Cloning, Expression, and Nutritional Regulation of the Mammalian Δ-6 Desaturase

Abstract

Arachidonic acid (20:4(n-6)) and docosahexaenoic acid (22:6(n-3)) have a variety of physiological functions that include being the major component of membrane phospholipid in brain and retina, substrates for eicosanoid production, and regulators of nuclear transcription factors. The rate-limiting step in the production of 20:4(n-6) and 22:6(n-3) is the desaturation of 18:2(n-6) and 18:3(n-3) by Delta-6 desaturase. In this report, we describe the cloning, characterization, and expression of a mammalian Delta-6 desaturase. The open reading frames for mouse and human Delta-6 desaturase each encode a 444-amino acid peptide, and the two peptides share an 87% amino acid homology. The amino acid sequence predicts that the peptide contains two membrane-spanning domains as well as a cytochrome b5-like domain that is characteristic of nonmammalian Delta-6 desaturases. Expression of the open reading frame in rat hepatocytes and Chinese hamster ovary cells instilled in these cells the ability to convert 18:2(n-6) and 18:3(n-3) to their respective products, 18:3(n-6) and 18:4(n-3). When mice were fed a diet containing 10% fat, hepatic enzymatic activity and mRNA abundance for hepatic Delta-6 desaturase in mice fed corn oil were 70 and 50% lower than in mice fed triolein. Finally, Northern analysis revealed that the brain contained an amount of Delta-6 desaturase mRNA that was several times greater than that found in other tissues including the liver, lung, heart, and skeletal muscle. The RNA abundance data indicate that prior conclusions regarding the low level of Delta-6 desaturase expression in nonhepatic tissues may need to be reevaluated.

Effect of dietary fatty acids on expression of lipogenic enzymes and fatty acid profile in tissues of bulls

“…D6d is involved in a complex process of biosynthesis of longer chain n-3 and n-6 fatty acids through conversion of linoleic and linolenic acids to their products (Stoffel et al, 2008). The molecular weights of ACC, SCD and D6d immunoreactive bands detected in this study were 150, 37 and 50 kDa respectively, which is consistent with the molecular weights of ACC, SCD and D6d proteins reported for other species (Tanabe et al, 1975;Cho et al, 1999;Moreau et al, 2006). In a case of the SCD protein expression (in muscle and subcutaneous adipose tissue) and muscle D6d, the two closely positioned immunoreactive bands were observed.…”

“…Similarly to ACC, the presence of D6d-immunoreactive proteins was also observed in both tissues (Figure 3b), and the signal was much higher in subcutaneous adipose tissue when compared with the muscle. The bands' size was approximately of 50 kDa, which is consistent with the molecular weight of mouse and human D6d (Cho et al, 1999).…”

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).…”

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.…”