Adipose Tissue Macrophage Phenotypes and Characteristics: The Key to Insulin Resistance in Obesity and Metabolic Disorders

Obesity is one of the most serious global health problems, with an incidence that increases yearly and coincides with the development of a variety of associated comorbidities (e.g., type 2 diabetes, nonalcoholic fatty liver disease, some immune‐related disorders). Although many studies have investigated the pathogenesis of overweight and obesity, multiple regulatory factors underlying the onset of obesity‐related metabolic disorders remain elusive. Macrophages contribute to modulation of obesity‐related inflammation and insulin resistance (IR); adipose tissue macrophages are particularly important in this context. Based on newly identified links between the chemokine system and obesity, macrophage polarization has become an essential target of new therapies for obesity‐related IR. The findings of multiple studies imply that variations in gut microbiota and its metabolites might contribute to the regulation of obesity and related metabolic disorders. Recently, several novel antidiabetic drugs, applied as treatment for weight loss, were shown to be effective for obesity‐induced IR and other comorbidities. The present review will discuss the properties and functions of macrophages in adipose tissue under conditions of obesity from three perspectives: the chemokine system, the gut microbiota, and antidiabetic drug application. It is proposed that macrophages might be a key therapeutic target for obesity‐induced complications.     

肥胖与脂肪组织巨噬细胞的研究进展

肥胖被认为是一种慢性促炎症疾病。近年来巨噬细胞在肥胖的发生过程中起的重要作用越来越被研究者们所重视。研究发现脂肪组织巨噬细胞(ATMs)的极化和招募在肥胖的发生过程中扮演着重要角色:在肥胖的脂肪组织中,巨噬细胞M1/M2的比例出现失衡即M1促炎巨噬细胞比例上调M2抑炎巨噬细胞比例下调导致脂肪组织慢性炎症;脂肪组织的局部炎症发生时周边组织巨噬细胞招募至脂肪组织也能够促进肥胖的发展进程。本文就肥胖的发生与脂肪组织巨噬细胞的极化和招募的关系作一综述。     

Adipose Tissue Macrophages Promote Myelopoiesis and Monocytosis in Obesity

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GLUT4 Defects in Adipose Tissue Are Early Signs of Metabolic Alterations in Alms1GT/GT,a Mouse Model for Obesity and Insulin Resistance

Dysregulation of signaling pathways in adipose tissue leading to insulin resistance can contribute to the development of obesity-related metabolic disorders. Alström Syndrome, a recessive ciliopathy, caused by mutations in ALMS1, is characterized by progressive metabolic alterations such as childhood obesity, hyperinsulinemia, and type 2 diabetes. Here we investigated the role of Alms1 disruption in AT expansion and insulin responsiveness in a murine model for Alström Syndrome. A gene trap insertion in Alms1 on the insulin sensitive C57BL6/Ei genetic background leads to early hyperinsulinemia and a progressive increase in body weight. At 6 weeks of age, before the onset of the metabolic disease, the mutant mice had enlarged fat depots with hypertrophic adipocytes, but without signs of inflammation. Expression of lipogenic enzymes was increased. Pre-adipocytes isolated from mutant animals demonstrated normal adipogenic differentiation but gave rise to mature adipocytes with reduced insulin-stimulated glucose uptake. Assessment of whole body glucose homeostasis revealed glucose intolerance. Insulin stimulation resulted in proper AKT phosphorylation in adipose tissue. However, the total amount of glucose transporter 4 (SLC4A2) and its translocation to the plasma membrane were reduced in mutant adipose depots compared to wildtype littermates. Alterations in insulin stimulated trafficking of glucose transporter 4 are an early sign of metabolic dysfunction in Alström mutant mice, providing a possible explanation for the reduced glucose uptake and the compensatory hyperinsulinemia. The metabolic signaling deficits either reside downstream or are independent of AKT activation and suggest a role for ALMS1 in GLUT4 trafficking. Alström mutant mice represent an interesting model for the development of metabolic disease in which adipose tissue with a reduced glucose uptake can expand by de novo lipogenesis to an obese state.     

