肺Ⅱ型上皮干细胞分化在放射性肺纤维化中作用

The role of lung typeⅡepithelial stem cell differentiation in radiation-induced pulmonary fibrosis

目的通过观察Ⅱ型肺泡上皮细胞表面活性蛋白C(proSP-C)、Ⅰ型肺上皮细胞标志蛋白(HOPX)、间质细胞标志蛋白波形蛋白(vimentin)及转化生长因子β1(TGF-β1)在肺组织表达的动态变化,以确定放射诱导肺纤维化的间质细胞是由Ⅱ型肺上皮细胞异分化所致,并探讨其可能的机制。方法给予8周龄C57BL/6j雌性小鼠胸部X线单次照射20 Gy,分别在照射后24 h、1周、1~6个月收集小鼠肺组织,通过对比肺组织(0 Gy)形态学变化,明确肺纤维化形成时间点。另通过免疫荧光染色观察proSP-C、HOPX、vimentin及TGF-β1表达改变,判断Ⅱ型上皮细胞在不同损伤阶段的动态表型,再用Western blot进行定量分析。结果单次20 Gy照后3个月肺组织发生局部纤维化。Ⅱ型细胞能共表达proSP-C/HOPX和proSP-C/vimentin;而Western blot显示这些蛋白和TGF-β1的表达量随肺损伤而发生改变。结论推测肺Ⅱ型上皮细胞在X线照射后因TGF-β1升高异分化为间质样细胞,这可能是放射性肺纤维化的主要诱因。

Objective To determine the role of typeⅡalveolar epithelial stem cells(AECⅡ)in radiation-induced pulmonary injury and investigate the potential mechanism by observing the dynamic changes in the expression levels of anti-prosurfactant protein C(proSP-C)proSP-C(AECⅡbiomarker),homeobox only protein X(HOPX,type I alveolar epithelial cell biomarker)or vimentin(a mesenchymal marker)and transforming growth factorβ1(TGF-β1),a profibrotic cytokine.Methods Eight-week old C57BL/6j female mice were exposed to X-ray thoracic irradiation.Mouse lungs were collected at 8 different time points of 24 h,1 week,1 to 6 months after irradiation.The histopathological changes of the lungs at different time points were observed with H&E staining to determine the time of formation of pulmonary fibrosis.In addition,the co-expression of proSP-C with HOPX or vimentin in AECⅡwas confirmed by immunofluorescence staining to track AECⅡphenotypes at different injury phases following thoracic irradiation.The expression levels of those proteins and TGF-β1 were quantitatively detected by Western blot.Results After thoracic exposure to a single dose of 20 Gy X-ray for 3 months,the fibrotic lesions in the lungs could be noted.The co-expression of proSP-C with vimentin or HOPX could be observed in AECⅡ.Western blot demonstrated that the expression levels of TGF-β1 and those proteins were also changed along with the lung injury.Conclusion AECⅡcan be differentiated into mesenchymal-like cells after X-ray irradiation due to the up-regulated expression of TGF-β1,which is a potential cause of radiation-induced pulmonary fibrosis.