Platelet-activating factor stimulates phospholipase C activity in human endometrium

Chromosomal location, structure, and temporal expression of the platelet-activating factor receptor (PAFr) gene in porcine endometrium and embryos relative to estrogen receptor alpha gene expression

Although platelet-activating factor receptor (PAFr) gene was well characterized in the human, little was known about it in domestic animals. Porcine PAFr gene was mapped using fluorescence in situ hybridization (FISH). The structure of this gene was investigated using a 5' rapid amplification of cDNA ends (RACE) technique. Temporal expression of PAFr and estrogen receptor alpha genes (ER), and distribution of the PAFr transcripts in porcine endometrial and embryonic tissues on days 0, 10, 12, 14, 16, and 18 were analyzed using DNA competitors and reverse transcription and polymerase chain reaction (RT-PCR). The porcine PAFr gene was mapped to SSC6q26-27. Alternative splicing of primary transcripts of the PAFr gene produced two different transcripts. Transcript 1 was expressed in all tissues and cells, and transcript 2 was detected in all tissues but white blood cells. The temporal expression of the PAFr gene in endometrial (P > 0.05) and embryonic (P < 0.05) tissues of pregnant sows increased from day 10 to 16. The temporal expression of ER genes in endometrial tissues of pregnant sows decreased from day 10 to 18 (P < 0.05). In addition, ER expression was detectable in 20-60% of embryonic tissue samples, which generally decreased. In combination with previously obtained data on PAF and estradiol-17beta (E(2)) concentrations in pregnant uterine luminal fluids (pULF), endometrial and embryonic tissues, the present results indicated that the increasing PAFr transcripts were positively associated with increasing levels of PAF. Both ER transcripts and E(2) found in pULF decreased correspondingly from day 13 to 16. These results indicate that via PAFr, PAF could play a dominant role in peri-implantation development in pigs as compared to E(2).

Platelet-activating factor (PAF) receptor and genetically engineered PAF receptor mutant mice

Platelet-activating factor (PAF, 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine) is a biologically active phospholipid mediator. Although PAF was initially recognized for its potential to induce platelet aggregation and secretion, intense investigations have elucidated potent biological actions of PAF in a broad range of cell types and tissues, many of which also produce the molecule. PAF acts by binding to a unique G-protein-coupled seven transmembrane receptor. PAF receptor is linked to intracellular signal transduction pathways, including turnover of phosphatidylinositol, elevation in intracellular calcium concentration, and activation of kinases, resulting in versatile bioactions. On the basis of numerous pharmacological reports, PAF is thought to have many pathophysiological and physiological functions. Recently advanced molecular technics enable us not only to clone PAF receptor cDNAs and genes, but also generate PAF receptor mutant animals, i.e., PAF receptor-overexpressing mouse and PAF receptor-deficient mouse. These mutant mice gave us a novel and specific approach for identifying the pathophysiological and physiological functions of PAF. This review also describes the phenotypes of these mutant mice and discusses them by referring to previously reported pharmacological and genetical data.

Platelet-activating factor may act as an endogenous pulse generator for sheep of luteolytic PGF2alpha release

