Agonist activation of f-actin-mediated eosinophil shape change and mediator release is dependent on Rac2

Potent CCR3 Receptor Antagonist, SB328437, Suppresses Colonic Eosinophil Chemotaxis and Inflammation in the Winnie Murine Model of Spontaneous Chronic Colitis

Eosinophils and their regulatory molecules have been associated with chronic intestinal inflammation and gastrointestinal dysfunctions; eosinophil accumulation in the gut is prominent in inflammatory bowel disease (IBD). The chemokine receptor CCR3 plays a pivotal role in local and systemic recruitment and activation of eosinophils. In this study, we targeted CCR3-ligand interactions with a potent CCR3 receptor antagonist, SB328437, to alleviate eosinophil-associated immunological responses in the Winnie model of spontaneous chronic colitis. Winnie and C57BL/6 mice were treated with SB328437 or vehicle. Clinical and histopathological parameters of chronic colitis were assessed. Flow cytometry was performed to discern changes in colonic, splenic, circulatory, and bone marrow-derived leukocytes. Changes to the serum levels of eosinophil-associated chemokines and cytokines were measured using BioPlex. Inhibition of CCR3 receptors with SB328437 attenuated disease activity and gross morphological damage to the inflamed intestines and reduced eosinophils and their regulatory molecules in the inflamed colon and circulation. SB328437 had no effect on eosinophils and their progenitor cells in the spleen and bone marrow. This study demonstrates that targeting eosinophils via the CCR3 axis has anti-inflammatory effects in the inflamed intestine, and also contributes to understanding the role of eosinophils as potential end-point targets for IBD treatment.

Alteration of lung tissues proteins in birch pollen induced asthma mice before and after SCIT

Subcutaneous immunotherapy (SCIT) is a classic form of allergen-specific immunotherapy that is used to treat birch pollen induced allergic asthma. To investigate the underlying molecular mechanisms of SCIT, we aimed to profile lung samples to explore changes in the differential proteome before and after SCIT in mice with allergic asthma. Fresh lungs were collected from three groups of female BALB/c mice: 1) control mice, 2) birch pollen-induced allergic mice, and 3) birch pollen-induced allergic mice with SCIT. Tandem mass tag (TMT) labelling coupled with liquid chromatography-tandem mass spectrometry (LC-MS/MS) was used to analyze the lung proteome in the mice. Ingenuity pathway analysis (IPA) and Gene Ontology (GO) classification analysis were applied to identify differentially expressed proteins (DEPs) and crucial pathways. The screened DEPs were validated by immunohistochemistry analysis. A total of 317 proteins were upregulated and 184 proteins were downregulated in the asthma group compared to those of the control group. In contrast, 639 DEPs (163 upregulated and 456 downregulated proteins) were identified after SCIT in comparison with those of the asthma group. Among the 639 DEPs, 277 proteins returned to similar levels as those of the relative non-asthma condition. Bioinformatic analysis revealed that the 277 proteins played a significant role in the leukocyte extravasation signaling pathway. The leukocyte extravasation signaling pathway and related DEPs were of crucial importance in birch pollen SCIT.

Eosinophil Shape Change and Secretion

The analysis of eosinophil shape change and mediator secretion is a useful tool in understanding how eosinophils respond to immunological stimuli and chemotactic factors. Eosinophils undergo dramatic shape changes, along with secretion of the granule-derived enzyme eosinophil peroxidase (EPX) in response to chemotactic stimuli including platelet-activating factor (PAF) and CCL11 (eotaxin-1). Here, we describe the analysis of eosinophil shape change by confocal microscopy analysis and provide an experimental approach for comparing unstimulated cells with those that have been stimulated to undergo chemotaxis. In addition, we illustrate two different degranulation assays for EPX using OPD and an ELISA technique and show how eosinophil degranulation may be assessed from in vitro as well as ex vivo stimulation.

