Role of TGFbeta superfamily in Broncopulmonary Dysplasia

描述(申请人提供)：支气管肺发育不良(BPD)继续影响大多数极早产儿，主要是一种由于发育中的囊状肺损伤而导致的肺泡停止形成的疾病。保护性策略在减少BPD方面一直无效，强调需要更好地了解潜在的发病机制，以使新疗法的开发成为可能。转化生长因子超家族信号调节ECM沉积，ECM沉积对正常肺发育至关重要，并在肺发育的球囊阶段动态调节。利用临床相关的BPD小鼠模型，将高氧性肺损伤限制在球囊阶段(在小鼠中为第0-4天)，以持续简化成人肺泡结构，我们确定在第4天，转化生长因子-β2(而不是转化生长因子-β1或3配体)唯一地被O2抑制。尽管过度的转化生长因子-β与BPD的发病机制有关，但它通常伴随着长期的O2暴露与迟发性纤维化(当BPD的表型已经确立时)；尚不清楚囊状发育受阻的急性期的配体特异性的转化生长因子-β信号是否与BPD的发病有关。除了转化生长因子-β2，我们发现在球状肺发育过程中，高氧下调了转化生长因子-β信号的完整机制途径，包括细胞内转化生长因子-β信号转导，pSmad3(在肺中占主导地位)，以及一种新的转化生长因子-β下游细胞外基质效应因子，？igH3。与高氧类似，基因敲除igH3会损害球状肺的发育。通过对我们生理性(高氧)和新型遗传(igH3缺失)囊状发育受阻小鼠模型中的转化生长因子-β信号通路的定向遗传分析，我们确定了BPD发病的已知和新的生物标志物：卵泡抑素和MSX2(负调控肌成纤维细胞分化)、CDKN1A(负调控细胞增殖)和IL6(重要的炎症调节因子)。我们假设，在球囊阶段对转化生长因子β信号的急性、短暂的抑制足以引起BPD，转化生长因子β2的下调是负责的关键配体，并通过抑制SMAD3的激活而起作用，导致ECM调节蛋白？igH3的下调。通过比较BPD的生理学和遗传学模型，我们将确定转化生长因子的错误调节是肺泡化受阻机制的积极参与者，还是仅仅是对肺损伤的代偿性反应。目的1将研究早期BPD是否以抑制的转化生长因子-β信号为特征，而持续高氧后随后的上调是对第二种修复机制的代偿反应。目的2将测试单独通过特异性丢失转化生长因子β2配体抑制转化生长因子β是否能够复制BPD。目的3将确定的机制(S)，通过下游的转化生长因子-β2效应细胞外基质蛋白的缺失，足以导致BPD。

DESCRIPTION (provided by applicant): Bronchopulmonary Dysplasia (BPD) continues to affect the majority of infants born extremely premature and is primarily a disease of arrested alveolarization resulting from injury to the developing saccular lung. Protective strategies have been ineffective in reducing BPD, underscoring the need to better understand the underlying pathogenesis to enable development of novel therapies. Transforming Growth Factor-¿ superfamily signaling regulates ECM deposition, which is critical to normal lung development, and is dynamically regulated during the saccular stage of lung development. Utilizing a clinically-relevant murine model of BPD that limits hyperoxic lung injury to the saccular stage (day 0-4 in mice) to persistently simplify adult alveolar structure, we determined TGF-¿2 (but not TGF-¿ 1 or 3 ligands) is uniquely suppressed by O2 by day 4. Although excessive TGF-¿ has been implicated in BPD pathogenesis, it is often following prolonged O2 exposure coincident with late-onset fibrosis (when BPD phenotype is already well-established); it is unclear if ligand-specific TGF-¿ signaling within the acute phase of arrested saccular development contributes to BPD pathogenesis. In addition to TGF-¿2, we show during saccular lung development that hyperoxia down-regulates the complete mechanistic pathway of TGF-¿ signaling, including intracellular TGF-¿ signal transducer, pSmad3 (which predominates in lung), as well as a novel TGF-¿ downstream ECM effector, ¿igH3. Similar to hyperoxia, genetic knockout of ¿igH3 impairs saccular lung development. Through targeted genetic analysis of TGF-¿ signaling pathways in both our physiologic (hyperoxia) and novel genetic (¿igH3 null) mouse models of arrested saccular development, we identified known and novel biomarkers of BPD pathogenesis: Follistatin and Msx2 (negatively regulates myofibroblast differentiation), Cdkn1a (negatively regulates cell proliferation), and IL6 (important modulator of inflammation). We hypothesize that acute, short-lived suppression of TGF-¿ signaling within the saccular stage is sufficient to cause BPD, and that Tgf-¿2 downregulation is the key ligand responsible and acts via suppression of Smad3 activation resulting in down-regulation of the ECM-modulating protein, ¿igH3. By comparing our physiologic and genetic models of BPD, we will determine whether TGF-¿ mis-regulation is an active participant in the mechanism of arrested alveolarization or merely a compensatory response to lung injury. Aim 1 will examine whether early phase BPD is characterized by suppressed TGF-¿ signaling while subsequent upregulation following prolonged hyperoxia is a compensatory response to 2nd reparative mechanisms. Aim 2 will test whether TGF-¿ suppression via specific loss of TGF-¿2 ligand alone is able to phenocopy BPD. Aim 3 will determine the mechanism(s) by which absence of the downstream TGF-¿2 effector ECM protein, ¿igH3, is sufficient to cause BPD.