Winter survival for many insects depends on cold hardiness adaptations as well as entry into a hypometabolic diapause state that minimizes energy expenditure. We investigated whether AMP-activated protein kinase (AMPK) could be involved in this adaptation in larvae of two cold-hardy insects, Eurosta solidaginis that is freeze tolerant and Epiblema scudderiana that uses a freeze avoidance strategy. AMPK activity was almost 2-fold higher in winter larvae (February) compared with animals collected in September. Immunoblotting revealed that phosphorylation of AMPK in the activation loop and phosphorylation of acetyl-CoA carboxylase (ACC), a key target of AMPK, were higher in Epiblema during midwinter whereas no seasonal change was seen in Eurosta. Immunoblotting also revealed a significant increase in ribosomal protein S6 phosphorylation in overwintering Epiblema larvae, and in both Eurosta and Epiblema, phosphorylation of eukaryotic initiation factor 4E-binding protein-1 dramatically increased in the winter. Pyruvate dehydrogenase (PDH) E1α subunit site 1 phosphorylation was 2-fold higher in extracts of Eurosta larvae collected in February versus September while PDH activity decreased by about 50% in Eurosta and 80% in February Eurosta larvae compared with animals collected in September. Glycogen phosphorylase phosphorylation was 3-fold higher in Epiblema larvae collected in February compared with September and also in these animals, triglyceride lipase activity increased by 70% during winter. Overall, our study suggests a re-sculpting of metabolism during insect diapause, which shifted to a more catabolic poise in freeze-avoiding overwintering Epiblema larvae, possibly involving AMPK.

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Keywords 4E-BP1, AMPK, Glycogen phosphorylase, Metabolic rate depression, PDH, Protein synthesis, RpS6, Triglyceride lipase
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Journal Journal of Insect Physiology
Rider, M.H. (Mark H.), Hussain, N. (Nusrat), Dilworth, S.M. (Stephen M.), Storey, J, & Storey, K. (2011). AMP-activated protein kinase and metabolic regulation in cold-hardy insects. Journal of Insect Physiology, 57(11), 1453–1462. doi:10.1016/j.jinsphys.2011.07.006