Hormonal regulation of oviductal glycoprotein 1 (OVGP1; MUC9) in the macaque cervix: a novel indicator of progestogen action

Abstract

Progestogen-only contraception is reported to act by suppressing ovulation and/or altering cervical mucus secretion. Unfortunately, the effect of contraceptives on mucus quality is difficult to assess accurately by traditional Insler score or post-coital tests, and the lack of a molecular test for mucus quality has created a roadblock to the development of new contraceptives that target the cervix. Oviductal glycoprotein 1 (OVGP1; MUC9) is a hormonally regulated, carbohydrate-rich glycoprotein secreted by oviductal epithelial cells [1]. In addition to the oviduct, the OVGP1 expression has been reported for the cervix of rabbits, [2] mice and women, but hormonal regulation of OVGP1 in the cervix is poorly understood. The objective of this study was to characterize hormonal regulation and localization of OVGP1 in the macaque cervix as a novel marker of progestogen action. Real-time PCR and immunohistochemical analysis of the macaque cervix. Adult ovariectomized rhesus macaques (Macaca mulatta) were treated sequentially with estradiol (E2) and then E2 plus progesterone (P) to create artificial menstrual cycles. Reproductive tracts were collected in the artificial proliferative phase (E2 alone; n=13) and in the artificial secretory phase after 1, 3, 7, and 14 days of P (n=4, 5, 5, and 10, respectively). Total RNA was isolated from cervical samples and analyzed for expression of OVGP1 by TaqMan® real-time PCR and presented relative to expression of ribosomal (S10) RNA. Representative samples were analyzed by immunohistochemistry on cryosections with polyclonal antibodies specific to OVGP1. Representative sections were also stained for estrogen receptor 1 (ESR1) and progesterone receptor (PGR) as independent assays for E2 and (P) action. OVGP1 transcript was upregulated in the proliferative phase, maximal in the late proliferative phase, and maintained through day 1 of the secretory phase. There was a significant decrease (P<0.01) in OVGP1 expression between secretory phase day 1 and day 3 and a further significant (P<0.05) decrease by secretory phase day 7 and 14. IHC revealed specific OVGP1 staining in columnar cells of the mid cervix. Staining was strongest in the apical portion of the epithelial cells consistent with secretion into the cervix mucus. As expected, ESR-1 and PGR was present in the cervix throughout the cycle. ESR1 and PGR staining was stronger in the cervix epithelium during the proliferative phase of the cycle. These results indicate that OVGP1 is expressed in the primate cervix as well as the primate oviduct, and strongly upregulated by estrogen in the proliferative phase and down-regulated by P during the secretory phase. The cervical epithelium would be easily accessible by biopsy or cervical brush, and OVGP1 could be assayed either by ELISA or by real-time PCR to provide a rapid and very sensitive method for identifying the effect of progestogen-based contraceptives on the cervix in clinical trials.