Mechanisms of IL-17A-mediated enhancement of asthma severity

描述(申请人提供)：哮喘是一种慢性炎症性肺部疾病，目前全球有超过3亿人患有哮喘。虽然哮喘是由Th2对过敏原的过度免疫反应介导的，但最近的证据表明，Th17细胞因子IL-17A的产生与更严重的疾病的发展有关。虽然重度哮喘患者在急性发作后发病或死亡的风险最大，而且对对轻度疾病患者高效的治疗可能难以奏效，但IL-17A促进严重过敏性哮喘发展的分子机制尚不明确。更好地了解IL-17A促进严重哮喘的分子机制将为目前治疗效果不佳的人群提供额外的治疗靶点。使用小鼠模型，我们提供的证据表明，严重哮喘与IL-17A的产生增加有关，并与IL17ra的表达增强和对IL-17A的反应性增强有关。IL-17A的产生和反应性的这些变化加剧了IL-13驱动的STAT6的激活、基因表达和呼吸道反应。我们的初步数据表明，IL-17A介导的增强IL-13驱动的应答在小鼠细胞中通过两种非相互独立的机制发生：1)通过引起包括IL-13R�1和TRAF3的复合体的解离，通常限制IL-13驱动的STAT6的磷酸化；2)通过激活转录因子(核因子-�B、C/EBPSTAT6和C/EBPSTAT6)来增强IL-13/STAT6驱动的基因表达。虽然这里提出的初步研究也表明类似的机制可能在人类细胞系中发挥作用，但在我们的小鼠模型中所做的观察在多大程度上适用于患有严重哮喘的人类尚不清楚。提出了三个特定的目标来确定IL-17A增强小鼠和人类哮喘严重程度的分子机制。具体目标1将确定在IL-17A存在下观察到的IL-13诱导的STAT6磷酸化和AHR增加是否是IL-17A信号启动后IL-13R�1：TRAF3复合体解离的结果。具体目的2将剖析IL-17A在体外和体内IL-13/IL-17A协同作用中对核因子-�B(典型和非典型)、C/eBP�和C/eBP�的激活的重要性。特异性目标3将直接测试IL-13和IL-17A之间的类似协同作用是否在哮喘相关的原代人类细胞中观察到。此外，我们将确定儿童中的严重哮喘是否与IL-17A产生、IL17RA表达和IL-17A反应性增加有关，就像在小鼠中一样。总的来说，本申请中提出的研究将使我们超越过敏性哮喘的“Th2范例”，开始描述Th17-产品引发严重过敏性哮喘的机制，并确定类似的机制是否可能在小鼠和人类身上发挥作用。更好地了解这些机制将使我们能够确定对严重哮喘患者进行治疗干预的新靶点，目前的治疗方法对这一人群的服务不足。

DESCRIPTION (provided by applicant): Asthma is a chronic, inflammatory disease of the lung that currently afflicts more than 300 million people worldwide. While asthma is mediated by an excessive Th2 immune response to allergens, recent evidence suggests that production of the Th17 cytokine, IL-17A, is associated with the development of more severe disease. While severe asthmatics are at greatest risk for morbidity or death following acute exacerbations, and can be refractory to therapies that are highly effective in individuals with mild disease, the molecular mechanisms whereby IL-17A contributes to the development of severe allergic asthma are ill-defined. A greater understanding of the molecular mechanisms through which IL-17A facilitates severe asthma would provide additional therapeutic targets for populations underserved by current therapies. Using a mouse model we provide evidence that severe asthma is associated with increased IL-17A production, and is compounded by enhanced Il17ra expression and elevated responsiveness to IL-17A. These alterations in IL-17A production and responsiveness exacerbate IL-13-driven STAT6 activation, gene expression, and airway responses. Our preliminary data suggests that IL-17A-mediated enhancement of IL-13-driven responses occur through two, non-mutually independent mechanisms in mouse cells; 1) by causing the dissociation of a complex including IL-13R�1 and TRAF3, which normally limits IL-13-driven STAT6 phosphorylation, and 2) by activating transcription factors (NF-�B, C/EBP� and C/EBP�) which can enhance IL-13/STAT6 driven gene expression. While preliminary studies presented here also suggest that similar mechanisms may operate in human cell lines, the extent to which the observations made in our mouse model apply to humans with severe asthma is unclear. Three specific aims are proposed to identify the molecular mechanisms through which IL-17A enhances asthma severity in mice, and humans. Specific Aim 1 will determine if the increased IL-13-driven STAT6 phosphorylation and AHR observed in the presence of IL-17A is the result of the dissociation of the IL- 13R�1:TRAF3 complex following initiation of IL-17A signaling. Specific Aim 2 will dissect the importance of IL- 17A-driven activation of NF-�B (canonical versus non-canonical), C/EBP� and C/EBP� in IL-13/IL-17A synergy in vitro and in vivo. Specific Aim 3 will directly test whether similar synergistic interactions between IL-13 and IL-17A are observed in asthma relevant, primary human cells. Additionally, we will determine whether severe asthma in children is associated, as it is in the mouse, with increased IL-17A production, IL17RA expression, and IL-17A responsiveness. Collectively, the studies proposed in this application will move us beyond the "Th2 paradigm" of allergic asthma, begin to characterize the mechanisms whereby Th17-products trigger the development of severe allergic asthma, and determine whether similar mechanisms may be at play in mice and humans. A better understanding of these mechanisms will enable us to identify novel targets for therapeutic interventions in individuals with severe asthma, a population underserved by current therapies.