Labour is associated with increased expression of type-IIA secretory phospholipase A2 but not type-IV cytosolic phospholipase A2 in human myometrium

Abstract

Human labour is associated with increased prostaglandin synthesis within the uterus. The aim of this study was to examine the expression of the type-IV cytosolic phospholipase A₂ (cPLA₂-IV) and the type IIA secretory phospholipase A₂ (sPLA₂-IIA) in myometrium in association with labour onset at term and preterm deliveries. These enzymes are important for the release of the prostaglandin precursor, arachidonic acid, from phospholipid membrane stores. RT–PCR was used to determine differences in gene expression between non-labour and labour groups. Expression of sPLA₂-IIA in human myometrium was significantly increased with pregnancy, and with labour, both at term and preterm. Expression of cPLA₂-IV in myometrium was not significantly altered with respect to pregnancy or labour. Immunohistochemical analysis demonstrated differences in the spatial localization of cPLA₂-IV and sPLA₂-IIA protein in upper and lower segment myometrium. cPLA₂-IV was predominantly in vascular endothelial cells, while sPLA₂-IIA was observed in vascular, endothelial and smooth muscle cells. In addition, sPLA₂-IIA showed a distinct nuclear or perinuclear localization in myometrial smooth muscle cells of the lower segment. We postulate that the increased expression of sPLA₂-IIA rather than cPLA₂-IV in the myometrium may play a role in the onset and/or maintenance of human parturition.