Pulsatile release of uterine prostaglandin F2alpha (PGF2alpha) induces luteolysis in ruminants. However, the mechanism(s) that initiates and maintains luteolysis has not been defined. The present study tested the hypothesis that the endogenous PGF2alpha pulse generator is uterine-derived platelet-activating factor (PAF). Ovariectomized ewes were given exogenous progesterone (P), estradiol (E), or both (P+E, mimicking the normal luteal phase). Only ewes treated with steroids released PAF into the uterine lumen and had increased PAF:acetylhydrolase activity in the uterine lumen. Steroid treatment also influenced the capacity of the uterus to release PGF2alpha in response to exogenous PAF. PAF infusion did not affect plasma PGF2alpha metabolite (PGFM) levels in control (no steroid treatment) ewes but increased plasma PGFM levels in P+E ewes (P < 0.001) and ewes treated with P or E alone (P < 0.05). Infusion of PAF followed by or coincident with oxytocin (OT) acted in a synergistic manner to increase plasma PGFM levels. Repeated infusion of PAF into the uterus at 1-h intervals induced tachyphylaxis of the PGFM response to PAF; however, sensitivity of the uterus to PAF returned spontaneously by the 6th h. Interferon-tau (IFN-tau) inhibits pulsatile release of PGF2alpha during pregnancy to prevent luteolysis. Exogenous recombinant ovine IFN-tau (50 microgram) inhibited the uterine response to PAF alone or the combined effects of PAF and OT. These results indicate that uterine PAF fulfills many of the criteria for an endogenous PGF2alpha pulse-generator: steroid induction of PAF production and uterine responsiveness to PAF-induced release of PGF; synergistic stimulation of PAF-induced PGF release by OT; inhibition of PAF effects by IFN-tau; and PAF's ability to induce pulses of PGF with a periodicity during a period of chronic exposure of the uterus to PAF.

Localization, quantification, and activation of platelet-activating factor receptor in human endometrium during the menstrual cycle: PAF stimulates NO, VEGF, and FAKpp125

Implantation is characterized by an inflammatory-like response with expansion of extracellular fluid volume, increased vascular permeability, and vasodilatation. These effects are believed to be mediated at the paracrine level by prostaglandin E2 and platelet-activating factor (PAF), but the cellular mechanism (or mechanisms) remains largely unknown. We demonstrate that PAF receptor (PAF-R) immunoreactivity and mRNA are detected in proliferative and secretory endometrial glands, however, the responsiveness of endometrium to physiological concentrations of PAF is confined predominantly to the secretory endometrium. Semiquantitative reverse transcription-polymerase chain reaction revealed that PAF-R transcript levels were highest in the mid-late proliferative and late secretory phases of the cycle. Interaction of PAF with its receptor resulted in the rapid release of nitric oxide (NO), increased expression of vascular endothelial growth factor (VEGF), and activation of FAKpp125, a focal adhesion kinase, demonstrating that the PAF-R is functionally active. Inhibition of NO synthesis by NG-monomethyl-L-arginine produced dose-dependent attenuation of PAF-evoked NO release, indicating NOS activation; the dependency of PAF-evoked NO release on PKC and extracellular Ca2+ was confirmed by PKC inhibitor Ro 31-8220 and by the removal of extracellular Ca2+. PAF up-regulated VEGF gene expression in a concentration- and time-dependent fashion in human endometrial epithelial cell lysates. Transcription of VEGF was rapidly followed by secretion of the protein. These data support our premise that this autocoid acts as an angiogenic mediator in the regeneration of the endometrium after menses and as a vasodilator to promote blastocyst attachment during the implantation process.

Platelet activating factor and conception

PURPOSE

This review provides evidence for the involvement of platelet activating factor (PAF) in the several facets of pregnancy establishment.

METHODS

A comprehensive literature review and new data.

RESULTS

PAF has a role in spermatozoal function, fertilization, embryo development, and implantation.

CONCLUSIONS

PAF is intimately involved in conception.

