Number and distribution of myofibroblasts and α-smooth muscle actin expression levels in fetal membranes with and without gestational complications.

The permeability and tension of fetal membranes (FMs) is associated with extracellular matrix proteins produced largely by myofibroblasts (MFBBs). alpha-smooth muscle actin (alpha-SMA) is involved in the contraction of MFBBs and has been implicated as a special biomarker of MFBBs in non-vessel FM. The present study demonstrated, by using immunohistochemistry, reverse-transcription polymerase chain reaction and western blotting, that MFBBs were mainly distributed in chorioamniotic mesoderm at 16-21 weeks and in chorionic mesoderm at 22-40 weeks, respectively, while overlapping with each other at 16-40 weeks. In addition, a quantity of MFBBs were identified in chorionic epithelia at 16-40 weeks. The MFBBs were distributed parallel to the FMs. The quantities of MFBBs and the expression levels of alpha-SMA were negatively associated with increasing gestational progress and of amniotic fluid indexes in full-term females (those from oligohydramnios were higher than polyhydramnios); however, the thickness of the FM's mesoderm remained unchanged. Of note, the number of MFBBs in early-onset severe pre-eclampsia (EOSP) was significantly decreased in comparison with that in EOSP controls and late-onset severe pre-eclampsia (LOSP), while that in LOSP was higher than that in LOSP controls. The present data indicated that the changes in the quantity and distribution of MFBBs in the FM affects the permeability and tension of the FM. In addition, the findings suggested that the expression levels of alpha-SMA in the FM also contributed to the properties of the FM. Simultaneously, the number and distribution of MFBBs and the expression levels of alpha-SMA in the FM may be involved in the mechanisms of development, apoptosis and trophoblast-MFBB transformation of the FM.