Matrix metalloproteinase-9 and tissue inhibitor of metalloproteinase-3 arekey regulators of extracellular matrix degradation by mouse embryos

Embryo implantation in humans and rodents is a highly invasive yet tightly controlled process involving extracellular matrix (ECM) degradation, Matrix metalloproteinase 9 (MMP-9) has been implicated as the major facilitator o f this ECM degradation. MMP-9 is expressed by the embryo's trophoblast cell s, whereas tissue inhibitor of metalloproteinases 3 (TIMP-3) is expressed b y the maternal uterine cells immediately adjacent to the trophoblast. We ex amined the functional roles of MMP-9 and TIMP-3 during in vitro ECM degrada tion by mouse embryos. Blastocysts were treated with either MMP-9 antisense or sense oligonucleotides and incubated on an ECM gel. The extent of ECM d egradation exhibited by the blastocysts due to proteinase secretion was qua ntified. Embryos exposed to MMP-9 antisense oligonucleotides exhibited redu ced ECM-degrading activity as compared with controls, and this reduced acti vity was correlated with the level of MMP-9 secreted by the embryos. The fu nctional role of TIMP-3 was then examined by incubating blastocysts on an E CM gel that had been impregnated with various amounts of TIMP-3. In a dose- dependent manner, increases in TIMP-3 resulted in a reduction in ECM degrad ation and were correlated with diminished MMP-9 activity. These results pro vide important functional evidence that in vitro ECM degradation is regulat ed by embryo-derived MMP-9 and ECM-derived TIMP-3.