Activation of human endometrial phospholipase D by bradykinin

Bradykinin may act as a promoter of endometrial regeneration. In [3H]myristate-labelled endometrial stromal cells, bradykinin and tetradecanoylphorbol acetate (TPA) mediated activation of phospholipase D (PLD) as measured by the accumulation of [3H]phosphatidylbutanol ([3H]PtdBut). Kinetics of bradykinin-evoked PLD activation was rapid and transient, whereas the TPA response was relatively slow in onset. Bradykinin induced a dose-dependent (EC50 0.11 nM) [3H]PtdBut accumulation at concentrations at which it stimulated DNA synthesis. In [3H]inositol-labelled cells, bradykinin evoked a rapid increase in inositol phosphates which preceded the increase in [3H]PtdBut formation. Chronic pretreatment with 400 nM TPA abolished PLD activation to subsequent treatment with either TPA and bradykinin. Staurosporine, an inhibitor of protein kinase C, strongly inhibited (IC50 96 nM) TPA-induced [3H]PtdBut formation, but bradykinin-stimulated [3H]PtdBut accumulation was only partially inhibited (IC50 65 microM). The effect of bradykinin and TPA on PLD activity was synergistic, suggesting that the two agents may act via different mechanisms. These results suggest PKC-dependent and independent pathways are involved in bradykinin-induced PLD activation and that the mitogenic activity of this vasoactive peptide on endometrial stromal cells may in part be mediated via the PLD pathway. This may have significance both to implantation and endometrial cancer.

Oestradiol-17 beta modulates PAF-evoked phospholipase D activity but not inositide-lipid hydrolysis in human endometrial cell line, HEC-1B

Platelet-activating factor (PAF) has been shown to stimulate phospholipase D (PLD) activity in human endometrium. The effect of 17 beta-oestradiol on PAF- and 12-O-tetradecanoylphorbol 13-acetate (TPA)-evoked PLD activity assayed as an accumulation of [3H]phosphatidylbutanol was examined in [3H]myristic acid labelled in a human endometrial epithelial cell line HEC-1B. TPA stimulated PLD activity in a dose-dependent manner whereas PAF had no significant effect on PLD activity. Following 48 h pretreatment with 100 nM 17 beta-oestradiol, PAF evoked PLD activity while leaving inositol trisphosphate accumulation in myo-[2-3H] inositol-labelled HEC-1B cells unaffected. In the 17 beta-oestradiol-treated cells, TPA-stimulated PLD activity was significantly elevated at 100 nM TPA (P < 0.05) and 1 microM TPA (P < 0.05) compared to responses in the untreated cells, suggesting that 17 beta-oestradiol may upregulate PKC activity. Interestingly, following a 30 min pretreatment of HEC-1B cells with a range of 17 beta-oestradiol concentrations. TPA (10 nM) and PAF (100 nM) stimulated PLD activity. However, TPA-stimulated PLD activity levels fell 10-fold while PAF-mediated PLD activity remained elevated at 10 nM and 100 nM concentrations of 17 beta-oestradiol suggesting a different mechanism of activation. These results indicate that 17 beta-oestradiol can upregulate PAF-induced PLD activity in HEC-1B cells.

Basic FGF activates phospholipase D in endothelial cells in the absence of inositol-lipid hydrolysis

In the absence of inositol-lipid hydrolysis, mitogenic concentrations of basic fibroblast growth factor (bFGF) stimulated phosphatidylbutanol formation in the presence of butan-1-ol in [3H]myristate-labeled human umbilical vascular endothelial (HUVE) cells, indicating that the fibroblast growth factor receptor was able to couple to the activation of phospholipase D (PLD). The ability of bFGF and 12-O-tetradecanoylphorbol-13-acetate (TPA) to stimulate PLD activity was completely abolished in cells pretreated with 400 nM TPA for 48 h to downregulate protein kinase C (PKC). bFGF-stimulated PLD activity was inhibited by genistein (5 microM; P < 0.02) and the PKC inhibitor 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H-7, 5 microM; P < 0.001) as well as by the removal of calcium from extracellular environment. bFGF induced DNA synthesis in a dose-dependent manner, and pretreatment of cells with H-7 inhibited the mitogenic activity of bFGF. These results indicate that activation of PKC is responsible for bFGF-induced PLD activation and the mitogenic activity of bFGF in HUVE cells. A coupled PLD/3-sn-phosphatidate phosphohydrolase pathway may play a role in the regulation of endothelial cell proliferation.

