Mitochondrial Dysfunction in Skeletal Muscle Pathologies

Influence of Amino Acids and Exercise on Muscle Protein Turnover, Particularly in Cancer Cachexia

Cancer cachexia is a multifaceted syndrome that impacts individuals with advanced cancer. It causes numerous pathological changes in cancer patients, such as inflammation and metabolic dysfunction, which further diminish their quality of life. Unfortunately, cancer cachexia also increases the risk of mortality in affected individuals, making it an important area of focus for cancer research and treatment. Several potential nutritional therapies are being tested in preclinical and clinical models for their efficacy in improving muscle metabolism in cancer patients. Despite promising results, no special nutritional therapies have yet been validated in clinical practice. Multiple studies provide evidence of the benefits of increasing muscle protein synthesis through an increased intake of amino acids or protein. There is also increasing evidence that exercise can reduce muscle atrophy by modulating protein synthesis. Therefore, the combination of protein intake and exercise may be more effective in improving cancer cachexia. This review provides an overview of the preclinical and clinical approaches for the use of amino acids with and without exercise therapy to improve muscle metabolism in cachexia.

Morroniside Protects C2C12 Myoblasts from Oxidative Damage Caused by ROS-Mediated Mitochondrial Damage and Induction of Endoplasmic Reticulum Stress

Oxidative stress contributes to the onset of chronic diseases in various organs, including muscles. Morroniside, a type of iridoid glycoside contained in Cornus officinalis, is reported to have advantages as a natural compound that prevents various diseases. However, the question of whether this phytochemical exerts any inhibitory effect against oxidative stress in muscle cells has not been well reported. Therefore, the current study aimed to evaluate whether morroniside can protect against oxidative damage induced by hydrogen peroxide (H2O2) in murine C2C12 myoblasts. Our results demonstrate that morroniside pretreatment was able to inhibit cytotoxicity while suppressing H2O2-induced DNA damage and apoptosis. Morroniside also significantly improved the antioxidant capacity in H2O2-challenged C2C12 cells by blocking the production of cellular reactive oxygen species and mitochondrial superoxide and increasing glutathione production. In addition, H2O2-induced mitochondrial damage and endoplasmic reticulum (ER) stress were effectively attenuated by morroniside pretreatment, inhibiting cytoplasmic leakage of cytochrome c and expression of ER stress-related proteins. Furthermore, morroniside neutralized H2O2-mediated calcium (Ca2+) overload in mitochondria and mitigated the expression of calpains, cytosolic Ca2+-dependent proteases. Collectively, these findings demonstrate that morroniside protected against mitochondrial impairment and Ca2+-mediated ER stress by minimizing oxidative stress, thereby inhibiting H2O2-induced cytotoxicity in C2C12 myoblasts.

Age-dependent loss of Crls1 causes myopathy and skeletal muscle regeneration failure

Skeletal muscle aging results in the gradual suppression of myogenesis, leading to muscle mass loss. However, the specific role of cardiolipin in myogenesis has not been determined. This study investigated the crucial role of mitochondrial cardiolipin and cardiolipin synthase 1 (Crls1) in age-related muscle deterioration and myogenesis. Our findings demonstrated that cardiolipin and Crls1 are downregulated in aged skeletal muscle. Moreover, the knockdown of Crls1 in myoblasts reduced mitochondrial mass, activity, and OXPHOS complex IV expression and disrupted the structure of the mitochondrial cristae. AAV9-shCrls1-mediated downregulation of Crls1 impaired muscle regeneration in a mouse model of cardiotoxin (CTX)-induced muscle damage, whereas AAV9-mCrls1-mediated Crls1 overexpression improved regeneration. Overall, our results highlight that the age-dependent decrease in CRLS1 expression contributes to muscle loss by diminishing mitochondrial quality in skeletal muscle myoblasts. Hence, modulating CRLS1 expression is a promising therapeutic strategy for mitigating muscle deterioration associated with aging, suggesting potential avenues for developing interventions to improve overall muscle health and quality of life in elderly individuals.

Adrenalectomy attenuates hyperalgesia but does not regulate muscle wasting in a female rat model of fibromyalgia

Although it is well established that fibromyalgia (FM) syndrome is characterized by chronic diffuse musculoskeletal hyperalgesia, very little is known about the effect of this pathology on muscle tissue plasticity. Therefore, the present study aimed to characterize the putative alterations in skeletal muscle mass in female rats subjected to a FM model by inducing chronic diffuse hyperalgesia (CDH) through double injections of acidic saline (pH 4.0) into the left gastrocnemius muscle at 5-day intervals. To determine protein turnover, the total proteolysis, proteolytic system activities and protein synthesis were evaluated in oxidative soleus muscles of pH 7.2 (control) and pH 4.0 groups at 7 days after CDH induction. All animals underwent behavioural analyses of mechanical hyperalgesia, strength and motor performance. Our results demonstrated that, in addition to hyperalgesia, rats injected with acidic saline exhibited skeletal muscle loss, as evidenced by a decrease in the soleus fibre cross-sectional area. This muscle loss was associated with increased proteasomal proteolysis and expression of the atrophy-related gene (muscle RING-finger protein-1), as well as reduced protein synthesis and decreased protein kinase B/S6 pathway activity. Although the plasma corticosterone concentration did not differ between the control and pH 4.0 groups, the removal of the adrenal glands attenuated hyperalgesia, but it did not prevent the increase in muscle protein loss in acidic saline-injected animals. The data suggests that the stress-related hypothalamic-pituitary-adrenal axis is involved in the development of hyperalgesia, but is not responsible for muscle atrophy observed in the FM model induced by intramuscular administration of acidic saline. Although the mechanisms involved in the attenuation of hyperalgesia in rats injected with acidic saline and subjected to adrenalectomy still need to be elucidated, the results found in this study suggest that glucocorticoids may not represent an effective therapeutic approach to alleviate FM symptoms.

Fuzhuan brick tea extract ameliorates obesity-induced skeletal muscle atrophy by alleviating mitochondrial dysfunction in mice

Fuzhuan brick tea (FBT) is a post-fermented tea fermented by the fungus Eurotium cristatum and is mainly produced in Hunan Province, China. Our previous study revealed that FBT extract prevents obesity by increasing energy expenditure and mitochondrial content in mice. Therefore, in this study, we hypothesized that FBT extract could be effective in alleviating obesity-induced muscle atrophy by addressing mitochondrial dysfunction, and aimed to explore the underlying molecular mechanism of FBT extract in high-fat diet-induced obese mice. FBT extract increased skeletal muscle weight and size, myosin heavy chain isoforms, and muscle performance in obese mice. Additionally, FBT extract reduced obesity-induced intramuscular lipids, skeletal muscle inflammation, and the expression of skeletal muscle atrophy markers, and increased the expression of fibronectin type III domain-containing protein 5 in skeletal muscles. Obesity-induced skeletal muscle mitochondrial dysfunction was improved by FBT extract as analyzed through mitochondrial morphology, fatty acid oxidation, respiratory chain complexes, and mitochondrial dynamics and biogenesis. Epigallocatechin, a major bioactive compound in FBT extract, attenuated palmitic acid-induced muscle atrophy by regulating mitochondrial functions in C2C12 cells. In conclusion, FBT extract may prevent obesity-induced muscle atrophy by alleviating mitochondrial dysfunction in mice.

Identifying Acss1, Mtfp1 and Oxct1 as key regulators and promising biomarkers of sarcopenia in various models

Mitochondrial dysfunction plays a critical role in muscular homeostasis, but the molecular mechanism underlying mitochondrial dynamics and sarcopenia awaits to be uncovered. We all know that malnutrition, cachexia, and type 2 diabetes are significant contributors to the development of sarcopenia.Therefore, we analyzed a bioinformatic analysis on cathectic differentially expressed genes (cDEGs), fasted differentially genes (fDEGs) and mitochondria-related genes. The overlapping genes identified were then validated by RT-qPCR and Western blotting experiments in various sarcopenia mice models and used to predict aging-related muscle loss in humans. First, the correlation analysis and PPI network indicated 6 overlapping candidates (Bdh1, Gdap1, Acss1, Mtfp1, Idh2, Oxct1) may constitute a regulatory effect in mitochondrial dynamics and muscle wasting. Next, we successfully established fasted, Lewis lung carcinoma (LLC) and Diabetes Mellitus (DM) induced sarcopenia mice models and verified that Acss1, Mtfp1 and Oxct1 shared common and significant variation tendency in these sarcopenia mice models. Further-more, Pearson correlation analysis showed that Acss1 was negatively related to the weight of gastrocnemius while Mtfp1 and Oxct1 displayed a significantly positive correlation with gastrocnemius weight in sarcopenic mice model induced by LLC, fasting and DM. What's more, ROC analysis based on human aging-related datasets indicated Acss1, Mtfp1, Oxct1 had outstanding diagnostic capabilities for sarcopenia. In general, we identified three hub genes (Acss1, Mtfp1 and Oxct1) that are strongly associated with mitochondrial dysfunction in sarcopenia and may provide novel and reliable indicators for screening, diagnosis, and prognosis, as well as potential therapeutic targets for patients with sarcopenia.

