Involvement of PTEN in airway hyperresponsiveness and inflammation in bronchial asthma

Mast cells can mediate vascular permeability through regulation of the PI3K-HIF-1alpha-VEGF axis

RATIONALE

Bronchial inflammation is usually accompanied by increased vascular permeability. Mast cells release a number of mediators that act directly on the vasculature, resulting in vasodilatation, increased permeability, and subsequent plasma protein extravasation. Vascular endothelial growth factor (VEGF) has been implicated to contribute to asthmatic tissue edema through its effect on vascular permeability. However, the effects of mast cells on VEGF-mediated signaling in allergic airway disease are not clearly understood.

OBJECTIVES

An aim of the present study was to investigate the role of mast cells on VEGF-mediated signal transduction in allergic airway disease.

METHODS

We used genetically mast cell-deficient WBB6F(1)-Kit(W)/Kit(W-v) (W/W(v)) mice and the congenic normal WBB6F(1)(+/+) mouse model for allergic airway disease to investigate the role of mast cells on VEGF-mediated signal transduction in allergic airway disease, more specifically in vascular permeability.

MEASUREMENTS AND MAIN RESULTS

Our present study, with ovalbumin (OVA)-sensitized without adjuvant and OVA-challenged mice, revealed the following typical pathophysiologic features of allergic airway diseases: increased inflammatory cells of the airways, airway hyperresponsiveness, increased vascular permeability, and increased levels of VEGF. However, levels of VEGF and plasma exudation in W/W(v) mice after OVA inhalation were significantly lower than levels in WBB6F(1)(+/+) mice. Moreover, mast cell-reconstituted W/W(v) mice restored vascular permeability and VEGF levels similar to those of the WBB6F(1)(+/+) mice. Our data also showed that VEGF expression was regulated by hypoxia-inducible factor-1alpha (HIF-1alpha) activation through the phosphatidylinositol 3-kinase (PI3K)-HIF-1alpha pathway in allergic airway disease.

CONCLUSIONS

These results suggest that mast cells modulate vascular permeability by the regulation of the PI3K-HIF-1alpha-VEGF axis.

Human rhinovirus 1B exposure induces phosphatidylinositol 3-kinase-dependent airway inflammation in mice

RATIONALE

Infection with rhinovirus (RV) triggers exacerbations of asthma and chronic obstructive lung disease.

OBJECTIVES

We sought to develop a mouse model of RV employing RV1B, a minor group serotype that binds to the low-density lipoprotein receptor.

METHODS

C57BL/6 mice were inoculated intranasally with RV1B, replication-deficient ultraviolet (UV)-irradiated RV1B, or RV39, a major group virus.

MEASUREMENTS AND MAIN RESULTS

Viral RNA was present in the lungs of RV1B-treated mice, but not in those exposed to UV-irradiated RV1B or RV39. Lung homogenates of RV-treated mice contained infectious RV 4 days after inoculation. RV1B exposure induced neutrophilic and lymphocytic airway inflammation, as well as increased lung expression of KC, macrophage-inflammatory protein-2, and IFN-alpha and IFN-beta. RV1B-exposed mice showed airway hyperresponsiveness 1 and 4 days after inoculation. UV-irradiated RV1B induced modest neutrophilic airway inflammation and hyperresponsiveness 1 day after exposure. Both RV1B and UV-irradiated RV1B, but not RV39, increased lung phosphorylation of Akt. Confocal immunofluorescence showed colocalization of RV1B and phospho-Akt in the airway epithelium. Finally, pretreatment with the phosphatidylinositol 3-kinase inhibitor LY294002 attenuated chemokine production and neutrophil infiltration.

CONCLUSIONS

We conclude that RV1B induces airway inflammation in vivo. Evidence is presented that viral replication occurs in vivo and is required for maximal responses. On the other hand, viral replication was not required for a subset of RV-induced responses, including neutrophilic inflammation, airway hyperresponsiveness, and Akt phosphorylation. Finally, phosphatidylinositol 3-kinase/Akt signaling is required for maximal RV1B-induced airway neutrophilic inflammation, likely via its essential role in virus internalization.

Caffeic acid phenethyl ester attenuates allergic airway inflammation and hyperresponsiveness in murine model of ovalbumin-induced asthma

Caffeic acid phenethyl ester (CAPE) is a biologically active ingredient of propolis, which has several interesting biological properties, including antioxidant and anti-inflammatory; however, its anti-allergic effects are poorly understood. The objective of this study was to determine whether treatment with CAPE results in significant inhibition of asthmatic reactions in a mouse model. Mice sensitized and challenged with ovalbumin (OVA) had the following typical asthmatic reactions: an increase in the number of eosinophils in bronchoalveolar lavage (BAL) fluid; a marked influx of inflammatory cells into the lung around blood vessels and airways, and airway luminal narrowing; the development of airway hyperresponsiveness (AHR); the presence of tumor necrosis factor-alpha (TNF-alpha) and Th2 cytokines, including IL-4 and IL-5, in the BAL fluid; and the presence of allergen-specific IgE in the serum. Five successive intraperitoneal administrations of CAPE before the last airway OVA challenge resulted in significant inhibition of characteristic asthmatic reactions. We determined that increased generation of reactive oxygen species (ROS) by inhalation of OVA was diminished via the administration of CAPE in BAL fluid, as well as nuclear factor-kappaB (NF-kappaB) DNA binding activity. These findings indicate that oxidative stress may have a crucial function in the pathogenesis of bronchial asthma, and that CAPE may be useful as an adjuvant therapy for the treatment of bronchial asthma.

A genetic variation in inositol polyphosphate 4 phosphatase a enhances susceptibility to asthma

RATIONALE

Microarray data from mouse studies have identified a number of genes to be differentially expressed in allergen-sensitized mice lungs.

OBJECTIVES

Taking leads from these datasets, we attempted to identify novel genes associated with atopic asthma in humans.

METHODS

We performed family-based genetic association analysis on selected markers within or in proximity of 21 human homologs of genes short-listed from ovalbumin-sensitized mouse studies in the Gene Expression Omnibus database of the National Center for Biotechnology Information. Family-based and case-control studies were undertaken for fine mapping and functional variation analysis of INPP4A (inositol polyphosphate 4 phosphatase type I). Western blot analysis was performed to analyze INPP4A protein stability from human platelets.

MEASUREMENTS AND MAIN RESULTS

Our genetic association studies of 21 human genes in 171 trios led to the identification of a biallelic repeat (rs3217304) in INPP4A, associated with atopic asthma (P = 0.009). Further studies using additional three single nucleotide polymorphisms (SNPs), +92031A/T, +92344C/T, and +131237C/T, and two microsatellite markers, D2S2311 and D2S2187, revealed significant genetic associations with loci +92031A/T (P = 0.0012) and +92344C/T (P = 0.004). A nonsynonymous SNP, +110832A/G (Thr/Ala), present within a sequence enriched with proline, glutamic acid, serine, and threonine (PEST), in proximity of these two loci, showed a significant association with atopic asthma (P = 0.0006). The association results were also replicated in an independent cohort of 288 patients and 293 control subjects (P = 0.004). PEST score and Western blot analyses indicated a functional role of this SNP in regulating INPP4A protein stability.

CONCLUSIONS

In our study, INPP4A was identified as a novel asthma candidate gene, whereby the +110832A/G (Thr/Ala) variant affected its stability and was significantly associated with asthma.

