Nitric Oxide Regulates Skeletal Muscle Fatigue, Fiber Type, Microtubule Organization, and Mitochondrial ATP Synthesis Efficiency Through cGMP-Dependent Mechanisms

Renshen Yangrong decoction for secondary malaise and fatigue: network pharmacology and Mendelian randomization study

Background

Renshen Yangrong decoction (RSYRD) has been shown therapeutic effects on secondary malaise and fatigue (SMF). However, to date, its bioactive ingredients and potential targets remain unclear.

Purpose

The purpose of this study is to assess the potential ingredients and targets of RSYRD on SMF through a comprehensive strategy integrating network pharmacology, Mendelian randomization as well as molecular docking verification.

Methods

Search for potential active ingredients and corresponding protein targets of RSYRD on TCMSP and BATMAN-TCM for network pharmacology analysis. Mendelian randomization (MR) was performed to find therapeutic targets for SMF. The eQTLGen Consortium (sample sizes: 31,684) provided data on cis-expression quantitative trait loci (cis-eQTL, exposure). The summary data on SMF (outcome) from genome-wide association studies (GWAS) were gathered from the MRC-IEU Consortium (sample sizes: 463,010). We built a target interaction network between the probable active ingredient targets of RSYRD and the therapeutic targets of SMF. We next used drug prediction and molecular docking to confirm the therapeutic value of the therapeutic targets.

Results

In RSYRD, network pharmacology investigations revealed 193 possible active compounds and 234 associated protein targets. The genetically predicted amounts of 176 proteins were related to SMF risk in the MR analysis. Thirty-seven overlapping targets for RSYRD in treating SMF, among which six (NOS3, GAA, IMPA1, P4HTM, RB1, and SLC16A1) were prioritized with the most convincing evidence. Finally, the 14 active ingredients of RSYRD were identified as potential drug molecules. The strong affinity between active components and putative protein targets was established by molecular docking.

Conclusion

This study revealed several active components and possible RSYRD protein targets for the therapy of SMF and provided novel insights into the feasibility of using Mendelian randomization for causal inference between Chinese medical formula and disease.

Expression of neuronal NO synthase α- and β-isoforms in skeletal muscle of mice

Knowledge of the primary structure of neuronal NO synthase (nNOS) in skeletal muscle is still conflicting and needs further clarification. To elucidate the expression patterns of nNOS isoforms at both mRNA and protein level, systematic reverse transcription (RT)-PCR and epitope mapping by qualitative immunoblot analysis on skeletal muscle of C57/BL6 mice were performed. The ability of the nNOS isoforms to form aggregates was characterized by native low-temperature polyacrylamide electrophoresis (LT-PAGE). The molecular analysis was focused on the rectus femoris (RF) muscle, a skeletal muscle with a nearly balanced ratio of nNOS α- and β-isoforms. RT-PCR amplificates from RF muscles showed exclusive exon-1d mRNA expression, either with or without exon-μ. Epitope mapping demonstrated the simultaneous expression of the nNOS splice variants α/μ, α/non-μ, β/μ and β/non-μ. Furthermore, immunoblotting suggests that the transition between nNOS α- and β-isoforms lies within exon-3. In LT-PAGE, three protein nNOS associated aggregates were detected in homogenates of RF muscle and tibialis anterior muscle: a 320 kDa band containing nNOS α-isoforms, while 250 and 300 kDa bands consist of nNOS β-isoforms that form homodimers or heterodimers with non-nNOS proteins.

Use of thiacalix[4]arene C-1193 for a directed influence on the functional activity of mitochondria and simulation of this process using a Petri nets

In molecular biological studies, considerable attention is paid to macrocyclic nanoscale compounds known as calix[4]arenes. An imperative concern in biochemical membranology and molecular biotechnology is the exploration of effectors capable of modifying the intensity of redox reactions within the inner mitochondrial membrane and influencing the activity of its Ca2+ transport systems. The simulation model development is relevant to formalize and generalize the experimental data and assess the conformity of experimental results with theoretical predictions. Experiments were carried out on a suspension of isolated rat myometrial mitochondria. The synthesized thiacalix[4]arene C-1193, containing four sulfur atoms, was employed. Demonstrations of time-dependent and concentration-dependent (0.01-10 μM) inhibition of Ca2+ accumulation and reactive oxygen species (ROS) formation by mitochondria in the presence of C-1193 were observed. While C-1193 inhibited the oxidation of NADH and FADH2, it did not induce mitochondrial swelling. The thiacalix[4]arene also inhibited the synthesis of nitric oxide, with a Ki of 5.5 ± 1.7 nM, positioning it as a high-affinity blocker of endogenous NO generation in mitochondria. These results are the basis for the possible application of the synthesized thiacalix[4]arene as a tool in researching biochemical processes in mitochondria. A simulation model employing functional hybrid Petri nets was developed, reproducing the functional activity of mitochondria, including simultaneous NADH oxidation, ROS formation, NO synthesis, and Ca2+ accumulation. The derived equations formalize and describe the time dependencies of the listed processes in the medium under the influence of thiacalix[4]arene C-1193.

Effects of Dietary Nitrate Supplementation on Performance during Single and Repeated Bouts of Short-Duration High-Intensity Exercise: A Systematic Review and Meta-Analysis of Randomised Controlled Trials

Inorganic nitrate (NO₃^-) has emerged as a potential ergogenic aid over the last couple of decades. While recent systematic reviews and meta-analyses have suggested some small positive effects of NO₃^- supplementation on performance across a range of exercise tasks, the effect of NO₃^- supplementation on performance during single and repeated bouts of short-duration, high-intensity exercise is unclear. This review was conducted following PRISMA guidelines. MEDLINE and SPORTDiscus were searched from inception to January 2023. A paired analysis model for cross-over trials was incorporated to perform a random effects meta-analysis for each performance outcome and to generate standardized mean differences (SMD) between the NO₃^- and placebo supplementation conditions. The systematic review and meta-analysis included 27 and 23 studies, respectively. Time to reach peak power (SMD: 0.75, p = 0.02), mean power output (SMD: 0.20, p = 0.02), and total distance covered in the Yo-Yo intermittent recovery level 1 test (SMD: 0.17, p < 0.0001) were all improved after NO₃^- supplementation. Dietary NO₃^- supplementation had small positive effects on some performance outcomes during single and repeated bouts of high-intensity exercise. Therefore, athletes competing in sports requiring single or repeated bouts of high-intensity exercise may benefit from NO₃^- supplementation.

