Background and aims
Excessive or unbalanced nutrient intake may cause diabetes. A growing body of evidence points to that mitochondrial dysfunction plays an important role in
Materials and methods
To enable the study we developed a high-throughput islet respirometry approach based on the XF24 platform, originally designed to study monolayers of cells. By applying drugs that act on the respiratory chain we can estimate the level of fuel-stimulated, uncoupled (reflecting proton leak), maximal as well as non-mitochondrial respiration under various conditions. Islets were derived from wildtype and high fat diet fed C57Bl6/J mice as well as from human donors.
β-cell dysfunction. The reason for this is likely that mitochondria stand in the center of nutrient metabolism. In this study we tested the hypothesis that islets from diabetic animals have defect mitochondrial respiratory function. Results
We found that due to increased proton leak, islets from diabetic high fat diet fed animals exhibit lower respiratory efficiency as compared to animals fed control chow. Examining the regulation of the leak we found that fuels that stimulate insulin secretion also increase uncoupled respiration, and that this may be mediated by reactive oxygen species. Moreover, dissecting the molecular mechanism, we show that the adenine nucleotide transporter contributes to one-third of the leak while uncoupling protein 2 and permeability transition pore appear not to contribute. Finally, we examined a cohort of human islets and found lower levels of uncoupled respiration as compared to mouse islets. However, as in the mouse islets glucose challenge induced increase in uncoupled respiration. Interestingly, there was a trend towards lower oxygen consumption rates in islets from obese donors.
Islets have relative high levels of proton leak, which is regulated by cellular fuels and reactive oxygen species. Adenine nucleotide transporter but not uncoupling protein 2 or permeability transition pore appears to contribute to the observed uncoupled respiration. Interestingly, levels of uncoupled respiration increase in a diabetes animal model. In theory, tuning islet mitochondrial efficiency may represent a therapeutic target.