Metabolic Benefits of Methionine Restriction in Adult Mice Do Not Require Functional Methionine Sulfoxide Reductase a (MsrA)

Methionine restriction (MR) extends lifespan and improves several markers of health in rodents. However, the proximate mechanisms of MR on these physiological benefits have not been fully elucidated. The essential amino acid methionine plays numerous biological roles and limiting its availability in the diet directly modulates methionine metabolism. There is growing evidence that redox regulation of methionine has regulatory control on some aspects of cellular function but interactions with MR remain largely unexplored. We tested the functional role of the ubiquitously expressed methionine repair enzyme methionine sulfoxide reductase A (MsrA) on the metabolic benefits of MR in mice. MsrA catalytically reduces both free and protein-bound oxidized methionine, thus playing a key role in its redox state. We tested the extent to which MsrA is required for metabolic effects of MR in adult mice using mice lacking MsrA. As expected, MR in control mice reduced body weight, altered body composition, and improved glucose metabolism. Interestingly, lack of MsrA did not impair the metabolic effects of MR on these outcomes. Moreover, females had blunted MR responses regardless of MsrA status compared to males. Overall, our data suggests that MsrA is not required for the metabolic benefits of MR in adult mice.

Inhibition of HDACs (Histone Deacetylases) Ameliorates High-Fat Diet–Induced Hypertension Through Restoration of the MsrA (Methionine Sulfoxide Reductase A)/Hydrogen Sulfide Axis

Hydrogen sulfide (H 2 S) is an endogenous gaseous antioxidant and antihypertensive molecule produced during the homocysteine metabolism. MsrA (methionine sulfoxide reductase A) enables the metabolism of homocysteine by reducing methionine sulfoxide to methionine. Although HDAC (histone deacetylase) inhibition has been reported to show blood pressure lowering effects, their effects on endogenous H 2 S production are largely unknown. Here, we assessed the relevance of MsrA in high-fat diet (HFD)-induced hypertension and the effect of HDAC inhibition on MsrA expression, H 2 S production, and hypertension. Male C57BL/6 mice were fed a normal diet or HFD. HFD increased blood pressure and activities of HDAC3 and 6 but downregulated MsrA in the mesenteric arteries and the serum H 2 S level. HFD upregulated 4 hydroxynonenal, TNF (tumor necrosis factor)-α, and IL (interleukin)-6, and vasocontractile proteins. The histone H3 acetylation of the MsrA promoter was decreased by HFD. In hypertensive HFD-fed mice, administration of the HDAC inhibitor CG200745 lowered blood pressure and increased serum H 2 S level. CG200745 increased acetylation of histone H3 and MsrA levels in the mesenteric arteries while downregulating oxidative stress, inflammation, and vasocontractile proteins. Silencing of MsrA in the vascular smooth muscle cells recapitulated HFD-induced in vivo hypertensive effects. CG200745 increased the histone H3 acetylation of the MsrA promoter, MsrA expression, and H 2 S production in vascular smooth muscle cells, supporting the in vivo results. Collectively, HFD-induced downregulation of MsrA plays a pivotal role in HFD-induced hypertension by reducing H 2 S levels. MsrA expression is epigenetically regulated by HDAC inhibitors, providing HDAC inhibitors as a therapeutic option and MsrA and H 2 S as novel therapeutic targets.

An unusual thioredoxin system in the facultative parasite Acanthamoeba castellanii

