胰高血糖素样肽1对胰腺β细胞的作用及其机制

胰高血糖素样肽1(GLP-1)是一种主要由肠道L细胞分泌的肠促胰素。GLP-1能通过葡萄糖依赖模式刺激胰岛素的分泌,同时有延缓胃排空、抑制胰高血糖素分泌、降低体重的作用,有利于维持体内血糖稳态。目前,基于GLP-1的药物作为新的糖尿病治疗手段已越来越受到重视。我们简要综述GLP-1对胰腺β细胞的作用及机制研究进展。     

胰高血糖素样肽-1与受体相互作用研究进展

胰高血糖素样肽-1(GLP-1)具有促胰岛素分泌、抑制胰高血糖素分泌、刺激胰岛β细胞的增殖和分化、抑制β细胞凋亡、抑制胃排空等作用,近年来成为治疗糖尿病药物研究中的热点。GLP-1与受体的相互作用一直备受关注,我们从4个方面对GLP-1与受体相互作用的研究进行了综述:GLP-1的二级结构、GLP-1单个残基改变及残基间的相互作用、GLP-1不同残基片段对GLP-1结合并激活受体的影响和GLP-1受体的相互作用模式。     

胰高血糖素样肽-1与Ⅰ型糖尿病治疗

近年来研究表明,胰高血糖素样肽-1（GLP-1）对胰岛β细胞的分化、增殖均起重要作用,包括抑制β细胞凋亡、刺激β细胞增生、诱导干细胞分化为胰腺内分泌细胞,从而使被破坏的胰岛细胞恢复分泌胰岛素的功能,这些作用为其治疗Ⅰ型糖尿病提供了证据,使其成为Ⅰ型糖尿病治疗领域研究的热点。     

GLP-1与2型糖尿病的研究进展

胰高血糖素样肽-1(glucagon-like peptide-1,GLP-1)具有促进胰岛素分泌、保护胰岛β细胞、降低食欲等多种重要功能,在控制体内血糖平衡的过程中发挥重要作用。2型糖尿病的发生伴随着胰高血糖素样肽-1生物应答功能受损。胰高血糖素样肽-1类似物、胰高血糖素样肽-1受体激动剂和胰高血糖素样肽-1降解酶抑制剂等糖尿病治疗药物已在临床上表现出很好的应用前景。     

胰高血糖素样肽-1保护胰岛β细胞相关分子机制的研究进展

胰高血糖素样肽-1(Glucagon-like peptide-1,GLP-1)是肠道L细胞分泌的一种重要的肠促胰岛素.大量研究表明,除刺激胰岛素分泌外,GLP-1可通过促进胰岛β细胞增殖,抑制β细胞凋亡而增加胰岛β细胞量,本文就其相关分子信号转导机制进行综述.     

胰高血糖素样多肽-1拮抗2型糖尿病胰岛细胞凋亡损伤

胰高血糖素样多肽-1（glucogen like peptide 1, GLP-1）在胰岛素分泌过程中扮演重要角色,并在改善β细胞功能方面有着令人瞩目的效应,但有关其作用机制尚需更深入研究。本研究探讨GLP-1对2型糖尿病（type 2 diabetes mellitus, T2DM）大鼠模型胰岛细胞损伤的影响,观察GLP-1在T2DM大鼠胰岛细胞凋亡损伤机制中所发挥的作用。HE染色结果发现,糖尿病大鼠胰岛损伤。ELISA结果表明,糖尿病患者和糖尿病大鼠血清中GLP-1表达水平上调。放射免疫结果表明,GLP-1和谷氧还蛋白1（Grx1）促进HIT-T 15细胞分泌胰岛素,Cd抑制胰岛素的分泌。免疫组化结果表明,糖尿病大鼠GLP-1加药处理后,各组与糖尿病组相比,药物提高了Grx1和胰岛素表达水平,降低了胰高血糖素表达水平,同时降低了活性胱天蛋白酶3（caspase-3）的表达。本研究结果提示,GLP-1在肥胖T2DM大鼠胰岛细胞凋亡中起保护作用,同时可调节胰岛素和胰高血糖素水平,其机制可能与Grx1相关     

胰高血糖素样肽1受体--治疗糖尿病新药的研究热点

胰高血糖素样肽l(glucagon—like peptide—l,GLP-1)与胰岛素分泌和糖代谢调节密切相关。GLP-1与其受体(GLP-1receptor,GLP-1R)结合后,主要通过cAMP和P13K两条信号途径,促进胰岛素的分泌,刺激胰岛β细胞的增殖和分化。对GLP-1R结构和信号传导机制的研究,有助于了解其在糖尿病病理进程中的作用,为开发新型糖尿病治疗药物指明方向。     

