UCP2 in pancreatic beta-cells : a radical way to short circuit glucose sensing?

Uncoupling proteins (UCPs) catalyse proton transport across the mitochondrial inner membrane, thereby uncoupling oxidative phosphorylation. UCP2 is expressed in several mammalian tissues including pancreatic β-cells. Since UCP2 activity uncouples the processes that link glucose metabolism (oxidation) to insulin secretion (phosphorylation), it is expected to attenuate glucose-stimulated insulin secretion (GSIS). Published studies using UCP2 over-expressing and UCP2 ablated β-cells support this hypothesis. Therefore, identifying regulators of β-cell UCP2 activity may help develop novel ways to treat type II diabetes. Furthermore, β-cells present a valuable system with which to study UCP2 activity in situ. Studies using isolated mitochondria have demonstrated that the superoxide radical and particular reactive alkenals activate UCP2, and that novel, mitochondrially-targeted antioxidants (mito-antioxidants) prevent activation of UCP2 by superoxide. Mito-antioxidants and reactive alkenals are thus useful tools to investigate pancreatic β-cell UCP2 activity in situ. I hypothesised that endogenously produced superoxide activates UCP2 in β-cells to negatively regulate GSIS, and tested this hypothesis by measuring UCP2 activity in isolated β-cell mitochondria and GSIS in intact β-cells. Mito-antioxidants prevented superoxide-activation of UCP2 in isolated β-cell mitochondria but, surprisingly, did not potentiate GSIS. These unexpected findings suggested that either UCP2 was endogenously inactive, or endogenous UCP2 activity is not inhibited by mito-antioxidants. I sought to distinguish between these possibilities using UCP2 overexpressing β-cells, and by investigating isolated mitochondria in which UCP2 appeared to be endogenously active. Certain reactive alkenals both activated UCP2 in β cell mitochondria and attenuated GSIS in intact cells, suggesting that may attenuate insulin secretion physiologically, or provide valuable tools to probe UCP2 activity in cells.EThOS - Electronic Theses Online ServiceGBUnited Kingdo