Tissue remodelling in the ovary by plasminogen activators and matrix metalloproteinases: Regulation and functional role revealed by gene deficient mice

Abstract

Proteolysis mediated by the plasminogen activator (PA) system and the metalloproteinase (MMP) system has been associated with various physiological processes in many organs including the ovary. Many studies suggest that these protease systems may play a role in several ovarian processes including degradation of the follicle wall during ovulation as well as formation and regression of corpus luteum (CL) after ovulation. To study the functional role of ovarian proteases in vivo, we have used gene deficient mice lacking tPA, uPA, PAI-1 or plasminogen. The ovulation efficiency in 25 day old mice during gonadotropin-induced ovulation, was found to be normal in mice with a single deficiency of tPA, uPAandPAI-1 but reduced by 17% and 26% in mice lacking plasminogen and PAs, respectively. In a physiological ovulation model, normally cycling adult plasminogen deficient mice was found to have a normal ovulation efficiency, suggesting that a compensatory mechanism may operate during physiological ovulation. Together our results suggest that plasmin may play a functional role in the ovulatory process, although this role may be less significant than earlier postulated. In a search for alternative ovarian proteases involved in the ovulatory process, we have studied the regulation of MMPs in the ovary. MMP-2 (gelatinase A) was found to be the main MMP expressed in the ovary, but there was no up-regulation at the time of ovulation. However, a 100 kDa MMP (most likely MMP-9) was also found. Interestingly, this MMP was up-regulated in plasminogen deficient mice. To study the functional role of MMPs and the possible co-operation between MMPs and PAs in the ovulatory process, we have treated wild-type and plasminogen deficient mice with the hydroxamate MMP inhibitor GM6001. Our data show that suppression of MMP activity in wild-type mice and plasminogen deficiency causes a similar (18%-19%) reduction of ovulation efficiency. Suppression of MMP activity in plasminogen deficient mice caused only an additive reduction of ovulation efficiency, suggesting that both enzyme systems play a role in this process and that they operate in an additive rather than synergistic manner. Using a pseudopregnant mouse model, we have also studied the expression of some members of the PA system and the MMP system during different luteal developmental stages. Northern blot and in situ hybridization revealed that tPA, uPA, PAI-I, tissue inhibitor of MMP 1 (TIMP-1), as well as the tumor-related stromelysin-3 and membrane type MMP (MT1-MMP) were temporally expressed to take part in corpus luteum formation and regression. Similar to the apoptotic correlated expression in CL, stromelysin -3 was also expressed in follicles destined to the degenerative process called atresia also mediated by apoptotic cell death.