Mitochondrial alterations and oxidative stress in an acute transient mouse model of muscle degeneration: implications for muscular dystrophy and related muscle pathologies

Changes in protein fluxes and gene expression in non-injured muscle tissue distant from an acute myotoxic injury in male mice

The response to acute myotoxic injury requires stimulation of local repair mechanisms in the damaged tissue. However, satellite cells in muscle distant from acute injury have been reported to enter a functional state between quiescence and active proliferation. Here, we asked whether protein flux rates are altered in muscle distant from acute local myotoxic injury and how they compare to changes in gene expression from the same tissue. Broad and significant alterations in protein turnover were observed across the proteome in the limb contralateral to injury during the first 10 days after. Interestingly, mRNA changes had almost no correlation with directly measured protein turnover rates. In summary, we show consistent and striking changes in protein flux rates in muscle tissue contralateral to myotoxic injury, with no correlation between changes in mRNA levels and protein synthesis rates. This work motivates further investigation of the mechanisms, including potential neurological factors, responsible for this distant effect. KEY POINTS: Previous literature demonstrates that stem cells of uninjured muscle respond to local necrotic muscle tissue damage and regeneration. We show that muscle tissue that was distant from a model of local necrotic damage had functional changes at both the gene expression and the protein turnover level. However, these changes in distant tissue were more pronounced during the earlier stages of tissue regeneration and did not correlate well with each other. The results suggest communication between directly injured tissue and non-affected tissues that are distant from injury, which warrants further investigation into the potential of this mechanism as a proactive measure for tissue regeneration from damage.

Changes in protein fluxes in skeletal muscle during sequential stages of muscle regeneration after acute injury in male mice

Changes in protein turnover play an important role in dynamic physiological processes, including skeletal muscle regeneration, which occurs as an essential part of tissue repair after injury. The inability of muscle tissue to recapitulate this regenerative process can lead to the manifestation of clinical symptoms in various musculoskeletal diseases, including muscular dystrophies and pathological atrophy. Here, we employed a workflow that couples deuterated water (2H2O) administration with mass spectrometry (MS) to systematically measure in-vivo protein turnover rates across the muscle proteome in 8-week-old male C57BL6/J mice. We compared the turnover kinetics of over 100 proteins in response to cardiotoxin (CTX) induced muscle damage and regeneration at unique sequential stages along the regeneration timeline. This analysis is compared to gene expression data from mRNA-sequencing (mRNA-seq) from the same tissue. The data reveals quantitative protein flux signatures in response to necrotic damage, in addition to sequential differences in cell proliferation, energy metabolism, and contractile gene expression. Interestingly, the mRNA changes correlated poorly with changes in protein synthesis rates, consistent with post-transcriptional control mechanisms. In summary, the experiments described here reveal the signatures and timing of protein flux changes during skeletal muscle regeneration, as well as the inability of mRNA expression measurements to reveal changes in directly measured protein turnover rates. The results of this work described here provide a better understanding of the muscle regeneration process and could help to identify potential biomarkers or therapeutic targets.

Intervention with metabolites emulating endogenous cell transitions accelerates muscle regeneration in young and aged mice

Tissue regeneration following an injury requires dynamic cell-state transitions that allow for establishing the cell identities required for the restoration of tissue homeostasis and function. Here, we present a biochemical intervention that induces an intermediate cell state mirroring a transition identified during normal differentiation of myoblasts and other multipotent and pluripotent cells to mature cells. When applied in somatic differentiated cells, the intervention, composed of one-carbon metabolites, reduces some dedifferentiation markers without losing the lineage identity, thus inducing limited reprogramming into a more flexible cell state. Moreover, the intervention enabled accelerated repair after muscle injury in young and aged mice. Overall, our study uncovers a conserved biochemical transitional phase that enhances cellular plasticity in vivo and hints at potential and scalable biochemical interventions of use in regenerative medicine and rejuvenation interventions that may be more tractable than genetic ones.

Mitochondrial protein and organelle quality control-Lessons from budding yeast

Mitochondria are essential for normal cellular function and have emerged as key aging determinants. Indeed, defects in mitochondrial function have been linked to cardiovascular, skeletal muscle and neurodegenerative diseases, premature aging, and age-linked diseases. Here, we describe mechanisms for mitochondrial protein and organelle quality control. These surveillance mechanisms mediate repair or degradation of damaged or mistargeted mitochondrial proteins, segregate mitochondria based on their functional state during asymmetric cell division, and modulate cellular fitness, the response to stress, and lifespan control in yeast and other eukaryotes.

Serum uric acid is independently associated with hypertension in patients with polymyositis and dermatomyositis

Serum uric acid (UA), as an antioxidant, has been associated with hypertension in the general population. Hypertension is highly prevalent in patients with polymyositis and dermatomyositis (PM/DM). Owning elevated levels of reactive oxygen species, patients with PM/DM have lower concentrations of UA in comparison with healthy people. We explored a potential association between UA levels and hypertension in PM/DM and evaluated whether this association is independent of hypertension risk factors, PM/DM characteristics and relevant drugs. A total of 472 PM/DM patients were assessed. UA and related laboratory data were measured. Demographic, hypertension-related factors, PM/DM characteristics and drug use were assessed as potential covariates. Results were analyzed using logistic models to test the independence of the association between UA and hypertension. UA levels were higher in hypertension subjects compared to non-hypertensive PM/DM patients [284.70 (239.93-357.38) vs 264.00(222.50-322.75), p = .017]. When adjusted for hypertension risk factors, PM/DM characteristics and drugs, the odds of being a hypertensive PM/DM patient per 1 μmol/L UA increase were significantly increased: odds ratio = 1.473 (95% confidence interval:1.063-2.042, p = .020). This cross-sectional study suggests that UA levels are independently associated with hypertension in PM/DM patients.

Mechanisms and effects of metformin on skeletal muscle disorders

Skeletal muscle disorders are mostly genetic and include several rare diseases. With disease progression, muscle fibrosis and adiposis occur, resulting in limited mobility. The long course of these diseases combined with limited treatment options affect patients both psychologically and economically, hence the development of novel treatments for neuromuscular diseases is crucial to obtain a better quality of life. As a widely used hypoglycemic drug in clinical practice, metformin not only has anti-inflammatory, autophagy-regulating, and mitochondrial biogenesis-regulating effects, but it has also been reported to improve the symptoms of neuromuscular diseases, delay hypokinesia, and regulate skeletal muscle mass. However, metformin's specific mechanism of action in neuromuscular diseases requires further elucidation. This review summarizes the evidence showing that metformin can regulate inflammation, autophagy, and mitochondrial biogenesis through different pathways, and further explores its mechanism of action in Duchenne muscular dystrophy, statin-associated muscle disorders, and age-related sarcopenia. This review clarifies the directions of future research on therapy for neuromuscular diseases.

