Liu Songling, Premont Richard T, Kontos Christopher D, Zhu Shoukang, Rockey Don C
Department of Cell Biology, Duke University Medical Center, Durham, North Carolina 27710, USA.
Nat Med. 2005 Sep;11(9):952-8. doi: 10.1038/nm1289. Epub 2005 Sep 4.
Nitric oxide (NO) production by endothelial cell nitric oxide synthase (eNOS) in sinusoidal endothelial cells is reduced in the injured liver and leads to intrahepatic portal hypertension. We sought to understand the mechanism underlying defective eNOS function. Phosphorylation of the serine-threonine kinase Akt, which activates eNOS, was substantially reduced in sinusoidal endothelial cells from injured livers. Overexpression of Akt in vivo restored phosphorylation of Akt and production of NO and reduced portal pressure in portal hypertensive rats. We found that Akt physically interacts with G-protein-coupled receptor kinase-2 (GRK2), and that this interaction inhibits Akt activity. Furthermore, GRK2 expression increased in sinusoidal endothelial cells from portal hypertensive rats and knockdown of GRK2 restored Akt phosphorylation and NO production, and normalized portal pressure. Finally, after liver injury, GRK2-deficient mice developed less severe portal hypertension than control mice. Thus, an important mechanism underlying impaired activity of eNOS in injured sinusoidal endothelial cells is defective phosphorylation of Akt caused by overexpression of GRK2 after injury.
在受损肝脏中，肝血窦内皮细胞中的内皮型一氧化氮合酶（eNOS）产生的一氧化氮（NO）减少，进而导致肝内门静脉高压。我们试图了解eNOS功能缺陷背后的机制。激活eNOS的丝氨酸 - 苏氨酸激酶Akt的磷酸化在受损肝脏的肝血窦内皮细胞中显著降低。在体内过表达Akt可恢复Akt的磷酸化和NO的产生，并降低门静脉高压大鼠的门静脉压力。我们发现Akt与G蛋白偶联受体激酶2（GRK2）存在物理相互作用，且这种相互作用会抑制Akt活性。此外，门静脉高压大鼠肝血窦内皮细胞中GRK2表达增加，敲低GRK2可恢复Akt磷酸化和NO产生，并使门静脉压力恢复正常。最后，肝损伤后，GRK2缺陷小鼠的门静脉高压程度比对照小鼠轻。因此，受损肝血窦内皮细胞中eNOS活性受损的一个重要机制是损伤后GRK2过表达导致Akt磷酸化缺陷。
