Extracellular matrix interactions in early human embryos: implications for normal implantation events

Abstract

To study the role of the extracellular matrix (ECM) proteins in supporting the development and implantation competence of human embryos. Expression of an implantation site adhesive glycoprotein, oncofetal fibronectin, and basement membrane collagen-degrading matrix metalloproteinase-2 and -9 were studied in cultured human embryos. The ability of exogenously added laminin and fibronectin to enhance hatching and matrix metalloproteinase-2 expression was quantitated also. Fifty-four women with tubal factor infertility enrolled in the IVF program at the University Hospital of Oulu agreed to participate by providing 20 residual oocytes and 227 residual early embryos for this study. The presence of oncofetal fibronectin immunoreactive protein was assayed by immunocytochemical staining with two specific monoclonal antibodies, FDC-6 and X18A4. These antibodies bind to specific and distinct epitopes within tumor and trophoblast-derived oncofetal fibronectin. Changes in embryo matrix metalloproteinase-2 production were measured by zymography and confirmed by immunocytochemical staining. Intracellular oncofetal fibronectin was identified within blastomeres of early stage embryos. The immunoreactivity of oncofetal fibronectin in the zona pellucida was associated with fragmentation and dissolution of the zona. Exogenously added laminin or adult-type fibronectin significantly increased the hatching rate of the cultured embryos. Embryos cultured with added adult-type fibronectin or trophoblast-derived oncofetal fibronectin stimulated the matrix metalloproteinase-2 production (72-kd type IV collagenase) by 2.25 +/- 0.16-fold when compared with control embryos (mean +/- SD). Embryonic production of specific ECM proteins, such as oncofetal fibronectin, appears to be important for the morphological and biochemical development of human preimplantation embryos. Moreover, ECM proteins promote acquisition of the adhesive and degradative properties required by human embryos for successful implantation.