Yoshiki Kobayashi

Physiological Levels of 15-Deoxy-Δ12,14-Prostaglandin J2 Prime Eotaxin-Induced Chemotaxis on Human Eosinophils through Peroxisome Proliferator-Activated Receptor-γ Ligation

15-Deoxy-Δ12,14-PGJ2 (15d-PGJ2), mainly produced by mast cells, is known as a potent lipid mediator derived from PGD2 in vivo. 15d-PGJ2 was thought to exert its effects on cells exclusively through peroxisome proliferator-activated receptor-γ (PPARγ) and chemoattractant receptor-homologous molecule expressed on Th2 cells (CRTH2), which are both expressed on human eosinophils. However, the physiological role of 15d-PGJ2 remains unclear, because the concentration generated in vivo is generally much lower than that required for its biological functions. In the present study we found that low concentrations (picomolar to low nanomolar) of 15d-PGJ2 and a synthetic PPARγ agonist markedly enhanced the eosinophil chemotaxis toward eotaxin, and the effect was decreased in a dose-dependent manner. Moreover, at a low concentration (10−10 M), 15d-PGJ2 and troglitazone primed eotaxin-induced shape change and actin polymerization. These priming effects were completely reversed by a specific PPARγ antagonist, but were not mimicked by CRTH2 agonist 13,14-dihydro-15-keto-PGD2, suggesting that the effects were mediated through PPARγ ligation. The effect exerted by 15d-PGJ2 parallels the enhancement of Ca2+ influx, but is not associated with the ERK, p38 MAPK, and NF-κB pathways. Furthermore, the time course and treatment of eosinophils with actinomycin D, an inhibitor of gene transcription, indicated that the transcription-independent pathway had a role in this process. PPARγ might interact with an eotaxin-induced cytosolic signaling pathway, because PPARγ is located in the eosinophil cytosol. Taken together with current findings, these results suggest that under physiological conditions, 15d-PGJ2 contributes to allergic inflammation through PPARγ, which plays a role as a biphasic regulator of immune response.

Gender difference in allergic airway remodelling and immunoglobulin production in mouse model of asthma

Epidemiological studies have shown that the prevalence of adult asthma and severe asthma is higher in women. It has also been reported that female mice are more susceptible than males to the development of allergic airway inflammation and airway hyperresponsiveness (AHR). The influence of gender difference in the pathogenesis of severe asthma, especially airway remodelling in an animal model, has been studied rarely. We investigated gender difference in the development of airway remodelling using a long‐term antigen‐challenged mouse asthma model.

Obesity and Eosinophilic Inflammation: Does Leptin Play a Role

It has been pointed out that obesity is a risk factor for, and is involved in the exacerbation of asthma. Mounting evidence about adipose tissue-derived proteins (adipokines) gave rise to the current understanding of obesity as a systemic inflammatory disorder. In this review, we summarized the involvement of leptin, focusing on eosinophil functions. Several studies have indicated that leptin can restrain eosinophil apoptosis, enhance migration, increase adhesion molecules and induce cytokine production. Since leptin also acts on a variety of immune cells related to allergic response, increased leptin in obese individuals potentially explains the mechanism by which obesity leads to an exacerbation of asthma. Further studies targeting adipokines will delineate the association between obesity and eosinophil-associated diseases.

Expression and functional roles of G-protein-coupled estrogen receptor (GPER) in human eosinophils