Neuroanatomical zones of human traumatic brain injury reveal significant differences in protein profile and protein oxidation: Implications for secondary injury events

Traumatic brain injury (TBI) causes significant neurological deficits and long-term degenerative changes. Primary injury in TBI entails distinct neuroanatomical zones, i.e., contusion (Ct) and pericontusion (PC). Their dynamic expansion could contribute to unpredictable neurological deterioration in patients. Molecular characterization of these zones compared with away from contusion (AC) zone is invaluable for TBI management. Using proteomics-based approach, we were able to distinguish Ct, PC and AC zones in human TBI brains. Ct was associated with structural changes (blood-brain barrier (BBB) disruption, neuroinflammation, axonal injury, demyelination and ferroptosis), while PC was associated with initial events of secondary injury (glutamate excitotoxicity, glial activation, accumulation of cytoskeleton proteins, oxidative stress, endocytosis) and AC displayed mitochondrial dysfunction that could contribute to secondary injury events and trigger long-term degenerative changes. Phosphoproteome analysis in these zones revealed that certain differentially phosphorylated proteins synergistically contribute to the injury events along with the differentially expressed proteins. Non-synaptic mitochondria (ns-mito) was associated with relatively more differentially expressed proteins (DEPs) compared to synaptosomes (Syn), while the latter displayed increased protein oxidation including tryptophan (Trp) oxidation. Proteomic analysis of immunocaptured complex I (CI) from Syn revealed increased Trp oxidation in Ct > PC > AC (vs. control). Oxidized W272 in the ND1 subunit of CI, revealed local conformational changes in ND1 and the neighboring subunits, as indicated by molecular dynamics simulation (MDS). Taken together, neuroanatomical zones in TBI show distinct protein profile and protein oxidation representing different primary and secondary injury events with potential implications for TBI pathology and neurological status of the patients.

Inflammation and Oxidative Stress in Snakebite Envenomation: A Brief Descriptive Review and Clinical Implications

Snakebite envenoming is a pathological condition which may occur in response to the injection of venom. Snake venoms contain a complex mixture of biologically active molecules which are responsible for a broad spectrum of clinical manifestations, ranging from local tissue injuries to fatal complications. Snake venom administration commonly provokes local tissue injury often associated with systemic effects, including neurotoxic and cardiotoxic manifestations, bleeding, acute kidney injury, and rhabdomyolysis. An important spectrum of pathogenesis of snake envenomation is the generation of reactive oxygen species (ROS), which can directly provoke tissue damage and also potentiate the deleterious consequences of inflammation at the bite site. Snake venom components known to induce oxidative stress include phospholipases A₂, metalloproteinases, three-finger toxins, and L-amino acid oxidase. Clear evidence is mounting suggesting that inflammation and oxidative stress participate in the destructive effects of envenoming, including acute renal failure, tissue necrosis, and unusual susceptibility to bleed (hemorrhage), mostly due to hypocoagulability, neuro/cardio toxicity, and myonecrosis. Impaired regulation of oxidative stress may also set the stage for secondary/long-term complications of snakebite envenomation such as musculoskeletal disabilities. Some aspects of natural antioxidant therapeutic options are discussed in this review.

Skeletal Muscle Regeneration in Cardiotoxin-Induced Muscle Injury Models

Skeletal muscle injuries occur frequently in daily life and exercise. Understanding the mechanisms of regeneration is critical for accelerating the repair and regeneration of muscle. Therefore, this article reviews knowledge on the mechanisms of skeletal muscle regeneration after cardiotoxin-induced injury. The process of regeneration is similar in different mouse strains and is inhibited by aging, obesity, and diabetes. Exercise, microcurrent electrical neuromuscular stimulation, and mechanical loading improve regeneration. The mechanisms of regeneration are complex and strain-dependent, and changes in functional proteins involved in the processes of necrotic fiber debris clearance, M1 to M2 macrophage conversion, SC activation, myoblast proliferation, differentiation and fusion, and fibrosis and calcification influence the final outcome of the regenerative activity.

Association of Oxidative Stress with Neurological Disorders

BACKGORUND

Oxidative stress is one of the main contributing factors involved in cerebral biochemical impairment. The higher susceptibility of the central nervous system to reactive oxygen species mediated damage could be attributed to several factors. For example, neurons use a greater quantity of oxygen, many parts of the brain have higher concentraton of iron, and neuronal mitochondria produce huge content of hydrogen peroxide. In addition, neuronal membranes have polyunsaturated fatty acids, which are predominantly vulnerable to oxidative stress (OS). OS is the imbalance between reactive oxygen species generation and cellular antioxidant potential. This may lead to various pathological conditions and diseases, especially neurodegenerative diseases such as, Parkinson's, Alzheimer's, and Huntington's diseases.

OBJECTIVES

In this study, we explored the involvement of OS in neurodegenerative diseases.

METHODS

We used different search terms like "oxidative stress and neurological disorders" "free radicals and neurodegenerative disorders" "oxidative stress, free radicals, and neurological disorders" and "association of oxidative stress with the name of disorders taken from the list of neurological disorders. We tried to summarize the source, biological effects, and physiologic functions of ROS.

RESULTS

Finally, it was noted that more than 190 neurological disorders are associated with oxidative stress.

CONCLUSION

More elaborated studies in the future will certainly help in understanding the exact mechanism involved in neurological diseases and provide insight into revelation of therapeutic targets.

Identification of a novel gene signature in second-trimester amniotic fluid for the prediction of preterm birth

Preterm birth affects approximately 5% to 7% of live births worldwide and is the leading cause of neonatal morbidity and mortality. Amniotic fluid supernatant (AFS) contains abundant cell-free nucleic acids (cfNAs) that can provide genetic information associated with pregnancy complications. In the current study, cfNAs of AFS in the early second-trimester before the onset of symptoms of preterm birth were analyzed, and we compared gene expression levels between spontaneous preterm birth (n = 5) and term birth (n = 5) groups using sequencing analysis. Differential expression analyses detected 24 genes with increased and 6 genes with decreased expression in the preterm birth group compared to term birth. Upregulated expressions of RDH14, ZNF572, VOPP1, SERPINA12, and TCF15 were validated in an extended AFS sample by quantitative PCR (preterm birth group, n = 21; term birth group, n = 40). Five candidate genes displayed a significant increase in mRNA expression in immortalized trophoblast HTR-8/SVneo cell with H₂O₂ treatment. Moreover, the expression of five candidate genes was increased to more than twofold by pretreatment with lipopolysaccharide in HTR-8/SVneo cells. Changes in gene expression between preterm birth and term birth is strongly correlated with oxidative stress and infection during pregnancy. Specific expression patterns of genes could be used as potential markers for the early identification of women at risk of having a spontaneous preterm birth.

