Trans10, cis12 conjugated linoleic acid increases triacylglycerol accumulation in goat mammary epithelial cells in vitro

Abstract

Trans10, cis12 conjugated linoleic acid (t10c12-CLA) is well-established in decreasing milk fat content and causing milk fat depression (MFD) in dairy cattle and goats. However, the detailed mechanisms of its effect are not completely understood. Therefore, we used goat mammary epithelial cells (GMECs) to further study the molecular mechanisms whereby t10c12-CLA regulates milk fat synthesis. The optimal concentration of t10c12-CLA (100 μmol/L) for cell culture was determined through a cell vitality and morphology assay, and evaluation of abundance of apoptosis-related proteins. Oil red O stain indicated that t10c12-CLA increased concentration of cytoplasmic lipid droplets. Furthermore, t10c12-CLA increased the intracellular triacylglycerol (TG) content (P < 0.05). Among 16 genes related to lipid metabolism that were measured by quantitative real-time PCR, t10c12-CLA down-regulated (P < 0.05) genes involved in de novo fatty acid synthesis including FASN, ACACA and SCD1, and also down-regulated the protein expression of FASN and SCD1 but up-regulated (P < 0.05) the expression of CD36 and ADRP. Overall, the data indicate that a side effect of de novo fatty acid synthesis inhibition by t10c12-CLA is the up-regulation of fatty acid uptake and accumulation of lipid droplets in GMECs. The biologic reason for such an effect merits further study.

Regulation of Key Genes for Milk Fat Synthesis in Ruminants

“…After BMECs was treated with 150 mol/L t10c12-CLA for 48 h, the abundance of SCD1 decreased significantly ( 63 ). T10c12-CLA could also inhibit SCD1 expression by affecting the binding of SREBP1 protein to SRE and NF-Y sites ( 105 ), which was consistent with Zhang et al ( 106 ) and Peterson et al ( 64 ). Foxo1 can inhibit the participation of SREBP1 in lipid metabolism in the liver of mice.…”

“…The mRNA abundance of CD36 was down-regulated by 56% after interfering PPARA in GMECs, which was the same as the positive regulatory effect of PPARA in the de novo synthesis of milk fat, however, interfering PPARA up-regulated the mRNA abundance of ACSL1 and also significantly increased TAG content, suggesting a stronger negative regulation of ACSL1 by PPARA and further interpreting the dominance of LCFA uptake in the blood ( 37 ). Several studies have confirmed that t10c12-CLA, PPARG and PPARD exhibit positive regulation of both CD36 ( 35 , 87 , 106 ) and ACSL1 ( 34 , 36 , 63 ), however, Shi et al ( 61 ) challenge the above view that t10c12-CLA A positively regulates CD36 and ACSL1, which may be related to factors such as the species, mode and amount of additives, the exact mechanism of action needs to be further verified by more in-depth experimental studies as well as large-scale populations. As previously described, 14-3-3γ, LXR, SREBP1 and CIDEC have positive regulatory roles in the de novo synthesis of milk fat, which perform similar functions during LCFA uptake ( 21 , 29 , 36 , 69 ).…”

“…t10c12-CLA can reduce TAG storage and enhance FA oxidation ( 106 ), which is beneficial to human health ( 59 ). After 5 days of perfusion of t10c12-CLA (13.6 g/d) into the abomasum of dairy cows, the fat production capacity of dairy cows decreased by 82%.…”

Effects of Fat Supplementation in Dairy Goats on Lipid Metabolism and Health Status

“…In particular, trans10-cis12-CLA has been demonstrated to be partly responsible for milk fat depression (MFD) in dairy cows [47,48]. In a study by Zhang et al [49], trans10-cis12-CLA downregulated the expression of various genes involved in de novo FA synthesis ( FASN, SCD1, ACACA ) in caprine mammary gland epithelium in vitro. The reason behind such an effect are still to be clarified.…”

“…In line with the latter finding are those of Suárez-Vega et al [57], who evidenced how MFD induced by CLA supplementation was characterized by a wider downregulation of adipogenic genes in dairy ewe mammary glands than fish oil-induced ones; moreover, CLA-induced MFD but not fish oil-induced MFD affected genes involved not only in FA synthesis, but also in immune response, as evidenced by the milk somatic cell transcriptome analysis. In this regard, Zhang et al [49] found that trans10-cis12-CLA increased the concentration of lipid droplets in caprine mammary gland cells. As discussed later on, an increase in lipid droplet content in the goat leukocyte cytoplasm is associated with the activation of immune and inflammatory mechanisms [58].…”