Elevated Circulating Insulin-Like Growth Factor Binding Protein-1 Is Sufficient to Cause Fetal Growth Restriction

IGF binding protein-1 (IGFBP-1) inhibits the mitogenic actions of the IGFs. Circulating IGFBP-1 is elevated in newborns and experimental animals with fetal growth restriction (FGR). To establish a causal relationship between high circulating IGFBP-1 and FGR, we have generated transgenic mice using the mouse α-fetoprotein gene promoter to target overexpression of human IGFBP-1 (hIGFBP-1) in the fetal liver. These transgenic mice (AFP-BP1) expressed hIGFBP-1 mainly in the fetal hepatocytes, starting at embryonic d 14.5 (E14.5), with lower levels in the gut. The expression peaked at 1 wk postnatally (plasma concentration, 474 ± 34 ng/ml). At birth, AFP-BP1 pups were 18% smaller [weighed 1.34 ± 0.02 g compared with 1.62 ± 0.04 g for wild type (WT); P < 0.05], and they did not demonstrate any postnatal catch-up growth. The placentas of the AFP-BP1 mice were larger than WT from E16.5 onwards (150 ± 12 for AFP-BP1 vs. 100 ± 5 mg for WT at E16.5; P < 0.05). Thus, this model of FGR is associated with a larger placenta, but without postnatal catch-up growth. Overall, these data clearly demonstrate that high concentrations of circulating IGFBP-1 are sufficient to cause FGR.