Mitochondrial Redox Signaling Research Articles

Mitochondrial superoxide disrupts the metabolic and epigenetic landscape of CD4+ and CD8+ T-lymphocytes

While the role of mitochondrial metabolism in controlling T-lymphocyte activation and function is becoming more clear, the specifics of how mitochondrial redox signaling contributes to T-lymphocyte regulation remains elusive. Here, we examined the global effects of elevated mitochondrial superoxide (O2-) on T-lymphocyte activation using a novel model of inducible manganese superoxide dismutase (MnSOD) knock-out. Loss of MnSOD led to specific increases in mitochondrial O2- with no evident changes in hydrogen peroxide (H2O2), peroxynitrite (ONOO−), or copper/zinc superoxide dismutase (CuZnSOD) levels. Unexpectedly, both mitochondrial and glycolytic metabolism showed significant reductions in baseline, maximal capacities, and ATP production with increased mitochondrial O2- levels. MnSOD knock-out T-lymphocytes demonstrated aberrant activation including widespread dysregulation in cytokine production and increased cellular apoptosis. Interestingly, an elevated proliferative signature defined by significant upregulation of cell cycle regulatory genes was also evident in MnSOD knock-out T-lymphocytes, but these cells did not show accelerated proliferative rates. Global disruption in T-lymphocyte DNA methylation and hydroxymethylation was also observed with increased mitochondrial O2-, which was correlated to alterations in intracellular metabolite pools linked to the methionine cycle. Together, these results demonstrate a mitochondrial redox and metabolic couple that when disrupted may alter cellular processes necessary for proper T-lymphocyte activation.

Mitochondria, Metabolism, and Redox Mechanisms in Psychiatric Disorders.

Significance: Our current knowledge of the pathophysiology and molecular mechanisms causing psychiatric disorders is modest, but genetic susceptibility and environmental factors are central to the etiology of these conditions. Autism, schizophrenia, bipolar disorder and major depressive disorder show genetic gene risk overlap and share symptoms and metabolic comorbidities. The identification of such common features may provide insights into the development of these disorders. Recent Advances: Multiple pieces of evidence suggest that brain energy metabolism, mitochondrial functions and redox balance are impaired to various degrees in psychiatric disorders. Since mitochondrial metabolism and redox signaling can integrate genetic and environmental environmental factors affecting the brain, it is possible that they are implicated in the etiology and progression of psychiatric disorders. Critical Issue: Evidence for direct links between cellular mitochondrial dysfunction and disease features are missing. Future Directions: A better understanding of the mitochondrial biology and its intracellular connections to the nuclear genome, the endoplasmic reticulum and signaling pathways, as well as its role in intercellular communication in the organism, is still needed. This review focuses on the findings that implicate mitochondrial dysfunction, the resultant metabolic changes and oxidative stress as important etiological factors in the context of psychiatric disorders. We also propose a model where specific pathophysiologies of psychiatric disorders depend on circuit-specific impairments of mitochondrial dysfunction and redox signaling at specific developmental stages.

Mitoquinone ameliorates pressure overload-induced cardiac fibrosis and left ventricular dysfunction in mice

