既往研究提示,高浓度葡萄糖是诱导糖尿病肾病纤维化的主要病理机制。高浓度的葡萄糖可诱导肾小管导管上皮细胞α-SMA表达[4-5],α-SMA为肌成纤维细胞的标志性蛋白,是反映上皮细胞转分化主要观察指标。目前发现,高糖促转分化的作用机制主要是通过上调各种细胞分化或基质增殖的蛋白水平,例如TGF-β1、PTHrP、Ⅰ型胶原及MMP-2等,TGF-β1、PTHrP信号通路在器官纤维化中的作用已经明确,其水平升高可以通过上调Smad系列蛋白表达,诱导细胞转分化为纤维细胞。而Ⅰ型胶原及MMP-2是参与基质沉积及积聚的主要调控蛋白,同时以自分泌及旁分泌方式作用本体细胞或邻近细胞,从而放大纤维化效应[4-7]。其他细胞包括血管内皮细胞、平滑肌细胞等不仅是单纯性高糖,间歇性高糖同样可以从多个水平影响细胞分化通路TGFβ1/Smad信号转导,从而加重纤维化进程[2-3]。
本研究发现,高浓度葡萄糖环境或间歇性高糖分别作用NRK-52EA细胞后,其TGF-β1、Ⅰ型胶原、MMP-2、α-SMA以及PTHrP表达水平均显著上调;间歇性高糖TGF-β1、MMP2以及α-SMA表达较持续性高糖作用更为显著,该结果与Polhill等[8]对肾小球系膜细胞研究结果—间歇性高糖可以促进肾小球系膜细胞纤维化相似,故推测间歇性高糖较持续性高糖可能更容易通过激活TGF-β1、MMP-2而诱导肾小管导管上皮细胞NRK-52EA转分化为含α-SMA的间充质细胞,加重肾脏纤维化。
本研究结果还发现,间歇性高糖能显著上调NRK-52EA细胞株的ROS含量,其水平高于单纯性高糖组。Quagliaro等[9]研究提示间歇性高糖能通过氧化应激作用促进ROS积聚,诱导各种炎症因子包括MMP等表达,而该系列炎症因子已经被证实参与诱导肾小管导管上皮转分化为间充质细胞进程[10],Jones等[11]也发现间歇性高糖能显著诱导人脐静脉内皮细胞氧化应激反应标记物硝基酪氨酸含量升高,从而促进细胞凋亡。故认为间歇性高糖诱导NRK-52EA细胞转分化作用比持续性高糖更显著,其机制可能是间歇性高糖诱导细胞内氧化应激更严重,从而促进肾小管导管上皮细胞TGF-β1、MMP-2等系列蛋白的表达以拮抗炎症反应,而TGF-β1、MMP-2蛋白表达上调,又进一步加重肾小管上皮细胞纤维化进程。
综上所述,间歇性高糖对肾小管上皮细胞的损害应该更予重视。提示临床控制血糖平稳是糖尿病治疗的重要基础,在此基础上适当抗氧化治疗有望减轻氧化应激, 保护肾小管上皮细胞, 迟滞其转分化, 可能会延缓糖尿病并发症的发展医.学.全.在.线www.med126.com。
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