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In the ovary, extensive tissue remodeling is required during both follicular development and the break down of the follicular wall at the time of ovulation. Extracellular proteases such as serine proteases and matrix metalloproteinases (MMPs) are thought to play pivotal roles in these processes. In this paper, we have used in situ hybridization to study the regulation and distribution of mRNA coding for MMP-2 (gelatinase A) and its cell surface activator membrane-type MMP1 (MT1-MMP) during gonadotropin induced ovulation in the rat. In ovaries of untreated immature (23 day old) rats, the levels of MT1-MMP and MMP-2 mRNA were low. MMP-2 mRNA was found in theca-interstitial cells while MT1-MMP mRNA was found in both granulosa and theca-interstitial cells and both messages were induced after stimulation with PMSG. After an ovulatory dose of hCG, the expression of MT1-MMP was dramatically down regulated in the granulosa cell layers of large preovulatory follicles but the expression remained and appeared to be up regulated together with MMP-2 in the theca-interstitial cells surrounding the large preovulatory follicles. The expression kinetics and tissue distribution supports the notion that MT1-MMP may have dual functions in the ovary. Initially MT1-MMP may act as a matrix degrading protease inside the follicle during follicular development and later, just prior to ovulation, as an activator of proMMP-2 in theca-interstitial cells surrounding preovulatory follicles.
Liu et al. (Sun,) studied this question.