Platelet-activating factor receptor (PAFR) regulates neuronal maturation and synaptic transmission during postnatal retinal development.

Introduction: Platelet-activating factor (PAF), PAF receptor (PAFR), and PAF- synthesis/degradation systems are involved in essential CNS processes such as neuroblast proliferation, differentiation, migration, and synaptic modulation. The retina is an important central nervous system (CNS) tissue for visual information processing. During retinal development, the balance between Retinal Progenitor Cell (RPC) proliferation and differentiation is crucial for proper cell determination and retinogenesis. Despite its importance in retinal development, the effects of PAFR deletion on RPC dynamics are still unknown. Methods: We compared PAFR knockout mice (PAFR-/-) retinal postnatal development proliferation and differentiation aspects with control animals. Electrophysiological responses were analyzed by electroretinography (ERG). Results and discussion: In this study, we demonstrate that PAFR-/- mice increased proliferation during postnatal retinogenesis and altered the expression of specific differentiation markers. The retinas of postnatal PAFR-/- animals decreased neuronal differentiation and synaptic transmission markers, leading to differential responses to light stimuli measured by ERG. Our findings suggest that PAFR signaling plays a critical role in regulating postnatal RPC cell differentiation dynamics during retinal development, cell organization, and neuronal circuitry formation.

Platelet-Activating Factor Receptor (PAFR) Regulates Retinal Progenitor/Stem Cells Profile in Ciliary Epithelium Cells.

The retina is a central nervous tissue essential to visual perception and highly susceptible to environmental damage. Lower vertebrate retinas activate intrinsic regeneration mechanisms in response to retinal injury regulated by a specialized population of progenitor cells. The mammalian retina does not have populations of progenitor/stem cells available to activate regeneration, but contains a subpopulation of differentiated cells that can be reprogrammed into retinal stem cells, the ciliary epithelium (CE) cells. Despite the regenerative potential, stem cells derived from CE exhibit limited reprogramming capacity probably associated with the expression of intrinsic regulatory mechanisms. Platelet-activating factor (PAF) is a lipid mediator widely expressed in many cells and plays an important role in stem cell proliferation and differentiation. During mammalian development, PAF receptor signaling showed important effects on retinal progenitors' cell cycle regulation and neuronal differentiation that need to be further investigated. In this study, our findings suggested a dynamic role for PAF receptor signaling in CE cells, impacting stem cell characteristics and neurosphere formation. We showed that PAF receptors and PAF-related enzymes are downregulated in retinal progenitor/stem cells derived from PE cells. Blocking PAFR activity using antagonists increased the expression of specific progenitor markers, revealing potential implications for retinal tissue development and maintenance.

Singlet oxygen from endoperoxide initiates an intracellular reactive oxygen species release in HaCaT keratinocytes.

Singlet oxygen (|1O2) is a selective intermediate reactive oxygen species generated naturally in biological systems by light- and non-light mediated processes. Although |1O2 plays an important role in cell signaling and in maintaining homeostasis, it can be toxic due to its ability to diffuse across considerable distances. Several in vitro studies have investigated the pathways by which |1O2 mediates oxidation of biological molecules and potential pathogenesis. However, understanding how singlet oxygen exerts cell injury through the production of subsequent reactive oxygen species remains unexplored. To study this, we used a hydrophobic endoperoxide as a source of |1O2. Endoperoxides are reagents that quantitatively generate singlet oxygen in solution at 35°C by thermal decomposition. Our chemiluminescence and cell viability assay data revealed that |1O2 stimulated a secondary intracellular reactive oxygen species production in a very short time. To determine the source of these reactive oxygen species with endo-peroxide exposure, cells were treated with inhibitors targeting NADPH oxidases and platelet activating factor receptors. Our results showed that addition of the platelet activating factor receptor antagonist, Apafant (WEB2086), alleviated cell injury and hydrogen peroxide levels following endoperoxide stimulation. Furthermore, intracellular calcium assay data demonstrated a potential calcium sensitive production of intracellular reactive oxygen species.

