Deletion of the Glutaredoxin-2 Gene Protects Mice from Diet-Induced Weight Gain, Which Correlates with Increased Mitochondrial Respiration and Proton Leaks in Skeletal Muscle

Abstract

Aims: The aim of this study was to determine whether deleting the gene encoding glutaredoxin-2 (GRX2) could protect mice from diet-induced weight gain. Results: Subjecting wild-type littermates to a high fat diet (HFD) induced a significant increase in overall body mass, white adipose tissue hypertrophy, lipid droplet accumulation in hepatocytes, and higher circulating insulin and triglyceride levels. In contrast, GRX2 heterozygotes (GRX2 +/-) fed an HFD had a body mass, white adipose tissue weight, and hepatic and circulating lipid and insulin levels similar to littermates fed a control diet. Examination of the bioenergetics of muscle mitochondria revealed that this protective effect was associated with an increase in respiration and proton leaks. Muscle mitochondria from GRX2 +/mice had a *2to 3-fold increase in state 3 (phosphorylating) respiration when pyruvate/malate or succinate served as substrates and a *4-fold increase when palmitoyl-carnitine was being oxidized. Proton leaks were *2to 3-fold higher in GRX2 +/muscle mitochondria. Treatment of mitochondria with either guanosine diphosphate, genipin, or octanoyl-carnitine revealed that the higher rate of O 2 consumption under state 4 conditions was associated with increased leaks through uncoupling protein-3 and adenine nucleotide translocase. GRX2 +/mitochondria also had better protection from oxidative distress. Innovation: For the first time, we demonstrate that deleting the Grx2 gene can protect from diet-induced weight gain and the development of obesity-related disorders. Conclusions: Deleting the Grx2 gene protects mice from diet-induced weight gain. This effect was related to an increase in muscle fuel combustion, mitochondrial respiration, proton leaks, and reactive oxygen species handling.

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

“…Mitochondria harbor a number of glutathionylation targets including Krebs cycle enzymes, respiratory complexes, solute anion carriers, antioxidant defense proteins, and factors involved in the induction of apoptosis and fission/fusion [ 4 ]. Reversible protein S-glutathionylation has also been recently identified as a negative feedback regulator for ROS production by pyruvate dehydrogenase (PDH), α-ketoglutarate dehydrogenase (KGDH), and complex I and indirectly prevents H 2 O 2 genesis through the induction of leaks by the uncoupling proteins (UCP) (reviewed in [ 4 , 5 ]). Furthermore, the reversible modification of proteins by glutathionylation was recently proposed to serve as a global cellular mechanism for the inhibition of ROS production, thereby serving as a keystone in desensitizing H 2 O 2 signals [ 6 ].…”

“…This was associated with a decrease in gonadal fat pad mass, augmented whole body energy expenditure, and increased respiration due to deglutathionylation and activation of proton leaks throughUCP3 in muscles [ 11 ]. Our group recently followed up on these seminal findings and revealed that male mice heterozygous for the Grx2 gene ( Grx2+/− ) are completely resistant to the development of DIO following exposure to a HFD for seven weeks [ 5 ]. This was associated with protection from abdominal fat pad accretion, intrahepatic lipid accumulation and glycogen granule depletion, and maintenance of circulating triglyceride and insulin levels that were comparable to littermates fed a control-matched diet [ 5 ].…”

“…Our group recently followed up on these seminal findings and revealed that male mice heterozygous for the Grx2 gene ( Grx2+/− ) are completely resistant to the development of DIO following exposure to a HFD for seven weeks [ 5 ]. This was associated with protection from abdominal fat pad accretion, intrahepatic lipid accumulation and glycogen granule depletion, and maintenance of circulating triglyceride and insulin levels that were comparable to littermates fed a control-matched diet [ 5 ]. These effects correlated strongly with a ∼50% decrease in the overall S-glutathionylation of skeletal muscle mitochondrial proteins, which included UCP3 and adenine nucleotide translocase (ANT) [ 5 ].…”

“…This was associated with protection from abdominal fat pad accretion, intrahepatic lipid accumulation and glycogen granule depletion, and maintenance of circulating triglyceride and insulin levels that were comparable to littermates fed a control-matched diet [ 5 ]. These effects correlated strongly with a ∼50% decrease in the overall S-glutathionylation of skeletal muscle mitochondrial proteins, which included UCP3 and adenine nucleotide translocase (ANT) [ 5 ]. This resulted in the activation of proton leaks through both proteins and an increase in mitochondrial fuel combustion by ∼four-fold [ 5 ].…”

“…These effects correlated strongly with a ∼50% decrease in the overall S-glutathionylation of skeletal muscle mitochondrial proteins, which included UCP3 and adenine nucleotide translocase (ANT) [ 5 ]. This resulted in the activation of proton leaks through both proteins and an increase in mitochondrial fuel combustion by ∼four-fold [ 5 ].…”