Oral L-glutamine pretreatment attenuates skeletal muscle atrophy induced by 24-h fasting in mice

Mechanisms of endurance and resistance exercise in type 2 diabetes mellitus: A Narrative review

In the treatment and management of type 2 diabetes mellitus (T2DM), exercise therapy has received increasing attention due to its accessibility and cost-effectiveness. Regular physical exercise improves glycemic control by ameliorating insulin resistance (IR) and reducing the risk of complications. However, the distinct mechanisms underlying the efficacy of endurance training (ET) and resistance training (RT) in T2DM remain incompletely understood. This review systematically compares the molecular pathways through which ET and RT improve IR, focusing on epigenetic regulation, metabolic reprogramming, and anti-inflammatory effects. We highlight that RT enhances protein synthesis via the IGF-1/PI3K/AKT/mTOR pathway, while ET predominantly improves mitochondrial biogenesis and lipid oxidation through AMPK/SIRT1/PGC-1α signaling. Additionally, ET exerts immunomodulatory effects by suppressing pro-inflammatory cytokines (e.g., TNF-α) and elevating anti-inflammatory myokines (e.g., IL-6). These findings provide a mechanistic basis for personalized exercise prescriptions in T2DM management.

Selected Nutrients to Oppose Muscle Disuse Following Arthroscopic Orthopedic Surgery: A Narrative Review

Background: Orthopedic surgery and the corresponding events (i.e., immobilization and muscle disuse) result in a cascade of biological events to promote healing but can come with the loss of skeletal muscle mass and strength. A good nutritional status of patients is associated with positive post-surgical outcomes, with macronutrients receiving the majority of emphasis in the research literature. However, beyond the surgical literature, there are other nutrients and nutritional supplements that have been established or postulated to improve skeletal muscle mass and strength. Objective: The purpose of this narrative review is to provide evidence for the utility of using creatine, vitamin D, omega-3 fatty acids, glutamine, essential amino acids-branched chain amino acids (EAA-BCAA) and beta-hydroxy-beta-methylbutyrate (HMB) supplementation and the role they may play in minimizing muscle atrophy and strength loss following orthopedic surgery. The review will also highlight areas of future research to support a better understanding of the efficacy of supplementing with these substances pre- and/or post-surgery.

Systemic regulation of retinal medium-chain fatty acid oxidation repletes TCA cycle flux in oxygen-induced retinopathy

Activation of anaplerosis takes away glutamine from the biosynthetic pathways to the energy-producing TCA cycle. Especially, induction of hyperoxia driven anaplerosis in neurovascular tissues such as the retina during early stages of development could deplete biosynthetic precursors from newly proliferating endothelial cells impeding physiological angiogenesis and leading to vasoobliteration. Using an oxygen-induced retinopathy (OIR) mouse model, we investigated the metabolic differences between OIR-resistant BALB/cByJ and OIR susceptible C57BL/6J strains at system levels to understand the molecular underpinnings that potentially contribute to hyperoxia-induced vascular abnormalities in the neural retina. Our systems level in vivo RNA-seq, proteomics, and lipidomic profiling and ex-vivo retinal explant studies show that the medium-chain fatty acids serves as an alternative source to feed the TCA cycle. Our findings strongly implicate that medium-chain fatty acids could suppress glutamine-fueled anaplerosis and ameliorate hyperoxia-induced vascular abnormalities in conditions such as retinopathy of prematurity.

Dexamethasone-induced muscle atrophy and bone loss in six genetically diverse collaborative cross founder strains demonstrates phenotypic variability by Rg3 treatment

Background

Osteosarcopenia is a common condition characterized by the loss of both bone and muscle mass, which can lead to an increased risk of fractures and disability in older adults. The study aimed to elucidate the response of various mouse strains to treatment with Rg3, one of the leading ginsenosides, on musculoskeletal traits and immune function, and their correlation.

Methods

Six Collaborative Cross (CC) founder strains induced muscle atrophy and bone loss with dexamethasone (15 mg/kg) treatment for 1 month, and half of the mice for each strain were orally administered Rg3 (20 mg/kg). Different responses were observed depending on genetic background and Rg3 treatment.

Results

Rg3 significantly increased grip strength, running performance, and expression of muscle and bone health-related genes in a two-way analysis of variance considering the genetic backgrounds and Rg3 treatment. Significant improvements in grip strength, running performance, bone area, and muscle mass, and the increased gene expression were observed in specific strains of PWK/PhJ. For traits related to muscle, bone, and immune functions, significant correlations between traits were confirmed following Rg3 administration compared with control mice. The phenotyping analysis was compiled into a public web resource called Rg3-OsteoSarco.

Conclusion

This highlights the complex interplay between genetic determinants, pathogenesis of muscle atrophy and bone loss, and phytochemical bioactivity and the need to move away from single inbred mouse models to improve their translatability to genetically diverse humans. Rg3-OsteoSarco highlights the use of CC founder strains as a valuable tool in the field of personalized nutrition.