长效GLP-1受体激动剂的研发进展

胰高血糖素样肽-1(glucagon-like Peptide-1,GLP-1)是机体在葡萄糖等刺激下释放的一类肠促胰岛素。GLP-1具有促进葡萄糖依赖性胰岛素分泌,促进胰岛β细胞增殖并抑制其凋亡、抑制摄食、减慢胃排空和减轻体重等作用。GLP-1在体内极不稳定,易被二肽基肽酶-IV(dipeptidyl peptidase-IV,DPP-IV)降解,半衰期短。从墨西哥巨蜥蜴唾液中分离得到GLP-1的天然类似物Exendin-4与其有着相似的作用,且不易被DPP-IV降解。以GLP-1及Exendin-4为基础,研发长效GLP-1受体激动剂,已成为研发新型糖尿病治疗药物的热点之一。本文就长效GLP-1受体激动剂的研发现状予以综述。     

胰高血糖素样多肽-1拮抗2型糖尿病胰岛细胞凋亡损伤（英文）

胰高血糖素样多肽-1(glucogen-like peptide-1,GLP-1)在胰岛素分泌过程中扮演重要角色,并在改善β细胞功能方面有着令人瞩目的效应,但有关其作用机制尚需更深入研究。本研究探讨GLP-1对2型糖尿病(type 2 diabetes mellitus,T2DM)大鼠模型胰岛细胞损伤的影响,观察GLP-1在T2DM大鼠胰岛细胞凋亡损伤机制中所发挥的作用。HE染色结果发现,糖尿病大鼠胰岛损伤。ELISA结果表明,糖尿病患者和糖尿病大鼠血清中GLP-1表达水平上调。放射免疫结果表明,GLP-1和谷氧还蛋白1(Grx1)促进HIT-T 15细胞分泌胰岛素,Cd抑制胰岛素的分泌。免疫组化结果表明,糖尿病大鼠GLP-1加药处理后,各组与糖尿病组相比,药物提高了Grx1和胰岛素表达水平,降低了胰高血糖素表达水平,同时降低了活性胱天蛋白酶3(caspase-3)的表达。本研究结果提示,GLP-1在肥胖T2DM大鼠胰岛细胞凋亡中起保护作用,同时可调节胰岛素和胰高血糖素水平,其机制可能与Grx1相关。     

新型降糖药物Exenatide研究进展及前景展望

Exenatide是胰高血糖素样肽-1（GLP-1）受体的一种激动剂,可模拟人体自身激素GLP-1的功能,具有促进胰腺p-细胞增殖、改善其功能,以及促进胰岛素分泌,增加机体对胰岛素的敏感性和延缓胃排空等作用,因而有着传统治疗糖尿病药物不可比拟的优点,近年来已经成为糖尿病治疗领域的研究热点,应用前景非常广阔。简要介绍了Exenatide的生物活性、作用机理和临床应用现状,并对Exenatide长效降糖方面的研究进行了展望。     

Two incretin hormones GLP-1 and GIP: comparison of their actions in insulin secretion and β cell preservation

Gastric inhibitory polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) are the two primary incretin hormones secreted from the intestine upon ingestion of glucose or nutrients to stimulate insulin secretion from pancreatic β cells. GIP and GLP-1 exert their effects by binding to their specific receptors, the GIP receptor (GIPR) and the GLP-1 receptor (GLP-1R), which belong to the G-protein coupled receptor family. Receptor binding activates and increases the level of intracellular cAMP in pancreatic β cells, thereby stimulating insulin secretion glucose-dependently. In addition to their insulinotropic effects, GIP and GLP-1 have been shown to preserve pancreatic β cell mass by inhibiting apoptosis of β cells and enhancing their proliferation. Due to such characteristics, incretin hormones have been gaining mush attention as attractive targets for treatment of type 2 diabetes, and indeed incretin-based therapeutics have been rapidly disseminated worldwide. However, despites of plethora of rigorous studies, molecular mechanisms underlying how GIPR and GLP-1R activation leads to enhancement of glucose-dependent insulin secretion are still largely unknown. Here, we summarize the similarities and differences of these two incretin hormones in secretion and metabolism, their insulinotropic actions and their effects on pancreatic β cell preservation. We then try to discuss potential of GLP-1 and GIP in treatment of type 2 diabetes.     

