Calcineurin/NFAT signalling regulates pancreatic beta-cell growth and function

The growth and function of organs such as pancreatic islets adapt to meet physiological challenges and maintain metabolic balance, but the mechanisms controlling these facultative responses are unclear. Diabetes in patients treated with calcineurin inhibitors such as cyclosporin A indicates that calcineurin/nuclear factor of activated T-cells (NFAT) signalling might control adaptive islet responses, but the roles of this pathway in beta-cells in vivo are not understood. Here we show that mice with a beta-cell-specific deletion of the calcineurin phosphatase regulatory subunit, calcineurin b1 (Cnb1), develop age-dependent diabetes characterized by decreased beta-cell proliferation and mass, reduced pancreatic insulin content and hypoinsulinaemia. Moreover, beta-cells lacking Cnb1 have a reduced expression of established regulators of beta-cell proliferation. Conditional expression of active NFATc1 in Cnb1-deficient beta-cells rescues these defects and prevents diabetes. In normal adult beta-cells, conditional NFAT activation promotes the expression of cell-cycle regulators and increases beta-cell proliferation and mass, resulting in hyperinsulinaemia. Conditional NFAT activation also induces the expression of genes critical for beta-cell endocrine function, including all six genes mutated in hereditary forms of monogenic type 2 diabetes. Thus, calcineurin/NFAT signalling regulates multiple factors that control growth and hallmark beta-cell functions, revealing unique models for the pathogenesis and therapy of diabetes.     

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.     

Autoimmune diabetes as a consequence of locally produced interleukin-2.

During cell differentiation in the thymus, self-reactive T cells can be generated. The majority of these seem to be deleted after intrathymic encounter with the relevant autoantigen. As all self antigens are unlikely to be present in the thymus, some autoreactive T cells may escape censorship. Here we study the fate of these cells using transgenic mice expressing the class I molecule H-2Kb (Kb) in the insulin-producing beta-cells of the pancreas. These mice were crossed with mice transgenic for genes encoding a Kb-specific T-cell antigen receptor (TCR) which could be detected using a clonotype-specific monoclonal antibody. Although T cells expressing the highest level of transgenic TCR were deleted intrathymically in double-transgenic mice, Kb-specific T cells were detected in the periphery. These cells caused the rejection of Kb-expressing skin grafts, but ignored islet Kb antigens even after priming. But when double-transgenic mice were crossed with transgenic mice expressing the lymphokine interleukin-2 in the pancreatic beta-cells, there was a rapid onset of diabetes. These results indicate that autoreactive T cells that ignore self antigens may cause autoimmune diabetes when provided with exogenous 'help' in the form of interleukin-2.     

T-cell clones from a type-1 diabetes patient respond to insulin secretory granule proteins

T LYMPHOCYTES reactive to pancreatic beta-cells are thought to have a central role in the autoimmune process leading to type 1 (insulin-dependent) diabetes, but the molecular targets of these T cells have not yet been defined. As identification of such antigens may enable measures to be developed to prevent the disease, we have characterized an antigen that is recognized by insulinoma membrane-reactive T-cell clones established from a newly diagnosed type-1 diabetes patient. Subcellular fractionation studies using rat insulinoma indicate that the antigenic determinant recognized by one of these clones is an integral membrane component of the insulin secretory granule. After a 5,000-fold purification, we have defined the antigen as a monomer of relative molecular mass 38,000. As granular membrane proteins are transiently exposed on the cell surface during exocytosis, their accessibility to components of the immune system may be a function of the secretory activity of beta-cells.     

Attenuation of FGF signalling in mouse beta-cells leads to diabetes

Fibroblast growth factor (FGF) signalling has been implicated in patterning, proliferation and cell differentiation in many organs, including the developing pancreas. Here we show that the FGF receptors (FGFRs) 1 and 2, together with the ligands FGF1, FGF2, FGF4, FGF5, FGF7 and FGF10, are expressed in adult mouse beta-cells, indicating that FGF signalling may have a role in differentiated beta-cells. When we perturbed signalling by expressing dominant-negative forms of the receptors, FGFR1c and FGFR2b, in the pancreas, we found that that mice with attenuated FGFR1c signalling, but not those with reduced FGFR2b signalling, develop diabetes with age and exhibit a decreased number of beta-cells, impaired expression of glucose transporter 2 and increased proinsulin content in beta-cells owing to impaired expression of prohormone convertases 1/3 and 2. These defects are all characteristic of patients with type-2 diabetes. Mutations in the homeobox gene Ipf1/Pdx1 are linked to diabetes in both mouse and human. We also show that Ipf1/Pdx1 is required for the expression of FGFR1 signalling components in beta-cells, indicating that Ipf1/Pdx1 acts upstream of FGFR1 signalling in beta-cells to maintain proper glucose sensing, insulin processing and glucose homeostasis.     

