Adipose-selective targeting of the GLUT4 gene impairs insulin action in muscle and liver

The earliest defect in developing type 2 diabetes is insulin resistance, characterized by decreased glucose transport and metabolism in muscle and adipocytes. The glucose transporter GLUT4 mediates insulin-stimulated glucose uptake in adipocytes and muscle by rapidly moving from intracellular storage sites to the plasma membrane. In insulin-resistant states such as obesity and type 2 diabetes, GLUT4 expression is decreased in adipose tissue but preserved in muscle. Because skeletal muscle is the main site of insulin-stimulated glucose uptake, the role of adipose tissue GLUT4 downregulation in the pathogenesis of insulin resistance and diabetes is unclear. To determine the role of adipose GLUT4 in glucose homeostasis, we used Cre/loxP DNA recombination to generate mice with adipose-selective reduction of GLUT4 (G4A-/-). Here we show that these mice have normal growth and adipose mass despite markedly impaired insulin-stimulated glucose uptake in adipocytes. Although GLUT4 expression is preserved in muscle, these mice develop insulin resistance in muscle and liver, manifested by decreased biological responses and impaired activation of phosphoinositide-3-OH kinase. G4A-/- mice develop glucose intolerance and hyperinsulinaemia. Thus, downregulation of GLUT4 and glucose transport selectively in adipose tissue can cause insulin resistance and thereby increase the risk of developing diabetes.     

胰岛素抵抗及高血糖对GFAT活性的影响

分别观察了胰岛素抵抗和高血糖水平对己糖胺途径限速酶GFAT活性的影响.在alloxan高血糖小鼠模型中,与正常对照组比较,血清果糖胺水平升高了15.9%,肾组织GFAT活性升高了32.8%;经胰岛素治疗后,血清果糖胺水平降低了9.7%,其肾组织GFAT活性也降低了l9.4%.在高糖高脂饲料诱导的胰岛素抵抗的IR小鼠中,与同批正常对照组比较,正糖钳实验中稳态时葡萄糖输注率G IR值降低了69.3%,胰岛素耐量实验中的AUC值升高了38.1%,其肾脏组织GFAT活性也增加了26.6%.在胰岛素诱导的具有胰岛素抵抗的IR-H IR c细胞模型中,与正常H IR c细胞比较,其10、25 nmol/L胰岛素诱导的葡萄糖摄取能力分别降低了25.3%、21.1%,而GFAT活性分别增加了29.7%、46.5%.可见,GFAT活性与一段时间的平均血糖水平和胰岛素抵抗状态密切正相关.     

Serum retinol binding protein 4 contributes to insulin resistance in obesity and type 2 diabetes

In obesity and type 2 diabetes, expression of the GLUT4 glucose transporter is decreased selectively in adipocytes. Adipose-specific Glut4 (also known as Slc2a4) knockout (adipose-Glut4(-/-)) mice show insulin resistance secondarily in muscle and liver. Here we show, using DNA arrays, that expression of retinol binding protein-4 (RBP4) is elevated in adipose tissue of adipose-Glut4(-/-) mice. We show that serum RBP4 levels are elevated in insulin-resistant mice and humans with obesity and type 2 diabetes. RBP4 levels are normalized by rosiglitazone, an insulin-sensitizing drug. Transgenic overexpression of human RBP4 or injection of recombinant RBP4 in normal mice causes insulin resistance. Conversely, genetic deletion of Rbp4 enhances insulin sensitivity. Fenretinide, a synthetic retinoid that increases urinary excretion of RBP4, normalizes serum RBP4 levels and improves insulin resistance and glucose intolerance in mice with obesity induced by a high-fat diet. Increasing serum RBP4 induces hepatic expression of the gluconeogenic enzyme phosphoenolpyruvate carboxykinase (PEPCK) and impairs insulin signalling in muscle. Thus, RBP4 is an adipocyte-derived 'signal' that may contribute to the pathogenesis of type 2 diabetes. Lowering RBP4 could be a new strategy for treating type 2 diabetes.     

