avb6-mediated TGFb activation in radiation lung fibrosis

描述（由申请人提供）：辐射诱导肺纤维化（RIPF）是胸部辐射的主要剂量限制性毒性之一。一般认为，纤维化细胞因子TGFbeta1对RIPF的发展是必需的，尽管这一假设尚未在动物模型中得到直接验证。由于TGFbeta1以潜伏形式分泌，TGFbeta1的活性由激活步骤控制。TGFbeta1的潜伏期是由于TGFbeta1与其前肽潜伏期相关肽（LAP）相互作用所致。TGFbeta1信号在LAP释放TGFbeta1后发生。我们发现LAP是一种上皮特异性整合素α - β 6的配体。在alphavbeta6结扎LAP后，TGFbeta1被释放。因此，上皮细胞通过表达alphavbeta6，局部激活TGFbeta1。缺乏α - β - 6的小鼠（β - 6-/-小鼠）在接触博来霉素后不会发生肺纤维化。最近，我们培育了TGFbeta1-LAP基因敲入突变的小鼠（TGFbeta1-RGE小鼠），该突变可消除整合素结合。这些小鼠的表型再现了TGFbeta1-/-小鼠的表型，表明整合素介导的TGFbeta1激活是产生活性TGFbeta1的主要（也许是唯一）机制。我们还发现β 6-/-小鼠不发生RIPF。此外，野生型小鼠在胸部照射后肺上皮中α - β 6的表达急剧上调，这是在RIPF发生之前发生的一个晚期事件。这些结果表明，RIPF需要alphavbeta6介导的TGFbeta1激活，并提出了两种治疗策略：抑制alphavbeta6功能和预防alphavbeta6上调。

DESCRIPTION (provided by applicant): Radiation-induced pulmonary fibrosis (RIPF) is one of the major dose-limiting toxicities of thoracic radiation. It is generally believed that the fibrogenic cytokine TGFbeta1 is necessary for the development of RIPF, although this hypothesis has not been directly tested in animal models. Because TGFbeta1 is secreted in a latent form, TGFbeta1 activity is controlled by an activation step. TGFbeta1 latency is due to interaction of TGFbeta1 with its propeptide, Latency-Associated Peptide (LAP). TGFbeta1 signaling occurs following release of TGFbeta1 from LAP. We discovered that LAP is a ligand for an epithelium-specific integrin, alphavbeta6. Following ligation of LAP by alphavbeta6, TGFbeta1 is released. Therefore, by expressing alphavbeta6, epithelial cells locally activate TGFbeta1. Mice lacking alphavbeta6 (beta6-/- mice) do not develop lung fibrosis after exposure to bleomycin. Recently, we generated mice with a knocked-in mutation in TGFbeta1-LAP that abrogates integrin binding (TGFbeta1-RGE mice). The phenotype of these mice reproduces that of TGFbeta1-/- mice, indicating that integrin-mediated TGFbeta1 activation is a major (and perhaps the only) mechanism for generating active TGFbeta1. We have also found that beta6-/- mice do not develop RIPF. Furthermore, wild type mice sharply upregulate alphavbeta6 expression in lung epithelium as a late event after thoracic irradiation, just prior to the onset of RIPF. These results suggest that alphavbeta6-mediated TGFbeta1 activation is required for RIPF, and suggest 2 treatment strategies: inhibition of alphavbeta6 function, and prevention of alphavbeta6 upregulation. Our overall goal is to treat and/or prevent RIPF by inhibiting the alphavbeta6-TGFbeta1 activation system. We propose 3 aims. First, we will confirm that TGFbeta1 is required for RIPF. This will be done by treating irradiated mice with a TGFbeta antagonist and also by measuring the fibrotic response of TGFbeta1+/- mice. Second, we will test whether an alphavbeta6 inhibitor (a murine anti-alphavbeta6 mAb) reverses and/or prevents RIPF. If this reagent works, it should be considered as a potential therapy in human RIPF, and perhaps in radiation fibrosis affecting other organs. Measuring the fibrotic response of TGFbeta1-RGE+/- mice will also test the role of integrin-mediated TGFbeta1 activation in RIPF. Third, we will test the hypothesis that alphavbeta6 upregulation in lung epithelium, which occurs just prior to the development of RIPF, is due to increased TGFbeta1 signaling.