Apoptosis rate and transcriptional response of pancreatic islets exposed to the PPAR gamma agonist Pioglitazone

Rodrigo N Lamounier,Maria Lúcia Corrêa-Giannella,Leonardo S Oliveira,Daniel Giannella-Neto,Peter White,Flavia L Costal,Cassio N Coimbra,Klaus H Kaestner

doi:10.1186/1758-5996-5-1

Abstract

To explore the molecular pathways underlying thiazolidinediones effects on pancreatic islets in conditions mimicking normo- and hyperglycemia, apoptosis rate and transcriptional response to Pioglitazone at both physiological and supraphysiological glucose concentrations were evaluated. Adult rat islets were cultured at physiological (5.6 mM) and supraphysiological (23 mM) glucose concentrations in presence of 10 μM Pioglitazone or vehicle. RNA expression profiling was evaluated with the PancChip 13k cDNA microarray after 24-h, and expression results for some selected genes were validated by qRT-PCR. The effects of Pioglitazone were investigated regarding apoptosis rate after 24-, 48- and 72-h. At 5.6 mM glucose, 101 genes were modulated by Pioglitazone, while 1,235 genes were affected at 23 mM glucose. Gene networks related to lipid metabolism were identified as altered by Pioglitazone at both glucose concentrations. At 23 mM glucose, cell cycle and cell death pathways were significantly regulated as well. At 5.6 mM glucose, Pioglitazone elicited a transient reduction in islets apoptosis rate while at 23 mM, Bcl2 expression was reduced and apoptosis rate was increased by Pioglitazone. Our data demonstrate that the effect of Pioglitazone on gene expression profile and apoptosis rate depends on the glucose concentration. The modulation of genes related to cell death and the increased apoptosis rate observed at supraphysiological glucose concentration raise concerns about Pioglitazone’s direct effects in conditions of hyperglycemia and reinforce the necessity of additional studies designed to evaluate TZDs effects on the preservation of β-cell function in situations where glucotoxicity might be more relevant than lipotoxicity.

Highlights

Type 2 diabetes is characterized by impaired insulin secretion and reduced peripheral insulin sensitivity
We evaluated five genes previously suggested as peroxisome proliferator-activated receptor γ (PPARγ) targets, Gck, Slc2a2, Abca1, Lpl and Ucp2, as well as the expression of Pparg, Ppara, Ins1 and Ins2
This study, designed to further investigate the direct effects of Pioglitazone on pancreatic islets, demonstrates that the effect of this TZD on islet apoptosis rate and gene expression profile depends on the glucose concentration

Summary

Introduction

Type 2 diabetes is characterized by impaired insulin secretion and reduced peripheral insulin sensitivity. Apoptosis constitutes the main form of β-cell death [12] and gluco- and/or lipotoxicity are two of the major mechanisms for islets dysfunction and apoptosis in pancreatic cells in type 2 diabetes [13]. While TZDs have been reported to have direct beneficial effects on β-cells by preventing these toxicities [14,15], by promoting antioxidative effects [16] and by preventing β-cell dysfunction under conditions of concomitant hyperglycemic and cytokine stress [17], this notion has been contested by others [18,19]. To further explore the molecular pathways underlying TZDs direct effects on pancreatic islets in conditions mimicking normo- and hyperglycemia, we have determined transcriptional response and apoptosis rate of rat islets to Pioglitazone, currently the only TZD in clinical use, at both physiological and supraphysiological glucose concentrations

Methods

Results

Conclusion