The influences of cycle stage and pregnancy upon cell glycosylation in the endometrium of the mare.

This study investigates how the stages of a horse’s reproductive cycle and pregnancy alter the sugar coating of cells in the endometrium. The research indicates that the glycosylation process, or the adding of sugars to proteins in cells, changes significantly during pregnancy.

Research Approach and Methods

The researchers used a method known as lectin histochemistry to examine the distribution and glycan (sugar) composition of uterine glycoproteins, which are proteins with added sugars meant for secretion by the cell. They wanted to determine how the presence of an embryo in the uterus impacts this glycosylation process in the endometrium, the mucous membrane lining the uterus.

Endometrial biopsies were carried out on mares at different stages: in heat, at Days 5, 8, 12 and 15 after ovulation (during diestrus cycle), and at Days 12 and 15 of pregnancy.

Findings and Conclusions

• During heat (estrus), the lumenal epithelial cells (cells lining the uterus) were found to be mostly non-ciliated (without hair-like projections) and contained glycosylated granules in the cytoplasm.
• Five days post-ovulation, these cells grew taller and had more highly glycosylated apical granules.
• By Days 12 and 15 after ovulation, these cells became more cube-like and some displayed fewer secretory granules.
• The cells showed stark differences by Days 12 and 15 of pregnancy. The ciliated cell were swollen, with numerous granules, while their non-ciliated counterparts had only a few in the apical cytoplasm.
• Glycosylation changed dramatically during pregnancy in the luminal (inner surface) and superficial gland epithelium. There were fewer fucosylated termini (a particular type of sugar structure), more N-acetyl galactosamine residues, coupled with a general decrease in sialic acid and several other sugar structures.
• Glycosylation in ciliated cells on Days 12 and 15 of pregnancy showed a close resemblance to that of the embryonic capsule.

The study concludes that the production of glycoproteins, proteins coated with sugar molecules, by lumenal epithelial cells, is likely influenced by the presence of a fetus. The researchers speculate that in addition to providing nourishment to the growing embryo, these secretory glycoproteins may contribute components to the capsule that only partly forms in embryos grown in vitro.