PDHK-2 Deficiency Is Associated with Attenuation of Lipase-Mediated Fat Consumption for the Increased Survival of Caenorhabditis elegans Dauers Sunhee Kim, E-Jin Shin, Jeong-Hoon Hahm, Pil-Jong Park, Ji-Eun Hwang, Young-Ki Paik* Department of Biochemistry and Integrated Omics for Biomedical Science, World Class University Program, College of Life Science and Biotechnology, Yonsei Proteome Research Center, Yonsei University, Seoul, Korea Abstract In Caenorhabditis elegans, slow fat consumption has been suggested to contribute to the extension of the survival rate during nutritionally adverse conditions. Here, we investigated the potential role of pyruvate dehydrogenase kinase (PDHK)- 2, the C. elegans homolog of mammalian PDK, effects on fat metabolism under nutritional conditions. PDHK-2 was expressed at low levels under well-fed conditions but was highly induced during long-term starvation and in the dauer state. This increase in pdhk-2 expression was regulated by both DAF-16 and NHR-49. Dauer-specific induction of PDHK-2 was abolished upon entry into the post-dauer stage. Interestingly, in the long-term dauer state, stored fat levels were higher in daf-2(e1370);pdhk-2 double mutants than in daf-2(e1370), suggesting a positive relationship between PDHK-2 activity and fat consumption. PDHK-2 deficiency has been shown to lead to greater preservation of residual fats, which would be predicted to contribute to survival during the dauer state. A test of this prediction showed that the survival rates of daf-2(e1370);pdhk- 2(tm3075) and daf-2(e1370);pdhk-2(tm3086) double mutants were higher than that of daf-2(e1370), suggesting that loss of either the ATP-binding domain (tm3075) or branched chain keto-acid dehydrogenase kinase domain (tm3086) of PDHK-2 leads to reduced fat consumption and thus favors increased dauer survival. This attenuated fat consumption in the long- term dauer state of C. elegans daf-2 (e1370);pdhk-2 mutants was associated with concomitant down-regulation of the lipases ATGL (adipose triglyceride lipase), HSL (hormone-sensitive lipase), and C07E3.9 (phospholipase). In contrast, PDHK-2 overexpression in wild-type starved worms induced lipase expression and promoted abnormal dauer formation. Thus, we propose that PDHK-2 serves as a molecular bridge, connecting fat metabolism and survival under nutritionally adverse conditions in C. elegans. Citation: Kim S, Shin E-J, Hahm J-H, Park P-J, Hwang J-E, et al. (2012) PDHK-2 Deficiency Is Associated with Attenuation of Lipase-Mediated Fat Consumption for the Increased Survival of Caenorhabditis elegans Dauers. PLoS ONE 7(7): e41755. doi:10.1371/journal.pone.0041755 Editor: Howard Riezman, University of Geneva, Switzerland Received June 18, 2012; Accepted June 25, 2012; Published July 27, 2012 Copyright: 2012 Kim et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This study was supported by the National Research Foundation of Korea (NRF) grant (No. 2011-0028112 to YKP) and WCU Program (R31-2008-000- 10086-0) funded by the Korean government (MEST), and the National Project for Personalized Genomic Medicine (A111218-11-CP01 to YKP). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: paikyk@yonsei.ac.kr Introduction It has been well documented that a close relationship exists between energy metabolism and aging processes in animals, including the nematode Caenorhabditis elegans [1,2]. In C. elegans, in particular, the critical role of insulin/insulin-like growth factor-1 (IGF-1) signaling (IIS) in metabolism and the control of aging has been well established. For example, suppression of the IIS pathway has been shown to cause a substantial increase in both mean lifespan (MLS) and fat accumulation [1–3]. This pathway also controls the dauer state, a non-aging condition that is important in determining the relationship between metabolism and aging [4,5]. When C. elegans encounters unfavorable growth conditions (e.g., lack of food or high temperatures) or high concentrations of dauer pheromones (daumones or ascarosides), it can enter the dauer state [5–10]. Studies on dauer entry in C. elegans have suggested that this process is compartmentalized according to metabolic phase and growth time [11]. When L2 larvae prepare for dauer entry, nutritional adaptation accompanies intestinal and hypodermal fat accumulation, enabling C. elegans to survive an extended dormant period [12]. The dauer state is controlled by an IIS mechanism in which DAF-16 serves as a downstream effector [11–13]. The dauer state is resistant to environmental stresses, such as heat and cold, as well as oxidative stress, and the metabolic activity of dauer larvae is generally reduced [12]. Because dauer larvae do not feed, they use mostly stored triglycerides (TGs) as an energy source [12,13]; TGs, in turn, are hydrolyzed to fatty acids by lipases [14]. Additional macronutrients that are stored and metabolized in dauer larvae include glycogen and trehalose [15]. Because their supply of stored nutrients is limited, dauers must suppress energy-consuming metabolic activities to survive [16]. Microarray and SAGE (serial analysis of gene expression) assays of dauer larvae, recovered dauers, and mixed-stage populations have suggested that the expression of enzymes involved in b-oxidation of fatty acids, glycolysis, glyoxylate, and gluconeogenesis pathways are enhanced under nutritionally adverse conditions, indicating that TGs are degraded by lipases and converted into sugars that are used for survival [17–21]. Slow energy release and tightly controlled energy consumption may be critical to long-term survival through diapause, hibernation, or long-term fasting in a PLoS ONE | www.plosone.org 1 July 2012 | Volume 7 | Issue 7 | e41755