Prostaglandin endoperoxide synthase-2 contributes to the endothelin/sarafotoxin-induced prostaglandin E2 synthesis in mouse osteoblastic cells (MC3T3-E1): evidence for a protein tyrosine kinase-signaling pathway and involvement of protein kinase C

Phospholipase D1 activity is crucial for cytosolic phospholipase A2 -dependent prostaglandin E2 formation in murine osteoblastic MC3T3-E1 cells

In bone, prostaglandin E2 (PGE2) is highly osteogenic and formed by osteoblasts, a key modulatory event in the regulation of bone cell activity. MC3T3-E1 cells are widely used as an in vitro model of osteoblast function. It is still not clear which pathways contribute to the release of AA in these cells. In this study we have focussed on the contribution of phospholipase D (PLD) enzymes to osteoblastic PGE2 formation after stimulation with endothelin-1 (ET-1). Using specific inhibitors of PLD1 and PLD2 we could show that PGE2 formation was strictly dependent on PLD1 but not PLD2 activity and cytosolic phospholipase A2 (cPLA2) was activated by triggering through PLD1. We have identified diacyl glycerol (DAG) as a possible effector molecule which may serve as a triggering signal for PKC activation and subsequent cPLA2 phosphorylation.

Ionomycin induces prostaglandin E2 formation in murine osteoblastic MC3T3-E1 cells via mechanisms independent of its ionophoric nature

Ionomycin and A23187 are divalent cation ionophores with a marked preference for calcium. Studies using these ionophores have almost exclusively interpreted their results in the light of calcium elevation. It was the aim of this study to investigate the effects of ionomycin in osteoblatic MC3T3-E1 cells that are not attributable to its ionophoric properties. Thus, we have found that in contrast to A23187, ionomycin shows similar effects on prostaglandin E2 formation as bradykinin and endothelin-1, being potentiated by extracellular nickel and inhibited by cholera toxin and pertussis toxin. Our data strongly suggest that inomycin, at least in part, exerts its effects via specific binding to a G-protein coupled receptor, thereby evoking downstream cellular events like arachidonate release with subsequent prostaglandin formation.

Potentiation of endothelin-1-induced prostaglandin E2 formation by Ni(2+) and Sr(2+) in murine osteoblastic MC3T3-E1 cells

Cation recognition mechanisms beyond calcium-sensing receptors are still largely unexplored and consequently there is surprisingly little information on linking of this primary event to key metabolic features of different cell systems, such as arachidonic acid metabolism. However, information on the modulatory role of extracellular cations in cellular function is scarce. In this study we have demonstrated, that Ni(2+) and Sr(2+) potentiate endothelin-1 induced prostaglandin E2 formation in the osteoblastic cell line, MC3T3-E1, even in the absence of extracellular calcium. The effect is strictly dependent of receptor-mediated signal transduction processes evoked by endothelin-1 and arachidonate release involves cytosolic phospholipase A2 activity. The ligation sites, at least for Ni(2+) are extracellular. The data suggest a novel activation mechanism for arachidonate release and subsequent prostaglandin formation that does not require calcium.

15-Deoxy-Δ12,14-prostaglandin J2 induces Cox-2 expression in human osteosarcoma cells through MAPK and EGFR activation involving reactive oxygen species

Prostaglandins (PGs), important modulators in bone biology, may also contribute to tumor formation and progression in human osteosarcoma. 15-Deoxy-Δ(12,14)-PGJ(2) (15d-PGJ(2)), a metabolite of PGD(2) and PPARγ-ligand, exerts a panel of biological activities via receptor-dependent and -independent mechanisms. As inducible cyclooxygenase-2 (Cox-2) is a candidate inflammatory marker in human osteosarcoma and a rate-limiting enzyme in PG biosynthesis, this study aimed at investigating intracellular redox status and signaling cascades leading to Cox-2 induction in human MG-63 osteosarcoma cells. 15d-PGJ(2) induced the accumulation of reactive oxygen species (ROS) that in turn may lead to upregulation of Cox-2 via two different routes in a PPARγ-independent manner. First, phosphorylation of p38 MAPK directly enhances Cox-2 expression by promoting mRNA stability. Second, 15d-PGJ(2) induces activation of epidermal growth factor receptors and downstream activation of Cox-2 via phosphorylation of p42/44 MAPK. Glutathione precursor molecules reversed enhanced ROS levels and Cox-2 expression. Functional activity of Cox-2 expression was tested by measurement of PGE(2) and PGF(2α). The synthetic compound 9,10-dihydro-15d-PGJ(2) lacking the α,β-unsaturated carbonyl group in the cyclopentenone ring did not exhibit the cellular responses observed with 15d-PGJ(2). We conclude that the electrophilic carbon atom of 15d-PGJ(2) is responsible for alterations in intracellular redox status and Cox-2 expression.

