Treatment with acetylcholine (ACh) of a b-escin-permeabilized intrapulmonary bronchial smooth muscle of the rat induced force when the Ca 2+ concentration was clamped at 1 mM. The AChinduced Ca 2+ sensitization of myo®laments was signi®cantly greater in antigen-induced airway hyperresponsive rats than in control rats. The ACh-induced Ca 2+ sensitization was completely blocked by treatment with Clostridium botulinum C3 exoenzyme, an inactivator of Rho family of proteins. Moreover, the protein level of RhoA in the intrapulmonary bronchi was signi®cantly increased in the airway hyperresponsive rats. Thus, increased airway smooth muscle contractility observed in asthmatics may be related to augmented agonist-induced, Rho-mediated Ca 2+ sensitization of myo®laments.

Interleukin-13 (IL-13) is one of the central mediators for development of airway hyperresponsiveness in asthma. However, its effect on bronchial smooth muscle (BSM) is not well known. Recent studies revealed an involvement of RhoA/Rho-kinase in BSM contraction, and this pathway has now been proposed as a new target for asthma therapy. To elucidate the role of IL-13 on the induction of BSM hyperresponsiveness, effects of IL-13 on contractility and RhoA expression in BSMs were investigated. Male BALB/c mice were sensitized and repeatedly challenged with ovalbumin antigen. In the repeatedly antigen-challenged mice, marked airway inflammation and BSM hyperresponsiveness with an up-regulation of IL-13 in bronchoalveolar lavage fluids were observed. In cultured human BSM cells, IL-13 caused an up-regulation of RhoA. The IL-13-induced up-regulation of RhoA was inhibited by leflunomide, an inhibitor of signal transducer and activator of transcription 6 (STAT6). In isolated BSM tissues of naive mice, the contractility was significantly enhanced by organ culture in the presence of IL-13. Moreover, in vivo treatment of airways with IL-13 by intranasal instillation caused a BSM hyperresponsiveness with an up-regulation of RhoA in naive mice. These findings suggest that IL-13/STAT6 signaling is critical for development of antigen-induced BSM hyperresponsiveness and that agents that specifically inhibit this pathway in BSM may provide a novel strategy for the treatment of asthma.

These findings suggest that RhoA expression is negatively regulated by miR-133a in BSMs. IL-13 might, at least in part, contribute to the reduction of miR-133a.

Background: It has recently been suggested that RhoA plays an important role in the enhancement of the Ca 2+ sensitization of smooth muscle contraction. In the present study, a participation of RhoA-mediated Ca 2+ sensitization in the augmented bronchial smooth muscle (BSM) contraction in a murine model of allergic asthma was examined.

Interleukin-13 (IL-13) is one of the central mediators for development of airway hyperresponsiveness in asthma. The signal transducer and activation of transcription 6 (STAT6) is one of the major signal transducers activated by IL-13, and a possible involvement of IL-13/STAT6 pathway in the augmented bronchial smooth muscle (BSM) contraction has been suggested. In the present study, the effect of a novel STAT6 inhibitor, AS1517499, on the development of antigen-induced BSM hyperresponsiveness was investigated. In cultured human BSM cells, IL-13 (100 ng/ml) caused a phosphorylation of STAT6 and an up-regulation of RhoA, a monomeric GTPase responsible for Ca2+ sensitization of smooth muscle contraction: both events were inhibited by co-incubation with AS1517499 (100 nM). In BALB/c mice that were actively sensitized and repeatedly challenged with ovalbumin antigen, an increased IL-13 level in bronchoalveolar lavage fluids and a phosphorylation of STAT6 in bronchial tissues were observed after the last antigen challenge. These mice had an augmented BSM contractility to acetylcholine together with an up-regulation of RhoA in bronchial tissues. Intraperitoneal injections of AS1517499 (10 mg/kg) 1 hour before each ovalbumin exposure inhibited both the antigen-induced up-regulation of RhoA and BSM hyperresponsiveness, almost completely. A partial but significant inhibition of antigen-induced production of IL-13 was also found. These findings suggest that the inhibitory effects of STAT6 inhibitory agents, such as AS1517499, both on RhoA and IL-13 up-regulations might be useful for asthma treatment.

Rationale: Uteroglobin-related protein (UGRP) 1, which is highly expressed in the epithelial cells of the airways, has been suggested to play a role in lung inflammation. Objectives: The aim of study was to understand the effect of overexpressed UGRP1 on lung inflammation in a mouse model of allergic airway inflammation. Methods: Ovalbumin-sensitized and -challenged mice, a model for allergic airway inflammation, were used in conjunction with recombinant adenovirus expressing UGRP1. Based on this result, we propose UGRP1 as a novel therapeutic candidate for treating lung inflammation such as is found in asthma. Measurements and Main Results

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Abstract. Airway hyperresponsiveness to nonspecific stimuli is one of the characteristic features of allergic bronchial asthma. An elevated contractility of bronchial smooth muscle has been considered as one of the causes of the airway hyperresponsiveness. The contraction of smooth muscles including airway smooth muscles is mediated by both Ca 2+ -dependent and Ca 2+-independent pathways. The latter Ca 2+ -independent pathway, termed Ca 2+ sensitization, is mainly regulated by a monomeric GTP-binding protein, RhoA, and its downstream target Rho-kinase. In animal models of allergic bronchial asthma, an augmented agonist-induced, RhoA-mediated contraction of bronchial smooth muscle has been suggested. The RhoA/Rho-kinase signaling is now proposed as a novel target for the treatment of airway hyperresponsiveness in asthma. Herein, we will discuss the mechanism of development of bronchial smooth muscle hyperresponsiveness, one of the causes of the airway hyperresponsiveness, based on the recent studies using animal models of allergic bronchial asthma and/or cultured airway smooth muscle cells. The possibility of RhoA as a therapeutic target in asthma, especially airway hyperresponsiveness, will also be described.