Glutathione peroxidase 3, a new retinoid target gene, is crucial for human skeletal muscle precursor cell survival

Pet Wellness and Vitamin A: A Narrative Overview

The health of companion animals, particularly dogs and cats, is significantly influenced by nutrition, with vitamins playing a crucial role. Vitamin A, in particular, is indispensable, with diverse roles ranging from vision to immune modulation and reproduction. Despite its importance, the metabolism and dietary requirements of vitamin A in companion animals remain complex and not fully understood. This review provides a comprehensive overview of the historical perspective, the digestion, the metabolism, the physiological roles, the deficiency, the excess, and the interactions with other micronutrients of vitamin A in companion animals. Additionally, it highlights future research directions and gaps in our understanding. Insights into the metabolism of vitamin A in companion animals, personalized nutrition strategies based on genetic variability, longitudinal studies tracking the status of vitamin A, and investigations into its immunomodulatory effects are crucial for optimizing pet health and wellness. Furthermore, understanding the stability and bioavailability of vitamin A in pet food formulations is essential for ensuring the provision of adequate micronutrients. Overall, this review underscores the importance of vitamin A in companion animal nutrition and the need for further research to enhance our understanding and to optimize dietary recommendations for pet health and well-being.

Current Understanding of Human Polymorphism in Selenoprotein Genes: A Review of Its Significance as a Risk Biomarker

Selenium has been proven to influence several biological functions, showing to be an essential micronutrient. The functional studies demonstrated the benefits of a balanced selenium diet and how its deficiency is associated with diverse diseases, especially cancer and viral diseases. Selenium is an antioxidant, protecting the cells from damage, enhancing the immune system response, preventing cardiovascular diseases, and decreasing inflammation. Selenium can be found in its inorganic and organic forms, and its main form in the cells is the selenocysteine incorporated into selenoproteins. Twenty-five selenoproteins are currently known in the human genome: glutathione peroxidases, iodothyronine deiodinases, thioredoxin reductases, selenophosphate synthetase, and other selenoproteins. These proteins lead to the transport of selenium in the tissues, protect against oxidative damage, contribute to the stress of the endoplasmic reticulum, and control inflammation. Due to these functions, there has been growing interest in the influence of polymorphisms in selenoproteins in the last two decades. Selenoproteins' gene polymorphisms may influence protein structure and selenium concentration in plasma and its absorption and even impact the development and progression of certain diseases. This review aims to elucidate the role of selenoproteins and understand how their gene polymorphisms can influence the balance of physiological conditions. In this polymorphism review, we focused on the PubMed database, with only articles published in English between 2003 and 2023. The keywords used were "selenoprotein" and "polymorphism". Articles that did not approach the theme subject were excluded. Selenium and selenoproteins still have a long way to go in molecular studies, and several works demonstrated the importance of their polymorphisms as a risk biomarker for some diseases, especially cardiovascular and thyroid diseases, diabetes, and cancer.

scTour: a deep learning architecture for robust inference and accurate prediction of cellular dynamics

Despite the continued efforts, a batch-insensitive tool that can both infer and predict the developmental dynamics using single-cell genomics is lacking. Here, I present scTour, a novel deep learning architecture to perform robust inference and accurate prediction of cellular dynamics with minimal influence from batch effects. For inference, scTour simultaneously estimates the developmental pseudotime, delineates the vector field, and maps the transcriptomic latent space under a single, integrated framework. For prediction, scTour precisely reconstructs the underlying dynamics of unseen cellular states or a new independent dataset. scTour's functionalities are demonstrated in a variety of biological processes from 19 datasets.

Loss of transcriptional heterogeneity in aged human muscle stem cells

Age-related loss of muscle mass and function negatively impacts healthspan and lifespan. Satellite cells function as muscle stem cells in muscle maintenance and regeneration by self-renewal, activation, proliferation and differentiation. These processes are perturbed in aging at the stem cell population level, contributing to muscle loss. However, how representation of subpopulations within the human satellite cell pool change during aging remains poorly understood. We previously reported a comprehensive baseline of human satellite cell (Hu-MuSCs) transcriptional activity in muscle homeostasis describing functional heterogenous human satellite cell subpopulations such as CAV1+ Hu-MUSCs. Here, we sequenced additional satellite cells from new healthy donors and performed extended transcriptomic analyses with regard to aging. We found an age-related loss of global transcriptomic heterogeneity and identified new markers (CAV1, CXCL14, GPX3) along with previously described ones (FN1, ITGB1, SPRY1) that are altered during aging in human satellite cells. These findings describe new transcriptomic changes that occur during aging in human satellite cells and provide a foundation for understanding functional impact.

Single cell analysis reveals satellite cell heterogeneity for proinflammatory chemokine expression

Background: The expression of proinflammatory signals at the site of muscle injury are essential for efficient tissue repair and their dysregulation can lead to inflammatory myopathies. Macrophages, neutrophils, and fibroadipogenic progenitor cells residing in the muscle are significant sources of proinflammatory cytokines and chemokines. However, the inducibility of the myogenic satellite cell population and their contribution to proinflammatory signaling is less understood.

Methods: Mouse satellite cells were isolated and exposed to lipopolysaccharide (LPS) to mimic sterile skeletal muscle injury and changes in the expression of proinflammatory genes was examined by RT-qPCR and single cell RNA sequencing. Expression patterns were validated in skeletal muscle injured with cardiotoxin by RT-qPCR and immunofluorescence.

Results: Satellite cells in culture were able to express Tnfa, Ccl2, and Il6, within 2 h of treatment with LPS. Single cell RNA-Seq revealed seven cell clusters representing the continuum from activation to differentiation. LPS treatment led to a heterogeneous pattern of induction of C-C and C-X-C chemokines (e.g., Ccl2, Ccl5, and Cxcl0) and cytokines (e.g., Tgfb1, Bmp2, Il18, and Il33) associated with innate immune cell recruitment and satellite cell proliferation. One cell cluster was enriched for expression of the antiviral interferon pathway genes under control conditions and LPS treatment. Activation of this pathway in satellite cells was also detectable at the site of cardiotoxin induced muscle injury.

Conclusion: These data demonstrate that satellite cells respond to inflammatory signals and secrete chemokines and cytokines. Further, we identified a previously unrecognized subset of satellite cells that may act as sensors for muscle infection or injury using the antiviral interferon pathway.

Decline of regenerative potential of old muscle stem cells: contribution to muscle aging

Muscle stem cells (MuSCs) are required for life-long muscle regeneration. In general, aging has been linked to a decline in the numbers and the regenerative potential of MuSCs. Muscle regeneration depends on the proper functioning of MuSCs, which is itself dependent on intricate interactions with its niche components. Aging is associated with both cell-intrinsic and niche-mediated changes, which can be the result of transcriptional, posttranscriptional, or posttranslational alterations in MuSCs or in the components of their niche. The interplay between cell intrinsic alterations in MuSCs and changes in the stem cell niche environment during aging and its impact on the number and the function of MuSCs is an important emerging area of research. In this review, we discuss whether the decline in the regenerative potential of MuSCs with age is the cause or the consequence of aging skeletal muscle. Understanding the effect of aging on MuSCs and the individual components of their niche is critical to develop effective therapeutic approaches to diminish or reverse the age-related defects in muscle regeneration.

Transcriptional reprogramming of skeletal muscle stem cells by the niche environment

Adult stem cells are indispensable for tissue regeneration, but their function declines with age. The niche environment in which the stem cells reside plays a critical role in their function. However, quantification of the niche effect on stem cell function is lacking. Using muscle stem cells (MuSC) as a model, we show that aging leads to a significant transcriptomic shift in their subpopulations accompanied by locus-specific gain and loss of chromatin accessibility and DNA methylation. By combining in vivo MuSC transplantation and computational methods, we show that the expression of approximately half of all age-altered genes in MuSCs from aged male mice can be restored by exposure to a young niche environment. While there is a correlation between gene reversibility and epigenetic alterations, restoration of gene expression occurs primarily at the level of transcription. The stem cell niche environment therefore represents an important therapeutic target to enhance tissue regeneration in aging.

