Procyanidin B2 Promotes Skeletal Slow-Twitch Myofiber Gene Expression through the AMPK Signaling Pathway in C2C12 Myotubes

GPCPD1 is regulated by METTL3/IGF2BP3 dependent m6A modification to affect pig muscle fiber type conversion

The N6-methyladenosine (m6A) modification is the most prevalent and abundant RNA modification in eukaryotes. In our previous study, we identified that the glycerophosphocholine phosphodiesterase 1 (GPCPD1) gene was differentially expressed and diverse m6A modificated in the pig soleus and extensor digitorum longus muscles. In this study, we further investigated the function of GPCPD1 gene in pig muscle development. We found that GPCPD1 inhibited myogenic differentiation and promoted the conversion of fast-twitch to slow-twitch fibers in both porcine muscle satellite cells (PSCs) and in mouse model. We also found that the expression of GPCPD1 was affected by m6A methyltransferase METTL3. The methylated GPCPD1 gene was recognized by the m6A reader protein IGF2BP3, which further modulated the stability of GPCPD1 mRNA. This study provided novel evidence into m6A regulation in pig muscle development and illustrated the new post-transcriptional regulation way in GPCPD1 expression.

Procyanidin B2 attenuates microvascular dysfunction in diabetic retinopathy via inhibition of caspase-1/GSDMD mediated pyroptosis

ETHNOPHARMACOLOGICAL RELEVANCE

In traditional Chinese medicine (TCM), grape seeds (Vitis vinifera) are believed to nourish the liver and kidney and improve blood circulation, which aligns with the pathophysiological needs of conditions characterized by microvascular dysfunction. Procyanidin B2 (PB2), a major active compound in grape seeds, has shown potent anti-inflammatory and vascular-protective effects. However, the specific role of PB2 in diabetic retinal microvasculature and its underlying molecular mechanisms remain unexplored.

AIMS OF THE STUDY

This study aimed to evaluate the therapeutic potential of Procyanidin B2 (PB2) in alleviating microvascular damage in diabetic retinopathy and the possible mechanisms.

MATERIALS AND METHODS

Pyroptosis in endothelial cells was analyzed under high glucose conditions and in the retinas of diabetic mice. The effects of PB2 on pyroptosis and endothelial dysfunction were examined through in vitro assays evaluating cell proliferation, migration, and tube formation. In vivo experiments using diabetic mouse models were conducted to assess retinal vascular integrity, with a focus on PB2's impact on endothelial pyroptosis and its associated molecular mechanisms.

RESULTS

PB2 significantly suppressed pyroptosis in endothelial cells exposed to high glucose by inhibiting the caspase-1/GSDMD signaling pathway. This suppression enhanced endothelial cell proliferation, migration, and tube formation. In diabetic mice, PB2 treatment effectively alleviated retinal microvascular dysfunction by reducing pyroptosis and preserving retinal vascular integrity.

CONCLUSION

These findings provide a molecular basis for PB2's therapeutic potential in DR and support its further development as an intervention for diabetic vascular complications.

CRISPR Screen Identifies the RNA-Binding Protein Eef1a1 as a Key Regulator of Myogenesis

Skeletal muscle myogenesis hinges on gene regulation, meticulously orchestrated by molecular mechanisms. While the roles of transcription factors and non-coding RNAs in myogenesis are widely known, the contribution of RNA-binding proteins (RBPs) has remained unclear until now. Therefore, to investigate the functions of post-transcriptional regulators in myogenesis and uncover new functional RBPs regulating myogenesis, we employed CRISPR high-throughput RBP-KO (RBP-wide knockout) library screening. Through this approach, we successfully identified Eef1a1 as a novel regulatory factor in myogenesis. Using CRISPR knockout (CRISPRko) and CRISPR interference (CRISPRi) technologies, we successfully established cellular models for both CRISPRko and CRISPRi. Our findings demonstrated that Eef1a1 plays a crucial role in promoting proliferation in C2C12 myoblasts. Through siRNA inhibition and overexpression methods, we further elucidated the involvement of Eef1a1 in promoting proliferation and suppressing differentiation processes. RIP (RNA immunoprecipitation), miRNA pull-down, and Dual-luciferase reporter assays confirmed that miR-133a-3p targets Eef1a1. Co-transfection experiments indicated that miR-133a-3p can rescue the effect of Eef1a1 on C2C12 myoblasts. In summary, our study utilized CRISPR library high-throughput screening to unveil a novel RBP, Eef1a1, involved in regulating myogenesis. Eef1a1 promotes the proliferation of myoblasts while inhibiting the differentiation process. Additionally, it acts as an antagonist to miR-133a-3p, thus modulating the process of myogenesis.