From raw materials to validated system: the construction of a genomic library and microarray to interpret systemic perturbations in Northern bobwhite

The limited availability of genomic tools and data for nonmodel species impedes computational and systems biology approaches in nonmodel organisms. Here we describe the development, functional annotation, and utilization of genomic tools for the avian wildlife species Northern bobwhite (Colinus virginianus) to determine the molecular impacts of exposure to 2,6-dinitrotoluene (2,6-DNT), a field contaminant of military concern. Massively parallel pyrosequencing of a normalized multitissue library of Northern bobwhite cDNAs yielded 71,384 unique transcripts that were annotated with gene ontology (GO), pathway information, and protein domain analysis. Comparative genome analyses with model organisms revealed functional homologies in 8,825 unique Northern bobwhite genes that are orthologous to 48% of Gallus gallus protein-coding genes. Pathway analysis and GO enrichment of genes differentially expressed in livers of birds exposed for 60 days (d) to 10 and 60 mg/kg/d 2,6-DNT revealed several impacts validated by RT-qPCR including: prostaglandin pathway-mediated inflammation, increased expression of a heme synthesis pathway in response to anemia, and a shift in energy metabolism toward protein catabolism via inhibition of control points for glucose and lipid metabolic pathways, PCK1 and PPARGC1, respectively. This research effort provides the first comprehensive annotated gene library for Northern bobwhite. Transcript expression analysis provided insights into the metabolic perturbations underlying several observed toxicological phenotypes in a 2,6-DNT exposure case study. Furthermore, the systemic impact of dinitrotoluenes on liver function appears conserved across species as PPAR signaling is similarly affected in fathead minnow liver tissue after exposure to 2,4-DNT.

Involvement of Rho and p38 MAPK in endothelin-1-induced expression of PGHS-2 mRNA in osteoblast-like cells

Prostaglandins (PGs) play an important role in bone remodeling because eicosanoids are local mediators of bone metabolism, which can induce physiological and pathological responses of bone tissue. Biosynthesis of PGs is catalyzed by constitutively expressed PG endoperoxide G/H synthase (PGHS) 1 and by the inducible isoform PGHS-2. In MC3T3-E1 osteoblast-like cells, expression of PGHS-2 was shown by mechanical forces, cytokines, growth factors, and hormones. Recently, endothelin (ET) 1-stimulated PGHS-2 mRNA expression was described, leading to a burst in prostaglandin E2 (PGE2) production. In this study, we investigated ET-1-induced signal transduction pathway(s) involved in the PGHS-2 mRNA production. Time course of PGHS-2 mRNA expression reaching the maximum within 45 minutes is in good agreement with the concept of an immediate early gene product. Inhibition of phospholipase C (PLC), phospholipase D (PLD), phosphatidylinositol-3 kinase (PI-3-kinase), and protein kinase C (PKC) had no influence on PGHS-2 synthesis. Using specific blockers of tyrosine kinases indicated involvement of p38 MAPK but not p42/44 MAPK. By preloading cells with exoenzyme C3, we were able to show requirement of the Rho family of G proteins for p38 MAPK phosphorylation and PGHS-2 mRNA synthesis, whereas pertussis toxin (PTX) and cholera toxin (CTX) had no remarkable effect.

