Chronic glucolipotoxic conditions in pancreatic islets impair insulin secretion due to dysregulated calcium dynamics, glucose responsiveness and mitochondrial activity

Abstract

BackgroundIn the progression towards diabetes, glucolipotoxicity is one of the main causes of pancreatic beta cell pathology. The aim of this study was to examine the in vitro effects of chronic glucolipotoxic conditions on cellular responses in pancreatic islets, including glucose and fat metabolism, Calcium mobilization, insulin secretion and insulin content.ResultsExposure of islets to chronic glucolipotoxic conditions decreased glucose stimulated insulin secretion in vitro. Reduced protein levels of Glut2/slc2a2, and decreased glucokinase and pyruvate carboxylase mRNA levels indicated a significant lowering in glucose sensing. Concomitantly, both fatty acid uptake and triglyceride accumulation increased significantly while fatty acid oxidation decreased. This general suppression in glucose metabolism correlated well with a decrease in mitochondrial number and activity, reduction in cellular ATP content and dampening of the TCA cycle. Further, we also observed a decrease in IP3 levels and lower Calcium mobilization in response to glucose. Importantly, chronic glucolipotoxic conditions in vitro decreased insulin gene expression, insulin content, insulin granule docking (to the plasma membrane) and insulin secretion.ConclusionsOur results present an integrated view of the effects of chronic glucolipotoxic conditions on known and novel signaling events, in vitro, that results in reduced glucose responsiveness and insulin secretion.

High Recovery of Functional Islets Stored at Low and Ultralow Temperatures

“…Insulin secretion function of freshly isolated and cryopreserved islets was assessed by performing GSIS according to a previously published protocol [29]. The medium-sized islets (4-6 in number) ranging from 100-150 µm, were handpicked and added to 24 well plates (Nunc A/S) in triplicate.…”

Curcumin pretreatment mediates antidiabetogenesis via functional regulation of adrenergic receptor subtypes in the pancreas of multiple low-dose streptozotocin-induced diabetic rats

“…Diabetic rats showed a significant reduction in the pancreatic IP3 content, leading to decreased calcium mobilization from endoplasmic reticulum in response to glucose and other secretagogue stimuli. [63]. Curcumin pre-treated rats were able to maintain a near control level of IP3 when compared to diabetic rats.…”

Bioenergetics and Type 2 Diabetes

“…Because in pancreatic islets ATP is co-secreted with insulin, it is difficult to dissociate between the effects of FA on ATP syntheses and changes of ATP content in insulin granules. In fact, the insulin content is decreased in islets chronically exposed to FFA [8].…”

“…In an attempt to model "glucolipotoxicity" in vitro, pancreatic islets are usually cultured for several days in high glucose and fatty acids (FA) concentrations. Studies have described multiple cellular processes involved in the pathogenesis of β-cell dysfunction, including changes in gene expression [1,2] intermediary metabolism [3], mitochondrial function [4], ion channel activity [5][6][7], insulin synthesis and exocytosis [8]. Different molecular mechanisms of FAinduced β-cell dysfunction have been proposed including accumulation of ceramide [9], apoptosis of β-cells due to oxidative [10][11] and endoplasmic reticulum (ER) stress [12,13] as well as others mechanisms [14,15].…”

“…The latest effect should lead to changes in oxygen consumption and oxidative ATP synthesis. However, such data are limited and related to insulinoma cells [45] and only measurements of total ATP reported in islets exposed to FA [8]. Because in pancreatic islets ATP is co-secreted with insulin, it is difficult to dissociate between the effects of FA on ATP syntheses and changes of ATP content in insulin granules.…”