Endogenous and Exogenous Antioxidants in Skeletal Muscle Fatigue Development during Exercise

Muscle fatigue is defined as a decrease in maximal force or power generated in response to contractile activity, and it is a risk factor for the development of musculoskeletal injuries. One of the many stressors imposed on skeletal muscle through exercise is the increased production of reactive oxygen species (ROS) and reactive nitrogen species (RNS), which intensifies as a function of exercise intensity and duration. Exposure to ROS/RNS can affect Na⁺/K⁺-ATPase activity, intramyofibrillar calcium turnover and sensitivity, and actin-myosin kinetics to reduce muscle force production. On the other hand, low ROS/RNS concentrations can likely upregulate an array of cellular adaptative responses related to mitochondrial biogenesis, glucose transport and muscle hypertrophy. Consequently, growing evidence suggests that exogenous antioxidant supplementation might hamper exercise-engendering upregulation in the signaling pathways of mitogen-activated protein kinases (MAPKs), peroxisome-proliferator activated co-activator 1α (PGC-1α), or mammalian target of rapamycin (mTOR). Ultimately, both high (exercise-induced) and low (antioxidant intervention) ROS concentrations can trigger beneficial responses as long as they do not override the threshold range for redox balance. The mechanisms underlying the two faces of ROS/RNS in exercise, as well as the role of antioxidants in muscle fatigue, are presented in detail in this review.

Stimulation of soluble guanylate cyclase by vericiguat reduces skeletal muscle atrophy of mice following chemotherapy

Background: The chemotherapeutic doxorubicin (DOX) promotes severe skeletal muscle atrophy, which induces skeletal muscle weakness and fatigue. Soluble guanylate cyclase (sGC) contributes to a variety of pathophysiological processes, but whether it is involved in DOX-induced skeletal muscle atrophy is unclear. The present study aimed to stimulate sGC by vericiguat, a new oral sGC stimulator, to test its role in this process. Methods: Mice were randomly divided into four groups: control group, vericiguat group, DOX group, and DOX + vericiguat group. Exercise capacity was evaluated before the mice were sacrificed. Skeletal muscle atrophy was assessed by histopathological and molecular biological methods. Protein synthesis and degradation were monitored in mice and C2C12 cells. Results: In this study, a significant decrease in exercise capacity and cross-sectional area (CSA) of skeletal muscle fibers was found in mice following DOX treatment. Furthermore, DOX decreased sGC activity in mice and C2C12 cells, and a positive correlation was found between sGC activity and CSA of skeletal muscle fibers in skeletal muscle. DOX treatment also impaired protein synthesis, shown by puromycin detection, and activated ubiquitin-proteasome pathway. Following sGC stimulation, the CSA of muscle fibers was elevated, and exercise capacity was enhanced. Stimulation of sGC also increased protein synthesis and decreased ubiquitin-proteasome pathway. In terms of the underlying mechanisms, AKT/mTOR and FoxO1 pathways were impaired following DOX treatment, and stimulation of sGC restored the blunted pathways. Conclusion: These results unravel sGC stimulation can improve skeletal muscle atrophy and increase the exercise capacity of mice in response to DOX treatment by enhancing protein synthesis and inhibiting protein degradation. Stimulation of sGC may be a potential treatment of DOX-induced skeletal muscle dysfunction.

Dietary Nitrate Supplementation Enhances Performance and Speeds Muscle Deoxyhaemoglobin Kinetics during an End-Sprint after Prolonged Moderate-Intensity Exercise

Short-term dietary nitrate (NO3−) supplementation has the potential to enhance performance during submaximal endurance, and short-duration, maximal-intensity exercise. However, it has yet to be determined whether NO3− supplementation before and during submaximal endurance exercise can improve performance during a short-duration, maximal-intensity end-sprint. In a randomised, double-blind, crossover study, 9 recreationally active men ingested NO3−-rich (BR: 8 mmol NO3−/day) and NO3−-depleted (PL: 0.75 mmol NO3−/day) beetroot powder for 7 days. On day 7, participants completed 2 h of moderate-intensity cycling, which immediately transitioned into a 60 s maximal-intensity end-sprint, with supplements ingested 2 h before and 1 h into the moderate-intensity exercise bout. Plasma [NO3−] and [NO2−] were higher in BR compared to PL pre- and post-exercise (p < 0.05). Post-exercise plasma [NO3−] was higher than pre-exercise (562 ± 89 µM vs. 300 ± 73 µM; p < 0.05) and plasma [NO2−] was not significantly different pre- (280 ± 58 nM) and post-exercise (228 ± 63 nM) in the BR condition (p > 0.05). Mean power output during the final 30 s of the end-sprint was greater after BR (390 ± 38 W) compared to PL (365 ± 41 W; p < 0.05). There were no differences between BR and PL in any muscle oxygenation variables during moderate-intensity cycling (p > 0.05), but muscle [deoxyhaemoglobin] kinetics was faster during the end-sprint in BR (6.5 ± 1.4 s) compared to PL (7.3 ± 1.4 s; p < 0.05). These findings suggest that NO3− supplementation has the potential to improve end-sprint performance in endurance events when ingested prior to and during exercise.

