PAI-1 and aging-related susceptibility to lung fibrosis

 描述(申请人提供)：特发性肺纤维化(IPF)是一种与年龄相关的进行性致死性肺部疾病，病因不明，也没有有效的治疗方法。肺泡II型上皮细胞(AEC2)凋亡和成纤维细胞(Myo)凋亡抵抗在IPF肺组织中明显存在，被认为是IPF发生和发展的关键。有趣的是，我们的研究表明，与年轻小鼠相比，老年小鼠经历了成纤维细胞凋亡的减少，而AEC2凋亡和纤维化反应的增加，这表明AEC2和成纤维细胞凋亡的失调可能是与衰老相关的IPF易感性的基础。然而，衰老过程中成纤维细胞和AEC2凋亡调节失调的机制尚不清楚。纤溶酶原激活物抑制物1(PAI-1)是组织型和尿激酶型纤溶酶原激活物(tPA和uPA)的主要抑制物，在肺纤维化的发生发展中起重要作用。重要的是，我们以前的研究/初步数据表明，PAI-1在小鼠肺成纤维细胞和AEC2中的表达随着年龄的增加而增加，抑制PAI-1的活性可以恢复老年小鼠肺成纤维细胞对凋亡的敏感性。我们以前的研究/初步数据进一步表明，抑制PAI-1的活性或用PAI-1 siRNA抑制PAI-1可诱导肺成纤维细胞的凋亡和肺成纤维细胞的凋亡，但抑制P53和AEC2的凋亡。基于这些数据，我们假设与衰老相关的PAI-1的增加导致AEC2和成纤维细胞凋亡的失调，这是老年人对肺纤维化易感性增加的基础。氧化还原失衡在老年动物和IPF中明显存在。然而，氧化还原失衡如何导致与衰老相关的IPF易感性尚不清楚。我们以前的研究/初步数据表明，随着年龄的增长，啮齿动物肺内最丰富的细胞内游离硫醇和重要抗氧化剂谷胱甘肽(GSH)的浓度下降，而产生活性氧(ROS)的重要生成物NADPH氧化酶4(NOX4)的表达增加。我们以前的研究还表明，NOX4来源的ROS通过修饰/抑制丝裂原活化蛋白激酶-1(MAPK-1)诱导成纤维细胞中的PAI-1，而谷胱甘肽通过阻断β/p38的激活选择性地抑制转化生长因子-JNK-JNK-1诱导的PAI-1。重要的是，我们的初步数据显示，老年小鼠肺中MKP-1的硫醇修饰增加，而MKP-1的活性降低。因此，我们进一步假设，衰老相关的氧化还原失衡通过改变/抑制MKPs(如MKP-1)诱导PAI-1，从而导致AEC2和成纤维细胞凋亡的失调。使用不同的动物模型，包括本实验室最近建立的新的PAI-1条件性基因敲除小鼠模型，提出了四个具体目标来验证我们的假设。一种用于肺纤维化的小分子PAI-1抑制剂的治疗潜力也将在老年小鼠身上进行测试。这些研究结果不仅将为IPF与衰老相关的易感性机制提供新的线索，而且可能导致新的范式转换概念以及治疗IPF的新疗法。

 DESCRIPTION (provided by applicant): Idiopathic pulmonary fibrosis (IPF) is an aging-related progressive fatal lung disorder with no known etiology and no effective treatment. Alveolar type II epithelial cell (AEC2) apoptosis and (myo)fibroblast apoptosis resistance are evident in IPF lungs and are believed to be a key in the initiation and progression of IPF. Interestingly, our studies show that old mice experience diminished fibroblast apoptosis but augmented AEC2 apoptosis and fibrotic response upon bleomycin challenge, compared to young mice, suggesting that dysregulation of AEC2 and fibroblast apoptosis may underlie the aging-related susceptibility to IPF. The mechanism underlying the dysregulation of fibroblast and AEC2 apoptosis during aging, however, is unknown. Plasminogen activator inhibitor 1 (PAI-1), a primary inhibitor of tissue-type and urokinase-type plasminogen activators (tPA and uPA), plays an important role in the development of lung fibrosis. Importantly, our previous studies/preliminary data show that PAI-1 expression is increased with age in mouse lung fibroblasts and AEC2 and that inhibition of PAI-1 activity restored the sensitivity of lung fibroblasts from old mice to apoptosis. Our previous studies/preliminary data further show that inhibition of PAI-1 activity or knockdown of PAI-1 with PAI-1 siRNA induces p53, a master controller of apoptosis, and apoptosis in lung fibroblasts but suppresses p53 and apoptosis in AEC2. Based on these data, we hypothesize that aging-related increase in PAI-1 leads to dysregulation of AEC2 and fibroblast apoptosis, which underlies the increased susceptibility of the elderly to lung fibrosis. Redox imbalance is evident in aged animals and in IPF. How redox imbalance contributes to aging-related susceptibility to IPF, however, is unclear. Our previous studies/preliminary data show that the concentrations of glutathione (GSH), the most abundant intracellular free thiol and an important antioxidant, decrease whereas the expression of NADPH oxidase 4 (Nox4), an important producer of reactive oxygen species (ROS), increases with age in rodent lungs. Our previous studies also showed that Nox4-derived ROS induced PAI-1 in fibroblasts through modifying/inhibiting MAPK phosphatase 1 (MKP-1) whereas GSH selectively inhibited TGF-β1-induced PAI-1 by blocking JNK/p38 activation. Importantly, our preliminary data show that MKP-1 thiol modification is increased whereas the activity of MKP-1 is decreased in the lung of old mice. Therefore, we further hypothesize that aging-related redox imbalance contributes to the dysregulation of AEC2 and fibroblast apoptosis through inducing PAI-1 by modifying/inhibiting MKPs (e.g. MKP-1). Four specific aims are proposed to test our hypotheses, using different animal models including novel PAI-1 conditional knockout mouse models recently generated in this lab. The therapeutic potential of a small molecule PAI-1 inhibitor for lung fibrosis will also be tested in aged mice. The results from these studies will nt only shed new light on the mechanism underlying aging-related susceptibility to IPF but may also lead to novel paradigm shifting concept as well as new therapeutics for the treatment of IPF.