Alison E. John

IL-13-Induced Airway Hyperreactivity During Respiratory Syncytial Virus Infection Is STAT6 Dependent

Airway damage and hyperreactivity induced during respiratory syncytial virus (RSV) infection can have a prolonged effect in infants and young children. These infections can alter the long-term function of the lung and may lead to severe asthma-like responses. In these studies, the role of IL-13 in inducing and maintaining a prolonged airway hyperreactivity response was examined using a mouse model of primary RSV infection. Using this model, there was evidence of significant airway epithelial cell damage and sloughing, along with mucus production. The airway hyperreactivity response was significantly increased by 8 days postinfection, peaked during days 10–12, and began to resolve by day 14. When the local production of Th1- and Th2-associated cytokines was examined, there was a significant increase, primarily in IL-13, as the viral response progressed. Treatment of RSV-infected mice with anti-IL-13 substantially inhibited airway hyperreactivity. Anti-IL-4 treatment had no effect on the RSV-induced responses. Interestingly, when IL-13 was neutralized, an early increase in IL-12 production was observed within the lungs, as was a significantly lower level of viral Ags, suggesting that IL-13 may be regulating an important antiviral pathway. The examination of RSV-induced airway hyperreactivity in STAT6−/− mice demonstrated a significant attenuation of the response, similar to the anti-IL-13 treatment. In addition, STAT6−/− mice had a significant alteration of mucus-producing cells in the airway. Altogether, these studies suggest that a primary factor leading to chronic RSV-induced airway dysfunction may be the inappropriate production of IL-13.

Integrin αvβ5-Mediated TGF-β Activation by Airway Smooth Muscle Cells in Asthma

Severe asthma is associated with airway remodeling, characterized by structural changes including increased smooth muscle mass and matrix deposition in the airway, leading to deteriorating lung function. TGF-β is a pleiotropic cytokine leading to increased synthesis of matrix molecules by human airway smooth muscle (HASM) cells and is implicated in asthmatic airway remodeling. TGF-β is synthesized as a latent complex, sequestered in the extracellular matrix, and requires activation for functionality. Activation of latent TGF-β is the rate-limiting step in its bioavailability. This study investigated the effect of the contraction agonists LPA and methacholine on TGF-β activation by HASM cells and its role in the development of asthmatic airway remodeling. The data presented show that LPA and methacholine induced TGF-β activation by HASM cells via the integrin αvβ5. Our findings highlight the importance of the β5 cytoplasmic domain because a polymorphism in the β5 subunit rendered the integrin unable to activate TGF-β. To our knowledge, this is the first description of a biologically relevant integrin that is unable to activate TGF-β. These data demonstrate that murine airway smooth muscle cells express αvβ5 integrins and activate TGF-β. Finally, these data show that inhibition, or genetic loss, of αvβ5 reduces allergen-induced increases in airway smooth muscle thickness in two models of asthma. These data highlight a mechanism of TGF-β activation in asthma and support the hypothesis that bronchoconstriction promotes airway remodeling via integrin mediated TGF-β activation.

Respiratory syncytial virus-induced CCL5/RANTES contributes to exacerbation of allergic airway inflammation

Severe respiratory syncytial virus (RSV) infection has a significant impact on airway function and may induce or exacerbate the response to a subsequent allergic challenge. In a murine model combining early RSV infection with later cockroach allergen (CRA) challenge, we examined the role of RSV‐induced CCL5/RANTES production on allergic airway responses. RSV infection increased CCL5 mRNAand protein levels, peaking at days 8 and 12, respectively. Administration of CCL5 antiserum during days 0–14 of the RSV infection did not significantly alter viral protein expression when comparedto mice treated with control serum. In mice receiving the combined RSV‐allergen challenge, lungs collected on day 22 exhibited significantly increased numbers of CD4‐ and CD8‐positive T cells. Thisincrease in T cell numbers was not observed in mice receiving α‐CCL5. On day 43, peribronchial eosinophilia and leukotriene levels were increased in RSV‐allergen mice. Pretreatment with CCL5 antiserum resulted in decreased recruitment of inflammatory cells to bronchoalveolar and peribronchial regions of the lungs and these reductions were associated with a reduction in both T cell recruitment into the bronchoalveolar space, leukotriene release and chemokine generation. Thus, CCL5 released during RSV infection has a significant effect on the inflammatory response to subsequent allergic airway challenges.