Increased expression of glutathione peroxidase 3 prevents tendinopathy by suppressing oxidative stress

Tendinopathy, a degenerative disease, is characterized by pain, loss of tendon strength, or rupture. Previous studies have identified multiple risk factors for tendinopathy, including aging and fluoroquinolone use; however, its therapeutic target remains unclear. We analyzed self-reported adverse events and the US commercial claims data and found that the short-term use of dexamethasone prevented both fluoroquinolone-induced and age-related tendinopathy. Rat tendons treated systemically with fluoroquinolone exhibited mechanical fragility, histological change, and DNA damage; co-treatment with dexamethasone attenuated these effects and increased the expression of the antioxidant enzyme glutathione peroxidase 3 (GPX3), as revealed via RNA-sequencing. The primary role of GPX3 was validated in primary cultured rat tenocytes treated with fluoroquinolone or H₂O₂, which accelerates senescence, in combination with dexamethasone or viral overexpression of GPX3. These results suggest that dexamethasone prevents tendinopathy by suppressing oxidative stress through the upregulation of GPX3. This steroid-free approach for upregulation or activation of GPX3 can serve as a novel therapeutic strategy for tendinopathy.

GPX2 Gene Affects Feed Efficiency of Pigs by Inhibiting Fat Deposition and Promoting Muscle Development

GPX2 has been recognized as a potential candidate gene for feed efficiency in pigs. This article aimed to elucidate polymorphism of GPX2 associated with feed efficiency and its related molecular mechanism. In this study, seven single nucleotide polymorphisms (SNP) of GPX2 were found among 383 Duroc pigs. In addition, seven SNPs and ALGA0043483 (PorcineSNP60 BeadChip data in 600 Duroc pigs), which are near the GPX2 gene, were identified in one haplotypes block. Furthermore, associated studies showed that the genotype of GPX2 has significant association with weaning weight and 100 kg BF in Duroc pigs. In addition, the AG had no effect when the backfat became thinner, and the FCR and RFI traits had a tendency to decrease in the G3 + TT combination genotype, accompanied by an increase of GPX2 expression in backfat and muscle tissues. At the cellular level, the adipocyte proliferation and ability of adipogenic differentiation were reduced, and the lipid degradation increased in 3T3-L1 when there was overexpression of GPX2. In contrast, overexpression of the GPX2 gene can promote the muscle cell proliferation and myogenic differentiation in C2C12 cells. In other words, GPX2 has the effect of reducing fat deposition and promoting muscle development, and it is a candidate gene for backfat and feed efficiency.

Selenoprotein: Potential Player in Redox Regulation in Chlamydomonas reinhardtii

Selenium (Se) is an essential micro-element for many organisms, including Chlamydomonas reinhardtii, and is required in trace amounts. It is obtained from the 21st amino acid selenocysteine (Sec, U), genetically encoded by the UGA codon. Proteins containing Sec are known as selenoproteins. In eukaryotes, selenoproteins are present in animals and algae, whereas fungi and higher plants lack them. The human genome contains 25 selenoproteins, most of which are involved in antioxidant defense activity, redox regulation, and redox signaling. In algae, 42 selenoprotein families were identified using various bioinformatics approaches, out of which C. reinhardtii is known to have 10 selenoprotein genes. However, the role of selenoproteins in Chlamydomonas is yet to be reported. Chlamydomonas selenoproteins contain conserved domains such as CVNVGC and GCUG, in the case of thioredoxin reductase, and CXXU in other selenoproteins. Interestingly, Sec amino acid residue is present in a catalytically active domain in Chlamydomonas selenoproteins, similar to human selenoproteins. Based on catalytical active sites and conserved domains present in Chlamydomonas selenoproteins, we suggest that Chlamydomonas selenoproteins could have a role in redox regulation and defense by acting as antioxidants in various physiological conditions.

Application of ATAC-Seq for genome-wide analysis of the chromatin state at single myofiber resolution

Myofibers are the main components of skeletal muscle, which is the largest tissue in the body. Myofibers are highly adaptive and can be altered under different biological and disease conditions. Therefore, transcriptional and epigenetic studies on myofibers are crucial to discover how chromatin alterations occur in the skeletal muscle under different conditions. However, due to the heterogenous nature of skeletal muscle, studying myofibers in isolation proves to be a challenging task. Single-cell sequencing has permitted the study of the epigenome of isolated myonuclei. While this provides sequencing with high dimensionality, the sequencing depth is lacking, which makes comparisons between different biological conditions difficult. Here, we report the first implementation of single myofiber ATAC-Seq, which allows for the sequencing of an individual myofiber at a depth sufficient for peak calling and for comparative analysis of chromatin accessibility under various physiological and disease conditions. Application of this technique revealed significant differences in chromatin accessibility between resting and regenerating myofibers, as well as between myofibers from a mouse model of Duchenne Muscular Dystrophy (mdx) and wild-type (WT) counterparts. This technique can lead to a wide application in the identification of chromatin regulatory elements and epigenetic mechanisms in muscle fibers during development and in muscle-wasting diseases.

cDNA Characterization and Expression of Selenium-Dependent CqGPx3 Isoforms in the Crayfish Cherax quadricarinatus under High Temperature and Hypoxia

Glutathione peroxidase 3 (GPx3) is the only extracellular selenoprotein (Sel) that enzymatically reduces H2O2 to H2O and O2. Two GPx3 (CqGPx3) cDNAs were characterized from crayfish Cherax quadricarinatus. The nerve cord CqGPx3a isoform encodes for a preprotein containing an N-terminal signal peptide of 32 amino acid residues, with the mature Sel region of 192 residues and a dispensable phosphorylation domain of 36 residues. In contrast, the pereiopods CqGPx3b codes for a precursor protein with 19 residues in the N-terminal signal peptide, then the mature 184 amino acid residues protein and finally a Pro-rich peptide of 42 residues. CqGPx3 are expressed in cerebral ganglia, pereiopods and nerve cord. CqGPx3a is expressed mainly in cerebral ganglia, antennulae and nerve cord, while CqGPx3b was detected mainly in pereiopods. CqGPx3a expression increases with high temperature and hypoxia; meanwhile, CqGPx3b is not affected. We report the presence and differential expression of GPx3 isoforms in crustacean tissues in normal conditions and under stress for high temperature and hypoxia. The two isoforms are tissue specific and condition specific, which could indicate an important role of CqGPx3a in the central nervous system and CqGPx3b in exposed tissues, both involved in different responses to environmental stressors.

A Bioassay-Guided Fractionation of Rosemary Leaf Extract Identifies Carnosol as a Major Hypertrophy Inducer in Human Skeletal Muscle Cells

A good quality of life requires maintaining adequate skeletal muscle mass and strength, but therapeutic agents are lacking for this. We developed a bioassay-guided fractionation approach to identify molecules with hypertrophy-promoting effect in human skeletal muscle cells. We found that extracts from rosemary leaves induce muscle cell hypertrophy. By bioassay-guided purification we identified the phenolic diterpene carnosol as the compound responsible for the hypertrophy-promoting activity of rosemary leaf extracts. We then evaluated the impact of carnosol on the different signaling pathways involved in the control of muscle cell size. We found that activation of the NRF2 signaling pathway by carnosol is not sufficient to mediate its hypertrophy-promoting effect. Moreover, carnosol inhibits the expression of the ubiquitin ligase E3 Muscle RING Finger protein-1 that plays an important role in muscle remodeling, but has no effect on the protein synthesis pathway controlled by the protein kinase B/mechanistic target of rapamycin pathway. By measuring the chymotrypsin-like activity of the proteasome, we found that proteasome activity was significantly decreased by carnosol and Muscle RING Finger 1 inactivation. These results strongly suggest that carnosol can induce skeletal muscle hypertrophy by repressing the ubiquitin-proteasome system-dependent protein degradation pathway through inhibition of the E3 ubiquitin ligase Muscle RING Finger protein-1.

