Human chorionic gonadotropin-dependent regulation of 17beta-hydroxysteroid dehydrogenase type 4 in preovulatory follicles and its potential role in follicular luteinization.

The research provides evidence that the expression of the enzyme 17Beta-hydroxysteroid dehydrogenase type 4 (17betaHSD4) is regulated in preovulatory follicles during ovulation caused by human chorionic gonadotropin (hCG). This enhanced expression could potentially play a role in reducing circulating levels of the hormone 17beta-estradiol after the LH (luteinizing hormone) surge in follicular luteinization.

Study Objective and Methodology

• The main aim of this investigation was to understand how 17betaHSD4 is regulated during hCG-induced ovulation or luteinization. Luteinization is a process that transforms the follicles in the ovary into a structure called the corpus luteum.
• To conduct this study, the researchers cloned the cDNA of equine 17betaHSD4, a protein that contains 735 amino acids and demonstrates high levels of similarity (81-87%) to other mammalian orthologs.

Findings

• Upon using RT-PCR and Southern blot analyses, the research showed that mRNA expression of 17betaHSD4 was present before the hCG treatment. However, there was a significant increase in follicles extracted 24 hours post hCG treatment.
• The researchers were also able to isolate granulosa and theca interna cells and found out that mRNA was present in both layers, but it was primarily expressed in the granulosa cells.
• A polyclonal antibody was also produced against a fragment of the equine protein to study the regulation of the 17betaHSD4 protein. Immunoblots, as well as immunohistochemical data, confirmed an increase in the full-length 17betaHSD4 protein post 24 hours of hCG treatment, supporting the mRNA findings.

Conclusion

• From this research, it could be inferred that the hCG-induced initiation of follicular luteinization is accompanied by a significant increase in the expression of 17betaHSD4.
• Given that 17betaHSD4 deactivates the hormone 17beta-estradiol, the enhanced presence of this enzyme in luteinizing preovulatory follicles could potentially offer an additional mechanism for reducing the circulating levels of 17beta-estradiol post the LH surge, contributing further to the process of luteinization.