庆大霉素对CIH子代大鼠听力及内耳Connexin26蛋白表达水平影响的研究

Effects of gentamicin on hearing and Connexin26 protein expression in the inner ear of CIH offspring rats

目的研究官内缺氧和庆大霉素（GM）双重影响对仔鼠内耳听力损伤影响的关系。方法建立宫内慢性缺氧（Intrauterine chronic hypoxia，CIH）孕鼠模型，24只SD孕大鼠分为正常组和缺氧组，每组12只。分娩后得正常仔鼠和缺氧仔鼠各12窝（每窝12-13只仔鼠）。仔鼠生后8周，随机选取正常仔鼠24只，分正常仔鼠组、正常＋GM仔鼠组；缺氧仔鼠24只，分缺氧仔鼠组、缺氧＋GM仔鼠组（各12只）。4组仔鼠做听性脑干反应（auditory brainstem response，ABR）检测听功能后，麻醉处死动物，取出内耳分别做Westernblot、实时定量PCR、亚硫酸氢盐测序法（BSP）甲基化检测等。结果孕鼠动脉血气分析：缺氧组孕鼠动脉血氧分压（PaO2）、动脉血氧饱和度（SaO2）水平和正常组比较，均显著下降，差异有统计学意义（P〈0．05或P〈0．01），缺氧组孕鼠与正常组间PaCO2及pH值差异均无统计学意义（P〉0．05）。ABR检测结果：缺氧＋GM仔鼠组的ABR阈值明显高于其他3组，差异有统计学意义（P〈0．01）。正常＋GM仔鼠组、缺氧仔鼠组之间ABR阈值差异无统计学意义（P〉0．05），但正常仔鼠组ABR阈值均低于正常＋GM仔鼠组、缺氧仔鼠组，差异均有统计学意义（P〈0．05）。实时定量PCR检测仔鼠内耳组织GJB2mRNA水平：缺氧＋GM仔鼠组GJB2mRNA水平明显低于其他3组，差异有统计学意义（P〈0．01）。正常＋GM仔鼠组、缺氧仔鼠组之间的GJB2 mRNA水平差异无统计学意义（P〉0．05），但正常仔鼠组的GJB2mRNA水平均高于正常＋GM仔鼠组、缺氧仔鼠组，差异均有统计学意义（P〈0．05）。Westernblot检测仔鼠内耳Connexin26蛋白表达的结果和GJB2mRNA表达水平一致。甲基化测序：GJB2基因启动子岛1、岛2区域甲基化分析，缺氧＋GM仔鼠组内耳组织中的GJB2基因启动子区域岛1、岛2位点甲基化率百分比明显高于其他3组，差异有统计学意义（P〈0．01）。正常＋GM仔鼠组和缺氧仔鼠组的GJB2基因启动子区域岛1、岛2位点甲基化率百分比水平差异无统计学意义（P〉0．05），但和正常仔鼠组比较明显升高，差异有统计学意义（P〈0．05）。结论妊娠期缺氧及GM可导致仔鼠听力损伤，并且有协同效应。主要是致聋基因GJB2基因启动子岛1、岛2区域甲基化水平上升，GJB2mRNA水平下降，Connexin26蛋白表达下降。

Objective To investigate the relationship between intrauterine hypoxia （CIH） and gentamiein （GM） on the development of inner ear in neonatal rats. Methods A CIH rat model was established. A total of 24 SD pregnant rats were divided into a normal group and a hypoxia group （n = 12）. After delivery, the two groups were randomly divided into four subgroups （n = 12） ： a normal group, a normal GM group, a hypoxia group, and a hypoxia GM group. All the rats were sacrificed after auditory brainstem response （ABR） was measured. The inner ear was examined by Western blot, real -time PCR, and bisulfite sequencing PCR. Results Analysis of arterial blood gas： the levels of PaO2 and SaO2 in pregnant rats in hypoxia group were significantly lower than those in the normal group （P 〈0.05 or P 〈0.01 ）, but no statistical difference was found in PaCO2 and pH （P 〉 0.05 ）. ABR ： compared with other groups, there was significant increase in ABR response threshold of the hypoxia GM group （P 〈 0.01 ）. There was no significant difference in ABR response threshold between the normal GM and hypoxia groups （ P 〈 0.05 ）. The normal group showed remarkable decreases in ABR response threshold compared with the normal GM and hypoxia GM groups （ P 〈 0.05 ）. Real time - PCR： There was a significant difference in the level of GJB2 mRNA between the hypoxia GM group compared with the other groups （P 〈 0.01 ）. There was no significant difference in GJB2 mRNA level between the normal GM and hypoxia groups （ P 〉 0. 05）. The normal group showed remarkable increases in GJB2 mRNA level compared with the normal GM and hypoxia GM groups （ P 〈 0.05 ）. The changes of Connexin26 protein level were consistent with those of GJB2 mRNA level. Methylation sequencing： GJB2 gene promoter island 1 and island 2 region methylation analysis showed that the percentage of methylation rate in the hypoxia GM group was significantly higher than that in the other three groups （ P 〈 0.05）. There was no difference between the normal GM and hypoxia groups （P 〉 0.05）. But compared with the normal group, the difference was statistically significant （ P 〈 0.05 ）. Conclusions Hypoxia and gentamicin in pregnancy can lead to hearing damage and synergistic effects. The methylation level of GJB2 gene promoter is increased, the level of GJB2 mRNA is decreased, and the expression of Connexin26 protein is decreased.