G-Protein-coupled receptor agonists differentially regulate basal or tumor necrosis factor-α-stimulated activation of interleukin-6 and RANTES in human airway smooth muscle 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.

Sphingosine-1-phosphate inhibits IL-1-induced expression of C-C motif ligand 5 via c-Fos-dependent suppression of IFN-β amplification loop

The neuroinflammation associated with multiple sclerosis involves activation of astrocytes that secrete and respond to inflammatory mediators such as IL-1. IL-1 stimulates expression of many chemokines, including C-C motif ligand (CCL) 5, that recruit immune cells, but it also stimulates sphingosine kinase-1, an enzyme that generates sphingosine-1-phosphate (S1P), a bioactive lipid mediator essential for inflammation. We found that whereas S1P promotes IL-1-induced expression of IL-6, it inhibits IL-1-induced CCL5 expression in astrocytes. This inhibition is mediated by the S1P receptor (S1PR)-2 via an inhibitory G-dependent mechanism. Consistent with this surprising finding, infiltration of macrophages into sites of inflammation increased significantly in S1PR2(-/-) animals. However, activation of NF-κB, IFN regulatory factor-1, and MAPKs, all of which regulate CCL5 expression in response to IL-1, was not diminished by the S1P in astrocytes. Instead, S1PR2 stimulated inositol 1,4,5-trisphosphate-dependent Ca(++) release and Elk-1 phosphorylation and enhanced c-Fos expression. In our study, IL-1 induced the IFNβ production that supports CCL5 expression. An intriguing finding was that S1P induced c-Fos-inhibited CCL5 directly and also indirectly through inhibition of the IFN-β amplification loop. We propose that in addition to S1PR1, which promotes inflammation, S1PR2 mediates opposing inhibitory functions that limit CCL5 expression and diminish the recruitment of immune cells.

Airway smooth muscle CXCR3 ligand production: regulation by JAK-STAT1 and intracellular Ca²⁺

In asthma, airway smooth muscle (ASM) chemokine (C-X-C motif) receptor 3 (CXCR3) ligand production may attract mast cells or T lymphocytes to the ASM, where they can modulate ASM functions. In ASM cells (ASMCs) from people with or without asthma, we aimed to investigate JAK-STAT1, JNK, and Ca²⁺ involvement in chemokine (C-X-C motif) ligand (CXCL)10 and CXCL11 production stimulated by interferon-γ, IL-1β, and TNF-α combined (cytomix). Confluent, growth-arrested ASMC were treated with inhibitors for pan-JAK (pyridone-6), JAK2 (AG-490), JNK (SP-600125), or the sarco(endo)plasmic reticulum Ca²⁺ATPase (SERCA) pump (thapsigargin), Ca²⁺ chelator (BAPTA-AM), or vehicle before and during cytomix stimulation for up to 24 h. Signaling protein activation as well as CXCL10/CXCL11 mRNA and protein production were examined using immunoblot analysis, real-time PCR, and ELISA, respectively. Cytomix-induced STAT1 activation was lower and CXCR3 ligand mRNA production was more sensitive to pyridone-6 and AG-490 in asthmatic than nonasthmatic ASMCs, but CXCL10/CXCL11 release was inhibited by the same proportion. Neither agent caused additional inhibition of release when used in combination with the JNK inhibitor SP-600125. Conversely, p65 NF-κB activation was higher in asthmatic than nonasthmatic ASMCs. BAPTA-AM abolished early CXCL10/CXCL11 mRNA production, whereas thapsigargin reduced it in asthmatic cells and inhibited CXCL10/CXCL11 release by both ASMC types. Despite these inhibitory effects, neither Ca²⁺ agent affected early activation of STAT1, JNK, or p65 NF-κB. In conclusion, intracellular Ca²⁺ regulated CXCL10/CXCL11 production but not early activation of the signaling molecules involved. In asthma, reduced ASM STAT1-JNK activation, increased NF-κB activation, and altered Ca²⁺ handling may contribute to rapid CXCR3 ligand production and enhanced inflammatory cell recruitment.

