The anorexigenic and catabolic effects of Angiotensin II during muscle wasting are redox dependent
Description
Previous experiments have shown that Angiotensin II (Ang II) infusion in mice causes marked skeletal muscle wasting via a reduction in appetite and a catabolic effect. In the cardiovascular system, several Ang II effects are mediated by increased generation of reactive oxygen species (ROS) via NADPH oxidase activation. However, the roles of oxidative stress and of NADPH Oxidase in the skeletal muscle wasting effects of Ang II are unknown. To address this issue, in vivo experiments were conducted in which mice were infused with Ang II (1500 ng/k/min) or vehicle via subcutaneously implanted minipumps for 1 week. Body weight and food intake were assessed daily. After 7 days, mice were sacrificed to record skeletal muscle weights and to collect tissues for further analysis. Pair-feeding groups were added to obtain insights into the role of oxidative stress in the anorexigenic and catabolic components of Ang II induced wasting. In the first series of experiments, p47 phox null mice were used to demonstrate that the absence of a functional NADPH oxidase attenuated the loss of body weight and skeletal muscle weight and completely blunted the loss of appetite during Ang II infusions. In the second group of experiments an oral antioxidant (N-acetylcysteine) prevented body weight and muscle weight reductions as well as anorexia, when administered concomitantly with Ang II to wild type mice. In vitro analysis of ROS production in the skeletal muscle indicated increased superoxide formation and increased oxidized to reduced glutathione ratios (GSSG/GSH) in response to Ang II. Both of these increases were prevented by the absence of a functional NADPH oxidase or by antioxidant treatment. In addition, our data demonstrated that Ang II increased both mitochondrial and NADPH oxidase derived ROS production. Finally, to demonstrate that the observed effects were not dependant on genetic background, experiments were conducted in a different mouse strain (FVB). Results of these experiments confirmed the link between Ang II induced ROS production and skeletal muscle wasting. In conclusion, our experiments used a genetic loss-of-function mutation and pharmacological inhibitors to demonstrate that both components of Ang II induced muscle wasting in vivo are critically dependent on increased oxidative stress that likely results from cross-talk between the membrane-bound NADPH oxidase and mitochondria