Common mouse models of chronic kidney disease are not associated with cachexia

The 5/6 nephrectomy and adenine-induced nephropathy mouse models have been extensively used to study Chronic Kidney Disease (CKD)-related cachexia. One common caveat of these CKD models is the cross-sectional nature of comparisons made versus controls. We here performed a comprehensive longitudinal assessment of body composition and energy metabolism in both models. The most striking finding is that weight loss is largely driven by reduced food intake which promotes rapid loss of lean and fat mass. However, in both models, mice catch up weight and lean mass a few days after the surgery or when they are switched back to standard chow diet. Muscle force and mass are fully recovered and no sign of cachexia is observed. Our data demonstrate that the time-course of kidney failure and weight loss are unrelated in these common CKD models. These data highlight the need to reconsider the relative contribution of direct and indirect mechanisms to muscle wasting observed in CKD.

Potential nutritional strategies to prevent and reverse sarcopenia in aging process: Role of fish oil-derived ω-3 polyunsaturated fatty acids, wheat oligopeptide and their combined intervention

INTRODUCTION

Nutritional support is potentially considered an essential step to prevent muscle loss and enhance physical function in older adults.

OBJECTIVES

This study aimed to assess the role of potential nutritional strategies, i.e., fish oil-derived ω-3 polyunsaturated fatty acids (PUFAs), wheat oligopeptide and their combined intervention, in preventing and reversing sarcopenia in aging process.

METHODS

One hundred 25-month-old Sprague-Dawley rats were randomly divided into 10 groups, and 10 newly purchased 6-month-old rats were included in young control group (n = 10). Fish oil (200, 400 or 800 mg/kg body weight), wheat oligopeptide (100, 200 or 400 mg/kg body weight), fish oil + wheat oligopeptide (800 + 100, 400 + 200 or 200 + 400 mg/kg body weight) or the equal volume of solvent were administered daily by gavage for 10 weeks. The effects of these interventions on natural aging rats were evaluated.

RESULTS

All intervention groups had a significant increase in muscle mass and grip strength and reduction in perirenal fat weight when compared to the aged control group (P < 0.05). The results of biochemical parameters, magnetic resonance imaging, proteomics and western blot suggested that the combination of wheat oligopeptide and fish oil-derived ω-3 PUFA, especially group WFM 2 (400 + 200 mg/kg body weight fish oil + wheat oligopeptide), was found to be more effective against aging-associated muscle loss than single intervention. Additionally, the interventions ameliorated fatty infiltration, muscle atrophy, and congestion in the intercellular matrix, and inflammatory cell infiltration in muscle tissue. The interventions also improved oxidative stress, anabolism, hormone levels, and inflammatory levels of skeletal muscle.

CONCLUSIONS

The combination of fish oil-derived ω-3 PUFA and wheat oligopeptide was found to be a promising nutritional support to prevent and reverse sarcopenia. The potential mechanism involved the promotion of protein synthesis and muscle regeneration, as well as the enhancement of muscle strength.

Oral glutamine supplementation relieves muscle loss in immobilized rats, altering p38MAPK and FOXO3a signaling pathways

BACKGROUND

Skeletal muscle synthesizes, stores, and releases body L-glutamine (GLN). Muscle atrophy due to disabling diseases triggers the activation of proteolytic and pro-apoptotic cell signaling, thus impairing the body's capacity to manage GLN content. This situation has a poor therapeutic prognosis.

OBJECTIVE

Evaluating if oral GLN supplementation can attenuate muscle wasting mediated by elevated plasma cortisol and activation of caspase-3, p38MAPK, and FOXO3a signaling pathways in soleus and gastrocnemius muscles of rats submitted to 14-day bilateral hindlimbs immobilization.

METHODS

Animals were randomly distributed into six groups: non-immobilized rats (Control), control orally supplemented with GLN (1 g kg-1) in solution with L-alanine (ALA: 0.61 g kg-1; GLN+ALA), control orally supplemented with dipeptide L-alanyl-L-glutamine (DIP; 1.49 g kg-1), hindlimbs immobilized rats (IMOB), IMOB orally GLN+ALA supplemented (GLN+ALA-IMOB), and IMOB orally DIP supplemented (DIP-IMOB). Plasma and muscle GLN concentration, plasma cortisol level, muscle caspase-3 activity, muscle p38MAPK and FOXO3a protein content (total and phosphorylated forms), and muscle cross-sectional area (CSA) were measured.

RESULTS

Compared to controls, IMOB rats presented: a) increased plasma cortisol levels; b) decreased plasma and muscle GLN concentration; c) increased muscle caspase-3 activity; d) increased total and phosphorylated p38MAPK protein content; e) increased FOXO3a and decreased phosphorylated FOXO3a protein content; f) reduced muscle weight and CSA befitting to atrophy. Oral supplementation with GLN+ALA and DIP was able to significantly attenuate these effects.