The Role of Mitochondrial Quality Control in Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) is a major cause of morbidity, mortality, and health care use worldwide with heterogeneous pathogenesis. Mitochondria, the powerhouses of cells responsible for oxidative phosphorylation and energy production, play essential roles in intracellular material metabolism, natural immunity, and cell death regulation. Therefore, it is crucial to address the urgent need for fine-tuning the regulation of mitochondrial quality to combat COPD effectively. Mitochondrial quality control (MQC) mainly refers to the selective removal of damaged or aging mitochondria and the generation of new mitochondria, which involves mitochondrial biogenesis, mitochondrial dynamics, mitophagy, etc. Mounting evidence suggests that mitochondrial dysfunction is a crucial contributor to the development and progression of COPD. This article mainly reviews the effects of MQC on COPD as well as their specific regulatory mechanisms. Finally, the therapeutic approaches of COPD via MQC are also illustrated.

Modulation of mitochondrial activity by sugarcane (Saccharum officinarum L.) top extract and its bioactive polyphenols: a comprehensive transcriptomics analysis in C2C12 myotubes and HepG2 hepatocytes

Age-related mitochondrial dysfunction leads to defects in cellular energy metabolism and oxidative stress defense systems, which can contribute to tissue damage and disease development. Among the key regulators responsible for mitochondrial quality control, peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) is an important target for mitochondrial dysfunction. We have previously reported that bioactive polyphenols extracted from sugarcane top (ST) ethanol extract (STEE) could activate neuronal energy metabolism and increase astrocyte PGC-1α transcript levels. However, their potential impact on the mitochondria activity in muscle and liver cells has not yet been investigated. To address this gap, our current study examined the effects of STEE and its polyphenols on cultured myotubes and hepatocytes in vitro. Rhodamine 123 assay revealed that the treatment with STEE and its polyphenols resulted in an increase in mitochondrial membrane potential in C2C12 myotubes. Furthermore, a comprehensive examination of gene expression patterns through transcriptome-wide microarray analysis indicated that STEE altered gene expressions related to mitochondrial functions, fatty acid metabolism, inflammatory cytokines, mitogen-activated protein kinase (MAPK) signaling, and cAMP signaling in both C2C12 myotubes and HepG2 hepatocytes. Additionally, protein-protein interaction analysis identified the PGC-1α interactive-transcription factors-targeted regulatory network of the genes regulated by STEE, and the quantitative polymerase chain reaction results confirmed that STEE and its polyphenols upregulated the transcript levels of PGC-1α in both C2C12 and HepG2 cells. These findings collectively suggest the potential beneficial effects of STEE on muscle and liver tissues and offer novel insights into the potential nutraceutical applications of this material.

Electroacupuncture alleviates multifidus muscle injury by modulating mitochondrial function and Ca2+ uptake

Multifidus muscles maintain the stability of the lumbar spine and play a crucial role in the pathogenesis of nonspecific lower back pain. Previous studies have shown that electroacupuncture (EA) can relieve the symptoms of low back pain and reduce injury to the lumbar multifidus muscles. In this study, a rat model of lumbar multifidus muscle injury was established by 0.05% bupivacaine injection and subsequently treated with EA at bilateral "Weizhong" (BL40) acupoints. Disruption of the function and structure of multifidus muscles, increased cytosolic Ca2+ in multifidus myocytes, and reduced mitochondrial fission and ATP production were observed in the model group. Additionally, increased expression of the mitochondrial calcium uniporter (MCU) promoted mitochondrial reuptake of Ca2+ , reversing the excessive increase in cytoplasmic Ca2+ . However, the excessive increase in MCU not only aggravated the increased cytoplasmic Ca2+ but also decreased the expression of the mitochondrial division proteins dynamin-related protein 1 (Drp1) and mitochondrial fission factor (MFF). EA inhibited the overexpression of MCU, promoted mitochondrial reuptake of Ca2+ , and reversed cytosolic Ca2+ overload. Furthermore, EA regulated the expression of the mitochondrial fission proteins Drp1 and MFF and promoted the production of ATP, helping the recovery of mitochondrial function after multifidus injury. Therefore, EA can protect against bupivacaine-induced mitochondrial dysfunction, possibly by attenuating MCU overexpression in the inner mitochondrial membrane and reducing Ca2+ overloading in muscle cells, thereby protecting mitochondrial function and maintaining the normal energy demand of muscle cells.

Modulation of sarcopenia phenotypes by glutathione peroxidase 4 overexpression in mice

Our laboratory previously showed lipid hydroperoxides and oxylipin levels are elevated in response to loss of skeletal muscle innervation and are associated with muscle pathologies. To elucidate the pathological impact of lipid hydroperoxides, we overexpressed glutathione peroxidase 4 (GPx4), an enzyme that targets reduction of lipid hydroperoxides in membranes, in adult CuZn superoxide dismutase knockout (Sod1KO) mice that show accelerated muscle atrophy associated with loss of innervation. The gastrocnemius muscle from Sod1KO mice shows reduced mitochondrial respiration and elevated oxidative stress (F2 -isoprostanes and hydroperoxides) compared to wild-type (WT) mice. Overexpression of GPx4 improved mitochondrial respiration and reduced hydroperoxide generation in Sod1KO mice, but did not attenuate the muscle loss that occurs in Sod1KO mice. In contrast, contractile force generation is reduced in EDL muscle in Sod1KO mice relative to WT mice, and overexpression of GPx4 restored force generation to WT levels in Sod1KO mice. GPx4 overexpression also prevented loss of muscle contractility at the single fibre level in fast-twitch fibres from Sod1KO mice. Muscle fibres from Sod1KO mice were less sensitive to both depolarization and calcium at the single fibre level and exhibited a reduced activation by S-glutathionylation. GPx4 overexpression in Sod1KO mice rescued the deficits in both membrane excitability and calcium sensitivity of fast-twitch muscle fibres. Overexpression of GPx4 also restored the sarco/endoplasmic reticulum Ca2+ -ATPase activity in Sod1KO gastrocnemius muscles. These data suggest that GPx4 plays an important role in preserving excitation-contraction coupling function and Ca2+ homeostasis, and in maintaining muscle and mitochondrial function in oxidative stress-induced sarcopenia. KEY POINTS: Knockout of CuZn superoxide dismutase (Sod1KO) induces elevated oxidative stress with accelerated muscle atrophy and weakness. Glutathione peroxidase 4 (GPx4) plays a fundamental role in the reduction of lipid hydroperoxides in membranes, and overexpression of GPx4 improves mitochondrial respiration and reduces hydroperoxide generation in Sod1KO mice. Muscle contractile function deficits in Sod1KO mice are alleviated by the overexpression of GPx4. GPx4 overexpression in Sod1KO mice rescues the impaired muscle membrane excitability of fast-twitch muscle fibres and improves their calcium sensitivity. Sarco/endoplasmic reticulum Ca2+ -ATPase activity in Sod1KO muscles is decreased, and it is restored by the overexpression of GPx4. Our results confirm that GPx4 plays an important role in preserving excitation-contraction coupling function and Ca2+ homeostasis, and maintaining muscle and mitochondrial function in oxidative stress-induced sarcopenia.

5-Heptadecylresorcinol Ameliorates Obesity-Associated Skeletal Muscle Mitochondrial Dysfunction through SIRT3-Mediated Mitophagy

Skeletal muscle dysfunction caused by obesity is characterized by the decline in mitochondrial content and function. 5-Heptadecylresorcinol (AR-C17) is a specific bioactive component derived from whole wheat and rye, which has been evidenced to improve obesity-associated skeletal muscle dysregulation. However, the mechanism underlying its protective activity requires further exploration. Herein, we found that AR-C17 (5, 10, and 20 μM) intervention reversed PA-induced (0.5 mM) reduction in mitochondrial content, mitochondrial membrane potential, and mitochondrial energy metabolism in C2C12 cells. Meanwhile, AR-C17 evidently alleviated PA-mediated myotube mitochondrial dysfunction via elevating mitochondria autophagy flux and upregulating the expression level of autophagy-related protein, while this effect was abolished by an autophagy inhibitor (3-MA). Further analysis showed that SIRT3-FOXO3A-PINK-Parkin-mediated mitophagy was involved in the modulation of myocyte mitochondrial dysfunction by AR-C17. In addition, AR-C17 administration (30 and 150 mg/kg/day) significantly improved high-fat-diet-induced mitochondrial dysregulation in mice skeletal muscle tissue via SIRT3-dependent mitophagy. Our findings indicate that skeletal muscle cells are responsive to AR-C17, which improves myogenesis and mitophagy in vitro and in vivo.