Targeting lung inflammation: novel therapies for the treatment of COPD

Chronic obstructive pulmonary disease (COPD) is a global health problem. As understanding of pathology of COPD has increased it has been established that COPD is associated with the progressive pulmonary inflammation and destruction of lung parenchyma (emphysema) that relate to disease severity. Therefore, it is anticipated that drugs that reduce pulmonary inflammation will provide effective, disease modifying therapy for COPD. Several specific therapies are directed against the influx of inflammatory cells into the airways and lung parenchyma that occurs in COPD; these include agents directed against cytokines and chemokines. Broad-range anti-inflammatory drugs are now in phase III development for COPD; they include inhibitors of phosphodiesterase 4 (PDE4). Other drugs that inhibit cell signaling include inhibitors of p38 mitogen-activated protein kinase (MAPK), nuclear factor-κB (NF-κB), and phosphoinositide-3-kinase (PI3K). There is also a search for inhibitors of proteinases and matrix metalloproteinases (MMPs) to prevent lung destruction and the development of emphysema. This review highlights studies on novel or potential anti-inflammatory agents that might be considered in the development of new future therapies for COPD.

Phosphoinositide lipid phosphatases: natural regulators of phosphoinositide 3-kinase signaling in T lymphocytes

The phosphoinositide 3-kinase signaling pathway has been implicated in a range of T lymphocyte cellular functions, particularly growth, proliferation, cytokine secretion, and survival. Dysregulation of phosphoinositide 3-kinase-dependent signaling and function in leukocytes, including B and T lymphocytes, has been implicated in many inflammatory and autoimmune diseases. As befits a pivotal signaling cascade, several mechanisms exist to ensure that the pathway is tightly regulated. This minireview focuses on two lipid phosphatases, viz. the 3'-phosphatase PTEN (phosphatase and tensin homolog deleted on chromosome 10) and SHIP (Src homology 2 domain-containing inositol-5-phosphatase). We discuss their role in regulating T lymphocyte signaling as well their potential as future therapeutic targets.

Inhibition of airway allergic disease by co-administration of flagellin with allergen

Bacterial flagellin, which activates Toll-like receptor 5 and cytosolic pattern recognition receptor Ipaf, has a strong immunomodulatory activity. In the present study, we examined whether intranasal co-administration of flagellin with allergen could modulate established airway hyperresponsiveness and Th2 response using an ovalbumin (OVA)-sensitized mouse model. Balb/c mice sensitized with OVA were treated with OVA-flagellin (FlaB) mixture three times at 1-week intervals. Seven days after the final OVA-FlaB administration, the mice were challenged with OVA inhalation, and airway responses and OVA-specific immune responses were evaluated. The OVA-FlaB treatment significantly suppressed OVA-induced airway hyperresponsiveness, airway eosinophilic inflammation, and OVA-specific Th2 cytokine productions in splenocytes. These results indicate that flagellin co-administered with allergen can modulate airway inflammatory response through inhibition of Th2 responses, and flagellin can be considered as a component for allergen-specific immunotherapy.

Ceramide inhibits LPS-induced production of IL-5, IL-10, and IL-13 from mast cells

Mast cells are central regulators of allergic inflammation through production of various chemical mediators and cytokines. Bacterial infection occasionally worsens allergic inflammation. Although the exact mechanism of this phenomenon remains unclear, we have previously reported that LPS stimulates mast cells to produce not only pro-inflammatory cytokines, such as IL-6 and TNF-alpha, but also Th2-type cytokines, such as IL-5 and IL-13, and a regulatory cytokine, IL-10. In the present study, we have studied the effect of ceramide on LPS-mediated cytokine production from mast cells, as ceramide modulates various cellular functions in many cell types. Administration of cell-permeable C8 ceramide reduced production of IL-5, IL-10, and IL-13 from LPS-stimulated mouse bone marrow-derived mast cells (BMMCs) apparently through transcriptional inhibition, but did not affect IL-6 or TNF-alpha production. Consistently, LPS-stimulated production of IL-5, IL-10, and IL-13 from BMMCs is significantly enhanced in the presence of fumonisin B1, a de novo ceramide synthesis inhibitor. Interestingly, the same C8 ceramide treatment showed opposite effects on cytokine production from LPS-stimulated macrophages, reducing IL-6 and TNF-alpha while not affecting IL-10 production. C8 ceramide pretreatment significantly reduced LPS-induced Akt phosphorylation in BMMCs, but not in macrophages. Furthermore, pretreatment of BMMCs by wortmannin, a specific inhibitor of PI3 kinase, inhibited LPS-stimulated expression of IL-5, IL-10, and IL-13, but not that of TNF-alpha or IL-6. Thus, ceramide appeared to down-regulate LPS-stimulated production of IL-5, IL-10, and IL-13 from mast cells by inhibiting PI3 kinase-Akt pathway in a cell type-specific manner.

Phosphoinositide 3-kinase signalling in lung disease: leucocytes and beyond

The family of lipid kinases termed phosphoinositide-3-kinase (PI3K) is known to contribute at multiple levels to innate and adaptive immune responses, and is hence an attractive target for drug discovery in inflammatory and autoimmune disease, including respiratory diseases. The development of isoform-selective pharmacological inhibitors, targeted gene manipulation and short interfering RNA (siRNA) target validation have facilitated a better understanding of the role that each member of this family of kinases plays in the physiology and pathology of the respiratory system. In this review, we will evaluate the evidence for the roles of specific PI3K isoforms in the lung and airways, and discuss their potential as targets for novel drug therapies.

Peroxisome proliferator-activated receptor gamma and retinoic acid receptor synergistically up-regulate the tumor suppressor PTEN in human promyeloid leukemia cells

Peroxisome proliferator-activated receptor gamma (PPARgamma) and retinoic acid receptors (RARs) have been a focus in chemotherapy for human cancers. The tumor suppressor PTEN plays a pivotal role in the growth of human cancer cells. We investigated whether costimulation of PPARgamma and RAR could synergistically up-regulate PTEN in human leukemia cells and consequently potentiate the inhibition of growth and cell cycle progression of these cells. We found that overexpression of PTEN with the adenoviral vector Ad/PTEN caused growth arrest at the G1 phase of the cell cycle of HL-60 cells. HL-60 cells treated with either a PPARgamma ligand (ciglitazone) or a RAR ligand (all-trans retinoic acid [ATRA]) up-regulated PTEN in HL-60 cells. The 2 compounds in combination showed synergistic effects on PTEN expression at the protein and messenger RNA levels. Moreover, the combination of ciglitazone and ATRA synergistically reduced cell growth rates and cell cycle arrest at the G1 phase. Our results suggest that, PPARgamma and RAR play an important role in controlling the growth of leukemia cells via the up-regulation of PTEN.