Relationship of Adipokines and Proinflammatory Cytokines Among Asian Indians With Obesity and Youth Onset Type 2 Diabetes

Objective: It is well known that inflammation is associated with diabetes, but it is unclear whether obesity mediates this association in individuals with youth-onset type 2 diabetes mellitus (T2DM-Y).Methods: We recruited individuals with T2DM-Y (age at onset <25 years) and age-matched normal glucose tolerance (NGT) subjects. Participants were further classified using Asia-Pacific body mass index cut-points for obesity and categorized as: nonobese NGT (n = 100), Obese NGT (n = 50), nonobese T2DM-Y (n = 50), and obese T2DM-Y (n = 50). We compared adipokines (adiponectin and leptin) and proinflammatory cytokines (tumor necrosis factor alpha &lsqb;TNF-α] and monocyte chemotactic protein-1 &lsqb;MCP-1]) across groups.Results: Compared to nonobese NGT, the other 3 groups (obese NGT, nonobese T2DM-Y, and obese T2DM-Y) were found to have lower adiponectin (7.7 vs. 5.7, 4.2, 3.8 μg/mL, P<.01), and higher leptin (3.6 vs. 5.4, 5.7, 7.9 μg/mL, P<.001) and MCP 1 (186 vs. 272, 340, 473 pg/mL, P<.001) respectively. However, TNF-α levels were higher only among nonobese T2DM-Y (112 pg/mL) and obese T2DM-Y (141 pg/mL, P<.01 for each). After adjusting for age, sex, waist, hypertension, homeostatic model assessment of insulin resistance (HOMA-IR), serum cholesterol, triglycerides, and family history of diabetes, adiponectin was associated with 33% and 41% lower odds of being nonobese T2DM and obese T2DM, respectively. However, adjusted for same factors, leptin, TNF-α, and MCP-1 were associated with markedly higher odds (5- to 14-fold) of nonobese and obese T2DM.Conclusion: In young Asian Indians, leptin and proinflammatory cytokines are positively, and adiponectin negatively, associated with both nonobese and obese T2DM-Y compared to nonobese NGT individuals.Abbreviations: BMI = body mass index CI = confidence interval FPG = fasting plasma glucose HOMA-IR = homeostatic model assessment of insulin resistance IGT = impaired glucose tolerance MCP-1 = monocyte chemotactic protein-1 NGT = normal glucose tolerance OGTT = oral glucose tolerance test OR = odds ratio T2DM-Y = youth-onset type 2 diabetes TNF-α = tumor necrosis factor-α     

Genetic Ablation of miR-33 Increases Food Intake,Enhances Adipose Tissue Expansion,and Promotes Obesity and Insulin Resistance

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饮食诱导肥胖及肥胖抵抗与脂肪细胞因子

Levin提出饮食诱导肥胖（DIO）与饮食诱导肥胖抵抗（DIO-R）的概念后,其发生机制受到了广泛关注。现代研究认为脂肪组织除了能调节能量代谢外,还可以分泌多种细胞因子,如瘦素、脂联素、肿瘤坏死因子-α（TNF-α）和抵抗素等。在已发现的脂肪细胞因子中,瘦素、TNF-α和脂联素等与肥胖的发生密切关联。DIO大鼠血清瘦素水平比DIO-R大鼠高,DIO大鼠瘦素敏感性降低,发生了瘦素抵抗。DIO小鼠血浆脂联素水平比DIO-R小鼠低。DIO组TNF-α水平明显高于DIO-R组。     

The Association of Cysteine with Obesity, Inflammatory Cytokines and Insulin Resistance in Hispanic Children and Adolescents

Context

Plasma total cysteine (tCys) independently relates to fat mass in adults. Dietary cyst(e)ine promotes adiposity and decreases glucose tolerance in some rodent models, but alleviates insulin resistance in others.

Objective

To investigate whether the association of tCys with body fat extends to children at particular risk of obesity, and whether tCys is associated with insulin resistance and obesity-associated inflammation.

Methods

We explored the cross-sectional relations of fasting plasma tCys and related metabolites with body composition measured by dual-energy X-ray absorptiometry in 984 Hispanic children and adolescents aged 4–19 years from the Viva La Familia Study. Linear and logistic regression and dose-response curves were used to evaluate relations of tCys with obesity, insulin resistance and inflammatory markers including interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-α), monocyte chemoattractant protein-1 (MCP-1) and C-reactive protein (CRP).