Orientin Promotes Antioxidant Capacity, Mitochondrial Biogenesis, and Fiber Transformation in Skeletal Muscles through the AMPK Pathway

The sleep-breathing condition obstructive sleep apnea (OSA) is characterized by repetitive upper airway collapse, which can exacerbate oxidative stress and free radical generation, thereby detrimentally impacting both motor and sensory nerve function and inducing muscular damage. OSA development is promoted by increasing proportions of fast-twitch muscle fibers in the genioglossus. Orientin, a water-soluble dietary C-glycosyl flavonoid with antioxidant properties, increased the expression of slow myosin heavy chain (MyHC) and signaling factors associated with AMP-activated protein kinase (AMPK) activation both in vivo and in vitro. Inhibiting AMPK signaling diminished the effects of orientin on slow MyHC, fast MyHC, and Sirt1 expression. Overall, orientin enhanced type I muscle fibers in the genioglossus, enhanced antioxidant capacity, increased mitochondrial biogenesis through AMPK signaling, and ultimately improved fatigue resistance in C2C12 myotubes and mouse genioglossus. These findings suggest that orientin may contribute to upper airway stability in patients with OSA, potentially preventing airway collapse.

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.

Procyanidin B2: A promising multi-functional food-derived pigment for human diseases

Natural edible pigments play a paramount part in the food industry. Procyanidin B2 (PB2), one of the most representative naturally occurring edible pigments, is usually isolated from the seeds, fruits, and leaves of lots of common plants, such as grapes, Hawthorn, black soybean, as well as blueberry, and functions as a food additive in daily life. Notably, PB2 has numerous bioactivities and possesses the potential to treat/prevent a wide range of human diseases, such as diabetes mellitus, diabetic complications, atherosclerosis, and non-alcoholic fatty liver disease, and the underlying mechanisms were partially elucidated, including mediating signaling pathways like NF-κB, MAPK, PI3K/Akt, apoptotic axis, and Nrf-2/HO-1. This paper presents a review of the natural sources, bioactivities, and the therapeutic/preventive potential of PB2 and the possible mechanisms, with the aim of promoting the development of PB2 as a functional food and providing references for its clinical application in the treatment of diseases.

"Biqi" Bayberry Extract Promotes Skeletal Muscle Fiber Type Remodeling by Increasing Fast Myofiber Formation via the Akt/FoxO1 Pathway in Mice

Bayberry is known to be a rich source of natural flavonoids and has been reported to have various health-promoting abilities. However, its function on regulating skeletal muscle fiber type remains unclear. This study examined whether bayberry extract affects skeletal muscle fiber type by promoting fast myofiber formation, as well as the potential molecular mechanism. After eight weeks, the "Biqi" bayberry extract (BBE) groups mice displayed markedly enhanced grip strength and improved metabolic rate compared to the control group mice. BBE also significantly increased myofibers size, LDH activity, MyHC-IIb (fast-twitch mRNA) expression, and the percentage of fast-twitch myofibers, while decreasing SDH activity, MyHC-I (slow-twitch mRNA) expression, and slow-twitch myofibers percentage in the skeletal muscle of the mice. The effect of BBE on regulating skeletal muscle fiber type remodeling is likely attributed to its activation of the Akt-FoxO1 pathway. Our findings indicated that BBE can effectively regulate the expression and proportion of fast-twitch fibers, making it a potential therapy for improving glucose homeostasis of skeletal muscle.

