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Characterization of the role of long-chain fatty acids in the regulation of lipogenic gene expression via LXRα in goat mammary epithelial cells
In dairy cows and goats, liver X receptor α (LXRα) is a nuclear receptor considered as a potentially important regulator of de novo long-chain fatty acid (LCFA) synthesis. Previous data in bovine MacT cells indicated that activation of LXRα with the agonist T0901317 (T09) up-regulates the expression of some lipogenic target genes, hence, could play a role in de novo FA synthesis regulation. In vitro, long-chain fatty acids (LCFA) could have an agonistic capacity on LXRα, thus, serving as an alternate mechanism for regulating milk fat synthesis. In order to characterize the roles of LXRα and LCFA in the regulation of lipid synthesis in goat mammary epithelial cells (GMEC), primary mammary cells isolated from mammary gland of Saanen dairy goats cultivated in lactogenic medium were cultured in triplicate and for 12 h with 50 μM of the specific LXRα agonist T0901317 (T09) or the specific LXRα antagonist GGPP (GP), 100 μM of several LCFA (16:0, 18:0, t10,c12- conjugated linoleic acid (CLA), docosahexaenoic acid (DHA), and eicosapentaenoic acid (EPA)), and a combination of GP with 100 μM of several LCFA (16:0, 18:0, t10,c12-CLA, DHA, and EPA) (for a total of 7 treatments excluding controls). Expression of 17 genes involved in LCFA plus 3 internal control genes was detected using qPCR. Data were statistically analyzed using the GLM of SAS. The multiple comparisons were corrected using Tukey’s test and accepted as significant at P < 0.05. Although T09 did not alter LXRα, data from the cells treated with GP alone revealed that a minimum activation of LXRα is essential for the up-regulation (P < 0.05) of INSIG1, LPIN1, FASN, SREBF1, AGPAT6, and SCD. The marked up-regulation (P < 0.05) of SREBF1, FASN, ACACA, and SCD with T09 vs. control suggests their expression is partly controlled by LXRα as reported in MacT cells. Expression of PPARG did not respond to T09 or GP but when the LCFA were combined with GP, its expression was up-regulated (P = 0.0001) by 13-18 fold over the control. Both 16:0 and 18:0 when combined with GP up-regulated (P < 0.05) SREBF1, INSIG1, SCD, ACSS2, AGPAT6, and LPIN1 but had no effect on ACACA or FASN. Data obtained with the combination of GP and LCFA revealed a complex scenario. However, data indicate that the LCFA effect could have been driven partly via PPARG as demonstrated previously in MacT cells. Overall, data suggest that LCFA could partly act as competitive agonists of LXRα in GMEC.
Keywords: nutrigenomics, milk fat synthesis, nuclear receptor