P-selectin mediates IL-13-induced eosinophil transmigration but not eotaxin generation in vivo: a comparative study with IL-4-elicited responses

An endothelial microRNA-1-regulated network controls eosinophil trafficking in asthma and chronic rhinosinusitis

BACKGROUND

Airway eosinophilia is a prominent feature of asthma and chronic rhinosinusitis (CRS), and the endothelium plays a key role in eosinophil trafficking. To date, microRNA-1 (miR-1) is the only microRNA known to be regulated in the lung endothelium in asthma models.

OBJECTIVE

We sought to determine the role of endothelial miR-1 in allergic airway inflammation.

METHODS

We measured microRNA and mRNA expression using quantitative RT-PCR. We used ovalbumin and house dust mite models of asthma. Endothelium-specific overexpression of miR-1 was achieved through lentiviral vector delivery or induction of a transgene. Tissue eosinophilia was quantified by using Congo red and anti-eosinophil peroxidase staining. We measured eosinophil binding with a Sykes-Moore adhesion chamber. Target recruitment to RNA-induced silencing complex was assessed by using anti-Argonaute2 RNA immunoprecipitation. Surface P-selectin levels were measured by using flow cytometry.

RESULTS

Serum miR-1 levels had inverse correlations with sputum eosinophilia, airway obstruction, and number of hospitalizations in asthmatic patients and sinonasal tissue eosinophilia in patients with CRS. IL-13 stimulation decreased miR-1 levels in human lung endothelium. Endothelium-specific overexpression of miR-1 reduced airway eosinophilia and asthma phenotypes in murine models and inhibited IL-13-induced eosinophil binding to endothelial cells. miR-1 recruited P-selectin, thymic stromal lymphopoietin, eotaxin-3, and thrombopoietin receptor to the RNA-induced silencing complex; downregulated these genes in the lung endothelium; and reduced surface P-selectin levels in IL-13-stimulated endothelial cells. In our asthma and CRS cohorts, miR-1 levels correlated inversely with its target genes.

CONCLUSION

Endothelial miR-1 regulates eosinophil trafficking in the setting of allergic airway inflammation. miR-1 has therapeutic potential in asthmatic patients and patients with CRS.

Intravital imaging of eosinophils: Unwrapping the enigma

Eosinophils are traditionally associated with allergic and parasitic inflammation. More recently, eosinophils have also been shown to have roles in diverse processes including development, intestinal health, thymic selection, and B-cell survival with the majority of these insights being derived from murine models and in vitro assays. Despite this, tools to measure the dynamic activity of eosinophils in situ have been lacking. Intravital microscopy is a powerful tool that enables direct visualization of leukocytes and their dynamic behavior in real-time in a wide range of processes in both health and disease. Until recently eosinophil researchers have not been able to take full advantage of this technology due to a lack of tools such as genetically encoded reporter mice. This mini-review examines the history of intravital microscopy with a focus on eosinophils. The development and use of eosinophil-specific Cre (EoCre) mice to create GFP and tdTomato fluorescent reporter animals is also described. Genetically encoded eosinophil reporter mice combined with intravital microscopy provide a powerful tool to add to the toolbox of technologies that will help us unravel the mysteries still surrounding this cell.

Inhibiting focal adhesion kinase (FAK) blocks IL-4 induced VCAM-1 expression and eosinophil recruitment in vitro and in vivo

Leukocyte recruitment plays a critical role during both normal inflammation and chronic inflammatory diseases, and ongoing studies endeavor to better understand the complexities of this process. Focal adhesion kinase (FAK) is well known for its role in cancer, yet it also has been shown to regulate aspects of neutrophil and B16 melanoma cell recruitment by rapidly influencing endothelial cell focal adhesion dynamics and junctional opening. Recently, we found that FAK related non-kinase (FRNK), a protein that is often used as a FAK dominant negative, blocked eosinophil transmigration by preventing the transcription of vascular cell adhesion molecule-1 (VCAM-1) and eotaxin-3 (CCL26). Surprisingly, the blocking occurred even in the absence of endogenous FAK. To better understand the role of FAK in leukocyte recruitment, we used a FAK-specific inhibitor (PF-573228) and determined the effect on IL-4 induced eosinophil recruitment in vitro and in vivo. PF-573228 prevented the expression of VCAM-1 and CCL26 expression in IL-4-stimulated human endothelial cells in vitro. As a result, eosinophil adhesion and transmigration were blocked. PF-572338 also prevented IL-4-induced VCAM-1 expression in vivo. Using brightfield intravital microscopy, we found that PF-573228 decreased leukocyte rolling flux, adhesion, and emigration. We specifically examined eosinophil recruitment in vivo by using an eosinophil-GFP reporter mouse and found PF-573228 attenuated eosinophil emigration. This study reveals that a FAK inhibitor influences inflammation through its action on eosinophil recruitment.