Cerebrovascular inflammation following subarachnoid hemorrhage

Aneurysmal subarachnoid hemorrhage frequently results in complications including intracranial hypertension, rebleeding and vasospasm. The extravasated blood is responsible for a cascade of reactions involving release of various vasoactive and pro-inflammatory factors (several of which are purported to induce vasospasm) from blood and vascular components in the subarachnoid space. The authors review the available evidence linking these factors to the development of inflammatory lesions of the cerebral vasculature, emphasizing: 1) neurogenic inflammation due to massive release of sensory nerve neuropeptides; 2) hemoglobin from lysed erythrocytes, which creates functional lesions of endothelial and smooth muscle cells; 3) activity, expression and metabolites of lipoxygenases cyclooxygenases and nitric oxide synthases; 4) the possible role of endothelin-1 as a pro-inflammatory agent; 5) serotonin, histamine and bradykinin which are especially involved in blood-brain barrier disruption; 6) the prothrombotic and pro-inflammatory action of complement and thrombin towards endothelium; 7) the multiple actions of activated platelets, including platelet-derived growth factor production; 8) the presence of perivascular and intramural macrophages and granulocytes and their interaction with adhesion molecules; 9) the evolution, origins, and effects of pro-inflammatory cytokines, especially IL-1, TNF-alpha and IL-6. Human and animal studies on the use of anti-inflammatory agents in subarachnoid hemorrhage include superoxide and other radical scavengers, lipid peroxidation inhibitors, iron chelators, NSAIDs, glucocorticoids, and serine protease inhibitors. Many animal studies claim reduced vasospasm, but these effects are not always confirmed in human trials, where symptomatic vasospasm and outcome are the major endpoints. Despite recent work on penetrating vessel constriction, there is a paucity of studies on inflammatory markers in the microcirculation.

Overexpression of cyclooxygenase-2 in rabbit basilar artery endothelial cells after subarachnoid hemorrhage

OBJECTIVE

We investigated the expression in rabbit basilar arteries of cyclooxygenase (COX)-2, which is the inducible isoform of the enzyme of prostaglandin (PG) production, and the concentrations of the proinflammatory cytokine tumor necrosis factor alpha (TNFalpha) and representative PGs in the cerebrospinal fluid (CSF) after experimental subarachnoid hemorrhage (SAH).

METHODS

Seven sets of basilar arteries were removed from control rabbits and from rabbits killed 1 and 3 days after induced SAH. The arteries were subjected to identical simultaneous immunolabeling for examination with a confocal microscope. One-half of each artery was stained for the constitutive form COX-1 and the other half for COX-2. CSF was sampled in control animals and at 6 hours, 1 day, and 3 days for assays of TNFalpha, PGE2, and 6-keto-PGF1 (metabolite of PGI2).

RESULTS

COX-1 immunoreactivity in the endothelial layer was similar in the three groups. Weak endothelial COX-2 immunoreactivity was found in arteries of control animals. COX-2 staining was higher in the group killed at 3 days compared with the control group (P < 0.05). The levels of PGE2 and 6-keto-PGF1alpha in the CSF peaked significantly at 6 hours, then decreased at 3 days to the basal level (PGE2) or significantly lower (6-keto-PGF1). TNFalpha was undetectable in control CSF, significantly higher (P < 0.001) at 6 hours, and undetectable at 3 days.

CONCLUSION

After SAH, endothelial COX-1 immunoreactivity does not change, whereas overexpression of COX-2 occurs at 3 days. This induction does not seem linked to TNFalpha production, nor is it responsible for early raised levels of PGE2 and PGI2 in the CSF. We suggest that the role of induced COX-2 may be to modify gene expression and hence alter the properties of the vessel wall after SAH.

Effect of the aminosteroid U73122 on prostaglandin E(2) production in a murine clonal osteoblast-like cell line, MC3T3-E1

Prostaglandin E(2) production stimulated by various agents (arachidonic acid, prostaglandin F(2alpha), ionomycin, the calcium ionophore A23187, and melittin) was investigated after pretreatment of murine osteoblast-like MC3T3-E1 cells with the putative phospholipase C blocker, U73122. The aminosteroid dose dependently inhibited prostaglandin E(2) production induced by all agonists, except arachidonic acid. The results suggest an inhibitory role of U73122 on phospholipase A(2) activity or activation.