Ontogeny of Carbon Monoxide-Related Gene Expression in a Deep-Diving Marine Mammal

Marine mammals such as northern elephant seals (NES) routinely experience hypoxemia and ischemia-reperfusion events to many tissues during deep dives with no apparent adverse effects. Adaptations to diving include increased antioxidants and elevated oxygen storage capacity associated with high hemoprotein content in blood and muscle. The natural turnover of heme by heme oxygenase enzymes (encoded by HMOX1 and HMOX2) produces endogenous carbon monoxide (CO), which is present at high levels in NES blood and has been shown to have cytoprotective effects in laboratory systems exposed to hypoxia. To understand how pathways associated with endogenous CO production and signaling change across ontogeny in diving mammals, we measured muscle CO and baseline expression of 17 CO-related genes in skeletal muscle and whole blood of three age classes of NES. Muscle CO levels approached those of animals exposed to high exogenous CO, increased with age, and were significantly correlated with gene expression levels. Muscle expression of genes associated with CO production and antioxidant defenses (HMOX1, BVR, GPX3, PRDX1) increased with age and was highest in adult females, while that of genes associated with protection from lipid peroxidation (GPX4, PRDX6, PRDX1, SIRT1) was highest in adult males. In contrast, muscle expression of mitochondrial biogenesis regulators (PGC1A, ESRRA, ESRRG) was highest in pups, while genes associated with inflammation (HMOX2, NRF2, IL1B) did not vary with age or sex. Blood expression of genes involved in regulation of inflammation (IL1B, NRF2, BVR, IL10) was highest in pups, while HMOX1, HMOX2 and pro-inflammatory markers (TLR4, CCL4, PRDX1, TNFA) did not vary with age. We propose that ontogenetic upregulation of baseline HMOX1 expression in skeletal muscle of NES may, in part, underlie increases in CO levels and expression of genes encoding antioxidant enzymes. HMOX2, in turn, may play a role in regulating inflammation related to ischemia and reperfusion in muscle and circulating immune cells. Our data suggest putative ontogenetic mechanisms that may enable phocid pups to transition to a deep-diving lifestyle, including high baseline expression of genes associated with mitochondrial biogenesis and immune system activation during postnatal development and increased expression of genes associated with protection from lipid peroxidation in adulthood.

Synthetic Retinoids Beyond Cancer Therapy

While the uses of retinoids for cancer treatment continue to evolve, this review focuses on other therapeutic areas in which retinoids [retinol (vitamin A), all-trans retinoic acid (RA), and synthetic retinoic acid receptor (RAR)α-, β-, and γ-selective agonists] are being used and on promising new research that suggests additional uses for retinoids for the treatment of disorders of the kidneys, skeletal muscles, heart, pancreas, liver, nervous system, skin, and other organs. The most mature area, in terms of US Food and Drug Administration-approved, RAR-selective agonists, is for treatment of various skin diseases. Synthetic retinoid agonists have major advantages over endogenous RAR agonists such as RA. Because they act through a specific RAR, side effects may be minimized, and synthetic retinoids often have better pharmaceutical properties than does RA. Based on our increasing knowledge of the multiple roles of retinoids in development, epigenetic regulation, and tissue repair, other exciting therapeutic areas are emerging. Expected final online publication date for the Annual Review of Pharmacology and Toxicology, Volume 62 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Redox Homeostasis in Muscular Dystrophies

In recent years, growing evidence has suggested a prominent role of oxidative stress in the pathophysiology of several early- and adult-onset muscle disorders, although effective antioxidant treatments are still lacking. Oxidative stress causes cell damage by affecting protein function, membrane structure, lipid metabolism, and DNA integrity, thus interfering with skeletal muscle homeostasis and functionality. Some features related to oxidative stress, such as chronic inflammation, defective regeneration, and mitochondrial damage are shared among most muscular dystrophies, and Nrf2 has been shown to be a central player in antagonizing redox imbalance in several of these disorders. However, the exact mechanisms leading to overproduction of reactive oxygen species and deregulation in the cellular antioxidants system seem to be, to a large extent, disease-specific, and the clarification of these mechanisms in vivo in humans is the cornerstone for the development of targeted antioxidant therapies, which will require testing in appropriately designed clinical trials.

Analysis of genes regulated by DUX4 via oxidative stress reveals potential therapeutic targets for treatment of facioscapulohumeral dystrophy

Muscles of patients with facioscapulohumeral dystrophy (FSHD) are characterized by sporadic DUX4 expression and oxidative stress which is at least partially induced by DUX4 protein. Nevertheless, targeting oxidative stress with antioxidants has a limited impact on FSHD patients, and the exact role of oxidative stress in the pathology of FSHD, as well as its interplay with the DUX4 expression, remain unclear. Here we set up a screen for genes that are upregulated by DUX4 via oxidative stress with the aim to target these genes rather than the oxidative stress itself. Immortalized human myoblasts expressing DUX4 (MB135-DUX4) have an increased level of reactive oxygen species (ROS) and exhibit differentiation defects which can be reduced by treating the cells with classic (Tempol) or mitochondria-targeted antioxidants (SkQ1). The transcriptome analysis of antioxidant-treated MB135 and MB135-DUX4 myoblasts allowed us to identify 200 genes with expression deregulated by DUX4 but normalized upon antioxidant treatment. Several of these genes, including PITX1, have been already associated with FSHD and/or muscle differentiation. We confirmed that PITX1 was indeed deregulated in MB135-DUX4 cells and primary FSHD myoblasts and revealed a redox component in PITX1 regulation. PITX1 silencing partially reversed the differentiation defects of MB135-DUX4 myoblasts. Our approach can be used to identify and target redox-dependent genes involved in human diseases.

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Double homeobox transcription factor DUX4 misregulates hundreds of genes and induces oxidative stress in human myoblasts.

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ROS, notably those of mitochondrial origin, contribute to the differentiation defects in myoblasts expressing DUX4.

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A subset of genes is deregulated by DUX4 indirectly, via oxidative stress.

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A strategy to identify the genes deregulated by DUX4 via oxidative stress was developed.

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PITX1 is deregulated by DUX4 via oxidative stress and can be targeted to improve myogenesis in DUX4-expressing myoblasts.

Dystrophin Deficiency Causes Progressive Depletion of Cardiovascular Progenitor Cells in the Heart

Duchenne muscular dystrophy (DMD) is a devastating condition shortening the lifespan of young men. DMD patients suffer from age-related dilated cardiomyopathy (DCM) that leads to heart failure. Several molecular mechanisms leading to cardiomyocyte death in DMD have been described. However, the pathological progression of DMD-associated DCM remains unclear. In skeletal muscle, a dramatic decrease in stem cells, so-called satellite cells, has been shown in DMD patients. Whether similar dysfunction occurs with cardiac muscle cardiovascular progenitor cells (CVPCs) in DMD remains to be explored. We hypothesized that the number of CVPCs decreases in the dystrophin-deficient heart with age and disease state, contributing to DCM progression. We used the dystrophin-deficient mouse model (mdx) to investigate age-dependent CVPC properties. Using quantitative PCR, flow cytometry, speckle tracking echocardiography, and immunofluorescence, we revealed that young mdx mice exhibit elevated CVPCs. We observed a rapid age-related CVPC depletion, coinciding with the progressive onset of cardiac dysfunction. Moreover, mdx CVPCs displayed increased DNA damage, suggesting impaired cardiac muscle homeostasis. Overall, our results identify the early recruitment of CVPCs in dystrophic hearts and their fast depletion with ageing. This latter depletion may participate in the fibrosis development and the acceleration onset of the cardiomyopathy.