Genome-wide analysis of circular RNA-mediated ceRNA regulation in porcine skeletal muscle development

BACKGROUND

As a diverse and abundant class of endogenous RNAs, circular RNAs (circRNAs) participate in various biological processes including cell proliferation and apoptosis. Nevertheless, few researchers have investigated the role of circRNAs in muscle development in cultivated pigs.

RESULTS

In this study, we used RNA-seq to construct circRNA expression profiles in skeletal muscle of Jinfen White pigs at the age of 1, 90, and 180 days. Among the 16,990 identified circRNAs, 584 circRNAs were differentially expressed. Moreover, the enrichment analysis of DE circRNA host genes showed that they were mainly involved in muscle contraction, muscle organ development and muscle system processes, as well as AMPK and cAMP-related signal pathways. We also constructed a circRNA-miRNA-mRNA co-expression network to find key circRNAs which many involved in the regulation of porcine skeletal muscle development through the competitive endogenous RNA (ceRNA) mechanism. It is noteworthy that circ_0018595/miR-1343/PGM1 axis may play a regulatory role in the development of porcine skeletal muscle.

CONCLUSIONS

This study identified the circRNAs and present the circRNA expression profile in the development of pigs, revealed that DE circRNA host genes participate in different cell fates and enriched the porcine ceRNA network. Thus, this work will become a valuable resource for further in-depth study of the regulatory mechanism of circRNA in the development of porcine skeletal muscle.

Effects of protocatechuic acid on antioxidant capacity, mitochondrial biogenesis and skeletal muscle fiber transformation

In skeletal muscle, the increased proportion of type I muscle fibers has the potential to improve muscle atrophy and prevent human metabolic diseases. Protocatechuic acid (PCA), as a kind of anthocyanin metabolite, has antioxidant and anti-inflammatory physiological activities. The purpose of this experiment was to use mice and C2C12 myotubes to examine if PCA can induce the transformation of muscle fiber and the mechanisms involved. We found that PCA significantly increased the expression of slow myosin heavy chain (MyHC), and markedly decreased the expression of fast MyHC in gastrocnemius muscle of mice and C2C12 myotubes. In addition, PCA also enhanced the antioxidant capacity and promoted mitochondrial biogenesis in mice. Importantly, the AMP-activated protein kinase (AMPK) signaling pathway was activated and AMPK inhibitor compound C attenuated the positive effect of PCA on myofiber conversion. To sum up, we revealed that PCA was able to promote the conversion of skeletal muscle fiber from type II to type I through the AMPK signaling pathway.

Molecular Mechanisms for the Carnosine-Induced Activation of Muscle-Brain Interaction

Carnosine is known to improve brain function. The molecular basis for the carnosine-mediated interaction between intestinal cells and neuronal cells is that carnosine acts on intestinal cells and stimulates exosome secretion, which can induce neurite outgrowth in neuronal cells. This study aimed to infer the carnosine-mediated interaction between muscle cells and neuronal cells. The results revealed that carnosine induces muscle cell differentiation, as well as the secretion of exosomes and myokines that can act on neuronal cells. Carnosine acts not only on intestinal cells but also on muscle cells, stimulating the secretion of secretory factors including exosomes that induce neurite outgrowth in neuronal cells, as well as myokines known to be involved in neuronal cell activation. As the miRNAs in exosomes secreted from intestinal cells and muscle cells upon carnosine treatment are different, it could be assumed that carnosine acts on each cell to interact with neuronal cell through separate factors and mechanisms.

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.

