Lower Glucose-stimulated Insulin Secretion Research Articles

Characteristics of research-focused human islet preparations from organ donors with type 2 diabetes

ABSTRACT Type 2 diabetes mellitus (T2D) affects 463 million individuals worldwide. β-cell dysfunction and relatively inadequate β-cell mass has been implicated in the pathogenesis of T2D. Primary human islets from T2D patients can reveal the islet dysfunction and the underlying mechanisms and thus have become valued resources for diabetes research. Our center (Human Islet Resource Center, China) has prepared a number of batches of human islets from T2D organ donors. The present study aims to characterize islet isolation processes, islet yields, and qualities of T2D pancreases by comparing with non-diabetic (ND) ones. Overall, 24 T2D and 80 ND pancreases were obtained with informed research consents. The digestion time, islet purity, yield, size distribution, islet morphology score, viability, and function in each islet preparation were analyzed. We found that at digestion stage, T2D pancreases need significantly longer digestion duration and have worse digestion rates and lower gross islet yields. At purification stage, T2D pancreases have poorer purity, purification rate, morphology score, and islet yields after purification. Functional evaluation by GSI assay showed that the human T2D islets have significantly lower glucose stimulated insulin secretion ability. In conclusion, the features of longer digestion duration, lower yields and quality, and impaired insulin secretion in T2D group are consistent with the pathological condition of this disease. Both islet yields and islet function evaluation results did not support human T2D islets as clinical transplantation resources. However, they could serve as good research models for T2D disease studies and promote the advancement of diabetes research.

1395-P: Maternal Exercise during Pregnancy Affects Offspring Adiposity through One Carbon Metabolism Cycle

Maternal obesity during pregnancy can adversely affect adult offspring adiposity and insulin resistance. The goal of this study was to determine if maternal exercise mitigates the adverse effects of maternal obesity on offspring health. Female (C57BL/6NJ) mice were fed from weaning a control diet (10%kcal fat; MC n=18) or western diet (45% kcal fat; MW n=15) to induce excess adiposity. After 13 weeks, the mice were bred and maintained on the diets, with (E) and without (S) access to a running wheel (exercise), throughout pregnancy and lactation. Offspring were weaned onto the control diet and fed for 13 weeks; male offspring were studied. Offspring from MWE dams had greater (p<0.05) retroperitoneal and mesenteric adipose tissue than offspring from MWS dams. This was not observed in offspring from dams fed the control diet. Offspring from exercised dams had lower glucose-stimulated insulin secretion compared to those from sedentary dams, independent of maternal diet. No differences in glucose and insulin tolerance were observed. One carbon metabolism is required for several physiological processes including DNA synthesis, amino and lipid metabolism, and the generation of methyl groups. Disturbances in one carbon metabolism occur in obesity. We hypothesized that maternal exercise mitigates the adverse effects of maternal obesity on offspring adiposity through changes in one carbon metabolism. MCE offspring had lower serum total homocysteine (6.3μmol/L) compared to MCS offspring (9.4μmol/L). This was not observed in the offspring from western diet-fed dams. Offspring from western diet-fed dams had higher hepatic methylenetetrahydrofolate reductase (Mthfr) mRNA expression compared to offspring from control diet-fed dams. Offspring from dams that exercised also had higher hepatic Mthfr mRNA; the highest expression was observed in MWE offspring. The findings from this study suggest that one carbon metabolism may play a role in developmental programing of offspring adiposity. Disclosure N. Boonpattrawong: None. A. Mehran: None. I. Laher: None. A.M. Devlin: None. Funding Canadian Institutes of Health Research

Chronically Increased Amino Acids Improve Insulin Secretion, Pancreatic Vascularity, and Islet Size in Growth-Restricted Fetal Sheep.

