Control of myofibroblast activation and pulmonary fibrosis by Na/K-ATPase

 描述（由申请方提供）：特发性肺纤维化（IPF）是一种进行性致死性疾病，其特征为肺实质纤维化和肺结构变形。IPF尚无有效的治疗方法，需要确定药物干预的新靶点。IPF的发病机制特征为伤口愈合紊乱且不消退。肺泡上皮细胞的损伤导致各种促炎和促纤维化介质的产生，其中转化生长因子-β（TGF-β）是最确定的。在TGF-β刺激下，肺泡成纤维细胞通过重新表达平滑肌特异性收缩蛋白，分泌细胞外基质蛋白和促纤维化因子、存活因子和生长因子，分化成肌成纤维细胞。这些肌成纤维细胞总是在肺纤维化患者的肺标本的组织切片上发现，并被认为在这种疾病的发病机制中起重要作用。因此，靶向肌成纤维细胞分化和生长/存活可能是预防/治疗肺纤维化的有吸引力的治疗策略。 Na/K-ATP酶（钠泵）是一种将3 Na+泵出细胞并将2K+泵入细胞的酶，因此在维持单价阳离子的电化学梯度和各种细胞中的电势中起关键作用。抑制Na/K-ATP酶的强心苷如地高辛或哇巴因已用于治疗心脏病数十年。我们的新发现表明Na/K-ATP酶在控制肌成纤维细胞分化和肺纤维化中的新作用，并表明强心苷的新治疗潜力。基于我们的初步数据，我们假设（i）Na/K-ATP酶的活性是响应于TGF-β的肌成纤维细胞活化所必需的，（ii）强心苷抑制Na/K-ATP酶通过一种新的双重机制导致体外肌成纤维细胞活化减弱，该双重机制涉及TGF-β受体-2表达的下调和环氧合酶-2表达的诱导，和（iii）强心苷在肺纤维化的小鼠模型中在低剂量下可能具有保护作用。 为了验证这些假设，我们提出了三个具体的目标：（i）检查通过抑制Na+/K+-ATP酶调节肌成纤维细胞活化及其在人肺成纤维细胞中的作用机制，（ii）检查地高辛对小鼠模型肺纤维化严重程度的潜在保护作用，以及（iii）检查其他强心类固醇在体外和体内的抗纤维化作用。

 DESCRIPTION (provided by applicant): Idiopathic pulmonary fibrosis (IPF) is a progressive, fatal disease characterized by parenchymal fibrosis and structural distortion of the lungs. There is no effective treatment for IPF and novel targets of pharmacologic intervention need to be identified. The pathogenesis of IPF is characterized by disordered and non-resolving wound healing. Injury of the alveolar epithelial cells results in the elaboration of various pro-inflammatory and pro-fibrotic mediators, of which Transforming Growth Factor-ß (TGF-ß) is the most established. Under stimulation with TGF-ß, alveolar fibroblasts differentiate into myofibroblasts, by de novo expression of smooth muscle-specific contractile proteins, and secretion of extracellular matrix proteins and of pro-fibrotic, survival and growth factors. These myofibroblasts are invariably found on histological sections of lung specimens from patients with pulmonary fibrosis and are believed to play an important role in the pathogenesis of this disease. Therefore, targeting myofibroblast differentiation and growth/survival could be an attractive therapeutic strategy for prevention/treatment of pulmonary fibrosis. Na/K-ATPase (sodium pump) is an enzyme that pumps 3Na+ out of the cell and 2K+ into the cell against their gradient, and thus plays a key role in the maintenance of electrochemical gradients of monovalent cations and of electrical potential in various cells. Cardiac glycosides such as digoxin or ouabain that inhibit Na/K- ATPase have been used for treatment of heart diseases for decades. Our new findings suggest a novel role of Na/K-ATPase in a control of myofibroblast differentiation and pulmonary fibrosis and suggest a new therapeutic potential of cardiac glycosides. Based on our preliminary data, we hypothesize that (i) the activity of Na/K-ATPase is required for myofibroblast activation in response to TGF-ß, (ii) inhibition of Na/K-ATPase by cardiac glycosides leads to attenuated myofibroblast activation in vitro through a novel dual mechanism involving downregulation of TGF-ß receptor-2 expression and induction of cyclooxygenase-2 expression, and (iii) cardiac glycosides may have a protective effect at low doses in mouse models of pulmonary fibrosis. To test these hypotheses, we propose three specific aims: (i) examine the regulation of myofibroblast activation through inhibition of Na+/K+-ATPase and the mechanisms of this effect in human lung fibroblasts, (ii) examine the potential protective effect of digoxin on the severity of pulmonary fibrosis in mouse models, and (iii) examine the anti-fibrotic effect of other cardiotonic steroids in vitro and in vivo.