Excessive expression and activity of cathepsin B in sheep cumulus cells compromises oocyte developmental competence

In vitro developmental competence of sheep oocytes is still relatively low. In this study, we investigated cathepsin B activity in sheep cumulus-oocyte complexes, the expression of cathepsin B and apoptosis rates in sheep cumulus cells, and the correlations between these indicies and in vitro developmental competence of sheep oocytes. The present result suggested that the active form of cathepsin B in cumulus-oocyte complexes was predominantly present in cumulus cells rather than oocytes. Cathepsin B activity in cumulus-oocyte complexes was strongly inhibited by cathepsin inhibitor E-64. RT-PCR analysis showed that cathepsin B expression in cumulus cells decreased during in vitro maturation. TUNEL staining and flow cytometry of cumulus cells showed that the apoptosis rate increased after in vitro maturation, and treatment with E-64 reduced both cathepsin B expression and apoptosis levels. Furthermore, E-64 treatment increased blastocyst rates of sheep.