Placental insufficiency is associated with reduced supply of amino acids to the fetus and leads to intrauterine growth restriction (IUGR). IUGR fetuses are characterized by lower glucose-stimulated insulin secretion, smaller pancreatic islets with less β-cells, and impaired pancreatic vascularity. To test whether supplemental amino acids infused into the IUGR fetus could improve these complications of IUGR we used acute (hours) and chronic (11 d) direct fetal amino acid infusions into a sheep model of placental insufficiency and IUGR near the end of gestation. IUGR fetuses had attenuated acute amino acid-stimulated insulin secretion compared with control fetuses. These results were confirmed in isolated IUGR pancreatic islets. After the chronic fetal amino acid infusion, fetal glucose-stimulated insulin secretion and islet size were restored to control values. These changes were associated with normalization of fetal pancreatic vascularity and higher fetal pancreatic vascular endothelial growth factor A protein concentrations. These results demonstrate that decreased fetal amino acid supply contributes to the pathogenesis of pancreatic islet defects in IUGR. Moreover, the results show that pancreatic islets in IUGR fetuses retain their ability to respond to increased amino acids near the end of gestation after chronic fetal growth restriction.

Pancreas-Specific Sirt1-Deficiency in Mice Compromises Beta-Cell Function without Development of Hyperglycemia.

Aims/HypothesisSirtuin 1 (Sirt1) has been reported to be a critical positive regulator of glucose-stimulated insulin secretion in pancreatic beta-cells. The effects on islet cells and blood glucose levels when Sirt1 is deleted specifically in the pancreas are still unclear.MethodsThis study examined islet glucose responsiveness, blood glucose levels, pancreatic islet histology and gene expression in Pdx1Cre; Sirt1ex4F/F mice that have loss of function and loss of expression of Sirt1 specifically in the pancreas.ResultsWe found that in the Pdx1Cre; Sirt1ex4F/F mice, the relative insulin positive area and the islet size distribution were unchanged. However, beta-cells were functionally impaired, presenting with lower glucose-stimulated insulin secretion. This defect was not due to a reduced expression of insulin but was associated with a decreased expression of the glucose transporter Slc2a2/Glut2 and of the Glucagon like peptide-1 receptor (Glp1r) as well as a marked down regulation of endoplasmic reticulum (ER) chaperones that participate in the Unfolded Protein Response (UPR) pathway. Counter intuitively, the Sirt1-deficient mice did not develop hyperglycemia. Pancreatic polypeptide (PP) cells were the only other islet cells affected, with reduced numbers in the Sirt1-deficient pancreas.Conclusions/InterpretationThis study provides new mechanistic insights showing that beta-cell function in Sirt1-deficient pancreas is affected due to altered glucose sensing and deregulation of the UPR pathway. Interestingly, we uncovered a context in which impaired beta-cell function is not accompanied by increased glycemia. This points to a unique compensatory mechanism. Given the reduction in PP, investigation of its role in the control of blood glucose is warranted.

Microarray analysis of isolated human islet transcriptome in type 2 diabetes and the role of the ubiquitin–proteasome system in pancreatic beta cell dysfunction

To shed light on islet cell molecular phenotype in human type 2 diabetes (T2D), we studied the transcriptome of non-diabetic (ND) and T2D islets to then focus on the ubiquitin–proteasome system (UPS), the major protein degradation pathway. We assessed gene expression, amount of ubiquitinated proteins, proteasome activity, and the effects of proteasome inhibition and prolonged exposure to palmitate. Microarray analysis identified more than one thousand genes differently expressed in T2D islets, involved in many structures and functions, with consistent alterations of the UPS. Quantitative RT-PCR demonstrated downregulation of selected UPS genes in T2D islets and beta cell fractions, with greater ubiquitin accumulation and reduced proteasome activity. Chemically induced reduction of proteasome activity was associated with lower glucose-stimulated insulin secretion, which was partly reproduced by palmitate exposure. These results show the presence of many changes in islet transcriptome in T2D islets and underline the importance of the association between UPS alterations and beta cell dysfunction in human T2D.