1544
Lipogenic gene network expression in bovine mammary epithelial cells in response to the “ideal” profile of Lys, Met, Thr, Phe, His, and Val
Amino acids (AA) not only are building blocks of proteins but also are key factors regulating protein synthesis. In regards to milk protein synthesis, the 6 essential AA (EAA) for which “ideal” recommendations have been proposed are Lys, Met, Thr, Phe, His, and Val. We hypothesized that the essential AA profile could affect the mRNA expression of genes regulating lipogenic gene networks in bovine MAC-T cells. The specific objective of this study was to study how changing the ratio of Lys to Thr, Lys to His, and Lys to Val affects the expression of lipogenic target genes. Triplicate cultures with the “optimal” AA ratio (OPAA; Lys:Met 2.9:1; Thr:Phe, 1.05:1; Lys:Thr, 1.8:1; Lys:His, 2.38:1; Lys:Val, 1.23:1) plus rapamycin (OPAARMC, control), OPAA, 2.1:1 Lys:Thr (LT2.1), 1.3:1 Lys:Thr (LT1.3), 3.05:1 Lys:His (LH3.0), and 1.62:1 Lys:Val (LV1.6) were incubated for 12 h. The expression of lipogenic gene networks was evaluated via quantitative PCR of 15 genes plus 3 internal control genes measured using qPCR. Data were log-transformed and statistically analyzed using the GLM of SAS with treatment as a fixed effect and replicate as random effect. The multiple comparisons were corrected using Tukey’s and significance set a P<0.05. Responses to LT2.1, LT1.3, LH3.0, and LV1.6 relative to the OPAARMC included greater expression of ACSS2, FABP3, ACACA, FASN, SCD, LPIN1, INSIG1, SREBF1, PPARD, and NR1H3. Furthermore, LV1.6 increased expression of ACSL1, DGAT1, and RXRA and reduced PPARG expression. Although no effect of OPAA on expression of PPARG was observed, OPAA increased expression of ACSS2, FABP3, ACACA, FASN, SCD, LPIN1, INSIG1, and SREBF1 compared with OPAARMC. Gene network analysis using Ingenuity Pathway Analysis revealed a potentially important role of EAA ratios in the coordination of milk fat synthesis via PPARG and SREBF1. The upregulation of lipogenic gene networks observed underscore a role of EAA in the regulation of milk fat synthesis during lactation.
Keywords: nutrigenomics, milk fat synthesis, mTOR