Regulation of Mucous Cell Metaplasia in Asthma

描述(由申请人提供)： 哮喘的临床表现部分是由于慢性炎症导致粘液细胞化生(MCM)，即在外周呼吸道出现粘液细胞，通常没有这些细胞。在哮喘小鼠模型中，系统免疫卵白蛋白(OVA)后，反复暴露于OVA气雾剂，最初会诱导炎症和MCM，而长期暴露会导致IFN-γ水平增加和MCM分解。在暴露于过敏原的小鼠中，滴注干扰素-γ可诱导促凋亡蛋白Bax的表达，并通过引起细胞凋亡来加速MCM的分解。缺乏Bax或Stat 1的小鼠在长期接触变应原期间不能分解MCM。Bax或Stat 1是IFNGamma必需的信号分子。IL-13可抑制干扰素-γ诱导的小鼠黏液细胞和正常人支气管上皮细胞Bax的表达和凋亡。我们的指导性假设是，IL-13诱导MCM，并通过Bax介导的途径在化生粘液细胞中抵消IFNGamma激活Stat 1和诱导细胞凋亡的作用。在目标1中，我们将确定IL-13抑制IFN-γ信号转导和Bax介导的MCM分解的途径。我们将确定IL-13是直接抑制Bax的表达还是激活Stat 3，这是已知的导致抗凋亡蛋白Bc l-2和BCI-1xL表达的原因。此外，我们将确定IL-13是否需要通过IL-4Rpha和Stat 6信号来抑制IFNGamma诱导的Bax表达。在目标2中，我们将确定干扰素-γ诱导变应原诱导的MCM中Bax表达的途径，以及Bax介导的途径是否是分解MCM所必需的。我们将研究干扰素-γ信号是否通过干扰素(R)和Stat-1在变应原诱导的MCM中诱导Bax，以及干扰素(诱导IL-13Ralpha2的表面表达是否通过Stat-6抑制IL-13信号的表达)。我们将通过滴注干扰素-γ来确定Bax在降低变应原诱导的MCM中的需求。我们对人体尸检组织和支气管刷检的初步结果表明，Bax在非哮喘患者的粘膜细胞中表达，而在哮喘患者中不表达。因此，在目标3中，我们将确定哮喘患者的炎性介质是否抑制Bax的表达，并促进粘膜细胞的存活。将使用尸检组织和支气管刷检查来研究哮喘、慢性支气管炎患者和无呼吸道疾病的对照组之间Bax表达细胞百分比的差异。此外，我们还将确定支气管肺泡灌洗液对HBE中MCM和Bax表达的影响。这些研究将为减少哮喘患者的粘液细胞数量提供新的策略。

DESCRIPTION (provided by applicant): Clinical manifestations of asthma result in part from chronic inflammation that leads to mucous cell metaplasia (MCM), the appearance of mucous cells in peripheral airways that are normally devoid of these cells. In a mouse model of asthma, systemic immunization with ovalbumin (OVA) followed by repeated exposures to OVA aerosols initially induces inflammation and MCM, while prolonged exposures cause increase of IFNgamma levels and resolution of MCM. Instillation of IFNgamma in allergen-exposed mice induces expression of Bax, a pro-apoptotic protein, and accelerates the resolution of MCM by causing apoptosis. Mice deficient in Bax or Stat 1, an obligatory signaling molecule for IFNgamma, do not resolve MCM during prolonged exposures to allergen. IL-13 inhibits IFNgamma-induced Bax expression and apoptosis in mucous cells of mice and in normal human bronchial epithelial cells (HBEs). Our guiding hypothesis is that IL-13 induces MCM and counteracts the role of IFNgamma to activate Stat 1 and induce apoptosis through a Bax-mediated pathway in metaplastic mucous cells. In Aim 1, we will determine the pathway by which IL-13 inhibits IFNgamma signaling and Bax mediated resolution of MCM. We will determine whether IL-13 directly inhibits Bax expression or activates Stat 3, which is known to cause expression of anti-apoptotic proteins, Bcl-2 and BcI-lxL. Furthermore, we will determine whether IL-13 requires signaling through IL-4Ralpha and Stat 6 to inhibit IFNgamma-induced Bax expression. In Aim 2, we will determine the pathway by which IFNgamma induces Bax expression in allergen-induced MCM and whether the Bax-mediated pathway is essential to resolve MCM. We will investigate whether IFNgamma signals through IFN(R and Stat 1 to induce Bax in allergen-induced MCM and whether IFN( induces surface expression of IL-13Ralpha2 to inhibit IL-13 signaling through Stat 6. We will determine the requirement of Bax in decreasing MCM by instilling IFNgamma in Bax-deficient mice that have allergen-induced MCM. Our preliminary results with human autopsy tissues and bronchial brushings show that Bax is expressed in mucous cells from non-asthmatics and is absent in asthmatics. Therefore, in Aim 3, we will determine whether inflammatory mediators from asthmatics suppress expression of Bax and enhance mucous cell survival. The difference in the percentages of Bax-expressing cells among subjects with asthma, chronic bronchitis, and controls without respiratory diseases will be investigated using autopsy tissues and bronchial brushings. Furthermore, we will determine the effect of bronchoalveolar lavage fluid in inducing MCM and Bax expression in HBEs. These studies will provide new strategies to reduce mucous cell numbers in asthmatic patients.