Low levels of naturally occurring regulatory T lymphocytes in blood of mares with early pregnancy loss.

Early pregnancy loss is a major reason for low reproductive efficiency in the horse. In humans and mice, low numbers of regulatory T cells (Treg cells) are linked to miscarriage. The percentage of Treg cells in oestrous mares at the start of the breeding season was evaluated in relation to the outcome of subsequent pregnancy. For identification and quantification of Treg cells, a highly sensitive and specific qPCR assay targeting the Treg-specific demethylated region in the equine forkhead box transcription factor (FOXP3) gene was established. In a total of 108 mares, pregnancy was followed until detection of early pregnancy loss (n=17), abortion without identification of an infectious or apparent cause (n=9) or birth of a viable foal (n=82). Measured Treg-cell levels did not significantly differ between mares that conceived (82%; 1.50±0.04%) or did not get pregnant (18%; 1.45±0.10%). The Treg-cell percentage at oestrus before breeding was significantly different (P<0.05) between mares that either underwent early pregnancy loss up to Day 40 of pregnancy (1.29±0.07%) and mares that aborted (1.61±0.15%) or gave birth to a live foal (1.52±0.05%). These results suggest that low levels of Treg cells in mares can contribute to pregnancy loss up to Day 40 after ovulation.

Exploration of global gene expression changes during the estrous cycle in equine endometrium.

The equine endometrium exhibits characteristic morphological and functional changes during the estrous cycle controlled by the interplay of progesterone and estradiol. A microarray analysis of endometrial tissue samples derived from five time points of the estrous cycle (Day [D] 0, D3, D8, D12, and D16) was performed to study the dynamics of equine endometrial gene expression. Statistical analysis revealed 4996 genes differentially expressed during the estrous cycle. Clustering of similar expression profiles was performed to find groups of coregulated genes. This revealed eight major profiles: highest mRNA concentrations on D0, from D0 to D3, on D3, from D3 to D8, on D8, from D8 to D12, from D12 to D16, and on D16. Bioinformatics analysis revealed distinct molecular functions and biological processes for the individual expression profiles characterizing the different phases of the estrous cycle (e.g., extracellular matrix and inflammatory response during the estrus phase, cell division and cell cycle during early luteal phase, and endoplasmic reticulum, protein transport, and lipid metabolism in the luteal phase). A comparison to dynamic gene expression changes in bovine endometrium identified common and species-specific gene regulations in cyclic endometrium. Analysis of expression changes during the estrous cycle for genes previously found to be differentially expressed on D12 of pregnancy provided new evidence for possible regulation of these genes. This study provides new insights regarding global changes of equine endometrial gene expression as molecular reflections of physiological changes in the cyclic equine endometrium with regard to the crucial role of this tissue for successful reproduction.