CORTICOSTEROID INDUCED APOPTOSIS IN AIRWAY EPITHELIUM

呼吸道上皮在维持呼吸道动态平衡方面起着重要作用，在哮喘等炎症性疾病中可能会受到广泛的损害。暴露在环境中的过敏原可能会部分通过导致上皮细胞脱落和细胞死亡而加重哮喘。虽然支气管上皮剥脱是哮喘病理的一个基本特征，但其机制尚不清楚。作为其在呼吸道的有效炎症作用的一部分，皮质类固醇可诱导迁移性嗜酸性粒细胞和T淋巴细胞的凋亡。我们实验室的新数据表明，无论是在培养的细胞中还是在动物模型中，皮质类固醇也可以诱导呼吸道上皮细胞凋亡。因此，皮质类固醇可能具有迄今未被认识到的不良后果：诱导上皮细胞凋亡和延长支气管上皮剥脱。持续的上皮损伤可能导致亚上皮纤维化和慢性气道重塑的发展。我们建议的中心假设是，皮质类固醇治疗对支气管上皮的存活是有害的，即使它促进了呼吸道炎症的消退。我们的目标是回答两个特定的假设：1)在过敏原刺激下，皮质类固醇是否诱导上皮细胞凋亡，并加剧上皮细胞凋亡；2)上皮细胞分化因子是否对抗皮质类固醇诱导的细胞凋亡。将使用特定的分析方法来确定培养物、呼吸道和肺组织切片中的细胞凋亡。糖皮质激素启动细胞凋亡的信号机制将通过Western印迹、荧光分析和RT-PCR进行检测。使用转基因的人呼吸道上皮细胞将决定分化因子，如转化生长因子-β和顺式维甲酸，是否减弱细胞凋亡和加速修复。一个小鼠模型将被用来证明皮质类固醇和分化因子治疗对体内上皮细胞的凋亡、修复和完整性的影响。这一模型将有助于确定呼吸道炎症和皮质类固醇治疗在上皮损伤发生中的相互作用。这些实验将阐明上皮细胞凋亡导致损伤后呼吸道粘膜修复受损的机制。糖皮质激素加重上皮细胞凋亡、脱落和死亡的证据表明，至少有一种慢性哮喘的病理发现可能是治疗该疾病的结果。这些数据将有助于为哮喘的治疗带来新的治疗思路和方式，以抑制炎症，同时防止粘膜损伤。

The airway epithelium has a major role in maintaining airway homeostasis and may be damaged extensively in inflammatory diseases such as asthma. Environmental exposure to allergen may worsen asthma in part by causing epithelial cell shedding and cell death. Although denudation of bronchial epithelium is a cardinal feature of the pathology of asthma, the mechanisms underlying this phenomenon remain unknown. As part of their potent inflammatory effects in airways, corticosteroids induce apoptosis in migratory eosinophils and T-lymphocytes. New data from our laboratory suggest that corticosteroids can also induce apoptosis in airway epithelium, both in cultured cells and in animal models. As such, corticosteroids may possess a heretofore unrecognized adverse consequence: induction of epithelial cell apoptosis and prolongation of bronchial epithelial denudation. Continued epithelial damage may lead to the development of sub- epithelial fibrosis and chronic airway remodeling. The central hypothesis of our proposal is that corticosteroid treatment is deleterious to bronchial epithelial survival, even though it promotes resolution of airway inflammation. Our goal is to answer two specific hypotheses: 1) whether corticosteroids elicit epithelial cell apoptosis, and worsen epithelial cell apoptosis during allergen challenge; and 2) whether differentiation factors for epithelial cells counter corticosteroid-induced apoptosis. Specific assays to determine apoptosis both in culture and in airway and lung tissue sections will be used. Signaling mechanisms for initiation of apoptosis by corticosteroids will be examined by Western blot, fluorescent assays, and RT-PCR. The use of transfected human airway epithelial cells will determine whether differentiation factors, such as transforming growth factor-beta and cis-retinoic acid, attenuate apoptosis and speed repair. A mouse model will be used to demonstrate the effect of corticosteroid and differentiation factor treatment on epithelial cell apoptosis, repair and integrity in vivo. This model will help determine the interplay between airway inflammation and corticosteroid treatment on the genesis of epithelial damage. These experiments will demonstrate mechanisms by which epithelial cell apoptosis leads to impaired repair of the airway mucosa after injury. Demonstration that corticosteroids worsen epithelial cell apoptosis, shedding and death would suggest that at least one of the pathologic findings in chronic asthma may be a result of treatment for the disease. These data would help lead to new therapeutic ideas and modalities in the treatment of asthma to suppress inflammation while preventing mucosal damage.