Mitochondrial Dysfunction in Rabies Virus-Infected Human and Canine Brains

Rabies is a fatal encephalitis caused by the Rabies lyssavirus (RABV). The presence of minimal neuropathological changes observed in rabies indicates that neuronal dysfunction, rather than neuronal death contributes to the fatal outcome. The role of mitochondrial changes has been suggested as a possible mechanism for neuronal dysfunction in rabies. However, these findings are mostly based on studies that have employed experimental models and laboratory-adapted virus. Studies on brain tissues from naturally infected human and animal hosts are lacking. The current study investigated the role of mitochondrial changes in rabies by morphological, biochemical and proteomic analysis of RABV-infected human and canine brains. Morphological analysis showed minimal inflammation with preserved neuronal and disrupted mitochondrial structure in both human and canine brains. Proteomic analysis revealed involvement of mitochondrial processes (oxidative phosphorylation, cristae formation, homeostasis and transport), synaptic proteins and autophagic pathways, with over-expression of subunits of mitochondrial respiratory complexes. Consistent with these findings, human and canine brains displayed elevated activities of complexes I (p < 0.05), IV (p < 0.05) and V (p < 0.05). However, this did not result in elevated ATP production (p < 0.0001), probably due to lowered mitochondrial membrane potential as noted in RABV-infected cells in culture. These could lead to mitochondrial dysfunction and mitophagy as indicated by expression of FKBP8 (p < 0.05) and PINK1 (p < 0.001)/PARKIN (p > 0.05) and ensuing autophagy, as shown by the status of LCIII (p < 0.05), LAMP1 (p < 0.001) and pertinent ultrastructural markers. We propose that altered mitochondrial bioenergetics and cristae architecture probably induce mitophagy, leading to autophagy and consequent neuronal dysfunction in rabies.

Mss51 deletion increases endurance and ameliorates histopathology in the mdx mouse model of Duchenne muscular dystrophy

Mitochondrial derangement is an important contributor to the pathophysiology of muscular dystrophies and may be among the earliest cellular deficits. We have previously shown that disruption of Mss51, a mammalian skeletal muscle protein that localizes to the mitochondria, results in enhanced muscle oxygen consumption rate, increased endurance capacity, and improved limb muscle strength in mice with wildtype background. Here, we investigate whether Mss51 deletion in the mdx murine model of Duchenne muscular dystrophy (mdx-Mss51 KO) counteracts the muscle pathology and mitochondrial irregularities observed in mdx mice. We found that mdx-Mss51 KO mice had increased myofiber oxygen consumption rates and an amelioration of muscle histopathology compared to mdx counterparts. This corresponded with greater treadmill endurance and less percent fatigue in muscle physiology, but no improvement in forelimb grip strength or limb muscle force production. These findings suggest that although Mss51 deletion ameliorates the skeletal muscle mitochondrial respiration defects in mdx and improves fatigue resistance in vivo, the lack of improvement in force production suggests that this target alone may be insufficient for a therapeutic effect.

Beneficial Role of Exercise in the Modulation of mdx Muscle Plastic Remodeling and Oxidative Stress

Duchenne muscular dystrophy (DMD) is an X-linked recessive progressive lethal disorder caused by the lack of dystrophin, which determines myofibers mechanical instability, oxidative stress, inflammation, and susceptibility to contraction-induced injuries. Unfortunately, at present, there is no efficient therapy for DMD. Beyond several promising gene- and stem cells-based strategies under investigation, physical activity may represent a valid noninvasive therapeutic approach to slow down the progression of the pathology. However, ethical issues, the limited number of studies in humans and the lack of consistency of the investigated training interventions generate loss of consensus regarding their efficacy, leaving exercise prescription still questionable. By an accurate analysis of data about the effects of different protocol of exercise on muscles of mdx mice, the most widely-used pre-clinical model for DMD research, we found that low intensity exercise, especially in the form of low speed treadmill running, likely represents the most suitable exercise modality associated to beneficial effects on mdx muscle. This protocol of training reduces muscle oxidative stress, inflammation, and fibrosis process, and enhances muscle functionality, muscle regeneration, and hypertrophy. These conclusions can guide the design of appropriate studies on human, thereby providing new insights to translational therapeutic application of exercise to DMD patients.

Loss of Parkin Results in Altered Muscle Stem Cell Differentiation during Regeneration

The high capacity of the skeletal muscle to regenerate is due to the presence of muscle stem cells (MuSCs, or satellite cells). The E3 ubiquitin ligase Parkin is a key regulator of mitophagy and is recruited to mitochondria during differentiation of mouse myoblast cell line. However, the function of mitophagy during regeneration has not been investigated in vivo. Here, we have utilized Parkin deficient (Parkin^-/-) mice to investigate the role of Parkin in skeletal muscle regeneration. We found a persistent deficiency in skeletal muscle regeneration in Parkin^-/- mice after cardiotoxin (CTX) injury with increased area of fibrosis and decreased cross-sectional area (CSA) of myofibres post-injury. There was also a significant modulation of MuSCs differentiation and mitophagic markers, with altered mitochondrial proteins during skeletal muscle regeneration in Parkin^-/- mice. Our data suggest that Parkin-mediated mitophagy plays a key role in skeletal muscle regeneration and is necessary for MuSCs differentiation.

High-Dimensional Single-Cell Quantitative Profiling of Skeletal Muscle Cell Population Dynamics during Regeneration

The interstitial space surrounding the skeletal muscle fibers is populated by a variety of mononuclear cell types. Upon acute or chronic insult, these cell populations become activated and initiate finely-orchestrated crosstalk that promotes myofiber repair and regeneration. Mass cytometry is a powerful and highly multiplexed technique for profiling single-cells. Herein, it was used to dissect the dynamics of cell populations in the skeletal muscle in physiological and pathological conditions. Here, we characterized an antibody panel that could be used to identify most of the cell populations in the muscle interstitial space. By exploiting the mass cytometry resolution, we provided a comprehensive picture of the dynamics of the major cell populations that sensed and responded to acute damage in wild type mice and in a mouse model of Duchenne muscular dystrophy. In addition, we revealed the intrinsic heterogeneity of many of these cell populations.

Cardiotoxin-induced skeletal muscle injury elicits profound changes in anabolic and stress signaling, and muscle fiber type composition

To improve muscle healing upon injury, it is of importance to understand the interplay of key signaling pathways during muscle regeneration. To study this, mice were injected with cardiotoxin (CTX) or PBS in the Tibialis Anterior muscle and were sacrificed 2, 5 and 12 days upon injection. The time points represent different phases of the regeneration process, i.e. destruction, repair and remodeling, respectively. Two days upon CTX-injection, p-mTORC1 signaling and stress markers such as BiP and p-ERK1/2 were upregulated. Phospho-ERK1/2 and p-mTORC1 peaked at d5, while BiP expression decreased towards PBS levels. Phospho-FOXO decreased 2 and 5 days following CTX-injection, indicative of an increase in catabolic signaling. Furthermore, CTX-injection induced a shift in the fiber type composition, characterized by an initial loss in type IIa fibers at d2 and at d5. At d5, new type IIb fibers appeared, whereas type IIa fibers were recovered at d12. To conclude, CTX-injection severely affected key modulators of muscle metabolism and histology. These data provide useful information for the development of strategies that aim to improve muscle molecular signaling and thereby recovery.

