脂联素受体及信号转导研究进展

脂联素是脂肪细胞特异分泌的细胞因子,有增强胰岛素敏感性、抗高血糖、抗动脉粥样硬化等效应.它在血清中有3种不同的低聚体形式,改变每种低聚体的相对量可以调节脂联素的活性.脂联素受体1(AdipoR1)在骨骼肌有丰富表达,脂联素受体2(AdipoR2)主要在肝脏表达.AdipoR1对脂联素球形结构域(gACRP30)有高度亲和性,AdipoR2对全长型脂联素及gACRP30有中度亲和性.已有研究表明脂联素通过激活腺苷酸活化蛋白激酶和增强胰岛素受体酪氨酸磷酸化作用等途径发挥作用.白介素-6、过氧化物酶体增殖物激活受体-γ影响脂联素的表达和分泌.     

脂联素受体及信号转导研究进展

脂联素是脂肪细胞特异分泌的细胞因子，有增强胰岛素敏感性、抗高血糖、抗动脉粥样硬化等效应。它在血清中有3种不同的低聚体形式，改变每种低聚体的相对量可以调节脂联素的活性。脂联素受体1(AdipoR1)在骨骼肌有丰富表达，脂联素受体2(AdipoR2)主要在肝脏表达。AdipoR1对脂联素球形结构域(gACRP30)有高度亲和性，AdipoR2对全长型脂联素及gACRP30有中度亲和性。已有研究表明脂联素通过激活腺苷酸活化蛋白激酶和增强胰岛素受体酪氨酸磷酸化作用等途径发挥作用。白介素-6、过氧化物酶体增殖物激活受体-γ影响脂联素的表达和分泌。     

吡格列酮对2型糖尿病大鼠骨骼肌脂联素受体1表达的影响

目的观察吡格列酮对2型糖尿病大鼠血清脂联素以及骨骼肌脂联素受体1(AdipoR1)表达的影响,探讨吡格列酮对2型糖尿病胰岛素抵抗的改善作用及机制。方法 40只8周龄健康雌性SD大鼠,随机分为正常对照组(n=10)、糖尿病组(n=15)及吡格列酮组(n=15)。用高糖高脂饲料加小剂量链脲佐菌素建立2型糖尿病大鼠模型,成模后吡格列酮组给予10 mg/(kg.d)吡格列酮灌胃,正常对照组和糖尿病组给予同体积生理盐水灌胃,共12周。3个月后股静脉取血,酶联免疫吸附法(ELISA)测定血清脂联素水平,留取大鼠骨骼肌,光、电镜观察骨骼肌结构,免疫组织化学染色法测定骨骼肌AdipoR1蛋白的表达。结果与正常对照组(1.73±0.32 mg/L)比较,糖尿病组血清脂联素(1.01±0.27 mg/L)水平显著降低,而吡格列酮组(1.34±0.43 mg/L)较糖尿病组显著升高,差异有统计学意义(P<0.05)。骨骼肌AdipoR1免疫组织化学染色正常对照组着色深且广泛,糖尿病组较正常对照组染色浅,吡格列酮组较糖尿病组染色深,但较正常对照组浅。光镜及电镜结果显示大鼠骨骼肌结构未见明显异常。结论 2型糖尿病大鼠血清脂联素水平及骨骼肌AdipoR1表达降低并导致糖脂代谢紊乱及胰岛素抵抗。吡格列酮可上调血清脂联素及骨骼肌AdipoR1的表达,从而调节糖脂代谢,改善胰岛素抵抗。     

2型糖尿病大鼠脂肪组织脂联素和骨骼肌组织脂联素受体R1基因表达的变化

半定量RT-PCR检测2型糖尿病大鼠模型脂肪组织脂联素及骨骼肌组织脂联素受体R1 mRNA表达。与正常大鼠比较，糖尿病大鼠骨骼肌组织脂联素受体R1基因表达无改变。糖尿病大鼠血清脂联素水平下降是由脂肪组织脂联素mRNA表达降低引起的，罗格列酮治疗可以使之改善。     

