Fisslthaler Beate, Fleming Ingrid, Keserü Benjamin, Walsh Kenneth, Busse Rudi
Institut für Kardiovaskuläre Physiologie, Johann Wolfgang Goethe-Universität, Frankfurt am Main, Germany.
Circ Res. 2007 Feb 2;100(2):e12-21. doi: 10.1161/01.RES.0000257747.74358.1c. Epub 2007 Jan 11.
The rate-limiting enzyme for cholesterol synthesis, the hydroxy-methylglutaryl coenzyme A reductase (HCR), is phosphorylated by the AMP-activated protein kinase (AMPK). As shear stress activates the AMPK in endothelial cells, we determined whether it affects HCR activity and subsequent HCR-dependent signaling. Shear stress (12 dynes cm(-2)) rapidly increased the phosphorylation and activity (6.5- and 4-fold, respectively) of the AMPK in cultured endothelial cells and the activated AMPK phosphorylated the HCR in vitro. Moreover, shear stress and the AMPK activator 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR) attenuated endothelial HCR activity by 37% and 33%, respectively. Inhibition of NO production attenuated the acute shear stress-induced phosphorylation of the AMPK and the decrease in HCR activity. Prolonged shear stress (18 hours) led to a significant (50%) decrease in HCR mRNA expression that was dependent on NO, AMPK, and the subsequent phosphorylation and degradation of FoxO1a. Correspondingly, the downregulation of FoxO (small interfering RNA) decreased HCR expression. Prolonged shear stress also attenuated the bradykinin-induced activation of Ras and extracellular signal-regulated kinase 1/2, a phenomenon that was comparable to the effects of cerivastatin and that was reversed by mevalonate and thus attributed to HCR inhibition. A decrease (35%) in HCR expression was also detected in femoral arteries from mice following voluntary exercise, and the bradykinin-induced vasodilatation of the mouse hindlimb was attenuated by both exercise and the HCR inhibitor cerivastatin. These data indicate that fluid shear stress regulates the activity and expression of the HCR in endothelial cells and determines responsiveness to stimuli, such as bradykinin via a mechanism involving NO, AMPK, FoxO1a, and p21Ras.
胆固醇合成的限速酶，即羟甲基戊二酰辅酶A还原酶（HCR），可被AMP激活的蛋白激酶（AMPK）磷酸化。由于剪切应力可激活内皮细胞中的AMPK，我们研究了其是否会影响HCR活性及随后的HCR依赖性信号传导。剪切应力（12达因/平方厘米）可迅速增加培养的内皮细胞中AMPK的磷酸化水平和活性（分别增加6.5倍和4倍），且激活的AMPK可在体外使HCR磷酸化。此外，剪切应力和AMPK激活剂5-氨基咪唑-4-甲酰胺核苷（AICAR）分别使内皮HCR活性降低37%和33%。抑制一氧化氮（NO）生成可减弱急性剪切应力诱导的AMPK磷酸化及HCR活性降低。长时间的剪切应力（18小时）导致HCR mRNA表达显著降低（50%），这依赖于NO、AMPK以及随后FoxO1a的磷酸化和降解。相应地，FoxO的下调（小干扰RNA）降低了HCR表达。长时间的剪切应力还减弱了缓激肽诱导的Ras和细胞外信号调节激酶1/2的激活，这一现象与西立伐他汀的作用类似，且可被甲羟戊酸逆转，因此归因于HCR抑制。在自愿运动后的小鼠股动脉中也检测到HCR表达降低（35%），且运动和HCR抑制剂西立伐他汀均可减弱缓激肽诱导的小鼠后肢血管舒张。这些数据表明，流体剪切应力可调节内皮细胞中HCR的活性和表达，并通过涉及NO、AMPK、FoxO1a和p21Ras的机制决定对缓激肽等刺激的反应性。
