Mechanisms of glucose hypersensitivity in beta-cells from normoglycemic, partially pancreatectomized mice.

Abstract

Increased ␤-cell sensitivity to glucose precedes the loss of glucose-induced insulin secretion in diabetic animals. Changes at the level of ␤-cell glucose sensor have been described in these situations, but it is not clear whether they fully account for the increased insulin secretion. Using a euglycemic-normolipidemic 60% pancreatectomized (60%-Px) mouse model, we have studied the ionic mechanisms responsible for increased ␤-cell glucose sensitivity. Two weeks after Px (Px14 group), Px mice maintained normoglycemia with a reduced ␤c e l l mass (0.88 ± 0.18 mg) compared with control mice (1.41 ± 0.21 mg). At this stage, the dose-response curve for glucose-induced insulin release showed a signific a n t displacement to the left (P < 0.001). Islets from the Px14 group showed oscillatory electrical activity and cytosolic Ca 2 + ([ C a 2 + ] i) oscillations in response to glucose concentrations of 5.6 mmol/l compared with islets from the control group at 11.1 mmol/l. All the above changes were fully reversible both in vitro (after 48-h culture of islets from the Px14 group) and in vivo (after regeneration of ␤-cell mass in islets studied 60 days after Px). No significant differences in the input resistance and ATP inhibition of ATP-sensitive K + (K AT P) channels were found between ␤-cells from the Px14 and control groups. The dose-response curve for glucoseinduced MTT (C,N-d i p h e n y l-N-4,5-dimethyl thiazol 2 yl tetrazolium bromide) reduction showed a significant displacement to the left in islets from the Px14 group (P < 0.001). These results indicate that increased glucose sensitivity in terms of insulin secretion and Ca 2 + s i gnaling was not due to intrinsic modifications of K AT P channel properties, and suggest that the changes are most likely to be found in the glucose metabolism.

Alginate Encapsulation of Human Embryonic Stem Cells to Enhance Directed Differentiation to Pancreatic Islet-Like Cells

“…Protein quantification using MagPix showed that the encapsulated UD hESCs expressed intracellular c-peptide (0.39 pg/mg total-protein) and glucagon (0.019 pg/mg total-protein). Although a previous study with primary mouse islets showed a c-peptide content of 9.93 ng/mg total-protein, 40 considering the present results are obtained with hESCs, this is indeed an encouraging step toward functional islet-like cell types from hESCs in 3D culture. Gene expression analysis showed that the required machinery necessary for glucose-stimulated insulin release was present by upregulation of the K ATP subunits SUR1 and KIR6.2 as well as glucokinase.…”

Regulation of Pancreatic β-Cell Regeneration in the Normoglycemic 60% Partial-Pancreatectomy Mouse

“…However, the confounding effects of hyperglycemia in these models on BCM compensation, the signaling pathways, and ␤-cell gene expression could not be excluded (2). In contrast, the 60% Px rodent model offers a significant advantage in examining BCM compensation since a vigorous, but transient, regeneration process ensues despite a 60% reduction in BCM (17,18).…”

“…Sixty percent Px was performed on 8-week-old male C57BL/6 mice (n ϭ 20 -25 per group) (Taconic), as described previously for rats (17) and mice (18). Mice were anesthetized with an intraperitoneal injection containing a mixture of ketamine (50 mg/kg) and xylazine (5 mg/kg).…”

Increased Glucose Sensitivity of Stimulus-Secretion Coupling in Islets FromPsammomys obesusAfter Diet Induction of Diabetes

“…It is thus possible that the sustained ␤-cell hyperactivity required to maintain normoglycemia in the face of insulin resistance, rather than hyperglycemia itself, leads to the observed changes in glucose sensitivity. The advantage of such a process is obvious as long as normoglycemia is preserved (42,49), but this physiological adaptation to increased insulin demands seems completely inoperative in the presence of persistent hyperglycemia.…”