CONCLUSIONS

These findings attest that oral GLN supplementation in GLN+ALA solution or DIP forms attenuates rats' skeletal muscle mass wasting caused by disuse-mediated muscle atrophy.

Changes in Skeletal Muscle Protein Metabolism Signaling Induced by Glutamine Supplementation and Exercise

AIM

To evaluate the effects of resistance exercise training (RET) and/or glutamine supplementation (GS) on signaling protein synthesis in adult rat skeletal muscles.

METHODS

The following groups were studied: (1) control, no exercise (C); (2) exercise, hypertrophy resistance exercise training protocol (T); (3) no exercise, supplemented with glutamine (G); and (4) exercise and supplemented with glutamine (GT). The rats performed hypertrophic training, climbing a vertical ladder with a height of 1.1 m at an 80° incline relative to the horizontal with extra weights tied to their tails. The RET was performed three days a week for five weeks. Each training session consisted of six ladder climbs. The extra weight load was progressively increased for each animal during each training session. The G groups received daily L-glutamine by gavage (one g per kilogram of body weight per day) for five weeks. The C group received the same volume of water during the same period. The rats were euthanized, and the extensor digitorum longus (EDL) muscles from both hind limbs were removed and immediately weighed. Glutamine and glutamate concentrations were measured, and histological, signaling protein contents, and mRNA expression analyses were performed.

RESULTS

Supplementation with free L-glutamine increased the glutamine concentration in the EDL muscle in the C group. The glutamate concentration was augmented in the EDL muscles from T rats. The EDL muscle mass did not change, but a significant rise was reported in the cross-sectional area (CSA) of the fibers in the three experimental groups. The levels of the phosphorylated proteins (pAkt/Akt, pp70S6K/p70S6K, p4E-BP1/4E-BP1, and pS6/S6 ratios) were significantly increased in EDL muscles of G rats, and the activation of p4E-BP1 was present in T rats. The fiber CSAs of the EDL muscles in T, G, and GT rats were increased compared to the C group. These changes were accompanied by a reduction in the 26 proteasome activity of EDL muscles from T rats.

CONCLUSION

Five weeks of GS and/or RET induced muscle hypertrophy, as indicated by the increased CSAs of the EDL muscle fibers. The increase in CSA was mediated via the upregulated phosphorylation of Akt, 4E-BP1, p70S6k, and S6 in G animals and 4E-BP1 in T animals. In the EDL muscles from T animals, a decrease in proteasome activity, favoring a further increase in the CSA of the muscle fibers, was reported.

Composition of gut microbiota involved in alleviation of dexamethasone-induced muscle atrophy by whey protein

Skeletal muscle atrophy is a condition associated with increased morbidity and mortality. While the concept of the gut-muscle axis has been proposed, the role of gut microbiota in dexamethasone (DEX)-induced skeletal muscle atrophy remains largely unknown, limiting its clinical applications. In this study, we found that administration of DEX caused a shift in the gut microbiota of mice, characterized by an increased ratio of Firmicutes/Bacteroidota and a reduction in alpha diversity. We also identified 480 new operational taxonomic units (OTUs), while 1168 specific OTUs were lost. Our Spearman correlation analysis revealed 28 key taxonomic genera of bacteria that were positively or negatively associated with skeletal muscle strength and weight (r: -0.881 to 0.845, p < 0.05). Moreover, supplementation with whey protein reshaped the gut microbiota structure in DEX-treated mice, making it more similar to that of the control group. Importantly, we further utilized a stepwise regression model to identify two enterotypes capable of predicting skeletal muscle function and weight. Notably, Ileibacterium and Lachnospiraceae_UCG-001 played significant roles in predicting both skeletal muscle function and weight. Our findings suggest that DEX causes shifts in the gut microbiota, which can be reversed by whey protein intervention. The enterotypes identified by our stepwise regression models predict muscle function and weight, underscoring the potential role of gut microbiota in modulating muscle atrophy and emphasizing the therapeutic opportunities of microbiota-altering interventions.

Quantification of Nτ -Methylhistidine and Nπ-Methylhistidine in Chicken Plasma by Liquid Chromatography-Tandem Mass Spectrometry

The concentration of N^τ-methylhistidine in plasma provides an index of skeletal muscle protein breakdown. This study aimed to establish a quantitative method for measuring the concentrations of N^τ-methylhistidine and its isomer N^π-methylhistidine in chicken plasma, using liquid chromatography-tandem mass spectrometry with stable isotope dilution analysis. The acceptable linear ranges of detection were 1.56-50.00 μmol/L for N^τ-methylhistidine and 0.78-25.00 μmol/L for N^π-methylhistidine. The proposed method detected changes in the plasma levels of N^τ-methylhistidine and N^π-methylhistidine in response to fasting and re-feeding. These results suggest that the method developed in this study can be used for the simultaneous measurement of N^τ-methylhistidine and N^π-methylhistidine in chicken plasma.

