Dietary Fish Oil Alters DNA Methylation of Genes Involved in Polyunsaturated Fatty Acid Biosynthesis in Muscle and Liver of Atlantic Salmon (Salmo salar)

Adequate dietary supply of eicosapentaenoic acid (20:5n-3) and docosahexaenoic acid (22:6n-3) is required to maintain health and growth of Atlantic salmon (Salmo salar). However, salmon can also convert α-linolenic acid (18:3n-3) into eicosapentaenoic acid (20:5n-3) and docosahexaenoic acid (22:6n-3) by sequential desaturation and elongation reactions, which can be modified by 20:5n-3 and 22:6n-3 intake. In mammals, dietary 20:5n-3 + 22:6n-3 intake can modify Fads2 expression (Δ6 desaturase) via altered DNA methylation of its promoter. Decreasing dietary fish oil (FO) has been shown to increase Δ5fad expression in salmon liver. However, it is not known whether this is associated with changes in the DNA methylation of genes involved in polyunsaturated fatty acid synthesis. To address this, we investigated whether changing the proportions of dietary FO and vegetable oil altered the DNA methylation of Δ6fad_b, Δ5fad, Elovl2, and Elovl5_b promoters in liver and muscle from Atlantic salmon and whether any changes were associated with mRNA expression. Higher dietary FO content increased the proportions of 20:5n-3 and 22:6n-3 and decreased Δ6fad_b mRNA expression in liver, but there was no effect on Δ5fad, Elovl2, and Elovl5_b expression. There were significant differences between liver and skeletal muscle in the methylation of individual CpG loci in all four genes studied. Methylation of individual Δ6fad_b CpG loci was negatively related to its expression and to proportions of 20:5n-3 and 22:6n-3 in the liver. These findings suggest variations in dietary FO can induce gene-, CpG locus-, and tissue-related changes in DNA methylation in salmon.     

Fatty acid elongase 6 plays a role in the synthesis of long-chain fatty acids in goat mammary epithelial cells

In nonruminants, it is well established that elongation of very long-chain fatty acid-like fatty acid elongase 6 (ELOVL6) catalyzes the synthesis of C18:0 from C16:0 in lipogenic tissues like adipose and liver. However, the role of ELOVL6 in regulating lipid metabolism in ruminant mammary gland remains unknown. In the present study, ELOVL6 was overexpressed or knocked down via adenoviral transfection to assess its role in goat mammary epithelial cells. Results revealed that ELOVL6 overexpression had a weak effect on the expression of genes related to triacylglycerol (TAG) synthesis and desaturation. Overexpression of ELOVL6 increased the content of C18:0 at the expense of C16:0, and increased the elongation index of C16:0. Overexpression of ELOVL6 had no significant effect on the elongation index of C16:1n-7 and the desaturation indices of C16:0 and C18:0. Knockdown of ELOVL6 had a negative effect on mRNA expression of the esterification genes GPAM and diacylglycerolacyltransferase 2 (DGAT2) and TAG concentration; however, it increased the concentration of C16:0 and decreased C18:1n-7 and C18:1n-9 in goat mammary epithelial cells. Accordingly, downregulation of ELOVL6 significantly decreased the elongation indices of C16:0 and C16:1n-7. The lack of change in the desaturation indices of C16:0 and C18:0 upon knockdown of ELOVL6 was consistent with the minor change in SCD1 expression. In conclusion, these are the first results highlighting an important role of ELOVL6 in long-chain fatty elongation and TAG synthesis in ruminant mammary cells.     

Synthesis of C20–38 Fatty Acids in Plant Tissues

Very-long-chain fatty acids (VLCFA) are involved in a number of important plant physiological functions. Disorders in the expression of genes involved in the synthesis of VLCFA lead to a number of phenotypic consequences, ranging from growth retardation to the death of embryos. The elongation of VLCFA in the endoplasmic reticulum (ER) is carried out by multiple elongase complexes with different substrate specificities and adapted to the synthesis of a number of products required for a number of metabolic pathways. The information about the enzymes involved in the synthesis of VLCFA with more than 26 atoms of Carbon is rather poor. Recently, genes encoding enzymes involved in the synthesis of both regular-length fatty acids and VLCFA have been discovered and investigated. Polyunsaturated VLCFA in plants are formed mainly by 20:1 elongation into new monounsaturated acids, which are then imported into chloroplasts, where they are further desaturated. The formation of saturated VLCFA and their further transformation into a number of aliphatic compounds included in cuticular waxes and suberin require the coordinated activity of a large number of different enzymes.     

纤细裸藻△9-脂肪酸延长酶基因在解脂耶氏酵母中的表达

从纤细裸藻c DNA中克隆出△9-脂肪酸延长酶基因,与解脂耶氏酵母整合载体p INA1297连接构建重组质粒p INA1297-△9E,用电击转化法将重组质粒转化到解脂耶氏酵母中,筛选得到阳性表达菌株YL△9E。在酵母浸出粉胨葡萄糖培养（YPD）条件下,工程酵母YL△9E的菌体生长速率高于对照菌株polf。对工程酵母YL△9E进行脂肪酸成分分析,结果表明△9-脂肪酸延长酶基因获得表达,产生了二十碳二烯酸（EDA）,其含量可高达14.8%。      

Solubilization of Acyl-CoA elongases from developing rapeseed (Brassica napus L.)

Acyl-CoA elongases are important in producing high-erucic acid rapeseed. The effects of Triton X-100,N-octyl-β-D-glucopyranoside and deoxycholate on the C18:1-CoA and C20:1-CoA elongase(s) have been studied by using a 15,000 ×g pellet from developing rapeseed. The synthesis of very long chain monounsaturated fatty acids (VLCMFA) and, in particular, that of erucic acid were stimulated by Triton X-100, whatever the substrate used. In the presence ofN-octyl-β-D-glucopyranoside, the elongase activity was practically unchanged, whereas deoxycholate strongly inhibited VLCMFA synthesis. Triton X-100 was chosen for the solubilization, at an optimal Triton X-100/protein (w/w) ratio of 2.5. Acyl-CoAs were the major products synthesized by the solubilized acyl-CoA elongase(s). The analysis of the reaction intermediates showed that the entire elongation complex has been solubilized and was still functional.     

Effects of dietary fish oil replacement with flaxseed oil on tissue fatty acid composition and expression of desaturase and elongase genes

BACKGROUND: This study was conducted to evaluate the effects of total or partial substitution of dietary fish oil (FO) by flaxseed oil (FlaxO) in Jade Tiger hybrid abalone on fatty acid composition of muscle, gonad and digestive gland, and the expression of desaturase and elongase genes. Abalone were fed five different experimental diets in which FO (control diet) was serially replaced by 25%, 50%, 75% and 100% FlaxO respectively. RESULTS: Muscle, gonad and digestive gland of abalone fed the control diet and the diets containing 25%, 50% and 75% FlaxO showed significantly higher (P < 0.05) levels of eicosapentaenoic acid (EPA), docosapentaenoic acid (DPA) and docosahexaenoic acid (DHA) compared to those fed the 100% FlaxO. The results also showed that Δ‐6 desaturase and elongase gene expression in muscle was increased in a graded manner by increasing dietary FlaxO. The expression of both genes was higher in abalone fed the FlaxO‐substituted diets compared to the abalone fed FO. CONCLUSION: The replacement of FO with FlaxO in commercial abalone diets at levels of 25–75% can improve the composition of health‐benefiting n‐3 polyunsturated fatty acids in tissues of cultured hybrid abalone, and achieve similar outcomes to FO supplementation. Copyright © 2011 Society of Chemical Industry