Pharmaceutical Agents for Contractile-Metabolic Dysfunction After Volumetric Muscle Loss

Volumetric muscle loss (VML) injuries represent a majority of military service member casualties and are common in civilian populations following blunt and/or penetrating traumas. Characterized as a skeletal muscle injury with permanent functional impairments, there is currently no standard for rehabilitation, leading to lifelong disability. Toward developing rehabilitative strategies, previous research demonstrates that the remaining muscle after a VML injury lacks similar levels of plasticity or adaptability as healthy, uninjured skeletal muscle. This may be due, in part, to impaired innervation and vascularization of the remaining muscle, as well as disrupted molecular signaling cascades commonly associated with muscle adaptation. The primary objective of this study was to assess the ability of four pharmacological agents with a strong record of modulating muscle contractile and metabolic function to improve functional deficits in a murine model of VML injury. Male C57BL/6 mice underwent a 15% multimuscle VML injury of the posterior hindlimb and were randomized into drug treatment groups (formoterol [FOR], 5-aminoimidazole-4-carboxamide riboside [AICAR], pioglitazone [PIO], or sildenafil [SIL]) or untreated VML group. At the end of 60 days, the injury model was first validated by comparison to age-matched injury-naive mice. Untreated VML mice had 22% less gastrocnemius muscle mass, 36% less peak-isometric torque, and 27% less maximal mitochondrial oxygen consumption rate compared to uninjured mice (p < 0.01). Experimental drug groups were, then, compared to VML untreated, and there was minimal evidence of efficacy for AICAR, PIO, or SIL in improving contractile and metabolic functional outcomes. However, FOR-treated VML mice had 18% greater peak isometric torque (p < 0.01) and permeabilized muscle fibers had 36% greater State III mitochondrial oxygen consumption rate (p < 0.01) compared to VML untreated mice, suggesting an overall improvement in muscle condition. There was minimal evidence that these benefits came from greater mitochondrial biogenesis and/or mitochondrial complex protein content, but could be due to greater enzyme activity levels for complex I and complex II. These findings suggest that FOR treatment is candidate to pair with a rehabilitative approach to maximize functional improvements in VML-injured muscle. Impact statement Volumetric muscle loss (VML) injuries result in deficiencies in strength and mobility, which have a severe impact on patient quality of life. Despite breakthroughs in tissue engineering, there are currently no treatments available that can restore function to the affected limb. Our data show that treatment of VML injuries with clinically available and FDA-approved formoterol (FOR), a beta-agonist, significantly improves strength and metabolism of VML-injured muscle. FOR is therefore a promising candidate for combined therapeutic approaches (i.e., regenerative rehabilitation) such as pairing FOR with structured rehabilitation or cell-seeded biomaterials as it may provide greater functional improvements than either strategy alone.

UPRmt activation improves pathological alterations in cellular models of mitochondrial diseases

Background

Mitochondrial diseases represent one of the most common groups of genetic diseases. With a prevalence greater than 1 in 5000 adults, such diseases still lack effective treatment. Current therapies are purely palliative and, in most cases, insufficient. Novel approaches to compensate and, if possible, revert mitochondrial dysfunction must be developed.

Results

In this study, we tackled the issue using as a model fibroblasts from a patient bearing a mutation in the GFM1 gene, which is involved in mitochondrial protein synthesis. Mutant GFM1 fibroblasts could not survive in galactose restrictive medium for more than 3 days, making them the perfect screening platform to test several compounds. Tetracycline enabled mutant GFM1 fibroblasts survival under nutritional stress. Here we demonstrate that tetracycline upregulates the mitochondrial Unfolded Protein Response (UPR^mt), a compensatory pathway regulating mitochondrial proteostasis. We additionally report that activation of UPR^mt improves mutant GFM1 cellular bioenergetics and partially restores mitochondrial protein expression.

Conclusions

Overall, we provide compelling evidence to propose the activation of intrinsic cellular compensatory mechanisms as promising therapeutic strategy for mitochondrial diseases.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-022-02331-8.

Nitric oxide and skeletal muscle contractile function

Nitric oxide (NO) is complex modulator of skeletal muscle contractile function, capable of increasing or decreasing force and power output depending on multiple factors. This review explores the effects and potential mechanisms for modulation of skeletal muscle contractile function by NO, from pharmacological agents in isolated muscle preparations to dietary nitrate supplementation in humans and animals. Pharmacological manipulation in vitro suggests that NO signaling diminishes submaximal isometric force, whereas dietary manipulation in vivo suggest that NO enhances submaximal force. The bases for these different responses are unknown but could reflect dose-dependent effects. Maximal isometric force is unaffected by physiologically relevant levels of NO, which do not induce overt protein oxidation. Pharmacological and dietary manipulation of NO signaling enhances the maximal rate of isometric force development, unloaded shortening velocity, and peak power. We hypothesize that these effects are mediated by post-translational modifications of myofibrillar proteins that modulate thick filament regulation of contraction (e.g., mechanosensing and strain-dependence of cross-bridge kinetics). NO effects on contractile function appear to have some level of fiber type and sex-specificity. The mechanisms behind NO-mediated changes in skeletal muscle function need to be explored through proteomics analysis and advanced biophysical assays to advance the development of small molecules and open intriguing therapeutic and ergogenic possibilities for aging, disease, and athletic performance.

Regulation of skeletal myogenesis in C2C12 cells through modulation of Pax7, MyoD, and myogenin via different low-frequency electromagnetic field energies

BACKGROUND: A low-frequency electromagnetic field (LF-EMF) exerts important biological effects on the human body. OBJECTIVE: We previously studied the immunity and atrophy of gastrocnemius muscles in rats with spinal cord injuries and found that LF-EMF with a magnetic flux density of 1.5 mT exerted excellent therapeutic and preventive effects on reducing myotubes and increasing spatium intermusculare. However, the effects of LF-EMF on all stages of skeletal myogenesis, such as activation, proliferation, differentiation, and fusion of satellite cells to myotubes as stimulated by myogenic regulatoryfactors (MRFs), have not been fully elucidated. METHODS: This study investigated the optimal LF-EMF magnetic flux density that exerted maximal effects on all stages of C2C12 cell skeletal myogenesis as well as its impact on regulatory MRFs. RESULTS: The results showed that an LF-EMF with a magnetic flux density of 2.0 mT could activate C2C12 cells and upregulate the proliferation-promoting transcription factor PAX7. On the other hand, 1.5 mT EMF could upregulate the expression of MyoD and myogenin. CONCLUSION: LF-EMF could prevent the disappearance of myotubes, with different magnetic flux densities of LF-EMF exerting independent and positive effects on skeletal myogenesis such as satellite cell activation and proliferation, muscle cell differentiation, and myocyte fusion.

