The Matrix Metalloproteinase System and Ovulation: Expression, Regulation and Function in the Human and the Rat.

The matrix metalloproteinases (MMPs) are postulated to facilitate ovulation by remodeling the follicular wall. The MMP family is comprised of 25 different proteinases, many of which share common structural and functional characteristics and, as such, are classified as the collagenases, the gelatinases, the stromelysins and the membrane type MMPs. In the present study, the expression, regulation and function of the MMPs during the periovulatory period was explored in the human and rat ovary. The dominant follicle was collected from women at 4 time points: prior to rhCG injection (preovulatory), early (12 to 18h), late (>18 to 34h), or post ovulatory (>44 to =70h). The follicle was processed for either immunohistochemistry or collection of granulosa cells and the theca layer. For the rodent experiments, intact rat ovaries, granulosa cells, and residual tissue (tissue remaining after granulosa cell collection) were isolated from PMSG-hCG-primed animals at different times after hCG. For the collagenases, there was a species difference in the expression patterns. Interstitial collagenase (MMP1) mRNA was increased in the human while MMP8 (neutrophil collagenase) and MMP13 were unchanged. However, only Mmp13 mRNA was stimulated by hCG in the rat ovary. As the rodent MMP13 is a homolog of the human interstitial collagenase (MMP1), this indicates an increase in collagenase in both species. The stromelysins (MMP3, 10, 11) are a class of proteinases within the MMP family that were originally named based upon their stromal-derived origin and capacity to degrade structural proteins of the extracellular matrix. Comparison of the stromelysins revealed that MMP10 mRNA was highly induced in human granulosa cells and the theca layer as well as intact rat ovaries, granulosa cells, and residual tissue. Localization of MMP10 to granulosa and theca cells in both human and rat ovarian follicles was confirmed by immunohistochemistry. MMP3 mRNA was unchanged in the human cells. MMP11 mRNA decreased following hCG treatment in human granulosa and theca cells as well as rat granulosa cells. The membrane type-MMPs (MT-MMPs) are a subgroup of six metalloproteinases with an additional transmembrane domain that anchors these proteases to the cell membrane. Expression of mRNA for MMP14 (MT1-MMP) and MMP16 (MT3-MMP) were increased in both the human and rat ovary after hCG. Functional studies blocking MMP14 activation or activity in vitro resulted in a decrease in the activation of the gelatinase MMP2, as well as a decrease in ovulation rate. These findings indicate that one of the roles of MMP14 is to activate other proteinases. Blocking gelatinase activity in granulosa cells revealed that this subgroup of MMPs was able to not only act on the extracellular matrix but also to shed proteins from the cell surface as well as cleave granulosa cell derived proteins. The present findings demonstrate that hCG induces specific members of the MMP family prior to ovulation. There are commonalities in the MMP expression patterns between the human and the rodent suggesting the importance of this family in the periovulatory events associated with breakdown of the follicle and extrusion of the oocyte. This paramount role is supported by findings that MMP inhibitors block oocyte release. Furthermore, the present findings demonstrate that the MMPs act outside of their classical action on the extracellular matrix as sheddases. Supported by NIH P20 RR15592, NIH HD057446.