The airway epithelium as regulator of inflammation patterns in asthma

Unravelling the complexity of tissue inflammation in uncontrolled and severe asthma

PURPOSE OF REVIEW

The clinical and inflammatory heterogeneity in asthma constitutes a major challenge for improved treatment. This review describes the nature of the inflammatory complexity and how it can be decoded to yield improved disease understanding and personalized treatment. The focus is on the difficult task of revealing the immunological complexity as it occurs inside diseased patient tissues.

RECENT FINDINGS

The inflammatory heterogeneity in asthma stretches beyond the classical division into allergic Th2 eosinophilic versus Th1 and/or Th17 neutrophilic (or paucigranulocytic) phenotypes. Rather than having one distinct type of inflammation, many patients display a patchwork of overlapping immune signatures. The patient diversity is further increased by differences in regard of distal lung involvement. Faced with this staggering complexity, calls have been made for a pragmatic biomarker-guided identification of treatable traits. In parallel, novel high-dimensional analyses and multiplex imaging aid the long-term goal of decoding the underlying molecular endotypes.

SUMMARY

Asthma is vastly heterogeneous with multiple and superimposed inflammatory and anatomical phenotypes. Despite the intensive research and introduction of highly immune-selective dugs, basic questions remain; especially as still too many of today's uncontrolled patients remain poorly understood. Here, pragmatic biomarker strategies, combined with novel methodological approaches that ultimately reveal the complete immunological complexity, will pave the way for improved differential diagnosis and personalized medication.

Recent progress regarding kaempferol for the treatment of various diseases

Kaempferol, also known as kaempferol-3 or kaempferide, is a flavonoid compound that naturally occurs in tea, as well as numerous common vegetables and fruits, including beans, broccoli, cabbage, gooseberries, grapes, kale, strawberries, tomatoes, citrus fruits, brussel sprouts, apples and grapefruit. The present review mainly summarizes the application of kaempferol in treating diseases and the underlying mechanisms that are currently being studied. Due to its anti-inflammatory properties, it may be used to treat numerous acute and chronic inflammation-induced diseases, including intervertebral disc degeneration and colitis, as well as post-menopausal bone loss and acute lung injury. In addition, it has beneficial effects against cancer, liver injury, obesity and diabetes, inhibits vascular endothelial inflammation, protects the cranial nerve and heart function, and may be used for treating fibroproliferative disorders, including hypertrophic scar.

Targeted inhibition of GATA-6 attenuates airway inflammation and remodeling by regulating caveolin-1 through TLR2/MyD88/NF-κB in murine model of asthma

The purpose of this study was to evaluate the effects of GATA-6 on airway inflammation and remodeling and the underlying mechanisms in a murine model of chronic asthma. Female BALB/c mice were randomly divided into four groups: phosphate-buffered saline control (PBS), ovalbumin (OVA)-induced asthma group (OVA), OVA+ siNC and OVA+ siGATA-6. In this mice model, GATA-6 expression level was significantly elevated and the expression in Caveolin-1 (Cav-1) inversely correlated with the abundance of GATA-6 in OVA-induced asthma of mice. Silencing of GATA-6 gene expression upregulated Cav-1 expression. Additionally, downregulation of GATA-6 dramatically decreased OVA-challenged inflammation, infiltration, and mucus production. Moreover, silencing of GATA-6 resulted in decreased levels of immunoglobulin E (IgE) and inflammatory mediators and reduced inflammatory cell accumulation, as well as inhibiting the expression of important mediators including matrix metalloproteinase (MMP)-2 and MMP-9, TGF-β1, and a disintegrin and metalloproteinase 8 (ADAM8) and ADAM33, which is related to airway remodeling. Further analysis confirmed that silencing of GATA-6 attenuated OVA-induced airway inflammation and remodeling through the TLR2/MyD88 and NF-κB pathway. In conclusion, these findings indicated that the downregulation of GATA-6 effectively inhibited airway inflammation and reversed airway remodeling via Cav-1, at least in part through downregulation of TLR2/MyD88/NF-κB, which suggests that GATA-6 represents a promising therapeutic strategy for human allergic asthma.

The PPARγ agonist, rosiglitazone, attenuates airway inflammation and remodeling via heme oxygenase-1 in murine model of asthma

AIM

Rosiglitazone is one of the specific PPARγ agonists showing potential therapeutic effects in asthma. Though PPARγ activation was considered protective in inhibiting airway inflammation and remodeling in asthma, the specific mechanisms are still unclear. This study was aimed to investigate whether heme oxygenase-1 (HO-1) related pathways were involved in rosiglitazone-activated PPARγ signaling in asthma treatment.

METHODS

Asthma was induced in mice by multiple exposures to ovalbumin (OVA) in 8 weeks. Prior to every OVA challenge, the mice received rosiglitazone (5 mg/kg, p.o.). After the mice were sacrificed, the bronchoalveolar lavage fluid (BALF), blood samples and lungs were collected for analyses. The activities of HO-1, MMP-2 and MMP-9 in airway tissue were assessed, and the expression of PPARγ, HO-1 and p21 proteins was also examined.

