Cellular and molecular mechanisms of muscle atrophy

The Interactome in the Evolution From Frailty to Sarcopenic Dependence

Biomarkers are essential tools for accurate diagnosis and effective prevention, but their validation is a pending challenge that limits their usefulness, even more so with constructs as complex as frailty. Sarcopenia shares multiple mechanisms with frailty which makes it a strong candidate to provide robust frailty biomarkers. Based on this premise, we studied the temporal evolution of cellular interactome in frailty, from independent patients to dependent ones. Overweight is a recognized cause of frailty in aging, so we studied the altered mechanisms in overweight independent elderly and evaluated their aggravation in dependent elderly. This evidence of the evolution of previously altered mechanisms would significantly support their role as real biomarkers of frailty. The results showed a preponderant role of autophagy in interactome control at both different functional points, modulating other essential mechanisms in the cell, such as mitochondrial capacity or oxidative stress. Thus, the overweight provoked in the muscle of the elderly an overload of autophagy that kept cell survival in apparently healthy individuals. This excessive and permanent autophagic effort did not seem to be able to be maintained over time. Indeed, in dependent elderly, the muscle showed a total autophagic inactivity, with devastating effects on the survival of the cell, which showed clear signs of apoptosis, and reduced functional capacity. The frail elderly are in a situation of weakness that is a precursor of dependence that can still be prevented if detection is early. Hence biomarkers are essential in this context.

Phytochemical‑rich herbal formula ATG‑125 protects against sucrose‑induced gastrocnemius muscle atrophy by rescuing Akt signaling and improving mitochondrial dysfunction in young adult mice

The antioxidant capability of herbal remedies has attracted widespread attention, but their molecular mechanisms in a muscle atrophy model have not been explored. The aim of the present study was to compare the bioactivity of sucrose challenged mice following treatment with ATG‑125. Here, through a combination of transcriptomic and biomedical analysis, herbal formula ATG‑125, a phytochemical‑rich formula, was identified as a protective factor against muscle atrophy in sucrose challenged mice. Gene ontology (GO) identified differentially expressed genes that were primarily enriched in the 'negative regulation of proteolysis', 'cellular amino acid metabolic process', 'lipoprotein particle' and 'cell cycle', all of which were associated with the ATG‑125‑mediated prevention of muscle atrophy, particularly with regard to mitochondrial biogenesis. In skeletal muscle, a set of mitochondrial‑related genes, including angiopoietin‑like 4, nicotinamide riboside kinase 2 (Nmrk2), pyruvate dehydrogenase lipoamide kinase isozyme 4, Asc‑type amino acid transporter 1 and mitochondrial uncoupling protein 3 (Ucp3) were markedly upregulated following ATG‑125 intervention. An increase in Nmrk2 and Ucp3 expression were noted after ATG‑125 treatment, in parallel with upregulation of the 'nicotinate and nicotinamide metabolism' pathway, as determined using the Kyoto Encyclopedia of Genes and Genomes (KEGG). Furthermore, KEGG pathway analysis revealed the downregulation of 'complement and coagulation cascades', 'cholesterol metabolism', 'biosynthesis of amino acids' and 'PPAR signaling pathway', which were associated with the downregulation of serine (or cysteine) peptidase inhibitor clade A member (Serpina)3, Serpina1b, Serpina1d, Serpina1e, apolipoprotein (Apo)a1 and Apoa2, all of which were cardiovascular and diabetes‑associated risk factors and were regulated by ATG‑125. In addition, ATG‑125 treatment resulted in downregulated mRNA expression levels of ATPase sarcoplasmic/endoplasmic reticulum Ca2+ transporting 2, troponin‑I1, troponin‑C1 and troponin‑T1 in young adult gastrocnemius muscle compared with the sucrose group. Nuclear factor‑κB‑hypoxia inducible factor‑1α‑TGFβ receptor type‑II‑vascular endothelial growth factor staining indicated that ATG‑125 decreased sucrose‑induced chronic inflammation. ATG‑125 was sufficient to prevent muscle atrophy, and this protective effect may be mediated through upregulation of AKT phosphorylation, upregulating the insulin growth factor‑1R‑insulin receptor substrate‑PI3K‑AKT pathway, which in turn resulted in a forkhead box O‑dependent decrease in protein degradation pathways, including regulation of atrogin1 and E3 ubiquitin‑protein ligase TRIM63. Peroxisome‑proliferator activated receptor γ coactivator 1α (PGC1α) was decreased in young adult mice challenged with sucrose. ATG‑125 treatment significantly increased PGC1α and significantly increased UCP‑1,2,3 expression levels, which suggested ATG‑125 poised the mitochondria for uncoupling of respiration. This effect is consistent with the increased SIRT1 levels and may explain an increase in mitochondria biogenesis. Taken together, the present study showed that ATG‑125, as an integrator of protein synthesis and degradative pathways, prevented muscle wasting.

The cellular basis of compensatory muscle growth in the teleost Odontesthes bonariensis

This study evaluates white muscle growth and in vivo cell proliferation during a fasting and refeeding trial, using pejerrey Odontesthes bonariensis as animal model, in order to better understand the cellular basis governing catch-up growth. Experiments consisted in two groups of fish, a control one continuously fed ad libitum, and a group fasted for 2 weeks and then fed for another 2 weeks. We examined how the formation of new muscle fibers and their increase in size were related to muscle precursor cell (MPC) proliferation under both experimental conditions. During fasting, the number of 5-ethynyl-2'-deoxyuridinepositive (EdU+) cells decreased along with myogenic regulatory factors (MRF) mRNA levels related to myoblast proliferation and differentiation, and the muscle stem cell-markerPax7 mRNA level increased. Analysis of myomere cross-sectional area, distribution of muscle fiber sizes and number of fibers per myomere showed that muscle hypertrophy but not hyperplasia was inhibited during fasting. Both higher igf2 mRNA level and the persistence of cell proliferation could be supporting new myofibre formation. On the other hand, an exacerbated MPC proliferation occurred during catch-up growth, and this increase in cell number could be contributing to the growth of both pre-existing and newly form small fibers. The finding that some MPCs proliferate during fasting and that muscle growth mechanisms, hyperplasia and hypertrophy, are differentially regulated could help to explain why re-fed fish could growth at higher rates, and why they return to the lost growth trajectory.

Myonuclear apoptosis via cleaved caspase-3 upregulation is related to macrophage accumulation underlying immobilization-induced muscle fibrosis

INTRODUCTION/AIMS

Although macrophage accumulation plays a key role in the development of immobilization-induced muscle fibrosis, the underlying mechanisms remain unclear. Therefore, we focused on the alterations of myonuclear apoptosis via cleaved caspase-3, and investigated whether these changes may be related to macrophage accumulation.

METHODS

Eight-week-old Wistar rats were divided into immobilization and control groups, and the soleus muscles were selected for analysis.

RESULTS

The mRNA and protein expression of collagen and the number of CD11b-positive cells were significantly higher in the immobilized rats than in the control rats at 1 and 2 weeks. TdT-mediated dUTP nick end-labeling (TUNEL)-positive myonuclei counts in 1- and 2-week control rats were 0.2 ± 0.1 and 0.2 ± 0.5, whereas they were 1.0 ± 0.6 and 1.1 ± 0.5 in 1- and 2-week immobilized rats. The cleaved caspase-3 protein expressions in 1- and 2-week control rats were 0.2 ± 0.1 and 0.2 ± 0.1, whereas they were 0.5 ± 0.1 and 0.4 ± 0.2 in 1- and 2-week immobilized rats. TUNEL-positive myonuclei counts and cleaved caspase-3 protein expression were significantly higher in immobilized rats than in control rats at 1 and 2 weeks. The numbers of myonuclei in 1- and 2-week control rats were 2.8 ± 0.1 and 2.6 ± 0.4, whereas they were 2.2 ± 0.4 and 2.2 ± 0.2 in 1- and 2-week immobilized rats. The numbers of myonuclei were significantly lower in immobilized than in control rats at both time-points.

DISCUSSION

Myonuclear apoptosis via the upregulation of cleaved caspase-3 might induce macrophage accumulation. These alterations are related to immobilization-induced muscle fibrosis.

Oyster Hydrolysates Attenuate Muscle Atrophy via Regulating Protein Turnover and Mitochondria Biogenesis in C2C12 Cell and Immobilized Mice

Sarcopenia, also known as skeletal muscle atrophy, is characterized by significant loss of muscle mass and strength. Oyster (Crassostrea gigas) hydrolysates have anti-cancer, antioxidant, and anti-inflammation properties. However, the anti-sarcopenic effect of oyster hydrolysates remains uninvestigated. Therefore, we prepared two different oyster hydrolysates, namely TGPN and PNY. This study aimed to determine the anti-muscle atrophy efficacy and molecular mechanisms of TGPN and PNY on both C2C12 cell lines and mice. In vitro, the TGPN and PNY recovered the dexamethasone-induced reduction in the myotube diameters. In vivo, TGPN and PNY administration not only improved grip strength and exercise endurance, but also attenuated the loss of muscle mass and muscle fiber cross-sectional area. Mechanistically, TGPN and PNY increased the expression of protein synthesis-related protein levels via phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt)/mammalian target of the rapamycin pathway, and reduced the expression of protein degradation-related protein levels via the PI3K/Akt/forkhead box O pathway. Also, TGPN and PNY stimulated NAD-dependent deacetylase sirtuin-1(SIRT1), peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC-1α), nuclear respiratory factor 1,2, mitochondrial transcription factor A, along with mitochondrial DNA content via SIRT1/PGC-1α signaling. These findings suggest oyster hydrolysates could be used as a valuable natural material that inhibits skeletal muscle atrophy via regulating protein turnover and mitochondrial biogenesis.