Identification of a Sesquiterpene Lactone from Arctium lappa Leaves with Antioxidant Activity in Primary Human Muscle Cells

Many pathologies affecting muscles (muscular dystrophies, sarcopenia, cachexia, renal insufficiency, obesity, diabetes type 2, etc.) are now clearly linked to mechanisms involving oxidative stress. In this context, there is a growing interest in exploring plants to find new natural antioxidants to prevent the appearance and the development of these muscle disorders. In this study, we investigated the antioxidant properties of Arctium lappa leaves in a model of primary human muscle cells exposed to H₂O₂ oxidative stress. We identified using bioassay-guided purification, onopordopicrin, a sesquiterpene lactone as the main molecule responsible for the antioxidant activity of A. lappa leaf extract. According to our findings, onopordopicrin inhibited the H₂O₂-mediated loss of muscle cell viability, by limiting the production of free radicals and abolishing DNA cellular damages. Moreover, we showed that onopordopicrin promoted the expression of the nuclear factor-erythroid-2-related factor 2 (Nrf2) downstream target protein heme oxygenase-1 (HO-1) in muscle cells. By using siRNA, we demonstrated that the inhibition of the expression of Nrf2 reduced the protective effect of onopordopicrin, indicating that the activation of the Nrf2/HO-1 signaling pathway mediates the antioxidant effect of onopordopicrin in primary human muscle cells. Therefore, our results suggest that onopordopicrin may be a potential therapeutic molecule to fight against oxidative stress in pathological specific muscle disorders.

Regulatory Phenomena in the Glutathione Peroxidase Superfamily

Significance: The selenium-containing Glutathione peroxidases (GPxs)1-4 protect against oxidative challenge, inhibit inflammation and oxidant-induced regulated cell death. Recent Advances: GPx1 and GPx4 dampen phosphorylation cascades predominantly via prevention of inactivation of phosphatases by H₂O₂ or lipid hydroperoxides. GPx2 regulates the balance between regeneration and apoptotic cell shedding in the intestine. It inhibits inflammation-induced carcinogenesis in the gut but promotes growth of established cancers. GPx3 deficiency facilitates platelet aggregation likely via disinhibition of thromboxane biosynthesis. It is also considered a tumor suppressor. GPx4 is expressed in three different forms. The cytosolic form proved to inhibit interleukin-1-driven nuclear factor κB activation and leukotriene biosynthesis. Moreover, it is a key regulator of ferroptosis, because it reduces hydroperoxy groups of complex lipids and silences lipoxygenases. By alternate substrate use, the nuclear form contributes to chromatin compaction. Mitochondrial GPx4 forms the mitochondrial sheath of spermatozoa and, thus, guarantees male fertility. Out of the less characterized GPxs, the cysteine-containing GPx7 and GPx8 are unique in contributing to oxidative protein folding in the endoplasmic reticulum by reacting with protein isomerase as an alternate substrate. A yeast 2-Cysteine glutathione peroxidase equipped with CP and CR was reported to sense H₂O₂ for inducing an adaptive response. Critical Issues: Most of the findings compiled are derived from tissue culture and/or animal studies only. Their impact on human physiology is sometimes questionable. Future Directions: The expression of individual GPxs and GPx-dependent regulatory phenomena are to be further investigated, in particular in respect to human health.

Lim K, Jaiswal JK, Chen YW. Membrane Repair Deficit in Facioscapulohumeral Muscular Dystrophy

Deficits in plasma membrane repair have been identified in dysferlinopathy and Duchenne Muscular Dystrophy, and contribute to progressive myopathy. Although Facioscapulohumeral Muscular Dystrophy (FSHD) shares clinicopathological features with these muscular dystrophies, it is unknown if FSHD is characterized by plasma membrane repair deficits. Therefore, we exposed immortalized human FSHD myoblasts, immortalized myoblasts from unaffected siblings, and myofibers from a murine model of FSHD (FLExDUX4) to focal, pulsed laser ablation of the sarcolemma. Repair kinetics and success were determined from the accumulation of intracellular FM1-43 dye post-injury. We subsequently treated FSHD myoblasts with a DUX4-targeting antisense oligonucleotide (AON) to reduce DUX4 expression, and with the antioxidant Trolox to determine the role of DUX4 expression and oxidative stress in membrane repair. Compared to unaffected myoblasts, FSHD myoblasts demonstrate poor repair and a greater percentage of cells that failed to repair, which was mitigated by AON and Trolox treatments. Similar repair deficits were identified in FLExDUX4 myofibers. This is the first study to identify plasma membrane repair deficits in myoblasts from individuals with FSHD, and in myofibers from a murine model of FSHD. Our results suggest that DUX4 expression and oxidative stress may be important targets for future membrane-repair therapies.

Aldehyde dehydrogenases contribute to skeletal muscle homeostasis in healthy, aging, and Duchenne muscular dystrophy patients

BACKGROUND

Aldehyde dehydrogenases (ALDHs) are key players in cell survival, protection, and differentiation via the metabolism and detoxification of aldehydes. ALDH activity is also a marker of stem cells. The skeletal muscle contains populations of ALDH-positive cells amenable to use in cell therapy, whose distribution, persistence in aging, and modifications in myopathic context have not been investigated yet.

METHODS

The Aldefluor® (ALDEF) reagent was used to assess the ALDH activity of muscle cell populations, whose phenotypic characterizations were deepened by flow cytometry. The nature of ALDH isoenzymes expressed by the muscle cell populations was identified in complementary ways by flow cytometry, immunohistology, and real-time PCR ex vivo and in vitro. These populations were compared in healthy, aging, or Duchenne muscular dystrophy (DMD) patients, healthy non-human primates, and Golden Retriever dogs (healthy vs. muscular dystrophic model, Golden retriever muscular dystrophy [GRMD]).

RESULTS

ALDEF⁺ cells persisted through muscle aging in humans and were equally represented in several anatomical localizations in healthy non-human primates. ALDEF⁺ cells were increased in dystrophic individuals in humans (nine patients with DMD vs. five controls: 14.9 ± 1.63% vs. 3.6 ± 0.39%, P = 0.0002) and dogs (three GRMD dogs vs. three controls: 10.9 ± 2.54% vs. 3.7 ± 0.45%, P = 0.049). In DMD patients, such increase was due to the adipogenic ALDEF⁺ /CD34⁺ populations (11.74 ± 1.5 vs. 2.8 ± 0.4, P = 0.0003), while in GRMD dogs, it was due to the myogenic ALDEF⁺ /CD34^- cells (3.6 ± 0.6% vs. 1.03 ± 0.23%, P = 0.0165). Phenotypic characterization associated the ALDEF⁺ /CD34^- cells with CD9, CD36, CD49a, CD49c, CD49f, CD106, CD146, and CD184, some being associated with myogenic capacities. Cytological and histological analyses distinguished several ALDH isoenzymes (ALDH1A1, 1A2, 1A3, 1B1, 1L1, 2, 3A1, 3A2, 3B1, 3B2, 4A1, 7A1, 8A1, and 9A1) expressed by different cell populations in the skeletal muscle tissue belonging to multinucleated fibres, or myogenic, endothelial, interstitial, and neural lineages, designing them as potential new markers of cell type or of metabolic activity. Important modifications were noted in isoenzyme expression between healthy and DMD muscle tissues. The level of gene expression of some isoenzymes (ALDH1A1, 1A3, 1B1, 2, 3A2, 7A1, 8A1, and 9A1) suggested their specific involvement in muscle stability or regeneration in situ or in vitro.