Perspective of a Pediatrician: Shared Pathogenesis of the Three Most Successful Pathogens of Children.

Highly successful invasive pathogens exploit host vulnerabilities by adapting tools to co-opt highly conserved host features. This is especially true when pathogens develop ligands to hijack trafficking routes or signaling patterns of host receptors. In this context, highly successful pathogens can be grouped together by the patterns of organs infected and diseases they cause. In the case of this perspective, the focus is on the historically most successful invasive bacterial pathogens of children that cause pneumonia, sepsis and meningitis: Streptococcus pneumoniae, Haemophilus influenzae, and Neisseria meningitidis. This triad shares a ligand to bind to PAF receptor to enter host cells despite early defenses by innate immunity. All three also target laminin receptor to cross endothelial barriers using a common set of molecular tools that may prove to be a design for a cross-protective vaccine.

Effect of acyl and alkyl analogs of platelet-activating factor on inflammatory signaling.

Platelet-activating factor (PAF), a bioactive ether phospholipid with significant pro-inflammatory properties, was identified almost half a century ago. Despite extensive study of this autocoid, therapeutic strategies for targeting its signaling components have not been successful, including the recent clinical trials with darapladib, a drug that targets plasma PAF-acetylhydrolase (PAF-AH). We recently provided experimental evidence that the previously unrecognized acyl analog of PAF, which is concomitantly produced along with PAF during biosynthesis, dampens PAF signaling by acting both as a sacrificial substrate for PAF-AH and probably as an endogenous PAF-receptor antagonist/partial agonist. If this is the scenario in vivo, PAF-AH needs to catalyze the selective hydrolysis of alkyl-PAF and not acyl-PAF. Accordingly, different approaches are needed for treating inflammatory diseases in which PAF signaling is implicated. The interplay between acyl-PAF, alkyl-PAF, PAF-AH, and PAF-R is complex, and the outcome of this interplay has not been previously appreciated. In this review, we discuss this interaction based on our recent findings. It is very likely that the relative abundance of acyl and alkyl-PAF and their interactions with PAF-R in the presence of their hydrolyzing enzyme PAF-AH may exert a modulatory effect on PAF signaling during inflammation.

Platelet activating factor receptor antagonists improve the efficacy of experimental chemo- and radiotherapy

Platelet activating factor is a lipid mediator of inflammation, and in recent decades, it has emerged as an important factor in tumor outcomes. Platelet activating factor acts by specific binding to its receptor, which is present in both tumor cells and cells that infiltrate tumors. Pro-tumorigenic effects of platelet activating factor receptor in tumors includes promotion of tumor cell proliferation, production of survival signals, migration of vascular cells and formation of new vessels and stimulation of dendritic cells and macrophages suppressor phenotype. In experimental models, blocking of platelet activating factor receptor reduced tumor growth and increased animal survival. During chemotherapy and radiotherapy, tumor cells that survive treatment undergo accelerated proliferation, a phenomenon known as tumor cell repopulation. Work from our group and others showed that these treatments induce overproduction of platelet activating factor-like molecules and increase expression of its receptor in tumor cells. In this scenario, antagonists of platelet activating factor markedly reduced tumor repopulation. Here, we note that combining chemo- and radiotherapy with platelet activating factor antagonists could be a promising strategy for cancer treatment.

[Antagonistic effect of ginkgolide homologues on PAF-induced platelet aggregation and neuroprotective effect].

To study the antagonistic effect of ginkgolide homologues on platelet-activating factor (PAF)-induced platelet aggregation and investigate its neuroprotective effect. PAF was used as a coagulant, and ginkgolides were added to the rabbit blood samples respectively. The inhibitory effect of each compound on platelet aggregation was detected by turbidimetry. In L-glutamate induced primary cortical neuron cell injury model, MTT assay was used to detect cell viability. Intracellular free Ca2+ concentration in neurons was measured by using the fluorescent Ca2+ indicator Fura-2 AM. Morphological observation and Hoechst 33258 staining were used to detect the inhibitory effect of ginkgolide on neuronal apoptosis. The results showed that the inhibitory effect on PAF-induced platelet aggregation activity in ginkgolide homologues was ginkgolide K (GK), ginkgolide B (GB), ginkgolide A (GA), ginkgolide C (GC), ginkgolide M (GM), ginkgolide J (GJ) and ginkgolide (GL) from high to low. GB and GK (1-100 µmol•L ⁻¹) could significantly reduce the cell damage caused by L-glutamate, with survival rate increasing, intracellular calcium concentration reducing and cell morphology restoring. This paper has identified the activities and characteristics of various compounds of ginkgolide homologues on PAF-induced platelet aggregation as well as its neuroprotective effect.

