Enzyme Methionine Sulfoxide Reductase Research Articles

About the many faces of autism spectrum disorder: from psychoanalysis to biological markers. Could the methionine sulfoxide reductase enzymes play a role?

Autism spectrum disorder is a dramatic condition for the affected children, their families and the entire society. Genetic and environmental factors are involved in its pathogenesis and oxidative stress appears to be the main trigger. Methionine sulfoxide reductase enzymes are physiologically involved in the contrast to oxidative stress and disorders in their expression/activity could result in several diseases. In the fight against autism spectrum disorder, this neglected biochemical feature should be taken into account.

Methionine sulfoxide reductase B5 plays a key role in preserving seed vigor and longevity in rice (Oryza sativa).

Oxidation of methionine leads to the formation of methionine S-sulfoxide and methionine R-sulfoxide, which can be reverted by two types of methionine sulfoxide reductase (MSR): MSRA and MSRB. Though the role of MSR enzymes has been elucidated in various physiological processes, the regulation and role of MSR in seeds remains poorly understood. In this study, through molecular, biochemical, and genetic studies using seed-specific overexpression and RNAi lines of OsMSRB5 in Oryza sativa, we demonstrate the role of OsMSRB5 in maintaining seed vigor and longevity. We show that an age-induced reduction in the vigor and viability of seeds is correlated with reduced MSR activity and increased methionine sulfoxide (MetSO) formation. OsMSRB5 expression increases during seed maturation and is predominantly localized to the embryo. Further analyses on transgenic lines reveal the role of OsMSRB5 in modulating reactive oxygen species (ROS) homeostasis to preserve seed vigor and longevity. We show that ascorbate peroxidase and PROTEIN l-ISOASPARTYL METHYLTRANSFERASE undergo MetSO modification in seeds that affects their functional competence. OsMSRB5 physically interacts with these proteins and reverts this modification to facilitate their functions and preserve seed vigor and longevity. Our results thus illustrate the role of OsMSRB5 in preserving seed vigor and longevity by modulating ROS homeostasis in seeds.

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.

Lack of the antioxidant enzyme methionine sulfoxide reductase A in mice impairs RPE phagocytosis and causes photoreceptor cone dysfunction

Methionine sulfoxide reductase A (MsrA) is a widely expressed antioxidant enzyme that counteracts oxidative protein damage and contributes to protein regulation by reversing oxidation of protein methionine residues. In retinal pigment epithelial (RPE) cells in culture, MsrA overexpression increases phagocytic capacity by supporting mitochondrial ATP production. Here, we show elevated retinal protein carbonylation indicative of oxidation, decreased RPE mitochondrial membrane potential, and attenuated RPE phagocytosis in msra−/− mice. Moreover, electroretinogram recordings reveal decreased light responses specifically of cone photoreceptors despite normal expression and localization of cone opsins. Impairment in msra−/− cone-driven responses is similar from 6 weeks to 13 months of age. These functional changes match dramatic decreases in lectin-labeled cone sheaths and reduction in cone arrestin in msra−/− mice. Strikingly, cone defects in light response and in lectin-labeled cone sheath are completely prevented by dark rearing. Together, our data show that msra−/− mice provide a novel small animal model of preventable cone-specific photoreceptor dysfunction that may have future utility in analysis of cone dystrophy disease mechanisms and testing therapeutic approaches aiming to alleviate cone defects.

Fecal Microbiota Transplantation Is a Promising Method to Restore Gut Microbiota Dysbiosis and Relieve Neurological Deficits after Traumatic Brain Injury.

