Differential expression of myometrial AP‐1 proteins during gestation and labour

Preterm labour (PTL) is a leading cause of perinatal mortality and postnatal morbidity. Contractions of the uterine muscle (myometrium) that determine the onset of labour depend on the expression of contraction‐associated proteins (CAPs, i.e. connexin43) regulated by dimeric AP‐1 transcription factors. Here, we examined subcellular (by immunoblotting) and tissue expression (by immunohistochemistry) of myometrial AP‐1 proteins (cJUN, JUNB, JUND, cFOS, FOSB, FRA1, FRA2) throughout gestation and TL in different species (mouse, rat and human). To identify the critical AP‐1 members associated with preterm birth, we studied their expression in mouse model of ‘infectious’ (LPS‐induced) and ‘sterile’ (RU486‐induced) PTL. We found that (1) myometrial AP‐1 composition is preserved in vivo between different species (rodents and human) indicating that Fos/Jun heterodimer (i.e. FRA2/JUND) may be indispensable for labour initiation. (2) Our in vivo study using murine models of gestation shows that there is a similarity in the myometrial AP‐1 protein composition during TL and pathological PTL of different aetiology suggesting the involvement of similar molecular machinery in the induction of labour. (3) This study is first comprehensive protein analysis of seven AP‐1 members in human labouring versus non‐labouring myometrium, showing their cellular expression and tissue distribution in relation to labour status.