Regulation of Stearoyl-Coenzyme A Desaturase 1 by trans-10,cis-12 Conjugated Linoleic Acid via SREBP1 in Primary Goat Mammary Epithelial Cells

摘要

trans-10,cis-12 Conjugated linoleic acid (t10c12-CLA) is a biohydrogenation intermediate in the rumen that inhibits mammary fatty acid de novo synthesis in lactating dairy goats. However, the underlying molecular pathways in milk-lipid metabolism affected by t10c12-CLA are not completely understood. The present study investigated the lipid-regulation mechanisms in goat mammary epithelial cells (GMECs) in response to t10c12-CLA. Gene-expression analysis indicated sterol-regulatory-element-binding transcription factor1 (SREBF1) and its putative target gene stearoyl-CoA desaturase (SCD1) were down-regulated (fold changes of 0.33 +/- 0.04, P 0.05, and 0.19 +/- 0.01, P 0.01, respectively). Concentrations of cellular palmitoleic acid (C16:1) and oleic acid (C18:1) were decreased (1.12 +/- 0.05 vs 1.69 +/- 0.11% and 15.70 +/- 0.44 vs 24.97 +/- 0.82%, respectively, P 0.01), whereas those of linoleic acid (C18:2) were increased (5.00 +/- 0.14 vs 3.81 +/- 0.25%, P 0.05); the desaturation indices of C16 and C18 were decreased in response to t10c12-CLA treatment (6.90 +/- 0.05 vs 8.00 +/- 0.30% and 61.41 +/- 0.65 vs 67.73 +/- 1.33%, respectively, P 0.05). A luciferase-activity assay indicated that deletion of the sterol-response-element (SRE) site and the nuclear-factor (NF-Y) site in the SCD1-promoter region (-511/+65 bp) suppressed the regulatory effect of t10c12-CLA. Overexpression of SREBF1 partly counteracted the inhibitory effect of t10c12-CLA on de novo fatty acid synthesis. Overall, t10c12-CLA causes an inhibition of fatty acid synthesis and desaturation and regulates SCD1 expression by affecting the binding of SREBP1 protein to the SRE and NF-Y sites.