Interleukin-6 attenuates insulin-mediated increases in endothelial cell signaling but augments skeletal muscle insulin action via differential effects on tumor necrosis factor-alpha expression.
OBJECTIVE
The cytokine interleukin-6 (IL-6) stimulates AMP-activated protein kinase (AMPK) and insulin signaling in skeletal muscle, both of which result in the activation of endothelial nitric oxide synthase (eNOS). We hypothesized that IL-6 promotes endothelial cell signaling and capillary recruitment in vivo, contributing to increased glucose uptake.


METHODS
The effect of IL-6 with and without insulin on AMPK, insulin, and eNOS signaling in and nitric oxide (NO) release from human aortic endothelial cells (HAECs) was examined. The physiological significance of these in vitro signaling events was assessed by measuring capillary recruitment in rats during control and euglycemic-hyperinsulinemic clamps with or without IL-6 infusion.


RESULTS
IL-6 blunted increases in insulin signaling, eNOS phosphorylation (Ser1177), and NO production and reduced phosphorylation of AMPK in HAEC in vitro and capillary recruitment in vivo. In contrast, IL-6 increased Akt phosphorylation (Ser473) in hindlimb skeletal muscle and enhanced whole-body glucose disappearance and glucose uptake during the clamp. The differences in endothelial cell and skeletal muscle signaling were mediated by the cell-specific, additive effects of IL-6 and insulin because this treatment markedly increased tumor necrosis factor (TNF)-alpha protein expression in HAECs without any effect on TNF-alpha in skeletal muscle. When HAECs were incubated with a TNF-alpha-neutralizing antibody, the negative effects of IL-6 on eNOS signaling were abolished.


CONCLUSIONS
In the presence of insulin, IL-6 contributes to aberrant endothelial cell signaling because of increased TNF-alpha expression.
Yuen
Derek Y C
DY
Cellular and Molecular Metabolism Laboratory, Baker IDI Heart and Diabetes Institute, Melbourne, Victoria, Australia.
Dwyer
Renee M
RM
Matthews
Vance B
VB
Zhang
Lei
L
Drew
Brian G
BG
Neill
Bronwyn
B
Kingwell
Bronwyn A
BA
Clark
Michael G
MG
Rattigan
Stephen
S
Febbraio
Mark A
MA
D000263:Adenylate Kinase / Q000187:drug effects / Q000378:metabolism; D000818:Animals; D001011:Aorta / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D004730:Endothelium, Vascular / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D006801:Humans; D007328:Insulin / Q000494:pharmacology / Q000502:physiology*; D015850:Interleukin-6 / Q000494:pharmacology*; D023421:Models, Animal; D018482:Muscle, Skeletal / Q000187:drug effects / Q000502:physiology*; D009569:Nitric Oxide / Q000378:metabolism; D010766:Phosphorylation; D051381:Rats; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D014409:Tumor Necrosis Factor-alpha / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism
D007328:Insulin; D015850:Interleukin-6; D014409:Tumor Necrosis Factor-alpha; D009569:Nitric Oxide; D000263:Adenylate Kinase