Tissue Engineering Strategies for Peripheral Nerve Regeneration

A peripheral nerve injury (PNI) has severe and profound effects on the life of a patient. The therapeutic approach remains one of the most challenging clinical problems. In recent years, many constructive nerve regeneration schemes are proposed at home and abroad. Nerve tissue engineering plays an important role. It develops an ideal nerve substitute called artificial nerve. Given the complexity of nerve regeneration, this review summarizes the pathophysiology and tissue-engineered repairing strategies of the PNI. Moreover, we discussed the scaffolds and seed cells for neural tissue engineering. Furthermore, we have emphasized the role of 3D printing in tissue engineering.

Loss of REDD1 prevents chemotherapy-induced muscle atrophy and weakness in mice

BACKGROUND

Chemotherapy is an essential treatment to combat solid tumours and mitigate metastasis. Chemotherapy causes side effects including muscle wasting and weakness. Regulated in Development and DNA Damage Response 1 (REDD1) is a stress-response protein that represses the mechanistic target of rapamycin (mTOR) in complex 1 (mTORC1), and its expression is increased in models of muscle wasting. The aim of this study was to determine if deletion of REDD1 is sufficient to attenuate chemotherapy-induced muscle wasting and weakness in mice.

METHODS

C2C12 myotubes were treated with carboplatin, and changes in myotube diameter were measured. Protein synthesis was measured by puromycin incorporation, and REDD1 mRNA and protein expression were analysed in myotubes treated with carboplatin. Markers of mTORC1 signalling were measured by western blot. REDD1 global knockout mice and wild-type mice were treated with a single dose of carboplatin and euthanized 7 days later. Body weight, hindlimb muscle weights, forelimb grip strength, and extensor digitorum longus whole muscle contractility were measured in all groups. Thirty minutes prior to euthanasia, mice were injected with puromycin to measure puromycin incorporation in skeletal muscle.

RESULTS

C2C12 myotube diameter was decreased at 24 (P = 0.0002) and 48 h (P < 0.0001) after carboplatin treatment. Puromycin incorporation was decreased in myotubes treated with carboplatin for 24 (P = 0.0068) and 48 h (P = 0.0008). REDD1 mRNA and protein expression were increased with carboplatin treatment (P = 0.0267 and P = 0.0015, respectively), and this was accompanied by decreased phosphorylation of Akt T³⁰⁸ (P < 0.0001) and S⁴⁷³ (P = 0.0006), p70S6K T³⁸⁹ (P = 0.0002), and 4E-binding protein 1 S⁶⁵ (P = 0.0341), all markers of mTORC1 activity. REDD1 mRNA expression was increased in muscles from mice treated with carboplatin (P = 0.0295). Loss of REDD1 reduced carboplatin-induced body weight loss (P = 0.0013) and prevented muscle atrophy in mice. REDD1 deletion prevented carboplatin-induced decrease of protein synthesis (P = 0.7626) and prevented muscle weakness.

CONCLUSIONS

Carboplatin caused loss of body weight, muscle atrophy, muscle weakness, and inhibition of protein synthesis. Loss of REDD1 attenuates muscle atrophy and weakness in mice treated with carboplatin. Our study illustrates the importance of REDD1 in the regulation of muscle mass with chemotherapy treatment and may be an attractive therapeutic target to combat cachexia.

H19X-encoded miR-322(424)/miR-503 regulates muscle mass by targeting translation initiation factors

BACKGROUND

Skeletal muscle atrophy is a debilitating complication of many chronic diseases, disuse conditions, and ageing. Genome-wide gene expression analyses have identified that elevated levels of microRNAs encoded by the H19X locus are among the most significant changes in skeletal muscles in a wide scope of human cachectic conditions. We have previously reported that the H19X locus is important for the establishment of striated muscle fate during embryogenesis. However, the role of H19X-encoded microRNAs in regulating skeletal mass in adults is unknown.

METHODS

We have created a transgenic mouse strain in which ectopic expression of miR-322/miR-503 is driven by the skeletal muscle-specific muscle creatine kinase promoter. We also used an H19X mutant mouse strain in which transcription from the locus is interrupted by a gene trap. Animal phenotypes were analysed by standard histological methods. Underlying mechanisms were explored by using transcriptome profiling and validated in the two animal models and cultured myotubes.

RESULTS

Our results demonstrate that the levels of H19X microRNAs are inversely related to postnatal skeletal muscle growth. Targeted overexpression of miR-322/miR-503 impeded skeletal muscle growth. The weight of gastrocnemius muscles of transgenic mice was only 54.5% of the counterparts of wild-type littermates. By contrast, interruption of transcription from the H19X locus stimulates postnatal muscle growth by 14.4-14.9% and attenuates the loss of skeletal muscle mass in response to starvation by 12.8-21.0%. Impeded muscle growth was not caused by impaired IGF1/AKT/mTOR signalling or a hyperactive ubiquitin-proteasome system, instead accompanied by markedly dropped abundance of translation initiation factors in transgenic mice. miR-322/miR-503 directly targets eIF4E, eIF4G1, eIF4B, eIF2B5, and eIF3M.

CONCLUSIONS

Our study illustrates a novel pathway wherein H19X microRNAs regulate skeletal muscle growth and atrophy through regulating the abundance of translation initiation factors, thereby protein synthesis. The study highlights how translation initiation factors lie at the crux of multiple signalling pathways that control skeletal muscle mass.

Overview of sialylation status in human nervous and skeletal muscle tissues during aging

Sialic acids (Sias) are a large and heterogeneous family of electronegatively charged nine-carbon monosaccharides containing a carboxylic acid and are mostly found as terminal residues in glycans of glycoproteins and glycolipids such as gangliosides. They are linked to galactose or N-acetylgalactosamine via α2,3 or α2,6 linkage, or to other Sias via α2,8 or more rarely α2,9 linkage, resulting in mono, oligo and polymeric forms. Given their characteristics, Sias play a crucial role in a multitude of human tissue biological processes in physiological and pathological conditions, ranging from development and growth to adult life until aging. Here, we review the sialylation status in human adult life focusing on the nervous and skeletal muscle tissues, which both display significant structural and functional changes during aging, strongly impacting on the whole human body and, therefore, on the quality of life. In particular, this review highlights the fundamental roles played by different types of glycoconjugates Sias in several cellular biological processes in the nervous and skeletal muscle tissues during adult life, also discussing how changes in Sia content during aging may contribute to the physiological decline of physical and nervous functions and to the development of age-related degenerative pathologies. Based on our current knowledge, further in-depth investigations could help to develop novel prophylactic strategies and therapeutic approaches that, by maintaining and/or restoring the correct sialylation status in the nervous and skeletal muscle tissues, could contribute to aging slowing and the prevention of age-related pathologies.

Exogenous insulin-like growth factor 1 attenuates cisplatin-induced muscle atrophy in mice

BACKGROUND

A reduction in the skeletal muscle mass worsens the prognosis of patients with various cancers. Our previous studies indicated that cisplatin administration to mice caused muscle atrophy. This is a concern for human patients receiving cisplatin. The insulin-like growth factor 1 (IGF-1)/phosphoinositide 3-kinase (PI3K)/Akt pathway stimulates the rate of protein synthesis in skeletal muscle. Thus, IGF-I can be a central therapeutic target for preventing the loss of skeletal muscle mass in muscle atrophy, although it remains unclear whether pharmacological activation of the IGF-1/PI3K/Akt pathway attenuates muscle atrophy induced by cisplatin. In this study, we examined whether exogenous recombinant human IGF-1 attenuated cisplatin-induced muscle atrophy.

METHODS

Male C57BL/6J mice (8-9 weeks old) were injected with cisplatin or saline for four consecutive days. On Day 5, quadriceps muscles were isolated. Mecasermin (recombinant human IGF-1) or the vehicle control was subcutaneously administered 30 min prior to cisplatin administration. A dietary restriction group achieving weight loss equivalent to that caused by cisplatin administration was used as a second control. C2C12 myotubes were treated with cisplatin with/without recombinant mouse IGF-1. The skeletal muscle protein synthesis/degradation pathway was analysed by histological and biochemical methods.

RESULTS

Cisplatin reduced protein level of IGF-1 by about 85% compared with the vehicle group and also reduced IGF-1/PI3K/Akt signalling in skeletal muscle. Under this condition, the protein levels of muscle ring finger protein 1 (MuRF1) and atrophy gene 1 (atrogin-1) were increased in quadriceps muscles (MuRF1; 3.0 ± 0.1 folds, atrogin-1; 3.0 ± 0.3 folds, P < 0.001, respectively). The administration of a combination of cisplatin and IGF-1 significantly suppressed the cisplatin-induced downregulation of IGF-1/PI3K/Akt signalling and upregulation of MuRF1 and atrogin-1 (up to 1.6 ± 0.3 and 1.5 ± 0.4 folds, P < 0.001, respectively), resulting in diminished muscular atrophy. IGF-1 showed similar effects in cisplatin-treated C2C12 myotubes, as well as the quadriceps muscle in mice.