Results

tCys, methionine and total homocysteine (tHcy) increased with age. Upper tCys quartile was independently associated with a 5-fold increased risk of obesity (95% CI 3.5–8.0, P<0.001), and 2-fold risk of insulin resistance (95% CI: 1.6-5.0, P<0.001; adjusted for body fat%). Within the overweight/obese subgroup, but not in normal-weight children, tCys accounted for 9% of the variability in body fat% (partial r = 0.30, P<0.001; adjusted for age and gender). tCys correlated positively with serum non-esterified fatty acids and leptin, partly independent of body fat, but was not associated with serum IL-6, TNF-α or MCP-1. A positive correlation with CRP disappeared after adjustment for BMI.

Conclusion

tCys is independently associated with obesity and insulin resistance in Hispanic children and adolescents, highlighting a previously underappreciated link between the sulfur amino acid metabolic pathway and obesity and cardiometabolic risk.     

HILPDA Uncouples Lipid Droplet Accumulation in Adipose Tissue Macrophages from Inflammation and Metabolic Dysregulation

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Regulation of Adipose Tissue Inflammation and Insulin Resistance by MAPK Phosphatase 5

Obesity and metabolic disorders such as insulin resistance and type 2 diabetes have become a major threat to public health globally. The mechanisms that lead to insulin resistance in type 2 diabetes have not been well understood. In this study, we show that mice deficient in MAPK phosphatase 5 (MKP5) develop insulin resistance spontaneously at an early stage of life and glucose intolerance at a later age. Increased macrophage infiltration in white adipose tissue of young MKP5-deficient mice correlates with the development of insulin resistance. Glucose intolerance in MKP5-deficient mice is accompanied by significantly increased visceral adipose weight, reduced AKT activation, enhanced p38 activity, and increased inflammation in visceral adipose tissue when compared with wild-type (WT) mice. Deficiency of MKP5 resulted in increased inflammatory activation in macrophages. These findings thus demonstrate that MKP5 critically controls inflammation in white adipose tissue and the development of metabolic disorders.     

Role of NKG2D in Obesity-Induced Adipose Tissue Inflammation and Insulin Resistance

The early events that initiate inflammation in the adipose tissue during obesity are not well defined. It is unclear whether the recruitment of CD8 T cells to the adipose tissue during onset of obesity occurs through antigen-dependent or -independent processes. We have previously shown that interaction between NKG2D (natural-killer group 2, member D) and its ligand Rae-1ε is sufficient to recruit cytotoxic T lymphocytes to the pancreas and induce insulitis. Here, we tested whether NKG2D–NKG2D ligand interaction is also involved in obesity-induced adipose tissue inflammation and insulin resistance. We observed a significant induction of NKG2D ligand expression in the adipose tissue of obese mice, especially during the early stages of obesity. However, mice lacking NKG2D developed similar levels of insulin resistance and adipose tissue inflammation compared to control mice when placed on a high-fat diet. Moreover, overexpression of Rae-1ε in the adipose tissue did not increase immune cell infiltration to the adipose tissue either in the setting of a normal or high-fat diet. These results indicate that, unlike in the pancreas, NKG2D–NKG2D ligand interaction does not play a critical role in obesity-induced inflammation in the adipose tissue.     

Crosstalk between Adipocytes and Immune Cells in Adipose Tissue Inflammation and Metabolic Dysregulation in Obesity

Recent findings, notably on adipokines and adipose tissue inflammation, have revised the concept of adipose tissues being a mere storage depot for body energy. Instead, adipose tissues are emerging as endocrine and immunologically active organs with multiple effects on the regulation of systemic energy homeostasis. Notably, compared with other metabolic organs such as liver and muscle, various inflammatory responses are dynamically regulated in adipose tissues and most of the immune cells in adipose tissues are involved in obesity-mediated metabolic complications, including insulin resistance. Here, we summarize recent findings on the key roles of innate (neutrophils, macrophages, mast cells, eosinophils) and adaptive (regulatory T cells, type 1 helper T cells, CD8 T cells, B cells) immune cells in adipose tissue inflammation and metabolic dysregulation in obesity. In particular, the roles of natural killer T cells, one type of innate lymphocyte, in adipose tissue inflammation will be discussed. Finally, a new role of adipocytes as antigen presenting cells to modulate T cell activity and subsequent adipose tissue inflammation will be proposed.     

