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

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 A(2) (cPLA(2)-IV) and the type IIA secretory phospholipase A(2) (sPLA(2)-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 sPLA(2)-IIA in human myometrium was significantly increased with pregnancy, and with labour, both at term and preterm. Expression of cPLA(2)-IV in myometrium was not significantly altered with respect to pregnancy or labour. Immunohistochemical analysis demonstrated differences in the spatial localization of cPLA(2)-IV and sPLA(2)-IIA protein in upper and lower segment myometrium. cPLA(2)-IV was predominantly in vascular endothelial cells, while sPLA(2)-IIA was observed in vascular, endothelial and smooth muscle cells. In addition, sPLA(2)-IIA showed a distinct nuclear or perinuclear localization in myometrial smooth muscle cells of the lower segment. We postulate that the increased expression of sPLA(2)-IIA rather than cPLA(2)-IV in the myometrium may play a role in the onset and/or maintenance of human parturition.