Sexual dimorphism in asthma links the estrogen and allergic immune responses. The function of estrogen was classically believed to be mediated through its nuclear receptors, i.e., estrogen receptors (ERs). However, recent studies established the important roles of G-protein-coupled estrogen receptor (GPER/GPR30) as a novel membrane receptor for estrogen. To date, the role of GPER in allergic inflammation is poorly understood. The purpose of this study was to examine whether GPER might affect the functions of eosinophils, which play an important role in the pathogenesis of asthma. Here, we demonstrated that GPER was expressed in purified human peripheral blood eosinophils both at the mRNA and protein levels. Although GPER agonist G-1 did not induce eosinophil chemotaxis or chemokinesis, preincubation with G-1 enhanced eotaxin (CCL11)-directed eosinophil chemotaxis. G-1 inhibited eosinophil spontaneous apoptosis and caspase-3 activities. The anti-apoptotic effect was not affected by the cAMP-phospodiesterase inhibitor rolipram or phosphoinositide 3-kinase inhibitors. In contrast to resting eosinophils, G-1 induced apoptosis and increased caspase-3 activities when eosinophils were co-stimulated with IL-5. No effect of G-1 was observed on eosinophil degranulation in terms of release of eosinophil-derived neurotoxin (EDN). The current study indicates the functional capacities of GPER on human eosinophils and also provides the previously unrecognized mechanisms of interaction between estrogen and allergic inflammation.

Soluble vascular cell adhesion molecule-1 induces human eosinophil migration

Background:  Tissue eosinophilia is one of the hallmarks of allergic diseases and Th2‐type immune responses including asthma. Adhesion molecules are known to play an important role in the accumulation of eosinophils in allergic inflammatory foci, and they contribute to eosinophil activation. Elevated levels of the soluble forms of adhesion molecules in the body fluid of asthmatic patients have been observed, although their pathophysiological significance remains to be fully elucidated.

Theophylline and Dexamethasone Induce Peroxisome Proliferator-Activated Receptor-γ Expression in Human Eosinophils

Eosinophils are major effector cells in allergic diseases including asthma. Peroxisome proliferator-activated receptor-γ (PPARγ) is a nuclear receptor that regulates immune reaction. We have previously demonstrated that human eosinophils express PPARγ and that stimulation with a synthetic agonist for PPARγ attenuated the factor-induced eosinophil survival and chemotaxis. However, the modulator of the eosinophil PPARγ expression has not yet been studied. In this study, we investigated the effect of theophylline and dexamethasone (widely used drugs in the treatment of asthma) on PPARγ expression in eosinophils. Purified human peripheral blood eosinophils were cultured, and therapeutic concentrations of theophylline and dexamethasone were added. Subsequently, PPARγ was measured using quantitative real-time RT-PCR and flow cytometry. Theophylline and dexamethasone markedly enhanced both mRNA and protein levels of PPARγ. These findings suggest that the increase in PPARγ expression on eosinophils may play a role in the anti-inflammatory effects of theophylline and dexamethasone.

RANTES and Eotaxin Enhance CD11b and CD18 Expression on Eosinophils from Allergic Patients with Eosinophilia in the Application of Whole Blood Flow Cytometry Analysis

Background: C-C chemokines and adhesion molecules expressed on eosinophils play an important role in the pathology of allergic inflammatory disease. C-C chemokines such as eotaxin or RANTES are involved in β2 integrin expression on purified eosinophils; so far we have no data on unpurified eosinophils in the peripheral blood. We measured β1 and β2 integrin activation after stimulation with eotaxin or RANTES in vitro using whole-blood flow-cytometric analysis. Methods: Heparinized whole blood obtained from allergic patients with eosinophilia or normal subjects was diluted with the same volume of RPMI 1640, and then cells were incubated in the presence or absence of PMA/ionomycin or chemokines for 45 min at 37°C. After hemolyzation with lysing solution, expression of CD11b, CD11a, CD18 and CD49d on eosinophils was measured using flow cytometry. Results: The expression of CD11b, CD11a and CD18 in allergic patients was significantly higher than that in normal subjects. CD11b and CD18 expression showed a significant increase after stimulation with C-C chemokines, which was remarkable in allergic patients. Conclusion: Eosinophils in the blood of allergic patients exhibited a higher expression of β2 integrins and were more sensitive to RANTES and eotaxin than those of normal subjects.

