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.

These results indicate that female mice experience more airway remodelling compared with male mice. These results suggest the involvement of sex hormones and gender differences in cellular functions in airway remodelling.

The CC chemokine eotaxin plays a pivotal role in local accumulation of eosinophils. Very little is known about the eotaxin signaling in eosinophils except the activation of the mitogen-activated protein (MAP) kinase family. The p21 G protein Rho and its substrate Rho-associated coiled-coil forming protein kinase (ROCK) regulate the formation of stress fibers and focal adhesions. In the present study, we studied the functional relevance of Rho and ROCK in eosinophils using the ROCK inhibitor (Y-27632) and exoenzyme C3, a specific Rho inhibitor. Eotaxin stimulates activation of Rho A and ROCK II in eosinophils. Exoenzyme C3 almost completely inhibited the ROCK activity, indicating that ROCK is downstream of Rho. We then examined the role of Rho and ROCK in eosinophil chemotaxis. The eotaxin-induced eosinophil chemotaxis was significantly inhibited by exoenzyme C3 or Y-27632. Because extracellular signal-regulated kinase (ERK)1/2 and p38 MAP kinases are activated by eotaxin and are critical for eosinophil chemotaxis, we investigated whether Rho and ROCK are upstream of these MAP kinases. C3 partially inhibited eotaxin-induced phosphorylation of ERK1/2 but not p38. In contrast, neither ERK1/2 nor p38 phosphorylation was abrogated by Y-27632. Both C3 and Y-27632 reduced reactive oxygen species production from eosinophils. We conclude that both Rho and ROCK are important for eosinophil chemotaxis and reactive oxygen species production. There is a dichotomy of downstream signaling pathways of Rho, namely, Rho-ROCK and Rho-ERK pathways. Taken together, eosinophil chemotaxis is regulated by multiple signaling pathways that involve at least ROCK, ERK, and p38 MAP kinase.

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PI3Kgamma might be involved in allergic airway inflammation, AHR, and airway remodeling by regulating the challenge/effector phase of allergic responses.