Mutations to the third cytoplasmic domain of the glucagon-like peptide 1 (GLP-1) receptor can functionally uncouple GLP-1-stimulated insulin secretion in HIT-T15 cells.

Glucagon-like peptide-1 (GLP-1) is an insulinotropic hormone with powerful antidiabetogenic effects that are thought to be mediated by adenylyl cyclase (AC). Recently, we generated two GLP-1 receptor mutant isoforms (IC3-1 and DM-1) that displayed efficient ligand binding and the ability to promote Ca2+ mobilization from intracellular stores but lacked the ability to couple to AC. In the present study, the wild-type rat GLP-1 receptor (WT-GLP-1 R) or the IC3-1 and DM-1 mutant forms were expressed for the first time in the insulin-producing HIT-T15 cells. Only cells expressing WT-GLP-1 R displayed dramatically elevated GLP-1-induced cAMP responses and elevated insulin secretion. The increase in GLP-1-stimulated secretion in cells expressing WT-GLP-1 R, however, was not accompanied by differences in glucose-stimulated insulin release. Prolonged exposure to GLP-1 (10 nM, 17 h), not only led to an increase in insulin secretion but also increased insulin mRNA levels, but only in cells expressing the WT-GLP-1 R and not the mutant isoforms. Electrophysiological analyses revealed that GLP-1 application enhanced L-type voltage-dependent Ca2+ channel (VDCC) currents > 2-fold and caused a positive shift in VDCC voltage-dependent inactivation in WT-GLP-1R cells only, not control or mutant (DM-1) cells. This action on the Ca2+ current was further enhanced by the VDCC agonist, BAYK8644, suggesting GLP-1 acts via a distinct mechanism dependent on cAMP. These studies demonstrate that the GLP-1 receptor efficiently couples to AC to stimulate insulin secretion and that receptors lacking critical residues in the proximal region of the third intracellular loop can effectively uncouple the receptor from cAMP production, VDCC activity, insulin secretion, and insulin biosynthesis.     

Systems analysis of GLP-1 receptor signaling in pancreatic β-cells

Glucagon-like peptide-1 (GLP-1) elevates intracellular concentration of cAMP ([cAMP]) and facilitates glucose-dependent insulin secretion in pancreatic β-cells. There has been much evidence to suggest that multiple key players such as the GLP-1 receptor, G(s) protein, adenylate cyclase (AC), phosphodiesterase (PDE), and intracellular Ca(2+) concentration ([Ca(2+)]) are involved in the regulation of [cAMP]. However, because of complex interactions among these signaling factors, the kinetics of the reaction cascade as well as the activities of ACs and PDEs have not been determined in pancreatic β-cells. We have constructed a minimal mathematical model of GLP-1 receptor signal transduction based on experimental findings obtained mostly in β-cells and insulinoma cell lines. By fitting this theoretical reaction scheme to key experimental records of the GLP-1 response, the parameters determining individual reaction steps were estimated. The model reconstructed satisfactorily the dynamic changes in [cAMP] and predicted the activities of cAMP effectors, protein kinase A (PKA), and cAMP-regulated guanine nucleotide exchange factor [cAMP-GEF or exchange protein directly activated by cAMP (Epac)] during GLP-1 stimulation. The simulations also predicted the presence of two sequential desensitization steps of the GLP1 receptor that occur with fast and very slow reaction rates. The cross talk between glucose- and GLP-1-dependent signal cascades for cAMP synthesis was well reconstructed by integrating the direct regulation of AC and PDE by [Ca(2+)]. To examine robustness of the signaling system in controlling [cAMP], magnitudes of AC and PDE activities were compared in the presence or absence of GLP-1 and/or the PDE inhibitor IBMX.(1).     

Emerging roles for β-arrestin-1 in the control of the pancreatic β-cell function and mass: New therapeutic strategies and consequences for drug screening

Defective insulin secretion is a feature of type 2 diabetes that results from inadequate compensatory increase in β-cell mass, decreased β-cell survival and impaired glucose-dependent insulin release. Pancreatic β-cell proliferation, survival and secretion are thought to be regulated by signalling pathways linked to G-protein coupled receptors (GPCRs), such as the glucagon-like peptide-1 (GLP-1) and the pituitary adenylate cyclase-activating polypeptide (PACAP) receptors. β-arrestin-1 serves as a multifunctional adaptor protein that mediates receptor desensitization, receptor internalization, and links GPCRs to downstream pathways such as tyrosine kinase Src, ERK1/2 or Akt/PKB. Importantly, recent studies found that β-arrestin-1 mediates GLP-1 signalling to insulin secretion, GLP-1 antiapoptotic effect by phosphorylating the proapoptotic protein Bad through ERK1/2 activation, and PACAP potentiation of glucose-induced long-lasting ERK1/2 activation controlling IRS-2 expression. Together, these novel findings reveal an important functional role for β-arrestin-1 in the regulation of insulin secretion and β-cell survival by GPCRs.     