Increasing evidence indicates that mitochondrial-associated redox signaling contributes to the pathophysiology of heart failure (HF). The mitochondrial-targeted antioxidant, mitoquinone (MitoQ), is capable of modifying mitochondrial signaling and has shown beneficial effects on HF-dependent mitochondrial dysfunction. However, the potential therapeutic impact of MitoQ-based mitochondrial therapies for HF in response to pressure overload is reliant upon demonstration of improved cardiac contractile function and suppression of deleterious cardiac remodeling. Using a new (patho)physiologically relevant model of pressure overload-induced HF we tested the hypothesis that MitoQ is capable of ameliorating cardiac contractile dysfunction and suppressing fibrosis. To test this C57BL/6J mice were subjected to left ventricular (LV) pressure overload by ascending aortic constriction (AAC) followed by MitoQ treatment (2 µmol) for 7 consecutive days. Doppler echocardiography showed that AAC caused severe LV dysfunction and hypertrophic remodeling. MitoQ attenuated pressure overload-induced apoptosis, hypertrophic remodeling, fibrosis and LV dysfunction. Profibrogenic transforming growth factor-β1 (TGF-β1) and NADPH oxidase 4 (NOX4, a major modulator of fibrosis related redox signaling) expression increased markedly after AAC. MitoQ blunted TGF-β1 and NOX4 upregulation and the downstream ACC-dependent fibrotic gene expressions. In addition, MitoQ prevented Nrf2 downregulation and activation of TGF-β1-mediated profibrogenic signaling in cardiac fibroblasts (CF). Finally, MitoQ ameliorated the dysregulation of cardiac remodeling-associated long noncoding RNAs (lncRNAs) in AAC myocardium, phenylephrine-treated cardiomyocytes, and TGF-β1-treated CF. The present study demonstrates for the first time that MitoQ improves cardiac hypertrophic remodeling, fibrosis, LV dysfunction and dysregulation of lncRNAs in pressure overload hearts, by inhibiting the interplay between TGF-β1 and mitochondrial associated redox signaling.

Olfactory proteotyping: towards the enlightenment of the neurodegeneration.

Olfactory proteotyping: towards the enlightenment of the neurodegeneration.

Endothelial Mitochondrial Preprotein Translocase Tomm7-Rac1 Signaling Axis Dominates Cerebrovascular Network Homeostasis.

Objective- Mitochondria are the important yet most underutilized target for cardio-cerebrovascular function integrity and disorders. The Tom (translocases of outer membrane) complex are the critical determinant of mitochondrial homeostasis for making organs acclimate physiological and pathological insults; however, their roles in the vascular system remain unknown. Approach and Results- A combination of studies in the vascular-specific transgenic zebrafish and genetically engineered mice was conducted. Vascular casting and imaging, endothelial angiogenesis, and mitochondrial protein import were performed to dissect potential mechanisms. A loss-of-function genetic screening in zebrafish identified that selective inactivation of the tomm7 (translocase of outer mitochondrial membrane 7) gene, which encodes a small subunit of the Tom complex, specially impaired cerebrovascular network formation. Ablation of the ortholog Tomm7 in mice recapitulated cerebrovascular abnormalities. Restoration of the cerebrovascular anomaly by an endothelial-specific transgenesis of tomm7 further indicated a defect in endothelial function. Mechanistically, Tomm7 deficit in endothelial cells induced an increased import of Rac1 (Ras-related C3 botulinum toxin substrate 1) protein into mitochondria and facilitated the mitochondrial Rac1-coupled redox signaling, which incurred angiogenic impairment that underlies cerebrovascular network malformation. Conclusions- Tomm7 drives brain angiogenesis and cerebrovascular network formation through modulating mitochondrial Rac1 signaling within the endothelium.

Mitochondrial-derived reactive oxygen species influence ADP sensitivity, but not CPT-I substrate sensitivity.