Antagonistic effect of ginkgolide homologues on PAF-induced platelet aggregation and neuroprotective effect / 中国中药杂志

To study the antagonistic effect of ginkgolide homologues on platelet-activating factor (PAF)-induced platelet aggregation and investigate its neuroprotective effect. PAF was used as a coagulant, and ginkgolides were added to the rabbit blood samples respectively. The inhibitory effect of each compound on platelet aggregation was detected by turbidimetry. In L-glutamate induced primary cortical neuron cell injury model, MTT assay was used to detect cell viability. Intracellular free Ca2+ concentration in neurons was measured by using the fluorescent Ca2+ indicator Fura-2 AM. Morphological observation and Hoechst 33258 staining were used to detect the inhibitory effect of ginkgolide on neuronal apoptosis. The results showed that the inhibitory effect on PAF-induced platelet aggregation activity in ginkgolide homologues was ginkgolide K (GK), ginkgolide B (GB), ginkgolide A (GA), ginkgolide C (GC), ginkgolide M (GM), ginkgolide J (GJ) and ginkgolide (GL) from high to low. GB and GK (1-100 μmol•L ⁻¹) could significantly reduce the cell damage caused by L-glutamate, with survival rate increasing, intracellular calcium concentration reducing and cell morphology restoring. This paper has identified the activities and characteristics of various compounds of ginkgolide homologues on PAF-induced platelet aggregation as well as its neuroprotective effect.

Hypoxia and hyperoxia potentiate PAF receptor-mediated effects in newborn ovine pulmonary arterial smooth muscle cells: significance in oxygen therapy of PPHN.

Platelet-activating factor (PAF) acting via its receptor (PAFR) is implicated in the pathogenesis of persistent pulmonary hypertension of the newborn (PPHN). Effects of long-term oxygen therapy on newborn lung are not well understood; therefore, we studied the effect of oxygen tension on ovine newborn pulmonary artery smooth muscle cells (NBPASMC). Our global hypothesis is that PPHN results from failure of newborn lamb pulmonary system to downregulate PAFR activity or to upregulate vasodilatory cyclic nucleotides (Cnucs) activity. NBPASMC from newborns 6-12 days old were studied in vitro at three different oxygen tensions (pO2, [Torr]: hypoxia, <40; normoxia, 80-100; and hyperoxia, >100 Torr often clinically imposed upon newborns with PPHN) PAFR- and Cnucs mediated effects were determined. PAFR and PKA Cα mRNA expression as well as prostacyclin, thromboxane, cAMP production, and DNA synthesis was studied to assess PAFR-mediated hypertrophy and/or hyperplasia. Hypoxia and hyperoxia increased specific PAFR binding. PAF treatment during hyperoxia increased PAFR gene, but decreased PKA-Cα gene expression. Hypoxia and hyperoxia increased NBPASMC proliferation via PAFR signaling. Baseline prostacyclin level was ninefold greater than in fetal PASMC, whereas baseline thromboxane was sevenfold less suggesting greater postnatal cyclooxygenase activity in NBPASMC PAF decreased, while forskolin and 8-Br-cAMP increased cAMP production. Decrease of PAFR effects by Cnucs indicates that normal newborn PA physiology favors vasodilator pathways to minimize PAF-induced hypertrophy or hyperplasia. We speculate that failure of newborn lung to anchor downregulation of vasoconstrictors with upregulation of vasodilators leads to PPHN.

