Arachidonic acid promotes ovarian development by modulating lipid metabolism and steroid hormone secretion in Chinese mitten crab (Eriocheir sinensis)

Abstract

In this study, two animal experiments were designed to assess the function of arachidonic acid (ARA) on the ovarian development of Chinese mitten crab (Eriocheir sinensis). In experiment 1, female crabs (35.55 ± 0.02 g) were fed seven experimental diets, each containing varying levels of ARA (0.01 %, 0.28 %, 0.48 %, 0.67 %, 0.86 %, 1.02 %, and 1.21 %) for 120 d. Dietary 0.48 %–0.86 % ARA significantly improved the growth performance of crabs, and more than dietary 0.67 % ARA significantly increased the gonadosomatic index (GSI), ovarian vitellogenin (VTG) and vitellin (Vn) contents (P < 0.05). The egg diameter was largest when dietary 0.86 % ARA. Moreover, dietary ARA also significantly affected the hepatopancreatic and ovarian fatty acid compositions and ARA content by increasing the relative expressions of phospholipase A2 (pla2), cyclooxygenase-1(cox-1), cyclooxygenase-2 (cox-2) and 5-lipoxygenase (5-lox), while decreasing the relative expressions of fatty acid synthase (fas), fatty acid desaturase (fad6), lipoprotein lipase (lpl) and fatty acid elongase (elo) (P < 0.05). Based on the GSI and egg diameter, the amount of 0.86 % ARA was selected to further investigate the mechanisms involved in ovarian development. In experiment 2, female crabs (73.34 ± 0.07 g) were fed ARA diets (0.01 % and 0.86 %) for 60 d. Results demonstrated that a diet supplemented with 0.86 % ARA notably increased the progesterone (PROG) and prostaglandins (PGs) contents in hepatopancreas, as well as the thromboxane A2 (TXA2), estradiol (E2), and estriol (E3) contents in ovaries of E. sinensis (P < 0.05). Immunohistochemical analyses showed that 0.86 % ARA significantly promoted the expression of E2 receptor. Moreover, transcriptome sequencing revealed that 15 KEGG pathways, including the mTOR and FoxO signalling pathways and steroid biosynthesis, were enriched in the differentially expressed genes (DEGs) of crabs fed 0.86 % ARA. In conclusion, dietary 0.86 % ARA accelerated the deposition of ARA in the hepatopancreas and ovaries by regulating ARA synthesis and metabolism-related genes, then subsequently providing energy for ovarian development. Meanwhile, ARA promoted steroid hormone secretion and ovarian development-related pathways by facilitating the generation of PGs and ultimately promoted ovarian development in Chinese mitten crabs.