Exogenous essential amino acids stimulate an adaptive unfolded protein response in the mammary glands of lactating cows

Abstract

The phosphorylation of mammalian target of rapamycin complex 1 (mTORC1) components and integrated stress response networks in the mammary glands of lactating cows have not accounted for the stimulation of milk protein yield by chronic supplementation with AA or glucose. Faster milk protein synthesis could be a consequence of increased milk protein mRNA per cell, the number of ribosomes per cell, the secretory capacity of cells, or the mammary cell number. To investigate these 4 possibilities using a translational and transcriptional approach, we performed protein and gene expression analyses of mammary and longissimus dorsi tissue collected from lactating dairy cows after 5 d of abomasal infusion with saline or 844 or 1,126 g/d of an essential AA (EAA) mixture, with and without 1,000 g/d glucose. Infusion with EAA increased milk protein yield but did not affect the phosphorylation of mTORC1-related proteins in the mammary gland. In skeletal muscle, phosphorylation of 4EBP1 (eIF4E-binding protein 1) increased in response to both EAA and glucose, and phosphorylated S6K1 (70-kDa ribosomal protein S6 kinase) increased with glucose. In response to EAA, mammary mRNA expression of the marker genes for milk proteins, ribosome biogenesis, and cell proliferation were not upregulated. Instead, reciprocal regulation of 2 arms of the unfolded protein response occurred. Infusion of EAA for 5 d activated XBP1 (X-box binding protein 1) mRNA, encoding a transcription factor for endoplasmic reticulum biogenesis, and it decreased the mRNA expression of genes encoding pro-apoptotic protein CHOP (C/EBP homologous protein) and downstream GADD34 (growth arrest and DNA damage-inducible 34). These findings implicate non-stress-related, adaptive capabilities of the unfolded protein response in the long-term nutritional regulation of milk protein yield in lactating dairy cows.

Mammary gland utilization of amino acids and energy metabolites differs when dairy cow rations are isoenergetically supplemented with protein and fat

“…Lactose synthesis may be largely regulated by mammary mechanisms independent of glucose supply, such as glucose phosphorylation and transport capacity, and concentrations of metabolites glucose-6-P and glucose-1-P . The synthetic processes for milk protein and fat may also play a role in determining total milk yield through stimulatory effects on cell signaling pathways dictating overall mammary synthetic capacity (Nichols et al, 2017) or through effects on hormones and enzymes controlling flux through the lactose synthesis pathway (Anderson et al, 2007). Taken together, results of previous studies along with data presented here suggest that although glucose is necessary to support lactose yield, glucose availability per se is not the driving force stimulating lactose synthesis in mid-lactation cows, and that mammary regulation of milk production is dependent on factors other than mammary glucose supply.…”

Methylome and transcriptome profiles in three yak tissues revealed that DNA methylation and transcription factor ZGPAT co-regulate milk production

“…Differentially methylated regions (DMRs) were identi ed using metilene (Version 0. [2][3][4][5][6] within a 500 bp sliding window at 250 bp steps with at least 10 CpGs covered by over 10× sequence reads, applying the thresholds of differential methylation β >=15%, FDR for two-dimensional Kolmogorov-Smirnov-Test p-value <0.05. [35].…”

“…Domestic yaks play an indispensable role in sustaining the livelihood of Tibetans and other ethnic groups on the Qinghai-Tibetan Plateau (QTP) and in the Himalayas and connecting Central Asian highlands by providing milk, meat, hide, ber, fuel, and transportation [1,2]. Milk is an important source of high-quality protein because of its high content of essential amino acids, such as lysine, which is de cient in many human diets [3], and because of its well-known physiological effects, such as immunomodulatory and gastrointestinal activities [4]. The milk protein content and composition in uence the technological properties of milk and are therefore important for the dairy industry, especially in Europe, where the majority of the milk produced is transformed into cheese.…”

Methylome and transcriptome analyses of yaks of different ages revealed that DNA methylation and transcription factor ZGPAT co-regulate milk production

“…Domestic yaks play an indispensable role in sustaining the livelihood of Tibetans and other ethnic groups on the Qinghai-Tibetan Plateau (QTP) and in the Himalayas and connecting Central Asian highlands by providing milk, meat, hide, fiber, fuel, and transportation [1,2]. Milk is an important source of high-quality protein because of its high content of essential amino acids, such as lysine, which is deficient in many human diets [3], and because of its well-known physiological effects, such as immunomodulatory and gastrointestinal activities [4]. The milk protein content and composition influence the technological properties of milk and are therefore important for the dairy industry, especially in Europe, where the majority of the milk produced is transformed into cheese.…”