Toll-like receptor 3 involvement in vascular function.

Maintaining endothelial cell (EC) and vascular smooth muscle cell (VSMC) integrity is an important component of human health and disease because both EC and VSMC regulate various functions, including vascular tone control, cellular adhesion, homeostasis and thrombosis regulation, proliferation, and vascular inflammation. Diverse stressors affect functions in both ECs and VSMCs and abnormalities of functions in these cells play a crucial role in cardiovascular disease initiation and progression. Toll-like receptors (TLRs) are important detectors of pathogen-associated molecular patterns derived from various microbes and viruses as well as damage-associated molecular patterns derived from damaged cells and perform innate immune responses. Among TLRs, several studies reveal that TLR3 plays a key role in initiation, development and/or protection of diseases, and an emerging body of evidence indicates that TLR3 presents components of the vasculature, including ECs and VSMCs, and plays a functional role. An agonist of TLR3, polyinosinic-polycytidylic acid [poly (I:C)], affects ECs, including cell death, inflammation, chemoattractant, adhesion, permeability, and hemostasis. Poly (I:C) also affects VSMCs including inflammation, proliferation, and modulation of vascular tone. Moreover, alterations of vascular function induced by certain molecules and/or interventions are exerted through TLR3 signaling. Hence, we present the association between TLR3 and vascular function according to the latest studies.

Prostaglandin E2 increases the expression of cyclooxygenase-2 in cultured rat microglia.

Prostaglandin E2 (PGE2) plays pivotal roles in controlling microglial activation with the EP2 receptor, a PGE2 receptor subtype. Activated microglia are often reported to increase cyclooxygenase (COX)-2 expression, followed by PGE2 production, but it is unclear whether extracellular PGE2 is involved in microglial PGE2 synthesis. In the present study, we report that PGE2 increases COX-2 protein in microglia. In a culture system, PGE2 at 10-6 M for 3 h increased COX-2 and microsomal PGE synthase (mPGES)-1 mRNA levels, and reduced mPGES-2, but did not affect COX-1 or cytosolic PGE synthase (cPGES) in microglia. PGE2 at 10-6 M for 3 h also increased the COX-2 protein level, but did not affect COX-1, mPGES-1, mPGES-2, or cPGES. An EP2 agonist, ONO-AE1-259-01, also increased COX-2 and mPGES-1 mRNA levels, and reduced mPGES-2, but did not affect COX-1 or cPGES, whereas an EP1 agonist, ONO-DI-004, an EP3 agonist, ONO-AE-248, and an EP4 agonist, ONO-AE1-329, had no effect. Similar to PGE2, ONO-AE1-259-01 increased the COX-2 protein level, but did not affect COX-1, mPGES-1, mPGES-2, or cPGES. In addition, the effects of PGE2 were inhibited by an EP2 antagonist, PF-04418948, but not by an EP1 antagonist, ONO-8713, an EP3 antagonist, ONO-AE3-240, or an EP4 antagonist, ONO-AE3-208, at 10-6 M. On the other hand, lipopolysaccharide (LPS) increased PGE2 production, but the LPS-induced PGE2 production was not affected by ONO-8713, PF-04418948, ONO-AE3-240, or ONO-AE3-208. These results indicate that PGE2 increases COX-2 protein in microglia through the EP2 receptor supporting the idea that extracellular PGE2 has a triggering aspect for microglial activation.

Gas Permeation Property of Silicon Carbide Membranes Synthesized by Counter-Diffusion Chemical Vapor Deposition.

An amorphous silicon carbide (SiC) membrane was synthesized by counter-diffusion chemical vapor deposition (CDCVD) using silacyclobutane (SCB) at 788 K. The SiC membrane on a Ni-γ-alumina (Al2O3) α-coated Al2O3 porous support possessed a H2 permeance of 1.2 × 10-7 mol·m-2·s-1·Pa-1 and an excellent H2/CO2 selectivity of 2600 at 673 K. The intermittent action of H2 reaction gas supply and vacuum inside porous support was very effective to supply source gas inside mesoporous intermediate layer. A SiC active layer was formed inside the Ni-γ-Al2O3 intermediate layer. The thermal expansion coefficient mismatch between the SiC active layer and Ni-γ-Al2O3-coated α-Al2O3 porous support was eased by the low decomposition temperature of the SiC source and the membrane structure.