Background Traumatic brain injury (TBI) can induce persistent fluctuation in the gut microbiota makeup and abundance. The present study is aimed at determining whether fecal microbiota transplantation (FMT) can rescue microbiota changes and ameliorate neurological deficits after TBI in rats. Methods A controlled cortical impact (CCI) model was used to simulate TBI in male Sprague-Dawley rats, and FMT was performed for 7 consecutive days. 16S ribosomal RNA (rRNA) sequencing of fecal samples was performed to analyze the effects of FMT on gut microbiota. Modified neurological severity score and Morris water maze were used to evaluate neurobehavioral functions. Metabolomics was used to screen differential metabolites from the rat serum and ipsilateral brains. The oxidative stress indices were measured in the brain. Results TBI induced significance changes in the gut microbiome, including the alpha- and beta-bacterial diversity, as well as the microbiome composition at 8 days after TBI. On the other hand, FMT could rescue these changes and relieve neurological deficits after TBI. Metabolomics results showed that the level of trimethylamine (TMA) in feces and the level of trimethylamine N-oxide (TMAO) in the ipsilateral brain and serum was increased after TBI, while FMT decreased TMA levels in the feces, and TMAO levels in the ipsilateral brain and serum. Antioxidant enzyme methionine sulfoxide reductase A (MsrA) in the ipsilateral hippocampus was decreased after TBI but increased after FMT. In addition, FMT elevated SOD and CAT activities and GSH/GSSG ratio and diminished ROS, GSSG, and MDA levels in the ipsilateral hippocampus after TBI. Conclusions FMT can restore gut microbiota dysbiosis and relieve neurological deficits possibly through the TMA-TMAO-MsrA signaling pathway after TBI.

Redox-mediated regulation of an evolutionarily conserved cross-β structure formed by the TDP43 low complexity domain

A methionine-rich low complexity (LC) domain is found within a C-terminal region of the TDP43 RNA-binding protein. Self-association of this domain leads to the formation of labile cross-β polymers and liquid-like droplets. Treatment with H2O2 caused phenomena of methionine oxidation and droplet melting that were reversed upon exposure of the oxidized protein to methionine sulfoxide reductase enzymes. Morphological features of the cross-β polymers were revealed by H2O2-mediated footprinting. Equivalent TDP43 LC domain footprints were observed in polymerized hydrogels, liquid-like droplets, and living cells. The ability of H2O2 to impede cross-β polymerization was abrogated by the prominent M337V amyotrophic lateral sclerosis-causing mutation. These observations may offer insight into the biological role of TDP43 in facilitating synapse-localized translation as well as aberrant aggregation of the protein in neurodegenerative diseases.

An NMR-Based Biosensor to Measure Stereospecific Methionine Sulfoxide Reductase Activities in Vitro and in Vivo*.

Oxidation of protein methionines to methionine-sulfoxides (MetOx) is associated with several age-related diseases. In healthy cells, MetOx is reduced to methionine by two families of conserved methionine sulfoxide reductase enzymes, MSRA and MSRB that specifically target the S- or R-diastereoisomers of methionine-sulfoxides, respectively. To directly interrogate MSRA and MSRB functions in cellular settings, we developed an NMR-based biosensor that we call CarMetOx to simultaneously measure both enzyme activities in single reaction setups. We demonstrate the suitability of our strategy to delineate MSR functions in complex biological environments, including cell lysates and live zebrafish embryos. Thereby, we establish differences in substrate specificities between prokaryotic and eukaryotic MSRs and introduce CarMetOx as a highly sensitive tool for studying therapeutic targets of oxidative stress-related human diseases and redox regulated signaling pathways.

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.

Higher Circulating Trimethylamine N-oxide Sensitizes Sevoflurane-Induced Cognitive Dysfunction in Aged Rats Probably by Downregulating Hippocampal Methionine Sulfoxide Reductase A.

