THE EXPRESSION AND FUNCTION OF CYSTATIN-C AND CATHEPSIN-B AND CATHEPSIN-L DURING MOUSE EMBRYO IMPLANTATION AND PLACENTATION

The implantation of the mouse embryo requires the controlled invasion of the uterine stroma by the embryonic trophoblast. This event is depe ndent, in part, on the secretion of matrix metalloproteinases and seri ne proteinases for the extracellular degradation of the uterine matrix , Proteinase activity is controlled by stromal decidualization and spe cific proteinase inhibitors, This work adds to our understanding of im plantation and placentation by reporting the expression and function o f another class of proteinases/inhibitors closely related to invasive cell behavior. We focused on the cysteine proteinases, cathepsins B an d L, and their inhibitor cystatin C, Northern blots showed that tropho blast expressed cathepsin B throughout the invasive period (days 5.5-1 0.5), Both cathepsin B message and cathepsin L protein were localized to the mature, invasive trophoblast giant cells, Substrate gel electro phoresis showed an increase in giant cell cathepsin activity with enzy me profiles changing at the end of the invasive period, Northern and w estern blotting showed that cystatin C, the main inhibitor of cathepsi ns, was a major product of the decidualizing stroma, Message levels fi rst increased in peripheral decidualizing cells, with the protein loca lizing close to the embryo during implantation (days 5.5-8.5). With th e regression of the decidua beginning on day 9.5, a coordinated upregu lation of both cathepsin B and cystatin C was observed implying a role for controlled cathepsin expression during apoptosis. E-64, a synthet ic inhibitor of cathepsins B and L, was injected into pregnant females at the stage of blastocyst attachment (days 4.5-5.5), High doses resu lted in the complete failure of implantation while lower doses resulte d in stunted embryos and a reduced decidual reaction. These results su ggested that cathepsins B and L are necessary for normal embryo develo pment and uterine decidualization, and that decidua contributes to the ir control by a coordinated expression of cystatin C within the implan tation site.