Gastric Cancer with Sarcopenia: an Area Worth Focusing On

OPINION STATEMENT

Gastric cancer (GC) is the fifth most common cancer and the third leading cause of cancer death worldwide, which seriously endangers human health. A number of studies have shown that sarcopenia occurs more frequently in patients with gastric cancer than in the general population and can significantly affect the disease status and survival of patients, which is of great significance in predicting the prognosis of gastric cancer. Patients with gastric cancer may suffer sarcopenia no matter before or after surgery, and the pathogenesis is complex. Abnormal nutrient metabolism and reduced exercise are the leading causes. In addition, surgical treatment and chemotherapy for gastric cancer might participate in the physiological and pathological mechanism of sarcopenia. Generally speaking, exercise and nutritional therapy are the main prevention and treatment methods for sarcopenia. But more prospective evidence is needed to establish reasonable interventions, and other drug treatments are in their infancy. For the diagnostic criteria of sarcopenia, the cut-off values of the skeletal muscle mass index obtained from CT images vary widely and need to be standardized and unified. We also need to explore simple predictors to facilitate sarcopenia risk assessment. More research is needed to formulate more appropriate treatments for gastric cancer patients with sarcopenia.

Autophagy in sarcopenia: Possible mechanisms and novel therapies

With global population aging, age-related diseases, especially sarcopenia, have attracted much attention in recent years. Characterized by low muscle strength, low muscle quantity or quality and low physical performance, sarcopenia is one of the major factors associated with an increased risk of falls and disability. Much effort has been made to understand the cellular biological and physiological mechanisms underlying sarcopenia. Autophagy is an important cellular self-protection mechanism that relies on lysosomes to degrade misfolded proteins and damaged organelles. Research designed to obtain new insight into human diseases from the autophagic aspect has been carried out and has made new progress, which encourages relevant studies on the relationship between autophagy and sarcopenia. Autophagy plays a protective role in sarcopenia by modulating the regenerative capability of satellite cells, relieving oxidative stress and suppressing the inflammatory response. This review aims to reveal the specific interaction between sarcopenia and autophagy and explore possible therapies in hopes of encouraging more specific research in need and unlocking novel promising therapies to ameliorate sarcopenia.

Mechanisms Underlying the Effects of the Green Tea Polyphenol EGCG in Sarcopenia Prevention and Management

Sarcopenia is prevalent among the older population and severely affects human health. Tea catechins may benefit for skeletal muscle performance and protect against secondary sarcopenia. However, the mechanisms underlying their antisarcopenic effect are still not fully understood. Despite initial successes in animal and early clinical trials regarding the safety and efficacy of (-)-epigallocatechin-3-gallate (EGCG), a major catechin of green tea, many challenges, problems, and unanswered questions remain. In this comprehensive review, we discuss the potential role and underlying mechanisms of EGCG in sarcopenia prevention and management. We thoroughly review the general biological activities and general effects of EGCG on skeletal muscle performance, EGCG's antisarcopenic mechanisms, and recent clinical evidence of the aforesaid effects and mechanisms. We also address safety issues and provide directions for future studies. The possible concerted actions of EGCG indicate the need for further studies on sarcopenia prevention and management in humans.

Cholic and deoxycholic acids induce mitochondrial dysfunction, impaired biogenesis and autophagic flux in skeletal muscle cells

BACKGROUND

Skeletal muscle is sensitive to bile acids (BA) because it expresses the TGR5 receptor for BA. Cholic (CA) and deoxycholic (DCA) acids induce a sarcopenia-like phenotype through TGR5-dependent mechanisms. Besides, a mouse model of cholestasis-induced sarcopenia was characterised by increased levels of serum BA and muscle weakness, alterations that are dependent on TGR5 expression. Mitochondrial alterations, such as decreased mitochondrial potential and oxygen consumption rate (OCR), increased mitochondrial reactive oxygen species (mtROS) and unbalanced biogenesis and mitophagy, have not been studied in BA-induced sarcopenia.

METHODS

We evaluated the effects of DCA and CA on mitochondrial alterations in C₂C₁₂ myotubes and a mouse model of cholestasis-induced sarcopenia. We measured mitochondrial mass by TOM20 levels and mitochondrial DNA; ultrastructural alterations by transmission electronic microscopy; mitochondrial biogenesis by PGC-1α plasmid reporter activity and protein levels by western blot analysis; mitophagy by the co-localisation of the MitoTracker and LysoTracker fluorescent probes; mitochondrial potential by detecting the TMRE probe signal; protein levels of OXPHOS complexes and LC3B by western blot analysis; OCR by Seahorse measures; and mtROS by MitoSOX probe signals.

RESULTS

DCA and CA caused a reduction in mitochondrial mass and decreased mitochondrial biogenesis. Interestingly, DCA and CA increased LC3II/LC3I ratio and decreased autophagic flux concordant with raised mitophagosome-like structures. In addition, DCA and CA decreased mitochondrial potential and reduced protein levels in OXPHOS complexes I and II. The results also demonstrated that DCA and CA decreased basal, ATP-linked, FCCP-induced maximal respiration and spare OCR. DCA and CA also reduced the number of cristae. In addition, DCA and CA increased the mtROS. In mice with cholestasis-induced sarcopenia, TOM20, OXPHOS complexes I, II and III, and OCR were diminished. Interestingly, the OCR and OXPHOS complexes were correlated with muscle strength and bile acid levels.

CONCLUSION

Our results showed that DCA and CA decreased mitochondrial mass, possibly by reducing mitochondrial biogenesis, which affects mitochondrial function, thereby altering potential OCR and mtROS generation. Some mitochondrial alterations were also observed in a mouse model of cholestasis-induced sarcopenia characterised by increased levels of BA, such as DCA and CA.

A Scoping Review Investigating the "Gene-Dosage Theory" of Mitochondrial DNA in the Healthy Skeletal Muscle

This review provides an overview of the evidence regarding mtDNA and valid biomarkers for assessing mitochondrial adaptions. Mitochondria are small organelles that exist in almost all cells throughout the human body. As the only organelle, mitochondria contain their own DNA, mitochondrial DNA (mtDNA). mtDNA-encoded polypeptides are subunits of the enzyme complexes in the electron transport chain (ETC) that are responsible for production of ATP to the cells. mtDNA is frequently used as a biomarker for mitochondrial content, since changes in mitochondrial volume are thought to induce similar changes in mtDNA. However, some exercise studies have challenged this "gene-dosage theory", and have indicated that changes in mitochondrial content can adapt without changes in mtDNA. Thus, the aim of this scoping review was to summarize the studies that used mtDNA as a biomarker for mitochondrial adaptions and address the question as to whether changes in mitochondrial content, induce changes in mtDNA in response to aerobic exercise in the healthy skeletal muscle. The literature was searched in PubMed and Embase. Eligibility criteria included: interventional study design, aerobic exercise, mtDNA measurements reported pre- and postintervention for the healthy skeletal muscle and English language. Overall, 1585 studies were identified. Nine studies were included for analysis. Eight out of the nine studies showed proof of increased oxidative capacity, six found improvements in mitochondrial volume, content and/or improved mitochondrial enzyme activity and seven studies did not find evidence of change in mtDNA copy number. In conclusion, the findings imply that mitochondrial adaptions, as a response to aerobic exercise, can occur without a change in mtDNA copy number.

Kcnma1 is involved in mitochondrial homeostasis in diabetes-related skeletal muscle atrophy

Uncontrolled diabetes causes a catabolic state with multi-organic complications, of which impairment on skeletal muscle contributes to the damaged mobility. Kcnma1 gene encodes the pore-forming α-subunit of Ca²⁺ - and voltage-gated K⁺ channels of large conductance (BK channels), and loss-of-function mutations in Kcnma1 are in regards to impaired myogenesis. Herein, we observed a time-course reduction of Kcnma1 expression in the tibialis anterior muscles of leptin receptor-deficient (db/db) diabetic mice. To investigate the role of Kcnma1 in diabetic muscle atrophy, muscle-specific knockdown of Kcnma1 was achieved by mice receiving intravenous injection of adeno-associated virus-9 (AAV9)-encoding shRNA against Kcnma1 under the muscle creatine kinase (MCK) promoter. Impairment on muscle mass and myogenesis were observed in m/m mice with AAV9-shKcnma1 intervention, while this impairment was more obvious in diabetic db/db mice. Simultaneously, damaged mitochondrial dynamics and biogenesis showed much severer in db/db mice with AAV9-shKcnma1 intervention. RNA sequencing revealed the large transcriptomic changes resulted by Kcnma1 knockdown, and changes in mitochondrial homeostasis-related genes were validated. Besides, the artificial alteration of Kcnma1 in mouse C2C12 myoblasts was achieved with an adenovirus vector. Consistent results were demonstrated by Kcnma1 knockdown in palmitate-treated cells, whereas opposite results were exhibited by Kcnma1 overexpression. Collectively, we document Kcnma1 as a potential keeper of mitochondrial homeostasis, and the loss of Kcnma1 is a critical event in priming skeletal muscle loss in diabetes.