Gut microbiota-derived metabolite trimethylamine N-oxide (TMAO) has recently been shown to promote oxidative stress and inflammation in the peripheral tissues, contributing to the pathogenesis of many diseases. Here we examined whether pre-existing higher circulating TMAO would influence cognitive function in aged rats after anesthetic sevoflurane exposure. Aged rats received vehicle or TMAO treatment for 3weeks. After 2weeks of treatment, these animals were exposed to either control or 2.6% sevoflurane for 4h. Oneweek after exposure, freezing as measured by fear conditioning test, microglia activity, proinflammatory cytokine expression and NADPH oxidase-dependent reactive oxygen species (ROS) production in the hippocampus (a key brain structure involved in learning and memory) were comparable between vehicle-treated rats exposed to control and vehicle-treated rats exposed to sevoflurane. TMAO treatment, which increased plasma TMAO before and 1week after control or sevoflurane exposure, significantly reduced freezing to contextual fear conditioning, which was associated with increases in microglia activity, proinflammatory cytokine expression and NADPH oxidase-dependent ROS production in the hippocampus in rats exposed to sevoflurane but not in rats exposed to control. Moreover, hippocampal expression of antioxidant enzyme methionine sulfoxide reductase A (MsrA) was reduced by TMAO treatment in both groups, and TMAO-induced reduction in MsrA expression was negatively correlated with increased proinflammatory cytokine expression in rats exposed to SEV. These findings suggest that pre-existing higher circulating TMAO downregulates antioxidant enzyme MsrA in the hippocampus, which may sensitize the hippocampus to oxidative stress, resulting in microglia-mediated neuroinflammation and cognitive impairment in aged rats after sevoflurane exposure.

Methionine Sulfoxide Reductase Enzymes: A Possible Virulence Factor for the Management of Antibiotic Resistance Crisis in the Climate Change Era

The problem of antibiotic resistance develops when bacteria are able to grow in the presence of conventional antimicrobial drugs and today represents a serious public health issue. The environmental effects of global warming, by unknown genomic mechanisms of adaption, could dramatically increase this phenomenon and support a more rapid progression to “post-antibiotic era”, in which common infections will be untreatable. Alternative approaches toward drug-resistant bacterial infections need to be explored to ensure effective therapies. Bacterial pathogens produce virulence factors that allow them to invade and to damage host cells. Methionine sulfoxide reductase (Msr) enzymes (MsrAs and MsrBs) are important, but poor studied, virulence factors for many bacterial strains. A deeper insight into their mechanism of action and regulation could help in developing novel therapeutic strategies toward drug-resistant bacteria, in order to overcome the antibiotic resistance crisis.

The presence of elevated circulating trimethylamine N-oxide exaggerates postoperative cognitive dysfunction in aged rats

Surgical trauma can cause brain oxidative stress and neuroinflammation, leading to postoperative cognitive dysfunction (POCD), especially in the elderly. Additionally, the pre-existing risk factors may enhance POCD. Gut microbiota-derived metabolite trimethylamine N-oxide (TMAO) has recently been shown to contribute to the pathogenesis of many diseases by increasing oxidative stress and inflammation in the peripheral tissues. Here we examined whether the presence of elevated circulating TMAO would influence surgery-induced cognitive decline. Aged rats were treated with vehicle or TMAO for 3 weeks. After two weeks of treatment, these rats underwent sham-operation or laparotomy. One week after surgery, rats underwent laparotomy exhibited hippocampal-dependent cognitive dysfunction as evidenced by reduced contextual freezing time, which was associated with elevated plasma proinflammatory cytokine levels, increased microglia-mediated neuroinflammation and reactive oxygen species (ROS) production in the hippocampus. Treatment with TMAO, which elevated plasma TMAO before and 1 week after surgery, further increased microglia-mediated neuroinflammation and ROS production in the hippocampus, resulting in exaggerated cognitive dysfunction in laparotomy group but not in sham-operation group. Moreover, TMAO treatment decreased expression of antioxidant enzyme methionine sulfoxide reductase (Msr) A in both groups. The results suggest that the presence of elevated circulating TMAO downregulates antioxidant enzyme MsrA in the hippocampus, which may increase the susceptibility to surgery-induced oxidative stress, contributing to exaggerations of neuroinflammation and cognitive decline in aged rats following surgery. Interventions to reduce circulating TMAO in the perioperative period may be a novel strategy to prevent the exaggeration of cognitive decline in elderly patients with high circulating TMAO.

