Cloning, Expression, and Fatty Acid Regulation of the Human Δ-5 Desaturase

Abstract

Arachidonic (20:4(n-6)), eicosapentaenoic (20:5(n-3)), and docosahexaenoic (22:6(n-3)) acids are major components of brain and retina phospholipids, substrates for eicosanoid production, and regulators of nuclear transcription factors. One of the two rate-limiting steps in the production of these polyenoic fatty acids is the desaturation of 20:3(n-6) and 20:4(n-3) by ⌬-5 desaturase. This report describes the cloning and expression of the human ⌬-5 desaturase, and it compares the structural characteristics and nutritional regulation of the ⌬-5 and ⌬-6 desaturases. The open reading frame of the human ⌬-5 desaturase encodes a 444-amino acid peptide which is identical in size to the ⌬-6 desaturase and which shares 61% identity with the human ⌬-6 desaturase. The ⌬-5 desaturase contains two membrane-spanning domains, three histidine-rich regions, and a cytochrome b 5 domain that all align perfectly with the same domains located in the ⌬-6 desaturase. Expression of the open reading frame in Chinese hamster ovary cells instilled the ability to convert 20:3(n-6) to 20:4(n-6). Northern analysis revealed that many human tissues including skeletal muscle, lung, placenta, kidney, and pancreas expressed ⌬-5 desaturase mRNA, but ⌬-5 desaturase was most abundant in the liver, brain, and heart. However, in all tissues, the abundance of ⌬-5 desaturase mRNA was much lower than that observed for the ⌬-6 desaturase. When rats were fed a diet containing 10% safflower oil or menhaden fish oil, the level of hepatic mRNA for ⌬-5 and ⌬-6 desaturase was only 25% of that found in the liver of rats fed a fat-free diet or a diet containing triolein. Finally, a BLAST and Genemap search of the human genome revealed that the ⌬-5 and ⌬-6 desaturase genes reside in reverse orientation on chromosome 11 and that they are separated by <11,000 base pairs.

Effect of supplementation of the maternal diet with fish oil or linseed oil on fatty-acid composition and expression of Δ5- and Δ6-desaturase in tissues of female piglets

“…Examples of the blots are given in Figure 1. The sizes of the immunoreactive bands for both enzymes were approximately 50 kDa, which is consistent with the molecular weights of D5d and D6d proteins reported in other species (Cho et al, 1999a and1999b). Across diets, the average expression of D5d protein was the highest in muscle, followed by subcutaneous adipose tissue, with the lowest level in the liver (Table 6).…”

Effects of fish oil and additional starch on tissue fatty acid profile and lipogenic gene mRNA abundance in lactating goats fed a diet containing sunflower-seed oil

“…It has been suggested that this inhibitory effect of carbohydrates on SCD1 mRNA abundance in the liver can be mediated by hormonal factors, such as leptinaemia (Lengi and Corl, 2007;Bernard et al, 2012), but no difference in the concentration of plasma leptin between the two experimental groups was observed in our study. On the other hand, the reduction in the mRNA abundance of FADS2 in the liver of goats fed the SFO diet, most likely caused by a negative effect of n-3 PUFA on the expression of this gene (Cho et al, 1999), might explain the decrease in the 18:3n-6 and 20:3n-6 concentrations in the liver, which could also be related to the lower supply of their precursor, 18:2n-6, in the SFO diet. In contrast, the different dietary treatments did not lead to changes in the mRNA abundance of the transcription factors regulating lipogenic gene expression (i.e.…”

Dietary myristic acid at physiologically relevant levels increases the tissue content of C20:5 n-3 and C20:3 n-6 in the rat

“…However, desaturase assays are routinely designed after fasting [15] because high variability in desaturase activities comes from the nutritional status of the animals. While dietary PUFA are known to suppress the expression and activity of ∆6-and ∆5-desaturases [23,24], the effect of individual saturated FA has been less explored.…”