Enhanced airway smooth muscle cell thromboxane receptor signaling via activation of JNK MAPK and extracellular calcium influx

Cyclosporin A up-regulated thromboxane A2 receptor through activation of MAPK and NF-κB pathways in rat mesenteric artery

Cyclosporin A (CsA) is an immunosuppressant used in transplantation patients and inflammatory diseases. CsA-induced local vasoconstriction can lead to serious side effects including nephrotoxicity and hypertension. However, the underlying mechanisms are not fully understood. Mesenteric artery rings of rats were cultured with CsA and specific inhibitors for mitogen-activating protein kinases (MAPK) and nuclear factor-κB (NF-κB) signaling pathways. A sensitive myograph recorded thromboxane (TP) receptor-mediated vasoconstriction. Protein levels of key signaling molecules were assessed by Western blotting. The results show that CsA up-regulated the TP receptor expression with the enhanced vasoconstriction in a dose- and time-dependent manner. Furthermore, the blockage of MAPKs or NF-κB activation markedly attenuated CsA-enhanced vasoconstriction and the TP receptor protein expression. Rats subcutaneously injected with CsA for three weeks showed increased blood pressure in vivo and increased contractile responses to a TP agonist ex vivo. CsA also enhanced TP receptor, as well as p-ERK1/2, p-p38, p- IκBα, p-NF-κB P65 protein levels and decreased IκBα protein expression, demonstrating that CsA induced TP receptor enhanced-vasoconstriction via activation of MAPK and NF-κB pathways. In conclusion, CsA up-regulated the expression of TP receptors via activation of MAPK and NF-κB pathways. The results may provide novel options for prevention of CsA-associated hypertension.

PM2.5 causes vascular hyperreactivity through the upregulation of the thromboxane A2 receptor and activation of MAPK pathways

Airborne fine particulate matter (PM_2.5) is a major cardiovascular disease environmental risk factor. However, the underlying mechanism of action is not fully understood. Thromboxane is widely known as an important vasoconstrictor substance that binds to G-protein-coupled receptors (GPCR) in arteries and is involved in various cardiovascular diseases. This study examined the effect of PM_2.5 on thromboxane A₂ receptor (TP) in the mesenteric arteries and the underlying intracellular signal mechanisms (by focusing on the mitogen-activated protein kinase (MAPK) pathway). Rat mesenteric artery segments were exposed to PM_2.5 in the presence of MAPK pathway inhibitors. The contractile reactivity of mesenteric arteries was analyzed using wire myography. The mRNA and protein expression of TP receptor and MAPK pathway molecules were detected by real-time PCR and Western blot. Mesenteric artery receptor localization was assessed by immunohistochemistry. The results showed that TP receptor-mediated maximum contraction response was achieved after exposing arteries to 1.0 μg/mL PM_2.5 for 16 h (Emax: 228 ± 16% of K⁺). Moreover, inhibitor U0126 (ERK1/2 inhibitor), SB203580 (p38 inhibitor), and SP600125 (JNK inhibitor) depressed the increased TP receptor-mediated contractile responses (reduced rage were 17.9 ~ 59.6%). These inhibitors also decreased the increased mRNA expression and protein of the TP receptor induced by PM_2.5 (reduced by more than 50% and 46%, respectively). The immunoreactivity of increased TP receptor expression was primarily localized in the cytoplasm. In addition, phosphorylation quantitative analysis showed that in the presence of MAPK inhibitors, the PM_2.5-induced phosphorylation of ERK1/2, p38, and JNK protein increased by more than 30.0 ~ 130.3%. These results suggest that PM_2.5 upregulates the TP receptor of rat mesenteric arteries through activation of the ERK1/2, p38, and JNK MAPK pathways.

The Biology of Prostaglandins and Their Role as a Target for Allergic Airway Disease Therapy

Prostaglandins (PGs) are a family of lipid compounds that are derived from arachidonic acid via the cyclooxygenase pathway, and consist of PGD₂, PGI₂, PGE₂, PGF₂, and thromboxane B₂. PGs signal through G-protein coupled receptors, and individual PGs affect allergic inflammation through different mechanisms according to the receptors with which they are associated. In this review article, we have focused on the metabolism of the cyclooxygenase pathway, and the distinct biological effect of each PG type on various cell types involved in allergic airway diseases, including asthma, allergic rhinitis, nasal polyposis, and aspirin-exacerbated respiratory disease.