胰岛素对大鼠骨骼肌细胞脂联素受体基因表达的影响

目的了解体外胰岛素对原代培养大鼠骨骼肌细胞脂联素受体1表达的影响。方法体外原代培养骨骼肌细胞,应用SYBRGreenⅠ染料建立一种快速、可靠的实时定量PCR,对其主要要素进行优化。观察不同胰岛素浓度不同作用时间下,大鼠骨骼肌细胞脂联素受体基因表达水平的动态变化。结果建立敏感、特异、快速检测脂联素受体1mRNA的实时定量PCR方法,随着胰岛素浓度的增加,脂联素受体1表达逐渐降低。在较低浓度（胰岛素浓度〈1nmol/L）时,脂联素受体1表达的降低无统计学意义,当胰岛素浓度增加到10nmol/L及以上时,骨骼肌细胞脂联素受体1表达的降低有统计学意义（P〈0.05）,这种抑制作用1h后出现,24h后达到高峰。结论成功地建立SYBRGreenⅠ实时定量PCR检测脂联素受体基因的表达方法,体外高胰岛素对骨骼肌细胞脂联素受体1mRNA表达有抑制作用,并呈时间和剂量依赖性。     

脂联素受体在正常SD大鼠乳鼠心肌细胞的分布和表达

目的通过体外培养SD大鼠乳鼠心肌细胞,研究脂联素受体1(AdipoR1)、脂联素受体2(AdipoR2)及T-钙黏蛋白(T-cadherin)三种脂联素受体在大鼠乳鼠心肌细胞上的分布和表达。方法采用酶消化法原代培养乳鼠心肌细胞,通过α-肌动蛋白免疫荧光法对原代培养的心肌细胞进行鉴定,并在倒置相差显微镜下观察细胞生长状态。选用原代培养96h的单层心肌细胞进行实验,使用RT-PCR和细胞免疫组织化学方法检测AdipoR1、AdipoR2、T-cadherin的mRNA和蛋白在心肌细胞中的表达情况。结果在SD大鼠乳鼠心肌细胞上均检测到了AdipoR1、AdipoR2、T-cadherin的mRNA和蛋白表达,其中以AdipoR1和T-cad-herin的mRNA和蛋白表达量高,与AdipoR2的表达量相比差异有统计学意义(P<0.01)。结论脂联素受体1、脂联素受体2和T-钙黏蛋白,三种脂联素受体在SD大鼠乳鼠心肌细胞上均有表达,并以脂联素受体1和T-钙黏蛋白的表达为主,脂联素受体2表达量较少。     

脂联素受体的表达与调节

脂联素受体1在骨骼肌中有丰富表达,而脂联素受体2主要在肝中表达。另外,两种脂联素受体也在胰岛β细胞、脂肪组织、单核细胞、巨噬细胞、成骨细胞、心肌组织和胎盘组织中表达。生长激素、胰岛素以及过氧化物酶体增殖物活化受体(PPAR)α、PPARγ和肝X受体激动剂等可影响脂联素受体的表达。研究脂联素受体在不同组织、细胞中的表达与调节可了解其组织特异性作用。     

脂联素与慢性肝病的关系研究进展

脂肪组织能够分泌多种脂肪因子,这些脂肪因子通过自分泌方式调节脂肪合成和分解代谢。脂联素是脂肪因子的一种,它除了能够促进糖和脂肪代谢之外还具有抗炎,增敏胰岛素和抗动脉粥样硬化等功能因而备受关注。一、脂联素与慢性肝病脂联素是在脂肪组织中特异表达的脂肪因子。在血浆中,脂联素以低分子量多聚体和高分子量多聚体的形式存在。脂联素存在两种受体:AdipoR1和AdipoR2。这两种受体在多种组织都有表达,但主要分布在骨骼肌和肝脏。血清脂联素水平与体脂肪含量、空腹胰岛素浓度、血浆甘油三酯水平密切相关。过氧化物酶激活物增值受体γ(P…     