Comparative label-free mass spectrometric analysis of temporal changes in the skeletal muscle proteome after impact trauma in rats

Proteomics offers the opportunity to identify and quantify many proteins and to explore how they correlate and interact with each other in biological networks. This study aimed to characterize changes in the muscle proteome during the destruction, repair, and early-remodeling phases after impact trauma in male Wistar rats. Muscle tissue was collected from uninjured control rats and rats that were euthanized between 6 h and 14 days after impact injury. Muscle tissue was analyzed using unbiased, data-independent acquisition LC-MS/MS. We identified 770 reviewed proteins in the muscle tissue, 296 of which were differentially abundant between the control and injury groups (P ≤ 0.05). Around 50 proteins showed large differences (≥10-fold) or a distinct pattern of abundance after injury. These included proteins that have not been identified previously in injured muscle, such as ferritin light chain 1, fibrinogen γ-chain, fibrinogen β-chain, osteolectin, murinoglobulin-1, T-kininogen 2, calcium-regulated heat-stable protein 1, macrophage-capping protein, retinoid-inducible serine carboxypeptidase, ADP-ribosylation factor 4, Thy-1 membrane glycoprotein, and ADP-ribosylation factor-like protein 1. Some proteins increased between 6 h and 14 days, whereas other proteins increased in a more delayed pattern at 7 days after injury. Bioinformatic analysis revealed that various biological processes, including regulation of blood coagulation, fibrinolysis, regulation of wound healing, tissue regeneration, acute inflammatory response, and negative regulation of the immune effector process, were enriched in injured muscle tissue. This study advances the understanding of early muscle healing after muscle injury and lays a foundation for future mechanistic studies on interventions to treat muscle injury.

Human muscle pathology is associated with altered phosphoprotein profile of mitochondrial proteins in the skeletal muscle

Analysis of human muscle diseases highlights the role of mitochondrial dysfunction in the skeletal muscle. Our previous work revealed that diverse upstream events correlated with altered mitochondrial proteome in human muscle biopsies. However, several proteins showed relatively unchanged expression suggesting that post-translational modifications, mainly protein phosphorylation could influence their activity and regulate mitochondrial processes. We conducted mitochondrial phosphoprotein profiling, by proteomics approach, of healthy human skeletal muscle (n = 10) and three muscle diseases (n = 10 each): Dysferlinopathy, Polymyositis and Distal Myopathy with Rimmed Vacuoles. Healthy human muscle mitochondrial proteins displayed 253 phosphorylation sites (phosphosites), which contributed to metabolic and redox processes and mitochondrial organization etc. Electron transport chain complexes accounted for 84 phosphosites. Muscle pathologies displayed 33 hyperphosphorylated and 14 hypophorphorylated sites with only 5 common proteins, indicating varied phosphorylation profile across muscle pathologies. Molecular modelling revealed altered local structure in the phosphorylated sites of Voltage-Dependent Anion Channel 1 and complex V subunit ATP5B1. Molecular dynamics simulations in complex I subunits NDUFV1, NDUFS1 and NDUFV2 revealed that phosphorylation induced structural alterations thereby influencing electron transfer and potentially altering enzyme activity. We propose that altered phosphorylation at specific sites could regulate mitochondrial protein function in the skeletal muscle during physiological and pathological processes.

Skeletal muscle: A review of molecular structure and function, in health and disease

Decades of research in skeletal muscle physiology have provided multiscale insights into the structural and functional complexity of this important anatomical tissue, designed to accomplish the task of generating contraction, force and movement. Skeletal muscle can be viewed as a biomechanical device with various interacting components including the autonomic nerves for impulse transmission, vasculature for efficient oxygenation, and embedded regulatory and metabolic machinery for maintaining cellular homeostasis. The "omics" revolution has propelled a new era in muscle research, allowing us to discern minute details of molecular cross-talk required for effective coordination between the myriad interacting components for efficient muscle function. The objective of this review is to provide a systems-level, comprehensive mapping the molecular mechanisms underlying skeletal muscle structure and function, in health and disease. We begin this review with a focus on molecular mechanisms underlying muscle tissue development (myogenesis), with an emphasis on satellite cells and muscle regeneration. We next review the molecular structure and mechanisms underlying the many structural components of the muscle: neuromuscular junction, sarcomere, cytoskeleton, extracellular matrix, and vasculature surrounding muscle. We highlight aberrant molecular mechanisms and their possible clinical or pathophysiological relevance. We particularly emphasize the impact of environmental stressors (inflammation and oxidative stress) in contributing to muscle pathophysiology including atrophy, hypertrophy, and fibrosis. This article is categorized under: Physiology > Mammalian Physiology in Health and Disease Developmental Biology > Developmental Processes in Health and Disease Models of Systems Properties and Processes > Cellular Models.

Tryptophan Oxidation in the UQCRC1 Subunit of Mitochondrial Complex III (Ubiquinol-Cytochrome C Reductase) in a Mouse Model of Myodegeneration Causes Large Structural Changes in the Complex: A Molecular Dynamics Simulation Study

Muscle diseases display mitochondrial dysfunction and oxidative damage. Our previous study in a cardiotoxin model of myodegeneration correlated muscle damage with mitochondrial dysfunction, which in turn entailed altered mitochondrial proteome and oxidative damage of mitochondrial proteins. Proteomic identification of oxidized proteins in muscle biopsies from muscular dystrophy patients and cardiotoxin model revealed specific mitochondrial proteins to be targeted for oxidation. These included respiratory complexes which displayed oxidative modification of Trp residues in different subunits. Among these, Ubiquinol-Cytochrome C Reductase Core protein 1 (UQCRC1), a subunit of Ubiquinol-Cytochrome C Reductase Complex or Cytochrome b-c1 Complex or Respiratory Complex III displayed oxidation of Trp395, which could be correlated with the lowered activity of Complex III. We hypothesized that Trp395 oxidation might contribute to altered local conformation and overall structure of Complex III, thereby potentially leading to altered protein activity. To address this, we performed molecular dynamics simulation of Complex III (oxidized at Trp395 of UQCRC1 vs. non-oxidized control). Molecular dynamic simulation analyses revealed local structural changes in the Trp395 site. Intriguingly, oxidized Trp395 contributed to decreased plasticity of Complex III due to significant cross-talk among the subunits in the matrix-facing region and subunits in the intermembrane space, thereby leading to impaired electron flow from cytochrome C.

Soluble epoxide hydrolase inhibitor, APAU, protects dopaminergic neurons against rotenone induced neurotoxicity: Implications for Parkinson's disease

Epoxyeicosatrienoic acids (EETs), metabolites of arachidonic acid, play a crucial role in cytoprotection by attenuating oxidative stress, inflammation and apoptosis. EETs are rapidly metabolised in vivo by the soluble epoxide hydrolase (sEH). Increasing the half life of EETs by inhibiting the sEH enzyme is a novel strategy for neuroprotection. In the present study, sEH inhibitors APAU was screened in silico and further evaluated for their antiparkinson activity against rotenone (ROT) induced neurodegeneration in N27 dopaminergic cell line and Drosophila melanogaster model of Parkinson disease (PD). In the in vitro study cell viability (MTT and LDH release assay), oxidative stress parameters (total intracellular ROS, hydroperoxides, protein oxidation, lipid peroxidation, superoxide dismutase, catalase, glutathione peroxidise, glutathione reductase, glutathione, total antioxidant status, mitochondrial complex-1activity and mitochondrial membrane potential), inflammatory markers (IL-6, COX-1 and COX-2), and apoptotic markers (JNK, phospho-JNK, c-jun, phospho-c-jun, pro and active caspase-3) were assessed to study the neuroprotective effects. In vivo activity of APAU was assessed in Drosophila melanogaster by measuring survival rate, negative geotaxis, oxidative stress parameters (total intracellular ROS, hydroperoxides, glutathione levels) were measured. Dopamine and its metabolites were estimated by LC-MS/MS analysis. In the in silico study the molecule, APAU showed good binding interaction at the active site of sEH (PDB: 1VJ5). In the in vitro study, APAU significantly attenuated ROT induced changes in oxidative, pro-inflammatory and apoptotic parameters. In the in vivo study, APAU significantly attenuates ROT induced changes in survival rate, negative geotaxis, oxidative stress, dopamine and its metabolites levels (p < 0.05). Our study, therefore, concludes that the molecule APAU, has significant neuroprotection benefits against rotenone induced Parkinsonism.

