Effect of dietary L-theanine supplementation on skeletal muscle fiber type transformation in vivo

Dietary protein restriction regulates skeletal muscle fiber metabolic characteristics associated with the FGF21-ERK1/2 pathway

Under conditions of dietary amino acid balance, decreasing the dietary crude protein (CP) level in pigs has a beneficial effect on meat quality. To further elucidate the mechanism, we explored the alteration of muscle fiber characteristics and key regulators related to myogenesis in the skeletal muscle of pigs fed a protein restricted diet. Compared to pigs fed a normal protein diet, dietary protein restriction significantly increased the slow-twitch muscle fiber proportion in skeletal muscle, succinic dehydrogenase (SDH) activity, the concentrations of ascorbate, biotin, palmitoleic acid, and the ratio of s-adenosylhomocysteine (SAM) to s-adenosylhomocysteine (SAH), but the fast-twitch muscle fiber proportion, lactate dehydrogenase (LDH) activity, the concentrations of ATP, glucose-6-phosphate, SAM, and SAH in skeletal muscle, and the ratio of serum triiodothyronine (T3) to tetraiodothyronine (T4) were decreased. In conclusion, we demonstrated that dietary protein restriction induced skeletal muscle fiber remodeling association the regulation of FGF21-ERK1/2-mTORC1 signaling in weaned piglets.

Metabolic signatures and potential biomarkers of sarcopenia in suburb-dwelling older Chinese: based on untargeted GC-MS and LC-MS

BACKGROUND

Untargeted metabolomics can be used to expand our understanding of the pathogenesis of sarcopenia. However, the metabolic signatures of sarcopenia patients have not been thoroughly investigated. Herein, we explored metabolites associated with sarcopenia by untargeted gas chromatography (GC)/liquid chromatography (LC)-mass spectrometry (MS) and identified possible diagnostic markers.

METHODS

Forty-eight elderly subjects with sarcopenia were age and sex matched with 48 elderly subjects without sarcopenia. We first used untargeted GC/LC-MS to analyze the plasma of these participants and then combined it with a large number of multivariate statistical analyses to analyze the data. Finally, based on a multidimensional analysis of the metabolites, the most critical metabolites were considered to be biomarkers of sarcopenia.

RESULTS

According to variable importance in the project (VIP > 1) and the p-value of t-test (p < 0.05), a total of 55 metabolites by GC-MS and 85 metabolites by LC-MS were identified between sarcopenia subjects and normal controls, and these were mostly lipids and lipid-like molecules. Among the top 20 metabolites, seven phosphatidylcholines, seven lysophosphatidylcholines (LysoPCs), phosphatidylinositol, sphingomyelin, palmitamide, L-2-amino-3-oxobutanoic acid, and palmitic acid were downregulated in the sarcopenia group; only ethylamine was upregulated. Among that, three metabolites of LysoPC(17:0), L-2-amino-3-oxobutanoic acid, and palmitic acid showed very good prediction capacity with AUCs of 0.887 (95% CI = 0.817-0.957), 0.836 (95% CI = 0.751-0.921), and 0.805 (95% CI = 0.717-0.893), respectively.

CONCLUSIONS

These findings show that metabonomic analysis has great potential to be applied to sarcopenia. The identified metabolites could be potential biomarkers and could be used to study sarcopenia pathomechanisms.

