50 Equine uterine fluid proteome on the fifth day after ovulation

Abstract

The characterisation of the uterine proteome before the entry of the embryo to the uterus is essential to know the factors involved in the physiological events of gestation. The objective of the study was to compare, by a proteomics approach, the uterine lumen of cyclic and inseminated mares on Day 5 after ovulation. Samples of endometrial secretion were collected over 2 cycles during Day 5 post-ovulation. The first cycle constituted the cyclic group (n=10), and in the following cycle, the same mares were inseminated and considered as the inseminated group (n=8). All samples were subjected to polyacrylamide gel electrophoresis with sodium sulfate in gels of 12.5%. A total of 107 spots were visualised by 2-dimensional polyacrylamide gel electrophoresis with sodium sulfate. Eight selected spots were extracted, digested by trypsin, and analysed by mass spectrometry for protein identification. Selected spots were considered representative of the differentially expressed proteins when it was shown that the intensity of the spots between the groups in the study was significantly different and considering that the protein was present in at least 50% of the gels (P<0.05). Student’s t-test was used to compare the relative percentage of expression of the spots. Four different proteins were identified by MASCOT (http://www.matrixscience.com/) and validated by the application SCAFFOLD, version 3.6.4 (http://www.proteomesoftware.com/products/scaffold/). In this study, ceruloplasmin was the main protein identified in the equine endometrium on Day 5 after ovulation. The results demonstrated statistically significant changes in ceruloplasmin expression for the inseminated group in comparison with the cyclic group (P=0.036). Our findings suggest that the increase of ceruloplasmin expression in the uterine fluid represents preparation of the endometrial for implantation and development of a potential equine embryo. The comparison of the proteic expression from the endometrium of cyclic and inseminated mares before the embryo moves into the uterus enhances understanding of the processes associated with conceptus-endometrium interaction during the maternal recognition period in the mare.