Hypoxia inhibits invasion of extravillous trophoblast cells through reduction of matrix metalloproteinase (MMP)-2 activation in the early first trimester of human pregnancy

During early pregnancy, extravillous trophoblast (EVT) cells are exposed to very low pO(2) values. In this study, we investigated the proteolytic functions and invasiveness of human primary EVT cells under hypoxic conditions to show the early placental pathophysiology. Placental samples (from 5 to 10 weeks gestation) were obtained at termination of pregnancy. Cytotrophoblast cells were separated by Percoll(®) gradient method and cultured on Matrigel(®) to obtain an invasive phenotype (similar to EVT). The invasion capacity (Matrigel-coated invasion assay), migration of the cells (wound healing assay), activity and expression of matrix metalloproteinase (MMP)-2 and tissue inhibitor for MMP (TIMP)-2 (gelatin gel zymography, ELISA, and quantitative RT-PCR), and expression of membrane-type (MT)1-MMP (western blot) were investigated. All cultures (except for quantitative RT-PCR) were performed under 20% oxygen, 5% oxygen, and 5% oxygen with 3 repetitions of 0.1% oxygen hypoxic stimulation for 1 h. Invasion and MMP2 activity of the cells were significantly increased in 20% and decreased in 0.1% oxygen. There was no significant difference in cell migration among the oxygen environments. Concentrations of MMP2 in the supernatant and expression of MT1-MMP were increased in both the 0.1% and 20% oxygen environments. The MMP2 mRNA level was increased after 1-h stimulation with 0.1% oxygen. The TIMP2 concentration was increased only in 20% oxygen, but the mRNA level was decreased in 0.1% oxygen. These results suggested that hypoxia might inhibit the invasive capacity and MMP2 activation of EVT cells in the early first trimester of pregnancy. Decrease in TIMP2 production may reduce the MMP2/TIMP2/MT1-MMP complex and lead to this unique behavior of EVT cells under hypoxic conditions.