TNF-α potentiates lysophosphatidic acid-induced COX-2 expression via PKD in human colonic myofibroblasts

The myofibroblast (MFB) has recently been identified as an important mediator of tumor necrosis factor-α (TNF-α)-associated colitis and cancer, but the mechanism(s) involved remains incompletely understood. Here, we show that treatment of 18Co cells, a model of human colonic MFBs, with TNF-α and lysophosphatidic acid (LPA) induced striking synergistic cyclooxygenase-2 (COX-2) protein expression and production of PGE(2). This effect was prevented by the LPA(1) receptor antagonist Ki16425, the G(iα)-specific inhibitor pertussis toxin, and by the preferential protein kinase (PK) C inhibitors GF109203X and Go6983. As a known downstream target of LPA and PKC, we tested whether PKD, recently implicated in the regulation of COX-2 expression in MFB, was involved in this response. TNF-α, while having no detectable effect on the activation of PKD when added alone, augmented PKD activation stimulated by LPA, as measured by PKD autophosphorylation at Ser(910). LPA-induced PKD activation was also inhibited by Ki16425, pertussis toxin, GF109203X, and Go6983. Transfection of 18Co cells with short interfering RNA targeting PKD completely inhibited the synergistic increase in COX-2 protein, demonstrating a critical role of PKD in this response. Our results imply that cross talk between TNF-α and LPA results in the amplification of COX-2 protein expression via a conserved PKD-dependent signaling pathway that appears to involve the LPA(1) receptor and the G protein G(iα). PKD plays a critical role in the expression of COX-2 in human colonic MFBs and may contribute to an inflammatory microenvironment that promotes tumor growth.

Lysophosphatidic acid inhibits CC chemokine ligand 5/RANTES production by blocking IRF-1-mediated gene transcription in human bronchial epithelial cells

Lysophosphatidic acid (LPA) is a phospholipid mediator that exerts a variety of biological responses through specific G-protein-coupled receptors (LPA(1)-LPA(5) and P2Y5). LPA is thought to be involved in airway inflammation by regulating the expression of anti-inflammatory and proinflammatory genes. Chemokines such as CCL5/RANTES are secreted from airway epithelium and play a key role in allergic airway inflammation. CCL5/RANTES is a chemoattractant for eosinophils, T lymphocytes, and monocytes and seems to exacerbate asthma. We stimulated CCL5/RANTES production in a human bronchial epithelial cell line, BEAS-2B, with IFN-γ and TNF-α. When LPA was added, CCL5/RANTES mRNA expression and protein secretion were inhibited, despite the presence of IFN-γ and TNF-α. The LPA effect was attenuated by Ki16425, a LPA(1)/LPA(3) antagonist, but not by dioctylglycerol pyrophosphate 8:0, an LPA(3) antagonist. Pertussis toxin, the inhibitors for PI3K and Akt also attenuated the inhibitory effect of LPA on CCL5/RANTES secretion. We also identify the transcription factor IFN regulatory factor-1 (IRF-1) as being essential for CCL5/RANTES production. Interestingly, LPA inhibited IFN-γ and TNF-α-induced IRF-1 activation by blocking the binding of IRF-1 to its DNA consensus sequence without changing IRF-1 induction and its nuclear translocation. Ki16425, pertussis toxin, and PI3K inhibitors attenuated the inhibitory effect of LPA on IRF-1 activation. Our results suggest that LPA inhibits IFN-γ- and TNF-α-induced CCL5/RANTES production in BEAS-2B cells by blocking the binding of IRF-1 to the CCL5/RANTES promoter. LPA(1) coupled to G(i) and activation of PI3K is required for this unique effect.

Regulation of G-protein-coupled signaling pathways in allergic inflammation

Allergic diseases such as asthma are elicited by maladaptive activation of immune cells such as mast cells and lymphocytes by otherwise innocuous allergens. The numerous mediators secreted by such cells promote both acute inflammation and, in many instances, chronic tissue remodeling. Most of these compounds exert their effects on end-organ targets such as epithelial and endothelial cells and airway smooth muscle by activating G-protein-coupled receptors (GPCRs), which are by far the most abundant type of cell surface receptor. Since GPCRs are also the most common target of allergy therapeutics, a better understanding of their intracellular signaling mechanisms is vital to improve the efficacy of such drugs or to develop new targets. In this review, we focus on some of the new regulatory elements that control the duration and amplitude of GPCR signal transduction pathways in immune effector cells and end-organ structural cells affected by allergic inflammation.

