MAPK and AP-1 proteins are increased in term pre-labour fetal membranes overlying the cervix: regulation of enzymes involved in the degradation of fetal membranes

Abstract

Fetal membranes overlying the cervix (i.e. supracervical site, SCS) are characterised by increased extracellular matrix (ECM) degradation. In non-gestational tissues, the mitogen activated protein kinase (MAPK) and activator protein (AP)-1 family are involved in the regulation of the ECM degrading enzyme metalloproteinase (MMP)-9. The aims of this study were (i) to compare the expression of AP-1 proteins in fetal membranes from the SCS and a distal site (DS), and (ii) determine if the MAPK/AP-1 pathway is involved in the regulation of MMP-9. Fetal membranes overlying the cervix were identified in situ in women undergoing term elective Caesarean section. Immunohistochemistry (n = 6) was used to localise the expression of the MAPK proteins ERK (total and phosphorylated), JNK (total and phosphorylated) and p38 MAPK (total and phosphorylated), and the AP-1 proteins JunB, cJun (total and phosphorylated), JunD, cFos and FosD. There was no difference in JNK, p38 MAPK, FosB, cJun and JunD protein expression between SC and distal fetal membranes. However, when compared to DS, the intensity and/or extent of staining of ERK, p-ERK, p-JNK, p-p38 MAPK, cFos, JunB and p-cJun were greater in amnion and chorion obtained from the SCS. In order to elucidate a role for these proteins in ECM degradation, pharmacological inhibitors of MAPK protein activation were utilised in primary amnion cells. The ERK inhibitor U0126, JNK inhibitor SP600125 and p38 MAPK inhibitor SB202190 all significantly decreased IL-β-induced MMP-9 gene expression and pro MMP-9 in human primary amnion cells. In summary, at term, non laboured SC fetal membranes are characterised by increased expression of MAPK and AP-1 proteins. MMP-9 expression and production was significantly suppressed by inhibitors of three key enzymes in the signalling cascades leading to AP-1 formation, ERK 1/2, JNK and p38 MAPK. Thus, the MAPK/AP-1 pathway may play a role in the degradation of the ECM at the SCS making it more susceptible to membrane rupture.