Integrin alphavbeta8 Inhibits Airway Epithelial Cell Growth

描述（由申请人提供）：慢性阻塞性肺疾病（COPD）治疗试验的失败反映了我们对该疾病的机制了解不足。该项目的长期目标是提高对COPD机制的理解。COPD导致气道阻塞的两个主要病理特征是肺泡壁丧失和小气道壁增厚（<2mm）。小气道改变随着COPD严重程度的增加而进展，因此是稳定或潜在逆转气道阻塞的治疗靶点。最近的研究表明，TGF¿可能通过调节气道上皮细胞和间充质细胞类型（统称为上皮-间充质营养单位（EMTU））之间平衡的自分泌和旁分泌相互作用，在COPD的壁增厚中发挥主要机制作用。这些自分泌和旁分泌的相互作用决定了肺发育过程中的细胞分化。这些相互作用的不平衡可能导致慢性气道损伤（如烟草烟雾）并导致气道重塑。TGF - γ异构体在EMTU内的所有细胞类型中表达，但几乎完全以非活性形式表达。因此，TGF¿的激活是TGF¿功能调控的重点。我们最近开发了人类EMTU的首批体外模型之一(Araya等人，Am。J. Path, 2006)，并利用它确定整合素在TGF激活以及随后气道上皮细胞与成纤维细胞之间的自分泌和旁分泌相互作用中起主要作用。使用人类COPD样本，我们发现在气道上皮和小气道成纤维细胞中¿8的表达增加，这与肺功能下降和气道壁增厚显著相关。这些发现使我们得出了我们的总体假设：COPD气道上皮细胞和成纤维细胞中TGF - 8依赖性激活的增加导致EMTU中形态发生程序的不适当再激活，从而导致气道重塑。利用与生理相关的原代人气道上皮细胞和成纤维细胞培养系统，我们将：1)确定气道上皮细胞和成纤维细胞在COPD中（38）表达增加的机制；2)确定av¿8介导的TGF¿激活增加在COPD中的机制；3)确定在气道上皮细胞和成纤维细胞类型之间的自分泌和旁分泌相互作用中，av - 8介导的TGF -活化增加的功能后果。TGF¿是已知的最具纤维化的细胞因子之一，但由于其在几乎所有组织中的正常稳态作用，针对TGF¿中和的治疗也会产生不希望的全身效应。TGF -激活整合素av - 8在COPD中上调，但在正常人体组织中的表达模式受到高度限制，这使得它可能成为特异性抑制TGF - 8在COPD中的治疗靶点。这一建议是测试抑制av¿8功能在COPD中的治疗潜力的第一步。

DESCRIPTION (provided by applicant): Failure of therapeutic trials for Chronic Obstructive Lung Disease (COPD) reflects our poor mechanistic understanding of the disease. The long term goal of this project is to improve the mechanistic understanding of COPD. The two major pathologic features of COPD that contribute to airway obstruction are loss of alveolar walls and wall thickening of small airways (<2mm). Small airway changes progress with increasing severity of COPD and therefore represent a therapeutic target to stabilize or potentially reverse airway obstruction. Recent investigation suggests that TGF¿ is likely to play a major mechanistic role in wall thickening in COPD by regulating the balanced autocrine and paracrine interactions between airway epithelial and mesenchymal cell types, collectively known as the epithelial-mesenchymal trophic unit (EMTU). These autocrine and paracrine interactions dictate cellular differentiation during lung development. Imbalances in these interactions could result from chronic airway injury (e.g. tobacco smoke) and lead to airway remodeling. TGF¿ isoforms are expressed by all cell types within the EMTU, but almost entirely in an inactive form. Hence, activation of TGF¿ is a major point of regulation of TGF¿ function. We have recently developed one of the first in vitro models of the human EMTU (Araya, et al, Am. J. Path, 2006) and have used it to determine that the integrin av¿8 plays a major role in TGF¿ activation, and subsequent autocrine and paracrine interactions between airway epithelial cells and fibroblasts. Using human COPD samples, we demonstrate increased ¿8 expression in both the airway epithelium and small airway fibroblasts, which significantly correlates with declining pulmonary function and airway wall thickening. These findings have led us to our overall hypothesis: Increased av¿8-dependent activation of TGF¿ in COPD airway epithelial cells and fibroblasts leads to inappropriate reactivation of morphogenic programs within the EMTU, which leads to airway remodeling. Using physiologically relevant primary human airway epithelial and fibroblast cell culture systems, we will: 1) determine the mechanism of increased (38 expression in COPD by airway epithelial cells and fibroblasts; 2) determine mechanism of increased av¿8-mediated activation of TGF¿ in COPD; 3) determine the functional consequence of increased av¿8-mediated activation of TGF¿ in autocrine and paracrine interactions between airway epithelial and fibroblast cell types. TGF¿ is one of the most fibrogenic cytokines known, but because of its normal homeostatic role in virtually all tissues, therapies targeted at global TGF¿ neutralization will also have undesired systemic effects. The TGF¿ activating integrin, av¿8, is upregulated in COPD but has a highly restricted pattern of expression in normal human tissues making it a possible therapeutic target to specifically inhibit TGF¿ in COPD. This proposal is the first step in testing the therapeutic potential of inhibiting av¿8 function in COPD.