A Concomitant Muscle Injury Does Not Worsen Traumatic Brain Injury Outcomes in Mice

Traumatic brain injury (TBI) often involves multitrauma in which concurrent extracranial injury occurs. We previously demonstrated that a long bone fracture exacerbates neuroinflammation and functional outcomes in mice given a TBI. Whether other forms of concomitant peripheral trauma that are common in the TBI setting, such as skeletal muscle injury, have similar effects is unknown. As such, here we developed a novel mouse multitrauma model by combining a closed-skull TBI with a cardiotoxin (CTX)-induced muscle injury to investigate whether muscle injury affects TBI outcomes. Adult male mice were assigned to four groups: sham-TBI + sham-muscle injury (SHAM); sham-TBI + CTX-muscle injury (CTX); TBI + sham-muscle injury (TBI); TBI + CTX-muscle injury (MULTI). Some mice were euthanized at 24 h post-injury to assess neuroinflammation and cerebral edema. The remaining mice underwent behavioral testing after a 30-day recovery period, and were euthanized at 35 days post-injury for post-mortem analysis. At 24 h post-injury, both TBI and MULTI mice had elevated edema, increased expression of GFAP (i.e., a marker for reactive astrocytes), and increased mRNA levels of inflammatory chemokines. There was also an effect of injury on cytokine levels at 35 days post-injury. However, the TBI and MULTI mice did not significantly differ on any of the measures assessed. These initial findings suggest that a concomitant muscle injury does not significantly affect preclinical TBI outcomes. Future studies should investigate the combination of different injury models, additional outcomes, and other post-injury time points.

Hsp60 in Skeletal Muscle Fiber Biogenesis and Homeostasis: From Physical Exercise to Skeletal Muscle Pathology

Hsp60 is a molecular chaperone classically described as a mitochondrial protein with multiple roles in health and disease, participating to the maintenance of protein homeostasis. It is well known that skeletal muscle is a complex tissue, rich in proteins, that is, subjected to continuous rearrangements, and this homeostasis is affected by many different types of stimuli and stresses. The regular exercise induces specific histological and biochemical adaptations in skeletal muscle fibers, such as hypertrophy and an increase of mitochondria activity and oxidative capacity. The current literature is lacking in information regarding Hsp60 involvement in skeletal muscle fiber biogenesis and regeneration during exercise, and in disease conditions. Here, we briefly discuss the functions of Hsp60 in skeletal muscle fibers during exercise, inflammation, and ageing. Moreover, the potential usage of Hsp60 as a marker for disease and the evaluation of novel treatment options is also discussed. However, some questions remain open, and further studies are needed to better understand Hsp60 involvement in skeletal muscle homeostasis during exercise and in pathological condition.

Drug Repurposing for Duchenne Muscular Dystrophy: The Monoamine Oxidase B Inhibitor Safinamide Ameliorates the Pathological Phenotype in mdx Mice and in Myogenic Cultures From DMD Patients

Oxidative stress and mitochondrial dysfunction play a crucial role in the pathophysiology of muscular dystrophies. We previously reported that the mitochondrial enzyme monoamine oxidase (MAO) is a relevant source of reactive oxygen species (ROS) not only in murine models of muscular dystrophy, in which it directly contributes to contractile impairment, but also in muscle cells from collagen VI-deficient patients. Here, we now assessed the efficacy of a novel MAO-B inhibitor, safinamide, using in vivo and in vitro models of Duchenne muscular dystrophy (DMD). Specifically, we found that administration of safinamide in 3-month-old mdx mice reduced myofiber damage and oxidative stress and improved muscle functionality. In vitro studies with myogenic cultures from mdx mice and DMD patients showed that even cultured dystrophic myoblasts were more susceptible to oxidative stress than matching cells from healthy donors. Indeed, upon exposure to the MAO substrate tyramine or to hydrogen peroxide, DMD muscle cells displayed a rise in ROS levels and a consequent mitochondrial depolarization. Remarkably, both phenotypes normalized when cultures were treated with safinamide. Given that safinamide is already in clinical use for neurological disorders, our findings could pave the way toward a promising translation into clinical trials for DMD patients as a classic case of drug repurposing.

Mitochondrial dysfunction in human skeletal muscle biopsies of lipid storage disorder

Mitochondria regulate the balance between lipid metabolism and storage in the skeletal muscle. Altered lipid transport, metabolism and storage influence the bioenergetics, redox status and insulin signalling, contributing to cardiac and neurological diseases. Lipid storage disorders (LSDs) are neurological disorders which entail intramuscular lipid accumulation and impaired mitochondrial bioenergetics in the skeletal muscle causing progressive myopathy with muscle weakness. However, the mitochondrial changes including molecular events associated with impaired lipid storage have not been completely understood in the human skeletal muscle. We carried out morphological and biochemical analysis of mitochondrial function in muscle biopsies of human subjects with LSDs (n = 7), compared to controls (n = 10). Routine histology, enzyme histochemistry and ultrastructural analysis indicated altered muscle cell morphology and mitochondrial structure. Protein profiling of the muscle mitochondria from LSD samples (n = 5) (vs. control, n = 5) by high-throughput mass spectrometric analysis revealed that impaired metabolic processes could contribute to mitochondrial dysfunction and ensuing myopathy in LSDs. We propose that impaired fatty acid and respiratory metabolism along with increased membrane permeability, elevated lipolysis and altered cristae entail mitochondrial dysfunction in LSDs. Some of these mechanisms were unique to LSD apart from others that were common to dystrophic and inflammatory muscle pathologies. Many differentially regulated mitochondrial proteins in LSD are linked with other human diseases, indicating that mitochondrial protection via targeted drugs could be a treatment modality in LSD and related metabolic diseases. Cover Image for this Issue: doi: 10.1111/jnc.14177.

