Matrix degrading proteases in the ovary : expression and function

Abstract

Extracellular matrix degrading proteases from the plasminogen (plg) activator (PA) and the matrix metalloproteinase (MMP) systems have been implicated as important mediators of ovulation and corpus luteum (CL) formation and regression. The aim of this thesis was to investigate the expression and regulation of PAs and MMPs in the ovary and to examine their functional roles for CL formation and function. The expression of membrane-type MMP-1 (MT1-MMP) and its substrate gelatinase A (MMP-2) mRNAs was studied during pregnant mare serum gonadotropin (PMSG)/human chorionic gonadotropin (hCG)-induced ovulation in immature rats. These proteases were coordinately regulated so that both were highly expressed in the theca cells of large preovulatory follicles. This suggests that MT1-MMP activates gelatinase A in preovulatory follicles to degrade the follicular wall during ovulation. In pseudopregnant (psp) rats, MT1-MMP mRNA was expressed in the CL throughout the luteal phase. Tissue inhibitor of metalloproteases type-1 (TIMP-1) mRNA was expressed during CL formation and regression. MMP-2 and collagenase-3 mRNAs were expressed during CL formation and regression, respectively. When the luteal phase was artificially prolonged or shortened, TIMP-1 and collagenase-3 mRNAs were induced only after the serum progesterone levels had decreased, indicating a close association with luteolysis in the rat. In psp mice, the expression of mRNAs coding for both PAs, seven MMPs, and five protease inhibitors was studied. Most of the studied molecules were coordinately expressed during formation or regression of the CL. However, uPA, MT1-MMP, and TIMP-3 mRNAs were expressed throughout the luteal phase. The role of uPA was examined in psp uPA deficient mice. These mice displayed no abnormalities in luteal function or vascularity. The role of uPA is thus either not essential or can be compensated by other proteases in the absence of uPA. In order to control the timing of the CL formation, a mouse model for PMSG/hCG-induced CL formation was developed. Five different protocols were evaluated. One of them provided CL that were stable for six days. In that protocol the mice were treated with prolactin (PRL), twice daily from day 2 of CL life onward. The expression of the steroid acute regulatory protein (StAR) mRNA in the psp CL was also characterized to assess its use as a molecular marker for CL development and regression. It was highly expressed in the forming and functional CL and downregulated at a late stage of CL regression. The functional role of plg and MMPs for CL formation and function was investigated in plg deficient mice treated with the MMP inhibitor galardin (GM6001). Both psp mice and PMSG/hCG +PRL-induced CL formation were used. Several molecular markers for CL development and regression were used to evaluate the health status of the CL. Our data showed that healthy and vascularized CL formed even in plg deficient mice treated with the inhibitor. However, serum progesterone levels were significantly reduced in these mice, an effect that was mainly attributable to the plg deficiency. In conclusion, neither plg nor MMPs, alone or in combination, seem to be essential for the development of a functional CL