Elevated chaperone proteins are a feature of winter freeze avoidance by larvae of the goldenrod gall moth, Epiblema scudderiana

Winter survival for many insect species includes a need to maintain metabolic homeostasis and structural/functional integrity of macromolecules not only over a wide range of cold temperatures but also in response to rapid temperature change. Chaperones are well-known to protect/stabilize protein structure with regard to heat stress but less is known about their potential involvement in long-term protection of the proteome at subzero temperatures. The present study assessed the participation of chaperone proteins in the cold hardiness of larvae of the goldenrod gall moth, Epiblema scudderiana (Clemens) (Lepidoptera, Olethreutidae), monitoring changes in nine proteins over the winter months as well as their responses to laboratory cold acclimation or anoxia exposure. Four heat shock proteins (HSPs: Hsp110, Hsp70, Hsp60, Hsp40), three glucose-regulated proteins (GRPs: Grp78, Grp 94, Grp170) and the tailless complex polypeptide 1 (TCP-1) as well as the heat shock transcription factor (HSF1) were investigated. In general, all were significantly elevated in larvae collected from an outdoor site between October and March, as compared with September values, and chaperone levels were reduced again in April. The October to March interval also includes the period of diapause followed by cold quiescence in the species. Relative expression of Hsp70, Hsp60 and Hsp40 rose by 2–3-fold, GRPs increased 1.5–3-fold, and levels of active (hyperphosphorylated) HSF1 increased by 4–4.8-fold over the midwinter months. Chilling from 15 °C to 4 °C in the laboratory upregulated Grp78 protein content that remained high as temperature was further reduced to −4 °C and then −20 °C whereas Hsp110, Hsp70 and HSF1 levels increased when larvae were exposed to −4 °C and −20 °C. Grp170 (also known as oxygen-regulated protein 150) was the only chaperone that increased significantly in the larvae in response to anoxia exposure at 4 °C. The data also indicated that multiple subcellular compartments received enhanced protection for their proteome since upregulation of chaperones included proteins known to occur in cytosolic (Hsp40, Hsp70), mitochondrial (Hsp60) and endoplasmic reticulum (Grp170) locations. Overall, the data indicate that chaperones have a significant role to play in the winter cold hardiness of E. scudderiana and identify declining temperatures (and perhaps also oxygen restriction) as potential modulators of chaperone production. The data add support to a relatively understudied area of insect cold hardiness – the long-term protection and stabilization of the proteome over the winter months.