Pin1 Regulates IL-5 Induced Eosinophil Polarization and Migration

Eosinophils become polarized in response to cytokines such IL-5 or eotaxin prior to directional migration. Polarization is preceded by F-actin assembly, but the mechanisms that regulate these events and how the shape change influences cell migration from the peripheral blood into the lung remain unclear. In this study, we show that the prolyl isomerase, Pin1, is required for IL-5-induced Eos polarization and migration. Co-immunoprecipitation and immunofluorescence analysis revealed that Pin1 directly interacts with members of Rho GTPase family. Mouse eosinophils lacking Pin1 or human cells treated with Pin1 inhibitors showed significantly reduced IL-5-induced GTPase activity and cofilin phosphorylation, resulting in reduced F-actin polymerization, cell polarization, and directional migration to chemokines. Our result suggests that Pin1 regulates cytoskeletal re-organization, eosinophil morphology, and cell migration through the modulation of Rho GTPase activity. Targeting Pin1 along with GTPases could provide a new approach to reduce pulmonary Eos accumulation during asthmatic exacerbations.

Molecular Biology of Eosinophils: Introduction

The eosinophil is an enigmatic cell with a continuing ability to fascinate. A considerable history of research endeavor on eosinophil biology stretches from the present time back to the nineteenth century. Perhaps one of the most fascinating aspects of the eosinophil is how accumulating knowledge has changed the perception of its function from passive bystander, modulator of inflammation, to potent effector cell loaded with histotoxic substances through to more recent recognition that it can act as both a positive and negative regulator of complex events in both innate and adaptive immunity. This book consists of chapters written by experts in the field of eosinophil biology that provide comprehensive clearly written protocols for techniques designed to underpin research into the function of the eosinophil in health and disease.

Cytokine trafficking of IL-9 and IL-13 through TfnRc+ vesicles in activated human eosinophils

Eosinophils are granulocytes that are elevated in lung mucosa in approximately half of patients with allergic asthma. These highly granulated cells can synthesize and secrete many cytokines, including IL-9 and IL-13. We hypothesized that IL-9 and IL-13 are found as preformed mediators in crystalloid granules and secreted using distinct trafficking pathways. Human eosinophils were purified from peripheral venous blood, adhered to coverslips, and stimulated with platelet activating factor (PAF). Cells were immunolabeled with antibodies to IL-9 or IL-13 and colocalized with markers for secretory organelles, using CD63 for crystalloid granules and transferrin receptor (TfnRc) for vesicles. Fixed cells were imaged using super-resolution microscopy and quantified by colocalization using Pearson's correlation coefficient. IL-9 immunofluorescence increased in a time-dependent manner to PAF, whereas colocalization of IL-9 and CD63 significantly increased from 0.52 to 0.67 after 5 min PAF. Colocalization of IL-9 with TfnRc significantly increased at 60 min of stimulation with PAF (0.54 at 0 min to 0.60 at 60 min). IL-13 showed lower colocalization with CD63 (0.55) than TfnRc (0.63) in unstimulated cells. Upon PAF stimulation, IL-13 intensity transiently decreased at 5 and 60 min, whereas colocalization of IL-13 with CD63 decreased throughout stimulation to 0.43. While colocalization of IL-13 with TfnRc transiently increased to 0.66 at 5 min PAF, it returned to near baseline levels (0.64) after 15 min PAF. Our results suggest that IL-9 and IL-13 are stored in crystalloid granules as well as endosomal structures, and that IL-9 is primarily trafficked to the cell surface via TfnRc⁺ endosome-like vesicles.

Atomic Force Microscopy Is a Potent Technique to Study Eosinophil Activation

Eosinophils are multifunctional cells with several functions both in healthy individuals, and those with several diseases. Increased number and morphological changes in eosinophils have been correlated with the severity of an acute asthma exacerbation. We measured eosinophils obtained from healthy controls and individuals with acute asthma using atomic force microscopy (AFM). In the control samples, cells showed more rounded morphologies with some spreading, while activated cells from symptomatic individuals were spreading, and presenting emission of multiple pseudopods. Eosinophils presenting separate granules close to the cells suggesting some degranulation was also increased in asthma samples. In comparison to histopathological techniques based on brightfield microscopy, AFM showed considerably more details of these morphological changes, making the technique much more sensitive to detect eosinophil morphological changes that indicate functional alteration of this cell. AFM could be an important tool to evaluate diseases with alterations in eosinophil functions.