Reactive oxygen species have a causal role in multiple forms of insulin resistance

Insulin resistance is a cardinal feature of type 2 diabetes and is characteristic of a wide range of other clinical and experimental settings. Little is known about why insulin resistance occurs in so many contexts. Do the various insults that trigger insulin resistance act through a common mechanism? Or, as has been suggested, do they use distinct cellular pathways? Here we report a genomic analysis of two cellular models of insulin resistance, one induced by treatment with the cytokine tumour-necrosis factor-alpha and the other with the glucocorticoid dexamethasone. Gene expression analysis suggests that reactive oxygen species (ROS) levels are increased in both models, and we confirmed this through measures of cellular redox state. ROS have previously been proposed to be involved in insulin resistance, although evidence for a causal role has been scant. We tested this hypothesis in cell culture using six treatments designed to alter ROS levels, including two small molecules and four transgenes; all ameliorated insulin resistance to varying degrees. One of these treatments was tested in obese, insulin-resistant mice and was shown to improve insulin sensitivity and glucose homeostasis. Together, our findings suggest that increased ROS levels are an important trigger for insulin resistance in numerous settings.     

Phosphorylation of the glucose transporter in vitro and in vivo by protein kinase C

The Ca2+- and phospholipid-dependent protein kinase (protein kinase C) is present in many mammalian tissues, and its important physiological protein substrates are only now beginning to be identified. A useful advance in identifying these intracellular substrates has been the recognition that the kinase is the receptor for phorbol esters, which stimulate phosphotransferase activity. Phorbol ester-induced changes in protein phosphorylation in intact cells may thus be taken, in part, as a probable indication of protein kinase C activation. The many cellular effects of phorbol esters include the stimulation of glucose uptake, although the response of glucose uptake to phorbol esters appears to be complex, apparently varying in response time and requirement for protein synthesis. Such observations prompted us to explore one possible explanation for the alteration of glucose uptake, namely, phosphorylation of the glucose transporter by protein kinase C. We report here that incubation of purified human erythrocyte glucose transporter with rat brain protein kinase C results in the phosphorylation of a protein of relative molecular mass (Mr) 50,000-60,000 which has subsequently been identified as the glucose transporter by specific immunoprecipitation with a monoclonal antibody. Immunoprecipitation of membrane proteins from 32P-labelled human erythrocytes revealed a phorbol ester-stimulated phosphorylation of the transporter. This covalent modification of the glucose transporter may thus, in part, underlie the ability of phorbol esters and certain hormones to stimulate glucose uptake.     

Decreased expression of the insulin-responsive glucose transporter in diabetes and fasting

Cellular resistance to insulin caused by a reduction in insulin-mediated glucose uptake can be produced in rats by chemically inducing diabetes with streptozotocin and by fasting. Two glucose transporter isoforms are expressed in fat cells: (1) the insulin-responsive species which is found only in fat and muscle, and (2) a species corresponding to the erythrocyte/Hep G2/rat brain transporter. We show here that fat cells isolated from streptozotocin diabetic rats and from fasted rats show a significant (60-80%) decrease in the amount of immunologically detectable insulin-sensitive glucose transporter and no change in the level of the Hep G2/rat brain transporter. Administration of insulin and refeeding, respectively, result in a return of the insulin-sensitive glucose transporter to levels that are normal or slightly above normal. Thus, peripheral tissue insulin resistance could be due to the specific reduction in the amount of insulin-sensitive glucose transporter.     

罗格列酮对老年2型糖尿病合并高血压患者血压的影响

目的:观察胰岛素增敏剂罗格列酮用于老年2型糖尿病合并高血压的患者时,降低血浆胰岛素水平以及改善胰岛素敏感性后对血压的影响。方法:23例老年2型糖尿病合并高血压患者口服罗格列酮(文迪雅)4mg～8mg,1次/日。治疗前后测定BMI、血压、HbA_(1C)、FBG、PBG、FINS、PINS,并按HOMA模型计算胰岛素抵抗指数、胰岛素分泌指数和药物的不良反应。结果:(1)罗格列酮治疗12周后,BMI治疗前后比较无显著性差异;血压治疗后明显下降,降压幅度达(6.75±0.03)/(7.25±0.53)mmHg,与治疗前比较有显著性差异。(2)治疗后HbA_(1C)、FBG、PBG、FINS、PINS均明显下降,治疗前后比较有显著性差异。(3)治疗后HOMA-IR下降,IAI升高,与治疗前比较有显著性差异,FINS/FBG无显著性差异。(4)我国老年患者使用罗格列酮的安全性及耐受性较好。结论:罗格列酮治疗中国老年2型糖尿病患者,能降低血浆胰岛素水平,改善IR,显著降低收缩压和舒张压;且其安全性、耐受性均较好。     