Prostaglandin E2 potentiates interferon-γ-induced nitric oxide production in cultured rat microglia.

Prostaglandin E2 (PGE2 ) plays crucial roles in managing microglial activation through the prostanoid EP2 receptor, a PGE2 receptor subtype. In this study, we report that PGE2 enhances interferon-γ (IFN-γ)-induced nitric oxide production in microglia. IFN-γ increased the release of nitrite, a metabolite of nitric oxide, which was augmented by PGE2 , although PGE2 by itself slightly affects nitrite release. The potentiating effect of PGE2 was positively associated with increased expression of inducible nitric oxide synthase. In contrast to nitrite release induced by IFN-γ, lipopolysaccharide-induced nitrite release was not affected by PGE2 . An EP2 agonist, ONO-AE1-259-01 also augmented IFN-γ-induced nitrite release, while an EP1 agonist, ONO-DI-004, an EP3 agonist, ONO-AE-248, or an EP4 agonist, ONO-AE1-329, did not. In addition, the potentiating effect of PGE2 was inhibited by an EP2 antagonist, PF-04418948, but not by an EP1 antagonist, ONO-8713, an EP3 antagonist, ONO-AE3-240, or an EP4 antagonist, ONO-AE3-208, at 10-6  M. Among the EP agonists, ONO-AE1-259-01 alone was able to accumulate cyclic adenosine monophosphate (AMP), and among the EP antagonists, PF-04418948 was the only one able to inhibit PGE2 -increased intracellular cyclic AMP accumulation. On the other hand, IFN-γ promoted phosphorylation of signal transducer and activator of transcription 1, which was not affected by PGE2 . Furthermore, other prostanoid receptor agonists, PGD2 , PGF2α , iloprost, and U-46119, slightly affected IFN-γ-induced nitrite release. These results indicate that PGE2 potentiates IFN-γ-induced nitric oxide production in microglia through the EP2 receptor, which may shed light on one of the pro-inflammatory aspects of PGE2 .

Prostaglandin E2 induces apoptosis in cultured rat microglia.

Prostaglandin E2 (PGE2) plays a critical role in the modulation of microglial function including migration and phagocytosis through EP2, which increases intracellular cyclic adenosine monophosphate (AMP) concentration. In the present study, we found that PGE2 reduces cell viability in microglia. PGE2 decreased 3-(4,5-dimethylthiazol-2-thiazolyl)-2,5-diphenyltetrazolium bromide (MTT) reduction and increased lactate dehydrogenase release, deoxyribonucleic acid fragmentation, and poly(ADP-ribose) polymerase cleavage after 24h incubation, suggesting that PGE2 induces apoptosis in these cells. An EP2 agonist, butaprost, and an EP4 agonist, PGE1 alcohol, also induced apoptosis, while an EP1 agonist, 17-phenyl trinor PGE2, or an EP3 agonist, sulprostone, at 10(-6)M did not. On the other hand, EP1-EP4 antagonists, SC-51322, AH6809, L-798106, or GW627368X, up to 10(-5)M did not affect the decrease in MTT reduction by PGE2. Intracellular cyclic AMP accumulation was induced by butaprost, but not 17-phenyl trinor PGE2, sulprostone, or PGE1 alcohol at 10(-6)M. Additionally, we previously reported that PGE2-induced intracellular cyclic AMP accumulation was reversed by AH6809. Besides EP receptors, one of other targets was thought to be prostaglandin transporter, but its inhibitors, bromocresol green or U-46619 up to 10(-5)M did not affect the decrease in MTT reduction by PGE2. These results suggest that PGE2 induces apoptosis in microglia independent of intracellular cyclic AMP concentration, and there are different mechanisms between PGE2-induced apoptosis and the modulation of microglial function.

Prostaglandin E2 reduces amyloid beta-induced phagocytosis in cultured rat microglia.