The free-living amoeba Acanthamoeba castellanii occurs worldwide in soil and water and feeds on bacteria and other microorganisms. It is, however, also a facultative parasite and can cause serious infections in humans. The annotated genome of A. castellanii (strain Neff) suggests the presence of two different thioredoxin reductases (TrxR), of which one is of the small bacterial type and the other of the large vertebrate type. This combination is highly unusual. Similar to vertebrate TrxRases, the gene coding for the large TrxR in A. castellanii contains a UGA stop codon at the C-terminal active site, suggesting the presence of selenocysteine. We characterized the thioredoxin system in A. castellanii in conjunction with glutathione reductase (GR), to obtain a more complete understanding of the redox system in A. castellanii and the roles of its components in the response to oxidative stress. Both TrxRases localize to the cytoplasm, whereas GR localizes to the cytoplasm and the large organelle fraction. We could only identify one thioredoxin (Trx-1) to be indeed reduced by one of the TrxRases, i.e., by the small TrxR. This thioredoxin, in turn, could reduce one of the two peroxiredoxins tested and also methionine sulfoxide reductase A (MsrA). Upon exposure to hydrogen peroxide and diamide, only the small TrxR was upregulated in expression at the mRNA and protein levels, but not the large TrxR. Our results show that the small TrxR is involved in the A. castellanii’s response to oxidative stress. The role of the large TrxR, however, remains elusive.

Molecular Expression of Bioactive Recombinant Methionine Sulfoxide Reductase A (MsrA)

Background: The increase in reactive oxygen species (ROS) production during cryopreservation of semen, leads to oxidation of biomolecules affecting the functionality of spermatozoa. Methionine residues in proteins are highly prone to oxidation and get converted into methionine sulfoxide (MetO). Methionine sulfoxide reductase A (MsrA) can improve the functionality of spermatozoa by reducing the MetO to methionine restoring the lost functionality of the affected proteins. Objective: The expression of catalytically active recombinant MsrA (rMsrA). Methods: The msrA gene was PCR amplified, cloned and sequenced. Further, the recombinant clone was used for protein expression and purification. The protein was getting precipitated during dialysis in Tris-buffer. Hence, the purified rMsrA was dialyzed at 4°C against the Tris-buffer pH 7.5 containing MgCl2, KCl, NaCl, urea and triton X-100. During dialysis, changes of buffer were done at every 12 h interval with stepwise reduction in the concentrations of NaCl, urea and triton X100. The final dialysis was done with buffer containing 10 mM MgCl2, 30 mM KCl, and 150 mM NaCl, 25 mM Tris–HCl pH 7.5. The activity of the rMsrA was checked spectrophotometrically. Results: The protein BLAST of buffalo MsrA with bovine sequence showed 14 amino acid mismatches. The rMsrA has been purified under denaturing conditions as it was forming inclusion bodies consistently during protein expression. After renaturation, the purified 33 kDa rMsrA was catalytically active by biochemical assay. Conclusion: The rMsrA expressed in prokaryotic system is catalytically active and can be used for supplementation to semen extender to repair the oxidatively damaged seminal plasma proteins that occur during cryopreservation.

The Antioxidant Enzyme Methionine Sulfoxide Reductase A (MsrA) Interacts with Jab1/CSN5 and Regulates Its Function

Methionine sulfoxide (MetO) is an oxidative posttranslational modification that primarily occurs under oxidative stress conditions, leading to alteration of protein structure and function. This modification is regulated by MetO reduction through the evolutionarily conserved methionine sulfoxide reductase (Msr) system. The Msr type A enzyme (MsrA) plays an important role as a cellular antioxidant and promotes cell survival. The ubiquitin- (Ub) like neddylation pathway, which is controlled by the c-Jun activation domain-binding protein-1 (Jab1), also affects cell survival. Jab1 negatively regulates expression of the cell cycle inhibitor cyclin-dependent kinase inhibitor 1B (P27) through binding and targeting P27 for ubiquitination and degradation. Here we report the finding that MsrA interacts with Jab1 and enhances Jab1′s deneddylase activity (removal of Nedd8). In turn, an increase is observed in the level of deneddylated Cullin-1 (Cul-1, a component of E3 Ub ligase complexes). Furthermore, the action of MsrA increases the binding affinity of Jab1 to P27, while MsrA ablation causes a dramatic increase in P27 expression. Thus, an interaction between MsrA and Jab1 is proposed to have a positive effect on the function of Jab1 and to serve as a means to regulate cellular resistance to oxidative stress and to enhance cell survival.