链脲佐菌素诱导的1型糖尿病大鼠肾脏脂联素受体的表达

目的 观察链脲佐菌素(STZ)诱导的糖尿病大鼠在不同时期其血清脂联素和脂联素受体(AdipoR)在肾脏组织的表达水平.方法 64只雌性SD大鼠按随机数字表法分为对照组和实验组(分别为2、6、10、12周,共8组):实验组大鼠32只,一次性空腹腹腔注射STZ 60 mg/kg,诱导糖尿病大鼠模型;对照组大鼠32只,腹腔注射等体积的枸橼酸缓冲液.分别于糖尿病大鼠成模后第2、6、10、12周两组各取8只,测体重、肾重、空腹血糖、24 h尿白蛋白定量;心内采血,离心取血清,检测血肌酐,空腹血清胰岛素;ELISA方法检测血、尿脂联素浓度.取左肾常规病理组织行糖原染色,在光镜下观察肾脏的病理组织学改变,免疫组化SP法检测肾脏2种受体AdipoR1和AdipoR2表达.结果 (1)实验组6、10、12周大鼠血清和尿脂联素高于对照组,差异有统计学意义(P＜0.01);且血清脂联素与24 h尿白蛋白排泄率、尿脂联素呈正相关(r值分别为0.806、0.696,均P＜0.01);尿脂联素与24 h尿白蛋白定量呈显著正相关(r=0.728,P＜0.01);逐步回归分析提示血清脂联素受24 h尿白蛋白定量影响最大(β=0.806,P＜0.01);(2)免疫组化半定量分析显示,AdipoR1和AdipoR2在正常大鼠肾组织中均有表达,主要分布于肾小管上皮细胞和肾小球内皮细胞.实验组造模成功6周时肾脏组织AdipoR1和AdipoR2表达,与对照组比较表达有所增强(F值分别为11.68、23.20,均P＜0.01),且与血清脂联素呈显著正相关(r值分别为0.666、0.684,均P＜0.01).结论 血清和尿脂联素水平与糖尿病肾病病程和AdipoR呈正相关,推测脂联素通过AdipoR直接作用于肾脏,尤其是作用于肾小管,在1型糖尿病肾脏病变中发挥保护作用.     

脂联素及受体、信号传导通路和相关疾病关系的研究进展

最早在白色脂肪细胞中发脂联素(APN)及其受体(AdipoR),现表明APN、AdipoR也在心肌细胞、骨骼肌细胞、成骨细胞、肾脏足细胞及胎盘、唾液腺上皮、脑垂体等组织中表达。APN与AdipoR结合后通过相应的信号传导途径发挥作用。APN、AdipoR水平下降或其信号传导途径中某一环节出现差错均可能导致胰岛素抵抗、糖尿病、动脉粥样硬化、代谢综合征发生,还可引起营养不良、肝纤维化、心肌梗死后心肌重构、自体骨质破坏、眼-肾-脑综合征疾病。     

Circulating adiponectin and expression of adiponectin receptors in human skeletal muscle: associations with metabolic parameters and insulin resistance and regulation by physical training