CONCLUSIONS

This study unveils the importance of the ALDH family of isoenzymes in the skeletal muscle physiology and homeostasis, suggesting their roles in tissue remodelling in the context of muscular dystrophies.

AIMTOR, a BRET biosensor for live imaging, reveals subcellular mTOR signaling and dysfunctions

Background

mTOR signaling is an essential nutrient and energetic sensing pathway. Here we describe AIMTOR, a sensitive genetically encoded BRET (Bioluminescent Resonance Energy Transfer) biosensor to study mTOR activity in living cells.

Results

As a proof of principle, we show in both cell lines and primary cell cultures that AIMTOR BRET intensities are modified by mTOR activity changes induced by specific inhibitors and activators of mTORC1 including amino acids and insulin. We further engineered several versions of AIMTOR enabling subcellular-specific assessment of mTOR activities. We then used AIMTOR to decipher mTOR signaling in physio-pathological conditions. First, we show that mTORC1 activity increases during muscle cell differentiation and in response to leucine stimulation in different subcellular compartments such as the cytosol and at the surface of the lysosome, the nucleus, and near the mitochondria. Second, in hippocampal neurons, we found that the enhancement of neuronal activity increases mTOR signaling. AIMTOR further reveals mTOR-signaling dysfunctions in neurons from mouse models of autism spectrum disorder.

Conclusions

Altogether, our results demonstrate that AIMTOR is a sensitive and specific tool to investigate mTOR-signaling dynamics in living cells and phenotype mTORopathies.

Creatine Phosphokinase Values during Low Starting Dose Isotretinoin Therapy

BACKGROUND

The value of creatine phosphokinase (CPK) monitoring during isotretinoin therapy is still a matter of debate because of the rarity of muscular and kidney damage in this setting. The aim of the study was to investigate the incidence of CPK elevation during a low starting dose isotretinoin regimen and to discuss the clinical approach to patients with increased CPK.

METHODS

We reviewed the records of the acne patients from 2015 to 2018 at the University of Ferrara and at the University of Modena and Reggio Emilia. Routine clinical and laboratory follow-up was analyzed.

RESULTS

The records of 328 patients were included in the study. Abnormal CPK levels were observed in 5.5% of cases. Revised Leeds acne scores and visual assessment scale (VAS) measurements decreased significantly after isotretinoin therapy.

DISCUSSION

The adoption of the low starting dose isotretinoin regimen is associated with low incidence of CPK elevation. The finding of CPK over the conventional value of 5 times above the limit was rarely observed and was never associated with kidney damage. Therefore, it should be interpreted as a relatively benign phenomenon that does not require the interruption of isotretinoin therapy and that should be managed mainly through the reassurance of the patient.

Role of Selenoproteins in Redox Regulation of Signaling and the Antioxidant System: A Review

Selenium is a vital trace element present as selenocysteine (Sec) in proteins that are, thus, known as selenoproteins. Humans have 25 selenoproteins, most of which are functionally characterized as oxidoreductases, where the Sec residue plays a catalytic role in redox regulation and antioxidant activity. Glutathione peroxidase plays a pivotal role in scavenging and inactivating hydrogen and lipid peroxides, whereas thioredoxin reductase reduces oxidized thioredoxins as well as non-disulfide substrates, such as lipid hydroperoxides and hydrogen peroxide. Selenoprotein R protects the cell against oxidative damage by reducing methionine-R-sulfoxide back to methionine. Selenoprotein O regulates redox homeostasis with catalytic activity of protein AMPylation. Moreover, endoplasmic reticulum (ER) membrane selenoproteins (SelI, K, N, S, and Sel15) are involved in ER membrane stress regulation. Selenoproteins containing the CXXU motif (SelH, M, T, V, and W) are putative oxidoreductases that participate in various cellular processes depending on redox regulation. Herein, we review the recent studies on the role of selenoproteins in redox regulation and their physiological functions in humans, as well as their role in various diseases.

The redox-dependent regulation of satellite cells following aseptic muscle trauma (SpEED): study protocol for a randomized controlled trial

Background

Muscle satellite cells (SCs) are crucial for muscle regeneration following muscle trauma. Acute skeletal muscle damage results in inflammation and the production of reactive oxygen species (ROS) which may be implicated in SCs activation. Protection of these cells from oxidative damage is essential to ensure sufficient muscle regeneration. The aim of this study is to determine whether SCs activity under conditions of aseptic skeletal muscle trauma induced by exercise is redox-dependent.

Methods/design

Based on the SCs content in their vastus lateralis skeletal muscle, participants will be classified as either high or low respondents. In a randomized, double-blind, crossover, repeated-measures design, participants will then receive either placebo or N-acetylcysteine (alters redox potential in muscle) during a preliminary 7-day loading phase, and for eight consecutive days following a single bout of intense muscle-damaging exercise. In both trials, blood samples and muscle biopsies will be collected, and muscle performance and soreness will be measured at baseline, pre-exercise, 2 and 8 days post exercise. Biological samples will be analyzed for redox status and SCs activity. Between trials, a 4-week washout period will be implemented.

Discussion

This study is designed to investigate the impact of redox status on SCs mobilization and thus skeletal muscle potential for regeneration under conditions of aseptic inflammation induced by exercise. Findings of this trial should provide insight into (1) molecular pathways involved in SCs recruitment and muscle healing under conditions of aseptic skeletal muscle trauma present in numerous catabolic conditions and (2) whether skeletal muscle’s potential for regeneration depends on its basal SCs content.

Trial registration

ClinicalTrials.gov, ID: NCT03711838. Registered on 19 Oct 2018.

Electronic supplementary material

The online version of this article (10.1186/s13063-019-3557-3) contains supplementary material, which is available to authorized users.

Effect of Gpx3 gene silencing by siRNA on apoptosis and autophagy in chicken cardiomyocytes

Glutathione peroxidase 3 (Gpx3), as an important selenoprotein, is the most crucial antioxidant defense in cardiomyocytes. However, the role of Gpx3 in Se-deficient cardiomyocyte damage still less reported. Here, we developed Gpx3 silence cardiomyocytes culture model (small interfering RNA; siRNA) for research the crosstalk between autophagy and apoptosis. Quantitative real-time PCR and western blot analysis are performed to detect the expression of apoptosis and autophagy-related genes. MDC stain, flow cytometry, AO/EB stain, and electron microscope were performed to observe the changes of cell morphology. Our results reveal that Gpx3 suppression can significant increases in ROS (p < 0.05) levels, which further induced apoptosis through upregulated the expression of Caspase-3 in cardiomyocytes. Meanwhile, we also found that the whole process is accompanied by the occurrence of autophagy, which are promoted by inhibiting the mTOR, and increasing the expression of ATG-7, ATG-10, and ATG-12. Altogether, we conclude that the apoptotic and autophagic response machineries share antagonistic function in Gpx3 knockdown cardiomyocytes.

Vitamin A Protects the Preterm Lamb Diaphragm Against Adverse Effects of Mechanical Ventilation

Background: Preterm infants are deficient in vitamin A, which is essential for growth and development of the diaphragm. Preterm infants often require mechanical ventilation (MV) for respiratory distress. In adults, MV is associated with the development of ventilation-induced diaphragm dysfunction and difficulty weaning from the ventilator. We assessed the impact of MV on the preterm diaphragm and the protective effect of vitamin A during MV.