Human Airway Smooth Muscle Cells from Asthmatic Individuals Have CXCL8 Hypersecretion Due to Increased NF-κB p65, C/EBPβ, and RNA Polymerase II Binding to the CXCL8 Promoter

CXCL8 is a neutrophil and mast cell chemoattractant that is involved in regulating inflammatory cell influx in asthma. Here, we investigated the transcriptional mechanism involved in CXCL8 induction by TNF-α in cultured human airway smooth muscle (HASM) cells and compared these in cells from nonasthmatic and asthmatic individuals. Transfection studies with mutated CXCL8 promoter constructs identified NF-κB, activating protein-1, and CAAT/enhancer binding protein (C/EBP)β as key transcription factors, and binding of these three transcription factors to the CXCL8 promoter after TNF-α stimulation was confirmed by chromatin immunoprecipitation analysis. Cells derived from asthmatic individuals produced significantly higher levels of CXCL8 than nonasthmatic cells both basally and following 24 h of stimulation with TNF-α (p < 0.001). Furthermore, chromatin immunoprecipitation studies detected increased binding of NF-κB p65 and RNA polymerase II to the CXCL8 promoter of asthmatic HASM cells both in the presence and absence of TNF-α stimulation. This was not due to either an increased activation or phosphorylation of NF-κB per se or to an increase in its translocation to the nucleus. Increased binding of C/EBPβ to the CXCL8 promoter of unstimulated cells was also detected in the asthmatic HASM cells. Collectively these studies show that HASM cells from asthmatic individuals have increased CXCL8 production due to the presence of a transcription complex on the CXCL8 promoter, which contains NF-κB, C/EBPβ, and RNA polymerase II. This is the first description of an abnormality in transcription factor binding altering chemokine expression in airway structural cells in asthma.

Discovery of a potent nanoparticle P-selectin antagonist with anti-inflammatory effects in allergic airway disease

The severity of allergic asthma is dependent, in part, on the intensity of peribronchial inflammation. P‐selectin is known to play a role in the development of allergen‐induced peribronchial inflammation and airway hyperreactivity. Selective inhibitors of P‐selectin‐ mediated leukocyte endothelial‐cell interactions may therefore attenuate the inflammatory processes associated with allergic airway disease. Novel P‐selectin inhibitors were created using a polyvalent polymer nanoparticle capable of displaying multiple synthetic, low molecular weight ligands. By assembling a particle that presents an array of groups, which as monomers interact with only low affinity, we created a construct that binds extremely efficiently to P‐ selectin. The ligands acted as mimetics of the key binding elements responsible for the high‐ avidity adhesion of P‐selectin to the physiologic ligand, PSGL‐1. The inhibitors were initially evaluated using an in vitro shear assay system in which interactions between circulating cells and P‐selectin‐coated capillary tubes were measured. The nanoparticles were shown to preferentially bind to selectins expressed on activated endothelial cells. We subsequently demonstrated that nanoparticles displaying P‐selectin blocking arrays were functionally active in vivo, significantly reducing allergen‐induced airway hyperreactivity and peribronchial eosinophilic inflammation in a murine model of asthma.

E- and P-selectins are essential for the development of cockroach allergen-induced airway responses.

Peribronchial inflammation contributes to the pathophysiology of allergic asthma. In many vascular beds, adhesive interactions between leukocytes and the endothelial surface initiate the recruitment of circulating cells. Previous studies using OVA-induced airway hyperreactivity indicated that P-selectin, a member of the selectin family expressed by activated platelets and endothelium, contributed to both inflammation and bronchoconstriction. The current study used cockroach allergen (CRA), an allergen that induces asthmatic responses in both humans and mice, to further investigate the role of selectins in the development of peribronchial inflammation and airway hyperreactivity. P- and E-selectin mRNAs were detected in extracts of CRA-sensitized animals beginning shortly after intratracheal challenge with CRA. The P-selectin mRNA was transiently induced at early time points while up-regulation of the E-selectin mRNA was more prolonged. Mice with targeted deletions in E-selectin (E−), P-selectin (P−), and both genes (E−/P−) showed 70–85% reductions in airway hyperreactivity, peribronchial inflammation, and eosinophil accumulation. The P− and E−/P− groups showed the most profound reductions. The transfer of splenic lymphocytes from CRA-primed E−/P− into naive wild-type (WT) mice produced the same level of airway hyperreactivity as transfers from CRA-primed WT into naive WT hosts, indicating that peripheral immunization was similar. The observed changes in the selectin-deficient animals were not related to inadequate sensitization, because CRA priming and challenge increased serum IgE levels. Furthermore, pulmonary Th2-type cytokines and chemokines in the E-selectin−/− and WT animals were similar. The findings indicate that both P- and E-selectin contribute to CRA-induced peribronchial inflammation and airway hyperreactivity.

Temporal Production of CCL28 Corresponds to Eosinophil Accumulation and Airway Hyperreactivity in Allergic Airway Inflammation

CCL28 is a recently identified chemokine ligand for CCR10 and CCR3 that has been identified in mucosal epithelial surfaces in diverse tissues. CCL28-mediated eosinophil chemotaxis and peroxidase release were inhibited by preincubation of cells with anti-CCR3. CCL28 was constitutively expressed in lung tissue collected from nonsensitized control mice but increased levels were found in mice sensitized and rechallenged with cockroach antigen (CRA). CCL28 levels peaked in the lungs 24 hours after intratracheal challenge with CRA, whereas eotaxin expression peaked at 8 hours. Increased expression of CCR3 but not CCR10 could be detected during the induction of the CRA-induced pulmonary inflammation. To investigate the role of CCL28 in allergic airway responses, mice were treated with CCL28 antiserum 1 hour before receiving the final CRA challenge. The level of airway hyperresponsiveness in mice treated with anti-CCL28 was significantly reduced at 24 hours, but not 8 hours, compared to mice receiving control serum. This reduction was not related to decreased Th2 cytokine, chemokine, or leukotriene levels at 24 hours although peribronchial eosinophilia was significantly reduced. Thus, CCL28 appears to play a role in regulating eosinophil recruitment to peribronchial regions of the lung possibly by coordinated temporal production with eotaxin.