CONCLUSIONS

The downregulation of IGF-1 expression in skeletal muscle might be one of the factors playing an important role in the development of cisplatin-induced muscular atrophy. Compensating for this downregulation with exogenous IGF-1 suggests that it could be a therapeutic target for limiting the loss of skeletal muscle mass in cisplatin-induced muscle atrophy.

Fermented Oyster Extract Attenuated Dexamethasone-Induced Muscle Atrophy by Decreasing Oxidative Stress

It is well known that oxidative stress induces muscle atrophy, which decreases with the activation of Nrf2/HO-1. Fermented oyster extracts (FO), rich in γ-aminobutyric acid (GABA) and lactate, have shown antioxidative effects. We evaluated whether FO decreased oxidative stress by upregulating Nrf2/HO-1 and whether it decreased NF-κB, leading to decreased IL-6 and TNF-α. Decreased oxidative stress led to the downregulation of Cbl-b ubiquitin ligase, which increased IGF-1 and decreased FoxO3, atrogin1, and Murf1, and eventually decreased muscle atrophy in dexamethasone (Dexa)-induced muscle atrophy animal model. For four weeks, mice were orally administered with FO, GABA, lactate, or GABA+Lactate, and then Dexa was subcutaneously injected for ten days. During Dexa injection period, FO, GABA, lactate, or GABA+Lactate were also administered, and grip strength test and muscle harvesting were performed on the day of the last Dexa injection. We compared the attenuation effect of FO with GABA, lactate, and GABA+lactate treatment. Nrf2 and HO-1 expressions were increased by Dexa but decreased by FO; SOD activity and glutathione levels were decreased by Dexa but increased by FO; NADPH oxidase activity was increased by Dexa but decreased by FO; NF-κB, IL-6, and TNF-α activities were increased by Dexa were decreased by FO; Cbl-b expression was increased by Dexa but restored by FO; IGF-1 expression was decreased by Dexa but increased by FO; FoxO3, Atrogin-1, and MuRF1 expressions were increased by Dexa but decreased by FO. The gastrocnemius thickness and weight were decreased by Dexa but increased by FO. The cross-sectional area of muscle fiber and grip strength were decreased by Dexa but increased by FO. In conclusion, FO decreased Dexa-induced oxidative stress through the upregulation of Nrf2/HO-1. Decreased oxidative stress led to decreased Cbl-b, FoxO3, atrogin1, and MuRF1, which attenuated muscle atrophy.

Amelioration of muscle wasting by gintonin in cancer cachexia

Cancer cachexia is characterized by systemic inflammation, protein degradation, and loss of skeletal muscle. Despite extensive efforts to develop therapeutics, only few effective treatments are available to protect against cancer cachexia. Here, we found that gintonin (GT), a ginseng-derived lysophosphatidic acid receptor (LPAR) ligand, protected C2C12 myotubes from tumor necrosis factor α (TNFα)/interferon γ (IFNγ)- induced muscle wasting condition. The activity of GT was found to be dependent on LPAR/Gαi2, as the LPAR antagonist Ki16425 and Gαi2 siRNA abolished the anti-atrophic effects of GT on myotubes. GT suppressed TNFα-induced oxidative stress by reducing reactive oxygen species and suppressing inflammation-related genes, such as interleukin 6 (IL-6) and NADPH oxidase 2 (NOX-2). In addition, GT exhibited anti-atrophy effects in primary normal human skeletal myoblasts. Further, GT protected against Lewis lung carcinoma cell line (LLC1)-induced cancer cachexia in a mouse model. Specifically, GT rescued the lower levels of grip strength, hanging, and cross-sectional area caused by LLC1. Collectively, our findings suggest that GT may be a good therapeutic candidate for protecting against cancer cachexia.

Indole-3-Propionic Acid, a Functional Metabolite of Clostridium sporogenes, Promotes Muscle Tissue Development and Reduces Muscle Cell Inflammation

Clostridium sporogenes (C. sporogenes), as a potential probiotic, metabolizes tryptophan and produces an anti-inflammatory metabolite, indole-3-propionic acid (IPA). Herein, we studied the effects of C. sporogenes and its bioactive metabolite, IPA, on skeletal muscle development and chronic inflammation in mice. In the in vivo study, the muscle tissues and serum samples of mice with C. sporogenes supplementation were used to analyze the effects of C. sporogenes on muscle metabolism; the IPA content was determined by metabonomics and ELISA. In an in vitro study, C2C12 cells were exposed to lipopolysaccharide (LPS) alone or LPS + IPA to verify the effect of IPA on muscle cell inflammation by transcriptome, and the involved mechanism was revealed by different functional assays. We observed that C. sporogenes colonization significantly increased the body weight and muscle weight gain, as well as the myogenic regulatory factors' (MRFs) expression. In addition, C. sporogenes significantly improved host IPA content and decreased pro-inflammatory cytokine levels in the muscle tissue of mice. Subsequently, we confirmed that IPA promoted C2C12 cells' proliferation by activating MRF signaling. IPA also effectively protected against LPS-induced C2C12 cells inflammation by activating Pregnane X Receptor and restoring the inhibited miR-26a-2-3p expression. miR-26a-2-3p serves as a novel muscle inflammation regulatory factor that could directly bind to the 3'-UTR of IL-1β, a key initiator factor in inflammation. The results suggested that C. sporogenes with its functional metabolite IPA not only helps muscle growth development, but also protects against inflammation, partly by the IPA/ miR-26a-2-3p /IL-1β cascade.

A large-scale transgenic RNAi screen identifies transcription factors that modulate myofiber size in Drosophila

Myofiber atrophy occurs with aging and in many diseases but the underlying mechanisms are incompletely understood. Here, we have used >1,100 muscle-targeted RNAi interventions to comprehensively assess the function of 447 transcription factors in the developmental growth of body wall skeletal muscles in Drosophila. This screen identifies new regulators of myofiber atrophy and hypertrophy, including the transcription factor Deaf1. Deaf1 RNAi increases myofiber size whereas Deaf1 overexpression induces atrophy. Consistent with its annotation as a Gsk3 phosphorylation substrate, Deaf1 and Gsk3 induce largely overlapping transcriptional changes that are opposed by Deaf1 RNAi. The top category of Deaf1-regulated genes consists of glycolytic enzymes, which are suppressed by Deaf1 and Gsk3 but are upregulated by Deaf1 RNAi. Similar to Deaf1 and Gsk3 overexpression, RNAi for glycolytic enzymes reduces myofiber growth. Altogether, this study defines the repertoire of transcription factors that regulate developmental myofiber growth and the role of Gsk3/Deaf1/glycolysis in this process.

Gintonin-enriched fraction improves sarcopenia by maintaining immune homeostasis in 20- to 24-month-old C57BL/6J mice

Background

Gintonin-enriched fraction (GEF) is a new non-saponin component glycolipoprotein isolated from ginseng root. This study examined the effect of GEF on age-related sarcopenia in old C57BL/6J mice.

Methods

Young (3–6 months) and old (20–24 months) C57BL/6J mice received oral GEF (50 mg/kg/day or 150 mg/kg/day) daily for 5 weeks. During the oral administration period, body weight and grip strength were measured weekly. After sacrifice, muscles from the hindlimb were excised and used for hematoxylin and eosin staining and western blotting to determine the effects of GEF on sarcopenia. The thymus was photographed to compare size, and flow cytometry was performed to examine the effect of GEF on immune homeostasis in the thymus and spleen. Blood samples were collected, and the concentrations of pro-inflammatory cytokines and IGF-1 were measured.

Results

GEF caused a significant increase in muscle strength, mass, and fiber size in old mice. GEF restored age-related disruption of immune homeostasis by maintaining T cell compartments and regulating inflammatory biomarkers. Thus, GEF reduced common low-grade chronic inflammatory parameters, which are the main cause of muscle loss.

Conclusion

GEF maintained immune homeostasis and inhibited markers of chronic inflammation, resulting in anti-sarcopenia effects in aged C57BL/6J mice. Thus, GEF is a potential therapeutic agent that slows sarcopenia in the elderly.

Integrated genomic and proteomic analyses identify stimulus-dependent molecular changes associated with distinct modes of skeletal muscle atrophy

Skeletal muscle atrophy is a debilitating condition that occurs with aging and disease, but the underlying mechanisms are incompletely understood. Previous work determined that common transcriptional changes occur in muscle during atrophy induced by different stimuli. However, whether this holds true at the proteome level remains largely unexplored. Here, we find that, contrary to this earlier model, distinct atrophic stimuli (corticosteroids, cancer cachexia, and aging) induce largely different mRNA and protein changes during muscle atrophy in mice. Moreover, there is widespread transcriptome-proteome disconnect. Consequently, atrophy markers (atrogenes) identified in earlier microarray-based studies do not emerge from proteomics as generally induced by atrophy. Rather, we identify proteins that are distinctly modulated by different types of atrophy (herein defined as “atroproteins”) such as the myokine CCN1/Cyr61, which regulates myofiber type switching during sarcopenia. Altogether, these integrated analyses indicate that different catabolic stimuli induce muscle atrophy via largely distinct mechanisms.

