasis convened with authorities from other medical specialties to discuss the recently described association between psoriasis, obesity and subsequent cardiovascular comorbidity. Similar to other diseases of increased systemic inflammation, psoriasis has been linked to a heightened risk of myocardial infarction, especially in the more severely affected, younger patients. However, unlike in other inflammatory diseases – such as rheumatoid arthritis – more severely affected patients with psoriasis are much more likely to be obese. Importantly, the pathophysiology of both psoriasis and obesity shows many shared cytokines that are known to contribute to features of the metabolic syndrome, such as hypertension, dyslipidaemia and insulin resistance. The strong association between psoriasis and obesity potentially makes psoriasis an important healthcare issue that requires an update in its standard of care. This meeting reviewed the evidence-based literature and addressed how, moving forward, dermatologists and other specialists may redefine the magnitude of health risk associated with more severe psoriasis and its comorbidities, while clarifying both the epidemiology and pathophysiology of the association with obesity.
Adipose tissue (AT) can accumulate macrophages and secrete several inflammatory mediators. Despite its pivotal role in the progression of chronic inflammatory processes such as atherosclerosis, the adaptive role of immunity in obesity remains poorly explored. Visceral AT of diet-induced obese C57BL/6 mice had higher numbers of both CD4(+) and CD8(+) T cells than lean controls, monitored by flow cytometry. When stimulated in vitro, T cells from obese AT produced more interferon (IFN)gamma than those from controls. AT from obese animals also had more cells expressing I-A(b), a mouse class II histocompatibility marker implicated in antigen presentation, as determined by immunostaining. Differentiated 3T3-L1 cells stimulated with recombinant IFNgamma or T-helper 1-derived supernatant produced several chemokines and their mRNAs. Obese IFNgamma-deficient animals had significantly reduced AT expression of mRNA-encoding inflammatory genes such as tumor necrosis factor-alpha and monocyte chemoattractant protein-1, decreased AT inflammatory cell accumulation, and better glucose tolerance than control animals consuming the same diet. Obese mice doubly deficient for IFNgamma receptor and apolipoprotein (Apo)E on a mixed 129SvEv/C57BL/6 (129/B6) genetic background, despite exhibiting similar AT mRNA levels of tumor necrosis factor-alpha and monocyte chemoattractant protein-1 as 129/B6-ApoE(-/-) controls, had decreased expression of important T cell-related genes, such as IFNgamma-inducible protein-10 and I-A(b), and lower plasma triglycerides and glucose. These results indicate a role for T cells and IFNgamma, a prototypical T-helper 1 cytokine, in regulation of the inflammatory response that accompanies obesity.
Obesity is linked to a variety of metabolic disorders, such as insulin resistance and atherosclerosis. Dysregulated production of fat-derived secretory factors, adipocytokines, is partly responsible for obesity-linked metabolic disorders. However, the mechanistic role of obesity per se to adipocytokine dysregulation has not been fully elucidated. Here, we show that adipose tissue of obese mice is hypoxic and that local adipose tissue hypoxia dysregulates the production of adipocytokines. Tissue hypoxia was confirmed by an exogenous marker, pimonidazole, and by an elevated concentration of lactate, an endogenous marker. Moreover, local tissue hypoperfusion (measured by colored microspheres) was confirmed in adipose tissue of obese mice. Adiponectin mRNA expression was decreased, and mRNA of C/EBP homologous protein (CHOP), an endoplasmic reticulum (ER) stress-mediated protein, was significantly increased in adipose tissue of obese mice. In 3T3-L1 adipocytes, hypoxia dysregulated the expression of adipocytokines, such as adiponectin and plasminogen activator inhibitor type-1, and increased the mRNAs of ER stress marker genes, CHOP and GRP78 (glucose-regulated protein, 78 kD). Expression of CHOP attenuated adiponectin promoter activity, and RNA interference of CHOP partly reversed hypoxia-induced suppression of adiponectin mRNA expression in adipocytes. Hypoxia also increased instability of adiponectin mRNA. Our results suggest that hypoperfusion and hypoxia in adipose tissues underlie the dysregulated production of adipocytokines and metabolic syndrome in obesity.
