Enhanced mitochondrial superoxide scavenging does not Improve muscle insulin action in the high fat-fed mouse

Improving mitochondrial oxidant scavenging may be a viable strategy for the treatment of insulin resistance and diabetes. Mice overexpressing the mitochondrial matrix isoform of superoxide dismutase (sod2(tg) mice) and/or transgenically expressing catalase within the mitochondrial matrix (mcat(tg) mice) have increased scavenging of O2(˙-) and H2O2, respectively. Furthermore, muscle insulin action is partially preserved in high fat (HF)-fed mcat(tg) mice. The goal of the current study was to test the hypothesis that increased O2(˙-) scavenging alone or in combination with increased H2O2 scavenging (mtAO mice) enhances in vivo muscle insulin action in the HF-fed mouse. Insulin action was examined in conscious, unrestrained and unstressed wild type (WT), sod2(tg), mcat(tg) and mtAO mice using hyperinsulinemic-euglycemic clamps (insulin clamps) combined with radioactive glucose tracers following sixteen weeks of normal chow or HF (60% calories from fat) feeding. Glucose infusion rates, whole body glucose disappearance, and muscle glucose uptake during the insulin clamp were similar in chow- and HF-fed WT and sod2(tg) mice. Consistent with our previous work, HF-fed mcat(tg) mice had improved muscle insulin action, however, an additive effect was not seen in mtAO mice. Insulin-stimulated Akt phosphorylation in muscle from clamped mice was consistent with glucose flux measurements. These results demonstrate that increased O2(˙-) scavenging does not improve muscle insulin action in the HF-fed mouse alone or when coupled to increased H2O2 scavenging

Enhanced Mitochondrial Superoxide Scavenging Does Not Improve Muscle Insulin Action in the High Fat-Fed Mouse

Improving mitochondrial oxidant scavenging may be a viable strategy for the treatment of insulin resistance and diabetes. Mice overexpressing the mitochondrial matrix isoform of superoxide dismutase (sod2tg mice) and/or transgenically expressing catalase within the mitochondrial matrix (mcattg mice) have increased scavenging of O2˙ˉ and H2O2, respectively. Furthermore, muscle insulin action is partially preserved in high fat (HF)-fed mcattg mice. The goal of the current study was to test the hypothesis that increased O2˙ˉ scavenging alone or in combination with increased H2O2 scavenging (mtAO mice) enhances in vivo muscle insulin action in the HF-fed mouse. Insulin action was examined in conscious, unrestrained and unstressed wild type (WT), sod2tg, mcattg and mtAO mice using hyperinsulinemic-euglycemic clamps (insulin clamps) combined with radioactive glucose tracers following sixteen weeks of normal chow or HF (60% calories from fat) feeding. Glucose infusion rates, whole body glucose disappearance, and muscle glucose uptake during the insulin clamp were similar in chow- and HF-fed WT and sod2tg mice. Consistent with our previous work, HF-fed mcattg mice had improved muscle insulin action, however, an additive effect was not seen in mtAO mice. Insulin-stimulated Akt phosphorylation in muscle from clamped mice was consistent with glucose flux measurements. These results demonstrate that increased O2˙ˉ scavenging does not improve muscle insulin action in the HF-fed mouse alone or when coupled to increased H2O2 scavenging

Summary of effects of diet and transgenic expression of SOD2 and/or catalase on oxidant production and cellular redox state.

<p>* Data adapted from Kang et al. 2012 [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0126732#pone.0126732.ref004" target="_blank">4</a>].</p

Divergent effects of SOD2 overexpression on muscle glucose uptake (Rg) and insulin signaling in HF-fed WT and <i>mcat</i>^<i>tg</i> mice.

<p>Non-metabolizable glucose analog [¹⁴C]2-deoxyglucose was administered as an intravenous bolus to determine muscle glucose uptake (Rg) using liquid scintillation counting in SOD2 overexpressing WT (<b>A</b>) and <i>mcat</i>^<i>tg</i> (<b>B</b>) mice. Insulin signaling was measured in tissue homogenates extracted from gastrocnemius, applied to 4–12% SDS-PAGE gel and Western blotted with anti-phospho-Akt (Ser⁴⁷³) or anti-total Akt antibodies. Values are expressed as mean ± SEM of integrated intensity and representative bands are presented (<b>C</b>). Ratio of phosphorylated-Akt to total Akt was calculated in SOD2 overexpressing WT (<b>D</b>) and mcat^tg (<b>E</b>) mice. n = 4–6. *<i>p</i><0.05 compared with <i>sod2</i>^<i>tg</i> or WT within a diet; ^#<i>p</i><0.05 compared with chow within a genotype. SVL, superficial vastus lateralis.</p

The relationship between glutathione redox state and muscle glucose uptake in chow and HF-fed mice.

<p>Rg determined by 2[¹⁴C]deoxyglucose during the insulin clamp plotted as a function of glutathione redox state (GSH/GSSG) in gastrocnemius of chow- (<b>A</b>) and HF-fed (<b>B</b>) mice. GSH/GSSG values were adapted from Kang et al. [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0126732#pone.0126732.ref004" target="_blank">4</a>].</p