Synthesis of omega-3 long-chain polyunsaturated fatty acid-rich triacylglycerols in an endemic goby, Gymnogobius isaza, from Lake Biwa, Japan

Abstract

It is commonly observed that freshwater fish contain lower amounts of omega-3 long-chain polyunsaturated fatty acids (LC-PUFAs), such as eicosapentaenoic acid (EPA, C20:5n-3) and docosahexaenoic acid (DHA, C22:6n-3), than marine fish species. In this study, we performed a detailed comparative analysis of phospholipids (PLs) and triacylglycerols (TAGs) from Gymnogobius isaza, a freshwater goby endemic to Lake Biwa inhabiting the lake bottom, and Gymnogobius urotaenia, a related goby that inhabits the shore of Lake Biwa. We found that tissues from G. isaza contain remarkably high amounts of omega-3 LC-PUFAs in both PLs and TAGs. Mass spectrometry analysis of TAGs demonstrated that the most abundant TAG molecular species were TAG (16:0/18:1/20:5), followed by TAG (14:0/18:1/20:5), in which EPA is incorporated into TAG at either the sn-1 or sn-3 positions. We isolated cDNAs encoding acyl-CoA: diacylglycerol acyltransferase designated as GiDGAT1 and GiDGAT2, from G. isaza. Expression studies using a neutral lipid-deficient Saccharomyces cerevisiae mutant strain demonstrated that both GiDGAT1 and GiDGAT2 possessed diacylglycerol acyltransferase activity, and preferential incorporation of LC-PUFA into TAG was observed in the presence of GiDGAT1. This study revealed the novel lipid profiles of G. isaza and identified the enzymes that were involved in the production of PUFA-containing TAGs.

Comparison of Fatty Acid Contents in Major Lipid Classes of Seven Salmonid Species from Siberian Arctic Lakes

“…Fish polar lipids are commonly considered as a physiologically crucial lipid class that are rich in LC-PUFA, mostly in DHA and, to a lesser extent, in EPA [19,37,39]. Indeed, percentages of DHA and EPA in PL of various wild marine and freshwater species ranged as 11.5-55.7% and 2.6-14.6%, with average values of 31.4% and 7.4%, respectively [40][41][42][43][44][45][46]. The average levels of EPA and DHA in the fish species from our study coincided with the above ranges, except the EPA value of whitefish, 16.6%, which was a bit higher than the known values.…”

“…Triacylglycerols are considered to be relatively poor in LC-PUFA and preferably accumulate monoenoic C16-22 FA [18,19,37]. According to the available data, levels of DHA and EPA in fish TAG varied in intervals of 2.3%-23.3% and 1.1%-14.1%, with average values of 8.8% and 5.3%, respectively [40][41][42][43][44][45][46]. The percentages of both EPA and DHA of TAG in the fish species from our study well coincided with the above ranges (Table 5).…”

Different mechanisms for selective transport of fatty acids using a single class of lipoprotein in Drosophila

“…The analysis of phospholipids, DAGs, and TAGs was performed on a Shimadzu LC-30AD HPLC system coupled to a triple-quadrupole LCMS-8040 mass spectrometer equipped with an electrospray source (32). Separation was performed on a Kinetex C8 column (2.6 m; 2.1 × 150 mm; Phenomenex) with a binary mobile phase having the following composition: 10 mM ammonium formate in water (mobile phase A) and 10 mM ammonium formate in 2-propanol/acetonitrile/water (45:45:10; v/v/v) (mobile phase B).…”

Functional expression of Δ12 fatty acid desaturase modulates thermoregulatory behaviour in Drosophila

“…Lipid analyses using gas chromatography (GC) were performed as described previously 5,50 . The extracted phospholipids were incubated in a 5% hydrogen chloride/methanol solution (Nacalai Tesque, Japan) at 100 °C for 3 h. Fatty acid methyl esters were then analysed using GC-14A (Shimadzu, Kyoto, Japan) with a flame ionisation detector and Supelco Omegawax Capillary GC columns (0.25 μm, 30 m × 0.25 mm; Sigma-Aldrich, USA).…”

“…LC-MS/MS analyses were performed using a high-performance liquid chromatography system LC-30AD (Shimadzu, Kyoto, Japan) coupled to a triple quadrupole mass spectrometer LC-MS-8040 (Shimadzu, Kyoto, Japan) that was equipped with an electrospray source as described previously 5,74 . The extracted phospholipids were separated using a Kinetex C8 column (2.6 μm, 2.1 × 150 mm) (Phenomenex, USA) with mobile phases comprising 10 mM ammonium formate in water (mobile phase A) and 10 mM ammonium formate in 2-propanol/acetonitrile/water (45/45/10) (mobile phase B).…”