Spatiotemporal Messenger Ribonucleic Acid Expression of Ovarian Tissue Inhibitors of Metalloproteinases throughout the Rat Estrous Cycle1

The tissue inhibitors of metalloproteinases (TIMPs) within the ovary closely regulate the matrix metalloproteinases, enzymes capable of degrading components of the extracellular matrix. The purpose of this study was to examine the spatial and temporal messenger RNA (mRNA) expression of the TIMPs in the ovaries of normally cycling rats. Ovaries were collected at 1100 h on each day of the 4-day estrous cycle, and TIMP mRNA expression was examined by Northern blot, RT-PCR, or in situ hybridization. TIMP-1 mRNA levels were significantly higher on estrus than on any other day. Although the 1.0-kb TIMP-2 transcript did not change across the cycle, the 3.5-kb transcript decreased significantly between metestrus and diestrus. Expression of TIMP-3 mRNA decreased significantly between proestrus and estrus. TIMP-1, TIMP-2, and TIMP-3 mRNAs were primarily localized to the theca, stroma, and corpora lutea (CL) on all days of the cycle, but with distinct cyclic changes. Thecal expression of TIMP-1 and TIMP–2 mRNAs was especially high immediately before and after ovulation. TIMP-1 and TIMP-3 mRNAs, which were low to undetectable in the granulosa cells of preovulatory follicles, were greatly increased in the luteinizing cells of newly forming CL on estrus. Although the presence of TIMP-1 mRNA in the granulosa cells of preovulatory follicles by in situ hybridization was near background levels, it was specifically identified in granulosa cells of follicles on all days of the cycle using laser capture microdissection and RT-PCR. Both TIMP-2 and TIMP-3 transcripts were up-regulated in luteinized follicles on proestrus and were present throughout the cycle in regressing CL. In summary, the unique and dynamic expression patterns of the TIMPs suggest that they have important, yet distinct, functions in the ovary. The high levels of TIMP-1 mRNA in the CL on estrus indicate a likely role for this inhibitor in luteal formation. The presence of TIMP-2 mRNA in regressing CL suggests an involvement in luteal demise, whereas TIMP-3 may play a role in the health of the follicle as well as in CL regression.