Insulin-like growth factor-binding proteins produced by Vero cells, human oviductal cells and human endometrial cells, and the role of insulin-like growth factor-binding protein-3 in mouse embryo co-culture systems

Co-culturing embryos on helper cells can mimic the in-vivo environment,thereby enhancing embryo development in vitro. Insulin-likegrowth factors (IGF) and their binding proteins (IGFBP) alsoenhance embryo development To investigate the kinds of IGFBPproduced by various cell monolayers and the effects of IGFBP-3on mouse embryo co-culture systems, 2-cell ICR mouse embryoswere cultured in either human tubal fluid medium alone or inthe presence of Vero cells, human oviductal cells or endometrialcells. The helper cells were analysed immunohisto-chemicallyto investigate the types of IGFBP produced by various cell monolayers.The concentrations of IGF-I and IGFBP-3 in media obtained fromthe culture of embryos alone, cells alone or cells plus embryoswere determined by radioimmunoassays. On day 7, more blastocystshatched in the co-culture groups (73% in the Vero cell group,76% in the endometrial cell group and 74% in the oviductal cellgroup) than in the control group (43%) (P < 0.0001). Theresults of immunohistochemistry revealed that (i) all threecell groups produced a lot of IGFBP-1, -2 and -3, but only alittle of IGFBP-4 and -5; and (ii) IGFBP-1, -2 and -3 were presentin blastocysts in either the presence or absence of helper cells.The IGF-I secreted by cell monolayers or embryos was undetectable(detection limit 0.83 ug/1). The IGFBP-3 concentrations in mediaobtained from co-cultured embryos and cells were significantlyhigher than in media without embryos (median values in oviductalcell culture medium, 165 versus 127 µg/1, P = 0.04; medianvalues in endometrial cell culture medium, 277.5 versus 183.5µg/1, P = 0.0002; median values in Vero cell culture medium,219 versus 120 µg/1, P = 0.011). Although IGFBP-3 concentrationin the medium that contained embryos alone was undetectableby radioimmuno-assay (detection limit 1.1 µg/1), immunohistochemistrydemonstrated the presence of IGFBP-3 in the embryos. Co-culturein systems in which there was an increased production of IGFBP-3led to an improved development of mouse embryos. IGFBP can improvethe binding of IGF to cell surface receptors of target tissue,and thus enhance the effect of limited IGF concentrations inpromoting embryo development in a co-culture system. We concludethat Vero cells, human endometrial cells and oviductal cellsproduce IGFBP-1, -2, -3, -4 and -5. IGFBP-3 may play a rolein embryotrophic potential by either regulating the action ofIGF or directly enhancing embryo development