Naringin induces skeletal muscle fiber type transformation via AMPK/PGC-1α signaling pathway in mice and C2C12 myotubes

Effect of ST36 electroacupuncture on the switch of skeletal muscle fibres in mice with sciatic nerve dissociation

Skeletal muscle is striated muscle that moves autonomously and is innervated by peripheral nerves. Peripheral nerve injury is very common in clinical treatment. However, the commonly used treatment methods often focus on the regeneration of the injured nerve but overlook the pathological changes in the injured skeletal muscle. Acupuncture, as the main treatment for denervated skeletal muscle atrophy, is used extensively in clinical practice. In the present study, a mouse model of lower limb sciatic nerve detachment was constructed and treated with electroacupuncture Stomach 36 to observe the atrophy of lower limb skeletal muscle and changes in skeletal muscle fibre types before and after electroacupuncture Stomach 36 treatment. Mice with skeletal muscle denervation showed a decrease in the proportion of IIa muscle fibres and an increase in the proportion of IIb muscle fibres, after electroacupuncture Stomach 36. The changes were reversed by specific activators of p38 MAPK, which increased IIa myofibre ratio. The results suggest that electroacupuncture Stomach 36 can reverse the change of muscle fibre type from IIb to IIa after denervation of skeletal muscle by inhibiting p38 MAPK. The results provide an important theoretical basis for the treatment of clinical peripheral nerve injury diseases with electroacupuncture, in addition to novel insights that could facilitate the study of pathological changes of denervated skeletal muscle.

Effect of resveratrol on skeletal slow-twitch muscle fiber expression via AMPK/PGC-1α signaling pathway in bovine myotubes

The purpose of this study was to evaluate the impact of resveratrol on slow-twitch muscle fiber expression in bovine myotubes. The results revealed that resveratrol enhanced slow myosin heavy chain (MyHC) and suppressed fast MyHC protein expression, accompanied by increased MyHC I/IIa and decreased MyHC IIx/IIb mRNA levels in bovine myotubes (P < 0.05). Resveratrol also enhanced the activities of succinic dehydrogenase (SDH), malate dehydrogenase (MDH) and the mitochondrial DNA (mtDNA) content, but reduced lactate dehydrogenase (LDH) activity (P < 0.05). Meanwhile, the protein and gene expression of AMPK, SIRT1 and PGC-1α were upregulated by resveratrol (P < 0.05). Furthermore, PGC-1α inhibitor SR-18292 could attenuate resveratrol-induced muscle fiber conversion from fast-twitch to slow-twitch. These results suggest that resveratrol might promote muscle fiber type transition from fast-twitch to slow-twitch through the AMPK/PGC-1α signaling pathway and mitochondrial biogenesis in bovine myotubes.

A Lignan from Alnus japonica Activates Myogenesis and Alleviates Dexamethasone-induced Myotube Atrophy

To find inhibitors against skeletal muscle loss, we isolated a lignan compound ((-)-(2R,3R-1,4-O-diferuloylsecoisolarciresinol, DFS) from the stem of Alnus japonica. C2C12 myoblasts were treated with DFS during differentiation. To induce an in vitro atrophic condition, differentiated myotubes were treated with dexamethasone (a synthetic glucocorticoid). DFS (10 nM) increased expression levels of myogenic factors and the number of multi-nucleated myotubes expressing myosin heavy chain (MHC). The myogenic potential of DFS could be attributed to p38 MAPK activation. DFS also protected against dexamethasone-induced damage, showing increased expression of MHC and mammalian target of rapamycin (mTOR), a major anabolic factor. Under atrophic condition, the anti-myopathy effect of DFS was associated with inactivation of NF-κB signaling pathway and the subsequent suppression of muscle degradative E3 ligases and myostatin. DFS treatment also restored fast muscle fiber (type II a, II b, and II x), known to be susceptible to dexamethasone. These results indicate that DFS isolated from A. japonica can stimulate myogenesis via p38 MAPK activation and alleviate muscle atrophy by modulating the expression of genes associated with muscle protein anabolism/catabolism. Thus, we propose that DFS can be used as a pharmacological and nutraceutical agent for increasing muscle strength or protecting muscle loss.

Effects of protocatechuic acid on antioxidant capacity, mitochondrial biogenesis and skeletal muscle fiber transformation

In skeletal muscle, the increased proportion of type I muscle fibers has the potential to improve muscle atrophy and prevent human metabolic diseases. Protocatechuic acid (PCA), as a kind of anthocyanin metabolite, has antioxidant and anti-inflammatory physiological activities. The purpose of this experiment was to use mice and C2C12 myotubes to examine if PCA can induce the transformation of muscle fiber and the mechanisms involved. We found that PCA significantly increased the expression of slow myosin heavy chain (MyHC), and markedly decreased the expression of fast MyHC in gastrocnemius muscle of mice and C2C12 myotubes. In addition, PCA also enhanced the antioxidant capacity and promoted mitochondrial biogenesis in mice. Importantly, the AMP-activated protein kinase (AMPK) signaling pathway was activated and AMPK inhibitor compound C attenuated the positive effect of PCA on myofiber conversion. To sum up, we revealed that PCA was able to promote the conversion of skeletal muscle fiber from type II to type I through the AMPK signaling pathway.