To examine whether obesity during childhood, adolescence, or adulthood is associated with an increased risk of multiple sclerosis (MS).
Women in the Nurses' Health Study (n = 121,700) and Nurses' Health Study II (n = 116,671) provided information on weight at age 18 and weight and height at baseline, from which body mass index was derived. Women also selected silhouettes representing their body size at ages 5, 10, and 20. Over the total 40 years of follow-up in both cohorts combined, we confirmed 593 cases of MS. Cox proportional hazards models, adjusting for age, latitude of residence, ethnicity, and cigarette smoking, were used to estimate the rate ratios and 95% confidence intervals (CI).
Obesity at age 18 (body mass index > or =30 kg/m(2)) was associated with a greater than twofold increased risk of MS (multivariate relative risk(pooled) = 2.25, 95% CI: 1.50-3.37, p trend <0.001). After adjusting for body size at age 20, having a large body size at ages 5 or 10 was not associated with risk of MS, whereas a large body size at age 20 was associated with a 96% increased risk of MS (95% CI: 1.33-2.89, p trend = 0.009). No significant association was found between adult body mass and MS risk.
Obese adolescents have an increased risk of developing multiple sclerosis (MS). Although the mechanisms of this association remain uncertain, this result suggests that prevention of adolescent obesity may contribute to reduced MS risk.
Obesity is associated with numerous inflammatory conditions including atherosclerosis, autoimmune disease and cancer. Although the precise mechanisms are unknown, obesity-associated rises in TNF-alpha, IL-6 and TGF-beta are believed to contribute. Here we demonstrate that obesity selectively promotes an expansion of the Th17 T-cell sublineage, a subset with prominent pro-inflammatory roles. T-cells from diet-induced obese mice expand Th17 cell pools and produce progressively more IL-17 than lean littermates in an IL-6-dependent process. The increased Th17 bias was associated with more pronounced autoimmune disease as confirmed in two disease models, EAE and trinitrobenzene sulfonic acid colitis. In both, diet-induced obese mice developed more severe early disease and histopathology with increased IL-17(+) T-cell pools in target tissues. The well-described association of obesity with inflammatory and autoimmune disease is mechanistically linked to a Th17 bias.
Obesity generates a proinflammatory environment in adipose tissue, but the factors that initiate this inflammatory cascade have been unclear. Three studies now show that alterations in the composition of adipose tissue T cells occur early in obesity and shape the relationship between immunity and metabolism (pages 914920, 921929 and 930939).
The immune system is closely linked to human metabolic diseases. Serum levels of IL-6 increase with obesity and insulin resistance. Not only does IL-6 decrease the insulin sensitivity of human cells such as adipocytes, but it also regulates the lineage commitment of naïve T cells into interleukin (IL)-17A-producing CD4(+) T (Th17) cells. Although IL-17A exerts a variety of effects on somatic tissues, its functional role in human adipocytes has not been identified. In this work, we show that IL-17A inhibits adipocyte differentiation in human bone marrow mesenchymal stem cells (hBM-MSCs), while promoting lipolysis of differentiated adipocytes. We find that IL-17A increases both mRNA and protein secretion of IL-6 and IL-8 during adipocyte differentiation in hBM-MSCs. IL-17A up-regulates cyclooxygenase (COX)-2 gene expression and thereby increases the level of prostaglandin (PG) E(2) in differentiated adipocyes. The suppression of anti-adipogenic PGE(2) by COX inhibitors such as aspirin and NS-398 partially blocked the effect of IL-17A on adipocyte differentiation in hBM-MSCs. Therefore, IL-17A exhibits its inhibitory effect in part via the COX-2 induction in differentiated adipocytes. In addition, treatment with anti-IL-17A antibody neutralizes IL-17A-mediated effects on adipocyte differentiation and function. These results suggest that IL-17A plays a regulatory role in both the metabolic and inflammatory processes of human adipocytes, similar to other pro-inflammatory cytokines such as IL-1, IFNgamma, and TNFalpha.
