Translational regulation of milk protein synthesis

点击翻译按钮获取中文摘要

The protein of milk supplies an ideal amino acid profile for infant growth. In addition, bioactive peptides derived from fermentation or digestion of milk proteins possess functional value in treatment and prevention of symptoms of the human metabolic syndrome including obesity, atherogenesis, arterial hypertension, and type 2 diabetes. The bovine milk proteome is 80% casein and 20% whey proteins. The four caseins, designated as1-, as2-, ß- and K-casein are amphipathic and aggregate into surfactant particles called casein micelles that have drawn attention in recent years due to their interesting properties as novel gastrointestinal nutrient and drug delivery nanoparticles. The process of micelle formation during casein translation and vesicular transport in the mammary epithelial cell, and the roles of each individual casein in the intravesicular aggregation process have not yet been fully elucidated. Our objectives are to study the translational regulation of casein synthesis using a combination of in vitro, in vivo and in silico techniques. We will use cell-free translation to generate hypotheses to explain differences in translational efficiency of human and bovine caseins. We will also scale up protein yields from the cell-free system to enable study of casein micelle formation and stability. We will apply silencing RNA protocols to probe the role of mammalian target of rapamycin (mTOR) and integrated stress response (ISR) networks in nutritional and hormonal manipulations of casein secretion from mammary epiothelial cells in culture. Our findings will lead to tests in vivo, using a split-udder protocol where mTOR and ISR inhibitors are infused into two unilateral quarters through the teat canals, and contralateral responses in phosphorylation state of mammary mTOR and ISR signalling proteins are evaluated. The data will be used to parametize a model of translational control of milk protein synthesis that can be used to design new experimental protocols. The focus on translation of milk protein mRNAs is novel for the dairy cow nutrition field and may generate significant new findings in terms of the casein profile in milk, the nutrient-encapsulating properties of casein micelles, and the ability to improve human nutrition.