Glutamine and leucine administration attenuates muscle atrophy in sepsis

AIMS

This study investigated whether l-glutamine (Gln) and/or l-leucine (Leu) administration could attenuate muscle atrophy in a mouse model of cecal ligation and puncture (CLP)-induced sepsis.

MATERIALS AND METHODS

Septic mice were given a daily intraperitoneal injection of Gln, Leu, or Gln plus Leu, and mice were sacrificed on either day 1 or 4 after CLP. Blood and muscles were collected for analysis of amino acid contents and markers related to protein degradation, muscle regeneration, and protein synthesis.

KEY FINDINGS

Leu treatment alone increased both muscle mass and total muscle protein content on day 4 after CLP. Gln administration reduced muscular Gln contents on day 1 and enhanced plasma Gln levels on day 4. Higher plasma branched-chain amino acid (BCAA) abundances and lower muscular BCAA levels were observed in Leu-treated mice on day 4. Gln and Leu individually suppressed muscle expressions of the E3 ubiquitin ligase genes, Trim63 and Fbxo32, on day 4 after CLP. As to muscle expressions of myogenic genes, both Gln and Leu upregulated Myog expression on day 1, but Leu alone enhanced Myf5 gene expression, whereas Gln plus Leu increased MyoD and Myog expression levels on day 4. Akt/mammalian target of rapamycin (mTOR) signaling was only activated by Gln and Leu when individually administered.

SIGNIFICANCE

Gln and/or Leu administration reduces sepsis-induced muscle degradation and promotes myogenic gene expressions. Leu treatment alone had more-pronounced effects on maintaining muscle mass during sepsis. A combination of Gln and Leu failed to show synergistic effects on alleviating sepsis-induced muscle atrophy.

Hydrolyzed whey protein enriched with glutamine dipeptide attenuates skeletal muscle damage and improves physical exhaustion test performance in triathletes

Purpose

To investigate the effects of hydrolyzed whey protein enriched with glutamine dipeptide on the percentage of oxygen consumption, second ventilatory threshold, duration and total distance covered, and skeletal muscle damage during an exhaustion test in elite triathletes.

Methods

The study was a randomized, double-blinded, placebo-controlled, crossover trial. Nine male triathletes performed a progressive incremental test on a treadmill ergometer (1.4 km h^-1·3 min^-1) 30 min after ingesting either 50 g of maltodextrin plus four tablets of 700 mg hydrolyzed whey protein enriched with 175 mg of glutamine dipeptide diluted in 250 ml of water (MGln) or four tablets of 700 mg maltodextrin plus 50 g maltodextrin diluted in 250 ml of water (M). Each athlete was submitted to the two dietary treatments and two corresponding exhaustive physical tests with an interval of one week between the interventions. The effects of the two treatments were then compared within the same athlete. Maximal oxygen consumption, percentage of maximal oxygen consumption, second ventilatory threshold, and duration and total distance covered were measured during the exhaustion test. Blood was collected before and immediately after the test for the determination of plasma lactate dehydrogenase (LDH) and creatine kinase (CK) activities and lactate concentration (also measured 6, 10, and 15 min after the test). Plasma cytokines (IL-6, IL-1β, TNF-α, IL-8, IL-10, and IL-1ra) and C-reactive protein levels were also measured.

Results

A single dose of MGln increased the percentage of maximal oxygen consumption, second ventilatory threshold duration, and total distance covered during the exhaustion test and augmented plasma lactate levels 6 and 15 min after the test. MGln also decreased plasma LDH and CK activities indicating muscle damage protection. Plasma cytokine and C-reactive protein levels did not change across the study periods.

Conclusion

Conditions including overnight fasting and a single dose of MGln supplementation resulted in exercising at a higher percentage of maximal oxygen consumption, a higher second ventilatory threshold, blood lactate levels, and reductions in plasma markers of muscle damage during an exhaustion test in elite triathletes. These findings support oral glutamine supplementation's efficacy in triathletes, but further studies require.

Urotensin receptor acts as a novel target for ameliorating fasting-induced skeletal muscle atrophy