Resistin,Adiponectin, Ghrelin,Leptin, and Proinflammatory Cytokines: Relationships in Obesity

Objective: To evaluate interactions among leptin, adiponectin, resistin, ghrelin, and proinflammatory cytokines [tumor necrosis factor receptors (TNFRs), interleukin‐6 (IL‐6)] in nonmorbid and morbid obesity. Research Methods and Procedures: We measured these hormones by immunoenzyme or radiometric assays in 117 nonmorbid and 57 morbidly obese patients, and in a subgroup of 34 morbidly obese patients before and 6 months after gastric bypass surgery. Insulin resistance by homeostasis model assessment, lipid profile, and anthropometrical measurements were also performed in all patients. Results: Average plasma lipids in morbidly obese patients were elevated. IL‐6, leptin, adiponectin, and resistin were increased and ghrelin was decreased in morbidly obese compared with nonmorbidly obese subjects. After adjusting for age, gender, and BMI in nonmorbidly obese, adiponectin was positively associated with HDLc and gender and negatively with weight (β = ?0.38, p < 0.001). Leptin and resistin correlated positively with soluble tumor necrosis factor receptor (sTNFR) 1 (β = 0.24, p = 0.01 and β = 0.28, p = 0.007). In the morbidly obese patients, resistin and ghrelin were positively associated with sTNFR2 (β = 0.39, p = 0.008 and β = 0.39, p = 0.01). In the surgically treated morbidly obese group, body weight decreased significantly and was best predicted by resistin concentrations before surgery (β = 0.45, p = 0.024). Plasma lipids, insulin resistance, leptin, sTNFR1, and IL‐6 decreased and adiponectin and ghrelin increased significantly. Insulin resistance improved after weight loss and correlated with high adiponectin levels. Discussion: TNFα receptors were involved in the regulatory endocrine system of body adiposity independently of leptin and resistin axis in nonmorbidly obese patients. Our results suggest coordinated roles of adiponectin, resistin, and ghrelin in the modulation of the obesity proinflammatory environment and that resistin levels before surgery treatment are predictive of the extent of weight loss after bypass surgery.     

Sphingolipid Content of Human Adipose Tissue: Relationship to Adiponectin and Insulin Resistance

Ceramides (Cer) are implicated in obesity‐associated skeletal muscle and perhaps adipocyte insulin resistance. We examined whether the sphingolipid content of human subcutaneous adipose tissue and plasma varies by obesity and sex as well as the relationship between ceramide content and metabolic indices. Abdominal subcutaneous adipose biopsies were performed on 12 lean adults (males = 6), 12 obese adults (males = 6) for measurement of sphingolipid content and activity of the main ceramide metabolism enzymes. Blood was sampled for glucose, insulin (to calculate homeostasis model assessment‐estimated insulin resistance (HOMA_IR)) adiponectin, and interleukin‐6 (IL‐6) concentrations. Compared to lean controls, total ceramide content (pg/adipocyte) was increased by 31% (P < 0.05) and 34% (P < 0.05) in obese females and males, respectively. In adipocytes from obese adults sphingosine, sphinganine, sphingosine‐1‐phosphate, C14‐Cer, C16‐Cer, and C24‐Cer were all increased. C18:1‐Cer was increased in obese males and C24:1‐Cer in obese females. For women only, there was a negative correlation between C16‐Cer ceramide and plasma adiponectin (r = ?0.77, P = 0.003) and a positive correlation between total ceramide content and HOMA_IR (r = 0.74, P = 0.006). For men only there were significant (at least P < 0.05), positive correlations between adipocyte Cer‐containing saturated fatty acid and plasma IL‐6 concentration. We conclude that the sexual dimorphism in adipose tissue behavior in humans extends to adipose tissue sphingolipid content its association with adiponectin, IL‐6 and insulin resistance.     

Abdominal Subcutaneous and Visceral Adipose Tissue and Insulin Resistance in the Framingham Heart Study

