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Modeling the pancreatic ?-cell: dual mechanisms of glucose suppression of glucagon secretion.

ABSTRACT: The mechanism by which glucose induces insulin secretion in ?-cells is fairly well understood. Despite years of research, however, the mechanism of glucagon secretion in ?-cells is still not well established. It has been proposed that glucose regulates glucagon secretion by decreasing the conductance of either outward ATP-dependent potassium channels (K(ATP)) or an inward store-operated current (SOC). We have developed a mathematical model based on mouse data to test these hypotheses and found that both mechanisms are possible. Glucose metabolism closes K(ATP) channels, which depolarizes the cell but paradoxically reduces calcium influx by inactivating voltage-dependent calcium and sodium channels and decreases secretion. Glucose metabolism also activates SERCA pumps, which fills the endoplasmic reticulum and hyperpolarizes the cells by reducing the inward current through SOC channels and again suppresses glucagon secretion. We find further that the two mechanisms can combine to account for the nonmonotonic dependence of secretion on glucose observed in some studies, an effect that cannot be obtained with either mechanism alone.

SUBMITTER: Watts M

PROVIDER: S-EPMC3944880 | biostudies-other | 2014 Feb

REPOSITORIES: biostudies-other

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Modeling the pancreatic α-cell: dual mechanisms of glucose suppression of glucagon secretion.

Watts Margaret M Sherman Arthur A

Biophysical journal 20140201 3

The mechanism by which glucose induces insulin secretion in β-cells is fairly well understood. Despite years of research, however, the mechanism of glucagon secretion in α-cells is still not well established. It has been proposed that glucose regulates glucagon secretion by decreasing the conductance of either outward ATP-dependent potassium channels (K(ATP)) or an inward store-operated current (SOC). We have developed a mathematical model based on mouse data to test these hypotheses and found t ...[more]

PMID: 24507615

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Project description:Inhibition of glucagon hypersecretion from pancreatic α-cells is an appealing strategy for the treatment of diabetes. Our hypothesis is that proteins that associate with glucagon within alpha cell secretory granules will regulate glucagon secretion, and may provide druggable targets for controlling abnormal glucagon secretion in diabetes. Recently, we identified a dynamic glucagon interactome within the secretory granules of the α cell line, αTC1-6, and showed that select proteins within the interactome could modulate glucagon secretion. In the present study, we show that one of these interactome proteins, the neuronal protein stathmin-2, is expressed in αTC1-6 cells and in mouse pancreatic alpha cells, and is a novel regulator of glucagon secretion. The secretion of both glucagon and Stmn2 was significantly enhanced in response to 55 mM K+, and immunofluorescence confocal microscopy showed co-localization of stathmin-2 with glucagon and the secretory granule markers chromogranin A and VAMP-2 in αTC1-6 cells. In mouse pancreatic islets, Stathmin-2 co-localized with glucagon, but not with insulin, and co-localized with secretory pathway markers. To show a function for stathmin-2 in regulating glucagon secretion, we showed that siRNA-mediated depletion of stathmin-2 in αTC1-6 cells caused glucagon secretion to become constitutive without any effect on proglucagon mRNA levels, while overexpression of stathmin-2 completely abolished both basal and K+-stimulated glucagon secretion. Overexpression of stathmin-2 increased the localization of glucagon into the endosomal-lysosomal compartment, while depletion of stathmin-2 reduced the endosomal localization of glucagon. Therefore, we describe stathmin-2 as having a novel role as an alpha cell secretory granule protein that modulates glucagon secretion via trafficking through the endosomal-lysosomal system. These findings describe a potential new pathway for the regulation of glucagon secretion, and may have implications for controlling glucagon hypersecretion in diabetes.

Dataset Information

Modeling the pancreatic ?-cell: dual mechanisms of glucose suppression of glucagon secretion.

Publications

Modeling the pancreatic α-cell: dual mechanisms of glucose suppression of glucagon secretion.

Similar Datasets

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