ROS and hypoxia signaling regulate periodic metabolic arousal during insect dormancy to coordinate glucose, amino acid, and lipid metabolism

Metabolic suppression is a hallmark of animal dormancy that promotes overall energy savings. Some diapausing insects and some mammalian hibernators have regular cyclic patterns of substantial metabolic depression alternating with periodic arousal where metabolic rates increase dramatically. Previous studies, largely in mammalian hibernators, have shown that periodic arousal is driven by an increase in aerobic mitochondrial metabolism and that many molecules related to energy metabolism fluctuate predictably across periodic arousal cycles. However, it is still not clear how these rapid metabolic shifts are regulated. We first found that diapausing flesh fly pupae primarily use anaerobic glycolysis during metabolic depression, but engage in aerobic respiration through the TCA cycle during periodic arousal. Diapausing pupae also clear anaerobic by products and regenerate many metabolic intermediates depleted in metabolic depression during arousal, consistent with patterns in mammalian hibernators. We found that decreased levels of reactive oxygen species (ROS) induced metabolic arousal, and elevated ROS extended the duration of metabolic depression. Our data suggest ROS regulate the timing of metabolic arousal by changing the activity of two critical metabolic enzymes, PDH (pyruvate dehydrogenase) and CPT1 (Carnitine palmitoyltransferase I), by modulating the levels of HIF (hypoxia inducible transcription factor) and phosphorylation of AMPK (AMP-activated protein kinase). While ROS and the flux of metabolic intermediates have been implicated in the regulation of insect diapause, our study is the first to describe patterns of intermediary metabolism during periodic arousal in insects and the first to show that ROS signaling can regulate periodic arousal in any multicellular organism.