Airborne fine particulate matter causes murine bronchial hyperreactivity via MAPK pathway-mediated M3 muscarinic receptor upregulation

Regarding the human health effects, airborne fine particulate matter 2.5 (PM_2.5 ) is an important environmental risk factor. However, the underlying molecular mechanisms are largely unknown. The present study examined the hypothesis that PM_2.5 causes bronchial hyperreactivity by upregulated muscarinic receptors via the mitogen-activated protein kinase (MAPK) pathway. The isolated rat bronchi segments were cultured with different concentration of PM_2.5 for different time. The contractile response of the bronchi segments were recorded by a sensitive myograph. The mRNA and protein expression levels of M₃ muscarinic receptors were studied by quantitative real-time PCR and immunohistochemistry, respectively. The muscarinic receptors agonist, carbachol induced a remarkable contractile response on fresh and DMSO cultured bronchial segments. Compared with the fresh or DMSO culture groups, 1.0 µg/mL of PM_2.5 cultured for 24 h significantly enhanced muscarinic receptor-mediated contractile responses in bronchi with a markedly increased maximal contraction. In addition, the expression levels of mRNA and protein for M₃ muscarinic receptors in bronchi of PM_2.5 group were higher than that of fresh or DMSO culture groups. SB203580 (p38 inhibitor) and U0126 (MEK1/2 inhibitor) significantly inhibited the PM_2.5 -induced enhanced contraction and increased mRNA and protein expression of muscarinic receptors. However, JNK inhibitor SP600125 had no effect on PM_2.5 -induced muscarinic receptor upregulation and bronchial hyperreactivity. In conclusion, airborne PM_2.5 upregulates muscarinic receptors, which causes subsequently bronchial hyperreactivity shown as enhanced contractility in bronchi. This process may be mediated by p38 and MEK1/2 MAPK pathways. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 371-381, 2017.

Airborne fine particulate matter induces an upregulation of endothelin receptors on rat bronchi

Airborne fine particulate matter (PM2.5) is a risk factor for respiratory diseases. However, little is known about the effects of PM2.5 on bronchi. The present study investigated the effect of airborne PM2.5 on rat bronchi and the underlying mechanisms. Isolated rat bronchial segments were cultured for 24 h. Endothelin (ET) receptor-mediated contractile responses were recorded using a wire myograph. The mRNA and protein expression levels of ET receptors were studied using quantitative real-time PCR, Western blotting, and immunohistochemistry. The results demonstrated that ETA and ETB receptor agonists induced remarkable contractile responses on fresh and cultured bronchial segments. PM2.5 (1.0 or 3.0 μg/ml) significantly enhanced ETA and ETB receptor-mediated contractile responses in bronchi with a markedly increased maximal contraction compared to the DMSO or fresh groups. PM2.5 increased the mRNA and protein expression levels of ETA and ETB receptors. U0126 (a MEK1/2 inhibitor) and SB203580 (a p38 inhibitor) significantly suppressed PM2.5-induced increases in ETB receptor-mediated contractile responses, mRNA and protein levels. SP600125 (a JNK inhibitor) and SB203580 significantly abrogated the PM2.5-induced enhancement of ETA receptor-mediated contraction and receptor expression. In conclusion, PM2.5 upregulates ET receptors in bronchi. ETB receptor upregulation is associated with MEK1/2 and p38 pathways, and the upregulation of ETA receptor is involved in JNK and p38 pathways.

Thromboxane A2 Receptor Inhibition Suppresses Multiple Myeloma Cell Proliferation by Inducing p38/c-Jun N-terminal Kinase (JNK) Mitogen-activated Protein Kinase (MAPK)-mediated G2/M Progression Delay and Cell Apoptosis

Multiple myeloma (MM) is a plasma cell malignancy without effective therapeutics. Thromboxane A2 (TxA2)/TxA2 receptor (T prostanoid receptor (TP)) modulates the progression of some carcinomas; however, its effects on MM cell proliferation remain unclear. In this study, we evaluated cyclooxygenase (COX) enzymes and downstream prostaglandin profiles in human myeloma cell lines RPMI-8226 and U-266 and analyzed the effects of COX-1/-2 inhibitors SC-560 and NS-398 on MM cell proliferation. Our observations implicate COX-2 as being involved in modulating cell proliferation. We further incubated MM cells with prostaglandin receptor antagonists or agonists and found that only the TP antagonist, SQ29548, suppressed MM cell proliferation. TP silencing and the TP agonist, U46619, further confirmed this finding. Moreover, SQ29548 and TP silencing promoted MM cell G2/M phase delay accompanied by reducing cyclin B1/cyclin-dependent kinase-1 (CDK1) mRNA and protein expression. Notably, cyclin B1 overexpression rescued MM cells from G2/M arrest. We also found that the TP agonist activated JNK and p38 MAPK phosphorylation, and inhibitors of JNK and p38 MAPK depressed U46619-induced proliferation and cyclin B1/CDK1 protein expression. In addition, SQ29548 and TP silencing led to the MM cell apoptotic rate increasing with improving caspase 3 activity. The knockdown of caspase 3 reversed the apoptotic rate. Taken together, our results suggest that TxA2/TP promotes MM cell proliferation by reducing cell delay at G2/M phase via elevating p38 MAPK/JNK-mediated cyclin B1/CDK1 expression and hindering cell apoptosis. The TP inhibitor has potential as a novel agent to target kinase cascades for MM therapy.