Role of the phosphoinositide 3-kinase p110delta in generation of type 2 cytokine responses and allergic airway inflammation

Phosphoinositide 3-kinases (PI3K) regulate immune activation via their roles in signal transduction of multiple classes of receptors. Here, we examined the effect of genetic inactivation of the hemopoietic cell-restricted PI3K isoform p110delta on systemic cytokine and chemokine responses and allergic airway inflammation. We found that type 2 cytokine responses (IL-4, IL-5 and IL-13) are significantly decreased in p110delta mutants, whereas type 1 cytokine responses (IFN-gamma and CXCL10) were robust. Elevated IFN-gamma production during the primary response to ovalbumin (OVA) was associated with reduced production of the regulatory cytokine IL-10. IFN-gamma and IL-10 production normalized after secondary OVA immunization; however, type 2 cytokine production was persistently reduced. Type 2 cytokine-dependent airway inflammation elicited by intranasal challenge with OVA was dramatically reduced, with reduced levels of eosinophil recruitment and mucus production observed in the lungs. Induction of respiratory hyper-responsiveness to inhaled methacholine, a hallmark of asthma, was markedly attenuated in p110delta-inactivated mice. Adoptive transfer of OVA-primed splenocytes from normal but not p110delta-inactivated mice could induce airway eosinophilia in naive, airway-challenged recipient mice. These data demonstrate a novel functional role for p110delta signaling in induction of type 2 responses in vivo and may offer a new therapeutic target for Th2-mediated airway disease.

Transactivation of Src, PDGF receptor, and Akt is involved in IL-1β-induced ICAM-1 expression in A549 cells

In previous study, interleukin-1beta (IL-1beta) has been shown to induce ICAM-1 expression through MAPKs and NF-kappaB in A549 cells. In addition to these pathways, transactivation of non-receptor tyrosine kinase (Src), PDGF receptors (PDGFRs), and phosphatidylinositol 3-kinase (PI3K)/Akt has been implicated in the expression of inflammatory genes. Here, we further investigated whether these different mechanisms participating in IL-1beta-induced ICAM-1 expression in A549 cells. We initially observed that IL-1beta-induced ICAM-1 promoter activity was attenuated by the inhibitors of Src (PP1), PDGFR (AG1296), PI3-K (LY294002 and wortmannin), and Akt (SH-5), revealed by reporter gene assay, Western blotting, and RT-PCR analyses. The involvement of Src and PI3-K/Akt in IL-1beta-induced ICAM-1 expression was significantly attenuated by transfection of A549 cells with dominant negative plasmids of Src, p85 and Akt, respectively. Src, PDGFR, and PI3K/Akt mediated the effects of IL-1beta because pretreatment with PP1, AG1296, and wortmannin also abrogated IL-1beta-stimulated Src, PDGFR, and Akt phosphorylation, respectively. Moreover, pretreatment with p300 inhibitor (curcumin) also blocked ICAM-1 expression. We further confirmed that p300 was associated with ICAM-1 promoter which was dynamically linked to histone H4 acetylation stimulated by IL-1beta, determined by chromatin immunoprecipitation assay. Association of p300 and histone-H4 to ICAM-1 promoter was inhibited by LY294002. Up-regulation of ICAM-1 enhanced the adhesion of neutrophils onto A549 cell monolayer exposed to IL-1beta, which was inhibited by PP1, AG1296, LY294002, wortmannin, and helenalin. These results suggested that Akt phosphorylation mediated through transactivation of Src/PDGFR promotes the transcriptional p300 activity and eventually leads to ICAM-1 expression induced by IL-1beta.

TNF-alpha induces MMP-9 expression via activation of Src/EGFR, PDGFR/PI3K/Akt cascade and promotion of NF-kappaB/p300 binding in human tracheal smooth muscle cells

TNF-alpha has been shown to induce matrix metalloproteinase-9 (MMP-9) expression, which, in turn, degrades extracellular matrix in the inflammatory responses. However, the inductive mechanisms of the MMP-9 by TNF-alpha remain unclear. In human tracheal smooth muscle cells, TNF-alpha induced MMP-9 expression and Akt phosphorylation in a time-dependent manner, which was attenuated by the inhibitors of Src (PP1), epidermal growth factor receptor (AG1478), PDGFR (AG1296), and PI3K (LY294002), respectively, revealed by reporter gene assay, RT-PCR, zymographic, and Western blot analyses. Transfection with the dominant negative mutants of c-Src (KM, K295M [kinase inactive mutant]), p85, and Akt (KA, K179A) also reduced MMP-9 expression. These findings indicated that MMP-9 expression was regulated by PI3K/Akt via the transactivation of growth factor receptors. Furthermore, LY294002 or wortmannin inhibited Akt phosphorylation but had no effect on NF-kappaB translocation, which was blocked by helenalin. Mutated NF-kappaB DNA binding element in the MMP-9 promoter and helenalin also attenuated MMP-9 expression, suggesting that PI3K/Akt and NF-kappaB independently regulated MMP-9 expression. To support this notion, immunofluorescence staining and immunoprecipitation were applied to characterize the transcription factors involved in these responses. The results showed that LY294002 and curcumin blocked Akt translocation into nucleus. In contrast, p300, acetyl-histone (H3), and NF-kappaB p65 were found to be coimmunoprecipitated with the phosphorylated Akt, indicating that these components associated with the MMP-9 promoter are revealed by chromatin immunoprecipitation assay. Thus, our study provides a new insight into the molecular mechanisms that TNF-alpha-stimulated Akt phosphorylation mediated through transactivation of Src and growth factor receptors may stimulate the recruitment of p300, assemble transcription factor (p65), and then lead to MMP-9 expression.

Cysteinyl leukotriene upregulates IL-11 expression in allergic airway disease of mice

BACKGROUND

Chronic airway inflammation and airway remodeling are important features of bronchial asthma. IL-11 is one of the important mediators involved in the process of airway inflammation and remodeling. Cysteinyl leukotrienes (cysLTs) play roles in recruitment of inflammatory cells, airway smooth muscle contraction, vascular leakage, increased mucus secretion, decreased mucociliary clearance, and airway fibrosis.

OBJECTIVE

An aim of the present study was to determine the effect of the cysLTs on the regulation of IL-11 expression.

METHODS

We used a C57BL/6 mouse model of allergic airway disease and murine tracheal epithelial cells to examine the effects of cysLTs on the regulation of IL-11 expression.

RESULTS

Our present study with an ovalbumin-induced murine model of allergic airway disease revealed that levels of leukotriene C(4) (LTC(4)) in bronchoalveolar lavage fluids were increased and that administration of montelukast or pranlukast reduced the increased levels of LTC(4); the increased expression of IL-11 protein and mRNA in lung tissues; airway inflammation, bronchial hyperresponsiveness; the increased levels of TGF-beta(1), IL-4, and IL-13 in bronchoalveolar lavage fluids and lung tissues; and airway fibrosis. In addition, LTC(4) stimulates epithelial cells to produce IL-11. Our results also showed that cysLT type 1 receptor antagonists downregulated the activity of a transcription factor, nuclear factor kappaB, and BAY 11-7085 substantially reduced the increased levels of IL-11 after ovalbumin inhalation.

CONCLUSION

These results suggest that cysLTs regulate the IL-11 expression in allergic airway disease.

CLINICAL IMPLICATIONS

These findings provide one of the molecular mechanisms for the effects of cysLTs on airway inflammation and fibrosis in allergic airway diseases.

Src homology 2 domain-containing inositol 5-phosphatase 1 deficiency leads to a spontaneous allergic inflammation in the murine lung

BACKGROUND

Src homology 2 domain-containing inositol 5-phosphatase 1 (SHIP-1) controls the intracellular level of the phosphoinositide 3-kinase product phosphotidylinositol-3,4,5-trisphosphate and functions as a negative regulator of cytokine and immune receptor signaling. Emerging evidence suggests that the phosphoinositide 3-kinase pathway might be involved in allergic inflammation in the lung. However, the functional relevance of SHIP-1 in the T(H)2 activation pathway has not been established. SHIP-1(-/-) mice have spontaneous myeloproliferative inflammation in the lung, the nature of which has not been elucidated. We hypothesized that SHIP-1 plays an important role as a regulator in pulmonary allergic inflammation and in maintaining lung homeostasis.