CONTEXT: Adiponectin, an adipocyte-secreted hormone, is associated with insulin resistance and the metabolic syndrome. OBJECTIVE: The physiological regulation of circulating adiponectin levels and mRNA expression of its receptors (AdipoR1 and AdipoR2) in skeletal muscle remains to be fully elucidated. DESIGN/PATIENTS: We assessed circulating adiponectin and AdipoR1/R2 mRNA expression in human skeletal muscle in a cross-sectional study of 140 subjects with normal or impaired glucose tolerance or type 2 diabetes. In the context of an interventional study, the same measurements were performed in 60 of these subjects (20/glucose tolerance group) before and after 4 wk of physical training. Finally, we measured these same variables in addition to protein levels of AMP kinase (AMPK), acetyl phosphorylated AMPK, coenzyme A carboxylase, phosphorylated coenzyme A carboxylase, and phosphatidylinositol 3-kinase in muscle before and after 3 h of intensive exercise in a subgroup of five subjects. SETTING: This study was performed at an academic clinical research center. RESULTS: Circulating adiponectin was negatively associated, whereas AdipoR1/R2 mRNA levels were positively associated with obesity, glucose and lipid levels, and insulin resistance. Physical training for 4 wk resulted in increased circulating adiponectin levels and AdipoR1/R2 mRNA expression in muscle. Exercise for 3 h increased AdipoR1/R2 mRNA expression as well as phosphorylation of AMPK and acetyl coenzyme A carboxylase in muscle, but had no effect on circulating adiponectin. CONCLUSIONS: Adiponectin, AdipoR1, and AdipoR2 are all associated with body composition, insulin sensitivity, and metabolic parameters. Physical training increases circulating adiponectin and mRNA expression of its receptors in muscle, which may mediate the improvement of insulin resistance and the metabolic syndrome in response to exercise.     

Adiponectin receptors gene expression and insulin sensitivity in non-diabetic Mexican Americans with or without a family history of Type 2 diabetes

Aims/hypothesis The recent discovery of two adiponectin receptors (AdipoR1 and AdipoR2) will improve our understanding of the molecular mechanisms underlying the insulin-sensitising effect of adiponectin. The aim of this study was to determine for the first time whether skeletal muscle AdipoR1 and/or AdipoR2 gene expression levels are associated with insulin resistance.Methods Using RT-PCR and northern analysis we measured AdipoR1 and AdipoR2 gene expression in skeletal muscle from healthy Mexican Americans with normal glucose tolerance who had (n=8) or did not have (n=10) a family history of Type 2 diabetes.Results Gene expression profiling indicated that the AdipoR1 and AdipoR2 isoforms are highly expressed in human skeletal muscle, unlike in mice where AdipoR2 expression was highest in the liver, and AdipoR1 was highest in skeletal muscle. In the study subjects, the expression levels of AdipoR1 (p=0.004) and AdipoR2 (p=0.04), as well as plasma adiponectin concentration (p=0.03) were lower in people with a family history of Type 2 diabetes than in those with no family history of the disease. Importantly, the expression levels of both receptors correlated positively with insulin sensitivity (r=0.64, p=0.004 and r=0.47, p=0.048 respectively).Conclusions/interpretation Collectively, these data indicate that both isoforms of the adiponectin receptor play a role in the insulin-sensitising effect of adiponectin.Abbreviations AdipoR1 adiponectin receptor-1 - AdipoR2 adiponectin receptor-2 - AMKP adenosine 5-monophosphate-activated protein kinase - FH+ with a family history of Type 2 diabetes - FH– with no family history of Type 2 diabetes - PPAR- peroxisome proliferator-activated receptor-     

Adiponectin receptors: expression in Zucker diabetic rats and effects of fenofibrate and metformin

The insulin-sensitizing adipokine, adiponectin, acts through 2 receptors, AdipoR1 and AdipoR2. A decreased expression of these receptors could contribute to insulin resistance and diabetes. We determined if the expression of adiponectin receptors is decreased in an experimental model, the Zucker diabetic rat (ZDF), and if a peroxisome proliferator-activated receptor alpha agonist, fenofibrate, and metformin could increase these expressions. The ZDF and control (L) rats were studied at 7, 14, and 21 weeks. After initial study at 7 weeks, ZDF received no treatment (n = 10), metformin (n = 10), or fenofibrate (n = 10) until final studies at 14 or 21 weeks. The L rats received no treatment. AdipoR1 and R2 expressions were measured in liver, muscle, and white adipose tissue (WAT). As expected, ZDF rats were insulin resistant at 7 weeks, had type 2 diabetes mellitus at 14 weeks, and had diabetes with insulin deficiency at 21 weeks. Compared with L rats, AdipoRs messenger RNA was decreased only in the WAT (P < .05) of 7-week-old ZDF rats, but was unchanged in muscle and increased in liver. Metformin and fenofibrate decreased plasma triacylglycerols (P < .01) as expected. The only effect of fenofibrate on AdipoRs was a moderate increase (P < .01) of both receptors' messenger RNA in liver. Metformin increased AdipoR1 and R2 expression in muscle (P < .01) and AdipoR1 (P < .01) in WAT. These results do not support an important role for decreased AdipoRs expression in the development of insulin resistance and diabetes. Parts of the actions of fenofibrate and of metformin could be mediated by a stimulation of the expression of these receptors in liver and in insulin-sensitive, glucose-utilizing tissues (muscle, WAT), respectively.     