Urotensin receptor (UT) is a G-protein-coupled receptor, whose endogenous ligand is urotensin-II (U-II). Skeletal muscle mass is regulated by various conditions, such as nutritional status, exercise, and diseases. Previous studies have pointed out that the urotensinergic system is involved in skeletal muscle metabolism and function, but its mechanism remains unclear, especially given the lack of research on the effect and mechanism of fasting. In this study, UT receptor knockout mice were generated to evaluate whether UT has effects on fasting induced skeletal muscle atrophy. Furthermore, the UT antagonist palosuran (3, 10, 30mg/kg) was intraperitoneally administered daily for 5 days to clarify the therapeutic effect of UT antagonism. Our results found the mice that fasted for 48hours exhibited skeletal muscle atrophy, accompanied by enhanced U-II levels in both skeletal muscles and blood. UT receptor knockout effectively prevented fasting-induced skeletal muscle atrophy. The UT antagonist ameliorated fasting-induced muscle atrophy in mice as determined by increased muscle strengths, weights, and muscle fiber areas (including fast, slow, and mixed types). In addition, the UT antagonist reduced skeletal muscle atrophic markers, including F-box only protein 32 (FBXO32) and tripartite motif containing 63 (TRIM63). Moreover, the UT antagonist was also observed to enhance PI3K/AKT/mTOR while inhibiting autophagy signaling. In summary, our study provides the first evidence that UT antagonism may represent a novel therapeutic approach for the treatment of fasting-induced skeletal muscle atrophy.

Maternal low-protein diet reduces skeletal muscle protein synthesis and mass via Akt-mTOR pathway in adult rats

Several studies have demonstrated that a maternal low-protein diet induces long-term metabolic disorders, but the involved mechanisms are unclear. This study investigated the molecular effects of a low-protein diet during pregnancy and lactation on glucose and protein metabolism in soleus muscle isolated from adult male rats. Female rats were fed either a normal protein diet or low-protein diet during gestation and lactation. After weaning, all pups were fed a normal protein diet until the 210th day postpartum. In the 7th month of life, mass, contractile function, protein and glucose metabolism, and the Akt-mTOR pathway were measured in the soleus muscles of male pups. Dry weight and contractile function of soleus muscle in the low-protein diet group rats were found to be lower compared to the control group. Lipid synthesis was evaluated by measuring palmitate incorporation in white adipose tissue. Palmitate incorporation was higher in the white adipose tissue of the low-protein diet group. When incubated soleus muscles were stimulated with insulin, protein synthesis, total amino acid incorporation and free amino acid content, glucose incorporation and uptake, and glycogen synthesis were found to be reduced in low-protein diet group rats. Fasting glycemia was higher in the low-protein diet group. These metabolic changes were associated with a decrease in Akt and GSK-3β signaling responses to insulin and a reduction in RPS6 in the absence of the hormone. There was also notably lower expression of Akt in the isolated soleus muscle of low-protein diet group rats. This study is the first to demonstrate how maternal diet restriction can reduce skeletal muscle protein and mass by downregulating the Akt-mTOR pathway in adulthood.

Mitigating sarcoplasmic reticulum stress limits disuse-induced muscle loss in hindlimb unloaded mice

Muscle disuse in the hindlimb unloaded (HU) mice causes significant atrophy and weakness. However, the cellular and molecular mechanisms driving disuse-muscle atrophy remain elusive. We investigated the potential contribution of proteins dysregulation by sarcoplasmic reticulum (SR), a condition called SR stress, to muscle loss during HU. Male, c57BL/6j mice were assigned to ground-based controls or HU groups treated with vehicle or 4-phenylbutyrate (4-PBA), a potent inhibitor of SR stress, once a day for three weeks. We report that the 4-PBA reduced the SR stress and partly reversed the muscle atrophy and weakness in the HU mice. Transcriptome analysis revealed that several genes were switched on (n = 3688) or differentially expressed (n = 1184) due to HU. GO, and KEGG term analysis revealed alterations in pathways associated with the assembly of cilia and microtubules, extracellular matrix proteins regulation, calcium homeostasis, and immune modulation during HU. The muscle restoration with 4-PBA partly reversed these changes along with differential and unique expression of several genes. The analysis of genes among the two comparisons (HU-v vs. control and HU-t vs. HU-v.) shows 841 genes were overlapped between the two comparisons and they may be regulated by 4-PBA. Altogether, our findings suggest that the pharmacological suppression of SR stress may be an effective strategy to prevent disuse-induced muscle weakness and atrophy.

Excess glutamine does not alter myotube metabolism or insulin sensitivity

Glutamine is an amino acid previously linked with improved skeletal muscle metabolism and insulin signaling, however, past observations often use cell culture models with only supraphysiological concentrations. Additionally, past reports have yet to simultaneously investigate both metabolic outcomes and insulin signaling. The present report utilized cell culture experiments and measured the effects of both physiological and supraphysiological levels of glutamine on myotube metabolism and insulin signaling/resistance. It was hypothesized the addition of glutamine at any level would increase cell metabolism and related gene expression, as well as improve insulin signaling versus respective control cells. C2C12 myotubes were treated with glutamine ranging from 0.25 mM-4 mM (or media control) for 24 h to capture a range of physiological and supraphysiological concentrations. qRT-PCR was used to measure metabolic gene expression. Mitochondrial and glycolytic metabolism were measured via oxygen consumption and extracellular acidification rate, respectively. Insulin sensitivity (indicated by pAkt:Akt) and metabolism following glucose/insulin infusion were also assessed. Glutamine treatment consistently increased mitochondrial and glycolytic metabolism versus true controls (cells treated with media void of glutamine), however, supraphysiological glutamine did not enhance metabolism beyond that of cells with physiological levels of glutamine. Neither physiological nor supraphysiological levels of glutamine altered insulin signaling regardless of insulin stimulation or insulin resistance when compared with respective controls. These data demonstrate excess glutamine does not appear to alter myotube metabolism or glucose disposal when base levels of glutamine are present. Moreover, glutamine does not appear to alter insulin sensitivity regardless of level of insulin resistance or presence of insulin stimulation.

