Leucine promotes differentiation of porcine myoblasts through the protein kinase B (Akt)/Forkhead box O1 signalling pathway

Leu promotes C2C12 cell differentiation by regulating the GSK3β/β-catenin signaling pathway through facilitating the interaction between SESN2 and RPN2

BACKGROUND

Leucine (Leu) is an essential amino acid that facilitates skeletal muscle satellite cell differentiation, yet its mechanism remains underexplored. Sestrin2 (SESN2) serves as a Leu sensor, binding directly to Leu, while ribophorin II (RPN2) acts as a signaling factor in multiple pathways. This study aimed to elucidate Leu's impact on mouse C2C12 cell differentiation and skeletal muscle injury repair by modulating RPN2 expression through SESN2, offering a theoretical foundation for clinical skeletal muscle injury prevention and treatment.

RESULTS

Leu addition promoted C2C12 cell differentiation compared to the control, enhancing early differentiation via myogenic determinant (MYOD) up-regulation. Sequencing revealed SESN2 binding to and interacting with RPN2. RPN2 overexpression up-regulated MYOD, myogenin and myosin heavy chain 2, concurrently decreased p-GSK3β and increased nuclear β-catenin. Conversely, RPN2 knockdown yielded opposite results. Combining RPN2 knockdown with Leu rescued increased p-GSK3β and decreased nuclear β-catenin compared to Leu absence. Hematoxylin and eosin staining results showed that Leu addition accelerated mouse muscle damage repair, up-regulating Pax7, MYOD and RPN2 in the cytoplasm, and nuclear β-catenin, confirming that the role of Leu in muscle injury repair was consistent with the results for C2C12 cells.

CONCLUSION

Leu, bound with SESN2, up-regulated RPN2 expression, activated the GSK3β/β-catenin pathway, enhanced C2C12 differentiation and expedited skeletal muscle damage repair. © 2024 Society of Chemical Industry.

Production of Proliferation- and Differentiation-Competent Porcine Myoblasts for Preclinical Studies in a Porcine Large Animal Model of Muscular Insufficiency

Muscular insufficiency is observed in many conditions after injury, chronic inflammation, and especially in elderly populations. Causative cell therapies for muscle deficiencies are not state of the art. Animal models to study the therapy efficacy are, therefore, needed. We developed an improved protocol to produce myoblasts suitable for pre-clinical muscle therapy studies in a large animal model. Myoblasts were isolated from the striated muscle, expanded by employing five different protocols, and characterized on transcript and protein expression levels to determine procedures that yielded optimized regeneration-competent myoblasts and multi-nucleated myotubes. We report that swine skeletal myoblasts proliferated well under improved conditions without signs of cellular senescence, and expressed significant levels of myogenic markers including Pax7, MyoD1, Myf5, MyoG, Des, Myf6, CD56 (p ≤ 0.05 each). Upon terminal differentiation, myoblasts ceased proliferation and generated multi-nucleated myotubes. Injection of such myoblasts into the urethral sphincter complex of pigs with sphincter muscle insufficiency yielded an enhanced functional regeneration of this muscle (81.54% of initial level) when compared to the spontaneous regeneration in the sham controls without myoblast injection (67.03% of initial level). We conclude that the optimized production of porcine myoblasts yields cells that seem suitable for preclinical studies of cell therapy in a porcine large animal model of muscle insufficiency.

Cell Therapy by Mesenchymal Stromal Cells Versus Myoblasts in a Pig Model of Urinary Incontinence

