The organs of the adult reproductive system can undergo extensive remodelling, experiencing rapid changes in tissue mass and function. Much of this matrix remodelling is attributed to the action of matrix metalloproteinases. Matrix metalloproteinase family members are expressed in a highly-regulated manner in many reproductive processes, including menstruation, ovulation, implantation, and uterine, breast, and prostate involution. Metalloproteinase concentrations and activity can be regulated by reproductive hormones, as well as by growth factors and cytokines that participate in reproductive events. In addition to playing a role in the loss of connective tissue mass, the metalloproteinases can influence the phenotype of the cellular components of the tissues, altering basic cellular functions such as proliferation, differentiation, and apoptosis. This review focuses on the expression of matrix metalloproteinases in reproductive tissues, and discusses the evidence supporting a role for these enzymes in modulating the structure and function of reproductive organs.
To explore the role of the matrix metalloproteinase matrilysin (MAT) in normal tissue remodeling, we cloned the murine homologue of MAT from postpartum uterus using RACE polymerase chain reaction and examined its pattern of expression in embryonic, neonatal, and adult mice. The murine coding sequence and the corresponding predicted protein sequence were found to be 75% and 70% identical to the human sequences, respectively, and organization of the six exons comprising the gene is similar to the human gene. Northern analysis and in situ hybridization revealed that MAT is expressed in the normal cycling, pregnant, and postpartum uterus, with levels of expression highest in the involuting uterus at early time points (6 h to 1.5 days postpartum). The mRNA was confined to epithelial cells lining the lumen and some glandular structures. High constitutive levels of MAT transcripts were also detected in the small intestine, where expression was localized to the epithelial Paneth cells at the base of the crypts. Similarly, MAT expression was found in epithelial cells of the efferent ducts, in the initial segment and cauda of the epididymis, and in an extra-hepatic branch of the bile duct. MAT transcripts were detectable only by reverse transcription-polymerase chain reaction in the colon, kidney, lung, skeletal muscle, skin, stomach, juvenile uterus, and normal, lactating, and involuting mammary gland, as was expression primarily late in embryogenesis. Analysis of MAT expression during postnatal development indicated that although MAT is expressed in the juvenile small intestine and reproductive organs, the accumulation of significant levels of MAT mRNA appears to correlate with organ maturation. These results show that MAT expression is restricted to specific organs in the mouse, where the mRNA is produced exclusively by epithelial cells, and suggest that in addition to matrix degradation and remodeling, MAT may play an important role in the differentiated function of these organs.
Rhesus monkeys are useful models in which to examine the hormonal regulation of endometrial matrix metalloproteinases (MMP) and to evaluate the role of MMP in uterine bleeding. Artificial 28 day menstrual cycles can be induced in ovariectomized monkeys by inserting an oestradiol implant for 2 weeks, then inserting a progesterone implant for 2 weeks, and then, with the oestradiol implant remaining in place, removing and reinserting the progesterone implant at 2 week intervals. To examine MMP during menses, we established such cycles and removed uteri by hysterectomy at closely spaced intervals before, during and after menses, as well as at later time points. Some samples were also obtained during menses induced by the withdrawal of both progesterone and oestradiol. We examined mRNA of the following MMP by Northern blotting: matrilysin, stromelysin-1, stromelysin-2, stromelysin-3 and the tissue inhibitor of MMP TIMP-1. The expression of these MMP mRNA increased substantially by 2-3 days after progesterone withdrawal, whether or not oestradiol was maintained. The expression of some of the MMP (stromelysins-1 and -2) returned very rapidly to baseline levels by 5 days after progesterone withdrawal, while the expression of others (matrilysin, stromelysin-3 and TIMP-1) declined more slowly, reaching a baseline level by 10 days after progesterone withdrawal, with little or no further decline after progesterone concentrations rose during the induced luteal phase. Immunocytochemical studies showed that matrilysin was expressed primarily in the glands of the upper functionalis. In other work with the rhesus monkey model, we used a s.c. endometrial autograft technique in which pieces of endometrium were autotransplanted to the abdominal skin. During menses in the grafts, matrilysin was expressed in the glands of the grafts similar to the glands in the eutopic endometrium. Endometrial autografts can serve as a useful model for the study of MMP in uterine bleeding.
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