Maternal organic selenium supplementation during gestation enhances muscle fiber area and muscle fiber maturation of offspring in porcine model

Background

Organic selenium supplementation during gestation improves the antioxidant status and reproductive performance of sows and increases the antioxidative capacity of the intestines of their offspring. This study was conducted to investigate the effect of maternal basel diet (control) supplemented with an organic Se, 2-hydroxy-4-methylselenobutanoic acid (HMSeBA), or inorganic sodium selenite (Na₂SeO₃) during gestation on the antioxidant status and development of muscle in newborn and weaned piglets. Newborn piglets before colostrum intake and weaned piglets were selected for longissimus dorsi (LD) muscle collection and analysis.

Results

The results showed that maternal HMSeBA supplementation increased the muscle area and content of Se in the LD muscle of newborn piglets, improved gene expression of selenoproteins, and decreased oxidative status in the LD muscle of both newborn and weaned piglets compared with the control. The expression of muscle development-related genes of newborn piglets in the HMSeBA group was lower than in the control group, whereas the expression of MRF4 in weaned piglets was higher in the HMSeBA group than in the control and Na₂SeO₃ groups. In addition, HMSeBA supplementation decreased the mRNA expressions of myosin heavy chains (MyHC) IIx and MyHC IIb and the percentage of MyHC IIb; increased the expression of PGC-1α in the LD muscle of newborn piglets; increased the gene expression of MyHC IIa; and decreased the protein expression of slow MyHC and the activity of malate dehydrogenase in the LD muscle of weaned piglets compared with the control group.

Conclusions

Maternal HMSeBA supplementation during gestation can improve the antioxidative capacity of the muscle of their offspring and promote the maturity of muscle fibres in weaned offspring.

Dihydromyricetin alters myosin heavy chain expression via AMPK signaling pathway in porcine myotubes

Dihydromyricetin (DHM) has attracted wide concern for its excellent biological function and pharmacological activities and was reported to have a positive effect on skeletal muscle insulin resistance, slow-twitch fibers expression and AMPK signaling. Thus, we took porcine myotubes derived from skeletal muscle satellite cells as the object to investigate the effects of DHM on myosin heavy chain (MyHC) expression and its mechanism in this study. Data showed that DHM up-regulated protein expression of MyHC I and down-regulated the protein expression of MyHC IIb, accompanied by an increase of MyHC I mRNA level and a decrease of MyHC IIb mRNA level. Besides, DHM increased the activities of malate dehydrogenase and succinic dehydrogenase and reduced lactate dehydrogenase activity. AMP-activated protein kinase (AMPK) was phosphorylated and AMPKα1 mRNA level was increased by DHM. The AMPK signaling-related factors including peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α), sirtuin1 (Sirt1), nuclear respiratory factor 1 (NRF1), and phospho-calmodulin-dependent protein kinase kinase-β (p-CaMKKβ) were increased by DHM. Inhibition of the AMPK signaling by compound C and AMPKα1 siRNA significantly attenuated the effects of DHM on expressions of MyHC I, MyHC IIb, PGC-1α and Sirt1. As a whole, DHM increased MyHC I expression and decreased MyHC IIb expression by the AMPK signaling.

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.

Hydroxysafflor yellow A triggered a fast-to-slow muscle fiber-type conversion via regulating FoxO1 in myocytes

Hydroxysafflor yellow A (HSYA) is the main bioactive component of safflower and has been reported to have significant health-promoting abilities. However, the regulation of HSYA on different types of skeletal myofibers is largely unknown. Here, in vitro experiments found that the water extract of safflower could significantly increase MyHC I, MB and Tnni1 mRNA expression while downregulating MyHC IIb mRNA expression. Furthermore, HSYA triggered fast-to-slow fiber-type switching and increased gene expression related to mitochondrial biosynthesis both in vitro and in vivo. Autodock analyses proved that FoxO1 is a potential target of HSYA, and qRT-PCR and western blotting further showed that HSYA significantly promoted the activation of the FoxO1 signaling pathway. Additionally, the levels of PGC1α, downstream of FoxO1, also significantly increased after HSYA treatment. Together, our findings suggested that HSYA triggered a fast-to-slow myofiber-type shift through the FoxO1 signaling pathway.

