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

Abstract

Highlights: Black-Right-Pointing-Pointer The impact of UCP-2 over expression on mitochondrial function is controversial. Black-Right-Pointing-Pointer We tested mitochondrial functions at defined levels of overexpression. Black-Right-Pointing-Pointer We find minor increases of fatty acid oxidation and uncoupling. Black-Right-Pointing-Pointer Effects were seen only at high level (fourfold) of over expression. Black-Right-Pointing-Pointer Hence it is doubtful whether these effects are of importance in diabetes. -- 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 48 h exposure to 1 {mu}g/ml of doxycycline (dox) induced UCP-2 fourfold (424 {+-} 113%, mean {+-} SEM) and 0.1 {mu}g/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-{sup 14}C]-glucose oxidation (+5 {+-} 9% at 11 mM glucose). Oxidation of [1-{sup 14}C]-oleate was increased from 4088 to 5797 fmol/{mu}g prot/2 h at 3.3 mM glucose, p < 0.03. Oxidationmore » of L-[{sup 14}C(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.« less

Authors:
 [1]; ;  [1]; ;  [2];  [3];  [1];  [1];  [4]
  1. Department of Cancer Research and Molecular Medicine, Norwegian University of Science and Technology (NTNU), Trondheim (Norway)
  2. Department of Molecular Medicine and Surgery, Karolinska Institute, Stockholm (Sweden)
  3. Department of Laboratory Medicine, NTNU, Trondheim (Norway)
  4. (Sweden)
Publication Date:
OSTI Identifier:
22207913
Resource Type:
Journal Article
Journal Name:
Biochemical and Biophysical Research Communications
Additional Journal Information:
Journal Volume: 423; Journal Issue: 2; Other Information: Copyright (c) 2012 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0006-291X
Country of Publication:
United States
Language:
English
Subject:
60 APPLIED LIFE SCIENCES; APOPTOSIS; ATP; CARBON 14; GLUCOSE; GLUTAMINE; INSULIN; METABOLISM; MITOCHONDRIA; OXIDATION; PHOSPHORUS 30; SCANNING ELECTRON MICROSCOPY; SECRETION

Citation Formats

Hals, Ingrid K., E-mail: ingrid.hals@ntnu.no, Ogata, Hirotaka, Pettersen, Elin, Ma, Zuheng, Bjoerklund, Anneli, Skorpen, Frank, Egeberg, Kjartan Wollo, Grill, Valdemar, and Department of Molecular Medicine and Surgery, Karolinska Institute, Stockholm. Marked over expression of uncoupling protein-2 in beta cells exerts minor effects on mitochondrial metabolism. United States: N. p., 2012. Web. doi:10.1016/J.BBRC.2012.05.101.
Hals, Ingrid K., E-mail: ingrid.hals@ntnu.no, Ogata, Hirotaka, Pettersen, Elin, Ma, Zuheng, Bjoerklund, Anneli, Skorpen, Frank, Egeberg, Kjartan Wollo, Grill, Valdemar, & Department of Molecular Medicine and Surgery, Karolinska Institute, Stockholm. Marked over expression of uncoupling protein-2 in beta cells exerts minor effects on mitochondrial metabolism. United States. doi:10.1016/J.BBRC.2012.05.101.
Hals, Ingrid K., E-mail: ingrid.hals@ntnu.no, Ogata, Hirotaka, Pettersen, Elin, Ma, Zuheng, Bjoerklund, Anneli, Skorpen, Frank, Egeberg, Kjartan Wollo, Grill, Valdemar, and Department of Molecular Medicine and Surgery, Karolinska Institute, Stockholm. Fri . "Marked over expression of uncoupling protein-2 in beta cells exerts minor effects on mitochondrial metabolism". United States. doi:10.1016/J.BBRC.2012.05.101.
@article{osti_22207913,
title = {Marked over expression of uncoupling protein-2 in beta cells exerts minor effects on mitochondrial metabolism},
author = {Hals, Ingrid K., E-mail: ingrid.hals@ntnu.no and Ogata, Hirotaka and Pettersen, Elin and Ma, Zuheng and Bjoerklund, Anneli and Skorpen, Frank and Egeberg, Kjartan Wollo and Grill, Valdemar and Department of Molecular Medicine and Surgery, Karolinska Institute, Stockholm},
abstractNote = {Highlights: Black-Right-Pointing-Pointer The impact of UCP-2 over expression on mitochondrial function is controversial. Black-Right-Pointing-Pointer We tested mitochondrial functions at defined levels of overexpression. Black-Right-Pointing-Pointer We find minor increases of fatty acid oxidation and uncoupling. Black-Right-Pointing-Pointer Effects were seen only at high level (fourfold) of over expression. Black-Right-Pointing-Pointer Hence it is doubtful whether these effects are of importance in diabetes. -- 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 48 h exposure to 1 {mu}g/ml of doxycycline (dox) induced UCP-2 fourfold (424 {+-} 113%, mean {+-} SEM) and 0.1 {mu}g/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-{sup 14}C]-glucose oxidation (+5 {+-} 9% at 11 mM glucose). Oxidation of [1-{sup 14}C]-oleate was increased from 4088 to 5797 fmol/{mu}g prot/2 h at 3.3 mM glucose, p < 0.03. Oxidation of L-[{sup 14}C(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.},
doi = {10.1016/J.BBRC.2012.05.101},
journal = {Biochemical and Biophysical Research Communications},
issn = {0006-291X},
number = 2,
volume = 423,
place = {United States},
year = {2012},
month = {6}
}