Effect of flavonoids on skeletal muscle mass, strength and physical performance in middle-aged and older adults with or without Sarcopenia: A meta-analysis of randomized controlled trials

The role of flavonoids in regulating the synthesis and function of skeletal muscles is increasingly recognized. However, randomized controlled trials have yielded inconsistent results on the influence of flavonoids on human muscular parameters. Therefore, we performed a meta-analysis to evaluate the possible effects of flavonoids on sarcopenia-related parameters in middle-aged and elderly people. Eligible literature and randomized controlled trials reports have been extensively searched from PubMed, Cochrane Library, Web of Science, and EMBASE databases until April 2022. A total of 20 articles involving 796 participants were available for the meta-analysis. There were significant benefits for participants in appendicular muscle mass gain (SMD = 0.29; 95% CI: 0.07, 0.52; P = 0.01) and 6-min walk distance (SMD = 0.37; 95% CI: 0.01, 0.73; P = 0.05). A subgroup analysis indicated that flavonoid significantly improves appendicular muscle mass (SMD = 0.50; 95% CI: 0.21, 0.80; P < 0.01) and Timed-Up and Go test (SMD = −0.47; 95% CI: −0.85, −0.09; P = 0.02) in Sarcopenia population. Our results provide insight into the effects of flavonoids on skeletal muscle mass and gait speed for those without exercise. However, there was no significant improvement in the subjects' muscle strength.

Antifatigue effect of naringin on improving antioxidant capacity and mitochondrial function and preventing muscle damage

The aim of this study was to explore effects of naringin (Nar) on antifatigue ability; the weight-loaded and non-loading swimming tests were performed. Compared with the control group, dietary supplementation of Nar significantly prolonged the weight-loaded swimming time to exhaustion of mice (P < 0.01). Nar significantly reduced the serum lactic acid (LD) level (P < 0.05) and lactate dehydrogenase (LDH) activity (P < 0.001), while increased the serum non-esterified free fatty acids (NEFA) level (P < 0.001). In addition, Nar significantly increased the liver glycogen and muscle glycogen contents (P < 0.05) and the phosphoenolpyruvate carboxykinase (PEPCK) (P < 0.01) and glucokinase (GCK) mRNA levels (P < 0.001) in liver and gastrocnemius (GAS) muscle. Furthermore, Nar significantly improved the antioxidant capacity, mitochondrial function, and muscle mitochondrial fatty acid β-oxidation (P < 0.05), and decreased inflammation and muscle damage-related gene expression (P < 0.05). These findings suggested that Nar can improve antifatigue effect by enhancing antioxidant capacity and mitochondrial function and preventing muscle damage.

Dihydromyricetin alters myosin heavy chain expression via AMPK signaling pathway in porcine myotubes

Dihydromyricetin (DHM) has attracted wide concern for its excellent biological function and pharmacological activities and was reported to have a positive effect on skeletal muscle insulin resistance, slow-twitch fibers expression and AMPK signaling. Thus, we took porcine myotubes derived from skeletal muscle satellite cells as the object to investigate the effects of DHM on myosin heavy chain (MyHC) expression and its mechanism in this study. Data showed that DHM up-regulated protein expression of MyHC I and down-regulated the protein expression of MyHC IIb, accompanied by an increase of MyHC I mRNA level and a decrease of MyHC IIb mRNA level. Besides, DHM increased the activities of malate dehydrogenase and succinic dehydrogenase and reduced lactate dehydrogenase activity. AMP-activated protein kinase (AMPK) was phosphorylated and AMPKα1 mRNA level was increased by DHM. The AMPK signaling-related factors including peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α), sirtuin1 (Sirt1), nuclear respiratory factor 1 (NRF1), and phospho-calmodulin-dependent protein kinase kinase-β (p-CaMKKβ) were increased by DHM. Inhibition of the AMPK signaling by compound C and AMPKα1 siRNA significantly attenuated the effects of DHM on expressions of MyHC I, MyHC IIb, PGC-1α and Sirt1. As a whole, DHM increased MyHC I expression and decreased MyHC IIb expression by the AMPK signaling.

SESN2 prevents the slow-to-fast myofiber shift in denervated atrophy via AMPK/PGC-1α pathway

BACKGROUND

Sestrin2 (SESN2), a stress-inducible protein, has been reported to protect against denervated muscle atrophy through unfolded protein response and mitophagy, while its role in myofiber type transition remains unknown.

METHODS

A mouse sciatic nerve transection model was created to evaluate denervated muscle atrophy. Myofiber type transition was confirmed by western blot, fluorescence staining, ATP quantification, and metabolic enzyme activity analysis. Adeno-associated virus (AAV) was adopted to achieve SESN2 knockdown and overexpression in gastrocnemius. AMPK/PGC-1α signal was detected by western blot and activated with 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR). C2C12 myotubes with rotenone treatment were adopted for in vitro experiments.