人类巨细胞病毒感染致1型糖尿病机制的初步探讨

目的通过对1型糖尿病患者的HCMV感染标志物、空腹血糖、空腹C肽、胰岛素自身抗体及抗胰岛细胞抗体的研究,初步探讨HCMV致1型糖尿病的机制。方法检测1型糖尿病患者的HCMV感染标志物（包括HCMV—IgG及其相对含量、HCMV—IgM及HCMV—pp65）、空腹血糖、C肽、抗胰岛素自身抗体及抗胰岛细胞抗体并进行统计学分析。结果HCMV感染与1型糖尿病患者抗胰岛素自身抗体之间无明显相关性,但与1型糖尿病患者空腹血糖、空腹C肽、抗胰岛细胞抗体存在明显的相关性,HCMV—pp65阳性的1型糖尿病患者中其空腹血糖明显高于该指标阴性者;抗HCMV—IgG阳性的1型糖尿病患者空腹血糖水平、抗胰岛细胞抗体均显著高于抗HCMV—IgG阴性者,而空腹C肽水平则明显低于抗HCMV—IgG阴性者,且抗HCMV—IgG抗体指数在4．1以上者,其抗胰岛细胞抗体阳性率显著高于抗HCMV—IgG抗体指数在4．0以下者。结论HCMV感染可能通过直接损伤胰岛免疫病理反应损伤胰岛细胞最终导致1型糖尿病的发生。     

Remission in models of type 1 diabetes by gene therapy using a single-chain insulin analogue

A cure for diabetes has long been sought using several different approaches, including islet transplantation, regeneration of beta cells and insulin gene therapy. However, permanent remission of type 1 diabetes has not yet been satisfactorily achieved. The development of type 1 diabetes results from the almost total destruction of insulin-producing pancreatic beta cells by autoimmune responses specific to beta cells. Standard insulin therapy may not maintain blood glucose concentrations within the relatively narrow range that occurs in the presence of normal pancreatic beta cells. We used a recombinant adeno-associated virus (rAAV) that expresses a single-chain insulin analogue (SIA), which possesses biologically active insulin activity without enzymatic conversion, under the control of hepatocyte-specific L-type pyruvate kinase (LPK) promoter, which regulates SIA expression in response to blood glucose levels. Here we show that SIA produced from the gene construct rAAV-LPK-SIA caused remission of diabetes in streptozotocin-induced diabetic rats and autoimmune diabetic mice for a prolonged time without any apparent side effects. This new SIA gene therapy may have potential therapeutic value for the cure of autoimmune diabetes in humans.     

胰岛炎症导致的2型糖尿病发病过程的动力学模型及治疗策略

为了揭示胰岛炎症导致2型糖尿病发生发展的机制,建立胰岛 β 细胞和巨噬细胞相互作用的数学模型,包括IL-1β 的产生和巨噬细胞的浸润过程,研究高浓度葡萄糖和游离脂肪酸对IL-1β 的共同作用,揭示胰岛炎症在2型糖尿病进程中的动力学机理.通过对模型中动力学参数的敏感性分析,提出针对不同患病情况的可能的优化治疗策略.     

HLA class II induction in human islet cells by interferon-gamma plus tumour necrosis factor or lymphotoxin

HLA class II molecules are surface glycoproteins which are essential in the initiation of immune responses. It has been postulated that induction of class II in epithelial cells such as endocrine cells, which are normally class II negative, may result in autoimmunity. In type I diabetes, islet beta cells, the target of the autoimmune process, selectively express class II antigens. But in contrast to most other cell types, islet beta cells are not stimulated to express class II by interferon-gamma (IFN-gamma) and thus the conditions under which this induction occurs have been particularly elusive. The cytotoxins tumour necrosis factor (TNF) and lymphotoxin (LT) synergize with IFN-gamma in a number of activities. We report here that IFN-gamma in combination with either TNF or LT induces islet cell class II expression. This finding has important implications for the pathogenesis of type I diabetes and the understanding of the differential control of class II expression.     

