Effects of estradiol exposure on lipid metabolism in male and female sea cucumber Apostichopus japonicus

Lipids are important energy storage nutrients and signalling molecules for reproduction. Steroid hormones, including estradiol (E₂), have been shown to play a key regulatory role in lipid metabolism in vertebrates. However, not much is known on the action of sex steroids in lipid metabolism in invertebrates. This study investigated the impact of exogenous E₂ administration in lipid metabolism of male and female sea cucumber Apostichopus japonicus. Control females had higher crude lipid content in the body wall, but not in the intestines, as compared to control males. E₂ administration significantly reduced the total lipid content in the intestine and body wall of females, but not males. The analysis of intestinal metabolites and gene expression of A. japonicus showed that E₂ significantly affected the expression of genes and the levels of metabolites related with lipid metabolism pathway. The metabolism of sex hormones, triglycerides and fatty acids in females was more active as compared to males. The fatty acid degradation and glycerophospholipid metabolism pathways were disturbed by E₂ administration in males. E₂ significantly inhibited the activity of catalase (CAT) in the coelomic fluid, and it is speculated that E₂ may have disrupted lipid metabolism by inducing oxidative imbalance in males by targeting the glycerophospholipid metabolism pathway. The study confirms that sex steroids play a significant role in regulating physiological functions in echinoderms and, in particular, that E₂ might modulate lipid metabolism, as described for vertebrates. The results also suggest that exogenous administration of sex steroids could be used as a tool to regulate reproductive function to improve the rearing of A. japonicus.