Thy-1+ dendritic epidermal T cells (dECs) express invariant gamma delta antigen receptors and are found in intimate contact
with keratinocytes in murine epidermis--thus raising the possibility that keratinocytes express a ligand for the antigen receptor
of these T cells. Thy-1+ dECs were stimulated to produce lymphokines by interaction with keratinocytes in vitro. This stimulation
was mediated through the dEC antigen receptor and did not appear to be restricted by the major histocompatibility complex.
Thus, dECs can recognize self antigens and may participate in immune surveillance for cellular damage rather than for foreign
antigens.
Tumor necrosis factor (TNF) is implicated in wasting syndromes and insulin resistance in chronic infection and obese-linked diabetes. TNF (10 ng/ml) inhibited adipocyte differentiation of 3T3-L1 cells, and in these TNF treated cells little insulin-stimulated glucose uptake was observed. Treatment of 3T3-L1 cells with troglitazone (1-10 microM) partially prevented this inhibitory effect of TNF on adipogenesis, and enhanced expression of C/EBP alpha and GLUT4, even in the presence of TNF. Troglitazone also prevented the inhibitory effects of interleukin-1, interleukin-6, and leukemia inhibitory factor, but not of transforming growth factor beta on adipocyte differentiation of 3T3-L1 cells. These effects might contribute to the antidiabetic effect of troglitazone in obese diabetic animals.
Adipocyte differentiation is coordinatedly regulated by several transcription factors. C/EBP beta, C/EBP delta and ADD-1/SREBP-1 are active early during the differentiation process and induce the expression and/or activity of the peroxisome proliferator activated receptor-gamma (PPAR gamma), the pivotal coordinator of the adipocyte differentiation process. Activated PPAR gamma induces exit from the cell cycle and triggers the expression of adipocyte-specific genes, resulting in increased delivery of energy to the cells. C/EBP alpha, whose expression coincides with the later stages of differentiation, cooperates with PPAR gamma in inducing additional target genes and sustains a high level of PPAR gamma in the mature adipocyte as part of a feedforward loop. Altered activity and/or expression of these transcription factors might underlie the pathogenesis of disorders characterized by increased or decreased adipose tissue depots.
We isolated the human adipose-specific and most abundant gene transcript, apM1 (Maeda, K., et al., Biochem. Biophys. Res. Commun. 221, 286-289, 1996). The apM1 gene product was a kind of soluble matrix protein, which we named adiponectin. To quantitate the plasma adiponectin concentration, we have produced monoclonal and polyclonal antibodies for human adiponectin and developed an enzyme-linked immunosorbent assay (ELISA) system. Adiponectin was abundantly present in the plasma of healthy volunteers in the range from 1.9 to 17.0 mg/ml. Plasma concentrations of adiponectin in obese subjects were significantly lower than those in non-obese subjects, although adiponectin is secreted only from adipose tissue. The ELISA system developed in this study will be useful for elucidating the physiological and pathophysiological role of adiponectin in humans.
Adipose tissue expresses tumor necrosis factor (TNF) and interleukin (IL)-6, which may cause obesity-related insulin resistance. We measured TNF and IL-6 expression in the adipose tissue of 50 lean and obese subjects without diabetes. Insulin sensitivity (S(I)) was determined by an intravenous glucose tolerance test with minimal-model analysis. When lean [body mass index (BMI) <25 kg/m(2)] and obese (BMI 30-40 kg/m(2)) subjects were compared, there was a 7.5-fold increase in TNF secretion (P < 0.05) from adipose tissue, and the TNF secretion was inversely related to S(I) (r = -0.42, P < 0.02). IL-6 was abundantly expressed by adipose tissue. In contrast to TNF, plasma (rather than adipose) IL-6 demonstrated the strongest relationship with obesity and insulin resistance. Plasma IL-6 was significantly higher in obese subjects and demonstrated a highly significant inverse relationship with S(I) (r = -0.71, P < 0.001). To separate the effects of BMI from S(I), subjects who were discordant for S(I) were matched for BMI, age, and gender. By use of this approach, subjects with low S(I) demonstrated a 3.0-fold increased level of TNF secretion from adipose tissue and a 2.3-fold higher plasma IL-6 level (P < 0.05) compared with matched subjects with a high S(I). Plasma IL-6 was significantly associated with plasma nonesterified fatty acid levels (r = 0.49, P < 0.002). Thus the local expression of TNF and plasma IL-6 are higher in subjects with obesity-related insulin resistance.