SIRT1 prevents pulmonary thrombus formation induced by arachidonic acid via downregulation of PAF receptor expression in platelets.

SIRT1, a class III histone deacetylase, is critically involved in cellular response to stress and modulates cardiovascular risk factors. However, its role in thrombus formation is largely unknown. Thus, this study investigated the effect of SIRT1 on pulmonary thrombus formation, and then identified its role in the modulation of platelet aggregation. In isolated human platelets, cell aggregation was increased by various platelet activators, such as platelet activating factor (PAF), arachidonic acid (AA), ADP, and thrombin. AA- and PAF-mediated platelet aggregations were suppressed by WEB2086, a PAF receptor (PAFR) antagonist. Pulmonary thrombus formation induced by PAF or AA was also attenuated by WEB2086, suggesting that PAFR plays a key role in AA-induced platelet aggregation. In platelets isolated from SIRT1-TG mice as well as in platelets treated with resveratrol or reSIRT1, PAFR expression was decreased, whereas this expressional downregulation by SIRT1 activators was inhibited in platelets treated with MG132 (a proteasome inhibitor) or NH4Cl (a lysosome inhibitor). Furthermore, platelet aggregation induced by AA was markedly attenuated by resveratrol and reSIRT1. Likewise, the increased pulmonary thrombus formation in mice treated with AA was also attenuated by SIRT1 activators. In line with these results, pulmonary thrombus formation was markedly attenuated in SIRT1-TG mice. Taken together, this study showed that SIRT1 downregulates PAFR expression on platelets via proteasomal and lysosomal pathways, and that this downregulation inhibits platelet aggregation in vitro and pulmonary thrombus formation in vivo.

Myeloperoxidase formation of PAF receptor ligands induces PAF receptor-dependent kidney injury during ethanol consumption.

Cytochrome P450 2E1 (CYP2E1) induction and oxidative metabolism of ethanol in hepatocytes inflame and damage liver. Chronic ethanol ingestion also induces kidney dysfunction, which is associated with mortality from alcoholic hepatitis. Whether the kidney is directly affected by ethanol or is secondary to liver damage is not established. We found that CYP2E1 was induced in kidney tubules of mice chronically ingesting a modified Lieber-deCarli liquid ethanol diet. Phospholipids of kidney tubules were oxidized and fragmented in ethanol-fed mice with accumulation of azelaoyl phosphatidylcholine (Az-PC), a nonbiosynthetic product formed only by oxidative truncation of polyunsaturated phosphatidylcholine. Az-PC stimulates the inflammatory PAF receptor (PTAFR) abundantly expressed by neutrophils and kidney tubules, and inflammatory cells and myeloperoxidase-containing neutrophils accumulated in the kidneys of ethanol-fed mice after significant hysteresis. Decreased kidney filtration and induction of the acute kidney injury biomarker KIM-1 in tubules temporally correlated with leukocyte infiltration. Genetic ablation of PTAFR reduced accumulation of PTAFR ligands and reduced leukocyte infiltration into kidneys. Loss of this receptor in PTAFR(-/-) mice also suppressed oxidative damage and kidney dysfunction without affecting CYP2E1 induction. Neutrophilic inflammation was responsible for ethanol-induced kidney damage, because loss of neutrophil myeloperoxidase in MPO(-/-) mice was similarly protective. We conclude that ethanol catabolism in renal tubules results in a self-perpetuating cycle of CYP2E1 induction, local PTAFR ligand formation, and neutrophil infiltration and activation that leads to myeloperoxidase-dependent oxidation and damage to kidney function. Hepatocytes do not express PTAFR, so this oxidative cycle is a local response to ethanol catabolism in the kidney.

A platelet-activating factor (PAF) receptor deficiency exacerbates diet-induced obesity but PAF/PAF receptor signaling does not contribute to the development of obesity-induced chronic inflammation.