Pancreatic amylin and calcitonin gene-related peptide cause resistance to insulin in skeletal muscle in vitro

Insulin resistance occurs in a variety of conditions, including diabetes, obesity and essential hypertension, but its underlying molecular mechanisms are unclear. In type 2 (non-insulin-dependent) diabetes mellitus, it is insulin-resistance in skeletal muscle, the chief site of insulin-mediated glucose disposal in humans, that predominantly accounts for the low rates of glucose clearance from the blood, and hence for impaired glucose tolerance. Human type 2 diabetes is characterized by a decrease in non-oxidative glucose storage (muscle glycogen synthesis), and by the deposition of amyloid in the islets of Langerhans. Amylin is a 37-amino-acid peptide which is a major component of islet amyloid and has structural similarity to human calcitonin gene-related peptide-2 (CGRP-2; ref. 8). CGRP is a neuropeptide which may be involved in motor activity in skeletal muscle. We now report that human pancreatic amylin and rat CGRP-1 are potent inhibitors of both basal and insulin-stimulated rates of glycogen synthesis in stripped rat soleus muscle in vitro. These results may provide a basis for a new understanding of the molecular mechanisms that cause insulin resistance in skeletal muscle.     

Prime role for an insulin epitope in the development of type 1 diabetes in NOD mice

A fundamental question about the pathogenesis of spontaneous autoimmune diabetes is whether there are primary autoantigens. For type 1 diabetes it is clear that multiple islet molecules are the target of autoimmunity in man and animal models. It is not clear whether any of the target molecules are essential for the destruction of islet beta cells. Here we show that the proinsulin/insulin molecules have a sequence that is a primary target of the autoimmunity that causes diabetes of the non-obese diabetic (NOD) mouse. We created insulin 1 and insulin 2 gene knockouts combined with a mutated proinsulin transgene (in which residue 16 on the B chain was changed to alanine) in NOD mice. This mutation abrogated the T-cell stimulation of a series of the major insulin autoreactive NOD T-cell clones. Female mice with only the altered insulin did not develop insulin autoantibodies, insulitis or autoimmune diabetes, in contrast with mice containing at least one copy of the native insulin gene. We suggest that proinsulin is a primary autoantigen of the NOD mouse, and speculate that organ-restricted autoimmune disorders with marked major histocompatibility complex (MHC) restriction of disease are likely to have specific primary autoantigens.     

Aurora-A对2型糖尿病小鼠模型中胰岛细胞增殖的影响

为研究Aurora-A在2型糖尿病小鼠中对胰岛细胞增殖的影响,通过Western blot、免疫组织化学染色、增殖细胞核抗原(proliferating cell nucler antigen,PCNA)染色等方法研究了Aurora-A在2型糖尿病小鼠胰腺组织中的表达以及抑制AuroraA后糖尿病小鼠胰岛细胞的增殖情况。将32只雄性C57BL/6J小鼠随机分为4组,每组8只,分别为空白组、高脂饮食组、模型组和治疗组。模型组和治疗组采用高脂饲料(high fat diet,HFD)联合链脲佐霉素(Streptozotocin,STZ)腹腔注射造模,造模成功后治疗组以Aurora-A抑制剂连续灌胃2周;模型组则以等量的生理盐水灌胃。经药物干预后采用PCNA染色检测各组小鼠胰岛细胞的增殖情况。结果表明:与空白组相比,Aurora-A在模型组胰腺组织中明显表达升高;与模型组相比,治疗组小鼠经Aurora-A抑制剂治疗后胰岛细胞增殖率明显降低。可见,Aurora-A在2型糖尿病小鼠胰腺组织中表达升高;并对胰岛细胞的增殖起着重要的作用。     

维生素A 对2 型糖尿病大鼠模型胰岛纤维增生的影响

摘要: 目的观察维生素A 对2 型糖尿病( T2DM) 大鼠胰岛纤维增生的影响。方法维生素A 补充2 周后,将GK大鼠胰腺石蜡切片行HE 和Masson 染色,观察胰岛纤维化区域变化。结果补充维生素A 组GK ( Goto-Kakizaki)大鼠胰岛纤维增生区域明显减少。结论外源性给予维生素A 能显著减少T2DM 胰岛纤维增生。     

Progression of autoimmune diabetes driven by avidity maturation of a T-cell population

