Abstract
Arginine (Arg) is a conditionally-essential amino acid that is taken up by bovine mammary gland in excess of its output in milk. In this study we evaluated the effects of Arg concentration on the expression of casein and signaling pathway-related genes in mammary epithelial cells. The treatments (applied for 24 h) were designed to be devoid of Arg 0X (control; 0.00 mg/L), resemble the profile of Arg in casein (Arg 1X; 278.00 mg/L), be deficient [Arg 0.25X (69.50 mg/L) and Arg 0.5X (139.00 mg/L)], or be in excess of the amount in casein [Arg 2X (556.00 mg/L), Arg 4X (1,112 mg/L), and Arg 8X (2,224 mg/L)]. The expression of CSN1S, CSN3 and mTOR in the experimental groups was higher than those of the control group (P<0.05). Except for Arg 0.25X and Arg 8X (P>0.05), the expression of CSN1S2, CSN2 and JAK2 in other experimental groups was higher (P<0.05) than those in the control group. Except for Arg 8X (P>0.05), the expression of STAT5 in the other experimental groups was higher than those of the control (P<0.05). It also was observed that except for Arg 0.5X, the S6K expression was higher in other experimental groups than the control (P<0.05). In contrast, except for Arg 0.25X the other experimental groups resulted in lower 4EBP1 expression than the control (P<0.05). Among groups, the expression of CSN1S1, CSN1S2, CSN2, CSN3, JAK2, STAT5, mTOR and S6K gene was highest with Arg 2X (P<0.05); the reverse was true for 4EBP1 gene, with the lowest expression in this group (P<0.05). Taken together, Arg appears to play an important role in the transcriptional regulation of casein genes and mTOR-related genes in bovine mammary epithelial cells.
Highlights
There is growing recognition that besides their role as building blocks of proteins and polypeptides, some amino acids (AA) regulate key metabolic pathways that are necessary for maintenance, growth, reproduction, and immunity [1]
A number of studies in monogastric animals have revealed that arginine plays several key functions including serving as precursor for the synthesis of nitric oxide and decreasing blood pressure [19], enhancing cell division [20], [21], and inducing the release of hormones and promoting protein and DNA synthesis [22]
Our preliminary in vitro studies showed that arginine increased the synthesis of casein in mammary epithelial cells from dairy cattle
Summary
There is growing recognition that besides their role as building blocks of proteins and polypeptides, some amino acids (AA) regulate key metabolic pathways that are necessary for maintenance, growth, reproduction, and immunity [1]. Except for its use during milk protein synthesis, those reviews concluded that the extra arginine might exert other unknown biological or metabolic functions in the mammary gland. The availability of AA in the lactating cow is critical for mammary protein synthesis [7]. Previous work on AA metabolism in dairy cattle have focused on achieving an optimal balance in the diet to provide the required precursors for maintaining and enhancing milk protein synthesis [5], [8]. Results revealed that cell signaling molecules involved in the regulation of milk protein synthesis responded differently to the various nutritional stimuli. Subsequent work by Appuhamy et al [10] revealed regulatory roles of essential AA other than arginine in mammary cell protein synthesis
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