Homozygous and heterozygous GH transgenesis alters fatty acid composition and content in the liver of Amago salmon (Oncorhynchus masou ishikawae)

Abstract

SummaryGrowth hormone (GH) transgenic Amago (Oncorhynchus masou ishikawae), containing the sockeye GH1 gene fused with metallothionein-B promoter from the same species, were generated and the physiological condition through lipid metabolism compared among homozygous (Tg/Tg) and heterozygous GH transgenic (Tg/+) Amago and the wild type control (+/+). Previously, we have reported that the adipose tissue was generally smaller in GH transgenic fish compared to the control, and that the Δ-6 fatty acyl desaturase gene was down-regulated in the Tg/+ fish. However, fatty acid (FA) compositions have not been measured previously in these fish. In this study we compared the FAs composition and content in the liver using gas chromatography. Eleven kinds of FA were detected. The composition of saturated and monounsaturated fatty acids (SFA and MUFA) such as myristic acid (14:0), palmitoleic acid (16:1n-7), and cis-vaccenic acid (cis-18:1n-7) was significantly (P<0.05) decreased in GH transgenic Amago. On the other hand, the composition of polyunsaturated fatty acids (PUFAs) such as linoleic acid (18:2n-6), arachidonic acid (20:4n-6), and docosapentaenoic acid (22:5n-3) was significantly (P<0.05) increased. Levels of serum glucose and triacylglycerol were significantly (P<0.05) decreased in the GH transgenics compared with +/+ fish. Furthermore, 3′-tag digital gene expression profiling was performed using liver tissues from Tg/Tg and +/+ fish, and showed that Mid1 interacting protein 1 (Mid1ip1), which is an important factor to activate Acetyl-CoA carboxylase (ACC), was down-regulated in Tg/Tg fish, while genes involved in FA catabolism were up-regulated, including long-chain-fatty-acid–CoA ligase 1 (ACSL1) and acyl-coenzyme A oxidase 3 (ACOX3). These data suggest that liver tissue from GH transgenic Amago showed starvation by alteration in glucose and lipid metabolism due to GH overexpression. The decrease of serum glucose suppressed Mid1ip1, and caused a decrease of de novo FA synthesis, resulting in a decrease of SFA and MUFA. This induced expression of ACSL1 and ACOX3 to produce energy through β-oxidation in the GH transgenic Amago.

The use of genetic engineering techniques to improve the lipid composition in meat, milk and fish products: a review

“…The lower lipid content in a growth-enhanced transgenic fish is probably due to a higher rate of metabolism and increased requirements for energy, which results in increased rate of use of fat reserves. Sugiyama et al (2012) reported a significant beneficial influence of growth hormone transgenesis on liver fatty-acid composition in Amago salmon (Oncorhynchus masou ishikawae); thus transgenic fish had decreased contents of SFAs and MUFAs, as well as an increased content of PUFAs, among others EPA and DPA. The impact of an enhanced metabolism rate on lipid changes was also evident in the case of a transgenic tilapia (Oreochromis hornorum) containing foreign growth hormone, with a significantly reduced cholesterol concentration in its blood serum Martínez et al (1999).…”

Fatty acid content in muscles of amago salmon homozygous or heterozygous for a growth hormone transgene

“…The mean weights of the homozygous (Tg/Tg), heterozygous (Tg/+) (note that all the heterozygotes were produced using eggs from transgenic fish and sperm from wild type), and age control (+/+) fish used in this experiment were 131 g, 109 g, and 85 g, respectively. Details of the production and detection of the transgenic fish using PCR were described in a previous study (Sugiyama et al, 2012).…”

“…Extraction and purification of total lipids were performed following the method of Folch et al Fatty acid contents (mg/g) in muscle tissue from homozygous (black), heterozygous (gray) of GH transgenic amago salmon, and from controls (white), compared with those in liver tissue (Sugiyama et al, 2012). Contents of fatty acids were calculated using heptadecanoic acid (17:0) as an internal standard.…”

“…×50 m, Shinwa Chemical Industries, Inc., Tokyo, Japan). Details of the procedure were described in a previous study (Sugiyama et al, 2012).…”

“…This change in catabolism caused an increase in β-oxidation of saturated (SFAs) and monounsaturated fatty acids (MUFAs) in homozygous (Tg/Tg) and heterozygous (Tg/+) amago salmon compared to the controls (Sugiyama et al, 2012). Expression of the Mid1 interacting protein 1 gene (Mid1ip1), which is important in enhancing de novo fatty acid synthesis, was down-regulated, and an increase in 3-hydroxybutyric acid (a ketone body) was observed in the livers of the GH transgenic fish.…”