Dietary cholesterol promotes growth and ecdysone signalling pathway by modulating cholesterol transport in swimming crabs (Portunus trituberculatus)

Cholesterol, as an indispensable nutrient, regulates molting and growth in crustacean. As crustaceans are unable to biosynthesize cholesterol de novo, it is central to understand how dietary cholesterol affects molting in crustaceans. An 8-week feeding trial was conducted to evaluate the effects of dietary cholesterol level (0.12%, 0.43%, 0.79%, 1.00%, 1.30% and 2.50%) on growth, cholesterol metabolism and expression of genes related to lipid and ecdysone metabolism in female swimming crabs (Portunus trituberculatus). A total of 192 crabs (1.41 ± 0.05 g) were randomly distributed into 192 aquaria. Each treatment had 4 replicates with each replicate containing 8 crabs. Crabs fed the 1.00% cholesterol diet showed best growth performance, and thus based on percent weight gain, the optimal dietary cholesterol requirement was calculated at 1.01%. Tissue cholesterol concentrations were positively correlated with dietary cholesterol level. The contents of functional fatty acids in hepatopancreas significantly increased as dietary cholesterol increased from 0.12% to 2.50% (P < 0.05). The expression levels of genes related to lipogenesis pathway, lipid catabolism and fatty acid oxidation were significantly down-regulated with increased dietary cholesterol level (P < 0.05). The highest expression levels of cholesterol transport genes, low-density lipoprotein receptor (ldlr) and low-density lipoprotein receptor-related protein 2 (lrp2) occurred in crabs fed the 1.30% cholesterol diet. Moreover, hormones related to molting such as crustacean hyperglycemic hormone (CHH), methyl farnesoate (MF), molt-inhibiting hormone (MIH), and ecdysone in hemolymph were significantly influenced by dietary cholesterol level (P < 0.05). The highest expression levels of ecdysone receptor (ecr) and chitinase 1 (chi1) in eyestalk and hepatopancreas were found in crabs fed the diet containing 1.00% cholesterol (P < 0.05). In conclusion, the optimal dietary level was beneficial to functional fatty acid accumulation, regulated lipid metabolism, promoted the ecdysone signalling pathway by improving the cholesterol transport, and improved the molting rate and growth of swimming crabs.