Preliminary Study On The Effect Of HUFA On The Lipid Metabolism In Grass Carp Ctenopharyngodon Idella

Highly unsaturated fatty acid can maintain the cell membrane structure of fish, the function integrity, certain enzyme activities, the constitution prostaglandin precursor and the enhancement immune system function. Some researchers have studied the different fatty acid and the fat source dietary influence the growth performance, fatty acid composition and body composition of fresh water fish, discovered that HUFA or fish oil have the function that promoting the growth performance and reducing body fat content. But its influence body fat deposition's function is because HUFA inhibited the lipid metabolism or transport, or promoted lipidolysis was not still clear, the further evaluation of the related mechanism was reqiured in freshwater fishes.We study the change on mRNA expresson of LXRα,SREBP-1,FAS,ACC,LPL which related to lipid metabolism in feeding process, its helpful to understand the molecular mechanism of fish lipid metabolism. The essential method about reseach of the rule of animal fat deposition was adipocytes culturing in vitro and monitoring the process of adipocyte proliferation with reseaching about development regulation of adipose tissue.Grass carp was used as the experimental animal in this study. After being treated with HUFA directly, the pattern of the change of gene expression which related lipid metabolism and cultured adipocytes in vitro was investigated. Based on the study on the rules of the adipocytes proliferation and differentiation, it is aimed to work over the effect and mechanism of HUFA on adipocyte development in grass carp, which is important to elucidate the development mechanism of adipocyte tissue, and beneficial to provide new train of thought and theoretic foundation on the regulation of lipid storage in cultured fish.The main results were as follows:1. The cDNA sequence of Liver X Receptorα(LXRα)(GenBank accession number FJ965309 ), and the partial cDNA sequence of sterol regulatory element- binding protein 1 (SREBP-1) (GenBank accession number GU339498 ), fatty acid sythetase(FAS)(GenBank accession number GQ466046 ), acety1 COA carboxylase (ACC) (GenBank accession number HM142590) were cloned.The obtained sequence is 1230bp, 899bp, 709bp, 467bp in length separately. Homology is 70.7%~100% with other species. Widely expressed in hepatopancreas, muscle, heart, gill, spleen, intestin, brain, kidney, testis, and intrapaneal fat body (IPF),with the highest expression level of LXRαgene was found in testis, lowest one in muscle (p<0.05).2. Preadipocytes active and differentiate spontaneously. After inducting the preadipocytes filled with lipid-rich droplets at a higher ratio, and the adipogenic gene expression was enhanced.3. DHA promote preadipocytes of grass carp proliferation, inhibit its differentiation.4. Dietary HUFA were very effectively incorporated into the fish body. Analysis of fatty acid indicated that a higher content of C22:6n-3(p<0.01) and HUFA (p<0.05) were found in intraperiotenal fat (IPF), and a higher content of n-3 (p<0.01) and HUFA (p<0.05) but lower C20:4n-6 content (p<0.05) in muscle of HUFA group. The content of n-3/n-6 was significantly higher in the hepatopancreas, IPF, and muscle in fish fed the HUFA diet compared to the control diet. The content of IPF and hepatopancreas lipid (p<0.05) was lower in the HUFA group. On the other hand, a significantly higher T-AOC activity, the lower LPL activity and LPL,LXRα, SREBP-1c, FAS, ACC mRNA expression(p<0.05) was observed in the hepatopancreas of fish fed the HUFA diet.From above, our study suggest that HUFA significantly regulate lipid metabolism of grass carp, through suppresses the expression of lipogenic gene mRNA,the exogenous application lipid enter to hepatopancreas and adipocytes differentiation, reduces the liver fat and abdomen fat content, fatty acid composition is affected by fatty acid composition of the diet, improving the quality level of the fish.