Signature of high altitude adaptation in the gluteus proteome of the yak.

Yak is the unique Bovidae species in the Qinghai-Tibetan Plateau. A previous proteomic study has compared the yak muscle tissue to one cattle strain using the isobaric tags for relative and absolute quantification approach. In this study, to further investigate the molecular mechanisms underlying yak adaptation, the proteomic profiles of gluteus were compared between yak and one moderate-altitude cattle strain (Tibetan cattle) and two low-altitude cattle strains (Holstein and Sanjiang cattle) using a label-free quantitative method. The comparisons identified 20, 364, 143 upregulated proteins and 4, 6, 37 downregulated proteins in yak, compared with Tibetan, Holstein, and Sanjiang cattle, respectively. Protein-protein interaction analysis indicated that these differentially expressed proteins were mainly related to "oxidative phosphorylation" and "electron transport chain." Further analysis revealed that NADH dehydrogenase [ubiquinone] 1 alpha subcomplex subunit 11, NADH dehydrogenase [ubiquinone] 1 beta subcomplex subunit 4, cytochrome C oxidase subunit 6A2, mitochondrial and cytochrome c oxidase subunit NDUFA4 were all increased in the yak, suggesting that yak might increase mitochondrial capacity to sustain metabolic rates under high altitude conditions, which might be a long-term adaptive mechanism underlying adaptation to high altitude environments. Yak increased the level of thioredoxin reductase 2 to protect themselves from oxidative damages. Moreover, the increased expression levels of phosphatidylinositol 4,5-bisphosphate 3-kinase catalytic subunit alpha isoform and caveolin-1 in yak suggested that yaks promoted glucose uptake for adaptation to high altitude. These results provided more information to better understand the molecular mechanisms underlying yak adaption.