title: Angiotensin II causes endothelial dysfunction via the GRK2/Akt/eNOS pathway in aortas from a murine type 2 diabetic model.
abstract: Nitric oxide (NO) production and endothelial function are mediated via the Akt/eNOS pathway. We investigated the reductions of these mechanism(s) in type 2 diabetes. Diabetic model (nicotinamide+streptozotocin-induced) mice were fed for 4 weeks on a normal diet either containing or not containing losartan, an AT₁ R antagonist. Relaxations and NO productions were measured in isolated aortas. G-protein coupled receptor kinase 2 (GRK2) protein levels and activities in the Akt/eNOS signaling-pathway were mainly assayed by Western blotting. Clonidine- and insulin-induced relaxations and NO productions, all of which were significantly decreased in aortas isolated from the diabetics, were normalized by 4 weeks' losartan administration. Plasma angiotensin II (Ang II) and GRK2 protein levels were increased in diabetes, and each was normalized by 4 week's losartan administration. Additionally, there was a direct correlation between the plasma Ang II and aortic GRK2 protein levels. In the diabetics, the clonidine-induced responses (but not the insulin-induced ones) were enhanced by GRK2-inhibitor. Akt phosphorylation was markedly below control in the clonidine-stimulated diabetes. The phosphorylation of Akt at Thr³⁰⁸ was significantly normalized and the phosphorylation of eNOS at Ser¹¹⁷⁷ tended to be increased by GRK2-inhibitor in the clonidine-stimulated diabetics. Our data suggest that (a) the Akt/eNOS pathway is downstream of GRK2, and that GRK2 inhibits Akt/eNOS activities, and (b) this pathway underlies the impaired NO production seen in type 2 diabetes, in which there are defective phosphorylations of Akt and eNOS that may be caused by an upregulation of GRK2 secondary to a high plasma Ang II level. Inhibitors of GRK2 warrant further investigation as potential new therapeutic agents in diabetes.
authors.affiliation: Department of Physiology and Morphology, Institute of Medicinal Chemistry, Hoshi University, Shinagawa-ku, Tokyo 142-8501, Japan.
authors.forename: Kumiko
authors.initials: K
authors.lastname: Taguchi
authors.forename: Tsuneo
authors.initials: T
authors.lastname: Kobayashi
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Takenouchi
authors.forename: Takayuki
authors.initials: T
authors.lastname: Matsumoto
authors.forename: Katsuo
authors.initials: K
authors.lastname: Kamata
mesh_terms: D000804:Angiotensin II / Q000097:blood / Q000378:metabolism*; D000818:Animals; D001011:Aorta / Q000378:metabolism / Q000503:physiopathology*; D003924:Diabetes Mellitus, Type 2 / Q000097:blood / Q000378:metabolism / Q000503:physiopathology*; D004730:Endothelium, Vascular / Q000378:metabolism / Q000503:physiopathology*; D054769:G-Protein-Coupled Receptor Kinase 2 / Q000097:blood / Q000378:metabolism*; D008297:Male; D051379:Mice; D009569:Nitric Oxide / Q000378:metabolism; D052250:Nitric Oxide Synthase Type III / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*
chemical_list: D000804:Angiotensin II; D009569:Nitric Oxide; D052250:Nitric Oxide Synthase Type III; D051057:Proto-Oncogene Proteins c-akt; C496568:GRK2 protein, mouse; D054769:G-Protein-Coupled Receptor Kinase 2