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The pancreatic islets comprising only 1%-2% of the volume are highly vascularized and innervated mini-organs. They contain five endocrine cell types, including β cells that secrete insulin, which is synthesized as a single polypeptide chain, preproinsulin, processed to proinsulin, and finally to insulin and C-peptide. This process is complex and regulated, involving the Golgi complex, the endoplasmic reticulum, and the secretory granules of the β cell.
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Insulin secretory vesicles release insulin to stimulate blood glucose uptake and regulate carbohydrate metabolism. When the blood glucose levels increase, glucose enters the pancreatic β-islet cells through glucose transporters. Once inside, glucose is metabolized through glycolysis, the citric acid cycle, and the electron transport chain, producing ATP. This increase in ATP concentration closes ATP-sensitive potassium channels, leading to depolarization of the membrane and the opening of...
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Insulin is released by beta cells of the pancreas when blood glucose levels are high. It facilitates glucose absorption and utilization in insulin-dependent cells with insulin receptors on their plasma membranes. Insulin promotes glucose uptake by increasing the number of glucose transport proteins in the cell membrane, allowing glucose to enter the cell. As a result, glucose utilization and ATP production are enhanced.
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Incretins include glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), which stimulate insulin secretion post-meals. In type 2 diabetes, GIP's efficacy is reduced, making GLP-1 a viable drug target. GIP originates from preproGIP.
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Insulin: The Receptor and Signaling Pathways01:28

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Insulin action is mediated through a receptor tyrosine kinase, akin to the IGF-1 receptor. The number of receptors per cell varies significantly, from 40 on erythrocytes to 300,000 on adipocytes and hepatocytes. The insulin receptor consists of linked α/β subunit dimers, forming a heterotetramer glycoprotein with two extracellular α subunits and two β subunits spanning the membrane. The α subunits inhibit the inherent tyrosine kinase activity of the β subunits, but...
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Dipeptidyl peptidase 4 (DPP-4) is a serine protease widely distributed in the body. It's involved in the inactivation of GLP-1 and GIP hormones, which are crucial for insulin regulation. DPP-4 inhibitors, such as sitagliptin (Januvia), saxagliptin (Onglyza), linagliptin (Tradjenta), alogliptin (Nesina), and vildagliptin (Galvus), help increase the proportion of active GLP-1, enhancing insulin secretion. These inhibitors work by competitively binding to DPP-4. This binding causes a...
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Updated: Nov 30, 2025

A Method for Mouse Pancreatic Islet Isolation and Intracellular cAMP Determination
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Insulinoma induces a hyperinsulinemia-mediated decrease of GLUT2 and GLP1 receptor in normal pancreatic β-cells.

H Sho1, K Fukui1, S Yoneda1

  • 1Departments of Metabolic Medicine, Graduate School of Medicine, Osaka University, Suita, Japan.

Biochemical and Biophysical Research Communications
|November 17, 2020
PubMed
Summary
This summary is machine-generated.

Insulinoma, a tumor producing insulin, causes lower expression of glucose transporter 2 (GLUT2) and glucagon-like peptide 1 receptor (GLP1R) in normal pancreatic beta cells. This downregulation may result from prolonged exposure to high insulin levels.

Keywords:
Glucagon-like peptide 1 receptorGlucose transporter 2InsulinomaPancreatic β-cellPostoperative hyperglycemia

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Area of Science:

  • Endocrinology
  • Molecular Biology
  • Oncology

Background:

  • Insulinoma is associated with transient hyperglycemia post-surgery.
  • The impact of insulinoma on normal pancreatic beta-cells remains unclear.
  • Understanding beta-cell function in insulinoma is crucial for metabolic health.

Purpose of the Study:

  • To investigate the expression of glucose transporter 2 (GLUT2) and glucagon-like peptide 1 receptor (GLP1R) in normal beta-cells of insulinoma patients.
  • To explore the in vitro effects of high insulin concentrations on GLUT2 and GLP1R expression in beta-cells.

Main Methods:

  • Comparative analysis of GLUT2 and GLP1R expression in non-tumorous islets from insulinoma patients and normal glucose tolerance (NGT) controls.
  • Quantitative real-time PCR (q-PCR) and Western blotting to assess gene and protein expression.
  • In vitro experiments exposing MIN6 beta-cells to high insulin concentrations.

Main Results:

  • Significantly lower expression rates of GLUT2 and GLP1R were observed in non-tumorous islets of insulinoma patients compared to NGT controls.
  • In vitro, high insulin exposure led to decreased GLUT2 protein levels after 12 hours and GLP1R protein levels after 24 hours.
  • No significant changes in GLUT2 and GLP1R mRNA levels were detected in response to high insulin concentrations.

Conclusions:

  • Insulinoma is associated with the downregulation of GLUT2 and GLP1R expression in adjacent normal pancreatic beta-cells.
  • Elevated insulin levels, characteristic of insulinoma, may be responsible for this observed downregulation.
  • These findings highlight a potential mechanism for altered beta-cell function in the presence of insulinoma.