Functional Role of Klf4 in Alveolarization and Ventilation-Induced Lung Injury of Newborn Mice

富氧气体（MV-O2）机械通气为呼吸衰竭早产儿提供了挽救生命的治疗，但也会促进通气诱导的肺损伤（VILI），这在新生儿中会导致肺泡形成受损和毛细血管发育不全，如新生儿慢性肺病（CLD）中所见。长期MV和O2补充导致的肺泡形成缺陷与肺细胞凋亡增加有关。II型肺泡上皮细胞（ATII）被认为是祖细胞，在肺损伤后肺泡形成和再生中至关重要。然而，MV-O2后肺泡上皮细胞存活和肺泡形成的潜在分子机制尚不清楚。Krüppel样因子4（Klf 4）是一种在上皮细胞的多能性、分化、存活和发育中具有多种调节作用的转录因子。我们最近发现，Klf 4的mRNA和蛋白在机械通气的5日龄小鼠的肺减少; Klf 4的表达也减少了培养的小鼠肺II型上皮细胞（MLE-12）暴露于周期性拉伸后。此外，我们发现MLE-12中Klf 4的缺失抑制细胞存活。因此，我们现在的目标是阐明Klf 4在正常肺发育和MV-O2后新生小鼠肺中观察到的肺泡化缺陷中的功能作用。为此，我们将提出三个具体目标：我们将（1）分析Klf 4在肺发育晚期的表达模式以及在此期间AT II细胞中Klf 4的缺失如何影响小鼠肺泡形成;（2）表征Klf 4在体外循环牵张±高氧期间AT II细胞存活中的功能作用;和（3）确定在MV期间AT II中Klf 4过表达是否保持肺泡形成并使新生小鼠的肺生长成为可能。资助这个项目应该定义Klf 4在AT II和肺泡化中作为细胞存活的调节剂的功能作用，并帮助开发新的策略来保护肺泡化和促进肺生长。

Mechanical ventilation with O2-rich gas (MV-O2) offers life-saving treatment for premature infants with respiratory failure, but also promotes Ventilation-Induced Lung Injury (VILI), which in neonates results in impaired formation of alveoli and capillary hypoplasia, as seen in neonatal Chronic Lung Disease (CLD). Defective alveolar formation by both prolonged MV and O2 supplementation has been linked to increased lung cell apoptosis. Type II alveolar epithelial cells (ATII) are recognized as progenitor cells, crucial in alveolar formation and regeneration subsequent to lung injury. However, the underlying molecular mechanisms regulating alveolar epithelial cell survival and alveolar formation in lungs after MV-O2is unclear. Krüppel-like factor 4 (Klf4) is a transcription factor with diverse regulatory roles in cell pluripotency, differentiation, survival and development in epithelial cells. We recently discovered that Klf4 mRNA and protein were reduced in lungs of mechanically ventilated 5-day old mice; Klf4 expression was also diminished in cultured mouse lung type II epithelial cells (MLE-12) after exposure to cyclic stretch. Moreover, we found that loss of Klf4 in MLE-12 inhibits cell survival. Therefore, we aim now to elucidate the functional role of Klf4 in normal lung development and in defective alveolarization seen in lungs of newborn mice after MV-O2. To this end, we will address three specific aims: we will (1) analyze the expression pattern of Klf4 during late lung development and how loss of Klf4 in AT II cells during this period affects alveolar formation in mice; (2) characterize the functional role of Klf4 in survival of AT II cells during cyclic stretch ± hyperoxia in vitro; and (3) determine if Klf4 overexpression in AT II preserves alveolar formation and enables lung growth in newborn mice during MV. Funding this project should define the functional role of Klf4 in AT II and alveolarization as a modulator of cell survival, and help to develop new strategies to preserve alveolarization and promote lung growth.