Song Ping, Wu Yong, Xu Jian, Xie Zhonglin, Dong Yunzhou, Zhang Miao, Zou Ming-Hui
Section of Endocrinology and Diabetes, Department of Medicine, University of Oklahoma Health Science Center, Oklahoma City, OK 73104, USA.
Circulation. 2007 Oct 2;116(14):1585-95. doi: 10.1161/CIRCULATIONAHA.107.716498. Epub 2007 Sep 17.
Oxidative stress plays a causal role in vascular injury in diabetes mellitus, but the mechanisms and targets remain poorly understood.
Exposure of cultured human umbilical vein endothelial cells to either peroxynitrite (ONOO-) or high glucose significantly inhibited both basal and insulin-stimulated Akt phosphorylation at Ser473 and Akt activity in parallel with increased apoptosis, phosphorylation, and activity of phosphatase and tensin homologue deleted on chromosome 10 (PTEN). Furthermore, protein kinase B/Akt inhibition induced by ONOO- or high glucose and apoptosis triggered by high glucose could be abolished by transfection of PTEN-specific small interfering RNA, suggesting that PTEN mediated the Akt inhibition by ONOO-. In addition, exposure of human umbilical vein endothelial cells to ONOO- or high glucose remarkably increased Ser428 phosphorylation of LKB1, a tumor suppressor. Interestingly, the ONOO(-)-enhanced PTEN phosphorylation and Akt inhibition can be blocked by LKB1-specific small interfering RNA. Consistently, LKB1 phosphorylated PTEN at Ser380/Thr382/383 in vitro, suggesting that LKB1 might act as an upstream kinase for PTEN. Compared with nondiabetic mice, the levels of PTEN, LKB1-Ser428 phosphorylation, and 3-nitrotyrosine (a biomarker of ONOO-) were significantly increased in the aortas of streptozotocin-induced diabetic mice, which was in parallel with a reduction in Akt-Ser473 phosphorylation and an increase in apoptosis. Furthermore, administration of PTEN-specific small interfering RNA suppressed diabetes-enhanced apoptosis and Akt inhibition. Finally, treatment with Tempol, a superoxide dismutase mimetic, and insulin, both of which reduced the ONOO- formation, markedly reduced diabetes-enhanced LKB1-Ser428 phosphorylation, PTEN, and apoptosis in the endothelium of mouse aortas.
We conclude that hyperglycemia triggers apoptosis by inhibiting Akt signaling via ONOO(-)-mediated LKB1-dependent PTEN activation.
氧化应激在糖尿病血管损伤中起因果作用，但其机制和靶点仍知之甚少。
将培养的人脐静脉内皮细胞暴露于过氧亚硝酸盐（ONOO-）或高糖环境中，可显著抑制丝氨酸473位点的基础及胰岛素刺激的Akt磷酸化和Akt活性，同时凋亡增加，10号染色体缺失的磷酸酶及张力蛋白同源物（PTEN）的磷酸化和活性增强。此外，过氧亚硝酸盐或高糖诱导的蛋白激酶B/Akt抑制以及高糖引发的凋亡可通过转染PTEN特异性小干扰RNA消除，提示PTEN介导了过氧亚硝酸盐对Akt的抑制作用。另外，将人脐静脉内皮细胞暴露于过氧亚硝酸盐或高糖环境中会显著增加肿瘤抑制因子LKB1丝氨酸428位点的磷酸化。有趣的是，LKB1特异性小干扰RNA可阻断过氧亚硝酸盐增强的PTEN磷酸化和Akt抑制。一致地，LKB1在体外可使PTEN丝氨酸380/苏氨酸382/383位点磷酸化，提示LKB1可能作为PTEN的上游激酶。与非糖尿病小鼠相比，链脲佐菌素诱导的糖尿病小鼠主动脉中PTEN、LKB1丝氨酸428位点磷酸化及3-硝基酪氨酸（过氧亚硝酸盐的生物标志物）水平显著升高，同时Akt丝氨酸473位点磷酸化减少且凋亡增加。此外，给予PTEN特异性小干扰RNA可抑制糖尿病增强的凋亡和Akt抑制。最后，用超氧化物歧化酶模拟物Tempol和胰岛素治疗，二者均可减少过氧亚硝酸盐的形成，显著降低糖尿病增强的LKB1丝氨酸428位点磷酸化、PTEN水平及小鼠主动脉内皮细胞凋亡。
我们得出结论，高血糖通过过氧亚硝酸盐介导的LKB1依赖的PTEN激活抑制Akt信号传导，从而引发细胞凋亡。