OBJECTIVE

To test our hypothesis, we characterized the pulmonary phenotype of SHIP-1(-/-) mice.

RESULTS

Analyses of lung histopathology and bronchoalveolar lavage cellularity revealed that the majority of SHIP-1(-/-) mice had progressive and severe pulmonary inflammation of macrophages, lymphocytes, neutrophils, and eosinophils; mucous hyperplasia; airway epithelial hypertrophy; and subepithelial fibrosis. These pathologic changes were accompanied by exaggerated production of T(H)2 cytokines and chemokines, including IL-4, IL-13, eotaxin, and monocyte chemoattractant protein 1, in the lung. Furthermore, the number of mast cells significantly increased, and many of these cells were undergoing degranulation, which was correlated with increased content and spontaneous release of histamine in the lung tissue of SHIP-1(-/-) mice.

CONCLUSION

These findings provide strong evidence that mice lacking SHIP-1 have an allergic inflammation in the lung, suggesting that SHIP-1 plays an important role in regulating the T(H)2 signaling pathway and in maintaining lung homeostasis.

CLINICAL IMPLICATIONS

SHIP-1 as a regulator might be a potential therapeutic target for controlling allergic inflammation in diseases such as asthma.

Vascular Endothelial Growth Factor Modulates Matrix Metalloproteinase-9 Expression in Asthma

RATIONALE

Vascular endothelial growth factor (VEGF) and matrix metalloproteinase-9 (MMP-9) are mediators of airway inflammation and remodeling in asthma.

OBJECTIVES

This study investigates a potential relationship between VEGF and MMP-9, and the mechanisms by which VEGF signaling regulates MMP-9 expression in asthma.

METHODS

We evaluated whether levels of VEGF correlated with levels of MMP-9 in the sputum of asthma patients, and the effect of VEGF receptor inhibitors on MMP-9 expression in murine model of asthma.

MEASUREMENTS AND MAIN RESULTS

We have found that levels of VEGF and MMP-9 are significantly higher in the sputum of patients with asthma than in healthy control subjects, and a significant correlation is found between the levels of VEGF and MMP-9. This study with the ovalbumin-induced model of asthma revealed the following typical pathophysiologic features of asthma in the lungs: increased numbers of inflammatory cells of the airways, airway hyperresponsiveness, increased vascular permeability, and increased levels of MMP-9 and VEGF. Administration of VEGF receptor inhibitors reduced the pathophysiologic signs of asthma and decreased the increased expression of MMP-9 after ovalbumin inhalation.

CONCLUSIONS

These results indicate that there is a close relationship between VEGF and MMP-9 expression and that inhibition of VEGF receptor down-regulates the expression of MMP-9. These findings suggest that VEGF signaling regulates MMP-9 expression and plays a critical role in initiation and maintenance of asthma.

Strategies for targeting T-cells in allergic diseases and asthma

T helper (Th) 2 lymphocytes play a crucial role in the initiation, progression and persistence of allergic diseases, including asthma. Drugs that interfere with the activation of T-cells or more selectively Th2-specific signaling molecules and drugs that prevent the selective migration into lung tissue are promising novel strategies for the treatment of allergic asthma. Although the mainstay asthma therapy of inhaled glucocorticoids is rather effective, targeting Th2 cells may be an important alternative in childhood. Regulatory T-cells (Treg cells) have a physiological role in protection of unwanted immune responses to auto-antigens and allergens. Literature data indicate that an imbalance between Th2 and Treg cells may underlie development and disease expression of allergic asthma. Drugs or immunotherapies that stimulate these counter-Treg cells may limit aberrant Th2 responses leading to suppression of symptoms. Furthermore, these types of treatments may offer the perspective of disease modification and long-term relief of symptoms.

Adenosine metabolism and murine strain-specific IL-4-induced inflammation, emphysema, and fibrosis

To define the factors that control the tissue effects of IL-4, we compared the effects of Tg IL-4 in Balb/c and C57BL/6 mice. In the former, IL-4 caused modest eosinophilic inflammation and mild airway fibrosis and did not shorten survival. In C57BL/6 mice, IL-4 caused profound eosinophilic inflammation, airway fibrosis, emphysematous alveolar destruction, and premature death. These differences could not be accounted for by changes in Th2 or Th1 cytokines, receptor components, STAT6 activation, MMPs, or cathepsins. In contrast, in C57BL/6 mice, alveolar remodeling was associated with decreased levels of tissue inhibitors of metalloproteinase 2, -3, and -4 and alpha1-antitrypsin, and fibrosis was associated with increased levels of total and bioactive TGF-beta1. Impressive differences in adenosine metabolism were also appreciated, with increased tissue adenosine levels and A(1), A(2B), and A(3) adenosine receptor expression and decreased adenosine deaminase (ADA) activity in C57BL/6 animals. Treatment with ADA also reduced the inflammation, fibrosis, and emphysematous destruction and improved the survival of C57BL/6 Tg animals. These studies demonstrate that genetic influences control IL-4 effector pathways in the murine lung. They also demonstrate that IL-4 has different effects on adenosine metabolism in Balb/c and C57BL/6 mice and that these differences contribute to the different responses that IL-4 induces in these inbred animals.

Geldanamycin treatment reduces neovascularization in a mouse model of retinopathy of prematurity

BACKGROUND

The benzoquinoid antibiotic 17-allylaminogeldanamycin (17-AAG) inhibits the Ras/Raf/MEK and PI3-Kinase signaling pathways and down-regulates vascular endothelial factor expression. Here we use a mouse model of oxygen-induced retinopathy to investigate the effect of 17-AAG on retinal neovascularization and vascular recovery.

MATERIAL AND METHODS

C57BL/6 mice were exposed to 75% oxygen from postnatal day 7 (P7) to P12 and recovered in room air thereafter. Beginning with P12 mice were treated for 5 days by daily IP injection of 17-AAG (12.5 mg/kg body weight) micro dispersed in an emulsion of 4% Lipoid EPC, 5% sucrose, and 0.9% NaCl or Wortmannin (100 microg/kg body weight). On P17, the retinal vascular and avascular area, neovascular blood vessel tufts, and main vessel tortuosity were quantified after perfusion of the mice with FITC-Concanavalin A. The mRNA levels of VEGF, angiopoietin 1 and 2 were quantified by real-time RT-PCR.

RESULTS

After 17-AAG treatment, a reduction of the vascular area was measured from 37.8 +/- 5.2% to 30.8 +/- 5.7% (P = 0.005), and an increase of the avascular area from 10.8 +/- 5.6% to 20.3 +/- 6.6% (P = 0.001). No alteration of the vascular pattern, the number of blood vessel tufts and the main vessel tortuosity was achieved by treatment with the PI-3 kinase inhibitor Wortmannin. After treatment with 17-AAG, the numbers of tufts (127.9 33.2) were different from the controls (173.7 +/- 55.2, P = 0.035), but not the main vessel tortuosity. No significant change in VEGF and angiopoietin 1 mRNA expression could be achieved with either of the treatments. Wortmannin treatment also did not change the angiopoietin 2 mRNA level, whereas the level was reduced in 17-AAG treated mice retina from 436-fold (+/- 64) to 200-fold (+/-55) (P = 0.035).