Regulation of endothelin-1-induced interleukin-6 production by Ca2+ influx in human airway smooth muscle cells

Endothelin-1 is considered to be an important mediator in the pathophysiology of asthma because it induces contraction, hypertrophy, and proliferation in airway smooth muscle cells as well as inflammatory responses in the airway. Airway smooth muscle cells have been suggested to contribute to airway inflammation in asthma by producing cytokines. Nevertheless, the role of intracellular Ca(2+) signal in cytokine production in human airway smooth muscle cells is still unclear. We investigated the mechanisms by which endothelin-1 induces production of interleukin (IL)-6, a pleiotropic cytokine, in primary cultured human airway smooth muscle cells. Levels of IL-6 protein and mRNA were significantly increased by endothelin-1 in dose- and time-dependent manners. Endothelin-1-induced IL-6 production was markedly attenuated by EGTA and various Ca(2+) channel inhibitors such as 3,5-bis(trifluoromethyl)-1H-pyrazole derivative (BTP-2), 1-[beta-[3-(4-methoxyphenyl)propoxy]-4-methoxyphenethyl]-1H-imidazole hydrochloride (SKF96365), and nifedipine. Endothelin-1-induced increases in intracellular Ca(2+) concentrations were significantly inhibited in Ca(2+)-free solution and by BTP-2, SKF96365, and nifedipine. The IL-6 synthesis was also inhibited by the extracellular signal-regulated kinase (ERK)1/2 inhibitor 1,4-diamino-2,3-dicyano-1,4-bis(o-aminophenylmercapto)-butadiene ethanolate (U0126) and the p38 inhibitor 4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)1H-imidazole (SB203580), but not by the c-Jun NH2-terminal kinase inhibitor anthra[1,9-cd]-pyrazol-6-(2H)-one (SP600125). Endothelin-1 significantly upregulated phosphorylation of ERK1/2 and p38 but blocking Ca(2+) influx pathways did not inhibit either upregulation. These findings demonstrate that endothelin-1-induced IL-6 synthesis in airway smooth muscle cells occurs via two parallel but independent events that include Ca(2+) influx and activation of ERK1/2 and p38.

Ion channel regulation of intracellular calcium and airway smooth muscle function

Airway hyper-responsiveness associated with asthma is mediated by airway smooth muscle cells (SMCs) and has a complicated etiology involving increases in cell contraction and proliferation and the secretion of inflammatory mediators. Although these pathological changes are diverse, a common feature associated with their regulation is a change in intracellular Ca(2+) concentration ([Ca(2+)](i)). Because the [Ca(2+)](i) itself is a function of the activity and expression of a variety of ion channels, in both the plasma membrane and sarcoplasmic reticulum of the SMC, the modification of this ion channel activity may predispose airway SMCs to hyper-responsiveness. Our objective is to review how ion channels determine the [Ca(2+)](i) and influence the function of airway SMCs and emphasize the potential of ion channels as sites for therapeutic approaches to asthma.

Expanded-polyglutamine huntingtin protein suppresses the secretion and production of a chemokine (CCL5/RANTES) by astrocytes

