Kjær Marte Avranden, Ruyter Bente, Berge Gerd Marit, Sun Yajing, Østbye Tone-Kari Knutsdatter
Nofima, Ås, Norway.
Nofima, Sunndalsøra, Norway.
PLoS One. 2016 Dec 14;11(12):e0168230. doi: 10.1371/journal.pone.0168230. eCollection 2016.
Limited availability of the n-3 fatty acids EPA and DHA have led to an interest in better understanding of the n-3 biosynthetic pathway and its regulation. The biosynthesis of alpha-linolenic acid to EPA and DHA involves several complex reaction steps including desaturation-, elongation- and peroxisomal beta-oxidation enzymes. The aims of the present experiments were to gain more knowledge on how this biosynthesis is regulated over time by different doses and fatty acid combinations. Hepatocytes isolated from salmon were incubated with various levels and combinations of oleic acid, EPA and DHA. Oleic acid led to a higher expression of the Δ6 fatty acid desaturase (fad) genes Δ6fad_a, Δ6fad_b, Δ6fad_c and the elongase genes elovl2 compared with cells cultured in medium enriched with DHA. Further, the study showed rhythmic variations in expression over time. Levels were reached where a further increase in specific fatty acids given to the cells not stimulated the conversion further. The gene expression of Δ6fad_a_and Δ6fad_b responded similar to fatty acid treatment, suggesting a co-regulation of these genes, whereas Δ5fad and Δ6fad_c showed a different regulation pattern. EPA and DHA induced different gene expression patterns, especially of Δ6fad_a. Addition of radiolabelled alpha-linolenic acid to the hepatocytes confirmed a higher degree of elongation and desaturation in cells treated with oleic acid compared to cells treated with DHA. This study suggests a complex regulation of the conversion process of n-3 fatty acids. Several factors, such as that the various gene copies are differently regulated, the gene expression show rhythmic variations and gene expression only affected to a certain level, determines when you get the maximum conversion of the beneficial n-3 fatty acids.
n-3脂肪酸二十碳五烯酸（EPA）和二十二碳六烯酸（DHA）的有限可得性引发了人们对更好地理解n-3生物合成途径及其调控的兴趣。从α-亚麻酸生物合成EPA和DHA涉及几个复杂的反应步骤，包括去饱和酶、延长酶和过氧化物酶体β-氧化酶。本实验的目的是进一步了解不同剂量和脂肪酸组合如何随时间调控这种生物合成。将从鲑鱼分离的肝细胞与不同水平和组合的油酸、EPA和DHA一起孵育。与在富含DHA的培养基中培养的细胞相比，油酸导致Δ6脂肪酸去饱和酶（fad）基因Δ6fad_a、Δ6fad_b、Δ6fad_c以及延长酶基因elovl2的表达更高。此外，研究表明表达随时间有节律性变化。当给予细胞的特定脂肪酸进一步增加时，达到了不再刺激进一步转化的水平。Δ6fad_a和Δ6fad_b的基因表达对脂肪酸处理的反应相似，表明这些基因存在共同调控，而Δ5fad和Δ6fad_c表现出不同的调控模式。EPA和DHA诱导不同的基因表达模式，尤其是Δ6fad_a。向肝细胞中添加放射性标记的α-亚麻酸证实，与用DHA处理的细胞相比，用油酸处理的细胞中延长和去饱和程度更高。这项研究表明n-3脂肪酸转化过程存在复杂的调控。几个因素，如各种基因拷贝受到不同调控、基因表达呈现节律性变化以及基因表达仅在一定水平上受到影响，决定了何时能实现有益n-3脂肪酸的最大转化。
