Naringin Promotes Skeletal Muscle Fiber Remodeling by the AdipoR1-APPL1-AMPK Signaling Pathway

Arginine Regulates Skeletal Muscle Fiber Type Formation via mTOR Signaling Pathway

The composition of skeletal muscle fiber types affects the quality of livestock meat and human athletic performance and health. L-arginine (Arg), a semi-essential amino acid, has been observed to promote the formation of slow-twitch muscle fibers in animal models. However, the precise molecular mechanisms are still unclear. This study investigates the role of Arg in skeletal muscle fiber composition and mitochondrial function through the mTOR signaling pathway. In vivo, 4-week C56BL/6J male mice were divided into three treatment groups and fed a basal diet supplemented with different concentrations of Arg in their drinking water. The trial lasted 7 weeks. The results show that Arg supplementation significantly improved endurance exercise performance, along with increased SDH enzyme activity and upregulated expression of the MyHC I, MyHC IIA, PGC-1α, and NRF1 genes in the gastrocnemius (GAS) and quadriceps (QUA) muscles compared to the control group. In addition, Arg activated the mTOR signaling pathway in the skeletal muscle of mice. In vitro experiments using cultured C2C12 myotubes demonstrated that Arg elevated the expression of slow-fiber genes (MyHC I and Tnnt1) as well as mitochondrial genes (PGC-1α, TFAM, MEF2C, and NRF1), whereas the effects of Arg were inhibited by the mTOR inhibitor rapamycin. In conclusion, these findings suggest that Arg modulates skeletal muscle fiber type towards slow-twitch fibers and enhances mitochondrial functions by upregulating gene expression through the mTOR signaling pathway.

Regulatory mechanism and therapeutic potentials of naringin against inflammatory disorders

Naringin is a natural flavonoid with therapeutic properties found in citrus fruits and an active natural product from herbal plants. Naringin has become a focus of attention in recent years because of its ability to actively participate in the body's immune response and maintain the integrity of the immune barrier. This review aims to elucidate the mechanism of action and therapeutic efficacy of naringin in various inflammatory diseases and to provide a valuable reference for further research in this field. The review provided the chemical structure, bioavailability, pharmacological properties, and pharmacokinetics of naringin and found that naringin has good therapeutic potential for inflammatory diseases, exerting anti-inflammatory, anti-apoptotic, anti-oxidative stress, anti-ulcerative and detoxifying effects in the disease. Moreover, we found that the great advantage of naringin treatment is that it is safe and can even alleviate the toxic side effects associated with some of the other drugs, which may become a highlight of naringin research. Naringin, an active natural product, plays a significant role in systemic diseases' anti-inflammatory and antioxidant regulation through various signaling pathways and molecular mechanisms.

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.

Punicalagin protects against impaired skeletal muscle function in high-fat-diet-induced obese mice by regulating TET2

The function of skeletal muscles can be markedly hampered by obesity. Ten-eleven translocation 2 (TET2) is an important therapeutic target for ameliorating skeletal muscle dysfunction. Our previous study revealed that punicalagin (PUN) regulated TET2 in obese mice; however, whether PUN can prevent obesity-induced skeletal muscle dysfunction by regulating TET2 remains unclear. In the present study, 40 male C57BL/6J mice were divided into four groups (n = 10 per group): the control (CON) group, the high-fat-diet (HFD, negative control) group, the resveratrol (positive control) group, and the PUN group. The ratio of gastrocnemius weight to body weight (0.0097 ± 0.0016 vs. 0.0080 ± 0.0011), the grip strength (120.04 g ± 11.10 vs. 98.89 g ± 2.79), and the muscle fiber count (314.56 per visual field ± 92.73 vs. 236.44 per visual field ± 50.58) in the PUN group were higher than those in the HFD group. Moreover, the levels of the TET2 protein, 5-hydroxymethylcytosine (5hmC), and 5-formylcytosine (5fC) in skeletal muscles were significantly lower in the HFD group than those in the CON group; these levels increased after PUN treatment. Compared with the HFD group, the phosphorylation level of AMP-activated protein kinase (AMPK) α in the PUN group was higher, which effectively enhanced the stability of the TET2 protein. Besides, the ratio of (succinic acid + fumaric acid)/α-ketoglutarate in the PUN group was lower than that in the HFD group (43.21 ± 12.42 vs. 99.19 ± 37.07), and a lower ratio led to a higher demethylase activity of TET2 in the PUN group than in the HFD group. This study highlights that PUN supplementation protects against obesity-induced impairment of the skeletal muscle function via regulating the protein stability of TET2 and the enzymatic activity of TET2 demethylation.

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.

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.

Sesamin Activates Skeletal Muscle FNDC5 Expression and Increases Irisin Secretion via the SIRT1 Signaling Pathway

Sesamin, a major lignin mainly found in sesame (Sesamum indicum) oil and sesame seeds, has been demonstrated to possess lipoclasis-promoting, antiobesity, and antidiabetic effects. Irisin is a newly discovered myokine that has attracted great interest as a key target to prevent/treat obesity and its related metabolic diseases. However, the effect and potential mechanism of sesamin on FNDC5/irisin are still vacant. In this study, we showed that sesamin treatment increased FNDC5/irisin activation and regulated SIRT1, PGC-1α, and p-SMAD3/SMAD3 expression in C2C12 cells. By using specific inhibitors and lentivirus in C2C12 cells, we found that the SIRT1/SMAD3 axis plays an important role in sesamin regulated FNDC5/irisin activation. We also found that sesamin treatment activated FNDC5 expression and regulated the SIRT1/SMAD3 signaling axis in mice's skeletal muscle. What is more, by the high-fat diet induced obese model, we further showed that sesamin improved the high-fat diet induced decrease in irisin production and secretion, which results in an improvement of body weight gain and skeletal muscle dysfunction. Our results suggested that sesamin could activate FNDC5 expression and stimulate irisin secretion through the SIRT1 pathway both in vitro and in vivo, which may provide a new strategy for preventing and improving irisin deficiency related diseases.