Glycyl- l-histidyl- l-lysine-Cu2+ rescues cigarette smoking-induced skeletal muscle dysfunction via a sirtuin 1-dependent pathway

BACKGROUND

Skeletal muscle dysfunction is an important co-morbidity in patients with chronic obstructive pulmonary disease (COPD) and is significantly associated with increased mortality. Oxidative stress has been demonstrated an important trigger for COPD-related skeletal muscle dysfunction. Glycine-histidine-lysine (GHK) is an active tripeptide, which is a normal component of human plasma, saliva, and urine; promotes tissue regeneration; and acts as an anti-inflammatory and antioxidant properties. The purpose of this study was to determine whether GHK is involved in COPD-related skeletal muscle dysfunction.

METHODS

The plasma GHK level in patients with COPD (n = 9) and age-paired healthy subjects (n = 11) were detected using reversed-phase high-performance liquid chromatography. The complex GHK with Cu (GHK-Cu) was used in in vitro (C2C12 myotubes) and in vivo experiments (cigarette smoking [CS]-exposure mouse model) to explore the involvement of GHK in CS-induced skeletal muscle dysfunction.

RESULTS

Compared with healthy control, plasma GHK levels were decreased in patients with COPD (70.27 ± 38.87 ng/mL vs. 133.0 ± 54.54 ng/mL, P = 0.009). And plasma GHK levels in patients with COPD were associated with pectoralis muscle area (R = 0.684, P = 0.042), inflammatory factor TNF-α (R = -0.696, P = 0.037), and antioxidative stress factor SOD2 (R = 0.721, P = 0.029). GHK-Cu was found to rescue CSE-induced skeletal muscle dysfunction in C2C12 myotubes, as evidenced by increased expression of myosin heavy chain, reduced expression of MuRF1 and atrogin-1, elevated mitochondrial content, and enhanced resistance to oxidative stress. In CS-induced muscle dysfunction C57BL/6 mice, GHK-Cu treatment (0.2 and 2 mg/kg) reduces CS-induced muscle mass loss (skeletal muscle weight (1.19 ± 0.09% vs. 1.29 ± 0.06%, 1.40 ± 0.05%; P < 0.05) and muscle cross-sectional area elevated (1055 ± 552.4 μm² vs. 1797 ± 620.9 μm² , 2252 ± 534.0 μm² ; P < 0.001), and also rescues CS-induced muscle weakness, indicated by improved grip strength (175.5 ± 36.15 g vs. 257.6 ± 37.98 g, 339.1 ± 72.22 g; P < 0.01). Mechanistically, GHK-Cu directly binds and activates SIRT1(the binding energy was -6.1 kcal/mol). Through activating SIRT1 deacetylation, GHK-Cu inhibits FoxO3a transcriptional activity to reduce protein degradation, deacetylates Nrf2 and contribute to its action of reducing oxidative stress by generation of anti-oxidant enzymes, increases PGC-1α expression to promote mitochondrial function. Finally, GHK-Cu could protect mice against CS-induced skeletal muscle dysfunction via SIRT1.

CONCLUSIONS

Plasma glycyl- l-histidyl- l-lysine level in patients with chronic obstructive pulmonary disease was significantly decreased and was significantly associated with skeletal muscle mass. Exogenous administration of glycyl- l-histidyl- l-lysine-Cu²⁺ could protect against cigarette smoking-induced skeletal muscle dysfunction via sirtuin 1.

Serum Retinol Binding Protein 4 as a Potential Biomarker for Sarcopenia in Older Adults

Sarcopenia is characterized by progressive loss of muscle mass and function due to aging. Retinol-binding protein 4 (RBP4) is an adipokine with pro-inflammatory effects. However, the change of RBP4 concentration and its role in sarcopenia remains unclear. The aim of this study was to evaluate the association of serum RBP4 level with sarcopenia in the older adults. A total of 816 community-dwelling older adults aged ≥60 years were enrolled. Serum RBP4 was measured by enzyme-linked immunosorbent assay. Appendicular skeletal muscle mass index (ASMI), grip strength, and gait speed were measured. We found that serum RBP4 levels were higher in patients with sarcopenia when compared with those without sarcopenias (44.3 [33.9-57.7] vs 38.0 [28.0-48.4] μg/mL). Receiver operating characteristic curve analysis indicated that the optimal cutoff value of serum RBP4 level that predicted sarcopenia was 38.79 μg/mL with a sensitivity of 67.8% and a specificity of 53.3%. Multivariate logistic regression analysis showed that the subjects with a higher level of RBP4 had a higher risk of sarcopenia (adjusted odds ratio [OR] = 2.036, 95% CI = 1.449-2.861). Serum RBP4 concentration was negatively correlated with grip strength (r = -.098), gait speed (r = -.186), and AMSI (r = -.096). Moreover, serum RBP4 levels were higher in patients with severe sarcopenia when compared with those with moderate sarcopenia (49.0 [37.3-61.2] vs 40.4 [31.3-51.2] μg/mL). Taken together, our results demonstrate that serum RBP4 level is correlated with the risk and severity of sarcopenia in the older adults, indicating that RBP4 might serve as a surrogate biomarker for the screening and evaluation of sarcopenia.

Mechanism of skeletal muscle atrophy after spinal cord injury: A narrative review

Spinal cord injury leads to loss of innervation of skeletal muscle, decreased motor function, and significantly reduced load on skeletal muscle, resulting in atrophy. Factors such as braking, hormone level fluctuation, inflammation, and oxidative stress damage accelerate skeletal muscle atrophy. The atrophy process can result in skeletal muscle cell apoptosis, protein degradation, fat deposition, and other pathophysiological changes. Skeletal muscle atrophy not only hinders the recovery of motor function but is also closely related to many systemic dysfunctions, affecting the prognosis of patients with spinal cord injury. Extensive research on the mechanism of skeletal muscle atrophy and intervention at the molecular level has shown that inflammation and oxidative stress injury are the main mechanisms of skeletal muscle atrophy after spinal cord injury and that multiple pathways are involved. These may become targets of future clinical intervention. However, most of the experimental studies are still at the basic research stage and still have some limitations in clinical application, and most of the clinical treatments are focused on rehabilitation training, so how to develop more efficient interventions in clinical treatment still needs to be further explored. Therefore, this review focuses mainly on the mechanisms of skeletal muscle atrophy after spinal cord injury and summarizes the cytokines and signaling pathways associated with skeletal muscle atrophy in recent studies, hoping to provide new therapeutic ideas for future clinical work.

Dietary interventions and molecular mechanisms for healthy musculoskeletal aging

Over the past decade, extensive efforts have focused on understanding age-associated diseases and how to prolong a healthy lifespan. The induction of dietary protocols such as caloric restriction (CR) and protein restriction (PR) has positively affected a healthy lifespan. These intervention ideas (nutritional protocols) have been the subject of human cohort studies and clinical trials to evaluate their effectiveness in alleviating age-related diseases (such as type II diabetes, cardiovascular disease, obesity, and musculoskeletal fragility) and promoting human longevity. This study summarizes the literature on the nutritional protocols, emphasizing their impacts on bone and muscle biology. In addition, we analyzed several CR studies using Gene Expression Omnibus (GEO) database and identified common transcriptome changes to understand the signaling pathway involved in musculoskeletal tissue. We identified nine novel common genes, out of which five were upregulated (Emc3, Fam134b, Fbxo30, Pip5k1a, and Retsat), and four were downregulated (Gstm2, Per2, Fam78a, and Sel1l3) with CR in muscles. Gene Ontology enrichment analysis revealed that CR regulates several signaling pathways (e.g., circadian gene regulation and rhythm, energy reserve metabolic process, thermogenesis) involved in energy metabolism. In conclusion, this study summarizes the beneficiary role of CR and identifies novel genes and signaling pathways involved in musculoskeletal biology.

Porous Se@SiO2 nanoparticles improve oxidative injury to promote muscle regeneration via modulating mitochondria

Background: Acute skeletal muscle injuries are common among physical or sports traumas. The excessive oxidative stress at the site of injury impairs muscle regeneration. The authors have recently developed porous Se@SiO₂ nanoparticles (NPs) with antioxidant properties. Methods: The protective effects were evaluated by cell proliferation, myogenic differentiation and mitochondrial activity. Then, the therapeutic effect was investigated in a cardiotoxin-induced muscle injury rat model. Results: Porous Se@SiO₂ NPs significantly protected the morphological and functional stability of mitochondria, thus protecting satellite cells from H₂O₂-induced damage to cell proliferation and myogenic differentiation. In the rat model, intervention with porous Se@SiO₂ NPs promoted muscle regeneration. Conclusion: This study reveals the application potential of porous Se@SiO₂ NPs in skeletal muscle diseases related to mitochondrial dysfunction.

