Effect of endothelium-specific insulin resistance on endothelial function in vivo.
OBJECTIVE
Insulin resistance is an independent risk factor for the development of cardiovascular atherosclerosis. A key step in the development of atherosclerosis is endothelial dysfunction, manifest by a reduction in bioactivity of nitric oxide (NO). Insulin resistance is associated with endothelial dysfunction; however, the mechanistic relationship between these abnormalities and the role of impaired endothelial insulin signaling versus global insulin resistance remains unclear.


METHODS
To examine the effects of insulin resistance specific to the endothelium, we generated a transgenic mouse with endothelium-targeted overexpression of a dominant-negative mutant human insulin receptor (ESMIRO). This receptor has a mutation (Ala-Thr(1134)) in its tyrosine kinase domain that disrupts insulin signaling. Humans with the Thr(1134) mutation are insulin resistant. We performed metabolic and vascular characterization of this model.


RESULTS
ESMIRO mice had preserved glucose homeostasis and were normotensive. They had significant endothelial dysfunction as evidenced by blunted aortic vasorelaxant responses to acetylcholine (ACh) and calcium ionophore. Furthermore, the vascular action of insulin was lost in ESMIRO mice, and insulin-induced endothelial NO synthase (eNOS) phosphorylation was blunted. Despite this phenotype, ESMIRO mice demonstrate similar levels of eNOS mRNA and protein expression to wild type. ACh-induced relaxation was normalized by the superoxide dismutase mimetic, Mn(III)tetrakis(1-methyl-4-pyridyl) porphyrin pentachloride. Endothelial cells of ESMIRO mice showed increased superoxide generation and increased mRNA expression of the NADPH oxidase isoforms Nox2 and Nox4.


CONCLUSIONS
Selective endothelial insulin resistance is sufficient to induce a reduction in NO bioavailability and endothelial dysfunction that is secondary to increased generation of reactive oxygen species. This arises independent of a significant metabolic phenotype.
Cardiovascular Division, Department of Cardiology, King's College, London, UK.
Edward R
ER
Duncan
Paul A
PA
Crossey
Simon
S
Walker
Narayana
N
Anilkumar
Lucilla
L
Poston
Gillian
G
Douglas
Vivienne A
VA
Ezzat
Stephen B
SB
Wheatcroft
Ajay M
AM
Shah
Mark T
MT
Kearney
Mark I
MI
Kearney
D000409:Alanine; D019943:Amino Acid Substitution; D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D003001:Cloning, Molecular; D004730:Endothelium, Vascular / Q000502:physiology*; D005951:Glucose Tolerance Test; D006706:Homeostasis; D006801:Humans; D007333:Insulin Resistance / Q000502:physiology*; D051379:Mice; D008822:Mice, Transgenic; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D019001:Nitric Oxide Synthase / Q000235:genetics; D052250:Nitric Oxide Synthase Type III / Q000235:genetics; D010957:Plasmids; D016133:Polymerase Chain Reaction; D011972:Receptor, Insulin / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013912:Threonine; D001616:beta-Galactosidase / Q000172:deficiency / Q000235:genetics
D001786:Blood Glucose; D013912:Threonine; D019001:Nitric Oxide Synthase; D052250:Nitric Oxide Synthase Type III; D011972:Receptor, Insulin; D001616:beta-Galactosidase; D000409:Alanine