Selective Myostatin Inhibition Spares Sublesional Muscle Mass and Myopenia-Related Dysfunction after Severe Spinal Cord Contusion in Mice

Clinically relevant myopenia accompanies spinal cord injury (SCI), and compromises function, metabolism, body composition, and health. Myostatin, a transforming growth factor (TGF)β family member, is a key negative regulator of skeletal muscle mass. We investigated inhibition of myostatin signaling using systemic delivery of a highly selective monoclonal antibody - muSRK-015P (40 mg/kg) - that blocks release of active growth factor from the latent form of myostatin. Adult female mice (C57BL/6) were subjected to a severe SCI (65 kdyn) at T9 and were then immediately and 1 week later administered test articles: muSRK-015P (40 mg/kg) or control (vehicle or IgG). A sham control group (laminectomy only) was included. At euthanasia, (2 weeks post-SCI) muSRK-015P preserved whole body lean mass and sublesional gastrocnemius and soleus mass. muSRK-015P-treated mice with SCI also had significantly attenuated myofiber atrophy, lipid infiltration, and loss of slow-oxidative phenotype in soleus muscle. These outcomes were accompanied by significantly improved sublesional motor function and muscle force production at 1 and 2 weeks post-SCI. At 2 weeks post-SCI, lean mass was significantly decreased in SCI-IgG mice, but was not different in SCI-muSRK-015P mice than in sham controls. Total energy expenditure (kCal/day) at 2 weeks post-SCI was lower in SCI-immunoglobulin (Ig)G mice, but not different in SCI-muSRK-015P mice than in sham controls. We conclude that in a randomized, blinded, and controlled study in mice, myostatin inhibition using muSRK-015P had broad effects on physical, metabolic, and functional outcomes when compared with IgG control treated SCI animals. These findings may identify a useful, targeted therapeutic strategy for treating post-SCI myopenia and related sequelae in humans.

Assessing the Use of the sGC Stimulator BAY-747, as a Potential Treatment for Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is a severe and progressive muscle wasting disorder, affecting one in 3500 to 5000 boys worldwide. The NO-sGC-cGMP pathway plays an important role in skeletal muscle function, primarily by improving blood flow and oxygen supply to the muscles during exercise. In fact, PDE5 inhibitors have previously been investigated as a potential therapy for DMD, however, a large-scale Phase III clinical trial did not meet its primary endpoint. Since the efficacy of PDE5i is dependent on sufficient endogenous NO production, which might be impaired in DMD, we investigated if NO-independent sGC stimulators, could have therapeutic benefits in a mouse model of DMD. Male mdx/mTR^G2 mice aged six weeks were given food supplemented with the sGC stimulator, BAY-747 (150 mg/kg of food) or food alone (untreated) ad libitum for 16 weeks. Untreated C57BL6/J mice were used as wild type (WT) controls. Assessments of the four-limb hang, grip strength, running wheel and serum creatine kinase (CK) levels showed that mdx/mTR^G2 mice had significantly reduced skeletal muscle function and severe muscle damage compared to WT mice. Treatment with BAY-747 improved grip strength and running speed, and these mice also had reduced CK levels compared to untreated mdx/mTR^G2 mice. We also observed increased inflammation and fibrosis in the skeletal muscle of mdx/mTR^G2 mice compared to WT. While gene expression of pro-inflammatory cytokines and some pro-fibrotic markers in the skeletal muscle was reduced following BAY-747 treatment, there was no reduction in infiltration of myeloid immune cells nor collagen deposition. In conclusion, treatment with BAY-747 significantly improves several functional and pathological parameters of the skeletal muscle in mdx/mTR^G2 mice. However, the effect size was moderate and therefore, more studies are needed to fully understand the potential treatment benefit of sGC stimulators in DMD.

Transcriptomic investigation of embryonic pectoral muscle reveals increased myogenic processes in Shitou geese compared to Wuzong geese

1.Embryonic stages before birth are crucial for poultry muscle development, as this determines muscle mass in adulthood. This study characterised the distinction in embryonic pectoral muscle development between Wuzong (WZE, small) and Shitou (STE, large) geese (two indigenous goose breeds in Guangdong Province, China) at embryonic days 15 (E15), 23 (E23) and the day of hatching (P1) to gain insights into the regulatory mechanisms of muscle development.2.The results showed that STE had significantly higher myofibre density during E15-P1 and had significantly larger myofibre diameter at E15 than WZE. By RNA-sequencing analysis, 19 507 genes were detected, and 7121 differentially expressed genes (DEGs) were identified.3.Gene expression distinctions between breeds began increasing from E23, and WZE had different gene expression profiles compared to STE. A GO analysis of DEGs indicated that myo-genes involved at E15 may influence distinct pectoral muscle development characteristics between WZE and STE. The RT-qPCR results were consistent with the RNA-sequencing analysis. Four muscle structure protein coding genes (MYL2, MYL3, TNNI2 and TNNC2 and three other functional genes (CAV3, CACNA1S and NOS1) were identified in a predicted interaction network. These functional genes may interact with muscle structural protein coding genes to regulate embryonic pectoral muscle development in WZE and STE geese.4.The study revealed that STE and WZE had divergent embryonic pectoral muscle development patterns and these differences may begin before E15.

Gasotransmitter signaling in energy homeostasis and metabolic disorders

Gasotransmitters are small molecules of gases, including nitric oxide (NO), hydrogen sulfide (H₂S), and carbon monoxide (CO). These three gasotransmitters can be endogenously produced and regulate a wide range of pathophysiological processes by interacting with specific targets upon diffusion in the biological media. By redox and epigenetic regulation of various physiological functions, NO, H₂S, and CO are critical for the maintenance of intracellular energy homeostasis. Accumulated evidence has shown that these three gasotransmitters control ATP generation, mitochondrial biogenesis, glucose metabolism, insulin sensitivity, lipid metabolism, and thermogenesis, etc. Abnormal generation and metabolism of NO, H₂S, and/or CO are involved in various abnormal metabolic diseases, including obesity, diabetes, and dyslipidemia. In this review, we summarized the roles of NO, H₂S, and CO in the regulation of energy homeostasis as well as their involvements in the metabolism of dysfunction-related diseases. Understanding the interaction among these gasotransmitters and their specific molecular targets are very important for therapeutic applications.