Methionine and leucine induce ARID1A degradation to promote mTOR expression and milk synthesis in mammary epithelial cells

Amino acids can activate mTOR to promote milk synthesis in mammary epithelial cells (MECs), but the underlying molecular mechanism is still largely unknown. The objective is to investigate the regulatory mechanism of amino acids (Met and Leu) in stimulating mRNA expression of mTOR in MECs. We found that the protein abundance of AT-rich interaction domain 1A (ARID1A) was poorly expressed in mouse mammary gland tissues of lactating period. ARID1A knockdown and gene activation experiments detected whether ARID1A negatively regulated milk protein and fat synthesis in bovine MECs, cell proliferation and the expression and activation of mTOR. ChIP-PCR detected that ARID1A, H3K27ac, H3K27me3 and H3K4me3 all bound to the mTOR promoter at -548∼-793 nt. Knockdown or gene activation of ARID1A enhanced or weakened the binding of H3K27ac on the mTOR promoter, respectively. The stimulation of Met and Leu on mTOR expression and phosphorylation were eliminated by ARID1A gene activation. Furthermore, Met and Leu decreased the protein level of ARID1A through ubiquitination and proteasomal degradation. TRIM21 bound to ARID1A, and TRIM21 knockdown blocked the stimulation of Met and Leu on ARID1A degradation. In summary, these data reveal that ARID1A blocks Met and Leu signaling to mTOR gene transcription through inhibiting H3K27ac deposition on its promoter, and Met and Leu decrease ARID1A protein level through TRIM21-mediated ubiquitination and proteasomal degradation. Our findings uncover that Met and Leu promote mTOR expression for milk synthesis through the TRIM21-ARID1A signaling pathway, providing a novel theoretical basis for the application of amino acids in milk production.

Endoplasmic Reticulum Stress and Autophagy Markers in Soleus Muscle Disuse-Induced Atrophy of Rats Treated with Fish Oil

Endoplasmic reticulum stress (ERS) and autophagy pathways are implicated in disuse muscle atrophy. The effects of high eicosapentaenoic (EPA) or high docosahexaenoic (DHA) fish oils on soleus muscle ERS and autophagy markers were investigated in a rat hindlimb suspension (HS) atrophy model. Adult Wistar male rats received daily by gavage supplementation (0.3 mL per 100 g b.w.) of mineral oil or high EPA or high DHA fish oils (FOs) for two weeks. Afterward, the rats were subjected to HS and the respective treatments concomitantly for an additional two-week period. After four weeks, we evaluated ERS and autophagy markers in the soleus muscle. Results were analyzed using two-way analysis of variance (ANOVA) and Bonferroni post hoc test. Gastrocnemius muscle ω-6/ω-3 fatty acids (FAs) ratio was decreased by both FOs indicating the tissue incorporation of omega-3 fatty acids. HS altered (p < 0.05) the protein content (decreasing total p38 and BiP and increasing p-JNK2/total JNK2 ratio, and caspase 3) and gene expressions (decreasing BiP and increasing IRE1 and PERK) of ERS and autophagy (decreasing Beclin and increasing LC3 and ATG14) markers in soleus. Both FOs attenuated (p < 0.05) the increase in PERK and ATG14 expressions induced by HS. Thus, both FOs could potentially attenuate ERS and autophagy in skeletal muscles undergoing atrophy.

Nutraceuticals in the Prevention and Treatment of the Muscle Atrophy

Imbalance of protein homeostasis, with excessive protein degradation compared with protein synthesis, leads to the development of muscle atrophy resulting in a decrease in muscle mass and consequent muscle weakness and disability. Potential triggers of muscle atrophy include inflammation, malnutrition, aging, cancer, and an unhealthy lifestyle such as sedentariness and high fat diet. Nutraceuticals with preventive and therapeutic effects against muscle atrophy have recently received increasing attention since they are potentially more suitable for long-term use. The implementation of nutraceutical intervention might aid in the development and design of precision medicine strategies to reduce the burden of muscle atrophy. In this review, we will summarize the current knowledge on the importance of nutraceuticals in the prevention of skeletal muscle mass loss and recovery of muscle function. We also highlight the cellular and molecular mechanisms of these nutraceuticals and their possible pharmacological use, which is of great importance for the prevention and treatment of muscle atrophy.