Methods: Preterm lambs delivered operatively at ∼131 days gestation (full gestation: 150 days) received respiratory support by synchronized intermittent mandatory ventilation for 3 days. Lambs in the treated group received daily (24 h) enteral doses of 2500 IU/kg/day vitamin A combined with 250 IU/kg/day retinoic acid (VARA) during MV, while MV control lambs received saline. Unventilated fetal reference lambs were euthanized at birth, without being allowed to breathe. The fetal diaphragm was collected to quantify mRNA levels of myosin heavy chain (MHC) isoforms, atrophy genes, antioxidant genes, and pro-inflammatory genes; to determine ubiquitin proteasome pathway activity; to measure the abundance of protein carbonyl, and to investigate metabolic signaling.

Results: Postnatal MV significantly decreased expression level of the neonatal MHC gene but increased expression level of MHC IIx mRNA level (p < 0.05). Proteasome activity increased after 3 days MV, accompanied by increased MuRF1 mRNA level and accumulated protein carbonyl abundance. VARA supplementation decreased proteasome activity and FOXO1 signaling, down-regulated MuRF1 expression, and reduced reactive oxidant production.

Conclusion: These findings suggest that 3 days of MV results in abnormal myofibrillar composition, activation of the proteolytic pathway, and oxidative injury of diaphragms in mechanically ventilated preterm lambs. Daily enteral VARA protects the preterm diaphragm from these adverse effects.

Comparing atmospheric and hypoxic cultured mesenchymal stem cell transcriptome: implication for stem cell therapies targeting intervertebral discs

Background

Mesenchymal stem cells (MSCs) represent an attractive avenue for cellular therapies targeting degenerative diseases. MSC in vitro expansion is required in order to obtain therapeutic numbers during the manufacturing process. It is known that culture conditions impact cellular properties and behavior after in vivo transplantation. In this study, we aimed at evaluating the benefit of hypoxic culturing of human bone marrow derived mesenchymal stem cells on cell fitness and whole genome expression and discussed its implication on cellular therapies targeting orthopedic diseases such as chronic lower back pain.

Methods

Human bone marrow mesenchymal stem cells (hBMMSCs) were isolated from fresh human anticoagulated whole bone marrow and were cultured side by side in atmospheric (20% O₂) and hypoxic (5% O₂) oxygen partial pressure for up to 3 passages. Stem cell fitness was assessed by clonogenic assay, cell surface marker expression and differentiation potential. Whole genome expression was performed by mRNA sequencing. Data from clonogenic assays, cell surface marker by flow cytometry and gene expression by quantitative PCR were analyzed by two-tailed paired Student’s t-test. Data from mRNA sequencing were aligned to hg19 using Tophat-2.0.13 and analyzed using Cufflinks-2.1.1.

Results

Hypoxic culturing of hBMMSCs had positive effects on cell fitness, as evidenced by an increased clonogenicity and improved differentiation potential towards adipocyte and chondrocyte lineages. No difference in osteoblast differentiation or in cell surface markers were observed. Only a small subset of genes (34) were identified by mRNA sequencing to be significantly dysregulated by hypoxia. When clustered by biological function, these genes were associated with chondrogenesis and cartilage metabolism, inflammation and immunomodulation, cellular survival, migration and proliferation, vasculogenesis and angiogenesis.

Conclusions

Hypoxic culturing positively impacted hBMMSCs fitness and transcriptome, potentially improving inherent properties of these cells that are critical for the development of successful cellular therapies. Hypoxic culturing should be considered for the in vitro expansion of hBMMSCs during manufacturing of cellular therapies targeting orthopedic disorders such as lower back pain.

Glucocorticoid-dependent REDD1 expression reduces muscle metabolism to enable adaptation under energetic stress

Background

Skeletal muscle atrophy is a common feature of numerous chronic pathologies and is correlated with patient mortality. The REDD1 protein is currently recognized as a negative regulator of muscle mass through inhibition of the Akt/mTORC1 signaling pathway. REDD1 expression is notably induced following glucocorticoid secretion, which is a component of energy stress responses.

Results

Unexpectedly, we show here that REDD1 instead limits muscle loss during energetic stresses such as hypoxia and fasting by reducing glycogen depletion and AMPK activation. Indeed, we demonstrate that REDD1 is required to decrease O₂ and ATP consumption in skeletal muscle via reduction of the extent of mitochondrial-associated endoplasmic reticulum membranes (MAMs), a central hub connecting energy production by mitochondria and anabolic processes. In fact, REDD1 inhibits ATP-demanding processes such as glycogen storage and protein synthesis through disruption of the Akt/Hexokinase II and PRAS40/mTORC1 signaling pathways in MAMs. Our results uncover a new REDD1-dependent mechanism coupling mitochondrial respiration and anabolic processes during hypoxia, fasting, and exercise.

Conclusions

Therefore, REDD1 is a crucial negative regulator of energy expenditure that is necessary for muscle adaptation during energetic stresses. This present study could shed new light on the role of REDD1 in several pathologies associated with energetic metabolism alteration, such as cancer, diabetes, and Parkinson’s disease.

Electronic supplementary material

The online version of this article (10.1186/s12915-018-0525-4) contains supplementary material, which is available to authorized users.

Regulation and function of avian selenogenome

BACKGROUND

Selenium (Se) is an essential micronutrient required by avian species. Dietary Se/vitamin E deficiency induces three classical diseases in chicks: exudative diathesis, nutritional pancreatic atrophy, and nutritional muscular dystrophy.

SCOPE OF REVIEW

This review is to summarize and analyze the evolution, regulation, and function of avian selenogenome and selenoproteome and their relationship with the three classical Se/vitamin E deficiency diseases.

MAJOR CONCLUSIONS

There are 24 selenoproteins confirmed in chicks, with two avian-specific members (SELENOU and SELENOP2) and two missing mammalian members (GPX6 and SELENOV). There are two forms of SELENOP containing 1 or 13 selenocysteine residues. In addition, a Gallus gallus gene was conjectured to be the counterpart of the human SEPHS2. Expression of selenoprotein genes in the liver, pancreas, and muscle of chicks seemed to be highly responsive to dietary Se changes. Pathogeneses of the Se/vitamin E deficient diseases in the chicks were likely produced by missing functions of selected selenoproteins in regulating cellular and tissue redox balance and inhibiting oxidative/reductive stress-induced cell death.

GENERAL SIGNIFICANCE

Gene knockout models, similar to those of rodents, will help characterize the precise functions of avian selenoproteins and their comparisons with those of mammalian species.

Protective effect of Rhus coriaria fruit extracts against hydrogen peroxide-induced oxidative stress in muscle progenitors and zebrafish embryos

Background and Purpose

Oxidative stress is involved in normal and pathological functioning of skeletal muscle. Protection of myoblasts from oxidative stress may improve muscle contraction and delay aging. Here we studied the effect of R. coriaria sumac fruit extract on human myoblasts and zebrafish embryos in conditions of hydrogen peroxide-induced oxidative stress.

Study Design and Methods

Crude ethanolic 70% extract (CE) and its fractions was obtained from sumac fruits. The composition of sumac ethyl acetate EtOAc fraction was studied by ¹H NMR. The viability of human myoblasts treated with CE and the EtOAc fraction was determined by trypan blue exclusion test. Oxidative stress, cell cycle and adhesion were analyzed by flow cytometry and microscopy. Gene expression was analyzed by qPCR.

Results

The EtOAc fraction (IC₅₀ 2.57 µg/mL) had the highest antioxidant activity and exhibited the best protective effect against hydrogen peroxide-induced oxidative stress. It also restored cell adhesion. This effect was mediated by superoxide dismutase 2 and catalase. Pre-treatment of zebrafish embryos with low concentrations of the EtOAc fraction protected them from hydrogen peroxide-induced death in vivo. ¹H NMR analysis revealed the presence of gallic acid in this fraction.

Conclusion

Rhus coriaria extracts inhibited or slowed down the progress of skeletal muscle atrophy by decreasing oxidative stress via superoxide dismutase 2 and catalase-dependent mechanisms.