Skeletal muscle wasting is caused by many catabolic stimuli, which were thought to act via shared mechanisms. Hunt et al. now show that distinct catabolic stimuli induce muscle wasting via largely different molecular changes. The authors identify atrophy-associated proteins (“atroproteins”) that may represent diagnostic biomarkers and/or therapeutic targets.

Restorative potential of (-)-epicatechin in a rat model of Gulf War illness muscle atrophy and fatigue

We examined in a rat model of Gulf War illness (GWI), the potential of (-)-epicatechin (Epi) to reverse skeletal muscle (SkM) atrophy and dysfunction, decrease mediators of inflammation and normalize metabolic perturbations. Male Wistar rats (n = 15) were provided orally with pyridostigmine bromide (PB) 1.3 mg/kg/day, permethrin (PM) 0.13 mg/kg/day (skin), DEET 40 mg/kg/day (skin) and were physically restrained for 5 min/day for 3 weeks. A one-week period ensued to fully develop the GWI-like profile followed by 2 weeks of either Epi treatment at 1 mg/kg/day by gavage (n = 8) or water (n = 7) for controls. A normal, control group (n = 15) was given vehicle and not restrained. At 6 weeks, animals were subjected to treadmill and limb strength testing followed by euthanasia. SkM and blood sampling was used for histological, biochemical and plasma pro-inflammatory cytokine and metabolomics assessments. GWI animals developed an intoxication profile characterized SkM atrophy and loss of function accompanied by increases in modulators of muscle atrophy, degradation markers and plasma pro-inflammatory cytokine levels. Treatment of GWI animals with Epi yielded either a significant partial or full normalization of the above stated indicators relative to normal controls. Plasma metabolomics revealed that metabolites linked to inflammation and SkM waste pathways were dysregulated in the GWI group whereas Epi, attenuated such changes. In conclusion, in a rat model of GWI, Epi partially reverses detrimental changes in SkM structure including modulators of atrophy, inflammation and select plasma metabolites yielding improved function.

Integration of proteomic and genetic approaches to assess developmental muscle atrophy

Muscle atrophy, or a decline in muscle protein mass, is a significant problem in the aging population and in numerous disease states. Unraveling molecular signals that trigger and promote atrophy may lead to a better understanding of treatment options; however, there is no single cause of atrophy identified to date. To gain insight into this problem, we chose to investigate changes in protein profiles during muscle atrophy in Manduca sexta and Drosophila melanogaster. The use of insect models provides an interesting parallel to probe atrophic mechanisms as these organisms undergo a normal developmental atrophy process during the pupal transition stage. Leveraging the inherent advantages of each model organism, we first defined protein signature changes during M. sexta intersegmental muscle (ISM) atrophy and then used genetic approaches to confirm their functional importance in the D. melanogaster dorsal internal oblique muscles (DIOMs). Our data reveal an upregulation of proteasome and peptidase components and a general downregulation of proteins that regulate actin filament formation. Surprisingly, thick filament proteins that comprise the A-band are increased in abundance, providing support for the ordered destruction of myofibrillar components during developmental atrophy. We also uncovered the actin filament regulator ciboulot (Cib) as a novel regulator of muscle atrophy. These insights provide a framework towards a better understanding of global changes that occur during atrophy and may eventually lead to therapeutic targets.

Cellular and molecular modulation of rotator cuff muscle pathophysiology

Rotator cuff (RC) tendon tears are common shoulder injuries that result in irreversible and persistent degeneration of the associated muscles, which is characterized by severe inflammation, atrophy, fibrosis, and fatty infiltration. Although RC muscle degeneration strongly dictates the overall clinical outcomes, strategies to stimulate RC muscle regeneration have largely been overlooked to date. In this review, we highlight the current understanding of the cellular processes that coordinate muscle regeneration, and the roles of muscle resident cells, including immune cells, fibroadipogenic progenitors, and muscle satellite cells in the pathophysiologic regulation of RC muscles following injury. This review also provides perspectives for potential therapies to alleviate the hallmarks of RC muscle degeneration to address current limitations in postsurgical recovery.

Allulose Attenuated Age-Associated Sarcopenia via Regulating IGF-1 and Myostatin in Aged Mice

SCOPE

Allulose is shown to increase the muscle weight in diet-induced obese mice. However, there are no studies on the effects of allulose in age-associated sarcopenia. This study aims to elucidate the mechanisms of action for allulose in age associated by analyzing the transcriptional patterns in aged mice.

METHODS AND RESULTS

The 48-week-old mice are fed with AIN-93diet containing allulose for 12 weeks. Allulose supplementation increases the muscle mass and grip strength in aged mice. Allulose increases the insulin-like growth factor 1 (IGF-1) and its downstream factor expressions which 40 are related protein synthesis, while inhibits the myostatin expression related protein degradation. In mRNA-seq analysis, allulose supplementation significantly decreases in Adiponectin, Adipsin, cell death inducing DFFA like effector (CIDEC), Haptoglobin, Neuroglobin, and stearoyl-CoA desaturase-1 (SCD1) and increases in cytokine-inducible SH2-containing protein (CISH) and ceramide synthase 1 (CerS1) that are regulate protein turn over in gastrocnemius. Also, allulose alleviates autophagy in muscle with regulated mammalian target of rapamycin (mTOR) signaling pathway and increases the anti-oxidant enzyme activity.

CONCLUSION

These findings suggest that allulose improves the age-associated sarcopenia with enhancing antioxidant properties by altering mRNA and protein expression.

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.

Thyroid Hormone Action in Muscle Atrophy

Skeletal muscle atrophy is a condition associated with various physiological and pathophysiological conditions, such as denervation, cachexia, and fasting. It is characterized by an altered protein turnover in which the rate of protein degradation exceeds the rate of protein synthesis, leading to substantial muscle mass loss and weakness. Muscle protein breakdown reflects the activation of multiple proteolytic mechanisms, including lysosomal degradation, apoptosis, and ubiquitin-proteasome. Thyroid hormone (TH) plays a key role in these conditions. Indeed, skeletal muscle is among the principal TH target tissue, where TH regulates proliferation, metabolism, differentiation, homeostasis, and growth. In physiological conditions, TH stimulates both protein synthesis and degradation, and an alteration in TH levels is often responsible for a specific myopathy. Intracellular TH concentrations are modulated in skeletal muscle by a family of enzymes named deiodinases; in particular, in muscle, deiodinases type 2 (D2) and type 3 (D3) are both present. D2 activates the prohormone T4 into the active form triiodothyronine (T3), whereas D3 inactivates both T4 and T3 by the removal of an inner ring iodine. Here we will review the present knowledge of TH action in skeletal muscle atrophy, in particular, on the molecular mechanisms presiding over the control of intracellular T3 concentration in wasting muscle conditions. Finally, we will discuss the possibility of exploiting the modulation of deiodinases as a possible therapeutic approach to treat muscle atrophy.

The Critical Role of Oxidative Stress in Sarcopenic Obesity

Sarcopenic obesity (SO) is a combination of obesity and sarcopenia that primarily develops in older people. Patients with SO have high fat mass, low muscle mass, low muscle strength, and low physical function. SO relates to metabolic syndrome and an increased risk of morbimortality. The prevalence of SO varies because of lacking consensus criteria regarding its definition and the methodological difficulty in diagnosing sarcopenia and obesity. SO includes systemic alterations such as insulin resistance, increased proinflammatory cytokines, age-associated hormonal changes, and decreased physical activity at pathophysiological levels. Interestingly, these alterations are influenced by oxidative stress, which is a critical factor in altering muscle function and the generation of metabolic dysfunctions. Thus, oxidative stress in SO alters muscle mass, the signaling pathways that control it, satellite cell functions, and mitochondrial and endoplasmic reticulum activities. Considering this background, our objectives in this review are to describe SO as a highly prevalent condition and look at the role of oxidative stress in SO pathophysiology.

DA-Raf and the MEK inhibitor trametinib reverse skeletal myocyte differentiation inhibition or muscle atrophy caused by myostatin and GDF11 through the non-Smad Ras-ERK pathway

Myostatin (Mstn) and GDF11 are critical factors that are involved in muscle atrophy in the young and sarcopenia in the elderly, respectively. These TGF-β superfamily proteins activate not only Smad signaling but also non-Smad signaling including the Ras-mediated ERK pathway (Raf-MEK-ERK phosphorylation cascade). Although Mstn and GDF11 have been shown to induce muscle atrophy or sarcopenia by Smad2/3-mediated Akt inhibition, participation of the non-Smad Ras-ERK pathway in atrophy and sarcopenia has not been well determined. We show here that both Mstn and GDF11 prevented skeletal myocyte differentiation but that the MEK inhibitor U0126 or trametinib restored differentiation in Mstn- or GDF11-treated myocytes. These MEK inhibitors induced the expression of DA-Raf1 (DA-Raf), which is a dominant-negative antagonist of the Ras-ERK pathway. Exogenous expression of DA-Raf in Mstn- or GDF11-treated myocytes restored differentiation. Furthermore, administration of trametinib to aged mice resulted in an increase in myofiber size, or recovery from muscle atrophy. The trametinib administration downregulated ERK activity in these muscles. These results imply that the Mstn/GDF11-induced Ras-ERK pathway plays critical roles in the inhibition of myocyte differentiation and muscle regeneration, which leads to muscle atrophy. Trametinib and similar approved drugs might be applicable to the treatment of muscle atrophy in sarcopenia or cachexia.