Nitric oxide's physiologic effects and potential as a therapeutic agent against COVID-19

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is responsible for COVID-19 pneumonia, a pandemic that precipitates huge pressures on the world's social and economic systems. Disease severity varies among individuals. SARS-CoV-2 infection can be associated with e.g. flu-like symptoms, dyspnoea, severe interstitial pneumonia, acute respiratory distress syndrome, multiorgan dysfunction, and generalized coagulopathy. Nitric oxide (NO), is a small signal molecule that impacts pleiotropic functions in human physiology, which can be involved in the significant effects of COVID-19 infection. NO is a neurotransmitter involved in the neural olfactory processes in the central nervous system, and some infected patients have reported anosmia as a symptom. Additionally, NO is a well-known vasodilator, important coagulation mediator, anti-microbial effector and inhibitor of SARS-CoV replication. Exhaled NO is strongly related to the type-2 inflammatory response found in asthma, which has been suggested to be protective against SARS-CoV-2 infection. Several reports indicate that the use of inhaled NO has been an effective therapy during this pandemic since the ventilation-perfusion ratio in COVID-19 patients improved afterwards and they did not require mechanical ventilation. The aim of this mini-review is to summarize relevant actions of NO that could be beneficial in the treatment of COVID-19.

Rapid, redox-mediated mechanical susceptibility of the cortical microtubule lattice in skeletal muscle

The highly ordered cortical microtubule lattice of skeletal muscle is disorganized in dystrophin-deficient mdx mice. Implicated mechanisms include loss of dystrophin binding, altered α-tubulin posttranslational modification, expression of a β-tubulin involved in regeneration, and reactive oxygen species (ROS). Here we show that the transverse microtubules in mdx muscle expressing miniaturized dystrophins are rapidly lost after eccentric contraction. Analysis of mdx lines expressing different dystrophin constructs demonstrate that spectrin-like repeats R4-15 and R20-23 were required for mechanically stable microtubules. Microtubule loss was prevented by the non-specific antioxidant N-acetylcysteine while inhibition of NADPH oxidase 2 had only a partial effect, suggesting that ROS from multiple sources mediate the rapid loss of transverse microtubules after eccentric contraction. Finally, ablation of α-dystrobrevin, β- or γ-cytoplasmic actin phenocopied the transverse microtubule instability of miniaturized dystrophins. Our data demonstrate that multiple dystrophin domains, α-dystrobrevin and cytoplasmic actins are necessary for mechanically stable microtubules.

Nitric oxide regulates ganoderic acid biosynthesis by the S-nitrosylation of aconitase under heat stress in Ganoderma lucidum

Nitric oxide (NO) is an important signalling molecule in stress response of organisms. We previously reported that NO decreases heat stress (HS)-induced ganoderic acid (GA) accumulation in Ganoderma lucidum. To explore the mechanisms by which NO modulates GA biosynthesis under HS, the effect of NO on the reactive oxygen species (ROS) content was examined. The results showed that NO decreased the production of mitochondrial ROS (mitROS) by 60% under HS. Further research revealed that NO reduced the mitROS content by inhibiting aconitase (Acon) activity. The GA content in Acon-silenced (Aconi) strains treated with NO donor did not differ significantly from that in untreated Aconi strains. To study the mechanism by which Acon activity is inhibited, the S-nitrosylation level of Acon was determined. Biotin-switch technology and mass spectrometry analysis were used to show that Acon is S-nitrosylated at the Cys-594 amino acid residue. Substitution of Cys-594 with a Ser, which cannot be S-nitrosylated, abolished the responsiveness of Acon to the NO-induced reduction in its enzymatic activity. These findings demonstrate that NO inhibits Acon activity through S-nitrosylation at Cys-594. In summary, these findings describe mechanism by which NO regulates GA biosynthesis via S-nitrosylation of Acon under HS condition in G. lucidum.

Targeting reactive oxygen species (ROS) to combat the age-related loss of muscle mass and function

The loss of muscle mass and function with age, termed sarcopenia, is an inevitable process, which has a significant impact on quality of life. During ageing we observe a progressive loss of total muscle fibres and a reduction in cross-sectional area of the remaining fibres, resulting in a significant reduction in force output. The mechanisms which underpin sarcopenia are complex and poorly understood, ranging from inflammation, dysregulation of protein metabolism and denervation. However, there is significant evidence to demonstrate that modified ROS generation, redox dis-homeostasis and mitochondrial dysfunction may have an important role to play. Based on this, significant interest and research has interrogated potential ROS-targeted therapies, ranging from nutritional-based interventions such as vitamin E/C, polyphenols (resveratrol) and targeted pharmacological compounds, using molecules such as SS-31 and MitoQ. In this review we evaluate these approaches to target aberrant age-related ROS generation and the impact on muscle mass and function.

PGC-1α, Inflammation, and Oxidative Stress: An Integrative View in Metabolism

Peroxisome proliferator-activated receptor-γ coactivator (PGC)-1α is a transcriptional coactivator described as a master regulator of mitochondrial biogenesis and function, including oxidative phosphorylation and reactive oxygen species detoxification. PGC-1α is highly expressed in tissues with high energy demands, and it is clearly associated with the pathogenesis of metabolic syndrome and its principal complications including obesity, type 2 diabetes mellitus, cardiovascular disease, and hepatic steatosis. We herein review the molecular pathways regulated by PGC-1α, which connect oxidative stress and mitochondrial metabolism with inflammatory response and metabolic syndrome. PGC-1α regulates the expression of mitochondrial antioxidant genes, including manganese superoxide dismutase, catalase, peroxiredoxin 3 and 5, uncoupling protein 2, thioredoxin 2, and thioredoxin reductase and thus prevents oxidative injury and mitochondrial dysfunction. Dysregulation of PGC-1α alters redox homeostasis in cells and exacerbates inflammatory response, which is commonly accompanied by metabolic disturbances. During inflammation, low levels of PGC-1α downregulate mitochondrial antioxidant gene expression, induce oxidative stress, and promote nuclear factor kappa B activation. In metabolic syndrome, which is characterized by a chronic low grade of inflammation, PGC-1α dysregulation modifies the metabolic properties of tissues by altering mitochondrial function and promoting reactive oxygen species accumulation. In conclusion, PGC-1α acts as an essential node connecting metabolic regulation, redox control, and inflammatory pathways, and it is an interesting therapeutic target that may have significant benefits for a number of metabolic diseases.

