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Long chain fatty acids alter expression of genes involved in lipid metabolism in goat mammary epithelial cells partly through PPARγ
Data from dairy cows and goats indicate a prominent role of PPARγ in regulating milk fat synthesis (MFS). The PPARγ binds and is activated by long-chain fatty acids (LCFA), hence is amenable for fine-tuning MFS. Previous data in MacT cells indicated an agonistic capacity of saturated LCFA but also the potential of LCFA to act through alternative transcriptional regulators. In order to determine the specificity of LCFA in modulating PPARγ in goats, triplicate cultures of primary mammary cells from Saanen goats cultivated in lactogenic medium were cultured for 24 h with 50 μM of the specific PPARγ activator rosiglitazone (ROSI) or the specific PPARγ inhibitor GW9662 (GW), 100 μM of several LCFA (16:0, 18:0, t10,c12-CLA, DHA, and EPA), and a combination of GW with each of LCFA (for a total of 12 treatments excluding controls). Expression of 28 genes involved in MFS plus 3 internal control genes was measured using qPCR. Data were log-transformed and statistically analyzed using the GLM of SAS. The multiple comparisons were corrected using Tukey’s test and significance set at P<0.05. The cells treated with GW alone allowed uncovering that a minimum activation of PPARγ is essential for the expression of LPIN1, PPARG, LXRA, LPL, ACSL1, FABP3, and FABP4. The combination of the data from GW and ROSI treatments allowed identification of SCD, FADS1, NR1H3, SREBF1, INSIG1, LPL, FABP3, and FABP4 as strong PPARγ target genes. The 16:0 and 18:0 had the strongest effect on most of the measured genes and stronger than ROSI. Among the unsaturated LCFA, the CLA had the strongest effect in decreasing expression of FASN, FADS1, LPIN1, SREBF1, SREBF2, INSIG1, RXRA, NCOR1, and FABP3. The combination with GW diminished but did not completely eliminate the effect of saturated LCFA and interacted in a complex manner with the effect of unsaturated LCFA. The expression of AGPAT6, PLIN2, and CD36 increased in all treatments compared with control. The expression of NR1H3 solely responded to ROSI and GW but not to LCFA. Results allowed pinpointing true PPARγ target genes in goat mammary cells, and confirmed that saturated LCFA are potent PPARγ agonists in ruminants but they act also through alternative transcriptional factors. Data established the lipid-depressing effect of unsaturated LCFA, particularly CLA. A complex mechanism for LCFA in regulating expression of lipid-related genes in goat mammary cells was uncovered.
Keywords: nuclear receptors, milk fat synthesis, nutrigenomics