Comprehensive Transcriptome Analysis Reveals the Role of lncRNA in Fatty Acid Metabolism in the Longissimus Thoracis Muscle of Tibetan Sheep at Different Ages

Long noncoding RNA (lncRNA) plays an important regulatory role in mammalian adipogenesis and lipid metabolism. However, their function in the longissimus thoracis (LT) muscle of fatty acid metabolism of Tibetan sheep remains undefined. In this study, fatty acid and fat content in LT muscle of Tibetan sheep were determined, and RNA sequencing was performed to reveal the temporal regularity of lncRNA expression and the effect of lncRNA-miRNA-mRNA ceRNA regulatory network on lipid metabolism of LT muscle in Tibetan sheep at four growth stages (4-month-old, 4 m; 1.5-year-old, 1.5 y; 3.5-year-old, 3.5 y; 6-year-old, 6 y). The results indicated that the intramuscular fat (IMF) content was highest at 1.5 y. Moreover, the monounsaturated fatty acid (MUFA) content in 1.5 y of Tibetan sheep is significantly higher than those of the other groups (P < 0.05), and it was also rich in a variety of polyunsaturated fatty acids (PUFA). A total of 360 differentially expressed lncRNAs (DE lncRNAs) were identified from contiguous period transcriptome comparative groups of 4 m vs. 1.5 y, 1.5 y vs. 3.5 y, 3.5 y vs. 6 y, and 4 m vs. 6 y, respectively. Kyoto encyclopedia of genes and genomes (KEGG) enrichment analysis found that the target genes in lncRNA trans-mRNA were significantly related to the protein digestion, absorption, and fatty acid biosynthesis pathways (P < 0.05), which demonstrated that DE lncRNA trans-regulated the target genes, and further regulated the growth and development of the LT muscle and intramuscular fatty acid metabolism in Tibetan sheep. We further analyzed the role of the lncRNA-miRNA-mRNA regulatory network in the lipid metabolism of Tibetan sheep. Additionally, GPD2, LIPE (lipase E hormone-sensitive enzyme), TFDP2, CPT1A, ACACB, ADIPOQ, and other mRNA related to fatty acid and lipid metabolism and the corresponding lncRNA-miRNA regulatory pairs were identified. The enrichment analysis of mRNA in the regulatory network found that the AMPK signaling pathway was the most significantly enriched (P = 0.0000112361). Comprehensive transcriptome analysis found that the LIPE, ADIPOQ, ACACB, and CPT1A that were regulated by lncRNA might change the formation of energy metabolism in Tibetan sheep muscle through the AMPK signaling pathway, and oxidized muscle fibers are transformed into glycolytic muscle fibers, reduced IMF content, and the fatty acid profile also changed.

Dietary lycopene supplementation improves meat quality, antioxidant capacity and skeletal muscle fiber type transformation in finishing pigs

This study aimed to investigate effects of dietary lycopene supplementation on meat quality, antioxidant ability and muscle fiber type transformation in finishing pigs. In a 70-day experiment, 18 Duroc × Landrace × Yorkshire barrows were randomly allocated to 3 dietary treatments including a basal diet supplemented with 0, 100 and 200 mg/kg lycopene, respectively. Each dietary treatment had 6 replicates with one pig each. Results showed that dietary 200 mg/kg lycopene supplementation increased muscle redness a∗ value, intramuscular fat and crude protein contents, and decreased muscle lightness L∗ and yellowness b∗ values (P < 0.05), suggesting that addition of 200 mg/kg lycopene to the diet of finishing pigs improved color, nutritional value and juiciness of pork after slaughter. Results also showed that dietary lycopene supplementation enhanced antioxidant capacity of finishing pigs (P < 0.05). Moreover, dietary supplementation of 200 mg/kg lycopene significantly increased slow myosin heavy chain (MyHC) protein level and slow-twitch fiber percentage, and decreased fast MyHC protein level and fast-twitch fiber percentage (P < 0.05), suggesting that the addition of 200 mg/kg lycopene to the diet of finishing pigs promoted muscle fiber type conversion from fast-twitch to slow-twitch. Together, we provide the first evidence that dietary 200 mg/kg lycopene supplementation improves meat quality, enhances antioxidant capacity and promotes muscle fiber type transformation from fast-twitch to slow-twitch in finishing pigs.

