Angiotensin II causes endothelial dysfunction via the GRK2/Akt/eNOS pathway in aortas from a murine type 2 diabetic model

Pharmacol Res. 2011 Nov;64(5):535-46. doi: 10.1016/j.phrs.2011.05.001. Epub 2011 May 6.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Angiotensin II / blood
  • Angiotensin II / metabolism*
  • Animals
  • Aorta / metabolism
  • Aorta / physiopathology*
  • Diabetes Mellitus, Type 2 / blood
  • Diabetes Mellitus, Type 2 / metabolism
  • Diabetes Mellitus, Type 2 / physiopathology*
  • Endothelium, Vascular / metabolism
  • Endothelium, Vascular / physiopathology*
  • G-Protein-Coupled Receptor Kinase 2 / blood
  • G-Protein-Coupled Receptor Kinase 2 / metabolism*
  • Male
  • Mice
  • Nitric Oxide / metabolism
  • Nitric Oxide Synthase Type III / metabolism*
  • Proto-Oncogene Proteins c-akt / metabolism*

Substances

  • Angiotensin II
  • Nitric Oxide
  • Nitric Oxide Synthase Type III
  • Proto-Oncogene Proteins c-akt
  • GRK2 protein, mouse
  • G-Protein-Coupled Receptor Kinase 2