Abdominal subcutaneous adipose tissue (SAT) occurs in two depots separated by a fascial plane: deep SAT and superficial SAT. In a recent study it was demonstrated that the amount of deep SAT has a much stronger relationship to insulin resistance than does superficial SAT. Because insulin resistance may be related to fatty acid release from adipose tissue, we hypothesized that the two SAT depots may have a different lipolytic activity.
To test this hypothesis, we obtained samples of deep and superficial SAT from patients undergoing elective abdominal surgery. The rate of lipolysis was determined in the collagenase-digested adipocytes obtained from the two fat depots by measuring glycerol release in the presence and absence of isoproterenol. In addition, the relative concentration of hormone-sensitive lipase was determined in both SAT depots by Western blot analysis.
Our results showed that the rate of isoproterenol-stimulated lipolysis was approximately 20% higher in cells from deep SAT compared with those from superficial SAT, indicating that the deep SAT is more lipolytically active. The concentration of hormone-sensitive lipase did not differ between the two adipose tissue depots.
These findings suggest that the higher lipolytic activity of deep SAT may account for its stronger association with insulin resistance. The mechanism seems to be independent of differences in hormone-sensitive lipase concentration.
When induced to differentiate, growth-arrested 3T3-L1 preadipocytes synchronously reenter the cell cycle and undergo mitotic clonal expansion (MCE) followed by expression of genes that produce the adipocyte phenotype. The preadipocytes traverse the G(1)S checkpoint synchronously as evidenced by the expressionactivation of cdk2-cyclin-EA, turnover of p27kip1, hyperphosphorylation of Rb, translocation of cyclin D(1) from nuclei to cytoplasm and GSK-3beta from cytoplasm to nuclei, and incorporation of [(3)H]thymidine into DNA. As the cells cross the G(1)S checkpoint, CEBPbeta acquires DNA-binding activity, initiating a cascade of transcriptional activation that culminates in the expression of adipocyte proteins. The mitogen-activated protein kinaseextracellular signal-regulated kinase kinase (MEK) inhibitor PD98059 delays, but does not block, MCE and differentiation, the extent of the delay causing a comparable delay in the expression of cell-cycle markers, MCE, and adipogenesis. The more potent and specific MEK inhibitor UO126 and the cyclin-dependent kinase inhibitor roscovitine, which inhibit the cell cycle at different points, block MCE, expression of cell cycle and adipocyte markers, as well as adipogenesis. These results show that MCE is a prerequisite for differentiation of 3T3-L1 preadipocytes into adipocytes.
The nuclear hormone receptor peroxisome proliferator-activated receptor gamma (PPARgamma) is a member of the PPAR family. The endogenous activators of all members of the PPAR family are a variety of fatty acids, which suggests that the PPARs are highly involved in lipid metabolism. In the present paper, the current understanding of the involvement of PPARgamma in adipocyte proliferation and adipose tissue formation is extensively reviewed, and it is stressed that PPARgamma seems to be a major regulator in the differentiation of adipocytes. Thiazoledinediones (TZDs) are a group of PPARgamma-agonists used in the treatment of type 2 diabetes (T2D) since 1997. They are characterized by their ability to decrease insulin resistance, and have been suggested to slow down the progression of insulin resistance. Treatment with TZD requires several weeks of treatment to decrease plasma glucose levels, but in addition they markedly decrease plasma triglycerides and free fatty acids. A major drawback of treatment with TZD is body fat gain, but some evidence suggests that the fat is redistributed in a favourable direction, that is, from visceral to subcutaneous depots. However, the effect of long-term treatment on weight gain following TZD treatment is unknown, and it may be questioned whether the use of these 'adipogenic compounds' is appropriate, considering that excess body fat is almost a prerequisite for the development of type 2 diabetes.
