ROS and hypoxia signaling regulate periodic metabolic arousal during insect dormancy to coordinate glucose, amino acid, and lipid metabolism Chao Chena,1, Rohit Maharb, Matthew E. Merrittb, David L. Denlingerc,d,1, and Daniel A. Hahna,e,1 aDepartment of Entomology and Nematology, The University of Florida, Gainesville, FL 32611-0620; bDepartment of Biochemistry and Molecular Biology, The University of Florida, Gainesville, FL 32610-0245; cDepartment of Entomology, 300 Aronoff Laboratory, The Ohio State University, Columbus, OH 43210; dDepartment of Evolution, Ecology, and Organismal Biology, The Ohio State University, 300 Aronoff Laboratory, Columbus, OH 43210; and eGenetics Institute, The University of Florida, Gainesville, FL 32610-3610 Contributed by David L. Denlinger, November 5, 2020 (sent for review August 20, 2020; reviewed by Kendra J. Greenlee and Vladimír Košál) Metabolic suppression is a hallmark of animal dormancy that dormant organisms maintain relatively constant lowered metabo- promotes overall energy savings. Some diapausing insects and lism, others including a few mammalian hibernators and a few some mammalian hibernators have regular cyclic patterns of diapausing insects regularly fluctuate between strong metabolic substantial metabolic depression alternating with periodic arousal depression and short bursts of higher metabolic activity, termed where metabolic rates increase dramatically. Previous studies, periodic arousal (5, 8). The flesh fly Sarcophaga crassipalpis Mac- largely in mammalian hibernators, have shown that periodic quart (Diptera: Sarcophagidae) shows dramatic metabolic sup- arousal is driven by an increase in aerobic mitochondrial metab- pression during their multiple-month pupal diapause with less than olism and that many molecules related to energy metabolism 10% of the CO2 output of nondiapausing pupae (9). However, this fluctuate predictably across periodic arousal cycles. However, it is strong metabolic depression predictably alternates with periods of still not clear how these rapid metabolic shifts are regulated. We arousal wherein the metabolic rates of diapausing pupae approxi- first found that diapausing flesh fly pupae primarily use anaerobic mate those of nondiapause pupae (9), akin to the periodic arousal glycolysis during metabolic depression but engage in aerobic cycles observed in some hibernating mammals (5). respiration through the tricarboxylic acid cycle during periodic In mammalian hibernators, periodic arousal has been associ- arousal. Diapausing pupae also clear anaerobic by-products and ated with multiple nonmutually exclusive functions including: PHYSIOLOGY regenerate many metabolic intermediates depleted in metabolic replenishing key metabolic substrates, restoring the energetic state, depression during arousal, consistent with patterns in mammalian purging metabolic waste, protein homeostasis, repairing damage hibernators. We found that decreased levels of reactive oxygen incurred during depression, sleep, and a number of other physio- species (ROS) induced metabolic arousal and elevated ROS ex- logical and biochemical events (5, 6). Even though changes in the tended the duration of metabolic depression. Our data suggest abundances of many transcripts, proteins, and metabolites (10–13) ROS regulates the timing of metabolic arousal by changing the are associated with periodic arousal, the molecular signals that activity of two critical metabolic enzymes, pyruvate dehydroge- nase and carnitine palmitoyltransferase I by modulating the levels Significance of hypoxia inducible transcription factor (HIF) and phosphorylation of adenosine 5′-monophosphate-activated protein kinase (AMPK). Organisms from bacterial spores, plant seeds, and invertebrate Our study shows that ROS signaling regulates periodic arousal in cysts to diapausing insects and mammalian hibernators dra- our insect diapasue system, suggesting the possible importance matically suppress metabolism to save energy during dormant ROS for regulating other types of of metabolic cycles in dormancy periods. Understanding regulatory mechanisms controlling as well. metabolic depression provides insights into fundamental con- trol of energy use during dormancy and offers perspectives ROS | hypoxia signaling | periodic arousal | diapause | hibernation that may allow artificial induction and breaking of dormancy. Some insects and mammalian hibernators show periodic any organisms have evolved dormancy strategies that allow arousal from metabolic depression during dormancy. We show Mthem to synchronize their lifecycles with favorable times that insects follow similar metabolic tactics during torpor and for growth and reproduction as well as to mitigate stressful times, periodic arousal as mammalian