cGMP: a unique 2nd messenger molecule - recent developments in cGMP research and development

Cyclic guanosine monophosphate (cGMP) is a unique second messenger molecule formed in different cell types and tissues. cGMP targets a variety of downstream effector molecules and, thus, elicits a very broad variety of cellular effects. Its production is triggered by stimulation of either soluble guanylyl cyclase (sGC) or particulate guanylyl cyclase (pGC); both enzymes exist in different isoforms. cGMP-induced effects are regulated by endogenous receptor ligands such as nitric oxide (NO) and natriuretic peptides (NPs). Depending on the distribution of sGC and pGC and the formation of ligands, this pathway regulates not only the cardiovascular system but also the kidney, lung, liver, and brain function; in addition, the cGMP pathway is involved in the pathogenesis of fibrosis, inflammation, or neurodegeneration and may also play a role in infectious diseases such as malaria. Moreover, new pharmacological approaches are being developed which target sGC- and pGC-dependent pathways for the treatment of various diseases. Therefore, it is of key interest to understand this pathway from scratch, beginning with the molecular basis of cGMP generation, the structure and function of both guanylyl cyclases and cGMP downstream targets; research efforts also focus on the subsequent signaling cascades, their potential crosstalk, and also the translational and, ultimately, the clinical implications of cGMP modulation. This review tries to summarize the contributions to the "9th International cGMP Conference on cGMP Generators, Effectors and Therapeutic Implications" held in Mainz in 2019. Presented data will be discussed and extended also in light of recent landmark findings and ongoing activities in the field of preclinical and clinical cGMP research.

Nifedipine inhibits oxidative stress and ameliorates osteoarthritis by activating the nuclear factor erythroid-2-related factor 2 pathway

Nifedipine is a voltage-gated calcium channel inhibitor widely used in the treatment of hypertension. Nifedipine has been reported to have antioxidant and anti-apoptotic effects and promotes cell proliferation. However, the effects of nifedipine on oxidative stress and apoptosis in osteoarthritic (OA) chondrocytes are still unclear. In this study, we sought to investigate whether nifedipine alleviates oxidative stress and apoptosis in OA through nuclear factor erythroid-2-related factor 2 (Nrf2) activation. The cytotoxicity of nifedipine against human chondrocytes was detected using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) kit, whereas mRNA and protein expression levels were measured using reverse transcription-polymerase chain reaction (RT-PCR) and Western blotting, respectively. The oxidative stress level was analyzed by measuring reactive oxygen species (ROS), glutathione peroxidase (GSH-px), catalase (CAT) and superoxide dismutase (SOD) activities. The role of Nrf2 in the effect of nifedipine on OA was analyzed using an Nrf2 inhibitor brusatol (BR). The result showed that nifedipine inhibited the expression of matrix metalloprotein(MMP)-13, interleukin (IL)-1β, IL-6, tumor necrosis factor (TNF)-α, cyclooxygenase (COX)-2, inducible nitric oxide (NO) synthase (iNOS), and prostaglandin E2 (PGE2), as well as reduced ROS production in human OA chondrocytes, which was partially reversed by BR. Nifedipine prevented cartilage degeneration and contributed to the expression of Nrf-2 in chondrocytes. These results indicate that nifedipine inhibited inflammation and oxidative stress in chondrocytes via activation of Nrf-2/HO-1 signaling.

Arginine promotes porcine type I muscle fibres formation through improvement of mitochondrial biogenesis

The present study aimed to investigate whether arginine (Arg) promotes porcine type I muscle fibres formation via improving mitochondrial biogenesis. In the in vivo study, a total of sixty Duroc × Landrace × Yorkshire weaning piglets with an average body weight of 6·55 (sd 0·36) kg were randomly divided into four treatments and fed with a basal diet or a basal diet supplemented with 0·5, 1·0 and 1·5 % l-Arg, respectively, in a 4-week trial. Results showed that dietary supplementation of 1·0 % Arg significantly enhanced the activity of succinate dehydrogenase, up-regulated the protein expression of myosin heavy chain I (MyHC I) and increased the mRNA levels of MyHC I, troponin I1, C1 and T1 (Tnni1, Tnnc1 and Tnnt1) in longissimus dorsi muscle compared with the control group. In addition, ATPase staining analysis indicated that 1·0 % Arg supplementation significantly increased the number of type I muscle fibres and significantly decreased the number of type II muscle fibres. Furthermore, 1·0 % Arg supplementation significantly up-regulated PPAR-γ coactivator-1α (PGC-1α), sirtuin 1 and cytochrome c (Cytc) protein expressions, increased PGC-1α, nuclear respiratory factor 1 (NRF1), mitochondria transcription factor B1 (TFB1M), Cytc and ATP synthase subunit C1 (ATP5G) mRNA levels and increased mitochondrial DNA content. In the in vitro study, mitochondrial complex I inhibitor rotenone (Rot) was used. We found that Rot annulled Arg-induced type I muscle fibres formation. Together, our results provide for the first time the evidence that Arg promotes porcine type I muscle fibres formation through improvement of mitochondrial biogenesis.

Regulation of mitochondria function by natriuretic peptides

Natriuretic peptides (NPs) are well known to promote renal Na⁺ excretion, counteracting the effects of the renin-angiotensin-aldosterone system. Thus, NPs serve as a key component in the maintenance of blood pressure, influencing fluid retention capabilities via osmoregulation. Recently, NPs have been shown to affect lipolysis and enhance lipid oxidation and mitochondrial respiration. Here, we provide an overview of current knowledge about the relationship between NPs and mitochondria-mediated processes such as reactive oxygen species production, Ca²⁺ signaling, and apoptosis. Establishing a clear physiological and mechanistic connection between NPs and mitochondria in the cardiovascular system will open new avenues of research aimed at understanding and potentially using it as a therapeutic target from a completely new angle.

