Quantitative bioassays for measuring biologically functional gonadotropins based on eel gonadotropic receptors

Area of Science:

• Aquaculture
• Reproductive Biology
• Biotechnology

Background:

• Eel stocks are declining globally, necessitating artificial reproduction for aquaculture.
• Current methods for inducing eel maturation rely on hormone injections (hCG, pituitary extract).
• Accurate measurement of gonadotropic hormones is essential for optimizing artificial reproduction protocols.

Purpose of the Study:

• To develop and validate bioassays for quantifying biologically active luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in eels.
• To establish a method for monitoring hormone levels in eel plasma for improved reproduction strategies.

Main Methods:

• Created stable HEK293 cell lines expressing Japanese eel LH receptor (ajLHR) and European eel FSH receptor (aaFSHR).
• Utilized a firefly luciferase reporter gene (CRE-Luc) responsive to cAMP signaling.
• Adapted a protocol to inactivate plasma toxins by heating (37°C for 24h) before bioassay analysis.

Main Results:

• The ajLHR-expressing cells showed a linear response to human chorionic gonadotropin (hCG) over a >100,000-fold concentration range.
• The aaFSHR-expressing cells responded linearly to salmon pituitary extract over a 1000-fold concentration range.
• Bioassays were validated using various hormone sources (hCG, human FSH, salmon, carp, and eel pituitary extracts), and plasma toxin inactivation was successful.

Conclusions:

• Developed novel, sensitive bioassays for eel LH and FSH using engineered HEK293 cells.
• The developed assays, after plasma toxin inactivation, enable effective monitoring of gonadotropic hormone levels in eels.
• These bioassays are valuable tools for advancing eel artificial reproduction and aquaculture.