RESULTS

SESN2 was found to be upregulated in denervated skeletal muscles and rotenone-treated C2C12 cells. Knockdown of SESN2 aggravated muscle atrophy and accelerated myofiber type transition from slow-twitch to fast-twitch. Moreover, AMPK/PGC-1α signaling was proven to be activated by SESN2 after denervation, which further induced the expression of hypoxia-inducible factor HIF2α. Exogenous activation of AMPK/PGC-1α signaling could counteract the addition of slow-to-fast myofiber shift caused by SESN2 knockdown and lead to the retainment of muscle mass after denervation.

CONCLUSION

Collectively, the present study indicates that SESN2 prevents myofiber type transition from slow-twitch to fast-twitch and preserves muscle mass in denervated atrophy via AMPK/PGC-1α signaling. These findings contribute to a better understanding of the pathogenesis of muscle atrophy and provide novel insights into the role of SESN2 in myofiber type transition.

Bioactive Compounds for Fibromyalgia-like Symptoms: A Narrative Review and Future Perspectives

Fibromyalgia (FM) is a prevalent, chronic condition without a cure or reliable therapy. The etiopathogenesis of this syndrome is ambiguous, which has heightened the challenge of discovering treatments to minimize patients’ painful symptoms. FM is characterized by diffuse musculoskeletal pain usually accompanied by functional pain syndromes, such as fatigue, sleep disturbances, cognitive difficulties, and mood issues. Currently available treatment options for FM are limited. Recent studies have suggested a potential role for dietary bioactive compounds in FM management. We performed a narrative review to evaluate the existing evidence regarding the dietary bioactive compounds for FM, and we proposed molecular mechanisms on this topic. The inclusion criteria were (i) human, in vivo, or in vitro studies, (ii) studies related to the effect of bioactive compounds on FM-like symptoms, (iii) peer-reviewed literature, and (iv) publications until February 2022 in PubMed and Google Scholar. Exclusion criteria were (i) study designs using CCI, SNI, or SNL models because they are more NP models rather than FM models, and (ii) studies published in a language other than English. Keywords were dietary bioactive compounds, fibromyalgia, cell, animals, humans. Here, we report the effects of commonly consumed bioactive compounds (capsaicin, ginger, curcumin, n-3 PUFA, grape seed extract, naringin, and genistein) on FM-like symptoms in cellular, animal, and human studies. Cellular studies demonstrated that these bioactive compounds reduce pro-inflammatory production and increase antioxidant capacity of neurons or myoblasts that regulate apoptosis/cell survival. Animal studies showed that these regularly consumed bioactive compounds have an effect on FM-like symptoms, as evidenced by decreased pain hypersensitivity and fatigue as well as improved social behaviors. Further studies are warranted to allow meaningful comparison and quantification of the efficacy of these bioactive compounds on FM-like symptoms across studies, in terms of actual changes in antioxidant capacity, pain hypersensitivity, fatigue, and social behaviors. To date, human studies regarding the efficacy of these bioactive compounds on FM-like symptoms are limited and inconclusive. Our review identifies this important knowledge gap and proposes that the development and use of improved preclinical FM models are needed, particularly concerning the usage of female animals to better mimic FM pathophysiology and symptomatology.

Anti-fatigue effect of quercetin on enhancing muscle function and antioxidant capacity

The aim of this study was to evaluate the anti-fatigue effect of quercetin in mice. Three-week-old male BALB/c mice, fed with/without 0.005% quercetin for 6 weeks, were randomly divided into two experimental sets (loaded swimming and non-loading swimming tests). Our data indicated that dietary quercetin supplementation prolonged the exhaustive swimming time. In addition, lactic acid (LD) and blood urea nitrogen (BUN) levels, lactate dehydrogenase (LDH) and creatine kinase (CK) activities in serum were significantly decreased, while the levels of non-esterified free fatty acids (NEFA) in serum and the content of liver glycogen and muscle glycogen were significantly enhanced in dietary quercetin supplementation group. Furthermore, dietary quercetin supplementation significantly enhanced the glutathione peroxidase (GPx) and catalase (CAT) activities in serum, liver and gastrocnemius muscle and enhanced the total superoxide dismutase (T-SOD) activity in gastrocnemius muscle, but decreased the malondialdehyde (MDA) content and reactive oxygen species (ROS) level. Meanwhile, dietary quercetin supplementation affected the mRNA expression of regulators factors involved in muscle damage and inflammation, glucose metabolism and gluconeogenesis, muscle mitochondrial fatty acid β-oxidation and antioxidant related genes. Together, our data confirm that dietary quercetin supplementation can promote anti-fatigue capacity by promoting the antioxidant capacity and glycogen storage, as well as enhancing muscle function. PRACTICAL APPLICATIONS: Quercetin is a natural polyphenolic flavonoid substance. Here we confirm that quercetin has anti-fatigue activity. Our study indicates that quercetin may be used as natural anti-fatigue functional food or drugs.