Insulin resistance is associated with central obesity and an increased risk of cardiovascular disease. Our objective is to examine the association between abdominal subcutaneous (SAT) and visceral adipose tissue (VAT) and insulin resistance, to determine which fat depot is a stronger correlate of insulin resistance, and to assess whether there was an interaction between SAT, VAT, and age, sex, or BMI. Participants without diabetes from the Framingham Heart Study (FHS), who underwent multidetector computed tomography to assess SAT and VAT (n = 3,093; 48% women; mean age 50.4 years; mean BMI 27.6 kg/m²), were evaluated. Insulin resistance was measured using the homeostasis model and defined as HOMA_IR ≥75th percentile. Logistic regression models, adjusted for age, sex, smoking, alcohol, menopausal status, and hormone replacement therapy use, were used to assess the association between fat measures and insulin resistance. The odds ratio (OR) for insulin resistance per standard deviation increase in SAT was 2.5 (95% confidence interval (CI): 2.2–2.7; P < 0.0001), whereas the OR for insulin resistance per standard deviation increase in VAT was 3.5 (95% CI: 3.1–3.9; P < 0.0001). Overall, VAT was a stronger correlate of insulin resistance than SAT (P < 0.0001 for SAT vs. VAT comparison). After adjustment for BMI, the OR of insulin resistance for VAT was 2.2 (95% CI: 1.9–2.5; P < 0.0001). We observed an interaction between VAT and BMI for insulin (P interaction = 0.0004), proinsulin (P interaction = 0.003), and HOMA_IR (P interaction = 0.003), where VAT had a stronger association in obese individuals. In conclusion, SAT and VAT are both correlates of insulin resistance; however, VAT is a stronger correlate of insulin resistance than SAT.     

RBP4 Activates Antigen-Presenting Cells,Leading to Adipose Tissue Inflammation and Systemic Insulin Resistance

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High-Fat Diet Triggers Inflammation-Induced Cleavage of SIRT1 in Adipose Tissue To Promote Metabolic Dysfunction

Adipose tissue plays an important role in storing excess nutrients and preventing ectopic lipid accumulation in other organs. Obesity leads to excess lipid storage in adipocytes, resulting in the generation of stress signals and the derangement of metabolic functions. SIRT1 is an important regulatory sensor of nutrient availability in many metabolic tissues. Here we report that SIRT1 functions in adipose tissue to protect from inflammation and obesity under normal feeding conditions, and to forestall the progression to metabolic dysfunction under dietary stress and aging. Genetic ablation of SIRT1 in adipose tissue leads to gene expression changes that highly overlap with changes induced by high-fat diet in wild-type mice, suggesting that dietary stress signals inhibit the activity of SIRT1. Indeed, we show that high-fat diet induces the cleavage of SIRT1 protein in adipose tissue by the inflammation-activated caspase-1, providing a link between dietary stress and predisposition to metabolic dysfunction.     

Both Subcutaneous and Visceral Adipose Tissue Correlate Highly with Insulin Resistance in African Americans

Objective: 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. Research Methods and Procedures: 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 (S_I) was determined from the minimal model using data obtained from the frequently sampled intravenous glucose tolerance test. Results: In men, both VAT and SAT were negatively correlated with S_I (r for both correlations = ?0.57; p < 0.01). In women, the correlation coefficient between VAT and S_I was ?0.50 (p < 0.01) and between SAT and S_I was ?0.67 (p < 0.01). In women, the correlation coefficient for S_I with SAT was significantly greater than the correlation coefficient with VAT (p = 0.02). Discussion: 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.     

舒芬太尼复合地佐辛镇痛对中老年胸科手术后胰岛素抵抗及促炎细胞因子的影响

目的:研究舒芬太尼复合地佐辛镇痛对中老年胸科手术后胰岛素抵抗及促炎细胞因子的影响。方法:选取2012年12月到2014年12月我院收治的中老年胸科手术患者80例,按照随机数字表法将患者分为研究组和对照组,每组40例。研究组给予舒芬太尼复合地佐辛镇痛,对照组给予舒芬太尼镇痛,比较两组术后2 h和24 h视觉模拟评分(VAS)和镇静程度评分(Ramsay),比较手术前、术后2 h和24 h两组胰岛素含量、胰岛素敏感性以及肿瘤坏死因子-a(TNF-a)、白介素-6(IL-6)情况。结果:术后2 h和24 h研究组VAS评分均显著低于对照组,Ramsay评分显著高于对照组,两组比较差异具有统计学意义(P0.05);两组术后2 h和24 h胰岛素含量、胰岛素敏感性比较差异具有统计学意义(P0.05);手术前两组TNF-a、IL-6水平比较均无统计学意义(P0.05),术后2 h和24 h研究组TNF-a、IL-6显著低于对照组,两组比较差异具有统计学意义(P0.05)。结论:舒芬太尼复合地佐辛应用于中老年胸科手术具有较好的术后镇痛效果,且具有抑制胰岛素抵抗和促炎细胞因子的作用。