The mechanisms regulating oxidative phosphorylation during exercise remain poorly defined; however, key mitochondrial proteins, including carnitine palmitoyltransferase-I (CPT-I) and adenine nucleotide translocase, have redox-sensitive sites. Interestingly, muscle contraction has recently been shown to increase mitochondrial membrane potential and reactive oxygen species (ROS) production; therefore, we aimed to determine if mitochondrial-derived ROS influences bioenergetic responses to exercise. Specifically, we examined the influence of acute exercise on mitochondrial bioenergetics in WT (wild type) and transgenic mice (MCAT, mitochondrial-targeted catalase transgenic) possessing attenuated mitochondrial ROS. We found that ablating mitochondrial ROS did not alter palmitoyl-CoA (P-CoA) respiratory kinetics or influence the exercise-mediated reductions in malonyl CoA sensitivity, suggesting that mitochondrial ROS does not regulate CPT-I. In contrast, while mitochondrial protein content, maximal coupled respiration, and ADP (adenosine diphosphate) sensitivity in resting muscle were unchanged in the absence of mitochondrial ROS, exercise increased the apparent ADP Km (decreased ADP sensitivity) ∼30% only in WT mice. Moreover, while the presence of P-CoA decreased ADP sensitivity, it did not influence the basic response to exercise, as the apparent ADP Km was increased only in the presence of mitochondrial ROS. This basic pattern was also mirrored in the ability of ADP to suppress mitochondrial H2O2 emission rates, as exercise decreased the suppression of H2O2 only in WT mice. Altogether, these data demonstrate that while exercise-induced mitochondrial-derived ROS does not influence CPT-I substrate sensitivity, it inhibits ADP sensitivity independent of P-CoA. These data implicate mitochondrial redox signaling as a regulator of oxidative phosphorylation.

Redox Regulation of Hexokinases.

Hexokinases are key enzymes that are responsible for the first reaction of glycolysis, but they also moonlight other cellular processes, including mitochondrial redox signaling regulation. Modulation of hexokinase activity and spatiotemporal location by reactive oxygen and nitrogen species as well as other gasotransmitters serves as the basis for a unique, underexplored method of tight and flexible regulation of these fundamental enzymes. Recent Advances: Redox modifications of thiols serve as a molecular code that enables the precise and complex regulation of hexokinases. Redox regulation of hexokinases is also used by multiple parasites to cause widespread and severe diseases, including malaria, Chagas disease, and sleeping sickness. Redox-active molecules affect each other, and the moonlighting activity of hexokinases provides another feedback loop that affects the cellular redox status and is hijacked in malignantly transformed cells. Several compounds affect the redox status of hexokinases in vivo. These include the dehydroascorbic acid (oxidized form of vitamin C), pyrrolidinium porrolidine-1-carbodithioate (contraceptive), peroxynitrite (product of ethanol metabolism), alloxan (a glucose analog), and isobenzothiazolinone ebselen. However, very limited information is available regarding which amino acid residues in hexokinases are affected by redox signaling. Except in cases of monogenic diabetes, direct evidence is absent for disease phenotypes that are associated with variations within motifs that are susceptible to redox signaling. Further studies should address the propensity of hexokinases and their disease-associated variants to participate in redox regulation. Robust and straightforward proteomic methods are needed to understand the context and consequences of hexokinase-mediated redox regulation in health and disease.

Control of mitochondrial superoxide production by reverse electron transport at complex I

The generation of mitochondrial superoxide (O2˙̄) by reverse electron transport (RET) at complex I causes oxidative damage in pathologies such as ischemia reperfusion injury, but also provides the precursor to H2O2 production in physiological mitochondrial redox signaling. Here, we quantified the factors that determine mitochondrial O2˙̄ production by RET in isolated heart mitochondria. Measuring mitochondrial H2O2 production at a range of proton-motive force (Δp) values and for several coenzyme Q (CoQ) and NADH pool redox states obtained with the uncoupler p-trifluoromethoxyphenylhydrazone, we show that O2˙̄ production by RET responds to changes in O2 concentration, the magnitude of Δp, and the redox states of the CoQ and NADH pools. Moreover, we determined how expressing the alternative oxidase from the tunicate Ciona intestinalis to oxidize the CoQ pool affected RET-mediated O2˙̄ production at complex I, underscoring the importance of the CoQ pool for mitochondrial O2˙̄ production by RET. An analysis of O2˙̄ production at complex I as a function of the thermodynamic forces driving RET at complex I revealed that many molecules that affect mitochondrial reactive oxygen species production do so by altering the overall thermodynamic driving forces of RET, rather than by directly acting on complex I. These findings clarify the factors controlling RET-mediated mitochondrial O2˙̄ production in both pathological and physiological conditions. We conclude that O2˙̄ production by RET is highly responsive to small changes in Δp and the CoQ redox state, indicating that complex I RET represents a major mode of mitochondrial redox signaling.

