Objectives: The IGF system is central to fetal growth. Recently, the relationships between cytokines and the IGF system have been shown in specific tissues. It is unknown whether these occur in the placenta. The aim of this study was to assess whether interleukin-6 (IL-6) modulated the IGF system.
Methods: Whole villous tissue and cord serum were collected from fetal growth restriction (FGR) neonates diagnosed before birth with altered Doppler velocimetry and controls. Sixteen FGR and 20 controls, born after week 32 of gestation from elective Caesarean sections, were compared. Total RNA was extracted from the placenta samples, reverse transcribed, and real-time quantitative reverse transcriptase (RT)-PCR was performed to quantify cDNA for IGF-I, IGF-II, IGF binding protein (IGFBP)-1, IGFBP-2, and IL-6. The same proteins were assayed in placenta lysates and cord serum using specific commercial kits and western immunoblotting.
Results: FGR subjects had significantly more IGFBPs-1 and -2, and IL-6 mRNA and corresponding proteins in the placenta. In particular, the less phosphorylated isoforms of IGFBP-1 were highly increased. IL-6 and IGFBPs-2 mRNA, and IL-6 and IGFBP-1 peptides were positively and significantly correlated in the placenta. The IGF-II peptide was also significantly increased in FGR placentas. In cord serum, IGFBPs-1 and -2 were significantly more elevated in the FGR neonates. Serum IL-6 was significantly and positively correlated with both IGFBP-1 and IGFBP-2.
Conclusions: The placenta of FGR neonates has higher IGF-II, IGFBP-1, IGFBP-2, and IL-6 contents compared with controls. At birth, IGFBPs-1 and -2 are increased in the cord blood of FGR neonates. IL-6 and IGFBP-2 gene expressions are closely related in the placenta. We suggest that the increase in IL-6 and IGFBP-2 could be subsequent to hypoxia and nutrient deficiency. As IGFBP-2 has a strong affinity for IGF-II, which is crucial for fetal growth, it could be an important bioregulator of IGF-II in the placenta.