Production of insulin-like growth factor binding proteins (IGFBPs) by human endometrial stromal cell is stimulated by the presence of embryos.

Abstract

To identify IGFBPs among endometrial secretory products and study their role in implantation and early embryo development. Two-cell CB6F1 mouse embryos were cultured alone or with human endometrial stromal cells in RPMI 1640 plus 10% fetal calf serum (FCS) with or without addition of IGF-I (20 micrograms/ml), IGF receptor antibody (0.1 microgram/ml), progesterone (P) (20 ng/ml) and relaxin (R) (20 micrograms/ml). On the designated day, the medium was changed to protein-free RPMI and incubated for 16 h. Both conditioned medium and conditioned protein-free medium were then collected for protein analysis and immunoradiometric assay. Cells were fixed with 4% paraformaldehyde for immunohistochemical staining. IGFBP1 (31 kDa), IGFBP2 (36 kDa), IGFBP3 (45 kDa and 50 kDa) and an unknown IGFBP (25 kDa) were identified in conditioned medium of human endometrial stromal cells cultured alone or cocultured with mouse embryos. Secretion of IGFBPs by endometrial stromal cells was stimulated in the presence of mouse embryos as well as by P and R. IGFBP3 appears to be more responsive to embryonic signals. On the other hand, the secretion of IGFBP1 was greatly stimulated by P and R. Immunolocalization revealed that all three BPs were present in both embryonic and endometrial cells and their immunological staining was heavily increased by P and R. Endometrial stromal cells were able to synthesize and secrete IGFBPs to modify IGF action on embryo development. Secretion of IGFBPs was stimulated by embryonic signals and was hormonally dependent. The fact that IGFBP3 was more responsive to embryonic signals suggests that it may be important in early implantation. On the other hand, IGFBP1 production was highly responsive to both P and R, suggesting that it may be important throughout pregnancy. In addition, the fact that IGFBPs were located in endometrial and embryonic cells may suggest that these secretory products have autocrine and/or paracrine effects on both types of cells.