| Extensive extracellular matrix (ECM) remodeling occurs in many physiological processes such as angiogenesis, ovulation, and bone development and many pathological processes such as tumor growth and metastasis, arthritis, and wound healing. The matrix metalloproteinases (MMPs) are a family of metal dependent enzymes that are largely responsible for degradation and restructuring of the ECM. Activity of the MMPs in the extracellular milieu is regulated by the tissue inhibitors of metalloproteinases (TIMPs). My hypothesis is that MMP and TIMP mRNA expression and activity are increased following a gonadotropin-induced LH surge. Specifically, an increase in gelatinase-A (MMP-2), collagenase (MMP-1 and MMP-13) and membrane-type MMP (MMP-14) is anticipated that results in the ultimate dissolution of the ECM resulting in follicle rupture. To test my hypothesis, I investigated the effect of a gonadotropin releasing hormone (GnRH)-induced LH surge on localization, expression, and activity of selected MMPS (MMP-1, 2, 13 and 14) and TIMPs (TIMPs 1–3). Following synchronization, bovine ovulatory follicles or new corpora lutea (CL) were collected by colpotomy at 0, 6, 12, 18, 24, and 48 h (CL) after a GnRH injection resulting in the LH surge (n = 5–8 per time point). MMP-14 expression, as well as TIMP-2 expression and activity, were increased following the LH surge, while MMP-2 mRNA expression and activity were unchanged. In addition, the collagenases MMP-1 and MMP-13 demonstrated increased mRNA expression following the LH surge. Of the two MMP-1 mRNA species detected, a 2.4 kb transcript was primarily expressed in the follicle, and a 1.8 kb transcript was predominant in the new CL. While TIMP-1 mRNA and activity were increased, TIMP-3 mRNA declined following the LH surge. Expression of MMP-14, MMP-2, and TIMP-3 mRNA was primarily localized to the theca cells, while TIMP-1 and TIMP-2 expression was localized to the granulosa cells. Based on their substrate specificity, intrafollicular localization, and increased mRNA expression following the LH surge, I conclude that MMP-1, MMP-13, and MAP-14 may mediate degradation of the type I and III collagen rich ECM in the theca layer and tunica albuginea. While MMP-2 mRNA remained unchanged, localization of MMP-2 activity to the cell surface may be important for basement membrane breakdown. (Abstract shortened by UMI.)... |
