An investigation into the impact of deleting one copy of the glutaredoxin-2 gene on diet-induced weight gain and the bioenergetics of muscle mitochondria in female mice fed a high fat diet.

Our group recently documented that male mice containing a deletion for one copy of the glutaredoxin-2 (Grx2) gene were completely protected from developing diet-induced obesity (DIO). Objectives: Here, we conducted a similar investigation but with female littermates. Results: In comparison to our recent publication using male mice, exposure of WT and GRX2+/- female mice to a HFD from 3-to-10 weeks of age did not induce any changes in body mass, circulating blood glucose, food intake, hepatic glycogen levels, or abdominal fat pad mass. Examination of the bioenergetics of muscle mitochondria revealed no changes in the rate of superoxide ( O 2 ∙ - )/hydrogen peroxide (H2O2) or O2 consumption under different states of respiration or alterations in lipid peroxidation adduct levels regardless of mouse strain or diet. Additionally, we measured the bioenergetics of mitochondria isolated from liver tissue and found that partial loss of GRX2 augmented respiration but did not alter ROS production. Discussion: Overall, our findings demonstrate there are sex differences in the protection of female GRX2+/- mice from DIO, fat accretion, intrahepatic lipid accumulation, and the bioenergetics of mitochondria from muscle and liver tissue.

C57BL/6J mice upregulate catalase to maintain the hydrogen peroxide buffering capacity of liver mitochondria.

Here, we demonstrate that the upregulation of catalase is required to compensate for the loss of nicotinamide nucleotide transhydrogenase (NNT) to maintain hydrogen peroxide (H2O2) steady-state levels in C57BL/6J liver mitochondria. Our investigations using the closely related mouse strains C57BL/6NJ (6NJ; +NNT) and C57BL/6J (6J; -NNT) revealed that NNT is required for the provision of NADPH and that the upregulation of isocitrate dehydrogenase-2 (IDH2) activity is not enough to compensate for the absence of NNT, which is consistent with previous observations. Intriguingly, despite the absence of NNT, 6J mitochondria had rates of H2O2 production (58.56 ±â€¯3.79 pmol mg-1 min-1) that were similar to samples collected from 6NJ mice (72.75 ±â€¯14.26 pmol mg-1 min-1) when pyruvate served as the substrate. However, 6NJ mitochondria energized with succinate produced significantly less H2O2 (59.95 ±â€¯2.13 pmol mg-1 min-1) when compared to samples from 6J mice (116.39 ±â€¯20.74 pmol mg-1 min-1), an effect that was attributed to the presence of NNT. Further investigations into the H2O2 eliminating capacities of these mitochondria led to the novel observation that 6J mitochondria compensate for the loss of NNT by upregulating catalase. Indeed, 6NJ and 6J mitochondria energized with pyruvate or succinate displayed similar rates for H2O2 elimination, quenching ~84% and ~86% of the H2O2, respectively, in the surrounding medium within 30 s. However, inclusion of palmitoyl-CoA, an NNT inhibitor, significantly limited H2O2 degradation by 6NJ mitochondria only (~55% of H2O2 eliminated in 30 s). Liver mitochondria from 6J mice treated with palmitoyl-CoA still cleared ~80% of the H2O2 from the surrounding environment. Inhibition of catalase with triazole compromised the capacity of 6J mitochondria to maintain H2O2 steady-state levels. By contrast, disabling NADPH-dependent antioxidant systems had a limited effect on the H2O2 clearing capacity of 6J mitochondria. Liver mitochondria collected from 6NJ mice, on the other hand, were more reliant on the GSH and TRX systems to clear exogenously added H2O2. However, catalase still played an integral in eliminating H2O2 in 6NJ liver mitochondria. Immunoblot analyses demonstrated that catalase protein levels were ~7.7-fold higher in 6J mitochondria. Collectively, our findings demonstrate for the first time that 6J liver mitochondria compensate for the loss of NNT by increasing catalase levels for the maintenance of H2O2 steady-state levels. In general, our observations reveal that catalase is an integral arm of the antioxidant response in liver mitochondria.

Sex-dependent Differences in the Bioenergetics of Liver and Muscle Mitochondria from Mice Containing a Deletion for glutaredoxin-2.

Our group recently published a study demonstrating that deleting the gene encoding the matrix thiol oxidoreductase, glutaredoxin-2 (GRX2), alters the bioenergetics of mitochondria isolated from male C57BL/6N mice. Here, we conducted a similar study, examining H2O2 production and respiration in mitochondria isolated from female mice heterozygous (GRX2+/-) or homozygous (GRX2-/-) for glutaredoxin-2. First, we observed that deleting the Grx2 gene does not alter the rate of H2O2 production in liver and muscle mitochondria oxidizing pyruvate, α-ketoglutarate, or succinate. Examination of the rates of H2O2 release from liver mitochondria isolated from male and female mice revealed that (1) sex has an impact on the rate of ROS production by liver and muscle mitochondria and (2) loss of GRX2 only altered ROS release in mitochondria collected from male mice. Assessment of the bioenergetics of these mitochondria revealed that loss of GRX2 increased proton leak-dependent and phosphorylating respiration in liver mitochondria isolated from female mice but did not alter rates of respiration in liver mitochondria from male mice. Furthermore, we found that deleting the Grx2 gene did not alter rates of respiration in muscle mitochondria collected from female mice. This contrasts with male mice where loss of GRX2 substantially augmented proton leaks and ADP-stimulated respiration. Our findings indicate that some fundamental sexual dimorphisms exist between GRX2-deficient male and female rodents.