Sarcopenia in pulmonary diseases is associated with elevated sarcoplasmic reticulum stress and myonuclear disorganization

Chronic obstructive pulmonary disease (COPD) is frequently associated with age-related muscle loss or sarcopenia. However, the exact molecular mechanism of muscle loss in COPD remains elusive. We investigated the association of chronic dysregulation of sarcoplasmic reticulum (SR) protein homeostasis (a condition called SR stress) and myonuclear disorganization with sarcopenia in patients with COPD. Markers of SR stress and their downstream consequences, including apoptosis and inflammation, were upregulated in patients with COPD. The maximal SR Ca²⁺ ATPase (SERCA) activity was significantly reduced in advanced COPD as compared to healthy controls. Single muscle fiber diameter and cytoplasmic domain per myonucleus were significantly smaller in patients with advanced COPD than in healthy controls. Increased disruption of myonuclear organization was found in the COPD patients as compared to healthy controls. These changes in SR dysfunction were accompanied by elevated global levels of oxidative stress, including lipid peroxidation and mitochondrial reactive oxygen species (ROS) production. Altogether, our data suggest that muscle weakness in advanced COPD is in part associated with the disruption of SR protein and calcium homeostasis and their pathological consequences.

The ERG1A K+ Channel Is More Abundant in Rectus abdominis Muscle from Cancer Patients Than that from Healthy Humans

BACKGROUND

The potassium channel encoded by the ether-a-gogo-related gene 1A (erg1a) has been detected in the atrophying skeletal muscle of mice experiencing either muscle disuse or cancer cachexia and further evidenced to contribute to muscle deterioration by enhancing ubiquitin proteolysis; however, to our knowledge, ERG1A has not been reported in human skeletal muscle.

METHODS AND RESULTS

Here, using immunohistochemistry, we detect ERG1A immunofluorescence in human Rectus abdominis skeletal muscle sarcolemma. Further, using single point brightness data, we report the detection of ERG1A immunofluorescence at low levels in the Rectus abdominis muscle sarcolemma of young adult humans and show that it trends toward greater levels (10.6%) in healthy aged adults. Interestingly, we detect ERG1A immunofluorescence at a statistically greater level (53.6%; p < 0.05) in the skeletal muscle of older cancer patients than in age-matched healthy adults. Importantly, using immunoblot, we reveal that lower mass ERG1A protein is 61.5% (p < 0.05) more abundant in the skeletal muscle of cachectic older adults than in healthy age-matched controls. Additionally, we report that the ERG1A protein is detected in a cultured human rhabdomyosarcoma line that may be a good in vitro model for the study of ERG1A in muscle.

CONCLUSIONS

The data demonstrate that ERG1A is detected more abundantly in the atrophied skeletal muscle of cancer patients, suggesting it may be related to muscle loss in humans as it has been shown to be in mice experiencing muscle atrophy as a result of malignant tumors.

Preventive effect of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) against endotoxin-induced muscle atrophy

BACKGROUND & AIMS

Muscle atrophy is a public health issue and inflammation is a major cause of muscle atrophy. While docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), which are typical ω-3 polyunsaturated fatty acids, are reported to have anti-inflammatory effects on endotoxin-induced inflammatory responses, their effects on inflammatory muscle atrophy have not been clarified. In this study, we aimed to investigate the effects of DHA and EPA on inflammatory muscle atrophy.

METHODS

DHA or EPA was added to C2C12 myotubes at a concentration of 25, 50, or 100 μM, and 1 h later, lipopolysaccharide (LPS) was added at a concentration of 1 μg/mL. Two hours after the first LPS addition, mRNA expression of atrogin-1 and Murf-1 in C2C12 myotubes was measured. The second LPS addition was performed 24 h after the first LPS addition, and myotube diameter, myofibrillar protein, and cell viability were measured. One-way ANOVA and Tukey's multiple comparison test were used for statistical processing of the results, and the significance level was set to less than 5 %.

RESULTS

The LPS-added group significantly decreased the myotube diameter and the myofibrillar protein content compared to the control group. The myotube diameter was significantly higher in the 25 μM, 50 μM DHA and 25 μM EPA-added groups compared to the LPS group. In the 25 μM DHA and EPA-added groups, the myofibrillar protein content was significantly higher than that in the LPS group. The mRNA expression levels of atrogin-1 and murf-1 were significantly suppressed in the 25 μM DHA and EPA-added groups compared to the LPS group. The cell viability did not change by the addition of LPS, DHA, and EPA.

CONCLUSIONS

The addition of DHA or EPA suppressed the decrease in myotube diameter and myofibrillar protein content and suppressed the increase in atrogin-1 and murf-1 induced by LPS. This study showed the preventive effect of DHA and EPA on endotoxin-induced muscle atrophy.

Associations between Grip Strength and Glycemic Control in Type 2 Diabetes Mellitus: the 2014-2019 Korea National Health and Nutrition Examination Survey

OBJECTIVES

Glycemic control is essential for preventing severe complications in patients with diabetes mellitus. This study investigated the association between grip strength and glycemic control in Korean adults with type 2 diabetes mellitus.

METHODS

From the Korea National Health and Nutrition Examination Survey, 2,498 participants aged over 19 years that patients with diabetes mellitus who did not have a history of cardiovascular disease or cancer were selected for analysis. Grip strength was assessed using a handheld dynamometer and was represented as age-specific and sex-specific tertiles. Multivariable logistic regression was performed to calculate the odds ratio (OR) and 95% confidence interval (CI) of glycemic control according to the grip strength tertiles.

RESULTS

A significantly lower probability (OR, 0.67; 95% CI, 0.47 to 0.97) for glycemic control was found in the lowest tertile of grip strength compared to the highest tertile. Furthermore, a subgroup analysis by sex only found significant associations between grip strength and glycemic control in males.

CONCLUSIONS

Lower grip strength was associated with poor glycemic control in patients with diabetes mellitus, especially in males. However, further studies are needed to confirm the causal relationship between grip strength and glycemic control.

Metabolic Syndrome and Sarcopenia

Skeletal muscle is a major organ of insulin-induced glucose metabolism. In addition, loss of muscle mass is closely linked to insulin resistance (IR) and metabolic syndrome (Met-S). Skeletal muscle loss and accumulation of intramuscular fat are associated with a variety of pathologies through a combination of factors, including oxidative stress, inflammatory cytokines, mitochondrial dysfunction, IR, and inactivity. Sarcopenia, defined by a loss of muscle mass and a decline in muscle quality and muscle function, is common in the elderly and is also often seen in patients with acute or chronic muscle-wasting diseases. The relationship between Met-S and sarcopenia has been attracting a great deal of attention these days. Persistent inflammation, fat deposition, and IR are thought to play a complex role in the association between Met-S and sarcopenia. Met-S and sarcopenia adversely affect QOL and contribute to increased frailty, weakness, dependence, and morbidity and mortality. Patients with Met-S and sarcopenia at the same time have a higher risk of several adverse health events than those with either Met-S or sarcopenia. Met-S can also be associated with sarcopenic obesity. In this review, the relationship between Met-S and sarcopenia will be outlined from the viewpoints of molecular mechanism and clinical impact.

Role of autophagy in muscle disease

Beside inherited muscle diseases many catabolic conditions such as insulin resistance, malnutrition, cancer growth, aging, infections, chronic inflammatory status, inactivity, obesity are characterized by loss of muscle mass, strength and function. The decrease of muscle quality and quantity increases morbidity, mortality and has a major impact on the quality of life. One of the pathogenetic mechanisms of muscle wasting is the dysregulation of the main protein and organelles quality control system of the cell: the autophagy-lysosome. This review will focus on the role of the autophagy-lysosome system in the different conditions of muscle loss. We will also dissect the signalling pathways that are involved in excessive or defective autophagy regulation. Finally, the state of the art of autophagy modulators that have been used in preclinical or clinical studies to ameliorate muscle mass will be also described.

Skeletal Muscle Deconditioning in Breast Cancer Patients Undergoing Chemotherapy: Current Knowledge and Insights From Other Cancers

Breast cancer represents the most commonly diagnosed cancer while neoadjuvant and adjuvant chemotherapies are extensively used in order to reduce tumor development and improve disease-free survival. However, chemotherapy also leads to severe off-target side-effects resulting, together with the tumor itself, in major skeletal muscle deconditioning. This review first focuses on recent advances in both macroscopic changes and cellular mechanisms implicated in skeletal muscle deconditioning of breast cancer patients, particularly as a consequence of the chemotherapy treatment. To date, only six clinical studies used muscle biopsies in breast cancer patients and highlighted several important aspects of muscle deconditioning such as a decrease in muscle fibers cross-sectional area, a dysregulation of protein turnover balance and mitochondrial alterations. However, in comparison with the knowledge accumulated through decades of intensive research with many different animal and human models of muscle atrophy, more studies are necessary to obtain a comprehensive understanding of the cellular processes implicated in breast cancer-mediated muscle deconditioning. This understanding is indeed essential to ultimately lead to the implementation of efficient preventive strategies such as exercise, nutrition or pharmacological treatments. We therefore also discuss potential mechanisms implicated in muscle deconditioning by drawing a parallel with other cancer cachexia models of muscle wasting, both at the pre-clinical and clinical levels.