Rho and Rac, but not ROCK, are required for secretion of human and mouse eosinophil-associated RNases

BACKGROUND

Eosinophil-associated RNases (EARs) are stored preformed in eosinophil cytoplasmic secretory granules and have a key role in eosinophil effector functions in host defence and inflammatory disorders. However, the secretion mechanisms of EARs are poorly understood.

OBJECTIVE

Our study aimed to understand the involvement of cytoskeleton machinery in EAR secretion.

METHODS

Fresh human and mouse eosinophils were stimulated with CCL11, and the secretion of enzymatically active EARs was detected using an RNase activity assay. The involvement of cytoskeletal elements or microtubules was probed using specific inhibitors.

RESULTS

We found that dynamic polymerization of microtubules and cytoskeletal elements, such as Rho and Rac, is required for chemokine-mediated EAR secretion from human and mouse eosinophils. However, inhibition of ROCK (Rho-associated protein kinase) increased EAR secretion in human and mouse eosinophils even in the absence of chemokine stimulation, suggesting ROCK negatively regulates EAR secretion.

CONCLUSIONS

Collectively, these data suggest a cytoskeleton-dependent mechanism of EAR secretion from eosinophils, findings that are pertinent to host defence, allergy and other eosinophil-associated diseases.

RAC2 promotes abnormal proliferation of quiescent cells by enhanced JUNB expression via the MAL-SRF pathway

Radiation-induced lung injury (RILI) occurs most often in radiotherapy of lung cancer, esophageal cancer, and other thoracic cancers. The occurrence of RILI is a complex process that includes a variety of cellular and molecular interactions, which ultimately result in carcinogenesis. However, the underlying mechanism is unknown. Here we show that Ras-related C3 botulinum toxin substrate 2 (RAC2) and transcription factor jun-B (JUNB) were upregulated in non-small cell carcinoma (NSCLC) tissues and were associated with poor prognoses for NSCLC patients. Ionizing radiation also caused increased expression of RAC2 in quiescent stage cells, and the reentry of quiescent cells into a new cell cycle. The activity of the serum response factor (SRF) was activated by RAC2 and other Rho family genes (RhoA, ROCK, and LIM kinase). Consequently, JUNB acted as an oncogene and induced abnormal proliferation of quiescent cells. Together, the results showed that RAC2 can be used as a target gene for radiation protection. A better understanding of the RAC2 and JUNB mechanisms in the molecular etiology of lung cancer will be helpful in reducing cancer risks and side effects during treatment of this disorder. Our study therefore provides a new perspective on the involvement of RAC2 and JUNB as oncogenes in the tumorigenesis of NSCLC.

Enhanced activation of eosinophils in peripheral blood and implications for eosinophilic esophagitis diagnosis

BACKGROUND AND AIM

Eosinophils are markers of the eosinophilic esophagitis (EoE) disease, and this work aimed to assess whether activation of eosinophils could be a noninvasive test to contribute for EoE diagnosis.

METHODS

The activation state of peripheral blood eosinophils in EoE patients and control subjects was assessed based on the morphological aspects of the eosinophil after adherence to slide. Cyclooxygenase-2 and 5-lipoxygenase expressions were evaluated by means of immunofluorescence microscopy to verify if and which eicosanoid pathway is triggered in eosinophils in blood in EoE.

RESULTS

The eosinophils of patients with EoE were significantly more activated than those of control individuals. The lowest percentage of normal eosinophils for control subjects was 40%, while the highest percentage of eosinophils of normal aspect for patients with EoE was 32%. Considering 36% as a cutoff for normal eosinophils, this value differentiated all individuals with EoE from individuals without the disease with a sensitivity of 100%, considering the diagnosis of EoE as currently defined. Eosinophils of EoE patients showed higher expression of cyclooxygenase-2 than those of control subjects.

CONCLUSIONS

The quantification of morphological changes in eosinophils is a feasible, easy, and reliable manner to identify EoE patients. Therefore, patients with symptoms of esophageal dysfunction showing higher than 36% activated eosinophils in peripheral blood could be a useful way to help definition and diagnostic criterion for EoE.