Adiponectin and adiponectin receptors

Metabolic syndrome is thought to result from obesity and obesity-linked insulin resistance. Obesity in adulthood is characterized by adipocyte hypertrophy. Adipose tissue participates in the regulation of energy homeostasis as an important endocrine organ that secretes a number of biologically active "adipokines."Heterozygous peroxisome proliferator-activated receptor-gamma knockout mice were protected from high-fat diet induced obesity, adipocyte hypertrophy, and insulin resistance. Systematic gene profiling analysis of these mice revealed that adiponectin/Acrp30 was overexpressed. Functional analyses including generation of adiponectin transgenic or knockout mice have revealed that adiponectin serves as an insulin-sensitizing adipokine. In fact, obesity-linked down-regulation of adiponectin was a mechanism whereby obesity could cause insulin resistance and diabetes. Recently, we have cloned adiponectin receptors in the skeletal muscle (AdipoR1) and liver (AdipoR2), which appear to comprise a novel cell-surface receptor family. We showed that AdipoR1 and AdipoR2 serve as receptors for globular and full-length adiponectin and mediate increased AMP-activated protein kinase, peroxisome proliferator-activated receptor-alpha ligand activities, and glucose uptake and fatty-acid oxidation by adiponectin. Obesity decreased expression levels of AdipoR1/R2, thereby reducing adiponectin sensitivity, which finally leads to insulin resistance, the so-called "vicious cycle." Most recently, we showed that osmotin, which is a ligand for the yeast homolog of AdipoR (PHO36), activated AMPK via AdipoR in C2C12 myocytes. This may facilitate efficient development of adiponectin receptor agonists. Adiponectin receptor agonists and adiponectin sensitizers should serve as versatile treatment strategies for obesity-linked diseases such as diabetes and metabolic syndrome.     

A potential role for skeletal muscle caveolin-1 as an insulin sensitivity modulator in ageing-dependent non-obese type 2 diabetes: studies in a new mouse model

Aims/hypothesis Type 2 diabetes mellitus is a common age-dependent disease. We discovered that male offspring of non-diabetic C57BL/6 and DBA/2 mice, called JYD mice, develop type 2 diabetes when they grow old. JYD mice show characteristics of insulin resistance, hyperglycaemia and hyperinsulinaemia in old age without obesity. We postulated that the mechanism of age-dependent type 2 diabetes in this model relates to caveolin-1 status in skeletal muscle, which appears to regulate insulin sensitivity in the mice. Methods We compared insulin sensitivity in aged C57BL/6 and JYD mice using glucose and insulin tolerance tests and ¹⁸F-fluorodeoxyglucose positron emission tomography. We also determined insulin signalling molecules and caveolin proteins using western blotting, and altered caveolin-1 levels in skeletal muscle of C57BL/6 and JYD mice using viral vector systems, to examine the effect of this on insulin sensitivity. Results In 30-week-old C57BL/6 and JYD mice, the basal levels of IRS-1, Akt and peroxisome proliferator-activated receptor-γ decreased, as did insulin-stimulated phosphorylation of Akt and insulin receptor β. However, caveolin-1 was only increased about twofold in 30-week-old JYD mice as compared with 3-week-old mice, whereas an eightfold increase was seen in C57BL/6 mice. Downregulation of caveolin-1 production in C57BL/6 mice caused severe impairment of glucose and insulin tolerance. Upregulation of caveolin-1 in aged diabetic JYD mice significantly improved insulin sensitivity with a concomitant increase of glucose uptake in the skeletal muscle. Conclusions/interpretation The level of skeletal muscle caveolin-1 is correlated with the progression of age-dependent type 2 diabetes in JYD mice. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorised users. Y. S. Oh and L.-Y. Khil contributed equally to this study. J.-W. Yoon passed away on 6 April 2006.     

