Role of β₁ integrins in human endometrium and decidua during implantation

The present study was undertaken to investigate the expression and function of β₁ integrins in human endometrium and decidua. Fluorescence-activated flow cytometry demonstrated the greater expression of the β₁, α₁, α₂, and as subunits of the β₁ integrin family in cultured stromal cells from the midsecretory phase than in those of the early proliferative phase. The addition of estradiol (E₂) and progesterone (P) to cultured stromal cells in the early proliferative phase increased the expression of β₁ integrins in vitro. The immunohistochemical distribution of β₁ integrins demonstrated predominantly glandular epithelial staining in the proliferative phase, and stromal and glandular staining in the midsecretory phase. flow cytometry also demonstrated the expression of β₁, α₁, α₂, α₃, α₅, and α₆ subunits of β₁ integrin family in cultured decidual cells. Immunohistochemistry confirmed the β₁ integrin cell surface phenotypes in cultured decidual cells observed by flow cytometry. In the subsequent experiment, the effects of antibodies against specific β₁ integrin heterodimers on mouse embryo attachment and spreading were tested to identify the role of β₁ integrins in early implantation. We developed assays for the attachment of mouse embryos and for trophoblastic spreading on cultured human decidual cells. The addition of antibodies directed against β₁ and α integrin subunits to cultured decidual cells did not affect the rates of hatching or attachment of the blastocysts, whereas the outgrowth of embryos on the decidual cells was inhibited by their antibodies in a dose-dependent manner. Thus, β₁ integrin in human endometrium and decidua may be important in mediating the organization of extracellular matrix proteins derived from embryos during the early stage of implantation.