Activation of the GLP-1 Receptor Signalling Pathway: A Relevant Strategy to Repair a Deficient Beta-Cell Mass

Recent preclinical studies in rodent models of diabetes suggest that exogenous GLP-1R agonists and DPP-4 inhibitors have the ability to increase islet mass and preserve beta-cell function, by immediate reactivation of beta-cell glucose competence, as well as enhanced beta-cell proliferation and neogenesis and promotion of beta-cell survival. These effects have tremendous implication in the treatment of T2D because they directly address one of the basic defects in T2D, that is, beta-cell failure. In human diabetes, however, evidence that the GLP-1-based drugs alter the course of beta-cell function remains to be found. Several questions surrounding the risks and benefits of GLP-1-based therapy for the diabetic beta-cell mass are discussed in this review and require further investigation

De la patogénesis al tratamiento de la diabetes tipo 2. El paradigma de la rata GK

Now that the reduction in beta-mass has been clearly established in humans with type 2 diabetes mellitus (T2D), the debate focuses on the possible mechanisms responsible for abnormal islet microenvironment, decreased beta-cell number and impaired beta-cell function, and their multifactorial aetiologies. The informations available in the Goto-Kakizaki (GK/Par line) rat, one of the best characterized animal models of spontaneous T2D, are reviewed in such a perspective. We propose that the defective beta-cell mass and function in the GK/Par model reflects the complex interactions of three pathogenic players: i) several independent loci containing genes responsible for some diabetic traits (but not decreased beta-cell mass); (ii) gestational metabolic impairment inducing a programming of endocrine pancreas (decreased beta-cell neogenesis) which is transmitted to the next generation; and (iii) secondary (acquired) loss of beta-cell differentiation due to chronic exposure to hyperglycaemia (glucotoxicity). An important message is that the «heritable» determinants of T2D do not simply rely on genetic factors, but probably involve transgenerational epigenetic responses. Finally, studies from our group have shown that pharmacological use of GLP-1 receptor agonist in vivo during the GK prediabetes period, induced beta-cell regeneration through activation of beta-cell replication and neogenesis, and doing so prevented the development of hyperglycaemia. This suggests a novel application of GLP-1 receptor agonists to the prevention of human diabetes by treatment of at risk individuals during the prediabetic period. Since we also demonstrated that GLP-1 acutely restores the glucose competence of the GK beta-cell, GLP-1 receptor agonists turn to be very attractive tools for the treatment of the decreased beta-cell functioning mass as encountered in T2D.Ahora que la reducción de la masa de la célula beta ha sido claramente establecida en humanos con diabetes mellitas tipo 2 (T2D), el debate se focaliza sobre los posibles mecanismos responsables de un microambiente anormal en el islote, del decrecido número de células beta, del alterado funcionamiento de ellas y de sus etiologías multifactoriales. Las eficaces informaciones proporcionadas por la rata Goto-Kakizaki (línea GK), uno de los mejor caracterizados modelos animales de T2D espontánea, están siendo revisadas para tales fines. Nosotros proponemos que la defectuosa masa y función de la célula beta en el modelo GK reflejan unas interacciones complejas de tres vertientes patogénicas: i) varios loci que contienen genes responsables de algunos indicios diabéticos (pero no de decrecida masa de célula beta); ii) daño metabólico gestacional que induce un programa de páncreas endocrino (decrecida neogénesis de célula beta), lo cual es transmitido a la próxima generación, y iii) secundaria (adquirida) pérdida de diferenciación de célula beta debida a una exposición crónica a hiperglucemia (glucotoxicidad). Un mensaje importante es que los determinantes «heredables» de T2D no descansan simplemente sobre factores genéticos, sino probablemente envuelven respuestas epigenéticas transgeneracionales. Finalmente, estudios de nuestro grupo han mostrado que el uso farmacológico de agonistas del receptor de GLP-1 in vivo, en el periodo de prediabetes de ratas GK, inducían regeneración de célula beta, a través de la activación de la replicación y neogénesis de célula beta y de esta forma prevenían el desarrollo de hiperglucemia. Esto sugiere una nueva aplicación del receptor agonista de GLP-1 para la prevención de diabetes humana por el tratamiento con éste, durante el periodo prediabético, a individuos de riesgo. Como nosotros mostramos, también, que el GLP-1 restaura de forma acusada la sensibilidad a la glucosa de la célula beta GK, los agonistas del receptor de GLP-1 vuelven a ser una herramienta atractiva para el tratamiento del decrecimiento de la masa funcionante de la célula beta lo cual es encontrada en T2D