CONCLUSION

An IP injection of 17-AAG is able to reduce angioproliferative retinopathy in a mouse model for oxygen-induced retinopathy. Our data indicate that the mechanism does not involve a direct or indirect reduction of the VEGF mRNA level, but acts downstream of the VEGF pathway. Thus, 17-AAG probably does not work by PI-3 kinase inhibition but via the Ras/Raf/MEK pathway. These data underline the potential utility of tyrosine kinase inhibitors in hypoxia induced neovascularization.

Inhibition of phosphoinositide 3-kinase delta attenuates allergic airway inflammation and hyperresponsiveness in murine asthma model

P110delta phosphoinositide 3-kinase (PI3K) plays a pivotal role in the recruitment and activation of certain inflammatory cells. Recent findings revealed that the activity of p110delta also contributes to allergen-IgE-induced mast cell activation and vascular permeability. We investigated the role of p110delta in allergic airway inflammation and hyperresponsiveness using IC87114, a selective p110delta inhibitor, in a mouse asthma model. BALB/c mice were sensitized with OVA and, upon OVA aerosol challenge, developed airway eosinophilia, mucus hypersecretion, elevation in cytokine and chemokine levels, up-regulation of ICAM-1 and VCAM-1 expression, and airway hyperresponsiveness. Intratracheal administration of IC87114 significantly (P<0.05) attenuated OVA-induced influx into lungs of total leukocytes, eosinophils, neutrophils, and lymphocytes, as well as levels of IL-4, IL-5, IL-13, and RANTES in a dose-dependent manner. IC87114 also significantly (P<0.05) reduced the serum levels of total IgE and OVA-specific IgE and LTC(4) release into the airspace. Histological studies show that IC87114 inhibited OVA-induced lung tissue eosinophilia, airway mucus production, and inflammation score. In addition, IC87114 significantly (P<0.05) suppressed OVA-induced airway hyperresponsiveness to inhaled methacholine. Western blot analyses of whole lung tissue lysates shows that IC87114 markedly attenuated the OVA-induced increase in expression of IL-4, IL-5, IL-13, ICAM-1, VCAM-1, RANTES, and eotaxin. Furthermore, IC87114 treatment markedly attenuated OVA-induced serine phosphorylation of Akt, a downstream effector of PI3K signaling. Taken together, our findings implicate that inhibition of p110delta signaling pathway may have therapeutic potential for the treatment of allergic airway inflammation.

Hydrogen peroxide induces vascular permeability via regulation of vascular endothelial growth factor

Oxidative stress plays critical roles in initiation and/or worsening of respiratory disease process. Although reactive oxygen species (ROS) are shown to cause vascular leakage, the mechanisms by which ROS induce an increase in vascular permeability are not clearly understood. In this study, we have used a murine model to evaluate the effect of hydrogen peroxide (H(2)O(2)) to examine roles of ROS and the molecular mechanism in vascular permeability. The results have revealed that ROS levels, vascular endothelial growth factor (VEGF) expression, hypoxia-inducible factor-1alpha protein level, airway hyperresponsiveness, and vascular permeability are increased after inhalation of H(2)O(2). Administration of antioxidants markedly reduced plasma extravasation and VEGF levels in lungs treated with H(2)O(2). These results indicate that ROS may modulate vascular permeability via upregulation of VEGF expression.

Regulation of phosphatidylinositol 3-kinase by polyisoprenyl phosphates in neutrophil-mediated tissue injury

Neutrophils play a central role in host defense, inflammation, and tissue injury. Recent findings indicate a novel role for polyisoprenyl phosphates (PIPPs) as natural down-regulatory signals in neutrophils. The relationship between PIPPs and neutrophil early activating signals, such as phosphoinositides, has not been previously determined. Here, we establish presqualene diphosphate (PSDP) as an endogenous PIPP regulator of phosphatidylinositol 3-kinase (PI3K). In human neutrophils, leukotriene B4 (LTB4) triggered rapid decreases in PSDP and reciprocal increases in PI3K activity. In addition, PSDP was identified by gas chromatography/mass spectrometry in p110gamma-PI3K immunoprecipitates obtained 30 s after LTB4, indicating a physical interaction between PSDP and PI3K in activated neutrophils. Moreover, PSDP (0.4-800 pmol) directly inhibited recombinant human p110gamma-PI3K activity. During an experimental model of lung injury and inflammation, a reciprocal relationship was also present in vivo for lung PSDP and PI3K activity. To investigate its therapeutic potential, we developed a new PSDP structural mimetic that blocked human neutrophil activation and mouse lung PI3K activity and inflammation. Together, our findings indicate that PSDP is an endogenous PI3K inhibitor, and suggest that in inflammatory diseases characterized by excessive neutrophil activation, PIPPs can serve as structural templates in a novel antineutrophil therapeutic strategy to limit tissue injury.

Epigallocatechin-3-gallate protects toluene diisocyanate-induced airway inflammation in a murine model of asthma

Epigallocatechin-3-gallate (EGCG), a major form of tea catechin, has anti-allergic properties. To elucidate the anti-allergic mechanisms of EGCG, we investigated its regulation of matrix metalloproteinase (MMP-9) expression in toluene diisocyanate (TDI)-inhalation lung tissues as well as TNF-alpha and Th2 cytokine (IL-5) production in BAL fluid. Compared with untreated asthmatic mice those administrated with EGCG had significantly reduced asthmatic reaction. Also, increased reactive oxygen species (ROS) generation by TDI inhalation was diminished by administration of EGCG in BAL fluid. These results suggest that EGCG regulates inflammatory cell migration possibly by suppressing MMP-9 production and ROS generation, and indicate that EGCG may be useful as an adjuvant therapy for bronchial asthma.

p38 and EGF receptor kinase-mediated activation of the phosphatidylinositol 3-kinase/Akt pathway is required for Zn2+-induced cyclooxygenase-2 expression

Cyclooxygenase 2 (COX-2) expression is induced by physiological and inflammatory stimuli. Regulation of COX-2 expression is stimulus and cell type specific. Exposure to Zn2+ has been associated with activation of multiple intracellular signaling pathways as well as the induction of COX-2 expression. This study aims to elucidate the role of intracellular signaling pathways in Zn2+-induced COX-2 expression in human bronchial epithelial cells. Inhibitors of the phosphatidylinositol 3-kinase (PI3K) potently block Zn2+-induced COX-2 mRNA and protein expression. Overexpression of adenoviral constructs encoding dominant-negative Akt kinase downstream of PI3K or wild-type phosphatase and tensin homolog deleted on chromosome 10, an important PI3K phosphatase, suppresses COX-2 mRNA expression induced by Zn2+. Zn2+ exposure induces phosphorylation of the tyrosine kinases, including Src and EGF receptor (EGFR), and the p38 mitogen-activated protein kinase. Blockage of these kinases results in inhibition of Zn2+-induced Akt phosphorylation as well as COX-2 protein expression. Overexpression of dominant negative p38 constructs suppresses Zn2+-induced increase in COX-2 promoter activity. In contrast, the c-Jun NH2-terminal kinase and the extracellular signal-regulated kinases have minimal effect on Akt phosphorylation and COX-2 expression. Inhibition of p38, Src, and EGFR kinases with pharmacological inhibitors markedly reduces Akt phosphorylation induced by Zn2+. However, the PI3K inhibitors do not show inhibitory effects on p38, Src, and EGFR. These data suggest that p38 and EGFR kinase-mediated Akt activation is required for Zn2+-induced COX-2 expression and that the PI3K/Akt signaling pathway plays a central role in this event.

