Gestation-Stage Related Changes in the IGF System Components in the Equine Placenta

Area of Science:

• Reproductive Biology
• Endocrinology
• Equine Science

Background:

• The insulin-like growth factor (IGF) system is vital for mammalian pregnancy, influencing placental development and angiogenesis.
• Limited information exists on the IGF system's role and its relationship with vascular endothelial growth factor (VEGF) in the equine placenta (chorioallantois; CA) and endometrium (EN) during gestation.

Purpose of the Study:

• To investigate the expression patterns of IGF system components (ligands, receptors, binding proteins) in equine CA and EN throughout gestation.
• To examine the correlation between IGF system expression, particularly IGF1 and IGF2, and VEGF expression in the equine CA.
• To determine the localization and serum concentrations of IGF1 during equine pregnancy.

Main Methods:

• Quantitative analysis of mRNA expression for IGF ligands (IGF1, IGF2), receptors (IGF1R, IGF2R, INSR), and binding proteins (IGFBPs, IGF2BPs) in equine CA and EN at various gestational ages (45 days to 11 months) and postpartum.
• Immunohistochemistry to localize IGF1 within the equine CA.
• Measurement of serum IGF1 concentrations across gestation.

Main Results:

• IGF1 mRNA expression in equine CA peaked at 6 months of gestation and correlated positively with VEGF expression (r = 0.62, p = 0.001).
• IGF2 mRNA was more abundant than IGF1 in equine CA throughout gestation, but its expression was not correlated with VEGF.
• IGFBP2 and IGF2BP2 were highly expressed early in gestation (day 45), while IGFBP3 and IGFBP5 increased postpartum. IGF1 localized to the chorionic epithelium, and serum IGF1 peaked at 9 months gestation.

Conclusions:

• The equine IGF system, especially IGF1, plays a significant role in placental development and angiogenesis.
• A strong positive correlation exists between IGF1 and VEGF expression in the equine chorioallantois during gestation, suggesting IGF1 regulates VEGF-mediated angiogenesis.
• Differential expression of IGF binding proteins suggests stage-specific roles throughout equine pregnancy.