Comparison of ultrastructural and nanomechanical signature of platelets from acute myocardial infarction and platelet activation

Acute myocardial infarction (AMI) initiation and progression follow complex molecular and structural changes in the nanoarchitecture of platelets. However, it remains poorly understood how the transformation from health to AMI alters the ultrastructural and biomechanical properties of platelets within the platelet activation microenvironment. Here, we show using an atomic force microscope (AFM) that platelet samples, including living human platelets from the healthy and AMI patient, activated platelets from collagen-stimulated model, show distinct ultrastructural imaging and stiffness profiles. Correlative morphology obtained on AMI platelets and collagen-activated platelets display distinct pseudopodia structure and nanoclusters on membrane. In contrast to normal platelets, AMI platelets have a stiffer distribution resulting from complicated pathogenesis, with a prominent high-stiffness peak representative of platelet activation using AFM-based force spectroscopy. Similar findings are seen in specific stages of platelet activation in collagen-stimulated model. Further evidence obtained from different force measurement region with activated platelets shows that platelet migration is correlated to the more elasticity of pseudopodia while high stiffness at the center region. Overall, ultrastructural and nanomechanical profiling by AFM provides quantitative indicators in the clinical diagnostics of AMI with mechanobiological significance.

Eosinophil cytokines, chemokines, and growth factors: emerging roles in immunity

Eosinophils derive from the bone marrow and circulate at low levels in the blood in healthy individuals. These granulated cells preferentially leave the circulation and marginate to tissues, where they are implicated in the regulation of innate and adaptive immunity. In diseases such as allergic inflammation, eosinophil numbers escalate markedly in the blood and tissues where inflammatory foci are located. Eosinophils possess a range of immunomodulatory factors that are released upon cell activation, including over 35 cytokines, growth factors, and chemokines. Unlike T and B cells, eosinophils can rapidly release cytokines within minutes in response to stimulation. While some cytokines are stored as pre-formed mediators in crystalloid granules and secretory vesicles, eosinophils are also capable of undergoing de novo synthesis and secretion of these immunological factors. Some of the molecular mechanisms that coordinate the final steps of cytokine secretion are hypothesized to involve binding of membrane fusion complexes comprised of soluble N-ethylmaleimide sensitive factor attachment protein receptors (SNAREs). These intracellular receptors regulate the release of granules and vesicles containing a range of secreted proteins, among which are cytokines and chemokines. Emerging evidence from both human and animal model-based research has suggested an active participation of eosinophils in several physiological/pathological processes such as immunomodulation and tissue remodeling. The observed eosinophil effector functions in health and disease implicate eosinophil cytokine secretion as a fundamental immunoregulatory process. The focus of this review is to describe the cytokines, growth factors, and chemokines that are elaborated by eosinophils, and to illustrate some of the intracellular events leading to the release of eosinophil-derived cytokines.

The Rho GTPase Rac1 is required for recycling endosome-mediated secretion of TNF in macrophages

Rho GTPases are required for many cellular events such as adhesion, motility, and membrane trafficking. Here we show that in macrophages, the Rho GTPases Rac1 and Cdc42 are involved in lamellipodia and filopodia formation, respectively, and that both of these Rho GTPases are essential for the efficient surface delivery of tumor necrosis factor (TNF) to the plasma membrane following TLR4 stimulation. We have previously demonstrated intracellular trafficking of TNF via recycling endosomes in lipopolysaccharide (LPS)-activated macrophages. Here, we further define a specific role for Rac1 in intracellular TNF trafficking, demonstrating impairment in TNF release following TLR4 stimulation in the presence of a Rac inhibitor, in cells expressing a dominant negative (DN) form of Rac1, and following small interfering RNA (siRNA) knockdown of Rac1. Rac1 activity was required for TNF trafficking but not for TLR4 signaling following LPS stimulation. Reduced TNF secretion was due to a defect in Rac1 activity, but not of the closely related Rho GTPase Rac2, demonstrated by the additional use of macrophages derived from Rac2-deficient mice. Labeling recycling endosomes by the uptake of fluorescent transferrin enabled us to show that Rac1 was required for the final stages of TNF trafficking and delivery from recycling endosomes to the plasma membrane. Thus, actin remodeling by the Rho GTPase Rac1 is required for TNF cell surface delivery and release from macrophages.

