Abstract
Evidence is conflicting as to the impact of elevated levels of uncoupling protein-2 (UCP-2) on insulin-producing beta cells. Here we investigated effects of a fourfold induction of UCP-2 protein primarily on mitochondrial parameters and tested for replication of positive findings at a lower level of induction.We transfected INS-1 cells to obtain a tet-on inducible cell line. A 48h exposure to 1μg/ml of doxycycline (dox) induced UCP-2 fourfold (424±113%, mean±SEM) and 0.1μg/ml twofold (178±29%, n=3).Fourfold induced cells displayed normal viability (MTT, apoptosis), normal cellular insulin contents and, glucose-induced insulin secretion (+27±11%) as well as d-[U-14C]-glucose oxidation (+5±9% at 11mM glucose). Oxidation of [1-14C]-oleate was increased from 4088 to 5797 fmol/μg prot/2h at 3.3mM glucose, p<0.03. Oxidation of l-[14C(U)]-glutamine was unaffected. Induction of UCP-2 did not significantly affect measures of mitochondrial membrane potential (Rhodamine 123) or mitochondrial mass (Mitotracker Green) and did not affect ATP levels. Oligomycin-inhibited oxygen consumption (a measure of mitochondrial uncoupling) was marginally increased, the effect being significant in comparison with dox-only treated cells, p<0.05. Oxygen radicals, assessed by dichlorofluorescin diacetate, were decreased by 30%, p<0.025. Testing for the lower level of UCP-2 induction did not reproduce any of the positive findings. A fourfold induction of UCP-2 was required to exert minor metabolic effects. These findings question an impact of moderately elevated UCP-2 levels in beta cells as seen in diabetes.
Published Version
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