Adiponectin is a 29-kDa adipocyte protein that has been linked to the insulin resistance of obesity and lipodystrophy. To better understand the regulation of adiponectin expression, we measured plasma adiponectin and adipose tissue adiponectin mRNA levels in nondiabetic subjects with varying degrees of obesity and insulin resistance. Plasma adiponectin and adiponectin mRNA levels were highly correlated with each other (r = 0.80, P < 0.001), and obese subjects expressed significantly lower levels of adiponectin. However, a significant sex difference in adiponectin expression was observed, especially in relatively lean subjects. When men and women with a BMI <30 kg/m(2) were compared, women had a twofold higher percent body fat, yet their plasma adiponectin levels were 65% higher (8.6 +/- 1.1 and 14.2 +/- 1.6 micro g/ml in men and women, respectively; P < 0.02). Plasma adiponectin had a strong association with insulin sensitivity index (S(I)) (r = 0.67, P < 0.0001, n = 51) that was not affected by sex, but no relation with insulin secretion. To separate the effects of obesity (BMI) from S(I), subjects who were discordant for S(I) were matched for BMI, age, and sex. Using this approach, insulin-sensitive subjects demonstrated a twofold higher plasma level of adiponectin (5.6 +/- 0.6 and 11.2 +/- 1.1 micro g/ml in insulin-resistant and insulin-sensitive subjects, respectively; P < 0.0005). Adiponectin expression was not related to plasma levels of leptin or interleukin-6. However, there was a significant inverse correlation between plasma adiponectin and tumor necrosis factor (TNF)-alpha mRNA expression (r = -0.47, P < 0.005), and subjects with the highest levels of adiponectin mRNA expression secreted the lowest levels of TNF-alpha from their adipose tissue in vitro. Thus, adiponectin expression from adipose tissue is higher in lean subjects and women, and is associated with higher degrees of insulin sensitivity and lower TNF-alpha expression.
Recent studies of the pathogenesis of rheumatoid arthritis (RA) have revealed that both synovial fibroblasts and T cells participate in the perpetuation of joint inflammation as dynamic partners in a mutual activation feedback, via secretion of cytokines and chemokines that stimulate each other. In this study, we investigated the role of IL-17, a major Th1 cytokine produced by activated T cells, in the activation of RA synovial fibroblasts. Transcripts of IL-17R (IL-17 receptor) and IL-17RB (IL-17 receptor B) were present in fibroblast-like synoviocytes (FLS) of RA patients. IL-17R responded with increased expression upon in vitro stimulation with IL-17, while the level of IL-17RB did not change. IL-17 enhanced the production of IL-6 and IL-8 in FLS, as previously shown, but did not affect the synthesis of IL-15. IL-17 appears to be a stronger inducer of IL-6 and IL-8 than IL-15, and even exerted activation comparable to that of IL-1beta in RA FLS. IL-17-mediated induction of IL-6 and IL-8 was transduced via activation of phosphatidylinositol 3-kinase/Akt and NF-kappaB, while CD40 ligation and p38 MAPK (mitogen-activated protein kinase) are not likely to partake in the process. Together these results suggest that IL-17 is capable of more than accessory roles in the activation of RA FLS and provide grounds for targeting IL-17-associated pathways in therapeutic modulation of arthritis inflammation.