Natriuretic peptide signaling is involved in the expression of oxidative metabolism-related and muscle fiber constitutive genes in the gastrocnemius muscle

Natriuretic peptides regulate cyclic guanosine monophosphate (cGMP) levels via their receptors and have various physiological effects. Natriuretic peptide receptor C (NPR-C) increases cGMP signaling by functioning as a clearance receptor. We analyzed the role of natriuretic peptides in the skeletal muscle, which increases in mass with bone elongation, of NPR-C- mice. High-fat diet (HFD)-fed NPR-C- mice exhibited obesity resistance and higher oxygen consumption. PGC1α gene expression was upregulated in the gastrocnemius muscle of HFD-fed NPR-C- mice compared with HFD-fed NPR-C+ (wild-type) mice. Gene expression of proliferator-activated receptor delta and estrogen-related receptor α, which upregulate oxidative metabolism, was increased in the gastrocnemius muscle of NPR-C- mice, irrespective of diet. Expression of myosin heavy chain 7, a component of type I slow-twitch fiber, was enhanced. Natriuretic peptide signaling may influence oxidative metabolism-related and slow-twitch fiber constitutive gene expression in the fast-twitch gastrocnemius muscle but not in slow-twitch muscles such as the soleus.

Persistent upregulation of the β-tubulin tubb6, linked to muscle regeneration, is a source of microtubule disorganization in dystrophic muscle

In healthy adult skeletal muscle fibers microtubules form a three-dimensional grid-like network. In the mdx mouse, a model of Duchenne muscular dystrophy (DMD), microtubules are mostly disordered, without periodicity. These microtubule defects have been linked to the mdx mouse pathology. We now report that increased expression of the beta 6 class V β-tubulin (tubb6) contributes to the microtubule changes of mdx muscles. Wild-type muscle fibers overexpressing green fluorescent protein (GFP)-tubb6 (but not GFP-tubb5) have disorganized microtubules whereas mdx muscle fibers depleted of tubb6 (but not of tubb5) normalize their microtubules, suggesting that increasing tubb6 is toxic. However, tubb6 increases spontaneously during differentiation of mouse and human muscle cultures. Furthermore, endogenous tubb6 is not uniformly expressed in mdx muscles but is selectively increased in fiber clusters, which we identify as regenerating. Similarly, mdx-based rescued transgenic mice that retain a higher than expected tubb6 level show focal expression of tubb6 in subsets of fibers. Tubb6 is also upregulated in cardiotoxin-induced mouse muscle regeneration, in human myositis and DMD biopsies, and the tubb6 level correlates with that of embryonic myosin heavy chain, a regeneration marker. In conclusion, modulation of a β-tubulin isotype plays a role in muscle differentiation and regeneration. Increased tubb6 expression and microtubule reorganization are not pathological per se but reflect a return to an earlier developmental stage. However, chronic elevation of tubb6, as occurs in the mdx mouse, may contribute to the repeated cycles of regeneration and to the pathology of the disease.

Neuronal nitric oxide synthase (nNOS) splice variant function: Insights into nitric oxide signaling from skeletal muscle

Defects in neuronal nitric oxide synthase (nNOS) splice variant localization and signaling in skeletal muscle are a firmly established pathogenic characteristic of many neuromuscular diseases, including Duchenne and Becker muscular dystrophy (DMD and BMD, respectively). Therefore, substantial efforts have been made to understand and therapeutically target skeletal muscle nNOS isoform signaling. The purpose of this review is to summarize recent salient advances in understanding of the regulation, targeting, and function of nNOSμ and nNOSβ splice variants in normal and dystrophic skeletal muscle, primarily using findings from mouse models. The first focus of this review is how the differential targeting of nNOS splice variants creates spatially and functionally distinct nitric oxide (NO) signaling compartments at the sarcolemma, Golgi complex, and cytoplasm. Particular attention is given to the functions of sarcolemmal nNOSμ and limitations of current nNOS knockout models. The second major focus is to review current understanding of cGMP-mediated nNOS signaling in skeletal muscle and its emergence as a therapeutic target in DMD and BMD. Accordingly, we address the preclinical and clinical successes and setbacks with the testing of phosphodiesterase 5 inhibitors to redress nNOS signaling defects in DMD and BMD. In summary, this review of nNOS function in normal and dystrophic muscle aims to advance understanding how the messenger NO is harnessed for cellular signaling from a skeletal muscle perspective.

Riociguat prevents hyperoxia-induced lung injury and pulmonary hypertension in neonatal rats without effects on long bone growth

Bronchopulmonary dysplasia (BPD) remains the most common and serious chronic lung disease of premature infants. Severe BPD complicated with pulmonary hypertension (PH) increases the mortality of these infants. Riociguat is an allosteric soluble guanylate cyclase stimulator and is approved by the FDA for treating PH in adults. However, it has not been approved for use in neonates due to concern for adverse effects on long bone growth. To address this concern we investigated if administration of riociguat is beneficial in preventing hyperoxia-induced lung injury and PH without side effects on long bone growth in newborn rats. Newborn rats were randomized to normoxia (21% O₂) or hyperoxia (85% O₂) exposure groups within 24 hours of birth, and received riociguat or placebo by once daily intraperitoneal injections during continuous normoxia or hyperoxia exposure for 9 days. In the hyperoxia control group, radial alveolar count, mean linear intercept and vascular density were significantly decreased, the pathological hallmarks of BPD, and these were accompanied by an increased inflammatory response. There was also significantly elevated vascular muscularization of peripheral pulmonary vessels, right ventricular systolic pressure and right ventricular hypertrophy indicating PH. However, administration of riociguat significantly decreased lung inflammation, improved alveolar and vascular development, and decreased PH during hyperoxia by inducing cGMP production. Additionally, riociguat did not affect long bone growth or structure. These data indicate that riociguat is beneficial in preventing hyperoxia-induced lung injury and PH without affecting long bone growth and structure and hence, suggests riociguat may be a potential novel agent for preventing BPD and PH in neonates.