Driving an Oxidative Phenotype Protects Myh4 Null Mice From Myofiber Loss During Postnatal Growth

Postnatal muscle growth is accompanied by increases in fast fiber type compositions and hypertrophy, raising the possibility that a slow to fast transition may be partially requisite for increases in muscle mass. To test this hypothesis, we ablated the Myh4 gene, and thus myosin heavy chain IIB protein and corresponding fibers in mice, and examined its consequences on postnatal muscle growth. Wild-type and Myh4^–/– mice had the same number of muscle fibers at 2 weeks postnatal. However, the gastrocnemius muscle lost up to 50% of its fibers between 2 and 4 weeks of age, though stabilizing thereafter. To compensate for the lack of functional IIB fibers, type I, IIA, and IIX(D) fibers increased in prevalence and size. To address whether slowing the slow-to-fast fiber transition process would rescue fiber loss in Myh4^–/– mice, we stimulated the oxidative program in muscle of Myh4^–/– mice either by overexpression of PGC-1α, a well-established model for fast-to-slow fiber transition, or by feeding mice AICAR, a potent AMP kinase agonist. Forcing an oxidative metabolism in muscle only partially protected the gastrocnemius muscle from loss of fibers in Myh4^–/– mice. To explore whether traditional means of stimulating muscle hypertrophy could overcome the muscling deficits in postnatal Myh4^–/– mice, myostatin null mice were bred with Myh4^–/– mice, or Myh4^–/– mice were fed the growth promotant clenbuterol. Interestingly, both genetic and pharmacological stimulations had little impact on mice lacking a functional Myh4 gene suggesting that the existing muscle fibers have maximized its capacity to enlarge to compensate for the lack of its neighboring IIB fibers. Curiously, however, cell signaling events responsible for IIB fiber formation remained intact in the tissue. These findings further show disrupting the slow-to-fast transition of muscle fibers compromises muscle growth postnatally and suggest that type IIB myosin heavy chain expression and its corresponding fiber type may be necessary for fiber maintenance, transition and hypertrophy in mice. The fact that forcing muscle metabolism toward a more oxidative phenotype can partially compensates for the lack of an intact Myh4 gene provides new avenues for attenuating the loss of fast-twitch fibers in aged or diseased muscles.

Effects of dietary grape seed proanthocyanidin extract supplementation on meat quality, muscle fiber characteristics and antioxidant capacity of finishing pigs

The aim of this study was to investigate effects of dietary grape seed proanthocyanidin extract (GSPE) supplementation on meat quality, muscle fiber characteristics and antioxidant capacity of finishing pigs. The data showed GSPE increased pH24 h, redness, crude protein content and decreased shear force, drip loss48 h, lactate content and glycolytic potential in longissimus dorsi (LD) muscle, accompanied by increased contents of total polyunsaturated fatty acid (PUFA), n-3 PUFA, and the ratio of PUFA to saturated fatty acid. GSPE promoted MyHC I mRNA and slow MyHC protein expression, and increased slow-twitch fiber percentage. The activities of total antioxidant capacity, total superoxide dismutase, catalase and glutathione peroxidase in LD muscle were increased by GSPE while malondialdehyde content was decreased. Together, this study demonstrated that dietary GSPE supplementation can effectively improve the color, water-holding capacity, tenderness and nutritional value of pork, and increase slow-twitch fiber percentage and antioxidant capacity of finishing pigs.

Therapeutic potential of PGC-1α in age-related macular degeneration (AMD) - the involvement of mitochondrial quality control, autophagy, and antioxidant response

INTRODUCTION

Age-related macular degeneration (AMD) is the leading, cause of sight loss in the elderly in the Western world. Most patients remain still without any treatment options. The targeting of Peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), a transcription co-factor, is a putative therapy against AMD.