Zc3h10 is a novel mitochondrial regulator

Mitochondria are the energy-generating hubs of the cell. In spite of considerable advances, our understanding of the factors that regulate the molecular circuits that govern mitochondrial function remains incomplete. Using a genome-wide functional screen, we identify the poorly characterized protein Zinc finger CCCH-type containing 10 (Zc3h10) as regulator of mitochondrial physiology. We show that Zc3h10 is upregulated during physiological mitochondriogenesis as it occurs during the differentiation of myoblasts into myotubes. Zc3h10 overexpression boosts mitochondrial function and promotes myoblast differentiation, while the depletion of Zc3h10 results in impaired myoblast differentiation, mitochondrial dysfunction, reduced expression of electron transport chain (ETC) subunits, and blunted TCA cycle flux. Notably, we have identified a loss-of-function mutation of Zc3h10 in humans (Tyr105 to Cys105) that is associated with increased body mass index, fat mass, fasting glucose, and triglycerides. Isolated peripheral blood mononuclear cells from individuals homozygotic for Cys105 display reduced oxygen consumption rate, diminished expression of some ETC subunits, and decreased levels of some TCA cycle metabolites, which all together derive in mitochondrial dysfunction. Taken together, our study identifies Zc3h10 as a novel mitochondrial regulator.

The influence of immunological stressors on traumatic brain injury

Traumatic brain injury (TBI) is a leading cause of death and disability worldwide, and typically involves a robust immune response. Although a great deal of preclinical research has been conducted to identify an effective treatment, all phase III clinical trials have been unsuccessful to date. These translational shortcomings are in part due to a failure to recognize and account for the heterogeneity of TBI, including how extracranial factors can influence the aftermath of TBI. For example, most preclinical studies have utilized isolated TBI models in young adult males, while clinical trials typically involve highly heterogeneous patient populations (e.g., different mechanisms of injury, a range of ages, presence of polytrauma or infection). This paper will review the current, albeit limited literature related to how TBI is affected by common concomitant immunological stressors. In particular, discussion will focus on whether extracranial trauma (i.e., polytrauma), infection, and age/immunosenescence can influence TBI pathophysiology, and thereby may result in a different brain injury than what would have occurred in an isolated TBI. It is concluded that these immunological stressors are all likely to be TBI modifiers that should be further studied and could impact translational treatment strategies.

A Futile Battle? Protein Quality Control and the Stress of Aging

There exists a phenomenon in aging research whereby early life stress can have positive impacts on longevity. The mechanisms underlying these observations suggest a robust, long-lasting induction of cellular defense mechanisms. These include the various unfolded protein responses of the endoplasmic reticulum (ER), cytosol, and mitochondria. Indeed, ectopic induction of these pathways, in the absence of stress, is sufficient to increase lifespan in organisms as diverse as yeast, worms, and flies. Here, we provide an overview of the protein quality control mechanisms that operate in the cytosol, mitochondria, and ER and discuss how they affect cellular health and viability during stress and aging.

Metabolic and vascular pattern in medial pterygoid muscle is altered by chronic stress in an animal model of hypodontia

Psychological stress is an important perpetuating, worsening and risk factor for temporomandibular disorders of muscular or articular origin. Occlusion instability, by the way, is considered a risk factor of this pathology and can be reproduced in some experimental animal models. The exact physiologic mechanism underlying these relations however, remains unclear. Our purpose was to test the hypothesis that chronic stress and unilateral exodontia induce metabolic and vascular changes in the medial pterygoid muscle of rats. Adult Wistar rats were submitted to chronic unpredictable stress and/or unilateral exodontia and their plasma and medial pterygoid muscle were removed for analysis. The parameters evaluated included plasma levels of corticosterone, metabolic activity by succinate dehydrogenase, oxidative capacity by nicotinamide adenine dinucleotide diaphorase, capillary density by laminin and alfa-CD staining and reactive oxidative species production. Chronic unpredictable stress as an isolated factor, increased oxidative metabolism, capillary density and reactive oxygen species production at medial pterygoid muscle. Conversely, exodontia has a main effect in metabolism, promoting glycolytic transformation of muscle fibers. Association of both factors induced a major glycolytic pattern in muscle and vascular changes. Our findings provide insights into the mechanisms, possibly inducing metabolic and vascular alterations on medial pterygoid muscle of rats, by which chronic stress and occlusal instabilities might be involved as risk factors in the pathophysiology of temporomandibular disorders with muscular components.

Co-expression Network Approach Reveals Functional Similarities among Diseases Affecting Human Skeletal Muscle

Diseases affecting skeletal muscle exhibit considerable heterogeneity in intensity, etiology, phenotypic manifestation and gene expression. Systems biology approaches using network theory, allows for a holistic understanding of functional similarities amongst diseases. Here we propose a co-expression based, network theoretic approach to extract functional similarities from 20 heterogeneous diseases comprising of dystrophinopathies, inflammatory myopathies, neuromuscular, and muscle metabolic diseases. Utilizing this framework we identified seven closely associated disease clusters with 20 disease pairs exhibiting significant correlation (p < 0.05). Mapping the diseases onto a human protein-protein interaction network enabled the inference of a common program of regulation underlying more than half the muscle diseases considered here and referred to as the “protein signature.” Enrichment analysis of 17 protein modules identified as part of this signature revealed a statistically non-random dysregulation of muscle bioenergetic pathways and calcium homeostasis. Further, analysis of mechanistic similarities of less explored significant disease associations [such as between amyotrophic lateral sclerosis (ALS) and cerebral palsy (CP)] using a proposed “functional module” framework revealed adaptation of the calcium signaling machinery. Integrating drug-gene information into the quantitative framework highlighted the presence of therapeutic opportunities through drug repurposing for diseases affecting the skeletal muscle.

Nanoparticles for CRISPR-Cas9 delivery

The DNA mutation that causes Duchenne muscular dystrophy in mice can be corrected, with minimal off-target effects, by gold nanoparticles carrying the CRISPR components.

Changes in Muscle Metabolism are Associated with Phenotypic Variability in Golden Retriever Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is an X-chromosome-linked disorder and the most common monogenic disease in people. Affected boys are diagnosed at a young age, become non-ambulatory by their early teens, and succumb to cardiorespiratory failure by their thirties. Despite being a monogenic condition resulting from mutations in the DMD gene, affected boys have noteworthy phenotypic variability. Efforts have identified genetic modifiers that could modify disease progression and be pharmacologic targets. Dogs affected with golden retriever muscular dystrophy (GRMD) have absent dystrophin and demonstrate phenotypic variability at the functional, histopathological, and molecular level. Our laboratory is particularly interested in muscle metabolism changes in dystrophin-deficient muscle. We identified several metabolic alterations, including myofiber type switching from fast (type II) to slow (type I), reduced glycolytic enzyme expression, reduced and morphologically abnormal mitochondria, and differential AMP-kinase phosphorylation (activation) between hypertrophied and wasted muscle. We hypothesize that muscle metabolism changes are, in part, responsible for phenotypic variability in GRMD. Pharmacological therapies aimed at modulating muscle metabolism can be tested in GRMD dogs for efficacy.