Platelet-activating factor (PAF) is a well-known phospholipid that mediates acute inflammatory responses. In the present study, we investigated whether PAF/PAF receptor signaling contributed to chronic inflammation in the white adipose tissue (WAT) of PAF receptor-knockout (PAFR-KO) mice. Body and epididymal WAT weights were higher in PAFR-KO mice fed a high-fat diet (HFD) than in wild-type (WT) mice. TNF-α mRNA expression levels in epididymal WAT and the infiltration of CD11c-positive macrophages into epididymal WAT, which led to chronic inflammation, were also elevated in HFD-fed PAFR-KO mice. HFD-fed PAFR-KO mice had higher levels of fasting serum glucose than HFD-fed WT mice as well as impaired glucose tolerance. Although PAF receptor signaling up-regulated the expression of TNF-α and lipopolysaccharide induced the expression of acyl-CoA:lysophosphatidylcholine acyltransferase 2 (LPCAT2) mRNA in bone marrow-derived macrophages, no significant differences were observed in the expression of LPCAT2 mRNA and PAF levels in epididymal WAT between HFD-fed mice and normal diet-fed mice. In addition to our previous finding in which energy expenditure in PAF receptor (PAFR)-deficient mice was low due to impaired brown adipose tissue function, the present study demonstrated that PAF/PAF receptor signaling up-regulated the expression of Ucp1 mRNA, which is essential for cellular thermogenesis, in 3T3-L1 adipocytes. We concluded that the marked accumulation of abdominal fat due to HFD feeding led to more severe chronic inflammation in WAT, which is associated with glucose metabolism disorders, in PAFR-KO mice than in WT mice, and PAF/PAF receptor signaling may regulate energy expenditure and adiposity.

Mechanism by which nuclear factor-kappa beta (NF-kB) regulates ovine fetal pulmonary vascular smooth muscle cell proliferation.

Platelet activating factor (PAF) modulates ovine fetal pulmonary hemodynamic. PAF acts through its receptors (PAFR) in pulmonary vascular smooth muscle cells (PVSMC) to phosphorylate and induce nuclear translocation of NF-kB p65 leading to PVSMC proliferation. However, the interaction of NF-kB p65 and PAF in the nuclear domain to effect PVSMC cell growth is not clearly defined. We used siRNA-dependent translation initiation arrest to study a mechanism by which NF-kB p65 regulates PAF stimulation of PVSMC proliferation. Our hypotheses are: (a) PAF induces NF-kB p65 DNA binding and (b) NF-kB p65 siRNA attenuates PAF stimulation of PVSMC proliferation. For DNA binding, cells were fed 10 nM PAF with and without PAFR antagonists WEB 2170, CV 3988 or BN 52021 and incubated for 12 h. DNA binding was measured by specific ELISA. For NF-kB p65 siRNA effect, starved cells transfected with the siRNA were incubated for 24 h with and without 10 nM PAF. Cell proliferation was measured by DNA synthesis while expression of NF-kB p65 and PAFR protein was measured by Western blotting. In both studies, the effect of 10% FBS alone was used as the positive control. In general, PAF stimulated DNA binding which was inhibited by PAFR antagonists. siRNAs to NF-kB p65 and PAFR significantly attenuated cell proliferation compared to 10% FBS and PAF effect. Inclusion of PAF in siRNA-treated cells did not reverse inhibitory effect of NF-kB p65 siRNA on DNA synthesis. PAFR expression was inhibited in siRNA-treated cells. These data show that PAF-stimulation of PVSMC proliferation occurs via a PAFR-NF-kB p65 linked pathway.

Effect of sodium tanshinone IIA sulfonate treatment in a rat model of preeclampsia.