Muscle fiber type-specific autophagy responses following an overnight fast and mixed meal ingestion in human skeletal muscle

The aim of the present study was to investigate the fiber type-specific abundance of autophagy-related proteins after an overnight fast and following ingestion of a mixed meal in human skeletal muscle. Twelve overweight, healthy young male volunteers underwent a 3-h mixed meal tolerance test following an overnight fast. Blood samples were collected in the overnight-fasted state and throughout the 180-min postmeal period. Skeletal muscle biopsies were collected in the fasted state, and at 30 and 90 min after meal ingestion. Protein content of key autophagy markers and upstream signaling responses were measured in whole muscle and pooled single fibers using immunoblotting. In the fasted state, type I fibers displayed lower LC3B-I but higher LC3B-II abundance and higher LC3B-II/LC3B-I ratio compared with type II fibers (P < 0.05). However, there were no fiber type differences in p62/SQSTM1, unc-51 like autophagy activating kinase (ULK1), ATG5, or ATG12 (P > 0.05). Compared with the fasted state, there was a reduction in LC3B-II abundance, indicative of lower autophagosome content, in whole muscle and in both type I and type II fibers following meal ingestion (P < 0.05). This reduction in autophagosome content occurred alongside similar increases in p-Akt^S473 and p-mTOR^S2448 in both type I and type II muscle fibers (P < 0.05). In human skeletal muscle, type I fibers have a greater autophagosome content than type II fibers in the overnight-fasted state despite comparable abundance of other key upstream autophagy proteins. Autophagy is rapidly inhibited in both fiber types following the ingestion of a mixed meal.NEW & NOTEWORTHY This study examined the fiber type-specific content of key autophagy proteins in human muscle. We showed that markers of autophagosome content are higher in type I fibers in the overnight-fasted state, whereas autophagy is rapidly inhibited in both type I and type II fibers after the ingestion of a mixed meal.

Extra Virgin Olive Oil (EVOO), a Mediterranean Diet Component, in the Management of Muscle Mass and Function Preservation

Aging results in a progressive decline in skeletal muscle mass, strength and function, a condition known as sarcopenia. This pathological condition is due to multifactorial processes including physical inactivity, inflammation, oxidative stress, hormonal changes, and nutritional intake. Physical therapy remains the standard approach to treat sarcopenia, although some interventions based on dietary supplementation are in clinical development. In this context, thanks to its known anti-inflammatory and antioxidative properties, there is great interest in using extra virgin olive oil (EVOO) supplementation to promote muscle mass and health in sarcopenic patients. To date, the molecular mechanisms responsible for the pathological changes associated with sarcopenia remain undefined; however, a complete understanding of the signaling pathways that regulate skeletal muscle protein synthesis and their behavior during sarcopenia appears vital for defining how EVOO might attenuate muscle wasting during aging. This review highlights the main molecular players that control skeletal muscle mass, with particular regard to sarcopenia, and discusses, based on the more recent findings, the potential of EVOO in delaying/preventing loss of muscle mass and function, with the aim of stimulating further research to assess dietary supplementation with EVOO as an approach to prevent or delay sarcopenia in aging individuals.

Bile Acids Induce Alterations in Mitochondrial Function in Skeletal Muscle Fibers

Cholestatic chronic liver disease is characterized by developing sarcopenia and elevated serum levels of bile acids. Sarcopenia is a skeletal muscle disorder with the hallmarks of muscle weakness, muscle mass loss, and muscle strength decline. Our previous report demonstrated that deoxycholic acid (DCA) and cholic acid (CA), through the membrane receptor TGR5, induce a sarcopenia-like phenotype in myotubes and muscle fibers. The present study aimed to evaluate the impact of DCA and CA on mitochondrial mass and function in muscle fibers and the role of the TGR5 receptor. To this end, muscle fibers obtained from wild-type and TGR5^−/− mice were incubated with DCA and CA. Our results indicated that DCA and CA decreased mitochondrial mass, DNA, and potential in a TGR5-dependent fashion. Furthermore, with TGR5 participation, DCA and CA also reduced the oxygen consumption rate and complexes I and II from the mitochondrial electron transport chain. In addition, DCA and CA generated more mitochondrial reactive oxygen species than the control, which were abolished in TGR5^−/− mice muscle fibers. Our results indicate that DCA and CA induce mitochondrial dysfunction in muscle fibers through a TGR5-dependent mechanism.

The Effect of Dietary Leucine Supplementation on Antioxidant Capacity and Meat Quality of Finishing Pigs under Heat Stress

This study examined the effects of dietary leucine supplements on antioxidant capacity and meat quality in growing-finishing pigs. A total of 24 crossbred (Duroc × Landrace × Yorkshire) pigs with an average initial weight of 68.33 ± 0.97 kg were randomly allotted to three treatment groups. All pigs were exposed to constant heat stress. Each group of pigs was fed a basal diet, or a diet supplemented with increasing levels of leucine (0.25% or 0.50%). The results showed that leucine intake could improve average daily gain and reduce feed/gain of finishing pigs under heat stress (p < 0.05). The supplementation of leucine could improve the carcass slant length (p = 0.09), and dramatically increased loin-eye area of the finishing pigs (p < 0.05) but had no significant effect on other carcass traits. Compared with the control group, 0.50% leucine markedly reduced drip loss and shear force of longissimus dorsi muscle, and increased pH value at 24 h after slaughter (p < 0.05). Dietary supplementation of 0.25% leucine increased the contents of inosine monophosphate and intramuscular fat in biceps femoris muscle (p < 0.05). Supplementation of 0.25% or 0.50% leucine significantly stimulated the activities of antioxidant enzymes while reduced the level of MDA in serum, liver and longissimus dorsi muscle (p < 0.05). Compared with the control group, 0.50% leucine supplementation markedly modulated the relative mRNA expression levels of genes related to muscle fiber type and mitochondrial function in longissimus dorsi muscle and the gene relative antioxidant in the liver (p < 0.05). In conclusion, dietary leucine supplementation could improve the growth performance and meat quality of the finishing pigs under heat stress, and the pathway of Keap1-NRF2 and PGC-1α-TFAM might be involved.

Elevated mir-145-5p is associated with skeletal muscle dysfunction and triggers apoptotic cell death in C2C12 myotubes

Skeletal muscle dysfunction is a common comorbidity of chronic obstructive pulmonary disease (COPD), and the molecular mechanisms regarding to the pathogenesis of this disease have not been elucidated. In this study, a novel miR-145-5p was significantly upregulated in the serum collected from patients with COPD-associated muscle atrophy, in contrast with the normal participants. Then, we evidenced that silencing of miR-145-5p suppressed cell death and elongated cell survival during cell culture process. Consistently, upregulation of miR-145-5p induced cell apoptosis and restrain cell viability in the C2C12 cells, suggesting that miR-145-5p contributes to cell death. Further experiments evidenced that miR-145-5p decreased the expression levels of phosphorylated PI3K (p-PI3K), Akt (p-Akt) and mTOR (p-mTOR) to inactivate the PI3K/Akt/mTOR pathway, and this pathway was also reactivated by miR-145-5p ablation. Finally, we proved that the protective effects of miR-145-5p ablation were abrogated by co-treating cells with PI3K inhibitor LY294002. Taken together, we concluded that miR-145-5p promoted cell death to facilitate muscle dysfunctions via inactivating the PI3K/Akt/mTOR pathway.

A High-Fat Diet Induces Muscle Mitochondrial Dysfunction and Impairs Swimming Capacity in Zebrafish: A New Model of Sarcopenic Obesity

Obesity is a highly prevalent disease that can induce metabolic syndrome and is associated with a greater risk of muscular atrophy. Mitochondria play central roles in regulating the physiological metabolism of skeletal muscle; however, whether a decreased mitochondrial function is associated with impaired muscle function is unclear. In this study, we evaluated the effects of a high-fat diet on muscle mitochondrial function in a zebrafish model of sarcopenic obesity (SOB). In SOB zebrafish, a significant decrease in exercise capacity and skeletal muscle fiber cross-sectional area was detected, accompanied by high expression of the atrophy-related markers Atrogin-1 and muscle RING-finger protein-1. Zebrafish with SOB exhibited inhibition of mitochondrial biogenesis and fatty acid oxidation as well as disruption of mitochondrial fusion and fission in atrophic muscle. Thus, our findings showed that muscle atrophy was associated with SOB-induced mitochondrial dysfunction. Overall, these results showed that the SOB zebrafish model established in this study may provide new insights into the development of therapeutic strategies to manage mitochondria-related muscular atrophy.

IL-6 Deficiency Attenuates Skeletal Muscle Atrophy by Inhibiting Mitochondrial ROS Production through the Upregulation of PGC-1α in Septic Mice

Current evidences indicate that both inflammation and oxidative stress contribute to the pathogenesis of sepsis-associated skeletal muscle atrophy. However, the interaction between inflammation and oxidative stress has not been completely understood in sepsis-associated skeletal muscle atrophy. Here in the present study, a murine model of sepsis has been established by cecal ligation and puncture (CLP) with wild-type and interleukin- (IL-) 6 knockout (KO) mice. Our results suggested that IL-6 KO largely attenuated skeletal muscle atrophy as reflected by reduced protein degradation, increased cross-sectional area (CSA) of myofibers, and improved muscle contractile function (all $P<0.05$ ). In addition, we observed that IL-6 KO promoted the expression of peroxisome proliferator-activated receptor γ coactivator–1alpha (PGC–1α) and inhibited CLP-induced mitochondrial reactive oxygen species (ROS) production in skeletal muscles (all $P<0.05$ ). However, the knockdown of PGC–1α abolished the protective effects of IL-6 KO in CLP-induced skeletal muscle atrophy and reversed the changes in mitochondrial ROS production (all $P<0.05$ ). Ex vivo experiments found that exogenous IL-6 inhibited PGC–1α expression, promoted mitochondrial ROS production, and induced proteolysis in C2C12 cells (all $P<0.05$ ). Together, these results suggested that IL-6 deficiency attenuated skeletal muscle atrophy by inhibiting mitochondrial ROS production through the upregulation of PGC–1α expression in septic mice.