Preclinical SPECT/CT Imaging of αvβ6 Integrins for Molecular Stratification of Idiopathic Pulmonary Fibrosis

Transforming growth factor β activation by the αvβ6 integrin is central to the pathogenesis of idiopathic pulmonary fibrosis. Expression of the αvβ6 integrin is increased in fibrotic lung tissue and is a promising therapeutic target for treatment of the disease. Currently, measurement of αvβ6 integrin levels in the lung requires immunohistochemical analysis of biopsy samples. This procedure is clinically impractical for many patients with pulmonary fibrosis, and a noninvasive strategy for measuring αvβ6 integrin levels in the lungs is urgently required to facilitate monitoring of disease progression and therapeutic responses. Methods: Using a murine model of bleomycin-induced lung injury, we assessed the binding of intravenously administered 111In-labeled αvβ6-specific (diethylenetriamine pentaacetate-tetra [DTPA]-A20FMDV2) or control (DTPA-A20FMDVran) peptide by nanoSPECT/CT imaging. Development of fibrosis was assessed by lung hydroxyproline content, and αvβ6 protein and itgb6 messenger RNA were measured in the lungs. Results: Maximal binding of 111In-labeled A20FMDV2 peptide to αvβ6 integrins was detected in the lungs 1 h after intravenous administration. No significant binding was detected in mice injected with control peptide. Integrin binding was increased in the lungs of bleomycin-, compared with saline-, exposed mice and was attenuated by pretreatment with αvβ6-blocking antibodies. Levels of 111In-labeled A20FMDV2 peptide correlated positively with hydroxyproline, αvβ6 protein, and itgb6 messenger RNA levels. Conclusion: We have developed a highly sensitive, quantifiable, and noninvasive technique for measuring αvβ6 integrin levels within the lung. Measurement of αvβ6 integrins by SPECT/CT scanning has the potential for use in stratifying therapy for patients with pulmonary fibrosis.

Respiratory syncytial virus-induced exaggeration of allergic airway disease is dependent upon CCR1-associated immune responses.

Severe respiratory syncytial virus (RSV) infection has a significant impact on airway function, and may alter subsequent development of asthma. CCR1 mRNA was significantly up‐regulated during primary RSV infection in BALB/c mice, and was also up‐regulated during allergen exposure in sensitized mice. Although CCR1–/– mice exhibited similar levels of airway hyperresponsiveness (AHR) as wild‐type mice in response to cockroach allergen alone, in animals treated with RSV prior to cockroach antigen (CRA) sensitization and challenge, a significant decrease in exacerbated AHR was observed in the CCR1–/– mice. The reduction in AHR after RSV and allergen challenge in CCR1–/– mice was not associated with changes in peribronchial eosinophilia, but was accompanied by significantly decreased IL‐13 levels in the lungs, as well as an absence of mucus cell staining within the airways. When T lymphocyte numbers were compared in animals receiving CRA to animals receiving a combination of RSV and allergen an increase in both CD4 and CD8 T lymphocytes could be detected in wild‐type but not CCR1–/– animals. Thus, these data suggest that CCR1‐mediated responses have a primary role for inducing severe disease during RSV infection, and may be responsible for altering the lung pathophysiological responses to subsequent allergen challenges via IL‐13‐mediated mechanisms.

Abnormal Histone Methylation Is Responsible for Increased Vascular Endothelial Growth Factor 165a Secretion from Airway Smooth Muscle Cells in Asthma

Vascular endothelial growth factor (VEGF), a key angiogenic molecule, is aberrantly expressed in several diseases including asthma where it contributes to bronchial vascular remodeling and chronic inflammation. Asthmatic human airway smooth muscle cells hypersecrete VEGF, but the mechanism is unclear. In this study, we defined the mechanism in human airway smooth muscle cells from nonasthmatic and asthmatic patients. We found that asthmatic cells lacked a repression complex at the VEGF promoter, which was present in nonasthmatic cells. Recruitment of G9A, trimethylation of histone H3 at lysine 9 (H3K9me3), and a resultant decrease in RNA polymerase II at the VEGF promoter was critical to repression of VEGF secretion in nonasthmatic cells. At the asthmatic promoter, H3K9me3 was absent because of failed recruitment of G9a; RNA polymerase II binding, in association with TATA-binding protein-associated factor 1, was increased; H3K4me3 was present; and Sp1 binding was exaggerated and sustained. In contrast, DNA methylation and histone acetylation were similar in asthmatic and nonasthmatic cells. This is the first study, to our knowledge, to show that airway cells in asthma have altered epigenetic regulation of remodeling gene(s). Histone methylation at genes such as VEGF may be an important new therapeutic target.