Preeclampsia is a disorder of pregnancy with a significant impact on maternal and fetal health. The complexity of this multifactorial condition has precluded development of effective therapies and, although many potential pathways have been investigated, the etiology still requires clarification. Our group has investigated the scavenger lectin-like oxidized LDL (LOX-1) receptor, which may respond to factors released from the distressed placenta that contribute to the vascular pathologies observed in preeclampsia. Given the known beneficial effects of sodium tanshinone IIA sulfonate (STS; a component of Salvia miltiorrhiza) on vasodilation, reduction of oxidative stress, and lipid profiles, we have investigated its role as a potential treatment strategy. We hypothesized that STS would improve vascular endothelial function and, combined with a reduction in oxidative stress, would improve pregnancy outcomes in a rat model of preeclampsia (reduced uteroplacental perfusion pressure, RUPP). We further hypothesized this may occur via the action of STS on the LOX-1 and/or platelet-activating factor (PAF) receptor axes. The RUPP model increased maternal blood pressure, vascular oxidative stress, and involvement of the vascular PAF receptor. Treatment with STS during pregnancy decreased both oxidative stress and involvement of the PAF receptor; however, it also increased involvement of the LOX-1 receptor, which is in line with the concept that scavenger receptors, such as LOX-1 and PAF, are upregulated in response to ligand binding and/or under pathological conditions. In this model of preeclampsia, however, the vascular actions of STS did not lead to improvements in pregnancy outcome such as fetal biometrics or maternal blood pressure.

Effect of PAF receptor antagonist on PGE2 content and COX-2 expression in gastric mucosa of young rats with endotoxemia / 解放军医学杂志

Objective To investigate the protective effect of prostaglandin E2 (PGE2), cyclooxygenase-2 (COX-2) and platelet activating factor (PAF) receptor antagonist on endotoxin-induced acute gastric mucosal injury in young rats. Methods Eighteen-day old Wistar rats were randomly divided into 4 groups: normal control group, model group (LPS group), PAF antagonist prevention group, and PAF antagonist treatment group. The model of endotoxemia in young rats was reproduced by intraperitoneal injection of endotoxin (5mg/kg of O55:B5 lipopolysaccharide). The rats in PAF prevention and treatment group received PAF antagonist BN52021 (Ginkgolide B, 5mg/kg) 0.5h before or after modeling. The rats in control group were given intraperitoneal injection of same amount of normal saline (1ml/kg). The animals were sacrificed 1.5, 3, 6, 24, 48 and 72h after intraperitoneal injection of endotoxin (8 in each group). The pathologic changes in gastric mucosa were observed after HE staining. The content of PGE2was measured by radioimmunoassay, the expression of COX-2 protein was determined by immunohistochemistry SP method, and the expression of COX-2 mRNA was assessed with RT-PCR method. Results Pathological changes in gastric mucosa were found to be edema of epithelial cells at 1.5h, and hyperemia and edema 3h after intraperitoneal injection of endotoxin in LPS group. The changes were most marked at 6h, including bleeding, karyorrhexis, pyknosis and apoptosis of epithelial cells of gastric mucosa. Exfoliation of the epithelium and neutrophil infiltration were observed at 24h, thinning of mucosa and a decrease in glands were observed at 48h, but no further changes were observed at 72h. However, all the above changes were significantly alleviated in prevention and treatment groups. The PGE2 content of gastric mucosa was lowered at 3h (P<0.05), and it was lowest at 6h (P<0.01) after endotoxin injection in LPS group, and significant difference was found between LPS group and control group. The PGE2 content of gastric mucosa was obviously increased at 3h and 6h in prevention group (P<0.05), and at 6h in treatment group (P<0.05). The differences at 6h were significant (P<0.01) among prevention group, treatment group and LPS group. No expression of COX-2 protein or mRNA was seen in gastric mucosal tissue of control group. In contrast with control group, cytoplasm COX-2 protein of gastric mucosal tissue was seen to express at 6h after endotoxin injection in LPS group, and it was obviously enhanced at 24, 48 and 72h (P<0.01), and the COX-2 mRNA level was also elevated. The expressions of COX-2 protein and mRNA were increased obviously at 6h in PAF antagonist prevention group and treatment group (P<0.01). The expressions of COX-2 protein at 6h and COX-2 mRNA at 24h were obviously elevated in prevention group and treatment group compared with those of LPS group (P<0.01). Conclusion PAF receptor antagonist may up-regulate the expression level of COX-2 protein and mRNA, increase PGE2 content, alleviate acute gastric mucosal injury, and promote the healing of gastric mucosal injury.

