The expression of interferon-stimulated gene 15 in equine endometrium.

This research article investigates the role of a particular protein (ISG15) in horse pregnancy, finding that the levels of this protein do not change significantly between the early stage of pregnancy and a non-pregnant state in horses. The authors suggest that, contrary to predictions from studies in other species, ISG15 modification may not be an active factor in horse pregnancy.

Study Context and Hypothesis

• The study revolves around a biological molecule known as the interferon-stimulated protein 15 kDa (ISG15), which has been found in different species to be increased during pregnancy. It is hypothesized that ISG15 plays a role in making the uterus receptive to embryo implantation and growth (conceptus development).
• This study aims to investigate the expression of ISG15 in the endometrium (uterine lining) of horses, including whether its levels change during pregnancy, and the location and identity of the proteins that are conjugated (bonded) with ISG15.

Methods and Observations

• The researchers examined the levels of ISG15 and related enzymes in the endometrium of horses on Day 14 of the luteal phase (a phase in the menstrual cycle) and at two points during pregnancy (Day 14 and Day 50).
• They found an increased expression of ISG15 at Day 14 of pregnancy compared to Day 14 of the cycle, but no change at Day 50 of pregnancy compared to Day 14 of the cycle.
• The researchers also conducted a Western blot analysis, a technique used to analyze proteins, with an anti-ISG15 antibody. This revealed bands indicating the presence of proteins conjugated with ISG15, but no free ISG15.
• Using immunohistochemistry (a process to locate proteins in cells), the researchers found that ISG15-associated proteins were primarily found in the luminal and glandular epithelial cells of the endometrium, while stromal cells (connective tissue cells) exhibited weaker staining.

Conclusions

• The results suggest that the expression of ISG15-conjugated proteins within the equine endometrium does not differ significantly between the early stage of pregnancy and a non-pregnant state.
• The researchers thus hypothesize that, in contrast to what has been observed in other species, ISG15’s role in horse pregnancy may not involve actively contributing to the interaction between the conceptus and the mother. Instead, the ISG15-conjugated proteins could mainly contribute to normal cellular function within the endometrium.