Anti- and Proinflammatory Effects of 15-Deoxy-Δ12,14-Prostaglandin J2(15d-PGJ2) on Human Eosinophil Functions

The cyclopentenone prostaglandin 15-deoxy-Δ12,14-prostaglandin J2 (15d-PGJ2) is recognized as a potent lipid mediator that is derived from PGD2, which is produced abundantly in allergic inflammatory sites. It is now established that 15d-PGJ2 negatively regulates cellular functions through its intracellular targets such as peroxisome proliferator-activated receptor-γ (PPARγ). However, recent studies revealed that 15d-PGJ2 appears to possess not only anti-inflammatory activities but also a proinflammatory potential depending on its concentration and the activation state of the target cell. For instance, at low concentrations, 15d-PGJ2 enhances eotaxin-induced chemotaxis, shape change, and actin reorganization in eosinophils through its ligation with PPARγ. Moreover, 15d-PGJ2 itself is a potent chemoattractant, and it induces calcium mobilization, and up-regulates CD11b expression through its membrane receptor – chemoattractant receptor-homologous molecule expressed on Th2 cells (CRTH2). Conversely, at high concentrations, 15d-PGJ2 inhibits eosinophil survival by inducing apoptosis in a PPARγ-independent manner. Here, we discuss the pathophysiological roles of 15d-PGJ2 that could act as a paracrine, autocrine, and intracrine substance to regulate eosinophil functions.

Adiponectin attenuates human eosinophil adhesion and chemotaxis: implications in allergic inflammation

Abstract Objective: Growing evidence has shown an association between obesity and asthma. Adiponectin, an adipocyte-derived cytokine, is known to have anti-inflammatory effects with reduced concentrations in obese subjects. Recent findings raised the intriguing possibility that adiponectin might play a role in allergic inflammation, although the mechanistic basis for their relationship remains unclear. The purpose of this study was to examine whether adiponectin might affect functions of eosinophils, which play an important role in the pathogenesis of asthma. Methods: Human peripheral blood eosinophils were purified to study expression of adiponectin receptors AdipoR1 and AdipoR2 using RT-PCR and flow cytometry. The effect of adiponectin on eosinophil survival was investigated using annexin V and propidium iodide staining. Eotaxin-induced cell adhesion was investigated using ICAM-1-coated plates. A Boyden chamber and real-time horizontal migration system were used for eotaxin-directed chemotaxis assay. Expression of eotaxin receptor CCR3 and intracellular calcium influx were assessed by flow cytometry. Results: AdipoR1 and AdipoR2 were expressed in human eosinophils. Adiponectin did not affect eosinophil survival or CCR3 expression; however, eotaxin-enhanced adhesion was inhibited by pretreatment with adiponectin. Adiponectin also diminished eotaxin-directed chemotactic responses by disturbing both velocity and directionality. Calcium influx in response to eotaxin was attenuated by adiponectin. Conclusions: These results indicate that adiponectin attenuates the eosinophil functions induced by eotaxin without affecting cell viability. The inhibitory effect was associated with diminished calcium signaling rather than altering of surface receptor expression. Increasing circulating adiponectin might be a novel therapeutic modality for treatment of asthma, especially in obese asthmatics.

Retinoic acids up-regulate functional eosinophil-driving receptor CCR3.

Eotaxins and their receptor CCR3 have a definitive role for tissue accumulation of eosinophils both under homeostatic and pathologic conditions. However, physiological stimuli that can up‐regulate CCR3 in blood‐derived human eosinophils have not been recognized. As a prior gene microarray study revealed up‐regulation of CCR3 in eosinophils stimulated with retinoic acids (RAs), the expression of functional CCR3 was examined. We found that 9‐cis RA and all‐trans RA (ATRA) significantly induced surface CCR3 expression regardless of the presence of IL‐3 or IL‐5. Pharmacological manipulations with receptor‐specific agonists and antagonists indicated that retinoic acid receptor‐α activation is critical for CCR3 up‐regulation. RA‐induced CCR3 was associated with its functional capacity, in terms of the calcium mobilization and chemotactic response to eotaxin‐1 (CCL11). Our study suggests an important role of vitamin A derivatives in the tissue accumulation of eosinophils.