Phospholipase A2 isozymes in pregnancy and parturition

Changes in Rat Uterine and Cervical Phospholipase A2 Activity Following Progesterone Agonist or Antagonist Administration at Term

Our previous study revealed that a fall in plasma progesterone (P(4)) level was associated with a transient increase in cytosolic phospholipase A(2) (PLA(2)) activity and prostaglandin F(2)alpha level in the rat uterus and cervix during natural parturition. This study determined the changes in the PLA(2) activities during modulated occurrence of delivery by P(4) antagonist or agonist late in pregnancy. In rats undergoing P(4) antagonist-induced preterm delivery, the PLA(2) activities of both uterine and cervical cytosol significantly decreased 12 h after the challenge and tended to be attenuated within 72 h. The plasma P(4) level altered in a similar pattern. Blockade of delivery by chronic treatment with P(4) agonist was not associated with changes in uterine PLA(2) activity compared with that in normally delivering rats, although there was a persistent rise in cervical PLA(2) activity. The obtained data indicates that the PLA(2) activities in rat uterine and cervical cytosol are not regulated solely by P(4) and that delivery can occur without activation of this enzyme.

The phospholipase A2 superfamily and its group numbering system

The superfamily of phospholipase A(2) (PLA(2)) enzymes currently consists of 15 Groups and many subgroups and includes five distinct types of enzymes, namely the secreted PLA(2)s (sPLA(2)), the cytosolic PLA(2)s (cPLA(2)), the Ca(2+) independent PLA(2)s (iPLA(2)), the platelet-activating factor acetylhydrolases (PAF-AH), and the lysosomal PLA(2)s. In 1994, we established the systematic Group numbering system for these enzymes. Since then, the PLA(2) superfamily has grown continuously and over the intervening years has required several updates of this Group numbering system. Since our last update, a number of new PLA(2)s have been discovered and are now included. Additionally, tools for the investigation of PLA(2)s and approaches for distinguishing between the different Groups are described.

The role and regulation of the nuclear factor kappa B signalling pathway in human labour

Within the discipline of reproductive biology, our understanding of one of the most fundamental biological processes is lacking--the cellular and molecular mechanisms that govern birth. This lack of understanding limits our ability to reduce the incidence of labour complications. The incidence of labour complications including: preterm labour; cervical incompetence; and post-date pregnancies has not diminished in decades. The key to improving the management of human labour and delivery is an understanding of how the multiple processes that are requisite for a successful labour and delivery are coordinated to achieve a timely birth. Processes of human labour include the formation of: contraction associated proteins; inflammatory mediators (e.g. cytokines); uterotonic phospholipid metabolites (e.g. prostaglandins); and the induction of extracellular matrix (ECM) remodelling. Increasingly, it is becoming evident that labour onset and birth are the result of cross-talk between multiple components of an integrated network. This hypothesis is supported by recent data implicating various upstream regulatory pathways in the control of key labour-associated processes, including the activity of enzymes involved in the formation of prostaglandins and extracellular matrix remodelling, and mediators of inflammation. Clearly, the biochemical pathways involved in the formation of these mediators represent potential sites for intervention that may translate to therapeutic interventions to delay or prevent preterm labour and delivery. Available data strongly implicate the nuclear factor-kappaB (NF-kappaB) family as candidate upstream regulators of multiple labour-associated processes. Not only do these data warrant further detailed analysis of the involvement of these pathways in the process of human labour but also promise new insights into the key mechanisms that trigger birth and the identification of new therapeutic interventions that will improve the management of labour.

