Aging-dependent changes in rat heart mitochondrial glutaredoxins—Implications for redox regulation

Abstract

Clinical and animal studies have documented that hearts of the elderly are more susceptible to ischemia/reperfusion damage compared to young adults. Recently we found that aging-dependent increase in susceptibility of cardiomyocytes to apoptosis was attributable to decrease in cytosolic glutaredoxin 1 (Grx1) and concomitant decrease in NF-κB-mediated expression of anti-apoptotic proteins. Besides primary localization in the cytosol, Grx1 also exists in the mitochondrial intermembrane space (IMS). In contrast, Grx2 is confined to the mitochondrial matrix. Here we report that Grx1 is decreased by 50–60% in the IMS, but Grx2 is increased by 1.4–2.6 fold in the matrix of heart mitochondria from elderly rats. Determination of in situ activities of the Grx isozymes from both subsarcolemmal (SSM) and interfibrillar (IFM) mitochondria revealed that Grx1 was fully active in the IMS. However, Grx2 was mostly in an inactive form in the matrix, consistent with reversible sequestration of the active-site cysteines of two Grx2 molecules in complex with an iron–sulfur cluster. Our quantitative evaluations of the active/inactive ratio for Grx2 suggest that levels of dimeric Grx2 complex with iron–sulfur clusters are increased in SSM and IFM in the hearts of elderly rats. We found that the inactive Grx2 can be fully reactivated by sodium dithionite or exogenous superoxide production mediated by xanthine oxidase. However, treatment with rotenone, which generates intramitochondrial superoxide through inhibition of mitochondrial respiratory chain Complex I, did not lead to Grx2 activation. These findings suggest that insufficient ROS accumulates in the vicinity of dimeric Grx2 to activate it in situ.

AP39, a mitochondria-targeting hydrogen sulfide (H2S) donor, protects against myocardial reperfusion injury independently of salvage kinase signalling

“…Although this result is comparable with our previously data (Boengler et al . ), others have reported higher RCR ratios (Chen et al ., ; Asemu et al ., ; Gao et al ., ). This could be due to either measuring oxygen consumption at 30°C instead of 25°C, using trypsin instead of nargase to release the IFM or stimulating the mitochondria with higher concentration of ADP than what was used in this study.…”

Glutaredoxin-1 Deficiency Causes Fatty Liver and Dyslipidemia by Inhibiting Sirtuin-1

“…However, gene expression of the thioredoxin system was unaltered in Glrx -/-mice. Furthermore, the mitochondrial isoform glutaredoxin-2, which is exclusively mitochondrial matrix localized (54) and controls ironsulfur clusters (24) as well as mitochondrial protein GSH adducts (19), showed no changes in gene expression.…”

The Important Functions of GSH-Dependent Enzyme Glutaredoxin 2 (Grx2)

“…However, most of the Grx2 is prominently in the inactive dimer formation. Only by exogenous superoxide production by xanthine oxidase was the dimer able to cleave to monomeric form [43]. H 2 O 2 had no effect on Grx2 activation.…”

“…Usually, with aging, there is a decline in antioxidant expression and activity. Interestingly, Gao et al first suggested that Grx2 is found to be increased nearly twofold in the mitochondrial matrix of cardiac muscle cells [43]. However, most of the Grx2 is prominently in the inactive dimer formation.…”