In vivo activation of AMP-activated protein kinase attenuates diabetes-enhanced degradation of GTP cyclohydrolase I.
In vivo activation of AMP-activated protein kinase attenuates diabetes-enhanced degradation of GTP cyclohydrolase I.
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作者：
Wang S;Xu J;Song P;Viollet B;Zou MH
已有报道通过激活AMP激活的蛋白激酶(AMPK)改善内皮功能。然而，AMPK在内皮细胞中的靶点仍然不明确。这项研究的目的是测试AMPK是否抑制GTP-环水解酶(GTPCH I)的降解，GTPCH I是糖尿病血管内皮功能障碍的关键事件。从链脲佐菌素注射糖尿病小鼠分离的人脐静脉内皮细胞和主动脉分别检测磷酸化AMPK(Thr172)、GTPCH I、四氢生物蝶呤(BH4)和内皮功能。给链脲佐菌素注射的小鼠口服二甲双胍(30 0 mg·kg-1·day-day，−1，4周)可显著抑制糖尿病引起的AMPK磷酸化水平的降低。二甲双胍治疗也使乙酰胆碱诱导的内皮松弛正常化，并增加GTPCH I和BH4水平。给予AMPK激活剂AICAR或AMPK组活性突变体的腺病毒过表达可阻断高糖(30 mmol/L)诱导的GTPCH I、BH4和BH4的减少，但对GTPCH I mRNA无影响。此外，AICAR或过表达AMPK可抑制高糖增强的26S蛋白酶体活性。一以贯之，MG132抑制蛋白酶体可消除高糖诱导的人脐静脉内皮细胞GTPCH I的减少。此外，从AMPKα2−/−小鼠分离的主动脉，其26S蛋白酶体活性升高，GTPCH I和BH4水平降低。最后，给予MG132或补充L-七叶蝶呤均可使AMPKα2−/−小鼠受损的主动脉内皮依赖性舒张功能恢复正常。我们的结论是，AMPK激活通过抑制26S蛋白酶体介导的糖尿病GTPCH I降解而使血管内皮细胞功能正常化。
The activation of AMP-activated protein kinase (AMPK) has been reported to improve endothelial function. However, the targets of AMPK in endothelial cells remain poorly defined. The aim of this study was to test whether AMPK suppresses the degradation of GTP-cyclohydrolase (GTPCH I), a key event in vascular endothelial dysfunction in diabetes. Both human umbilical vein endothelial cells and aortas isolated from streptozotocin-injected diabetic mice were assayed for phospho-AMPK (Thr172), GTPCH I, tetrahydrobiopterin (BH4), and endothelial functions. Oral administration of metformin (300 mg · kg−1 · day−1, 4 weeks) in streptozotocin-injected mice significantly blunted the diabetes-induced reduction of AMPK phosphorylation at Thr172. Metformin treatment also normalized acetylcholine-induced endothelial relaxation and increased the levels of GTPCH I and BH4. The administration of AICAR, an AMPK activator, or adenoviral overexpression of a constitutively active mutant of AMPK abolished the high-glucose–induced (30 mmol/l) reduction of GTPCH I, biopeterins, and BH4 but had no effect on GTPCH I mRNA. Furthermore, AICAR or overexpression of AMPK inhibited the high-glucose–enhanced 26S proteasome activity. Consistently, inhibition of the proteasome by MG132 abolished high-glucose–induced reduction of GTPCH I in human umbilical vein endothelial cells. Further, aortas isolated from AMPKα2−/− mice, which exhibited elevated 26S proteasome activity, had reduced levels of GTPCH I and BH4. Finally, either administration of MG132 or supplementation of l-sepiapterin normalized the impaired endothelium-dependent relaxation in aortas isolated from AMPKα2−/− mice. We conclude that AMPK activation normalizes vascular endothelial function by suppressing 26S proteasome-mediated GTPCH I degradation in diabetes.
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影响因子：
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