Characterization of Protein‐Ligand Interactions in MsrA from E. coli

The amino acid methionine is highly susceptible to oxidation via reactive oxygen species, resulting in loss of function in proteins containing oxidized methionines. This loss of protein function has been implicated in numerous neurodegenerative and age‐related diseases such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis (Lou Gehrig's Disease), emphysema, and arthritis. The enzyme methionine sulfoxide reductase (MsrA) catalyzes the stereospecific reduction of oxidized methionine in free amino acids, peptides, and proteins, restoring function in the latter. The catalytic mechanism of MsrA has been studied extensively, but less is known about how MsrA is able to recognize its large variety of substrates, from single amino acids or small molecules to oxidized methionines in the context of a protein. Earlier work from our lab using intrinsic and extrinsic fluorescence spectroscopy suggests that the presence of sulfoxide group on a methionine in a target protein enhances existing weak hydrophobic interactions with MsrA. The current study builds on these findings using fluorescence spectroscopy to characterize how MsrA of E. coli recognizes its substrates and repairs specific oxidized methionine residues in an intrinsically‐disordered form of staphylococcal nuclease and a nonapeptide derived from it.Support or Funding InformationThis work was supported by a Research Corporation award (grant number CC5482) to VFS. The Office of Naval Research supported Trident Scholar research by JS. MJW was supported by a Garrigues Program scholarship award.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Redox State Controls Phase Separation of the Yeast Ataxin-2 Protein via Reversible Oxidation of Its Methionine-Rich Low-Complexity Domain

Yeast ataxin-2, also known as Pbp1, senses the activity state of mitochondria in order to regulate TORC1. A domain of Pbp1 required to adapt cells to mitochondrial activity is of low sequence complexity. The low-complexity (LC) domain of Pbp1 forms labile, cross-β polymers that facilitate phase transition ofthe protein into liquid-like or gel-like states. Phasetransition for other LC domains is reliant upon widely distributed aromatic amino acids. In place of tyrosine or phenylalanine residues prototypically used for phase separation, Pbp1 contains 24 similarly disposed methionine residues. Here, we show that the Pbp1 methionine residues are sensitive to hydrogen peroxide (H2O2)-mediated oxidation invitro and in living cells. Methionine oxidation melts Pbp1 liquid-like droplets in a manner reversed by methionine sulfoxide reductase enzymes. These observations explain how reversible formation of labile polymers by the Pbp1 LC domain enables the protein to function as a sensor of cellular redox state.

Chemoenzymatic Deracemization of Chiral Sulfoxides.

The highly enantioselective enzyme methionine sulfoxide reductase A was combined with an oxaziridine-type oxidant in a biphasic setup for the deracemization of chiral sulfoxides. Remarkably, high ee values were observed with a wide range of substrates, thus providing a practical route for the synthesis of enantiomerically pure sulfoxides.

Chemoenzymatic Deracemization of Chiral Sulfoxides

AbstractThe highly enantioselective enzyme methionine sulfoxide reductase A was combined with an oxaziridine‐type oxidant in a biphasic setup for the deracemization of chiral sulfoxides. Remarkably, high ee values were observed with a wide range of substrates, thus providing a practical route for the synthesis of enantiomerically pure sulfoxides.

Methionine sulfoxide reductase B3 requires resolving cysteine residues for full activity and can act as a stereospecific methionine oxidase.

The oxidation of methionine residues in proteins occurs during oxidative stress and can lead to an alteration in protein function. The enzyme methionine sulfoxide reductase (Msr) reverses this modification. Here, we characterise the mammalian enzyme Msr B3. There are two splice variants of this enzyme that differ only in their N-terminal signal sequence, which directs the protein to either the endoplasmic reticulum (ER) or mitochondria. We demonstrate here that the enzyme can complement a bacterial strain, which is dependent on methionine sulfoxide reduction for growth, that the purified recombinant protein is enzymatically active showing stereospecificity towards R-methionine sulfoxide, and identify the active site and two resolving cysteine residues. The enzyme is efficiently recycled by thioredoxin only in the presence of both resolving cysteine residues. These results show that for this isoform of Msrs, the reduction cycle most likely proceeds through a three-step process. This involves an initial sulfenylation of the active site thiol followed by the formation of an intrachain disulfide with a resolving thiol group and completed by the reduction of this disulfide by a thioredoxin-like protein to regenerate the active site thiol. Interestingly, the enzyme can also act as an oxidase catalysing the stereospecific formation of R-methionine sulfoxide. This result has important implications for the role of this enzyme in the reversible modification of ER and mitochondrial proteins.

