Molecular Mechanisms of Ghrelin-Mediated Endothelial Nitric Oxide Synthase Activation

• Published in: Endocrinology (Philadelphia) Vol. 149; no. 8; pp. 4183 - 4192
• Main Authors: Xu, Xiangbin, Sook Jhun, Bong, Hoon Ha, Chang, Jin, Zheng-Gen
• Format: Journal Article
• Language: English
• Published: Bethesda, MD Endocrine Society 01.08.2008; The Endocrine Society
• Subjects: AMP-Activated Protein Kinases; Animals; Biological and medical sciences; Cattle; Cell Adhesion - drug effects; Cells, Cultured; Endothelial Cells - drug effects; Endothelial Cells - metabolism; Endothelial Cells - physiology; Enzyme Activation - drug effects; Fundamental and applied biological sciences. Psychology; Ghrelin - pharmacology; Humans; Male; Mice; Mice, Inbred C57BL; Multienzyme Complexes - metabolism; Multienzyme Complexes - physiology; Nitric Oxide - metabolism; Nitric Oxide Synthase Type III - metabolism; Oncogene Protein v-akt - metabolism; Oncogene Protein v-akt - physiology; Phosphorylation - drug effects; Protein-Serine-Threonine Kinases - metabolism; Protein-Serine-Threonine Kinases - physiology; Receptors, Ghrelin - physiology; U937 Cells; Vertebrates: endocrinology; Enzyme; Ghrelin; Blood vessel; Activation; Circulatory system; Oxidoreductases; Nitric-oxide synthase; Endothelium
• ISSN: 0013-7227; 1945-7170
• DOI: 10.1210/en.2008-0255

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.