小肠缺血再灌注损伤恢复期骨形成蛋白-4促进肠黏膜屏障恢复的实验研究

Experimental study of bone morphogenetic protein-4 in promoting recovery of small intestinal mucosal barrier during recovery period of intestine ischemia-reperfusion injury

目的探讨在小肠缺血再灌注(I/R)损伤恢复期时小肠上皮细胞中骨形成蛋白-4(BMP4)促进肠黏膜屏障功能恢复的机制。方法 28只6~8周龄C57BL/6J雄性小鼠,采取随机数字表法随机抽取24只小鼠用于I/R操作,余下4只小鼠进行假手术(SO)操作。I/R后分别于6、12、24、48 h时随机抽取4只小鼠处死用于观察小鼠小肠黏膜的形态学变化并检测其空肠上皮细胞中BMP4 mRNA表达的变化,另外8只小鼠分配用于肠黏膜损伤恢复期(根据预实验结果,选择I/R后24 h时作为观察时间点)的实验观察。对I/R后恢复期即I/R后24 h时的小鼠腹腔内分别注射浓度为30 ng/(m L·kg)的重组人BMP4蛋白(I/R-24 h-BMP4组)和生理盐水(I/R-24 h-NS组),对不注射任何液体的小鼠作为对照组(I/R-24 h-空白组),采用随机数字表法每组随机分配4只小鼠,然后检测各组小鼠空肠黏膜组织跨膜电阻抗(TER)的变化,同时采用Western blot法检测各组小鼠小肠上皮细胞中BMP4蛋白、紧密连接蛋白(occludin、ZO-1)、Notch信号通路蛋白(Notch1、Jagged1)及磷酸化Smad6蛋白(p-Smad6)的蛋白表达变化。结果在小鼠小肠I/R后24 h时,小肠黏膜绒毛上皮层损伤明显减轻、水肿减轻、肠绒毛少部分断裂、脱落。与SO小鼠比较,I/R后6、12、24、48 h时空肠上皮细胞中BMP4 mRNA表达呈逐渐增高趋势。小鼠I/R损伤后恢复期即I/R后24 h时发现,给予外源性BMP4蛋白刺激后,I/R-24 h-BMP4组空肠黏膜组织中TER值、BMP4、occludin、ZO-1、Notch1、Jagged1、p-Smad6蛋白表达均较I/R-24 h-NS组和I/R-24 h-空白组升高。结论从本研究初步研究结果看,在小肠I/R损伤后恢复期,空肠黏膜屏障通透性增大、BMP4表达增加,其可能是通过激活Notch信号通路(Notch1、Jagged1)和Smad经典信号通路(p-Smad6)与促进紧密连接蛋白(occludin和ZO-1)表达增加来促进肠黏膜屏障功能的恢复,从而减轻肠黏膜屏障功能损伤。

Objective To investigate the mechanism of bone morphogenetic protein-4(BMP4) in promoting the recovery of small intestinal mucosal barrier function during the recovery period of small intestine ischemia-reperfusion(I/R) injury. Methods Twenty-eight C57 BL/6 J male mice aged 6–8 weeks were randomly selected and assigned to small intestine I/R group(n=24) and sham operation(SO) group(n=4) by random number table method. Small intestine I/R injury models of 24 mice were established, then 4 mice were randomly selected at 6, 12, 24 and 48 h after I/R established modeling and killed to observe the morphological changes of small intestinal mucosa and detect the expression of BMP4 mRNA in the jejunal epithelial cells, the other 8 mice were allocated for the experimental observation at the recovery period of small intestine I/R injury(24 h after I/R was selected as the observation time point of recovery period of small intestine I/R injury according to the pre-experimental results). Twelve mice were randomly divided into I/R-24 hBMP4 group(recombinant human BMP4 protein was injected intraperitoneally), I/R-24 h-NS(normal saline) group(NS was injected intraperitoneally), and I/R-24 h-blank group(did nothing), 4 mice in each group. Then the small intestinal transmembrane electrical impedance(TER) was measured by Ussing chamber. The expressions of BMP4 protein and tight junction proteins(occludin and ZO-1), Notch signaling pathway proteins(Notch1 and Jagged1), and Smad6 protein were detected by Western blot. Results At 24 h after I/R injury, the injuries of villous epithelium, edema, and a small part of villi were alleviated. The BMP4 mRNA expressions at 6, 12, 24 and 48 h after I/R injury in the small intestinal epithelial cells were increased as compared with the SO group. Compared with the I/R-24 h-NS group and the I/R-24 h-blank group,the TER was increased, and the expression levels of occludin, ZO-1, p-Smad6, Notch1, Jagged1 were increased in the I/R-24 h-BMP4 group. Conclusion From the preliminary results of this study, during recovery period of small intestine I/R injury, the expression of BMP4 in small intestinal epithelial cells is increased, permeability of jejunal mucosal barrier is increased, which might promote the recovery of small intestinal mucosal barrier function by activating the Notch signaling pathway(Notch1 and Jagged1), Smad classic signaling pathway, and promoting the increase of tight junction protein expression(occludin and ZO-1).