小鼠肺臟上皮幹細胞於高氧肺損傷之角色探討

Abstract

高氧治療 (hypeorxic ventilation)廣泛應用於早產兒的呼吸維持，然而此治療造成肺部損傷以及疾病。肺部支氣管發育不良BPD (bronchopulmonary dysplasia)為一種慢性肺部疾病，好發於使用高氧治療之早產兒。其症狀包括肺部發炎，肺泡肥大，肺部發育失調以及終生心肺功能不良。成體幹細胞 (adult stem cell)在組織發育以及修復當中扮演重要的角色。在先前的研究中，小鼠肺臟幹細胞 (mouse pulmonary stem/progenitor cells) 可從肺臟初級培養中取得，並在誘導條件下分化形成第一型肺泡細胞。雖然各種治療肺部支氣管發育不良之療法已被研發，肺臟幹細胞於此疾病之進程中扮演何種角色仍不明。使用高氧處理(90% O2 )使肺臟幹細胞之分化被阻止。於已經分化之肺臟幹細胞中，高氧處理造成細胞群落之凋亡，此細胞群落介於於幹細胞及末端分化第一型肺泡細胞之間。高氧處理造成之細胞凋亡可被在乙醯基半胱氨酸阻止。使用雙氧水處理肺臟幹細胞可造成類似之細胞凋亡型態，顯示高氧處理誘發細胞凋亡由活性氧化物 (Reactive Oxygen Species)所造成。在不同氧濃度處理當中，40% O2明顯的延緩肺臟幹細胞之凋亡，顯示肺臟幹細胞能承受40% O2之高氧環境。本研究顯示肺臟幹細胞在誘導分化成第一型肺泡細胞之進程中，在不同階段對於氧化壓力有不同之承受力。分化中之肺臟細胞承受力低於肺臟幹細胞以及第一型肺泡細胞。

Hyperoxic ventilation has been widely used to support respiratory function for preterm infants. However, such treatment causes injuries and diseases. BPD (bronchopulmonary dysplasia) is the most predominant chronic lung disease among children after hyperoxia ventilation treatment. Its syndrome includes inflammation, alveolar hypertrophy, lung development impairment and respiratory malfunction among the entire lifespan. It is believed that adult stem cell play critical roles in tissue development and injury repair. In previous studies, we have isolated pulmonary stem/progenitor cells (mPSCs) via primary culture of lung tissues. Under induction condition, the mPSCs underwent differentiation into type-1 pneumocytes. Although various therapies were proposed, there was little information about the roles of pulmonary stem/progenitor cell behaved in the treatment. In our study, hyperoxic condition (90% O2 ) arrested differentiation of mPSCs into alveolar lineage by inducing cells apoptosis.Treatment of hyperoxia on differentiating mPSCs resulted in an apoptotic cells area between stem/progenitor cells and terminal differentiated type-1 pneumocytes, where a differentiation switch was believed to be turn on. Apoptosis of mPSCs could be rescued by treatment with NAC (N-acetyl cysteine). This phenotype could be reproduced by treating the cells with H2O2 , which generates enormous ROS. In different hyperoxic condition, a significant reduction of apoptotic cells numbers was observed in treatment with 40 % O2, which indicate the marginal level of hyperoxic tolerance for mPSCs. Taken together, we proposed that mPSCs undergoing an alveolar differentiation lineage had a weaker resistance to ROS hazards; compared to stem/progenitor cells incorporated terminal differentiated type-1 pneumocytes.