Therapeutic Targets for Regulating Oxidative Damage Induced by Ischemia-Reperfusion Injury: A Study from a Pharmacological Perspective

Ischemia-reperfusion (I-R) injury is damage caused by restoring blood flow into ischemic tissues or organs. This complex and characteristic lesion accelerates cell death induced by signaling pathways such as apoptosis, necrosis, and even ferroptosis. In addition to the direct association between I-R and the release of reactive oxygen species and reactive nitrogen species, it is involved in developing mitochondrial oxidative damage. Thus, its mechanism plays a critical role via reactive species scavenging, calcium overload modulation, electron transport chain blocking, mitochondrial permeability transition pore activation, or noncoding RNA transcription. Other receptors and molecules reduce tissue and organ damage caused by this pathology and other related diseases. These molecular targets have been gradually discovered and have essential roles in I-R resolution. Therefore, the current study is aimed at highlighting the importance of these discoveries. In this review, we inquire about the oxidative damage receptors that are relevant to reducing the damage induced by oxidative stress associated with I-R. Several complications on surgical techniques and pathology interventions do not mitigate the damage caused by I-R. Nevertheless, these therapies developed using alternative targets could work as coadjuvants in tissue transplants or I-R-related pathologies

Iron supplementation is sufficient to rescue skeletal muscle mass and function in cancer cachexia

Cachexia is a wasting syndrome characterized by devastating skeletal muscle atrophy that dramatically increases mortality in various diseases, most notably in cancer patients with a penetrance of up to 80%. Knowledge regarding the mechanism of cancer-induced cachexia remains very scarce, making cachexia an unmet medical need. In this study, we discovered strong alterations of iron metabolism in the skeletal muscle of both cancer patients and tumor-bearing mice, characterized by decreased iron availability in mitochondria. We found that modulation of iron levels directly influences myotube size in vitro and muscle mass in otherwise healthy mice. Furthermore, iron supplementation was sufficient to preserve both muscle function and mass, prolong survival in tumor-bearing mice, and even rescues strength in human subjects within an unexpectedly short time frame. Importantly, iron supplementation refuels mitochondrial oxidative metabolism and energy production. Overall, our findings provide new mechanistic insights in cancer-induced skeletal muscle wasting, and support targeting iron metabolism as a potential therapeutic option for muscle wasting diseases.

Multi-omics research in sarcopenia: Current progress and future prospects

Sarcopenia is a systemic disease with progressive and generalized skeletal muscle dysfunction defined by age-related low muscle mass, high content of muscle slow fibers, and low muscle function. Muscle phenotypes and sarcopenia risk are heritable; however, the genetic architecture and molecular mechanisms underlying sarcopenia remain largely unclear. In recent years, significant progress has been made in determining susceptibility loci using genome-wide association studies. In addition, recent advances in omics techniques, including genomics, epigenomics, transcriptomics, proteomics, and metabolomics, offer new opportunities to identify novel targets to help us understand the pathophysiology of sarcopenia. However, each individual technology cannot capture the entire view of the biological complexity of this disorder, while integrative multi-omics analyses may be able to reveal new insights. Here, we review the latest findings of multi-omics studies for sarcopenia and provide an in-depth summary of our current understanding of sarcopenia pathogenesis. Leveraging multi-omics data could give us a holistic understanding of sarcopenia etiology that may lead to new clinical applications. This review offers guidance and recommendations for fundamental research, innovative perspectives, and preventative and therapeutic interventions for sarcopenia.

Role of Creatine Supplementation in Conditions Involving Mitochondrial Dysfunction: A Narrative Review

Creatine monohydrate (CrM) is one of the most widely used nutritional supplements among active individuals and athletes to improve high-intensity exercise performance and training adaptations. However, research suggests that CrM supplementation may also serve as a therapeutic tool in the management of some chronic and traumatic diseases. Creatine supplementation has been reported to improve high-energy phosphate availability as well as have antioxidative, neuroprotective, anti-lactatic, and calcium-homoeostatic effects. These characteristics may have a direct impact on mitochondrion's survival and health particularly during stressful conditions such as ischemia and injury. This narrative review discusses current scientific evidence for use or supplemental CrM as a therapeutic agent during conditions associated with mitochondrial dysfunction. Based on this analysis, it appears that CrM supplementation may have a role in improving cellular bioenergetics in several mitochondrial dysfunction-related diseases, ischemic conditions, and injury pathology and thereby could provide therapeutic benefit in the management of these conditions. However, larger clinical trials are needed to explore these potential therapeutic applications before definitive conclusions can be drawn.

Advanced oxidation protein products contribute to chronic kidney disease-induced muscle atrophy by inducing oxidative stress via CD36/NADPH oxidase pathway

BACKGROUND

Sarcopenia with chronic kidney disease (CKD) progression is associated with life prognosis. Oxidative stress has attracted interest as a trigger for causing CKD-related muscular atrophy. Advanced oxidation protein products (AOPPs), a uraemic toxin, are known to increase oxidative stress. However, the role of AOPPs on CKD-induced muscle atrophy remains unclear.

METHODS

In a retrospective case-control clinical study, we evaluated the relationship between serum AOPPs levels and muscle strength in haemodialysis patients with sarcopenia (n = 26, mean age ± SEM: 78.5 ± 1.4 years for male patients; n = 22, mean age ± SEM: 79.1 ± 1.5 for female patients), pre-sarcopenia (n = 12, mean age ± SEM: 73.8 ± 2.0 years for male patients; n = 4, mean age ± SEM: 74.3 ± 4.1 for female patients) or without sarcopenia (n = 12, mean age ± SEM: 71.3 ± 1.6 years for male patients; n = 7, mean age ± SEM: 77.7 ± 1.6 for female ). The molecular mechanism responsible for the AOPPs-induced muscle atrophy was investigated by using 5/6-nephrectomized CKD mice, AOPPs-overloaded mice, and C2C12 mouse myoblast cells.

RESULTS

The haemodialysis patients with sarcopenia showed higher serum AOPPs levels as compared with the patients without sarcopenia. The serum AOPPs levels showed a negative correlation with grip strength (P < 0.01 for male patients, P < 0.01 for female patients) and skeletal muscle index (P < 0.01 for male patients). Serum AOPPs levels showed a positive correlation with cysteinylated albumin (Cys-albumin), a marker of oxidative stress (r2  = 0.398, P < 0.01). In the gastrocnemius of CKD mice, muscle AOPPs levels were also increased, and it showed a positive correlation with atrogin-1 (r2  = 0.538, P < 0.01) and myostatin expression (r2  = 0.421, P < 0.05), but a negative correlation with PGC-1α expression (r2  = 0.405, P < 0.05). Using C2C12 cells, AOPPs increased atrogin-1 and myostatin expression through the production of reactive oxygen species via CD36/NADPH oxidase pathway, and decreased myotube formation. AOPPs also induced mitochondrial dysfunction. In the AOPPs-overloaded mice showed that decreasing running time and hanging time accompanied by increasing AOPPs levels and decreasing cross-sectional area in gastrocnemius.

CONCLUSIONS

Advanced oxidation protein products contribute to CKD-induced sarcopenia, suggesting that AOPPs or its downstream signalling pathway could be a therapeutic target for the treatment of CKD-induced sarcopenia. Serum AOPPs or Cys-albumin levels could be a new diagnostic marker for sarcopenia in CKD.

Experimental models of lipid overload and their relevance in understanding skeletal muscle insulin resistance and pathological changes in mitochondrial oxidative capacity

It remains essential to decipher some of the pathological mechanisms that link obesity with deteriorating human health. Insulin resistance, due to enhanced free fatty acid substrate delivery, results in disrupted glucose homeostasis and altered mitochondrial oxidative capacity, which is a characteristic feature of an obese state. In fact, as a major site for regulating glucose homeostasis and energy production in response to insulin, the skeletal muscle has become an interesting target tissue to understand the impact of lipid overload on the development of insulin resistance and impaired mitochondrial respiratory function. In addition to systematically retrieving the discussed data, the current review brings an essential perspective in understanding the relevance of experimental models of lipid overload such as high fat diets in understanding the pathological link between insulin resistance and pathological changes in mitochondrial oxidative capacity. Importantly, inclusion of evidence from transgenic model highlights some of the unique molecular targets that are implicated in the development of insulin resistance and inefficient mitochondrial respiration processes within an obese state. Importantly, saturation with lipid products such as ceramides and diacylglycerols, especially within the skeletal muscle, appears to be instrumental in paving the path leading to worsening of metabolic complications. These metabolic consequences mostly interfere with the efficiency of the mitochondrial electron transport chain, leading to overproduction of toxic reactive oxygen species. Therefore, therapeutic agents that reverse the effects of lipid overload by improving insulin sensitivity and mitochondrial oxidative capacity are crucial for the management or even treatment of metabolic diseases.

