Antisense oligonucleotide inhibition of type II phospholipase A2 expression, release and activity in vitro

Spinal phospholipase A2 in inflammatory hyperalgesia: role of the small, secretory phospholipase A2

Current work emphasizes that peripheral tissue injury and inflammation results in a heightened sensitivity to subsequent noxious input (hyperalgesia) that is mediated in large part by the spinal synthesis and release of eicosanoids, in particular prostaglandins. Secreted phospholipase A(2)s (sPLA(2)s) form a class of structurally related enzymes that release arachidonic acid from cell membranes that is further processed to produce eicosanoids. We hypothesized that spinal sPLA(2)s may contribute to inflammation-induced hyperalgesia. Spinal cord tissue and cerebrospinal fluid were collected from rats for assessment of sPLA(2) protein expression and sPLA(2) activity. A basal sPLA(2) protein expression and activity was detected in spinal cord homogenate (87+/-17 pmol/min/mg), though no activity could be detected in cisternal cerebrospinal fluid, of naive rats. The sPLA(2) activity did not change in spinal cord tissue or cerebrospinal fluid assessed over 8 h after injection of carrageenan into the hind paw. However, the sPLA(2) activity observed in spinal cord homogenates was suppressed by addition of LY311727, a selective sPLA(2) inhibitor. To determine the role of this spinal sPLA(2) in hyperalgesia, we assessed the effects of lumbar intrathecal (IT) administration of LY311727 in rats with chronic IT catheters in three experimental models of hyperalgesia. IT LY311727 (3-30 microg) dose-dependently prevented intraplantar carrageenan-induced thermal hyperalgesia and formalin-induced flinching, at doses that had no effect on motor function. IT LY311727 also suppressed thermal hyperalgesia induced by IT injection of substance P (30 nmol). Using in vivo spinal microdialysis, we found that IT injection of LY311727 attenuated prostaglandin E(2) release into spinal dialysate otherwise evoked by the IT injection of substance P. Taken together, this work points to a role for constitutive sPLA(2)s in spinal nociceptive processing.

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 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.

Transcriptional regulation of genes for enzymes of the prostaglandin biosynthetic pathway

Numerous studies over the years have demonstrated changes in prostaglandin (PG) levels in intrauterine tissues in association with labour, and PG administration has long been used to induce delivery. While it is now widely accepted that PGs play a major role in human parturition, the complex regulation of their levels is still being elucidated, with the focus on the transcriptional control of the enzymes responsible for the various steps in PG biosynthesis and catabolism.

Phospholipase A2 isozymes in pregnancy and parturition

Mammalian cells contain several structurally different phospholipase (PLA2) enzymes that exhibit distinct localisation, function and mechanisms of regulation. PLA2 isozymes have been postulated to play significant roles in the parturition process. Both secretory and cytosolic PLA2 isozymes have been identified in human gestational tissues, and there is differential expression of these PLA2 isozymes in human fetal membranes and placenta obtained at preterm and term. The aims of this commentary are: (1) to review recent data concerning the expression, role and regulation of PLA2 isozymes in human gestational tissues; and (2) to present novel data demonstrating the regulation of PLA2 isozymes in human gestational tissues by nuclear factor-kappa B (NF-kappaB) and peroxisome proliferator-activated receptor (PPAR)-g.

Syncytial fusion of human trophoblast depends on caspase 8

Differentiation of human placental villous trophoblast includes syncytial fusion of cytotrophoblast forming syncytiotrophoblast. Early stages of the apoptosis cascade were described to be involved in this differentiation process. We investigated the role of the initiator caspase 8 in syncytial fusion in vitro, cultivating placental villous explants with or without caspase 8 antisense oligonucleotides or peptide inhibitors for up to 120 h. Trophoblast fusion and differentiation were assessed by confocal microscopy, immunohistochemistry and Western blot analysis. Culture with caspase 8 antisense oligonucleotides or peptide inhibitors reduced the fusion of cytotrophoblast with the syncytiotrophoblast, and resulted in multilayered cytotrophoblast. Caspase 8 expression was suppressed by antisense oligonucleotides and caspase 8 activities were reduced by peptide inhibitors. The organic anion-transporter hOAT-4 normally expressed in the cytotrophoblast and transferred into the syncytiotrophoblast by syncytial fusion was retained in the cytotrophoblast due to lack of fusion. We conclude that expression and activity of caspase 8 is a prerequisite for differentiation and syncytial fusion of cytotrophoblast cells.