Novel peptides from sea cucumber intestines hydrolyzed by neutral protease alleviate exercise-induced fatigue via upregulating the glutaminemediated Ca2+ /Calcineurin signaling pathway in mice

Sea cucumber intestines are considered a valuable resource in the sea cucumber processing industry due to their balanced amino acid composition. Studies have reported that peptides rich in glutamate and branched-chain amino acids have anti-fatigue properties. However, the function of the sea cucumber intestine in reducing exercise-induced fatigue remains unclear. In this study, we enzymatically hydrolyzed low molecular weight peptides from sea cucumber intestines (SCIP) and administered SCIP orally to mice to examine its effects on exercise-induced fatigue using swimming and pole-climbing exhaustion experiments. The results revealed that supplementation with SCIP significantly prolonged the exhaustion time of swimming in mice, decreased blood lactate and urea nitrogen levels, and increased liver and muscle glycogen levels following a weight-loaded swimming test. Immunofluorescence analysis indicated a notable increase the proportion of slow-twitch muscle fiber and a significant decrease the proportion of fast-twitch muscle fiber following SCIP supplementation. Furthermore, SCIP upregulated mRNA expression levels of Ca2+ /Calcineurin upstream and downstream regulators, thereby contributing to the promotion of skeletal muscle fiber type conversion. This study presents the initial evidence establishing SCIP as a potential enhancer of skeletal muscle fatigue resistance, consequently providing a theoretical foundation for the valuable utilization of sea cucumber intestines.

Myosin heavy chain isoform expression and meat quality characteristics of different muscles in yak (Bos grunniens)

Myosin heavy chain (MHC) isoforms and meat quality characteristics of different muscles were investigated to explore their potential relationships in yaks. Results showed that semitendinosus (ST), longissimus thoracis (LT), and infraspinatus (IS) have a greater ratio of MHC IIb (47.84%), MHC IIa (73.27%), and MHC I (24.26%), respectively, than the other two muscles. Compared with LT or ST, IS exhibited more intense color, greater water-holding capacity, and initial tenderness with higher intermuscular fat (IMF) and collagen (of lower cross-linking level), presenting overall better quality. Variations in MHC isoforms accounted for the muscle-specific meat quality. Specifically, MHC I was positively associated with redness, myoglobin, IMF, collagen, pH, and thermal stability and negatively associated with myofibril fragmentation index, fiber thickness, collagen cross-linking, and drip loss. These results provide insights into the relationships between MHC isoforms and meat quality in yaks and the MHC I isoform has an extensive influence on meat quality.

Dietary Supplementation with Lauric Acid Improves Aerobic Endurance in Sedentary Mice via Enhancing Fat Mobilization and Glyconeogenesis

BACKGROUND

Lauric acid (LA), a major, natural, medium-chain fatty acid, is considered an efficient energy substrate for intense exercise and in patients with long-chain fatty acid β-oxidation disorders. However, few studies have focused on the role of LA in exercise performance and related glucolipid metabolism in vivo.

OBJECTIVES

We aimed to investigate the effect of dietary supplementation with LA on exercise performance and related metabolic mechanisms.

METHODS

Male C57BL/6N mice (14 wk old) were fed a basal diet or a diet containing 1% LA, and a series of exercise tests, including a high-speed treadmill test, aerobic endurance exercises, a 4-limb hanging test, and acute aerobic exercises, were performed.

RESULTS

Dietary supplementation with 1.0% LA accelerated the recovery from fatigue after explosive exercise (P < 0.05) and improved aerobic endurance and muscle strength in sedentary mice (P = 0.039). Lauric acid intake not only changed muscle fatty acid profiles, including increases in C12:0 and n-6/n-3 PUFAs (P < 0.001) and reductions in C18:0, C20:4n-6, C22:6n-3, and n-3 PUFAs (P < 0.05) but also enhanced fat mobilization from adipose tissue and fatty acid oxidation in the liver, at least partly via the AMP-activated protein kinase-acetyl CoA carboxylase pathway (P < 0.05). Likewise, LA supplementation promoted liver glyconeogenesis and conserved muscular glycogen during acute aerobic exercise (P < 0.05), which was accompanied by an increase in the mitochondrial DNA copy number and Krebs cycle activity in skeletal muscle (P < 0.05).

CONCLUSIONS

Dietary supplemental LA serves as an efficient energy substrate for sedentary mice to improve aerobic exercise endurance and muscle strength through regulation of glucolipid metabolism. These findings imply that LA supplementation might be a promising nutritional strategy to improve aerobic exercise performance in sedentary people.