Lipopolysaccharide and TNF-α Activate the Nuclear Factor Kappa B Pathway in the Human Placental JEG-3 Cells

Up-regulation of pro-inflammatory cytokines, cyclooxygenase (COX-2) and prostaglandins is a critical factor driving human term labour and inflammation-associated preterm labour. Nuclear factor kappa B (NF-kappaB) is activated in response to a number of inflammatory mediators, including cytokines and lipopolysaccharide (LPS). The aim of this study was (i) to investigate if TNF-alpha and LPS activate the NF-kappaB pathway; and (ii) to use short interfering RNA (siRNA) against inhibitor kappaB kinase (IKK)-beta to confirm the role of the NF-kappaB pathway in the regulation of pro-inflammatory mediators in human placental JEG-3 cells. JEG-3 cells (3 independent experiments) were (i) incubated in the presence or absence of 10 microg/ml LPS or 20 ng/ml TNF-alpha, or (ii) transfected with 100 nM IKK-beta siRNA. Incubation of JEG-3 cells with LPS and TNF-alpha increased the expression of cytoplasmic IKK-beta and phosphorylated IkappaB-alpha, and nuclear NF-kappaB proteins p50 and p65. This was associated with a concurrent increase in COX-2 protein, and IL-6 and PGF2alpha release from JEG-3 cells. Treatment of cells with BAY 11-7082 at 50 microM significantly inhibited basal, LPS- and TNF-alpha-induced NF-kappaB and COX-2 expression, and IL-6 and PGF2alpha release. Transfection of JEG-3 cells with IKK-beta siRNA significantly decreased IL-6 and PGF2alpha release. The data presented in this study demonstrate that pro-inflammatory mediators regulate the NF-kappaB transcription pathway in human JEG-3 cells, and the IKK-beta/NF-kappaB pathway is a regulator of inflammatory mediators in placental JEG-3 cells.

Accelerated expansion of group IID-like phospholipase A2 genes in Bos taurus

Low-molecular-weight, calcium-dependent phospholipase A2 genes (PLA2s) that belong to the secreted type of PLA2s are clustered within a syntenic group on human 1p35-p36 and mouse 4qD3. We reassembled trace files available from the Whole Genome Sequencing (WGS) Project, obtaining an 86-kb contig with three tandem PLA2G2D duplications in the Hereford strain. We used mate-pair data to monitor the assembly and to exclude chimeric clones, demonstrating that the current WGS data may be assembled even in a highly repetitive region with a coverage exceeding fivefold. The genomic structure indicated that most of the PLA2G2D transcripts are formed by four exons. Two alternative first exons were present in all duplications. In two duplications insertions of satellite DNA in the third intron created a novel exon that gave rise to a two-exon product. Linkage and comparative mapping placed the bovine PLA2G2 locus on BTA2, indicating that it evolved from an ancestral PLA2G2D locus common to human, cattle, and rodents. Bovine PLA2G2D variants were capable of encoding 147-amino-acid polypeptides that consisted of putative signal peptide and metal-binding domains. Cysteine residues were conserved in positions analogous to those forming the seven disulfide bonds characteristic of PLA2G2 genes. Quantitative PCR analysis of bovine PLA2G2D transcripts indicated that their expression levels varied between the dry period and lactation in the mammary gland samples and that their expression was polymorphic in liver tissue. The recent burst of duplication and divergence of the bovine PLA2G2D genes and their polymorphic nature are typical of innate immune response genes.

Secretory phospholipase A2 of group IIA: Is it an offensive or a defensive player during atherosclerosis and other inflammatory diseases?

Since its discovery in the serum of patients with severe inflammation and in rheumatoid arthritic fluids, the secretory phospholipase A2 of group IIA (sPLA2-IIA) has been chiefly considered as a proinflammatory enzyme, the result of which has been very intense interest in selective inhibitors of sPLA2-IIA in the hope of developing new and efficient therapies for inflammatory diseases. The recent discovery of the antibacterial properties of sPLA2-IIA, however, has raised the question of whether the upregulation of sPLA2-IIA during inflammation is to be considered uniformly negative and the hindrance of sPLA2-IIA in every instance beneficial. The aim of this review is for this reason, along with the results of various investigations which argue for the proinflammatory and proatherogenic effects of an upregulation of sPLA2-IIA, also to array data alongside which point to a protective function of sPLA2-IIA during inflammation. Thus, it could be shown that sPLA2-IIA, apart from the bactericidal effects, possesses also antithrombotic properties and indeed plays a possible role in the resolution of inflammation and the accelerated clearance of oxidatively modified lipoproteins during inflammation via the liver and adrenals. Based on these multipotent properties the knowledge of the function of sPLA2-IIA during inflammation is a fundamental prerequisite for the development and establishment of new therapeutic strategies to prevent and treat severe inflammatory diseases up to and including sepsis.

