Human chorionic gonadotropin-dependent up-regulation of epiregulin and amphiregulin in equine and bovine follicles during the ovulatory process.

The research article explores the role of two specific molecules, epiregulin (EREG) and amphiregulin (AREG), in the ovulation process of large monoovulatory animal species, specifically horses and cows, with particular focus on how these molecules are regulated by another molecule, human chorionic gonadotropin (hCG).

Primary Objective

The main aim of the research was to gain a better understanding of how EREG and AREG expression operates in the ovarian follicles of monoovulatory animals. Crucially, researchers were keen on investigating how the aforementioned molecules are regulated by hCG leading up to ovulation.

Study Methodology

• Ovarian follicle extracts were prepared from horses collected during estrus between 0 and 39 hours after the application of hCG.
• Analytical techniques like RT-PCR/Southern blot and immunohistochemistry/immunoblot analyses were used to study the levels of EREG and AREG mRNAs and proteins, respectively.
• Samples from the female reproductive organs (corpora lutea) were also collected on the 8th day of the estrous cycle for further investigation.
• In-vitro studies were carried out on bovine granulosa cells to examine the impact of Epidermal Growth Factor Receptor (EGFR) activation on the expression of ovulation-related genes. An EGFR inhibitor PD153035 was used to observe any changes in the induction of ovulation-related transcripts. Moreover, the introduction of EGF, an analogue of EREG and AREG to the granulosa cultures, helped to understand their function further.

Key Findings

The results revealed that:

• The level of EREG and AREG mRNAs were initially quite low in the follicles (at 0 hour), but they saw a significant increase with time, showing maximum levels between 33-39 hours post-hCG application.
• The substantial increase was noted in both the granulosa and theca cells. Furthermore, these two peptides were found in greater concentration in follicles closer to ovulation.
• ADAM17, an enzyme which releases soluble bioactive form of EREG and AREG, was found to be present in high levels and remained constant throughout the period studied.
• The upsurge of both EREG and AREG transcripts in bovine preovulatory follicles post-hCG application was transient and primarily observed at 6h.
• When EGFR activation was suppressed, this resulted in reduced induction of several key ovulation-related transcripts, such as PTGS2, PTGER2, TNFAIP6, PGR, MMP1, VEGFA, and CTSL2 mRNAs.’

Conclusion and Significance

The study highlighted some essential differences in the temporal and cellular location of EREG and AREG expression in equine and bovine preovulatory follicles. The investigators further emphasized the potential role of follicular EGFR activation in the regulation of ovulation-regulated genes in large monoovulatory species.