Sepsis induces muscle atrophy by inhibiting proliferation and promoting apoptosis via PLK1-AKT signalling

Sepsis and sepsis-induced skeletal muscle atrophy are common in patients in intensive care units with high mortality, while the mechanisms are controversial and complicated. In the present study, the atrophy of skeletal muscle was evaluated in sepsis mouse model as well as the apoptosis of muscle fibres. Sepsis induced atrophy of skeletal muscle and apoptosis of myofibres in vivo and in vitro. In cell-based in vitro experiments, lipopolysaccharide (LPS) stimulation also inhibited the proliferation of myoblasts. At the molecular level, the expression of polo-like kinase 1 (PLK1) and phosphorylated protein kinase B (p-AKT) was decreased. Overexpression of PLK1 partly rescued LPS-induced apoptosis, proliferation suppression and atrophy in C2C12 cells. Furthermore, inhibiting the AKT pathway deteriorated LPS-induced atrophy in PLK1-overexpressing C2C12 myotubes. PLK1 was found to participate in regulating apoptosis and E3 ubiquitin ligase activity in C2C12 cells. Taken together, these results indicate that sepsis induces skeletal muscle atrophy by promoting apoptosis of muscle fibres and inhibiting proliferation of myoblasts via regulation of the PLK1-AKT pathway. These findings enhance understanding of the mechanism of sepsis-induced skeletal muscle atrophy.

Growth hormone secretagogue receptor-1a mediates ghrelin's effects on attenuating tumour-induced loss of muscle strength but not muscle mass

BACKGROUND

Ghrelin may ameliorate cancer cachexia (CC) by preventing anorexia, muscle, and fat loss. However, the mechanisms mediating these effects are not fully understood. This study characterizes the pathways involved in muscle mass and strength loss in the Lewis lung carcinoma (LLC)-induced cachexia model, and the effects of ghrelin in mice with or without its only known receptor: the growth hormone secretagogue receptor-1a ((GHSR-1a), Ghsr+/+ and Ghsr-/- ).

METHODS

Five to 7-month-old male C57BL/6J Ghsr+/+ and Ghsr-/- mice were inoculated with 1 × 106 heat-killed (HK) or live LLC cells (tumour implantation, TI). When tumours were palpable (7 days after TI), tumour-bearing mice were injected with vehicle (T + V) or ghrelin twice/day for 14 days (T + G, 0.8 mg/kg), while HK-treated mice were given vehicle (HK + V). Body weight and grip strength were evaluated before TI and at termination (21 days after TI). Hindlimb muscles were collected for analysis.

RESULTS

Less pronounced body weight (BW) loss (87.70 ± 0.98% vs. 83.92 ± 1.23%, percentage of baseline BW in tumour-bearing Ghsr+/+ vs. Ghsr-/- , P = 0.008), and lower upregulation of ubiquitin-proteasome system (UPS, MuRF1/Trim63, 5.71 ± 1.53-fold vs. 9.22 ± 1.94-fold-change from Ghsr+/+ HK + V in tumour-bearing Ghsr+/+ vs. Ghsr-/- , P = 0.036) and autophagy markers (Becn1, Atg5, Atg7, tumour-bearing Ghsr+/+  < Ghsr-/- , all P < 0.02) were found in T + V Ghsr+/+ vs. Ghsr-/- mice. Ghrelin attenuated LLC-induced UPS marker upregulation in both genotypes, [Trim63 was decreased from 5.71 ± 1.53-fold to 1.96 ± 0.47-fold in Ghsr+/+ (T + V vs. T + G: P = 0.032) and 9.22 ± 1.94-fold to 4.72 ± 1.06-fold in Ghsr-/- (T + V vs. T + G: P = 0.008)]. Only in Ghsr+/+ mice ghrelin ameliorated LLC-induced grip strength loss [improved from 89.24 ± 3.48% to 97.80 ± 2.31% of baseline (T + V vs. T + G: P = 0.042)], mitophagy markers [Bnip3 was decreased from 2.28 ± 0.56 to 1.38 ± 0.14-fold (T + V vs. T + G: P ≤ 0.05)], and impaired mitochondrial respiration [State 3u improved from 698.23 ± 73.96 to 934.37 ± 95.21 pmol/min (T + V vs. T + G: P ≤ 0.05)], whereas these markers were not improved by ghrelin Ghsr-/- . Compared with Ghsr+/+ , Ghsr-/- tumour-bearing mice also showed decreased response to ghrelin in BW [T + G-treated Ghsr+/+ vs. Ghsr -/- : 91.75 ± 1.05% vs. 86.18 ± 1.13% of baseline BW, P < 0.001)], gastrocnemius (T + G-treated Ghsr+/+ vs. Ghsr-/- : 96.9 ± 2.08% vs. 88.15 ± 1.78% of Ghsr+/+ HK + V, P < 0.001) and quadriceps muscle mass (T + G-treated Ghsr+/+ vs. Ghsr-/- : 96.12 ± 2.31% vs. 88.36 ± 1.94% of Ghsr+/+ HK + V, P = 0.01), and gastrocnemius type IIA (T + G-treated Ghsr+/+ vs. Ghsr-/- : 1250.49 ± 31.72 vs. 1017.62 ± 70.99 μm2 , P = 0.027) and IIB fibre cross-sectional area (T + G-treated Ghsr+/+ vs. Ghsr-/- : 2496.48 ± 116.88 vs. 2183.04 ± 103.43 μm2 , P = 0.024).

CONCLUSIONS

Growth hormone secretagogue receptor-1a mediates ghrelin's effects on attenuating LLC-induced weakness but not muscle mass loss by modulating the autophagy-lysosome pathway, mitophagy, and mitochondrial respiration.

Dicer-mediated miRNA processing is not involved in controlling muscle mass during muscle atrophy

Muscle atrophy occurs in a variety of physiological and pathological conditions. Specific molecular networks that govern protein synthesis and degradation play important roles in controlling muscle mass under diverse catabolic states. MicroRNAs (miRNAs) were previously found to be regulators of protein synthesis and degradation, and their expressions in skeletal muscle were altered in muscle wasting conditions. However, functional roles of miRNAs in muscle atrophy are poorly understood. In this study, we generated tamoxifen-inducible Dicer knockout (iDicer KO) mice and subjected them to 2 weeks of single hindlimb denervation. The expression of Dicer mRNA was significantly reduced in muscle of the iDicer KO mice compared to that of WT mice. The loss of Dicer moderately reduced levels of muscle-enriched miRNAs, miR-1, miR-133a and miR-206 in both innervated and denervated muscles of the iDicer KO mice. We also found that the extent of denervation-induced muscle atrophy as well as changes of signaling molecules related to protein synthesis/degradation pathways in the iDicer KO mice were comparable to these in WT mice. Taken together, Dicer knockout in adult skeletal muscle did not affect denervation-induced muscle atrophy.

Impedance-based measures of muscle mass can be used to predict severity of hepatic steatosis in pediatric nonalcoholic fatty liver disease

OBJECTIVES

The objective of this study was to investigate the association between measures of body composition based on bioelectrical impedance analysis (BIA) and histologic severity of liver disease in a pediatric cohort with nonalcoholic fatty liver disease (NAFLD).

METHODS

This was a cross-sectional study of patients < 20 y old with histologically confirmed NAFLD followed in our Steatohepatitis Center from 2017 to 2019. Contemporaneous body-composition data were obtained using a multifrequency octopolar BIA device (InBody 370, InBody, Seoul, South Korea). BIA data collected were skeletal muscle mass, appendicular muscle mass, and percentage body fat. Skeletal and appendicular muscle mass were corrected for height (dividing by the square of height), generating their respective indices. Univariate linear and logistic regression, followed by multivariable logistic regression analyses, were used.

RESULTS

Of the 79 children included (27% female, 73% male; 38% Hispanic; median age, 13 y; median body mass index Z-score, 2.43), the median NAFLD Activity Score was 4 (interquartile range, 3-5). In multivariable regression analyses, the skeletal muscle mass index was negatively associated with hepatic steatosis after controlling for confounders (odds ratio, 0.76; 95% confidence interval, 0.62-0.93). Similarly, the appendicular muscle mass index was negatively associated with severity of hepatic steatosis severity (odds ratio, 0.69; 95% confidence interval, 0.53-0.90). In contrast, percentage body fat was not associated with hepatic steatosis. NAFLD Activity Score, lobular inflammation, ballooning scores, and fibrosis stage were not associated with measures of body composition.

CONCLUSIONS

There is an inverse association between BIA-based measures of muscle mass and severity of hepatic steatosis in children with NAFLD. BIA data could further inform clinical decision making in this context.

Cell Types Used for Cultured Meat Production and the Importance of Myokines

The world’s population continues to increase, meaning we require more consistent protein supply to meet demand. Despite the availability of plant-based protein alternatives, animal meat remains a popular, high-quality protein source. Research studies have focused on cultured meat (meat grown in vitro) as a safe and more efficient alternative to traditional meat. Cultured meat is produced by in vitro myogenesis, which involves the processing of muscle satellite and mature muscle cells. Meat culture efficiency is largely determined by the culture conditions, such as the cell type and cell culture medium used and the biomolecular composition. Protein production can be enhanced by providing the optimum biochemical and physical conditions for skeletal muscle cell growth, while myoblasts play important roles in skeletal muscle formation and growth. This review describes the cell types used to produce cultured meat and the biological effects of various myokines and cytokines, such as interleukin-6, leukemia inhibitory factor, interleukin-4, interleukin-15, and interleukin-1β, on skeletal muscle and myogenesis and their potential roles in cultured meat production.

