Phenylalanine and valine differentially stimulate milk protein synthetic and energy-mediated pathway in immortalized bovine mammary epithelial cells

Abstract

Studies on promoting milk protein yield by supplementation of amino acids have been globally conducted. Nevertheless, there is a lack of knowledge of what pathways affected by individual amino acid in mammary epithelial cells that produce milk in practice. Phenylalanine (PHE) and valine (VAL) are essential amino acids for dairy cows, however, researches on mammary cell levels are still lacking. Thus, the aim of this study was conducted to evaluate the effects of PHE and VAL on milk protein synthesis-related and energy-mediated cellular signaling in vitro using immortalized bovine mammary epithelial (MAC-T) cells. To investigate the effects of PHE and VAL, the following concentrations were added to treatment medium: 0, 0.3, 0.6, 0.9, 1.2, and 1.5 mM. The addition of PHE or VAL did not adversely affect cell viability compared to control group. The concentrations of cultured medium reached its maximum at 0.9 mM PHE and 0.6 mM VAL (p < 0.05). Therefore, aforementioned 2 treatments were analyzed for proteomics. Glucose transporter 1 and mammalian target of rapamycin mRNA expression levels were up-regulated by PHE (166% and 138%, respectively) (p < 0.05). Meanwhile, sodium-dependent neutral amino acids transporter type 2 (ASCT2) and β-casein were up-regulated by VAL (173% in ASCT2, 238% in and 218% in β-casein) (p < 0.05). A total of 134, 142, and 133 proteins were detected in control group, PHE treated group, and VAL treated group, respectively. Among significantly fold-changed proteins, proteins involved in translation initiation or energy metabolism were detected, however, expressed differentially between PHE and VAL. Thus, pathway analysis showed different stimulatory effects on energy metabolism and transcriptional pathways. Collectively, these results showed different stimulatory effects of PHE and VAL on protein synthesis-related and energy-mediated cellular signaling in MAC-T cells.

Effect of Heat Stress on Bovine Mammary Cellular Metabolites and Gene Transcription Related to Amino Acid Metabolism, Amino Acid Transportation and Mammalian Target of Rapamycin (mTOR) Signaling

“…Phenylalanine (Phe) was confirmed as a potentially limiting amino acid for milk protein synthesis in BMECs [ 40 ]. The extraction of Phe by the mammary gland was shown to be equal to its amount secreted in milk [ 18 ].…”

D-Methionine and 2-hydroxy-4-methylthiobutanoic acid i alter beta-casein, proteins and metabolites linked in milk protein synthesis in bovine mammary epithelial cells

“…The addition of HMBi upregulated the elongation protein eukaryotic translation initiation factor 3 subunit (EIF3A) but downregulated the ribosomal proteins RPS12 and RPS21. Supplementation with D-Met stimulated phosphoinositide 3 (PI3) kinase, an upstream mTOR activator [ 19 , 28 , 33 , 34 ]. The list of all upregulated and downregulated proteins are listed in Tables 8 and 9 .…”

Enhancement of BCAT2-Mediated Valine Catabolism Stimulates β-Casein Synthesis via the AMPK-mTOR Signaling Axis in Bovine Mammary Epithelial Cells

“…We found Val acutely stimulated β-casein synthesis in the BMECs in a dose-dependent manner, especially at concentrations of 1.2 and 0.8 mM, while Val absence inhibited β-casein synthesis. However, Kim et al found that β-casein expression increased only at Val concentrations of 0.3 and 1.5 mM. Further studies are needed to investigate the underlying mechanisms by which Val affects β-casein synthesis.…”