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

富氧机械通气(MV-O2)为呼吸衰竭的早产儿提供了挽救生命的治疗，但也促进了呼吸机诱导的肺损伤(VILI)，这在新生儿中会导致肺泡形成障碍和毛细血管发育不良，如新生儿慢性肺病(CLD)。长期的MV和O2补充导致的肺泡形成缺陷与增加肺细胞的凋亡有关。肺泡II型上皮细胞(ATII)是公认的前体细胞，在肺损伤后肺泡的形成和再生中起关键作用。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-like factor4(KLF4)是一种转录因子，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。我们最近发现，机械通气5日龄小鼠肺组织中KLF4的mRNA和蛋白表达减少；周期性拉伸暴露后，培养的小鼠肺II型上皮细胞(MLE-12)中KLF4的表达也减少。此外，我们还发现MLE-12中KLF4的缺失抑制了细胞的存活。因此，我们现在的目标是阐明KLF4在正常肺发育和MV-O2后新生小鼠肺泡形成中的功能作用。为此，我们将解决三个具体目标：(1)我们将分析KLF4在肺发育后期的表达模式，以及在此期间KLF4在AT II细胞中的丢失如何影响小鼠肺泡的形成；(2)研究KLF4在体外周期性拉伸和高氧条件下AT II细胞存活中的功能作用；以及(3)确定KLF4在AT II中的过表达是否保留了肺泡的形成，并使新生小鼠在MV期间能够生长。资助该项目将明确KLF4在AT II和肺泡化中作为细胞存活调节器的功能作用，并有助于开发新的策略来保存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.