iTRAQ-based quantitative proteomic analysis of porcine uterine fluid during pre-implantation period of pregnancy

Proteins in the uterine luminal fluid are essential for embryo development and regulation of embryo-maternal interaction in porcine. However, little is known about the profile of proteins in uterine luminal fluid of porcine during the pre-implantation period. The present study, applied iTRAQ proteomics technology to identify and analyze uterine luminal fluid proteins on day 9 of estrus cycle and days 9, 12, and 15 of pregnancy. A total of 964 proteins were identified in the present study. Principal component analysis and hierarchical clustering revealed the dynamic developmental characteristics of embryo implantation, which indicated significant differences on day 12 or 15 of pregnancy. In addition, further analysis conducted in the present study identified 279 differentially abundance proteins among the three groups, five clusters were generated using SOTA clustering to examine changes in of the differentially abundant proteins. Results of the current study also found that the proteins in the cluster are involved in some important processes such as regulation of low-density lipoproteins and regulation of TGF-β secretion. Notably, it was found that regulation of TGF-β is essential for porcine embryonic morphological transformation. Furthermore, proteins that play vital roles in implantation, such as CTSC, CTSB, and ACP5 were identified through protein-protein interaction network. Therefore, these findings of the present study provide a basis for understanding embryo development mechanisms and implantation in pigs. SIGNIFICANCE: Proteins are directly acting molecules for the functioning of organisms. It is important to study the regulation mechanism of embryo implantation from the perspective of protein function. In the current study, iTRAQ proteomics technology was employed to identify and explore uterine luminal fluid proteins on day 9 of estrus cycle and days 9, 12, and 15 of pregnancy. The findings provide novel insights into the process of porcine early embryo implantation. Furthermore, it is also helpful to clarify the mechanism of embryonic development and implantation.