Effect of ginkgolide B on TLR4 and inflammatory protein expression in high glucose treated human umbilical vein endothelial cells / 中国药理学通报

Aim To investigate the effect of ginkgolide B on TLR4 expression in glucose-treated endothelial cells.Methods Human umbilical vein endothelial cells (HUVECs)were stimulated by high concentra-tion of glucose.TLR4,inflammatory protein expression and Akt phosphorylation were analyzed by Western blot.Transcription factor NF-κB nuclear translocation was analyzed by immunofluorescence.Results The expression of TLR4 and PAF receptor was increased in high glucose-treated HUVECs. In contrast, both ginkgolide B and CV3988 dose-dependently decreased TLR4 and PAF receptor expression in high glucose-treated cells,respectively.Ginkgolide B decreased in-flammatory protein ICAM-1 ,VCAM-1 expression.Mo-reover,ginkgolide B potently abolished Akt phospho-rylation and NF-κB p65 nuclear translocation.Conclu-sion Ginkgolide B can reduce TLR4,PAF receptor, ICAM-1 and VCAM-1 expression in high dose of glu-cose-treated HUVECs,the mechanism might be linked to inhibition of Akt phosphorylation and NF-κB activa-tion.

Phosphorylcholine and SpaA, a choline-binding protein, are involved in the adherence of Erysipelothrix rhusiopathiae to porcine endothelial cells, but this adherence is not mediated by the PAF receptor.

A crucial event in the initiation of many bacterial infections is the adherence of the bacteria to host cells, and bacterial surface structures and their interactions with host cell receptors play an important role in this process. Erysipelothrix rhusiopathiae is the causative agent of swine erysipelas, which may cause acute septicemia or chronic endocarditis and polyarthritis. To study the pathogenic mechanism of the widespread vascular disease observed in the acute form of swine erysipelas, we investigated the role of phosphorylcholine (PCho), a component of the E. rhusiopathiae capsule, in bacterial adherence to porcine endothelial cells (PECs) in vitro. We found that adherence of E. rhusiopathiae strain Fujisawa to PECs was twice that of adherence to control COS-7 cells and that the adherence rates of PCho-defective mutants were approximately 30-50% lower than those of the Fujisawa strain. The adherence of the Fujisawa strain to COS-7 cells transfected with the porcine platelet-activating factor receptor (PAFR) gene, which encodes a G protein-coupled receptor that has been shown to directly bind to Streptococcus pneumoniae via PCho in the bacterial cell wall, was not enhanced. Treatment with a PAFR antagonist (WEB-2086) did not inhibit bacterial adherence to PECs. Incubation of the bacterial cells with an antibody against PCho or SpaA, a choline-binding protein anchored to PCho of the Fujisawa strain, reduced the adherence of the strain to PECs. This effect was not observed when PCho-defective mutants were used. These results suggest that E. rhusiopathiae adheres to PECs via PCho and SpaA and that the PCho-mediated adherence is independent of PAFR.

Epidermal growth factor induces platelet-activating factor production through receptors transactivation and cytosolic phospholipase A2 in ovarian cancer cells.

BACKGROUND: Among the pro-inflammatory lipid mediators, platelet-activating factor (PAF) is a major primary and secondary messenger that binds to the PAF-receptor (PAFR). Epidermal growth factor (EGF) is a polypeptide growth factor that binds to the EGF-receptor (EGFR). Evidence suggests that both PAF and EGF play a significant role in oncogenic transformation, tumor growth, neoangiogenesis and metastasis, including ovarian cancer. PAF has the potential to transactivate EGFR in ovarian cancer cells. This study explores the mechanisms involved in EGF-induced PAF production. METHODS: The effect of EGF on PAF production in ovarian cancer cells was observed using enzyme-linked immunosorbent assay. The receptors transactivation and the role of cytosolic phospholipase A2 (cPLA2) in modulating PAF production induced by EGF was assessed using pharmacological inhibitors, si-RNA knockdown, targeted gene overexpression and immunocytochemistry. The signaling pathways invovled in PAF production induced by EGF in ovarian cancer cells were assessed. RESULTS: We demonstrate that EGF increases the production of PAF in CAOV3 and SKOV3 ovarian cancer cell lines. EGF induces the transactivation of PAFR, which can be blocked by an EGFR inhibitor. Inhibition of EGFR and/or PAFR blocks PAF production in response to EGF. EGF-induced PAF production involves the phosphorylation of extracellular-regulated protein kinase (ERK) and cytosolic phospholipase A2 (cPLA2). A cPLA2 inhibitor blocks EGF-induced PAF production as well as si-cPLA2, while overexpression of cPLA2 increases PAF production. CONCLUSIONS: These results indicate that EGF stimulates PAF production in ovarian cancer cells in a manner that requires cPLA2. We have also determined that crosstalk can occur bidirectionally between EGFR and PAFR, suggesting that EGF-induced PAF production could result in positive feedback that acts on the PAF-receptor to promote ovarian cancer progression.