Treatment with amyloid beta(1-42) (Abeta(1-42)) at 1microM for 60min increased phagocytosis of latex beads by cultured rat microglia. This increase was reduced dose-dependently by prostaglandin E(2) (PGE(2)), but PGD(2), PGF(2alpha), iloprost, or U-46619 had no effects. PGE(2) also reduced the phagocytosis of fluorescent-labeled Abeta(1-42). Abeta(1-42)-induced phagocytosis was reduced by butaprost but not by 17-phenyl trinor PGE(2), sulprostone, or PGE(1) alcohol. The reduction effect of PGE(2) on phagocytosis was reversed by AH6809, an E-prostanoid receptor 2 (EP2) antagonist, which inhibited cyclic adenosine monophosphate (AMP) accumulation induced by PGE(2). Butaprost, but not 17-phenyl trinor PGE(2), sulprostone, or PGE(1) alcohol increased intracellular cyclic AMP accumulation. In western blotting analysis, EP2-like immunoreactivity was detected in the crude membrane fraction of microglia. On the other hand, Abeta(1-42)-induced phagocytosis was not affected by SC-560, a cyclooxygenase-1 (COX-1) inhibitor, NS-398, a COX-2 inhibitor, or ibuprofen, a non-specific COX inhibitor. Abeta(1-42) or PGE(2) had little effect on the expression levels of COX-1 or COX-2. These results indicate that Abeta(1-42)-induced microglial phagocytosis is reduced by PGE(2) through EP2.

Prostaglandin E2 reduces extracellular ATP-induced migration in cultured rat microglia.

Treatment with 100 microM adenosine triphosphate (ATP) for 120 min augmented migration of cultured rat microglia by about 4-fold. This augmentation was effectively reduced by 0.1-10 microM prostaglandin E(2) (PGE(2)). PGE(2)-mediated reduction was reversed by the EP2 antagonist AH6809 at 10 microM. The EP2 agonist butaprost also reduced ATP-induced migration at 10 microM, whereas the EP1 agonist 17-phenyl trinor PGE(2), the EP3 agonist sulprostone, and the EP4 agonist PGE(1) alcohol all had no effect at 10 microM. In addition, ATP-induced migration was reduced by the adenylate cyclase activator forskolin at 100 microM, whereas the adenylate cyclase inhibitor SQ22536 reversed the effect of PGE(2) on ATP-induced migration at 100 microM. Over the same experimental duration, PGE(2), butaprost, and forskolin had little effect on cell viability. These findings indicate that ATP-induced microglial migration is reduced by PGE(2) through EP2 and adenylate cyclase.

Topics on the Na+/Ca2+ exchanger: responses of Na+/Ca2+ exchanger to interferon-gamma and nitric oxide in cultured microglia.

The Na(+)/Ca(2+) exchanger (NCX) plays a role in regulation of intracellular Ca(2+) levels, but little is known about the functional role of NCX in microglia. To clarify the role of NCX in microglia, we studied the responses of NCX to pathological conditions such as interferon-gamma or nitric oxide (NO) exposure. Treatment with interferon-gamma caused a biphasic increase in NCX activity. The delayed increase in NCX activity was accompanied by increases in the mRNA and protein levels. Pharmacological studies show that protein kinase C and tyrosine kinase are involved in the transient and delayed increases in NCX activity, and the extracellular signal-regulated protein kinase is involved in the delayed increase in NCX activity. On the other hand, NO causes apoptotic cell death in cultured microglia. We observed, using the specific NCX inhibitor SEA0400, that NO activates NCX activity and NCX is involved in NO-induced depletion of Ca(2+) in the endoplasmic reticulum (ER), leading to ER stress. These results suggest that NCX is involved in the regulation of Ca(2+) levels in the ER. The responses of NCX to interferon-gamma and NO implies that NCX plays a key role in microglial function.

Lipopolysaccharide sensitizes microglia toward Ca(2+)-induced cell death: mode of cell death shifts from apoptosis to necrosis.