L-Glutamine Supplementation Enhances Strength and Power of Knee Muscles and Improves Glycemia Control and Plasma Redox Balance in Exercising Elderly Women

We investigated the effects of oral L-glutamine (Gln) supplementation, associated or not with physical exercises, in control of glycemia, oxidative stress, and strength/power of knee muscles in elderly women. Physically active (n = 21) and sedentary (n = 23) elderly women aged 60 to 80 years were enrolled in the study. Plasma levels of D-fructosamine, insulin, reduced (GSH) and oxidized (GSSG) glutathione, iron, uric acid, and thiobarbituric acid-reactive substances (TBARs) (lipoperoxidation product), as well as knee extensor/flexor muscle torque peak and average power (isokinetic test), were assessed pre- and post-supplementation with Gln or placebo (30 days). Higher plasma D-fructosamine, insulin, and iron levels, and lower strength/power of knee muscles were found pre-supplementation in the NPE group than in the PE group. Post-supplementation, Gln subgroups showed higher levels of GSH, GSSG, and torque peak, besides lower D-fructosamine than pre-supplementation values. Higher muscle average power and plasma uric acid levels were reported in the PE + Gln group, whereas lower insulin levels were found in the NPE + Gln than pre-supplementation values. TBARs levels were diminished post-supplementation in all groups. Gln supplementation, mainly when associated with physical exercises, improves strength and power of knee muscles and glycemia control, besides boosting plasma antioxidant capacity of elderly women.

Targeted assessment of the metabolome in skeletal muscle and in serum of dairy cows supplemented with conjugated linoleic acid during early lactation

In the dairy cow, late gestation and early lactation are characterized by a complexity of metabolic processes required for the homeorhetic adaptation to the needs of fetal growth and milk production. Skeletal muscle plays an important role in this adaptation. The objective of this study was to characterize the metabolome in skeletal muscle (semitendinosus muscle) and in serum of dairy cows in the context of the physiological changes occurring in early lactation and to test the effects of dietary supplementation (from d 1 in milk onwards) with conjugated linoleic acids (sCLA; 100 g/d; supplying 7.6 g of cis-9,trans-11 CLA and 7.6 g of trans-10,cis-12 CLA per cow/d; n = 11) compared with control fat-supplemented cows (CTR; n = 10). The metabolome was characterized in skeletal muscle samples collected on d 21 and 70 after calving in conjunction with their serum counterpart using a targeted metabolomics approach (AbsoluteIDQ p180 kit; Biocrates Life Sciences AG, Innsbruck, Austria). Thereby 188 metabolites from 6 different compound classes (acylcarnitines, amino acids, biogenic amines, glycerophospholipids, sphingolipids, and hexoses) were quantified in both sample types. In both groups, dry matter intake increased after calving. It was lower in sCLA than in CTR on d 21, which resulted in reduced calculated net energy and metabolizable protein balances. On d 21, the concentrations of dopamine, Ala, and hexoses in the skeletal muscle were higher in sCLA than in CTR. On d 21, the changed metabolites in serum were mainly long-chain (>C24) diacyl phosphatidylcholine PC (PC-aa) and acyl-alkyl phosphatidylcholine (PC-ae), along with lysophosphatidylcholine acyl (lysoPC-a) C26:1 that were all lower in sCLA than in CTR. Supplementation with CLA affected the muscle concentrations of 22 metabolites on d 70 including 10 long-chain (>C22) sphingomyelin (SM), hydroxysphingomyelin [SM(OH)], PC-aa, and PC-ae along with 9 long-chain (>C16) lysoPC-a and 3 metabolites related to amino acids (spermine, citrulline, and Asp). On d 70, the concentrations of lysoPC-a C18:2 and C26:0 in serum were higher in the sCLA cows than in the CTR cows. Regardless of treatment, the concentrations of Ile, Leu, Phe, Lys, His, Met, Trp, and hydroxybutyrylcarnitine (C4-OH) decreased, whereas those of ornithine, Gln, and trans-4-hydroxyproline (t4-OH-Pro) increased from d 21 to 70 in muscle. The significantly changed metabolites in serum with time of lactation were 28 long-chain (>C30) PC-ae and PC-aa, 7 long-chain (>C16) SM and SM(OH), along with lysoPC-a C20:3 that were all increased. In conclusion, in addition to other significantly changed metabolites, CLA supplementation mainly led to changes in muscle and serum concentrations of glycerophospholipids and sphingolipids that might reflect the phospholipid compositional changes in muscle. The metabolome changes observed in sCLA on d 21 seem to be, at least in part, due to the lower DMI in these cows. The changes in the muscle concentrations of AA from d 21 to 70, which coincided with the steady energy and MP balances, might reflect a shift of protein synthesis/degradation balance toward synthesis.

