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Articles by B Viollet
Total Records ( 2 ) for B Viollet
  S Wang , M Zhang , B Liang , J Xu , Z Xie , C Liu , B Viollet , D Yan and M. H. Zou

Rational: AMP-activated protein kinase (AMPK) is an energy sensor and ubiquitously expressed in vascular cells. Recent studies suggest that AMPK activation improves endothelial function by counteracting oxidative stress in endothelial cells. How AMPK suppresses oxidative stress remains to be established.

Objective: The aim of this study is to examine the effects of AMPK in regulating NAD(P)H oxidase, oxidative stress, and endothelial function.

Methods and Results: The markers of oxidative stress, NAD(P)H oxidase subunit expression (gp91phox, p47phox, p67phox, NOX1 to -4), NAD(P)H oxidase–mediated superoxide production, 26S proteasome activity, IB degradation, and nuclear translocation of nuclear factor (NF)-B (p50 and p65) were examined in cultured human umbilical vein endothelial cells and mouse aortas isolated from AMPK2 deficient mice. Compared to the wild type, acetylcholine-induced endothelium-dependent relaxation was significantly impaired in parallel with increased production of oxidants in AMPK2–/– mice. Further, pretreatment of aorta with either superoxide dismutase (SOD) or tempol or apocynin significantly improved acetylcholine-induced endothelium-dependent relaxation in AMPK2–/– mice. Analysis of aortic endothelial cells from AMPK2–/– mice and human umbilical vein endothelial cells expressing dominant negative AMPK or AMPK2-specific siRNA revealed that loss of AMPK activity increased NAD(P)H oxidase subunit expression (gp91phox, p47phox, p67phox, NOX1 and -4), NAD(P)H oxidase–mediated superoxide production, 26S proteasome activity, IB degradation, and nuclear translocation of NF-B (p50 and p65), whereas AMPK activation by AICAR or overexpression of constitutively active AMPK had the opposite effect. Consistently, we found that genetic deletion of AMPK2 in low-density lipoprotein receptor knockout (LDLr–/–) strain markedly increased 26S proteasome activity, IB degradation, NF-B transactivation, NAD(P)H oxidase subunit overexpression, oxidative stress, and endothelial dysfunction, all of which were largely suppressed by chronic administration of MG132, a potent cell permeable proteasome inhibitor.

Conclusions: We conclude that AMPK2 functions as a physiological suppressor of NAD(P)H oxidase and ROS production in endothelial cells. In this way, AMPK maintains the nonatherogenic and noninflammatory phenotype of endothelial cells.

  B Benziane , M Bjornholm , L Lantier , B Viollet , J. R Zierath and A. V. Chibalin

Muscle contraction and metabolic stress are potent activators of AMP-activated protein kinase (AMPK). AMPK restores energy balance by activating processes that produce energy while inhibiting those that consume energy. The role of AMPK in the regulation of active ion transport is unclear. Our aim was to determine the effect of the AMPK activator A-769662 on Na+-K+-ATPase function in skeletal muscle cells. Short-term incubation of differentiated rat L6 myotubes with 100 µM A-769662 increased AMPK and acetyl-CoA carboxylase (ACC) phosphorylation in parallel with decreased Na+-K+-ATPase 1-subunit abundance at the plasma membrane and ouabain-sensitive 86Rb+ uptake. Notably, the effect of A-769662 on Na+-K+-ATPase was similar in muscle cells that do not express AMPK 1- and 2-catalytic subunits. A-769662 directly inhibits the 1-isoform of the Na+-K+-ATPase, purified from rat and human kidney cells in vitro with IC50 57 µM and 220 µM, respectively. Inhibition of the Na+-K+-ATPase by 100 µM ouabain decreases sodium pump activity and cell surface abundance, similar to the effect of A-769662, without affecting AMPK and ACC phosphorylation. In conclusion, the AMPK activator A-769662 inhibits Na+-K+-ATPase activity and decreases the sodium pump cell surface abundance in L6 skeletal muscle cells. The effect of A-769662 on sodium pump is due to direct inhibition of the Na+-K+-ATPase activity, rather than AMPK activation. This AMPK-independent effect on Na+-K+-ATPase calls into question the use of A-769662 as a specific AMPK activator for metabolic studies.

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