Glucose-induced O? consumption activates hypoxia inducible factors 1 and 2 in rat insulin-secreting pancreatic beta-cells.

ABSTRACT:

Background

Glucose increases the expression of glycolytic enzymes and other hypoxia-response genes in pancreatic beta-cells. Here, we tested whether this effect results from the activation of Hypoxia-Inducible-factors (HIF) 1 and 2 in a hypoxia-dependent manner.

Methodology/principal findings

Isolated rat islets and insulin-secreting INS-1E cells were stimulated with nutrients at various pO? values or treated with the HIF activator CoCl?. HIF-target gene mRNA levels and HIF subunit protein levels were measured by real-time RT-PCR, Western Blot and immunohistochemistry. The formation of pimonidazole-protein adducts was used as an indicator of hypoxia. In INS-1E and islet beta-cells, glucose concentration-dependently stimulated formation of pimonidazole-protein adducts, HIF1 and HIF2 nuclear expression and HIF-target gene mRNA levels to a lesser extent than CoCl? or a four-fold reduction in pO?. Islets also showed signs of HIF activation in diabetic Lepr(db/db) but not non-diabetic Lepr(db/+) mice. In vitro, these glucose effects were reproduced by nutrient secretagogues that bypass glycolysis, and were inhibited by a three-fold increase in pO? or by inhibitors of Ca²? influx and insulin secretion. In INS-1E cells, small interfering RNA-mediated knockdown of Hif1? and Hif2?, alone or in combination, indicated that the stimulation of glycolytic enzyme mRNA levels depended on both HIF isoforms while the vasodilating peptide adrenomedullin was a HIF2-specific target gene.

Conclusions/significance

Glucose-induced O? consumption creates an intracellular hypoxia that activates HIF1 and HIF2 in rat beta-cells, and this glucose effect contributes, together with the activation of other transcription factors, to the glucose stimulation of expression of some glycolytic enzymes and other hypoxia response genes.

SUBMITTER: Bensellam M 

PROVIDER: S-EPMC3250482 | biostudies-literature | 2012

REPOSITORIES: biostudies-literature