Sickle erythrocytes and platelets augment lung leukotriene synthesis with downregulation of anti-inflammatory proteins: relevance in the pathology of the acute chest syndrome.

Initiation, progression, and resolution of vaso-occlusive pain episodes in sickle cell disease (SCD) have been recognized as reperfusion injury, which provokes an inflammatory response in the pulmonary circulation. Some 5-lipoxygenase (5-lox) metabolites are potent vasoconstrictors in the pulmonary circulation. We studied stimulation of production of the inflammatory eicosanoids leukotrienes (LTs) and prostaglandin E2 (PGE2) by isolated rat lungs perfused with sickle (HbSS) erythrocytes. Our hypothesis is that HbSS erythrocytes produce more LTs than normal (HbAA) erythrocytes, which can induce vaso-occlusive episodes in SCD patients. Lung perfusates were collected at specific time points and purified by high-pressure liquid chromatography, and LTC4 and PGE2 contents were measured by enzyme-linked immunosorbent assay (ELISA). Rat lung explants were also cultured with purified HbAA and HbSS peptides, and 5-lox, cyclooxygenase 1/2, and platelet-activating factor receptor (PAFR) proteins were measured by Western blotting, while prostacyclin and LTs produced by cultured lung explants were measured by ELISA. Lung weight gain and blood gas data were not different among the groups. HbSS-perfused lungs produced more LTC4 and PGE2 than HbAA-perfused lungs: 10.40 ± 0.62 versus 0.92 ± 0.2 ng/g dry lung weight (mean ± SEM; P = 0.0001) for LTC4. Inclusion of autologous platelets (platelet-rich plasma) elevated LTC4 production to 12.6 ± 0.96 and 7 ± 0.60 ng/g dry lung weight in HbSS and HbAA perfusates, respectively. HbSS lungs also expressed more 5-lox and PAFR. The data suggest that HbSS erythrocytes and activated platelets in patient's pulmonary microcirculation will enhance the synthesis and release of the proinflammatory mediators LTC4 and PGE2, both of which may contribute to onset of the acute chest syndrome in SCD.

Common mechanism in endothelin-3 and PAF receptor function for anti-inflammatory responses.

Platelet-activating factor (PAF) is a potent lipid mediator that is implicated in numerous inflammatory diseases. Under inflammatory conditions, PAF is biosynthesized through the remodelling pathway and elicits many inflammatory responses through binding to its specific PAF receptor. Endogenous bioactive endothelins (ETs: ET-1, -2, and -3) are also considered potent inflammatory mediators that play a critical role in many inflammatory diseases. In this perspective, we provide a brief overview of possible common mechanisms in ETs and PAF receptor function for inflammatory responses. Accumulating evidence strongly suggests that ET-3, but not ET-1 and ET-2, can attenuate PAF-induced inflammation through direct binding of the Tyr-Lys-Asp (YKD) region in the peptide to PAF and its metabolite/precursor lyso-PAF, followed by inhibition of binding between PAF and its receptor. Additionally, YKD sequence-containing peptides may be useful as a novel type of anti-inflammatory drugs targeting this mechanism. These findings should lead to new treatment strategies for numerous inflammatory diseases by targeting the common mechanism in ET and PAF receptor function.