MAB5310 Sigma-AldrichAnti-Glutathione Antibody, clone D8

Potassium and sodium displacements across the skeletal muscle membrane during exercise may cause fatigue and are in part controlled by the Na,K-ATPase. Regulation of the Na,K-ATPase is therefore important for muscle functioning. We investigated the effect of oxidative stress (glutathionylation) on Na,K-ATPase activity. Ten male subjects performed three bouts of 4-min submaximal exercise followed by intense exercise to exhaustion with and without beta2-adrenergic stimulation with terbutaline. Muscle biopsies were obtained from m. vastus lateralis at rest (Control samples) and at exhaustion. In vitro glutathionylation reduced (P less than  0.05) maximal Na,K-ATPase activity in a dose-dependent manner. Na,K-ATPase α subunits, purified by immunoprecipitation and tested by glutathione (GSH) antibodies, had a basal glutathionylation in Control samples and no further glutathionylation with exercise and beta2-adrenergic stimulation. Immunoprecipitation with an anti-GSH antibody and subsequent immunodetection with β1 antibodies showed approximately 20% glutathionylation in Control samples and further glutathionylation after exercise (to 32%) and beta2-adrenergic stimulation (to 38%, P less than  0.05). Combining exercise and beta2-adrenergic stimulation raised the β1 glutathionylation to 45% (P less than  0.05). In conclusion, both α and β1 subunits of the Na,K-ATPase were glutathionylated in Control samples, which indicates that the maximal Na,K-ATPase activity is overestimated if based on protein density only. β1 subunits are further glutathionylated by exercise and beta2-adrenergic stimulation. Our data suggest that glutathionylation contributes to the complex regulation of Na,K-ATPase function in human skeletal muscle. Glutathionylation of the Na,K-ATPase may explain reductions in maximal Na,K-ATPase activity after exercise, which may be involved in muscle fatigue.

Dietary supplementation with ursolic acid (UA) prevents monocyte dysfunction in diabetic mice and protects mice against atherosclerosis and loss of renal function. The goal of this study was to determine the molecular mechanism by which UA prevents monocyte dysfunction induced by metabolic stress.Metabolic stress sensitizes or "primes" human THP-1 monocytes and murine peritoneal macrophages to the chemoattractant MCP-1, converting these cells into a hyper-chemotactic phenotype. UA protected THP-1 monocytes and peritoneal macrophages against metabolic priming and prevented their hyper-reactivity to MCP-1. UA blocked the metabolic stress-induced increase in global protein-S-glutathionylation, a measure of cellular thiol oxidative stress, and normalized actin-S-glutathionylation. UA also restored MAPK phosphatase-1 (MKP1) protein expression and phosphatase activity, decreased by metabolic priming, and normalized p38 MAPK activation. Neither metabolic stress nor UA supplementation altered mRNA or protein levels of glutaredoxin-1, the principal enzyme responsible for the reduction of mixed disulfides between glutathione and protein thiols in these cells. However, the induction of Nox4 by metabolic stress, required for metabolic priming, was inhibited by UA in both THP-1 monocytes and peritoneal macrophages.UA protects THP-1 monocytes against dysfunction by suppressing metabolic stress-induced Nox4 expression, thereby preventing the Nox4-dependent dysregulation of redox-sensitive processes, including actin turnover and MAPK-signaling, two key processes that control monocyte migration and adhesion. This study provides a novel mechanism for the anti-inflammatory and athero- and renoprotective properties of UA and suggests that dysfunctional blood monocytes may be primary targets of UA and related compounds.

AMP-activated protein kinase (AMPK) is a cellular and whole body energy sensor with manifold functions in regulating energy homeostasis, cell morphology and proliferation in health and disease. Here we apply multiple, complementary in vitro and in vivo interaction assays to identify several isoforms of glutathione S-transferase (GST) as direct AMPK binding partners: Pi-family member rat GSTP1 and Mu-family members rat GSTM1, as well as Schistosoma japonicum GST. GST/AMPK interaction is direct and involves the N-terminal domain of the AMPK β-subunit. Complex formation of the mammalian GSTP1 and -M1 with AMPK leads to their enzymatic activation and in turn facilitates glutathionylation and activation of AMPK in vitro. GST-facilitated S-glutathionylation of AMPK may be involved in rapid, full activation of the kinase under mildly oxidative physiological conditions.

Na,K-ATPase is highly sensitive to changes in the redox state, and yet the mechanisms of its redox sensitivity remain unclear. We have explored the possible involvement of S-glutathionylation of the catalytic α subunit in redox-induced responses. For the first time, the presence of S-glutathionylated cysteine residues was shown in the α subunit in duck salt glands, rabbit kidneys, and rat myocardium. Exposure of the Na,K-ATPase to oxidized glutathione (GSSG) resulted in an increase in the number of S-glutathionylated cysteine residues. Increase in S-glutathionylation was associated with dose- and time-dependent suppression of the enzyme function up to its complete inhibition. The enzyme inhibition concurred with S-glutathionylation of the Cys-454, -458, -459, and -244. Upon binding of glutathione to these cysteines, the enzyme was unable to interact with adenine nucleotides. Inhibition of the Na,K-ATPase by GSSG did not occur in the presence of ATP at concentrations above 0.5 mm. Deglutathionylation of the α subunit catalyzed by glutaredoxin or dithiothreitol resulted in restoration of the Na,K-ATPase activity. Oxidation of regulatory cysteines made them inaccessible for glutathionylation but had no profound effect on the enzyme activity. Regulatory S-glutathionylation of the α subunit was induced in rat myocardium in response to hypoxia and was associated with oxidative stress and ATP depletion. S-Glutathionylation was followed by suppression of the Na,K-ATPase activity. The rat α2 isoform was more sensitive to GSSG than the α1 isoform. Our findings imply that regulatory S-glutathionylation of the catalytic subunit plays a key role in the redox-induced regulation of Na,K-ATPase activity.

The 20 S proteasome complexes are major contributors to the intracellular protein degradation machinery in mammalian cells. Systematic administration of proteasome inhibitors to combat disease (e.g. cancer) has resulted in positive outcomes as well as adversary effects. The latter was attributed to, at least in part, a lack of understanding in the organ-specific responses to inhibitors and the potential diversity of proteomes of these complexes in different tissues. Accordingly, we conducted a proteomic study to characterize the 20 S proteasome complexes and their postulated organ-specific responses in the heart and liver. The cardiac and hepatic 20 S proteasomes were isolated from the same mouse strain with identical genetic background. We examined the molecular composition, complex assembly, post-translational modifications and associating partners of these proteasome complexes. Our results revealed an organ-specific molecular organization of the 20 S proteasomes with distinguished patterns of post-translational modifications as well as unique complex assembly characteristics. Furthermore, the proteome diversities are concomitant with a functional heterogeneity of the proteolytic patterns exhibited by these two organs. In particular, the heart and liver displayed distinct activity profiles to two proteasome inhibitors, epoxomicin and Z-Pro-Nle-Asp-H. Finally, the heart and liver demonstrated contrasting regulatory mechanisms from the associating partners of these proteasomes. The functional heterogeneity of the mammalian 20 S proteasome complexes underscores the concept of divergent proteomes among organs in the context of an identical genome.