Discovery and development of next generation sGC stimulators with diverse multidimensional pharmacology and broad therapeutic potential

Nitric oxide (NO)-sensitive soluble guanylyl cyclase (sGC), an enzyme that catalyzes the conversion of guanosine-5'-triphosphate (GTP) to cyclic guanosine-3',5'-monophophate (cGMP), transduces many of the physiological effects of the gasotransmitter NO. Upon binding of NO to the prosthetic heme group of sGC, a conformational change occurs, resulting in enzymatic activation and increased production of cGMP. cGMP modulates several downstream cellular and physiological responses, including but not limited to vasodilation. Impairment of this signaling system and altered NO-cGMP homeostasis have been implicated in cardiovascular, pulmonary, renal, gastrointestinal, central nervous system, and hepatic pathologies. sGC stimulators, small molecule drugs that synergistically increase sGC enzyme activity with NO, have shown great potential to treat a variety of diseases via modulation of NO-sGC-cGMP signaling. Here, we give an overview of novel, orally available sGC stimulators that Ironwood Pharmaceuticals is developing. We outline the non-clinical and clinical studies, highlighting pharmacological and pharmacokinetic (PK) profiles, including pharmacodynamic (PD) effects, and efficacy in a variety of disease models.

Relation of nNOS isoforms to mitochondrial density and PGC-1alpha expression in striated muscles of mice

The expression of neuronal NO synthase (nNOS) alpha- and beta-isoforms in skeletal muscle is well documented but only little information is available about their regulation/functions. Using different mouse models, we now assessed whether the expression of nNOS-isoforms in muscle fibers is related to mitochondria content/activity and regulated by peroxisome proliferator-activated receptor gamma coactivator-1alpha (PGC-1alpha). Catalytic histochemistry revealed highest nNOS-concentrations to be present in type-2 oxidative muscle fibers. Differences in mitochondrial density between nNOS-KO-mice and WT-littermates established by morphometry after transmission electron microscopy were significant in the oxidative portion of the tibialis anterior muscle (TA) but not in rectus femoris muscle (RF) indicating an nNOS-dependent mitochondrial pool in TA. Quantitative immunoblotting displayed the nNOS alpha-isoform to preponderate in those striated muscles of C57BL/6-mice that comprise of many type-2 oxidative fibers, e.g. TA, while roughly even levels of the two nNOS-isoforms were expressed in those muscles that mainly consist of type-2 glycolytic fibers, e.g. RF. Differences in citrate synthase-activity in muscle homogenates between nNOS-KO-mice and WT-littermates were positively related to nNOS alpha-isoform levels. In transgenic-mice over-expressing muscular PGC-1alpha compared to WT-littermates, immunoblotting revealed a significant shift in nNOS-expression in favor of the alpha-isoform in six out of eight striated muscles (exceptions: soleus muscle and tongue) without consistent relationship to changes in the expression of mitochondrial markers. In summary, our study demonstrated the nNOS alpha-isoform expression to be related to mitochondrial content/activity and to be up-regulated by up-stream PGC-1alpha in striated muscles, particularly in those enriched with type-2 oxidative fibers implying a functional convergence of the two signaling systems in these fibers.

A phase 3 randomized placebo-controlled trial of tadalafil for Duchenne muscular dystrophy

OBJECTIVE

To conduct a randomized trial to test the primary hypothesis that once-daily tadalafil, administered orally for 48 weeks, lessens the decline in ambulatory ability in boys with Duchenne muscular dystrophy (DMD).

METHODS

Three hundred thirty-one participants with DMD 7 to 14 years of age taking glucocorticoids were randomized to tadalafil 0.3 mg·kg^-1·d^-1, tadalafil 0.6 mg·kg^-1·d^-1, or placebo. The primary efficacy measure was 6-minute walk distance (6MWD) after 48 weeks. Secondary efficacy measures included North Star Ambulatory Assessment and timed function tests. Performance of Upper Limb (PUL) was a prespecified exploratory outcome.

RESULTS

Tadalafil had no effect on the primary outcome: 48-week declines in 6MWD were 51.0 ± 9.3 m with placebo, 64.7 ± 9.8 m with low-dose tadalafil (p = 0.307 vs placebo), and 59.1 ± 9.4 m with high-dose tadalafil (p = 0.538 vs placebo). Tadalafil also had no effect on secondary outcomes. In boys >10 years of age, total PUL score and shoulder subscore declined less with low-dose tadalafil than placebo. Adverse events were consistent with the known safety profile of tadalafil and the DMD disease state.

CONCLUSIONS

Tadalafil did not lessen the decline in ambulatory ability in boys with DMD. Further studies should be considered to confirm the hypothesis-generating upper limb data and to determine whether ambulatory decline can be slowed by initiation of tadalafil before 7 years of age.

CLINICALTRIALSGOV IDENTIFIER

NCT01865084.

CLASSIFICATION OF EVIDENCE

This study provides Class I evidence that tadalafil does not slow ambulatory decline in 7- to 14-year-old boys with Duchenne muscular dystrophy.

Reactive Oxygen Species/Nitric Oxide Mediated Inter-Organ Communication in Skeletal Muscle Wasting Diseases

SIGNIFICANCE

Cachexia is defined as a complex metabolic syndrome that is associated with underlying illness and a loss of muscle with or without loss of fat mass. This disease is associated with a high incidence with chronic diseases such as heart failure, cancer, chronic obstructive pulmonary disease (COPD), and acquired immunodeficiency syndrome (AIDS), among others. Since there is currently no effective treatment available, cachectic patients have a poor prognosis. Elucidation of the underlying mechanisms is, therefore, an important medical task. Recent Advances: There is accumulating evidence that the diseased organs such as heart, lung, kidney, or cancer tissue secrete soluble factors, including Angiotensin II, myostatin (growth differentiation factor 8 [GDF8]), GDF11, tumor growth factor beta (TGFβ), which act on skeletal muscle. There, they induce a set of genes called atrogenes, which, among others, induce the ubiquitin-proteasome system, leading to protein degradation. Moreover, elevated reactive oxygen species (ROS) levels due to modulation of NADPH oxidases (Nox) and mitochondrial function contribute to disease progression, which is characterized by loss of muscle mass, exercise resistance, and frailty.

CRITICAL ISSUES

Although substantial progress was achieved to elucidate the pathophysiology of cachexia, effectice therapeutic strategies are urgently needed.

FUTURE DIRECTIONS

With the identification of key components of the aberrant inter-organ communication leading to cachexia, studies in mice and men to inhibit ROS formation, induction of anti-oxidative superoxide dismutases, and upregulation of muscular nitric oxide (NO) formation either by pharmacological tools or by exercise are promising approaches to reduce the extent of skeletal muscle wasting. Antioxid. Redox Signal. 26, 700-717.