For unknown reasons, autoimmune diseases such as type 1 diabetes develop after prolonged periods of inflammation of mononuclear cells in target tissues. Here we show that progression of pancreatic islet inflammation to overt diabetes in nonobese diabetic (NOD) mice is driven by the 'avidity maturation' of a prevailing, pancreatic beta-cell-specific T-lymphocyte population carrying the CD8 antigen. This T-lymphocyte population recognizes two related peptides (NRP and NRP-A7) in the context of H-2Kd class I molecules of the major histocompatibility complex (MHC). As pre-diabetic NOD mice age, their islet-associated CD8+ T lymphocytes contain increasing numbers of NRP-A7-reactive cells, and these cells bind NRP-A7/H-2Kd tetramers with increased specificity, increased avidity and longer half-lives. Repeated treatment of pre-diabetic NOD mice with soluble NRP-A7 peptide blunts the avidity maturation of the NRP-A7-reactive CD8+ T-cell population by selectively deleting those clonotypes expressing T-cell receptors with the highest affinity and lowest dissociation rates for peptide-MHC binding. This inhibits the local production of T cells that are cytotoxic to beta cells, and halts the progression from severe insulitis to diabetes. We conclude that avidity maturation of pathogenic T-cell populations may be the key event in the progression of benign inflammation to overt disease in autoimmunity.     

SIRT1与糖脂代谢及在运动医学领域的研究展望

SIRT1(silent mating type information regulation 2 homolog1),哺乳动物sir2同系物,一种NAD+依赖的组蛋白脱乙酰化酶。越来越多的证据表明SIRT1通过其脱乙酰化酶活性参与糖脂代谢,其对胰岛β细胞功能和胰岛素信号通路起着正性调节作用,对改善胰岛素的敏感性和维持糖脂代谢稳态具有重要作用。运动疗法是防治2型糖尿病、非酒精性脂肪肝和动脉粥样硬化等慢性疾病主要方法之一,但运动改善慢性疾病的机理还未完全阐明。已有研究表明运动训练能够诱导大鼠骨骼肌和心肌组织中SIRT1表达。运动改善慢性疾病机理是否与SIRT1有关尚不确定。在总结SIRT1与糖脂代谢关系的基础上,结合运动与SIRT1的研究现状,展望SIRT1在运动医学领域的研究前景。     

Identification of susceptibility loci for insulin-dependent diabetes mellitus by trans-racial gene mapping

INSULIN-dependent (type I) diabetes mellitus (IDDM) follows an autoimmune destruction of the insulin-producing beta-cells of the pancreas. Family and population studies indicate that predisposition is probably polygenic. At least one susceptibility gene lies within the major histocompatibility complex and is closely linked to the genes encoding the class II antigens, HLA-DR and HLA-DQ (refs 3, 4). Fine mapping of susceptibility genes by linkage analysis in families is not feasible because of infrequent recombination (linkage disequilibrium) between the DR and DQ genes. Recombination events in the past, however, have occurred and generated distinct DR-DQ haplotypes, whose frequencies vary between races. DNA sequencing and oligonucleotide dot-blot analysis of class II genes from two race-specific haplotypes indicate that susceptibility to IDDM is closely linked to the DQA1 locus and suggest that both the DQB1 (ref. 7) and DQA1 genes contribute to disease predisposition.     

Innate immunity and intestinal microbiota in the development of Type 1 diabetes

Type 1 diabetes (T1D) is a debilitating autoimmune disease that results from T-cell-mediated destruction of insulin-producing beta-cells. Its incidence has increased during the past several decades in developed countries, suggesting that changes in the environment (including the human microbial environment) may influence disease pathogenesis. The incidence of spontaneous T1D in non-obese diabetic (NOD) mice can be affected by the microbial environment in the animal housing facility or by exposure to microbial stimuli, such as injection with mycobacteria or various microbial products. Here we show that specific pathogen-free NOD mice lacking MyD88 protein (an adaptor for multiple innate immune receptors that recognize microbial stimuli) do not develop T1D. The effect is dependent on commensal microbes because germ-free MyD88-negative NOD mice develop robust diabetes, whereas colonization of these germ-free MyD88-negative NOD mice with a defined microbial consortium (representing bacterial phyla normally present in human gut) attenuates T1D. We also find that MyD88 deficiency changes the composition of the distal gut microbiota, and that exposure to the microbiota of specific pathogen-free MyD88-negative NOD donors attenuates T1D in germ-free NOD recipients. Together, these findings indicate that interaction of the intestinal microbes with the innate immune system is a critical epigenetic factor modifying T1D predisposition.     

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.