谷氨酰胺对急性肺损伤大鼠肺泡上皮屏障功能的影响

Effects of glutamine on alveolar epithelial barrier function in rats with acute lung injury

目的:观察谷氨酰胺对急性肺损伤大鼠肺泡上皮屏障功能及紧密连接(TJ)特征性蛋白occludin和黏附连接蛋白E-cadherin的影响。方法:40只SD大鼠随机分为对照组、谷氨酰胺处理组(Gln组)、内毒素处理组(LPS组)、谷氨酰胺并内毒素处理组(Gln+LPS组)。测定支气管肺泡渗透性、运用免疫印迹测定和RT-PCR测定肺泡Ⅱ型上皮细胞中occludin和E-cadherin的蛋白及mRNA表达。结果:内毒素导致支气管肺泡上皮渗透性明显增高2倍左右(P<0.01);补充谷氨酰胺可以明显改善由内毒素处理引起的支气管肺泡上皮渗透性增高(P<0.05),但Gln+LPS组支气管肺泡渗透性仍较对照组及Gln组增高(P<0.05)。免疫印迹和RT-PCR显示在LPS组的occludin和E-cadherin蛋白和mRNA表达水平均较对照组及Gln组的低(P<0.01);在Gln+LPS组中occludin和E-cadherin的蛋白和mRNA表达水平较LPS组的高(P<0.05),而较对照组及Gln组的表达水平低(P<0.05)。结论:实验提示内毒素通过降低TJ分子occludin和E-cadherin的mRNA、蛋白表达水平导致肺泡上皮屏障功能受损,补充谷氨酰胺通过上调其mRNA、蛋白表达水平而对肺泡上皮屏障功能有保护作用。

Objective To investigate the effects of glutamine （Gin） on alveolar epithelial barrier function and the expressions of tight junction protein occludin and adherens junction protein E-cadherin in rats with acute lung injury. Methods 40 rats were randomized to control, LPS, Gin, or Gln/LPS group. Bronchoalveolar epithelial permeability was detected and alveolar type II cells were isolated. The protein and mRNA expressions of occludin and E-cadherin in the cells were examined by immunoblotting and RT-PCR. Results The bronchoalveolar epithelial permeability had an approximate 2-fold increase after treatment with LPS （P 〈 0.01 ） and Gin supplementation significantly attenuated this enhanced permeability （P〈 0.05）. However, the permeability in Gln/LPS group was still higher than that in both control and Gin group （P 〈 0.05 ）. Immunoblotting and RT-PCR showed that the expression levels of occludin and E-cadherin mRNA and proteins in LPS group were significantly lower than those in both control and Gin group （P 〈 0.01 ）. The expression levels of occludin and E-cadherin mRNA and proteins in Gln/LPS group were markedly higher than those in LPS group （P 〈 0.05） but lower than those in both control and Gin group （P 〈 0.05）. Conclusions LPS impairs alveolar epithelial barrier function through down-regulating the mRNA and protein expressions of occludin and E-cadherin. Gin supplementation plays a role in protecting the barrier function via up-regulating the mRNA and protein expressions.