Requirements for successful mitochondrial transplantation

Maintenance of mitochondrial oxidative phosphorylation capacity and other mitochondrial functions are essential for the prevention of mitochondrial dysfunction-related diseases such as neurodegenerative, cardiovascular, and liver diseases. To date, no well-known treatment modality has been developed to prevent or reduce mitochondrial dysfunction. However, a novel approach that transplants fully functional mitochondria directly into defective cells has recently caught the attention of scientists. In this review, we provide an overview of the cell/tissue source of the mitochondria to prompt cell regeneration or tissue repair in vitro and in vivo applications. The animal and human models entail that effective procedures should be used in the isolation and confirmation of mitochondrial membrane potential and function. We believe that these procedures for mitochondrial transplantation for tissue or cell culture will confirm intact, viable, and free from contamination isolated mitochondria from the appropriate sources.

Loss of zebrafish atp6v1e1b, encoding a subunit of vacuolar ATPase, recapitulates human ARCL type 2C syndrome and identifies multiple pathobiological signatures

The inability to maintain a strictly regulated endo(lyso)somal acidic pH through the proton-pumping action of the vacuolar-ATPases (v-ATPases) has been associated with various human diseases including heritable connective tissue disorders. Autosomal recessive (AR) cutis laxa (CL) type 2C syndrome is associated with genetic defects in the ATP6V1E1 gene and is characterized by skin wrinkles or loose redundant skin folds with pleiotropic systemic manifestations. The underlying pathological mechanisms leading to the clinical presentations remain largely unknown. Here, we show that loss of atp6v1e1b in zebrafish leads to early mortality, associated with craniofacial dysmorphisms, vascular anomalies, cardiac dysfunction, N-glycosylation defects, hypotonia, and epidermal structural defects. These features are reminiscent of the phenotypic manifestations in ARCL type 2C patients. Our data demonstrates that loss of atp6v1e1b alters endo(lyso)somal protein levels, and interferes with non-canonical v-ATPase pathways in vivo. In order to gain further insights into the processes affected by loss of atp6v1e1b, we performed an untargeted analysis of the transcriptome, metabolome, and lipidome in early atp6v1e1b-deficient larvae. We report multiple affected pathways including but not limited to oxidative phosphorylation, sphingolipid, fatty acid, and energy metabolism together with profound defects on mitochondrial respiration. Taken together, our results identify complex pathobiological effects due to loss of atp6v1e1b in vivo.

Cutis laxa syndromes are pleiotropic disorders of the connective tissue, characterized by skin redundancy and variable systemic manifestations. Cutis laxa syndromes are caused by pathogenic variants in genes encoding structural and regulatory components of the extracellular matrix or in genes encoding components of cellular trafficking, metabolism, and mitochondrial function. Pathogenic variants in genes coding for vacuolar-ATPases, a multisubunit complex responsible for the acidification of multiple intracellular vesicles, cause type 2 cutis laxa syndromes, a group of cutis laxa subtypes further characterized by neurological, skeletal, and rarely cardiopulmonary manifestations. To investigate the pathomechanisms of vacuolar-ATPase dysfunction, we generated zebrafish models that lack a crucial subunit of the vacuolar-ATPases. The mutant zebrafish models show morphological and functional features reminiscent of the phenotypic manifestations in cutis laxa patients carrying pathogenic variants in ATP6V1E1. In-depth analysis at multiple -omic levels identified biological signatures that indicate impairment of signaling pathways, lipid metabolism, and mitochondrial respiration. We anticipate that these data will contribute to a better understanding of the pathogenesis of cutis laxa syndromes and other disorders involving defective v-ATPase function, which may eventually improve patient treatment and management.

Mitochondrial Dysfunction Is a Common Denominator Linking Skeletal Muscle Wasting Due to Disease, Aging, and Prolonged Inactivity

Skeletal muscle is the most abundant tissue in the body and is required for numerous vital functions, including breathing and locomotion. Notably, deterioration of skeletal muscle mass is also highly correlated to mortality in patients suffering from chronic diseases (e.g., cancer). Numerous conditions can promote skeletal muscle wasting, including several chronic diseases, cancer chemotherapy, aging, and prolonged inactivity. Although the mechanisms responsible for this loss of muscle mass is multifactorial, mitochondrial dysfunction is predicted to be a major contributor to muscle wasting in various conditions. This systematic review will highlight the biochemical pathways that have been shown to link mitochondrial dysfunction to skeletal muscle wasting. Importantly, we will discuss the experimental evidence that connects mitochondrial dysfunction to muscle wasting in specific diseases (i.e., cancer and sepsis), aging, cancer chemotherapy, and prolonged muscle inactivity (e.g., limb immobilization). Finally, in hopes of stimulating future research, we conclude with a discussion of important future directions for research in the field of muscle wasting.

Is Upregulation of Sarcolipin Beneficial or Detrimental to Muscle Function?

Sarcolipin (SLN) is a regulator of sarco/endo plasmic reticulum Ca²⁺-ATPase (SERCA) pump and has been shown to be involved in muscle nonshivering thermogenesis (NST) and energy metabolism. Interestingly, SLN expression is significantly upregulated both during muscle development and in several disease states. However, the significance of altered SLN expression in muscle patho-physiology is not completely understood. We have previously shown that transgenic over-expression of SLN in skeletal muscle is not detrimental, and can promote oxidative metabolism and exercise capacity. In contrast, some studies have suggested that SLN upregulation in disease states is deleterious for muscle function and ablation of SLN can be beneficial. In this perspective article, we critically examine both published and some new data to determine the relevance of SLN expression to disease pathology. The new data presented in this paper show that SLN levels are induced in muscle during systemic bacterial (Salmonella) infection or lipopolysaccharides (LPS) treatment. We also present data showing that SLN expression is significantly upregulated in different types of muscular dystrophies including myotubular myopathy. These data taken together reveal that upregulation of SLN expression in muscle disease is progressive and increases with severity. Therefore, we suggest that increased SLN expression should not be viewed as the cause of the disease; rather, it is a compensatory response to meet the higher energy demand of the muscle. We interpret that higher SLN/SERCA ratio positively modulate cytosolic Ca²⁺ signaling pathways to promote mitochondrial biogenesis and oxidative metabolism to meet higher energy demand in muscle.

Specialized, pro-resolving mediators as potential therapeutic agents for alleviating fibromyalgia symptomatology

OBJECTIVE

To present a hypothesis on a novel strategy in the treatment of fibromyalgia (FM).

DESIGN

A narrative review.

SETTING

FM as a disease remains a challenging concept for numerous reasons, including undefined etiopathogenesis, unclear triggers and unsuccessful treatment modalities. We hypothesize that the inflammatome, the entire set of molecules involved in inflammation, acting as a common pathophysiological instrument of gut dysbiosis, sarcopenia, and neuroinflammation, is one of the major mechanisms underlying FM pathogenesis. In this setup, dysbiosis is proposed as the primary trigger of the inflammatome, sarcopenia as the peripheral nociceptive source, and neuroinflammation as the central mechanism of pain sensitization, transmission and symptomatology of FM. Whereas neuroinflammation is highly-considered as a critical deleterious element in FM pathogenesis, the presumed pathogenic roles of sarcopenia and systemic inflammation remain controversial. Nevertheless, sarcopenia-associated processes and dysbiosis have been recently detected in FM individuals. The prevalence of pro-inflammatory factors in the cerebrospinal fluid and blood has been repeatedly observed in FM individuals, supporting an idea on the role of inflammatome in FM pathogenesis. As such, failed inflammation resolution might be one of the underlying pathogenic mechanisms. In accordance, the application of specialized, inflammation pro-resolving mediators (SPMs) seems most suitable for this goal.

CONCLUSIONS

The capability of various SPMs to prevent and attenuate pain has been repeatedly demonstrated in laboratory animal experiments. Since SPMs suppress inflammation in a manner that does not compromise host defense, they could be attractive and safe candidates for the alleviation of FM symptomatology, probably in combination with anti-dysbiotic medicine.

