Cyclic-glycine-proline accelerates mammary involution by promoting apoptosis and inhibiting IGF-1 function

Area of Science:

• Reproductive Biology
• Cellular Biology
• Endocrinology

Background:

• Post-lactational mammary involution involves epithelial cell apoptosis, linked to decreased insulin-like growth factor-1 (IGF-1) expression.
• Cyclic-glycine-proline (cGP), an IGF-1 metabolite, modulates IGF-1 function and bioavailability in disease states.

Purpose of the Study:

• To investigate the impact of cGP on the physiological decline of IGF-1 function during post-lactational mammary involution in rats.
• To determine if cGP influences mammary cell apoptosis and tissue remodeling during involution.

Main Methods:

• Rat dams were administered cGP (3 mg/kg) or saline daily from postnatal day 8-22.
• Mammary glands were assessed at different involution stages: early (natural), mid (24-hr engorgement), and late (72-hr engorgement).
• Apoptosis, cell survival factors (Bcl-xl, IGF-1R), and IGF-1R phosphorylation were analyzed.

Main Results:

• cGP accelerated mammary cell loss via apoptosis and earlier clearance of secretory alveoli during early involution.
• Early upregulation of Bcl-xl and IGF-1R was observed in cGP-treated glands.
• cGP reduced IGF-1 bioactivity in late involution, indicated by decreased IGF-1R phosphorylation.
• Maternal cGP administration did not affect milk production or composition.

Conclusions:

• cGP accelerates post-lactational mammary involution by promoting apoptosis.
• The study demonstrates cGP's role in enhancing the physiological decline of IGF-1 function during involution.
• cGP impacts mammary gland remodeling and cell survival pathways during the post-lactational period.