Prenatal development is linked to bronchial reactivity: epidemiological and animal model evidence

Chronic cardiorespiratory disease is associated with low birthweight suggesting the importance of the developmental environment. Prenatal factors affecting fetal growth are believed important, but the underlying mechanisms are unknown. The influence of developmental programming on bronchial hyperreactivity is investigated in an animal model and evidence for comparable associations is sought in humans. Pregnant Wistar rats were fed either control or protein-restricted diets throughout pregnancy. Bronchoconstrictor responses were recorded from offspring bronchial segments. Morphometric analysis of paraffin-embedded lung sections was conducted. In a human mother-child cohort ultrasound measurements of fetal growth were related to bronchial hyperreactivity, measured at age six years using methacholine. Protein-restricted rats' offspring demonstrated greater bronchoconstriction than controls. Airway structure was not altered. Children with lesser abdominal circumference growth during 11–19 weeks' gestation had greater bronchial hyperreactivity than those with more rapid abdominal growth. Imbalanced maternal nutrition during pregnancy results in offspring bronchial hyperreactivity. Prenatal environmental influences might play a comparable role in humans.

KCNQ (Kv7) potassium channel activators as bronchodilators: combination with a β2-adrenergic agonist enhances relaxation of rat airways

KCNQ (Kv7 family) potassium (K(+)) channels were recently found in airway smooth muscle cells (ASMCs) from rodent and human bronchioles. In the present study, we evaluated expression of KCNQ channels and their role in constriction/relaxation of rat airways. Real-time RT-PCR analysis revealed expression of KCNQ4 > KCNQ5 > KCNQ1 > KCNQ2 > KCNQ3, and patch-clamp electrophysiology detected KCNQ currents in rat ASMCs. In precision-cut lung slices, the KCNQ channel activator retigabine induced a concentration-dependent relaxation of small bronchioles preconstricted with methacholine (MeCh; EC50 = 3.6 ± 0.3 μM). Bronchoconstriction was also attenuated in the presence of two other structurally unrelated KCNQ channel activators: zinc pyrithione (ZnPyr; 1 μM; 22 ± 7%) and 2,5-dimethylcelecoxib (10 μM; 24 ± 8%). The same three KCNQ channel activators increased KCNQ currents in ASMCs by two- to threefold. The bronchorelaxant effects of retigabine and ZnPyr were prevented by inclusion of the KCNQ channel blocker XE991. A long-acting β2-adrenergic receptor agonist, formoterol (10 nM), did not increase KCNQ current amplitude in ASMCs, but formoterol (1-1,000 nM) did induce a time- and concentration-dependent relaxation of rat airways, with a notable desensitization during a 30-min treatment or with repetitive treatments. Coadministration of retigabine (10 μM) with formoterol produced a greater peak and sustained reduction of MeCh-induced bronchoconstriction and reduced the apparent desensitization observed with formoterol alone. Our findings support a role for KCNQ K(+) channels in the regulation of airway diameter. A combination of a β2-adrenergic receptor agonist with a KCNQ channel activator may improve bronchodilator therapy.

Secondhand smoke exposure causes bronchial hyperreactivity via transcriptionally upregulated endothelin and 5-hydroxytryptamine 2A receptors

BACKGROUND

Cigarette smoke exposure is strongly associated with airway hyperreactivity (AHR) which is the main characteristic seen in asthma. The intracellular MAPK signaling pathways are suggested to be associated with the airway damage to the AHR. In the present study, we hypothesize that secondhand cigarette smoke (SHS) exposure upregulates the bronchial contractile receptors via activation of the Raf/ERK/MAPK pathway.

METHODOLOGY/PRINCIPAL FINDINGS

Rats were exposed to SHS for 3 h daily for up to 8 weeks. The receptor agonists-induced bronchial contractile reactivity was analyzed with a sensitive myograph system. The mRNA transcription and protein translation of the target receptors and the kinases in Raf/ERK/MAPK pathway were investigated by real-time PCR, Western blotting and immunofluorescence, respectively. Compared with exposure to fresh air, SHS induced enhanced bronchial contractile responses mediated by the 5-hydroxytryptamine 2A (5-HT(2A)) receptors as well as the endothelin type B (ET(B)) and type A (ET(A)) receptors. The response curves were shifted toward the left with an increased maximal contraction (E(max)) demonstrating that SHS induced AHR. Additionally, the mRNA and protein levels of the 5-HT(2A), ET(B) and ET(A) receptors were increased. Furthermore, SHS exposure increased the phosphorylation of Raf-1 and ERK1/2, but it did not alter p38 or JNK. A Raf-1 inhibitor (GW5074) suppressed the SHS-induced increase in the expression of 5-HT(2A) and ET(A) receptors and the receptor-mediated AHR.