The leading cause of stress urinary incontinence (SUI) in women is the urethral sphincter muscle deficiency caused by mechanical stress during pregnancy and vaginal delivery. In men, prostate cancer surgery and injury of local nerves and muscles are associated with incontinence. Current treatment often fails to satisfy the patient's needs. Cell therapy may improve the situation. We therefore investigated the regeneration potential of cells in ameliorating sphincter muscle deficiency and UI in a large animal model. Urethral sphincter deficiency was induced surgically in gilts by electrocautery and balloon dilatation. Adipose tissue-derived stromal cells (ADSCs) and myoblasts from Musculus semitendinosus were isolated from male littermates, expanded, characterized in depth for expression of marker genes and in vitro differentiation, and labeled. The cells were injected into the deficient sphincter complex of the incontinent female littermates. Incontinent gilts receiving no cell therapy served as controls. Sphincter deficiency and functional regeneration were recorded by monitoring the urethral wall pressure during follow-up by two independent methods. Cells injected were detected in vivo during follow-up by transurethral fluorimetry, ex vivo by fluorescence imaging, and in cryosections of tissues targeted by immunofluorescence and by polymerase chain reaction of the sex-determining region Y (SRY) gene. Partial spontaneous regeneration of sphincter muscle function was recorded in control gilts, but the sphincter function remained significantly below levels measured before induction of incontinence (67.03% ± 14.00%, n = 6, p < 0.05). Injection of myoblasts yielded an improved sphincter regeneration within 5 weeks of follow-up but did not reach significance compared to control gilts (81.54% ± 25.40%, n = 5). A significant and full recovery of the urethral sphincter function was observed upon injection of ADSCs within 5 weeks of follow-up (100.4% ± 23.13%, n = 6, p < 0.05). Injection of stromal cells provoked slightly stronger infiltration of CD45pos leukocytes compared to myoblasts injections and controls. The data of this exploratory study indicate that ADSCs inherit a significant potential to regenerate the function of the urethral sphincter muscle.

Taurine promotes muscle fiber type transformation through CaN/NFATc1 signaling in porcine myoblasts

This study investigated the effect of taurine (TAU) on the muscle fiber type transformation in porcine myoblasts and its molecular mechanisms. The findings revealed that TAU augmented the protein expression of slow MyHC and the enzyme activities of oxidative metabolism markers like malate dehydrogenase and succinic dehydrogenase. Conversely, it curtailed the expression of fast MyHC and glycolytic metabolism enzyme activity of lactate dehydrogenase. Moreover, TAU elevated the expression of genes associated with oxidative fiber while diminishing the expression of those linked to glycolytic fibers, suggesting that TAU promoted the muscle fiber type transformation from glycolytic fiber to oxidative fiber. Additionally, TAU notably enhanced the expression of key molecules of calcineurin (CaN)/nuclear factor of activated T cells c1 (NFATc1) signaling and the CaN activity in porcine myoblasts. However, CaN inhibitor cyclosporine A abolished these effects induced by TAU. Our results indicated that TAU regulated the muscle fiber type transformation from glycolytic to oxidative fiber by activation of CaN/NFATc1 signaling.

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.

Ellagic Acid Alters Muscle Fiber-Type Composition and Promotes Mitochondrial Biogenesis through the AMPK Signaling Pathway in Healthy Pigs

Ellagic acid (EA), because of its remarkable health-promoting ability, has aroused widespread interest in the fields of nutrition and medicine. However, no reports showed that EA regulates mitochondrial biogenesis as well as muscle fiber-type composition in pigs. Our study found that dietary 75 and 150 mg/kg EA obviously augmented the slow myosin heavy chain (MyHC) protein level, the number of slow-twitch muscle fibers, and the activity of malate dehydrogenase (MDH) in the longissimus thoracis (LT) muscle of growing-finishing pigs. In contrast, dietary 75 and 150 mg/kg EA decreased the fast MyHC level, the number of fast-twitch muscle fibers, and the activity of lactate dehydrogenase (LDH) in the LT muscle. In addition, our further study found that dietary 75 and 150 mg/kg EA promoted the mitochondrial DNA (mtDNA) content, the mRNA expressions of ATP synthase (ATP5G), mtDNA transcription factor A (TFAM), AMP-activated protein kinase α1 (AMPKα1), peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) and sirtuin 1 (Sirt1), and the level of phospho-LKB1 (P-LKB1), phospho-AMPK (P-AMPK), Sirt1, and PGC-1α in the LT muscle. In vitro, 5, 10, and 20 μmol/L EA treatment upregulated the level of slow MyHC, but only 10 μmol/L EA treatment decreased fast MyHC protein expression in porcine skeletal muscle satellite cells (PSCs). In addition, our data again found that 10 μmol/L EA treatment promoted the mtDNA content, the mRNA levels of ATP5G, mitochondrial transcription factor b1 (TFB1M), citrate synthase (Cs), AMPKα1, PGC-1α, and Sirt1, and the protein expressions of P-AMPK, P-LKB1, PGC-1α, and Sirt1 in PSCs. What is more, inhibition of the AMPK signaling pathway by AMPKα1 siRNA significantly eliminated the improvement of EA on muscle fiber-type composition as well as the mtDNA content in PSCs. In conclusion, EA altered muscle fiber-type composition and promoted mitochondrial biogenesis through the AMPK signaling pathway.

