Identification of potential differences in salivary proteomic profiles between estrus and diestrus stage of estrous cycle in dairy cows.

In the present study, a comparative global high-throughput proteomic analysis strategy was used to identify proteomic differences between estrus and diestrus stage of estrous cycle in dairy cows. Saliva was collected from cows during estrus and diestrus, and subjected to LC-MS/MS-based proteomic analysis. A total of 2842 proteins were detected in the saliva of cows, out of which, 2437 and 1428 non-redundant proteins were identified in estrous and diestrous saliva, respectively. Further, it was found that 1414 and 405 salivary proteins were specific to estrus and diestrus, respectively while 1023 proteins were common to both groups. Among the significantly dysregulated proteins, the expression of 56 proteins was down-regulated (abundance ratio <0.5) while 40 proteins were up-regulated (abundance ratio > 2) in estrous compared to diestrous saliva. The proteins, such as HSD17B12, INHBA, HSP70, ENO1, SRD5A1, MOS, AMH, ECE2, PDGFA, OPRK1, SYN1, CCNC, PLIN5, CETN1, AKR1C4, NMNAT1, CYP2E1, and CYP19A1 were detected only in the saliva samples derived from estrous cows. Considerable number of proteins detected in the saliva of estrous cows were found to be involved in metabolic pathway, PI3K-Akt signaling pathway, toll-like receptor signaling pathway, steroid biosynthesis pathway, insulin signaling pathway, calcium signaling pathway, estrogen signaling pathway, oxytocin signaling pathway, TGF-β signaling pathway and oocyte meiosis. On the other hand, proteins detected in saliva of diestrous cows were involved mainly in metabolic pathway. Collectively, these data provide preliminary evidence of a potential difference in salivary proteins at different stages of estrous cycle in dairy cows.