Metabolomic responses of sea cucumber Apostichopus japonicus to thermal stresses

Elevated water temperature is generally considered as one of the most widespread and problematic stressors on Apostichopus japonicus farming. To date, however, little is known about the intrinsic mechanisms of A. japonicus to cope with the rising temperature at the metabolic level. In the present study, the metabolomic responses were characterized in the muscles of A. japonicus at two thermal points, 20 °C and 25 °C by 1H NMR-based metabolomics. The results showed that both temperatures disturbed energy metabolism and induced osmotic regulation based on the metabolic biomarkers such as elevated threonine, alanine, arginine, glutamate, tyrosine, histidine, glycine, fumarate, glucose, and AMP and decreased ATP, aspartate, hypotaurine, and choline after exposure for 0 days and 3 days. At 7 days of thermal-stress, several metabolites were similarly altered including the increased glutamine, glycine, glucose, AMP, tyrosine, and histidine and the decreased ATP at 20 °C. Surprisingly, a large amount of amino acids (valine, leucine, isoleucine, threonine, arginine, glutamate, phenylalanine) markedly declined at 25 °C. In addition, the mRNA expression levels of HSP70 and ATP synthase as well as SOD activity and MDA content were also investigated, and their expression levels were significantly altered at different exposure conditions. Our present results provided new insights into thermal-stressed effects on A. japonicus at metabolic responses.