Little is known about the effect of microglial activation on cell death. This study examines the effects of lipopolysaccharide (LPS) and interferon-gamma (IFN-gamma), triggers of microglial activation, on cell death induced by several agents in cultured rat microglia. For comparison, the effect of LPS on cell death is also examined in cultured astrocytes. LPS or IFN-gamma enhanced cell death induced by thapsigargin or ionomycin, an agent that increases intracellular Ca2+ concentration, although LPS or IFN-gamma alone did not affect cell viability. Thapsigargin or ionomycin induced apoptosis in LPS-untreated microglia, while they induced necrosis in LPS-treated microglia, which were partially reversed by O,O'-bis(2-aminophenyl)ethyleneglycol-N,N,N',N'-tetraacetic acid tetraacetoxymethyl ester (BAPTA-AM, an intracellular Ca2+ chelator). In contrast, LPS treatment did not affect tunicamycin- or staurosporine-induced apoptosis, while it inhibited S-nitroso-N-acetylpenicillamine-induced apoptosis. The effect of LPS on thapsigargin or ionomycin-induced apoptosis was not observed in astrocytes. These results indicate that microglial activation sensitizes the cells toward cell death induced by the change in intracellular Ca2+ concentration and shifts the mode of cell death from apoptosis to necrosis.

SEA0400, a specific inhibitor of the Na+-Ca2+ exchanger, attenuates sodium nitroprusside-induced apoptosis in cultured rat microglia.

1. Using SEA0400, a potent and selective inhibitor of the Na+-Ca2+ exchanger (NCX), we examined whether NCX is involved in nitric oxide (NO)-induced disturbance of endoplasmic reticulum (ER) Ca2+ homeostasis followed by apoptosis in cultured rat microglia. 2. Sodium nitroprusside (SNP), an NO donor, decreased cell viability in a dose- and time-dependent manner with apoptotic cell death in cultured microglia. 3. Treatment with SNP decreased the ER Ca2+ levels as evaluated by measuring the increase in cytosolic Ca2+ level induced by exposing cells to thapsigargin, an irreversible inhibitor of ER Ca2+-ATPase. 4. The treatment with SNP also increased mRNA expression of CHOP and GPR78, makers of ER stress. 5. SEA0400 at 0.3-1.0 microM protected microglia against SNP-induced apoptosis. 6. SEA0400 blocked not only the SNP-induced decrease in ER Ca2+ levels but also SNP-induced increase in CHOP and GRP78 mRNAs. 7. SEA0400 did not affect capacitative Ca2+ entry in the presence and absence of SNP. 8. SNP increased Na+-dependent 45Ca2+ uptake and this increase was blocked by SEA0400. 9. These results suggest that SNP induces apoptosis via the ER stress pathway and SEA0400 attenuates SNP-induced apoptosis via suppression of the ER stress in cultured microglia. Our findings imply that NCX plays a role in ER Ca2+ depletion under pathological conditions.

Up-regulation of Na(+)-Ca2+ exchange activity by interferon-gamma in cultured rat microglia.

The Na(+)-Ca2+ exchanger (NCX) plays a role in regulating intracellular Ca2+ concentration, but little is known about NCX in microglia. We examined mRNA expression of NCX isoforms in cultured rat microglia and the effect of interferon-gamma (IFN-gamma) on NCX activity. RT-PCR showed that all of the known NCX isoforms, NCX1-3, are expressed in cultured microglia. Ouabain and monensin increased 45Ca2+ uptake and intracellular Ca2+ concentration in microglia, suggesting the presence of NCX activity in the reverse mode. Treatment with IFN-gamma (100 U/mL) caused a biphasic increase in NCX activity. The transient increase in NCX activity by IFN-gamma for 1 h was blocked by the protein kinase C (PKC) inhibitors, staurosporine and GF109203X, and the tyrosine kinase inhibitor, herbimycin A. The delayed increase in NCX activity by IFN-gamma for 24 h was blocked by the protein synthesis inhibitor cycloheximide and actinomycin D. Treatment with IFN-gamma for 24 h increased NCX mRNA and protein levels. The increase in NCX activity and NCX protein by IFN-gamma for 24 h was blocked by staurosporine, GF109203X, herbimycin A and the extracellular signal-regulated kinase inhibitor, PD98059. These findings suggest that NCX is up-regulated by IFN-gamma in a biphasic manner in microglia. Moreover, PKC and tyrosine kinase are involved in the up-regulation of NCX and the extracellular signal-regulated protein kinase is also involved in the delayed increase in NCX activity.