Ulk1-mediated autophagy plays an essential role in mitochondrial remodeling and functional regeneration of skeletal muscle

Autophagy is a conserved cellular process for degrading aggregate proteins and dysfunctional organelle. It is still debatable if autophagy and mitophagy (a specific process of autophagy of mitochondria) play important roles in myogenic differentiation and functional regeneration of skeletal muscle. We tested the hypothesis that autophagy is critical for functional regeneration of skeletal muscle. We first observed time-dependent increases (3- to 6-fold) of autophagy-related proteins (Atgs), including Ulk1, Beclin1, and LC3, along with reduced p62 expression during C2C12 differentiation, suggesting increased autophagy capacity and flux during myogenic differentiation. We then used cardiotoxin (Ctx) or ischemia-reperfusion (I/R) to induce muscle injury and regeneration and observed increases in Atgs between days 2 and 7 in adult skeletal muscle followed by increased autophagy flux after day 7 Since Ulk1 has been shown to be essential for mitophagy, we asked if Ulk1 is critical for functional regeneration in skeletal muscle. We subjected skeletal muscle-specific Ulk1 knockout mice (MKO) to Ctx or I/R. MKO mice had significantly impaired recovery of muscle strength and mitochondrial protein content post-Ctx or I/R. Imaging analysis showed that MKO mice have significantly attenuated recovery of mitochondrial network at 7 and 14 days post-Ctx. These findings suggest that increased autophagy protein and flux occur during muscle regeneration and Ulk1-mediated mitophagy is critical for recovery for the mitochondrial network and hence functional regeneration.

Gene co-expression network analysis of dysferlinopathy: Altered cellular processes and functional prediction of TOR1AIP1, a novel muscular dystrophy gene

Dysferlinopathy, caused by a dysferlin gene mutation, is a clinically heterogeneous autosomal recessive muscle disease characterized by progressive muscle degeneration. The dysferlin protein's functions and dysferlinopathy disease pathogenesis are not fully explored, and there is no specific treatment available that can alter the disease progression. This study uses publicly available dysferlinopathy patient microarray data to construct a gene co-expression network and investigates significant cellular pathways and their key players in dysferlinopathy pathogenesis. Extracellular matrix deposition, inflammation, mitochondrial abnormalities and protein degradation were found to be important in dysferlinopathy. Out of the hub genes, OXR1 and TIMP1 were selected through literature search as candidate genes for possible biomarker and molecular therapeutic target studies. A recently identified muscular dystrophy gene TOR1AIP1 was detected as a hub gene in dysferlinopathy. Co-expression and protein sequence feature analysis were adopted to predict TOR1AIP1's function. Our results suggest that LAP1 protein encoded by TOR1AIP1 may play a role in protein degradation possibly through transcriptional regulation in muscle tissue. These findings extend dysferlinopathy pathogenesis by presenting key genes and also suggest a novel function for a poorly characterized gene.

Forty years later: Mitochondria as therapeutic targets in muscle diseases

The hypothesis that mitochondrial dysfunction can be a general mechanism for cell death in muscle diseases is 40 years old. The key elements of the proposed pathogenetic sequence (cytosolic Ca2+ overload followed by excess mitochondrial Ca2+ uptake, functional and then structural damage of mitochondria, energy shortage, worsened elevation of cytosolic Ca2+ levels, hypercontracture of muscle fibers, cell necrosis) have been confirmed in amazing detail by subsequent work in a variety of models. The explicit implication of the hypothesis was that it "may provide the basis for a more rational treatment for some conditions even before their primary causes are known" (Wrogemann and Pena, 1976, Lancet, 1, 672-674). This prediction is being fulfilled, and the potential of mitochondria as pharmacological targets in muscle diseases may soon become a reality, particularly through inhibition of the mitochondrial permeability transition pore and its regulator cyclophilin D.

Curcumin Monoglucoside Shows Improved Bioavailability and Mitigates Rotenone Induced Neurotoxicity in Cell and Drosophila Models of Parkinson's Disease

Curcumin (CUR), a dietary polyphenol has diverse pharmacologic effects, but is limited by poor bioavailability. This is probably due to decreased solubility, cellular uptake and stability. In order to enhance its solubility and bioavailability, we synthesized the CUR bioconjugate curcumin monoglucoside (CMG) and tested its bioavailability, neuroprotective and anti-apoptotic propensity against rotenone (ROT) induced toxicity in N27 dopaminergic neuronal cells and Drosophila models. Our results elucidate that CMG showed improved bioavailability than CUR in N27 cells. Pre-treatment with CMG protected against ROT neurotoxicity and exerted antioxidant effects by replenishing cellular glutathione levels and significantly decreasing reactive species. CMG pre-treatment also restored mitochondrial complex I and IV activities inhibited by ROT. ROT-induced nuclear damage was also restored by CMG as confirmed by comet assay. CMG induced anti-apoptotic effects was substantiated by decreased phosporylation of JNK3 and c-jun, which in turn decreased the cleavage of pro-caspase 3. Q-PCR analysis of redox genes showed up-regulation of NOS2 and down-regulation of NQO1 upon ROT exposure and this was attenuated by CMG pre-treatment. Studies in the Drosophila ROT model revealed that, CMG administration showed better survival rate and locomotor activity, improved antioxidant activity and dopamine content than ROT treated group and was comparable with the CUR group. Based on these data, we surmise that CMG has improved bioavailability and offered neuroprotection comparable with CUR, against ROT-induced toxicity both in dopaminergic neuronal cell line and Drosophila models, with therapeutic implications for PD.

Development and evaluation of a simple and effective real time PCR assay for mitochondrial quantification in racing camels

Camel racing is a popular sport in the Middle East region, where the demand is high for racing camels with higher stamina and endurance. Devising a technique to measure oxidative capacity and endurance in camels should be useful. Mitochondria are highly specialized organelles involved in metabolism in all higher organisms for sustaining life and providing energy for physical functions. The ratio of mitochondrial DNA (mtDNA) to nuclear DNA (nDNA) is often used as an estimate for the metabolic status of the tissue. A greater quantity of mitochondria per unit of tissue translates into greater oxidative capacity and endurance. In this report, we describe a simple, sensitive and efficient real-time PCR assay for the quantification of blood mitochondria in racing camels. The primer sequences selected for the SYBR green-based PCR assay included mitochondrial D-loop region, mitochondrial ATP6ase gene and the nuclear β-actin gene. The assay was validated using two groups of camels comprising racing and dairy camels. The racing camels demonstrated a higher mtDNA/nDNA ratio compared with dairy camels based on the ΔΔCt values, with a higher variability among racing camels. The mean ΔΔCt values of adult and young racing camels did not vary considerably. The findings show that the present assay can be used as an evaluative tool for racing camels.