Huntington's disease (HD) is a hereditary neurological disease caused by expended CAG repeats in the HD gene, which codes for a protein called Huntingtin (Htt). The resultant mutant Huntingtin (mHtt) forms aggregates in neurons and causes neuronal dysfunction. In astrocytes, the largest population of brain cells, mHtt also exists. We report herein that astrocyte-conditioned medium (ACM) collected from astrocytes of R6/2 mice (a mouse model of HD) caused primary cortical neurons to grow less-mature neurites, migrate more slowly, and exhibit lower calcium influx after depolarization than those maintained in wild-type (WT) ACM. Using a cytokine antibody array and ELISA assays, we demonstrated that the amount of a chemokine [chemokine (C-C motif) ligand 5 (CCL5)/regulated on activation normal T cell expressed and secreted (RANTES)] released by R6/2 astrocytes was much less than that by WT astrocytes. When cortical neurons were treated with the indicated ACM, supplementation with recombinant CCL5/RANTES ameliorated the neuronal deficiency caused by HD-ACM, whereas removing CCL5/RANTES from WT-ACM using an anti-CCL5/RANTES antibody mimicked the effects evoked by HD-ACM. Quantitative PCR and promoter analyses demonstrated that mHtt hindered the activation of the CCL5/RANTES promoter by reducing the availability of nuclear factor kappaB-p65 and, hence, reduced the transcript level of CCL5/RANTES. Moreover, ELISA assays and immunocytochemical staining revealed that mHtt retained the residual CCL5/RANTES inside R6/2 astrocytes. In line with the above findings, elevated cytosolic CCL5/RANTES levels were also observed in the brains of two mouse models of HD [R6/2 and Hdh((CAG)150)] and human HD patients. These findings suggest that mHtt hinders one major trophic function of astrocytes which might contribute to the neuronal dysfunction of HD.

Increased secretion of leukemia inhibitory factor by immature airway smooth muscle cells enhances intracellular signaling and airway contractility

Airway smooth muscle cells (ASMC) play a major role in airway inflammation, hyperresponsiveness, and obstruction in asthma. However, very little is known regarding the relation between inflammatory mediators and cytokines and immature ASMC. The aim of this study was to evaluate 1) the secretion of leukemia inhibitory factor (LIF) (an IL-6 family neurotrophic cytokine) by ASMC; 2) intracellular calcium concentration ([Ca(2+)](i)) signaling; and 3) the effect of LIF on mast cell chemotaxis and rat airway contractility. Immature and adult human ASMC were cultured. ELISA and real-time PCR were performed to assess LIF protein secretion and mRNA production, [methyl-(3)H]thymidine incorporation to quantify ASMC DNA synthesis, a Boyden chamber to evaluate the effect of LIF on mast cell chemotaxis, microspectroflurimetry using indo-1 (at baseline and after stimulation bradykinin, U-46619, histamine, and acetylcholine, in the presence or absence of LIF or TNF-alpha) for [Ca(2+)](i) signaling, and isolated rat pup tracheae to determine the effect of LIF on airway contractility to ACh. TNF-alpha-stimulated immature ASMC produce more LIF mRNA and protein than adult ASMC, although this cytokine induces a moderate increase in DNA synthesis (+20%) in adult ASMC only. Human recombinant LIF exerts no chemotactic effect on human mast cells. In immature ASMC, ACh-induced [Ca(2+)](i) response was enhanced twofold after incubation with LIF, whereas TNF-alpha increased the [Ca(2+)](i) to U-46619 threefold. In TNF-alpha-exposed adult ASMC, [Ca(2+)](i) responses to ACh were of greater magnitude (sixfold increase) than in immature ASMC. Human recombinant LIF increased contractility to ACh by 50% in immature, isolated rat tracheae. Stimulated immature human ASMC greatly secrete LIF, thus potentially contributing to neuroimmune airway inflammation and subsequent remodeling. Increased LIF secretion enhances airway reactivity and [Ca(2+)](i) signaling.

The neuropeptide neuromedin U promotes IL-6 production from macrophages and endotoxin shock

Neuromedin U (NMU) is a neuropeptide involved in appetite, circadian rhythm, and pronociception. However, the NMU receptor NMU-R1 has been shown to be expressed in immune cells and NMU promotes mast cell-dependent inflammation. In this study, we demonstrated that NMU plays an important role in IL-6 production in macrophages. NMU-deficient mice were resistant against cecal ligation puncture- as well as LPS-induced septic shock. IL-6 but not TNF-alpha levels were markedly reduced in LPS-treated NMU-deficient mice compared with wild type mice. Both NMU and NMU-R1 were expressed in wild type peritoneal macrophages, and treatment with LPS resulted in up-regulation of NMU but down-regulation of NMU-R1 expression, however, no down-regulation of NMU-R1 was observed in NMU-deficient macrophages where LPS-induced IL-6 production was severely reduced. These data suggest that LPS-induced IL-6 expression is partly dependent on autocrine/paracrine activation of the NMU-NMU-R1 signals in macrophages.