Selenium-Dependent Glutathione Peroxidases During Tumor Development

Five out of eight human glutathione peroxidases (GPxes) are selenoproteins and thus their expression depends on the selenium (Se) supply. Most Se-dependent GPxes are downregulated in tumor cells, while only GPx2 is considerably upregulated. Whether expression profiles of GPxes predict tumor development and patient survival is controversially discussed. Also, results from in vitro and in vivo studies modulating the expression of GPx isoforms provide evidence for both anti- and procarcinogenic mechanisms. GPxes are able to reduce hydroperoxides, which otherwise would damage DNA, possibly resulting in DNA mutations, modulate redox-sensitive signaling pathways affecting proliferation, differentiation, and cellular metabolism or initiate cell death. Considering these different processes, the role and functions of individual Se-dependent GPx isoforms will be discussed herein in the context of tumorigenesis.

Glutathione peroxidases as oncotargets

Oxidative stress is a disturbance in the equilibrium among free radicals, reactive oxygen species, and endogenous antioxidant defense mechanisms. Oxidative stress is a result of imbalance between the production of reactive oxygen and the biological system's ability to detoxify the reactive intermediates or to repair the resulting damage. Mounting evidence has implicated oxidative stress in various physiological and pathological processes, including DNA damage, proliferation, cell adhesion, and survival of cancer cells. Glutathione peroxidases (GPxs) (EC 1.11.1.9) are an enzyme family with peroxidase activity whose main biological roles are to protect organisms from oxidative damage by reducing lipid hydroperoxides as well as free hydrogen peroxide. Currently, 8 sub-members of GPxs have been identified in humans, all capable of reducing H₂O₂ and soluble fatty acid hydroperoxides. A large number of publications has demonstrated that GPxs have significant roles in different stages of carcinogenesis. In this review, we will update recent progress in the study of the roles of GPxs in cancer. Better mechanistic understanding of GPxs will potentially contribute to the development and advancement of improved cancer treatment models.

Redox Control of Skeletal Muscle Regeneration

Skeletal muscle shows high plasticity in response to external demand. Moreover, adult skeletal muscle is capable of complete regeneration after injury, due to the properties of muscle stem cells (MuSCs), the satellite cells, which follow a tightly regulated myogenic program to generate both new myofibers and new MuSCs for further needs. Although reactive oxygen species (ROS) and reactive nitrogen species (RNS) have long been associated with skeletal muscle physiology, their implication in the cell and molecular processes at work during muscle regeneration is more recent. This review focuses on redox regulation during skeletal muscle regeneration. An overview of the basics of ROS/RNS and antioxidant chemistry and biology occurring in skeletal muscle is first provided. Then, the comprehensive knowledge on redox regulation of MuSCs and their surrounding cell partners (macrophages, endothelial cells) during skeletal muscle regeneration is presented in normal muscle and in specific physiological (exercise-induced muscle damage, aging) and pathological (muscular dystrophies) contexts. Recent advances in the comprehension of these processes has led to the development of therapeutic assays using antioxidant supplementation, which result in inconsistent efficiency, underlying the need for new tools that are aimed at precisely deciphering and targeting ROS networks. This review should provide an overall insight of the redox regulation of skeletal muscle regeneration while highlighting the limits of the use of nonspecific antioxidants to improve muscle function. Antioxid. Redox Signal. 27, 276-310.

[Correction of the oxidant-antioxidant balance in lungs during hyperoxia by liposomal alpha-tocopherol and retinoids in the experiment]

The influence of inhaled liposomes, containing dipalmitoyl phosphatidylcholine and a-tocopherol, and liposomes containing dipalmitoyl phosphatidylcholine, retinol and retinoic acid, on parameters of the oxidantantioxidant system in lungs of newborn guinea pigs exposed to hyperoxia during 3 and 14 days has been studied. Administration of both types of liposomes under conditions of prolonged hyperoxia (14 days) results in normalization of glutathione peroxidase activity and prevents elevation of the levels of lipid and protein peroxidation products in bronchoalveolar lavage fluid. Unlike liposomes with a-tocopherol, administration of liposomes containing retinoids did not cause the normalizing effect on the content of nonprotein SH-compounds in the bronchoalveolar fluid and contributed to significant reduction of the a-tocopherol level in lung tissues.

Are Antioxidants a Potential Therapy for FSHD? A Review of the Literature

Facioscapulohumeral muscular dystrophy (FSHD) is an inherited myopathy affecting approximately 1 in 7500 individuals worldwide. It is a progressive disease characterised by skeletal muscle weakness and wasting. A genetic mutation on the 4q35 chromosome results in the expression of the double homeobox 4 gene (DUX4) which drives oxidative stress, inflammation, toxicity, and atrophy within the skeletal muscle. FSHD is characterised by oxidative stress, and there is currently no cure and a lack of therapies for the disease. Antioxidants have been researched for many years, with investigators aiming to use antioxidants therapeutically for oxidative stress-associated diseases. This has included both natural and synthetic antioxidants. The use of antioxidants in preclinical or clinical models has been largely successful with a plethora of research reporting positive results. However, when translated to clinical trials, the use of antioxidants as a therapeutic intervention for a variety of disease has been largely unsuccessful. Moreover, specifically focusing on FSHD, limited research has been conducted on the use of antioxidants as a therapy in either preclinical or clinical models. This review summarises the current state of antioxidant use in the treatment of FSHD and discusses their potential avenue for therapeutic use for FSHD patients.

Retinoic acid maintains human skeletal muscle progenitor cells in an immature state

Muscle satellite cells are resistant to cytotoxic agents, and they express several genes that confer resistance to stress, thus allowing efficient dystrophic muscle regeneration after transplantation. However, once they are activated, this capacity to resist to aggressive agents is diminished resulting in massive death of transplanted cells. Although cell immaturity represents a survival advantage, the signalling pathways involved in the control of the immature state remain to be explored. Here, we show that incubation of human myoblasts with retinoic acid impairs skeletal muscle differentiation through activation of the retinoic-acid receptor family of nuclear receptor. Conversely, pharmacologic or genetic inactivation of endogenous retinoic-acid receptors improved myoblast differentiation. Retinoic acid inhibits the expression of early and late muscle differentiation markers and enhances the expression of myogenic specification genes, such as PAX7 and PAX3. These results suggest that the retinoic-acid-signalling pathway might maintain myoblasts in an undifferentiated/immature stage. To determine the relevance of these observations, we characterised the retinoic-acid-signalling pathways in freshly isolated satellite cells in mice and in siMYOD immature human myoblasts. Our analysis reveals that the immature state of muscle progenitors is correlated with high expression of several genes of the retinoic-acid-signalling pathway both in mice and in human. Taken together, our data provide evidences for an important role of the retinoic-acid-signalling pathway in the regulation of the immature state of muscle progenitors.

Contribution of mammalian selenocysteine-containing proteins to carcinogenesis

Oxidative stress caused by a sharp growth of free radicals in the organism is a major cause underlying the occurrence of all kinds of malignant formations. Selenium is an important essential trace element found in selenoproteins in the form of selenocysteine, an amino acid differing from cysteine for the presence of selenium instead of sulfur and making such proteins highly active. To date the role of selenium has been extensively investigated through studying the functions of selenoproteins in carcinogenesis. Analysis of the obtained results clearly demonstrates that selenoproteins can act as oncosuppressors, but can also, on the contrary, favor the formation of malignant tumors.