Muscle biopsies from human muscle diseases with myopathic pathology reveal common alterations in mitochondrial function

Muscle diseases are clinically and genetically heterogeneous and manifest as dystrophic, inflammatory and myopathic pathologies, among others. Our previous study on the cardiotoxin mouse model of myodegeneration and inflammation linked muscle pathology with mitochondrial damage and oxidative stress. In this study, we investigated whether human muscle diseases display mitochondrial changes. Muscle biopsies from muscle disease patients, represented by dysferlinopathy (dysfy) (dystrophic pathology; n = 43), polymyositis (PM) (inflammatory pathology; n = 24), and distal myopathy with rimmed vacuoles (DMRV) (distal myopathy; n = 31) were analyzed. Mitochondrial damage (ragged blue and COX-deficient fibers) was revealed in dysfy, PM, and DMRV cases by enzyme histochemistry (SDH and COX-SDH), electron microscopy (vacuolation and altered cristae) and biochemical assays (significantly increased ADP/ATP ratio). Proteomic analysis of muscle mitochondria from all three muscle diseases by isobaric tag for relative and absolute quantitation labeling and liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis demonstrated down-regulation of electron transport chain (ETC) complex subunits, assembly factors and Krebs cycle enzymes. Interestingly, 80 of the under-expressed proteins were common among the three pathologies. Assay of ETC and Krebs cycle enzyme activities validated the MS data. Mitochondrial proteins from muscle pathologies also displayed higher tryptophan (Trp) oxidation and the same was corroborated in the cardiotoxin model. Molecular modeling predicted Trp oxidation to alter the local structure of mitochondrial proteins. Our data highlight mitochondrial alterations in muscle pathologies, represented by morphological changes, altered mitochondrial proteome and protein oxidation, thereby establishing the role of mitochondrial damage in human muscle diseases. We investigated whether human muscle diseases display mitochondrial changes. Muscle biopsies from dysferlinopathy (Dysfy), polymyositis (PM), and distal myopathy with rimmed vacuoles (DMRV) displayed morphological and biochemical evidences of mitochondrial dysfunction. Proteomic analysis revealed down-regulation of electron transport chain (ETC) subunits, assembly factors, and tricarboxylic acid (TCA) cycle enzymes, with 80 proteins common among the three pathologies. Mitochondrial proteins from muscle pathologies also displayed higher Trp oxidation that could alter the local structure. Cover image for this issue: doi: 10.1111/jnc.13324.

Characterization of age-dependent changes in the striatum: Response to the mitochondrial toxin 3-nitropropionic acid

Neurodegenerative phenomena are associated with mitochondrial dysfunction and this could be exacerbated by aging. Age-dependence of mitochondrial response to toxins could help understand these mechanisms and evolve novel therapeutics. 3-Nitropropionic acid (3-NPA) is a mitochondrial toxin that induces neurotoxicity in the striatum via inhibition of complex II. We investigated the age-related events that contribute to 3-NPA toxicity. 3-NPA induced neuronal death, oxidative stress and altered mitochondrial structure in neuronal cells. 3-NPA injection in vivo caused motor impairment, mitochondrial dysfunction and oxidative damage with different trend in young and adult mice. To understand the age-dependent mechanisms, we carried out proteomic analysis of the striatal protein extract from young mice (control: YC vs. 3-NPA treated: YT) and adult mice (control: AC vs. 3-NPA treated: AT). Among the 3752 identified proteins, 33 differentially expressed proteins (mitochondrial, synaptic and microsomal proteins) were unique either to YT or AT. Interestingly, comparison of the proteomic profile in AC and YC indicated that 161 proteins (linked with cytoskeletal structure, neuronal development, axogenesis, protein transport, cell adhesion and synaptic function) were down-regulated in AC compared to YC. We surmise that aging contributes to the cellular and molecular architecture in the mouse striatum with implications for neurodegeneration.

Disruption of nuclear factor (erythroid-derived-2)-like 2 antioxidant signaling: a mechanism for impaired activation of stem cells and delayed regeneration of skeletal muscle

Recently we have reported that age-dependent decline in antioxidant levels accelerated apoptosis and skeletal muscle degeneration. Here, we demonstrate genetic ablation of the master cytoprotective transcription factor, nuclear factor (erythroid-derived-2)-like 2 (Nrf2), aggravates cardiotoxin (CTX)-induced tibialis anterior (TA) muscle damage. Disruption of Nrf2 signaling sustained the CTX-induced burden of reactive oxygen species together with compromised expression of antioxidant genes and proteins. Transcript/protein expression of phenotypic markers of muscle differentiation, namely paired box 7 (satellite cell) and early myogenic differentiation and terminal differentiation (myogenin and myosin heavy chain 2) were increased on d 2 and 4 postinjury but later returned to baseline levels on d 8 and 15 in wild-type (WT) mice. In contrast, these responses were persistently augmented in Nrf2-null mice suggesting that regulation of the regeneration-related signaling mechanisms require Nrf2 for normal functioning. Furthermore, Nrf2-null mice displayed slower regeneration marked by dysregulation of embryonic myosin heavy chain temporal expression. Histologic observations illustrated that Nrf2-null mice displayed smaller, immature TA muscle fibers compared with WT counterparts on d 15 after CTX injury. Improvement in TA muscle morphology and gain in muscle mass evident in the WT mice was not noticeable in the Nrf2-null animals. Taken together these data show that the satellite cell activation, proliferation, and differentiation requires a functional Nrf2 system for effective healing following injury.-Shelar, S. B., Narasimhan, M., Shanmugam, G., Litovsky, S. H., Gounder, S. S., Karan, G., Arulvasu, C., Kensler, T. W., Hoidal, J. R., Darley-Usmar, V. M., Rajasekaran, N. S. Disruption of nuclear factor (erythroid-derived-2)-like 2 antioxidant signaling: a mechanism for impaired activation of stem cells and delayed regeneration of skeletal muscle.

The transcriptional repressor Sum1p counteracts Sir2p in regulation of the actin cytoskeleton, mitochondrial quality control and replicative lifespan in Saccharomyces cerevisiae

Increasing the stability or dynamics of the actin cytoskeleton can extend lifespan in C. elegans and S. cerevisiae. Actin cables of budding yeast, bundles of actin filaments that mediate cargo transport, affect lifespan control through effects on mitochondrial quality control. Sir2p, the founding member of the Sirtuin family of lifespan regulators, also affects actin cable dynamics, assembly, and function in mitochondrial quality control. Here, we obtained evidence for novel interactions between Sir2p and Sum1p, a transcriptional repressor that was originally identified through mutations that genetically suppress sir2∆ phenotypes unrelated to lifespan. We find that deletion of SUM1 in wild-type cells results in increased mitochondrial function and actin cable abundance. Furthermore, deletion of SUM1 suppresses defects in actin cables and mitochondria of sir2∆ yeast, and extends the replicative lifespan and cellular health span of sir2∆ cells. Thus, Sum1p suppresses Sir2p function in control of specific aging determinants and lifespan in budding yeast.

Circulating Biomarkers for Duchenne Muscular Dystrophy

Duchenne muscular dystrophy is the most common form of muscular dystrophy. Genetic and biochemical research over the years has characterized the cause, pathophysiology and development of the disease providing several potential therapeutic targets and/or biomarkers. High throughput - omic technologies have provided a comprehensive understanding of the changes occurring in dystrophic muscles. Murine and canine animal models have been a valuable source to profile muscles and body fluids, thus providing candidate biomarkers that can be evaluated in patients. This review will illustrate known circulating biomarkers that could track disease progression and response to therapy in patients affected by Duchenne muscular dystrophy. We present an overview of the transcriptomic, proteomic, metabolomics and lipidomic biomarkers described in literature. We show how studies in muscle tissue have led to the identification of serum and urine biomarkers and we highlight the importance of evaluating biomarkers as possible surrogate endpoints to facilitate regulatory processes for new medicinal products.