PS5-16. Single Cell Analysis of Endometrial Remodeling After Pregnancy Loss in Beef Cattle.

Abstract

Pregnancy loss has a large economic impact on the beef industry. Nearly half of the cows that are bred each year experience embryonic mortality during the first trimester of their pregnancy. Successful recovery of the endometrium following pregnancy loss is important for successful subsequent pregnancies which need to be timely in order to remain in the herd. Despite this importance, the cellular and molecular mechanisms involved in the remodeling of the endometrium after spontaneous abortion in cattle remain unclear. Previous studies have relied on a bulk transcriptomics approach to characterize endometrium remodeling, which has limitations in cell-type-specific gene expression resolution. Therefore, the objective of this study was to characterize the cell populations and changes in gene expression following spontaneous pregnancy resorption using single-nuclei RNA-sequencing. Six Angus cows were synchronized using the 7&7 protocol and bred by artificial insemination. Five of six animals were confirmed pregnant by ultrasound at day 35. By day 50, three animals resorbed pregnancy and two remained pregnant. Caruncular endometrial tissue was collected opportunistically from all open (n = 1), pregnant (n = 2), and resorbed (n = 3) Angus cows at day 50 post insemination and immediately snap frozen in liquid nitrogen. Nuclei isolation and single-nuclei RNA-sequencing was performed using the 10X Genomics Chromium platform. Clustering at a resolution of 0.5 and differential expression of genes across clusters was performed using Seurat v5 in RStudio. A total of 14, 19, and 15 clusters were identified in open, pregnant, and resorbed caruncular endometrial samples, respectively. These clusters included epithelial, stroma, mesenchymal, and immune cell types. Differences in immune, stromal, and epithelial cell populations were observed in resorbed samples compared with pregnant and open. These findings suggest that endometrial remodeling following spontaneous abortion involves an influx of immune cells and the rebuilding of stromal and epithelial populations within the endometrium. Furthermore, this study provides a single-cell atlas of bovine endometrial remodeling following spontaneous resorption. By determining cell-type-specific responses, these results advance the previous understanding of the endometrium recovery mechanisms that prepare the uterus for subsequent pregnancies, and provide a foundation for identifying biomarkers to improve reproductive efficiency in beef cattle.