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Diabetes. 2008 Feb;57(2):424-31. Epub 2007 Nov 8.

Cyclical and alternating infusions of glucose and intralipid in rats inhibit insulin gene expression and Pdx-1 binding in islets.

Author information

1
DVM, Montreal Diabetes Research Center, Centre de Recherche du Centre Hospitalier de l'Université de Montréal, Technopole Angus, 2901 Rachel Est, Montréal, QC, H1W 4A4, Canada.

Abstract

OBJECTIVE:

Prolonged exposure of isolated islets of Langerhans to elevated levels of fatty acids, in the presence of high glucose, impairs insulin gene expression via a transcriptional mechanism involving nuclear exclusion of pancreas-duodenum homeobox-1 (Pdx-1) and loss of MafA expression. Whether such a phenomenon also occurs in vivo is unknown. Our objective was therefore to ascertain whether chronic nutrient oversupply inhibits insulin gene expression in vivo.

RESEARCH DESIGN AND METHODS:

Wistar rats received alternating 4-h infusions of glucose and Intralipid for a total of 72 h. Control groups received alternating infusions of glucose and saline, saline and Intralipid, or saline only. Insulin and C-peptide secretion were measured under hyperglycemic clamps. Insulin secretion and gene expression were assessed in isolated islets, and beta-cell mass was quantified by morphometric analysis.

RESULTS:

Neither C-peptide secretion nor insulin sensitivity was different among infusion regimens. Insulin content and insulin mRNA levels were lower in islets isolated from rats infused with glucose plus Intralipid. This was associated with reduced Pdx-1 binding to the endogenous insulin promoter, and an increased proportion of Pdx-1 localized in the cytoplasm versus the nucleus. In contrast, MafA mRNA and protein levels and beta-cell mass and proliferation were unchanged.

CONCLUSIONS:

Cyclical and alternating infusions of glucose and Intralipid in normal rats inhibit insulin gene expression without affecting insulin secretion or beta-cell mass. We conclude that fatty acid inhibition of insulin gene expression, in the presence of high glucose, is an early functional defect that may contribute to beta-cell failure in type 2 diabetes.

PMID:
17991758
PMCID:
PMC2979006
DOI:
10.2337/db07-1285
[Indexed for MEDLINE]
Free PMC Article

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