Isocitrate dehydrogenase 2 protects mice from high-fat diet-induced metabolic stress by limiting oxidative damage to the mitochondria from brown adipose tissue

Lee et al. Experimental & Molecular Medicine (2020) 52:238–252 https://doi.org/10.1038/s12276-020-0379-z ARTICLE Experimental & Molecular Medicine Open Access Isocitrate dehydrogenase 2 protects mice from high-fat diet-induced metabolic stress by limiting oxidative damage to the mitochondria from brown adipose tissue 1234567890():,; 1234567890():,; 1234567890():,; 1234567890():,; Jae-Ho Lee1, Younghoon Go2,3,4, Do-Young Kim1, Sun Hee Lee1, Ok-Hee Kim5, Yong Hyun Jeon6, Taeg Kyu Kwon7, Jae-Hoon Bae1, Dae-Kyu Song 1, Im Joo Rhyu8, In-Kyu Lee2,3, Minho Shong9, Byung-Chul Oh5, Christopher Petucci10,11, Jeen-Woo Park12, Timothy F. Osborne13 and Seung-Soon Im 1 Abstract Isocitrate dehydrogenase 2 (IDH2) is an NADP+-dependent enzyme that catalyzes the oxidative decarboxylation of isocitrate to α-ketoglutarate in the mitochondrial matrix, and is critical for the production of NADPH to limit the accumulation of mitochondrial reactive oxygen species (ROS). Here, we showed that high-fat diet (HFD) feeding resulted in accelerated weight gain in the IDH2KO mice due to a reduction in whole-body energy expenditure. Moreover, the levels of NADP+, NADPH, NAD+, and NADH were significantly decreased in the brown adipose tissue (BAT) of the HFD-fed IDH2KO animals, accompanied by decreased mitochondrial function and reduced expression of key genes involved in mitochondrial biogenesis, energy expenditure, and ROS resolution. Interestingly, these changes were partially reversed when the antioxidant butylated hydroxyanisole was added to the HFD. These observations reveal a crucial role for IDH2 in limiting ROS-dependent mitochondrial damage when BAT metabolism is normally enhanced to limit weight gain in response to dietary caloric overload. Introduction Brown adipose tissue (BAT) is a major metabolic organ in mammals, and has a key role in regulating whole-body thermogenesis, energy expenditure, and glucose metabolism1. Uncoupled respiration in the BAT is increased to prevent weight gain and insulin resistance when mice are fed a high-fat diet (HFD)2. A potentially unhealthy complication of elevated uncoupled respiration is the generation of mitochondrial reactive oxygen species (ROS), which must be limited to prevent oxidative damage to the Correspondence: Timothy F. Osborne () or Seung-Soon Im () 1 Department of Physiology, Keimyung University School of Medicine, Daegu 42601, Republic of Korea 2 Department of Internal Medicine, School of Medicine Kyungpook National University, Kyungpook National University Hospital, Daegu 41944, Republic of Korea Full list of author information is available at the end of the article. enzyme complexes of the electron transport (ET) chain and the tricarboxylic acid (TCA) cycle3,4. Proper coordinated action of key mitochondrial ET and TCA enzymes is required to modulate substrate flow and balance electron transfer. One of the key steps in the TCA cycle is the oxidative decarboxylation of isocitrate to generate α-ketoglutarate (αKG), which is catalyzed by isocitrate dehydrogenase (IDH) in the mitochondrial matrix. There are three mammalian IDH isoforms (IDH1, IDH2, and IDH3). The reaction catalyzed by IDH3 is irreversible, and this protein is thought to be the isoform responsible for the bulk of carbon flux through the TCA cycle, in which the electron capture is paired with the nicotinamide adenine dinucleotide (NAD+) and nicotinamide adenine dinucleotide hydrogen (NADH) cofactors. In contrast, both IDH1 and IDH2 catalyze reversible reactions, are paired with nicotinamide adenine dinucleotide © The Author(s) 2020 Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/. Official journal of the Korean Society for Biochemistry and Molecular Biology 239 Lee et al. Experimental & Molecular Medicine (2020) 52:238–252 phosphate (NADP+) and nicotinamide adenine dinucleotide hydrogen phosphate (NADPH), and reside in the cytosol and mitochondrial matrix, respectively. IDH1 and IDH2 have been proposed to balance cytoplasmic and mitochondrial redox, respectively, as their major roles5. Mitochondrial NADPH is essential to provide reducing equivalents to maintain glutathione (GSH) for the glutathione peroxidase (GPX)-dependent scavenging of mitochondrial ROS, which protects against the oxidative damage that occurs during times of elevated ET chain activity6,7. Although IDH2 is considered a unique enzyme in the regulation of mitochondrial ROS, its contribution to mitochondrial function during metabolic stresses such as HFD-dependent obesity is unknown. In this study, we showed that HFD-challenged IDH2KO mice gained significantly more weight than WT mice fed the same diet. The excess weight gains in the IDH2KO group occurred more rapidly than those in the WT group, and were accompanied by increased levels of cellular ROS and reduced energy expenditure in the BAT. The excess weight gain and impaired BAT activity were reversed when the antioxidant butylated hydroxyanisole (BHA) was added to the HFD. These studies uncover a critical role for IDH2 in balancing the ROS levels in the BAT when defending against body weight gain in response to the metabolic challenge of excess calorie consumption. Materials and methods Animal studies All procedures were performed in accordance with the Institutional Animal Care and Use Committees at Keimyung University School of Medicine, Daegu, South Korea (KM-2015-32R3). Four-week-old male IDH2KO mice8 and WT littermates with the same genetic background (C57BL/6J) were used for this study. No randomization of the mice was used. All animals were kept under 12-h light–dark cycles (6 a.m.–6 p.m. light, 6 p.m.–6 a.m. light) at 22–24 °C and 60–70% humidity with free access to water in a specific pathogen-free facility. These mice were fed either a low-fat diet (LFD, Research Diet: D12450J, containing 10% fat [kcal%]) or a HFD (Research Diet: D12492, containing 60% fat [kcal %]), and 7.5 g/kg BHA (Sigma Aldrich, St. Louis, Missouri, USA) using a modified protocol from a previous study9. We mixed the purchased HFD and LFD with butylated hydroxyanisole by grinding the BHA together with the HFD or LFD pellets, and provided the combined mixture to the different groups (...truncated)