Effect of linseed dietary supplementation on adipose tissue development, fatty acid composition, and lipogenic gene expression in lambs

Abstract

The objective of this study was to examine the effect of linseed supplementation on growth and carcass parameters, adipocyte cellularity, lipogenic enzyme activity, fatty acid (FA) composition and expression of lipogenic genes in subcutaneous (SC) adipose tissue and intramuscular (IM) adipose tissue of longissimus thoracis muscle of lambs. Thirty-six male Navarra breed lambs allocated into 3 experimental groups (15.2±0.18kg) were fed a control diet (containing barley and soya) and two experimental diets (5% and 10% linseed, L5 and L10 respectively) and slaughtered at 26.5±0.28kg. In the SC adipose tissue and muscle, the activity of fatty acid synthetase (FAS), glycerol 3-phosphate dehydrogenase (G3PDH), glucose 6-phosphate dehydrogenase (G6PDH) and NADP-Isocitrate dehydrogenase (ICDH) was studied and the expression of lipoprotein lipase (LPL), acetyl-CoA carboxylase 1or alpha (ACACA), stearoyl-CoA desaturase (SCD), fatty acid desaturase 1 (FADS1) and 2 (FADS2) and fatty acid elongase 5 (ELOVL5) was quantified. Addition of linseed, rich in α-linolenic acid (C18:3n−3), had no effect on growth and carcass parameters. Linseed supplementation increased C18:3n−3, C18:1t10 + C18:1t11 and total n−3 polyunsaturated fatty acid (PUFA) contents of SC and IM fat (P<0.001) and decreased C18:2n−6 and C18:3n−6 (P<0.05). The n−6/n−3 ratio was also decreased by linseed addition (P<0.05). There were no significant effects of linseed on C18:2c9,t11, eicosapentaenoic acid (C20:5n−3), docosapentaenoic acid (C22:5n−3) and docosahexaenoic acid (C22:6n−3) contents of SC and IM depots. In the SC fat, expression of ACACA and SCD was downregulated in L10 compared to C group (P<0.001) and LPL was upregulated in L5 group (P<0.001); however, there were no effects of diet on FADS1, FADS2 and ELOVL5 mRNA levels. In the IM fat, downregulation of ACACA (L5 and L10), SCD (L10), FADS1 (L5 and L10) and FADS2 (L5) was observed (P<0.001). Expression of LPL was upregulated in L5 compared to C group (P<0.01). It was concluded that dietary linseed raised C18:3n−3 and n−3 PUFA in SC and IM fat in Navarra breed lambs and modified the FA synthesis through the regulation of key-lipogenic gene expression. Dietary linseed regulated de novo FA synthesis and shifted monounsaturated FA formation at the transcriptional level by downregulating ACACA and SCD, respectively. Hence, linseed supplementation did not appear to enhance the synthesis of C18:2c9,t11. Moreover, dietary PUFA affected the expression of genes involved in long chain PUFA synthesis (FADS1, FADS2 and ELOVL5) in a tissue-specific manner.