Aberrant expression of redox regulatory proteins in patients with concomitant primary Sclerosing cholangitis/inflammatory bowel disease

ObjectivePrimary Sclerosing Cholangitis (PSC) is a severe cholestatic liver disease characterized by progressive peri-biliary tract inflammation, elevated oxidative stress and hepatocellular injury. A hallmark of PSC patients is the concurrent diagnosis of Inflammatory Bowel Disease occurring in approximately 70%–80% of PSC patients (PSC/IBD). We previously reported dysregulation of key anti-oxidant pathways in PSC/IBD. The objective of this study was to expand previous data by examining the abundance of thioredoxins (Trx) in PSC/IBD. MethodsUsing hepatic tissue and whole cell extracts isolated from age-matched healthy humans and patients diagnosed with end stage PSC/IBD, the protein abundance of thioredoxin, thioredoxin reductase (TrxR1), and their downstream substrates peroxiredoxins was assessed. ResultsWestern blot analyses of thioredoxin and peroxiredoxin abundance revealed significant increases in abundance of Trx1 and TrxR1 whereas expression of thioredoxin-interacting protein was significantly decreased in PSC/IBD. Concurrently, abundance of cytosolic peroxiredoxins was not significantly impacted. The abundance of mitochondrial Trx2, along with peroxiredoxins 3, 5 and 6 were significantly decreased by concurrent PSC/IBD. Histological staining of Trx1/TrxR1 revealed elevated nuclear Trx1 and TrxR1 staining within cholangiocytes as well as an overall periportal increase in expression in PSC/IBD. An examination of additional anti-oxidant responses reveal suppression of gamma-glutamylcysteine synthetase and heme oxygenase (HO-1) whereas expression of the protein chaperone glucose regulated protein 78 increased suggesting elevated cellular stress in PSC/IBD. ConclusionsResults herein suggest that in addition to severe dysregulation of anti-oxidant responses, cholestasis impacts both cytosolic/nuclear (Trx1) as well as mitochondrial (Trx2) redox signaling and control pathways.

Mitochondrial Na + import controls oxidative phosphorylation and hypoxic redox signaling

All metazoans depend on O2 delivery and consumption by the mitochondrial oxidative phosphorylation (OXPHOS) system to produce energy. A decrease in O2 availability (hypoxia) leads to profound metabolic rewiring. In addition, OXPHOS uses O2 to produce reactive oxygen species (ROS) that can drive cell adaptations through redox signalling, but also trigger cell damage1–4, and both phenomena occur in hypoxia4–8. However, the precise mechanism by which acute hypoxia triggers mitochondrial ROS production is still unknown. Ca2+ is one of the best known examples of an ion acting as a second messenger9, yet the role ascribed to Na+ is to serve as a mere mediator of membrane potential and collaborating in ion transport10. Here we show that Na+ acts as a second messenger regulating OXPHOS function and ROS production by modulating fluidity of the inner mitochondrial membrane (IMM). We found that a conformational shift in mitochondrial complex I during acute hypoxia11 drives the acidification of the matrix and solubilization of calcium phosphate precipitates. The concomitant increase in matrix free-Ca2+ activates the mitochondrial Na+/Ca2+ exchanger (NCLX), which imports Na+ into the matrix. Na+ interacts with phospholipids reducing IMM fluidity and mobility of free ubiquinone between complex II and complex III, but not inside supercomplexes. As a consequence, superoxide is produced at complex III, generating a redox signal. Inhibition of mitochondrial Na+ import through NCLX is sufficient to block this pathway, preventing adaptation to hypoxia. These results reveal that Na+ import into the mitochondrial matrix controls OXPHOS function and redox signalling through an unexpected interaction with phospholipids, with profound consequences in cellular metabolism.

Sodium nitrate supplementation alters mitochondrial H2O2 emission but does not improve mitochondrial oxidative metabolism in the heart of healthy rats.