Adipogenesis is the developmental process by which a multipotent mesenchymal stem cell differentiates into a mature adipocyte. This process involves a highly regulated and coordinated cascade of transcription factors that together lead to the establishment of the differentiated state. In the presence of the correct hormonal cues, committed pre-adipocytes express the bZIP factors C/EBPb and C/EBPd. These factors in turn induce the expression of C/EBPa and peroxisome proliferator-activated receptor g (PPARg). C/EBPa and PPARg together promote differentiation by activating adipose-specific gene expression and by maintaining each others expression at high levels. We have investigated the relative contributions of PPARg and C/EBPa to adipogenesis by selectively ablating these genes in mouse embryonic fibroblasts (MEFs). MEFs that lack C/EBPa are able to undergo adipogenesis, but only when PPARg is ectopically expressed. Interestingly, these cells are not sensitive to the metabolic actions of insulin. By way of contrast, cells that lack PPARg are utterly incapable of adipogenic conversion, even when supplemented with high levels of C/EBPa. Our current investigations are centered on the identification of novel adipogenic transcription factors, utilizing a variety of techniques, ranging from BAC transgenics to computational approaches. These approaches will be discussed, along with the roles of some new transcriptional players in adipogenesis, including the O/E family of proteins.
Close relationships have been demonstrated between adipose tissue and the inflammatory/immune system. Furthermore, obesity is increasingly considered as a state of chronic inflammation. Cytofluorometric analysis reveals the presence of significant levels of lymphocytes in the stroma-vascular fraction of white adipose tissues. In epididymal (EPI) fat, lymphocytes display an "ancestral" immune system phenotype (up to 70% of natural killer (NK), gammadelta+ T and NKT cells among all lymphocytes) whereas the inguinal (ING) immune system presents more adaptive characteristics (high levels of alphabeta+ T and B cells). The percentage of NK cells in EPI fat was decreased in obese mice fed with a high-fat diet, whereas gammadelta positive cells were significantly increased in ING fat. These data support the notion that adipose tissue may elaborate immunological mechanisms to regulate its functions which might be altered in obesity.
Obesity and lipoatrophy are major risks for insulin resistance, non-insulin-dependent diabetes and cardiovascular disease. In the past three decades, significant advances have been made in delineating the key transcription factors of adipogenesis, as well as extracellular effectors and intracellular signalling pathways that regulate fat cell formation. This review focuses on in vitro models of adipocyte differentiation, and on the balance between pro- and anti-adipogenic factors that drive the adipocyte differentiation process. Full understanding of the mechanisms of adipose tissue differentiation represents a major issue to develop a comprehensive strategy to prevent and treat obesity.
Ancestral lymphoid cells reside in adipose tissues, and their numbers are highly altered in obesity. Leptin, production of which is correlated to fat mass, is strongly involved in the relationships between adipose tissues and immune system. We investigated in epididymal (EPI) and inguinal (ING) fat pads to determine whether 1) lymphocyte phenotypes were correlated to the tissue weight and 2) leptin was involved in such relationships. Immunohistological analyses revealed a tight relationship between the T and NK lymphocytes of the stromal vascular fraction and adipocytes. We identified a significant negative and positive correlation between EPI weight and the percentage of NK and total T cells respectively by cytofluorometric analyses. The NK and ancestral gammadelta T cell contents were directly dependent of leptin since they increased significantly in high-fat (HF) diet mice but not in leptin-deficient (ob/ob) mice as compared to control. By contrast, the alphabeta T cell content seemed independent of leptin because their percentages increased significantly with the EPI weight whatever the type of mice (control, HF, ob/ob). The present study suggests that adipose tissues present, according to their localization, different immunological mechanisms that might be involved in the regulation of adipose cells functions and proliferations.
In adipogenesis, growth factors play a crucial role. Using serum depleted condition, we studied the causal role of endothelin-1 (ET-1) and epidermal growth factor (EGF), separately or together, in adipocyte differentiation of 3T3-L1 cells. ET-1 stimulation caused an anti-adipogenic response and this effect was potentiated upon treatment with EGF. Co-treatment with EGF and ET-1 blocked the expression of C/EBPalpha and PPARgamma, the adipogenic markers. The inhibition of adipogenesis was preceded by a biphasic (early and late) attenuation of Akt phosphorylation. We suggest that treatment with ET-1 and EGF together induce a more potent anti-adipogenic response, involving increased Erk1/2 phosphorylation and biphasic attenuation of Akt phosphorylation.
