Molecular mechanisms of ghrelin-mediated endothelial nitric oxide synthase activation.
Metabolic syndrome accelerates the atherosclerotic process, and the earliest event of which is endothelial dysfunction. Ghrelin, a newly discovered gastric peptide, improves endothelial function and inhibits proatherogenic changes. In particular, low ghrelin concentration has been associated with several features of metabolic syndrome, including obesity, insulin resistance, and high blood pressure. However, the molecular mechanisms underlying ghrelin vascular actions remain largely unclear. Here, we showed that ghrelin activated endothelial nitric oxide (NO) synthase (eNOS) in cultured endothelial cells (ECs) and in intact vessels. Specifically, ghrelin rapidly induced phosphorylation of eNOS on an activation site and production of NO in human umbilical vein ECs and bovine aortic ECs. The eNOS phosphorylation was also observed in mouse aortas ex vivo perfused with ghrelin and in aortic tissues isolated from mice injected with ghrelin. Mechanistically, ghrelin stimulated AMP-activated protein kinase (AMPK) and Akt activation in cultured ECs and intact vessels. Inhibiting AMPK and Akt with their pharmacological inhibitors, small interference RNA and adenoviruses carried dominant-negative mutants, markedly attenuated ghrelin-induced eNOS activation, and NO production. Furthermore, ghrelin receptor/Gq protein/calcium-dependent pathway mediates activation of AMPK, Akt, and eNOS, and calmodulin-dependent kinase kinase is a potential convergent point to regulate Akt and AMPK activation in ghrelin signaling. Importantly, eNOS activation is critical for ghrelin inhibition of vascular inflammation. Together, both in vitro and in vivo data demonstrate a new role of ghrelin signaling for eNOS activation, and highlight the therapeutic potential for ghrelin to correct endothelial dysfunction associated with atherosclerotic vascular diseases and metabolic syndrome.
Xu
Xiangbin
X
Aab Cardiovascular Research Institute and Department of Medicine, University of Rochester Medical Center, 601 Elmwood Avenue, Box 679, Rochester, New York 14642, USA.
Jhun
Bong Sook
BS
Ha
Chang Hoon
CH
Jin
Zheng-Gen
ZG
D055372:AMP-Activated Protein Kinases; D000818:Animals; D002417:Cattle; D002448:Cell Adhesion / Q000187:drug effects; D002478:Cells, Cultured; D042783:Endothelial Cells / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D004789:Enzyme Activation / Q000187:drug effects; D054439:Ghrelin / Q000494:pharmacology*; D006801:Humans; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009097:Multienzyme Complexes / Q000378:metabolism / Q000502:physiology; D009569:Nitric Oxide / Q000378:metabolism; D052250:Nitric Oxide Synthase Type III / Q000378:metabolism*; D051058:Oncogene Protein v-akt / Q000378:metabolism / Q000502:physiology; D010766:Phosphorylation / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism / Q000502:physiology; D054440:Receptors, Ghrelin / Q000502:physiology; D020298:U937 Cells
D054439:Ghrelin; D009097:Multienzyme Complexes; D054440:Receptors, Ghrelin; D009569:Nitric Oxide; D052250:Nitric Oxide Synthase Type III; D051058:Oncogene Protein v-akt; D017346:Protein Serine-Threonine Kinases; D055372:AMP-Activated Protein Kinases