Colocalization of acidic and basic fibroblast growth factor (FGF) in human placenta and the cellular effects of bFGF in trophoblast cell line JEG-3

The placenta undergoes extensive angiogenesis and cellular proliferation to establish adequate blood supply to the fetus. The aim of this study was to compare and contrast the immunolocalization of acidic and basic fibroblast growth factor (FGF) in both first trimester and term placenta and gestational decidua. Human choriocarcinoma cell line JEG-3 were employed as a model of cytotrophoblast and the effect of basic FGF on cell proliferation and phospholipase C and D activation investigated. Basic FGF-immunoreactivity (IR) was detected in or around cytotrophoblast cells and in extravillous trophoblast in first trimester placenta by immunohistochemistry using primary polyclonal rabbit antibodies. Identical staining patterns were produced by acidic FGF antibodies indicating colocalization of acidic FGF and basic FGF. At term, weaker and more diffuse staining was seen in the syncytiotrophoblast surrounding the placenta villi and strong staining was present in the smooth muscle cells of mid and large size placental vessels and in some endothelial cells. Endothelial cells and extravillous trophoblast stained strongly within the decidua at first trimester, whereas the glandular epithelium was weakly stained. Basic FGF induced [3H]thymidine incorporation in JEG-3 cells in a dose dependent manner and caused an increase in inosital phosphate accumulation in cells pre-labelled with myo-[3H]inosital at similar concentrations, suggesting a role of phospholipase C in JEG-3 cell proliferation. However, basic FGF failed to stimulate phospholipase D activity in cells pre-labelled with [3H]myristic acid. The detection of acid FGF and basic FGF on both maternal and fetal side of the placenta during early pregnancy suggests a role for FGF in angiogenesis, whereas localisation of the growth factor at term, when extensive angiogenesis has diminished, would indicate that FGF may be associated with more differentiated functions of the trophoblast. The nuclear localization of basic FGF in dividing but not non-dividing placental cells together with the effect of basic FGF on JEF-3 cells, strongly supports a role for basic FGF in cytotrophoblast proliferation in vivo.

Platelet-activating factor production from in vitro and in vivo fertilized murine embryos is similar

PROBLEM

This study measured platelet-activating factor (PAF) production of in vitro and in vivo fertilized murine embryos to ascertain whether site of fertilization impacted subsequent embryonic PAF production.

METHOD

Oocytes and embryo were collected from stimulated B6D2F1 mice. PAF production throughout the preimplantation phase from the two-celled stage through expanded blastocysts was measured and compared among normally developing embryos with the only difference being site of fertilization.

RESULTS

A striking increase in PAF production was noted for both in vivo and in vitro fertilized embryos over the four days of culture. Significantly higher (P < .001) levels of PAF production were noted with development from the two-celled stage (47.22 +/- 4.13; 44.30 +/- 2.43) to expanded blastocysts (254.31 +/- 24.01; 255.11 +/- 5.35 ng/embryo/24 h) for both in vitro and in vivo fertilized embryos, respectively. There was no significant difference (P > .05) in PAF production between the two groups of embryos.

CONCLUSIONS

Embryonic PAF production in the mouse increases in a stage-specific manner, and specifically the site of fertilization in vitro versus in vivo does not affect PAF production in normally developing embryos.

Embryonic platelet activating factor production in the rabbit increases during the preimplantation phase

OBJECTIVE

This study measured platelet activating factor (PAF) production by rabbit embryos in vitro and ascertained if there is increased PAF production associated with advancing embryonic development.

STUDY DESIGN

Two-cell rabbit embryos were recovered from superovulated New Zealand White does and cultured in vitro for 96 hr. Every 24 hr embryos were scored for developmental stage and PAF activity from the corresponding culture medium was measured by platelet aggregation and organic phosphate analyses.

RESULTS

PAF was detected in culture medium at all stages from two cells to blastocysts and rose significantly (P < 0.001) at each 24-hr interval, reaching maximal levels at the expanded blastocyst stage.

CONCLUSION

Maximal PAF production by expanded blastocysts may be an embryonic paracrine signal that facilitates implantation.