Regulation of mammary lipogenic genes in dairy cows fed crushed sunflower seeds

摘要

The main objective of this study was to investigate the effects of increasing dietary supplementation of crushed sunflower seeds (CSS) in dairy cow diet on mammary expression of genes involved in de novo fatty acid (FA) synthesis, FA desaturation, FA transport/uptake, cholesterol homeostasis, and regulation of transcription. Twenty-four cows were allocated to one of four diets supplemented with CSS at 0% (Control), 5%, 10%, or 15% of dry matter in randomized block design. After a five week experimental period, mammary tissue was biopsied, and milk and plasma samples were obtained. Milk proportion of preformed FA was increased at all levels of CSS supplementation while the proportion of FA <= C16 was reduced. This change in milk fat composition was reflected in a sustained mammary transcription of genes involved in FA transport, i.e. Lipoprotein Lipase (LPL), Fatty Acid Binding Protein 3 (FABP3), and FA Translocase, and a reduced transcription of a gene involved in regulation of transcription, i.e. Sterol Response Element Binding Factor 1 (SREBF1) as well as genes involved in FA synthesis in cows supplemented with CSS. Milk proportion of unsaturated fatty acids (UFA) was increased from 27.5% in control to 40.3% and 43.0% of total FA in cows supplemented with 10 and 15% CSS, respectively, in spite of reduced mammary transcription of two desaturase enzymes, i.e. Stearoyl CoA Desaturase 1 (SCD1) and FA Desaturase 1 (FADS1) in these two treatment groups. Transcription of Sterol Response Element Binding Protein Cleavage Activating Protein (SCAP), Niemann Pick disease type 1C (NPC1) and Acetyl-CoA Carboxylase alpha (ACAC) were also reduced by CSS supplementation to various degrees. Transcription of Insulin Induced Gene 1 (INSIG1), FA Desaturase 2 (FADS2), and ATP Binding Cassette, sub-family G member 2 (ABCG2) was not significantly changed by CSS supplementation. Our data show a coordinated down-regulation of mammary transcription of major lipogenic transcription factor, SREBF1, its target genes FAS and ACAC, and its activator protein SCAP during lipid supplementation even though overall milk fat secretion was unaltered.