hibernators, characterized by such as the cold of winter and periods of drought. Diapause is a anaerobic metabolism during depression and aerobic metabo- programmed dormancy strategy entered into by many insects in lism during arousal, emphasizing fundamental similarities in anticipation of stress (1, 2). Metabolic suppression is one of the metabolic regulation. Physiological levels of ROS regulate the hallmarks of dormancy from seed banks in the soil to mamma- switch from metabolic depression to periodic arousal thereby lian hibernators to insects in diapause. The majority of insects do controlling substrate flow into the tricarboxylic acid cycle. not feed during diapause and must use nutrient reserves accu- mulated prior to dormancy to fuel the long dormant period as Author contributions: C.C., M.E.M., D.L.D., and D.A.H. designed research; C.C., R.M., and well as the catabolic and anabolic demands of resuming the M.E.M. performed research; R.M. and M.E.M. contributed new reagents/analytic tools; C.C., R.M., M.E.M., and D.A.H. analyzed data; and C.C., M.E.M., D.L.D., and D.A.H. wrote lifecycle after dormancy (3, 4). Understanding how organisms the paper. naturally switch between high active metabolic rates and severe Reviewers: K.J.G., North Dakota State University; and V.K., Biology Centre CAS, v.v.i. metabolic depression has a wide range of implications from Institute of Entomology. building models for how climate change will affect dormant or- The authors declare no competing interest. ganisms to inducing or terminating dormant states artificially in Published under the PNAS license. whole organisms, recovery from ischemia in live tissues, main- 1To whom correspondence may be addressed. Email: [email protected], denlinger.1@ tenance of ex vivo organs for transplant, or even metabolic ma- osu.edu, or [email protected]. nipulation of specific groups of cells (e.g., cancer) (5–7). Thus, the This article contains supporting information online at https://www.pnas.org/lookup/suppl/ mechanisms regulating metabolic suppression during dormancy doi:10.1073/pnas.2017603118/-/DCSupplemental. have been an active source of study for decades. While some Published December 28, 2020. PNAS 2021 Vol. 118 No. 1 e2017603118 https://doi.org/10.1073/pnas.2017603118 | 1of10 Downloaded by guest on September 27, 2021 trigger metabolic arousal from depression have not yet been elu- and reactive oxygen species (ROS) can regulate metabolic cycles cidated for mammalian hibernators. It has been suggested that (15–19). mitochondria are activated during the periodic arousal, and cyclic Redox signaling has long been recognized as playing roles in changes in key metabolites associated with mitochondrial oxidative both insect diapause (20) and mammalian hibernation (21–23) phosphorylation may be a fundamental driving force for the met- with a recent study showing ROS regulates insect diapause abolic cycles (14). Studies from other systems, such as the budding through insulin signaling (24). Cyclic changes in ROS have been yeast metabolic cycle (YMC), have shown cyclic changes in associated with periodic arousal cycles in mammalian hiberna- abundance of molecules involved in redox signaling, such as re- tors (22, 25), and it has been proposed that ROS may even play a duced nicotinamide-adenine dinucleotide phosphate (NADP[H]) regulatory role (24). It is well recognized that an excess of ROS A C D G E B F H I Fig. 1. Metabolite and transcript abundances fluctuate with metabolic depression and arousal in a pattern that suggests anaerobic glycolysis in depression and aerobic metabolism during arousal. (A) A representative metabolic trajectory (CO2) from an individual diapausing pupa showing the metabolic cycle and defining our sampling points as arousal from metabolic depression (AD) was sampled ∼6 h after the initial uptick in CO2 production; interbout of metabolic arousal (IBA) was sampled ∼15 h after the initial uptick in CO2 production; EN (entering depression) was sampled ∼30 h after the initial uptick in CO2 production; early depression (ED) was sampled ∼48 h after the initial CO2 uptick in production and after CO2 levels came back down; late depression (LD) was sampled 5 to 6 d after entering metabolic depression. (B) Fold-change differences in metabolites that differed the most across any two of the five sampling points across the metabolic cycles. (C) Representative temporal patterns of key metabolites across the cycle. (D) AMP:ATP ratio increases during depression and ATP is recharged during arousal. (E) NADP reducing equivalents were depleted during depression and recharged during arousal. (F) L-acetylcarnitine increases from early depression and peaks during arousal. (G) Temporal expression patterns of glycolysis/gluconeogenesis genes. Hexokinase-A