Supplementation with dietary inorganic nitrate ([Formula: see text]) is increasingly recognized to confer cardioprotective effects in both healthy and clinical populations. While the mechanism(s) remains ambiguous, in skeletal muscle oral consumption of NaNO3 has been shown to improve mitochondrial efficiency. Whether NaNO3 has similar effects on mitochondria within the heart is unknown. Therefore, we comprehensively investigated the effect of NaNO3 supplementation on in vivo left ventricular (LV) function and mitochondrial bioenergetics. Healthy male Sprague-Dawley rats were supplemented with NaNO3 (1 g/l) in their drinking water for 7 days. Echocardiography and invasive hemodynamics were used to assess LV morphology and function. Blood pressure (BP) was measured by tail-cuff and invasive hemodynamics. Mitochondrial bioenergetics were measured in LV isolated mitochondria and permeabilized muscle fibers by high-resolution respirometry and fluorometry. Nitrate decreased ( P < 0.05) BP, LV end-diastolic pressure, and maximal LV pressure. Rates of LV relaxation (when normalized to mean arterial pressure) tended ( P = 0.13) to be higher with nitrate supplementation. However, nitrate did not alter LV mitochondrial respiration, coupling efficiency, or oxygen affinity in isolated mitochondria or permeabilized muscle fibers. In contrast, nitrate increased ( P < 0.05) the propensity for mitochondrial H2O2 emission in the absence of changes in cellular redox state and decreased the sensitivity of mitochondria to ADP (apparent Km). These results add to the therapeutic potential of nitrate supplementation in cardiovascular diseases and suggest that nitrate may confer these beneficial effects via mitochondrial redox signaling.

MITF acts as an anti-oxidant transcription factor to regulate mitochondrial biogenesis and redox signaling in retinal pigment epithelial cells

There is increasing evidence that the mechanisms protecting the retinal pigment epithelium (RPE) against oxidative stress are important for preventing retinal degenerative diseases. Little, however, is known about these mechanisms. Here we show that MITF, a transcription factor responsible for RPE development and function, regulates redox signaling by acting through PGC1α, a master regulator of mitochondrial biogenesis. Mitf deficiency in mice leads to significantly higher levels of reactive oxygen species (ROS) in both RPE and retina, suggesting that Mitf dysfunction might lead to oxidative damage in the RPE and, by extension, in the retina. Furthermore, overexpression of MITF in the human RPE cell line ARPE-19 indicates that MITF up-regulates antioxidant gene expression and mitochondrial biogenesis by regulating PGC1α and protects cells against oxidative stress. Our findings provide new insights into understanding the redox function of MITF in RPE cells and its potential contribution to prevention of RPE-associated retinal degenerations.

Mechanisms and Mitochondrial Redox Signaling in Photobiomodulation.

Photobiomodulation (PBM) involves the use of red or near-infrared light at low power densities to produce a beneficial effect on cells or tissues. PBM therapy is used to reduce pain, inflammation, edema, and to regenerate damaged tissues such as wounds, bones, and tendons. The primary site of light absorption in mammalian cells has been identified as the mitochondria and, more specifically, cytochrome c oxidase (CCO). It is hypothesized that inhibitory nitric oxide can be dissociated from CCO, thus restoring electron transport and increasing mitochondrial membrane potential. Another mechanism involves activation of light or heat-gated ion channels. This review will cover the redox signaling that occurs in PBM and examine the difference between healthy and stressed cells, where PBM can have apparently opposite effects. PBM has a marked effect on stem cells, and this is proposed to operate via mitochondrial redox signaling. PBM can act as a preconditioning regimen and can interact with exercise on muscles.

Altered Redox Homeostasis in Branched-Chain Amino Acid Disorders, Organic Acidurias, and Homocystinuria.

