Background and Aim: 

We previously tested the effects of 18h culture in 2, 5, 10 and 30 mM glucose (G2, G5, G10 and G30) on the transcriptome of rat islets and found that the mRNA levels of most glycolytic enzymes and other Hypoxia Inducible Factor (HIF) target genes are markedly up-regulated by G30 vs. G5. Thus, high glucose, which increases O₂ consumption in b-cells, may induce a relative hypoxia and thereby cause glucotoxicity. Here, we tested whether overnight culture in high glucose activates HIF in rat beta-cells.

Results: 

Stimulation by high glucose of HIF target genes (Adm, Gapdh, AldoA) was mimicked by hypoxia (1%vs. 20% O₂) and CoCl₂ (3–100 mmol/l) in rat islets and INS1-E cells. Other genes with a similar expression profile in response to glucose were not affected by hypoxia nor CoCl₂ treatment (Txnip, Aldob). In parallel, high glucose increased HIF1a and HIF2a protein levels by ~4 fold in INS1-E nuclear extracts and activated the nuclear translocation of their dimerization partner HIF1b. These glucose effects were prevented by culture under hyperoxic conditions (60%vs. 20% O₂) and by pharmacological agents that inhibit the glucose stimulation of Ca²⁺ influx and insulin secretion (1 mmol/l nimodipine, 250 mmol/l diazoxide and 1 mmol/l clonidine).

Conclusion: 

These results suggest that high glucose induces a state of relative hypoxia not only in whole rat islets but also in INS1-E cells cultured as monolayers, leading to the activation of HIF1/2a and increased expression of HIF target genes. These effects, which likely result from increased O₂ consumption by pancreatic beta-cells following the glucose-mediated acceleration of mitochondrial metabolism, may play a role in beta-cell glucotoxicity.