Development of a Ratiometric Fluorescent Probe with Two ­Reactive Sulfoxides for Monitoring the Activity of Methionine Sulfoxide Reductase A

Biological oxidation of methionine side chains in proteins is a process that affects the functions of many proteins. One of the key regulators of this signaling is the enzyme methionine sulfoxide reductase A (MsrA). MsrA is implicated in a number of diseases, but detailed understanding of its function is hindered by the lack of tools for monitoring the enzyme’s activity. We have designed and synthesized a probe named (S,S)-Sulfox-2 that is based on a BODIPY fluorophore and is equipped with two chiral sulfoxide units of defined stereochemistry. (S,S)-Sulfox-2 is shown to be highly responsive to MsrA and allows tracing of the MsrA activity by a significant change in the fluorescence profile.

Kinetic resolution of phenyl methyl sulfoxides by mammalian methionine sulfoxide reductase A

Chiral sulfoxides are widely used in organic synthesis as chiral auxiliaries. There are numerous strategies for the preparation of enantiomerically pure sulfoxides, based either on the enantioselective oxidation of sulphides or the enantiospecific reduction of sulfoxides. For both cases, bioconversion techniques have been developed and proposed for large-scale synthesis. Methionine sulfoxide reductase enzymes (MsrA and MsrB) catalyse the stereoselective conversion of methionine sulfoxide to methionine. MsrA can also catalyse the reduction of other exogenous sulfoxides, including p-tolyl methyl sulfoxide. However, the stereoselectivity towards this type of substrate is not yet well characterized. The activity and enantioselectivity of MsrA toward several aryl methyl sulfoxides is presented in this paper.

Inhibition of sympathetic activity by rilmenidine reverses angiotensin II-induced hypertension, blood pressure variability and cardiac remodeling

