Pyropia yezoensis Protein Supplementation Prevents Dexamethasone-Induced Muscle Atrophy in C57BL/6 Mice

Zebrafish Model for Studying Dexamethasone-Induced Muscle Atrophy and Preventive Effect of Maca (Lepidium meyenii)

Loss of myofibers during muscle atrophy affects functional capacity and quality of life. Dexamethasone, an inducer of rapid atrophy of skeletal myofibers, has been studied as a glucocorticoid receptor in muscle atrophy or motor neurodegeneration. In this study, we examined dexamethasone-induced muscle atrophy using zebrafish (Danio rerio), a vertebrate model, and assessed whether administration of Lepidium meyenii (maca) as a dietary supplement can prevent muscle atrophy. Changes in skeletal myofibers in zebrafish were evaluated after exposure to dexamethasone for different periods and at different concentrations. Under optimized conditions, zebrafish pre-fed with maca for 3 days were exposed to 0.01% dexamethasone for 1 h/day for 7 days. Thereafter, myofiber loss, damaged muscle contractile proteins, and abnormal exploratory behavior due to the structural and functional impairment of skeletal muscle associated with muscle atrophy were investigated using hematoxylin-eosin, immunofluorescence staining, and behavioral analyses. Our findings suggest that dexamethasone induces muscle atrophy in zebrafish, inhibiting exploratory behavior by inducing myofiber loss, inhibiting muscle contraction, and causing changes in endurance and velocity. Thus, the zebrafish model can be used to screen pharmaceutical agents and to study muscle atrophy. Furthermore, maca is a potential dietary supplement to prevent muscle atrophy, as it protects muscle fibers.

20(s)‑ginseonside‑Rg3 modulation of AMPK/FoxO3 signaling to attenuate mitochondrial dysfunction in a dexamethasone‑injured C2C12 myotube‑based model of skeletal atrophy in vitro

Muscle atrophy, a side effect from administration of the anti‑inflammatory medication dexamethasone (DEX), is preventable by concomitant administration of the major monomeric constituent of Panax ginseng C.A. Meyer, 20(S)‑ginsenoside Rg3 (S‑Rg3). Putative S‑Rg3‑associated prevention of DEX‑induced muscle atrophy may involve S‑Rg3 mitigation of DEX‑induced mitochondrial dysfunction. In the present study, MTT assays revealed enhanced cell viability following S‑Rg3 treatment of DEX‑injured C2C12 myotubes. Subsequent PCR and western blotting results demonstrated S‑Rg3‑induced reduction of expression of muscle atrophy F‑box protein (atrogin‑1) and muscle RING‑finger protein‑1, proteins previously linked to muscle atrophy. Additionally, S‑Rg3 treatment of DEX‑injured myotubes led to aggregation of Rg3 monomers in cells and dose‑dependent increases in cellular mitochondrial basal respiratory oxygen consumption rate and intracellular ATP levels compared with their levels in untreated DEX‑injured myotubes. In addition, S‑Rg3 treatment significantly reversed DEX‑induced reductions of expression of key mitochondrial respiratory electron transport chain subunits of protein complexes II, III and V in DEX‑injured myotube cells. Furthermore, S‑Rg3 alleviation of mitochondrial dysfunction associated with DEX‑induced injury of C2C12 myotubes was linked to S‑Rg3‑associated decreases in both forkhead box O3 (FoxO3) protein expression and phosphorylation of AMP‑activated protein kinase (AMPK). Collectively, these results implicate S‑Rg3 modulation of signaling within the AMPK‑FoxO3 pathway as a putative mechanism underlying S‑Rg3 alleviation of DEX‑induced muscle atrophy.

Mountain ginseng inhibits skeletal muscle atrophy by decreasing muscle RING finger protein-1 and atrogin1 through forkhead box O3 in L6 myotubes

ETHNOPHARMACOLOGICAL RELEVANCE

Mountain ginseng (Panax ginseng C.A. Meyer) is a medicinal herb with immune effects, muscle damage protection and energy metabolism effects. However, the pharmacological role of mountain ginseng in dexamethasone (DEXA)-induced muscle atrophy through the forkhead box O (FOXO) family is not understood. Therefore, we hypothesized that mountain ginseng inhibits skeletal muscle atrophy by decreasing muscle RING finger protein-1 (MuRF1) and atrogin1 through FOXO3 in L6 myotubes.

METHODS

Rat myoblast (L6) cells or Sprague-Dawley (SD) rats were exposed to DEXA and mountain ginseng. The expressions of muscle atrophy targets such as MuRF1, atrogin1, MyHC (myosin heavy chain), HSP90, p-Akt, Akt, p-ERK1/2, ERK, FOXO3a, FOXO1, myostatin, and follistatin were analyzed by using Western blot analysis or real-time PCR. The diameter of myotubes was measured. Recruitment of glucocorticoid receptor (GR) or FOXO3a was analyzed by performing a chromatin immunoprecipitation (ChIP) assay.

RESULTS

Mountain ginseng treatment reduced muscle weight loss and collagen deposition in DEXA-induced rats. Mountain ginseng treatment led to decreases in MuRF1, atrogin1, p-ERK1/2, FOXO3a, FOXO1, and myostatin. Also, mountain ginseng treatment led to increases in the diameter of myotubes, MyHC, HSP90, p-Akt, and follistatin. Treatment with mountain ginseng reduced enrichment of GR, FOXO3a, and RNA polymerase II on the promoters.