Effect of dietary dihydromyricetin supplementation on lipid metabolism, antioxidant capacity and skeletal muscle fiber type transformation in mice

This study aimed to investigate the effect of dietary dihydromyricetin (DHM) supplementation on lipid metabolism, antioxidant capacity and muscle fiber type transformation. Twenty-four male Kunming mice were randomly allotted to either control (basal diet) or DHM diets (supplemented with 300 mg/kg DHM). Our data showed that DHM administration decreased the triglycerides (TG) and low-density lipoprotein cholesterol (LDL-C) contents, and increased the catalase (CAT), total superoxide dismutase (T-SOD) and glutathione peroxidase (GSH-Px) activities in serum. In the liver, DHM decreased the TG and malondialdehyde (MDA) levels and increased the T-SOD and GSH-Px activities. For the tibialis anterior (TA) muscle, DHM increased the total antioxidant capacity (T-AOC) level and T-SOD activities. Western blotting and real-time quantitative PCR analysis showed that DHM increased the protein and mRNA levels of MyHC I and MyHC IIa and decreased the protein and mRNA levels of MyHC IIb in TA muscle, which may be achieved by activating the AMP-activated protein kinase (AMPK) signal. The mRNA levels of several regulatory factors related to mitochondrial function were up-regulated by DHM. In conclusion, dietary 300 mg/kg DHM supplementation improved lipid metabolism and antioxidant capacity and promoted the transformation of muscle fiber type from glycolysis to oxidation in mice.

Fermented Feed Modulates Meat Quality and Promotes the Growth of Longissimus Thoracis of Late-Finishing Pigs

This study investigated the effect of fermented diet on growth performance, carcass traits, meat quality and growth of longissimus thoracis (LT) of finishing pigs. A total of 48 finishing pigs [Duroc × (Landrace × Large White), male, 126 ± 5-d-old] weighing 98.76 ± 1.27 kg were randomly assigned to two treatments (eight pens per treatment and three pigs per pen) for a 28-d feeding trial, including control diet and fermented diet. Fermented diet significantly increased the loin eye area and lean mass percentage, decreased backfat thickness and improved meat quality of LT by decreasing the shear force and drip loss at 48 h post slaughter and improving meat sensory characteristics compared with control diet. A fermented diet also significantly increased the abundance of insulin, insulin receptor (IR), myoblast determination protein (MyoD) and myosin heavy chain-I (MyHC-I) transcripts, and the phosphorylation levels of AKT, mTORC1, 4EBP1 and S6K1 in LT, while decreasing the expression of muscle atrophy F-box (MAFbx) and forkhead Box O1 (Foxo1) mRNA transcripts. Moreover, proteomic analysis revealed that differentially expressed proteins predominantly involved in protein synthesis and muscle development were modulated by fermented diet. Our results indicated that a fermented diet improved meat quality and enhanced LT growth of finishing pigs by increasing insulin/AKT/mTORC1 protein synthesis cascade and activating the Foxo1/MAFbx pathway, along with the regulation of ribosomal protein and proteins involved in muscle contraction and muscle hypertrophy.

Leucine Improved Growth Performance, Muscle Growth, and Muscle Protein Deposition Through AKT/TOR and AKT/FOXO3a Signaling Pathways in Hybrid Catfish Pelteobagrus vachelli × Leiocassis longirostris