S SELECTED FOR PRESENTATION 14.4 Inhibition of sympathetic activity by rilmenidine reverses angiotensin II-induced hypertension, blood pressure variability and cardiac remodeling R. Sabharwal, R.N. El Accaoui, R.M. Weiss, M.K. Davis, F.M. Abboud, M.W. Chapleau Department of Internal Medicine, University of Iowa Veterans Affairs Medical Center, USA The relative contribution of increased sympathetic activity to angiotensin II (Ang II)-induced hypertension and end-organ damage is controversial. To determine the importance of the sympathetic nervous system, we examined whether sustained inhibition of sympathetic activity induced by intracerebroventricular infusion of rilmenidine (RIL) attenuates Ang II-induced hypertension, blood pressure variability and left ventricular (LV) remodeling. Blood pressure (BP) and heart rate (HR) were measured by telemetry in C57BL/6 mice (n= 7) and mice deficient in the antioxidant enzyme methionine sulfoxide reductase A (MsrA) (n= 8), before and during four weeks of Ang II infusion (1000 ng/kg/min, SC). LV end-diastolic volume (EDV), ejection fraction and mass were measured by echocardiography. Subgroups of mice were administered RIL (2.5 mg/kg/day, ICV, n = 4) over the last 2 weeks of Ang II infusion. Ang II infusion increased mean BP, BP variability, cardiac and vasomotor sympathetic tone, and LVEDV/mass ratio; and decreased cardiac vagal tone and spontaneous baroreflex sensitivity (sequence technique) (P b 0.05). All measures of dysfunction were exacerbated in MsrA−/− mice. As expected, RIL decreased sympathetic tone in all mice. Remarkably, RIL completely reversed Ang II-induced hypertension, BP variability, autonomic dysregulation, and LV remodeling in C57BL/6 andMsrA−/− mice (P b 0.05). RIL also increased (normalized) LV ejection fraction and locomotor activity in Ang II-infused MsrA−/− mice (P b 0.05). We conclude that Ang II-induced hypertension, BP variability and LV remodeling are critically dependent on increased sympathetic activity. The results strongly support therapeutic targeting of the brain to inhibit sympathetic activity in hypertension. (HL14388, VA). doi:10.1016/j.autneu.2015.07.320 14.5 Brain and renal alterations following denervation of ischemic kidney in renovascular hypertension E.E. Nishi, C.T. Bergamaschi, G.N. Gomes, J.C. Perry, G.S. Lincevicius, R.R. Campos Physiology Dpt., Universidade Federal de Sao Paulo, Brazil Psychobiology Dpt., Universidade Federal de Sao Paulo, Brazil Our aim was to investigate whether renal nerves play a role in the renal injury process and modulation of AngII receptors expression in the central nuclei and kidneys in renovascular hypertension. Denervation of clipped kidney (RD: visible bundles were dissected + 10% phenol) was performed in Wistar male rats (n = 5/group) 4–5 weeks after clip implantation (gap width: 0.2 mm). Ten days after RD, blood pressure (BP) was significantly reduced in the 2 K-1C rats. AT1R and AT2R upregulation within the rostral ventrolateral medulla (RVLM) and paraventricular nucleus of the hypothalamus (PVN) in the 2 K-1C group was normalized after RD. No change in the expression of either AngII receptor was found within the nucleus of the tractus solitarius (NTS). Following RD, there was no change in plasma renin activity in control and 2 K-1C rats. In order to distinguish the effects of RD from the reduction in BP, 2 K-1C rats were treated orally with hydralazine (25 mg/kg/day for seven consecutive days). Hydralazine significantly reduced BP and AT1R within the PVN in the 2 K-1C rats, but there were no changes in AT1R or AT2R within the RVLM and NTS. Following RD, renal injury was attenuated in both ischemic and contralateral kidneys of hypertensive rats, although hydralazine decreased injury only in the contralateral kidney. These results demonstrate that the renal nerves may modulate AngII receptors within the RVLM and renal injury in the ischemic kidney independent of BP and plasma renin activity in the 2 K-1C model of arterial hypertension. Supported by FAPESP and CNPq. doi:10.1016/j.autneu.2015.07.321 Symposium 15: Sleep and autonomic nervous system: At the crossroad between health and disease 15.1 Cardiovascular alterations induced by acute paradoxical sleep deprivation in rats

MsrA Overexpression Targeted to the Mitochondria, but Not Cytosol, Preserves Insulin Sensitivity in Diet-Induced Obese Mice.

There is growing evidence that oxidative stress plays an integral role in the processes by which obesity causes type 2 diabetes. We previously identified that mice lacking the protein oxidation repair enzyme methionine sulfoxide reductase A (MsrA) are particularly prone to obesity-induced insulin resistance suggesting an unrecognized role for this protein in metabolic regulation. The goals of this study were to test whether increasing the expression of MsrA in mice can protect against obesity-induced metabolic dysfunction and to elucidate the potential underlying mechanisms. Mice with increased levels of MsrA in the mitochondria (TgMito MsrA) or in the cytosol (TgCyto MsrA) were fed a high fat/high sugar diet and parameters of glucose homeostasis were monitored. Mitochondrial content, markers of mitochondrial proteostasis and mitochondrial energy utilization were assessed. TgMito MsrA, but not TgCyto MsrA, mice remain insulin sensitive after high fat feeding, though these mice are not protected from obesity. This metabolically healthy obese phenotype of TgMito MsrA mice is not associated with changes in mitochondrial number or biogenesis or with a reduction of proteostatic stress in the mitochondria. However, our data suggest that increased mitochondrial MsrA can alter metabolic homeostasis under diet-induced obesity by activating AMPK signaling, thereby defining a potential mechanism by which this genetic alteration can prevent insulin resistance without affecting obesity. Our data suggest that identification of targets that maintain and regulate the integrity of the mitochondrial proteome, particular against oxidative damage, may play essential roles in the protection against metabolic disease.