CONCLUSIONS

These results suggest that mountain ginseng inhibits skeletal muscle atrophy by decreasing MuRF1 and atrogin1 through FOXO3a in L6 myotubes.

Tissue-Engineered Human Myobundle System as a Platform for Evaluation of Skeletal Muscle Injury Biomarkers

Traditional serum biomarkers used to assess skeletal muscle damage, such as activity of creatine kinase (CK), lack tissue specificity and sensitivity, hindering early detection of drug-induced myopathies. Recently, a novel four-factor skeletal muscle injury panel (MIP) of biomarkers consisting of skeletal troponin I (sTnI), CK mass (CKm), fatty-acid-binding protein 3 (Fabp3), and myosin light chain 3, has been shown to have increased tissue specificity and sensitivity in rodent models of skeletal muscle injury. Here, we evaluated if a previously established model of tissue-engineered functional human skeletal muscle (myobundle) can allow detection of the MIP biomarkers after injury or drug-induced myotoxicity in vitro. We found that concentrations of three MIP biomarkers (sTnI, CKm, and Fabp3) in myobundle culture media significantly increased in response to injury by a known snake venom (notexin). Cerivastatin, a known myotoxic statin, but not pravastatin, induced significant loss of myobundle contractile function, myotube atrophy, and increased release of both traditional and novel biomarkers. In contrast, dexamethasone induced significant loss of myobundle contractile function and myotube atrophy, but decreased the release of both traditional and novel biomarkers. Dexamethasone also increased levels of matrix metalloproteinase-2 and -3 in the culture media which correlated with increased remodeling of myobundle extracellular matrix. In conclusion, this proof-of-concept study demonstrates that tissue-engineered human myobundles can provide an in vitro platform to probe patient-specific drug-induced myotoxicity and performance assessment of novel injury biomarkers to guide preclinical and clinical drug development studies.

Enriched environment ameliorates dexamethasone effects on emotional reactivity and metabolic parameters in mice

Convincing evidence shows that stress is associated with the development and course of psychiatric and metabolic disorders. The hypothalamic-pituitary-adrenal (HPA) axis mediates the stress response, a cascade of events that culminate in the release of glucocorticoids from the adrenal cortex. Chronic hypercortisolism typically characterizes stress-related illnesses, such as depression, anxiety, and metabolic syndrome. Considering previous studies pointing that environmental enrichment (EE) mitigates the deleterious effects of stress on neurobiological systems, we hypothesized that EE can confer resiliency against prolonged glucocorticoid administration-induced behavioral and metabolic alterations in mice. In this regard, three-month-old male Swiss mice were exposed to a four-week period of standard environment (SE) or EE. After this period, still in the respective environments, dexamethasone was administered intraperitoneally (i.p.) at a dose of 4 mg/kg, for 21 consecutive days, in order to generate the emotional-related behavioral outcomes, as previously described. It is demonstrated herein that EE prevents the dexamethasone-induced anxiety-like and passive stress-coping behaviors, as observed in the open field and tail suspension tests. Moreover, EE mitigated the hyperproteinemia and body weight loss induced by excess dexamethasone and decreased basal glucose levels. Taken together, these results support the hypothesis that EE attenuates the effects of chronic administration of synthetic glucocorticoids in mice, a strategy that may be translated to the clinical perspective.

Undaria pinnatifida extract feeding increases exercise endurance and skeletal muscle mass by promoting oxidative muscle remodeling in mice

Dietary habits can alter the skeletal muscle performance and mass, and Undaria pinnatifida extracts are considered a potent candidate for improving the muscle mass and function. Therefore, in this study, we aimed to assess the effect of U pinnatifida extracts on exercise endurance and skeletal muscle mass. C57BL/6 mice were fed a 0.25% U pinnatifida extract-containing diet for 8 weeks. U pinnatifida extract-fed mice showed increased running distance, total running time, and extensor digitorum longus and gastrocnemius muscle weights. U pinnatifida extract supplementation upregulated the expression of myocyte enhancer factor 2C, oxidative muscle fiber markers such as myosin heavy chain 1 (MHC1), and oxidative biomarkers in the gastrocnemius muscles. Compared to the controls, U pinnatifida extract-fed mice showed larger mitochondria and increased gene and protein expression of molecules involved in mitochondrial biogenesis and oxidative phosphorylation, including nuclear respiratory factor 2 and mitochondrial transcription factor A. U pinnatifida extract supplementation also increased the mRNA expression of angiogenesis markers, including VEGFa, VEGFb, FGF1, angiopoietin 1, and angiopoietin 2, in the gastrocnemius muscles. Importantly, U pinnatifida extracts upregulated the estrogen-related receptor γ and peroxisome proliferator-activated receptor gamma co-activator 1-alpha (PGC-1α)/AMP-activated protein kinase (AMPK)/sirtuin 1 (SIRT1) networks, which are partially increased by fucoxanthin, hesperetin, and caffeic acid treatments. Collectively, U pinnatifida extracts enhance mitochondrial biogenesis, increase oxidative muscle fiber, and promote angiogenesis in skeletal muscles, resulting in improved exercise capacity and skeletal muscle mass. These effects are attributable to fucoxanthin, hesperetin, and caffeic acid, bioactive components of U pinnatifida extracts.