山楂叶总黄酮防治大鼠胰岛素抵抗及脂肪肝的实验研究

观察山楂叶总黄酮(FHB)对胰岛素抵抗大鼠高血脂、氧化损伤及脂肪肝的防治作用,并对山楂叶总黄酮增强胰岛素敏感性和防治脂肪肝的作用机理进行初步探讨.高糖高脂饲料建立胰岛素抵抗大鼠模型,分为正常组、模型组、FHB组和阳性药物对照文迪雅组.12周末观察FHB对血清血糖、血脂、血清胰岛素含量、脂质过氧化和肝功能等的影响.结果表明,FHB组和模型组比较可以显著降低胰岛素抵抗大鼠血清FFA和TG水平,提高HDL-C水平;降低ALT和AST活性,降低肝指数,防止肝脏组织脂肪性病变,同时,明显提高总抗氧化能力和肝脏组织中SOD活性,降低MDA含量.由此得出结论,FHB对胰岛素抵抗大鼠高血脂和氧化损伤起到了良好的防治作用,能够改善病鼠胰岛素抵抗状态,增强其胰岛素敏感性,并具有良好的防治脂肪肝作用.     

Mechanisms linking obesity to insulin resistance and type 2 diabetes

Obesity is associated with an increased risk of developing insulin resistance and type 2 diabetes. In obese individuals, adipose tissue releases increased amounts of non-esterified fatty acids, glycerol, hormones, pro-inflammatory cytokines and other factors that are involved in the development of insulin resistance. When insulin resistance is accompanied by dysfunction of pancreatic islet beta-cells - the cells that release insulin - failure to control blood glucose levels results. Abnormalities in beta-cell function are therefore critical in defining the risk and development of type 2 diabetes. This knowledge is fostering exploration of the molecular and genetic basis of the disease and new approaches to its treatment and prevention.     

胰岛素瘤切除术后对血清激素、癌胚抗原水平及胰岛功能的影响

 探究了胰岛素瘤切除术前后患者血清激素、癌胚抗原（carcinoembryonic antigen，CEA）及胰岛功能指标水平变化，发现术后1 d患者胰岛β细胞功能指数（homeostasis model assess-ment-β，HOMA-β）、胰岛素敏感性指数（insulin sensitivity index，ISI）降低，胰岛素抵抗指数（homeostasis model assessment of insulin resistance，HOMA-IR）及血糖水平升高，CEA水平先增后降，差异有统计学意义（P<0.05）；与术后5 d相比，术后10 d及15 d患者HOMA-β、ISI水平升高，HOMA-IR水平降低；术后15 d胰岛素水平为（14.16±3.06）μU/L，但显著低于术前（32.07±5.75）μU/L，血糖水平降至（4.62±0.31）mmol/L，显著高于术前（2.12±0.59）mmol/L，术后1 d患者CEA水平高于术前，随后逐渐降低，差异有统计学意义（P>0.05）。CEA水平与各指标显著相关。胰岛功能指标、血清激素及CEA水平术后短时间内可引起胰岛素水平的异常降低和血糖水平的急剧升高，可作为预后指标。     

Insulin signalling and the regulation of glucose and lipid metabolism.

The epidemic of type 2 diabetes and impaired glucose tolerance is one of the main causes of morbidity and mortality worldwide. In both disorders, tissues such as muscle, fat and liver become less responsive or resistant to insulin. This state is also linked to other common health problems, such as obesity, polycystic ovarian disease, hyperlipidaemia, hypertension and atherosclerosis. The pathophysiology of insulin resistance involves a complex network of signalling pathways, activated by the insulin receptor, which regulates intermediary metabolism and its organization in cells. But recent studies have shown that numerous other hormones and signalling events attenuate insulin action, and are important in type 2 diabetes.     