An anti-inflammatory role for a phosphoinositide 3-kinase inhibitor LY294002 in a mouse asthma model

Phosphoinositide 3-kinase (PI3K) exhibits broad functional effects in immune cells. We investigated the role of PI3K in allergic airway inflammation using LY294002, a specific PI3K inhibitor, in a mouse asthma model. BALB/c mice were sensitized and challenged with ovalbumin (OVA), and developed airway eosinophilia, mucus hypersecretion, elevation in cytokine levels, and airway hyperresponsiveness. Intratracheal administration of LY294002 significantly inhibited OVA-induced increases in total cell counts, eosinophil counts, and IL-5, IL-13, and eotaxin levels in bronchoalveolar lavage fluid. Histological studies show that LY294002 dramatically inhibited OVA-induced lung tissue eosinophilia and airway mucus production. In addition, LY294002 significantly suppressed OVA-induced airway hyperresponsiveness to inhaled methacholine. Western blot analysis of whole lung lysates shows that LY294002 markedly attenuated OVA-induced serine phosphorylation of Akt, a direct downstream substrate of PI3K. Taken together, our findings suggest that inhibition of PI3K signaling pathway can suppress T-helper type 2 (Th2) cytokine production, eosinophil infiltration, mucus production, and airway hyperresponsiveness in a mouse asthma model and may have therapeutic potential for the treatment of allergic airway inflammation.

Negative regulation of myofibroblast differentiation by PTEN (Phosphatase and Tensin Homolog Deleted on chromosome 10)

RATIONALE

Myofibroblasts are primary effector cells in idiopathic pulmonary fibrosis (IPF). Defining mechanisms of myofibroblast differentiation may be critical to the development of novel therapeutic agents.

OBJECTIVE

To show that myofibroblast differentiation is regulated by phosphatase and tensin homolog deleted on chromosome 10 (PTEN) activity in vivo, and to identify a potential mechanism by which this occurs.

METHODS

We used tissue sections of surgical lung biopsies from patients with IPF to localize expression of PTEN and alpha-smooth muscle actin (alpha-SMA). We used cell culture of pten(-/-) and wild-type fibroblasts, as well as adenoviral strategies and pharmacologic inhibitors, to determine the mechanism by which PTEN inhibits alpha-SMA, fibroblast proliferation, and collagen production.

RESULTS

In human lung specimens of IPF, myofibroblasts within fibroblastic foci demonstrated diminished PTEN expression. Furthermore, inhibition of PTEN in mice worsened bleomycin-induced fibrosis. In pten(-/-) fibroblasts, and in normal fibroblasts in which PTEN was inhibited, alpha-SMA, proliferation, and collagen production was upregulated. Addition of transforming growth factor-beta to wild-type cells, but not pten(-/-) cells, resulted in increased alpha-SMA expression in a time-dependent fashion. In pten(-/-) cells, reconstitution of PTEN decreased alpha-SMA expression, proliferation, and collagen production, whereas overexpression of PTEN in wild-type cells inhibited transforming growth factor-beta-induced myofibroblast differentiation. It was observed that both the protein and lipid phosphatase actions of PTEN were capable of modulating the myofibroblast phenotype.

CONCLUSIONS

The results indicate that in IPF, myofibroblasts have diminished PTEN expression. Inhibition of PTEN in vivo promotes fibrosis, and PTEN inhibits myofibroblast differentiation in vitro.

Efficacy of a traditional Korean medicine, Chung-Sang-Bo-Ha-Tang, in a murine model of chronic asthma

Traditional herbal medicines may be viable alternatives to corticosteroid therapy for treatment of asthma. However, the therapeutic mechanisms of herbal compounds remain a matter of considerable debate. This study was performed to evaluate the effects of Chung-Sang-Bo-Ha-Tang (CSBHT), a herbal compound administrated therapeutically to asthma patients for centuries, on airway inflammation and remodeling in a murine model of chronic asthma. BALB/c mice sensitized to ovalbumin (OVA) were chronically challenged with aerosolized OVA for 6 weeks. During the last 2 weeks, some mice were treated daily with CSBHT by intragastric feeding. Dexamethasone (Dex)-treated, phosphate-buffered saline (PBS)-treated, and naive mice served as controls. The effects of CSBHT on airway inflammation, lung pathology, and cytokine production were evaluated. Mice exposed to recurrent airway challenge with OVA had chronic inflammation and characteristics of airway remodeling, including subepithelial fibrosis, epithelial hypertrophy, and goblet cell hyperplasia. CSBHT was as effective as Dex at moderately reducing these changes compared to the PBS-treated mice. In addition, IL-5 and IFN-gamma levels in supernatants of Concanavalin A (Con A)-activated splenocyte cultures were reduced in mice treated with CSBHT. Treatment with CSBHT during the last 2 weeks of challenge modulated airway inflammation and remodeling in a murine model of chronic asthma. Thus, CSBHT may effectively delay the progression of airway inflammation and remodeling.

Impact of PTEN on the expression of insulin-like growth factors (IGFs) and IGF-binding proteins in human gastric adenocarcinoma cells

PTEN is a tumor suppressor gene that is frequently mutated or deleted in a variety of human cancers including human gastric cancer. PTEN functions primarily as a lipid phosphatase and plays a key role in the regulation of the PI3 kinase/Akt pathway, thereby modulating cell proliferation and cell survival. On the other hand, the IGF system plays an important role in cell proliferation and cell survival via the PI3 kinase/Akt and MAP kinase pathways in many cancer cells. To characterize the impact of PTEN on the IGF-IGFR-IGFBP axis in gastric cancer, we overexpressed PTEN using an adenovirus gene transfer system in human gastric adenocarcinoma cells, SNU-484 and SNU-663, which lack PTEN. Overexpression of PTEN inhibited serum-induced as well as IGF-I-induced cell proliferation as compared to control cells. PTEN overexpression resulted in a significant decrease in the expression of IGF-I, -II, and IGF-IR. Interestingly, amongst the six IGFBPs, only IGFBP-3 was upregulated by PTEN, whereas IGFBP-4 and -6 were reduced. The IGFBP-3 promoter activity assay and Western immunoblotting demonstrate that PTEN regulates IGFBP-3 at the transcriptional level. In addition, the PI3 kinase inhibitor, LY294002, upregulates IGFBP-3 expression but downregulates IGF-I and IGF-II, indicating that PTEN controls IGFBP-3 and IGFs by an Akt-dependent pathway. These findings suggest that PTEN may inhibit antiapoptotic IGF actions not only by blocking the IGF-IGFR-induced Akt activity, but also by regulating expression of components of the IGF system, in particular, upregulation of IGFBP-3, which is known to exert antiproliferative effects through IGF-dependent and IGF-independent mechanisms in cancer cells.