Inborn errors of metabolism (IEMs) are a group of monogenic disorders characterized by dysregulation of the metabolic networks that underlie development and homeostasis. Emerging evidence points to oxidative stress and mitochondrial dysfunction as major contributors to the multiorgan alterations observed in several IEMs. The accumulation of toxic metabolites in organic acidurias, respiratory chain, and fatty acid oxidation disorders inhibits mitochondrial enzymes and processes resulting in elevated levels of reactive oxygen species (ROS). In other IEMs, as in homocystinuria, different sources of ROS have been proposed. In patients' samples, as well as in cellular and animal models, several studies have identified significant increases in ROS levels along with decreases in antioxidant defences, correlating with oxidative damage to proteins, lipids, and DNA. Elevated ROS disturb redox-signaling pathways regulating biological processes such as cell growth, differentiation, or cell death; however, there are few studies investigating these processes in IEMs. In this review, we describe the published data on mitochondrial dysfunction, oxidative stress, and impaired redox signaling in branched-chain amino acid disorders, other organic acidurias, and homocystinuria, along with recent studies exploring the efficiency of antioxidants and mitochondria-targeted therapies as therapeutic compounds in these diseases.

Role of Placental Mitochondria in Development of Pre-eclampsia: Focus on Mitochondrial Dynamics, Redox Signaling and Apoptosis

Role of Placental Mitochondria in Development of Pre-eclampsia: Focus on Mitochondrial Dynamics, Redox Signaling and Apoptosis

Assessing Spatiotemporal and Functional Organization of Mitochondrial Networks.

The functional and spatiotemporal organization of mitochondrial redox signaling networks can be studied in detail in cardiac myocytes and neurons by assessing the time-resolved signaling traits of their individual mitochondrial components. Perturbations of the mitochondrial network through oxidative stress can lead to coordinated, cluster-bound behavior in the form of synchronized limit-cycle oscillations of mitochondrial inner membrane potentials. These oscillations are facilitated by both structural coupling through changes in the local redox balance and signaling microdomains and functional coupling that is yet poorly understood. Thus, quantifiable measures of both coupling mechanisms, local dynamic mitochondrial coupling constants and functional clustering coefficients, are likely to offer valuable information on mitochondrial network organization. We provide step-by-step methodologies on how to acquire and assess these measures for inner membrane potential fluorescence fluctuations in laser-scanning two-photon microscope recordings of cardiac myocytes and neurons, that can be applied to other tissues as well.

Redox Equivalents and Mitochondrial Bioenergetics.

Mitochondrial energy metabolism depends upon high-flux and low-flux electron transfer pathways. The former provide the energy to support chemiosmotic coupling for oxidative phosphorylation. The latter provide mechanisms for signaling and control of mitochondrial functions. Few practical methods are available to measure rates of individual mitochondrial electron transfer reactions; however, a number of approaches are available to measure steady-state redox potentials (E h) of donor/acceptor couples, and these can be used to gain insight into rate controlling reactions as well as mitochondrial bioenergetics. Redox changes within the respiratory electron transfer pathway are quantified by optical spectroscopy and measurement of changes in autofluorescence. Low-flux pathways involving thiol/disulfide redox couples are measured by redox Western blot and mass spectrometry-based redox proteomics. Together, the approaches provide the opportunity to develop integrated systems biology descriptions of mitochondrial redox signaling and control mechanisms.

Mitochondrial ROS contribute to oridonin-induced HepG2 apoptosis through PARP activation.