AREAS COVERED

The characteristics of AMD and their possible connection with PGC-1α as well as the transcriptional and post-transcriptional control of PGC-1α are discussed. The PGC-1α-driven control of mitochondrial functions, and its involvement in autophagy and antioxidant responses are also examined. Therapeutic possibilities via drugs and epigenetic approaches to enhance PGC-1α expression are discussed. Authors conducted a search of literature mainly from the recent decade from the PubMed database.

EXPERT OPINION

Therapy options in AMD could include PGC-1α activation or stabilization. This could be achieved by a direct elevation of PGC-1α activity, a stabilization or modification of its upstream activators and inhibitors by chemical compounds, like 5-Aminoimidazole-4-carboxamide riboside, metformin, and resveratrol. Furthermore, manipulations with epigenetic modifiers of PGC-1α expression, including miRNAs, e.g. miR-204, are considered. A therapy aimed at PGC-1α up-regulation may be possible in other disorders besides AMD, if they are associated with disturbances in the mitochondria-antioxidant response-autophagy axis.

Naringin Promotes Skeletal Muscle Fiber Remodeling by the AdipoR1-APPL1-AMPK Signaling Pathway

Naringin, a natural flavonoid mainly found in citrus fruit, has been reported to exert a positive effect on improving skeletal muscle health. However, the effects and potential mechanisms of naringin on skeletal muscle fiber switching is still unclear. Here, we discovered that oral administration of naringin increased the low-speed running time, four-limb hanging time, body oxygen consumption in mice, enhanced aerobic enzyme activity, MyHC I expression, and slow-twitch fiber percentage in mice skeletal muscle. By contrast, naringin decreased α-GPDH enzyme activity, MyHC IIb expression, and fast-twitch fiber percentage. Moreover, naringin increased the concentration of serum adiponectin and activated the expression of AdipoR1, APPL1, AMPK, and PGC-1α. Furthermore, by the in vitro experiment and AdipoR1 knockdown, we found that inhibition of the AdipoR1 signaling pathway significantly reduced the effect of naringin on slow-twitch fiber-/fast-twitch fiber-related gene and protein expression. In conclusion, our results indicated that naringin could induce skeletal muscle fiber transition from fast twitch to slow twitch via the AdipoR1 signaling pathway. This study may provide new strategy for improving exercise endurance and slow muscle fiber deficiency-related diseases.

Effects of dietary ferulic acid supplementation on growth performance and skeletal muscle fiber type conversion in weaned piglets

BACKGROUND

Ferulic acid (FA) is a common polyphenolic compound. The purpose of this study was to explore the effect of dietary FA supplementation on growth performance and muscle fiber type conversion in weaned piglets. In this study, eighteen 21-day-old DLY (Duroc × Landrace × Yorkshire) weaned piglets were randomly divided into control, 0.05% FA, and 0.45% FA groups.

RESULTS

Our study showed that dietary FA supplementation had no effect on growth performance, but it could upregulate the expression of slow myosin heavy chain (MyHC) protein, increase the activities of succinic dehydrogenase and malate dehydrogenase, and downregulate the expression of fast MyHC protein. Dietary FA supplementation also increased the expression levels of phosphorylated AMP-activated protein kinase, sirtuin 1 (Sirt1), peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), myocyte enhancer factor 2C, and troponin I-SS, increased the proportion of slow-twitch fiber, and decreased the proportion of fast-twitch fiber. In addition, our results showed that dietary FA supplementation increased the messenger RNA abundance of mitochondrial nuclear transcription genes, including ATP synthase membrane subunit c locus 1, cytochrome oxidase subunit 1, nuclear respiratory factor 1, mitochondrial transcription factor A, mitochondrial transcription factor B1, and cytochrome c.

