Regulation of FADS2 expression and activity in European sea bass (Dicentrarchus labrax, L.) fed a vegetable diet

Abstract

Supplies of marine fish oils are limited, and continued growth in aquaculture production dictates that lipid substitutes in fish diets must be used without compromising fish health and product quality. In this study, the total substitution of a fish meal and fish oil by a blend of vegetable meals (corn, soybean, wheat and lupin) and linseed oil in the diet of European sea bass (Dicentrachus labrax) was investigated. Two groups of European sea bass were fed with fish diet (FD) or vegetable diet (VD) for 9months. VD, totally deprived of eicosapentaenoate (EPA; 20:5n-3) and docosahexaenoate (DHA; 22:6n-3), revealed a nutritional deficiency and affected growth performance. Whilst VD induced a significant increase in fatty acid desaturase 2 (FADS2) and sterol binding regulatory element-binding protein 1 (SREBP-1) mRNA levels, the desaturation rate of [1-(14)C]18:3n-3 into [1-(14)C]18:4n-3, analysed in microsomal preparations using HPLC method, did not show an upregulation of FADS2 activities in liver and intestine of fish fed VD. Moreover Western-blot analysis did not revealed any significant difference of FADS2 protein amount between the two dietary groups. These data demonstrate that sea bass exhibits a desaturase (FADS2) activity whatever their diet, but a post-transcriptional regulation of fads2 RNA prevents an increase of enzyme in fish fed a HUFA-free diet. This led to a lower fish growth and poor muscle HUFA content.

Marginal efficiencies of long chain-polyunsaturated fatty acid use by barramundi (Lates calcarifer) when fed diets with varying blends of fish oil and poultry fat

“…In the latter example, the authors argued that DHA was probably used as a substrate for energy production at lower dietary intake. Many studies have demonstrated that despite up regulation of genes involved in FA synthesis pathways, most fish species are unable to completely compensate for a lack of dietary LC-PUFA (Alhazzaa et al, 2011;Betancor et al, 2014;Francis et al, 2007;Geay et al, 2010;Tu et al, 2013). Interestingly in this study, the reduced retention of EPA may be attributable in part, to the apparent concomitant appearance of DPA via elongation of C20 to C22.…”

Effects of alternate feeding with different lipid sources on fatty acid composition and bioconversion in European sea bass (Dicentrarchus labrax)

“…There has recently been significant interest in the regulation of lipid metabolism genes such as SREBP-1 (Brown and Goldstein, 1997;Eberle et al, 2004), PPAR-α, delta-6 desaturase (Δ6D) and also fatty acid elongases (ELOVLS) (Tocher et al, 2006), as regulators of FA biosynthesis. Results from a number of studies have also suggested that the lower capability of marine fish species to synthesize EPA or DHA from shorter chain precursors could be due to an absence of the regulation of desaturase and elongase activity (Mourente and Dick, 2002;Zheng et al, 2004;Mourente et al, 2005;Geay et al, 2010). However, little information is available on commercially important cultured marine teleosts with respect to the implication of factors such as SREBP-1 and PPAR-α activities in relation to fatty acid bioconversion (Geay et al, 2010;Morais et al, 2011;Castro et al, 2014).…”

“…Results from a number of studies have also suggested that the lower capability of marine fish species to synthesize EPA or DHA from shorter chain precursors could be due to an absence of the regulation of desaturase and elongase activity (Mourente and Dick, 2002;Zheng et al, 2004;Mourente et al, 2005;Geay et al, 2010). However, little information is available on commercially important cultured marine teleosts with respect to the implication of factors such as SREBP-1 and PPAR-α activities in relation to fatty acid bioconversion (Geay et al, 2010;Morais et al, 2011;Castro et al, 2014). Even though the LC-PUFA biosynthetic pathways in teleosts are known to be further regulated by environmental (e.g.…”

miR-17 is involved in the regulation of LC-PUFA biosynthesis in vertebrates: Effects on liver expression of a fatty acyl desaturase in the marine teleost Siganus canaliculatus

“…Moreover, it was hypothesized that post-transcriptional regulation of Δ6 Fad expression may also take place in European sea bass as suggested by the inconsistent levels of Fad mRNA and protein in liver and intestine [21].…”