Dietary Taurine Supplementation Improves the Meat Quality, Muscle Fiber Type, and Mitochondrial Function of Finishing Pigs

This study investigated the effects of dietary supplementation with taurine (TAU) on the meat quality, muscle fiber type, and mitochondrial function of finishing pigs. The results demonstrated that TAU significantly increased the a* value while decreasing b*45 min, L*24 h, and drip loss24 h and drip loss48 h in the longissimus dorsi (LD) muscle. Dietary supplemented with TAU reduced the content of lactate and the glycolytic potential (GP) in the LD muscle. Dietary supplemented with TAU enhanced the oxidative fiber-related gene expression as well as increased succinic dehydrogenase and malate dehydrogenase activities while reducing lactate dehydrogenase activity. Furthermore, dietary supplementation with TAU increased the contents of mtDNA and ATP and mitochondrial function-related gene expression. Moreover, TAU enhanced the mRNA expressions of calcineurin (CaN) and nuclear factor of activated T cells c1 (NFATc1) and protein expressions of CNA and NFATc1. The results indicate that dietary TAU supplementation improves meat quality and mitochondrial biogenesis and function and promotes muscle fiber-type conversion from the glycolytic fiber to the oxidative fiber via the CaN/NFATc1 pathway.

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

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

Effect of hypobaric hypoxia on the fiber type transition of skeletal muscle: a synergistic therapy of exercise preconditioning with a nanocurcumin formulation

Hypobaric hypoxia (HH) leads to various adverse effects on skeletal muscles, including atrophy and reduced oxidative work capacity. However, the effects of HH on muscle fatigue resistance and myofiber remodeling are largely unexplored. Therefore, the present study aimed to explore the impact of HH on slow-oxidative fibers and to evaluate the ameliorative potential of exercise preconditioning and nanocurcumin formulation on muscle anti-fatigue ability. C2C12 cells (murine myoblasts) were used to assess the effect of hypoxia (0.5%, 24 h) with and without the nanocurcumin formulation (NCF) on myofiber phenotypic conversion. To further validate this hypothesis, male Sprague Dawley rats were exposed to a simulated HH (7620 m) for 7 days, along with NCF administration and/or exercise training. Both in vitro and in vivo studies revealed a significant reduction in slow-oxidative fibers (p < 0.01, 61% vs. normoxia control) under hypoxia. There was also a marked decrease in exhaustion time (p < 0.01, 65% vs. normoxia) in hypoxia control rats, indicating a reduced work capacity. Exercise preconditioning along with NCF supplementation significantly increased the slow-oxidative fiber proportion and exhaustion time while maintaining mitochondrial homeostasis. These findings suggest that HH leads to an increased transition of slow-oxidative fibers to fast glycolytic fibers and increased muscular fatigue. Administration of NCF in combination with exercise preconditioning restored this myofiber remodeling and improved muscle anti-fatigue ability.

Effects of dietary l-theanine supplementation on pork quality and muscle fiber type transformation in finishing pigs

BACKGROUND

This experiment aimed to investigate effects of dietary l-theanine supplementation on pork quality and muscle fiber type transformation in finishing pigs. In a 30-day experiment, 18 healthy Duroc × Landrace × Yorkshire (DLY) pigs with an average body weight of 86.03 ± 0.83 kg were randomly divided into three groups (a basal diet or a basal diet supplemented with 500 and 1000 ppm l-theanine, respectively), with six duplicates and one pig per replicate.