Bufei Jianpi Formula Improves Mitochondrial Function and Suppresses Mitophagy in Skeletal Muscle via the Adenosine Monophosphate-Activated Protein Kinase Pathway in Chronic Obstructive Pulmonary Disease

Skeletal muscle dysfunction, a striking systemic comorbidity of chronic obstructive pulmonary disease (COPD), is associated with declines in activities of daily living, reductions in health status and prognosis, and increases in mortality. Bufei Jianpi formula (BJF), a traditional Chinese herbal formulation, has been shown to improve skeletal muscle tension and tolerance via inhibition of cellular apoptosis in COPD rat models. This study aimed to investigate the mechanisms by which BJF regulates the adenosine monophosphate-activated protein kinase (AMPK) pathway to improve mitochondrial function and to suppress mitophagy in skeletal muscle cells. Our study showed that BJF repaired lung function and ameliorated pathological impairment in rat lung and skeletal muscle tissues. BJF also improved mitochondrial function and reduced mitophagy via the AMPK signaling pathway in rat skeletal muscle tissue. In vitro, BJF significantly improved cigarette smoke extract-induced mitochondrial functional impairment in L6 skeletal muscle cells through effects on mitochondrial membrane potential, mitochondrial permeability transition pores, adenosine triphosphate production, and mitochondrial respiration. In addition, BJF led to upregulated expression of mitochondrial biogenesis markers, including AMPK-α, PGC-1α, and TFAM and downregulation of mitophagy markers, including LC3B, ULK1, PINK1, and Parkin, with increased expression of downstream markers of the AMPK pathway, including mTOR, PPARγ, and SIRT1. In conclusion, BJF significantly improved skeletal muscle and mitochondrial function in COPD rats and L6 cells by promoting mitochondrial biogenesis and suppressing mitophagy via the AMPK pathway. This study suggests that BJF may have therapeutic potential for prophylaxis and treatment of skeletal muscle dysfunction in patients with COPD.

SARS-CoV-2/Renin-Angiotensin System: Deciphering the Clues for a Couple with Potentially Harmful Effects on Skeletal Muscle

Severe acute respiratory syndrome coronavirus (SARS-CoV-2) has produced significant health emergencies worldwide, resulting in the declaration by the World Health Organization of the coronavirus disease 2019 (COVID-19) pandemic. Acute respiratory syndrome seems to be the most common manifestation of COVID-19. A high proportion of patients require intensive care unit admission and mechanical ventilation (MV) to survive. It has been well established that angiotensin-converting enzyme type 2 (ACE2) is the primary cellular receptor for SARS-CoV-2. ACE2 belongs to the renin–angiotensin system (RAS), composed of several peptides, such as angiotensin II (Ang II) and angiotensin (1-7) (Ang-(1-7)). Both peptides regulate muscle mass and function. It has been described that SARS-CoV-2 infection, by direct and indirect mechanisms, affects a broad range of organ systems. In the skeletal muscle, through unbalanced RAS activity, SARS-CoV-2 could induce severe consequences such as loss of muscle mass, strength, and physical function, which will delay and interfere with the recovery process of patients with COVID-19. This article discusses the relationship between RAS, SARS-CoV-2, skeletal muscle, and the potentially harmful consequences for skeletal muscle in patients currently infected with and recovering from COVID-19.

Role of Oxidative Stress in Hepatic and Extrahepatic Dysfunctions during Nonalcoholic Fatty Liver Disease (NAFLD)

Nonalcoholic fatty liver disease (NAFLD) is a pathology that contains a broad liver dysfunctions spectrum. These alterations span from noninflammatory isolated steatosis until nonalcoholic steatohepatitis (NASH), a more aggressive form of the disease characterized by steatosis, inflammatory status, and varying liver degrees fibrosis. NAFLD is the most prevalent chronic liver disease worldwide. The causes of NAFLD are diverse and include genetic and environmental factors. The presence of NASH is strongly associated with cirrhosis development and hepatocellular carcinoma, two conditions that require liver transplantation. The liver alterations during NAFLD are well described. Interestingly, this pathological condition also affects other critical tissues and organs, such as skeletal muscle and even the cardiovascular, renal, and nervous systems. Oxidative stress (OS) is a harmful state present in several chronic diseases, such as NAFLD. The purpose of this review is to describe hepatic and extrahepatic dysfunctions in NAFLD. We will also review the influence of OS on the physiopathological events that affect the critical function of the liver and peripheral tissues.

The Effects of Calcium-β-Hydroxy-β-Methylbutyrate on Aging-Associated Apoptotic Signaling and Muscle Mass and Function in Unloaded but Nonatrophied Extensor Digitorum Longus Muscles of Aged Rats

Beta-hydroxy-beta-methylbutyrate (HMB), a naturally occurring leucine metabolite, has been shown to attenuate plantar flexor muscle loss and increase myogenic stem cell activation during reloading after a period of significant muscle wasting by disuse in old rodents. However, it was less clear if HMB would alter dorsiflexor muscle response to unloading or reloading when there was no significant atrophy that was induced by unloading. In this study, we tested if calcium HMB (Ca-HMB) would improve muscle function and alter apoptotic signaling in the extensor digitorum longus (EDL) of aged animals that were unloaded but did not undergo atrophy. The EDL muscle was unloaded for 14 days by hindlimb suspension (HS) in aged (34-36 mo.) male Fisher 344 × Brown Norway rats. The rats were removed from HS and allowed normal cage ambulation for 14 days of reloading (R). Throughout the study, the rats were gavaged daily with 170 mg of Ca-HMB or water 7 days prior to HS, then throughout 14 days of HS and 14 days of recovery after removing HS. The animals' body weights were significantly reduced by ~18% after 14 days of HS and continued to decline by ~22% during R as compared to control conditions; however, despite unloading, EDL did not atrophy by HS, nor did it increase in mass after R. No changes were observed in EDL twitch contraction time, force production, fatigue resistance, fiber cross-sectional area, or markers of nuclear apoptosis (myonuclei + satellite cells) after HS or R. While HS and R increased the proapoptotic Bax protein abundance, BCL-2 abundance was also increased as was the frequency of TUNEL-positive myonuclei and satellite cells, yet muscle mass and fiber cross-sectional area did not change and Ca-HMB treatment had no effect reducing apoptotic signaling. These data indicate that (i) increased apoptotic signaling preceded muscle atrophy or occurred without significant EDL atrophy and (ii) that Ca-HMB treatment did not improve EDL signaling, muscle mass, or muscle function in aged rats, when HS and R did not impact mass or function.

Cholic acid and deoxycholic acid induce skeletal muscle atrophy through a mechanism dependent on TGR5 receptor

Skeletal muscle atrophy is characterized by the degradation of myofibrillar proteins, such as myosin heavy chain or troponin. An increase in the expression of two muscle-specific E3 ligases, atrogin-1 and MuRF-1, and oxidative stress are involved in muscle atrophy. Patients with chronic liver diseases (CLD) develop muscle wasting. Several bile acids increase in plasma during cholestatic CLD, among them, cholic acid (CA) and deoxycholic acid (DCA). The receptor for bile acids, TGR5, is expressed in healthy skeletal muscles. TGR5 is involved in the regulation of muscle differentiation and metabolic changes. In this paper, we evaluated the participation of DCA and CA in the generation of an atrophic condition in myotubes and isolated fibers from the muscle extracted from wild-type (WT) and TGR5-deficient (TGR5^-/- ) male mice. The results show that DCA and CA induce a decrease in diameter, and myosin heavy chain (MHC) protein levels, two typical atrophic features in C₂ C₁₂ myotubes. We also observed similar results when INT-777 agonists activated the TGR5 receptor. To evaluate the participation of TGR5 in muscle atrophy induced by DCA and CA, we used a culture of muscle fiber isolated from WT and TGR5^-/- mice. Our results show that DCA and CA decrease the fiber diameter and MHC protein levels, and there is an increase in atrogin-1, MuRF-1, and oxidative stress in WT fibers. The absence of TGR5 in fibers abolished all these effects induced by DCA and CA. Thus, we demonstrated that CS and deoxycholic acid induce skeletal muscle atrophy through TGR5 receptor.

Angiotensin (1-7) Decreases Myostatin-Induced NF-κB Signaling and Skeletal Muscle Atrophy

Myostatin is a myokine that regulates muscle function and mass, producing muscle atrophy. Myostatin induces the degradation of myofibrillar proteins, such as myosin heavy chain or troponin. The main pathway that mediates protein degradation during muscle atrophy is the ubiquitin proteasome system, by increasing the expression of atrogin-1 and MuRF-1. In addition, myostatin activates the NF-κB signaling pathway. Renin–angiotensin system (RAS) also regulates muscle mass. Angiotensin (1-7) (Ang-(1-7)) has anti-atrophic properties in skeletal muscle. In this paper, we evaluated the effect of Ang-(1-7) on muscle atrophy and signaling induced by myostatin. The results show that Ang-(1-7) prevented the decrease of the myotube diameter and myofibrillar protein levels induced by myostatin. Ang-(1-7) also abolished the increase of myostatin-induced reactive oxygen species production, atrogin-1, MuRF-1, and TNF-α gene expressions and NF-κB signaling activation. Ang-(1-7) inhibited the activity mediated by myostatin through Mas receptor, as is demonstrated by the loss of all Ang-(1-7)-induced effects when the Mas receptor antagonist A779 was used. Our results show that the effects of Ang-(1-7) on the myostatin-dependent muscle atrophy and signaling are blocked by MK-2206, an inhibitor of Akt/PKB. Together, these data indicate that Ang-(1-7) inhibited muscle atrophy and signaling induced by myostatin through a mechanism dependent on Mas receptor and Akt/PKB.