Adiponectin--a key adipokine in the metabolic syndrome

Adiponectin is a recently described adipokine that has been recognized as a key regulator of insulin sensitivity and tissue inflammation. It is produced by adipose tissue (white and brown) and circulates in the blood at very high concentrations. It has direct actions in liver, skeletal muscle and the vasculature, with prominent roles to improve hepatic insulin sensitivity, increase fuel oxidation [via up-regulation of adenosine monophosphate-activated protein kinase (AMPK) activity] and decrease vascular inflammation. Adiponectin exists in the circulation as varying molecular weight forms, produced by multimerization. Recent data indicate that the high-molecular weight (HMW) complexes have the predominant action in the liver. In contrast to other adipokines, adiponectin secretion and circulating levels are inversely proportional to body fat content. Levels are further reduced in subjects with diabetes and coronary artery disease. Adiponectin antagonizes many effects of tumour necrosis factor-alpha(TNF-alpha) and this, in turn, suppresses adiponectin production. Furthermore, adiponectin secretion from adipocytes is enhanced by thiazolidinediones (which also act to antagonize TNF-alpha effects). Thus, adiponectin may be the common mechanism by which TNF-alpha promotes, and the thiazolidinediones suppress, insulin resistance and inflammation. Two adiponectin receptors, termed AdipoR1 and AdipoR2, have been identified and these are ubiquitously expressed. AdipoR1 is most highly expressed in skeletal muscle and has a prominent action to activate AMPK, and hence promote lipid oxidation. AdipoR2 is most highly expressed in liver, where it enhances insulin sensitivity and reduces steatosis via activation of AMPK and increased peroxisome-proliferator-activated receptor alpha ligand activity. T-cadherin, which is expressed in endothelium and smooth muscle, has been identified as an adiponectin-binding protein with preference for HMW adiponectin multimers. Given the low levels of adiponectin in subjects with the metabolic syndrome, and the beneficial effect of the adipokine in animal studies, there is exciting potential for adiponectin replacement therapy in insulin resistance and related disorders.     

Skeletal muscle neuronal nitric oxide synthase micro protein is reduced in people with impaired glucose homeostasis and is not normalized by exercise training

Skeletal muscle inducible nitric oxide synthase (NOS) protein is greatly elevated in people with type 2 diabetes mellitus, whereas endothelial NOS is at normal levels. Diabetic rat studies suggest that skeletal muscle neuronal NOS (nNOS) micro protein expression may be reduced in human insulin resistance. The aim of this study was to determine whether skeletal muscle nNOSmicro protein expression is reduced in people with impaired glucose homeostasis and whether exercise training increases nNOSmicro protein expression in these individuals because exercise training increases skeletal muscle nNOSmicro protein in rats. Seven people with type 2 diabetes mellitus or prediabetes (impaired fasting glucose and/or impaired glucose tolerance) and 7 matched (sex, age, fitness, body mass index, blood pressure, lipid profile) healthy controls aged 36 to 60 years participated in this study. Vastus lateralis muscle biopsies for nNOSmicro protein determination were obtained, aerobic fitness was measured (peak pulmonary oxygen uptake [Vo(2) peak]), and glucose tolerance and insulin homeostasis were assessed before and after 1 and 4 weeks of cycling exercise training (60% Vo(2) peak, 50 minutes x 5 d wk(-1)). Skeletal muscle nNOSmicro protein was significantly lower (by 32%) in subjects with type 2 diabetes mellitus or prediabetes compared with that in controls before training (17.7 +/- 1.2 vs 26.2 +/- 3.4 arbitrary units, P < .05). The Vo(2) peak and indicators of insulin sensitivity improved with exercise training in both groups (P < .05), but there was no effect of exercise training on skeletal muscle nNOSmicro protein in either group. In conclusion, individuals with impaired glucose homeostasis have reduced skeletal muscle nNOSmicro protein content. However, because exercise training improves insulin sensitivity without influencing skeletal muscle nNOSmicro protein expression, it seems that changes in skeletal muscle nNOSmicro protein are not central to the control of insulin sensitivity in humans and therefore may be a consequence rather than a cause of diabetes.     