Phosphoinositide-3 kinases critically regulate the recruitment and survival of eosinophils in vivo: importance for the resolution of allergic inflammation

The phosphatidylinositol-3 kinase (PI3K) family of signaling enzymes plays a crucial role in leukocyte recruitment and activation and hence, likely regulates the induction and propagation phases of inflammation. However, little data have emerged showing a role for these processes in the resolution phase in models of in vivo inflammation. Here, we have evaluated the role of PI3K for the migration and survival of eosinophils in a model of allergic pleurisy in mice. Eosinophil accumulation in PI3Kgamma-deficient mice was inhibited at 48 h, as compared with wild-type mice but not at earlier time-points (6 and 24 h). Experiments with adoptive transfer of bone marrow showed that PI3Kgamma in eosinophils but not in non-bone marrow-derived cells was required for their accumulation. Systemic treatment with PI3K inhibitors before antigen challenge prevented the recruitment of eosinophils. This was associated with decreased Akt phosphorylation, interleukin-5 production, and eosinophil release from the bone marrow. Treatment with PI3K inhibitors 24 h after antigen challenge markedly cleared the accumulated eosinophils, an effect associated with inhibition of Akt phosphorylation and an increased number of apoptotic events. Altogether, our data demonstrate an important role of PI3Kgamma for the maintenance of eosinophilic inflammation in vivo, whereas other isoforms of PI3K may be relevant for the recruitment process.

Quantitative profiling of plasma peptides in asthmatic mice using liquid chromatography and mass spectrometry

Asthma is increasing in prevalence worldwide as a result of factors associated with a Western lifestyle. However, simple and reliable diagnostic and prognostic markers are yet to be found. In an attempt to identify protein biomarker profiles among small molecular weight ranges, we employed an approach combining liquid chromatography with mass spectrometry, instead of two-dimensional gel electrophoresis (2-DE), which has previously been used to analyze protein expression patterns. Here we described its application to compare plasma peptides from control and chronic asthma mice. Peptides were quantitatively profiled as a multidimensional peptide mass fingerprint by a combination of reverse-phase high-performance liquid chromatography and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. They were identified by peptide mass fingerprinting using matrix-assisted laser desorption/ionization time-of-flight/time-of-flight tandem mass spectrometry. In this study, we quantitatively identified the fragment f of complement 3 (C3f), which is important in inflammation. C3f was significantly higher in controls than chronic asthma mice. Our strategy allowed the detection and identification of different plasma peptides between control and chronic asthma mice on a proteomic scale. Therefore, these results suggest that native small peptides detected by non-2-DE techniques may be useful and specific biomarkers of disease.

PPAR-gamma modulates allergic inflammation through up-regulation of PTEN

The ligand-activated nuclear receptor peroxisome proliferator-activated receptor gamma (PPARgamma) has been shown to regulate cell activation, differentiation, proliferation, and/or apoptosis. PPARgamma is also associated with anti-inflammatory responses. However, the signaling mechanism remains elusive. We have used a mouse model for asthma to determine the effect of PPARgamma agonists, rosiglitazone or pioglitazone, and PPARgamma on allergen-induced bronchial inflammation and airway hyperresponsiveness. Administration of PPARgamma agonists or adenovirus carrying PPARgamma cDNA (AdPPARgamma) reduced bronchial inflammation and airway hyperresponsiveness. Expression of PPARgamma was increased by ovalbumin (OVA) inhalation, and the increase was further enhanced by the administration of the PPARgamma agonists or AdPPARgamma. Levels of IL-4, IL-5, IL-13, and eosinophil cationic protein were increased after OVA inhalation, and the increased levels were significantly reduced by the administration of PPARgamma agonists or AdPPARgamma. The results also showed that the administration of PPARgamma agonists or AdPPARgamma up-regulated phosphatase and tensin homologue deleted on chromosome ten (PTEN) expression in allergen-induced asthmatic lungs. This up-regulation correlated with decreased phosphatidylinositol 3-kinase activity as measured by reduced phosphorylation of Akt. These findings demonstrate a protective role of PPARgamma in the pathogenesis of the asthma phenotype through regulation of PTEN expression.

The complexity of PTEN: mutation, marker and potential target for therapeutic intervention

Phosphatase and tensin homologue deleted on chromosome 10 (PTEN) is a phosphatase that removes phosphates primarily from lipids. It has also been called mutated in multiple advanced cancers 1 and transforming growth factor-beta regulated epithelial cell-enriched phosphatase 1. The best described substrate of PTEN is phosphatidyliniositol (3,4,5)-tris-phosphate [PtdIns(3,4,5)P3]. PTEN removes the phosphate in PtdIns(3,4,5)P(3) to generate PtdIns(4,5)P(2). PTEN serves to counter-balance the effects of phosphoinositide 3' kinase, which normally adds a phosphate to PtdIns(4,5)P(2) to generate PtdIns(3,4,5)P(3). PtdIns(3,4,5)P(3) recruits kinases such as phosphoinositide-dependent kinase 1, which in turn phosphorylate Akt, which phosphorylates other downstream proteins involved in regulation of apoptosis and cell-cycle progression. PTEN removal of the phosphate from PtdIns(3,4,5)P(3) inhibits this pathway by preventing localisation of proteins with pleckstrin homology domains to the cell membrane. Alterations of the PTEN gene are associated with cancer and other diseases. Novel therapeutic approaches have been developed to counteract the deletion/mutation of PTEN in human cancer. This review will discuss the role of PTEN in signal transduction and cancer as well as pharmacological approaches to combat PTEN loss in human cancer.

Prostaglandin E(2) inhibits fibroblast migration by E-prostanoid 2 receptor-mediated increase in PTEN activity

An increased migratory phenotype exists in lung fibroblasts derived from patients with fibroproliferative lung disease. Prostaglandin E(2) (PGE(2)) suppresses fibroblast migration, but the receptor(s) and mechanism(s) mediating this action are unknown. Our data confirm that treatment of human lung fibroblasts with PGE(2) inhibits migration. Similar effects of butaprost, an E-prostanoid (EP) 2 receptor-specific ligand, implicate the EP2 receptor in migration-inhibitory signaling. Further, migration in fibroblasts deficient for the EP2 receptor cannot be inhibited by PGE(2) or butaprost, confirming the central role of EP2 in mediating these effects. Our previous data suggested that phosphatase and tensin homolog on chromosome ten (PTEN), a phosphatase that opposes the actions of phosphatidylinositol-3-kinase (PI3K), may be important in regulating lung fibroblast motility. We now report that both PGE(2) and butaprost increase PTEN phosphatase activity, without a concomitant increase in PTEN protein levels. This contributes to EP2-mediated migration inhibition, because migration in PTEN-null fibroblasts is similarly unaffected by EP2 receptor signaling. Increased PTEN activity in response to EP2 stimulation is associated with decreased tyrosine phosphorylation on PTEN, a mechanism known to regulate enzyme activity. Collectively, these data describe the novel mechanistic finding that PGE(2), via the EP2 receptor, decreases tyrosine phosphorylation on PTEN, resulting in increased PTEN enzyme activity and inhibition of fibroblast migration.

The pattern of methacholine responsiveness in mice is dependent on antigen challenge dose

Background

Considerable variation exists in the protocols used to induce hyperresponsiveness in murine models of allergic sensitisation. We examined the effect of varying the number of antigen exposures at challenge on the development of methacholine responsiveness in systemically sensitised mice.

Methods

BALB/c mice were sensitised with ovalbumin (OVA), challenged with 1, 3 or 6 OVA aerosols. Lung function was measured using low frequency forced oscillations and partitioned into components representing the airways (R_aw) and lung parenchyma (tissue damping (G) and tissue elastance (H)). Responsiveness to inhaled methacholine (MCh), inflammatory cell profile and circulating IgE were assessed 24 and 48 hours after challenge. The threshold dose of MCh required to elicit a detectable response (sensitivity) and response to 30 mg.mL^-1 (maximal response) were determined for each compartment.

