高氧致慢性肺疾病早产大鼠P16基因启动子区甲基化

p16 promoter methylation in premature rats with chronic lung disease induced by hyperoxia

目的探讨高氧致慢性肺疾病早产大鼠肺组织p16基因的启动子甲基化状态。方法将早产Wistar大鼠80只随机分为高氧组（吸人氧浓度0．90）和对照组（吸人氧浓度0．21），每组均为40只。分别采用半巢式甲基化特异性聚合酶链反应技术和甲基化特异性聚合酶链反应技术检测肺组织p16基因的启动子甲基化状态。同时，应用逆转录-聚合酶链反应技术、Western印迹及免疫组织化学方法检测肺组织p16基因mRNA和蛋白的表达水平。结果应用半巢式甲基化特异性聚合酶链反应技术和甲基化特异性聚合酶链反应技术，对照组中不同日龄早产大鼠均未发现有甲基化发生。半巢式甲基化特异性聚合酶链反应技术检测高氧组甲基化发生率为52．5％（21／40），高于甲基化特异性聚合酶链反应技术检测甲基化的发生率（42．5％，17／40），但差异无统计学意义。高氧组肺组织p16mRNA表达水平在7、14、21d时分别为1．73±0．40，1．29±0．19和0．95±0．25，均低于对照组（分别为2．11±0．37、1.60±0．27和1.72±0．34），t分别为2．19、2．95和10．43，P均〈0．05。高氧组肺组织p16蛋白表达水平在7、14、21d时分别为88．1±8．7、65．7±4．5和50．4±4．9，也低于对照组（分别为95．0±4．1、83．5士13．6和86．7±11．9），t分别为2．27、3．95和13．40，P均〈O．05。甲基化大鼠肺组织p16mRNA表达水平为1．06±0．61，蛋白表达水平为62．32±25．65，均低于非甲基化大鼠，分别为1．63±0．62和94．93±22．21，差异均有统计学意义（t=2．95，OR=0．86，P〈0．01；t=4．28，OR=0．85，P％0．01）。结论高氧可导致早产大鼠的肺组织p16基因启动子甲基化异常，且其甲基化的发生率随高氧暴露时间的延长而逐渐增加，高氧诱导的p16基因启动子高甲基化状态可能是p16mRNA及蛋白的低水平表达的机制之一，但并非基因沉默。

Objective To investigate p16 promoter methylation in premature rats with chronic lung disease induced by hyperoxia. Methods Eighty premature Wistar rats were randomly divided into two groups., hyperoxia group （fraction of inspiratory oxygen） 0.90 and control group （fraction of inspiratory oxygen 0.21）, 40 rats for each group. Semi-nested methylation specific polymerase chain reaction and methylation specific polymerase chain reaction were applied respectively to detect p16 promoter methylation in lung tissues. Additionally, p16 mRNA and protein expressions in lung tissue were detected by reverse transcription-polymerase chain reaction, Western blot and immunohistochemistry method. Results The methylation was not found in control group by semi- nested methylation specific polymerase chain reaction and methylation specific polymerase chain reaction, while was found in different aged rats of the hyperoxia group. The methylation detection rate was higher by using the semi-nested methylation-specific polymerase chain reaction （52.5%, 21/40） than that by methylation specific polymerase chain reaction （42.5%, 17/40） in the hyperoxia group, but there was no statistically significant difference between the two methods. The p16 mRNA in the hyperoxia group were significantly lower than in the control group at day 7, 14 and 21（1.73 ±0.40 vs 2.11±0.37,1.29±0.19 vs 1.60±0.27,0.95±0.25 vs 1.72±0.34, t=2.19, 2.95 and 10.43,P〈0.05）. The p16 protein expressions by western blot in the hyperoxia group were significantly lower than in the control group at day？, 14 and 21 also （88. 1±8.7 vs 95.0±4.1,65.7＋4.5 vs 83.5± 13.6 and 50.4±4.9 vs 86.7±11.9, t±2.27,3.95 and 13.40,P〈0.05）. The expression of p16 rnRNA （1.06±0.61） and protein （62.32±25.65） in lung tissues of rats with methylation was lower than that without methylation （1.63±0.62 and 94.93±22.21, respectively） （t=2.95, OR=0.86; t=4.28, OR=0. 85,P%0.01, respectively）. Conclusions Exposure to hyperoxia might induce p16 promoter methylation in lung tissues in premature rats. Methylation risk increases as exposure time extends, p16 promoter methylation induced by hyperoxia might participate in the mechanism of lowering p16 mRNA and protein expression, but might not result in p16 gene silence.