Prostaglandin E2-dependent production of latent matrix metalloproteinase-9 in cultures of human fetal membranes

Studies in our laboratory have shown that structural changes in cervical biopsied fetal membranes, prior to labour, coincide with differences in the expression of the gelatinase enzyme, latent matrix metalloproteinase-9 (MMP-9). Concurrently, in vivo,there is an increase in the expression of prostaglandins, notably prostaglandin E-2 (PGE(2)), which has been shown to regulate the expression of MMPs in other systems. The aim of this study was to test the hypothesis (using an in-vitro culture model) that endogenously produced PGE(2) has a role in the elevation of MMP-9 described in vivo. Non-infected fetal membranes sampled from women undergoing elective Caesarean section were stimulated with 10% (v/v) fetal bovine serum (FBS), a known inducer of prostaglandins. This activation resulted in a time-dependent increase in the secretion of PGE(2) into the media, as determined by enzyme-linked immunosorbent assay (day 1: 19 +/- 9 pg/ml/24 h to 358 +/- 54 pg/ml/24 h by day 4). A similar pattern of secretion of latent MMP-9 was observed in parallel with the increase in PGE(2) in the same culture media (day 1: 1.63 +/- 0.17 ng/ml/24 h to 4.2 +/- 1.4 ng/ml/24 h by day 4). When both molecules were compared, a significant (P < 0.01) positive correlation (r = 0.623) was observed. Secretion of the tissue inhibitor of MMPs-9 (TIMP-1) was not significantly different between untreated (3.07 +/- 0.266 <mu>g/ml/24 h) and FBS-treated (3.85 +/- 0.24 mug/ml/24 h) cultures during the first 4 days in culture. Prostaglandin synthesis inhibition studies using indomethacin (100 mu mol/l) resulted in a 70-80% reduction in the activated secretion of latent MHP-9. Direct PGE(2) stimulation of cultures resulted in the bell shaped dose-response curve with concentrations of 1-100 nmol/l (which are within the range secreted in culture in response to FBS), stimulating significant latent MMP-9 secretion. These results suggest a link between endogenous PGE(2) and latent MPP-9 production in human fetal membranes, raising the possibility that PGE(2) has a role in the mechanism of fetal membrane structural changes and, hence, in parturition-associated membrane rupture.