The role of oxidative stress in skeletal muscle injury and regeneration: focus on antioxidant enzymes

Reactive oxygen species (ROS) are generated in skeletal muscle both during the rest and contractile activity. Myogenic cells are equipped with antioxidant enzymes, like superoxide dismutase, catalase, glutathione peroxidase, γ-glutamylcysteine synthetase and heme oxygenase-1. These enzymes not only neutralise excessive ROS, but also affect myogenic regeneration at several stages: influence post-injury inflammatory reaction, enhance viability and proliferation of muscle satellite cells and myoblasts and affect their differentiation. Finally, antioxidant enzymes regulate also processes accompanying muscle regeneration-induce angiogenesis and reduce fibrosis. Elevated ROS production was also observed in Duchenne muscular dystrophy (DMD), a disease characterised by degeneration of muscle tissue and therefore-increased rate of myogenic regeneration. Antioxidant enzymes are consequently considered as target for therapies counteracting dystrophic symptoms. In this review we present current knowledge regarding the role of oxidative stress and systems of enzymatic antioxidant defence in muscular regeneration after both acute injury and persistent muscular degeneration.

Mineralocorticoid receptors are present in skeletal muscle and represent a potential therapeutic target

Early treatment with heart failure drugs lisinopril and spironolactone improves skeletal muscle pathology in Duchenne muscular dystrophy (DMD) mouse models. The angiotensin converting enzyme inhibitor lisinopril and mineralocorticoid receptor (MR) antagonist spironolactone indirectly and directly target MR. The presence and function of MR in skeletal muscle have not been explored. MR mRNA and protein are present in all tested skeletal muscles from both wild-type mice and DMD mouse models. MR expression is cell autonomous in both undifferentiated myoblasts and differentiated myotubes from mouse and human skeletal muscle cultures. To test for MR function in skeletal muscle, global gene expression analysis was conducted on human myotubes treated with MR agonist (aldosterone; EC50 1.3 nM) or antagonist (spironolactone; IC50 1.6 nM), and 53 gene expression differences were identified. Five differences were conserved in quadriceps muscles from dystrophic mice treated with spironolactone plus lisinopril (IC50 0.1 nM) compared with untreated controls. Genes down-regulated more than 2-fold by MR antagonism included FOS, ANKRD1, and GADD45B, with known roles in skeletal muscle, in addition to NPR3 and SERPINA3, bona fide targets of MR in other tissues. MR is a novel drug target in skeletal muscle and use of clinically safe antagonists may be beneficial for muscle diseases.

Selenoproteins protect against avian nutritional muscular dystrophy by metabolizing peroxides and regulating redox/apoptotic signaling

Nutritional muscular dystrophy (NMD) of chicks is induced by dietary selenium (Se)/vitamin E (Vit. E) deficiencies and may be associated with oxidative cell damage. To reveal the underlying mechanisms related to the presumed oxidative cell damage, we fed four groups of 1-day-old broiler chicks (n = 40/group) with a basal diet (BD; 10 μg Se/kg; no Vit. E added, -Se -Vit. E) or the BD plus all-rac-α-tocopheryl acetate at 50mg/kg (-Se +Vit. E), Se (as sodium selenite) at 0.3mg/kg (+Se -Vit. E), or both of these nutrients (+Se +Vit. E) for 6 weeks. High incidences of NMD (93%) and mortality (36%) of the chicks were induced by the BD, starting at week 3. Dietary Se deficiency alone also induced muscle fiber rupture and coagulation necrosis in the pectoral muscle of chicks at week 3 and thereafter, with increased (P < 0.05) malondialdehyde, decreased (P < 0.05) total antioxidant capacity, and diminished (P < 0.05) glutathione peroxidase activities in the muscle. To link these oxidative damages of the muscle cells to the Se-deficiency-induced NMD, we first determined gene expression of the potential 26 selenoproteins in the muscle of the chicks at week 2 before the onset of symptoms. Compared with the +Se chicks, the -Se chicks had lower (P < 0.05) muscle mRNA levels of Gpx1, Gpx3, Gpx4, Sepp1, Selo, Selk, Selu, Selh, Selm, Sepw1, and Sep15. The -Se chicks also had decreased (P < 0.05) production of 6 selenoproteins (long-form selenoprotein P (SelP-L), GPx1, GPx4, Sep15, SelW, and SelN), but increased levels (P < 0.05) of the short-form selenoprotein P in muscle at weeks 2 and 4. Dietary Se deficiency elevated (P < 0.05) muscle p53, cleaved caspase 3, cleaved caspase 9, cyclooxygenase 2 (COX2), focal adhesion kinase (FAK), phosphatidylinositol 3-kinase (PI3K), phospho-Akt, nuclear factor-κB (NF-κB), p38 mitogen-activated protein kinase (p38 MAPK), phospho-p38 MAPK, phospho-JNK, and phospho-ERK and decreased (P < 0.05) muscle procaspase 3, procaspase 9, and NF-κB inhibitor α. In conclusion, the downregulation of SelP-L, GPx1, GPx4, Sep15, SelW, and SelN by dietary Se deficiency might account for induced oxidative stress and the subsequent peroxidative damage of chick muscle cells via the activation of the p53/caspase 9/caspase 3, COX2/FAK/PI3K/Akt/NF-κB, and p38 MAPK/JNK/ERK signaling pathways. Metabolism of peroxides and redox regulation are likely to be the mechanisms whereby these selenoproteins prevented the onset of NMD in chicks.

Downregulation of glutathione peroxidase 3 is associated with lymph node metastasis and prognosis in cervical cancer

Glutathione peroxidase 3 (GPX3) is a member of the glutathione peroxidase family of selenoproteins and is one of the key defensive enzymes against oxidative damages to host cells. Downregulation of GPX3 due to its promoter hypermethylation has been documented in several different types of cancer, indicating that GPX3 functions as a possible tumor suppressor. In the present study, we showed that GPX3 is also significantly downregulated in cervical cancer tissues compared to normal cervical tissues by qRT-PCR analyses and immunohistostainings. GPX3 expression was significantly related to lymph node metastasis and prognosis in cervical cancer patients. Treatment of cervical cancer cells with 5-aza-2'-deoxycytidine restored the expression of GPX3 and methylation-specific PCR (MSP) confirmed the CpG methylation of the GPX3 gene. Our results indicate that promoter methylation is one of the major causes of GPX3 downregulation in cervical cancer and GPX3 could serve as a predictive biomarker for lymph node metastasis and prognosis of cervical cancer.

Epigallocatechin-3-gallate improves plantaris muscle recovery after disuse in aged rats

Aging exacerbates muscle loss and slows the recovery of muscle mass and function after disuse. In this study we investigated the potential that epigallocatechin-3-gallate (EGCg), an abundant catechin in green tea, would reduce signaling for apoptosis and promote skeletal muscle recovery in the fast plantaris muscle and the slow soleus muscle after hindlimb suspension (HLS) in senescent animals. Fischer 344 × Brown Norway inbred rats (age 34 months) received either EGCg (50 mg/kg body weight), or water daily by gavage. One group of animals received HLS for 14 days and a second group of rats received 14 days of HLS, then the HLS was removed and they recovered from this forced disuse for 2 weeks. Animals that received EGCg over the HLS followed by 14 days of recovery, had a 14% greater plantaris muscle weight (p<0.05) as compared to the animals treated with the vehicle over this same period. Plantaris fiber area was greater after recovery in EGCg (2715.2±113.8 μm(2)) vs. vehicle treated animals (1953.0±41.9 μm(2)). In addition, activation of myogenic progenitor cells was improved with EGCg over vehicle treatment (7.5% vs. 6.2%) in the recovery animals. Compared to vehicle treatment, the apoptotic index was lower (0.24% vs. 0.52%), and the abundance of pro-apoptotic proteins Bax (-22%), and FADD (-77%) was lower in EGCg treated plantaris muscles after recovery. While EGCg did not prevent unloading-induced atrophy, it improved muscle recovery after the atrophic stimulus in fast plantaris muscles. However, this effect was muscle specific because EGCg had no major impact in reversing HLS-induced atrophy in the slow soleus muscle of old rats.