Adiponectin receptor gene expression in human skeletal muscle cells is not regulated by fibrates and thiazolidinediones

BACKGROUND: Thiazolidinediones as PPARgamma agonists and fibrates as PPARalpha agonists improve insulin sensitivity in insulin-responsive tissues. Recent data show an induction of adiponectin receptor 2 (AdipoR2) by PPARalpha and PPARgamma agonists in human macrophages. OBJECTIVE: In this study, we examined the effects of thiazolidinediones and fibrates on the expression of adiponectin receptors in human skeletal muscle cells, an important cell type in the context of insulin resistance. RESULTS AND METHODS: In vitro differentiated human myotubes treated with troglitazone or rosiglitazone (20 h) showed no significant changes in AdipoR1 and AdipoR2 mRNA expression. PPARgamma activation was controlled by determination of PPARgamma mRNA induction. Likewise, differentiated myotubes treated with Wy-14,643 or fenofibrate (20 h) revealed no significant regulation of AdipoR1 and AdipoR2 mRNA. PPARalpha activation was assessed by measuring PDHK4 mRNA expression. CONCLUSION: Induction of AdipoR gene expression in human skeletal muscle cells is not involved in the insulin-sensitizing effects of thiazolidinediones or fibrates.     

Adiponectin, skeletal muscle adiponectin receptor expression and insulin resistance following dexamethasone

Objective Skeletal muscle is a major site of adiponectin action and of glucocorticoid‐induced insulin resistance. Little human data exist however, regarding the impact of exogenous glucocorticoids on adiponectin receptors in skeletal muscle. Design and patients Twelve subjects with type 2 diabetes and 12 controls underwent blood sampling and muscle biopsy of vastus lateralis before and after 4 days of 4 mg dexamethasone. Measurements (i) Total and high molecular weight (HMW) plasma adiponectin, glucose and insulin; (ii) Skeletal muscle adiponectin receptor AdipoR1 and AdipoR2 mRNA levels by quantitative real time RT‐PCR. Results Baseline total adiponectin (8·0 ± 0·89 vs. 12·5 ± 1·46 µg/ml, P = 0·013), HMW adiponectin (2·8 ± 0·44 vs. 5·9 ± 1·04 µg/ml, P = 0·014) and AdipoR2 mRNA levels (mean ΔC_T 14·71 ± 0·35 vs. 13·37 ± 0·28, P = 0·017) were significantly lower in diabetic subjects. After dexamethasone, AdipoR2 mRNA fell in the controls but there was no change in the diabetic group, while there was a significant increase in total (P = 0·002) and HMW adiponectin (P < 0·001) across both groups. Total and HMW plasma adiponectin correlated with clinical and biochemical measures of insulin sensitivity. However following dexamethasone which increased insulin resistance, the relationship between adiponectin and the biochemical measures was lost. Conclusions Plasma adiponectin and skeletal muscle AdipoR2 mRNA expression are reduced in subjects with diabetes; both are likely to contribute to the observed insulin resistance. Dexamethasone inhibits AdipoR2 mRNA expression in nondiabetic subjects, while there is a small rise in plasma adiponectin levels. The close relationship between plasma adiponectin and biochemical measures of insulin sensitivity is lost in the setting of glucocorticoid‐induced insulin resistance.