Macrophage-specific PPARgamma controls alternative activation and improves insulin resistance

Obesity and insulin resistance, the cardinal features of metabolic syndrome, are closely associated with a state of low-grade inflammation. In adipose tissue chronic overnutrition leads to macrophage infiltration, resulting in local inflammation that potentiates insulin resistance. For instance, transgenic expression of Mcp1 (also known as chemokine ligand 2, Ccl2) in adipose tissue increases macrophage infiltration, inflammation and insulin resistance. Conversely, disruption of Mcp1 or its receptor Ccr2 impairs migration of macrophages into adipose tissue, thereby lowering adipose tissue inflammation and improving insulin sensitivity. These findings together suggest a correlation between macrophage content in adipose tissue and insulin resistance. However, resident macrophages in tissues display tremendous heterogeneity in their activities and functions, primarily reflecting their local metabolic and immune microenvironment. While Mcp1 directs recruitment of pro-inflammatory classically activated macrophages to sites of tissue damage, resident macrophages, such as those present in the adipose tissue of lean mice, display the alternatively activated phenotype. Despite their higher capacity to repair tissue, the precise role of alternatively activated macrophages in obesity-induced insulin resistance remains unknown. Using mice with macrophage-specific deletion of the peroxisome proliferator activated receptor-gamma (PPARgamma), we show here that PPARgamma is required for maturation of alternatively activated macrophages. Disruption of PPARgamma in myeloid cells impairs alternative macrophage activation, and predisposes these animals to development of diet-induced obesity, insulin resistance, and glucose intolerance. Furthermore, gene expression profiling revealed that downregulation of oxidative phosphorylation gene expression in skeletal muscle and liver leads to decreased insulin sensitivity in these tissues. Together, our findings suggest that resident alternatively activated macrophages have a beneficial role in regulating nutrient homeostasis and suggest that macrophage polarization towards the alternative state might be a useful strategy for treating type 2 diabetes.     

多囊卵巢综合征诊断指标与雌激素代谢的关系

探讨多囊卵巢综合征(PCOS)Rotterdam标准的不同诊断指标与我国患者雌激素合成以及糖代谢之间的关系.对8例对照、PCOS患者的17例多囊组(PCO组)、14例高雄组(OHA组)和21例复合组(PCOS组)妇女行卵巢兴奋试验(hMGl50IU hCG 5000IU),分别观察睾酮和雌二醇的血浓度变化,并计算芳香化酶功能指标和代谢指标.与对照组比较,PCOS三组均有雌二醇合成亢进,但程度有差异,芳香化酶状态以OHA组最高.三组患者的雌激素水平较正常对照组高,而且hMG刺激后均升高,但不同组的患者hMG刺激后雌激素升高的程度不同.雌激素过多升高导致FSH下降可能是PCOS卵泡发育停滞不排卵的一个因素.     

New drug targets for type 2 diabetes and the metabolic syndrome.

An insidious increase in features of the 'metabolic syndrome' - obesity, insulin resistance and dyslipidaemia -- has conspired to produce a worldwide epidemic of type 2 insulin-resistant diabetes mellitus. Most current therapies for this disease were developed in the absence of defined molecular targets or an understanding of disease pathogenesis. Emerging knowledge of key pathogenic mechanisms, such as the impairment of glucose-stimulated insulin secretion and the role of 'lipotoxicity' as a probable cause of hepatic and muscle resistance to insulin's effects on glucose metabolism, has led to a host of new molecular drug targets. Several have been validated through genetic engineering in mice or the preliminary use of lead compounds and therapeutic agents in animals and humans.     

不同糖耐量人群尿C肽肌酐比值与胰岛β细胞功能和胰岛素抵抗的关系研究

目的探讨不同糖耐量人群尿C肽肌酐比值与胰岛β细胞功能和胰岛素抵抗的关系.方法选取内分泌科就诊患者,根据75 g葡萄糖耐量检查结果分为正常糖耐量组72例,糖调节受损组54例,Ⅱ型糖尿病组94例.行静脉葡萄糖耐量实验,检测0~10 min胰岛素水平,计算急性胰岛素反应(AIR3-5)、0~10 min胰岛素曲线下面积(AUC)、稳态模型胰岛素抵抗指数(HOMA-IR)、胰岛β细胞功能指数(HOMA-β);留取受试者清晨空腹第1次、第2次尿液样和24 h尿样本,酶法检测尿肌酐值,化学发光法检测C肽水平,计算C肽肌酐比值.结果糖调节受损组、Ⅱ型糖尿病组空腹血糖、餐后2 h血糖、空腹胰岛素、餐后2 h胰岛素、糖化血红蛋白、HOMA-IR均明显高于正常糖耐量组,差异具有统计学意义(P0.05);而肾小球滤过率在3组间差异无统计学意义(P0.05).糖调节受损组、Ⅱ型糖尿病组AIR3-5、AUC、HOMA-β、第1次尿C肽肌酐比值、第2次尿C肽肌酐比值、24 h尿C肽明显高于正常糖耐量组,差异具有统计学意义(P0.05).第1次和第2次尿C肽/尿肌酐比值与AIR3-5,AUC,HOMA-β呈负相关,与HOMA-IR呈正相关,其中以第2次C肽尿肌酐比值相关性最佳.结论尿C肽肌酐比值在Ⅱ型糖尿病及糖调节受损个体中明显升高,且与胰岛β细胞第一时相分泌功能、胰岛素抵抗有直接相关性.     