β-hydroxybutyrate as an Anti-Aging Metabolite

The ketone bodies, especially β-hydroxybutyrate (β-HB), derive from fatty acid oxidation and alternatively serve as a fuel source for peripheral tissues including the brain, heart, and skeletal muscle. β-HB is currently considered not solely an energy substrate for maintaining metabolic homeostasis but also acts as a signaling molecule of modulating lipolysis, oxidative stress, and neuroprotection. Besides, it serves as an epigenetic regulator in terms of histone methylation, acetylation, β-hydroxybutyrylation to delay various age-related diseases. In addition, studies support endogenous β-HB administration or exogenous supplementation as effective strategies to induce a metabolic state of nutritional ketosis. The purpose of this review article is to provide an overview of β-HB metabolism and its relationship and application in age-related diseases. Future studies are needed to reveal whether β-HB has the potential to serve as adjunctive nutritional therapy for aging.

β-hydroxybutyrate as an Anti-Aging Metabolite

The ketone bodies, especially β-hydroxybutyrate (β-HB), derive from fatty acid oxidation and alternatively serve as a fuel source for peripheral tissues including the brain, heart, and skeletal muscle. β-HB is currently considered not solely an energy substrate for maintaining metabolic homeostasis but also acts as a signaling molecule of modulating lipolysis, oxidative stress, and neuroprotection. Besides, it serves as an epigenetic regulator in terms of histone methylation, acetylation, β-hydroxybutyrylation to delay various age-related diseases. In addition, studies support endogenous β-HB administration or exogenous supplementation as effective strategies to induce a metabolic state of nutritional ketosis. The purpose of this review article is to provide an overview of β-HB metabolism and its relationship and application in age-related diseases. Future studies are needed to reveal whether β-HB has the potential to serve as adjunctive nutritional therapy for aging.

β-hydroxybutyrate as an Anti-Aging Metabolite

The ketone bodies, especially β-hydroxybutyrate (β-HB), derive from fatty acid oxidation and alternatively serve as a fuel source for peripheral tissues including the brain, heart, and skeletal muscle. β-HB is currently considered not solely an energy substrate for maintaining metabolic homeostasis but also acts as a signaling molecule of modulating lipolysis, oxidative stress, and neuroprotection. Besides, it serves as an epigenetic regulator in terms of histone methylation, acetylation, β-hydroxybutyrylation to delay various age-related diseases. In addition, studies support endogenous β-HB administration or exogenous supplementation as effective strategies to induce a metabolic state of nutritional ketosis. The purpose of this review article is to provide an overview of β-HB metabolism and its relationship and application in age-related diseases. Future studies are needed to reveal whether β-HB has the potential to serve as adjunctive nutritional therapy for aging.

Trimetazidine and exercise provide comparable improvements to high fat diet-induced muscle dysfunction through enhancement of mitochondrial quality control

Obesity induces skeletal muscle dysfunction. The pathogenesis of which appears to substantially involve mitochondrial dysfunction, arising from impaired quality control. Exercise is a major therapeutic strategy against muscle dysfunction. Trimetazidine, a partial inhibitor of lipid oxidation, has been proposed as a metabolic modulator for several cardiovascular pathologies. However, the effects of Trimetazidine on regulating skeletal muscle function are largely unknown. Our present study used cell culture and obese mice models to test a novel hypothesis that Trimetazidine could improve muscle atrophy with similar results to exercise. In C2C12 cells, high palmitic acid-induced atrophy and mitochondrial dysfunction, which could be reversed by the treatment of Trimetazidine. In our animal models, with high-fat diet-induced obesity associated with skeletal muscle atrophy, Trimetazidine prevented muscle dysfunction, corrected metabolic abnormalities, and improved mitochondrial quality control and mitochondrial functions similarly to exercise. Thus, our study suggests that Trimetazidine successfully mimics exercise to enhance mitochondrial quality control leading to improved high-fat diet-induced muscle dysfunction.

Synergic association of diabetes mellitus and chronic kidney disease with muscle loss and cachexia: results of a 16-year longitudinal follow-up of a community-based prospective cohort study

Muscle loss is a serious complication in patients with diabetes mellitus (DM) and chronic kidney disease (CKD). However, studies on a long-term change in muscle mass presence or absence of DM and CKD are scarce. We included 6247 middle-aged adults from the Korean Genome and Epidemiology Study (KoGES) between 2001 and 2016. Bioimpedance analysis (BIA) was performed biennially. Patients were classified into four groups according to the presence or absence of DM and CKD. The primary outcome was muscle depletion, which was defined as a decline in fat-free mass index (FFMI) below the 10th percentile of all subjects. The secondary outcomes included the occurrence of cachexia, all-cause mortality, and the slopes of changes in fat-free mass and weight. During 73,059 person-years of follow-up, muscle depletion and cachexia occurred in 460 (7.4%) and 210 (3.4%), respectively. In the multivariable cause-specific hazards model, the risk of muscle depletion was significantly higher in subjects with DM alone than in those without DM and CKD (HR, 1.37; 95% CI, 1.04-1.80) and was strongly pronounced in subjects with both conditions (HR, 3.38; 95% CI, 1.30-8.75). The secondary outcome analysis showed consistent results. The annual decline rates in FFMI, fat mass, and body mass index (BMI) were the steepest in subjects with DM and CKD among the four groups. DM and CKD are synergically associated with muscle loss over time. In addition, the mortality risk is higher in individuals with muscle loss.

Effects of Geniposide and Geniposidic Acid on Fluoxetine-Induced Muscle Atrophy in C2C12 Cells

Fluoxetine, an antidepressant known as a selective 5-hydroxytryptamine reuptake inhibitor (SSRI), can cause side effects such as muscle atrophy with long-term use, but the mechanism is not fully understood. Geniposide (GPS) and geniposidic acid (GPSA), the main components of Gardenia jasminoides fruit, have been shown to have biological activity in disease prevention, but their role in preventing FXT-related side effects such as muscle atrophy remains unclear. The process of muscle atrophy is a complex physiological mechanism involving the balance of protein synthesis and catabolism. In this study, we hypothesized that FXT may suppress hypertrophy signaling and activate the atrophy mechanisms, resulting in proteolysis and reduced protein synthesis, while geniposide (GPS) and geniposide acid (GPSA) may be beneficial in improving muscle weakness caused by FXT. The C2C12 cell model was used to examine the expression of hypertrophy signaling (PI3K, Akt, and mTOR) and protein break signals (FOXO, MuRF-1, and MyHC). Our data indicated that FXT inhibited MyHC and promoted MuRF-1 protein expression by downregulating the signaling pathways of p-ERK1/2, p-Akt, p-mTOR, and p-FOXO, resulting in a decrease in differentiation and myotube formation in C2C12 muscle cells, which further resulted in muscle atrophy. However, GPS and GPSA can positively regulate the atrophy mechanism induced by FXT in muscle cells, thereby ameliorating the imbalance in muscle synthesis. In conclusion, GPS and GPSA have the potential to attenuate the muscle loss caused by long-term FXT administration, diseases, or the aging process.

Role of Protein Arginine Methyltransferases and Inflammation in Muscle Pathophysiology

Arginine methylation mediated by protein arginine methyltransferases (PRMTs) is a post-translational modification of both histone and non-histone substrates related to diverse biological processes. PRMTs appear to be critical regulators in skeletal muscle physiology, including regeneration, metabolic homeostasis, and plasticity. Chronic inflammation is commonly associated with the decline of skeletal muscle mass and strength related to aging or chronic diseases, defined as sarcopenia. In turn, declined skeletal muscle mass and strength can exacerbate chronic inflammation. Thus, understanding the molecular regulatory pathway underlying the crosstalk between skeletal muscle function and inflammation might be essential for the intervention of muscle pathophysiology. In this review, we will address the current knowledge on the role of PRMTs in skeletal muscle physiology and pathophysiology with a specific emphasis on its relationship with inflammation.

Musashi-2 contributes to myotonic dystrophy muscle dysfunction by promoting excessive autophagy through miR-7 biogenesis repression

Skeletal muscle symptoms strongly contribute to mortality of myotonic dystrophy type 1 (DM1) patients. DM1 is a neuromuscular genetic disease caused by CTG repeat expansions that, upon transcription, sequester the Muscleblind-like family of proteins and dysregulate alternative splicing of hundreds of genes. However, mis-splicing does not satisfactorily explain muscle atrophy and wasting, and several other contributing factors have been suggested, including hyperactivated autophagy leading to excessive catabolism. MicroRNA (miR)-7 has been demonstrated to be necessary and sufficient to repress the autophagy pathway in cell models of the disease, but the origin of its low levels in DM1 was unknown. We have found that the RNA-binding protein Musashi-2 (MSI2) is upregulated in patient-derived myoblasts and biopsy samples. Because it has been previously reported that MSI2 controls miR-7 biogenesis, we tested the hypothesis that excessive MSI2 was repressing miR-7 maturation. Using gene-silencing strategies (small interfering RNAs [siRNAs] and gapmers) and the small molecule MSI2-inhibitor Ro 08-2750, we demonstrate that reducing MSI2 levels or activity boosts miR-7 expression, represses excessive autophagy, and downregulates atrophy-related genes of the UPS system. We also detect a significant upregulation of MBNL1 upon MSI2 silencing. Taken together, we propose MSI2 as a new therapeutic target to treat muscle dysfunction in DM1.

