Hepatic transcriptome profiles reveal the hepatoprotective effects of dietary quercetin and sodium quercetin-5′-sulfonates supplementation in hybrid grouper (Epinephelus fuscoguttatus♀ × Epinephelus polyphekadion♂)

Plant flavonoids, such as quercetin (QE), are traditionally used to treat liver injuries. Given the limited bioavailability of quercetin, sodium quercetin-5′-sulfonates (QS) were synthesised and characterised. Although beneficial effects of QE on the fatty liver are observed in vertebrates, the exact mechanism is still unclear, particularly in fish livers. As a result, RNA-sequencing was conducted on hepatic libraries from hybrid groupers (Epinephelus fuscoguttatus♀ × Epinephelus polyphekadion♂) after QE and QS exposure for 56 d. In total, 49,411 unigenes were generated with a control group (FM, 0 mmol/kg), QE (QE, 3.2 mmol/kg), and QS (QS, 3.2 mmol/kg) supplementation group. The N50 for the unigenes is 2047 bp, whereas the mean length is 1198.55 bp. Compared with FM, we identified 788 and 848 differentially expressed unigenes (DEGs) in the liver in response to QE and QS, including 423 up- and 365 down-regulated in the QE group and 402 up- and 446 down-regulated in the QS group. Furthermore, ten genes were selected for real-time quantitative PCR to verify the reliability of our transcriptome data, and the result has shown that both up-and down-regulated genes were consistent with the RNA-seq results. Results showed that QE down-regulated hepatic genes involved in the steroid biosynthesis pathway, while QS up-regulated genes related to polyamine synthesis. More importantly, glutaminase1 (GLS1) is the initial and rate-limiting enzyme responsible for glutamine catabolism, down-regulated by QE and QS exposure. Our results will provide valuable information to help understand the underlying molecular mechanism for QE and QS preventing fatty liver of grouper.