Transient neonatal diabetes mellitus gene Zac1 impairs insulin secretion in mice through Rasgrf1

The biallelic expression of the imprinted gene ZAC1/PLAGL1 underlies ≈ 60% of all cases of transient neonatal diabetes mellitus (TNDM) that present with low perinatal insulin secretion. Molecular targets of ZAC1 misexpression in pancreatic β cells are unknown. Here, we identified the guanine nucleotide exchange factor Rasgrf1 as a direct Zac1/Plagl1 target gene in murine β cells. Doubling Zac1 expression reduced Rasgrf1 expression, the stimulus-induced activation of mitogen-activated protein kinase (MAPK) and phosphoinositide 3-kinase (PI3K) pathways, and, ultimately, insulin secretion. Normalizing Rasgrf1 expression reversed this phenotype. Moreover, the transplantation of Zac1-overexpressing β cells failed to reinstate euglycemia in experimental diabetic mice. In contrast, Zac1 expression did not interfere with the signaling of the glucagon-like peptide 1 receptor (GLP-1R), and the GLP-1 analog liraglutide improved hyperglycemia in transplanted experimental diabetic mice. This study unravels a mechanism contributing to insufficient perinatal insulin secretion in TNDM and raises new prospects for therapy.     

Oleoyl-lysophosphatidylinositol enhances glucagon-like peptide-1 secretion from enteroendocrine L-cells through GPR119

The gastrointestinal tract is increasingly viewed as critical in controlling glucose metabolism, because of its role in secreting multiple glucoregulatory hormones, such as glucagon like peptide-1 (GLP-1). Here we investigate the molecular pathways behind the GLP-1- and insulin-secreting capabilities of a novel GPR119 agonist, Oleoyl-lysophosphatidylinositol (Oleoyl-LPI). Oleoyl-LPI is the only LPI species able to potently stimulate the release of GLP-1 in vitro, from murine and human L-cells, and ex-vivo from murine colonic primary cell preparations. Here we show that Oleoyl-LPI mediates GLP-1 secretion through GPR119 as this activity is ablated in cells lacking GPR119 and in colonic primary cell preparation from GPR119^?/? mice. Similarly, Oleoyl-LPI-mediated insulin secretion is impaired in islets isolated from GPR119^?/? mice. On the other hand, GLP-1 secretion is not impaired in cells lacking GPR55 in vitro or in colonic primary cell preparation from GPR55^?/? mice. We therefore conclude that GPR119 is the Oleoyl-LPI receptor, upstream of ERK1/2 and cAMP/PKA/CREB pathways, where primarily ERK1/2 is required for GLP-1 secretion, while CREB activation appears dispensable.     

Molecular Characterisation of Small Molecule Agonists Effect on the Human Glucagon Like Peptide-1 Receptor Internalisation

The glucagon-like peptide receptor (GLP-1R), which is a G-protein coupled receptor (GPCR), signals through both Gαs and Gαq coupled pathways and ERK phosphorylation to stimulate insulin secretion. The aim of this study was to determine molecular details of the effect of small molecule agonists, compounds 2 and B, on GLP-1R mediated cAMP production, intracellular Ca²⁺ accumulation, ERK phosphorylation and its internalisation. In human GLP-1R (hGLP-1R) expressing cells, compounds 2 and B induced cAMP production but caused no intracellular Ca²⁺ accumulation, ERK phosphorylation or hGLP-1R internalisation. GLP-1 antagonists Ex(9–39) and JANT-4 and the orthosteric binding site mutation (V36A) in hGLP-1R failed to inhibit compounds 2 and B induced cAMP production, confirming that their binding site distinct from the GLP-1 binding site on GLP-1R. However, K334A mutation of hGLP-1R, which affects Gα_s coupling, inhibited GLP-1 as well as compounds 2 and B induced cAMP production, indicating that GLP-1, compounds 2 and B binding induce similar conformational changes in the GLP-1R for Gα_s coupling. Additionally, compound 2 or B binding to the hGLP-1R had significantly reduced GLP-1 induced intracellular Ca²⁺ accumulation, ERK phosphorylation and hGLP-1R internalisation. This study illustrates pharmacology of differential activation of GLP-1R by GLP-1 and compounds 2 and B.