(1) Background: l-leucine (Leu) plays a positive role in regulating protein turnover in skeletal muscle in mammal. However, the molecular mechanism for the effects of Leu on muscle growth and protein deposition is not clearly demonstrated in fish. This study investigated the effects of dietary Leu on growth performance and muscle growth, protein synthesis, and degradation-related signaling pathways of hybrid catfish (Pelteobagrus vachelli♀ × Leiocassis longirostris♂). (2) Methods: A total of 630 hybrid catfish (23.19 ± 0.20 g) were fed 6 different experimental diets containing graded levels of Leu at 10.0 (control), 15.0, 20.0, 25.0, 30.0, 35.0, and 40.0 g Leu kg^-1 for 8 weeks. (3) Results: Results showed that dietary Leu increased percent weight gain (PWG), specific growth rate (SGR), FI (feed intake), feed efficiency (FE), protein efficiency ratio (PER), muscle fibers diameter, and muscle fibers density; up-regulated insulin-like growth factor I (IGF-I), insulin-like growth factor I receptor (IGF-IR), proliferating cell nuclear antigen (PCNA), myogenic regulation factors (MyoD, Myf5, MyoG, and Mrf4), and MyHC mRNA levels; increased muscle protein synthesis via regulating the AKT/TOR signaling pathway; and attenuated protein degradation via regulating the AKT/FOXO3a signaling pathway. (4) Conclusions: These results suggest that Leu has potential role to improve muscle growth and protein deposition in fish, which might be due to the regulation of IGF mRNA expression, muscle growth related gene, and protein synthesis and degradation-related signaling pathways. Based on the broken-line model, the Leu requirement of hybrid catfish (23.19-54.55 g) for PWG was estimated to be 28.10 g kg^-1 of the diet (73.04 g kg^-1 of dietary protein). These results will improve our understanding of the mechanisms responsible for muscle growth and protein deposition effects of Leu in fish.

Betaine alleviates high glucose‑induced mesangial cell proliferation by inhibiting cell proliferation and extracellular matrix deposition via the AKT/ERK1/2/p38 MAPK pathway

Diabetic nephropathy (DN) is a major cause of chronic renal failure in diabetic patients worldwide. Betaine, a zwitterionic quaternary ammonium salt compound, is involved in numerous biological processes. The present study aimed to investigate the effects of betaine on mouse mesangial cells (MMCs) cultured under high glucose (HG) conditions and its underlying mechanisms. MMCs were treated with betaine under HG conditions. Cell proliferation and the cell cycle distribution were investigated with an MTT assay and flow cytometry, respectively. Western blotting and reverse transcription‑quantitative polymerase chain reaction analyses were applied to respectively determine protein and mRNA expression levels. The results suggested that betaine decreased cell proliferation in a dose‑dependent manner, while G1‑phase arrest was significantly induced in MMCs. Compared with the control group, the expression levels of p21 and p27 decreased under HG conditions, but were reversed by betaine. Furthermore, the expression levels of fibronectin and type IV collagen were significantly decreased in cells treated with betaine compared with the HG group. Additionally, betaine decreased the phosphorylation of Akt, extracellular‑signal‑regulated kinase (Erk)1/2 and p38 mitogen‑activated protein kinase (MAPK), but was enhanced under HG conditions. Overall, the results of the present study indicated that betaine serves a protective role in HG‑induced MMCs by inhibiting cell proliferation and extracellular matrix deposition via regulating regulation of the Akt/Erk1/2/p38 MAPK signaling pathway.

Leucine promotes porcine myofibre type transformation from fast-twitch to slow-twitch through the protein kinase B (Akt)/forkhead box 1 signalling pathway and microRNA-27a

Muscle fibre types can transform from slow-twitch (slow myosin heavy chain (MyHC)) to fast-twitch (fast MyHC) or vice versa. Leucine plays a vital effect in the development of skeletal muscle. However, the role of leucine in porcine myofibre type transformation and its mechanism are still unclear. In this study, effects of leucine and microRNA-27a (miR-27a) on the transformation of porcine myofibre type were investigatedin vitro. We found that leucine increased slow MyHC protein level and decreased fast MyHC protein level, increased the levels of phospho-protein kinase B (Akt)/Akt and phospho-forkhead box 1 (FoxO1)/FoxO1 and decreased the FoxO1 protein level. However, blocking the Akt/FoxO1 signalling pathway by wortmannin attenuated the role of leucine in porcine myofibre type transformation. Over-expression of miR-27a decreased slow MyHC protein level and increased fast MyHC protein level, whereas inhibition of miR-27a had an opposite effect. We also found that expression of miR-27a was down-regulated following leucine treatment. Moreover, over-expression of miR-27a repressed transformation from fast MyHC to slow MyHC caused by leucine, suggesting that miR-27a is interdicted by leucine and then contributes to porcine muscle fibre type transformation. Our finding provided the first evidence that leucine promotes porcine myofibre type transformation from fast MyHC to slow MyHC via the Akt/FoxO1 signalling pathway and miR-27a.