RESULTS

The results showed that dietary 1000 ppm l-theanine supplementation significantly reduced (P < 0.05) b*_{24 h} and drip loss. Dietary 1000 ppm l-theanine supplementation significantly increased (P < 0.05) slow myosin heavy chain (MyHC) protein expression and the percentage of slow-twitch fibers, as well as significantly decreased (P < 0.05) fast MyHC protein expression and the percentage of fast-twitch fibers, accompanied by an increase in succinate dehydrogenase (SDH) and malate dehydrogenase (MDH) activities and a decrease in lactate dehydrogenase (LDH) activity. In addition, the adenosine monophosphate (AMP)-activated protein kinase (AMPK) signaling pathway was activated by l-theanine.

CONCLUSION

Together, this study demonstrated for the first time that dietary supplementation of 1000 ppm l-theanine can improve pork color and drip loss and promote muscle fiber type transformation from fast-twitch to slow-twitch in finishing pigs. © 2022 Society of Chemical Industry.

Effect of dietary L-theanine supplementation on skeletal muscle fiber type transformation in weaning piglets

The aim of this study was to explore the effect of dietary L-theanine (LT) supplementation on skeletal muscle fiber type transformation in weaning piglets. Our data showed that LT significantly increased the slow-twitch fiber-related genes expression and the percentage of slow oxidative fiber, and decreased the MyHC IIb mRNA expression and the percentage of fast glycolytic fiber. In addition, LT significantly increased the succinic dehydrogenase (SDH) and malate dehydrogenase (MDH) activities and increased the LDH activities. In addition, LT significantly affected mitochondrial biogenesis and function and antioxidative related genes expression, and increased the protein expression of p-adenosine monophosphate (AMP)-activated protein kinase (AMPK) and peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α), nuclear factor E2-related factor 2 (Nrf2), NADPH quinone oxidoreductase-1 (NQO1) and heme oxygenase-1 (HO-1) and decreased the Keap1 protein levels. Furthermore, our data indicated that LT significantly increased the mRNA and protein expression of prospero-related homeobox 1 (Prox1), calcineurin A (CnA), and NFATc1, suggesting that dietary LT supplementation promoted skeletal muscle fiber transition from types II to I might be via activation of calcineurin signaling pathway. Taken together, these findings suggested that LT promoted the transformation of muscle fiber types from slow oxidative to fast glycolytic by increasing antioxidant capacity and improving mitochondrial biogenesis and function and activation of calcineurin signaling pathway.

Effect of dietary resveratrol supplementation on muscle fiber types and meat quality in beef cattle

In order to investigate the effect of dietary resveratrol supplementation on muscle fiber types and meat quality in beef cattle, a feeding experiment was undertaken. Longissimus lumborum, Psoas major and Semitendinosus muscles were collected 24 h post-mortem from two groups of cattle, which were fed with a total mixed ration (Control - CON) or supplemented with resveratrol (5 g/animal/day, RES) for 120 d before slaughter. The results showed that dietary resveratrol increased the gene expression of MyHC I and enhanced the proportion of type I fibers in three muscles. The cooking loss and Warner-Bratzler shear force of all muscles during aging for 21 days were decreased. However, the increased proportion of type I fibers resulted in a darker initial color, but did improve color stability, as the a* value of RES samples was lower initially but higher in the later stage of aging. This study indicates the supplementation potential of resveratrol for beef cattle for tenderness and color stability.

L-theanine induces skeletal muscle fiber type transformation by activation of prox1/CaN signaling pathway in C2C12 myotubes

The aim of this study was to investigate the effect and mechanism of L-theanine (LT) on muscle fiber type transformation in C2C12 myotubes. Our data showed that LT exhibited significantly higher slow oxidative muscle fiber expression and lower glycolytic fibers expression. In addition, LT significantly increased the activities of malate dehydrogenase (MDH) and succinic dehydrogenase (SDH), and decreased lactate dehydrogenase (LDH) activity, the calcineurin (CaN) activity and the protein expressions of nuclear factor of activated T cell 1 (NFATc1), prospero-related homeobox1 (prox1), and calcineurin A (CnA) were significantly increased. However, inhibition of CaN activity by cyclosporine A (CsA) abolished LT-induced increase of slow oxidative muscle fiber expression and decrease of glycolytic fibers expression. Moreover, inhibition of prox1 expression by prox1-siRNA disrupted LT-induced activation of CaN signaling pathway and muscle fiber type transformation. Taken together, these results indicated that LT could promote skeletal muscle fiber type transformation from type II to type I via activation of prox1/CaN signaling pathway.