Fetal pancreatic b-cell growth and insulin-like growth factors relationship in undernourished rats

Resumen del trabajo presentado al 38th EASD Annual Meeting of the European Association for the Study of Diabetes, celebrado en Budapest (Humgria) del 1 al 5 de septiembre de 2002.[Background and Aims] We have previously shown that Wistar fetuses from protein- caloric undernourished pregnant rats (U) at 21 days post coitum (dpc) exhibit increased β cell-mass. This alteration is correlated with increased insulinemia and total pancreatic insulin content, a pattern reminiscent to that reported in infants of mild diabetic mothers. Both Insulinlike Growth Factor (IGF)-I and -2 are essential players for growth and development during the fetal period. The aim of the present study was to investigate in the U fetuses at 21 dpc: 1) serum IGFs levels, 2) IGFs gene expression in the liver and pancreas, and 3) in vitro mitogenic effect of IGFs in isolated fetal islets using BrdU labelling index (LI). All values were compared to those in Wi star control fetuses (C). [Methods] Serum concentrations of IGF-I and IGF-2 were measured by radioimmuno assay and radioreceptor assay respectively. RNase protection assay was performed using RNA from pancreas and liver to evaluate IGFs or IGFBPs gene expression in both tissues. [Results] Similar serum IGF-I and-2levels were observed in U and C. IGF-I and IGF-2 mRNAs were detected in liver and pancreas of both C and U fetuses. Despite being decreased in the liver, IGF-l mRNA level was increased in U pancreases as compared to C. Concerning IGF-2 gene expression it was diminished in U pancreas while being normal in the liver as compared to C. No difference in IGFBP-I, -2 and -3 mRNA levels was detected in U liver when compared to C. However, gene expression of IGFBP-2 was increased and that of IGFBP-3 was decreased in U pancreases. Finally, the in vitro study showed a normal BrdU LI in U isolated fetal islets under basal conditions while it was found significantly increased twice in response to both IGF-I and IGF-2 (lOOng/ml) as compared to fetal C islets. [Conclusion] Our data suggest that in U fetuses at 21 dpc: I) the increased β-cell mass can be related to the stimulation of replicative β-cell response due to locally increased IGF-I in the pancreas 2) such IGF-I action is perhaps favored by an enhanced IGFBP-2 gene expression in pancreas, and 3) at variance with previous reports in several models of decreased intrapancreatic IGF-2 expression in fetuses, the low IGF-2 mRNA level as it is observed in the present U model does not correlate with a decreased β-cell growth.Peer Reviewe

Diabetic β-Cells Can Achieve Self-Protection against Oxidative Stress through an Adaptive Up-Regulation of Their Antioxidant Defenses

Background Oxidative stress (OS), through excessive and/or chronic reactive oxygen species (ROS), is a mediator of diabetes-related damages in various tissues including pancreatic β-cells. Here, we have evaluated islet OS status and β-cell response to ROS using the GK/Par rat as a model of type 2 diabetes. Methodology/Principal Findings Localization of OS markers was performed on whole pancreases. Using islets isolated from 7-day-old or 2.5-month-old male GK/Par and Wistar control rats, 1) gene expression was analyzed by qRT-PCR; 2) insulin secretion rate was measured; 3) ROS accumulation and mitochondrial polarization were assessed by fluorescence methods; 4) antioxidant contents were quantified by HPLC. After diabetes onset, OS markers targeted mostly peri-islet vascular and inflammatory areas, and not islet cells. GK/Par islets revealed in fact protected against OS, because they maintained basal ROS accumulation similar or even lower than Wistar islets. Remarkably, GK/Par insulin secretion also exhibited strong resistance to the toxic effect of exogenous H2O2 or endogenous ROS exposure. Such adaptation was associated to both high glutathione content and overexpression (mRNA and/or protein levels) of a large set of genes encoding antioxidant proteins as well as UCP2. Finally, we showed that such a phenotype was not innate but spontaneously acquired after diabetes onset, as the result of an adaptive response to the diabetic environment. Conclusions The GK/Par model illustrates the effectiveness of adaptive response to OS by beta-cells to achieve self-tolerance. It remains to be determined to what extend such islet antioxidant defenses upregulation might contribute to GK/Par beta-cell secretory dysfunction