2型糖尿病伴随高脂血症大鼠模型的建立及二甲双胍的干预

目的研究5%蔗糖饮水和高脂饮食加链脲佐菌素诱导2型糖尿病伴随高脂血症大鼠模型的建立及二甲双胍的治疗作用。方法SD大鼠一次性腹腔注射30 mg/kg链脲佐菌素,给予高脂饮食和5%蔗糖水喂养68 d后进行糖耐量实验,采血检测空腹血糖、血脂、胰岛素、抗氧化水平。结果与对照组比较,模型大鼠空腹血糖、糖耐量试验2 h后血糖、糖化血红蛋白、血清胰岛素和胰岛素抵抗指数显著升高(P<0.05),胰岛素敏感指数显著降低(P<0.05),TG、TC和FFA含量明显升高(P<0.05),SOD活力明显降低(P<0.05),MDA含量显著增加(P<0.05);二甲双胍组胆固醇、游离脂肪酸、空腹血糖、糖耐量异常、糖化血红蛋白、血清胰岛素和胰岛素抵抗指数、MDA显著降低(P<0.05),胰岛素敏感指数和SOD活力显著提高(P<0.05)。结论5%蔗糖饮水能改善大鼠的厌食症状,加上链脲佐菌素的小剂量注射和高脂饮食,可成功复制2型糖尿病大鼠模型,伴随高脂血症和抗氧化损伤。二甲双胍具有降糖、降脂、抗氧化、改善胰岛素抵抗作用,可作为2型糖尿病伴随高脂血症大鼠模型研究的阳性治疗药物。     

补肾活血颗粒对多囊卵巢综合征大鼠血清性激素水平、 血糖及胰岛素的影响

目的 观察补肾活血颗粒对多囊卵巢综合征（PCOS）模型大鼠血清性激素水平、血糖及胰岛素的影响。方法 采用颈背部皮下注射脱氢表雄酮（DHEA）造模法建立PCOS大鼠模型,将72只雌性SD大鼠随机分为正常对照组、模型组、二甲双胍组、中药高剂量组、中药中剂量组、中药低剂量组,每组12只,各组给予相应药物连续灌胃 20 d,用酶联免疫吸附测定法测定血清17-羟孕酮（17-OHP）、促黄体生成素（LH）、睾酮（T）、促卵泡素（FSH）、空腹 血糖（FPG）及胰岛素（INS）水平。结果模型组血清中17-OHP、LH、T、FSH、FPG、INS水平明显高于正常对照组 (P<0.01 ,P<0. 05 ),中药高剂量组降低大鼠血清LH、T、FSH及INS水平最为明显(P<0.01),二甲双胍组、中药中剂量组显著降低FPG（P<0. 01）,中药各治疗组均能降低17-OHP（P<0. 05）。结论 补肾活血颗粒能对PCOS 大鼠有一定的治疗作用,可改善激素水平、血糖及胰岛素的异常     

基因芯片研究小檗碱对胰岛素抵抗卵巢颗粒细胞基因表达的影响

应用基因芯片技术研究小檗碱对胰岛素抵抗卵巢颗粒细胞基因表达谱的影响。方法采用胰岛素信号转导通路调节糖代谢的关键分子——PI-3K的特异性阻断剂沃漫青霉素作用于猪卵巢颗粒细胞,人工诱导胰岛素抵抗(IR)的细胞模型;同时应用小檗碱作用在细胞模型上,作用48h后提取细胞总RNA,应用猪全基因组单通道芯片对样本基因进行筛查,得出差异表达基因数据并进行分析。结果显示,中药小檗碱作用模型细胞后差异表达基因42个。差异表达基因主要涉及的功能有:物质代谢、炎症与免疫反应、信号转导等。由此可得出结论:小檗碱可通过多种途径在基因水平上对胰岛素抵抗卵巢颗粒细胞起作用。