Marked over expression of uncoupling protein-2 in beta cells exerts minor effects on mitochondrial metabolism

► The impact of UCP-2 over expression on mitochondrial function is controversial. ► We tested mitochondrial functions at defined levels of overexpression. ► We find minor increases of fatty acid oxidation and uncoupling. ► Effects were seen only at high level (fourfold) of over expression. ► Hence it is doubtful whether these effects are of importance in diabetes. 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