Conditions such as pre-eclampsia and intrauterine growth restriction highlight the importance of normal placental cell turnover for successful pregnancy outcome. In these conditions abnormal levels of proliferation and increased apoptosis have been reported; aberrations in components of the IGF axis have also been observed. IGFs regulate proliferation and survival in other cellular systems but their ability to influence human placental cell function remains to be established.
First trimester placental tissue explants were cultured in serum free (SF) conditions at 20% oxygen for 2 days in the presence of BrdU (100 μM) ± IGF-I (10 nM) or IGF-II (10 nM). Immunohistochemical analysis using BrdU antisera revealed that both IGF-I and IGF-II significantly enhance cytotrophoblast proliferation (from 13.9±4.3% to 43.3±7.5%, P=0.02; 31.5±3.4%, P=0.01 respectively). Similar experiments performed in the presence of signalling inhibitors suggest the MAPK pathway as the key mediator of this response, as the percentage of IGF-I-induced BrdU-positive cytotrophoblasts was reduced in explants cultured with the IGF1R inhibitor PPP (5 μM; from 68.9±6.4% to 26.3±5.2%, P=0.01) or the MAPK inhibitor PD98059 (50 μM; 22.6±3.3%, P=0.02). The PI3K inhibitor LY294002 (200 nM) had no effect.
The ability of IGFs to rescue trophoblast from apoptosis was determined using TUNEL assays. Following explant culture in SF medium for 4 days, the level of apoptosis in villous cytotrophoblast was 37.4±4.0%. Culture with both IGF-I and IGF-II significantly decreased apoptosis (to 10.39±3.0%, P=0.0003; 15.1±4.5%, P=0.006 respectively). PPP or LY294002 inhibited the survival effect of IGF-I (from 20.1±3.6% apoptosis to 44.1±2.0%, P=0.0002 and 48.1±5.8%, P=0.003 respectively). No significant difference in the ability of IGF to rescue cells from apoptosis was observed in the presence of PD98059, demonstrating the survival effect of IGF is mediated by the PI3K pathway.
This study demonstrates the importance of IGF-initiated signalling events in regulating cell turnover in the human placenta.
06 - 07 Nov 2006
Society for Endocrinology