Eosinophil shape change and secretion

The analysis of eosinophil shape change and mediator secretion is a useful tool in understanding how eosinophils respond to immunological stimuli and chemotactic factors. Eosinophils undergo dramatic shape changes, along with secretion of the granule-derived enzyme eosinophil peroxidase (EPX) in response to chemotactic stimuli including platelet-activating factor and CCL11 (eotaxin-1). Here, we describe the analysis of eosinophil shape change by confocal microscopy analysis and provide an experimental approach for comparing unstimulated cells with those that have been stimulated to undergo chemotaxis. In addition, we illustrate two different degranulation assays for EPX using OPD and an enzyme-linked immunosorbent assay technique and show how eosinophil degranulation may be assessed from in vitro as well as ex vivo stimulation.

An essential role for Rab27a GTPase in eosinophil exocytosis

Eosinophil degranulation has been implicated in inflammatory processes associated with allergic asthma. Rab27a, a Rab-related GTPase, is a regulatory intracellular signaling molecule expressed in human eosinophils. We postulated that Rab27a regulates eosinophil degranulation. We investigated the role of Rab27a in eosinophil degranulation within the context of airway inflammation. Rab27a expression and localization in eosinophils were investigated by using subcellular fractionation combined with Western blot analysis, and the results were confirmed by immunofluorescence analysis of Rab27a and the granule membrane marker CD63. To determine the function of eosinophil Rab27a, we used Ashen mice, a strain of Rab27a-deficient animals. Ashen eosinophils were tested for degranulation in response to PAF and calcium ionophore by measuring released EPX activity. Airway EPX release was also determined by intratracheal injection of eosinophils into mice lacking EPX. Rab27a immunoreactivity colocalized with eosinophil crystalloid granules, as determined by subcellular fractionation and immunofluorescence analysis. PAF induced eosinophil degranulation in correlation with redistribution of Rab27a(+) structures, some of which colocalized with CD63(+) crystalloid granules at the cell membrane. Eosinophils from mice had significantly reduced EPX release compared with normal WT eosinophils, both in vitro and in vivo. In mouse models, Ashen mice demonstrated reduced EPX release in BAL fluid. These findings suggest that Rab27a has a key role in eosinophil degranulation. Furthermore, these findings have implications for Rab27a-dependent eosinophil degranulation in airway inflammation.

Morphological changes in eosinophils are reliable markers of the severity of an acute asthma exacerbation in children

BACKGROUND

Early identification of the severity of asthma exacerbation would be helpful for the management of patients. We aimed to evaluate the correlation of morphological change in activated eosinophils and the severity of an asthma exacerbation.

METHODS

Blood was collected from 55 asthmatic children: 40 of whom were having an exacerbation, 15 symptom-free, and 15 healthy controls. The percentage of eosinophils with morphological changes (emission of single or multiple pseudopods, presence of cytoplasmic vacuoles, releasing a small, moderate, or large quantity of granules, spreading, eosinophil death, and presence of cluster of free eosinophil granules) was quantified after the adherence to a slide and compared using the Mann-Whitney test. The correlation between the severity of the asthma exacerbation and the percentage changed eosinophils was tested with Spearman's correlation.

RESULTS

The proportion of activated eosinophils was higher in asthmatic symptom-free children than in the control group, and acute asthma exacerbation produced an additional increase in eosinophil activation (P < 0.01). More significantly increased morphological changes were emissions of multiple pseudopods, presence of cytoplasmic vacuoles, spreading, and presence of a cluster of free eosinophil granules (P < 0.001). The following were correlated with the severity of an asthma exacerbation: ≥14% of eosinophils emitting single pseudopod, 8% emitting multiple pseudopods, 17% with vacuoles, 28% eosinophils releasing a large quantity of granules, and 66% of spread eosinophils.

CONCLUSIONS

Quantifying the morphological changes in eosinophils is a feasible, easy, and reliable manner to identify the severity of an asthma exacerbation and therefore might improve the clinical management of asthmatic children.