Oridonin, the main active constituent of Rabdosia rubescens, is known to exert antitumor activity via the induction of apoptosis in numerous types of human cancer cells. However, the underlying regulatory mechanisms of mitochondrial ROS in oridonin-induced HepG2 apoptosis remain largely unknown, due to limitations of subcellular imaging resolution. Previously, it has been suggested that mitochondria serve a potential role in sensing and signaling cellular redox changes in vital biological processes such as cell death and the abiotic stress response, based on studies involving the mitochondrial-targeted redox-sensitive green fluorescent protein (GFP). To address this, a mitochondrial-targeted Grx1-roGFP2 (mtGrx1-roGFP2) biosensor was implemented to monitor real-time mitochondrial redox changes of HepG2 cells in response to either H2O2/DTT or oridonin/SS31 treatment. It was determined that oridonin caused a perturbation in mitochondrial redox status, which in turn contributed to oridonin-induced apoptosis. Furthermore, a novel mechanism underlying the regulation of mitochondrial redox changes in oridonin-induced HepG2 apoptosis, presumably dependent on PARP cleavage, was proposed. In conclusion, the present study provides evidence in support of mitochondrial redox changes as a potential mediator in the apoptotic activities of oridonin in HepG2 cells, which provides insight into the molecular mechanisms by which mitochondrial redox signaling regulates oridonin-induced apoptosis in cancer therapy, and the development of mitochondria-specific oridonin as a promising novel anticancer therapeutic strategy.

6 - Differential Redox Changes in Liver Mitochondrial Proteomes from Phenotypically Distinct Mouse Models of Glutathione Deficiency

Intrahepatocyte generation of free radicals and depletion of glutathione (GSH) are believed to be key mediators involved in the cellular pathogenic events underlying fatty liver disease (FLD). As the most abundant intracellular non-protein thiol, GSH has an important biochemical role in electrophile detoxification and oxidant elimination. Additionally, changes in GSH/GSSG (its oxidized form) redox couple may modify protein functions via redox post-translational modification. We have developed two unique transgenic mouse models in which hepatic GSH synthesis is repressed by abolishing the expression of the catalytic (GCLC) or the modifier (GCLM) subunit of glutamate-cysteine ligase, the rate-limiting enzyme in GSH biosynthesis. Our previous studies show that these mice have GSH deficiencies at different levels but exhibit either resistance to steatosis (GCLM knockout mice) or develop spontaneous liver pathologies featuring all clinical stages of FLD (liver-specific GCLC knockout mice). Importantly our studies show that functional integrity of the mitochondria is a key determinant of the hepatic phenotype under conditions of chronic GSH deficiency. The purpose of the current study is to investigate the hypothesis that GSH plays an important regulatory role in mitochondrial redox signaling network. We performed redox proteomics analysis of liver mitochondrial proteomes derived from two phenotypically distinct mouse models. Cellular redox buffering couples (GSH-GSSG, NADH-NAD and NADPH-NADP) were measured in parallel. The proteomics analysis revealed phenotype-associated Cysteine redox profiles of mitochondrial proteins that are involved in oxidative phosphorylation, lipid metabolism, xenobiotic metabolism, and cellular stress response. Biochemically, decreased NAD/NADH ratio appears to correlate with a protective phenotype. In conclusion, our preliminary data suggest a redox-based role of GSH in modulating mitochondrial pathways that are mechanistically linked to the pathogenesis of FLD.

Mitochondrial redox signaling enables repair of injured skeletal muscle cells.

Strain and physical trauma to mechanically active cells, such as skeletal muscle myofibers, injures their plasma membranes, and mitochondrial function is required for their repair. We found that mitochondrial function was also needed for plasma membrane repair in myoblasts as well as nonmuscle cells, which depended on mitochondrial uptake of calcium through the mitochondrial calcium uniporter (MCU). Calcium uptake transiently increased the mitochondrial production of reactive oxygen species (ROS), which locally activated the guanosine triphosphatase (GTPase) RhoA, triggering F-actin accumulation at the site of injury and facilitating membrane repair. Blocking mitochondrial calcium uptake or ROS production prevented injury-triggered RhoA activation, actin polymerization, and plasma membrane repair. This repair mechanism was shared between myoblasts, nonmuscle cells, and mature skeletal myofibers. Quenching mitochondrial ROS in myofibers during eccentric exercise ex vivo caused increased damage to myofibers, resulting in a greater loss of muscle force. These results suggest a physiological role for mitochondria in plasma membrane repair in injured cells, a role that highlights a beneficial effect of ROS.