| Budget Amount *help |
¥3,860,000 (Direct Cost: ¥3,500,000、Indirect Cost: ¥360,000)
Fiscal Year 2007: ¥1,560,000 (Direct Cost: ¥1,200,000、Indirect Cost: ¥360,000)
Fiscal Year 2006: ¥2,300,000 (Direct Cost: ¥2,300,000)
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| Research Abstract |
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 make clear 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. Both in vitro(human BSM cells and mouse BSM tissues) and in vivo(intranasal instillation into mouse airways) effects of IL-13 were also tested. In the repeatedly antigen-challenged mice, marked airway inflammation and BSM hyperresponsiveness with an upregulation of IL-13 in bronchoalveolar lavage fluids were observed In cultured human BSM cells, IL-13 caused an activation of signal transducer and activator of transcription
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6(STAT6) and an upregulation of RhoA : both of them were inhibited by a STAT6 inhibitor leflunomide. 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 1L-13 caused a BSM hyperresponsiveness with an upregulation 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 treatment of asthma. Next, 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 upregulation of RhoA, a monomeric GTPase responsible for Ca^<2+> sensitization of smooth muscle contraction : both events were inhibited by co-incubation with AS 1517499(100 nM). In BALB/c mice that were actively sensitized and repeatedly challenged with ovalbumin antigen, an increased 1L-13 level in bronchoalveolar lavage fluids and a phosphorylation of STAT6 in BSMs were observed after the last antigen challenge. These mice had an augmented BSM contractility to acetylcholine together with an upregulation of RhoA in BSMs. Intraperitoneal injections of AS1517499(10mg/kg) 1h before each ovalbumin exposure inhibited both the antigen-induced upregulation 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 M-13, generated by antigen exposure, upregulates RhoA via an activation of STAT6 in BSM cells directly, resulting in an augmented BSM contraction, which is one of the causes of the airway hyperresponsiveness. The inhibitory effects of AS1517499 both on RhoA and IL-13 upregulations might be useful for asthma treatment. Less
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