CONCLUSIONS/SIGNIFICANCE

Our findings show that SHS exposure induces transcriptional upregulation of the 5-HT(2A), ET(B) and ET(A) receptors in rat bronchial smooth muscle cells, which mediates AHR. The Raf/ERK/MAPK pathway is involved in SHS-associated receptor upregulation and AHR.

Inhibition of aldose reductase prevents endotoxin-induced inflammation by regulating the arachidonic acid pathway in murine macrophages

The bacterial endotoxin lipopolysaccharide (LPS) is known to induce release of arachidonic acid (AA) and its metabolic products, which play important roles in the inflammatory process. We have shown earlier that LPS-induced signals in macrophages are mediated by aldose reductase (AR). Here we have investigated the role of AR in LPS-induced release of AA metabolites and their modulation using a potent pharmacological inhibitor, fidarestat, and AR siRNA ablation in RAW264.7 macrophages and AR-knockout mouse peritoneal macrophages and heart tissue. Inhibition or genetic ablation of AR prevented the LPS-induced synthesis and release of AA metabolites such as PGE2, TXB, PGI2, and LTBs in macrophages. LPS-induced activation of cPLA2 was also prevented by AR inhibition. Similarly, AR inhibition also prevented the calcium ionophore A23187-induced cPLA2 and LTB4 in macrophages. Further, AR inhibition by fidarestat prevented the expression of AA-metabolizing enzymes such as COX-2 and LOX-5 in RAW264.7 cells and AR-knockout mouse-derived peritoneal macrophages. LPS-induced expression of AA-metabolizing enzymes and their catalyzed metabolic products was significantly lower in peritoneal macrophages and heart tissue from AR-knockout mice. LPS-induced activation of redox-sensitive signaling intermediates such as MAPKs, transcription factor NF-κB, and EGR-1, a transcriptional regulator of mPGES-1, which in collaboration with COX-2 leads to the production of PGE2, was also significantly prevented by AR inhibition. Taken together, our results indicate that AR mediates LPS-induced inflammation by regulating the AA-metabolic pathway and thus provide a novel role for AR inhibition in preventing inflammatory complications such as sepsis.

Secondhand smoke exposure induces Raf/ERK/MAPK-mediated upregulation of cerebrovascular endothelin ETA receptors

BACKGROUND

Cigarette smoking enhances the risk of stroke. However, the underlying molecular mechanisms are largely unknown. The present study established an in vivo rat secondhand cigarette smoking (SHS) model and examined the hypothesis that SHS upregulates endothelin receptors with increased cerebrovascular contraction via the Raf/extracellular signal-regulated kinase (ERK)/mitogen-activated protein kinases (MAPK) pathway.

RESULTS

Rats were exposed to SHS for up to 8 weeks. The cerebral artery vasoconstriction was recorded by a sensitive myograph. The mRNA and protein expressions for endothelin receptors in cerebral arteries were studied by real-time PCR and Western blot. Compared to fresh air exposed rats, cerebral arteries from SHS rats exhibited stronger contractile responses (P < 0.05) mediated by endothelin type A (ETA) receptors. The expressions of mRNA and protein for ETA receptors in the cerebral arteries from SHS rats were higher (P < 0.05) than that in control. SHS did not affect endothelin type B (ETB) receptor-mediated contractions, mRNA or protein levels. The results suggest that SHS upregulates ETA, but not ETB receptors in vivo. After SHS exposure, the mRNA levels of Raf-1 and ERK1/2, the protein expression of phosphorylated (p)-Raf-1 and p-ERK1/2 were increased (P < 0.05). Raf-1 inhibitor, GW5074 suppressed the enhanced ETA receptor-mediated contraction, mRNA and protein levels induced by SHS. In addition, GW5074 inhibited the SHS-caused increased mRNA and phosphorylated protein levels of Raf-1 and ERK1/2, suggesting that SHS induces activation of the Raf/ERK/MAPK pathway.

CONCLUSIONS

SHS upregulates cerebrovascular ETA receptors via the Raf/ERK/MAPK pathway, which provides novel understanding of mechanisms involved in SHS-associated stroke.