Exercise Training Attenuates Ubiquitin-Proteasome Pathway and Increases the Genes Related to Autophagy on the Skeletal Muscle of Patients With Inflammatory Myopathies

BACKGROUND/OBJECTIVE

The aim of this study was to evaluate the effects of exercise training on the ubiquitin-proteasome system (UPS) and genes related to autophagy on the skeletal muscle of patients with dermatomyositis (DM) and immune-mediated necrotizing myopathies (IMNMs).

METHODS

Seven DM patients and 6 IMNM patients were treated for 12 weeks with a twice-weekly aerobic and resistance training exercise program. Aerobic capacity, muscle strength, and expression of genes in the skeletal muscle related to UPS and to autophagy were evaluated at the baseline and after the intervention. Moreover, only at the baseline, 10 healthy control individuals were also evaluated.

RESULTS

The age of DM and IMNM patients was 49.8 and 58.5 years, respectively. Genes related to UPS were upregulated, whereas genes related to autophagy and antioxidative systems were downregulated only in the DM group when compared with control group. After completion of the exercise training program, several genes related to UPS were downregulated, whereas genes related to autophagy, mitochondrial pathways, and antioxidative systems were upregulated in both the DM and IMNM groups.

CONCLUSIONS

Exercise training can increase genes related to autophagy, mitophagy, and lysosomal biogenesis in the skeletal muscle of patients. These results suggest an increase in the recycling of damaged proteins and organelles, which may also contribute to the performance and endurance of skeletal muscles in these patients. Furthermore, in patients with myositis, exercise training led to a decrease in genes related to UPS and an increase in genes related to antioxidative capacity. Therefore, this may also contribute to an attenuation of skeletal muscle loss and of the deleterious effects of oxidative stress on the skeletal muscle of these patients.

Lifelong Exercise in Age Rats Improves Skeletal Muscle Function and MicroRNA Profile

PURPOSE

Lifelong exercise is known to attenuate sarcopenia (age-associated reduction in muscle mass and function); however, the underlying molecular mechanisms remain unclear. As microRNAs are widely involved in the regulation of skeletal muscle growth and development, we aimed to evaluate the effects of lifelong regular exercise on age-related alterations in muscle microRNA expression profiles as well as on skeletal muscle atrophy, apoptosis, and mitochondria and autophagy dysfunction.

METHODS

Female 8-month-old Sprague-Dawley rats were divided into four groups; 1) 18 months of moderate-intensity continuous training (MICT) initiated at 8 months (adult-MICT, n = 12), 2) 8 months of MICT initiated at 18 months (presarcopenia-MICT, n = 12), 3) 8-month-old adult sedentary controls (adult-SED), and 4) 26-month-old aging sedentary controls (old-SED). Age skeletal muscles were then subjected to quantitative reverse transcription-polymerase chain reaction, Kyoto Encyclopedia of Genes and Genomes, immunoblotting, and miR-486 3' untranslated region luciferase reporter gene analyses.

RESULTS

Age-related loss of miR-486 expression was improved, skeletal muscle atrophy and apoptosis were downregulated, and mitochondrial activity and autophagy were upregulated in the adult-MICT group. Kyoto Encyclopedia of Genes and Genomes analysis revealed that the PI3K/Akt pathway was upregulated in adult-MICT rats compared with that in old-SED. In vitro analyses in rat skeletal muscle L6 cells further confirmed that miR-486 targets PTEN, not SAV1, thereby activating the PI3K/Akt pathway and indirectly inhibiting HIPPO signaling.

CONCLUSIONS

Compared with presarcopenia-MICT rats, adult-MICT rats experienced greater beneficial effects regarding ameliorated age-related alterations in muscle miRNA expression profile, skeletal muscle atrophy, apoptosis, and mitochondria and autophagy dysfunction, which is potentially associated with the increased miR-486 expression and concomitant targeting of the PTEN/Akt signaling pathway.

Paraspinal muscle morphology and composition in adolescent idiopathic scoliosis: A histological analysis

BACKGROUND

Adolescent idiopathic scoliosis (AIS) is a condition resulting in spinal deformity and tissue adaptation of the paraspinal muscles. Although prior studies have demonstrated asymmetries in fiber type and other energetic features of muscle on the concave side of the curve, muscle morphology, architecture, and composition have not been evaluated. Therefore, the purpose of this study was to compare differences in paraspinal muscle microarchitecture and composition between concave and convex sides of a scoliotic curve in individuals with AIS.

METHODS

Paraspinal muscle biopsies were obtained at the apex of the scoliotic curve in 29 individuals with AIS undergoing surgical deformity correction. Histological assays were performed to quantify fiber size, evidence of muscle degeneration and regeneration, and tissue composition (proportion of muscle, collagen, and fat). Differences between contralateral muscle samples were compared using two-tailed paired Student's t tests, and relationships between clinical characteristics (age and curve severity) and muscle characteristics were investigated using Pearson correlations.

RESULTS

Muscle fibers were significantly larger on the convex side of the curve apex (P = .001), but were lower than literature-based norms for healthy paraspinal muscle. There were no differences in amount of degeneration/regeneration (P = .490) or the proportion of muscle and collagen (P > .350) between the concave and convex sides, but high levels of collagen were observed. There was a trend toward higher fat content on the concave side (P = .074). Larger fiber size asymmetries were associated with greater age (r = .43, P = .046), and trended toward an association with greater curve severity (r = .40, P = .069).

CONCLUSIONS

This study demonstrates that although muscle fibers are larger on the convex side of the scoliotic curve in AIS, muscles on both sides are atrophic compared to non-scoliotic individuals, and demonstrate levels of collagen similar to severe degenerative spinal pathologies. These findings provide insight into biological maladaptations occurring in paraspinal muscle in the presence of AIS.

Interaction of Fibromodulin and Myostatin to Regulate Skeletal Muscle Aging: An Opposite Regulation in Muscle Aging, Diabetes, and Intracellular Lipid Accumulation

The objective of this study was to investigate fibromodulin (FMOD) and myostatin (MSTN) gene expressions during skeletal muscle aging and to understand their involvements in this process. The expressions of genes related to muscle aging (Atrogin 1 and Glb1), diabetes (RAGE and CD163), and lipid accumulation (CD36 and PPARγ) and those of FMOD and MSTN were examined in CTX-injected, aged, MSTN^−/−, and high-fat diet (HFD) mice and in C2C12 myoblasts treated with ceramide or grown under adipogenic conditions. Results from CTX-injected mice and gene knockdown experiments in C2C12 cells suggested the involvement of FMOD during muscle regeneration and myoblast proliferation and differentiation. Downregulation of the FMOD gene in MSTN^−/− mice, and MSTN upregulation and FMOD downregulation in FMOD and MSTN knockdown C2C12 cells, respectively, during their differentiation, suggested FMOD negatively regulates MSTN gene expression, and MSTN positively regulates FMOD gene expression. The results of our in vivo and in vitro experiments indicate FMOD inhibits muscle aging by negatively regulating MSTN gene expression or by suppressing the action of MSTN protein, and that MSTN promotes muscle aging by positively regulating the expressions of Atrogin1, CD36, and PPARγ genes in muscle.

MyD88-mediated signaling intercedes in neurogenic muscle atrophy through multiple mechanisms

Skeletal muscle atrophy is a debilitating complication of many chronic disease states and disuse conditions including denervation. However, molecular and signaling mechanisms of muscle wasting remain less understood. Here, we demonstrate that the levels of several toll-like receptors (TLRs) and their downstream signaling adaptor, myeloid differentiation primary response 88 (MyD88), are induced in skeletal muscle of mice in response to sciatic nerve denervation. Muscle-specific ablation of MyD88 mitigates denervation-induced skeletal muscle atrophy in mice. Targeted ablation of MyD88 suppresses the components of ubiquitin-proteasome system, autophagy, and FOXO transcription factors in skeletal muscle during denervation. We also found that specific inhibition of MyD88 reduces the activation of canonical nuclear factor-kappa (NF-κB) pathway and expression of receptors for inflammatory cytokines in denervated muscle. In contrast, inhibition of MyD88 stimulates the activation of non-canonical NF-κB signaling in denervated skeletal muscle. Ablation of MyD88 also inhibits the denervation-induced increase in phosphorylation of AMPK without having any effect on the phosphorylation of mTOR. Moreover, targeted ablation of MyD88 inhibits the activation of a few components of the unfolded protein response (UPR) pathways, especially X-box protein 1 (XBP1). Importantly, myofiber-specific ablation of XBP1 mitigates denervation-induced skeletal muscle atrophy in mice. Collectively, our experiments suggest that TLR-MyD88 signaling mediates skeletal muscle wasting during denervation potentially through the activation of canonical NF-κB signaling, AMPK and UPR pathways.