Effects of increasing temperature and aestivation on biogenic amines, signal transduction pathways and metabolic enzyme activities in the sea cucumber (Apostichopus japonicus)

Marine invertebrates are facing increasing pressure from climate change, such as increasing temperature. Sea cucumber (Apostichopus japonicus) is an ectotherm and marine model organism for the study of aestivation, a state of dormancy caused by high temperature. The adaptive mechanism of successive temperature stress and aestivation remains unclear in A. japonicus. This study experimentally exposed A. japonicus to constant temperature (14 ℃) in 20 days, successive increasing temperature (14–20 and 14–26 ℃) in 15 days and then constant aestivation temperature (20 ℃ and 26 ℃) in 5 days, aiming to explore how biogenic amines and signal transduction pathways regulated energy metabolism to response to temperature increasing and aestivation in the A. japonicus. Together with correlation analysis, this experiment suggested that (1) when temperature increased, serotonin might react first to down-regulate cyclic AMP and protein kinase A signal transduction pathway through the receptor 5-HT1A, which led to the suppression of key metabolic enzymes; (2) during aestivation, calmodulin (CaM) and AMP-activated protein kinase (AMPK) increased, and then up-regulated the catabolism of carbohydrates and proteins to provide energy for aestivation. The sea cucumber on aestivation under the higher temperature stress (26 ℃) showed the higher contents of CaM and AMPK, and similar trends were found in glycogen phosphorylase and pyruvate kinase activities, meaning a higher energy catabolism; this implied that under the scenario of successive heatwaves happened in ocean, the aestivation mechanism itself might not be able to guarantee the sea cucumber's survival in the future.