Abstract
To investigate the physiological roles of dietary arachidonic acid (ARA) in fish, a feeding trial with Japanese seabass was conducted, followed by a hepatic transcriptome assay. Six experimental diets differing basically in ARA level (0.05%, 0.22%, 0.37%, 0.60%, 1.38% and 2.32% of dry matter) were used in the feeding trial. Liver samples from fish fed diets with 0.05% and 0.37% ARA were subjected to transcriptomic assay, generating a total of 139 differently expressed unigenes, which were primarily enriched in lipid metabolism and cell cycle-related signaling pathways. Then, qRT-PCR validation on lipid metabolism and cell cycle-related genes as well as corresponding enzyme-linked immunosorbent assay of selected proteins were conducted with liver samples from all six groups. Moderated ARA levels reduced lipogenesis and stimulated β-oxidation concurrently, but high ARA levels seemed to affect lipid metabolism in complicated ways. Both gene expression and protein concentration of cell cycle-related proteins were decreased by moderate levels of dietary ARA. The lipid content and fatty acid composition in fish confirmed the transcription and protein concentration results related to lipid metabolism. In conclusion, moderate levels of dietary ARA (0.37% and 0.60%) reduced lipid accumulation and tended to inhibit cell cycle progression in the liver of Japanese seabass.
Highlights
Arachidonic acid (ARA, C20:4n-6), as an n-6 long chain-polyunsaturated fatty acid (LC-PUFA), has been demonstrated to be an essential fatty acid for marine fish[1]
With Japanese seabass cultured in seawater, we have investigated the nutritional effects of a series of fatty acids and lipid sources such as DHA, EPA, arachidonic acid (ARA), α-linolenic acid (LNA), oleic acid (OA), steric acid (SA), palmic acid (PA), steric acid (SA), medium chain-fatty acid (MCA), fish oil, soybean oil, and linseed oil[6,29,30,31]
Genetic properties of some fatty acid/ lipid metabolism-related proteins such as Δ6 fatty acid desaturase (FADS2), sterol-regulatory element binding proteins (SREBP), peroxisome proliferator-activated receptor (PPAR), fatty acid-binding proteins (FABP), and FATP7,8,32,33, as well as their response to different dietary fatty acids/lipids have been investigated in these studies
Summary
Arachidonic acid (ARA, C20:4n-6), as an n-6 long chain-polyunsaturated fatty acid (LC-PUFA), has been demonstrated to be an essential fatty acid for marine fish[1]. In our previous studies with Japanese seabass, we have investigated the effects of dietary ARA on growth performances, non-specific immunity, as well as gene expressions of fatty acid-binding proteins (FABP) and fatty acid transport proteins (FATP) in various tissues[6,7,8]. With another marine fish species tongue sole (Cynoglossus semilaevis), we investigated the influence of dietary ARA on the gonadal steroidogenesis[9]. The results will provide useful information for better understanding the physiological roles of ARA in fish
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