Human chorionic gonadotropin-induced amphiregulin stimulates aromatase expression in human granulosa-lutein cells: a mechanism for estradiol production in the luteal phase.

STUDY QUESTION

Does amphiregulin (AREG), the most abundant and important epidermal growth factor receptor (EGFR) ligand in the follicular fluid, regulate aromatase expression in human granulosa-lutein (hGL) cells?

SUMMARY ANSWER

AREG mediates the hCG-induced up-regulation of aromatase expression and estradiol (E2) production in hGL cells.

WHAT IS KNOWN ALREADY

AREG expression and secretion are rapidly induced by hCG in hGL cells and mediate physiological functions of LH/hCG in the ovary. EGFR protein is expressed in follicles not only in the pre-ovulatory phase but also throughout the luteal phase of the menstrual cycle. After the LH surge, the human corpus luteum secretes high levels of E2, which regulates various luteal cell functions. Aromatase is an enzyme responsible for a key step in the biosynthesis of E2. However, whether AREG regulates aromatase expression and E2 production in hGL cells remains unexplored.

STUDY DESIGN, SIZE, DURATION: This study is an experimental study performed over a 1-year period. In vitro investigations examined the role of AREG in the regulation of aromatase expression and E2 production in primary hGL cells.

PARTICIPANTS/MATERIALS, SETTING, METHODS: Primary hGL cells were obtained from women undergoing IVF treatment in an academic research center. Aromatase mRNA and protein levels were examined after exposure of hGL cells to recombinant human AREG, hCG or LH. The EGFR tyrosine kinase inhibitor AG1478, PI3K inhibitor LY294002 and siRNAs targeting EGFR, LH receptor, StAR and AREG were used to verify the specificity of the effects and to investigate the underlying molecular mechanisms. Reverse transcription quantitative real-time PCR (RT-qPCR) and western blot were used to measure the specific mRNA and protein levels, respectively. Follicular fluid and serum were collected from 65 infertile women during IVF treatment. Pearson's correlation analysis was performed to examine the correlation coefficient between two values.

MAIN RESULTS AND THE ROLE OF CHANCE

Treatment of hGL cells with AREG-stimulated aromatase expression and E2 production. Using pharmacological inhibitors and specific siRNAs, we revealed that AREG-stimulated aromatase expression and E2 production via EGFR-mediated activation of the protein kinase B (AKT) signaling pathway. In addition, inhibition of EGFR activity and AREG knockdown attenuated hCG-induced up-regulation of aromatase expression and E2 production. Importantly, the protein levels of AREG in the follicular fluid were positively correlated with the E2 levels in serum after 2 days of oocyte pick-up and in the follicular fluid of IVF patients.

LARGE-SCALE DATA: N/A.

LIMITATIONS, REASONS FOR CAUTION: The in vitro setting of this study is a limitation that may not reflect the real intra-ovarian microenvironment. Clinical data were obtained from a small sample size.

WIDER IMPLICATIONS OF THE FINDINGS

Our results provide the first evidence that hCG-induced AREG contributes to aromatase expression and E2 production in the luteal phase of the menstrual cycle. A better understanding of the hormonal regulation of female reproductive function may help to develop new strategies for the treatment of clinical infertility.

STUDY FUNDING/COMPETING INTEREST(S): This work was supported by the National Natural Science Foundation of China for Young Scientists (81601253), the specific fund of clinical medical research of Chinese Medical Association (16020160632) and the Foundation from the First Affiliated Hospital of Zhengzhou University for Young Scientists to Lanlan Fang. This work was also supported by an operating grant from the National Natural Science Foundation of China (81820108016) to Ying-Pu Sun. All authors declare no conflict of interest.