Gestation age-related increase in 50-kDa rat uterine calcium-independent phospholipase A2 expression influences uterine sensitivity to polychlorinated biphenyl stimulation

Phospholipase A2 (PLA2) enzymes catalyze the rate-limiting step in eicosanoid production by liberating arachidonic acid from membrane phospholipids. There is limited information regarding the expression pattern and activity of uterine PLA2 enzymes during pregnancy. Polychlorinated biphenyls (PCBs) are a group of persistent environmental toxicants previously associated with decreased gestation length that are capable of activating PLA2. The purpose of the present study was to determine whether uterine sensitivity to PCB stimulation is dependent on PLA2 expression, comparing rat uterine PLA2 expression in Gestational Day (gd) 10 versus gd20. Western blot analysis revealed a significant increase in the expression of calcium-dependent PLA2G2A and a 50-kDa protein immunoreactive to calcium-independent PLA2G6 antibody in gd20 compared to gd10 rat uterine tissue. The increased expression of the 50-kDa PLA2G6 was associated with a gestational age-related increase in endometrial calcium-independent PLA2 activity that was sensitive to inhibition by bromoenol lactone (P < 0.05). Longitudinal uterine strips isolated from gd10 or gd20 rat were suspended in muscle baths to evaluate uterine contractions following exposure to the ortho substituted congener PCB 50. Exposure to 50 and 100 microM PCB 50 significantly increased the frequency of gd20, but not gd10, uteri compared to solvent (dimethyl sulfoxide) controls (P < 0.05). Pharmacologic inhibition of PLA2G6, but not PLA2G2A, attenuated PCB-induced stimulation of gd20 uterine contractions (P < 0.05). These data suggest that PCB 50 stimulates uterine contractions by activating endometrial PLA2G6. Furthermore, gestation age-related sensitivity to PCB is associated with an increase in the expression of a previously unidentified 50-kDa PLA2G6 in rat uterus.

Activation of phospholipase A2 is associated with generation of placental lipid signals and fetal obesity

CONTEXT

Obesity and diabetes during pregnancy are associated with increased insulin resistance and higher neonatal adiposity. In turn, insulin resistance triggers inflammatory pathways with accumulation of placental cytokines.

OBJECTIVE

To determine placental signals that translate into development of excess adipose tissue, we investigated the role of phospholipases A2 (PLA2) as targets of inflammatory mediators.

SETTING

The study was conducted at Case Western Reserve University, Department of Reproductive Biology.

SUBJECTS

Volunteers gave informed written consent in accordance with the Institutional Review Board guidelines. Placenta and cord blood samples were obtained at the time of elective cesarean section in 15 term pregnancies.

INTERVENTION

Neonatal anthropometric measurements were performed within 48 h of delivery. Placentas were grouped based on neonatal percentage body fat as obese (body fat > or = 16%) and lean control (body fat < or = 8%).

MAIN OUTCOME MEASURES

The primary outcomes were placenta PLA2 expression and fatty acid concentration.

RESULTS

Expression of PLA2G2A and PLA2G5, the main placenta phospholipases, was greater (P < 0.05) in placenta of obese compared with control neonates and was associated with increased 20:3 and 20:5 omega-3 polyunsaturated fatty acids. TNF-alpha and leptin content was increased 3-fold in placenta of obese neonates. TNF-alpha and leptin both induced a time-dependent activation of PLA2G2 and PLA2G5 in placental cells.

CONCLUSION

Accumulation of omega-3 fatty acids through secretory PLA2 activation is associated with high neonatal adiposity. We propose that the generation of placental lipid mediators through TNF-alpha and leptin stimulation represents a key mechanism to favor excess fetal fat accretion.

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.