Balanced branched-chain amino acids modulate meat quality by adjusting muscle fiber type conversion and intramuscular fat deposition in finishing pigs

BACKGROUND

Pork is an important food for humans and improving the quality of pork is closely related to human health. This study was designed to investigate the effects of balanced branched-chain amino acid (BCAA)-supplemented protein-restricted diets on meat quality, muscle fiber types, and intramuscular fat (IMF) in finishing pigs.

RESULTS

The results showed that, compared with the normal protein diet (160 g kg-1 crude protein), the reduced-protein diet (120 g kg-1 crude protein) supplemented with BCAAs to the ratio of 2:1:2 not only had higher average daily gain (P < 0.05) and carcass weight (P < 0.05) but also improved meat tenderness and juiciness by decreasing shear force (P < 0.05) and increasing water-holding capacity (P < 0.05). In particular, this treatment showed higher (P < 0.05) levels of phospho-acetyl-CoA carboxylase (P-ACC) and peroxisome proliferation-activated receptor-γ (PPARγ), and lower (P < 0.05) levels of P-adenosine 5'-monophosphate (AMP)-activated protein kinase (P-AMPK), increasing the composition of IMF and MyHC I (P < 0.05) in the longissimus dorsi muscle (LDM). In terms of health, this group increased eicosapentaenoic acid (EPA) (P < 0.01) and desirable hypocholesterolemic fatty acids (DHFA) (P < 0.05), and decreased atherogenicity (AI) (P < 0.01) and hypercholesterolemic saturated fatty acids (HSFA) (P < 0.05).

CONCLUSION

Our findings suggest a novel role for a balanced BCAA-supplemented restricted protein (RP) diet in the epigenetic regulation of more tender and healthier pork by increasing IMF deposition and fiber type conversion, providing a cross-regulatory molecular basis for revealing the nutritional regulation network of meat quality. © 2021 Society of Chemical Industry.

Comprehensive Analysis of Long Noncoding RNA Modified by m6A Methylation in Oxidative and Glycolytic Skeletal Muscles

N⁶-methyladenosine (m⁶A) is the most common modification in eukaryotic RNAs. Accumulating evidence shows m⁶A methylation plays vital roles in various biological processes, including muscle and fat differentiation. However, there is a lack of research on lncRNAs’ m⁶A modification in regulating pig muscle-fiber-type conversion. In this study, we identified novel and differentially expressed lncRNAs in oxidative and glycolytic skeletal muscles through RNA-seq, and further reported the m⁶A-methylation patterns of lncRNAs via MeRIP-seq. We found that most lncRNAs have one m⁶A peak, and the m⁶A peaks were preferentially enriched in the last exon of the lncRNAs. Interestingly, we found that lncRNAs’ m⁶A levels were positively correlated with their expression homeostasis and levels. Furthermore, we performed conjoint analysis of MeRIP-seq and RNA-seq data and obtained 305 differentially expressed and differentially m⁶A-modified lncRNAs (dme-lncRNAs). Through QTL enrichment analysis of dme-lncRNAs and PPI analysis for their cis-genes, we finally identified seven key m⁶A-modified lncRNAs that may play a potential role in muscle-fiber-type conversion. Notably, inhibition of one of the key lncRNAs, MSTRG.14200.1, delayed satellite cell differentiation and stimulated fast-to-slow muscle-fiber conversion. Our study comprehensively analyzed m⁶A modifications on lncRNAs in oxidative and glycolytic skeletal muscles and provided new targets for the study of pig muscle-fiber-type conversion.