Reactive nitrogen species induced by hyperglycemia suppresses Akt signaling and triggers apoptosis by upregulating phosphatase PTEN (phosphatase and tensin homologue deleted on chromosome 10) in an LKB1-dependent manner.
BACKGROUND
Oxidative stress plays a causal role in vascular injury in diabetes mellitus, but the mechanisms and targets remain poorly understood.


RESULTS
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.


CONCLUSIONS
We conclude that hyperglycemia triggers apoptosis by inhibiting Akt signaling via ONOO(-)-mediated LKB1-dependent PTEN activation.
Song
Ping
P
Section of Endocrinology and Diabetes, Department of Medicine, University of Oklahoma Health Science Center, Oklahoma City, OK 73104, USA.
Wu
Yong
Y
Xu
Jian
J
Xie
Zhonglin
Z
Dong
Yunzhou
Y
Zhang
Miao
M
Zou
Ming-Hui
MH
D000091162:AMP-Activated Protein Kinase Kinases; D000818:Animals; D017209:Apoptosis / Q000502:physiology; D002478:Cells, Cultured; D003921:Diabetes Mellitus, Experimental / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology; D004730:Endothelium, Vascular / Q000201:enzymology* / Q000473:pathology; D006801:Humans; D006943:Hyperglycemia / Q000188:drug therapy / Q000378:metabolism* / Q000473:pathology*; D007004:Hypoglycemic Agents / Q000494:pharmacology; D007328:Insulin / Q000494:pharmacology; D008297:Male; D051379:Mice; D051059:PTEN Phosphohydrolase / Q000378:metabolism*; D030421:Peroxynitrous Acid / Q000378:metabolism; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D026361:Reactive Nitrogen Species / Q000378:metabolism*; D012694:Serine / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D013912:Threonine / Q000378:metabolism; D014471:Umbilical Veins / Q000166:cytology; D015854:Up-Regulation / Q000502:physiology
D007004:Hypoglycemic Agents; D007328:Insulin; D026361:Reactive Nitrogen Species; D030421:Peroxynitrous Acid; D013912:Threonine; D012694:Serine; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; C109790:STK11 protein, human; D000091162:AMP-Activated Protein Kinase Kinases; D051059:PTEN Phosphohydrolase; C494929:PTEN protein, human; C487757:Pten protein, mouse