Regulation of lysophosphatidic acid-induced COX-2 expression by ERK1/2 activation in cultured feline esophageal epithelial Cells

Allergen inhalation generates pro-inflammatory oxidised phosphatidylcholine associated with airway dysfunction

Oxidised phosphatidylcholines (OxPCs) are produced under conditions of elevated oxidative stress and can contribute to human disease pathobiology. However, their role in allergic asthma is unexplored. The aim of this study was to characterise the OxPC profile in the airways after allergen challenge of people with airway hyperresponsiveness (AHR) or mild asthma. The capacity of OxPCs to contribute to pathobiology associated with asthma was also to be determined.Using bronchoalveolar lavage fluid from two human cohorts, OxPC species were quantified using ultra-high performance liquid chromatography-tandem mass spectrometry. Murine thin-cut lung slices were used to measure airway narrowing caused by OxPCs. Human airway smooth muscle (HASM) cells were exposed to OxPCs to assess concentration-associated changes in inflammatory phenotype and activation of signalling networks.OxPC profiles in the airways were different between people with and without AHR and correlated with methacholine responsiveness. Exposing patients with mild asthma to allergens produced unique OxPC signatures that associated with the severity of the late asthma response. OxPCs dose-dependently induced 15% airway narrowing in murine thin-cut lung slices. In HASM cells, OxPCs dose-dependently increased the biosynthesis of cyclooxygenase-2, interleukin (IL)-6, IL-8, granulocyte-macrophage colony-stimulating factor and the production of oxylipins via protein kinase C-dependent pathways.Data from human cohorts and primary HASM cell culture show that OxPCs are present in the airways, increase after allergen challenge and correlate with metrics of airway dysfunction. Furthermore, OxPCs may contribute to asthma pathobiology by promoting airway narrowing and inducing a pro-inflammatory phenotype and contraction of airway smooth muscle. OxPCs represent a potential novel target for treating oxidative stress-associated pathobiology in asthma.

12-HETE is a regulator of PGE2 production via COX-2 expression induced by a snake venom group IIA phospholipase A2 in isolated peritoneal macrophages

The snake venom miotoxin (MT)-III is a group IIA secreted phospholipase A₂ (sPLA₂) with pro-inflammatory activities. Previous studies have demonstrated that MT-III has the ability to stimulate macrophages to release inflammatory lipid mediators derived from arachidonic acid metabolism. Among them, we highlight prostaglandin (PG)E₂ produced by the cyclooxygenase (COX)-2 pathway, through activation of nuclear factor (NF)-κB. However, the mechanisms coordinating this process are not fully understood. This study investigates the regulatory mechanisms exerted by other groups of bioactive eicosanoids derived from 12-lipoxygenase (12-LO), in particular 12-hydroxyeicosatetraenoic (12-HETE), on group IIA sPLA₂-induced (i) PGE₂ release, (ii) COX-2 expression, and (iii) activation of signaling pathways p38 mitogen-activated protein kinases(p38MAPK), protein C kinase (PKC), extracellular signal-regulated kinase 1/2 (ERK1/2), and NF-κB. Stimulation of macrophages with group IIA sPLA₂ resulted in release of 12-HETE without modification of 12-LO protein levels. Pre-treatment of these cells with baicalein, a 12-LO inhibitor, decreased the sPLA₂-induced PGE₂ production, significantly reduced COX-2 expression, and inhibited sPLA₂-induced ERK; however, it did not affect p38MAPK or PKC phosphorylation. In turn, sPLA₂-induced PGE₂ release and COX-2 expression, but not NF-κB activation, was attenuated by pre-treating macrophages with PD98059 an inhibitor of ERK1/2. These results suggest that, in macrophages, group IIA sPLA₂-induced PGE₂ release and COX-2 protein expression are distinctly mediated through 12-HETE followed by ERK1/2 pathway activation, independently of NF-κB activation. These findings highlight an as yet undescribed mechanism by which 12-HETE regulates one of the distinct signaling pathways for snake venom group IIA sPLA₂-induced PGE₂ release and COX-2 expression in macrophages.

