Expression pattern of matrix metalloproteinases changes during folliculogenesis in the cat ovary

Matrix metalloproteinase (MMP) has been implicated as having roles in ovarian folliculogenesis. Here, we determined the expression pattern of six MMPs (MMP1, MMP2, MMP3, MMP7, MMP9 and MMP13) and their endogenous tissue inhibitor, TIMP1, during cat follicle growth. Different developmental stage follicles were mechanically isolated and gene expression analysed by real-time qPCR while MMP1, 2, 9 and 13 localization was determined by immunohistochemistry. With the exception of MMP13, the amount of MMP mRNA was lowest in primordial follicles and increased thereafter. Peak levels were detected in early antral follicles for MMP1 (72.2-fold increase above primordial follicle amount), MMP2 (10-fold), MMP3 (57-fold) and MMP9 (2.8-fold). MMP7 transcripts increased 2-fold by the primary follicle stage and then plateaued. MMP13 mRNA peaked in primary follicles (2.5-fold) and was lower in more advanced counterparts. TIMP1 sharply increased (6-fold) in secondary follicles and gradually declined in the later stages. MMP1 and MMP9 expression were expressed in the granulosa cells of all follicle stages. MMP2 was immunoreactive in early and antral follicles, especially at granulosa cells adjacent to the antral cavity. By contrast, the MMP13 was weakly detected in primary follicles onward. In summary, there are distinctive and consistent changes in MMPs and TIMP1 expression during follicle development, suggesting that these enzymes play one or more roles in cat folliculogenesis. In particular, high mRNA and protein expression levels of MMP1 and MMP2, especially at the antral stage, indicate that these enzymes likely are involved in antrum formation and expansion.