Role of TGFbeta superfamily in Broncopulmonary Dysplasia

描述（由申请人提供）：支气管肺发育不良（BPD）继续影响大多数极早产儿，主要是一种由发育中的囊状肺损伤引起的肺泡化停滞疾病。保护性策略在减少BPD方面无效，强调需要更好地了解潜在的发病机制，以开发新的治疗方法。转化生长因子超家族信号传导调节ECM沉积，这对正常肺发育至关重要，并且在肺发育的囊状阶段期间被动态调节。利用临床相关的BPD小鼠模型，将高氧肺损伤限制在囊状阶段（小鼠中的0-4天），以持续简化成年肺泡结构，我们确定TGF-β 2（但不是TGF-β 1或3配体）在第4天被O2唯一抑制。虽然过度的TGF-β BPD的发病机制中涉及，通常是在长时间的O2暴露与迟发性纤维化（当BPD表型已经很好地建立时）相一致之后;目前尚不清楚在囊状发育停滞的急性期内的配体特异性TGF-β信号传导是否有助于BPD的发病机制。除了TGF-β 2，我们发现在囊状肺发育过程中，高氧下调TGF-β信号传导的完整机制途径，包括细胞内TGF-β信号转导子pSmad 3（在肺中占主导地位），以及一种新的TGF-β下游ECM效应子<$igH3。类似于高氧，基因敲除的免疫球蛋白3损害囊状肺的发展。通过在我们的生理（高氧）和新的遗传（igH 3无效）小鼠模型中对TGF-β信号通路进行靶向遗传分析，我们确定了BPD发病机制的已知和新的生物标志物：卵泡抑素和Msx 2（负调节肌成纤维细胞分化），Cdkn 1a（负调节细胞增殖）和IL 6（重要的炎症调节因子）。我们假设，在囊状期内，TGF-β信号的急性、短暂抑制足以引起BPD，TGF-β 2下调是负责的关键配体，并通过抑制Smad 3活化而起作用，从而导致ECM调节蛋白β igH 3的下调。通过比较我们的BPD生理和遗传模型，我们将确定TGF-β的失调是否是肺泡化受阻机制的积极参与者，或者仅仅是对肺损伤的代偿反应。目的1将检查早期BPD是否以抑制TGF-β信号传导为特征，而随后在长时间高氧后的上调是对第二修复机制的代偿反应。目的2将测试通过单独的TGF-β 2配体的特异性损失的TGF-β抑制是否能够复制BPD的表型。目的3将确定下游TGF-β 2效应ECM蛋白，β igH 3的缺乏足以引起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.