CONCLUSION

We provided the first evidence that FA could promote muscle fiber type conversion from fast-twitch to slow-twitch via the Sirt1/AMP-activated protein kinase/PGC-1α signaling pathway and could improve the mitochondrial function in weaned piglets. This means that FA can be used as a dietary supplement to improve the quality of pork. © 2021 Society of Chemical Industry.

Procyanidin B2 induces porcine skeletal slow-twitch myofiber gene expression by AMP-activated protein kinase signaling pathway

In this study, our aim is to investigate the effect of dimer procyanidin B2 [epicatechin-(4β-8)-epicatechin] (PB2) on porcine skeletal myofiber gene expression in vitro. Our data showed PB2 promoted the protein expression of slow myosin heavy chain (MyHC) in porcine myotubes, concomitant with the increases in mRNA levels of MyHC I, MyHC IIa and Tnni1. We also found PB2 activated AMPK signaling in porcine myotubes. NRF1 and CaMKKβ that are two important upstream factors of AMPK, and Sirt1 and PGC-1α that are two major downstream factors of AMPK, were also up-regulated by PB2. The mechanism study showed the effect of PB2 on slow-twitch myofiber gene expression was abolished by AMPK inhibitor compound C or by AMPKα1 siRNA. Together, we found PB2 induced porcine skeletal slow-twitch myofiber gene expression by AMPK signaling pathway.

Activation of IGF-1 pathway and suppression of atrophy related genes are involved in Epimedium extract (icariin) promoted C2C12 myotube hypertrophy

The regenerative effect of Epimedium and its major bioactive flavonoid icariin (ICA) have been documented in traditional medicine, but their effect on sarcopenia has not been evaluated. The aim of this study was to investigate the effects of Epimedium extract (EE) on skeletal muscle as represented by differentiated C2C12 cells. Here we demonstrated that EE and ICA stimulated C2C12 myotube hypertrophy by activating several, including IGF-1 signal pathways. C2C12 myotube hypertrophy was demonstrated by enlarged myotube and increased myosin heavy chains (MyHCs). In similar to IGF-1, EE/ICA activated key components of the IGF-1 signal pathway, including IGF-1 receptor. Pre-treatment with IGF-1 signal pathway specific inhibitors such as picropodophyllin, LY294002, and rapamycin attenuated EE induced myotube hypertrophy and MyHC isoform overexpression. In a different way, EE induced MHyC-S overexpression can be blocked by AMPK, but not by mTOR inhibitor. On the level of transcription, EE suppressed myostatin and MRF4 expression, but did not suppress atrogenes MAFbx and MuRF1 like IGF-1 did. Differential regulation of MyHC isoform and atrogenes is probably due to inequivalent AKT and AMPK phosphorylation induced by EE and IGF-1. These findings suggest that EE/ICA stimulates pathways partially overlapping with IGF-1 signaling pathway to promote myotube hypertrophy.

Lycopene increases the proportion of slow-twitch muscle fiber by AMPK signaling to improve muscle anti-fatigue ability

Lycopene has a wide range of biological functions, especially its antioxidant capacity. However, effects of lycopene on muscle fatigue resistant and muscle fiber type conversion are unknown. In this study, we found that lycopene significantly prolonged the swimming time to exhaustion in mice. We also showed that lycopene increased the proportion of slow-twitch muscle fiber by promoting muscle fiber type conversion from fast-twitch to slow-twitch in mice and in C2C12 myotubes. The AMP-activated protein kinase (AMPK) signaling was activated by lycopene. AMPK upstream and downstream regulators including nuclear respiratory factor 1, calcium calmodulin-dependent protein kinase kinase-β, sirtuin 1 and peroxisome proliferator activated receptor-γ coactivator-1ɑ were also increased by lycopene. AMPK inhibitor compound C markedly attenuated the lycopene-induced skeletal muscle fiber type conversion in C2C12 myotubes. Taken together, we provided the first evidence that lycopene increases the proportion of slow-twitch muscle fiber through AMPK signaling pathway to improve fatigue resistant of skeletal muscle.