RESULTS

Rosiglitazone administration significantly attenuated airway inflammation and remodeling in mice with OVA-induced asthma, which were evidenced by decreased counts of total cells, eosinophils and neutrophils, and decreased levels of IL-5 and IL-13 in BALF, and by decreased airway smooth muscle layer thickness and reduced airway collagen deposition. Furthermore, rosiglitazone administration significantly increased PPARγ, HO-1 and p21 expression and HO-1 activity, decreased MMP-2 and MMP-9 activities in airway tissue. All the therapeutic effects of rosiglitazone were significantly impaired by co-administration of the HO-1 inhibitor ZnPP.

CONCLUSION

Rosiglitazone effectively attenuates airway inflammation and remodeling in OVA-induced asthma of mice by activating PPARγ/HO-1 signaling pathway.

Fluticasone Induces Epithelial Injury and Alters Barrier Function in Normal Subjects

Objective

The airway epithelium has a number of roles pivotal to the pathogenesis of asthma, including provision of a physical and immune barrier to the inhaled environment. Dysregulated injury and repair responses in asthma result in loss of airway epithelial integrity. Inhaled corticosteroids are a corner stone of asthma treatment. While effective in controlling asthma symptoms, they fail to prevent airway remodeling. Direct cytopathic effects on the airway epithelium may contribute to this.

Methods

This study examined the effects of a 4-week treatment regimen of inhaled fluticasone 500 μg twice daily in healthy human subjects. Induced sputum was collected for cell counts and markers of inflammation. Barrier function was examined by diethylenetriaminepentacetic acid (DTPA) clearance measured by nuclear scintillation scan, and albumin concentration in induced sputum.

Results

Steroid exposure resulted in epithelial injury as measured by a significant increase in the number of airway epithelial cells in induced sputum. There was no change in airway inflammation by induced sputum inflammatory cell counts or cytokine levels. Epithelial shedding was associated with an increase in barrier function, as measured by both a decrease in DTPA clearance and decreased albumin in induced sputum. This likely reflects the normal repair response.

Conclusion

Inhaled corticosteroids cause injury to normal airway epithelium. These effects warrant further evaluation in asthma, where the dysregulated repair response may contribute to airway remodeling.

Thymic stromal lymphopoietin is induced by respiratory syncytial virus-infected airway epithelial cells and promotes a type 2 response to infection

BACKGROUND

Respiratory viral infection, including respiratory syncytial virus (RSV) and rhinovirus, has been linked to respiratory disease in pediatric patients, including severe acute bronchiolitis and asthma exacerbation.

OBJECTIVE

The study examined the role of the epithelial-derived cytokine thymic stromal lymphopoietin (TSLP) in the response to RSV infection.

METHODS

Infection of human airway epithelial cells was used to examine TSLP induction after RSV infection. Air-liquid interface cultures from healthy children and children with asthma were also tested for TSLP production after infection. Finally, a mouse model was used to directly test the role of TSLP signaling in the response to RSV infection.

RESULTS

Infection of airway epithelial cells with RSV led to the production of TSLP via activation of an innate signaling pathway that involved retinoic acid induced gene I, interferon promoter-stimulating factor 1, and nuclear factor-κB. Consistent with this observation, airway epithelial cells from asthmatic children a produced significantly greater levels of TSLP after RSV infection than cells from healthy children. In mouse models, RSV-induced TSLP expression was found to be critical for the development of immunopathology.

CONCLUSION

These findings suggest that RSV can use an innate antiviral signaling pathway to drive a potentially nonproductive immune response and has important implications for the role of TSLP in viral immune responses in general.

Kaempferol suppresses eosionphil infiltration and airway inflammation in airway epithelial cells and in mice with allergic asthma

The airway epithelium is thought to play an important role in the pathogenesis of asthma. Airway epithelial activation may contribute to inflammatory and airway-remodeling events characteristic of asthma. Kaempferol, a flavonoid with antioxidative and antitumor properties, has been studied as an antiinflammatory agent. However, little is known regarding its effects on allergic asthma. Human airway epithelial BEAS-2B cells and eosinophils were used to investigate the effects of kaempferol on endotoxin- or cytokine-associated airway inflammation. Kaempferol, nontoxic at 1-20 μmol/L, suppressed LPS-induced eotaxin-1 protein expression that may be mediated, likely via Janus kinase 2 (JAK2) JAK2 signaling. Additionally, 1-20 μmol/L kaempferol dose-dependently attenuated TNFα-induced expression of epithelial intracellular cell adhesion molecule-1 and eosinophil integrin β2, thus encumbering the eosinophil-airway epithelium interaction. Kaempferol blunted TNFα-induced airway inflammation by attenuating monocyte chemoattractant protein-1 transcription, possibly by disturbing NF-κB signaling. This study further investigated antiallergic activity of kaempferol in BALB/c mice sensitized with ovalbumin (OVA) and challenged with a single dose of OVA. Oral administration of kaempferol attenuated OVA challenge-elevated expression of eotaxin-1 and eosinophil major basic protein via the blockade of NF-κB transactivation, thereby blunting eosinophil accumulation in airway and lung tissue. Therefore, dietary kaempferol is effective in ameliorating allergic and inflammatory airway diseases through disturbing NF-κB signaling.