iTRAQ-mediated analysis of the relationship between proteomic changes and yak longissimus lumborum tenderness over the course of postmortem storage

To identify differentially expressed proteins associated with energy metabolism and tenderness during the postmortem aging of yak longissimus lumborum muscle samples, we collected tissue

samples from yaks raised at different altitudes. At 12 h post-slaughter, we identified 290 differentially expressed proteins (DEPs) in these samples, whereas 436 such DEPs were detected

after 72 h. Identified DEPs were clustered into four main functional categories: cell structural proteins, glycogen metabolic proteins, energy reserve metabolic proteins, and cellular

polysaccharide metabolic proteins. Further bioinformatics analysis revealed that these proteins were associated with carbon metabolism, glycolysis, and the biosynthesis of amino acids. Our

functional insights regarding these identified proteins contribute to a more detailed molecular understanding of the processes of energy metabolism in yak muscle tissue, and represent a

valuable resource for future investigations.

Hypoxic conditions can cause mammalian cells and tissues to express a number of different glucose transporters and enzymes that ultimately lead them to shift their metabolic activity such

that they favor anaerobic glycolysis rather than aerobic respiration, leading to ATP generation that coincides with the reduced production of toxic reactive oxygen species (ROS)1. In rat

heart tissue, for example, acute hypoxia can result in a significant increase in phosphofructokinase (PFK) activity and lactate production together with a net reduction in cardiac ATP

levels2. Comparable findings have also been made in different studies of yak breeds that reside between 1500 and 5000 m of elevation in southwestern China3,4,5. As they are adapted to high

altitude conditions, yaks exhibit more robust energy metabolism and superior disease resistance relative to other cattle species. Importantly, under low oxygen conditions yaks of the Tibetan

Plateau are able to readily induce the expression of certain proteins that allow their cells to better adapt to hypoxia so as to improve circulation and preserve cellular functionality. We

have previously shown that yaks raised at high altitudes exhibit significantly reduced tissue glycogen levels that coincide with significant increases in hemoglobin and lactate levels in

blood samples from these same animals6. Cooking loss of the longissimus dorsi of low altitude Simmental cattle is lower than that of Yushu yak and Gannan yak, but the difference is not

significant. The L* and b* values of Simmental are slightly lower than Yushu yak and Gannan yak, and the a* value is higher than Yushu yak and Gannan yak. Cooking loss of the three groups

first increased significantly with the maturation time (0–72 h) (P  50, with scores > 75% corresponding to a phosphorylation event. Differential protein expression was detected via

comparisons between groups, with samples being compared via Student’s t tests with a P  1.5 or P