The human embryo produces basement membrane collagen (type IV collagen)-degrading protease activity

The biochemical basis and mechanism of embryo implantation is poorly understood. The human embryo has to penetrate the endometrial basement membrane and the thick decidual wall during implantation, a process which resembles the active spreading of invasive tumour cells where the degradation of type IV collagen (basement membrane collagen) plays an important role. This study reports that human embryos produce type IV collagen-degrading enzyme activity and the secretion of this enzyme increases with time in culture. The type IV collagen-degrading enzyme activity might facilitate the penetration of the embryo through the decidua, thus emphasizing an active role of the embryo in implantation. On the other hand, unfertilized oocytes secrete low, stable amounts of type IV collagen-degrading enzyme activity in vitro. It was also found that follicular granulosa cells secrete high amounts of type IV collagenolytic activity in culture. It has been previously shown that there is a pre-ovulatory peak in type IV collagenolytic activity in follicular fluid, and it can be assumed that the appearance of this enzyme in the follicular fluid is probably connected to follicular rupture and that it is produced by granulosa cells.