Role of NAD(P)H Oxidase in Superoxide Generation and Endothelial Dysfunction in Goto-Kakizaki (GK) Rats as a Model of Nonobese NIDDM

Background: Cardiovascular disease is the leading cause of mortality in diabetics, and it has a complex etiology that operates on several levels. Endothelial dysfunction and increased generation of reactive oxygen species are believed to be an underlying cause of vascular dysfunction and coronary artery disease in diabetes. This impairment is likely the result of decreased bioavailability of nitric oxide (NO) within the vasculature. However, it is unclear whether hyperglycemia per se stimulates NADPH oxidase-derived superoxide generation in vascular tissue. Methods and Results: This study focused on whether NADPH oxidase-derived superoxide is elevated in vasculature tissue evoking endothelial/smooth muscle dysfunction in the hyperglycemic (16964 mg%) Goto-Kakizaki (GK) rat. By dihydroethidine fluorescence staining, we determined that aorta superoxide levels were significantly elevated in 9 month-old GK compared with age matched Wistar (GK; 19566%, Wistar; 10063.5%). Consistent with these findings, 10 26 mol/L acetylcholine-induced relaxation of the carotid artery was significantly reduced in GK rats compared with age matched Wistar (GK; 4167%, Wistar; 10065%) and measurements in the aorta showed a similar trend (p =.08). In contrast, relaxation to the NO donor SNAP was unaltered in GK compared to Wistar. Endothelial dysfunction was reversed by lowering of superoxide with apocynin, a specific Nox inhibitor. Conclusions: The major findings from this study are that chronic hyperglycemia induces significant vascular dysfunction i

Global microRNA expression profiles in insulin target tissues in a spontaneous rat model of type 2 diabetes

AIMS/HYPOTHESIS: MicroRNAs regulate a broad range of biological mechanisms. To investigate the relationship between microRNA expression and type 2 diabetes, we compared global microRNA expression in insulin target tissues from three inbred rat strains that differ in diabetes susceptibility. METHODS: Using microarrays, we measured the expression of 283 microRNAs in adipose, liver and muscle tissue from hyperglycaemic (Goto-Kakizaki), intermediate glycaemic (Wistar Kyoto) and normoglycaemic (Brown Norway) rats (n = 5 for each strain). Expression was compared across strains and validated using quantitative RT-PCR. Furthermore, microRNA expression variation in adipose tissue was investigated in 3T3-L1 adipocytes exposed to hyperglycaemic conditions. RESULTS: We found 29 significantly differentiated microRNAs (p(adjusted) < 0.05): nine in adipose tissue, 18 in liver and two in muscle. Of these, five microRNAs had expression patterns that correlated with the strain-specific glycaemic phenotype. MiR-222 (p(adjusted) = 0.0005) and miR-27a (p(adjusted) = 0.006) were upregulated in adipose tissue; miR-195 (p(adjusted) = 0.006) and miR-103 (p(adjusted) = 0.04) were upregulated in liver; and miR-10b (p(adjusted) = 0.004) was downregulated in muscle. Exposure of 3T3-L1 adipocytes to increased glucose concentration upregulated the expression of miR-222 (p = 0.008), miR-27a (p = 0.02) and the previously reported miR-29a (p = 0.02). Predicted target genes of these differentially expressed microRNAs are involved in pathways relevant to type 2 diabetes. CONCLUSION: The expression patterns of miR-222, miR-27a, miR-195, miR-103 and miR-10b varied with hyperglycaemia, suggesting a role for these microRNAs in the pathophysiology of type 2 diabetes, as modelled by the Gyoto-Kakizaki rat. We observed similar patterns of expression of miR-222, miR-27a and miR-29a in adipocytes as a response to increased glucose levels, which supports our hypothesis that altered expression of microRNAs accompanies primary events related to the pathogenesis of type 2 diabetes