No abstract

A transcriptome analysis was conducted to provide the first detailed overview of dietary taurine intervention on liver lipid accumulation caused by high–fat in groupers. After an eight-week feeding, the fish fed 15% fat diet (High–fat diet) had higher liver lipid contents vs. fish fed 10% fat diet (Control diet). 15% fat diet with 1% taurine (Taurine diet) improved weight gain and feed utilization, and decreased hepatosomatic index and liver lipid contents vs. the High–fat diet. In the comparison of the Control vs. High–fat groups, a total of 160 differentially expressed genes (DEGs) were identified, of which up- and down-regulated genes were 72 and 88, respectively. There were 49 identified DEGs with 26 and 23 of up- and down-regulated in the comparison to High–fat vs. Taurine. Several key genes, such as cysteine dioxygenase (CDO1), ADP–ribosylation factor 1/2 (ARF1_2), sodium/potassium–transporting ATPase subunit alpha (ATP1A), carnitine/acylcarnitine translocase (CACT), and calcium/calmodulin–dependent protein kinase II (CAMK) were obtained by enrichment for the above DEGs. These genes were enriched in taurine and hypotaurine metabolism, bile secretion, insulin secretion, phospholipase D signaling pathway, and thermogenesis pathways, respectively. The present study will also provide a new insight into the nutritional physiological function of taurine in farmed fish.

A lipidomic analysis was conducted to provide the first detailed overview of lipid molecule profiles in response to dietary lipid and taurine and associations of liver lipid-lowering effects of dietary taurine with lipid molecular species and the positional distributions of fatty acids in the liver of juvenile orange-spotted groupers (Epinephelus coioides). The results indicated that the liver was more sensitive to varied dietary lipid and taurine contents than the muscle with regard to lipid molecules. A total of 131 differential lipid molecules (DLMs) were observed in the liver of groupers when dietary taurine was increased from 0 to 1% at 15% lipid, among which all the up and down-regulated DLMs are phospholipids (PLs) and triglycerides (TGs), respectively. The liver content of TGs containing 18:2n-6 attached at the sn-2 and sn-3 positions on the glycerol backbone increased with increasing dietary lipid from 10 to 15% but decreased with increasing dietary taurine from 0 to 1%. Therefore, dietary taurine can not only reduce lipid accumulation through decreasing the contents of TGs containing 18:2n-6 at the sn-2 and sn-3 positions but also enhance the anti-inflammatory capacity and health status of groupers. This study will also provide a new insight into the function of taurine in farmed fish.

An 8-week feeding trial was conducted to investigate how dietary taurine supplementation attenuates the lipid deposition induced by dietary high lipid in juvenile orange-spotted grouper (Epinephelus coioides). Three isonitrogenous (47% crude protein) semipurified diets were formulated to contain two levels of lipid and termed as 10% lipid diet, 15% lipid diet, and 15% lipid with 1% taurine (namely, diet 10L, diet 15L, and diet 15L + T, respectively). Groupers fed diet 15L + T showed higher weight gain and feed efficiency compared with diet 15L. Groupers fed diet 15L showed higher liver lipid contents, plasma total cholesterol (TC), and leptin contents vs. those fed diet 10L. Diet 15L + T decreased hepatosomatic index, liver lipid content, and plasma TC and adiponectin contents, and increased liver 3-hydroxy-3-methy1 glutary1 coenzyme A reductase content compared with diet 15L. Fish fed diet 15L had higher contents of chenodeoxycholic acid, deoxycholic acid, and lithocholic acid, and lower contents of glycodeoxycholic acid (GDCA), glycolithocholic acid, glycoursodeoxycholic acid, taurodeoxycholic acid (TDCA), and β-, γ-, and ω-muricholic acid (MCA) when compared with fish fed diet 10L. Diet 15L + T downregulated the contents of glycocholic acid, glycochenodeoxycholic acid, taurohyodeoxycholic acid, tauromuricholic acid, TDCA, ursodeoxycholic acid, GDCA, and β-MCA vs. diet 15L. Diet 15L upregulated expression of peroxisome proliferator-activated receptor α (pparα) gene but downregulated expression of acyl-CoA carboxylase (acc), fatty acid synthase (fas), and glucose-6-phosphate dehydrogenase (g6pd) genes in comparison with diet 10L. The gene expression level of fas and 6pgd was downregulated and the pparα gene expression level was upregulated in fish fed diet 15L + T compared with those in fish fed diet 15L. Overall, this study indicated that dietary taurine supplementation can attenuate the liver lipid deposition of groupers caused by feeding 15% lipid through accelerating lipid absorption of taurine-conjugated bile acids and fatty acid β-oxidation and inhibiting lipogenesis.

Examination of the molecular mechanism of taurine regulation of lipid metabolism in fish is limited. In this study, an oleic acid (OA)-induced hepatocyte steatosis model of orange-spotted grouper (Epinephelus coioides) was established for the first time. The model was used to test the effect of taurine on steatosis hepatocytes in Control, High-fat (0.4 mM OA) and Taurine (0.4 mM OA + 2 mM taurine) experimental groups of fish. Hepatocyte samples were subjected to transcriptome analysis. A total of 99634 unigenes was assembled, 69982 unigenes were annotated and 1831 differentially expressed genes (DEGs) in Control vs High-fat group, and 526 DEGs in the High-fat vs Taurine group were identified, of which 824 DEGs (Control vs High-fat) and 237 DEGs (High-fat vs Taurine) were observed to be upregulated, and 1007 DEGs (Control vs High-fat) and 289 DEGs (High-fat vs Taurine) were downregulated after taurine intervention. These genes are involved in peroxisome proliferator-activated receptor (PPAR) and 5' AMP-activated protein kinase (AMPK) signaling pathways, fatty acid elongation, primary bile acid biosynthesis, glycerophospholipid and glycerolipid metabolism. The findings provide new clues in understanding the regulatory role of taurine in lipid and fatty acid metabolism of fish. It is hoped that the obtained results will help in the design of feed formulations to improve grouper growth from the perspective of aquaculture nutrition.