Effect of lysophosphatidic acid on the immune inflammatory response and the connexin 43 protein in myocardial infarction

Lysophosphatidic acid (LPA) is an intermediate product of membrane phospholipid metabolism. Recently, LPA has gained attention for its involvement in the pathological processes of certain cardiovascular diseases. The aim of the present study was to clarify the association between the effect of LPA and the immune inflammatory response, and to investigate the effects of LPA on the protein expression levels of connexin 43 during myocardial infarction. Surface electrocardiograms of myocardial infarction rats and isolated rat heart tissue samples were obtained in order to determine the effect of LPA on the incidence of arrhythmia in rats that exhibited changes in immune status. The results demonstrated that the incidence of arrhythmia decreased when the rat immune systems were suppressed, and the incidence of arrhythmia increased when the rat immune systems were enhanced. The concentration levels of tumor necrosis factor (TNF)-α were determined by ELISA, and the results demonstrated that LPA induced T lymphocyte synthesis and TNF-α release. Using a patch-clamp technique, LPA was shown to increase the current amplitude of the voltage-dependent potassium channels (K_v) and calcium-activated potassium channels (K_Ca) in Jurkat T cells. The protein expression of connexin 43 (Cx43) was determined by immunohistochemical staining. The results indicated that LPA caused the degradation of Cx43 and decreased the expression of Cx43. This effect was associated with the immune status of the rats. There was a further decrease in Cx43 expression in the rats of the immune-enhanced group. To the best of our knowledge, these results provide the first evidence that LPA causes arrhythmia through the regulation of immune inflammatory cells and the decrease of Cx43 protein expression. The present study provided an experimental basis for the treatment of arrhythmia and may guide clinical care.

The Protective Effect of Eupatilin against Hydrogen Peroxide-Induced Injury Involving 5-Lipoxygenase in Feline Esophageal Epithelial Cells

In this study, we focused to identify whether eupatilin (5,7-dihydroxy-3',4',6-trimethoxyflavone), an extract from Artemisia argyi folium, prevents H₂O₂-induced injury of cultured feline esophageal epithelial cells. Cell viability was measured by the conventional MTT reduction assay. Western blot analysis was performed to investigate the expression of 5-lipoxygenase by H₂O₂ treatment in the absence and presence of inhibitors. When cells were exposed to 600 µM H₂O₂ for 24 hours, cell viability was decreased to 40%. However, when cells were pretreated with 25~150 µM eupatilin for 12 hours, viability was significantly restored in a concentration-dependent manner. H₂O₂-treated cells were shown to express 5-lipoxygenase, whereas the cells pretreated with eupatilin exhibited reduction in the expression of 5-lipoxygenase. The H₂O₂-induced increase of 5-lipoxygenase expression was prevented by SB202190, SP600125, or NAC. We further demonstrated that the level of leukotriene B₄ (LTB₄) was also reduced by eupatilin, SB202190, SP600125, NAC, or nordihydroguaiaretic acid (a lipoxygenase inhibitor) pretreatment. H₂O₂ induced the activation of p38MAPK and JNK, this activation was inhibited by eupatilin. These results indicate that eupatilin may reduce H₂O₂-induced cytotoxicity, and 5-lipoxygenase expression and LTB₄ production by controlling the p38 MAPK and JNK signaling pathways through antioxidative action in feline esophageal epithelial cells.

Compressive force inhibits adipogenesis through COX-2-mediated down-regulation of PPARgamma2 and C/EBPalpha

Various mechanical stimuli affect differentiation of mesoderm-derived cells such as osteoblasts or myoblasts, suggesting that adipogenesis may also be influenced by mechanical stimulation. However, effects of mechanical stimuli on adipogenesis are scarcely known. Compressive force was applied to a human preadipocyte cell line, SGBS. Levels of gene expression were estimated by real-time reverse transcription-polymerase chain reaction. The accumulation of lipids was evaluated by Sudan III or Oil Red O staining. In SGBS cells subjected to a compressive force of 226 Pa for 12 h before adipogenic induction, adipogenesis was inhibited. Compressive force immediately after adipogenic induction did not affect the adipogenesis. The expression of peroxisome proliferator-activated receptor (PPAR) gamma2 and CCAAT/enhancer binding protein (C/EBP) alpha mRNA during adipogenesis was inhibited by compressive force, whereas C/EBPbeta and C/EBPdelta mRNA levels were unaffected. In preadipocytes, compressive force increased mRNA levels of Krüppel-like factor 2, preadipocyte factor 1, WNT10b, and cyclooxygenase-2 (COX-2) which are known as negative regulators for the PPARgamma2 and C/EBPalpha genes. Furthermore, a COX-2 inhibitor completely reversed the inhibition of adipogenesis by compressive force. In conclusion, compressive force inhibited adipogenesis by suppressing expression of PPARgamma2 and C/EBPalpha in a COX-2-dependent manner.