Equine oviduct-specific glycoprotein is modulated by hormones and sperm cells.

Equine oviduct-specific glycoprotein (OVGP1) expression varies throughout the estrous cycle and is influenced by hormones, inflammatory factors, and sperm presence, suggesting it plays a key role in oviduct function and sperm-mare interactions.

Background and Importance of OVGP1

• OVGP1 is a glycoprotein specific to the oviduct that is essential for the oviduct’s physiological functions.
• The oviduct is divided into segments: infundibulum, ampulla, and isthmus, each playing different reproductive roles.
• Hormones such as β-estradiol (E) and progesterone (P), and factors like oxytocin (OXT) and tumor necrosis factor-α (TNFα), affect oviduct function mainly through prostaglandin regulation.
• Understanding how these hormones and factors modulate OVGP1 can provide insight into reproduction and potentially improve assisted reproductive technologies in horses.

Objective

• To evaluate the expression of OVGP1 in different segments of the equine oviduct (infundibulum, ampulla, isthmus) during various phases of the estrous cycle.
• To study the in vitro effects of hormones (E, P, OXT, TNFα) and sperm cells on OVGP1 gene transcription and protein secretion by oviduct tissue.

Methods Used

• Gene transcription was measured using real-time PCR to quantify OVGP1 mRNA levels.
• Protein expression was analyzed by western blotting to detect and quantify OVGP1 protein in tissue samples.
• Protein production was measured using enzyme immunoassay (EIA) to quantify secreted OVGP1.
• Experiments were conducted on equine oviduct tissues collected at different estrous cycle phases: follicular, early-luteal, and mid-luteal phases.
• In vitro treatments included hormones (E, P, OXT, TNFα) and exposure of oviduct explants to sperm cells, either in direct contact or separated by a permeable barrier.

Key Findings

• Estrous Cycle-Dependent Expression: OVGP1 mRNA significantly increased in the ampulla during the early-luteal phase, suggesting heightened gene activity at this stage.
• Protein Expression: OVGP1 protein levels were higher during the follicular phase across all oviduct segments, indicating a temporal lag between transcript and protein abundance.
• Hormonal Effects on Transcription:
  • Oxytocin and TNFα increased OVGP1 mRNA in the ampulla during the follicular phase.
  • Estradiol stimulated OVGP1 transcripts in the early-luteal phase.
  • Progesterone increased OVGP1 expression in the mid-luteal phase.
  • The influence of OXT and TNFα may occur indirectly through prostaglandin-mediated pathways.
  • Endogenous estradiol during the follicular phase may “prime” or prepare oviduct tissue to respond to estradiol in the early-luteal phase.
  • Progesterone’s stimulatory effect during the mid-luteal phase could play a role in supporting early embryo development.
• Hormone Effects on OVGP1 Protein Production: In vitro, OVGP1 secretion was not significantly altered by treatment with E, P, OXT, or TNFα, suggesting transcriptional changes may not immediately translate to protein secretion changes.
• Sperm Effects: The presence of sperm cells increased OVGP1 production in the isthmus, both with direct contact and indirect contact (separated by a barrier), indicating that sperm signals or contact stimulates OVGP1 secretion.

Interpretation and Implications

• There is a temporal disconnect between OVGP1 mRNA levels and protein expression, suggesting complex regulation to maintain optimal oviduct function throughout the estrous cycle.
• Hormonal modulation of OVGP1 transcription is phase-dependent and may coordinate preparation of the oviduct environment for fertilization and early embryonic development.
• Oxytocin and TNFα, known inflammatory and signaling molecules, may influence OVGP1 expression through prostaglandin pathways, highlighting the interplay between immune signaling and reproductive function.
• The stimulation of OVGP1 production by sperm cells suggests a dynamic cross-talk between male gametes and the female reproductive tract, which may optimize sperm survival, capacitation, or embryo formation.
• Understanding OVGP1 regulation could improve assisted reproductive technologies by enhancing oviductal environment mimicry and facilitating better sperm-oviduct interactions.