Results

Sensitivity; All three OVA protocols resulted in an increased sensitivity to MCh in R_aw but not in G or H. These responses where present at 24 and 48 hrs, except 1 OVA aerosol in which changes had resolved by 48 hrs. Maximal response; 1 OVA aerosol increased maximal responses in R_aw, G and H at 24 hrs, which was gone by 48 hrs. Three OVA aerosols increased responses in H at 48 hrs only. Six OVA challenges caused increases in R_aw, G and H at both 24 and 48 hrs. Eosinophils increased with increasing antigen challenges. IgE was elevated by OVA sensitisation but not boosted by OVA aerosol challenge.

Conclusions

The pattern of eosinophilia, IgE and MCh responsiveness in mice was determined by antigen dose at challenge. In this study, increased sensitivity to MCh was confined to the airways whereas increases in maximal responses occurred in both the airway and parenchymal compartments. The presence of eosinophilia and IgE did not always coincide with increased responsiveness to inhaled MCh. These findings require further systematic study to determine whether different mechanisms underlie airway and parenchymal hyperresponsiveness post antigen challenge.

Blockade of airway hyperresponsiveness and inflammation in a murine model of asthma by a prodrug of cysteine, L-2-oxothiazolidine-4-carboxylic acid

Oxidative stress plays an important role in the pathogenesis of bronchial asthma. An excess production of reactive oxygen species (ROS) and defective endogenous antioxidant defense mechanisms may be present in asthma. Reduced glutathione (GSH) is one of the most important reducing agents against oxidant free radicals. A reducing agent, L-2-oxothiazolidine-4-carboxylic acid (OTC), a prodrug of cysteine, increases intracellular GSH. We have used a mouse model for asthma to determine effects of OTC on allergen-induced bronchial inflammation and airway hyper-responsiveness. The administration of OTC reduced bronchial inflammation and airway hyper-responsiveness. ROS generation in bronchoalveolar lavage fluids was increased by ovalbumin (OVA) inhalation, but this increase was diminished by administration of OTC. The increased IL-4, IL-5, IL-13, and eosinophil cationic protein levels in lungs after OVA inhalation were significantly reduced by the administration of OTC. In addition, the increased expression of ICAM-1, VCAM-1, RANTES, and eotaxin in lungs after OVA inhalation was significantly reduced by the administration of OTC. We also showed that the increased NF-kappaB levels in nuclear protein extracts of lung tissues at 72 h after OVA inhalation were decreased by the administration of OTC. These findings suggest that OTC may reduce airway inflammation and hyper-responsiveness through regulation of NF-kappaB activity.

Blockade of inflammation and airway hyperresponsiveness in immune-sensitized mice by dominant-negative phosphoinositide 3-kinase-TAT

Phosphoinositide 3-kinase (PI3K) is thought to contribute to the pathogenesis of asthma by effecting the recruitment, activation, and apoptosis of inflammatory cells. We examined the role of class IA PI3K in antigen-induced airway inflammation and hyperresponsiveness by i.p. administration into mice of Δp85 protein, a dominant negative form of the class IA PI3K regulatory subunit, p85α, which was fused to HIV-TAT (TAT-Δp85). Intraperitoneal administration of TAT-Δp85 caused time-dependent transduction into blood leukocytes, and inhibited activated phosphorylation of protein kinase B (PKB), a downstream target of PI3K, in lung tissues in mice receiving intranasal FMLP. Antigen challenge elicited pulmonary infiltration of lymphocytes, eosinophils and neutrophils, increase in mucus-containing epithelial cells, and airway hyperresponsiveness to methacholine. Except for modest airway neutrophilia, these effects all were blocked by treatment with 3–10 mg/kg of TAT-Δp85. There was also significant reduction in IL-5 and IL-4 secretion into the BAL. Intranasal administration of IL-5 caused eosinophil migration into the airway lumen, which was attenuated by systemic pretreatment with TAT-Δp85. We conclude that PI3K has a regulatory role in Th2-cell cytokine secretion, airway inflammation, and airway hyperresponsiveness in mice.

Integrin alpha4beta1 regulates migration across basement membranes by lung fibroblasts: a role for phosphatase and tensin homologue deleted on chromosome 10

Idiopathic pulmonary fibrosis is a disease that is characterized by fibroblast accumulation and activation in the distal airspaces of the lung. We hypothesized that fibrotic lung fibroblasts migrate/invade across basement membranes by integrin-mediated mechanisms as a means of entering alveoli. We demonstrate that in lung fibroblasts derived from patients with idiopathic pulmonary fibrosis, fibronectin signaling is both necessary and sufficient for basement membrane migration/invasion across basement membranes. This effect is mediated through the alpha5beta1 integrin because blockade of fibronectin-alpha5 integrin ligation attenuated this response. In contrast, ligation of alpha4beta1 integrin inhibits basement membrane invasion by normal lung fibroblasts but not by fibrotic lung fibroblasts. This phenotypic difference is not related to surface expression of the alpha4beta1 integrin, as demonstrated by flow cytometry. In normal lung fibroblasts but not in fibrotic lung fibroblasts, we show that ligation of alpha4beta1 integrin induces a significant increase in phosphatase and tensin homologue deleted on chromosome 10 (PTEN) activity. Fibrotic lung fibroblasts express constitutively less PTEN mRNA and protein as well as phosphatase activity in comparison to normal lung fibroblasts. Together, these data suggest that a loss of alpha4beta1 signaling via PTEN confers a migratory/invasive phenotype to fibrotic lung fibroblasts. Furthermore, this study implicates a loss of PTEN function in the pathophysiology of idiopathic pulmonary fibrosis.

Zinc-induced PTEN protein degradation through the proteasome pathway in human airway epithelial cells

The tumor suppressor PTEN is a putative negative regulator of the phosphatidylinositol 3-kinase/Akt pathway. Exposure to Zn2+ ions induces Akt activation, suggesting that PTEN may be modulated in this process. Therefore, the effects of Zn2+ on PTEN were studied in human airway epithelial cells and rat lungs. Treatment with Zn2+ resulted in a significant reduction in levels of PTEN protein in a dose- and time-dependent fashion in a human airway epithelial cell line. This effect of Zn2+was also observed in normal human airway epithelial cells in primary culture and in rat airway epithelium in vivo. Concomitantly, levels of PTEN mRNA were also significantly reduced by Zn2+ exposure. PTEN phosphatase activity evaluated by measuring Akt phosphorylation decreased after Zn2+ treatment. Pretreatment of the cells with a proteasome inhibitor significantly blocked zinc-induced reduction of PTEN protein as well as the increase in Akt phosphorylation, implicating the involvement of proteasome-mediated PTEN degradation. Further study revealed that Zn2+-induced ubiquitination of PTEN protein may mediate this process. A phosphatidylinositol 3-kinase inhibitor blocked PTEN degradation induced by Zn2+, suggesting that phosphatidylinositol 3-kinase may participate in the regulation of PTEN. However, both the proteasome inhibitor and phosphatidylinositol 3-kinase inhibitor failed to prevent significant down-regulation of PTEN mRNA expression in response to Zn2+. In summary, exposure to Zn2+ ions causes PTEN degradation and loss of function, which is mediated by an ubiquitin-associated proteolytic process in the airway epithelium.