VEGF controls lung Th2 inflammation via the miR-1-Mpl (myeloproliferative leukemia virus oncogene)-P-selectin axis

Asthma, the prototypic Th2-mediated inflammatory disorder of the lung, is an emergent disease worldwide. Vascular endothelial growth factor (VEGF) is a critical regulator of pulmonary Th2 inflammation, but the underlying mechanism and the roles of microRNAs (miRNAs) in this process have not been defined. Here we show that lung-specific overexpression of VEGF decreases miR-1 expression in the lung, most prominently in the endothelium, and a similar down-regulation occurs in lung endothelium in Th2 inflammation models. Intranasal delivery of miR-1 inhibited inflammatory responses to ovalbumin, house dust mite, and IL-13 overexpression. Blocking VEGF inhibited Th2-mediated lung inflammation, and this was restored by antagonizing miR-1. Using mRNA arrays, Argonaute pull-down assays, luciferase expression assays, and mutational analysis, we identified Mpl as a direct target of miR-1 and showed that VEGF controls the expression of endothelial Mpl during Th2 inflammation via the regulation of miR-1. In vivo knockdown of Mpl inhibited Th2 inflammation and indirectly inhibited the expression of P-selectin in lung endothelium. These experiments define a novel VEGF-miR-1-Mpl-P-selectin effector pathway in lung Th2 inflammation and herald the utility of miR-1 and Mpl as potential therapeutic targets for asthma.

Eosinophils and Trichinella infection: toxic for the parasite and the host?

Peripheral blood and tissue eosinophilia characterize trichinellosis in humans, and present in addition to the increased total IgE levels that occur in many helminth infections. Both processes are the consequence of T-helper 2 activation. Blood and tissue eosinophilia begins with eosinophilopoiesis in the bone marrow, which is followed by the migration of eosinophils through the circulatory system, the eosinophil infiltration of tissues at the inflammatory foci and, finally, degranulation and cell death. Recently, some aspects of eosinophilia caused by Trichinella spiralis infection have been elucidated; however, the protective role of this population of cells against Trichinella parasites remains controversial. Furthermore, when eosinophils are numerous, they can be toxic for host tissues. This review discusses these issues in both human and rodent infection models.

CD34 facilitates the development of allergic asthma

Asthma is a pulmonary inflammatory disease dependent on eosinophil and mast cell infiltration into the lung. CD34 is a sialomucin expressed by both of these cell types, and we have used CD34(-/-) mice and a standard mouse model of asthma to evaluate the importance of CD34 expression on disease development. In comparison with wild-type (wt) mice, CD34(-/-) mice exhibited a dramatic reduction in all hallmarks of allergic asthma, including lowered airway inflammatory cell infiltration, airway hyperresponsiveness, and mast-cell recruitment. Bone marrow transplantation experiments confirmed that these defects are due to CD34 expression by bone marrow-derived cells. This was not, however, due to an inability to respond to antigen as, on a per cell basis, wt and CD34(-/-) inflammatory cells exhibit identical responses in cytokine production. We found a striking reduction in mobility of CD34(-/-) eosinophils in vitro, the major component of inflammatory infiltrates, which was consistent with proposed models for CD34 as an inhibitor of cell-cell adhesion. In summary, our data suggest that CD34 enhances mast-cell and eosinophil invasiveness and that its expression by these cells is a prerequisite for development of allergic asthma.

Junctional adhesion molecule-C regulates the early influx of leukocytes into tissues during inflammation

Leukocyte recruitment from blood to inflammatory sites occurs in a multistep process that involves discrete molecular interactions between circulating and endothelial cells. Junctional adhesion molecule (JAM)-C is expressed at different levels on endothelial cells of lymphoid organs and peripheral tissues and has been proposed to regulate neutrophil migration by its interaction with the leukocyte integrin Mac-1. In the present study, we show that the accumulation of leukocytes in alveoli during acute pulmonary inflammation in mice is partially blocked using neutralizing Abs against JAM-C. To confirm the function of JAM-C in regulating leukocyte migration in vivo, we then generated a strain of transgenic mice overexpressing JAM-C under the control of the endothelial specific promotor Tie2. The transgenic animals accumulate more leukocytes to inflammatory sites compared with littermate control mice. Intravital microscopy shows that this is the result of increased leukocyte adhesion and transmigration, whereas rolling of leukocytes is not significantly affected in transgenic mice compared with littermates. Thus, JAM-C participates in the later steps of the leukoendothelial adhesion cascade.