New insights in equine steroidogenesis: an in-depth look at steroid signaling in the placenta.

This study delves into the process of steroid production and signaling in the placenta of equine species during pregnancy. It proposes hypotheses and gives direction to future research in equine endocrine study.

Research Methodology

• The researchers sequenced the chorioallantois, part of the placenta crucial for nutrient and gas exchange, and the endometrium, the lining of the uterus, throughout various stages of gestation. They examined the transcripts related to the synthesis, conjugation, transportation, and signaling of steroids.
• These tissues were analyzed at different stages of pregnancy: 45 days, 4 months, 6 months, 10 months and 11 months. Post-partum samples were also taken for the chorioallantois. For the endometrium, the non-pregnant (diestrus) stage was also examined.

Key Findings

• Different isoforms of the enzyme HSD17B, which is involved in the synthesis of steroids, were expressed among tissues. HSD17B1 was found to be highly present in the chorioallantois while HSD17B2 was dominant in the endometrium. These enzymes play critical roles in hormone balance and metabolic processes.
• A new isoform akin to SULT1A1, an enzyme responsible for the detoxification and metabolism of hormones, was the chief sulfotransferase transcript in the chorioallantois. This discovery could be pivotal in understanding the metabolic process of steroids in horses at different stages of pregnancy.
• Nuclear estrogen (ESR1, ESR2) and progesterone (PGR) receptors were insignificantly present or even non-existent in the chorioallantois and the endometrium during pregnancy. These findings suggest that the usual pathway of steroid hormone action may not be prominent during gestation in horses.

Implications and Hypotheses

• From the data gathered, the study also put forth some hypotheses. One proposition is that the 45-day old chorioallantois may be capable of synthesizing steroids de novo, meaning from the beginning, using acetate as a base molecule. This suggests that steroidogenesis, the biological process by which steroids are produced from cholesterol, might start from scratch in the early stages of gestation in horses.
• Another hypothesis put forward is that horses could be using a process called glucuronidation to dispel estrogens from the endometrium during estrous, the recurring period of sexual receptivity and fertility, but not during pregnancy. This indicates that hormonal balance is likely maintained differently in pregnant and non-pregnant states in equines.

Conclusion

• The study provides a comprehensive exploration of equine steroid-related transcripts through various stages of gestation, which may direct future research and breakthroughs in the field of equine endocrinology.