The white adipose tissue, especially of humans, is now recognized as the central player in the mild inflammatory state that is characteristic of obesity. The question is how the increased accumulation of lipid seen in obesity causes an inflammatory state and how this is linked to the hypertension and type 2 diabetes that accompanies obesity. Once it was thought that adipose tissue was primarily a reservoir for excess calories that were stored in the adipocytes as triacylglycerols. In times of caloric deprivation these stored lipids were mobilized as free fatty acids and the insulin resistance of obesity was attributed to free fatty acids. It is now clear that in humans the expansion of adipose tissue seen in obesity results in more blood vessels, more connective tissue fibroblasts, and especially more macrophages. There is an enhanced secretion of some interleukins and inflammatory cytokines in adipose tissue of the obese as well as increased circulating levels of many cytokines. The central theme of this chapter is that human adipose tissue is a potent source of inflammatory interleukins plus other cytokines and that the majority of this release is due to the nonfat cells in the adipose tissue except for leptin and adiponectin that are primarily secreted by adipocytes. Human adipocytes secrete at least as much plasminogen activator inhibitor-1 (PAI-1), MCP-1, interleukin-8 (IL-8), and IL-6 in vitro as they do leptin but the nonfat cells of adipose tissue secrete even more of these proteins. The secretion of leptin, on the other hand, by the nonfat cells is negligible. The amount of serum amyloid A proteins 1 & 2 (SAA 1 & 2), haptoglobin, nerve growth factor (NGF), macrophage migration inhibitory factor (MIF), and PAI-1 secreted by the adipocytes derived from a gram of adipose tissue is 144%, 75%, 72%, 37%, and 23%, respectively, of that by the nonfat cells derived from the same amount of human adipose tissue. However, the release of IL-8, MCP-1, vascular endothelial growth factor (VEGF), TGF-beta1, IL-6, PGE(2), TNF-alpha, cathepsin S, hepatocyte growth factor (HGF), IL-1beta, IL-10, resistin, C-reactive protein (CRP), and interleukin-1 receptor antagonist (IL-1Ra) by adipocytes is less than 12% of that by the nonfat cells present in human adipose tissue. Obesity markedly elevates the total release of TNF-alpha, IL-6, and IL-8 by adipose tissue but only that of TNF-alpha is enhanced in adipocytes. However, on a quantitative basis the vast majority of the TNF-alpha comes from the nonfat cells. Visceral adipose tissue also releases more VEGF, resistin, IL-6, PAI-1, TGF-beta1, IL-8, and IL-10 per gram of tissue than does abdominal subcutaneous adipose tissue. In conclusion, there is an increasing recognition that adipose tissue is an endocrine organ that secretes leptin and adiponectin along with a host of other paracrine and endocrine factors in addition to free fatty acids.
IL-17A and its receptor are the founding members of a recently described cytokine family, with unique sequences and functions in the immune system and elsewhere. Consisting of six ligands (IL-17A-F) and five receptors (IL-17RA-IL-17RE) in mammals, these molecules have distinct primary amino acid structures with only minimal homology to other cytokine families. By far the best studied of these cytokines to date are IL-17A and its receptor, IL-17RA. IL-17A is produced primarily by T cells, and is the hallmark cytokine of a newly defined T helper cell subset that appears to be involved in generation of autoimmunity. Despite its production by the adaptive immune system, IL-17A exhibits proinflammatory activities similar to innate immune cytokines such as IL-1beta and TNF-alpha and appears to play important and nonredundant roles in regulating granulocytes in vivo. As a result, IL-17A also plays key roles in host defense. In contrast to the restricted expression of IL-17A, the IL-17RA receptor is ubiquitously expressed, and thus most cells are potential physiological targets of IL-17A. This chapter describes the major molecular properties, biological activities, and known signaling pathways of the IL-17 family, with an emphasis on IL-17A and IL-17RA.