Role of TGFbeta superfamily in Broncopulmonary Dysplasia

描述（由申请人提供）：支气管肺发育不良（BPD）持续影响大多数极早产婴儿，主要是一种由发育中的囊状肺损伤引起的肺泡发育受阻的疾病。保护性策略在减少BPD方面是无效的，这强调了更好地了解潜在发病机制以开发新疗法的必要性。转化生长因子-超家族信号调节ECM沉积，这对正常肺发育至关重要，并在肺发育的囊状阶段受到动态调节。利用临床相关的BPD小鼠模型，将高氧肺损伤限制在囊状期（小鼠0-4天），以持续简化成人肺泡结构，我们确定TGF-¿2（但不包括TGF-¿1或3配体）在第4天受到O2的独特抑制。虽然过量的TGF-¿与BPD的发病机制有关，但它通常是在长时间的O2暴露与晚发性纤维化（当BPD表型已经确定时）同时发生的；目前尚不清楚在囊性发育阻滞的急性期，配体特异性TGF-¿信号是否有助于BPD的发病。除了TGF- 2，我们发现在囊状肺发育过程中，高氧下调TGF-信号传导的完整机制通路，包括细胞内TGF-信号转导器pSmad3（在肺中占主导地位），以及一种新的TGF-下游ECM效应物- igH3。与高氧相似，基因敲除igH3会损害肺囊性发育。通过对我们的生理（高氧）和新型遗传（¿igH3 null）小鼠模型中TGF-信号通路的靶向遗传分析，我们确定了已知的和新的BPD发病机制的生物标志物：Follistatin和Msx2（负调节肌成纤维细胞分化），Cdkn1a（负调节细胞增殖）和IL6（重要的炎症调节剂）。我们假设，囊状期TGF-¿信号的急性、短期抑制足以引起BPD， TGF-¿2下调是关键配体，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的生理模型和遗传模型，我们将确定TGF-¿错误调控是肺泡阻滞机制的积极参与者，还是仅仅是对肺损伤的代偿反应。目的1将研究早期BPD是否以TGF-¿信号抑制为特征，而随后长时间高氧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TGF- 2配体特异性缺失抑制TGF-¿是否能够表型BPD。目的3将确定缺乏下游TGF- 2效应ECM蛋白igH3足以导致BPD的机制。

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.