Host cell glutamine metabolism as a potential antiviral target

A virus minimally contains a nucleic acid genome packaged by a protein coat. The genome and capsid together are known as the nucleocapsid, which has an envelope containing a lipid bilayer (mainly phospholipids) originating from host cell membranes. The viral envelope has transmembrane proteins that are usually glycoproteins. The proteins in the envelope bind to host cell receptors, promoting membrane fusion and viral entry into the cell. Virus-infected host cells exhibit marked increases in glutamine utilization and metabolism. Glutamine metabolism generates ATP and precursors for the synthesis of macromolecules to assemble progeny viruses. Some compounds derived from glutamine are used in the synthesis of purines and pyrimidines. These latter compounds are precursors for the synthesis of nucleotides. Inhibitors of glutamine transport and metabolism are potential candidate antiviral drugs. Glutamine is also an essential nutrient for the functions of leukocytes (lymphocyte, macrophage, and neutrophil), including those in virus-infected patients. The increased glutamine requirement for immune cell functions occurs concomitantly with the high glutamine utilization by host cells in virus-infected patients. The development of antiviral drugs that target glutamine metabolism must then be specifically directed at virus-infected host cells to avoid negative effects on immune functions. Therefore, the aim of this review was to describe the landscape of cellular glutamine metabolism to search for potential candidates to inhibit glutamine transport or glutamine metabolism.

Zanthoxylum alkylamides improve amino acid metabolism in type 2 diabetes mellitus rats

To investigate the effect of Zanthoxylum alkylamides (ZA) on amino acid metabolism of type 2 diabetes mellitus (T2DM), the present study was performed with T2DM rats model induced with high fat and sugar fodder combined with low-dose of streptozotocin. ZA were fed to rats at three different doses of 2, 4, and 8 mg/kg for 28 days and metformin was fed to rats at 135 mg/kg as positive control. The results showed that compared with the normal control, the amino acid levels and the expression of related carrier genes were disordered in T2DM rats. Compared with the model, different doses of ZA could significantly resist (p < .05) the decrease in body weight of T2DM rats and improve hyperglycemia, with the best result observed with the high dose (8 mg/kg). Different doses of ZA could ameliorate the levels of 19 kinds of amino acid in the plasma, jejunum, liver, and skeletal muscle of T2DM rats by regulating the expression of related amino acid transporters including LAT1, SNAT2, CAT1, et al. to thereby ameliorating amino acid metabolism disorder in T2DM rats. PRACTICAL APPLICATIONS: Previous studies showed that Zanthoxylum alkylamides (ZA) could promote the amino acid metabolism in the jejunum of healthy SD rats, improve protein metabolism disorder of type 1 diabetic rats, and also reduce the risk of metabolic syndrome in fat rats model. Herein, we investigated the effect of ZA on amino acid metabolism in type 2 diabetes mellitus (T2DM) rats. The results indicated that ZA could remarkably improve the abnormal expression of amino acid carriers in the jejunum, liver, and skeletal muscle, thereby ameliorating the disorder of amino acid metabolism in the plasma, jejunum, liver, and skeletal muscle of T2DM rats. Therefore, ZA are potential antidiabetic food/medicine product for the T2DM treatment.

Glutamine depletion disrupts mitochondrial integrity and impairs C2C12 myoblast proliferation, differentiation, and the heat-shock response

Glutamine and glucose are both oxidized in the mitochondria to supply the majority of usable energy for processes of cellular function. Low levels of plasma and skeletal muscle glutamine are associated with severe illness. We hypothesized that glutamine deficiency would disrupt mitochondrial integrity and impair cell function. C2C12 mouse myoblasts were cultured in control media supplemented with 5.6 mmol/L glucose and 2 mmol/L glutamine, glutamine depletion (Gln^-) or glucose depletion (Glc^-) media. We compared mitochondrial morphology and function, as well as cell proliferation, myogenic differentiation, and heat-shock response in these cells. Glc^- cells exhibited slightly elongated mitochondrial networks and increased mitochondrial mass, with normal membrane potential (ΔΨm). Mitochondria in Gln^- cells became hyperfused and swollen, which were accompanied by severe disruption of cristae and decreases in ΔΨm, mitochondrial mass, the inner mitochondrial membrane remodeling protein OPA1, electron transport chain complex IV protein expression, and markers of mitochondrial biogenesis and bioenergetics. In addition, Gln^- increased the autophagy marker LC3B-II on the mitochondrial membrane. Notably, basal mitochondrial respiration was increased in Glc^- cells as compared to control cells, whereas maximal respiration remained unchanged. In contrast, basal respiration, maximal respiration and reserve capacity were all decreased in Gln^- cells. Consistent with the aforementioned mitochondrial deficits, Gln^- cells had lower growth rates and myogenic differentiation, as well as a higher rate of cell death under heat stress conditions than Glc^- and control cells. We conclude that glutamine is essential for mitochondrial integrity and function; glutamine depletion impairs myoblast proliferation, differentiation, and the heat-shock response.